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Quantitative Assessment of Dynamic Control of Fingertip Forces After Pollicization
Nina Lightdale-Miric, MD1; Nicole M. Mueske, MS1; Jamie Berggren, OT1; Jennifer Loiselle, OT1; Francisco Valero-Cuevas, PhD2; Sudarshan Dayanidhi, PhD3; Tishya A. L. Wren, PhD1
1Children's Hospital Los Angeles, Los Angeles, CA; 2University of Southern California, Los Angeles, CA; 3University of San Diego, San Diego, CA

Background: Manual dexterity in children after finger pollicization is critical to functional outcomes. Dexterous manipulation requires independent finger movements, speed, strength, hand-eye coordination, and precise control of fingertip forces. Most tests of hand function evaluate a combination of these properties. This study used a novel Strength-Dexterity (S-D) test to isolate and quantify a specific aspect of dexterous manipulation, the dynamic control of fingertip forces, after finger pollicization in children.
Methods: We evaluated 10 pollicized and 5 non-pollicized hands from 8 participants ages 4-17 years. Participants attempted to compress and hold an instrumented spring between the thumb and next most radial finger to assess dynamic control of fingertip forces (S-D score). They also completed traditional functional tests including grip, lateral pinch, and tripod pinch strength, Box and Blocks Test, and 9-hole peg test and were graded using the Manual Ability Classification System and Total Active Motion measure. Retrospective chart and x-ray review provided clinical information. Pearson's correlation evaluated the relationship among age-normalized Z-scores from the S-D test and the other functional tests. Patient characteristics were compared between hands with good versus poor S-D outcome using Mann-Whitney rank sum tests.
Results: Six of 10 pollicized hands and all non-pollicized hands had S-D scores within the normal range. In contrast, almost all pollicized hands scored below the normal range for the traditional functional tests. S-D Z-scores were moderately correlated with Z-scores from all other functional tests (r = 0.42-0.61), but the correlations were generally weaker than the correlations amongst the other functional measures (r = 0.59-0.93), suggesting that the S-D test captures a different domain of function. The only clinical characteristic distinguishing hands with good vs. poor S-D outcome was a higher incidence of radial absence in the hands with poor S-D scores (3/4) compared with hands having normal S-D scores (0/6) (p = 0.02).
Conclusions: Manual dexterity is a key component in many activities of daily living, and it is an important outcome to evaluate after finger pollicization. The S-D results suggest that most pollicized hands achieved dynamic control of fingertip forces similar to age-matched norms. This may indicate that after pollicization children exhibit the necessary neuromuscular plasticity to acquire normal levels of control over dynamic fingertip forces, which may help them in performing tasks such as typing or holding a pencil. However, they may still lack the strength and/or gross motor coordination needed to achieve normal hand function.


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