Version June 2024
| Condition | Mechanism & historical features | Common symptoms | Key examination findings | Additional comments |
| Anterior and medial knee pain | ||||
| Patellofemoral pain | History of overuse, often involving running | Diffuse, anterior peri-patellar pain Knee may feel "unstable" Pain increases with squatting, prolonged sitting, running (especially downhill), climbing or descending stairs | Patellar undersurface may be tender (medial or lateral) Weak terminal knee extension and VMO atrophy common Weak hip flexion, abduction, & external rotation common Hamstring tightness common Patellofemoral compression test may be positive Normal knee motion Effusion rare | PFPS accounts for over 70 percent of outpatient visits for knee pain Structural intra-articular damage must be ruled out if recurrent effusions or unusual findings (eg, abnormal knee motion or laxity detected) present Patient may describe knee weakness (or "giving out"), likely due to reflex inhibition of quadriceps from pain Chondromalacia patella presents with similar history and examination, but advanced imaging reveals pathologic changes |
| Patellar tendinopathy | History of overuse, typically involving sports with jumping or sudden direction change Gradual onset of pain that steadily increases over time if ballistic activity continues | Pain at tendon or inferior pole of patella with ballistic movements (eg, jumping, sprinting, cutting) | Tendon tender at inferior pole of patella (most common), along tendon, or at tibial tuberosity Tendon may feel thick compared to normal (contralateral) one Often associated with tight quadriceps and/or hip flexors Knee motion normal Squat or hop reproduces pain | US shows characteristic changes of tendinopathy Much more common than quadriceps tendinopathy In skeletally immature, consider apophysitis |
| Chronic patella subluxation | History of patella dislocation or hypermobility syndrome | Pain around medial border of patella Knee or knee-cap "gives way" or feels unstable "Clicking" from superolateral part of patella with movement | VMO atrophy and weakness common Patellar apprehension test usually positive | Plain radiographs may show patella alta (high-riding patella) or shallow femoral sulcus |
| Pes anserine tendinopathy and bursitis | Insidious onset of medial-anterior knee pain Associated with repeated valgus strain (eg, breast stroke), genu valgus ("knock knees"), or medial knee instability | Pain around area of pes anserine insertion | Swelling at proximal medial-anterior tibia Area of pes anserine insertion often tender Resisted knee flexion or hip adduction elicits pain | US may reveal characteristic changes of tendinopathy or fluid around bursa |
| Prepatellar or infrapatellar bursitis | Swelling develops over days just inferior to the patella History of continual pressure on affected area (eg, laborer working while kneeling) | Pain and swelling just below patella | Swollen boggy bursa: early swelling below distal patella tendon insertion & around tibial tubercle; gradually swelling increases to cover tubercle & surrounding area Overlying skin erythematous Knee motion normal | Not truly a chronic condition, but does not cause acute onset of pain and not associated with sudden trauma US shows fluid under distal patellar tendon; fluid extends further into soft tissue as swelling increases Aspiration may be needed to rule out septic bursitis |
| Osteoarthritis flare | Generally occurs in adults over 50 years Pain develops with activity; joint stiffness present with inactivity | Delayed swelling (12 to 24 hours post activity) Pain around joint line or diffuse | Effusion Joint line tenderness (may not be prominent) Ligaments stable; meniscus testing negative or equivocal Inability to fully extend or flex knee common | Standing knee x-rays show arthritic changes (eg, sclerosis, joint narrowing) US shows narrow joint, bone spurring, and fluid extending into suprapatellar pouch |
| Degenerative medial meniscus tear | Develops over years and presents in older adults without inciting trauma | Symptoms often mild but may complain of baseline discomfort Pain with pivoting or knee twisting Knee may catch or lock | Medial joint line tenderness Knee motion may not be smooth and range may be limited Provocative tests (eg, Thesaly, McMurray) usually positive Pain increases with deep squat | US may show calcifications, fraying of peripheral meniscus, and cysts in regions of swelling |
| Tibial tuberosity or infrapatellar apophysitis | Common in athletes in early to mid teens whose sports involve cutting and jumping Often occurs during growth spurt while athlete is very active Pain increases with activity and decreases with rest | Pain around tibial tubercle or inferior patellar pole | Tenderness at tibial tubercle or inferior patellar pole Focal swelling & warmth directly over apophysis Knee stable and motion normal | Osgood Schlatter, apophysitis at tibial tubercle, is far more common than Sinding Larsen Johansson, apophysitis at inferior pole of patella Plain x-rays show open apophysis, often with fragmentation US shows open apophysis & fluid over tuberosity |
