Review of Adult Foot Radiology

Home , Calcific bursitis, Chondrolysis, Involucrum, Oligoarthritis, Sequestrum

LAWRENCE OSHER

In the workup of a hallux valgus deformity the practi- Metabolic disease (dystrophies included) tioner is often faced with unexpected radiographic Infections and inflammatory processes findings. Usually, the first course of action is to order Tumor and tumor-like conditions additional pedal studies, which may provide the addi- Degenerative disease and ischemic necrosis tional detail needed to help resolve or localize the apparent pathology. If the problem is within the pur- However, this approach is presumptive; not only is view of conventional radiography, a library text, if an understanding of these basic bone radiographic available, is often hurriedly consulted. changes clearly required, but one is expected to iden- It is clearly not possible to encompass all of pedal tify and then classify any lesion(s). Many radiographic radiology within the confines of a single chapter of bony abnormalities simply cannot be categorized at this volume. Designed for the physician already famil- first glance by the average physician, despite the ability iar with basic musculoskeletal radiographic terminol- to correctly describe the basic pathologic changes. For ogy, the following information will serve as a handy these practitioners, a more intuitive approach utilizing outline of foot pathology that may be encountered in clinical and laboratory data is required (studies clearly the routine workup of the patient with hallux valgus show improved accuracy in the reading of radiographs deformity. Particular effort has been given to simplify when appropriate clinical and laboratory data are pro- the process of generating basic differential diagnoses. vided). The following steps are recommended: Pictorial examples are provided throughout this chapter. 1. Identify the given views. 2. Discern normal from abnormal by describing any pathology in standard objective radiographic termi- RECOMMENDED APPROACH TO nology. THE PEDAL RADIOGRAPH 3. Note available clinical and laboratory data. 4. Synthesize objective radiographic findings (item 2, Basic radiographic findings are not necessarily com- above) with the significant clinical and laboratory monly seen. Their correct description, utilizing objec- data (3) to designate a spectrum of possible disease tive radiologic terminology and subsequent categori- states in which both the radiographic and the zation, is vital to the generation of an appropriate clinical data could occur. differential. Traditional radiographic approaches often 5. Rank individual diseases of this spectrum (4) as to prescribe that, for every bone lesion, the following their probability of occurrence, that is, most likely disease categories must be routinely considered: to least probable. This is the essence of differential diagnosis. Developmental anomalies 6. Suggest additional radiographic or other studies Trauma that might assist further in the differential diag- Dysplasias and dysostoses nosis. 67 68 HALLUX VALGUS AND FOREFOOT SURGERY

Fig. 4-1. (A) Reference anteroposterior view. (B) Reference lateral view. (C) Thirty-degree medial oblique foot view demonstrating incomplete calcaneonavicular coalition. Note separation between second and third cunei- forms.

A standard bone survey should be ordered when- 1. Medial oblique (-15° to 30°) (Fig. 4-1C) ever there is suspicion of multiple areas of involve- Jone's fracture/base of fifth metatarsal ment other than the foot. The standard bone survey Lateral digits comprises these radiographs: Posterolateral talar process Most accessory bones except os tibial externum Two views of skull Lesser metatarsal head and base pathology Two views of lumbar or thoracic spine Lateral plantar calcaneus/foraminae Anteroposterior view of pelvis Subungual exostosis Anteroposterior views of arms and thighs Fibular sesamoid (10° study) 2. Isherwood medial oblique 45°-60°. This view will not visualize middle subtalar joint detail (Fig. 4-2). Anterior facet of talocalcaneal joint REVIEW OF INDICATIONS FOR Anterior process os calcis THE BASIC ADJUNCT Calcaneonavicular coalition PEDAL VIEWS Steidas process of talus 3. Lateral oblique (15°-30°) (Fig. 4-3) It will be helped to first study the reference anteropos- Accessory navicular (os tibial externum) terior (Fig. 4-1A) and reference lateral views (Fig. Haglund's disease/navicular pathology 4-1B) before reviewing the following lists. Cornuate/“gorilloid” navicular REVIEW OF ADULT FOOT RADIOLOGY 69

Interphalangeal sesamoid Subungual exostoses and osteochondroma Plantar cortex of distal phalanx 5. Harris-Beath (Fig. 4-4A) T-C coalitions (Fig. 4-4B), posterior and middle facet evaluation. (The anterior facet cannot be visualized adequately.) Coronoaxial skyline of the sustentaculum tali. Fractures of the os calcis, to evaluate posterior facet for longitudinal split as well as calcaneal foreshortening. These may be combined with various oblique axial views (Broden, Anthon- sen, etc.). Arthritic changes of the subtalar joint. 6. Calcaneal axial Skyline of os calcis, which images cortical loss, protrusions, or promontories. The subtalar joint is not imaged. True space occupying lesions of the calcaneal body should be discriminated from a pseudo- cystic foramen calcaneum. Varus deformity of os calcis. Post trauma to rearfoot. 7. Forefoot (sesamoid) axial (Fig. 4-5A) Hypertrophic plantar metatarsal condyles Structural abnormalities of metatarsals, best visualized in coronal plane Changes to cristae Differentiation of symmetrically placed medial first metatarsal head erosions from cysts (Fig. 4-5B) Sesamoid detail Fig. 4-2. Isherwood medial oblique demonstrating normal Fractures shape of anterior calcaneal process. Note separation be- Arthritic changes (cysts, erosions, bony prolif- tween third cuneiform and cuboid bones. erations, fusions) Sesamoid position (preoperative evaluation) Foreign bodies in plantar forefoot Base of metatarsal bones

Fracture medial cuneiform First metatarsophalangeal joint (MPJ) and medial hallux detail Possible talonavicular coalition Subungual exostosis/osteochondroma distal THE BASIC PEDAL phalanx RADIOGRAPHIC DIFFERENTIALS Tibial sesamoid bone (45°-60°) The following section is intended as a summation of 4. Hallux lateral commonly encountered pathologic conditions in Skyline hallux pedal radiology. Topics such as bone tumors and con- Distraction, sesamoid fracture at MPJ 70 HALLUX VALGUS AND FOREFOOT SURGERY

Fig. 4-3. Lateral oblique foot study.

A B

Fig. 4-4 (A) Normal Harris-Beath study. (B) Harris-Beath view of a middle facet subtalar joint coalition.

REVIEW OF ADULT FOOT RADIOLOGY 71

Fig. 4-5. (A) Normal forefoot axial study. (B) Magnification of forefoot axial study showing large (10.0-mm.) medial first metatarsal head erosion in a patient with chronic gouty arthritis. Note cystic/erosive change tibial sesamoid bone. genital disorders are beyond the scope of this chapter mately 15 percent of patients. These may be and are not included. asymmetric initially, but eventually are bilaterally and symmetrically distributed in the joints. The Common Arthropathies Remissions and exacerbations may occur, with the remission period not exceeding 3 months. Adult Rheumatoid Arthritis Occurrence is bilateral and symmetrical. 1. General features Typical forefoot target zones Articular complaints of the small joints of hands Fifth MPJ, most common medically and later- and feet; initial pedal onset occurs in approxi- ally 72 HALLUX VALGUS AND FOREFOOT SURGERY

Medial interphalangeal joint (IPJ) hallux Cysts/pseudocysts Medial aspects of first through fourth metatar- Erosive involvement of base of proximal pha- sal heads langes 2. Early radiographic features (predominantly MPJs Osseous "island" formation (fifth metatarsal (metatarsal heads) and medial IPJ hallux) head) Fusiform soft tissue swelling Digital deformities; deviations and subluxations Juxta-articular osteopenia Nonosseous (fibrous) ankylosis (exceptions; car- Concentric joint space narrowing pus and tarsus) Small para-articular cystic erosions (<5 mm) 4. Midfoot and rearfoot radiographic findings (fore- 3. Progressive forefoot radiographic findings (Fig. foot involvement typically precedes rearfoot by 4-6) many years) Rigid flatfoot deformity common Bony ankylosis of tarsal joints Concentric narrowing of tarsal/intertarsal joints, which may lack juxta-articular osteoporosis and typically lack periarticular erosive changes Secondary osteoarthritis, especially talonavicular joint and posterior facet of subtalar joint "Bywater's" retrocalcaneal bursal lytic lesions

Spondyloarthropathies (Seronegative Arthritides) 1. Clinical characteristics of the seronegative arthritides Familial tendency Sacroiliitis Mucocutaneous affectations Major types (considerable clinical overlap exists) Psoriatic arthritis Reiter's disease Enteropathic arthritis Ankylosing spondylitis Target sites Early digital and heel involvement with enthe- sopathic findings MPJs, proximal interphalangeal joints (PIPJs), and distal interphalangeal joints (DIPJs) Hallucal sesamoids Calcaneus, ankle and knee joints 2. Pedal radiographic changes of seronegative arthritis (Figs. 4-7 to 4-10) Fig. 4-6. Progressive forefoot radiographic changes. Exten- Early changes soft tissues are nonspecific. sive erosive changes are noted of the first, second, third, and Asymmetric dactylitis (Fig. 4-7) exhibits pro- fifth metatarsal heads. In addition, the medial aspect of the found fusiform digital soft tissue swelling sec- hallux IP joint is involved. Note the absence of PIP and DIP joint involvement and presence of cyst formation on fifth ondary to joint effusions, and flexor teno- metatarsal head. synovitis with or without periostitis. REVIEW OF ADULT FOOT RADIOLOGY 73

3. General comparison of adult rheumatoid arthritis versus seronegative arthritis Seronegative arthritis lacks nodules. Bilateral asymmetric presentation is common in seronegative arthritis (oligoarticular). These following joints are uncommonly involved in adult rheumatoid arthritis: DIPJs PIPJs (in foot only) Sacroiliac (SI) joints (symmetric) Thoracolumbar joint Dactylitis and enthesopathies are common (initial) complaints in seronegative arthritis; early heel complaints occur in seronegative arthropathies. Seronegative arthritis often lacks profound osteopenia. Seronegative arthritis lacks significant cystic de- generation. Rheumatoid arthritis lacks periostitis and acrolysis. Medial, lateral, and central erosive changes to IP hallux occur in rheumatoid arthritis.

