Finite element analysis of medial closing and lateral opening wedge osteotomies of the distal femur in relation to hinge fractures

Abstract Purpose Intraoperative hinge fractures in distal femur osteotomies represent a risk factor for loss of alignment and non‐union. Using finite element analysis, the goal of this study was to investigate the influence of different hinge widths and osteotomy corrections on hinge fractures in medial closed‐wedge and lateral open‐wedge distal femur osteotomies. Methods The hinge was located at the proximal margin of adductor tubercle for biplanar lateral open‐wedge and at the upper border of the lateral femoral condyle for biplanar medial closed‐wedge distal femur osteotomies, corresponding to optimal hinge positions described in literature. Different hinge widths (5, 7.5, 10 mm) were created and the osteotomy correction was opened/closed by 5, 7.5 and 10 mm. Tensile and compressive strain of the hinge was determined in a finite element analysis and compared to the ultimate strain of cortical bone to assess the hinge fracture risk. Results Doubling the correction from 5 to 10 mm increased mean tensile and compressive strain by 50% for lateral open‐wedge and 48% for medial closed‐wedge osteotomies. A hinge width of 10 mm versus 5 mm showed increased strain in the hinge region of 61% for lateral open‐wedge and 32% for medial closed‐wedge osteotomies. Medial closed‐wedge recorded a higher fracture risk compared to lateral open‐wedge osteotomies due to a larger hinge cross‐section area (60–67%) for all tested configurations. In case of a 5 mm hinge, medial closed‐wedge recorded 71% higher strain in the hinge region compared to lateral open‐wedge osteotomies. Conclusion Due to morphological features of the medial femoral condyle, finite element analysis suggests that lateral‐open wedge osteotomies are the preferable option if larger corrections are intended, as a thicker hinge can remain without an increased hinge fracture risk.