What Causes Patellar Tracking Disorder?
Patellar tracking disorder occurs when the kneecap (patella) shifts out of its normal path as the leg bends or straightens. The patella typically glides smoothly within the trochlear groove, a V-shaped channel at the end of the thigh bone (femur), held in place by surrounding tendons and ligaments. When it deviates from this alignment, it can cause discomfort and impaired knee function.
Muscle Strength and Flexibility
Imbalances or weaknesses in specific muscle groups contribute to patellar tracking disorder. The quadriceps muscles, on the front of the thigh, play a key role in knee extension and patellar stability. The vastus medialis obliquus (VMO) muscle, on the inner side of the thigh, is important. Its oblique fibers provide a stabilizing pull on the patella, counteracting the outward pull from other quadriceps components.
When the VMO is weak or less active compared to the vastus lateralis (outer thigh muscle), an imbalanced pull can occur, drawing the kneecap laterally from its groove. This muscular imbalance prevents the patella from tracking correctly during leg movements. Weakness in hip abductor muscles, such as the gluteus medius, and hip external rotators also affects patellar alignment. These hip muscles help control the rotation and stability of the thigh bone.
Insufficient strength in these hip muscles can lead to excessive inward rotation of the femur, altering knee joint mechanics and causing improper patellar tracking. Tightness in muscles like the iliotibial band (a thick band of tissue along the outside of the thigh) or hamstrings can increase tension around the knee, pulling the kneecap out of its path. This combination of weak stabilizing muscles and tight opposing structures creates an environment conducive to patellar tracking issues.
Bone and Joint Alignment
Structural and anatomical factors play a role in predisposing individuals to patellar tracking disorder. Variations in the shape of the patella or the trochlear groove can affect how the kneecap glides. A shallow or irregularly shaped trochlear groove provides less bony constraint, making it easier for the patella to shift out of place.
The Q-angle, or quadriceps angle, measures the angle formed by the line of pull of the quadriceps muscle relative to the patellar tendon. An increased Q-angle, typically greater than 15 degrees in men and 18 degrees in women, indicates a more outward pull on the patella, increasing lateral displacement. This angle is influenced by factors like wider hips or increased pronation of the feet.
Structural issues like flat feet (pes planus) or differences in leg length can alter lower limb biomechanics. Flat feet can lead to increased inward rolling of the foot and inward rotation of the tibia, affecting knee alignment and patellar tracking. A difference in leg length can create compensatory movements, placing abnormal stress on the knee joint and influencing the patella’s movement within its groove.
Repetitive Strain and Activity
Certain activities and training errors can lead to patellar tracking disorder through repetitive strain. Movements involving repeated bending and straightening of the knee, common in sports like running, cycling, or jumping, can overload the patellofemoral joint. If tracking is even slightly off, this repetitive motion can cause irritation and inflammation.
Sudden increases in the intensity, duration, or frequency of physical activity, without adequate preparation, can contribute to the condition. For example, rapidly increasing running mileage or jumping volume can place excessive stress on the kneecap and its supporting structures before they adapt. This overload can disrupt the smooth tracking of the patella over time, leading to pain and dysfunction.
Improper technique during exercises or sports exacerbates the risk. Incorrect squatting form, where the knees collapse inward, can alter patellar mechanics and increase lateral stress on the kneecap. Over time, micro-traumas from repetitive, misaligned movements can wear down the articular cartilage beneath the patella and compromise the stability of its tracking.
Direct Impact and Injury
Acute traumatic events can cause patellar tracking disorder. A direct blow to the front of the knee, such as from a fall or a collision during sports, can displace the kneecap. This impact can push the patella completely out of its groove, resulting in a dislocation or partial dislocation (subluxation).
Beyond direct impacts, sudden twisting motions of the knee, particularly when the foot is planted, can injure the structures that stabilize the patella. These injuries often involve damage to the medial patellofemoral ligament (MPFL), a ligament on the inner side of the knee that helps prevent the kneecap from shifting outward. A tear or rupture of this ligament can lead to patellar instability.
Such acute injuries can alter the natural mechanics of the patellofemoral joint, even after the initial trauma has healed. Damage to supporting ligaments or the surrounding retinaculum (a fibrous tissue network) can leave the patella prone to recurrent instability and improper tracking, even with everyday activities. These acute events represent a distinct pathway to developing patellar tracking issues.