Patellar Instability

The patella is stabilized by several key structures, with the medial patellofemoral ligament (MPFL) being the primary stabilizer. The MPFL connects the inner side of the kneecap to the femur, keeping the patella aligned in its groove during knee movement. In addition, the quadriceps tendon links the quadriceps muscle to the patella, while the patellar tendon attaches the patella to the tibia (shin bone), forming a strong support system for the knee.

However, various factors can disrupt this delicate balance, leading to dislocation or subluxation (partial dislocation) of the patella. When the kneecap moves out of its groove, it can cause joint instability and significant discomfort.

Acute kneecap dislocations are often the result of a sports injury, a fall, or a direct blow to the knee. These incidents can force the patella out of its normal track, leading to pain, swelling, and an immediate loss of knee function. However, certain anatomical factors can predispose individuals to patellar instability. These include:

• Patella Alta: A condition where the kneecap sits higher than normal in the knee joint.
• Trochlear Dysplasia: A shallow groove in the femur that prevents the patella from staying securely in place.
• Misalignment: Abnormal alignment of the kneecap and tibia, often characterized by an increased Q-angle or rotational deformities.

In addition, women and girls are more prone to lateral patellar dislocations due to naturally looser ligaments and differences in joint structure. As a result, patellar instability is a common injury among young, active females.

Once a person experiences an initial patellar dislocation, the risk of future dislocations increases significantly. According to medical studies, 15 to 44% of patients who suffer a traumatic dislocation will experience recurrent dislocations, and the risk increases to 49% after two or more dislocations.

Key risk factors for recurrent patellar dislocations include:

• Young age: Adolescents and young adults are more likely to experience recurrent dislocations due to ongoing growth and physical activity.
• Sports-related injuries: High-impact sports increase the likelihood of kneecap dislocations.
• Patella Alta and Trochlear Dysplasia: Structural abnormalities in the knee joint make dislocations more likely.
• Laxity of the MPFL: Injuries to the MPFL, such as stretching or tearing, contribute to knee instability.

Repeated dislocations are often caused by underlying anatomical issues rather than trauma. For instance, a shallow trochlear groove or weak quadriceps muscles can increase the likelihood of the patella slipping out of place.

Chronic patellar instability can significantly impact an individual’s quality of life, causing persistent knee pain and limiting participation in physical activities. Common symptoms of chronic patellar instability include:

• Swelling and bruising: Swelling around the knee joint, especially after physical activity or a dislocation.
• Pain: Discomfort in the front of the knee, particularly when sitting for extended periods or standing up.
• Joint stiffness: Difficulty bending or straightening the knee.
• Knee buckling or catching: A sensation that the knee is unstable or might give way during movement.
• Creaking sound: A grinding or creaking sound during knee movement.
• Difficulty walking: Walking becomes painful, especially when the knee feels unstable.

For people living with chronic knee instability, the fear of recurrent dislocations can be as debilitating as the physical symptoms, severely limiting daily activities and sports participation.

Proper diagnosis of patellar instability is essential for effective treatment. During an initial consultation, the doctor will review the patient’s medical history, including any prior dislocations or subluxations, and perform a physical examination to assess the movement of the kneecap during a range of motion.

To confirm the diagnosis, imaging tests such as X-rays, MRIs, or CT scans may be ordered. These tests provide valuable information about the alignment of the knee bones, the depth of the trochlear groove, and any soft tissue injuries, such as a torn MPFL. An MRI, in particular, can detect loose bodies, cartilage damage, and bone bruising resulting from the patella’s dislocation.