Small changes of femoral torsion in varus or valgus distal femoral osteotomy using patient-specific instruments

Purpose Hinge fractures show a relatively high incidence in varus and valgus distal femoral osteotomy (DFO) and can lead to delayed- or non-union. Another observed complication of a hinge fracture is an unintentional change of the postoperative femoral torsion of up to + 9.5 degrees in conventionally performed DFO. We hypothesize that the change of femoral torsion in case of a hinge fracture is less pronounced when DFO is performed using patient-specific instruments (PSI) compared to the literature of conventionally performed DFO. Methods All patients who underwent varus or valgus DFO using PSI from January 2014 to September 2023 were included. Radiographs and computed tomography (CT) scans were used to screen for hinge fractures. Pre- and postoperative femoral torsion was measured in CT. Results Thirty-five medial closing-wedge DFO (MCW-DFO), 27 lateral closing-wedge DFO (LCW-DFO), and 27 lateral opening-wedge DFO (LOW-DFO) were included, resulting in a total of 89 included osteotomies. A total of 55 hinge fractures (61.8%) were observed. The femoral torsion changed significantly from 20.5 degrees +/- 7.7 degrees to 15.5 degrees +/- 8.1 degrees (p < 0.001) in LOW-DFO with a hinge fracture, whereas the other two techniques showed no significant change of femoral torsion. Conclusion The use of PSI in varus and valgus DFO showed only small changes of the postoperative femoral torsion, even in case of a hinge fracture. The change of femoral torsion was depending on the type of DFO and was only significant in LOW-DFO, however, not exceeding a mean change of 5 degrees.