Coxa Vara: Features, Symptoms, Causes, and Biomechanical Consequences

What Are the Features of Coxa Vara?

Coxa vara is a hip deformity characterized by a decreased angle between the head and neck of the femur and its shaft, typically less than 120-135 degrees, leading to altered biomechanics, gait abnormalities, and potential pain.

Introduction to Coxa Vara

Coxa vara, derived from Latin ("coxa" meaning hip, "vara" meaning bent inward), describes a specific anatomical deviation of the proximal femur. In a healthy adult hip, the angle formed by the femoral neck and the shaft of the femur, known as the femoral neck-shaft angle (or caput-collum-diaphyseal angle), typically ranges from 125 to 135 degrees. This angle is crucial for optimal hip joint mechanics, distributing forces efficiently and allowing for effective muscle leverage. When this angle is significantly reduced, often below 120 degrees, the condition is termed coxa vara. This structural change has profound implications for hip stability, muscle function, and overall lower limb biomechanics.

Key Anatomical and Biomechanical Features

The defining characteristics of coxa vara are rooted in its anatomical presentation and the subsequent biomechanical consequences:

• Decreased Femoral Neck-Shaft Angle: This is the hallmark feature. The femoral neck appears to be bent downwards relative to the shaft. This angle is typically measured on an anterior-posterior (AP) radiograph of the pelvis.
• Shortened Femened Femoral Neck: In many cases, especially developmental forms, the femoral neck itself may be shorter than average.
• Relative Elevation of the Greater Trochanter: As the femoral neck angles downward, the greater trochanter, the attachment site for key hip abductor muscles (gluteus medius and minimus), moves relatively superiorly. This reduces the mechanical advantage (lever arm) of these muscles.
• Increased Shear Forces at the Femoral Neck: The altered angle changes the distribution of forces across the femoral neck, increasing shear stress, particularly at the growth plate (physis) in growing individuals. This can predispose to further deformity or complications like slipped capital femoral epiphysis (SCFE) in adolescents.
• Reduced Mechanical Advantage of Hip Abductors: Due to the elevated greater trochanter and altered geometry, the hip abductor muscles become less efficient. This necessitates greater muscle force to stabilize the pelvis during single-leg stance.

Clinical Presentation and Symptoms

Individuals with coxa vara may present with a variety of signs and symptoms, depending on the severity, cause, and duration of the condition:

• Limp (Trendelenburg Gait): This is one of the most common and noticeable features. Due to the weakness and inefficiency of the hip abductor muscles, the pelvis drops on the unsupported side during the swing phase of gait. The individual may compensate by leaning their trunk over the stance leg (Trendelenburg sign) to shift their center of gravity.
• Pain: Pain is frequently experienced in the groin, hip, buttock, or thigh. It often worsens with activity and can be attributed to increased joint stress, muscle fatigue, or compensatory movements.
• Leg Length Discrepancy: The affected limb may appear shorter than the unaffected limb, contributing to gait abnormalities and potential compensatory changes in the spine or pelvis.
• Limited Range of Motion: Restricted hip abduction and internal rotation are common findings. External rotation may appear relatively increased.
• Prominent Greater Trochanter: The elevated position of the greater trochanter can make it more palpable and visually prominent on the affected side.
• Waddling Gait: In cases of bilateral coxa vara, a characteristic waddling gait may be observed due to the combined abductor weakness.
• Fatigue: Due to the increased effort required for ambulation and stabilization, individuals may experience generalized fatigue or specific muscle fatigue in the hip and thigh.

Potential Causes of Coxa Vara

Coxa vara can arise from various etiologies, categorized broadly into congenital, developmental, and acquired forms:

• Congenital Coxa Vara: Present at birth, often due to a developmental defect in the growth of the proximal femur.
• Developmental Conditions:
  • Slipped Capital Femoral Epiphysis (SCFE): While primarily a posterior and inferior displacement of the femoral head, it can lead to a secondary coxa vara deformity.
  • Perthes Disease: Avascular necrosis of the femoral head, which can lead to deformity and, in some cases, coxa vara.
• Acquired Causes:
  • Trauma: Femoral neck fractures, especially those that heal with malunion.
  • Metabolic Bone Diseases: Conditions like rickets or osteomalacia can weaken bone and lead to deformity.
  • Infection: Osteomyelitis of the proximal femur.
  • Tumors: Benign or malignant lesions affecting the femoral neck.
  • Paget's Disease: A chronic bone disorder that can cause bone deformity.

Associated Biomechanical Consequences

Beyond the immediate features, coxa vara can lead to a cascade of biomechanical issues:

• Increased Stress on Hip Joint Cartilage: The altered joint forces can lead to accelerated wear and tear of the articular cartilage, increasing the risk of early-onset osteoarthritis.
• Compensatory Muscle Overactivity: Muscles like the tensor fascia latae (TFL) and gluteus maximus may become overactive in an attempt to compensate for the weakened gluteus medius and minimus, leading to muscle imbalances and pain.
• Spinal and Pelvic Adaptations: To manage the leg length discrepancy and gait abnormalities, the pelvis may tilt, and the spine may develop compensatory curves (scoliosis), potentially leading to back pain.
• Altered Lower Limb Alignment: The changes at the hip can influence the alignment of the knee and ankle, potentially contributing to issues in these joints over time.

Diagnosis of Coxa Vara

Diagnosis typically involves a combination of:

• Clinical Examination: Assessment of gait, range of motion, leg length, and palpation for tenderness or prominence.
• Radiographic Imaging: X-rays of the pelvis and hips are essential to measure the femoral neck-shaft angle and identify any associated bone deformities or pathologies. Specific views may be required.

Management Considerations

While the focus here is on features, understanding the implications for management is key for fitness professionals. Management of coxa vara varies based on its cause and severity. In younger individuals, surgical correction (osteotomy) may be performed to restore a more physiological neck-shaft angle, improve biomechanics, and prevent long-term complications. For adults, conservative management involving pain control, physical therapy to strengthen surrounding musculature (especially hip abductors and core), and gait training may be employed, though surgical intervention might be considered for severe cases or those with significant functional limitations.

Conclusion

Coxa vara is a significant orthopedic condition characterized by a reduced femoral neck-shaft angle, leading to distinctive anatomical, biomechanical, and clinical features. For fitness enthusiasts, personal trainers, and student kinesiologists, recognizing these features – from the characteristic limp and pain to the underlying abductor weakness and altered joint mechanics – is crucial. A comprehensive understanding allows for appropriate exercise modifications, targeted strengthening programs, and referral to medical professionals when necessary, ultimately contributing to better client outcomes and injury prevention strategies.