Biomedical subjects

K T Palmer

Publications and source records attributed to K T Palmer.

At least 19 recordsLinked to original sources

PubMed2006

Does knee pain in the community behave like a regional pain syndrome? Prospective cohort study of incidence and persistence.

OBJECTIVES: To investigate whether knee pain in the community behaves like a regional pain syndrome, determined by its association with mental health, self-rated health (SRH) and beliefs about prognosis. METHODS: An 18-month postal follow-up was conducted in 1798 working-aged subjects, sampled from the community. At baseline questions were asked about pain in the knee lasting > or =1 day in the previous 12 months, mental health (Short-Form 36), somatising tendency (elements of the Brief Symptom Inventory), SRH and concern about 12-month prognosis. At follow-up we asked about knee pain during the last 4 weeks, and whether it had been present for > or =14 days or prescription-treated. Associations with incidence and persistence were explored using logistic regression. RESULTS: The 1256 participants (70% response) comprised 468 with knee pain at baseline and 788 without. Among the former, 49% had persistent knee pain at follow-up, while among the latter, 15% reported new symptoms. Incident prescription-treated knee pain was strongly associated with all of the mental health variables and with SRH. The odds of knee pain persisting were significantly raised in the least versus most favourable bands of somatising tendency and SRH, and persistence was also significantly more common among those who at baseline were concerned that they would still have a problem in 12 months. CONCLUSIONS: Our observations support the hypothesis that knee pain in the community shares risk factors in common with other non-specific regional pain syndromes.

Adult↗

PubMed2006

Upper limb pain in primary care: health beliefs, somatic distress, consulting and patient satisfaction.

BACKGROUND: Beliefs and mental well-being could influence decisions to consult about upper limb pain and satisfaction with care. OBJECTIVES: To describe beliefs about upper limb pain in the community and explore associations of beliefs and mental health with consulting and dissatisfaction. METHODS: Questionnaires were mailed to 4998 randomly chosen working-aged patients from general practices in Avon. We asked about upper limb pain, consulting, beliefs about symptoms, dissatisfaction with care, somatizing tendency (using elements of the Brief Symptom Inventory) and mental well-being (using the Short-Form 36). Associations were explored by logistic regression. RESULTS: Among 2632 responders, 1271 reported arm pain during the past 12 months, including 389 consulters. A third or more of responders felt that arm pain sufferers should avoid physical activity, that problems would persist beyond 3 months, that a doctor should be seen straightaway and that neglect could lead to permanent harm. Consulters were significantly more likely to agree with these statements than other upper limb pain sufferers. The proportion of consultations attributable to such beliefs was substantial. Dissatisfaction with care was commoner in those with poor mental health: the OR for being dissatisfied (worst versus best third of the distribution) was 3.2 (95% CI 1.2-8.5) for somatizing tendency and 2.4 (95% CI 1.3-4.7) for SF-36 score. Both factors were associated with dissatisfaction about doctors' sympathy, communication and care in examining. CONCLUSIONS: Negative beliefs about upper limb pain are common and associated with consulting. Somatizers and those in poorer mental health tend, subsequently, to feel dissatisfied with care.

Activities of Daily Living↗

PubMed2006

A prospective cohort study of arm pain in primary care and physiotherapy--prognostic determinants.

