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A patient-specific guide system has been used to facilitate bilateral shoulder arthrodesis in a Pekinese, and could be applied in other settings where alignment and reduction are anticipated particularly challenging, and / or when bone stock is limited.
Principles of osteotomy and reduction guide creation are similar to those described for limb deformity correction and fracture reduction. CT data is processed to obtain a 3D representations of the shoulder (Figure 1). This is imported into CAD software, and virtual 3D models of the humerus and scapula created. Virtual reduction of the shoulder is performed ensuring optimal alignment in all planes; virtual osteotomies of the glenoid and humeral head are then made (Figure 2). For each bone a virtual osteotomy guide is created; key features include a contact surface comprising an inverted virtual representation of a segment of cortex (such that the finished guide fits onto the cortex in a unique position), an osteotomy plane to guide the oscillating saw blade, and two Ellis pin channels (Figure 3). Subsequently a virtual reduction guide is created; when applied over the Ellis pins, the planned orientation of the ostectomised scapular and humerus results (Figure 4). These guides, as well as the original humerus and scapula, and the reduced humeroscapular unit, are 3D printed (Figure 5). Plates can be pre-contoured to the latter model (Figure 6), and can be applied with minimal further contouring time after guided osteotomy and reduction in theatre (Figure 7). Post-operative and follow-up radiographs from this case are shown in Figure 8.