This study reports on the incidence of a synostosis between the ring-small metacarpal bases in patients with Apert syndrome and describes a technique to resect the synostosis and insert silicone sheets to improve hand function. Records of 9 patients (18 hands) were evaluated. Average age at follow-up was 9.5 years. Three relationships between the ring-small metacarpals were observed. Type I hands (22%) had no abnormal interconnections; type II hands (33%) possessed a synostosis since birth; type III hands (44%) did not possess a synostosis at birth, but one later developed at average age of 79 months. Total incidence of synostosis was 77%. Five patients underwent excision of the synostosis. At an average of 16 postoperative months, 4 of these patients experienced improvement in hand prehension. In patients with Apert syndrome, resection of abnormal interconnections between the ring-small metacarpals is highly recommended to improve hand prehension based on the high incidence of a synostosis in this region.