Patellar Instability - Kneecap Dislocation 

What is Patellar Instability? 

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 Type 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 with jumping or decelerating and is very common in females playing soccer. This type of dislocation usually goes back in place on its own. The young athlete may experience a lot of pain and swelling in the front of the knee and have difficulty sitting. When they try and walk they may also experience pain and have feelings of instability or catching. 

The Patella dislocates on its own

The patient is able to 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 painful symptoms start. 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. 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, as well as a focused examination of the knee. Emphasis will also be placed on how the patella tracks with range of motion of the knee. 

• 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 on 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, in the ER, the doctor might be able to relocate the kneecap in its groove. However, if not, they may recommend sedation to help put the kneecap back in place. 
• 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 will be transitioned to a different type of knee brace that allows for more motion in the knee. 
• Rehabilitation exercises and a visit to physiotherapy will address strengthening the core, hip and thigh muscles and work on regaining complete motion in the knee. 
• The final steps of the rehabilitation involve more sport specific training to help with return to sports. Final return to play time depends on progression through the rehabilitation process but usually takes 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 a 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 done to stabilize the damaged cartilage or if irreparable, remove it. 
• In addition, measurements taken from xrays and MRI will be used to determine if any other 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 time. This will depend on the type of surgery the patient has to reconstruct/repair the patellar instability. 

Patellar Instability by the Numbers: 

• Patellar instability is one of the most common knee injuries in the pediatric and adolescent patient populations. 
• Incidence of primary patellar dislocation is 5.6 per 100,000 can increase to 29 in the 10 to 17 year old age group 
• Established risk factors for patellar instability are being a young female and having a history of previous patellar dislocation 
• Recurrence rate for dislocation between 15-44% (17% commonly quoted) 
• If there is another subsequent dislocation, rate of recurrence jumps up to 50% for another one. 

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 use of a patellar knee brace for high impact sporting activities. 
• Maintaining good core strength is essential to minimize recurrent dislocations in the future.