Dorsal femoral head coverage width index

The dorsal femoral head coverage width index (or dorsal acetabular femoral head coverage width index) is a measurement used to assess the anatomy of the hip joint in dogs. It quantifies the extent of lateral and dorsal coverage of the femoral head and is used to score coxofemoral dysplasia.

The dorsal femoral head coverage width index is determined from a ventrodorsal radiograph of the hips. The dog is placed dorsal recumbency and the pelvic limbs are extended caudally, the femurs are parallel to each other. Positioning is considered satisfactory if :

• the pelvis is symmetrical (iliums and obturator foramina are symmetrical)

• the femur cortex pass through the middle of the sesamoid bones of the gastrocnemius muscle

• the patellas are centered on the trochlea of femur.

A best fit circle outlining the head of femur is drawn to define its center. Femoral head diameter is drawn perpendicular to and bisecting the corresponding dorsal acetabular margin to measure the width of the dorsal acetabulum that overlays the femoral head at this level. The dorsal femoral head coverage width index is calculated by dividing the width of dorsal acetabular coverage by the femoral head diameter

Mostafa et al (2022) measured the following dorsal femoral head coverage width index in adult Labrador Retrievers (mean ± SD (range):

• Normal hip joints: 0.56 ± 0.05 (0.55–0.57)

• Near normal hip joints: 0.53 ± 0.06 (0.52–0.55)

• Mild hip dysplasia: 0.47 ± 0.06 (0.45–0.49)

• Moderate hip dysplasia: 0.39 ± 0.09 (0.36–0.41)

• Severe hip dysplasia: 0.28 ± 0.09 (0.26–0.30)