Systematic Approach to the Interpretation of Pelvis and Hip

Home , Pelvic inlet, Pelvic outlet, Pelvis

Volume 37 • Number 26 December 31, 2014

Systematic Approach to the Interpretation of Pelvis and Hip Radiographs: How to Avoid Common Diagnostic Errors Through a Checklist Approach MAJ Matthew Minor, MD, and COL (Ret) Liem T. Bui-Mansﬁ eld, MD After participating in this activity, the diagnostic radiologist will be better able to identify the anatomical landmarks of the pelvis and hip on radiography, and become familiar with a systematic approach to the radiographic interpretation of the hip and pelvis using a checklist approach.

initial imaging examination for the evaluation of hip or CME Category: General Radiology Subcategory: Musculoskeletal pelvic pain should be radiography. In addition to the com- Modality: Radiography plex anatomy of the pelvis and hip, subtle imaging fi ndings often indicating signifi cant pathology can be challenging to the veteran radiologist and even more perplexing to the Key Words: Pelvis and Hip Anatomy, Radiographic Checklist novice radiologist given the paradigm shift in radiology residency education. Radiography of the pelvis and hip is a commonly ordered examination in daily clinical practice. Therefore, it is impor- tant for diagnostic radiologists to be profi cient with its inter- The initial imaging examination for the evaluation pretation. The objective of this article is to present a simple of hip or pelvic pain should be radiography. but thorough method for accurate radiographic evaluation of the pelvis and hip. With the advent of cross-sectional imaging, a shift in residency training from radiography to CT and MR imag- Systematic Approach to the Interpretation of Pelvis ing has occurred; and as a result, the art of radiographic and Hip Radiographs interpretation has suffered dramatically. However, the Common views of the pelvis and proximal femur include the AP projection of the pelvis, anterior and posterior 45-degree oblique (Judet) projections of the pelvis, AP pro- Dr. Minor is Radiology Resident, SAUSHEC, Fort Sam Houston, Texas; and Dr. Bui-Mansfi eld is Chief, Musculoskeletal Radiology Section, Department of jection of the hip, and frog-leg lateral or straight lateral (Dan Radiology, Brooke Army Medical Center, Fort Sam Houston, Texas, and Miller) projection of the hip. More specifi c views of the hip Associate Professor, Department of Radiology, Uniformed Services University and pelvis to include pelvic inlet and outlet (Ferguson) views of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814; E-mail: liem.mansfi [email protected]. may be obtained depending on the clinical presentation. Each The authors and all staff in a position to control the content of this CME activity projection has advantages for visualization of the complex and their spouses/life partners (if any) have disclosed that they have no relation- pelvic anatomy. For example, the posterior column of the ships with, or fi nancial interests in, any commercial organizations pertaining to pelvis is best visualized on the Judet view; the sacroiliac this educational activity. joints are best appreciated on the pelvic outlet view; and the The opinions and assertions contained herein are those of the authors and should not be construed as offi cial or as representing the opinions of the Department of anterior and posterior aspects of the femoral neck are best the Army, Department of the Air Force, or the Department of Defense. seen on the frog-leg lateral view.1-3

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CCDRv37n26.inddDRv37n26.indd 1 111/17/141/17/14 9:369:36 PMPM The proximal femur, which can be divided into the femoral head, femoral neck, trochanters, and femoral shaft, articulates with the pelvis at the acetabulum. Normal angu- lation of the femoral head is approximately 125 to 135 degrees with respect to the long axis of the femoral shaft, with approximately 25 to 30 degrees of anteversion.3 The femoral neck, composed of the subcapital, transcervical, and basicervical segments, has characteristic compressive (vertically oriented) and tensile (arc-shaped) trabeculae. The intertrochanteric line (anterior) and the intertrochanteric crest (posterior) mark the transition between the femoral neck and the shaft. From the fusion of the 3 pelvic bones and articulation of the femur with the pelvis, several distinct Figure 1. This AP view of the pelvis shows the Hilgenreiner (H, radiographic lines, rings, and arcs are formed and are essen- horizontal dashed line) and Perkins (P, perpendicular solid line) lines on the right. On the left, the pubis (blue), ischium (yellow), tial to the analysis of pelvic radiographs. Table 1 outlines and ilium (red) are shown. the basic checklist approach for the evaluation of pelvic and hip radiographs.

