Review Question - QID 218085

In the setting of preaxial Wassel type IV polydactyly with thumbs of equal size, the radial-sided appendaged should be excised to avoid injury to the 1st metacarpophalangeal (MCP) joint ulnar collateral ligament (UCL), which would result in valgus instability and weakness with pinch activities.

Polydactyly can be classified as preaxial (thumb duplication), postaxial (small finger duplication), or central (index, long, or ring finger duplication). The Wassel classification is specific to thumb polydactyly and describes the level at which the duplication occurs, progressing more proximally with increasing Wassel type. Wassel Type IV (duplicated proximal phalanx) is the most common type of preaxial polydactyly (43%), with Type II the second most common (15%). Reconstruction of the thumb usually involves resection of the smaller thumb, although the remaining larger digit is almost never normal size. Ideally, the ulnar-sided thumb is preserved to maintain the 1st MCP UCL and, in most cases, the ulnar-sided thumb is the larger of the two.

Comer et al. published a 2018 review on polydactyly, describing the classifications and treatment modalities. For preaxial polydactyly, the most common surgical approach for the management of thumb duplication is the excision of the less well-developed digit and reconstruction of the retained thumb. Frequently, the ulnar thumb is preserved and the radial digit is excised because the radial digit is oftentimes more hypoplastic than the ulnar digit. Also, the native UCL, which is vital for pinch and grip function, is maintained on the ulnar digit. Additionally, the radial collateral ligament and a strip of distal continuous periosteum (to provide increased length) are transferred from the ablated digit to the retained thumb to maintain joint stability.

Wall and Goldfarb published a 2015 surgical technique on reconstruction for Type IV radial polydactyly. The authors state that although surgery can be performed at any age, they prefer to wait until the child is older than 12 months to minimize the anesthetic risk and allow time for thumb growth. The authors’ approach to the type IV thumb is to reconstruct the larger thumb, more often the ulnar thumb which maintains the ulnar collateral ligament, and use portions of the radial thumb as necessary.

Figure A is a radiograph demonstrating Wassel Type IV preaxial polydactyly. Illustration A depicts the Wassel classification. Illustration B depicts a preoperative plan for the management of type IV radial polydactyly, including excision of the less developed thumb and reconstruction of the retained digit.

Incorrect answers:

Answer 1: This describes an injury to the dorsal capsular structures, which would not be involved in an ulnar-sided resection.
Answer 2: This describes an injury to the volar capsular structures, which would not be involved in an ulnar-sided resection.
Answer 4: This describes an injury to the radial collateral ligament, which would not be involved in an ulnar-sided resection.
Answer 5: This describes an injury to the extensor pollicis longus, which would not be involved in an ulnar-sided resection.