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.
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
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.
Your surgeon diagnoses the condition by collecting your medical history and physical findings. He may also order certain tests such as X-rays, MRI or CT scans to confirm the diagnosis.
Treatment for instability depends on the severity of condition and based on the diagnostic reports. Initially your surgeon may recommend conservative treatments such as physical therapy, use of braces and orthotics. Pain relieving medications may be prescribed for symptomatic relief. However, when these conservative treatments yield unsatisfactory response surgical correction may be recommended.
Considering the type and severity of injury surgeon decides on the surgical correction. A lateral retinacular release may be performed where your surgeon releases, or cuts, the tight ligaments on the lateral side (outside) of the patella enabling the patella to slide more easily in the femoral groove.
Your surgeon may also perform a procedure to realign the quadriceps mechanism by tightening the tendons on the inside or medial side of the knee.
If the misalignment is severe tibial tubercle transfer (TTT) will be performed. This procedure involves the surgeon removing a section of bone where the patellar tendon attaches on the tibia. The bony section is then shifted and properly realigned with the patella and reattached to the tibia with two screws.
Following the surgery rehabilitation program may be recommended for better outcomes and quicker recovery.
Patellar Dislocation/Patellofemoral Dislocation
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).
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 (luxation). 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.
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 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.
Your doctor will examine your knee and suggests diagnostic tests such as X-ray, CT scan, and MRI scan to confirm condition and provide treatment. There are non-surgical and surgical ways of treating patellofemoral dislocation.
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. Physiotherapist will extend your knee and applies direct lateral to medial pressure to the knee which helps in relocation. It includes straightening and strengthening exercises of the hip muscles and other exercises which will improve range of motion.
Surgical treatment is recommended for those individuals who have recurrent patella dislocation. 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.
- 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 tendon using screws. The grafts are either taken from the same individuals (autograft) or from a donor (allograft). This procedure is also performed using an arthroscope.
- Tibia tubercle realignment or transfer – Tibia tubercle is a bony attachment below the patella tendon which sits on the tibia. In this procedure, the tibia tubercle is moved towards the center which is then held by two screws. The screws hold the bone in place and allow faster healing and prevent the patella to slide out of the groove. This procedure is also performed using an arthroscope.
After the surgery, your doctor will suggest you use crutches 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.