The complex anatomy of the pelvis derives from the sym- In the absence of trauma, an avulsion injury metric fusion of 3 pelvic bones: the ilium, ischium, and pubis of the pelvis or proximal femur in an adult at the acetabulum (Figure 1). Initially, the 3 pelvic bones are should raise concern of an underlying bone connected by a Y-shaped growth plate, the triradiate cartilage, neoplasm. which fuses at approximately 14 to 16 years of age.4-6 Anteriorly, the right and left pubis, composed of a body and superior and inferior pubic rami, articulate at the pubic sym- On every pelvic radiograph, the white cortical margins or physis. Posteriorly, the body of the ilium articulates with the lines of the pelvis and femur should be closely scrutinized sacrum forming the sacroiliac joints, which are composed of for evidence of disruption. Loss of the white cortical line is a synovial component at the lower one third and a syndes- due most commonly to fracture, followed by neoplasm, infec- motic component at the upper two thirds of the joint. Key tion, and erosion from arthritis. An example of a fracture components of the ilium include the iliac crest and the ante- disrupting the cortical white line of the ilium is an isolated rior inferior and anterior superior iliac spines. The ischium, impaction fracture or Duverney fracture7 (Figure 2). In young which forms the posterior border of the acetabulum, also is athletic individuals, traumatic pelvic avulsion injuries will composed of a body and 2 rami. Spines arising from the result in disruption of the cortical white margin; however, it ischium and ilium form the greater and lesser sciatic notches should be noted that in the absence of trauma an avulsion posteriorly. The obturator foramen, which is anterior, is injury in an adult should raise concern for an underlying bone formed by the fusion of the superior and inferior pubic rami neoplasm.8 Similarly, the pelvic and obturator rings should and the inferior ischial ramus.5 be smooth and continuous. Disruption of the pelvic or obturator ring requires 2 fractures or a fracture and dislocation, most frequently described by the hard pretzel analogy. Initially, the 3 pelvic bones are connected at the Therefore, whenever a radiologist detects a fracture in either acetabulum by the triradiate cartilage, which the pelvic or obturator ring, it is incumbent upon him or her fuses at approximately age 14 to 16 years. to search for a second fracture or a diastasis of either the sacroiliac joint or symphysis pubis.

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CCDRv37n26.inddDRv37n26.indd 2 111/17/141/17/14 9:369:36 PMPM Table 1. Radiographic Evaluation of the Pelvis and Hip Joint • Check for presence of white cortical line or margin • Symphysis pubis should be less than 5 mm in width • Sacroiliac joint should be 2 to 4 mm in width • Pelvic ring should have no disruption • Obturator ring should have no disruption • Sacral foraminal lines should be visible • Check transverse processes of lower lumbar vertebrae for fracture • Check obturator internus fascial plane for hematoma or mass • Check iliopectineal line for: 1. disruption = fracture of anterior column 2. thickening = Paget disease, idiopathic hyperphosphatasia (rare) 3. destruction = neoplasm or infection • Check ilioischial line for: Figure 2. This AP radiograph of the pelvis shows irregularity of 1. disruption = fracture of posterior column the left iliac wing white cortical line (thick arrow) due to an isolated 2. destruction = neoplasm or infection iliac wing fracture (Duverney fracture). Note the normal white • Radiographic U or teardrop should be visible cortical line (thin arrow) of the right iliac bone. • Teardrop distance should be symmetric • Check acetabular roof or supra-acetabular line • Check for presence of anterior lip of the acetabulum • Check for presence of posterior lip of the acetabulum • Line of Klein drawn along the superior edge of the femoral neck should intersect the epiphysis • Shenton arc, drawn between the medial border of the femoral neck and the superior border of obturator foramen, should be a smooth, continuous arc • The greater trochanter should be below the acetabulum • Check for the presence of intertrochanteric crest and line

Although often obscured by bowel gas or bowel contents, the sacral foraminal lines representing the superior margin of the sacral foramina should be continuous, symmetric, Figure 3. This AP radiograph of the pelvis reveals absent inferior and smooth. The superior 2 to 3 sacral foraminal lines sacral foraminal lines due to a lytic bone lesion involving the should be visible if not obscured by bowel gas or bowel sacrum and coccyx (check mark). Symmetric superior sacral contents and any disruption or irregularity may represent foraminal lines are present (arrow). subtle clues to traumatic or insufficiency fractures. Alternatively, the absence of a sacral foraminal line may is typically thicker laterally than medially because of indicate a destructive process (Figure 3). Likewise, the weight-bearing. Absence or disruption of the sharp supra- acetabular roof or supra-acetabular line should be sym- acetabular line is a reliable indicator of a disease process metric, continuous, and smooth. The supra-acetabular line involving the acetabulum (Figure 4).

