Impaired ossification coupled with accelerated cartilage degeneration in developmental dysplasia of the hip: evidences from μCT arthrography in a rat model

BACKGROUND Developmental dysplasia of the hip (DDH) always leads to cartilage degeneration and osteoarthritis of the hip joint. However, the diagnosis of early cartilage degeneration in DDH is still a clinical challenge. This study aims to investigate the dynamic changes of bone and cartilage in the hip of a rat model of DDH and to explore the potential application of microcomputed tomography (μCT) arthrography to detect early cartilage degeneration in DDH. METHODS Newborn Wistar rats were used to induce DDH by hindlimb swaddling. The bone and cartilage of the hip in model and control group were analyzed by μCT arthrography and histology examination at postnatal day 10, week 4, 6 and 8. RESULTS Hip dysplasia developed with age, became obvious at postnatal week 6 and further progressed at week 8. μCT analysis showed that bone mineral density (BMD) and bone volume density (bone volume over total volume, BV/TV) of the femoral head and neck region (FHNR) in model group were both significantly lower than those in control group, and they increased dramatically from postnatal week 4 to week 6 but maintained at a similar level at week 8. Contrast-enhanced μCT (CE-μCT) arthrography and histology data showed age-dependent increase in cartilage attenuation (CA) and decrease in safranin O staining intensity (SI) in model group, respectively. Moreover, the model group revealed remarkably higher CA and lower SI than control group, respectively. In addition, significant changes of CA and SI were both observed from postnatal week 6 to week 8 in model group. A strong linear correlation (r2=0.789, P <0.001) was found between CA and SI in model group. Furthermore, BMD was negatively correlated with SI (t=-2.683, P <0.05), whereas specific bone surface (bone surface over bone volume, BS/BV) was positively correlated with SI (t =4.501, P <0.01), in model group. CONCLUSIONS Impaired ossification coupled with continuous loss of sGAG in cartilage matrix was found in the dysplasia hip during the disease progression of DDH. Cartilage degeneration in the dysplasia hip may occur early at childhood, accelerated with age and become irreversible at young adult stage. All these abnormal changes could be quantitatively assessed by μCT arthrography.