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 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 extended + 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 visualization of greater trochanters in profile 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 weightbearing 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 CLINICAL PEARLS Hip OA Classification = Tonnis grade 0 = normal grade 1 = sclerosis of femoral head + acetabulum, slight joint space narrowing, slight lipping at joint margins grade 2 = small cysts in femoral head/acetabulum, moderate joint space narrowing, moderate loss of head sphericity grade 3 = large cysts in femoral head/acetabulum, joint space obliteration/severe narrowing, severe femoral head deformity vs. AVN Recommended views weightbearing AP pelvis AP lateral Findings joint space narrowing (JSN) osteophytes eburnation of bone subchondral sclerosis/cysts Hip osteonecrosis Classification = Steinberg Steinberg Classification (modification of Ficat classification) Stage Radiographs MRI Images 0 normal normal MRI and bone scan I normal abnormal MRI and/or bone scan II cystic or sclerosis changes abnormal MRI and/or bone scan III crescent sign (subchondral collapse) abnormal MRI and/or bone scan IV flattening of femoral head abnormal MRI and/or bone scan V narrowing of joint abnormal MRI and/or bone scan VI advanced degenerative changes abnormal MRI and/or bone scan Recommended views AP frog leg lateral Findings subchondral sclerosis/cysts crescent sign = subchondral collapse joint space narrowing Treatment criteria nonoperative treatment acceptable if precollapse AVN (Ficat stages 0-II) core decompression with or without bone grafting if early AVN, before subchondral collapse occurs reversible etiology rotational osteotomy if small lesions (<15%) in which the lesion can be rotated away from a weight bearing surface curettage and bone grafting through Mont trapdoor technique or Merle D'Aubigne lightbulb technique if precollapse AVN (Ficat stages 0-II) vascularized free-fibula transfer if pre-collapse and collapsed AVN in young patient reversible etiology preferred total hip arthroplasty if younger patient with crescent sign or more advanced femoral head collapse, +/- acetabular DJD irreversible etiology (chronic steroid use) patients >40 with large lesions total hip resurfacing if in advanced DJD with small, isolated focus of AVN requires adequate bone to support resurfacing component contraindicated in underlying disease process or chronic steroid use causing AVN (poor bone quality) and renal disease (metal ions from metal-on-metal implant) hip arthrodesis if very young patient in a labor intensive occupation Adult dysplasia of the hip Classification Crowe Crowe Classfication Grade Proximal displacement Femoral head subluxation I <10% vertical height of pelvis proximal migration of head neck junction from inter-teardrop line <50% of femoral head vertical diameter II 10-15% 50-75% III 15-20% 75-100% IV > 20% >100% Hartofilakidis Hartofilakidis Classification Dysplasia (Type A) Femoral head within acetabulum despite some subluxation. Segmental deficiency of the superior wall. Inadequate true acetabulum depth. Low dislocation (Type B) Femoral head creates a false acetabulum superior to the true acetabulum. There is complete absence of the superior wall. Inadequate depth of the true acetabulum. High dislocation (Type C) Femoral head is completely uncovered by the true acetabulum and has migrated superiorly and posteriorly. There is a complete deficiency of the acetabulum and excessive anteversion of the true acetabulum. Recommended views AP lateral Findings decreased femoral head sphericity crossover sign results from increased retroversion decreased lateral center-edge angle < 20° angle between vertical line + line from femoral head to lateral acetabulum assess on AP view normal 25-40° increased tonnis angle > 10° angle between horizontal line + line along superior acetabulum measures inclination of weightbearing zone assess on AP view normal 0-10° decreased head-neck offset ratio distance between line parallel to femoral neck through anterior femoral neck + anterior femoral head divided by diameter of femoral head assess on lateral view normal > 0.15 Treatment criteria nonoperative treatment acceptable as first-line periacetabular osteotomy +/- femoral osteotomy if symptomatic dysplasia in an adolescent or adult with concentrically reduced hip congruous joint with good joint space salvage pelvic osteotomy (chiari, shelf) if unreduced hip patients with inadequate femoral head coverage and an incongruous joint (a salvage procedure) hip resurfacing if Crowe type I or II disease total hip arthroplasty if last resort for those with severe arthritis older patients (>50) and those with advanced structural changes Idiopathic transient osteoporosis of the hip Recommended views AP lateral Findings (xray findings in femoral head and neck lag behind clinical signs by 4-8wks) subchondral cortical loss diffuse osteopenia of femoral head and neck joint effusion joint space is always preserved Treatment criteria nonoperative treatment acceptable always THA templating Recommended views AP pelvis AP hip frog leg lateral Steps establish radiographic landmarks pelvis/acetabulum acetabular roof = superolateral margin of acetabulum ilioischial line base of teardrop = created by superposition of the most distal part of the medial wall of the acetabulum and the tip of the anterior/posterior horn of acetabulum ischial tuberosities femur medullary canal greater trochanter lesser trochanter saddle point = most distal part of the junction between the superior aspect of the femoral neck and the greater trochanter evaluate for leg length discrepancy draw horizontal reference line through base of both teardrops (interteardrop line) vs. distal aspect of ischial tuberosities (bi-ischial line) ensure the line extends beyond