Novel Ultrasonographic Thickness and Strength Assessments of the Flexor Digitorum: A Reliability Analysis

Abstract

OBJECTIVES: Clinical conditions such as focal dystonia often require the assessment of atrophy and weakness of the finger muscles. However, due to a lack of well-established protocols, the current investigation focused on assessing the reliability of thickness and strength assessments of the flexor digitorum (FD) muscle, including both the superficialis and profundus components. As a secondary assessment, the reliability of the strength measurement of the extensor digitorum muscle was examined as well. METHODS: Different thickness measurements of the FD were taken via ultrasonography and averaged to estimate the mean thickness of the FD. Likewise, individual finger strength measurements taken by a custom-made finger pressure device were averaged to compute the mean strength of the flexor and extensor digitorum muscles. Test-retest reliability of the above measurements performed at two different time points (about 6 months apart) were examined on the right and left hands of 10 participants. RESULTS: Findings indicated excellent test-retest reliability (ICC > 0.92) for the mean thickness assessment of the FD and mean strength of the flexor and extensor digitorum for both dominant and non-dominant hands. The standard error of measurement was ≤4.3% for all three mean assessments, indicating high sensitivity. Likewise, the smallest detectable change was also sufficiently small for the mean thickness and mean strength of the flexor digitorum (≤5.1%) and moderately small (≤12%) for the strength of the extensor digitorum. CONCLUSIONS: Results indicated an excellent relative and absolute reliability, for both hands, for the mean thickness and strength assessments of the flexor digitorum muscle and for the mean strength of the extensor digitorum (measured for both hands). These measurements can be used for future investigations and can contribute to the establishment of more precise methods for assessing the muscles in the forearms which serve the hand.

Long-Term Muscular Atrophy and Weakness Following Cessation of Botulinum Toxin Type A Injections in the Flexor Digitorum Muscle of Musicians with Focal Hand Dystonia

“…However, results deriving from the strength assessment of the extensor digitorum should be interpreted with caution. Besides its excellent intraclass correlation coefficient (>0.92), reported by Ioannou et al [24], strength assessments of the extensor digitorum showed a larger detectable change (≤12%) as compared to the detectable change of the thickness and strength of the flexor digitorum (≤5.1%). This may also explain the larger variability of data in this particular assessment (see Figure 1).…”

“…That strength can be gained without a major increase in muscle size was shown using MRI cross-section images of healthy participants before and after a strength training protocol [35,36]. A possible explanation could be an adaptation of the nervous system that allows greater force generation without any morphological changes in the muscle itself [24,37,38].…”

“…The control group consisted of 12 healthy musicians (plus 4 healthy matched controls for the patients who were currently under the BoNT effect), all matched for handedness, instrument, gender, and as closely as possible for age [24]. Exclusion criteria for both groups were possible orthopedic or other neurological disorders (e.g., surgery, nerve damage, recent broken bones, neuromuscular disorders, etc.)…”

“…For dystonic musicians in particular, an adaptation of their repertoire, the shift from a solo to a teaching career, the high treatment cost, the alternative available treatment options such as sensorimotor retraining, and an insufficient response/benefit of the injection therapy are reasons why they decide to terminate their BoNT treatment [15,23]. Therefore, besides adding to the limited findings on human subjects, the current study attempted to objectively assess muscular atrophy and weakness via ultrasonography and finger strength assessments [24] in dystonic musicians who have terminated their BoNT treatment therapy. The main research question of the current investigation was the following: to what degree do atrophy and weakness persist/recover over time in focal hand dystonia patients after the cessation of a multiple BoNT injection therapy?…”

Bending-Sensitive Optical Waveguide Sensor With Carbon-Fiber Layer for Monitoring Grip Strength

“…The current assessment approach focuses on assessing the thickness and activity of the flexor digitorum muscle, which includes both the superficialis and profundus components. It is also necessary to examine the strength of the extensor digitorum muscle as a second assessment standard [28]. This illustrates that the main muscles that generate force when a person clenches a fist are flexor digitorum muscle and extensor digitorum muscle.…”