Hinge Fracture in Lateral Closed-wedge Distal Femoral Osteotomy in Knees Undergoing Double-level Osteotomy: Assessment of Postoperative Change in Rotational Alignment Using CT Evaluation

Purpose: The purpose of this study was to examine the radiological features of hinge fracture occurring at the distal medial femoral cortex in knees undergoing biplanar lateral closed-wedge distal femoral osteotomy (LCW-DFO) in double-level osteotomy (DLO) based on pre- and postoperative CT image analyses. It was hypothesised that medial hinge fractures in LCW-DFO would occur with a similar incidence to that in high tibial osteotomy, and its occurrence would affect the clinical/radiological outcomes and induce unintended change in alignment depending on the fracture type (direction of the fracture).

Methods: A consecutive series of 36 knees (31 patients) with primary varus osteoarthritis undergoing DLO comprised the study population. The mean age at surgery was 62.0 ± 5.9 years. Presence of hinge fracture was assessed on radiographs and CT images at 1 week. The fracture type was classified depending on the direction of the fracture line: crack propagation in line with the osteotomy (type 1) and fractures extending proximally (type 2) or distally (type 3) from the tip of the wedge. Computer-assisted assessments of bony limb alignment and bony geometry were conducted on a full-length weight-bearing radiograph and CT images using image analysis software. In addition, subjective clinical results were evaluated using the Knee Injury and Osteoarthritis Outcome Score (KOOS). Radiological and clinical follow-up results at 1 and 2 years were compared to the preoperative data, while comparative analysis was made between the subjects with and without a hinge fracture.

Results: Postoperative image examinations revealed type 1 and 2 medial femoral hinge fractures in 4 and 7 knees, while no type 3 fracture was identified in the study population. Consequently, the overall incidence of the hinge fracture was 30.6% (11 of the 36 knees). Four of those 11 fractures (36.4%) could not be detected on plain radiographs. CT image analysis for three-dimensional bony geometry showed greater increase in internal rotation of the distal bony segment (increased femoral antetorsion by 9.5° on average) after surgery compared to the knees without a hinge fracture (P = 0.01). Clinical evaluation using the KOOS at 2 years showed no significant difference between the groups with and without hinge fractures.

Conclusion: In LCW-DFO, medial femoral hinge fractures occurred in 30.6% of the cases. Knees with type 1 hinge fracture exhibited significantly greater increase in femoral antetorsion as compared to those without hinge fracture. In this case series, postoperative weight-bearing protocol was delayed for knees with hinge fracture. Consequently, surgical results were not affected by the occurrence of hinge fracture for up to 2 years.

Level Of Evidence: IV (case series).