Fixation of the mobile fragment in periacetabular osteotomy: a clinical study of two- vs. three-screw fixation with 4-week partial weight bearing

Aim Fixation of periacetabular osteotomy (PAO) has been a matter of interest since development of the procedure. Despite the stability of the construct, no consensus regarding the minimum number of screws needed for fixation is present. The aim of this study was to compare two-screw and three-screw fixation techniques in the clinical setting. Methods The study included a consecutive series of 100 hips that had undergone PAO surgery by a single surgeon between January 2022 and July 2023 with complete radiographic follow-up. The mobile fragment was fixed using three screws in 27 hips and two screws in 73 hips . Both groups did not significantly differ in any morphometric measure. Lateral center edge angle (LCEA), Acetabular index (AI), extrusion index (EI), anterior wall (AWI), and posterior wall index (PWI) were measured by two independent investigators preoperatively, immediately after surgery and at 1 year follow-up and interobserver agreement measured. Analysis of variance (ANOVA) was used for comparison. Results No change of correction of > 4° was observed in any hip in both groups. Both groups did not significantly differ regarding any change in radiographic measure in ΔLCEA (1.09 ± 2.46 vs. 0.52 ± 3.11, p = 0.34), ΔEI (− 1.94% ± 2.97% vs. − 0.44% ± 5.75%, p = 0.25), ΔAI (− 0.10 ± 1.71° vs. 0.21 ± 1.83, p = 0.72), ΔAWI (0.25% ± 7.78% vs. 0.02% ± 12.05%, p = 0.57), ΔPWI (4.03% ± 9.94% vs. 3.43% ± 10.79%, p = 0.38). There was no difference in complications between groups. The rate of non-union at 1 year was lower in the two screw group, although not significant (7% vs. 17%, p = 0.38). Conclusion The results emphasize the inherent stability of the PAO construct and demonstrate that the use of two screws for fixation of the mobile fragment is sufficient in PAO surgery, provided that the fragment was fully mobilized during surgery and at least 50% bony contact on the iliac wing was achieved. Furthermore, a 4 week partial weight bearing regimen is also adequate during the healing phase.