Morphologic characteristic of the first web space in congenital thumb duplication and the treatment strategy

Abstract

Objective To analyze the morphologic characteristics of the first web space in thumb duplication based on Wassel classifications, and propose corresponding treatment strategies. Methods Sixty thumb duplication patients (68 thumbs) were operated on between February and June of 2016. The special vernier caliper and goniometer used for hand function assessment were used to measure the first web space distance, the intermetacarpal distance (IMD) and intermetacarpal angle (DIMA) between the first and second metacarpal. Paired t test was used to compare the differences of these parameters between thumb duplication and the normal side. Emphasis was given to analyzing the first web space in Wassel type Ⅳ with the first metacarpal head ulnar deviation and Wassel typeⅤ, Ⅵ, Ⅶ. Results There were 23 thumbs in total in Wassel typeⅠ, Ⅱ, Ⅲ and type Ⅳ without ulnar deviation of the first metacarpal. The first web space distance were (2.56±0.46) cm and (2.32±0.39) cm for the normal and abnormal sides, respectively, with a statistically significant difference (t=3.115, P=0.006). The IMD were (3.32±0.27) cm and (3.24±0.28) cm, and the DIMA were (41.84±3.22)° and (41.79±3.39)° for the normal and abnormal sides, respectively. There were no statistically significant differences in IMD (t=1.529, P=0.144) and DIMA (t=0.224, P=0.826). There were 45 thumbs in Wassel type Ⅳ and Wassel typeⅤ, Ⅵ, Ⅶ with ulnar deviation of the first metacarpal head. The first web space distance were (2.62±0.34) cm, (2.21±0.44) cm for the normal and abnormal sides, respectively, with a statistically significant difference (t=5.238, P=0.000). The IMD were (3.38±0.36) cm and (3.03±0.53) cm, the DIMA were (43.32±3.87)°and (35.35±6.73)° respectively. There were statistically significant differences in IMD (t=4.585, P=0.000) and DIMA (t=7.730, P=0.000). Conclusion The first web space narrowing in thumb duplication was mainly seen in Wassel type Ⅳ with ulnar deviation of the first metacarpal head and Wassel typeⅤ, Ⅵ, Ⅶ. We recommended metacarpal osteotomy to realign the skeleton when the soft tissue is relaxed. If the soft tissue is tight, we prefer to perform Z-plasty or index finger dorsal flap transfer to open the first web space. Key words: Hand deformities, congenital; Thumb; The first web space; Treatment strategy