Correction of Excessive Tibial Plateau Angle and Limb Shortening in a Juvenile Dog Using a Hinged Circular Fixator Construct and Distraction Osteogenesis

Figure 3

Sagittal deformity correction plan and projected results. (a) The proximal tibial axis (orange line) was established by defining the tibial plateau (red line) and transferring the mechanical caudal proximal tibial angle as measured on the contralateral normal tibia (63°; tibial plateau angle (TPA) of 27°) and positioning that angle to extend proximally through the tibial eminences. The distal tibial mechanical axis (Kelly green line) was estimated based on the position this line extended proximally from the talus on the normal, contralateral limb. The intersection of these two axes defined the neutral center of rotation of angulation (CORA). The transverse bisecting line (purple dashed line), which is a line passing through the neutral CORA and located equidistant (78°) from the proximal and distal tibial axes, was drawn. An opening CORA, located cranially on the transverse bisecting line at the apex of the tibial tuberosity (large black dot), was selected for the location of the hinge axis. (b) A radial osteotomy was planned in the region of the proximal tibial metaphyseal-diaphyseal junction. Distraction would result in rotation of the proximal tibial segment about the hinge axis (magenta arrows) and separation of both the cranial and caudal tibial cortices along the osteotomy margin resulting in lengthening of the limb segment as the TPA was sequentially reduced to 7°. Locating the hinge axis on the transverse bisecting line was done to reduce the TPA and perform lengthening without inducing a secondary translational deformity. During distraction the position of the tibial eminences, which were used as the proximal landmark to define the mechanical tibial axis, were translated slightly cranial which also translated the final mechanical tibial axis (forest green line) cranial. (c) Regenerate bone (orange stippled area) would form in the distraction gap establishing a confluent column of tibial bone.

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(b)

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