EOS-based cup navigation: Randomised controlled trial in 78 total hip arthroplasties.

BACKGROUND: Minimising the risk of cup implantation outside the safe zone is among the objectives of navigation during total hip arthroplasty (THA). However, given the technical challenges raised by navigation when the patient is lying on the side, many surgeons still use the freehand technique. We conducted a randomised controlled trial to evaluate the new navigation system NAVEOS in the iliac plane, which is easily identified in the lateral decubitus position, with the objective of determining whether NAVEOS navigation decreased the frequency of cup implantation outside the safe zone compared to freehand cup positioning, without increasing the operative time or the frequency of complications.

HYPOTHESIS: NAVEOS navigation decreases the frequency of cup positioning outside the safe zone compared to freehand positioning.

MATERIAL AND METHODS: This randomised controlled trial compared cup positioning using NAVEOS navigation versus the freehand technique in patients undergoing primary THA. The safe zone was defined according to Lewinnek as 15±10° of radiological anteversion and 40±10° of radiological inclination. Cup position parameters were measured on computed tomography images obtained 3months after THA. The images were read by two independent observers who were blinded to group assignment. The primary evaluation criterion was cup position within the safe zone.

RESULTS: A 1:1 randomisation scheme was used to assign 78 patients (mean age, 68years; age range, 44-91years) to NAVEOS navigation or freehand cup positioning. The two groups were comparable for age, gender distribution, body mass index, and preoperative functional scores. In the NAVEOS group, navigation was discontinued prematurely in 6 patients, because of technical difficulties (n=2) or a marked discrepancy with clinical findings (n=4); however, the intention-to-treat approach was used for the analysis. The proportion of cups in the safe zone was 67% (28/39) in the NAVEOS group and 38% (17/39) in the freehand group (P=0.012). Anteversion was within the 5-25° range for 72% (28/39) cups in the NAVEOS group and 46% (18/39) in the freehand group (P=0.021). Inclination was within the 30-50° range for 95% (37/39) of cups with NAVEOS navigation and 85% (33/39) with freehand positioning (P=0.135). The odds ratio for cup implantation outside the safe zone was significantly lower with NAVEOS compared to freehand positioning (0.54; 95% confidence interval, 0.31-0.91). Mean operative time was 74 (range, 45-115) minutes with NAVEOS navigation and 70 (range, 40-105) minutes with freehand positioning (P=0.382). Complications consisted of 1 case each of anterior dislocation and infection, both in the freehand group.

DISCUSSION: Compared to freehand positioning, NAVEOS navigation significantly lowered the risk of cup positioning outside the safe zone, chiefly via improved achievement of the anteversion target. NAVEOS was not associated with increases in operative time or morbidity.

LEVEL OF EVIDENCE: II, randomised controlled trial with limited statistical power.