FIRST RESULTS OF A NOVEL NAVIGATION SYSTEM FOR TOTAL HIP ARTHROPLASTY

Abstract

Purpose of the study: Most systems used for computer-assisted total hip arthroplasty require preparatory computed tomography acquisition or use of multiple bone markers fixed on the pelvis. In order to overcome these problems, we developed a novel system for CT-free computer assisted hip surgery based on a functional approach to the hip joint. The concept is to orient the cup within a cone describing hip motion. The purpose of the present study was to analyze preliminary results obtained with this new system.

Material and methods: This new system was used to implant 18 primary total hip arthroplasties in 16 women and 2 men (mean age 68±7.8 years, age range 54–83 years) with degenerative disease. Two optoelectronic captors were fixed percutaneously on the pelvis and the distal femur. The acetabulum was reamed, then the femur prepared with instruments of increasing caliber. The last reamer positioned in the shaft carried an upper head which matched the size of the prepared acetabulum. Hip joint motion was recorded to determine the cone of maximal hip mobility. The system then oriented the cup so that this cone was completely included the cone described by the prosthesis.

Results: There was one traumatic posterior dislocation (fall in stairs) at three weeks, without recurrence. The Postel Merle d’Aubigné score improved from 8±2.9 (3–12) preoperatively to 17±0.8 (16–18) at last follow-up. None of the patients complained about the sites where the percutaneous markers were inserted and ther were no cases of hematoma or fracture. Mean leg length discrepancy was 5.6±7.5 mm (range 0–25 mm) before surgery and 0.6±3 mm (range −5 to 10 mm) at last follow-up. Mean anteversion of the femoral implant was 22.3±6.7° (14–31). Anatomic anteversion of the cup (measured from a marker linked to the pelvis and thus independently of the position of the pelvis) was 25.9±10.4° (12–40). The sum of the femoral and acetabular anteversions was 48.2±14.6° (range 27–71°).

Conclusion: This method can be used in routine practice without lengthening operative time excessively. It provides a safe way to control the length of the limb and helps position the cup. This study demonstrated that there is no ideal position for the cup that can be applied for all patients. Because of the wide spread of the inclination and anteversion figures, half of the cases were outside the safety range recommended by Lewinnek.