A novel system integrating load cell for assessing shoulder muscle strength

Muscle strength assessment is considered one of the most important outcome measures of shoulder function in patients with orthopedic dysfunction. Several methods and instruments are employed to assess isometric muscle strength. Isometric testing with hand-held dynamometer (HHD) are mostly used in clinical practice due to their easy mode of use, cost-effectiveness, and portability. However, variability in force data arises due to examiner strength and height, subject testing position, and HHD placement side. Recent literature explores advanced measurement devices like load cells, praised for high accuracy and data reliability. In this paper, in order to improve measurements reproducibility, we proposed a novel system for force measurement with a twofold aim: to estimate the shoulder muscle strength in clinical settings and to comparatively assess the performance of commercially available devices used to perform the mentioned measures. The proposed system was based on a load cell force and torque sensor. The load cell was fixed into a modular bracket. This configuration allows adjusting the system to fulfil the test specifications and the physical characteristics of the patient. A preliminary assessment of the proposed system capability of measuring shoulder muscle strength in clinical setting was carried out on a young healthy volunteer during the execution of six upper limb movements. In addition, a comparative analysis was conducted to evaluate the performance of commercially available HHD in relation to the discussed system. The novel system, along with a custom algorithm, showed promising capabilities in measuring shoulder muscular strength while performing several movements in a clinical environment. In addition, the system integrating the load cell force and torque sensor allowed the evaluation of performance of a commercially available device. The preliminary results showed differences between the measurements estimated by using the two instruments. Biases of 62.5 N and 47.1 N were observed among devices, considering the average and maximum force values achieved, respectively, when the subject flexed his elbow. This novel system integrating load cell may be considered a first effort to reliably evaluate shoulder muscle strength in a clinical scenario.