The term coxa comes from the Latin and refers to the hip. Vara refers to the angle of the neck at the top of the femur (thigh bone) between the shaft of the long bone and the round head at the top.
The femoral neck angle is usually about 150 degrees at birth. With time, growth and development, and weight-bearing, this angle decreases. By adulthood, it is more in the range of 125 to 135 degrees.
Some experts suggest coxa vara occurs when the angle between the ball and the shaft of the femur is less than 120 degree (in adults). This figure is closer to 110 degrees in children. The condition may or may not be painful but usually results in a limp because one leg is shorter than the other.
Surgery is done to help restore a more normal angle. The hope is to reduce any pain that may be present, improve hip motion, and get rid of the limp. The exact procedure that is done depends on the cause, location, and extent of the problem.
Children with a straightforward coxa vara deformity have a fairly good prognosis. Results improve function and are long-lasting. Prognosis is poor for children with multiple other deformities associated with the coxa vara. Abnormal features of the bone and cartilage cause hip instability in children.
If surgery is done too early, further growth spurts cause the problem to recur (come back). It’s not uncommon for these children to develop degenerative arthritis in early adulthood. You would need further details about your nephew to know what kinds of results are expected. Hopefully, all will go well with a good result. The surgeon will have a better idea what to expect after the operation is completed.