Abstract
Sagittal pelvic tilt (PT) has been shown to effect the functional position of acetabular components in patients with total hip replacements (THR). This change in functional component position may have clinical implications including increased likelihood of wear or dislocation. Surgeons can use computer-assisted navigation intraoperatively to account for a patient's pelvic tilt and to adjust the position of the acetabular component. However, the accuracy of this technique has been questioned due to the concern that PT may change after THR. The purpose of this study was to measure the change in PT after THR, and to determine if preoperative clinical and radiographic parameters can predict PT changes after THR.
138 consecutive patients who underwent unilateral THR by one surgeon received standing bi-planar lumbar spine and lower extremity radiographs preoperatively and six weeks postoperatively. Patients with prior contralateral THR, conversion THR and instrumented lumbosacral fusions were excluded. PT and pelvic incidence (PI) were measured preoperatively for each patient, and PT was measured on the postoperative imaging. A negative value for PT indicated posterior pelvic tilt. Patient demographics were collected from the chart.
Average age was 56.8±10.9 years, average BMI was 28.3±6.0 kg/m2, and 67 patients (48.6%) were female. Mean preoperative pelvic tilt was 0.6°±7.3° (range: −19.0° to 17.9°). We found greater than 10° of sagittal PT in 23 out of 138 (16.6%) patients in this sample. Mean post-operative pelvic tilt was 0.3°±7.4° (range: −18.4° to 15.0°). Mean change in pelvic tilt was −0.3°±3.6° (range: −9.6° to 13.5°). PT changed by less than 5° in 119 of 138 patients (86.2%). The mean difference in pre-operative and post-operative PT is not statistically significant (p = 0.395). Pre-operative PT was strongly correlated with post-operative PT (r2 = 0.88, p = 0.0001) (Figure 1). There was not a statistically significant relationship between PI and change in PT (r2 = −0.16, p = 0.06).
In conclusion, based on the variability in pelvic tilt in this study population and the relatively small change in pelvic tilt following THA tilt-adjustment of the acetabular component position based on standing pre-operative imaging is likely to be of benefit in the majority of patients undergoing navigated THA. However, we have been unable to predict the relatively rare occurrence of a large change in pelvic tilt, which would confound tilt-adjusted component position.
