Effect of surgical experience on imageless computer-assisted femoral component positioning in hip resurfacing--a preclinical study

Abstract

Background: The clinical outcome of hip resurfacing (HR) as a demanding surgical technique associated with a substantial learning curve depends on the position of the femoral component. The aim of the study was to investigate the effects of the level of surgical experience on computer-assisted imageless navigation concerning precision of femoral component positioning, notching, and oversizing rate, as well as operative time.

Methods: Three surgeons with different levels of experience in both HR and computer-assisted surgery (CAS) prepared the femoral heads of 54 synthetic femurs using the Durom(TM) Hip Resurfacing (Zimmer, Warsaw, IN, USA) system. Each surgeon prepared a total of 18 proximal femurs using the Navitrack® system (ORTHOsoft Inc., Montreal, Canada) or the conventional free-hand Durom(TM) K-wire positioning jig. The differences between planned and postoperative stem shaft angle (SSA) and anteversion angle in standardized x-rays were measured and the operative time, not including the time for calibrating the CAS-system, was documented. Notching was evaluated by the three surgeons in a randomized manner. Oversizing was determined by the difference of the preoperative determined cap and the cap size advised by the CAS-system.

Results: CAS significantly reduced the overall mean deviation between planned and postoperative SSA in comparison with the conventional procedure (mean ± SD, 1 ± 1.7° vs. 7.4 ± 4.4°, P < 0.01) regardless of the surgeon's level of experience. The incidence of either varus or valgus SSA deviations exceeding 5° were 1/27 for CAS and 15/27 for the conventional method, respectively (P < 0.001), corresponding to a reduction by 97%. Using CAS, the rate of notching was reduced by 100%.

Conclusions: The accuracy of femoral HR component orientation is significantly increased by use of CAS regardless of the surgeon's level of experience in our preclinical study. Thus, imageless computer-assisted navigation can be a valuable tool to improve implant positioning in HR for surgeons at any stage of their learning curve.

Figure 1

Screenshot from the Navitrack® Software: The left (axial) and the right (ap) illustration show the digitalized femur. The template in the middle demonstrates risks for possible notching in each quadrant of the neck (red quadrants).

Figure 2

Head/neck morphology of the three types of synthetic femurs used in this study. Anterior (a), top (b), and posterior (c) view: normal configuration, osteophytes, slipped epiphysis (right to left).

Figure 3

Experimental setup mimicking the position of the proximal femur after exposure by dorsal approach during hip resurfacing procedure. Overview (a), side view (b), and close up (c).

Figure 4

Representative X-ray image including CCD angle (here 130.3°), planned position (here stem shaft angle 134°), and size (here “44”) of the femoral component.

Figure 5

Deviation between planned and achieved stem shaft angle in degree comparing conventional jig and computer-assisted surgery.

Figure 6

Notching events in the superior (a) and posterior (b) quadrant (arrows).