Bifid thumb type IV in children: transferring an epiphyseal segment of the proximal phalanx with insertion of the abductor pollicis brevis tendon.

Objective: To evaluate the clinical and functional results of the surgical treatment of bifid thumb type IV in children.

Materials And Methods: A retrospective study was undertaken from January 1995 to December 2006. Clinical and radiographic evaluations were made according to Wassel's classification. The patients were performed by transferring an epiphyseal segment of the proximal phalanx with insertion of the abductor pollicis brevis tendon into the radial side of the epiphyseal proximal phalanx of the ulnar thumb. All patients were operated using one of five surgical procedures for bicephalous metacarpus, cartilaginous connection between the radial and ulnar proximal phalanges, the angular deformity of the metacarpophalangeal joint (MPJ) is >20°, and zigzag deformities. The postoperative results of the patients were evaluated for both function and cosmesis according to Tien's modified Tada scoring system.

Results: One hundred and sixty-four patients (102 females, 62 males) were included in this study. The MPJ was stable in 170 thumbs, 15 thumbs had 10° of radial instability, and new collateral ligaments were augmented in 27 thumbs. The alignment was normal in 75 thumbs, with alignment of the interphalangeal joint (IPJ) in 101 thumbs and alignment of the MPJ in 75 thumbs. Postoperatively, there were zigzag deformities in four thumbs (developed zigzag in two thumbs, recurrent zigzag in two thumbs); there was no first web space in those hands. There were four of 185 thumbs with thumb stiffness. The abductor function of 185 thumbs was as follows: >70° in 158 thumbs (85.4%), 50°-70° in 21 thumbs (11.4%), and <50° in six thumbs (3.2%). At the latest follow-up evaluation, no evidence of physeal growth injury or growth arrest was observed in any patient. Overall, we attained good results in 140 thumbs (75.7%), fair results in 36 thumbs (19.4%), and poor results in nine thumbs (4.9%).

Conclusion: We recommend the use of an epiphyseal segment of the proximal phalanx with insertion of the abductor pollicis brevis tendon into the radial side of the epiphyseal proximal phalanx of the ulnar thumb and to restore anatomical insertion of the abductor pollicis brevis muscle. The technique is simple, safe, and effective for thumb abductor function in the treatment of bifid thumb type IV in children.