Psoriatic Arthritis

1. Correlative clinical data of psoriatic arthritis Fig. 4-7. Asymmetric dactylitis with periostitis of second Good correlation between nail changes and ar- and fourth toes in a patient with Reiter's disease. thritis (not skin) Bilateral asymmetric oligoarthritis Underlying osseous changes may be present in Five patterns of arthritic attack approximately 50 percent of patients. Asymmetric oligoarthritis (70 percent) Periosteal apposition adjacent to symptomatic Symmetric polyarthritis (15 percent) joints and tendoligamentous attachments oc- DIP joint only (5 percent) curs during symptomatic periods. Arthritis mutilans (5 percent) Osteosclerosis is common but osteoporosis is Ankylosing spondylitis (5 percent) lacking. Target sites Poorly defined juxta-articular erosions are com- IP hallux (considered the most destructive ar- mon with marginal "whiskering periostitis." thropathy of the hallucal IP joint) Intra-articular bony ankylosis is also common, es- PIPs, DIPs, and MPs pecially psoriatic arthritis (Fig. 4-8). Sesamoids Joint space narrowing is uniform. Calcaneus (Resnick's sites 2-5) Acrolysis is present (Fig. 4-9). Ankle joint Minimal cyst formation occurs. 2. Radiographic changes of psoriatic arthritis in foot Erosive and proliferative bony calcaneal changes Normodensity or osteopenia seen during acute phases (typically ephemeral) occur (Fig. 4-10). 74 HALLUX VALGUS AND FOREFOOT SURGERY

Fig. 4-8. Generalized bony ankylosis along with a large "fluffy" infracalcaneal spur in a patient with mutilating psoriatic arthritis.

Bony ankylosis of DIPJs, PIPJs, and MPJs as well as Reiter's Disease tarsal bones (Note: As many as 30 percent of joints in psoriatic arthritis fuse) (Fig. 4-8) 1. Correlative clinical data of Reiter's disease Joint space widening and narrowing Young males Subchondral sclerosis Urethritis (typically nongonococcal) or enteritis Localized osteosclerosis Conjunctivitis Marginal joint "mouse-ear" erosions that may be Mucocutaneous lesions obscured by periosteal reaction Keratodermia blennorrhagicum Resorption and proliferative osseous changes Balanitis that may lead to arthritis mutilans with typical Mouth "pencil-and-cup" deformities or to digital con- Arthritis tractions/subluxations Not common in upper extremities "Ivory phalanx syndrome," or profound osteo- Dactylitis or heel pain a common initial com- sclerosis of hallucal distal phalanx secondary plaint to condensation of bone on periosteal and Joint deformity not as severe as in psoriatic endosteal surfaces (Fig. 4-9) arthritis Generalized sclerosis of os calcis and large, Forefoot joint involvement typically monoar- poorly defined "fluffy" spurs during symptom- ticular atic periods End-stage arthritis mutilans rare (Launois' de- Asymmetric digital dactylitis (Fig. 4-7) formity) Distal phalangeal tuft resorption (acro-osteoly- Pedal target sites sis) (Fig. 4-9) MTP joints REVIEW OF ADULT FOOT RADIOLOGY 75

Fig. 4-9. Psoriatic arthritis. Visible is an "ivory" osteosclerotic distal phalanx of hallux. Note the acrolysis as well as Fig. 4-10. Seronegative heel showing typical erosive find- intra-articular bony ankylosis of the IP joint. ing of retrocalcaneal bursal area and also large "fluffy" heel spur at infracalcaneal attachment of plantar fascia/intrinsics. Note generalized sclerosis of os calcis. First IP joint, medial and lateral Early loss of retrocalcaneal recess along with Calcaneus achilles tendon swelling is common; subjacent Achilles tendon erosive and proliferative calcaneal lesions Ankle joint (sites 1, 2, & 4) occur in Reiter's disease (Fig. 2. Radiographic features of Reiter's disease versus 4-10). psoriatic arthritis Joint space widening is not uncommon in pso- Except for the hallux IP joint, DIP and PIP joint riatic arthritis. involvement is not as common as in psoriatic arthritis. Osteoarthritis (Degenerative Joint Disease) There is a greater tendency for osteopenic changes in Reiter's, particularly during acute 1. Correlative clinical data of pedal Osteoarthritis phases (which last longer). Normal mineraliza- This is typically a secondary Osteoarthritis. It is tion then returns. commonly accepted that an association exists There is also a lesser tendency for bony ankylosis with pathomechanics/altered stress patterns in Reiter's disease. 76 HALLUX VALGUS AND FOREFOOT SURGERY

across joint(s) associated with the following: First MPJ axis of motion/instant center altera- tion Angle of metatarsus adductus First ray pathomechanics with pronation Sagittal plane elevation of first metatarsal/ray Other typical forms of secondary pedal osteoarthritis Trauma: osteochondritis dissecans, Freiberg's infraction, post sprains and fractures Congenital: tarsal coalitions, hereditary multiple exostosis, multiple epiphyseal dysplasia Arthritides: rheumatoid arthritis, calcium pyrophosphate dihydrate deposition disease (CPPD). Iatrogenic: after hallux abducto valgus surgery Common pedal target sites First MP joint(s) Medial column joints (greater mobility with pronation) Joints previously traumatized 2. Radiographic changes in osteoarthritis (Fig. 4-11) Unilaterally or bilaterally asymmetric Minimal soft tissue signs Asymmetric/focal (symmetric narrowing late) joint space narrowing Subchondral sclerosis/eburnation Subchondral cysts Marginal osteophytes Fig. 4-11. Typical osteoarthritic changes of the first meta- Paucity of periarticular fragmentation tarsophalangeal joint include focal narrowing, subchondral Absent erosions sclerosis, and marginal osteophytosis/proliferative changes including sesamoids. Erosive Osteoarthritis 1. Key clinical data of erosive osteoarthritis Occur predominantly in postmenopausal First MPJ arthritis (65 percent initially, 90 per- women cent at some time) Pedal target sites most often IP joints Hallux IP joint 2. Radiographic changes in erosive osteoarthritis Tarsometatarsal joint (see Fig. 4-13) Soft tissue swelling Ankle joint Marginal osteophyte formation 2. Early radiographic changes (Fig. 4-12A) Central joint space erosive changes producing a Extreme periarticular soft tissue swelling typical "seagull" appearance Significant osseous changes absent Bony ankylosis common and may dominate ra- Typically monoarticular diographic picture 3. Late (chronic) changes Joint space preserved until late Gouty Arthritis Asymmetric polyarticular (chronic) Erosions (Fig. 4-12B and C) 1. Correlative clinical data of gouty arthritis Juxta-articular/para-anicular Pedal target sites may involve any site in the foot. May be extra-articular

Fig. 4-12. (A) Acute gouty arthritis of the first metatarsophalangeal joint. (B) Chronic gouty arthritis. Visible is a large erosive change of hallucal proximal phalanx (10.0 mm) that is clearly both extra-articular as well as periarticular. Note eccentric soft tissue tophae of IPJ and MPJ. (C) Large erosive change of medial hallucal proximal phalanx along with lateral erosive change at IP joint margin. These changes are unusual in adult rheumatoid 77 arthritis. Note the subchondral density is normal. 78 HALLUX VALGUS AND FOREFOOT SURGERY

Large size (often >5.0 mm) with "punched- out" appearance Overhanging, proliferative margins (Martel's sign) Sclerotic lining Tophi (Fig. 4-12B) Eccentric focal soft tissue masses typically with subjacent erosions (versus rheumatoid arthritis nodules) May rarely become calcified Subchondral bony density typically unchanged (normodensity) Bony ankylosis and periostitis not overall promi- nent features Osseous infarcts End-stage osteolysis may mimic malignancy or somewhat resemble Charcot joint disease (especially when midfoot is involved) (Fig. 4-13)

