The effect of osteotomy type on the initial stiffness of the bone-implant construct in lateral opening-wedge distal femoral osteotomy (LOWDFO) using a uniplanar compared with a biplanar technique has been investigated. However, no study has explored the biomechanical risk factors for medial hinge fracture. This study aimed to compare the biomechanical strength of uniplanar versus biplanar LOWDFO regarding the risk for medial hinge fracture during gap opening. Twelve composite femora were divided into two groups (six in each group) based on the distal femoral osteotomy technique: uniplanar versus biplanar LOWDFO. All LOWDFO models were subjected to incremental static loading. The gap distance was expanded by 1 mm, and displacement values were recorded as anterior and posterior gap distances (mm). The average force values of all samples at certain gap distances were recorded, and the head distance was measured. The uniplanar group had higher load values than the biplanar group at all anterior gap distances. These differences were only significant at 2- and 3-mm gap distances (p = 0.025 and 0.037). At all posterior gap distances, the uniplanar group had higher load values than the biplanar group, but these differences only reached statistical significance at 2 mm (p = 0.037). Both groups had similar anterior, posterior, and average gap distances (p = 0.75, 0.522, 0.873). The uniplanar group had a higher head insertion distance (15.3 ± 5.7) than the biplanar group (14.7 ± 2.9), but it was not significant (p = 0.87). The uniplanar group had a lower average load before medial hinge fracture (46.41 ± 13.91 N) than the biplanar group (54.92 ± 31.94, p = 0.81). The biplanar group had an average maximum load value of 64.18 ± 25.6 N, while the uniplanar group had 57.90 ± 12.21 N (p = 0.81). This study revealed that the biplanar osteotomy technique allows a wider opening wedge gap with less risk of a medial hinge fracture than uniplanar LOWDFO.Level of evidence was level 3, case-control series.
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