OBJECTIVE: To investigate outcome and prognostic determinants for arm pain presenting to primary care and physiotherapy services. METHODS: Patients with arm pain were recruited as they presented to primary care and physiotherapy services, and were followed for 12 months. At baseline, they were classified by diagnosis using a validated examination schedule. Depression, somatizing tendency, health anxiety, fear-avoidance beliefs and chronic pain outside the arm were ascertained using standard definitions. Three outcomes were considered: same-site pain during the final month of follow-up (continuing pain); pain present on most days of that month; and pain present without a break of 7 days over follow-up ('unremitting' pain). Associations were explored in multi-level logistic regression models and summarized as odds ratios (ORs) with 95% confidence intervals (95% CIs). RESULTS: Altogether, 313 (83%) of 375 subjects completed follow-up, including 53% with 'continuing' and 24% with 'unremitting' pain. 'Continuing' pain was predicted most strongly by male sex (OR 1.9, 95% CI 1.2-3.2) (this association was restricted largely to the elbow), higher frequency of pain in the past month at baseline (OR 2.5, 95% CI 1.1-5.6), chronic pain at sites outside the arm (ORs 1.6-2.4 for different sites) and current smoking (OR 3.3, 95% CI 1.6-6.6). There were also indications that mental health and fear-avoidance beliefs influenced prognosis. Predictors for the other two adverse outcomes were similar. CONCLUSION: Arm pain often persists in patients who consult medical services. Predictors of persistence include male sex (elbow only), frequency of pain at baseline, chronic pain at other sites and smoking.

Adolescent↗

PubMed2006

Inflammatory responses to the occupational inhalation of metal fume.

Occupational exposure to metal fume promotes a reversible increase in the risk of pneumonia, but by mechanisms which are unclear. To investigate, the current authors measured various markers of host defence function in welders and nonwelders. Induced sputum and venous blood samples were collected from 27 welders with regular long-term exposure to ferrous metal fume and 31 unexposed matched controls. In sputum, the present authors measured cell counts, the soluble and cellular iron concentration, and levels of interleukin-8, tumour necrosis factor-alpha, myeloperoxidase, matrix metalloproteinase-9, immunoglobulin (Ig)A, alpha(2)-macroglobulin and unsaturated iron-binding capacity. Blood samples were assayed for evidence of neutrophil activation and pneumococcal IgG antibodies. Welders had significantly higher iron levels and a substantially lower unsaturated iron-binding capacity in their sputum, but, despite a high iron challenge, there was a noteworthy absence of an inflammatory response. Only blood counts of eosinophils and basophils were significantly related to the extent of welding. Weak nonsignificant trends were observed for several other measures, consistent with low-grade priming of neutrophils. In conclusion, these data suggest that chronic exposure to metal fume blunts responsiveness to inhaled particulate matter. However, the mechanism behind the lack of detectable local inflammatory response requires further investigation.

Adolescent↗

PubMed2005

Employment characteristics and job loss in patients awaiting surgery on the hip or knee.

AIMS: To investigate the factors, including size of organisation, associated with job loss in patients awaiting surgery to the hip or knee joint. METHODS: A questionnaire was mailed to 498 consecutive patients of working age listed at a district general hospital for major joint replacement, knee arthroscopy, or periacetabular osteotomy. Questions were asked about level of physical disability, duration of symptoms, employment circumstances at the time the joint problem began, and job changes since the onset of symptoms with their reasons. Analysis focused on those in work when their health problem began. Cox regression was used to examine risk factors for job loss related and unrelated to the joint problem, and results were summarised as adjusted hazard ratios (HRs) with 95% confidence intervals (95% CI). RESULTS: Responses came from 370 (74%) of those mailed, including 278 who were in work when their joint problem began. Of these, 82 (30%) had left their original job mainly or partly because of their joint disorder. Such job loss was more common in those employed in small businesses (HR for <10 v > or =10 employees: 1.9, 95% CI 1.2-3.0) and those whose work involved standing for >2 hours per day (HR 2.7, 95% CI 1.2-6.1) No similar associations were found when jobs were left for other reasons. After adjustment for non-sedentary work the association with small business employment remained but was weaker (HR 1.5, 95% CI 0.9-2.5). Modifications to work and access to occupational health advice were not associated with better job retention. CONCLUSIONS: In subjects with disabling hip or knee disease, job retention is poorer in those from small companies-a matter of concern given the rising prevalence of serious joint disease in the British workforce and the tendency of businesses to downsize and subcontract services to smaller enterprises.

Adult↗

PubMed2004

Quantifying the advantages and disadvantages of pre-placement genetic screening.

