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 kneecap and thighbone. 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 alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place.
Causes of Patellofemoral Instability
Patellofemoral instability can be caused because of variations in the shape of the patella or its trochlear groove as the knee bends and straightens. Normally, the patella moves up and down within the trochlear groove when the knee is bent or straightened. Patellofemoral instability occurs when the patella moves either partially (subluxation) or completely (dislocation) out of the trochlear groove.
A combination of factors can cause this abnormal tracking and include the following:
- Anatomical defect: Flat feet or fallen arches and congenital abnormalities in the shape of the patella bone can cause misalignment of the knee joint.
- Abnormal Q angle: The high Q angle (angle between the hips and knees) often results in mal tracking of the patella such as in patients with knock knees.
- Patellofemoral arthritis: Patellofemoral arthritis occurs when there is a loss of the articular cartilage on the back of the kneecap. This can eventually lead to abnormal tracking of the patella.
- Improper muscle balance: Weak quadriceps (anterior thigh muscles) can lead to abnormal tracking of the patella, causing it subluxate or dislocate.
- Damage or rupture to the medial patella-femoral ligament due to previous dislocation.
Young active individuals involved in sports activities are more prone to patellofemoral instability.
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.
Diagnosis of Patellofemoral Instability
Your doctor evaluates 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.
Conservative Treatments for Patellofemoral Instability
If your kneecap is only partially dislocated (subluxation), your physician may recommend non-surgical treatments, such as pain medications, rest, ice, physiotherapy, knee-bracing, and orthotics. 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 Treatments for Patellofemoral Instability
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 help maintain the patella tracking normally in the trochlea groove. This is most commonly done with a reconstruction of the medial patella-femoral ligament. If there is also an underlying bone abnormality an additional procedure to may be performed to realign the kneecap in the groove and to decrease the Q angle.
Postoperative Care Following Treatment of Patellofemoral Instability
Your doctor 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. Crutches may be 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 may be advised for a speedy recovery.
Risks and Complications Following Surgical Treatment of Patellofemoral Instability
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
Patients with patellofemoral instability have problems with the alignment of the kneecap. Therefore, treatment is necessary to bring the kneecap back into normal alignment. Your surgeon will decide which procedure is appropriate for your situation.