Dynamometric assessment of the upper extremity in upholstered furniture workers

For preventing the onset of disorders of the upper extremity, in upholstered furniture workers, it was decided to monitor their handgrip applying a method previously developed to 262 volunteers recruited among upholstered furniture workers. At the test time, only 23 subjects had clinical symptoms referable to upper limb work-related musculoskeletal disorders (clinical symptomatic group), while the remaining 239 subjects made up the clinical asymptomatic group. The measurement system consists of a dynamometer combining a handle screwed to a load cell constrained by a rigid metal framework and connected to 8-bit datalogger. The device was designed to ensure that the handgrip could be exerted without the subject being able to perceive any movement of the test device. Dynamometer signals were sampled at 110 Hz and relayed to a personal computer. The test protocol requires to apply and to maintain a Maximum Voluntary Contraction immediately on hearing a starting beep. After 3 s a second beep indicates the end of the contraction phase and so release of the handgrip. Therefore, the subject exerts an explosive auxometric contraction followed by an isometric contraction until the beginning of the release phase. Four performance indexes were taken into account, related to: 1) the maximum force of the dominant limb; 2) the ratio between the maximum force of the dominant versus the maximum force of the non-dominant limb; 3) the power developed during the auxometric contraction and the capacity to control the isometric contraction. The fourth was a global index obtained from the sum of the three performance indexes yielded. Handgrip test gave a positive response in 66 subjects (25.2%); 18 persons showed a severe functional limitations; all of them (true positive) belonged to the clinical symptomatic group and suffered for intense pain. The remaining 5 persons of the clinical symptomatic group, were classified as negative (false negative); 2 of those subjects did not refer pain o- - f the hand and the others only mild or moderate pain. One hundred ninety-one subjects (out of 239 clinically asymptomatic subjects) resulted true negatives and 48 mild positive. Among this mild positive group 27 persons were considered as true positive because they have had previous pathologies of the upper limb which can explain the poor performance; 18 persons were considered as false positive because they had no any relevant clinical history; the 3 persons developed upper limb pathologies in the two months after test were indentified among the true positives. In conclusion the adopted procedure showed 91% of sensitivity and 91% of specificity both higher than those obtained using only the maximum force exerted during handgrip (68% of sensitivity and 80% of specificity). The hardware features, the specific test protocol and the four indexes defined were able to identify cases with a reduced functional capacity confirming the clinical assessment in patients with severe pain. Functional limitations were also revealed in healthy subjects who have had relevant pathologies and in three cases in healthy subjects who developed symptoms of Upper Limb work-related musculoskeletal disorders. These results were obtained maintaining an acceptable incidence of false negative (2%) and false positive (7%). Thus, the proposed method could be used as a tool to monitor the presence of diseases of the upper extremities, while it must be further tested to verify its prognostic capacities.