Objective:To investigate the effects of periacetabular osteotomy (PAO) in treating borderline developmental dysplasia of the hip (DDH).Methods:The patients with borderline DDH [lateral center-edge angle (LCEA): 18°-25°) who received PAO with follow-up duration for more than 2 years from January 2011 to January 2018 in our hospital were retrospectively analyzed. The patients in the control group were matched on a 1∶2 ratio based on gender, age, body mass index (BMI) and follow-up duration. There were 66 patients in the 0°≤LCEA<10° group and 66 patients in the 10°≤LCEA<18° group. The LCEA, anterior center-edge angle (ACEA), T?nnis angle, femoral head extrusion index, femoro-epiphyseal acetabular roof (FEAR) index, femoral anteversion angle, West Ontario and McMaster University (WOMAC) index and International Hip Outcome Tool (iHOT-12) were compared among the three groups before operation and the last follow-up.Results:In the preoperative 18°≤LCEA<25° group, three of 33 patients (9.1%) had LCEA, because the only imaging feature suggested acetabular dysplasia, while other parameters were evaluated within the normal range. There were 17 patients with ACEA <20° (51.5%), 24 patients (72.7%) with T?nnis angle >10°, 12 patients (36.4%) with ACEA <20° and T?nnis angle >10°. The positive rate of posterior wall signs in the 18°≤LCEA<25° group (72.7%) was lower than that in the 10°≤LCEA<18° group (77.3%) and the 0°≤LCEA<10° group (90.9%) with statistically significant difference (χ 2=6.417, P=0.040) at preoperation. The positive rate of cross sign (27.3%) and ischial spine sign (48.5%) in the 18°≤LCEA<25° group were higher than those in the 10°≤LCEA<18° group (10.6% and 18.2%, respectively, χ 2=7.002, P=0.030) and the 0°≤LCEA<10° groups (9.1% and 13.6%, respectively, χ 2=16.497, P<0.001). The FEAR index in the 18°≤LCEA<25° group (3.7±8.0) lower than that in the 10°≤LCEA<18° group (4.3±7.9) and the 0°≤LCEA<10° group (11.0±8.8) with significant difference ( F=12.703, P<0.001). In the 18°≤LCEA<25° group, postoperative LCEA increased from 20.4°±1.8° to 37.8°±7.1°, ACEA increased from 18.3°±7.8° to 36.3°±6.3°. T?nnis angle decreased from 12.7°±6.2° to -5.6°±9.2°, the femoral head extrusion index decreased from 22.9%±6.7% to 10.7%±12.2%, the WOMAC index decreased from 20.1±13.4 to 6.0±6.3, and the iHOT-12 score increased from 50.2±19.9 to 90.0±13.7. The above difference before and after surgery was statistically significant ( P<0.05). At the last follow-up, the WOMAC score in the 18°≤LCEA<25° group was 6.0±6.3, wich was less than 10°≤LCEA<18° group (9.3±9.6) and 0°≤LCEA<10° group (12.0±16.0) ( F=6.515, P=0.002). The iHOT-12 score in the 18°≤LCEA<25° group was 90.0±13.7, which was greater than 10°≤LCEA<18° group (77.7±17.3) and 0°≤LCEA<10° group (78.1±20.5) ( F=15.833, P<0.001). Conclusion:After 2 years follow-up, PAO significantly improved bone coverage of femoral head and hip function in patients with borderline DDH. Before surgery, we should pay attention to the comprehensive evaluation of different radiological parameters of the acetabulum, to make better preoperative planning.

Objective:To investigate the stability and feasibility of using absorbable screws during Bernese periacetabular osteotomy.Methods:A retrospective analysis was conducted on a 36 year-old woman diagnosed with developmental dysplasia of the hip, who had undergone Bernese periacetabular osteotomy. Finite element analysis was used to simulate the stability of the acetabulum under loads of 10%, 20%, 50%, and 100% of the patient's weight. The structural stiffness of the pelvis and the maximum equivalent stress on the absorbable screws were observed under different conditions, including whether the acetabular bone block and the ilium were in contact, whether 3 or 4 screws were used, and whether a graft (including fibular cortical bone and PEEK grafts) was used.Results:The structural stiffness of the pelvis fixed with four screws increased by 67%-94% compared to that with three screws. After using a graft, the structural stiffness of the pelvis increased by 50%-83%. As the load increased, the maximum equivalent stress on the screws also increased. When the acetabular bone block and the ilium had no contact, no graft was used, and only three screws were used for fixation, the maximum equivalent stress could reach 518.9 MPa, while this value dropped to 61% when four screws were used (318.7 MPa). When the acetabular bone block and the ilium were in contact, the maximum equivalent stress was about 12% of that when there was no contact, regardless of the number of screws used. When a cortical bone graft or a PEEK graft was used, the maximum equivalent stress could drop to 21%-26% of that without a graft. When the screw strength was 130 MPa, a load of 20% of body weight was applied, and only three screws were used without a graft, the equivalent stress could exceed the strength of the screw; if four screws were used, the equivalent stress was slightly higher than the strength of the screw when a load of 50% of body weight was applied. However, when a graft was used (either cortical bone or PEEK), even when a load of 100% of body weight was applied, the equivalent stress was slightly lower than the strength of the screw.Conclusion:Absorbable screws can provide sufficient stability for Bernese periacetabular osteotomy. The contact between the acetabular bone block and the ilium, an increase in the number of screws, and the use of grafts (cortical bone and PEEK grafts) can further improve stability. Therefore, absorbable screws have broad application prospects in Bernese periacetabular osteotomy.