The pelvic floor of standing, healthy dogs is consistently nearly horizontal, but the orientation of the lumbar spine varies more widely.

The ischiopubic symphysis is a more reliable reference than the lumbar spine for preoperative acetabular cup planning in canine total hip replacement.

This prospective observational study evaluated lumbar, sacral, and pelvic orientation in 17 healthy, client-owned dogs using standardized full-length lateral radiographs obtained in a standing position. Composite images were constructed from stitched radiographs, and multiple anatomical axes were measured relative to the horizontal plane. The primary aim was to characterize interindividual variability in spinal and pelvic orientation and to determine whether standing acetabular orientation could be predicted from other postural parameters. Key findings revealed that the ischiopubic symphysis (pelvic floor) remained consistently nearly horizontal across all dogs, demonstrating low interindividual variability. In contrast, lumbar spinal orientation was substantially more variable and did not reliably approximate a horizontal plane. Standing acetabular orientation was highly variable among individuals and showed no significant correlation with most postural parameters. The strongest predictor of standing acetabular orientation was the acetabular-pubic angle (R² = 0.70), though even this relationship has limitations given the variability observed. These findings have direct implications for preoperative planning in canine total hip replacement (THR), where accurate acetabular cup positioning is critical to implant longevity and function. The study suggests that using the lumbar spine as a reference for estimating functional acetabular orientation—a common clinical assumption—may be unreliable. Instead, the ischiopubic symphysis may serve as a more consistent and reproducible anatomical reference for surgical planning in canine THR procedures.

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