Thinking Cap for the Kneecap - Patella Dislocations

It may seem like a small bone, but it plays a huge role in the functions of the knee. This bone that I talk about is the patella, or more fondly referred to as the knee cap. Nestled at the front of the knee joint, it sits somewhat between the thigh and leg bones.

The patella is enveloped by the tendons that are on the upper and lower parts of it. These tendons are called the quadriceps and patella tendon. Extension or straightening of the knee depends on the proper function of these tendons. The patella enhances this function by increasing the lever arm and thus increasing the vector of pull of the tendons. Put simply, this little bone significantly increases the strength of knee extension. Studies have shown that removing the patella will reduce the strength by up to 30 percent.

One of the more commonly encountered problems with regards to this bone is dislocation of the patella. This can occur as a result of trauma or less commonly as a result of anatomical abnormality of the structures that keep it stable. So, let's take a step back and look at what these structures are.

Starting from the inside, this oval shaped bone glides between a groove formed by the thigh bone in the knee. This valley shaped groove is called the trochlear groove. The trochlear groove is like two mountains, in between which is the valley. And instead of a river running through it (like a scenic painting), it’s the patella that glides between them. However, in certain patients, these mountain-like structures are not formed properly. Because of this, the patella tends to slide outwards and out of position instead of sliding between them like how it’s supposed to.

The next structure is the ligament that holds it in place, called the medial patellofemoral ligament (MPFL). This particular ligament acts as a checkrein to keep the patella in place, similar to checkrein used in horse riding. Running from the  patella on its medial side, injury to it can result in the patella dislocating to the side. The final structure that plays a big role in stabilising the patella are the quadriceps muscles, more specifically a part of the muscle called the vastus medialis obliqus (VMO). This is just a fancy name for the muscle that is just above the patella on its medial side that keeps it in place with muscle tone and during contraction.

As with any other conditions in orthopaedic, diagnosis of patella dislocation can be made clinically based on the history. As mentioned above, patella dislocation can be a result of trauma (like a fall or a sporting injury), or as a result of anatomical abnormalities. In any cases of patella dislocation, the immediate treatment would be to reduce the dislocation or in other words to put it back where it is supposed to be.

Further treatment in terms of surgery depends on many factors. For example, your doctor might ask, how many times have this happened before? This is because in cases of recurrent dislocations, patient will need to be treated operatively. So, this is where this article gets the name of its title form.

Diagnosing a patella dislocation is just the beginning. Being able to identify the root cause of why it's happening is where things get a little bit tricky. By now we already know that there are multiple anatomical structures responsible in maintaining the patella’s position. So how will your doctor find out which structures are causing the problem? This is done through thorough examination of the patient as a whole as well as the affected limb in specific.

One will need to identify, through physical examination, if the patient has generalized laxity of the joints, meaning if he or she is “loose jointed”, to check if the patella is able to be pushed in and out of position and if the patient’s limb is malrotated in any way. This coupled with imaging studies such as Xrays, CT scans and MRI scans will be able to guide the doctor in the direction of the best treatment plan.

Before any surgery is considered, patients should undergo a period of physiotherapy that should focus on strengthening the core as well as the quadriceps muscles and the muscles around the hip. These will help strengthen the muscles that act as dynamic stabilisers of the patella. Surgical treatment on the other hand will aim to correct any anatomical abnormalities detected. This is done by reconstructing the MPFL. In addition to that, further correction of the bony structures around the knee might be necessary.

Apart from patella dislocations, another common condition seen is patellofemoral arthritis. This is a condition whereby the cartilage on the patella is worn down. Although this condition is common in the elderly, it can also be seen in patients in their 30s as well. This is because, like in patella dislocation, anatomical abnormalities might cause the patella to not glide smoothly on the underlying trochlear. This would eventually lead to their cartilage being worn down. Treatment on cartilage defects were covered in my previous article, titled The Slippery Slope.

However, treating the underlying cause of it, as with patella dislocations will require thorough examination and meticulous planning. This is because treating conditions affecting the kneecap very so often requires one to put on the thinking cap.