Coxa vara is a hip deformity where the angle between the thighbone’s neck and shaft is smaller than normal, typically 120 degrees or less. In a healthy adult hip, this angle averages around 130 degrees, allowing the leg to bear weight efficiently and the hip muscles to function properly. When that angle decreases, it changes the mechanics of the entire hip joint, often leading to a limp, leg length differences, and limited range of motion.
How the Hip Angle Works
Your thighbone (femur) isn’t a straight rod. Near the top, it angles inward at the neck before connecting to the ball-shaped head that sits in your hip socket. The angle where the neck meets the shaft is called the neck-shaft angle, and it plays a critical role in how force transfers from your leg to your pelvis when you walk, run, or stand. A CT-based study of 800 adult hips found the average angle was about 130 degrees for men and 132 degrees for women, with a normal range roughly between 120 and 135 degrees.
When this angle drops below 120 degrees, the condition is classified as coxa vara. In more severe cases, the angle falls to 110 degrees or less. The opposite problem, where the angle exceeds 135 degrees, is called coxa valga. Both extremes alter how weight is distributed through the hip and can cause problems over time, but coxa vara tends to produce more noticeable symptoms because it shortens the affected leg and weakens the hip’s leverage system.
Types and Causes
Coxa vara falls into several broad categories depending on when and why the angle decreases.
Developmental coxa vara appears in early childhood, usually between ages one and six, when the growth plate in the upper femur doesn’t develop properly. The exact cause isn’t always clear, though theories include localized growth plate abnormalities, vascular problems during bone development, and metabolic factors. A characteristic feature on X-rays is a triangular fragment of unhealed bone along the inner lower edge of the femoral neck.
Congenital coxa vara is present at birth and often accompanies broader skeletal conditions. It’s particularly common in certain forms of skeletal dysplasia, where multiple bones throughout the body develop abnormally. In some of these cases, the growth plate between the femoral head and neck is present but barely functional, leading to overgrowth of the greater trochanter (the bony bump on the outer hip) relative to the femoral head.
Acquired coxa vara develops later in life as a consequence of another condition or injury. Common causes include fractures of the upper femur that heal at a reduced angle, loss of blood supply to the femoral head (avascular necrosis), infections of the hip joint, and a condition called slipped capital femoral epiphysis where the growth plate shifts in adolescence. Metabolic bone diseases also play a significant role: nutritional rickets, vitamin D-resistant rickets, kidney-related bone disease, fibrous dysplasia, and osteogenesis imperfecta (brittle bone disease) can all weaken the bone enough for the angle to gradually collapse under body weight.
Symptoms and How It Affects Walking
The most visible sign of coxa vara is an altered gait. Because the reduced angle effectively shortens the leg on the affected side, you may notice a limp that can be either painful or painless depending on the underlying cause. One of the hallmark findings is called a Trendelenburg gait: when you stand on the affected leg, the hip muscles on that side can’t hold the pelvis level, so the opposite side of the pelvis drops. To compensate, you might lean your upper body toward the affected side with each step to keep your balance. This creates a noticeable side-to-side sway.
When both hips are affected, which is more common in metabolic bone diseases and skeletal dysplasias, the pelvis drops to alternating sides with each step. This produces what’s described as a waddling gait. Beyond the limp, people with coxa vara often experience reduced ability to move the leg outward (limited abduction), pain in the hip or groin during activity, and fatigue in the hip muscles. Children may also develop a visible difference in leg length that becomes more apparent as they grow.
How It’s Diagnosed
Diagnosis starts with a physical exam, checking for leg length differences, range of motion, and the Trendelenburg sign. Standard hip X-rays confirm the diagnosis by showing the reduced neck-shaft angle. In children with developmental coxa vara, doctors also measure something called the Hilgenreiner epiphyseal angle, which assesses the steepness of the growth plate. This measurement helps predict whether the deformity will worsen over time.
A Hilgenreiner angle below 45 degrees is unlikely to progress on its own. Between 45 and 60 degrees, progression is possible, and the child needs regular monitoring. Above 60 degrees, progression is likely and surgical correction is typically recommended. CT scans or MRI may be used in certain cases to rule out tumors, infections, or metabolic bone disease as underlying causes.
Treatment: When Surgery Is Needed
Not every case of coxa vara requires surgery. A study comparing long-term outcomes in children with congenital coxa vara found that those managed without surgery tended to have milder deformities to begin with, averaging a neck-shaft angle of 122 degrees and a Hilgenreiner angle of 34 degrees. Most of these children maintained normal growth rates in the femoral neck, though only about 21% saw their varus angle fully resolve on its own. In contrast, children who needed surgery had more severe starting deformities, averaging a neck-shaft angle of 90 degrees. After correction, both groups had similar outcomes at long-term follow-up.
When surgery is needed, the standard approach is a valgus osteotomy. The surgeon cuts the bone just below the hip joint and repositions it to restore a more normal neck-shaft angle. The goal is twofold: correct the angle itself and reorient the growth plate to a more horizontal position, which encourages healthier bone growth going forward. The bone is then held in place with a metal plate and screws while it heals.
After surgery, patients are typically limited to partial weight bearing for four to six weeks while the bone heals at its new angle. Physical therapy follows to rebuild hip strength, particularly the abductor muscles that were mechanically disadvantaged by the deformity.
What Happens Without Treatment
Mild cases that remain stable may never cause significant problems. But moderate to severe coxa vara that goes untreated tends to worsen, especially in growing children. Over time, the femoral head and hip socket can become severely deformed. The abnormal mechanics accelerate wear on the joint surfaces, leading to early-onset arthritis. In the most severe untreated cases, a false joint (pseudoarthrosis) can develop between the femoral head and neck, making later surgical correction far more difficult and the results less predictable.
Early intervention in childhood, when the growth plate is still active, gives the best chance for the bone to remodel and grow normally after correction. Adults with coxa vara from childhood who develop significant arthritis may eventually need hip replacement, though correcting the underlying angle first (or at the same time) is important for the replacement to function properly.