Evaluation of three acetabular measurement methods for total hip replacement in dogs.

Objective: To compare three measurement methods for acetabular sizing and evaluate the influence of osteoarthritis (OA) on the accuracy of measurements.

Study design: Observational study.

Sample: Radiographic images of 73 hip joints from 60 dogs with cementless cups.

Methods: Radiographs were anonymized and measured independently by three observers. One observer measured 12 sets of radiographs three times. A best-fit acetabular circle (AC) and cranial-caudal acetabular line (AL) were measured on ventral-dorsal (VD) radiographic view and open leg lateral (OLL) view. A best-fit femoral head circle (FHC) was measured on VD, OLL, and craniocaudal horizontal beam (CCHB) views. Two observers scored the OA in each hip joint. Intra- and interobserver consistency and repeatability and bias relative to implanted cup size were calculated and analyzed.

Results: Intraobserver consistency and repeatability were excellent for all measurements. Interobserver consistency was excellent (ICC > 0.9) for AC_VD and AC_OLL and was good (0.75 < ICC ≤ 0.9) for all other methods. Bias was small for AC and AL measurements (range, -0.46 to 0.45 mm) and large for FHC measurements (-3.58 to -2.42 mm). OA score significantly influenced bias for all acetabular measurement methods (p < 0.05).

Conclusion: All acetabular measurement methods were highly consistent within an observer. Interobserver consistency was highest for AC_VD and AC_OLL. FHC measurements underestimated cup size. Higher OA scores decreased the accuracy of all acetabular measurement methods.

Clinical significance: Superimposing a circle on the acetabulum seen on VD radiographic view accurately measures the acetabulum before cementless cup placement.