Figure 4. This coned-down AP view of the pelvis shows destruction of the right acetabular roof or supra-acetabular line (thin arrow) secondary to a lytic bone lesion (thick arrow). 3

CCDRv37n26.inddDRv37n26.indd 3 111/17/141/17/14 9:369:36 PMPM Figure 5. This AP view of the pelvis reveals absence of the right iliopectineal line (arrow) and supra-acetabular line due to a lytic osseous lesion with associated soft-tissue mass. The right proximal femur also is involved. Figure 6. This AP view of the pelvis shows thickening of the left ilioischial line (thin arrow) secondary to fi brous dysplasia of the left ischial tuberosity (thick arrow). Note a second focus of fi brous dysplasia in the right intertrochanteric region (check mark). Whenever a fracture in either the pelvic or obturator ring is detected, a second pelvic fracture or a diastasis of either the sacroiliac The teardrop or radiographic U is a projectional phenom- joint or symphysis pubis must be excluded. enon secondary to the summation of shadows of the medial acetabular wall. Bone lesions or osteomyelitis may destroy the teardrop (Figure 7). Radiographically, the teardrop dis- The iliopectineal line formed by the superomedial linear tance is being measured from the lateral edge of the teardrop bony ridge of the superior pubic ramus in continuation with to the femoral head, and this distance should be bilaterally the arcuate line of the ilium serves as the anterior border of symmetric and measure less than 1 cm. Asymmetry of the the anterior column. Conditions affecting the anterior col- teardrop distance greater than 2 mm may provide subtle clues umn such as Paget disease or idiopathic hyperphosphatasia about an underlying pathologic process. Differential consid- may result in thickening of the iliopectineal line, whereas erations for widening of the teardrop distance include hip other pathologic processes may result in discontinuity or joint effusion, developmental dysplasia of the hip with supe- destruction of the line9,10 (Figure 5). The ilioischial line, rior and lateral subluxation of femoral head, intra-articular which defi nes the posterior column of the pelvis, extends body from recent hip fracture dislocation, or intra-articular along the medial border of the ischium inferiorly to the mass. The anterior lip of the acetabulum can be located by ischial tuberosity. Fractures and osseous lesions (e.g., fi brous following the superior pubic ramus laterally and superiorly, dysplasia) of the posterior column will result in discontinuity whereas the posterior lip of the acetabulum can be located or deviation of this typically smooth line (Figure 6). Of note, by following the inferior pubic ramus laterally and superiorly. the iliopectineal and ilioischial lines are best appreciated on Normally, the anterior lip of the acetabulum is located medial the Judet views. to the posterior lip of the acetabulum.

Figure 7. This AP view of the pelvis demonstrates loss of the right teardrop or radiographic U (thick arrow) secondary to an aneurysmal bone cyst. Note normal left teardrop (thin arrow). 4

CCDRv37n26.inddDRv37n26.indd 4 111/17/141/17/14 9:369:36 PMPM Figure 8. This frog-leg view of the pelvis reveals an abnormal left line of Klein (thin arrow) secondary to a slipped capital femoral epiphysis. Also, note the subtle widening of the left physis (thick arrow). On the right, the normal line of Klein (K, dashed arrow) intersects the epiphysis.

Radiographically, the teardrop distance is measured from the lateral edge of the teardrop to the femoral head and normally should measure less than 1 cm.

The line of Klein is drawn along the long axis of the superior aspect of the femoral neck and normally intersects the proximal femoral epiphysis. In the setting of slipped capital femoral epiphysis (SCFE), the normal relationship of the line of Klein will be lost (Figure 8). Likewise, the smooth curvilinear line connecting the medial aspect of the femoral neck with the undersurface of the superior pubic ramus forms the Shenton arc. Disruption of the Shenton arc may be secondary to hip dislocation, femoral neck fracture, or chronic developmental dysplasia of the hip with supe- Figure 10. This AP view of the pelvis shows traumatic widening rior and lateral subluxation of the femoral head (Figure 9). of the pubic symphysis of greater than 5 mm (arrow). At the femoroacetabular joint, horizontal (Hilgenreiner line) and perpendicular (Perkins line) lines deﬁ ne the 4 quadrants of the joint in which the femoral head should reside in the lower inner quadrant. The Hilgenreiner line connects the triradiate cartilages, and Perkins line extends vertically through the lateral edge of the acetabulum and perpendicular to the Hilgenreiner line (see Figure 1).

