Patient-Specific Flanged Acetabular Component Failure Is Associated With Excess Lateral Position Relative to Planned Position and Excess Cranial Position Relative to Anatomic Hip Center.

Abstract

Patient-specific custom flanged acetabular components (CFACs) are custom implants used in complex acetabular revision. Although CFACs are designed for precise positioning, accurate placement can be challenging. It is unclear whether placement accuracy of CFACs impacts aseptic loosening and survivorship. This study aimed to 1) evaluate accuracy of CFAC placement relative to (a) planned position and (b) anatomic hip center (AHC) and 2) determine whether placement accuracy is associated with radiographic failure or re-revision. A retrospective review of 99 CFAC procedures in 94 patients (mean age 62, range, 37 to 82) from 2004 to 2017 was performed. Postoperative radiographs were used to compare the distance between the postoperative final CFAC position and the preoperatively planned position. Implant distance from AHC (as defined by the Fujii modification of the Ranawat hip center) was also measured. Aseptic failure was defined as radiographic failure or revision involving CFAC removal for aseptic loosening. At a mean follow-up of 11.7 years, 16 cases (16.2%) underwent subsequent re-revision; and eight additional cases (8.1%) developed radiographic loosening. Only 34 implants (40.0%) were placed within five mm of the planned position. The mean distance from the planned position was 7.1 mm (0.4 to 34.7) and from the AHC was 18.5 mm (2.8 to 65.8; P < 0.0001). Revised CFACs were placed more laterally to the planned position compared to maintained implants (5.7 mm lateral versus 3.0 mm lateral; P = 0.04). Implants greater than seven mm lateral to plan were more likely to undergo CFAC revision (57.1 versus 11.3%; P = 0.004). Failed CFACs were placed more cranially relative to AHC than nonfailed FACs (13.0 mm cranial versus 7.3 mm cranial; P = 0.048). Patient-specific CFACs were placed greater than five mm from the planned position in 60% of cases. Excess lateral placement relative to plan was associated with re-revision. Excess proximal position relative to AHC was associated with failure. Surgeons should aim for accurate CFAC placement relative to the plan and anatomical alignment with the hip center, especially in the craniocaudal axis.