Femoral head bone mineral density patterns may identify hips at risk of degeneration

Developmental dysplasia of the hip (DDH) is a common abnormality that causes elevated contact stress and early onset osteoarthritis (OA). We hypothesized that adaptation of femoral head bone mineral density (BMD) patterns to focal loading during postnatal development could be used to identify hips at risk of degeneration. Evolving BMD patterns of the femoral head secondary center of ossification (SCO) were quantified and tested for differences with hip subluxation and degeneration. BMD was measured using quantitative computed tomography of hips in a canine model of DDH from 4 weeks to early skeletal maturity at 32 weeks. During body weight and SCO volumetric growth deceleration, SCO mean BMD increased rapidly and local regions of high BMD formed. Greater subluxation was associated with a lower mean BMD up to 14 weeks. At 32 weeks, greater subluxation was associated with a larger area of high BMD that was more laterally located and had a greater maximum BMD. BMD differences were associated with a higher probability of cartilage degeneration. Measurement and visualization of BMD pattern changes due to altered mechanical loading provide a basis for identifying hips at risk of early onset OA and a tool for surgical planning of contact stress reduction procedures.