the medial femoral cortices bilaterally interteardrop line is more accurate due to closer proximity to center of rotation of hip joints bi-ischial line may have decreased accuracy due to further distance from center of rotation of hip joints leading to more effect of rotation of pelvis mark the top (proximal-most point) of both lesser trochanters on the AP pelvis radiograph measure the distance between the inter-tuberosity line and the line drawn at the most proximal aspect of the lesser trochanters pelvic obliquity lumbrosacral hyperlordosis causes AP view to appear as inlet view hip contracture = adduction vs. adduction acetabular retroversion template acetabulum position cup in 40° +/- 10° of abduction increased abduction can lead to posterosuperior dislocation and eccentric poly wear decreased abduction can lead to inferior dislocaion and impingement in flexion position cup in 5-25° of anteversion increased anteversion can lead to anterior dislocation decreased anteversion can lead to posterior dislocation size cup so medial border approximates ilioischial line and has adequate lateral bone coverage with minimal removal of supportive subchondral bone if using cemented cup, allow for cement mantle of 2-3 mm if lateral bone coverage is incomplete, measure uncovered area in order to reproduce during surgery ensures adequate inclination mark center of rotation compare center of rotation to contralateral hip to determine differences in vertical distance from reference line and horizontal distance from teardrop line used to compensate limb length and offset during femoral templating note location of cysts in acetabular roof can be grafted or used as anchoring holes for cemented fixation note location of osteophytes to be removed intraoperatively failure to remove medial osteophytes can cause lateralization of acetabular component evaluate for protrusio acetabuli if present, measure width of protruded medial wall to determine width of medial particulate bone graft needed to fill defect intraoperatively evaluate for hip dysplasia dysplastic hips can have insufficient acetabular coverage and superolateral migration of femoral head if present, measure uncovered anterolateral portion of cup and reproduce during surgery to ensure adequate cup inclination can obtain more coverage intraoperatively by placing cup more proximal or medial, or by using portion of resected femoral head as bone graft template femur assess morphology of femur via radiographic indexes proposed by singh + dorr may influence decision to use cemented vs. cementless stem Dorr classification (based on ratio of inner canal diameter at level of lesser trochanter and 10 cm distal) type A = < 0.5 visible cortices on AP and lateral views no cement indicated type B = 0.5-0.75 thinning of posterior cortex on lateral view no cement indicated type C = > 0.75 thinning of cortices on AP and lateral views cement indicated determine insertion depth with goal of minimizing limb length inequality amount of limb-length change is based on vertical distance between center of rotation of femoral component and center of rotation of acetabular component placing the new femoral head center of rotation superior to the acetabular center of rotation will lengthen the limb commonly determined by line perpendicular to femoral shaft at level of greater trochanter can be unreliable due to relationship with neck-shaft angle if coxa valga, center of rotation is located superior to tip of greater trochanter determine height of femoral head component increased size leads to increased head-neck ratio/jump distance, leading to decreased dislocation determine size of femoral stem component/choose an appropriate sized femoral implant to fill medullary canal if using cementless proximally fitted stem, achieve contact between lateral and medial endosteal cortex if using fully porous-coated stem, achieve endosteal contact in diaphysis if using cemented stem, allow for 2 mm circumferential cement mantle plan location of proximal femoral opening in proximity of piriformis fossa on AP and lateral views too anterior or posterior opening point can cause eccentric reaming and subsequent perforation/fracture and noncircumferential cement mantle restore femoral offset can determine from contralateral hip by measuring distance from cener of rotation of head to tip of greater trochanter increased by medialization of femoral head increased femoral neck length decreased neck-shaft angle trochanteric advancement stem with increased offset mark new center of rotation of femoral head component and angle/level of neck osteotomy note distance from proximal aspect of lesser trochanter to center of rotation of femoral head component note distance from proximal aspect of lesser trochanter to proposed neck cut note width of femoral neck medial to stem to aid in assessing varus/valgus alignment of stem intraoperatively use lesser trochanter for posterior approach use saddle point for anterior approach if using cemented stem, determine optimal diameter of distal centralizer, plug size, and depth of insertion position stem in 10-15° of anteversion THA dislocation Recommended views AP cross-table lateral Findings increased acetabular inclination > 60° increased acetabular anteversion > 20° aceabular retroversion look for eccentric position of femoral head as an indication of polyethylene wear and risk for impending dislocation Treatment criteria nonoperative treatment acceptable in most cases polyethylene exchange if stable well-aligned implants with extensive polyethylene wear thought to be sole reason for dislocation revision arthroplasty if 2 or more dislocations with evidence of implant malalignment vertical acetabular component acetabular retroversion implant failure polyethylene wear conversion to hemiarthroplasty with larger femoral head if soft tissue deficiency or dysfunction contraindicated if acetabular bone is compromised