Patella Instability
Patella instability refers to a spectrum of symptoms relating to the instability of the kneecap joint. There are a large variety of symptoms that are experienced with this condition and include the feeling of the knee cap wanting to move too far laterally, but not completely out of joint (subluxation), all the way to having a complete kneecap dislocation. When complete kneecap dislocation occurs more than once in the same knee is it referred to as Episodic Patella Instability (EPI). After one patella dislocation, the chance of EPI occurring can be as high as 70%.
EPI can cause significant short and long-term problems to the knee. In the short term, recurrent dislocations cause pain and prolonged rehabilitation once the patella is reduced. The dislocation itself often leads to rupture of the Medial Patellofemoral Ligament (MPFL) and may be associated with damage to the knee cartilage in up to 90% of cases. The MPFL acts as a restraint to patella dislocations, so if it is torn during the first dislocation, it is often a factor contributing to EPI. In the long term if EPI is left untreated, it is often associated with the progression of arthritis within the patellofemoral compartment of the knee.
There are multiple contributing factors to EPI. The shape of the patellofemoral joint and especially how the patella and femur match up with each other is the issue in most patients.
The most common anatomical problem observed is related to the groove on the end of the femur, where the patella is supposed to articulate. When this groove (trochlea) is misshapen it is called trochlea dysplasia (TD). TD has varying degrees of severity, ranging from flattening of the groove all the way to having a bump or convex surface rather than a groove. TD is mild in most patients with EPD and it occurs in up to 96% of patients with EPI compared to 3% of patients without EPI.
Other common causes of EPI include the patella being positioned too high above the trochlea (patella alta) and malalignment of the lower limb. Often there is more than one anatomical cause, and there is usually associated poor function of the injured MPFL.
The diagnosis as to which factors are involved in EPI are incredibly variable, and are assessed by physical examination and medical imaging. The latter usually involved plain x-rays and an MRI. Based on the analysis of your physical examination and medical imaging you will then be able to discuss the options available to you for treatment.
Initial non surgical treatment in the form of physiotherapy is usually the first step in recovery from a patella dislocation. Ongoing non-surgical treatment is usually prescribed when there has been only one patella dislocation without an anatomical cause. Physiotherapy is very useful in this scenario to strengthen the weakened quadriceps muscles, in particular vastus medialis obliquus (VMO). Other treatment instituted may include stretching exercises for the lateral soft tissues around the knee as well as patella taping and bracing.
Surgical treatment is usually recommended when non surgical treatment has been exhausted or when there is a cartilage injury that needs surgical intervention with a primary patella dislocation. Surgical treatment aims to correct the various anatomical factors leading to the patella dislocation. Multiple factors can be addressed during the one operation.