Coxa valga is a structural change affecting the femur, the long bone of the thigh, which forms the ball component of the hip’s ball-and-socket joint. This condition involves a deformity in the proximal femur, specifically an alteration in the angle at which the femoral neck connects the head to the main shaft of the bone. The resulting change in hip structure can lead to instability, altered gait patterns, and functional limitations for the affected individual.
Anatomical Definition and Measurement
Coxa valga is defined by an abnormal increase in the angle between the femoral neck and the shaft of the femur, known as the Neck-Shaft Angle (NSA) or caput-collum-diaphyseal (CCD) angle. In a healthy adult hip, this angle averages between 125 and 135 degrees; coxa valga is diagnosed when the angle exceeds 140 degrees, making the femoral neck appear more upright. This increased angle shifts the position of the femoral head within the acetabulum, the hip socket. The greater the angle, the less efficient the primary hip muscles become because the increased NSA shortens the abductor lever arm. This significantly reduces the mechanical advantage of hip abductor muscles, such as the gluteus medius, contributing to instability and increasing the risk of subluxation due to inadequate acetabular coverage.
Developmental and Acquired Causes
The development of the neck-shaft angle is a dynamic process influenced by weight-bearing and muscle forces during early childhood. Newborns naturally have a larger angle, often around 150 degrees, which gradually remodels to the adult range as they begin walking. Coxa valga occurs when this normal remodeling process fails or when abnormal forces act upon the developing bone.
Developmental causes include conditions present from birth, such as generalized skeletal dysplasias, which involve abnormal bone modeling. The most common acquired causes are linked to neuromuscular disorders that create a significant muscle imbalance around the hip joint, such as cerebral palsy and spina bifida. In these cases, spasticity in the hip flexors and adductors exerts an abnormal pull on the femur, while weakened abductor muscles fail to counteract this force, resulting in the progressive increase of the neck-shaft angle.
Recognizing the Signs
Mild cases may be entirely asymptomatic and only discovered incidentally during imaging. However, a substantial increase in the neck-shaft angle often leads to noticeable functional impairments related to compromised hip mechanics. A primary clinical presentation is an abnormal gait, frequently observed as a limp or a Trendelenburg gait, which occurs because inefficient hip abductor muscles cannot stabilize the pelvis during walking. Patients may also report hip pain, typically felt in the groin or on the lateral side of the hip, especially after physical activity. Other signs include a reduced range of motion in the hip joint and, in unilateral cases, a measurable leg length discrepancy.
Diagnostic Methods and Treatment Approaches
The diagnosis of coxa valga is confirmed through imaging studies, with a standard anteroposterior (AP) X-ray of the pelvis being the fundamental diagnostic tool. The radiograph allows for the precise measurement of the caput-collum-diaphyseal angle to determine the degree of the valgus deformity.
For mild, asymptomatic cases, particularly in children where further growth and remodeling may occur, the initial approach is non-operative observation with regular radiographic follow-up. Physical therapy may be recommended to strengthen the muscles surrounding the hip joint to improve overall stability and function.
When the deformity is severe, painful, or leads to progressive hip subluxation, surgical intervention is necessary. The primary surgical treatment is a varus osteotomy, which involves cutting and realigning the femur to decrease the neck-shaft angle. The goal of the varus osteotomy is to restore optimal hip biomechanics, improve the mechanical advantage of the abductor muscles, and enhance the coverage of the femoral head within the acetabulum to stabilize the joint.