BACKGROUND: Tests of genotype may enable workers at unusual risk of future ill-health to be identified. Using them to select for employment, however, entails gains and losses to employers and employees. Ensuring a fair balance between the rights and obligations of each group requires a value judgement, but the advantages and disadvantages to interested parties must first be quantified in a meaningful way. METHOD AND RESULTS: The purposes of pre-employment screening are reviewed, and several simple measures relevant to the separate interests of employers and job applicants proposed-number screened to prevent a single adverse outcome; number excluded to prevent a case; expected incidence of the adverse outcome in those excluded; and preventable fraction. The derivation of these measures is illustrated, and the factors that influence them (the prevalence of the prognostic trait, the relative risk that it carries for an adverse outcome, and the overall incidence of disease) are related algebraically and graphically, to aid judgement on the utility of screening under different circumstances. CONCLUSIONS: In sensitive areas such as genetic testing the onus should be on the employer to justify plans for pre-placement screening. Several quantitative measures can be used to inform the ethical and economic debate about screening and to evaluate alternative strategies for prevention.

Cost-Benefit Analysis↗

PubMed2004

Mortality of workers exposed to ethylene oxide: extended follow up of a British cohort.

AIMS: To obtain further information about the risks of cancer associated with occupational exposure to ethylene oxide METHODS: Follow up was extended by 13 years for a cohort of 2876 men and women with definite or potential exposure to ethylene oxide in the chemical industry or in hospital sterilising units. Subjects were traced through National Health Service and social security records, and their mortality was compared with that expected from rates in the national population by the person-years method. RESULTS: Analysis was based on 565 deaths, of which 339 had occurred during the additional period of follow up. Mortality was close to or below expectation for all causes (565 deaths v 607.6 expected), all cancers (188 v 184.2), and for all specific categories of malignancy including stomach cancer (10 v 11.6), breast cancer (11 v 13.2), non-Hodgkin's lymphoma (7 v 4.8), and leukaemia (5 v 4.6). All five deaths from leukaemia occurred in the subset of subjects with greatest potential for exposure to ethylene oxide, but even in this group the excess of deaths was small (2.6 expected). CONCLUSIONS: The balance of evidence from this and other epidemiological investigations indicates that any risk of human cancer from ethylene oxide is low, particularly at the levels of occupational exposure that have occurred in Britain over recent decades. This may reflect the capacity of human cells to repair DNA damage caused by the chemical, which is a potent genotoxin and animal carcinogen.

Cause of Death↗

PubMed2004

Cigarette smoking, occupational exposure to noise, and self reported hearing difficulties.

AIMS: To explore the interaction of smoking and occupational exposure to noise as risk factors for hearing difficulty in the general population. METHODS: A questionnaire was mailed to 21 201 adults of working age, selected at random from the age-sex registers of 34 British general practices, and to 993 members of the armed services, randomly selected from pay records. Questions were asked about smoking habits, years spent in a noisy occupation, difficulty in hearing conversation, and wearing of a hearing aid. Associations of hearing difficulty with smoking habit were examined by logistic regression and compared across strata of noise exposure, with adjustment for potential confounders. RESULTS: Around half of the respondents had ever smoked, and half of these still smoked. Among 10 418 who provided details on hearing, 348 were classed as having moderate and 311 as having severe hearing difficulty. Risk of hearing difficulty was 3-5-fold higher in those employed for >5 years in noisy work compared with those never employed in a noisy job. Within strata of noise exposure (including those who had never worked in a noisy job), ex- and current smokers had a higher risk of hearing difficulty than lifetime non-smokers. The additional risks were small compared with those of long term noise exposure, and the combination of effects was more consistent with an additive than a multiplicative interaction. CONCLUSIONS: Smoking may adversely affect hearing, and workers should be encouraged to refrain from both smoking and exposure to noise. However, the extra risk to hearing incurred by smoking in high ambient noise levels is small relative to that from the noise itself, which should be the main target for preventive measures.

Adolescent↗

PubMed2003

Smoking and musculoskeletal disorders: findings from a British national survey.