Systemic Lupus Erythermatosus

1. Correlative clinical data of systemic lupus erythermatosus (SLE) Young females, increased incidence in blacks. Deforming, nonerosive arthritis of two or more joints Multisystem, including central nervous system (CNS) (seizures, etc.), pulmonary (effusions, pleuritis, etc.), renal (to 50 percent glomeru- Fig. 4-13. Extensive osteolysis base of fourth metatarsal lonephritis), cardiac, and skin (malar butterfly bone in a patient with chronic gouty arthritis. The changes or discoid plaquelike scaling may otherwise resemble charcot joint arthropathy. Pedal target sites MPJs Terminal phalangeal tufts (occasionally) Septic Arthritis 2. Radiographic changes in SLE 1. Correlative clinical data of septic arthritis Bilateral and symmetrical joint involvement This is an acute, red, hot monoarticular arthritis. Soft tissue swelling It may occur secondary to hematogenous osteo- Juxta-articular osteopenia myelitis in adults and infants or otherwise in Minimal/absent joint space narrowing certain joints in children where the metaphysis Deforming, nonerosive arthropathy involving is intra-articular (e.g., hip). MPJs (reversible) with subluxations and dislo- Associated signs and conditions in adult patients cations Debilitation Symmetric polyarthritis I.V. drug user Osteonecrosis/Freiberg-like deformities Prosthetic joint Soft tissue calcifications Direct trauma Occasional acrolysis of distal phalanges Contiguous osteomyelitis Post gonorrheal infection REVIEW OF ADULT FOOT RADIOLOGY 79

2. Radiographic changes in suppurative (pyogenic) ar- Diabetes mellitus thritis Tertiary syphilis Soft tissue swelling about joint Congenital indifference to pain Poorly marginated osseous erosions (peripheral Other neuropathic etiologies periarticular "bare" areas and/or central in- Syringomyelia volvement) Spina bifida Central joint space erosions Charcot-Marie-Tooth disease (rare) Rapid (1-3 weeks) concentric chondrolysis/joint Post-trauma space narrowing Pyrophosphate arthropathy (talonavicular joint) Reactive sclerosis (lacks osteopenia) Idiopathic osteonecrosis of navicular Eventual intra-articular bony ankylosis Avascular necrosis of talus Involvement of adjacent bony structures produc- Hemophilia ing classic picture of osteomyelitis Primary amyloidosis 3. Radiographic changes in nonsuppurative, tubercu- Post sympathectomy lous arthritis 2. Correlative clinical data of diabetic Charcot joint Phemister's triad arthropathy Gradual (slow) loss of joint space About 1 percent incidence among diabetic pa- Juxta-articular osteoporosis tients Peripheral osseous erosions Signs typically worse than symptoms Subchondral osseous erosions, central and pe- Soft tissue swelling with increased range of mo- ripheral (peripheral are seen more often in tion (ROM) and subsequent decreased ROM hip/knee/ankle) often with crepitus Tendency toward fibrous ankylosis Associated with long-standing diabetes, poor Late joint space loss control, and diabetic neuropathy Less periostitis than pyogenic and gonorrheal Pedal target sites 4. Correlative clinical data of gonococcal arthritis Weight-bearing "hypertrophic": Male > female Ankle joint (Fig. 4-14) Onset sudden or insidious Lisfranc's joint (Fig. 4-15.) Days 1 to 3 Systemic signs/symptoms Rash and fever/chills Days 4 to 6 Pauciarticular or polyarticular Small joints of foot Enthesopathy, calcaneous Knee > ankle > wrist > shoulder > foot > spine Lower extremities > upper extremities Associated with multiple joints and tenosynovitis 5. Radiographic findings in gonococcal arthritis As with pyogenic if untreated Osteoporosis and soft tissue swelling if treated

Charcot Joint Arthropathy

1. Differential diagnosis of disorders that may produce a radiographic picture of neuropathic joint Fig. 4-14. "Hypertrophic" Charcot joint deformity of the disease ankle in a patient with underlying neuropathy. 80 HALLUX VALGUS AND FOREFOOT SURGERY

A Fig. 4-15. (A) Anteroposterior view of hypertrophic Charcot joint deformity of Lisfranc's joint with resultant cube- foot deformity. (B) Lateral view of cube-foot deformity (same patient as in Fig. 4-15A).

Chopart's joint Note: The radiographic changes in this stage Subtalar joints (rarer) mimic acute, direct-extension osteomyelitis. Non-weight-bearing atrophic: However, the presence of osteopenia and IP and MP joints lysis suggests an intact vascular supply, and Ankle joint (rare) should not be misconstrued as a criterion to 3. Radiographic findings in diabetic neuroarthropathy amputate. (Charcot joints) Late, with significant weight-bearing (see Figs. Early 4-14 and 4-15) Soft tissue swelling Generalized sclerosis adjacent to site Digital subluxation Variable joint space narrowing Well-defined metaphyseal cortical defects Extensive osseous fragmentation Circumscribed zone of osteopenia Hypertrophic "bulky" osteophytes Subchondral "picture-framing" osteopenia Severe destruction/disorganization Possible underlying fracture "Cube foot" forefoot abduction (Fig. 4-15A Progressive and B) Poorly defined metaphyseal cortical defects Occasional bony ankylosis Periosteal reaction Late, without significant weight-bearing (Fig. Extensive osseous erosion and lysis (Fig. 4-16B) 4-16A) Sclerotic "pointed tubular bone" deformity Fragmentation with diaphyseal sparing REVIEW OF ADULT FOOT RADIOLOGY 81

A B

Fig. 4-16. (A) Progressive stage of diabetic osteolysis of the fifth toe. These changes are radiographically indistin- guishable from acute osteomyelitis (direct-extension type). (B) End-stage pointed tubular bone deformities in a patient with underlying neuropathy.

Overt osteolysis Benign nature of complaints; back stiffness with Restitution of integrity (forefoot) mild pain, talalgia, "tennis elbow," dysphagia Arthritis mutilans Not a true arthropathy Ankylosis not uncommon Pedal target areas, attachments of major soft tissue tendons and ligaments into bone (pure Diffuse Idiopathic Skeletal Hyperostosis enthesopathy) 2. Pedal radiographic findings (Fig. 4-17), entheso- 1. Correlative clinical data for diffuse idiopathic pathic osseous spurring skeletal hyperostosis (DISH) Common in dorsal midfoot Older than 50 years Calcaneus: large, poorly defined osseous apposi- Common axial syndesmophyte disease with ap- tions frequent at all major attachment sites pendicular manifestations Base of fifth metatarsal Males > females Anteriomedial navicular 82 HALLUX VALGUS AND FOREFOOT SURGERY

A B Fig. 4-17. (A) Anteroposterior view of midfoot of 91-year-old woman with underlying diffuse idiopathic skeletal hyperostosis. Extensive osseous apposition is noted at attachments sites of the flexor hallucis brevis (sesamoids), peroneus brevis, and anterior tibial tendons. (B) DISH. This lateral view of same patient in Fig. 4-15A shows extensive dorsal midfoot spurring as well as calcaneal and deltoid ligamentous involvements.

Medial first cuneiform Reaction to chronic soft tissue inflammation Hallucal sesamoids Reaction to trauma/hematoma subperiosteal space Forefoot joint capsular ossific spurring late (>75 Healing fracture. years) Metatarsal shafts (inconsistent) Soft tissue ossification/calcifications not un- Basic Differentials of Generalized common (Symmetric) Solid Periostitis 3. Postoperative new bone formation of implants of Adults 1. Primary (familial, idiopathic) hypertrophic os- Basic Differentials of teoarthropathy "Solid" Periostitis Radiographic Tarsals, metatarsals, and phalanges Solid periostitis is basically a reaction to some sub- Diaphyseal/metaphyseal/epiphyseal periosteal or extraperiosteal irritant. Common causes "Shaggy" irregular periostitis (spiculated) include the following: Ligamentous ossification 2. Secondary hypertrophic osteoarthropathy (HOA) Osteomyelitis (Fig. 4-18) Arthritis (seronegative, etc) Underlying primary lesion (often bronchogenic Bone tumor cancer) REVIEW OF ADULT FOOT RADIOLOGY 83

A B

Fig. 4-18. (A & B) Secondary HOA. "Solid," linear periosteal new bone formation of metatarsal shafts 2, 3, and 4 bilaterally are seen in a patient with underlying oat cell lung carcinoma.

