Ann Isabel Kryger

Validity of questionnaire self-reports on computer, mouse and keyboard usage during a four-week period

Objective: To examine the validity and potential biases in self-reports of computer, mouse and keyboard usage times, compared with objective recordings. Methods: A study population of 1211 people was asked in a questionnaire to estimate the average time they had worked with computer, mouse and keyboard during the past four working weeks. During the same period, a software program recorded these activities objectively. The study was part of a one-year follow-up study from 2000–1 of musculoskeletal outcomes among Danish computer workers. Results: Self-reports on computer, mouse and keyboard usage times were positively associated with objectively measured activity, but the validity was low. Self-reports explained only between a quarter and a third of the variance of objectively measured activity, and were even lower for one measure (keyboard time). Self-reports overestimated usage times. Overestimation was large at low levels and declined with increasing levels of objectively measured activity. Mouse usage time proportion was an exception with a near 1:1 relation. Variability in objectively measured activity, arm pain, gender and age influenced self-reports in a systematic way, but the effects were modest and sometimes in different directions. Conclusion: Self-reported durations of computer activities are positively associated with objective measures but they are quite inaccurate. Studies using self-reports to establish relations between computer work times and musculoskeletal pain could be biased and lead to falsely increased or decreased risk estimates.

The role of physical examinations in studies of musculoskeletal disorders of the elbow

Objectives: To present data on pain and physical findings from the elbow region, and to discuss the role of diagnostic criteria in epidemiological studies of epicondylitis. Methods: From a cohort of computer workers a subgroup of 1369 participants, who reported at least moderate pain in the neck and upper extremities, were invited to a standardised physical examination. Two independent physical examinations were performedone blinded and one not blinded to the medical history. Information concerning musculoskeletal symptoms was obtained by a baseline questionnaire and a similar questionnaire completed on the day of examination. Results: 349 participants met the authors criteria for being an arm case and 249 were elbow cases. Among the 1369 participants the prevalence of at least mild palpation tenderness and indirect tenderness at the lateral epicondyle was 5.8. The occurrence of physical findings increased markedly by level of pain score. Only about one half with physical findings fulfilled the authors pain criteria for having lateral epicondylitis. A large part with physical findings reported no pain at all in the elbow in any of the two questionnaires, 28 and 22, respectively. Inter-examiner reliability between blinded and not blinded examination was found to be low kappa value 0.340.40. Conclusion: Very few with at least moderate pain in the elbow region met common specific criteria for lateral epicondylitis. The occurrence of physical findings increased markedly by level of pain score and the associations were strongest with pain intensity scores given just before the examination. Physical signs were commonly found in subjects with no pain complaints. No further impact was achieved if the physical examination was not blinded to the medical history. Furthermore, the authors propose that pain, clinical signs and disability are studied as separate outcomes, and that the diagnoses of lateral epicondylitis should be used only for cases with classical signs of inflammation reflected by severe pain, which for example conveys some disability.

Muscle fatigue in relation to forearm pain and tenderness among professional computer users

BackgroundTo examine the hypothesis that forearm pain with palpation tenderness in computer users is associated with increased extensor muscle fatigue.MethodsEighteen persons with pain and moderate to severe palpation tenderness in the extensor muscle group of the right forearm and twenty gender and age matched referents without such complaints were enrolled from the Danish NUDATA study of neck and upper extremity disorders among technical assistants and machine technicians. Fatigue of the right forearm extensor muscles was assessed by muscle twitch forces in response to low frequency (2 Hz) percutaneous electrical stimulation. Twitch forces were measured before, immediately after and 15 minutes into recovery of an extensor isometric wrist extension for ten minutes at 15 % Maximal Voluntary Contraction (MVC).ResultsThe average MVC wrist extension force and baseline stimulated twitch forces were equal in the case and the referent group. After the fatiguing contraction, a decrease in muscle average twitch force was seen in both groups, but the decrease was largest in the referent group: 27% (95% CI 17–37) versus 9% (95% CI -2 to 20). This difference in twitch force response was not explained by differences in the MVC or body mass index.ConclusionComputer users with forearm pain and moderate to severe palpation tenderness had diminished forearm extensor muscle fatigue response. Additional studies are necessary to determine whether this result reflects an adaptive response to exposure without any pathophysiological significance, or represents a part of a causal pathway leading to pain.

Associations of work activities requiring pinch or hand grip or exposure to hand-arm vibration with finger and wrist osteoarthritis: a meta-analysis

OBJECTIVE We systematically reviewed the epidemiologic evidence linking finger and wrist osteoarthritis (OA) with work activities requiring pinch or hand grip or exposure to hand-arm vibration (HAV). METHODS PubMed and Embase databases were searched up to June 2013. We selected studies assessing the associations of radiographic diagnosed finger and/or wrist joint OA with work activities involving pinch or hand grip or exposure to HAV. We used specific criteria to evaluate completeness of reporting, potential confounding, and bias. Pooled odds ratios (OR) were computed using random-effects meta-analyses. RESULTS Of the 19 studies included, 17 were cross-sectional, 1 was a prospective cohort, and 1 a case-control study. The meta-analyses of studies that controlled their estimates for at least age and gender showed the associations of pinch grip work with proximal interphalangeal joint [OR 1.56, 95% confidence interval (95% CI) 1.09-2.23] and the first carpometacarpal joint OA (OR 2.10, 95% CI 1.06-4.17), but not with distal interphalangeal, metacarpalphalangeal, or wrist joints OA. Hand grip work and exposure to HAV were not associated with any finger or wrist OA. CONCLUSION Epidemiological studies provide limited evidence that pinch grip may increase the risk of wrist or finger OA, but causal relation cannot be resolved because of cross-sectional designs and inadequate characterization of biomechanical strain to the hand and wrist.