Design of custom-made navigational template of femoral head and pilot research in total hip resurfacing arthroplasty

Abstract

Background: To develop a novel custom-made navigational template for accurate prosthesis implantation in total hip resurfacing arthroplasty (THRA) by computer-aided technology.

Methods: The template was produced based on data preoperatively acquired from computed tomography (CT) scan. The position of the drill guide was obtained according to the anatomical axis of the femoral neck which was defined by the point of the femoral head center and another point of the femoral neck center. The final direction of the drill guide was confirmed by a valgus angle. The surface of the template was constructed based on the inverse of the femoral neck surface. Then the template was made of acrylate resin by using rapid prototyping (RP) technique. Finally, all the templates were verified in 17 cadavers arranged for THRA and postoperative medical images were employed to evaluate the accuracy and validity of the template.

Results: The templates had achieved a high fitting with the femoral neck surface, and there were no guide failures. Postoperative evaluation revealed that the Kirschner-wires pass through the center of the femoral head and femoral neck, presenting a relative expected and acceptable valgus angle to the central axis of the femoral neck. The lateral offset showed the relative valgus angle achieved as expected, the horizontal offset showed that no obvious antero-posterior deviation occured. The comparison between the preoperative Neck-shaft angle (NSA) and the postoperative Stem-shaft angle (SSA) showed there is no significant difference(P > 0.05).

Conclusion: The novel custom-made navigational template of femoral head can effectively assist surgeons for accurately implanting the femoral head components to the desired position in THRA.

Keywords: Anatomical axis of the femoral neck; Computer assisted surgery; Custom-made navigational template; Rapid prototyping; Total hip resurfacing Arthroplasty.

Fig. 1

Calculating the anatomical central axis of femoral neck. a Calculating the femoral head center by fitting a suitable sphere (yellow point). b Calculating the the proximal femur centerline and the femoral neck center (red point)

Fig. 2

Virtual location of the drill guide. The initial position (red) was consistent with the central axis of the femoral neck. The final direction (green) was confirmed by a small valgus angle of 5°-10° around the femoral head center

Fig. 3

The design of navigational template. a The direction of the template was consistent in the drill guide. b The virtual surface of template matched the femoral neck surface perfectly

Fig. 4

The actual model of the navigational template produced by rapid prototyping

Fig. 5

Cadaveric experiment. a The exposure and dislocation of the femoral head. b The navigational template fitted the femoral neck perfectly and a Kirschner wire was nailed in for fixation

Fig. 6

Postoperative x-rays and CT reconstruction show the perfect and accurate position of Kirschner wire. a Postoperative x-rays show the anteroposterior and lateral position of the Kirschner wire. b 3D reconstruction of postoperative CT scan shows the optimal postion of the Kirschner wire

Fig. 7

The NSA preoperative and SSA postoperative. Data are expressed as mean ± SD, and there is no significant difference (P > 0.05)

Fig. 8

Folded diagram of the lateral offset and the horizontal offset. The horizontal coordinates describes the number of included specimens, and the vertical coordinates describes the degree of lateral offset angle (black) and horizontal offset angle (gray) postoperative. As we can see from the diagram, the lateral offset shows expected requirement of relative valgus angle was achieved, the horizontal offset shows no obvious antero-posterior deviation had occured