Patellar Dislocation: Why Girls Are More Prone, Risk Factors, and Prevention

Why do girls have more patellar dislocations than boys?

The higher incidence of patellar dislocations in girls compared to boys is a complex issue stemming from a combination of anatomical, biomechanical, hormonal, and neuromuscular factors unique to the female physiology, particularly during growth and development.

Understanding Patellar Dislocation

Patellar dislocation occurs when the patella, or kneecap, displaces from its normal position within the trochlear groove of the femur (thigh bone), most commonly shifting laterally (outward). This can be a painful and debilitating injury, often resulting from non-contact twisting movements, direct trauma, or an inherent predisposition. While it can affect anyone, statistical data consistently shows a higher prevalence in adolescent girls and young women.

Anatomical and Biomechanical Predispositions in Females

Several structural and functional differences contribute significantly to the increased risk in females:

• Increased Q-Angle: The Q-angle (quadriceps angle) is the angle formed by a line from the anterior superior iliac spine (ASIS) of the pelvis through the center of the patella, and a line from the center of the patella to the tibial tubercle. Females typically have a wider pelvis, which naturally results in a larger Q-angle. A larger Q-angle increases the lateral pull of the quadriceps muscle on the patella, making it more susceptible to dislocating laterally out of the trochlear groove.
• Femoral Trochlear Dysplasia: The trochlear groove, the indentation at the end of the femur where the patella sits, can be shallower or flatter in some individuals. This anatomical variation, more commonly observed in females, provides less bony restraint for the patella, increasing its instability.
• Patella Alta: This condition refers to a patella that sits higher than normal in the trochlear groove. A high-riding patella has less contact with the groove, particularly in the early degrees of knee flexion, making it less stable and more prone to dislocation.
• Generalized Ligamentous Laxity: Females often exhibit greater generalized joint laxity or hypermobility compared to males, influenced by hormonal factors. Increased laxity in the ligaments surrounding the knee (e.g., medial patellofemoral ligament, MPFL) can lead to reduced stability of the patellofemoral joint, making it easier for the patella to displace.
• Genu Valgum (Knock-Knees): A slight degree of genu valgum is more common in females. This alignment issue places increased valgus stress on the knee, which can contribute to lateral patellar tracking and instability.

Hormonal Influences

The role of hormones, particularly estrogen, is increasingly recognized in musculoskeletal injury patterns in females.

• Estrogen's Effect on Collagen and Ligaments: Estrogen receptors are found in ligaments and tendons. Fluctuations in estrogen levels, especially during the menstrual cycle, are thought to influence collagen synthesis and turnover, potentially leading to transient increases in ligamentous laxity and a reduction in the stiffness and strength of connective tissues. This can make joints, including the knee, less stable and more vulnerable to injury.

Neuromuscular Control and Strength Disparities

Differences in muscle activation patterns, strength, and movement mechanics also play a crucial role.

• Quadriceps Muscle Imbalance: A common imbalance seen in females is a relative weakness or delayed activation of the vastus medialis obliquus (VMO) muscle compared to the vastus lateralis (VL). The VMO is crucial for pulling the patella medially and stabilizing it within the groove, while the VL pulls it laterally. An imbalance can lead to the patella tracking excessively laterally.
• Hip Abductor and External Rotator Weakness: Weakness in the gluteal muscles, particularly the gluteus medius and maximus, can lead to dynamic knee valgus (the knee collapsing inward) during activities like jumping, landing, and cutting. This "knock-knee" position increases the lateral force on the patella, predisposing it to dislocation.
• Landing Mechanics: Research indicates that females often exhibit different landing mechanics compared to males, characterized by:
  • Less Knee and Hip Flexion: Leading to a more upright posture and increased reliance on passive structures (ligaments) rather than active muscular absorption.
  • Greater Knee Valgus Moment: The inward collapse of the knee, which is a direct risk factor for patellar dislocation and other knee injuries.
  • Increased Ground Reaction Forces: Stiffer landings can transmit higher impact forces through the patellofemoral joint.

Activity Patterns and Training Considerations

Participation in sports that involve frequent cutting, pivoting, jumping, and rapid changes of direction (e.g., soccer, basketball, volleyball, gymnastics) inherently carries a higher risk for patellar dislocations. While both genders participate in these sports, the underlying anatomical, biomechanical, and neuromuscular factors mean that females may be at a disproportionately higher risk when engaging in such activities without targeted preventative training.

Prevention and Management Strategies

Understanding these multifactorial risks is key to developing effective prevention programs. Targeted interventions can significantly mitigate the risk of patellar dislocations in females.

• Neuromuscular Training Programs: These programs focus on improving proprioception, balance, agility, and dynamic stability. They include exercises to teach proper landing mechanics (soft knees, wide base, knees aligned over toes), cutting techniques, and deceleration strategies.
• Strength Training: Emphasize strengthening the hip abductors, external rotators, gluteal muscles, and the vastus medialis obliquus (VMO) to improve knee alignment and patellar tracking. Balanced quadriceps and hamstring strength is also vital for overall knee stability.
• Flexibility and Mobility: Addressing tightness in structures like the iliotibial (IT) band, lateral retinaculum, and hamstrings can reduce lateral pulling forces on the patella.
• Biomechanical Assessment: For athletes and individuals with recurrent dislocations, a professional assessment by a physical therapist or sports medicine specialist can identify specific anatomical and biomechanical deficits.
• Education: Athletes, coaches, and parents should be educated on the risk factors and the importance of proper training techniques and injury prevention strategies.

Conclusion

The higher incidence of patellar dislocations in girls is not due to a single cause but rather a complex interplay of inherent anatomical differences, hormonal influences, and distinct neuromuscular control patterns and movement mechanics. While these factors predispose females to a greater risk, a proactive and targeted approach to strength training, neuromuscular re-education, and biomechanical optimization can significantly reduce the likelihood of these injuries, enabling girls to participate safely and effectively in sports and physical activities.