Patella (Knee Cap) Instability

Anatomy

The knee joint is the junction between the femur (thigh) bone and the tibia (shin bone). The end of the femur is referred to as the distal femur and the top of the tibia is referred to as the proximal tibia or tibial plateau.  The kneecap is referred to as the patella. The knee is said to have three compartments – medial (inside), lateral (outside), and patellofemoral (directly behind the patella).  Articular cartilage covers the end of the femur, top of the tibia, and behind the patella and allow the bone to glide easily with one another. A ligament is a tight band of tissue that connects bone to bone and helps to increase stability. The primary stabilizer of the patella is the medial patellofemoral ligament (MPFL) which keeps the patella in the groove of the femur called the trochlea when the knee is moved from flexion to extension.

What is Patella Instability?

Patella instability or patellofemoral instability, is when the patella dislocates, or slips out of the trochlea. This occurs most commonly from a fall or sports injury. Some risk factors for patella dislocation include a shallow groove (trochlear dysplasia), high kneecap (patella alta), misalignment of the kneecap and tibia (rotational deformities, increase Q-angle), patients with loose ligaments.

Symptoms of Patella Instability

• Feeling like your knee dislocated.

• Swelling and bruising.

• Knee stiffness.

• Pain in the front of the knee.

• Pain when sitting and standing.

• Apprehension to knee flexion.

• Knee buckling and catching.

Diagnosing an Patellar Instability

A thorough patient history and physical exam can help to identify patients with patellar instability. X-ray images and MRI are useful diagnostic tools to help rule out other injuries and to confirm the diagnosis. 

Treatment for ACL Tears 

Nonsurgical Options - most commonly used for first time dislocations.

• Activity modifications and brace.

• Anti-inflammatory medications.

• Physical therapy.

Surgery: Usually needed with recurrent dislocations or with loose body in the knee. The over goal is to correct the underlying cause of the dislocation