Fig. 1.

A scattergram of cup orientation plots cup anteversion against cup inclination. All cups inserted with navigation are within the Lewinnek safe zone (outer rectangle). Dislocation occurred more frequently in the nonnavigation group (eight hips) than in the navigation group (no hips), but there was no difference in the dislocation rate between hips inside and outside the safe zone. The impingement-related mechanical complications comprised four revisions and seven neck erosions, all of which were seen in the nonnavigation group. The true safe zone without dislocation or mechanical complications seems to be 36° to 45° of inclination and 10° to 24° of anteversion (inner dotted rectangle).