Introduction In this study, we described a positioner which allows a combination of preoperative plan and intraoperative insertion of the cup to improve the reconstruction of the rotation center of the hip. Materials and methods A retrospective study was conducted on 32 consecutive patients (group A) using this positioner and 40 consecutive patients (group B) using conventional method; radiological parameters and clinical measurements before operation and at last follow-up were collected and evaluated. Results Group A had a reconstructed center of rotation (COR) that was 0.19 mm closer to the anatomic COR in height ( P < 0.005), compared with group B with 3.45 mm vertical dislocation. There were no statistically significant differences in the horizontal displacement between the two groups. The accuracy of cup inclination was 42.14 ± 3.57 in the group A and 38.73 ± 7.65 in the group B ( P = 0.015). The accuracy of cup anteversion was 14.82 ± 1.44 in the group A and 13.08 ± 5.95 in the group B ( P = 0.082). All cups in the group A were radiologically stable, while one cup in the group B was radiologically unstable and was successfully treated with second-stage revision. Both of the groups obtained a higher mean postoperative Harris Hip Score. Conclusions Utilizing this positioner helps to restore the COR position more precisely and provides satisfactory radiological and clinical outcomes in the short term, and more studies are required before its widespread adoption for complicated cases.

Introduction: To invest the auxiliary role of Patient specific Instrument(PSI) used as osteotomy guide plate in total knee arthroplasty(TKA) with valgus knee. Hypotheses: PSI osteotomy guide plate is applicable for total knee arthroplasty with valgus knee. Methods: A retrospective analysis was performed on 21 patients with valgus knee, including 5 males and 16 females, who underwent TKA in joint surgery department I of ZhengZhou Orthopaedic Hospital from March 2016 to February 2018. All the operations were performed with the assistance of PSI, and the radiographic and clinical evaluations including femoral tibial joint ectropion angle(FTA) before and after operation, range of motion(ROM) and the Hospital for Special Surgery (HSS) knee score were reviewed, and surgical complications were recorded. Results: All the 21 patients werefollowed up for 10 ˜ 26 months (mean 16 months).All the incisions healed by first intention. The FTA was reduced significantly to 6.3 °±1.2° after operation from 17.6 ° + 5.7 °(P < 0.05), the ROM was improved significantly from preoperative 71.3° ±5.8° to postoperative 102.4°±7.5° (P < 0.05), the HSS score at the last follow-up was improved from 38.2±5.7 to 87.5-3.5(P < 0.05). During the follow-up, no complications such as infection, loosening, sinking and valgus were observed. Conclusion: Providing accurate osteotomy, effective correction of the force line, simple operation and satisfactory clinical effect, the PSI osteotomy guide plate is applicable for total knee arthroplasty with valgus knee.