In reconstructing the Wassel type IV thumb duplication in infants, a deviation deformity of the retained thumb may be corrected by a closing transverse wedge osteotomy of the metacarpal neck. In older children and adults, this technique may cause avascular necrosis of the retained metacarpal condyle. We have addressed this problem by using an oblique wedge osteotomy of the metacarpal condyle. Ten patients (mean age, 18.9 years) underwent this procedure between 1993 and 2007. Patients with deviation angles of 30° or less had a closing wedge osteotomy, while those with deviation angles exceeding 30° had a rotational bone graft osteotomy. Deviation angles were corrected from a mean of 32° (range, 16° to 55°) to 0° in eight thumbs and 10° in two thumbs. There were no cases of avascular necrosis. All patients achieved good results by Tada's criteria. This technique effectively restores bony alignment of the thumb and preserves vascularity of the retained condyle.