High yield findings High yield findings Finding Importance Segond sign Small lateral tibial avulsion fracture that indicates a ACL tear Reverse Segond sign Small medial tibial avulsion fracture that indicates a PCL tear Arcuate sign Fibular head avulsion fracture that indicates a PLC injury Pellegrini Stieda sign Medial femoral condyle avulsion fracture that indicates a chronic MCL injury Patella alta Patellofemoral pathology Patella baja Arthrofibrosis Fairbanks changes DJD - post meniscectomy (square condyle, peak eminences, ridging, narrowing) Lateral MFC lesion OCD Crescent-shaped MFC lesion Spontanous osteonecrosis of the knee (SONK) Square lateral femoral condyle, cupped lateral tibial plateau Discoid meniscus 3 sagittal MRI images Discoid meniscus Bipartite patella Must differentiate from fracture Radiographic Standard Radiographs Weightbearing preferred for evaluation of joint space 45 degree PA flexion view (Rosenberg view) best for early tibiofemoral arthritis, posterior wear best for early tibiofemoral arthritis, posterior wear best for early tibiofemoral arthritis, posterior wear Merchant or sunrise view to evaluate patellofemoral space, tilt, and alignment best for early tibiofemoral arthritis, posterior wear Stress Radiographs Varus-valgus stress radiographs two diagnostic indications physeal fractures in children MCL / LCL injuries Posterior stress radiographs isolated PCL injury (10-12 mm posterior displacement) PCL and PLC injury (>12 mm posterior displacement) MRI Views sagittal evaluate menisci, cruciates, cartilage, extensor mechanism coronal evaluate menisci, cruciates, collaterals, cartilage axial evaluate patellofemoral joint, cruciates, popliteal fossa Sequences T1 water dark, fat bright best for showing anatomy, but not pathology T2 fat dark, water bright well suited for imaging edema and pathology STIR (Short T1 Inversion Recovery) fat suppression technique improved quality imaging in the presence of orthopedic prostheses Excellent for meniscal injury medial meniscal extrusion >3mm is associated with severe meniscal degeneration, a large meniscal tear, or tear of the root radial meniscal tears are more common in patients following prior meniscal surgery (32% prevalence of radial meniscal tears in post-op knees compared to 14% in patients without prior surgery) 3.0 T MRI has accuracy, sensitivity, and specificity of >90% for detecting medial and lateral meniscus tears ligament tear increased signal intensity, thickening, and cysts within and adjacent to ACL are common findings, and clinically insignificant (no instability) bone bruise near sulcus terminalis osteochondral injury PLC corner injuries can routinely visualize LCL and popliteus tendon with MRI, other structures are more rarely seen edema posterior to popliteus tendon can indicate an injury to the underlying structures of the PLC Ultrasound Excellent for fluid collections useful to evaluate bursae and fluid collections about the knee arthrofibrosis effective in detecting arthrofibrosis of the knee following TKA key findings for arthrofibrosis are synovial thickening and neovascularity