Knee ligament injuries are often the result of rotational movement of the knee joint (e.g., cutting and pivoting movements in sports). Injuries to the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) result in knee pain and instability. Various maneuvers aid in demonstrating knee instability and are usually sufficient for the diagnosis of collateral ligament tears. An MRI is the best confirmatory test for cruciate ligament tears. Isolated ligament injuries are usually treated conservatively, but surgery is recommended for complex injuries, severe knee instability, and patients with physically demanding occupations.
- ACL and PCL connect the femur to the tibia.
- The MCL merges with the joint capsule of the knee.
- The LCL connects the femur and the fibula; It does not merge with the joint capsule of the knee.
Mechanism of injury
- Low-energy noncontact: sports injuries with a twisting mechanism, e.g., football, soccer, basketball, baseball, alpine skiing, and gymnastics 
- High-velocity contact injuries (less common): direct blows to the knee causing forced hyperextension or valgus deformity of the knee
- History: Patients often report a popping sound shortly before the onset of symptoms.
Physical examination findings
- Knee swelling (e.g., due to hemarthrosis), pain, and instability
- Positive Lachman test (most sensitive test)
- Positive anterior drawer test
- Positive pivot shift test
Commonly associated injuries
- Most commonly lateral meniscus damage (often together with acute ACL and MCL injury)
- Unhappy triad: simultaneous injury of the ACL, MCL, and medial meniscus (the medial meniscus is attached to the MCL)
- Conservative treatment: for mild knee instability, less physically demanding occupations, premorbid inactivity, or postoperatively
- Arthroscopic surgery: for multiligament injuries, chronic knee instability, and for highly competitive athletes
- Mechanism of injury
- Initially vague symptoms: minimal (or absent) posterior knee pain, swelling, decreased functional range of motion
- Positive posterior drawer test
- Positive posterior sag sign
- Positive quadriceps active test
- Positive posterolateral drawer test
Collateral ligament injury
|Overview of collateral ligament injuries|
|Medial collateral ligament injury||Lateral collateral ligament injury|
|Mechanism of injury|| || |
|Clinical features|| |
| || |
- Location: knee joint (tibiofemoral articulation)
Mechanism of injury: usually caused by high-energy trauma, e.g., dashboard injury, fall from a height; low-energy trauma possible (especially in obese individuals)
- Anterior dislocation (tibia is anterior to the femur condyles): hyperextension of the knee joint driving the femur posterior to the tibia
- Posterior dislocation (tibia is posterior to the femur condyles): direct impact to the proximal tibia displacing the tibia posterior to the femur
- Medial/lateral dislocation (tibia is medial or lateral to the femur condyles): due to varus or valgus force
- Clinical features
- Immediate evaluation (due to potential severe neurovascular injuries), which includes:
- Reevaluation after immediate treatment, which includes:
Knee dislocations are frequently associated with severe neurovascular injuries and should be treated immediately.