Preoperative angulation as a predictor for operations of Wassel type IV polydactyly

The aim of this study was to find the degree of preoperative metacarpophalangeal (MCP) joint angulation that determines the need for corrective osteotomy and to compare the result for Wassel type IV thumb polydactyly operated by soft tissue reconstruction alone or with corrective osteotomy. The surgical options for correction of the angular deformity of the MCP joint in Wassel type IV thumb polydactyly were retrospectively reviewed. The preoperative angular deformity of the MCP joint and the last postoperative residual deformity at MCP joint were measured from the radiograph of thumb posteroanterior view. The cut-off point of the preoperative MCP angulation that provided less residual deformity in patients who were treated by soft tissue procedures alone was identified from receiver operating characteristic curve. A total of 45 patients with 46 thumb polydactyly (Wassel type IV) were studied. Mean pre and postoperative MCP angulation were 24.01 (range 0-68°) and 14.65 (range 0-39°), respectively. Thirty-four thumbs from 33 patients (73.91%) were operated on by soft tissue procedures alone and 12 thumbs (26.09%) needed corrective osteotomy. The best cut-off point of preoperative MCP angulation that showed less significant residual deformity when treated by soft tissue procedure alone was 30° (96.43% sensitivity and 100% specificity). In MCP angulation ≤30°, soft tissue reconstruction alone was an effective method for correction of angular deformity with predictable outcome of no significant residual deformity (0/27 thumbs). In MCP angulation >30°, corrective osteotomy is recommended over soft tissue procedure alone due to achieve proper thumb position and adequate soft tissue balance. There is also a statistical decrease in significant residual deformity [from 85.71% (6/7 cases, treated by soft tissue procedure alone) to 30% (3/10 cases, treated by corrective osteotomy), P < 0.05]. This study proposes the use of preoperative MCP joint angular deformity as a guide to the type of surgical intervention in Wassel type IV thumb polydactyly.