Figure 9. This AP view of the pelvis reveals loss of the normal Shenton arc on the right, widening of right teardrop distance (arrow), and superolateral subluxation of the right femoral head Figure 11. This AP view of the pelvis reveals widening of the right due to chronic developmental dysplasia of the hip. Normal inferior sacroiliac joint with increased subcortical sclerosis (arrow) Shenton arc is seen on the left (S, dashed line). of the right ilium secondary to septic sacroiliitis. 5

CCDRv37n26.inddDRv37n26.indd 5 111/17/141/17/14 9:369:36 PMPM are some of the most diffi cult fi ndings on radiography even The line of Klein is drawn along the long axis of for the experienced radiologist. the superior aspect of the femoral neck on the The pubic symphysis should be less than 5 mm in width frog-leg lateral view of the hip and normally and may be widened in traumatic symphyseal diastasis, blad- intersects the proximal femoral epiphysis. der exstrophy, or septic arthritis. Widening greater than 10 mm in males and 15 mm in females suggests instability. With widening greater than 25 mm, associated sacroiliac No discussion of the pelvis would be complete without a joint diastasis is expected (Figure 10). Interestingly, in the discussion of the soft tissues and joint spaces. The subtle third trimester of pregnancy, pubic symphysis mobility fi ndings associated with soft-tissue masses and joint diseases increases up to 8 to 12 mm.

Figure 12. A: This AP view of the pelvis shows displacement of the left gluteal fat stripe superiorly (thick arrow) in the setting of a left hip joint B effusion in comparison with the normal right gluteal fat stripe (thin arrow). The left arrowhead denotes the inferior extent of the hip joint capsule. B: This coronal T1 MR image of the pelvis shows displacement of the left gluteal fat stripe superiorly (thick arrow) in the setting of a left hip joint effusion in comparison with the normal, nondisplaced right gluteal fat stripe (thin arrow). The left arrowhead denotes the inferior extent of the hip joint capsule. C: Coronal STIR MR image of the pelvis shows distension of C the left hip joint (arrows) by a large left hip joint effusion. 6

CCDRv37n26.inddDRv37n26.indd 6 111/17/141/17/14 9:369:36 PMPM Figure 13. AP view of the pelvis reveals medial displacement of the right obturator internus fat stripe (arrow) secondary to an extraosseous soft-tissue mass (lymphoma) arising from the right acetabulum. The lymphoma was better seen on MR imaging (not shown).

The normal sacroiliac joints should be 2 to 4 mm in Conclusion width. Widening of the sacroiliac joints may be seen in the The anatomy of the pelvis and hip is complex. Therefore, setting of septic sacroiliitis (Figure 11) and traumatic dia- a systematic approach to the radiographic interpretation is stasis. The cortical margins of the sacroiliac joint also essential. A checklist of the common anatomical landmarks should be thin and continuous without sclerosis or erosions. in the pelvis and hip aids in the interpretation of hip and Although beyond the extent of this article, the femoroac- pelvis radiography. This CME activity emphasizes that etabular joints are involved in numerous infectious, neo- abnormal, asymmetric, or absent appearance of any of these plastic, and degenerative processes. It should always be anatomic structures may provide a clue to underlying pathol- remembered that an infectious process will affect both ogy and guide the diagnostic radiologist in further imaging sides of the hip joint with disruption of the cortical lines workup. of the femoral head, acetabular roof, or teardrop. Fascial planes created by the interface of fat with adjacent soft tissues are of particular importance in the evaluation of References pelvic radiographs. These fascial planes include the gluteal 1. Campbell SE. Radiography of the hip: lines, signs, and patterns of disease. Semin Roentgenol. 2005;40(3):290-319. fat stripe, which parallels the superior aspect of the femoral 2. Berquist TH, Coventry MB. The pelvis and hips. In: Berquist TH, ed. Imaging neck on the AP radiograph and depicts the fat plane between of Orthopedic Trauma and Surgery. Philadelphia, PA: WB Saunders; the gluteus minimus tendon and the ischiofemoral ligament. 1986:181-276. 3. Greenspan A. Lower Limb 1: Pelvic Girdle and Proximal Femur, in In the setting of a hip joint effusion, the gluteal fat stripe will Orthopedic Radiology: A Practical Approach. 2nd ed. Philadelphia, PA: be displaced superiorly (Figure 12). Inferior to the iliopsoas Lippincott Williams & Wilkins; 1995;197-226. tendon, the iliopsoas fat stripe, which also may be displaced 4. Armbuster TG, Guerra J Jr, Resnick D, et al. The adult hip: an anatomic study. Part 1: the bony landmarks. Radiology. 1978;128:1-10. in a hip joint effusion, can be identifi ed. The obturator inter- 5. Strandring S. Pelvic Girdle and Lower Limb, in Grays’ Anatomy. 40th ed. nus fat stripe, which can be seen paralleling the iliopectineal London, UK: Churchill-Livingstone; 2009. line, is formed by the fat adjacent to the obturator internus 6. Ponseti IV. Growth and development of the acetabulum in the normal child. Anatomical, histological, and roentgenographic studies. J Bone Joint Surg muscle. In the setting of trauma, the obturator internus fat Am. 1978;60:575-585. stripe may be displaced by a hematoma; otherwise, subtle 7. Young JW, Burgess AR, Brumback JW, et al. Lateral compression fractures displacement of the obturator internus fat stripe may be seen of the pelvis: the importance of plain radiographs in the diagnosis and surgi- cal management. Skeletal Radiol. 1986;15:103-109. in the setting of an extraosseous soft-tissue mass arising from 8. Bui-Mansfi eld LT, Chew FS, Lenchik L, et al. Nontraumatic avulsions of the the acetabulum (Figure 13). Although other fascial planes pelvis. AJR Am J Roetgenol. 2002;178:423-427. may be evident on pelvic radiographs, the above-mentioned 9. Saks BJ. Normal acetabular anatomy for acetabular fracture assessment: CT and plain fi lm correlation. Radiology. 1986;159:139-145. fascial planes represent those most commonly associated with 10. Whitehouse RW. Paget’s disease of bone. Semin Musculoskelet Radiol. pelvic pathologic processes. 2002;6:307-312.