Joint symptoms and signs worse in 30 to 40 Wavy or undulating cortical hyperostosis percent Other findings Radiographic Epiphyseal, invagination and hypertrophy Metatarsals and phalanges Metaphyseal widening, cupping, and shorten- Diaphyseal/metaphyseal ing Often linear or laminated, regular or irregular Premature closure of growth plates periostitis 5. Vascular insufficiency Periarticular osteoporosis and swelling 6. Chronic venous stasis (tibial periostitis) Differential diagnosis, DISH and juvenile rheu- 7. Polyarteritis nodosum matoid arthritis 8. Tuberous sclerosis 3. Thyroid acropachy 9. Fluorosis Hyperthyroidism 10. DISH (occasional) Clubbing Periostitis Selected Disorders of Increased Exopthalmos Tubular Bony Diameters Soft tissue swelling/myxedema (and also Acropachy) Radiographic 1. Diaphyseal Diaphyseal Acromegaly Shaggy, spiculated periostitis Paget's disease 4. Hypervitaminosis A (may be residual in adults) 2. Metaphyseal Radiographic Osteopetrosis (osteosclerotic) Metatarsals Pyle's disease (no osteosclerosis) Diaphyseal only, periostitis Gaucher's disease (no osteosclerosis) 84 HALLUX VALGUS AND FOREFOOT SURGERY

Shortened Tubular Bone Deformities 4. Neuroarthropathy (Brachydactyly) Diabetes Tabes dorsales 1. Hallux Syringomyelia Diabetic neurotrophic osteoarthropathy 5. Hyperparathyroidism 2. Phalanges and metatarsals 6. Vascular Diabetic neurotrophic osteoarthropathy TAO Idiopathic, isolated anomaly Raynaud's disease Rheumatoid arthritis 7. Leprosy Pseudohypoparathyroidism (especially first and 8. Post Injury fourth metatarsals) Frostbite Pseudopseudohypoparathyroidism Burns Turner syndrome (especially fourth metatarsal) 9. Polyvinylchloride (PVC) workers Basal cell nevus syndrome 10. Dilantin and ergot therapy Hereditary multiple exostoses 11. Chronic gout (asymmetric) Juvenile rheumatoid arthritis 12. Epidermolysis bullosa Infarction Trauma (fracture, burn, etc.) "Bone Within a Bone" Appearance Sickle cell disease 3. Flattened metatarsal heads 1. Osteopetrosis Freiberg's infraction 2. Sickle cell disease Diabetic neurotrophic osteoarthropathy 3. Sickle cell-ß-thalassemia disease 4. Some heavy metal intoxications (e.g., phosphorus) 5. Chronic osteomyelitis Some Disorders of Decreased 6. Congenital syphilis Tubular Bony Diameters 1. Acromegaly Selected Sclerotic Disorders (Internal 2. Diabetic neuro-osteoarthropathy (DNOAP) Osseous Disorders) 3. Juvenile rheumatoid arthritis 1. Transverse metaphyseal banding 4. Congenital syphilis Heavy metal (lead) poisoning Osteopetrosis Phosphorus osteopathy Selected Pointed Tubular Scurvy Bone Deformities Congenital syphilis (metaphysitis) 1. DNOAP Hypervitaminosis A and D 2. Psoriatic arthritis Leukemia (acute) 3. Alcoholic neuroarthropathy Reinforcement lines of osteoporosis 4. Scleroderma, dermatomyositis 2. Solitary circumscribed foci of osteosclerosis 5. Seronegative arthropathies Enostoses (bone islands) 6. Buerger's disease (TAO) Osteoid osteoma (medullary) 7. Arteriosclerosis obliterans Osteoma 8. Raynaud's disease Focal infarct (Fig. 4-19) Old nutrient foraminae (especially calcaneus) Healed fibrous bone lesion Acrolysis 3. Multiple circumscribed foci of osteosclerosis 1. Idiopathic Osteopoikilosis 2. Scleroderma Gardner syndrome (osteomata) 3. Psoriasis (see Fig. 4-9) Medullary fat necrosis/infarction REVIEW OF ADULT FOOT RADIOLOGY 85

Fig. 4-19. (A) Base of hallucal proximal focal osteosclerotic infarct in a patient with alcoholic pancreatitis. (B) Focal osteosclerotic lesion of os calcis (same patient as in Fig. 4-19A). Considering the nonhealing fifth metatarsal fracture, sickle cell disease remained a primary disorder to rule out.

4. Patchy-diffuse osteosclerosis/sclerotic foci Metaphyseal bone infarction: Previous infarct (may have serpiginous qualities) Sickle cell disease Endosteal fracture "callus" Infiltrated collagen vasculitides diagnosis Fibrous dysplasia Infections in juxtametaphyses Sclerosing osteitis in infection Pancreatitis (Fig. 4-20). Chronic osteomyelitis Steroids (pheochromocytoma) Osteoblastic metastases (breast, prostate) Rheumatoid arthritis Idiopathic osteonecrosis (navicular) Granuloma Paget's disease 5. Diffuse sclerosis of bones Secondary hyperparathyroidism Osteopetrosis/pycnodysostosis Primary osteogenic bone tumors Paget's disease Fairbank disease Hematopoietic disorders: mastocystosis, ane- Epiphyseal bone infarction: mias, myelofibrosis, leukemias Osteochondroses Metastases Post-traumatic Hypervitaminosis A and D Systemic lupus erythematosus 86 HALLUX VALGUS AND FOREFOOT SURGERY

Fig. 4-20. (A) Patchy-diffuse intramedullary osteosclerosis of the distal tibia. Osteosclerotic metatases must be ruled out. (B) Distal tibia (same patient as in Fig. 4-20A).

Hypo/pseudohypo- and pseudopseudohypo- 3. Generalized/nonregional (*, pediatric) parathyroidism Senile osteoporosis Fluorosis Osteomalacia (osteoporosis with bending) Melorheostosis Rickets (osteoporosis with bending)* Chronic osteomyelitis Chronic alcoholism Malabsorption/malnutrition Selected Osteopenic Disorders Vitamin C (scurvy) deficiency* Neuromuscular diseases/cerebral palsy 1. Subperiosteal resorption (rapid) Osteogenesis imperfecta* Hyperparathyroidism Endocrine: Reflex sympathetic dystrophy syndrome (RSDS) Hyperparathyroidism/Renal Osteodystrophy* Tendon avulsion (e.g., cortical desmoid) Hypogonadism 2. Spotted deossification (rapid) Diabetes mellitus (long-standing, poor con- Reflex sympathetic dystrophy syndrome (RSDS) trol) (Fig. 4-21) Cushing's disease Disuse osteoporosis (occasionally) Hyperthyroidism REVIEW OF ADULT FOOT RADIOLOGY 87

Fig. 4-21. "Spotty" juxta-articular or cancellous bony deossification in a patient with underlying reflex sympathetic dystrophy syndrome.

Hypothyroidism Hypervitaminosis A, excess osteoclastic activity in Collagen diseases metaphysis with active new bone proliferation Chronic anemias (e.g., iron deficiency)* in diaphysis Multiple myeloma Hypovitaminosis C, scurvy (Barlow's disease) Metastatic disease 6. Reticular areas of radiolucency Iatrogenic (steroids, heparin therapy) Sickle cell anemia 4. Localized osteopenia Anemias, thalessemia RSDS (may be seen as early as 3-4 weeks) 7. Regional osteopenic disorders/speckled or patchy Post-traumatic disuse/immobilization atrophy multiple radiolucencies (may mimic "moth-eaten" (seen at about 8-10 weeks) destruction; typically involve cancellous bone) Note: Hawkin's sign, a favorable radiographic Reflex sympathetic dystrophy syndrome (RSDS) sign suggesting the potential to heal, is merely Rapidly forming osteoporoses the presence of a thin zone of subchondral 8. Focal osteopenia lucency of the talar dome at a time (usually 8— Internal lysis 10 weeks post trauma) when disuse os- Acute osteomyelitis (see Fig. 4-22) teoporosis is radiographically apparent elsewhere. Calcifications Paget's disease (lytic phase I) Calcifications are typically classified into three catego- Regional migratory osteopenia ries. The first is metastatic, a disturbance of Ca and PO4 Tumor metabolism (Ca x PO >60-70); the second is calci- Juvenile rheumatoid arthritis 4 nosis, in which Ca and PO4 metabolism is normal; and Early osteomyelitis (Fig. 4-22) third, dystrophic, wherein calcium is deposited in de- 5. Multiple radiolucencies, primarily in multiple met- vitalized tissues. aphyses (modulation of normal growth pattern at the epiphyseal plate and metaphyseal junction) 1. Associated pathologies with metastatic calcification Congenital syphilis Widespread bone resorption 88 HALLUX VALGUS AND FOREFOOT SURGERY

