The knee joint is where the femur (thighbone) meets the tibia (shinbone), with the patella (kneecap) gliding in a groove at the front. A true knee dislocation is an extremely severe injury defined by the complete separation of the articular surfaces of the tibia and femur. This is distinct from a patellar dislocation, which only involves the kneecap slipping out of its groove. The joint is held together by strong ligaments, and their rupture allows the joint to separate, indicating a high-energy trauma injury.
Recognizable Signs of a Dislocated Knee
The most immediate sign of a tibiofemoral dislocation is a gross, visible deformity of the knee joint. The leg may appear severely misaligned, bent at an unnatural angle, or shortened compared to the uninjured limb. This physical displacement is typically accompanied by a feeling of the joint “giving way” or “popping out” at the moment of injury.
Intense, agonizing pain occurs instantly, often disproportionate to other joint injuries. Rapid swelling follows as internal bleeding and fluid accumulate within the joint capsule. The force required for the bones to separate causes extensive damage to surrounding soft tissues.
An inability to bear any weight on the injured leg is absolute, and any attempt to move the limb is impossible due to mechanical blockage and extreme pain. The knee will feel extremely unstable to the touch, and bruising may develop quickly. Even if the joint spontaneously slips back into place (which occurs in about 50% of cases), severe pain, rapid swelling, and profound instability will persist.
Associated Risks and Medical Urgency
A knee dislocation is a limb-threatening emergency due to the close relationship between the bones and the major vascular and nervous structures passing behind the knee. The most concerning complication is damage to the popliteal artery, the main blood vessel supplying the lower leg. Because the artery is tethered above and below the knee, violent displacement can stretch, tear, or sever it.
Vascular injury to the popliteal artery occurs in 18% to 32% of cases. This damage leads to acute ischemia, or loss of blood flow, which can result in irreversible muscle and nerve death within six to eight hours. Nerve damage is also common, with the common peroneal nerve injured in approximately 25% of dislocations, potentially causing foot drop and loss of sensation.
Immediate Safety Measures Before Professional Help Arrives
The most important immediate action is to call emergency services. While waiting for professional help, the priority is to protect the limb from further damage. Do not attempt to move, manipulate, or straighten the injured leg, and never try to force the joint back into its socket. Such attempts can worsen existing nerve damage or convert a partial arterial tear into a complete transection.
The injured leg must be immobilized exactly in the position in which it was found. Use pillows, rolled towels, or makeshift splints to support the joint above and below the knee. Check for signs of circulation in the foot by assessing the skin’s color and temperature or trying to feel a pulse. If available, ice wrapped in a cloth can be applied to manage swelling, provided it does not interfere with the limb’s supported position.
Professional Treatment and Rehabilitation
Upon arrival at the hospital, diagnostic imaging begins immediately with X-rays to confirm the dislocation and check for associated fractures. Due to the high risk of vascular injury, blood flow is promptly assessed using an ankle-brachial index (ABI) or a vascular study, such as computed tomography angiography (CTA). If vascular injury is suspected, the first acute treatment is closed reduction, where the bones are gently guided back into alignment under sedation or anesthesia.
If the popliteal artery is damaged, emergency vascular surgery must be performed within the six-to-eight-hour window to restore blood flow and prevent amputation. Following reduction and any necessary vascular repair, magnetic resonance imaging (MRI) is used to assess the extent of ligament and soft tissue damage. A true knee dislocation involves multiple torn ligaments, including the anterior and posterior cruciate ligaments, which require subsequent surgical reconstruction to restore joint stability.
The rehabilitation process is extensive and prolonged, starting with immobilization followed by physical therapy focused on restoring range of motion, strength, and stability. Full recovery can take nine to twelve months or longer, depending on the severity of damage to the ligaments, cartilage, nerve, or vascular structures. The goal of rehabilitation is to safely return the patient to full function while minimizing the long-term risk of chronic instability and post-traumatic arthritis.