A knee dislocation is a severe injury where the thighbone (femur) and shinbone (tibia) are forced out of alignment. This differs from a dislocated kneecap (patellar dislocation), which only involves the patella. A true knee dislocation is a medical emergency due to potential serious complications.
Immediate Sensations and Signs
When a knee dislocates, an individual experiences immediate, overwhelming pain. This pain is often accompanied by a feeling of the knee “giving out” or “popping out of place.” Many also report hearing an audible “pop” or “snap” at the moment of injury.
The injury typically results in a noticeable visual deformity of the knee. The leg may appear twisted, bent at an unnatural angle, or significantly misshapen. The individual will find it impossible to bear weight on the affected leg or to move it normally.
Accompanying Symptoms and Potential Complications
Beyond initial sensations, a dislocated knee quickly develops significant swelling and bruising around the joint. The knee will feel unstable, making movement excruciating. These injuries can also lead to serious complications involving surrounding structures.
Nerve damage, particularly to the peroneal nerve, may manifest as numbness, tingling, or weakness in the leg or foot below the knee. This type of nerve injury occurs in approximately 10% to 40% of cases. Vascular damage, impacting blood flow to the lower leg, is a critical concern, potentially causing the foot to feel cool or appear pale. Vascular injuries are reported in 5% to 15% of all knee dislocations, though some types may have higher rates, up to 40%.
Immediate Actions and Medical Care
If a knee dislocation is suspected, do not attempt to move the joint or force it back into place. Manipulating the knee without proper medical knowledge can cause additional damage to nerves, blood vessels, or surrounding tissues. Instead, call emergency services immediately.
Medical assessment begins with a physical examination and a detailed account of the injury. Imaging tests confirm the diagnosis and evaluate damage.
X-rays confirm dislocation and identify any associated fractures, while an MRI provides detailed images of soft tissues like ligaments and cartilage. A CT angiography may also assess for blood vessel damage. Initial medical treatment involves carefully repositioning the joint, often under sedation, and managing pain. Hospital admission is often necessary for close monitoring of vascular status.
Causes and Risk Factors
Knee dislocations primarily result from high-energy traumatic events. Common causes include motor vehicle accidents, significant falls from heights, or direct, forceful blows to the knee. These forces disrupt the ligamentous structures that stabilize the knee joint.
Sports injuries, particularly those involving high-impact collisions or extreme twisting motions, can also lead to knee dislocations. Less commonly, knee dislocations can occur from lower-energy mechanisms in individuals with pre-existing conditions like extreme ligamentous laxity or morbid obesity. However, it remains an injury associated with significant trauma.