In isolated acetabular revision surgery, surgeons must place the cup at an appropriate angle with various retained stem anteversion angles to prevent postoperative dislocation. For accurate acetabular cup position, various navigation systems have been used. Nevertheless, no publications have reported combined cup and stem anteversion and dislocation rates after isolated acetabular revision, especially comparing the use of navigation with manual implantation. Therefore we performed a retrospective comparative study to answer the following questions: (1) What is the combined anteversion after isolated acetabular revision with computed tomography-based navigation? (2) Does navigation improve the accuracy of cup angle and combined anteversion, (3) reduce dislocation rate, and (4) reduce operative time?

A navigation system makes combined anteversion near the target angle in isolated acetabular revision.

We conducted a retrospective study of 32 hips in 24 patients who underwent isolated acetabular revision total hip arthroplasty using computed tomography-based navigation system. The control group comprised 8 hips in 8 patients who underwent the same procedure without navigation.

In the navigation group, average Widmer's combined anteversion was 39.0°±8.7° (range, 25.3°–56.6°). Cup positions were 40.3°±2.9° (range, 29.0°–49.0°) for radiographic abduction angle, 24.3°±8.0° (range, 4.6°–42.6°) for radiographic anteversion. In the control group, Widmer's combined anteversion was 47.2°±15.1° (range, 27.0°–74.3°, p=0.048). The average cup positions for radiographic abduction angle and anteversion were 36.7°±8.9° (range, 24.5°–54.9°) and 29.1°±7.3° (range, 17.2°–38.8°), respectively (p>0.05). Widmer's combined anteversion deviated from the target angle by a smaller amount in the navigation group than in the control group: errors in measurement of Widmer's combined anteversion were 7.2°±5.1° (range, 0.74°–19.6°) in the navigation group and 13.9°±11.1° (range, 3.6°–37.3°) in the control group (p=0.135). Postoperative dislocation occurred in none of the 32 hips (0%) in the navigation group and in one of the 8 hips (12.5%) in the control group (p=0.2).

Using the navigation system, combined anteversion is made near the target angle in isolated acetabular revision surgery and more accurately than manual implantation. These results should be considered as preliminary since this is a limited cohort, but it brings new knowledge in navigation considering the very limited number of series using of navigation in isolated cup revision of total hip arthroplasty. In addition this is the first study to investigate combined cup and stem anteversion in isolated acetabular revision. The use of CT-scan is helpful to diagnose error in stem anteversion and to adapt the orientation of the new cup.

III, Retrospective case control study.