WHAT IS THE ACCURACY OF HIP CENTERING ACQUIRED WITH IMAGE-FREE SYSTEMS

Abstract

Purpose of the study: Knee prosthesis surgery has reached a high level of reproducibility, providing very satisfactory results in the large majority of patients. There remains however a certain lack of precision concerning this surgical procedure concerning the determination of the hip center. This point is used to establish the mechanical axis of the femur for positioning the prosthesis. Navigation systems can be used to localize this center. We conducted a cadaver study to determine the accuracy and repeatability of this method for determining the center of the hip joint.

Material and methods: A computerized navigation system was applied to seven fresh cadavers with normal hips. We compared the anatomic center of the hip joint with the point determined with the navigation system. We also compared the navigation technique using different navigation techniques: marker fixed on the iliac crest and without marker fixed on the iliac crest. We also determined the accuracy of the result as a function of hip circumduction during acquisition (5°, 8°, 10°).

Results: There was no statistical difference between investigator A (0.66±0.15, max error: 0.99) and B (0.68±0.10, max error: 0.87), p=0.98 (inter or intra-observer) for comparisons between the anatomic center of the hip joint and the point determined by the navigation system. The results were not statistically different between the navigation techniques (with and without a marker fixed on the iliac crest):(mean < 0.71 ± 032, max. error: 1.91) for each hip with the iliac marker (0.66 ± 0.20, max. error max: 0.99) or without the iliac marker (0.61 ± 0.41, max. error: 1.29) for hip 1. Accuracy was better for hip movement at 10° (0.60 ± 0.21, max. error: 0.92) than at 8° (0.81 ± 0.52, max. error: 1.91) or at 5° (0.67 ± 0.46, max. error: 1.91). In addition, without an iliac crest marker, 75% of the errors were less than 1, and 95% less than 1.5.

Discussion: Acquisition of the hip center of rotation using a computerized navigation system with or without use of markers fixed on the iliac crest is remarkably accurate.

Conclusion: New algorithms and control systems should help improve reproducibility above that obtained with the conventional technique.