American Association for Hand Surgery
Theme: Beyond Innovation

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Biomechanical Analysis of Extensor Indicis Proprius versus Abductor Digiti Minimi Tendon Transfers for Restoration of Thumb Opposition
Kyle Gabrick, MD1; David Tsai, MD2; Scott Persing, MD2; Rajiv Iyengar, MD3; Marc E. Walker, MD, MBA4; John Smetona, MD2; Ean Saberski, MD2; James E Clune, MD3; Michael Alperovich, MD, MSc3; Douglas van Citters, Ph.D.5; Michael Matthew, MD6
1Section of Plastic and Reconstructive Surgery, Yale University School of Medicine,, New Haven, CT, 2Yale University School of Medicine, New Haven, CT, 3Yale University, New Haven, CT, 4Section of Plastic and Reconstructive Surgery, Yale University School of Medicine, New Haven, CT, 5Dartmouth College, Hanover, NH, 6Plastic Surgery, Dartmouth University, Lebanon, NH

Background
Thumb opposition is essential for many activities of daily living. Lack of opposition can be devastating to the function of the hand. Abductor Digiti Minimi (ADM) and Extensor Indicis Proprius (EIP) both have application in the restoration of opposition in the setting of high median nerve palsy. The purpose of this biomechanical study was to quantify the work (J) of opposition (WOO) of these two motor groups to guide clinical decision making.
Methods:
WOO was calculated in five fresh-frozen cadaveric arms using a custom mechanical apparatus (Instron). Opposition was considered full when the thumb reached the longitudinal plane of the long finger. WOO was calculated as the force (N) required for full opposition (m). The Huber Transfer (ADM) and EIP opponensplasty were the tendon transfers performed and tested in each cadaver arm. Analysis of Variance (ANOVA) was used to compare the results obtained in each of the five cadaver arms. Significance was defined as p < 0.05.
Results:
The EIP required the greater mean amount of work (0.153 J) than ADM (0.068 J) to achieve full opposition. This observation was observed and reached significance in four of the five cadaver arms (p = 0.001, p < 0.001, p < 0.001, p = 0.015). In one arm ADM required the greatest work of opposition (0.115 J) for opposition (p = 0.006).
Conclusion:
Both EIP and ADM are acceptable and safe methods to restore thumb opposition in the setting of a high median nerve palsy. Our data shows that ADM requires less work to achieve full opposition when compared to EIP.


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