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Cruciate Ligament Tears
Definition: A partial or complete discontinuity in the connective tissue fibre matrix comprising the cruciate ligament(s).
Causes: Anterior cruciate ligament tears are a common sports injury usually occurring as an athlete rapidly decelerates whilst changing direction.
The occurrence of posterior cruciate tears is less common than their anterior counter-parts. This is due to its shorter length and greater width. The most common cause of posterior cruciate ligament tears result from direct trauma to the anterior aspect of the tibia resulting in its posterior translation about the femur, usually when the knee is bent. Posterior cruciate tears rarely occur in isolation, usually involving the lateral meniscus and collateral ligaments.
Women are particularly susceptible to cruciate tears due to anatomical differences and hormone-related ligamentous laxity coinciding with the menstrual cycle.
Examination: Anterior cruciate tears tend to present as pain in the affected knee with associated instability, and depending on the severity of the tear, ecchymoses, oedema, and heat in the back of the knee. The patient may report hearing a "popping" sound at the time of injury. The mechanism of injury is also important in the diagnosis of anterior cruciate tears. Patients suffering from anterior cruciate tears are usually asymptomatic walking in straight line, but have difficulty managing corners.
Orthopaedic tests for anterior cruciate tears:
Anterior drawer test and Lachman's: with the patient lying supine on the examining table and the involved knee flexed at 90° and the leg internally rotated, passively draw the tibia posteriorly than anteriorly. A posterior cruciate tear can give a false positive for an anterior cruciate tear. This test depends largely on clinical interpretation and one should look out for excessive anterior glide of the tibia on the femur when the anterior cruciate ligament is torn.
Posterior cruciate tears rarely occur in isolation, therefore the menisci, collateral ligaments, and capsule should also be assessed.
Orthopaedic tests for posterior cruciate tears:
Posterior drawer test: with the patient lying supine on the examining table and the involved knee flexed at 90° and the leg internally rotated, passively draw the tibia posteriorly. A positive is indicated when there is excessive posterior draw of the tibia on the femur. An MRI is warranted to check the integrity of the surrounding structures.