Wedge volume and osteotomy surface depend on surgical technique for distal femoral osteotomy

Purpose: Biplanar distal femoral osteotomy (DFO) is thought to promote rapid bone healing due to the increased cancellous bone surface compared to other DFO techniques. However, precise data on the bone surface area and wedge volume resulting from both open- and closed-wedge DFO techniques remain unknown. We hypothesized that biplanar rather than uniplanar DFO better reflects the ideal geometrical requirements for bone healing, representing a large cancellous bone surface combined with a small wedge volume. Methods: Femoral saw bones were assigned to 4 different groups of varization distal femur osteotomies: group 1, lateral open-wedge uniplanar DFO; group 2, medial closed-wedge uniplanar DFO; group 3, lateral open-wedge biplanar DFO; and group 4, medial closed-wedge biplanar DFO. Bone surface areas of all osteotomy planes were quantified. Wedge volumes were determined using a prism-based algorithm, applying standardized wedge heights of 5, 10 and 15 mm. Results: The biplanar osteotomy techniques (groups 3 and 4) created significantly larger femoral surface compared to the uniplanar groups (groups 1 and 2) (p = 0. 036). Bone surfaces after the lateral biplanar open-wedge technique (group 3) were slightly larger than the medial biplanar closed-wedge technique (group 4) and biplane techniques significantly larger than the uniplanar techniques (groups 1 and 2). Wedge volumes were significantly higher in the lateral uniplanar open-wedge (group 1) and biplanar open-wedge (group 3) techniques compared to the closed-wedge techniques (groups 2 and 4) that have nearly absent wedge volumes. Conclusion: Bone geometry following DFO suggests that the medial biplanar closed-wedge technique simultaneously creates smaller wedge volume and larger bone surface areas compared to the lateral biplanar open-wedge and the uniplanar DFO techniques. The horizontal cuts of the biplane DFO techniques are positioned behind the trochlear area in better healing metaphysial bone, which further enhances bone healing potential. Although this idealized geometric view on bony geometry excludes all biological factors that influence bone healing, the current data confirm the general rule for osteotomy techniques: reducing the amount of slow gap healing and wedge volumes and simultaneously increasing the area of faster contact healing by larger bone surface areas may be beneficial for osteotomy healing.