Abstract
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.