OBJECTIVES: To explore the relation between smoking habits and regional pain in the general population. METHODS: A questionnaire was mailed to 21 201 adults, aged 16-64 years, selected at random from the registers of 34 British general practices, and to 993 members of the armed services, randomly selected from pay records. Questions were asked about pain in the low back, neck, and upper and lower limbs during the past 12 months; smoking habits; physical activities at work; headaches; and tiredness or stress. Associations were examined by logistic regression and expressed as prevalence ratios (PRs). RESULTS: Questionnaires were completed by 12 907 (58%) subjects, including 6513 who had smoked at some time, among whom 3184 were current smokers. Smoking habits were related to age, social class, report of headaches, tiredness or stress, and manual activities at work. After adjustment for potential confounders, current and ex-smokers had higher risks than lifetime non-smokers for pain at all of the sites considered. This was especially so for pain reported as preventing normal activities (with PRs up to 1.6 in current v never smokers). Similar associations were found in both sexes, and when analysis was restricted to non-manual workers. CONCLUSIONS: There is an association between smoking and report of regional pain, which is apparent even in ex-smokers. This could arise from a pharmacological effect of tobacco smoke (for example, on neurological processing of sensory information or nutrition of peripheral tissues); another possibility is that people with a low threshold for reporting pain and disability are more likely to take up and continue smoking.

Adolescent↗

PubMed2003

The relative importance of whole body vibration and occupational lifting as risk factors for low-back pain.

AIMS: To explore the impact of occupational exposure to whole body vibration (WBV) on low back pain (LBP) in the general population and to estimate the burden of LBP attributable to occupational WBV in comparison with that due to occupational lifting. METHODS: A questionnaire including sections on WBV at work, LBP, and potential risk factors was mailed to a community sample of 22 194 men and women of working age. Sources and durations of exposure to occupational WBV were ascertained for the past week and personal vibration doses (eVDV) were estimated. Analysis was confined to subjects reporting exposures in the past week as typical of their work. Associations of LBP with eVDV, driving industrial vehicles, and occupational lifting were explored by logistic regression and attributable numbers were calculated. RESULTS: Significant associations were found between daily lifting of weights greater than 10 kg at work and LBP, troublesome LBP (which made it difficult to put on hosiery), and sciatica (prevalence ratios 1.3 to 1.7); but the risk of these outcomes in both sexes varied little by eVDV and only weak associations were found with riding on industrial vehicles. Assuming causal associations, the numbers of cases of LBP in Britain attributable to occupational WBV were estimated to be 444 000 in men and 95 000 in women. This compared with an estimated 940 000 male cases and 370 000 female cases of LBP from occupational lifting. CONCLUSIONS: The burden of LBP in Britain from occupational exposure to WBV is smaller than that attributable to lifting at work.

Adolescent↗

PubMed2002

Good medical practice: guidance for occupational physicians.

Following a catalogue of serious, highly publicized medical misdemeanours, the General Medical Council (GMC) has introduced plans for a new system of medical licensing in the UK called 'revalidation'. Under this, the onus will fall on individual doctors, including occupational physicians, to demonstrate their continuing fitness to practice. Doctors will need to show that they meet basic minimum standards in terms of the care they provide, their own continuing professional development, and other aspects of professional life like probity and ethical behaviour. As part of the process, the Faculty of Occupational Medicine, Royal College of Physicians, has produced its own guidance on good medical practice for occupational physicians, following an extensive consultation exercise. This paper summarizes the background to the initiative, the development process and the standards that have been recommended to aid professional accountability.

Clinical Competence↗

PubMed2002

Musculoskeletal disorders in farmers and farm workers.

