Patellar Instability

Patellar instability is where the kneecap dislocates from its groove and moves out of its normal position, either partially or completely. It can affect anyone but is more commonly seen in adolescents and young adults with anatomically at-risk knees. It particularly affects children who are physically active or participate in sports that involve jumping or pivoting movements, such as basketball, soccer, gymnastics, and volleyball, with underlying anatomy that places them at higher risk of having a dislocation. However, one in five dislocations occur during the usual activities of daily life. Females are more likely to experience patellar instability than males due to anatomy, hormones, and neuromuscular control differences. Patellar dislocation is a risk factor for patellofemoral arthritis that can develop from recurrent patellar instability over time.

Patellar instability is caused by abnormal tracking of the patella in its groove, causing it to dislocate. It can be caused by a variety of factors, including:

• Trauma: A sudden blow or impact to the knee can cause the patella to dislocate from its normal position.
• Anatomic abnormalities: Certain anatomic factors can increase the risk of patellar instability, such as a shallow trochlear groove (the groove in the femur where the patella sits), patella alta (patella is higher in the knee than it should be), or abnormal alignment of the lower extremity. Trochlea dysplasia is where the kneecap temporarily slides out of its groove.
• Muscle weakness or imbalance: Weakness or imbalance in the quadriceps muscles, which attach to the patella, can lead to instability and abnormal patellar tracking.
• Ligamentous laxity: Increased flexibility in the ligaments that support the knee can cause excessive movement and instability of the patella.
• Neuromuscular disorders: Certain neurological or neuromuscular conditions, such as cerebral palsy or muscular dystrophy, can increase the risk of patellar instability.
• Overuse injuries: Repetitive stress on the knee joint, such as from running or jumping, can lead to inflammation, irritation, and instability of the patella.
• Genetic factors: Some studies suggest that there may be a genetic component to patellar instability, although the specific genes involved are not yet known.

The symptoms of patellar instability can vary depending on the severity of the condition. Common symptoms include:

• Pain in the front of the knee, particularly around or behind the patella.
• Swelling and inflammation in the knee joint.
• A feeling of the knee giving way or buckling, particularly when standing, walking, or climbing stairs.
• A popping or grinding sensation in the knee joint.
• Stiffness and restricted range of motion in the knee.
• Visible deformity of the knee.
• Numbness or tingling in the leg or foot, particularly if nerves around the knee are affected.
• Chronic instability causes the patella to slip out of its groove during flexion and extension, impacting walking ability.
• Discomfort with activity and pain around the kneecap may be called “patellofemoral pain syndrome.”

Knee surgeon, Dr. Daniel Kaplan, will take a detailed history of the injury, inquire about a family history of instability, and whether this is the first dislocation. He will thoroughly examine the ligaments and soft tissues, the location and alignment of the patella, and check for tenderness. He will order imaging studies, including X-rays to evaluate the bones and an MRI of the soft tissues and cartilage.