Effect of remodeling on correction of tibia vara using the circular hexapod external fixator.

Abstract

Background: We aimed to evaluate if there would be loss of some correction achieved (caused by remodeling) after correcting tibia vara deformity with hexapod circular fixators and if that loss of correction would influence clinical outcomes.

Hypothesis: The hypothesis of the study was that remodeling at the osteotomy site would lead to loss of some correction over time.

Patients and methods: This retrospective study included 18 patients with tibial varus deformity as a sequela of adolescent tibia vara who underwent proximal tibial deformity correction using the Hexapod External Fixator between August 2020 and August 2023. We assessed clinical outcomes using the Limb Deformity-Scoliosis Research Society (LD-SRS) score and radiographic parameters such as Mechanical Axis Deviation (MAD) and Mechanical Axis Angle (MAA) measured preoperatively, post-correction, and at the final follow-up. Statistical analyses were performed to quantify the statistical significance of limb alignment change at final follow-up and to attempt to define a cut-off angle to be achieved at the end of correction that would result in no deviation in limb alignment in the long run.

Results: After a mean follow-up duration of 18.7 mo, there was a significant improvement in both functional and radiographic measures. The mean LD-SRS score improved from 3.4 ± 0.5 preoperatively to 4.6 ± 0.4 at the final follow-up. Radiographic parameters showed notable correction, with the mean MAA improving from 25.1º ± 8.7 (varus alignment) preoperatively to 1.7º ± 2.5 (valgus alignment) at the end of correction, and to 2.4º ± 3.3 (varus alignment) at the final follow-up. Similarly, the mean MAD value improved from 87.4 ± 29.5 mm (medial deviation) preoperatively to 7.3 ± 9.6 mm (medial deviation) at the end of correction, and to 6.1 ± 11.5 mm (lateral deviation) at the final follow-up.

Discussion: When treating adolescents with tibia vara deformity using hexapod fixators, it is advisable to over correct the MAA by 5° (valgus overcorrection) and the MAD by 7-9 mm to counteract the loss of some correction over time caused by the effect of remodeling.

Level of evidence: III; retrospective study.