Level II, diagnostic study--investigating a diagnostic test.

Open-wedge high tibial osteotomy (HTO) is becoming increasingly popular for the treatment of varus gonarthrosis in the active patient. The various implants used in HTO differ with regard to its design, the fixation stability and osteotomy technique. It is assumed that the combination of a plate fixator with a biplanar, v-shaped osteotomy supports bone healing. So far, there are no biomechanical studies that quantify the stabilizing effect of a biplanar versus uniplanar osteotomy. We hypothesized that a significant increase in primary stability of bone-implant constructs is achieved when using a biplanar as opposed to a uniplanar osteotomy. Twenty-four fresh-frozen human tibiae were mounted in a metal cylinder, and open-wedge osteotomy (12 mm wedge size) was performed in a standardized fashion. Proximal and distal tibial segments were marked with tantalum markers of 0.8 mm diameter. Two different plates with locking screws were used for fixation: a short spacer plate (group 1, n = 12) and a plate fixator (group 2, n = 12). In six specimens of each group, a biplanar V-shaped osteotomy with a 110 degrees angulated anterior cut behind the tuberosity parallel to the ventral tibial shaft axis was performed. In the remaining six specimens of each group, a simple uniplanar osteotomy was performed in an oblique fashion. Axial compression of the tibiae was performed using a material testing machine under standardized alignment of the loading axis. Load-controlled cyclical staircase loading tests were performed. The specimens were radiographed simultaneously in two planes together with a biplanar calibration cage in front of a film plane with and without load after each subcycle. Radiostereometry allowed for serial quantification of plastic and elastic micromotion at the osteotomy site reflecting the stability provided by the combination of implant and osteotomy technique. No significant additional stabilizing effect of a biplanar osteotomy in craniocaudal and mediolateral plane was found. However, additional stability was achieved in anteroposterior (AP) and all rotational planes in those specimens fixated with a short spacer plate. In this biomechanical set-up with axial load, the additional stabilizing effect of a biplanar osteotomy did not come into effect in the presence of a long and rigid plate fixator. However, biplanar osteotomy increased the fixation stability significantly in AP and rotational planes when a short spacer plate was used. Clinically, the biplanar osteotomy promotes bone healing regardless of the implant used. Biomechanically, biplanar osteotomy is advantageous for shorter plate designs to increase primary stability of the bone-implant construct.

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