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Home , Prepatellar bursitis, Sequestrum

Imaging of Disclosures: Musculoskeletal Infection • Consultant: BioClinica • Advisory Board: GE, Philips Jon A. Jacobson, M.D. • Book Royalties: Elsevier

Professor of Radiology Director, Division of Musculoskeletal Radiology University of Michigan Note: ultrasound images from the textbook Fundamentals of Musculoskeletal Ultrasound are copyrighted by Elsevier Inc.

Objectives: Outline: 1. Understand mechanism of • Mechanisms musculoskeletal infection • infection 2. Recognize imaging findings of • Septic musculoskeletal infection • 3. Differentiate osteomyelitis from neuropathic joint – Neuropathic joint – Discitis

Mechanisms: Infection: hematogenous • Hematogenous • Abscess (pyomyositis) – Children, intravenous drug abusers • Septic • Contiguous source • Septic arthritis – Diabetic ulcer – Acromioclavicular, sternoclavicular • Direct implantation – Sacroiliac – Penetrating • Osteomyelitis – Surgery – Vascular patterns differ with age

1 Normal Vascular Patterns Sites of Hematogenous Osteomyelitis

Infant Child >1 year Adult Infant Child >1 year Adult

From: Ortho Clin North Am 1998; 29:41 From: Ortho Clin North Am 1998; 29:41

Osteomyelitis: Contiguous Source Retained Cat Tooth

From: Ortho Clin North Am 1998; 29:41

Outline: • : • Mechanisms – Dermis, subdermis • Soft tissue infection – Erythema, warmth, edema • Cause: disruption of skin • Septic arthritis – Staph. Aureus – Strep. pyogenes From: RadioGraphics 2007; 27:1723 • Osteomyelitis • Susceptible: – Neuropathic joint – Vascular disease – Discitis – Indwelling objects

From: Skeletal Radiol 2010 in print

2 Cellulitis Cellulitis: ultrasound • Radiography and CT: • Early (<3 days): – Soft tissue swelling – Thick subcutaneous tissues, increase echogenicity – Increased density • Advanced: – Distorted, anechoic channels • Severe, advanced: – Fluctuating purulent fluid – Guided aspiration: efficacy similar to surgery • Late: abscess formation

J Ultrasound Med 2000; 19:743

Cellulitis: ultrasound Cellulitis • MRI: – Abnormal fluid signal – Isolated: subcutaneous tissues

Advanced Early T1w T2w + FS Gado

Differential Diagnosis • Fat necrosis Necrotizing – Pain, palpable, focal • Infection: – Thigh, women – Into deep fascia: progressive – No erythema – Necrosis: subcutaneous – Normal WBC • Gas-forming: – Anaerobes, aerobic gram negative • Life threatening emergency – 70 – 80% mortality if delayed diagnosis T1w T2w+ FS Gado From: RadioGraphics 2007; 27:1723 J Ultrasound Med 2008; 27:1751

3 Abscess • Deep fascia – Thick, enhancing • Staph. aureus: 77% – Non-specific • Direct spread or • Gas: hematogenous – Radiography, CT • Usually one muscle: From: RadioGraphics 2007; 27:1723 – MRI: signal void – Quads > gluteal > iliopsoas – US: echogenic, dirty • Pyomyositis: bacterial shadow – Common: HIV • Muscle abscesses RadioGraphics 2004; 24:1472 From: Skeletal Radiol 2010 in print

Abscess: Radiography and CT Abscess • CT: – Fluid collection + ring enhancement • Ultrasound: – Fluid: hypoechoic to hyperechoic

– May appear solid Gas • MRI: – Fluid signal + ring enhancement – T1w: high signal rim* Radiology 1995; 197:279

Abscess: ultrasound

MRI Abscess: calf

Hypoechoic

Hyperechoic

• Dynamic compression T1w T2w + FS Gado • Through- Anechoic Isoechoic transmission

4 Differential Diagnosis Differential Diagnosis • Diabetic muscle infarction • Retained foreign body • Imaging: – Surgical material – Not homogeneous fluid signal – Gossypiboma – Relatively normal muscle – Looks like hetergeneous fluid T1w architecture – Low signal gas on MRI • History: – – Long standing) – Normal WBC • Thigh > calf T1w T2w + FS Gado T2w + FS Gado AJR 2000; 174:165 AJR 2000; 174:165

Flexor Tendon Sheaths Infective Tenosynovitis • Uncommon • Puncture, bite: hand, foot • Hand: T T – Flexor tendon sheaths: • Thumb connects to little finger – Extensors: separate sheaths • Imaging: – Fluid distention: complex – Wrist: dorsal Foot: dorsal

From: www.sportnetdoc.com

Infective Tenosynovitis: wrist Septic Bursitis • Direct inoculation • Olecranon & prepatellar • Spread from joint • Radiography: – Swelling, possible gas • Ultrasound / MRI: – Fluid collection in expected location of a bursa – Possible gas Axial T2w + FS Axial post-gad

