Reliability of Sagittal Spinopelvic Alignment Measurements After Total Hip Arthroplasty.

STUDY DESIGN: This is a observational study.

OBJECTIVE: To evaluate the reliability of measuring sagittal spinopelvic alignment after hip arthroplasty.

SUMMARY OF BACKGROUND DATA: Pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), and lumbar lordosis (LL) are widely used in planning the treatment of people with spinal and hip disorders. Previously, these measures have proved reliable when hip heads are intact. Thus far, it is not known whether they are also reliable after total hip replacement.

MATERIALS AND METHODS: Two observers assessed PI, SS, PT, and LL in the radiographs of 97 patients who had undergone total hip replacement. Test-retest (intraobserver) and interobserver reliability were estimated.

RESULTS: The intraclass correlation coefficient ranged from 0.92 to 0.97 and 0.85 to 0.94 for the intraobserver and interobserver settings, respectively, indicating an almost perfect correlation between observers or observations. The absolute intrarater measurement errors were 1.41 [95% confidence interval (CI), 0.98-2.03) for PI, 1.16 (95% CI, 0.78-1.74) for SS, 0.49 (95% CI, 0.31-0.76) for PT, and 1.75 (95% CI, 1.22-2.51) degrees for LL. The respective interrater figures were 2.82 (95% CI, 2.04-3.9), 2.44 (95% CI, 1.78-3.35), 0.73 (95% CI, 0.48-1.13), and 2.28 (95% CI, 1.55-3.34) degrees.

CONCLUSIONS: It seems that total hip arthroplasty does not affect the reliability of spinopelvic sagittal alignment measurements.

LEVEL OF EVIDENCE: Level II.