Postinfection, infestation Ehlers-Danlos syndrome Neoplasms/tumor necrosis Trauma Connective tissue diseases Vascular disease Neuropathy Hematoma Injection sites Blunt trauma 4. Generalized calcinosis Calcinosis interstitialis universalis Longitudinal direction, plaque-like Skin and subcutaneous; occasionally tendons and muscles suggesting myositis, but no true bone formation occurs Tumoral calcinosis Often periarticular Large, solid, lobulated Collagen vascular diseases Dermatomyositis Fine, often reticular Associated with malignancies Often circumscribed (calcinosis circum- Fig. 4-22. Focal osteopenia of the medial first metatarsal scripta) head in acute osteomyelitis. An erosion of the terminal pha- Scleroderma with calcinosis (Thibierge-Weis- langeal tuft is also apparent. senbach syndrome) Achilles tendon Primary and secondary hyperparathyroidism Forefoot Hypoparathyroidism Tuftal Pseudohypoparathyroidism Leg; streaky or diffuse linear Massive bone destructive processes Circumscribed, lobulated or flocculent Metastatic tumors 5. Periarticular calcification(s) Multiple myeloma Synovial osteochondromatoses Leukemia Calcific tendinitis Miscellaneous, such as gut absorption Collagen vascular diseases Sarcoidosis Systemic lupus erythematosis Hypervitaminosis D Hyperparathyroidism and renal osteodystrophy Idiopathic hypercalcemia Hypoparathyroidism Immobilization/paralysis Hypervitaminosis D Milk-alkali syndrome Milk-alkali syndrome Cystic fibrosis Tumoral calcinosis Hyperphosphatemia Calcinosis universalis 2. Idiopathic calcinosis Articular disorders Calcinosis interstialis universalis CPPD Tumoral calcinosis Calcium hydroxyapatite deposition Calcine peritendinitis and bursitis Gout 3. Dystrophic calcification associations Infection REVIEW OF ADULT FOOT RADIOLOGY 89

6. Bursal, tendinous, or ligamentous calcifications 4. Underlying calcifying disorder (especially second- Calcific bursitis ary hyperparathyroidism in younger patients) Gout and pseudogout (Fig. 4-23) 5. Premature atherosclerosis Hypervitaminosis D Nephrotic syndrome Calcium hydroxyappetite deposition disease Hypothyroidism Ochronosis, Wilson's disease Diabetes Secondary hyperparathyroidism (occasionally Cushing syndrome primary) 7. Acral calcification Raynaud's disease Soft Tissue Ossification Systemic lupus 1. Neoplasm (e.g., parosteal osteosarcoma) Scleroderma/CREST syndrome 2. Post-traumatic ossification Dermatomyositis 3. Ossifying hematoma Calcinosis circumscripta universalis 4. Surgical scar 5. Severe burns Vascular Calcifications 6. Paralysis 7. Myositis ossificans 1. Monckeberg's medial sclerosis Heterotopic ossification of soft tissue with meta- 2. Calcific arteriosclerosis plasia of the intermuscular connective tissue 3. Intravascular phleboliths (rare in forefoot) (not secondary to muscle inflammation) Calcifications in veins 8. Radiographic findings Maffucci syndrome when pedal involvement is Soft tissue mass, early (possible association with extensive (hemangiomas) periostitis, 7-10 days) Hemangioma Peripheral osteoid (lacy new bone) formation 4-6 weeks post injury Lucent, cystic central changes Maturity, 5-6 months; trabeculation apparent Radiolucent band (zone) between myositic mass and subjacent bone cortex Ectopic bone, usually lying along axis of involved muscle

Appearance of Loose Intra-Articular Ossific Bodies 1. Avulsion fracture 2. Synovial osteochondromatoses 3. Osteochondral fracture 4. Degenerative joint disease 5. Freiberg's infraction 6. CPPD 7. DISH

Dactylitis

1. Seronegative arthritis (with enthesopathy) Fig. 4-23. CPPD. Note the fine, linear calcification in the 2. Sickle cell anemia achilles tendon. 3. Spina ventosa/tuberculosis 90 HALLUX VALGUS AND FOREFOOT SURGERY

4. Syphilis that of plain film radiography in that it is able to "ef- 5. Sarcoidosis (occasionally) face" the overlying bony cortex to allow for visualiza- 6. Traumatic periostitis tion of internal medullary osseous lesions. With respect to image quality, the orientation of x-ray tube travel can be significant in that maximum blurring oc- Coarsened Trabecular Pattern curs when the longitudinal axis of the part to be stud- 1. Paget's disease ied is perpendicular to the direction of tube travel. 2. Hemoglobinopathies Most pedal techniques employ 0.5-cm-slice thick- 3. Gaucher's disease ness with wide-angle tomography (30°- 50°). Wide- angle tomography is best for tissues with high inher- ent contrast (bone) but result in unacceptable soft Heel Pad Thickening tissue detail. In the foot, the true extent of geographic This anomaly is defined with a non-weight-bearing lat- destruction within cancellous bone(s) may not be ap- eral pedal view; in women, it is greater than 21 mm. preciated with plain film radiography. Tomography and in men, greater than 23 mm. can often elucidate the extent of this involvement. However, prolonged exposure times to ionizing radia- 1. Acromegaly tion are typically required. Largely replaced by com- 2. Dilantin therapy puted tomography (CT) scanning, tomography of the 3. Obesity foot still has one great advantage over modern CT 4. Peripheral edema scans, that is, the ability to directly image sagittal plane 5. Myxedema detail in all patients. 6. Infection Primary Disadvantages of Tomography 1. Radiation dosage OVERVIEW OF PEDAL 2. Ghost images APPLICATIONS FOR THE 3. Availability (particularly pleuridirectional units) NEWER, "STATE-OF-THE-ART" 4. Poor soft tissue visualization ANCILLARY IMAGING 5. Superimposed blurring MODALITIES Tomography: Overview Major Pedal Indications and Advantages 1. Orthogonal plane imaging of the tarsal bones (es- Tomography is primarily indicated for imaging planar pecially sagittal plane) detail in areas of complex osseous anatomy. The to- 2. Infection (bony involvement) mographic principle allows for the "focusing-in" of a Determination of the limits/extent of destruc- cross-sectioned anatomic plane by blurring all super- tion, particularly when cancellous bone is in- imposed image detail outside of a predetermined fo- volved cal plane. This focal plane lies at the system fulcrum, Periosteal reactions around which the x-ray tube head and film move in Sequestrum opposite directions. Those factors that increase the 3. Tarsal coalitions width of the blur (increasing angular arc, distance 4. Imaging of destruction/tumors/internal margin- from film or focal plane), as well as the efficiency of ation of bone blurring motion, improve the quality of the resultant Small caliber, lacking significant osteosclerosis studies. (e.g., medullary osteoid osteoma) Effective pedal imaging can usually be attained with Geographic and/or moth-eaten destruction in either linear or circular tomography. However, the cancellous bony areas resolving power of complex or pleuridirectional (tris- Cortical erosion piral and hypocycloidal) tomography is superior to Matrix details inferior to CT scans REVIEW OF ADULT FOOT RADIOLOGY 91

