Coxa Vara Deformity

Coxa vara is a hip deformity characterized by an abnormal decrease in the angle between the femoral neck and the femoral shaft. The normal neck-shaft angle in adults ranges from 125 to 135 degrees (slightly higher in children, decreasing with age). Coxa vara is defined as a neck-shaft angle of less than 120 degrees, with severe coxa vara having angles less than 100 degrees. The condition has multiple etiologies broadly classified as congenital (developmental, present at birth or early childhood) or acquired (developing later in life from trauma, infection, or other causes).

Etiologies and classification: 1) Congenital coxa vara — developmental coxa vara is the most common form, with multiple subtypes: a) Idiopathic developmental coxa vara — isolated condition, presents in early childhood, possible genetic component but specific gene unknown; characterized by progressive deformity during growth with delayed walking, painless limp; b) Cleidocranial dysplasia (RUNX2 mutations) — autosomal dominant, multiple skeletal anomalies including coxa vara, delayed clavicle ossification, dental anomalies, supernumerary teeth; c) Osteogenesis imperfecta — multiple fractures, blue sclerae, brittle bones, with secondary coxa vara from femoral neck deformity; d) Mucopolysaccharidoses (Hurler, Hunter, Morquio) — multiorgan involvement with skeletal dysplasia; e) Fibrocartilaginous dysplasia of femoral neck — rare, isolated; f) Skeletal dysplasias (camptomelic, Stickler, achondroplasia rarely); 2) Acquired coxa vara: a) Post-traumatic — following femoral neck fracture with malunion, SCFE (slipped capital femoral epiphysis) with chronic slip leading to coxa vara; b) Post-infectious — septic arthritis of hip in childhood with growth plate damage; osteomyelitis of femoral neck; c) Post-Perthes disease — Legg-Calvé-Perthes disease with femoral head deformity and secondary coxa vara; d) Metabolic bone disease — rickets (vitamin D deficiency), osteomalacia, fibrous dysplasia, Paget disease, hyperparathyroidism; e) Post-irradiation — radiation therapy to growing bone affecting growth plate; f) Idiopathic acquired in adults (rare).

Pathophysiology: 1) Mechanical disadvantage at hip — decreased neck-shaft angle reduces lever arm of hip abductors (especially gluteus medius), causing weakness and Trendelenburg gait; 2) Increased shear stress at femoral neck — predisposes to insufficiency fracture and SCFE; 3) Limb length discrepancy — affected leg shorter from displaced position of femoral head closer to acetabulum; 4) Altered hip mechanics — leads to abnormal cartilage loading and premature osteoarthritis; 5) Decreased range of motion — particularly abduction (limited by coxa vara) and internal rotation; 6) Stress fracture risk — particularly at the femoral neck; 7) Femoral head subluxation — in severe cases; 8) Secondary changes including capsular contracture, abductor weakness atrophy, gait pattern alterations.

Clinical presentation: 1) Childhood presentation (developmental) — painless limp typically noted by parents, delayed walking, abnormal gait pattern, leg length discrepancy noted clinically, no significant pain initially, may progress through growth; 2) Adolescent presentation (acquired SCFE) — painful limp with antalgic gait, hip pain often referred to thigh or knee, decreased hip range of motion especially internal rotation; 3) Adult presentation (acquired with osteoarthritis) — chronic hip pain with weight-bearing, decreased range of motion, Trendelenburg gait, leg length discrepancy; 4) Specific physical examination findings: a) Trendelenburg test positive (single-leg stance — pelvis tilts toward unaffected side due to gluteus medius weakness on affected side); b) Trendelenburg gait (waddling, lurching toward affected side); c) Leg length discrepancy (2-5 cm typical); d) Decreased hip range of motion (limited abduction, internal rotation); e) Hip adductor contracture; f) Greater trochanter elevation (above interpalatine line — Bryant triangle, palpable); g) Tenderness over greater trochanter; h) Decreased ipsilateral pelvic tilt; 5) Long-term complications include premature osteoarthritis of hip joint (50+ percent require hip replacement by 50 years if untreated), chronic pain, functional disability, gait abnormalities.