A dislocation of the patella
occurs when the kneecap is pulled out of the groove on the end of the thigh bone. The kneecap is always pulled to the outside of the groove. Once a patella dislocation occurs, it is much more likely to occur again in the future.
Understanding why the kneecap dislocation occurred is the key to determining the appropriate treatment. In some people, the bone alignment or anatomy may be an issue, in others there may be a torn ligament. If it is decided that surgery is the best treatment option, then determining the specific surgery is the most important step to prevent future dislocations.
Traditionally, after a first-time patella dislocation, non-surgical treatment is recommended. Non-surgical treatment usually consists of physical therapy
to strengthen the muscles around the knee as well as the use of a brace to help hold the kneecap in proper position. How effective non-surgical treatment is at preventing future dislocations is debatable, but many doctors feel that it is important to determine if this was a one-time event, or if it is likely to be a recurrent problem. Immediate surgery after a first-time dislocation has not been proven to be beneficial.
Most surgeons agree, if the kneecap dislocates multiple times, then surgery should be considered. When the kneecap dislocates, it is possible to damage the cartilage in the knee, leading to an increased chance of knee arthritis. When multiple dislocations occur, patellar stabilization surgery should be considered.
A lateral release
is the simplest and most commonly performed surgery to address patellar instability. Because the kneecap is being pulled to the outside of the knee, the lateral release cuts the knee joint capsule (retinaculum) on the outside of the knee joint. The idea is to loosen the pull to the outside and hopefully better center the kneecap within the groove on the end of the thigh bone. A lateral release may be performed along with a medial imbrication or MPFL reconstruction (see below).
A medical imbrication is a procedure to tighten the tissue on the inner side of the knee. Just as a lateral release loosens the structures pulling the kneecap to the outside, a medial imbrication tightens the structures on the inner side of the knee. The most common method of tightening the medial side of the knee is to advance the attachment of the quadriceps muscles on the kneecap on the inner side of the knee.
The most modern procedure being performed for patellar dislocation addresses an important ligament called the medial patellofemoral ligament, or MPFL. The MPFL is the tether between the end of the thigh bone (femur) and the inner side of the kneecap (patella). When the kneecap dislocates, the MPFL is always torn.
In acute injuries, it may be possible to repair the MPFL. This is only true in first-time dislocations that are addressed with immediate surgery. Therefore, some surgeons are advocating immediate surgery after an initial patella dislocation to repair the MPFL, despite the fact that this has not been shown to decrease the chance of repeat dislocation.
After repeat dislocations, in order to fix the MPFL, a new ligament must be made. This can be done using a ligament or tendon from elsewhere in your body, or from a donor (cadaver). The new MPFL ligament is created, and attached to the thigh bone and kneecap. This newly reconstructed MPFL then holds the kneecap in proper position.
Bone Realignment/Fulkerson Procedure:
In some patients, their anatomy is abnormal and contributes to the kneecap coming out of joint. The problem may be a shallow groove on the end of the thigh bone, or abnormal alignment of the lower extremity
In these situations, the usual surgery is to change the alignment of the extremity by shifting the position of the tibial tubercle on the shin bone. The tibial tubercle, the bump at the top of the shin bone, is the attachment of the patellar tendon. By moving the position of the tibial tubercle, the patella is pulled more to the inner side of the knee.
There are numerous variations of surgery that accomplish this task. The most common is the so-called Fulkerson procedure, named after the physician that described this technique. There are a number of other similar procedures that also move the position of the tibial tubercle.
Rehab After Surgery:
Rehab after surgery to realign the patella is variable. The least lengthy rehab is with a lateral release, and the longest rehab is with a bone realignment procedure. No matter what the procedure performed, the most common complication after surgery is stiffness of the knee
. Getting normal strength and mobility recovered after surgery can take months or longer.
As mentioned at the outset of this article, the most important step is to determine the best surgery to perform based on each individual situation. Not all kneecap dislocations occur for the same reason, and therefore not all treatments are the same. Seeing a surgeon who is familiar with causes and treatments for kneecap dislocations is important.
While dislocations of the patella can occur after surgery they are much less common. Most patients are able to resume their pre-injury level of activity without having the risk of dislocating their kneecap.
Hing CB, et al. "Surgical versus non-surgical interventions for treating patellar dislocation" Cochrane Database Syst Rev. 2011 Nov 9;11:CD008106.
Andrish J. "The management of recurrent patellar dislocation" Orthop Clin North Am. 2008 Jul;39(3):313-27.