Wedge volume and osteotomy surface depend on surgical technique for high tibial osteotomy

Biplanar open-wedge high tibial osteotomy (HTO) is thought to promote rapid bone healing due to the increased cancellous bone surface compared to other HTO techniques. However, precise data on the bone surface area and wedge volume resulting from both open- and closed-wedge HTO techniques remain unknown. We hypothesized that biplanar rather than uniplanar HTO better reflects the ideal geometrical requirements for bone healing, representing a large cancellous bone surface combined with a small wedge volume. Tibial saw bones were assigned to 4 different groups of valgisation high tibial osteotomies: group 1: open-wedge uniplanar HTO; group 2: open-wedge biplanar HTO with ascending frontal cut; group 3: open-wedge biplanar HTO with descending frontal cut (retrotubercule osteotomy technique), and group 4: closed-wedge uniplanar HTO. 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. The open-wedge biplanar osteotomy with a descending frontal cut (group 3) created significantly larger bone surfaces compared to the "classic" biplanar technique with an ascending frontal cut (group 2) and compared to all uniplanar techniques. Bone surfaces after the classic open-wedge technique (group 2) were slightly larger compared to all uniplanar techniques (group 1 and 4). No significant differences of wedge volumes were found between the retrotubercle (group 3) and classic open-wedge techniques (group 2). Wedge volumes were significantly higher in the uniplanar open-wedge technique (group 1) compared to the biplanar open-wedge techniques (group 2 and 3). Bone geometry following HTO suggests that the biplanar open-wedge techniques simultaneously create smaller wedge volumes and larger bone surface areas compared to the uniplanar open-wedge techniques. The relatively neglected closed-wedge technique still offers in theory the best healing potential, characterized by an almost absent wedge volume and a large bone-to-bone contact area. Although this idealized geometric view on bony geometry excludes all biologic factors that influence bone healing, the current data suggest a general rule for the applied standard osteotomy techniques and all of their surgical modifications: reducing the amount of slow gap healing and simultaneously increasing the area of faster contact healing may be beneficial for osteotomy healing. Thus, a biplanar rather than a uniplanar osteotomy may be performed for high tibial osteotomy in clinical practice.