Correction of severe lower limb deformity with digital hexapod external fixator based on CT data

Abstract purpose: The current study aimed to investigate the therapeutic effect of our self-developed digital six-axis external fixator technique for correction of severe deformities of the lower extremities.Patients and Methods: From January 2017 to December 2020, our institution used self-developed digital hexapod external fixator technology（QSF） based on CT data to slowly correct 28 severe tibial deformities, and 15 femurs underwent osteotomy and internal fixation. The mean age was 32.6±14.3 years, and the mean follow-up was 23.3±16.1 months. MAD, mFTA, MPTA, LLD, mLDFA at preoperative and final follow-up, and LEFS, KSS and functional score at preoperative and final follow-up were compared.Results: The QSF adjustment time was 21.4±10.8 days, and the healing time of the tibial osteotomy site was 17.6±7.0 weeks. Preoperative MAD, mFTA, MPTA were 54.1±26.2 mm, 167.7±15.7°, 75.2±12.0°, respectively. At last follow-up, MAD was 8.2±9.9 mm, mFTA was 177.6±3.4°, and MPTA was 87.6±2.4°. Significant improvement was achieved after operation. Preoperative LLD, mLDFA were 13.8±18mm, 83.7±10.8°, at last follow-up were 7.6±7.6mm, 87.8±2.6mm, no significant difference before and after operation. The LEFS, KSS and functional scores improved from 51.6 ± 11.2, 68.5 ± 11.7, 67.8 ± 11.2 to 72.3 ± 6.1, 92.9 ± 3.4, 94.2 ± 6.3, respectively. Conclusions: The QSF technique can accurately correct severe multiplanar deformities of the tibia in adults. Combined with femoral osteotomy to correct femoral deformity, satisfactory lower extremity alignment can be obtained. The technology has the advantages of simple operation, reliable fixation, less trauma and less complications.Level of Evidence: Level IV, case series.