| Quadriceps tendinopathy | Patient often a runner or active in sport involving jumping or sprinting Pain steadily increases over time if ballistic activity continues | Pain around superior pole of patella with jumping, running, squatting, and other ballistic activities | Focal tenderness between superior patellar border & body of quadriceps Pain with resisted knee flexion Quadriceps and hip flexor tightness may be present VMO atrophy may be present | US often shows characteristic changes to tendon, and bone spurs & calcifications Patellar tendinopathy much more common |
| Medial plica syndrome | History of trauma to medial peripatellar area or dislocation/subluxation of patella Runners with genu valgus ("knock knees") at risk | Pain around medial patella that increases with movement (knee flexion and extension) | Thickened plica palpable under medial patella Patella tracks abnormally during knee flexion-extension Audible pop from medial patella area during flexion-extension | US shows thickened plica |
| Patella stress fracture | History may be unclear Most common in active people training in ballistic sports Athletes who have increased training volume and/or intensity over past weeks to months | Anterior knee pain made worse by activity, particularly ballistic movements (jumping) | Patella tenderness (depends on severity of fracture) Normal knee motion | Fracture may not be apparent in plain radiographs; MRI may be required for diagnosis |
| Lateral and posterior knee pain | ||||
| Iliotibial band syndrome | Insidious onset of lateral knee pain related to overuse Occurs primarily in runners but also in cyclists In runners, pain can vary with pace & increases on sloped surfaces Pain increases over time if activity continues | Pain where ITB crosses lateral femoral condyle Pain increases with prolonged exercise but may persist afterwards | Tender ITB where it crosses lateral femoral condyle Weak hip abduction is common | Generally two patient types: Novice or female runner with weak hip abduction and internal knee rotation (genu valgum) OR Advanced runner with reduced hip adduction and external knee rotation (genu varum) |
| Popliteus tendinopathy | Gradual onset of posterolateral knee pain Often caused by excessive running (especially downhill) or sprinting, also by hiking downhill | Posterior knee pain Pain increases when runner is "braking" or trying to prevent acceleration while running downhill | Tenderness at posterior aspect of lateral femoral condyle (palpate popliteal tendon with patient in figure-of-4 position) Resisted tibial external rotation may elicit pain | US reveals characteristic changes of tendinopathy |
| Biceps femoris (lateral hamstring) tendinopathy | Gradual onset of posterolateral knee pain Often caused by excessive downhill running or sprinting | Posterolateral knee pain around tendon insertion | Tenderness at tendon insertion Pain increases with resisted knee flexion (perform with foot externally rotated) | US reveals characteristic changes of tendinopathy |
| Semimembranosus (medial hamstring) tendinopathy | Gradual onset of posteromedial knee pain Often caused by sprinting or downhill running | Posteromedial knee pain around tendon insertion | Tenderness at tendon insertion Pain increases with resisted knee flexion (perform with foot internally rotated) | US reveals characteristic changes of tendinopathy |
| Semimembranosus-gastrocnemius bursitis | Associated with overuse Pain increases when climbing stairs, running hills, or sprinting | Pain and tightness at proximal medial calf Swelling around posterior knee & proximal calf that increases after activity | Swelling and tenderness at medial-posterior knee Resisted knee flexion and eccentric testing of gastrocnemius (lowering heel while standing on step) may elicit pain | Can be mistaken for joint effusion of deep vein thrombosis US shows enlarged bursa |
| Degenerative lateral meniscus tear | Develops over years and presents in older adults, typically without inciting trauma | Symptoms often mild but may complain of baseline discomfort Pain with pivoting or knee twisting Knee may catch or lock | Lateral joint line tenderness Knee motion may not be smooth and range may be limited Provocative tests (eg, Thesaly, McMurray) usually positive Pain increases with deep squat | US may show calcifications, fraying of peripheral meniscus, and cysts in regions of swelling |
| Popliteal (Baker's) cyst | Damaged protruding posterior knee capsule with many potential causes | Posterior knee pain and tightness | Palpable swollen cystic structure in popliteal fossa | Often associated with intra-articular pathology or knee osteoarthritis If cyst ruptures, knee pain & tightness typically resolve; fluid may track into calf causing swelling US shows compressible fluid-filled mass, typically medial to vascular bundle |
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