NORMAL ANATOMY Osteology Distal femur anterior/posterior view lateral view Proximal tibia anterior/posterior view Patella anterior/posterior view Attachments Muscle anterior view posterior view lateral view Ligament/tendon anterior/posterior view lateral view RADIOGRAPHIC VIEWS AP/PA View Positioning patient supine (AP) vs. prone (PA) knee extended + leg IR 3-5° beam aim 1.5cm distal to apex of patella Indications fracture joint alignment OA PA view preferred over AP view weightbearing view preferred over non-weightbearing view Critique symmetrical femoral + tibial condyles fibular head should be bisected by the tibia visualization of intercondylar eminence in intercondylar fossa Weightbearing AP/PA (Rosenberg) view Positioning patient AP = erect + knees extended PA/Rosenberg = erect + knees flexed 45° beam obtain bilateral knees aim 1.5cm distal to apex of patella Indications OA = PA/Rosenberg view preferred over AP view to detect joint space narrowing given typical location of cartilage wear Critique equal distribution of body weight on both feet symmetrical femoral + tibial condyles patella centralized (rotational guide) visualization of intercondylar eminence in intercondylar fossa Full-length weightbearing AP (PCA) view Positioning patient erect knees extended + 18" apart beam obtain 3 films of bilateral lower extremities then splice together for hip/femur film, aim between ASIS + symphysis pubis for knee film, aim 1.5cm distal to apex of patella for tib-fib/ankle film, aim at mid-tibiotalar joint Indications OA = pre-op planning tip: if obtained, don't forget to check for hip OA even if complaining of just knee pain Deformity quantification Leg length measurement Critique equal distribution of body weight on both feet patella facing directly anterior knee flexion contractures can effect quality and accuracy of measurements Lateral View Positioning patient rolled lateral (mediolateral) = lateral decubitus on ipsilateral side + knee flexed 20-30° horizontal ray (lateromedial) = supine + knee extended beam aim 2.5cm distal to medial epicondyle tilt 5-7° cephalad (if rolled lateral) Indications fracture OA patella fracture = horizontal ray view to avoid displacement patella alta/baja = requires knee in 30° flexion trochlear dysplasia joint effusion Critique visualization of suprapatellar fat pad = via knee flexion < 30° appropriate IR/ER superimposition of posterior aspect of femoral condyles superimposition of fibular head + tibia open patellofemoral joint no visualization of adductor tubercle appropriate cephalad angulation = open tibiofemoral joint Oblique View Positioning patient AP = supine + knee extended + leg IR/ER 45° PA = prone + knee flexed 10° + leg IR/ER 45° beam aim 1.5cm distal to apex of patella Indications fracture = femoral condyle, patella OA intercondylar fossa pathology = loose bodies OCD lesions Critique superimposition of patella + ipsilateral femoral condyle asymmetrical tibiofemoral joint spaces Tangential View Positioning METHOD PATIENT BEAM Sunrise/Settegast supine vs. prone knee flexed 90° inf-sup 10-20° cephalad Hughston prone knee flexed 50-60° inf-sup 45° cephalad Merchant supine knee flexed 40° sup-inf 30° caudad Laurine semi-recumbent knee flexed 30° inf-sup 30° cephalad Indications patellar malalignment or tilt trochlear groove depth OA vertical patella fracture Critique visualization of femoral condyles + trochlear groove no superimposition of patella + femur open patellofemoral joint Intercondylar View Positioning METHOD PATIENT BEAM Beclere supine knee flexed 40° AP 40° cephalad Camp Coventry/Tunnel prone knee flexed 40° PA 40° caudad Holmblad erect vs. kneeling knee flexed 70° PA 0° Indications OCD = displaced cartilage congenital slipped patella = flattening/underdevelopment of lateral femoral condyle hemophilia = intercondylar widening intercondylar fossa pathology = loose bodies Critique superimposition of patella + ipsilateral femoral condyle asymmetrical tibiofemoral joint spaces NORMAL FINDINGS Normal anatomy Normal variants fabella sesamoid bone in lateral head of gastrocnemius best seen on lateral view cyamella sesamoid bone in popliteus tendon usually present in lateral aspect of distal femur in popliteal groove best seen on AP view cortical desmoid cortical lucency in posteromedial aspect of distal femur represents origin of medial head of gastrocnemius + insertion of adductor magnus seen in adolescents (10-15 yo) bipartite/tripartite patella usually superolateral with smooth margins CLINICAL PEARLS Knee OA Classification = Kellgren & Lawrence Kellgren & Lawrence (based on AP weightbearing