A true knee dislocation, also known as a tibiofemoral dislocation, involves the complete separation of the shin bone (tibia) from the thigh bone (femur) at the knee joint. This injury is uncommon, occurring in about 1 per 100,000 people per year, and is considered a medical emergency due to its potential for severe complications. It results from significant trauma, such as a high-speed car accident, a fall from a height, or a severe sports injury. Approximately half of these dislocations may spontaneously reduce before medical attention is sought.
Identifying Visual Signs
A dislocated knee presents with a profound visual deformity. The leg will appear noticeably misaligned or “crooked,” disrupting the normal knee joint shape. This can include the leg appearing shorter or longer than the uninjured limb, depending on the direction of the displacement. You might observe an abnormal prominence or a “dent” where the bones have shifted out of place.
Rapid, significant swelling around the joint is common, often developing quickly due to internal bleeding. Bruising or discoloration may also appear rapidly. Even if the joint spontaneously returns to its normal position, swelling and bruising can still be present, indicating the underlying injury.
Accompanying Symptoms
Beyond the visible changes, a dislocated knee is accompanied by immediate, excruciating pain. This intense pain makes weight-bearing impossible. Movement of the knee or leg may be severely limited or entirely impossible, sometimes presenting as an abnormal floppiness of the limb.
Numbness, tingling, or coolness in the foot or lower leg are critical warning signs. These symptoms indicate potential damage to nerves or blood vessels, serious complications of knee dislocations. Weakness in the foot or ankle may also occur, indicating nerve involvement.
Immediate Actions to Take
If a true knee dislocation is suspected, call emergency services immediately. Prompt medical attention is necessary due to the risk of significant complications. Do not attempt to move or straighten the injured leg.
Trying to force the knee back into place can cause further damage to surrounding tissues, blood vessels, or nerves. The individual should be kept as still and comfortable as possible while waiting for medical help to arrive. If feasible, the injured leg can be gently supported without any attempt to reposition it. Inform emergency responders of any numbness, tingling, or changes in foot color or temperature, as these details are important for assessing potential vascular or nerve damage.
Understanding the Distinction
Differentiating between a true knee (tibiofemoral) dislocation and a patellar (kneecap) dislocation is important, as they are often confused. A true knee dislocation involves the main bones of the leg, the femur and tibia, separating at the knee joint. This injury is a medical emergency due to the high risk of damage to blood vessels and nerves.
In contrast, a patellar dislocation occurs when only the kneecap (patella) slips out of its groove, typically to the side of the knee. While painful and requiring medical attention, a patellar dislocation generally does not carry the same immediate limb-threatening risks of vascular or nerve damage as a true knee dislocation. A dislocated kneecap might appear as a visible bump on the side of the knee where the kneecap has shifted. It is a more common injury and often has a less complex recovery than a true knee dislocation.