Accuracy of the hexapod external fixator in treating tibial angular deformities with or without limb length discrepancy: a retrospective study.

Abstract

Hexapod external fixator systems allow simultaneous deformity correction in multiple planes as well as limb lengthening. The aim of this study is to evaluate the accuracy of a hexapod frame (smart correction frame) in different types of tibial deformities requiring correction with or without lengthening. A total of 54 tibial angular deformities and limb length discrepancies operated with a hexapod frame between January 2015 and January 2021 were classified into four groups: "Group A ( n  = 13): only lengthening," "Group B ( n  = 14): lengthening and uniplanar correction," "Group C ( n  = 16): only uniplanar correction," and "Group D ( n  = 11): biplanar correction." The accuracy of angular deformity correction/lengthening was calculated by dividing the actual correction/lengthening achieved after frame removal by the preoperative planned lengthening/correction. The lengthening accuracy in Group A and Group B was 96.3 ± 7.1% and 95.7 ± 5.9%, respectively ( P  = 0.685). The angular deformity correction accuracy was 85.1 ± 9.9% for Group B, 85.2 ± 13.9% for Group C, and 80.2 ± 18.4% for Group D ( P  = 0.852). A revision program was performed in six cases (1 in Group B, 1 in Group C, and 4 in Group D) for full correction of the deformities. The accuracy of tibial lengthening is high with the hexapod frame and is minimally affected by simultaneous deformity correction; however, the accuracy of angular correction slightly reduces as the deformity becomes more complex. Surgeons should be aware that reprogramming may be required after complex deformity correction.