resection arthroplasty if all options have been exhausted significant bone loss and soft tissue deficiency psychiatric patients who are dislocating for secondary gain THA periprosthetic fracture Classification femur intra-op = Vancouver Vancouver Classification & Treatment - Intraoperative Periprosthetic Fracture Type Description Treatment Image A1 Proximal metaphysis, cortical perforation bone graft alone (e.g. from acetabular reaming) A2 Proximal metaphysis, nondisplaced crack cerclage wire before inserting stem(to prevent crack propagation) ignore the fracture if fully porous coated stem is used (provided there is no distal propagation) A3 Proximal metaphysis, displaced unstable fracture fully porous coated stem, or tapered fluted stem provided wires/cables/claw plate for isolated GT fractures B1 Diaphyseal, cortical perforation (usually during cement removal) fully porous coated stem (bypass by 2 cortical diameters) ± strut allograft B2 Diaphyseal, nondisplaced crack (from increased hoop stress during broaching or implant placement) cerclage wire (if implant stable) fully porous coated stem to bypass defect (if implant unstable) ± strut allograft PWB and observation (if detected postop) B3 Diaphyseal, displaced unstable fracture (usually during hip dislocation, cement removal, stem insertion) fully porous coated stem to bypass defect ± strut allograft C1 Distal to stem tip, cortical perforation (during cement removal) morcellized bone graft, fully porous coated stem to bypass defect, strut allograft C2 Distal to stem tip, nondisplaced fracture cerclage wire, strut allograft C3 Distal to stem tip, displaced unstable fracture ORIF post-op = Vancouver Vancouver Classification & Treatment - Postoperative Periprosthetic Fracture Type Description Treatment Image A Fracture in trochanteric region. Commonly associated with osteolysis. AG (greater trochanter) fractures caused by retraction, broaching, actual implant insertion, previous hip screws. Often requires treatment that addresses the osteolysis. AG fractures with <2cm displacement, treat nonoperatively with partial WB and allow fibrous union. AG fractures >2cm needs ORIF (loss of abductor function leads to instability) with trochanteric claw/cables. B1 Fracture around stem or just below it, with a well fixed stem ORIF using cerclage cables and locking plates B2 Fracture around stem or just below it, with a loose stem but good proximal bone stock Revision of the femoral component to a long porous-coated cementless stems and fixation of the fracture fragment. Revision of the acetabular component if indicated B3 Fracture around stem or just below it, with proximal bone that is poor quality or severely comminuted Femoral component revision with proximal femoral allograft or proximal femoral replacement C Fracture occurs well below the prosthesis ORIF with plate- leave the hip and acetabular prosthesis alone Recommended views AP cross-table lateral judet if acetabular fracture full-length femur films to evaluate extent of fracture Findings acetabulum = pelvic discontinuity asymmetrical obturator rings medial migration of inferior hempelvis disruption of Kohler line Treatment criteria acetabulum nonoperative treatment acceptable if stable ORIF vs. revision if unstable femur intra-op fracture stem removal, cabling, and reinsertion if longitudinal calcar split trochanteric fixation with wires, cables, or claw-plate if proximal femur fractures removal of implant with insertion of longer stem prosthesis if complete (two-part) fractures of middle region removal of implant, internal fixation with plate, reinsertion of prosthesis if distal fractures that cannot be bypassed with a long-stemmed prosthesis post-op fracture nonoperative treatment acceptable if non-displaced periprosthetic fractures of greater trochanter non-displaced fractures of lesser trochanter ORIF greater trochanter with wires, cables, or claw-plate if displaced periprosthetic fractures of the greater trochanter ORIF femoral shaft with locking plate and cerclage wires if Vancouver B1 fractures Vancouver C fractures femoral component revision with long-stem prosthesis if Vancouver B2 fractures some Vancouver B3 fractures femoral component revision with proximal femoral allograft if Vancouver B3 fractures in young patients femoral component revision with proximal femoral replacement if Vancouver B3 fractures in elderly, low-demand patients THA aseptic loosening Recommended views AP lateral Findings (xrays are not sensitive for osteolysis and typically underestimate extent of involvement) lucency > 2 mm at cement-bone or metal-bone interface component motion with stress views femoral component subsidence > 1 cm fracture of cement mantle change in peg-neck angle can also represent femoral head necrosis/collapse, femoral neck fracture decreased distance from tip of peg to lateral femoral cortex can also represent femoral head necrosis/collapse narrowing of femoral neck after 3 years or > 10% can also represent impingement acetabular component migration or change in position/inclination wearing of polyethylene liner leads to asymmetric superior location of femoral head within acetabular cup Treatment criteria nonoperative treatment acceptable if stable implant with minimal symptoms revision arthroplasty if pain due to aseptic loosening pain with evidence of osteolysis extensive osteolysis that would compromise revision surgery in the future THA leg length discrepancy Recommended views AP Findings leg length discrepancy insertion depth superior placement of femoral head relative to acetabulum lengthens limb inferior placement of femoral head relative to acetabulum shortens limb increased neck length increasing femoral offset will not increase limb length Treatment criteria nonoperative treatment acceptable in most cases revision arthroplasty if significant LLD that affect quality of life and has not resolved over 6 to 12 months