Use of patient-specific instrumentation for hip resurfacing arthroplasty: Measurement of accuracy using pre and postoperative CT-scan.

Abstract

Background: Hip resurfacing arthroplasty (HRA) is a valuable option for the treatment of primary osteoarthritis in young patients. However, the learning curve for femoral component implantation remains long. Few data are dedicated to patient-specific instrumentation (PSI) in this indication, and merely applied to limited study groups using X-rays as tool to assess accuracy of the method. Therefore, we conducted a prospective study assessing the results of PSI for HRA using pre- and postoperative CT scans based aiming to: 1) assess the accuracy of the planned axis in the axial and coronal planes, 2) evaluate if 3D planning could reproduce the native head diameter by a maximum deviation of one implant size (2 mm) from the component ultimately implanted.

Hypothesis: Our hypothesis was that PSI-assisted femoral component implantation would achieve an average accuracy within 5 ° of the planned axis in the axial and coronal planes.

Materials and methods: This prospective study analyzed 49 patients (51 HRA) with complete data from an initial cohort of 50 patients. On pre- and post-operative CT scans, the native caput-collum-diaphyseal (CCD) angle, stem-shaft angle (SSA), femoral anteversion and head diameter were measured. The objectives for the PSI jig were to restore head diameter, femoral anteversion and to implant the femoral component with a planned +5 ° valgus alignment in the coronal plane.

Results: During the surgery, the calcar-guided PSI (inferior jig) was used in 39 cases (76.4%), and the posterior neck-guided PSI (posterior jig) was used in 12 cases (23.6%). No jig failures were observed. Native femoral anteversion averaged 20 ° (range, 15-24) compared to 18.5 ° (range, 10-27 °) postoperatively (p = 0,3). The mean preoperative CCD was 132.5 ° (range, 126-137). The planned SSA was 138 ° (range, 132-143) while the postoperative SSA was 136.5 ° (range, 129-143) (p = 0,1). With accurate positioning being defined as placement within 5 ° of the planned anteversion and SSA, 48 cases (94.1%) achieved the desired femoral component positioning. The mean acetabular cup and femoral head diameters were respectively 58 mm (range, 54-64) and 52 mm (range, 48-58). The native head diameter averaged 51.5 mm (range, 47-57) (p = 0,2).

Discussion: The accuracy of the HRA position was excellent, with more than 94% of cases achieving desired positioning. The maximum difference between the planned and implanted head sizes was 2 mm (1 size), confirming our hypothesis. These findings support the use of this type of PSI for the HRA procedure.

Level of evidence: IV; prospective case series.