Does pelvic tilt change with a peri-acetabular osteotomy?

Change in pelvic tilt (PT) during and after peri-acetabular osteotomy (PAO) is important for surgical planning. The aims of this study were to (i) determine how PT varies throughout the course of treatment in patients undergoing PAO, (ii) test what factors influence the change in PT and (iii) assess whether changes in PT influenced achieved correction. This is an retrospective, single-centre, consecutive case series of 111 patients treated with PAO for global (n = 79), posterior (n = 49) or anterior dysplasia (n = 6) (mean age: 27.3 +/- 7.7 years; 85% females). PT was determined on supine, anteroposterior pelvic radiographs pre-, intra-, 1 day, 6 weeks and 1 year post-operatively, using the sacro-femoralpubic (SFP) angle, a validated, surrogate marker of PT. An optimal acetabular correction was based on the lateral centre-edge angle (25 degrees-40 degrees), acetabular index (-5 degrees to 10 degrees) and cross-over ratio (<20%). There was a significant difference across pre-(70.1 degrees +/- 4.8 degrees), 1-day (71.7 degrees +/- 4.3 degrees; P < 0.001) and early post-operative SFP (70.6 degrees +/- 4.7 degrees; P = 0.004). The difference in SPF between pre-operative and 1-year post-operative was -0.5 degrees +/- 3.1 degrees (P = 0.043), with 9% of cases having a difference of >5 degrees. The difference in SFP did not correlate with age, sex, body mass index, type of dysplasia or achievement of optimal acetabular correction (P = 0.1-0.9). In the early post-operative period, PT is reduced, leading to a relative appearance of acetabular retroversion, which gradually corrects and is restored by annual follow-up. The degree of change in PT during PAO did not adversely affect fragment orientation. PT does not significantly change in most patients undergoing PAO and therefore does not appear to be a compensatory mechanism.