Knee dislocation
A knee dislocation is an injury in which there is disruption of the knee joint between the tibia and the femur. Symptoms include pain and instability of the knee. Complications may include injury to an artery, most commonly the popliteal artery behind the knee, or compartment syndrome. About half of cases are the result of major trauma and about half as a result of minor trauma. About 50% of the time, the joint spontaneously reduces before arrival at hospital. Typically there is a tear of the anterior cruciate ligament, posterior cruciate ligament, and either the medial collateral ligament or lateral collateral ligament. If the ankle–brachial pressure index is less than 0.9, CT angiography is recommended to detect blood vessel injury. Otherwise repeated physical exams may be sufficient. More recently, the FAST-D protocol, assessing the posterior tibial and dorsalis pedis arteries for a ‘tri-phasic wave pattern’ with ultrasound, has been shown to be reliable in ruling out significant arterial injury. If the joint remains dislocated, reduction and splinting is indicated; this is typically carried out under procedural sedation. If signs of arterial injury are present, immediate surgery is generally recommended. Multiple surgeries may be required. In just over 10% of cases, an amputation of part of the leg is required. Knee dislocations are rare, occurring in about 1 per 100,000 people per year. Males are more often affected than females. Younger adults are most often affected. Descriptions of this injury date back to at least 20 BC by Meges of Sidon. Signs and symptoms Symptoms include knee pain. The joint may also have lost its normal shape and contour. A joint effusion may, or may not, be present. Complications Complications may include injury to the artery behind the knee (popliteal artery) in about 20% of cases or compartment syndrome. Damage to the common peroneal nerve or tibial nerve may also occur. Nerve problems, if they occur, often persist to a variable degree. Cause About half are the result of major trauma, the other half as a result of minor trauma. Major trauma may include mechanisms such as falls from a significant height, motor vehicle collisions, or a pedestrian being hit by a motor vehicle. Cases due to major trauma often have other injuries. Minor trauma may include tripping while walking or while playing sports. Risk factors include obesity. The condition may also occur in a number of genetic disorders such as Ellis–van Creveld syndrome, Larsen syndrome, and Ehlers–Danlos syndrome. Diagnosis As the injury may have self-reduced before arrival at hospital, the diagnosis may not be readily apparent. Diagnosis may be suspected based on the history of the injury and physical examination which may include anterior drawer test, valgus stress test, varus stress test, and posterior sag test. An accurate physical exam can be difficult due to pain. Plain X-rays, CT scan, ultrasonography, or MRI may help with the diagnosis. Findings on X-ray that may be useful among those who have already reduced include a variable joint space, subluxation of the joint,