Duplication or split thumb is a common congenital difference. Type IV is the most common type of duplication. Treatment is not simple ablation, but rather complex reconstruction involving the use of “spare parts” surgery. Surgical treatment for a specific sub-type of a Type IV thumb is discussed. The Type IV-D duplicated thumb represents a convergent type, which has the most complex anomalies and is difficult to treat.
The authors noted that a Type IV-D thumb often has a conjoined A-2 pulley with a split flexor pollicis longus tendon that bifurcates distal to this A-2 pulley. The flexor pollicis longus subsequently inserts eccentrically onto the distal phalanges and is believed to be the mechanism for the convergent alignment. Based upon this understanding of the pathoanatomy, the authors designed a surgical procedure that allows centralization of the flexor pollicis longus, reconstruction of the A-2 pulley, tightening of the collateral ligament, and reattachment of the abductor pollicis brevis tendon.
Over a four year period, four children underwent reconstruction of a Type IV-D thumb. The preoperative examination showed the duplicated thumb is divergent at the MP joint and convergent at the distal phalanges. During surgery, a conjoined A-2 pulley was always identified, as was a bifurcated flexor pollicis longus tendon. The surgical technique is described in this report, and consists of reconstruction of A-2 pulley and realignment of flexor pollicis longus tendon. In addition, the widened metacarpal head is reshaped by cutting off the radial part that articulated with the ablated radial component. The detached abductor pollicis brevis tendon is reattached to the restore abduction function. A longituidinal Kirschner wire is used for four weeks time.
Postoperative joints range of motion was assessed at both the MP and IP joints. A scoring system was used based upon range motion joints the overall alignment. For all four patients, the alignment of the reconstructive thumb was well maintained. Range of follow-up was between 2.5 and 4.7 years. Range of motion at the MP joint averaged 32 degrees, and at the IP joint 17 degrees. X-rays showed no evidence of recurrent angular deformity. Three cases were graded as good and one as fair.
Reconstruction of the duplicated thumb remains a challenging task. The goal is to achieve a stable thumb that is well aligned and functional. This particular type of Type IV duplication is especially difficult to treat. The authors noted this unique anatomic finding with bifurcation of the flexor pollicis longus tendon and eccentric insertion. Addressing the A-2 pulley and FPL insertion point leads to uniformed good results. Addressing the abnormal anatomy directly may avoid osteotomy and this operation should be considered in children with this particular type of thumb duplication.
Thumb, Duplication, Reconstruction
J Pediatr Orthop