Knee Instability

1. What is a Patellar (kneecap) Dislocation?

A patellar dislocation occurs when the kneecap slips off the end of the femur to the outside of the knee. In this circumstance, the kneecap is “dislocated” and can either slip back in by itself or may require one to straightened one’s knee out and push it back in place or presenting to an emergency room to have it reduced. In general, these knee injuries are significant and need to be assessed as to ones underlying native anatomy and also if there are any fractures of bone cartilage that present with this injury. The most important structure to prevent a kneecap dislocation from happening is called the medial patellofemoral ligament, or MPFL. A tear of the medial patellofemoral ligament can result in recurrent risk of a kneecap dislocation going forward. A complete evaluation is necessary to determine ones risk because ones underlying bony anatomy is a major determinate as to whether one has a chance of having a successful rehabilitation without surgery versus having a lower chance of a successful rehabilitation depending on further patellar dislocation.

2. What is a Patellar Subluxation?

A patellar subluxation occurs when a kneecap slips towards the outside of the knee but does not completely dislocate. In most circumstances, patients have a feeling that the kneecap is slipping out but not completely slipping or dislocating out of the knee joint. This can be quite disabling and repeated episodes of subluxation can also result in cartilage wear and a development of arthritis over time.

3. What is Knee Instability After a Lateral Recess?

A lateral recess is primarily a historical procedure that was performed to try to provide improved stability of the knee or to prevent extra stress in the knee cap which was developing arthritis on the outside part of the kneecap. We have since found out that lateral releases actually increase lateral patellar instability and in some circumstances when they have performed aggressively can result in the knee cap slipping to the inside. Medial patellar instabilities almost always occur after surgery (iatrogenic) and often can be quite disabling. It is very difficult for patients to determine if their kneecap is slipping to the inside or outside and many patients who have medial patellar instability after a lateral recess actually feel that there their kneecap is slipping laterally. Using a program of reverse McConnell taping can help to validate if the kneecap slipping to the inside or outside in these circumstances. In this circumstance, surgery to reverse the lateral release can often be successful.

4. What are the Risk Factors for Repeat Patellar Dislocations?

There are many factors that need to be assessed when one is looking at patellar instability. First, a tear of the ligaments that hold the kneecap towards the inside of the knee, primarily the medial patellofemoral ligament, or MPFL, is important to assess. Other factors are if the patella is high riding, called patella alta, and of the thigh bone, called the trochlea, is flat or is in a more V or U shaped.

A flat trochlea is known as trochlea dysplasia and because the bone is flat there is not much bony inherent stability and these patients have a higher risk of having a patellar dislocation. In addition, if one is knocked knee or in valgus alignment, there is also a higher risk of having the patellar dislocate laterally.

Therefore, all of these factors need to be assessed in determining ones risk of a recurrent lateral patellar dislocation.

In general, the redislocation rate for patients who have normal bony anatomy, indicating the patella is not too high riding, the trochlea is V-shaped rather than relatively flat, and who have neutral or a bowlegged alignment, the risk of redislocation can be less than 10% with a proper rehabilitation program. However, if one does have some patella alta, trochlea dysplasia and/or a knocked knee appearance (valgus alignment), there can be up to a 40% or more rate of kneecap redislocation, even with a well-directed rehabilitation program.

In general, for patients who do not have any significant pieces of cartilage and bone knocked off due to the kneecap dislocation, we would recommend proceeding with a rehabilitation program first, but also recognizing and following  these patients closely who do have underlying bony anatomy which puts them at a higher risk of having the patella redislocate.

5. What is Patellar Taping for Instability?

A program of taping is often useful to determine if the patient is slipping or subluxing laterally with their activities. It can also be used to help hold the patella in a better position to allow ones muscle strength to return back to high levels of function. The program with taping, most commonly McConnell taping, involves taping the patella to pull it towards the inside of the knee. This helps to make up for a stretched out, or deficient, medial patellofemoral ligament (MPFL). A positive response to kneecap taping may indicate that the patella is slipping laterally and that these patients may need a reconstruction of the MPFL, as well as the complete workup to determine if other structures need to be addressed with patellar instability surgery, after an appropriate period of rehabilitation.

In some patients, almost always in those who have had a previous lateral recess, a program of McConnell taping will make their symptoms worse. This is because after the lateral recess they are dislocating their patella medially, and these patients will be indicated for a program of reverse McConnell taping. It is considered a “reverse” of McConnell taping because in most circumstances the patella dislocates laterally and pulling it medial is desired. However, if the patella is dislocating medially after a lateral release, McConnell taping will often make their symptoms worse.

It is unfortunate that many patients that we send for reverse McConnell taping actually undergo McConnell taping because the physical therapist may misinterpret our recommendations, and these patients somewhat validate their pathology because their symptoms become much worse when the patella is pulled further medially. We try to stress with our patients which way the patella should be pulled when they go for a reverse McConnell taping to ensure that there taping program is correct and they obtain a correct diagnosis with this validation of pathology treatment program.

6. What Causes Knee Pain with Patellar Instability?

Unfortunately, it is not uncommon that when one dislocates their patella laterally that when the patella slips back in the joint some of the cartilage on the kneecap can be sheared off, sometimes with bone or sometimes just with the cartilage. In addition, the edge or rim of the trochlea can often have cartilage and/or bone sheared off when the patella dislocates.

Repeated episodes of lateral patellar dislocation can often result in more and more cartilage changes over time. It is important to recognize that if one has been told that they have “chondromalacia” that this is a kind term for arthritis because any damage to the cartilage is a form of arthritis.

Therefore, when one does have problems with pain and swelling with patellar subluxation and dislocation, one has to be concerned that they are having arthritis develop and should be seen sooner rather than later to try to minimize the further progression of this arthritis. Treatment with cartilage surgeries for the kneecap joint are nowhere near as affective as other areas of the knee, so trying to prevent this type of arthritis from progressing is important to ensure that once has good function over their lifetime.