NORMAL ANATOMY Osteology & Attachments Anterior view Posterior view Lateral view Superior view RADIOGRAPHIC VIEWS AP view Positioning patient supine leg IR 15-20° beam aim between ASIS + symphysis pubis Critique no rotation of pelvis superimposition of ischial spine with pelvic brim open obturator foramen no visualization of lesser trochanters too much external rotation of leg leads to increased visualization of lesser trochanter superimposition of ischial spine with pelvic brim Lateral view Positioning METHOD PATIENT BEAM Rolled lateral supine hip abducted 45° + knee flexed 90° mid-femoral neck n/a Horizontal ray/cross-table supine contralateral hip flexed 90° + ipsilateral hip IR 15-20° femoral head 45° cephalad Modified Dunn supine hip flexed 45° + abducted 20° 2.5 cm above pubic symphysis n/a Frog leg supine hip abducted 45° + knee flexed 30-40° 2.5 cm above pubic symphysis n/a Lowenstein semi-lateral 45° on ipsilateral side hip flexed 90° mid-femoral neck 20-25° cephalad False profile erect hip flexed 90°pelvis ER 65° toward ipsilateral side femoral head n/a Indications horizontal ray/cross-table useful in trauma patients where positioning is limited by pain modified dunn better demonstrates relationship of femoral head with acetabulum useful for confirming femoroacetabular impingement (alpha angle) frog leg better demonstrates shape of femoral head + head/neck transition useful for confirming epiphysiolysis, SCFE, Perthes disease lowenstein useful as alternative to frog leg view, as it is technically easier to obtain false profile provides true lateral projection of femoral head/neck and oblique view of acetabulum demonstrates anterior acetabular coverage of femoral head useful for determining anterior center-edge angle Critique horizontal ray/cross-table visualization of greater trochanter increased cephalad angle leads to increased visualization of greater trochanter off femoral neck but will distort/elongate femoral neck no obstructing soft tissue artifact via adequate elevation of contralateral leg modified dunn no overhang of greater trochanter over posterior margin visualization of lesser trochanter frog leg/lowenstein symmetrical obturator foramen + iliac wing concavity superimposition of greater trochanter + femoral neck false profile visualization of lesser trochanter too much ER leads to nonvisualization of lesser trochanter demonstration of bullet sign = superimposition of ischial tuberosity Oblique view Positioning METHOD PATIENT BEAM Hsieh semi-prone contralateral hip elevated 40-45° femoral head n/a Lillenfeld lateral decubitus on ipsilateral side pelvis tilted anteriorly 15° greater trochanter n/a Teufel semi-prone contralateral hip elevated 38° 2 cm above greater trochanter 12° cephalad Indications hsieh = posterior hip dislocation lillenfeld = posterolateral pelvis teufel = fovea capitis Critique NORMAL FINDINGS VIEW MEASUREMENT TECHNIQUE NORMAL FINDINGS SIGNIFICANCE Leg-length discrepancy AP line along inferior ischial tuberosity + line along superior aspect of lesser trochanter 0 cm Neck-shaft angle AP angle between femoral neck + femoral shaft 125-140° coxa vara < 120°; coxa valga > 140° Lateral center-edge angle/angle of wiberg AP angle between vertical line through femoral head + line along lateral acetabulum 25-40° assesses superolateral coverage: dysplasia < 20°; overcoverage > 40° Femoral head extrusion index AP % of femoral head not covered by acetabulum < 25% dysplasia > 25% Acetabular depth AP relationship of ilioischial line with acetabular floor vs. femoral head lateral coxa profunda = acetabular floor touches/medial to ilioischial line; protrusion acetabuli = femoral head touches/medial to ilioischial line Acetabular inclination/acetabular roof angle of tonnis AP angle between line through inferior sourcil parallel to inter-teardrop line + line from inferior to lateral sourcil 0-10° hip instability > 10°; pincer-type FAI < 0° Acetabular version AP crossover/figure-of-8 sign = relationship of anterior + posterior rim before reaching lateral sourcil 5-25° anteverted anteverted = no crossover; retroverted = crossover, also deficient posterior wall (femoral head lateral to posterior acetabulum) + prominent ischial spine, increased by increased pelvic tilt/rotation Hip center position AP distance from medial femoral head to ilioischial line < 10 mm lateralized > 10 mm Joint space width AP weight bearing minimum distance between femoral head + acetabulum 4 mm OA < 4 mm Head-neck offset AP vs. lateral relationship of anterior + posterior femoral head-neck junction symmetric radius of curvature decreased = anterior concavity > posterior; increased = anterior convexity Head-neck offset ratio lateral distance between line parallel to femoral neck through anterior femoral neck + anterior femoral head divided by diameter of femoral head > 0.15 cam lesion < 0.15 Alpha angle lateral angle between line from femoral head to anterolateral head-neck junction (where radius of femoral head becomes larger than neck) + line through femoral head/neck < 42° Cam lesion > 50-55° Head sphericity AP + lateral displacement of femoral head from reference circle < 2 mm aspherical > 2 mm Anterior center-edge angle/angle of lequesne false profile angle between vertical line through femoral head + line along femoral head/anterior acetabulum > 20° assesses anterior coverage; can have crossover sign but no posterior wall deficiency