Midterm Surgical Outcomes of Duplicated Thumbs According to New Classification

Area of Science:

• Orthopedic Surgery
• Hand Surgery
• Congenital Hand Anomalies

Background:

• Thumb duplication is a common congenital hand anomaly.
• Surgical outcomes for duplicated thumbs vary significantly based on the specific anatomical presentation.
• A need exists for a refined classification system to predict surgical success.

Purpose of the Study:

• To introduce a novel classification system for thumb duplication based on radiographic anatomy.
• To correlate this new classification with surgical outcomes in a large patient cohort.
• To provide guidance for surgical management strategies based on thumb duplication type.

Main Methods:

• A retrospective review of 562 duplicated thumbs in 529 patients was conducted.
• A new classification system (Distal, Proximal, Metacarpal types) was developed based on branching level and bone shape from radiographs.
• Surgical outcomes were assessed using the Japanese Society for Surgery of the Hand evaluation form after an average 10.2-year follow-up.

Main Results:

• The classification included Distal (D-type), Proximal (P-type), and Metacarpal (MC-type) thumbs.
• Good surgical outcomes (90%) were achieved in D-type and Proximal-type Po thumbs.
• Pa-, Pb-, Pc-, and MC-type thumbs showed lower scores, with specific joint instability patterns observed based on type.

Conclusions:

• The new classification system effectively identifies potential surgical challenges associated with each thumb duplication type.
• D-type and Po-type thumbs have excellent prognoses with appropriate surgical intervention.
• Specific reconstructive considerations are highlighted for Pa-, Pb-, Pc-, and MC-type thumbs to optimize functional outcomes.