Patellofemoral Instability and Dislocation
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 alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place.
Patella (knee cap) is a protective bone attached to the quadriceps muscles of the thigh by quadriceps tendon. Patella attaches with the femur bone and forms a patellofemoral joint. Patella is protected by a ligament which secures the kneecap from gliding out and is called as medial patellofemoral ligament (MPFL).
What is patellofemoral instability and dislocation?
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.
Patellar (knee cap) instability results from one or more dislocations or partial dislocations (subluxations). Patella is the small piece of bone in front of the knee that slides up and down the femoral groove (groove in the femur bone) during bending and stretching movements. The ligaments on the inner and outer sides of patella hold it in the femoral groove and avoid dislocation of patella from the groove.
Any damage to these ligaments may cause patella to slip out of the groove either partially (subluxation) or completely (dislocation). This misalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee cap in place. Once damaged, these soft structures are unable to keep the patella (knee cap) in position. Repeated subluxation or dislocation makes the knee unstable and the condition is called as knee instability.
Dislocation of the patella occurs when the patella moves out of the patellofemoral groove, (called as trochlea) onto a bony head of the femur. If the knee cap partially comes out of the groove, it is called as subluxation and if the kneecap completely comes out, it is called as dislocation. Patella dislocation is commonly observed in young athletes between 15 and 20 years and commonly affects women because of the wider pelvis creates lateral pull on the patella.
What causes the patella to dislocate?
Some of the causes for patellar dislocation include direct blow or trauma, twisting of the knee while changing the direction, muscle contraction, and congenital defects. It also occurs when the MPFL is torn. The common symptoms of acute patellofemoral instability or dislocation include pain, tenderness, swelling around the knee joint, restricted movement of the knee, numbness below the knee, and discoloration of the area where the injury has occurred.
Why may my patella be unstable?
Various factors and conditions may cause patellar instability. Often 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 "Q" angle is a medical term used to describe the angle between the hips and knees. The higher the "Q" angle, such as in patients with Knock Knees, the more the quadriceps pull on the patella causing misalignment.
- Patellofemoral Arthritis: Patellar misalignment causes uneven wear and tear and can eventually lead to arthritic changes to the joint.
- Improper Muscle Balance: Quadriceps, the anterior thigh muscles, function to help hold the kneecap in place during movement. Weak thigh muscles can lead to abnormal tracking of the patella, causing it subluxate or dislocate.
Young active individuals involved in sports activities are more prone to patellofemoral instability.
What are symptoms of patellofemoral instability problems?
Patients with knee instability experience different signs and symptoms such as:
- Pain, especially when standing up from a sitting position
- Feeling of unsteadiness or tendency of the knee to "give way" or "buckle"
- Recurrent subluxation
- Recurrent Dislocation
- Severe pain, swelling and bruising of the knee immediately following subluxation or dislocation
- Visible deformity and loss of function of the knee often occurs after subluxation or dislocation
- Sensation changes such as numbness or even partial paralysis can occur below the dislocation because of pressure on nerves and blood vessels
How do you diagnose patellofemoral instability and dislocation?
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.
How do you manage patellofemoral instability problems?
If your kneecap is only partially dislocated (subluxation), your physician may recommend non-surgical treatments, such as pain medications, rest, ice, physical therapy, 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.
Non-surgical or conservative treatment includes:
- PRICE (protection, rest, ice, compression, and elevation)
- Non-steroidal anti-inflammatory drugs and analgesics to treat pain and swelling
- Braces or casts which will immobilize the knee and allows the MPF ligament to heal
- Footwear to control gait while walking or running and decreases the pressure on the kneecap.
- Physical therapy is recommended which helps to control pain and swelling, prevent formation of scar of soft tissue, and helps in collagen formation. It includes straightening and strengthening exercises of the hip and knee muscles and other exercises which will improve range of motion.
Will surgery be necessary?
Surgical treatment is recommended for those individuals who have recurrent patella dislocation or instability and have failed non-surgical management. Some of the surgical options include:
- Lateral-release: It is done to loosen or release the tight lateral ligaments that pull the kneecap from its groove which increases pressure on the cartilage and causes dislocation. In this procedure, the ligaments that tightly hold the kneecap are cut using an arthroscope. This procedure is often combined with one of the other surgical procedures to address instability.
- Medial patellofemoral ligament reconstruction: In this procedure, the torn MPF ligament is removed and reconstructed using grafting technique. Grafts are usually harvested from the hamstring tendons, located at the back of the knee and are fixed to the patella and femur using screws and anchors.
- Tibia tubercle realignment or transfer: The tibial tubercle is the bony attachment of the patella tendon which on the tibia. In cases where the malalignment is more severe, a procedure called a tibial tubercle transfer (TTT) may be performed. In this procedure, the tibial tubercle is surgically fractured and moved towards the center of the tibia which is then held by two screws to allow stable healing.
After the surgery, your doctor will may suggest you use crutches and a brace for few weeks, prescribe medications to control pain and swelling, and recommend physical therapy which will help you to return to your sports activities at the earliest. 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.
What are some of the risks of 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
Patients with patellofemoral instability may have complex problems with the alignment of the limb and the knee cap. Therefore, the aims of treatment are to both bring the knee cap back into normal alignment and to hold it there. Your surgeon will decide which procedure is appropriate for your situation.