5. Postoperative complications ing frequencies (about 42.5 million cycles per second Bone graft incorporation in a 1.0-tesla (T) magnet and 64 megahertz in 1.5 T), Metallic implant problems known as the Larmor frequency, fall into the radio 6. Trauma wavelength bands of the electromagnetic spectrum. General evaluation of tarsal bony fracture(s) These nuclei are then stimulated (perturbed, tipped) Talar stiedas process fractures by a series of short radio wave burst/pulse cycles to Ankle joint pathology, e.g., osteochondral frac- various tip angles; the hydrogen atoms then "relax" to tures their previous, unexcited alignments, concurrently Evaluation of fracture healing or nonunions emitting magnetic radiance signals. These data are 7. Joints then used to reconstruct an image. Locate/identify juxta-articular and periarticular The microenvironment of hydrogen may change calcific and ossific bodies. from tissue to tissue throughout the body. This affects Evaluate joint space integrity of tarsal joints the behavior of the hydrogen atom during imaging (complex anatomy). and therefore the emitted signals after excitation. These effects can be observed through the measurement of Tl and T2 relaxation time constants of hydro- Magnetic Resonance Imaging: gen for certain tissues. Simply put, one Tl interval Brief Overview represents an exponential regrowth constant in the Magnetic resonance is the phenomenon of resonating original magnetic field direction and is the time it interaction between magnets (magnetic materials or takes for hydrogen nuclei to emit 63 percent of the atoms) and magnetic fields. In essence, certain sub- energy absorbed from the stimulating pulse. Tl time stances can undergo the absorption of energy from constant values are dependent on the external mag- externally applied electromagnetic field waves when netic field strengths. One T2 interval represents the the frequency is properly "tuned." When properly exponential decay of phase coherence in a plane per- tuned, just like sound waves resonating within a wine pendicular to the main magnetic field and is the time glass, all the atomic nuclei of a given species act in required for 63 percent of the signal to be lost by concert (spin coherently in "phase"). They simulta- dephasing. T2 time constants are largely independent neously start to "tip" (perturb) in a different direction of the applied external magnetic field strength. with an angle determined by the duration of applica- It is important to realize Tl and T2 relaxation times tion. The law of entropy dictates that these excited form the basis of tissue characterization and contrast. substances must release electromagnetic radiation of a The values of Tl and T2 are approximately the same in similar frequency in returning to their original energy pure water (e.g., urine and cerebrospinal fluid). In the states when the radiofrequency field waves are no complex microenvironments of living body tissues, longer applied. water may be impure; it is often in solution, it can be In applying this concept to the imaging of living in motion or tightly bound in a crystal lattice, or it may tissues, the nuclei of certain atoms can behave like be attached to macromolecules, compartmentalized, small magnets and develop "poles." These nuclei typi- subjected to thermal effects, viscosity, and so on. In cally have unpaired protons or neutrons and therefore contradistinction to pure water values, both Tl and T2 possess spinning electrical charges that generate a are greatly shortened and the signal fades correspond- magnetic field. In selecting atoms to optimally image ingly faster. The effects of flow are variable. Paramag- living tissues, one might intuitively look for atoms that netic substances such as methemoglobin formation emit the best (strongest) signals and are found (old hematoma) or intravenous gadolinium injection throughout all body tissues; hydrogen, a component shorten Tl and greatly shorten T2 relaxation times of of water, proves to be the best choice. tissues. When the patient is placed within the strong mag- It is, however, impossible to discriminate between netic field gantry of the magnetic resonance image Tl and T2 effects with a single stimulating pulse be- (MRI) scanner, hydrogen atoms tend to align and os- cause only regional hydrogen concentration would be cillate with the external magnetic field. Their oscillat- measured. Discrimination is accomplished largely 92 HALLUX VALGUS AND FOREFOOT SURGERY through the employment of various radiofrequency pulse along with two opposing magnetic gradients pulsing techniques or the injection of paramagnetic that first dephase and then ultimately rephase nu- contrast agents. With respect to pulse sequences, to clei ("gradient reversal"). This yields a free induc- evince these differences and therefore maximally con- tion decay (FID) echo. Depending on the tech- trast tissue signals, two or more pulses are applied in nique, gradient-echo methods can substantially rapid succession. Employing such pulse sequences, reduce MRI scan times (1 sec per scan is not un- images can be "weighted" to maximize either their Tl common). The signal intensities of tissues may vary or T2 signal characteristics. The time interval between in that marrow signals are typically darker and hya- repetitive pulses is the "time to repeat" (TR) and the line cartilage can be substantially brighter (from user-determined time interval between pulse and sig- afar, these images may mimic T2-weighted spin- nal measurement or echo return from the patient is echo images). Soft tissue contrast is poor when the "time to echo" (TE). In standard spin-echo pulse compared to standard spin-echo imaging, although sequences, a short TR and TE will yield Tl-weighted gradient-echo techniques can often improve imag- images whereas a long TR and TE interval will yield ing of hematoma and calcifications. T2-weighted images. Long TR and short TE times produce the "balanced," proton density image. c. Saturation pulse sequence (e.g., CHESS) techniques In general, a TR greater than 1.5 seconds (1,500 can effectively cancel the signals emanating from msec) and a TE greater than 0.4 seconds (40 msec) are protons bound to either fat or water in a given considered long. Tl-weighted images are often ac- voxel. Additionally, post-contrast Tl with gadoli- quired with 500/20 (millisecond) TR/TE combina- nium-DTPA fat saturation often improves the Tl tis- tions, respectively, and T2-weighted images with sue (marrow) contrast. 2,000/80 TR/TE combinations, respectively. Pathology often alters the normal relaxation time of Surface coils are commonly used to yield a small a given tissue, and thus allows for this delineation field of view (FOV) and maximize detail (maximize from normal tissues. In general, shortened Tl and signal-to-noise ratio). The smallest coil possible lengthened T2 relaxation times produce brighter sig- should be employed to fit the body part in foot and nal intensities and vice versa. Although absolute signal ankle imaging. Two knee coils, and occasionally head intensities can change considerably with changes in coils, are used. Flat surface coils are often best for both TR and TE, the relative intensities do not change achilles tendon imaging. Even though MR imaging of significantly between many tissues. the foot and ankle is now commonplace in podiatric It is standard procedure to employ spin-echo pulse medical practice, the practitioner must be wary of cycle imaging in the foot to provide proton density sending patients for scanning to hospitals or imaging (balanced), Tl- and T2-weighted images. Newer pulse- centers that do not routinely perform pedal MR scans sequence methods are yielding exciting results while or to institutions that prefer not to do them. Studies reducing MRI patient scanning times: are often suboptimal under these circumstances. a. Short-tau inversion recovery techniques (STIR) are The MRI Gray Scale: Normal now performed along with Tl-weighted and T2 fat Signal Intensities saturation images to improve the contrast between 1. High intensity: normal and pathologic tissues. Occasionally, in the Fat workup of infection, STIR images along with only Marrow Tl images are acquired. In these instances, the ad- 2. Low to intermediate intensity: dition of T2-weighted images may contribute useful Muscle information and eliminate some false-positive read- Hyaline cartilage ings (e.g., septic arthritis with possible osteomyeli- 3. Very low intensity: tis). Cortical bone b. Gradient-echo techniques (FLASH, GRASS) employ Air a single partial flip angle (usually from 5° to 30°) RF Ligaments and tendons Fibrocartilage REVIEW OF ADULT FOOT RADIOLOGY 93

4. Variable intensity (low-intensity Tl; high with T2): Common MRI Overlap Inflammatory or edematous tissue (Look-Alike) Pathologies Neoplastic tissue 1. Healed osteomyelitis Hemorrhage (interstitial) 2. Fracture Hematoma (intensity varies with age of hema- 3. Infarct toma) 4. Diabetic neuropathic bone disease (noninfective Increased initial Tl and T2 bone disease; osteolysis) Progressive decrease of Tl greater than T2 5. Septic arthritis (may evoke abnormal signal intensi- (effect seen with field strengths >1.0 T) ties in adjacent bone marrow) Fluid-filled structures General Advantages of MRI General Pedal Applications of MRI 1. Superior soft tissue contrast 1. Infection (osteomyelitis, cellulitis, absecesses) 2. Safety (nonionizing) 2. Avascular necrosis 3. Sensitivity to blood flow 3. Reflex sympathetic dystrophy syndrome 4. Multiplanar/triplanar pedal imaging; true ortho- 4. Neoplasms (bony and soft tissue, including meta- gonal planes can be acquired, any plane can be stases and true neuroma from Morton's neuroma) imaged 5. Hematoma 5. Contrast enhancement with minimal risk; contrast Fluid collections agents can be employed Postoperative dead space 6. Highly sensitive to many pathologies; however, not 6. Joint Evaluation specific Arthritis (low-signal synovial hypertrophy, carti- laginous narrowing) Limitations of MRI Subchondral cysts 1. MRI has longer scanning times than CT. Newer Internal derangements pulse sequencing may soon minimize this prob- Ligament (ankle) and tendon pathology lem. Tenosyovitis 2. Although the sensitivity for pathology often ap- Chronic tendinitis proaches 100 percent (e.g., osteomyelitis), the spe- Tendon rupture, total and partial cificity is considerably less for many osseous abnor- Effusion, bursitis malities, particularly those involving abnormal Fibrosis marrow signals. In these instances, the morpho- 7. Post-trauma logic appearance may be more reliable than the Stress fracture/insufficiency fracture marrow signal. Osteochondritis dessicans (acute and old) 3. Large metallic objects in the vicinity of the scanner, 8. Marrow pathology particularly ferromagnetic objects, can cause signifi- 9. Nonmetallic foreign bodies; nonferromagnetic me- cant image disruption/distortion. In addition, a sig- tallic foreign bodies nificant health hazard to the patient may occur with smaller ferromagnetic objects (orthopedic hard- Computed Tomographic Imaging ware, pellets) secondary to either dislodgment or heating during the actual scanning procedure. The basic principle employed in computed tomo- 4. Imaging of calcifications (except gradient echo/ graphic (CT) scanning is that the internal structure of FLASH) is provided. the body may be reconstructed in orthogonal planes 5. Negative imaging of the bony cortex is available. by gathering attenuation data from multiple x-ray pro- 6. Tissue heating occurs with MRI, although it is mild. jections in many different directions. These x-ray 7. MRI is contraindicated with cardiac pacemakers. beam scanning projections course through a fairly thin 8. MRI has a high cost. body plane, and the transmitted radiation registers 9. MRI must be interpreted in the clinical context. with highly sensitive scintillation crystal detectors or

