Acetabular cup placement in navigated and non-navigated total hip arthroplasty (THA): results of two consecutive series using a cementless short stem.

BACKGROUND

Acetabular component malposition has been linked to increased rates of dislocation, impingement, pelvic osteolysis, cup migration, leg length discrepancy and polyethylene wear in patients undergoing total hip arthroplasty (THA).

OBJECTIVE

Compare the acetabular component positioning and the operative time in two consecutive short-stem cementless THA series without and with using an imageless navigation.

MATERIAL AND METHOD: The retrospective study consisted of 31 cases of short-stem cementless THA without navigation (NNAV) and 30 cases with navigation (NAV). CT scans were performed in all cases at two-month or later postoperatively. The abduction and anteversion angles measured on postoperative CT were compared between two groups using t-test. The percentage of cup placement (abduction, anteversion and combined) within the safe zone for each group was compared using Chi-square test at a 0.05 level of significance. The operative time was compared between two groups using t-test.

RESULTS

The mean abduction was 43.97 (range, 33-52, SD 4.44) in NNAV group and 41.37 (range, 37-45, SD 2.01) in NAV group. This difference was significant (p = 0.004). The mean anteversion was 22.58 (range, 2-39, SD 10.68) in NNAV group and 13.57 (range, 7-18, SD 3.28) in NAV group. This difference was significant (p < 0.001). According to the criteria of Lewinnek et al, 96.8% in NNAV group were placed within the safe zone for abduction, 51.6% for anteversion, and 48.4% for both abduction and anteversion. In NAV group, all 30 cups (100%) were placed within the safe zone for abduction, anteversion, and both. There were significant differences in the percentage of cup placement within the safe zone for anteversion (p < 0.001), for both abduction and anteversion (p < 0.001) but not significant for abduction (p = 0.32) between two groups. The mean operative time was 107.09 and 110.67 minutes for NNAV and NAV group respectively, this difference was not significant (p = 0.49).

CONCLUSION

The present study demonstrated a significant increase in the placement of acetabular cups within the safe zone using imageless navigation compared to freehand technique, especially at anteversion angle.