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In Vivo Measurement of the Thenar Muscles and First Dorsal Interosseous in Thumb Carpometacarpal Joint Osteoarthritis Using Ultrasound Imaging
Eric Pridgen, PhD; Deborah Kenney, MS; Eugene Roh, MD; Amy Ladd, MD
Stanford University, Stanford, CA

Introduction: Osteoarthritis (OA) of the thumb carpometacarpal (CMC) joint is a significant medical problem, with an age-adjusted incidence of 7% in men and 15% in women. For the thumb CMC joint, stability has been implicated as one of the causes of OA. The focus of this study was to understand the role muscle integrity plays in thumb CMC OA pathogenesis by investigating whether the size of the abductor pollicis brevis (APB), opponens pollicis (OP), and first dorsal interosseous (FDI) varies between healthy control subjects and CMC OA patients.
Methods: APB, OP, and the distal FDI cross-sectional area (CSA) as well as first metacarpal (MC) bone length were measured using ultrasound. 13 control subjects (7 females, 6 males; ages 23-78) and 3 CMC OA patients with bilateral disease (2 females, 1 male; ages 46-49) participated in the study. A hand surgeon determined clinical and radiographic CMC OA. The CSA of each muscle was scaled by the MC length to account for differences in hand size. The effect of hand dominance on scaled CSA was evaluated using a paired, 2-tailed t test. The effect of OA on scaled CSA was determined using an unpaired, 2-tailed t test.
Results: The scaled CSA values for the APB, OP, and distal FDI muscles were compared between dominant and non-dominant hand in control subjects. The mean values are shown below along with p-values that indicate that there is no significant difference based on handedness. The scaled CSA for each muscle was compared between healthy hands and hands with OA. There was a significant difference between the two groups in the distal FDI, but not in the other muscles.

  Dominant Hand


Mean (SD)

Non-dominant Hand


Mean (SD)








Mean (SD)

Healthy Hands


Mean (SD)

APB 0.38 (0.12) 0.40 (0.08) 0.72 0.31 (0.06) 0.39 (0.10) 0.10
OP 0.48 (0.13) 0.46 (0.10) 0.57 0.37 (0.19) 0.47 (0.11) 0.08
FDI 0.67 (0.09) 0.70 (0.13) 0.46 0.68 (0.11) 0.43 (0.19) 0.0001

Conclusions: This study demonstrated that ultrasound is an effective method for measurement of hand muscles. Using this method, the study established that there is a decrease in scaled CSA in each of the muscles, with the distal FDI having a statistically significant decrease. Future prospective studies could be used to further evaluate the association between changes in muscle CSA and CMC OA disease, and determine if this method is viable for identification of at-risk patients and evaluation of interventions.

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