94 HALLUX VALGUS AND FOREFOOT SURGERY xenon gas ionization chamber detection systems. 1.0 Hounsfield units (1.0 H.U. = 0.1 percent of the Since the inception of CT, each newer generation of density of water). CT scanners has resulted in dramatic decreases in 3. In comparison to conventional tomography, CT overall scanning time over the previous generation. scanning offers the great advantage of producing Concurrently, image quality has improved with ad- cross-sectional images of superior contrast and de- vances in computers as well as their image reconstruc- tail without the superimposed blur or ghost image tion algorithms. "Pencil-thin" x-ray beams have been distortion. replaced with fan-shaped beams, and rotating detector 4. In comparison with both conventional radiography systems have largely been supplanted by stationary and tomography, CT scans yield superior soft tissue rings of detectors lining the scanning gantry. contrast/delineation (through windowing) com- In CT image reconstruction, a body plane is sub- bined with the added capability of assigning divided into many smaller blocks of tissue (voxel; vol- Houndsfield (CT) attenuation values to pathologic ume element) and then each block face (pixel on a tissue (Table 4-1). This can often help characterize picture screen readout) is assigned a number (linear the basic tissue makeup. attenuation coefficient) correlated to its x-ray beam 5. Three-dimensional CT imaging holds promise in attenuating power in that projection. These numbers, the construction of preoperative models in areas of so-called "CT numbers," are based on the Hounsfield complex anatomy. scale and allow the computer to assign gray-scale val- 6. Although ancillary MRI has largely supplanted CT ues to the image. Basically, the image may be centered scanning of the soft tissue anatomy/pathology, in around a given tissue's Hounsfield unit (either osse- most aspects CT imaging remains a superior imag- ous or soft tissue) with a range of gray tones extending ing modality for imaging of the skeletal system and a variable, user-determined width (window width) soft tissue calcifications/ossifications. above and below this numeric center point (window 7. CT can be used with cardiac pacemakers. level). At the extremes of this range of gray tones are 8. CT can be used with ferromagnetic materials. pure black and pure white. In common practice, bone 9. CT may also be used with contrast studies such as and/or soft tissue windows are acquired. arthrography. Although MRI has largely replaced CT scanning for soft tissue and marrow imaging, CT scanning is supe- Overall Limitations of CT Scanning rior in visualization of calcific and bony cortical lesions. Additionally, soft tissue-osseous interface pa- 1. X-ray image has limitations; image is generally infe- thology (e.g., tendinous impingement) may be rior to MR imaging soft tissue contrast. accurately imaged with CT. Other pedal applications 2. CT scans produce ionizing radiation with potential include diagnosing pathology not clearly delineated long-term effects. with plain film radiographs (usually occult around tar- 3. Pregnant female patients should not be scanned sal bones and ankle joint) and also surgical planning unless absolutely necessary. (e.g., osteochondritis dessicans, tumor, complex frac- 4. Invasive contrast studies are often routinely em- tures, rearfoot surgery). ployed.

Overall Advantages of CT Scanning Table 4-1. Hounsfield Units Despite the following list of advantages, plain film ra- (quantized attenuation values) diographs should always be obtained before ordering Heavy metal >>> 1,000 CT scans. Compact/cortical bone 1,000 Calcification 200 – 800 (600–1,000) Clotted blood 40 – 60 1. Short scan times range between 1 and 5 seconds Blood 25 – 40 Muscle 20 – 40 per slice. Water 0 2. Precise imaging of regional density differences. Fat -20 – -100 Newer CT scanners can measure tissue density to Air -1,000 REVIEW OF ADULT FOOT RADIOLOGY 95

5. Physical constraints of the scanning gantry limits Charcot joints (to ascertain degree of lysis, eluci- imaging to predominantly the transverse plane. date loose bodies, etc.) 6. Sagittal plane imaging of the foot cannot generally 7. Infarction be obtained directly. Basic CT scanner design pre- Osteonecrosis of navicular cludes direct sagittal plane imaging of the foot in Distal tibia most patients. Although the computer is capable of 8. Muscles (pyomyositis) reformatting (reconstructing) those anatomic planes not directly imaged, such images suffer from significant degradation of image quality. However, BRIEF REVIEW OF in about 30 to 40 percent of patients, direct sagittal RADIOGRAPHIC plane imaging can be accomplished via internal BIOMECHANICAL EVALUATION (occasionally external) leg rotation with the knees flexed. The biomechanical evaluation is performed from the 7. CT scanning is not devoid of some significant re- anteroposterior and lateral pedal radiographs. Stan- construction artifacts; some of the more important dardization of foot position is essential for biomechan- ones include motion artifacts, streak artifacts, and ical radiographic evaluation. The accepted standard in beam-hardening artifacts. Note: Although the pres- podiatric medicine is proper placement of the patient ence of a ferrometallic object(s) does not preclude in their midstance angle and base of gait. Inasmuch as scanning, streak artifacts of many metallic objects first and fifth ray angles, indices, and bunion criteria may significantly distort or totally obscure image are reviewed elsewhere in this text, they are not cov- detail (even more than MRI) when the object is ered in this section. The succeeding axis descriptions large and lies within the image plane. should not be construed as axes of motion.

Common Pedal Applications Anteroposterior View for CT Scanning 1. Metatarsus adductus angle (Fig. 4-24) 1. Bony cortex/cortical pathology Usual upper limit: 14°-17° 2. Calcifications Normal adult range: 5°-17° 3. Evaluation of neoplasms (H.U. assignments) (par- Pathologic: >20° ticularly bone tumors) Values increase slightly with supination and de- Internal margination/destructive typing crease moderately with pronation. Matrix Method (Fig. 4-24) Periosteal reaction The angle is formed by the longitudinal axis of 4. Trauma/nonunion the lesser tarsus and the second metatarsal Tarsal bony fractures longitudinal axis. A transection to the lesser Fractures of the os calcis (tendinous impinge- tarsal bones must first be constructed by ment) identifying the four corners of a trapezoid Osteochondritis dessicans that approximates these bones. Care must Lisfranc fracture evaluation (image fracture pat- be taken not to utilize the lateral fourth me- tern/elucidate osseous fragments) tatarsocuboid joint margin or the styloid 5. Infection (especially chronic) process of the fifth metatarsal base. Involucrum Alternate method (Engel et al; not depicted) Cortex/sequestrum The four corners of the second cuneiform are Abscesses/plantar space infections defined by points, and a longitudinal bisec- 6. Joints tion to this cuneiform is then constructed. Subtalar joint arthritis The intersection of this bisection with the Evaluation of tarsal coalitions bisection of the second metatarsal bone de- Prosthesis (may be limited by artifacts) fines the metatarsus adductus angle. This 96 HALLUX VALGUS AND FOREFOOT SURGERY

Fig. 4-25. Line AC is drawn to actual point of talonavicular articulation; line N is drawn to the average normal point spanning 75 percent of the articular surface of the taler head. Angle A is the talonavicular angle; B, the cuboid abduction angle; C, the talocuboid angle; D, the talocalcaneal angle. Fig. 4-24. The metatarsus adductus angle.

method is much faster and reliably pro- duces angular values about 3° higher than method (a). Decreased in subtalar joint supination 2. Talocalcaneal angle (Fig. 4-25) (angle of Kite; The angle is formed by the intersection of the Harris-Beath angle) longitudinal bisection of the talar neck (column Normal ranges tali) and longitudinal axis of the rearfoot. The Infants, 30°-50° longitudinal calcaneal axis (column calcanei) is Age 1-10, about 30° typically substituted for the longitudinal rearfoot Adolescents >5 years, 20°-35° axis. This axis can be constructed with either a Adults, 17°-21° line parallel to the anteriolateral surface of the REVIEW OF ADULT FOOT RADIOLOGY 97

calcaneus or perpendicular to the plane of the 7. Forefoot adductus angle (Fig. 4-26) inferior calcaneocuboid articulation Normal range: 0°-10° 3. Cuboid abduction angle (calcaneocuboid angle) The angle is formed by the intersection of the (see Fig. 4-25) column calcanei (or longitudinal axis of rearfoot, Normal range: 0°-5° Increased with midtarsal joint pronation Decreased with midtarsal joint supination The angle is formed by the intersection of the column calcanei and the longitudinal axis of the cuboid. A line drawn parallel to the lateral surfaces of each of these bones usually suffices (in lieu of geometric bisection). 4. Talonavicular angle (see Fig. 4-25) Normal range: 70° ± 10° Increased in supination Decreased in pronation The angle is formed by the column tali and the transection of the lesser tarsal bones. Alternate method The angle is formed by the bisection of the talar neck and a tangent to the proximal effective articular surface of the navicular. Inasmuch as the concave portion of any convex-concave articulation typically displays a thin subchondral sclerotic line spanning the joint, this easily delin- eates the effective articular surface. Although this method is faster, it is less commonly employed. 5. Talonavicular articulation (percent articulation of talus) Normal range: 75 percent of talar head articulates with navicular Decreases in pronation Increases in supination Inasmuch as the articulating surface limits of the talar head must be defined to form the distal bisecting segment of the column tali, the percent of talonavicular articulation can be accurately approximately by creating 45° angles to the mid- point of this segment (see Fig. 4-25). 6. Talocuboid angle (see Fig. 4-25) Normal range: 31° ± 2° Increases in pronation Decreases in supination Possible associations (36° moderate increase in IM) The angle is formed by the intersection of the longitudinal bisection of the talus and a line drawn parallel to the lateral surface of the cu- Fig. 4-26. The forefoot adductus angle. A comparison of two different methods of forming the longitudinal rearfoot boid. axis yields two parallel lines in this case. 98 HALLUX VALGUS AND FOREFOOT SURGERY