5 Trochanteric Bursa: infection + gas Prepatellar Bursitis

Patella PT PT

T1w Greater Trochanter Sagittal Axial

Epitrochlear Lymph Nodes: hyperplastic Cat scratch disease = infection • Animal scratch: usually a cat – Bartonella henselae • Child or adolescent: – Most common T2w + FS • Elbow: – Lymphadenopathy – Epitrochlear lymph node (medial)

Gado

Outline: Septic Arthritis • Hematogenous: • Mechanisms – S. aureus > • Soft tissue infection • Usually large joint • Also, joints with acronyms • Septic arthritis – ACJ, SCJ, SIJ • Osteomyelitis – Small vessels, slow flow – Increased risk of infection – Neuropathic joint • Irreversible joint damage: – Discitis – 48 hours

6 Septic Arthritis Septic Arthritis • Radiography / CT: • Ultrasound: – Periarticular – Joint effusion: Talonavicular – Joint space widening • Variable echogenicity • Acute lax joint, chronic infection • Anechoic to echogenic – Uniform joint space narrowing – Hyperemia: – Indistinct subchondral • Lack of flow does not plate exclude infection* – Synovial thickening – Erosions – Guided aspiration – Bone destruction RadioGraphics 1999; 19:1585 *AJR 1998; 206:731 Metatarsophalangeal

T1w Septic Arthritis Joint Recesses: • MRI: • Shoulder: biceps, posterior – Synovial enhancement (98%) Biceps Shoulder • Elbow: posterior – Perisynovial edema (84%) • Wrist: dorsal – Adjacent marrow edema (84%) • Hip: anterior femoral neck – Joint effusion: T2w + FS • : superior, medial, • 91% of large joints lateral to patella Elbow Knee • 54% of small joints • Ankle: anterior – Synovial thickening (22%): • MCP, MTP: dorsal atypical infection recesses Hip Ankle AJR 2004; 182:119

Septic Joint: sternoclavicular Septic Joint: fungal

T1w T2w + FS Gado

10 days later

7 Septic Joint: fungal Septic Arthritis: diagnosis • Joint aspiration: – Fluoroscopic or ultrasound-guided • Prior to fluoroscopic aspiration:

T1w T2w + FS Gado – Must have cross-sectional imaging – Exclude overlying bursa or abscess – Avoid contamination of a sterile joint by passing needle through overlying bursa – Screen for post-operative fluid collections

Gado

Iliopsoas Bursal Fluid Hip Arthroplasty: infection

Femur IP

Femoral Head Coronal Radiograph Axial T1w post-gadolinium

Osteomyelitis Osteomyelitis: Outline: Contiguous • Source • Mechanisms – HIV: atypical Mycobacteria • Blood cultures: • Soft tissue infection – Only positive in 50% • Septic arthritis (hematogenous) • Radiographs: • Osteomyelitis – Abnormal after 14 – 21 days – Neuropathic joint • Serology: – ESR elevated – Discitis – WBC: often elevated – : variable From: RadioGraphics 2007; 27:1723

8 Osteomyelitis: mechanism Osteomyelitis: acute versus chronic • Hematogenous: • Acute: – Infection begins in medullary space of bone – Bone destruction – Spreads out from bone – : in children (loose periosteum) – Children, intravenous drug abusers, septic • Chronic: • Contiguous source: – Extensive periostitis, sclerosis – Soft tissue abnormality (ulcer) extends to bone – Brodie’s abscess • Direct implantation – Sequestrum, cloaca, – Surgery (2%), cat bite, puncture wound

Acute Osteomyelitis: Osteomyelitis: adult versus child Radiography • Adult: • If ulcer: – Often direct spread: ulcer – Look at adjacent bone – Periostitis: only when subacute / chronic – Early: discontinuous cortex • Child: – Later: bone destruction – Hematogenous – Periostitis: not a feature – Metaphyseal equivalent (100%)* • Single bone (63%), contiguous (37%)* • If no ulcer: • Subperiosteal abscess: early finding** – Look for permeative • Periostitis: early sign (acute) appearance of bone – Adjacent soft tissue abscess (55%)* • Up to 3 weeks to identify *AJR 2007; 189:867 **Pediatr Radiol 1996; 26:291 Follow-up

Acute Osteomyelitis: Osteomyelitis: MRI MRI: criteria • Inversion recovery and T2w fat saturation:* • If ulcer: – Highest sensitivity for osteomyelitis (not specific) – Highest negative predictive value 1. Extends from ulcer to bone • T1-weighted images:** 2. Cortex disrupted T1w – Adds specificity 3. T1w: low signal – If high T2w and normal T1w: reactive edema 4. T2w: high signal • Intravenous gadolinium: 5. Contrast: + enhancement – If normal T2w: contrast not needed*** *More criteria, higher likelihood of – Delineates soft tissues: abscess osteomyelitis *Radiology 1998; 207:625 T2w + FS **AJR 2005; 185:386 ***AJR 2009; 192:1232

