[Comparison of the acetabular orientation after minimally-invasive total hip arthroplasty with and without computer-navigation: a clinical report of 106 hip in 87 patients].

OBJECTIVE: To evaluate the acetabular angle after minimally-invasive total hip arthroplasty (MIS-THA) with or without computer-navigation.

METHODS: 87 consecutive orthopedic patients (106 hips) underwent MIS-THA with computer-navigation (40 cases with 53 hips) or without computer-navigation (47 cases with 53 hips). The full leg length and pelvis were measured with radiography preoperatively and post-operatively.

RESULTS: The average length of incision of the navigation group was 8.9 cm (7.8 - 10.5 cm), and the average length of incision of the non-navigation group was 9.1 cm (7.5 - 11 cm) The average cup inclination on the plain post-operative radiography of the navigation group was 40.58 degrees +/- 5.09 degrees (30 degrees - 54 degrees ), only the cup abduction being 54 degrees , significantly less steep than that of the control group [44.17 degrees +/- 8.71 degrees (28 degrees - 70 degrees , t' = 2.56. P = 0.012). Among the 47 control cases 40 cases showed the cup abduction of 30 degrees - 50 degrees , 3 showed the cup abduction of < 30 degrees , and 10 showed the cup abduction of > 50 degrees . The computer-navigation MIS-THA was significantly more accurate than the conventional MIS-THA. Pearson chi-square test showed that there was not significant difference in the percentage of cases with acetabular abduction < 30 degrees , between these two groups (chi(2) = 1.37, P = 0.24), and there was a significant difference in the percentage of cases with acetabular abduction > 50 degrees , between these two groups (chi(2) = 8.22, P = 0.0042). There was a significant difference in the percentage of cases with the acetabular abduction < 30 degrees and > 50 degrees calculated together between these 2 groups (chi(2) = 11.85, P = 0.0006),

CONCLUSION: MIS-THA with computer-navigation allows accurate orientation of the cup implant components without direct visualization of the bony landmarks.