when obtainable) and the longitudinal axis of the Decreases in supination second metatarsal. The angle is formed by the intersection of the lateral talar axis (column tali) and the weight- bearing reference line. The talar declination an- Lateral View gle equals the lateral talocalcaneal angle minus 1. Lateral cyma line (Fig. 4-27) the calcaneal inclination angle. Normal range: Two continuous/conjoined hyper- 3. Calcaneal inclination angle (see Fig. 4-28) bolic curves Normal range: 18°-23° Anterior break: Pronation 0°-10°, very low (flatfoot) Posterior break: Supination 10°-20°, low to medium An ideally continuous S -shaped line formed 20°-30° medium by a tracing through the talonavicular and calca- >30°, high (posterior pes cavus) neocuboid articular surfaces. Disruption is sug- The angle is formed by the intersection of the gestive of abnormal rearfoot/subtalar joint me- weight-bearing reference line and a line connect- chanics. When a discontinuity occurs, the relative ing the most posterior inferior point of the os position of the talonavicular joint surface with calcis with the anterior inferior osseous limit of respect to the calcaneocuboid joint surface deter- the os calcis at the calcaneocuboid joint. Older mines the naming of the "break" (anterior or methods suggest this line connect the posterior posterior). Invariably, when the arc formed by inferior and the anterior inferior osseous land- the talonavicular surface transects the calca- marks of the calcaneus. neocuboid joint, the cyma line is anterioinfe- 4. Lateral talocalcaneal angle (see Fig. 4-28) riorly displaced. With a posterior cyma line, the Normal range: 45° ± 3° two joint surface tracings do not intersect. Increases in pronation 2. Talar declination angle (Fig. 4-28) Decreases in supination Normal range: 21° ± 4° The angle is formed by the intersection of the Increases in pronation column tali and the column calcanei. This be-

Fig. 4-27. A normal cyma line. REVIEW OF ADULT FOOT RADIOLOGY 99

Fig. 4-28. Angle E is the calcaneal inclination angle; F, the talar declination angle; G, the lateral talocalcaneal angle; H, the metatarsal (first) declination angle.

comes the external angle of a triangle with oppo- 7. Posterior Facet (declination) angle (not depicted) site angles of talar declination and calcaneal incli- Normal range Approximately 45° nation angle. The lateral talocalcaneal angle Increases in pronation therefore equals talar declination plus calcaneal Decreases in supination inclination angles. The posterior facet angle, which is formed by 5. Metatarsal declination angle(s) (see Fig. 4-28) the intersection of a line tracing through the pos- Normal ranges (from S. Fuson and S. Smith) terior facet and the weight-bearing surface, is a 23° ± 8°, first metatarsal gross indicator of pathology. 25° ± 4°, second metatarsal 15° ± 4°, fifth metatarsal Increases in supination/pes cavus SUGGESTED READINGS Decreases in pronation/flatfoot The angle is formed by the intersection of the longitudinal axis of the respective metatarsal and General the weight-bearing reference line. Aegerter E, Kirkpatrick JAJr: Orthopedic Diseases. WB Saun- 6. Lateral talometatarsal angle (not depicted) (talo- ders, Philadelphia, 1975 first metatarsal angle; Meary's angle) Berquist TH: Radiology of the Foot and Ankle. Raven Press, Normal range: 0°-14° New York, 1989 15° or greater: cavus foot Brower A: Arthritis in Black and White. WB Saunders, Phila- Age 5 years or less: negative angle delphia, 1988 Adult negative angle: pronation/flatfoot Chapman S, Nakielny R: Aids to Radiological Differential Di- The angle is formed by the intersection of the agnosis. Bailliere Tindall, London, 1990 lateral talar axis and the longitudinal bisection of Dahnert W: Radiology Review Manual. Williams & Wilkens, the first metatarsal. The intersection of these two Baltimore, 1991 lines suggests the apex of deformity, particularly Edeiken J: Roentgen Diagnosis of Diseases of Bone. Williams in cavus foot deformities. In a rectus foot, the & Wilkins, Baltimore, 1989 Felson B, Reeder M: Gamuts in Radiology. Audiovisual Radi- column tali typically passes through the first ology of Cincinnati, Cincinnati 1987 metatarsal. In a pronated foot (or metatarsus pri- Forrester DM, Kricun ME: Imaging of the Foot and Ankle. mus elevatus), the column tali passes inferior to Aspen. 1988 the first metatarsal head and vice versa with ante- Greenfield G: Radiology of Bone Disease. JB Lippincott, New rior cavus/supination. York, 1990 100 HALLUX VALGUS AND FOREFOOT SURGERY

Keats T: An Atlas of Normal Roentgen Variants That May Wolf GL, Popp C: NMR—A Primer for Medical Imaging. Simulate Disease. Year Book Medical Publishers, Chicago, Slack, Thorofare, NJ, 1984 1984 Kinsman S, Kroeker R: Leg-Podiatry Radiography. California Biomechanics State Dept. of Health, Sacramento, California, 1973 McCarty DJ: Arthritis & Allied Conditions. Lea & Febiger, Altman ML: Sagittal plane angles of the talus and calcaneus in Philadelphia, 1985 the developing foot. J Am Podiatry Assoc 58:191, 1968 Meschan I: Roentgen Signs in Diagnostic Imaging. Vol. 2. Coleman SS: Complex Foot Deformities in Children Lea & Appendicular Skeleton. WB Saunders, Philadelphia, 1985 Febiger, Philadephia, 1983 Montagne J, Chevrot A, Galmiche JM: Atlas of Foot DiGiovanni JE, Smith SD: Normal biomechanics of the adult Radiology. Masson, New York, 1981 rearfoot. J Am Podiatry Assoc 66:812, 1976 Ravin CE, Cooper C: Review of Radiology. WB Saunders, Engel E, Erlick N, Krems I: A simplified metatarsus adductus Philadelphia, 1990 angle. J Am Podiatry Assoc 73:620, 1983 Resnick D: Common disorders of synovium-lined joints: Fuson SM, Smith SD: Angular relationships of the metatarsal, pathogenesis, imaging abnormalities, and complications. talus, and calcaneus. J Am Podiatry Assoc 68:463, 1978 AJR 151:1079, 1988 Gamble FO, Yale I: Clinical Foot Roentgenology. Kreiger, Resnick D, Niwayama G: Diagnosis of Bone and Joint Disor- Huntington, NY, 1975 ders. Vols. 1-6. WB Saunders, Philadelphia 1988 Giannestras JJ: Foot Disorders: Medical and Surgical Man- Sartoris DJ, Resnick D: Radiological evaluation of patients agement. Lea & Febiger, Philadelphia, 1973 with arthritis. Pathol Annu 86:293, 1986 Greenberg GS: Relationship of Hallux Abductus Angle and Silverman FN: Caffey's Pediatric x-ray diagnosis. Yearbook First Metatarsal Angle to Severity of Pronation. J Am Podia- Medical, Chicago, 1985 try Assoc 69:29, 1979 Weissman S: Radiology of the Foot. Williams & Wilkins, Balti- Kaschak TJ, Laine W: Surgical radiology. Clin Podiatr Med more, 1989 Surg 5:797, 1988 LaPorta GA, Scarlet J: Radiographic changes in the pronated Ancillary Imaging Modalities and supinated foot. J Am Podiatry Assoc 67:334, 1977 Meary R: On the measurement of the angle between the Berquist TH: Magnetic Resonance of the Musculoskeletal talus and the first metatarsal. Symposium sur le pied System. Raven Press, New York, 1987 creux essentiel. Rev Chir Orthop 53:389, 1967 Curry TS, Dowdey JE, Murry RC Jr: Christensen's Physics of Montagne J, Chevrot A, Galmiche JM: Atlas of Foot Diagnostic Radiology, Lea & Febiger Philadelphia, 1990 Radiology. Masson, New York, 1981 Edelman R, HesselinkJR: Clinical Magnetic Resonance Imag- Root ML, Orien WP, Weed JH: Clinical Biomechanics. Vol. II. ing. WB Saunders, Philadelphia, 1990 Normal and Abnormal Function of the Foot. Clinical Bio- Horowitz AL: MRI Physics for Radiologists. A visual Ap- mechanics, Los Angeles, 1977 proach. Springer-Verlag, New York, 1992 Sgarlato TE: A Compendium of Podiatric Biomechanics. Cali- Hounsfield GN: Computerized transverse axial scanning (to- fornia College of Podiatric Medicine, 1971 mography). Br J Radiol 46:1016, 1973 Solomon M: Roentgenographic Biomechanical Evaluation of Oloff-Solomon J, Solomon MA: Computed tomographic the Foot. Johnathan Douglass, 1973 scanning of the foot and ankle. Clin Podiat Med Surg Templeton AW, McAlister WH, Zim ID: Standardization of 5:931, 1988 terminology and evaluation of osseous relationships in Oloff-Solomon J, Solomon MA: Magnetic Resonance Imaging congenitally abnormal feet. AJR 93:374, 1965 in the Foot and Ankle. Clin Podiatr Med Surg 5:945, 1988 Whitney AK: Radiographic Charting Technique. Pennsyl- Resnick D: Bone and Joint Imaging. WB Saunders, Philadel- vania College of Podiatric Medicine, 1978 phia, 1989