9 Osteomyelitis: adult diabetic

Osteomyelitis: MRI Soft tissue ulcer? Yes No • MRI with fat-suppression and contrast: – 88% sensitivity, 93% specificity* T2w: High Signal Normal (probably) None • MRI unenhanced: High – 98% sensitivity, 75% specificity** • Decreased T1w marrow signal concordant T1w Signal No osteomyelitis Normal with abnormal signal on T2w and post- Low intravenous contrast images Osteomyelitis Reactive Edema – 100% osteomyelitis*** *Radiology 1993; 189:251 **Radiology 1991; 180:533 Supporting Evidence: cortical destruction ***AJR 2005; 185:386

Osteomyelitis: 5th metatarsal Osteomyelitis: 1st distal phalanx

Axial T1w

Coronal T1w

T1wT2w + FS Gado Coronal T2w

Osteomyelitis: hematogenous Reactive Edema

T1w T2w + fat sat Sagittal T1w Sagittal T2w + FS

Diagnosis: Cocciodiomycosis

10 Subperiosteal Abscess: tibia Osteomyelitis: femur

T1w T2w + FS

Sinus track

Gado

Chronic Osteomyelitis Osteomyelitis: chronic • Radiography: – Remodeled, sclerotic, lucent – Exuberant periostitis • CT: – Sequestrum: – Scan without and with contrast • MRI: – Less fluid signal – Brodie’s abscess *Radiology 1998; 207:625 Patient #1 Patient #2 **AJR 2005; 185:386 ***Radiology 1997; 203:849

Chronic Osteomyelitis Osteomyelitis: chronic • Terminology: – Brodie’s abscess: chronic abscess of bone with surrounding fibrosis/sclerosis T1w – Sequestrum: dead bone separated from normal bone – Cloaca: passage into bone leading to cavity and sequestrum – Involucrum: envelope of new bone surrounding sequestrum Gado

11 Chronic Osteomyelitis: sequestrum, periostitis

T1w T2w FS

4 weeks earlier Gado Non-contrast

Chronic Osteomyelitis Neuropathic Foot

• Loss of proprioception and deep sensation • Relaxation, hypotonia • Recurrent injury • Malalignment • Joint destruction and disorganization • Location: determined by disease – Diabetes: lower extremity, esp. midfoot *Can become – Syrinx: upper extremity, spine septic after percutaneous aspiration

Neuropathic Foot Neuropathic Foot vs Osteomyelitis • Absence of ulceration: • Bone marrow edema: – Osteomyelitis unlikely: no need for MRI* – High T2w • Other findings: exclude infection: – T1w: variable, often normal – Location: midfoot • No adjacent ulcer – Thin rim enhancement of effusion – Subchondral cysts, intra-articular bodies • Multiple joints: esp. midfoot • Findings: superimposed infection** th st – Osteomyelitis: 5 MT > 1 MT > calcaneus – Sinus track, abnormal soft tissues, fluid collection • Subluxation – Diffuse abn marrow: low T1, high T2, +enhancement

Radiology 2002; 224:649 *J Am Coll Radiol 2008; 5:881 **Radiology 2006; 238:622

12 Neuropathic Foot Neuropathic Foot

T1wT2w + FS Gado

Neuropathic Foot Neuropathic Foot

T1w T2w + FS T2w + FS Gado

Discitis Discitis: acute • Adult: – Begins subchondral bone: anterolateral • Radiography: – Spreads into disc and next vertebra – Ill-defined endplate – Possible disc space narrowing – Focal lucency: anterior subchondral bone • MRI: – Endplates: fluid signal – Disc: fluid signal • Child: may begin in disc (usually < 7 years old) • May not be uniform – Annulus fibrosus: vascular / lymphatic supply up to 20 years – Paraspinal abscesses: TB Sem Musculoskel Radiol 2004; 8:215

13 Discitis: acute Discitis: acute

T1wT2w FS Gado

1 year earlier

Differential Diagnosis Discitis: chronic • Degenerative changes: • Radiographs / CT: – Modic 1: fluid signal – Ill-defined endplates – Modic 2: fat signal – Sclerotic – Modic 3: low signal • MRI: • Signal of disc: helpful – Improvement in fluid – If low: degeneration signal – If high: suspect infection T2w + FS

Note low signal of disc

Take Home Points: Take Home Points: • Osteomyelitis: adult – Look at bone adjacent to ulcer • Neuropathic joint: – Radiograph: loss of cortical line – No ulcer: osteomyelitis rare – MRI: • Septic hip or shoulder: • High T2, low T1 = osteomyelitis – Screen soft tissues with cross-sectional • High T2, normal T1 = reactive edema imaging before fluoroscopic aspiration • Osteomyelitis: child – Subperiosteal abscess, periostitis

14 Syllabus on line and other educational material: www.jacobsonmskus.com Twitter handle: @jjacobsn

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