Version June 2024
| Condition | Mechanism & historical features | Common symptoms | Key examination findings | Additional comments |
| Significant knee swelling | ||||
| Anterior cruciate ligament (ACL) tear | Sudden change in direction or landing from a jump (non-contact injury most common) Audible "pop" at time of injury Rapid swelling | Knee feels unstable Pain variable | Substantial effusion Positive Lachman, anterior drawer, & pivot shift tests | Female athletes at higher risk |
| Large meniscus tear | Sudden, forceful twisting of the knee with foot planted Tearing or popping sensation at time of injury | Knee pain and swelling Knee is popping, locking, catching, not moving properly, or feels unstable Knee may not fully extend & may give way with rotation Pain increases with squatting or pivoting | Substantial effusion Joint line tenderness Loss of smooth passive flexion & extension May not be able to achieve full active flexion or extension Positive McMurray test Positive bounce home test Pain with compression and twisting of knee (eg, positive Thessaly test) | Severity of symptoms & signs varies with extent and location of tear |
| Intra-articular fracture | Large valgus stress on knee, possibly during landing from jump or fall Trauma may be minor in osteoporotic women or elder men Rapid swelling | Knee pain and swelling | Joint line tenderness (usually lateral) Ligamentous instability absent | Lateral tibial plateau most often affected Imaging studies (eg, CT) needed for diagnosis Aspiration fluid may be bloody and contain fat globules |
| Osteochondral defect | Vigorous activity involving sudden change in direction and/or jumping Immediate pain and rapid swelling | Knee pain and swelling (effusion varies with size of defect) | Ligamentous instability absent (distinguishes from ACL injury) | Medial femoral condyle at greatest risk Can occur from direct trauma or overuse |
| Patellar dislocation | Pivoting or sudden change in direction | Knee "out of place" (typically lateral) Many reduce spontaneously prior to presentation | Effusion Patella may be dislocated or subluxed Tenderness often present along medial patellar border | Patients with hypermobility may have recurrent dislocation with milder symptoms and physical findings More common among young females |
| Posterior lateral corner tear | Patients may not recall trauma If recalled, trauma may involve blow to proximal anterior tibia | Posterior knee pain and instability Pain at posterior knee with pivoting | Focal tenderness at posterior lateral corner of knee Positive dial test | May occur with ACL or LCL injury |
| Posterior cruciate ligament (PCL) tear | Direct blow to proximal anterior tibia | Posterior knee pain Instability (may not be present): knee feels like it may hyperextend | Positive sag sign Positive posterior drawer test | History may be unclear: Patient may not associate current symptoms with past trauma |
| Patellar tendon tear | Sudden forceful flexion of a knee already flexed 60 degrees or more | Knee pain and swelling Cannot extend knee | Infrapatellar swelling & ecchymosis Tenderness (and possible tendon defect) at inferior patellar border Painful knee extension with partial tear Unable to extend knee with complete tear | Anabolic steroid use and quinolone antibiotics increase risk |
| Quadriceps tendon tear | Sudden fall backward while foot is fixed and knee flexed; athlete tackled while in this position (American football; rugby) | Anterior knee pain and swelling Cannot extend knee Difficulty bearing weight | Suprapatellar swelling & ecchymosis Tenderness (and possible tendon defect) at superior patellar border Painful knee extension with partial tear Unable to extend knee with complete tear | Uncommon but can occur spontaneously in athletes over 40 |
| Knee (tibiofemoral) dislocation | Typically high energy trauma involving direct blow to anterior knee causing hyperextension Can occur in obese individuals who fall | Knee pain, swelling, and instability May reduce spontaneously prior to presentation | Substantial effusion Ligamentous instability in multiple planes | Dangerous injury that can compromise blood flow to leg |
| Limited knee swelling | ||||
| Small or moderate meniscus tear | Sudden forceful twisting of the knee with foot planted Tearing or popping sensation at time of injury | Knee is popping, locking, catching, not moving properly, or feels unstable Pain increases with squatting or pivoting | Joint line tenderness Positive McMurray test Pain with compression and twisting of knee (eg, positive Thessaly test) | Severity of symptoms & signs varies with extent and location of tear |
| Medial collateral ligament (MCL) strain | Twisting of leg or direct blow to lateral knee creating valgus force | Medial knee pain Medial knee feels unstable with "cutting" or lateral movements | Focal tenderness over MCL Positive valgus stress test | Medial meniscal tear often accompanies MCL tear |
| Lateral collateral ligament (LCL) strain | Twisting of leg or direct blow to medial knee creating varus force | Lateral knee pain Lateral knee feels unstable with "cutting" or lateral movements | Focal tenderness over LCL Positive varus stress test | LCL tear requires greater force than MCL so injuries to cruciate ligaments (ACL, PCL) can occur |
| Patellar subluxation | History as above for patellar dislocation | Anterior knee pain Crepitation along superior lateral corner of patella | Effusion mild or absent Hypermobile patella Apprehension test may be positive | Increased risk with hypermobility syndromes More common with shallow patellar groove |
| Partial ACL tear | History as above for ACL tear | Symptoms as above but generally milder | Ligamentous instability may be mild or absent | |
| Partial PCL tear | History as above for PCL tear | Symptoms as above but generally milder | Ligamentous instability may be mild or absent | |
| Patella fracture | Direct trauma to anterior knee | Anterior knee pain, ecchymosis, and swelling | Focal patella tenderness | Perform plain radiographs including sunrise view Must assess integrity of knee extensor mechanism and PCL |
| Fibular neck or head fracture | Direct trauma to lateral knee, or associated with severe ankle sprain or fracture | Lateral knee pain | Focal tenderness over proximal fibula | |
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