The patella is a small bone at the front of the knee that connects the thighbone (femur) to the shin bone (tibia) and helps move the leg. It sits in a groove at the end of the thighbone, called the trochlea and slides up and down with knee movements.
Patellar instability is a complex condition in which the kneecap (patella) does not track properly in the knee joint and can come out of the groove. Patellar instability can occur when the patella tracking is off-center, when the groove is shallow, or when the muscles and ligaments around the knee are not working properly. Patellar instability commonly affects young and active people and eventually progresses to pain, functional decline, and arthritis.
Patellar instability can be caused by a number of factors, including:
- Risk of recurrent patellar instability increases after an initial patellar dislocation or subluxation. A dislocated patella (patellar dislocation) is when the kneecap pops out of the trochlea. A subluxed patella (patellar subluxation) is when the kneecap partially pops out of the trochlea. This can happen due to an acute traumatic injury, such as blow to the knee from a fall or a sudden twisting of the knee with the foot planted during sports like tennis, football, soccer, basketball, and gymnastics. Most dislocations occur in patients aged 10-17 years and in females more than males.
- Naturally loose ligaments. Some patients have generally lax ligaments and connective tissue which gives the kneecap more mobility. These ligaments provide static stability but can predispose these patients to instability.
- Tightness or weakness in the muscles that surround the knee, such as the quadriceps, hamstrings, and/or adductors. Muscles provide dynamic stability by their ability to contract. Thus, the stronger and more conditioned the muscles the more stable the knee cap position and tracking remain.
- Some people have an underlying bony abnormality that predisposes them to patellar instability.
When the patella dislocates or partially dislocates it stretches and tears the ligaments that hold the patella in place. Stretched and torn ligaments allow the kneecap to slip out of its groove. It also usually causes cartilage damage when the patella moves back into its groove. It can also cause fractures.
After a single traumatic dislocation the risk of repeated dislocations increases significantly, especially if the torn ligaments are not surgically repaired. Repeated dislocations and repetitive cartilage damage can cause not only instability but also pain. Chronic knee pain impacts the patient’s ability to participate in every day physical activities.
- A sense of instability in the knee
- Knee pain in the front of the knee
- Swelling and stiffness
- difficulty walking and climbing up or down stairs
- a popping sound as the patella leaves its groove
- knee buckling, catching, or locking
Dr. Patel will review your medical history, ask about your symptoms and history of dislocations, and perform an orthopaedic examination testing your knee bending and straightening. He will order x-rays to view the bones, reveal loose fragments of bone and cartilage in the joint, and rule out fractures. He will also order imaging studies like an MRI and a CT scan to evaluate soft tissue damage and review your kneecap alignment. Cartilage damage is common with a dislocation or subluxation.
Treatment varies based on whether this is your first case of instability, or you have chronic instability and the severity of the damage. Generally, when this is your first dislocation, with no joint damage and no loose bodies, Dr. Patel may recommend conservative treatment including immobilization with a brace, rest, over the counter anti-inflammatory medications, activity modification and physical therapy to restore range of motion and strength. However, the recurrence rate after conservative treatment ranges from 15-44%.
Patellar stabilization surgery is performed to repair the knee joint and help the patella track properly. It will be recommended when conservative treatment fails, when there is cartilage and bone damage with loose bodies, and chronic instability. Loose bodies may be removed with arthroscopic debridement.
There are a number of different surgical procedures that can be performed, depending on the cause of the patellar instability.
The most common type of surgery for patellar instability is surgical reconstruction of the medial patellofemoral ligament which is always torn when the kneecap dislocates. Sometimes the torn ligament may be able to be repaired if this is a first dislocation.
Other types of surgery for patellar instability include:
- Trochleoplasty – This procedure involves reshaping the trochlea to help the patella track properly.
- Tibial Tubercle Transfer – This procedure involves moving the tendon that attaches the patella to the shinbone (tibia) to a new location on the tibia. This helps to realign the knee joint and allow the patella to track properly.
- Osteotomy – This procedure involves cutting and realigning the bones around the knee joint. This helps to realign the joint and allow the patella to track properly.
Patellar instability is a common cause of knee pain and disability. With surgical stabilization and rehabilitation most patients can return to their pre-injury level of activity.
Dr. Ronak M. Patel is a double board-certified orthopaedic surgeon and sports medicine physician trained at Northwestern University and received a fellowship at the Cleveland Clinic. He specializes in the treatment of complex knee, shoulder and elbow injuries and degenerative conditions. Contact him to schedule a consultation to learn more about how he can help you return to the life you love and the activities that make life worth living. He serves teens and adults in Chicagoland and NW Indiana.
At a Glance
Ronak M. Patel M.D.
- Double Board-Certified, Fellowship-Trained Orthopaedic Surgeon
- Past Team Physician to the Cavaliers (NBA), Browns (NFL) and Guardians (MLB)
- Published over 49 publications and 10 book chapters
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