The kneecap (patella) is a small bone situated at the front of the knee joint. Its primary function is to act as a lever, increasing the mechanical advantage of the thigh muscles when the leg straightens. Patellar tracking refers to the path the kneecap follows as the knee bends and straightens. When this movement is smooth and centered, the knee functions without issue, but any deviation can lead to pain and dysfunction.
The Mechanics of Normal Patellar Movement
The patella moves within the trochlear groove, a specific channel on the end of the femur. This groove is shallowest when the leg is straight and deepens as the knee bends, providing a bony constraint. The kneecap is suspended by the quadriceps tendon above it and the patellar ligament below it. The patella begins to engage with the groove around 20 to 30 degrees of knee flexion. For the patella to remain centered, the pulling forces must be balanced by the vastus medialis obliquus (VMO), which pulls the patella inward (medially) to counteract the natural outward (lateral) pull.
Defining Patellar Tracking Disorder
A patellar tracking disorder occurs when the kneecap consistently moves outside of its proper path within the trochlear groove. The most common pattern involves the patella shifting toward the outside of the knee, known as lateral deviation. When the kneecap deviates, the cartilage on the underside rubs against the femur with abnormal friction or pressure. This repeated stress can irritate soft tissues and lead to patellofemoral pain syndrome (PFPS). In severe cases, the friction causes softening and breakdown of the cartilage, called chondromalacia patellae. The sensation of clicking, grinding, or popping (crepitus) is often associated with this irregular movement.
Primary Causes of Maltracking
The reasons for patellar maltracking are categorized into issues with soft tissue balance and underlying anatomical structure.
Soft Tissue Imbalance
Weakness in the muscles that pull the patella inward is a frequent soft tissue contributor. If the Vastus Medialis Obliquus (VMO) is significantly weaker than the outer quadriceps muscles, the kneecap is pulled too strongly toward the lateral side. Tightness in structures on the outside of the knee also exerts an abnormal lateral pull. The iliotibial band (IT band) and the lateral retinaculum can become tight, overpowering the VMO and forcing the patella out of alignment.
Structural Factors
Structural factors relate to the inherited shape and alignment of the bones in the leg. A shallow trochlear groove, called trochlear dysplasia, provides inadequate bony restraint to keep the patella centered. A kneecap that sits too high (patella alta) delays the engagement of the patella into the groove, increasing the risk of lateral instability. Alignment issues, such as a large Q-angle (the angle formed between the hip and the kneecap), also increase the outward pulling force on the patella, making maltracking more likely.
Diagnosis and Management of Tracking Issues
Diagnosis typically begins with a physical examination to assess symptoms, which often include pain around the kneecap that worsens with activities like squatting or climbing stairs. Clinicians observe patellar movement during knee flexion and extension and may check for the “J-sign,” where the kneecap deviates sharply outward at the end of leg extension. Imaging studies like X-rays check for structural abnormalities such as patella alta or an increased Q-angle, while an MRI evaluates the condition of the cartilage beneath the kneecap.
Management
Management of patellar tracking issues is overwhelmingly non-surgical and centers on physical therapy to restore muscle balance. Treatment focuses on strengthening the VMO for dynamic control over the patella and strengthening the hip abductor muscles to stabilize the entire leg alignment. Stretching addresses tightness in the lateral structures, such as the IT band or lateral retinaculum. Supportive measures like patellar taping or specialized braces can temporarily guide the kneecap into a more optimal path during rehabilitation. If non-surgical management fails or if the patella has a history of recurrent dislocation, surgical intervention may be considered. Common surgical procedures include a lateral release or a tibial tubercle transfer.