Patellar Instability - Kneecap Dislocation 

The kneecap, or patella bone, is the largest sesamoid bone in the human body. A Sesamoid bone is a bone that is embedded in a tendon and functions to modify friction, diminish pressure, and control the direction of muscle pull. The patella sits in a groove in the thigh bone (femur). When the geometry of the groove or how the patella sits is abnormal or a traumatic accident occurs, the patella dislocates and no longer tracks appropriately in the groove. This is referred to as patellar instability.

What Are the Types of Patellar Injuries?

Traumatic Injury

This type of patellar dislocation occurs with an outward twisting force at the knee with the foot planted. This typically occurs during jumping or deceleration and is very common among female soccer players. This type of dislocation usually returns to its original position on its own. The young athlete may experience significant pain and swelling in the front of the knee and difficulty sitting. When they try to walk, they may also experience pain and have feelings of instability or catching.

The Patella Dislocates on Its Own

The patient can have the kneecap slide in and out with knee motion. This may or may not be painful. It is important to have your child see a doctor as soon as possible if your child has painful symptoms. Patellar instability can damage the cartilage of the kneecap and the thighbone and stretch and damage the soft tissue on the medial side of the knee. In the long term, this can lead to early arthritis of the knee joint.

What Are Some of the Signs and Symptoms of Patellar Instability?

• Patella tracks off to the side
• Pain and swelling in the front of the knee
• Popping or creaking sound with knee motion
• Tenderness to palpation along the medial border of the patella
• Stiffness and pain with straightening of the knee

How Is It Diagnosed?

The doctor will perform a thorough history and physical examination. On exam, they will be looking at the rotational profile of the lower extremities, underlying looseness or laxity of the ligaments and muscles, and a focused examination of the knee. Emphasis will also be placed on how the patella tracks during the knee's range of motion.

• Radiographs will also be an essential part of the initial evaluation
• MRI may be ordered after a traumatic dislocation if the knee remains very unstable in range of motion or there is suspicion for an injury to the cartilage of the kneecap or femur that is loose in the joint.

What Are the Treatment Options?

Nonsurgical Treatment:

• If your child’s kneecap dislocates traumatically, they should go to an emergency room (ER) if the knee remains out of place. Most of the time, it will slide back into the groove with little to no assistance.
• If it is still out of place, the doctor in the ER might be able to relocate the kneecap back into its groove. However, if not, they may recommend sedation to help reposition the kneecap.
• After the kneecap is relocated, your child will be placed in a knee immobilizer to keep the knee straight for two weeks.
• For the next two weeks, your child can walk around using the knee immobilizer and crutches. Rest, ice, and elevation of the leg/knee will help reduce pain and swelling.
• At the two-week follow-up, the patient will be examined again and transitioned to a different knee brace that allows greater knee motion.
• Rehabilitation exercises and a visit to physiotherapy will address strengthening the core, hip, and thigh muscles and help regain full knee motion.
• The final steps of the rehabilitation involve more sport-specific training to help with the return to sports. The final return-to-play time depends on progression through the rehabilitation process but is usually around 3 months.
• If the patella remains unstable with motion and continues to slide to the side, or if pain and swelling have not improved, as noted above, an MRI may be ordered to look for damage to the cartilage or soft tissue structures of the knee that occurred from the dislocation.

Surgical Intervention:

• If an MRI shows loose cartilage or tears in the ligament, your child might need surgery to tighten the ligaments and make the area around the knee stronger. Surgery can also be performed to stabilize the damaged cartilage or, if irreparable, to remove it.
• In addition, X-ray and MRI measurements will be used to determine whether additional surgery is necessary to improve the geometry of the patella as it sits in the groove.
• After surgery, your child will probably wear a brace and walk with crutches for six weeks and go to physical therapy.
• The goal is to have the child return to their sport in 4-6 months. This will depend on the type of surgery the patient had to reconstruct/repair the patellar instability.

What Does the Return to Sports Look Like for My Child?

• Usually, you can return to sports after completion of a stepwise rehabilitation program. We recommend using a patellar knee brace for high-impact sports.
• Maintaining strong core strength is essential to minimize recurrent dislocations.