Knee sprains and meniscal injuries

[Michiko]

Sprains of the external (medial and lateral collateral) or internal (anterior and posterior cruciate) ligaments or injuries of the menisci may result from knee trauma. Symptoms include pain, joint effusion, instability (with severe sprains), and locking (with some meniscal injuries). Diagnosis is by physical examination and sometimes MRI. Treatment is PRICE (protection, rest, ice, compression, elevation) and, for severe injuries, casting or surgical repair.
(See also Overview of Sprains and Other Soft-Tissue Injuries.)
Many structures that help stabilize the knee are located mainly outside the joint; they include muscles (eg, quadriceps, hamstrings), their insertions (eg, pes anserinus), and extracapsular ligaments. The lateral collateral ligament is extracapsular; the medial (tibial) collateral ligament has a superficial extracapsular portion and a deep portion that is part of the joint capsule.
Inside the knee, the joint capsule and the posterior and highly vascular anterior cruciate ligaments help stabilize the joint. The medial and lateral menisci are intra-articular cartilaginous structures that act mainly as shock absorbers but provide some stabilization (see figure Ligaments of the knee).
The most commonly injured knee structures are the

Medial collateral ligament
Anterior cruciate ligament

The mechanism of injury predicts the type of injury:

Inward (valgus) force: Usually, the medial collateral ligament, followed by the anterior cruciate ligament, then the medial meniscus (this mechanism is the most common and is usually accompanied by some external rotation and flexion, as when being tackled in football)
Outward (varus) force: Often, the lateral collateral ligament, anterior cruciate ligament, or both (this mechanism is the 2nd most common)
Anterior or posterior forces and hyperextension: Typically, the cruciate ligaments
Weight bearing and rotation at the time of injury: Usually, menisci