Development of a measurement strategy for recording musculoskeletal strain on the distal upper extremity, in particular the thumb, during manual therapeutic activities

Status:

completed 06/2025

Aims:

The literature has shown the working conditions of physiotherapists and occupational therapists typically to be physically demanding, and at times associated with negative strain upon the spine, with resulting complaints in the lower back and the shoulders and neck. Indications also exist of elevated strain upon the elbows, hands and wrists (distal upper extremity) during performance of manual techniques such as joint mobilisation, massage and soft tissue techniques. To date, only a limited number of studies have demonstrated a risk of work-related thumb and hand complaints in these two occupational groups, or even among massage therapists.

To enable the cumulative strain in the distal upper extremity to be described on the basis of measured values, the Institute for Occupational Safety and Health of the DGUV (IFA) was tasked by the German Social Accident Insurance Institution for the health and welfare services (BGW) with developing a new measurement strategy for recording the exposure of the thumb and the distal upper extremity to physical strain. This approach was to be used in the long term to create registers of exposure. As yet, however, a corresponding occupational disease has not been formally recognized in Germany.

Activities/Methods:

A total of 15 test subjects (physiotherapists), 11 female and 4 male, were studied under laboratory conditions. All test subjects had been working in the profession for several years (between 2.5 and 40 years) and therefore possessed extensive practical experience.

Mobile dynamometry (e.g. force measurement with sensor pads), mobile electromyography (Cometa) and kinematic data capture (XSENS and XSENS Metagloves) were used to record the exposure to strain of the hand, fingers and, in particular, the thumbs during manual physiotherapy activities performed by physiotherapists and occupational therapists (n = 15) in a laboratory study. Four core therapy techniques were analysed: conventional massage, manual therapy, manual lymphatic drainage and trigger point therapy, in each case supplemented by selected sub-techniques. The kinematic data of the distal upper extremity were analysed for known kinematic parameters such as posture, repetition, motion velocity and range of motion. Dynamic data (action forces) and electromyographic data (muscle activity) were also used to determine the musculoskeletal workload on the thumb, fingers and wrist. The measurement system used was tested in field studies for its practicability.

Results:

A standardised test report and a suitable measurement strategy were developed for recording of the data. These proved reliable and were applied successfully on all test subjects.

Examination of the upper distal extremity during performance of these manual techniques yielded the following results:

Shoulder: Cumulative evaluation of repetitive movements in the shoulder joint indicates elevated strain during performance of all the therapy techniques studied. Strain caused by activities at or above shoulder height did not occur to any relevant degree during any of the techniques studied, however.

Wrist: Assessment by means of HAL-TLV (to ACGIH, 2018) revealed that all techniques presented at least a moderate risk of musculoskeletal complaints developing. Regular monitoring and checks of the strain are therefore advised, in accordance with the ACGIH recommendations. Some techniques even indicated an elevated risk, which is associated in the literature with an elevated prevalence of musculoskeletal disorders, such as carpal tunnel syndrome.

Thumb: Particular attention was paid to the carpometacarpal (CMC) joint of the thumb, which is considered a risk region for the development of trapeziometacarpal (TMC) arthritis resulting from manual therapy techniques. End-range movements in this joint were monitored in all techniques studied. However, a standardised method for objective assessment of strain on the CMC joint is not yet available.

The results obtained can be transferred to an exposure register and provide an initial insight into the strain patterns expected from a future field study. The standardised division into sub-techniques proved particularly useful, as it permitted differentiated analysis.

Comprehensive assessment of the total strain over an entire work shift requires a field study, however, since in practice, different techniques are combined in varying proportions. The measurement strategy developed is also suitable for use in such a field study. Based on the experience gained in the laboratory study, a reduction in the scale of the measurement systems is also intended: for example, an EMG need be recorded only on the dominant arm, as no significant differences in muscle activity were observed between the right and left sides.

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