Patellofemoral Instability

What is patellofemoral instability?

The knee can be divided into three compartments: patellofemoral, medial and lateral compartment. The patellofemoral compartment is the compartment in the front of the knee between the knee cap and thigh bone. The medial compartment is the area on the inside portion of the knee, and the lateral compartment is the area on the outside portion of the knee joint. Patellofemoral instability means that the patella (kneecap) moves out of its normal pattern of movement or alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place.

Malalignment has 3 categories (all degrees of the same problem):

  1. Excess Lateral Pressure Syndrome ELPS
  2. The kneecap is permanently but slightly out of place laterally and these patients have knee pain especially on bending activities.

  3. Lateral Patella Subluxation LPS
  4. The kneecap moves laterally and the patient tells you that they felt the kneecap move out but it went back in straight away.

  5. Lateral Patella Dislocation LPD
  6. The kneecap pops out laterally and stays out till something is done to put it back.

What are the causes of patellofemoral instability?

Normally, the patella moves up and down within the trochlear groove when the knee is bent or straightened. Patellofemoral instability can be caused by:

  1. Variations in the shape of the patella or its trochlear groove (dysplasia) as the knee bends and straightens.
  2. Abnormal Q angle-The high Q angle (angle between the centre of the patella and the patella tendon insertion).
  3. Patella Alta: This occurs when the patella tendon is too long and the patella rides high where it is more unstable.
  4. Patients with knock knees.
  5. Improper muscle balance- Weak quadriceps (anterior thigh muscles) can lead to abnormal tracking of the patella, causing it to subluxate or dislocate.
  6. Imbalance of soft tissue retinacula ligament restraints on the medial (inner) side of the patella which are often loose and the lateral (outer) retinacula ligament which are often tight.

Young active individuals involved in sports activities are more prone to patellofemoral instability and repeated maltracking leads to Patellofemoral arthritis.

Patellofemoral arthritis occurs when there is a loss of the articular cartilage on the back of the kneecap. This can eventually lead severe kneecap pain on all bending activities.

What are the symptoms of patellofemoral instability?

Patellofemoral instability causes pain when standing up from a sitting position and a feeling that the knee may buckle or give way. When the kneecap slips partially or completely you may have severe pain, swelling, bruising, visible deformity and loss of function of the knee. You may also have sensational changes such as numbness or even partial paralysis below the dislocation because of pressure on nerves and blood vessels.

How is patellofemoral instability diagnosed?

We will evaluate the source of patellofemoral instability based on your medical history and physical examination. Other diagnostic tests such as X-rays, MRI and CT scan may be done to determine the cause of your knee pain and to rule out other conditions.

What are the treatment options for patellofemoral instability?

Conservative treatment

If your kneecap is only partially dislocated (subluxation), we may recommend non-surgical treatments, such as pain medications, rest, ice, physiotherapy, knee-bracing. If the kneecap has been completely dislocated, the kneecap may need to be repositioned back in its proper place in the groove. This process is called closed reduction.

Surgical treatment

Surgery is sometimes needed to help return the patella to a normal tracking path when other non-surgical treatments have failed. The aim of the surgery is to realign the kneecap in the groove and to correct the anatomical abnormalities where possible.

Patellar realignment surgery is broadly classified into proximal re-alignment procedures and distal re-alignment procedures.

  1. Proximal re-alignment procedures: During this procedure, structures that limit the movements on the outside of the patella are lengthened or ligaments on the inside of the patella are shortened. This includes lateral release which can be performed arthroscopically without the need for open surgery.
  2. Distal re-alignment procedures: During this open procedure, the Q angle is decreased by moving the tibial tubercle towards the inner side of the knee.

The surgery is performed under sterile conditions in the operating room under spinal or general anaesthesia. We will make two small cuts around your knee. The arthroscope, a narrow tube with a tiny camera on the end is inserted through one of the incisions to view the knee joint. Specialized instruments are inserted into the joint through other small incisions. The camera attached to the arthroscope displays the image of the joint on the monitor. A sterile solution will be pumped into your knee to stretch the knee and provide a clear view and room for us to work. With the images from the arthroscope as a guide I can look for any pathology or anomaly and repair it through the other incisions with various instruments.

After the evaluation is completed, a larger incision is made if needed over the front of the knee to also tighten the tendons on the inside, or medial side of the knee to realign the quadriceps.

In cases where the malalignment is severe, a procedure called a tibial tubercle transfer (TTT) will be performed. In this procedure, a section of bone where the patellar tendon attaches to the tibia is removed. This bony section is then shifted and properly realigned with the patella and reattached to the tibia using screws.

What are the postoperative care instructions?

We will recommend pain medications to relieve pain. To help reduce the swelling you will be instructed to elevate the leg and apply ice packs over the knee.

If open surgery has been performed crutches are necessary for the first few weeks to prevent weight bearing on the knee. A knee immobilizer may be used to stabilize the knee. You will be instructed about the activities to be avoided and exercises to be performed for a faster recovery. A rehabilitation program will be advised for a speedy recovery.

What are the risks and complications associated with surgery?

Possible risks and complications associated with the surgery include:

  • Loss of ability to extend the knee
  • Recurrent dislocations or subluxations
  • Arthrofibrosis (thick fibrous material around the joint)
  • Persistent pain
  • Later development of arthritis (usually present in its early form at the time of surgery)