Positioning of custommade acetabular components at revision hip arthroplasty: do they really match as “a key and a lock”?

Purposes are to determine 1) what frequency and what degree is of custom acetabular implants malposition in comparison with planned position, 2) what the reason of malposition is and 3) what the malposition consequences we can wait for. Patients and methods. The observation group included 20 patients (18 women and 2 men) with severe acetabular defects. Mean age of patients made up 53 (22-72) years. Position of the implants was compared with the parameters of preoperative planning using 5 postoperative CT indices (inclination, anteversion of semi- spherical part of the implant, spatial location of the rotation center in three axes). More than 10° deviation for inclination or anteversion and 5° dislocation of the rotation center in any axis was considered as a malposition of the component. Results. Only 5 of 20 constructions matched conditionally permissible limits by all the parameters. Most often excessive dislocation of the rotation center in lateral direction (10 cases) and excessive anteversion (9 cases) were observed. During 6 weeks follow up no complications related to the acetabular component position were recorded. Conclusion. It was shown that at revision arthroplasty with custom-made implants the probability of implant malposition as compared to the preoperative plan. The main reason could be the complexity of intraoperative orientation under conditions of abnormal hip anatomy. Malposition of the implants beyond the stated values did not result in complications within the early postoperative period. The longer follow up is required for the assessment of the long-term results.