XRs) Grade 0 • no joint space narrowing (JSN) or reactive changes Grade 1 • possible osteophytic lipping + doubtful JSN Grade 2 • definite osteophytes + possible JSN Grade 3 • moderate osteophytes + definite JSN + some sclerosis + possible bone end deformity Grade 4 • large osteophytes + marked JSN + severe sclerosis + definite bone end deformity Recommended views weightbearing AP weightbearing lateral semi-flexed 45° PA most sensitive for early joint space narrowing (JSN) tangential Findings joint space narrowing (JSN) osteophytes eburnation of bone subchondral sclerosis/cysts TKA templating AP/PA view for true assessment, need full-length scanogram view (can be fooled by standard AP/PA view) assess mechanical axis of limb line from the center of femoral head to center of talus neutral = bisects knee varus = passes medial to center of knee valgus = passes lateral to center of knee important because restoration of neutral axis distributes weight-bearing loads equally to minimize risk of implant wear + aseptic loosening determine extent of coronal deformity tibiofemoral angle angle between AAF + AAT normal 7° ± 1° valgus hip-knee-ankle angle angle between MAF + MAT normal 0° determine femoral resection angle MAF – AAF normal varies by individual important because >7° valgus leads to increased Q angle, which can lead to patellofemoral maltracking determine tibial bone cut line perpendicular to MAT thickness of cut is determined by thickness of the tibial components important to place cut at level of pre-arthritic tibial plateau because: elevating joint line > 8mm --> mid-flexion instability, patellofemoral maltracking, pseudopatella baja leading to increased force at patellofemoral joint + extensor mechanism dysfunction lowering joint line --> flexion instability, extension lag, patellar subluxation, retropatellar pain Lateral view determine tibial slope angle between line along articular surface of tibia + line perpendicular to anterior cortex of tibia normal 5-15° in cruciate retaining knee typically maintain close to native slope (~5-7°) too much slope can lead to flexion/AP instability too little slope can lead to overstuffing of the flexion gap and limited ROM if using PS implant aim for 0-3° slope less slope needed as removal of the PCL opens the flexion gap avoid CAM/post impingement assess for presence of patella baja requires lateral XR with knee in 30° flexion calculate Insall-Salvati ratio ratio of patellar tendon length to patellar bone length patella baja if < 0.8 important because presence of patella baja can make exposure more difficult and cause decreased ROM due to impingement assess for history of patellectomy important because can lead to loss of extension strength and overload PCL consider using PS or dished CR implant for optimal outcomes Sunrise/Tangetial view determine patellar shift distance between apex of lateral femoral condyle + lateral edge of patella normal 0mm determine patellar tilt angle between line drawn along femoral condyles + lateral facet of patella normal > 12° TKA periprosthetic fracture Classification distal femur Lewis & Rorabeck Lewis and Rorabeck Classification (1997) Type I Nondisplaced; component intact Type II Displaced: component intact Type III Displaced; component loose or failing Su Su and Associates' Classification of Supracondylar Fractures of the Distal Femur Type I Fracture is proximal to the femoral component Type II Fracture originates at the proximal aspect of the femoral component and extends proximally Type III Any part of the fracture line is distal to the upper edge of anterior flange of the femoral component proximal tibia = Felix Felix and Associates' Classification of Periprosthetic Fractures of the Tibia Associated with TKA Type I Fracture of tibial plateau Type II Fracture adjacent to tibial stem Type III Fracture of tibial shaft, distal to component Type IV Fracture of tibial tubercle patella = Goldberg Goldberg Classification Type I Fracture not involving implant/cement interface or quadriceps mechanism Type II Fracture involving implant/cement interface and/or quadriceps mechanism Type III Type A: inferior pole fracture with patellar ligament ruptureType B: inferior pole fracture without patellar ligament rupture Type IV All types with fracture dislocations Recommended views AP lateral consider CT scan for better delineation of fracture pattern and proximity to implant Treatment criteria distal femur nonoperative treatment acceptable if nondisplaced fractures with stable prosthesis retrograde IMN if intact/stable prosthesis with open-box design to accommodate nail