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Is MPFL surgery necessary for a dislocated kneecap?

A kneecap which keeps dislocating can cause significant problemsMPFL surgery (medial patellofemoral ligament surgery) is an operation performed for a dislocating or unstable kneecap (patella). Other terms are kneecap instability, patellar instability, patellar subluxation and recurrent patellar dislocation. I often see patients who have dislocated their kneecap. One episode may not mean surgery. A complete assessment is needed to recommend correct treatment…

What causes a kneecap dislocation?

MPFL surgery is used for patellar dislocationsThe MPFL is a ligament which helps to keep the kneecap in place. It works when the knee is bending and straightening. The MPFL attaches between the kneecap and the inner side of the end of the thigh bone (femur). If you have a patellar dislocation, this usually results in a tear of the MPFL. The MPFL may heal after such an injury. If this is the case then you may not have any further patellar dislocations. If, however you have a second dislocation, it usually means that the MPFL did not heal. Further dislocations are therefore highly likely.

Besides the MPFL, there are anatomical factors which can make a patellar dislocation more likely. The groove in which the patellar runs during flexion of the knee is called the trochlea. An abnormally shaped or flattened trochlea is called trochlear dysplasia. People who have this are more prone to dislocation. Normally the patella is located at a specific height relative to the knee joint. In some people the patella is slightly higher than normal. This is called patella alta. This also increases the risk of a dislocation. Small rotational and angulation differences in the lower limbs may also predispose to instability and dislocation.

If you have one kneecap dislocation, surgery is usually not necessary. The exception is if the dislocation resulted in loose cartilage or bone in the knee joint. This should then be removed. If the kneecap has dislocated more than once then surgery is recommended. Surgery may also be recommended if the kneecap has dislocated only one time but there are additional risk factors. These risk factors include trochlear dysplasia or patella alta as described above.

What does a torn MPFL feel like?

If the MPFL is torn the kneecap many become unstable. It may feel as if the kneecap is coming out of place from time to time. This is called subluxation. This can occur with activities such as dancing. It can also occur with any activity which involves a sudden turning or pivoting movement. Sometimes it can occur during normal day-to-day activities. It is usually described as an uncomfortable feeling which causes apprehension.

If you have a complete dislocation the kneecap moves completely out of place. It “jumps” out of its normal groove and it gets “stuck” on the side of the knee. It always dislocates to the outer side of knee. This is usually very painful and you are not able to stand. Patients often collapse to the ground when this occurs. Sometimes the kneecap goes back into place on its own. If it does not it will need to be “put back” or reduced at a hospital. This is possible in the casualty department under a light sedation. When your pain is controlled and you are sedated the leg is straightened. In most cases this is enough to put the kneecap back in place.

What does MPFL surgery involve?

There are many ways to perform MPFL surgery. My preferred technique is to “borrow” a small hamstring tendon from the back of your knee. This is used to create a new ligament. Small tunnels are created in your kneecap and femur. The ligament is secured in these tunnels by absorbable screws. The new ligament acts as a “check reign” to prevent the kneecap from dislocating again.

Usually an arthroscopy is performed at the same time (read: Knee arthroscopy – what is involved?). This is to inspect the tracking of the kneecap before and after the surgery. Damaged areas of cartilage under the kneecap can be smoothed off. Any loose pieces of cartilage can be removed. An inspection of the trochlea for abnormal shape or flattening (dysplasia) can be made. Arthroscopy can also help document the status of the rest of the knee for future reference.

Occasionally, a bony re-alignment procedure (osteotomy) must also be performed. This is needed if there are significant anatomical risk factors for recurrent dislocations. The kneecap is attached to the shin bone (tibia) via the patellar tendon. This tendon is attached to an area of bone called the tibial tuberosity. A re-alignment osteotomy involves cutting the tibial tuberosity loose. It is then moved to the desired position, and fixed with screws. This procedure is not necessary in the majority of cases.

How long does it take to recover from MPFL surgery?

After MPFL surgery you normally spend one night in hospital. This is to make sure you are comfortable and that your pain is under control. Once you have seen the physiotherapist you are discharged the following day. I recommend a period of four weeks of partial weight bearing. During this time I prefer you to be in a brace. You will also need crutches. Thereafter you may begin full weight-bearing and walking on the on the leg. Although you will be able to get around soon after the surgery, getting back to sports takes much longer. It may take between 4 to 6 months for you to play sports again.

Is MPFL reconstruction surgery painful?

I would like to be upfront – most  patients who have an MPFL reconstruction report this it was fairly painful. Sometimes more extensive surgery must be performed in addition to the MPFL reconstruction. This includes a bony cut (osteotomy) to correct alignment and/or patellar height issues. This may add to discomfort after the procedure.

The good news is that the pain is bearable and we have many ways to minimise the discomfort. The surgery is done under general anaesthetic so you feel and remember nothing during the actual operation. Alternatively a spinal anaesthetic may be given. This will make your legs numb and you will not feel any pain. Should this anaesthetic be chosen a light sedation is given to help you sleep. My preference is to do the operation under a general anaesthetic. In this way you will be able to mobilise faster after the surgery. Your risk of a blood clot (DVT) will be lower.

Every effort is made to control your pain after the surgery. During the surgery I use the local anaesthetic injection to the skin and to the capsule of the knee joint. This is done to numb the area where the surgery is performed. While still in hospital we are able to give you intravenous and/or intramuscular injections for pain if needed. When you are discharged you are supplied with oral prescription-strength painkillers. Other pain-relieving measures include elevation and icing.

In conclusion…

MPFL surgery is necessary for a kneecap which keeps dislocating. An unstable kneecap may result in arthritis of the kneecap (patellofemoral arthritis) in later years. This is because each time the patella dislocates, the smooth cartilage lining the kneecap may be damaged. Every effort is made to minimise pain after the procedure. The results are usually good, but post-operative physiotherapy is essential for a successful outcome.

Yours in good health,

Dr Warren Matthee

MB BCh (Wits), MRCS (England), MMed (Ortho Surg), FC Orth (SA)

Orthopaedic Surgeon

(011) 304 6784

About the author…

I am an orthopaedic surgeon with a special interest in sports injuries and minimally invasive (arthroscopic) surgery of the knee and shoulder. I treat patients at Waterfall Hospital in Waterfall/Midrand and Morningside Mediclinic in Sandton. Besides these, I also treat patients from other areas as well, including Rosebank, Sunninghill and Fourways.

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    Patellar dislocation may require surgery