We studied the intra- and inter-rater reliability of muscle thickness and cross-sectional area measurements of thenar muscles with a water bath ultrasonography technique in eight healthy volunteers and 16 patients with trapeziometacarpal osteoarthritis. Thickness and cross-sectional area of the opponens pollicis, abductor pollicis brevis, flexor pollicis brevis, first dorsal interosseous and adductor pollicis muscle were measured. The results showed changes in the morphometric properties of the thenar muscles in patients with trapeziometacarpal osteoarthritis (TMC OA) compared with the healthy volunteers. In the dominant-sided patients ( n = 14), there were lower cross-sectional area values for the abductor pollicis brevis and opponens pollicis muscles. In the non-dominant-sided patients ( n = 10), there were lower cross-sectional area values for the abductor pollicis brevis and flexor pollicis brevis and lower muscle thickness of the abductor pollicis brevis. The water bath ultrasonography technique could be used to diagnose and treat diseases where changes in thenar muscle thickness and cross-sectional area can be expected. Level of evidence: III

BackgroundMuscle thickness and cross-sectional area (CSA) of the thenar muscles can vary depending on different pathologies (such as neuropathies, arthritis etc.). It is important to evaluate these muscles throughout the diagnosis and treatment processes to understand the pathophysiology of diseases and to identify new treatment strategies. Ultrasonographic imaging has been shown to be valid and reliable tool for the measurement of the muscle thickness and CSA of the particular thenar muscles,1–2 however there are no studies demonstrating normative values of all thenar muscles.ObjectivesThe purpose of this study is to obtain normative thickness and CSA values for the thenar muscles in healthy individuals by ultrasound and to assess the inter-rater reliability of sonographic muscle assessments.MethodsThe thenar muscles was examined ultrasonographically in eleven healthy volunteers. The assessment was carried out using Shimadzu SDU 1200-Pro US system working with 8–10 MHz linear probe. A custom-made foam cast was used for standardised positioning of the probe. The thickness and CSA parameters of FDI, OP, APB, flexor pollicis brevis (FPB), adductor pollicis (AdP) muscles were examined by two different investigators on the same image. Measurements were made from the palm side of the hand for APB, FPB, OP muscles and from the dorsal side of the hand for AdP and FDI muscles, using five different positions.3 To analyse inter-rater reliability, the examinations of both raters were compared.ResultsEleven healthy female subjects (mean age: 24.45±2.77 years; BMI: 21.43±2.48 kg/m2) were included in this study. Nine subjects had right hand dominancy and 2 had left hand dominancy. The reliability between two assessors, expressed as an interclass correlation coefficient (ICC), was excellent for all muscles (ICC range min:0.759, max:0.993 p<0.05).The mean thickness values of muscles were ordered from thick to thin in longitudinal assessment as AP, FDI, FPB, OP, APB. The mean thickness values of muscles were ordered from thick to thin in transverse assessment as AP, FDI, FPB, OP, APB. The mean CSA values of muscles were ordered from thick to thin as AP, FPB, FDI, APB, OP.Abstract AB1404-HPR – Table 1D: dominant, ND: non-dominantConclusionsUltrasonography can be used to reliably assess the thenar muscle architecture. This study is important to reveal the normative thickness and CSA values of the thenar muscles in healthy subjects. This data may provide a more comprehensive understanding of musculoskeletal problems and underlying pathophysiological mechanisms which consequently may have an impact on clinical decision making.References[1] Mohseny, B., Nijhuis, T. H., Hundepool, C. A., Janssen, W. G., Selles, R. W., &Coert, J. H. (2015). Ultrasonographic quantification of intrinsic hand muscle cross-sectional area; reliability and validity for predicting muscle strength. Archives of physical medicine and rehabilitation, 96(5),845–853.[2] Simon, N. G., Ralph, J. W., Lomen-Hoerth, C., Poncelet, A. N., Vucic, S., Kiernan, M. C., & Kl...

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