fracture proximal to femoral component (Su Type I) fracture that originates at the proximal femoral component and extends proximally (Su Type II) ORIF with fixed angle device if intact/stable prosthesis Lewis-Rorabeck II or Su Types I or II (described above) unable to accommodate intramedullary device fracture distal to flange of anterior femoral component (Su Type III) revision to long stem prosthesis if loose femoral component Lewis-Rorabeck III or Su Type III (described above) with poor bone stock distal femoral replacement if elderly patients with loose (Su type III) or malpositioned components and poor bone stock proximal tibia nonoperative treatment acceptable if nondisplaced fracture with stable prosthesis ORIF if unstable fracture with stable prosthesis long-stem revision prosthesis if displaced fractures with loose tibial component patella nonoperative treatment acceptable if stable implants with intact extensor mechanism non-displaced fractures ORIF vs. revision arthroplasty vs. patellectomy if loose patellar component extensor mechanism disruption TKA aseptic loosening Recommended views AP tibial osteolysis readily visible on AP femoral osteolysis may be difficult to detect on AP as lesions are typically located in posterior condyles and are obscured by the femoral component lateral helpful for identifying femoral osteolysis good quality lateral view is critical oblique often more helpful for identifying femoral osteolysis Findings radiolucent area around implant or cement with sclerotic border especially radiolucencies > 2 mm change in position of the implant varus or valgus subsidence of tibial component progressive widening of cement-bone or bone-prosthesis interface cement cracking or fragmentation Treatment criteria nonoperative treatment acceptable if stable implant with minimal symptoms revision TKA if pain due to aseptic loosening pain with evidence of osteolysis extensive osteolysis that would compromise revision surgery in the future TKA instability Classification extension = varus/valgus instability flexion = AP, occurs when the flexion gap exceeds the extension gap mid-flexion = malrotation when the knee is flexed between 45 and 90 degrees global = laxity of both flexion and extension gaps, as well as varus/valgus instability genu recurvatum = fixed valgus deformity and iliotibial band contracture Recommended views weightbearing AP used to assess joint line symmetry full-length AP used to assess overall mechanical alignment lateral used to assess femoral component sizing (assess posterior condylar offset compared to native), tibial slope, tibial subluxation, recurvatum flexion lateral can often see paradoxical rollback in PCL incompetent CR knees Findings extension instability excessive distal femoral resection oversized femoral component reverse tibial slope flexion instability overresection of posterior femoral condyles undersized femoral component increased tibial slope mid-flexion instability anterior or proximal placement of femoral component (look at the joint line to fibular head distance for evidence of joint line elevation) genu recurvatum TKA patellar maltracking Recommended views AP used to assess placement of femoral component and Q angle lateral used to assess femoral component anterior offset (overstuffing) tangential used to assess subluxation of patella, placement of patellar component, angle of patellar resection, and patellar tilt Findings laterally subluxed patella increased Q angle anterior placement of femoral component asymmetric patellar resection lateral placement of patellar component lateral osteophyte on patella TKA patellar prosthesis loosening Recommended views lateral tangential Findings loss of radiolucent space in patellofemoral joint with contact between patella bone and femoral component seen on lateral view dissociated patellar component patellar component adjacent/superficial to patella seen on lateral and tangential views thinning of polyethylene seen on tangential view TKA heterotopic ossification Classification = Furia & Pelligrini class I = island of bone localized to suprapatellar soft tissues class II = bone organized into areas of ossification contiguous with the anterior distal femur grade A = ≤ 5 cm grade B = > 5 cm Recommended views AP lateral Findings ossification along anterior distal aspect of femur and within quadriceps mechanism typically visible 3-4 weeks post-operatively and matures within 1-2 years Treatment criteria nonoperative treatment acceptable in most cases excision if quadriceps muscle snapping patellofemoral tracking difficulties patellofemoral instability