MCP flexion averaged 55 degrees in reconstructed thumbs, compared to 75 degrees in the contralateral thumb. Ablation with collateral ligament reconstruction
Advantages:
The reconstructed joints tend to remain flexible. Also, it preserves the nail bed and physis, this increases the prevention of nail deformities over time. Disadvantages:
Although surgeons try to obtain a stable thumb of appropriate size, instability of the IP and MCP joint may occur, as well as a size mismatch. Thumbs are defined as unacceptable if IP joint deviation exceeds 15 degrees, MCP joint deviation exceeds 30 degrees, and thumb size is inappropriate based on the examiners assessment. Also, thumb size one-third greater or less than the contralateral thumb is defined as unacceptable. On-top plasty procedure
No surgical outcomes studies exist for evaluating the function of the thumbs after an on-top plasty reconstruction. Central polydactyly
Few clinical outcome studies exist regarding the treatment of central polydactyly. Tada and colleagues note that satisfactory surgical correction of central polydactyly is difficult to achieve and that outcomes are generally poor. In Tadas study, 12 patients were reviewed. All patients required secondary surgical procedures to address flexion contractures and angular deviation at the IP joint level. However, several primary factors contribute to the complexity of central polydactyly reconstruction. Hypoplastic joints and soft tissues that predispose the reconstructed finger to joint contracture, and angular deformities as well as complex tendon anomalies, are often difficult to address. Therefore, treatment is wholly dependent on the anatomic components present, the degree of syndactyly, and the function of the duplicated finger.
The surgical technique is analogous to radial polydactyly, in which the level of duplication and anatomical components should guide operative treatment. The pedicled ulnar extra digit can be removed by  suture ligation to devise the skin bridge of the newborn child. This might be easier than an excision of the extra digit when the child is 6 to 12 months old. Ligation occludes the vascular supply to the duplicated digit, resulting in dry gangrene and subsequent autoamputation. This must be done with consideration of the presence of a neurovascular bundle, even in very small skin bridges. When the ligation is done inappropriately it can give a residual nubbin. Also, a neuroma can develop in the area of the scar. An excision can prevent the development of a residual nubbin and the sensitivity due to a neuroma. For infants with ulnar type B polydactyly the recommended treatment is ligation in the neonatal nursery. Studies have shown that excision of the extra digit in the neonatal nursery is a safe and simple procedure with a good clinical and cosmetic outcome. Radial polydactyly
Because neither of the two thumb components is normal, a decision should be taken on combining which elements to create the best possible composite digit. Instead of amputating the most hypoplastic thumb, preservation of skin, nail, collateral ligaments and tendons is needed to augment the residual thumb. Surgery is recommended in the first year of life, generally between 9 and 15 months of age. Surgical options depend on type of polydactyly.