Aim: The purpose of the study was to develop an instrument for positioning a resurfacing femoral component.

Materials and Methods: A new alignment device was developed, which references the natural anatomy of the patient and positions the implant in valgus, slight ante-version and centrally in the femoral neck.

Results: The device was used to position a resurfacing femoral component in 20 cadaveric femora (Group A) and in 15 patients (Group B). In the cadaver group, the valgus and version angles as well as the position of the component relative to the femoral neck centerline were assessed, using pre- and post-operative radiographs and transverse slices of the femoral necks along the component center line. In group A, the achieved valgus and ante-version angles were 9.95 ± 2.35 degrees and 1.87 ± 3.85 degrees, respectively. In the vertical plane, the implant was 0.50 ± 1.52 mm superior and in the horizontal plane, 0.57 ± 1.84 mm posterior to the centreline of the femoral neck. In the patient group, the valgus angle was 9.79 ± 5.38 degrees and the implant was 0.67 ± 1.27 mm inferior in the vertical plane. There was no notching in any of the cases. There was a very strong correlation between the pre op Neck Shaft angle and the postoperative valgus achieved (r =0.902)

Conclusion: The alignment device was quick and easy to use and positioned the femoral resurfacing component accurately and reproducibly referencing the native anatomy. The small size of the instrument makes it useful in minimally invasive techniques. The self-centering three-point design proved to be stable and superior to other currently available instruments.

Aim: The purpose of the study was to compare the placement of the guide wire for the femoral components in hip resurfacing, implanted using computer navigation and a new alignment device(jig).

Materials and Methods: The study was conducted on 13 cadaveric femora. Registration of the femoral head was carried out using Computer Aided Navigation system, Brainlab (BL) by the senior author. Guide wires were inserted using BL by the senior author and subsequently with the alignment device (jig) by the junior author. The junior author was blinded to the templated position and implanted the wire using the jig. In 6 femurs the implantation of the prosthesis was carried out in the position suggested by the BL and in 7 by the jig. All the femora were sectioned transversely after implantation and measurements were taken using callipers and subsequently using Autocad.

Results: There was no notching of the superior femoral neck in either of the groups. The mean and standard deviation of the anatomic neck-shaft angles was 124.91° ± 14.25°. The wire-shaft angle in the BL group was 131.46° ± 5.27° and in the jig group 134.08° ± 3.80°. In the BL group the wire was in 0.85° ± 2.15° of retroversion as compared to 1.38° ± 4.19° of anteversion in Jig group. The position of the wires at the narrowest cross section of the femoral neck is shown in figure.

Conclusion: The alignment device consistently positioned the wire more valgus and anteverted than Computer aided navigation, which was desired. In all cases, the wire position was well within acceptable limits. Computer aided navigation does not seem to offer distinct advantages in resurfacing hip replacements.