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.

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.

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.

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).

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.

IV; prospective case series.