Knee Dislocation

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Physical Therapy Videos - Knee

Basic Anatomy

Your knee is a joint located between your femur (thigh) bone and your tibia (lower leg) bone. Your knee joint includes a bone called the patella (kneecap). The ends of your bones are covered with a smooth surface called articular cartilage. This cartilage cushions your knee joint and lets you bend your knee. The strong muscles in the front of your thigh (quadriceps) and the back of your thigh (hamstrings) give you the power to bend and straighten your knee. Your knee also has many ligaments that connect one bone to another bone. These include the ACL (anterior cruciate ligament), PCL (posterior cruciate ligament), MCL (medial collateral ligament) and LCL (lateral collateral ligament). These ligaments help hold your bones together as you bend and straighten your knee. They can be injured during sports or other activities.

A knee dislocation is when your tibia moves away from your femur so that the bones are no longer in contact. Your bones no longer line up with each other correctly. This is different from when the patella dislocates. After a patella dislocation, the tibia and femur still line up correctly, but the kneecap is out of joint. Patella dislocations are more common than knee dislocations.

X-rays of a normal knee.
Figure 1: X-rays of a normal knee.

 

X-ray showing the locations of the various ligaments in the knee: MCL, ACL, PCL, and LCL.
Figure 2: X-ray showing the locations of the various ligaments in the knee: MCL, ACL, PCL, and LCL.

 

Model views of the knee from the front and the side.
Figure 3: Model views of the knee from the front and the side.

Mechanism and Epidemiology

Knee dislocations are uncommon. They can result from a high-energy event like a car or motorcycle collision, or from a low impact twisting event, such as walking down a slippery driveway and twisting your leg. Low-energy knee dislocations are more common in overweight patients. With either type, there is a tear in the ligaments in your knee, which allows the bones to separate and become “dislocated” (not lined up correctly) from each other. Dislocations can happen in many different directions: your tibia can move to the front, back or either side of your femur. The direction the tibia dislocates can indicate what ligaments may be injured.

X-ray of a knee dislocation in which the tibia is in front of the femur.
Figure 4: X-ray of a knee dislocation in which the tibia is in front of the femur.

 

X-rays of a knee dislocation in which the tibia has dislocated to the side of the femur.
Figure 5: X-rays of a knee dislocation in which the tibia has dislocated to the side of the femur.

 

X-ray of a patellar dislocation. The red arrow points to the patella. It has dislocated laterally (toward the outside of the leg). This is the most common way patellas dislocate. This is not the same as a knee dislocation.
Figure 6: X-ray of a patellar dislocation. The red arrow points to the patella. It has dislocated laterally (toward the outside of the leg). This is the most common way patellas dislocate. This is not the same as a knee dislocation.

Initial Treatment

Knee dislocations are painful and make it difficult to move your knee. Knee dislocations require a visit to an emergency room, where a healthcare provider will check the blood supply and nerve function of your leg. X-rays or other imaging scans will be taken. A reduction (putting the bones back in the correct place) may be done in the emergency room, or if necessary, the operating room.

It is common to have an injury to your nerves or blood vessels after a knee dislocation. If there is concern for an injury to the blood vessels of the leg, your doctor may request further tests, including scans in which dye is injected into the blood vessels. The dye will show if there is a tear. If you have damaged the blood supply to your leg, you may require an emergency operation to restore your blood supply. An orthopaedic surgeon and a vascular surgeon may need to work together to realign your leg and repair your damaged blood vessels.

After your bones are put back in position, you may have to wear a brace that keeps your knee in the right place. If your knee is unstable (loose) and will not stay in place, you may need to have an external fixator instead of a brace. This requires a surgery to put pins into your femur and tibia bones. The pins stick out of the skin and are connected by bars and clamps that hold the bones in the right position.

After a knee dislocation, you will be watched for a condition called compartment syndrome. This is when the swelling or pressure in your leg gets so high that your muscles are not getting enough blood flow. You may have a pressure monitor placed in the emergency room or after surgery to determine the health of the muscles in your leg. Compartment syndrome may require surgery to make cuts in your leg to release the pressure. Later, you will need more operations to repair the cuts in your leg.

Patient with an external fixator bridging the knee.
Patient with an external fixator bridging the knee.
Figures 7-8: Two different patients with an external fixator bridging the knee.

General Treatment

Knee dislocations are typically treated one of two ways. The first is to keep your knee from bending for a while. You will not be allowed to put weight on your leg, and your knee with be kept in the correct position using either a brace or an external fixator. This lets your ligaments and other soft tissues to heal on their own. The second way is to have your knee ligaments surgically repaired and/or replaced. This surgery is commonly done by an orthopaedic surgeon who a specializes in knee ligament injuries (usually an orthopaedic “sports” surgeon).
 

X-rays of a knee that was dislocated and had the ligaments repaired. The different screws and small plates all represent areas where ligaments were repaired.
Figure 9: X-rays of a knee that was dislocated and had the ligaments repaired. The different screws and small plates all represent areas where ligaments were repaired.

Post-Operative Care

The amount of time you need to be in a brace or external fixator will be determined by your orthopaedic surgeon. A brace or external fixator may be kept in place for several months. You may need another operation to remove the external fixator, check the stability of your knee, and/or manipulate your knee to regain motion. You will likely need physical therapy to help you move your knee. Since your knee has not moved for some time, it will be stiff and your muscles will be weak. Therapy can be hard and may take a long time to complete.

If you have your knee ligaments fixed or replaced, your surgeon will have a detailed plan for what you can do in the weeks and months after. You will likely need a long course of therapy to help your recovery.

Long Term

Recovering after a knee dislocation is a long process that can be difficult. Generally, your affected knee will be stiffer and weaker than your other knee. You may also develop arthritis in that knee. If you had damage to a nerve, using your leg may be more difficult. Unfortunately, if you injured the nerves that work the muscles of your foot, they may or may not heal fully. Braces or shoes that keep your foot from dragging on the ground may be needed. If you injured the blood vessels to your leg, it could lead to long-term problems with blood flow to that area. Injuries to a leg that limit movement or the ability to bear weight may put you at risk for blood clots. This may require use of medication to try to decrease your chances of developing a blood a clot. It is very important to follow the instructions of your treating orthopaedic surgeon to help prevent complications.

Occasionally, the damage to blood vessels and/or nerves after a knee dislocation is so bad that your leg may not be able to be saved, requiring an amputation.

Physical Therapy Videos - Knee

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Christopher Domes, MD
Edited by the OTA Patient Education Committee
All x-rays and pictures taken from the personal collections of Dr. Domes, Lisa Taitsman, MD, MPH, and Gerald Lang, MD