Resection of 4th-5th Metacarpal Synostosis and Fascial Interposition for Creation of a Functional Grip /Pinch in the Apert Hand.

Introduction: The 4th-5th metacarpal synostosis, present in over 80% of Apert hands, flattens the metacarpal arch, restricts metacarpal descent, may prevent opposition of border rays, and combined with symphalangism, negates any functional flexion. Ironically, the fifth ray including the digit is the most intact finger within the hand. Restoration of both position and mobility with arthroplasty changes the cardinal plane of flexion and enables both pinch and grip in these compromised hands. This report summarizes the evolution of our technique over five decades.

Methods: In a cohort of 184 Apert patients (368 hands) the presence, anatomy, and level of the metacarpal synostosis with a classification was determined. The present technique consists of incision along ulnar border of hand, wide excision of the skeletal coalition, release of dorsal structures, soft tissue interposition (with cadaveric fascia lata graft) with the fifth metacarpal flexed and supinated. During the past two decades the fascia was also wrapped around the fifth metacarpal in a subperiosteal plane. No fixation is needed. The arthroplasty was commonly combined with a thumb lengthening procedure, such as opening wedge osteotomy plus autogenous bone graft at 2-6 years or distraction lengthening and bone graft at 11-13 years old. Silicone blocks, silicone sheeting, and autogenous tendon were also used as interpositions early in our experience were not included. Data was generated over a 46 period and consisted of clinical and operative records, serial molds, serial X-rays, and OT records. Follow-up ranged from 3 to 44 years.

Results: 80% of the hands (N=147 patients) had bilateral 4-5th metacarpal synostoses, the extent of which correlated with the Apert hand classification3. In 72 patients (144 hands) the synostosis was resected and cadaveric fascia interposed. The 7 hands that had silicone blocks, silicone sheets, or tendon interposition were not included in the final results. Synostosis refusion occurred in 38 hands, all of which were performed early in the series and under the age of 6 years. Despite refusion, the position of the 5th digit was improved and the flat transverse arch tin a more curved or cupped posture. Eight of refused synostoses were re-released, usually in conjunction with thumb distraction lengthening. Distance between the opposing border rays was always improved and a new grip and pinch mechanism created.

Conclusion: Aggressive ostectomy of synostosis and fascial interposition places the ulnar side of the hand in a much more functional position. In conjunction with thumb lengthening, opposition between the thumb and fifth finger becomes a clinical reality in Apert children who are born with diminutive thumbs and minimal interphalangeal joint motion.