Objectives
To date, there remains a scarcity of evidence evaluating hinge fractures after closing wedge lateral distal femoral osteotomy (LCW-DFO) for varus malalignment. The aim of this study was to evaluate the morphology, incidence, and complications of hinge fractures following LCW-DFO and to identify technical and constitutional risk factors predisposing for hinge fracture and associated complications.

Methods

Seventy-nine consecutive cases of LCW-DFO for symptomatic varus malalignment (47 ± 12 years, 66% male) between 01/2007 and 03/2018 with a minimum of two-year postoperative follow-up were included in this monocentric retrospective study. Medical and surgical records were assessed. The incidence and morphology of medial cortical hinge fractures was assessed based on postoperative anterior–posterior knee radiographs and measurements evaluating the two-dimensional location of the hinge and osteotomy cut (wedge height, cut length, hinge angle) were performed. Technical and constitutional factors associated with an increased incidence of a medial cortical hinge fracture and complications were analyzed. A total sample size of 76 subjects to detect a difference of 1.5 mm of absolute correction, at a calculated effect size of 0.66 in order to achieve a statistical power of 0.8 was determined in an a priori power analysis. Statistical Analysis

Results

Medial cortical hinge fractures were detected in 48%. A novel classification is proposed based on fracture morphology, differentiating extension (68%), proximal (21%) and distal fracture types (11%). An increased wedge height in mm (6.5±1.9 vs. 7.9±3; p=0.040), an increased length of the osteotomy cut in mm (53.1±10.9 vs. 57.7±9.6; p=0.049) as well as position of the hinge in the medial sector of an established sector grid (p=0.049) were observed to be significantly associated with the incidence of a hinge fracture. Regarding complications, malunions after hinge fracture (14%) were significantly increased after mediolateral dislocation of the medial cortical bone > 2mm (p<0.05).

Conclusion

Hinge fractures can be detected in a substantial part of LCW-DFO cases. With increasing osteotomy wedge height and a hinge position close to the medial cortex, the risk of sustaining a hinge fracture is increased. A dislocation of medial hinge fracture >2mm should be avoided, as an association to malunion could be shown.