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1. All of the following are radiographic ﬁ ndings on an AP radio- 6. All of the following are differential considerations for widening graph of the pelvis consistent with possible osteolytic meta- of the teardrop distance, except static disease, except A. hip joint effusion A. destruction of an ilioischial line B. developmental dysplasia of the hip B. destruction of multiple sacral foraminal lines C. intra-articular body from recent fracture dislocation of C. thickening of an iliopectineal line the hip D. destruction of a supra-acetabular line D. intra-articular hip mass E. avulsion of a femoral lesser trochanter in a nontrauma- E. osteoarthritis of the hip tized adult 7. On an AP radiograph of the pelvis, sacral foraminal lines 2. An afebrile 14-year-old boy presents with worsening pain in represent his left hip. A frog-leg lateral view of the pelvis reveals an A. inferior margin of the sacral foramina abnormal left line of Klein and subtle widening of the left B. superior margin of the sacral foramina femoral physis. The most likely diagnosis is C. lateral margin of the sacral foramina A. left slipped capital femoral epiphysis D. medial margin of the sacral foramina B. left hip joint effusion 8. After a motor vehicle accident, a 25-year-old man complains C. stress fracture of the left femoral neck of left-sided pelvic pain. His AP radiograph of the pelvis D. septic arthritis of the left hip reveals a Duverney fracture. The location of the fracture is E. fracture of the left acetabulum A. iliac wing 3. According to the authors, which of the following is/are impor- B. sacrum tant parts of the systematic approach of the radiographic C. pubis evaluation of the pelvis and hips? D. ischium A. Intact teardrop or radiographic U E. femoral neck B. Sacroiliac joint width of 2 to 4 mm 9. Which one of the following imaging examinations should be C. Intact iliopectineal line performed initially for the evaluation of hip or pelvic pain? D. Intact supra-acetabular line A. CT E. All of the above B. MRI 4. All of the following conditions may cause disruption of the C. Bone scintigraphy Shenton arc on an AP radiograph of the pelvis, except D. Radiography A. hip dislocation E. Ultrasound B. nondisplaced acetabular fracture 10. Which one of the following radiographic projections is the C. femoral neck fracture best to visualize the posterior column of the pelvis? D. chronic developmental dysplasia of the hip with superior A. Pelvic outlet view and lateral subluxation of the femoral head B. AP projection 5. After severe injury to the pelvis of a 35-year-old man, the C. Judet view width of the symphysis pubis on an AP radiograph of the D. Dan Miller projection of hip pelvis is greater than 25 mm. What other pelvic injury should E. Pelvic inlet view the radiologist suspect? A. Posterior dislocation of a hip B. Anterior dislocation of a hip C. Comminuted fracture of the sacrum D. Sacroiliac joint diastasis E. Femoral neck fracture

CCDRv37n26.inddDRv37n26.indd 8 111/17/141/17/14 9:369:36 PMPM