Farming is a physically arduous occupation and this places farm workers at potential risk of musculoskeletal disorders such as osteoarthritis (OA) of the hip and knee, low back pain (LBP), neck and upper limb complaints, and hand-arm vibration syndrome (HAVS). This review considers the epidemiological evidence concerning such risks. The strongest evidence relates to OA of the hip, for which the public health impact is likely to be considerable. There is also weaker, but suggestive evidence that farmers more often have knee OA and LBP than workers in occupations with fewer physical demands. Tractor drivers, in particular, seem to have more LBP. Relatively little information exists on the risks of soft tissue rheumatism in the limbs and neck. For some outcomes, the link with occupational risk factors (such as heavy loading of joints and whole-body vibration) is sufficient to suggest the course that future prevention should take, but for several outcomes more research is first needed.

Adolescent↗

PubMed2002

Reliability of the Southampton examination schedule for the diagnosis of upper limb disorders in the general population.

BACKGROUND: Epidemiological research in the field of soft tissue neck and upper limb disorders has been hampered by the lack of an agreed system of diagnostic classification. In 1997, a United Kingdom workshop agreed consensus definitions for nine of these conditions. From these criteria, an examination schedule was developed and validated in a hospital setting. OBJECTIVE: To investigate the reliability of this schedule in the general population. METHODS: Ninety seven adults of working age reporting recent neck or upper limb symptoms were invited to attend for clinical examination consisting of inspection and palpation of the upper limbs, measurement of active and passive ranges of motion, and clinical provocation tests. A doctor and a trained research nurse examined each patient separately, in random order and blinded to each other's findings. RESULTS: Between observer repeatability of the schedule was generally good, with a median kappa coefficient of 0.66 (range 0.21 to 0.93) for each of the specific diagnoses considered. CONCLUSION: As expected, the repeatability of tests is poorer in the general population than in the hospital clinic, but the Southampton examination schedule is sufficiently reproducible for epidemiological research in the general population.

Adult↗

PubMed2002

Occupational exposure to noise and the attributable burden of hearing difficulties in Great Britain.

AIMS: To determine the prevalence of self reported hearing difficulties and tinnitus in working aged people from the general population, and to estimate the risks from occupational exposure to noise and the number of attributable cases nationally. METHODS: A questionnaire was mailed to 22 194 adults of working age selected at random from the age-sex registers of 34 British general practices (21 201 subjects) and from the central pay records of the British armed services (993 subjects). Information was collected on years of employment in a noisy job; and whether the respondent wore a hearing aid, had difficulty in hearing conversation, or had experienced persistent tinnitus over the past year. Associations of hearing difficulty and tinnitus with noise exposure were examined by logistic regression, with adjustment for age, sex, smoking habits, and frequent complaints of headaches, tiredness, or stress. The findings were expressed as prevalence ratios (PRs) with associated 95% confidence intervals (CIs). Attributable numbers were calculated from the relevant PRs and an estimate of the prevalence of occupational exposure to noise nationally. RESULTS: Some 2% of subjects reported severe hearing difficulties (wearing a hearing aid or having great difficulty in both ears in hearing conversation in a quiet room). In men, the prevalence of this outcome rose steeply with age, from below 1% in those aged 16-24 years to 8% in those aged 55-64. The pattern was similar in women, but severe hearing loss was only about half as prevalent in the oldest age band. Tinnitus was far more common in subjects with hearing difficulties. In both sexes, after adjustment for age, the risk of severe hearing difficulty and persistent tinnitus rose with years spent in a noisy job. In men older than 35 years with 10 or more years of exposure, the PR for severe hearing difficulty was 3.8 (95% CI 2.4 to 6.2) and that for persistent tinnitus 2.6 (95% CI 2.0 to 3.4) in comparison with those who had never had a noisy job. Nationally, some 153 000 men and 26 000 women aged 35-64 years were estimated to have severe hearing difficulties attributable to noise at work. For persistent tinnitus the corresponding numbers were 266 000 and 84 000. CONCLUSIONS: Significant hearing difficulties and tinnitus are quite common in men from the older working age range. Both are strongly associated with years spent in a noisy occupation--a predominantly male exposure. The national burden of hearing difficulties attributable to noise at work is substantial.

Adolescent↗

PubMed2002

Raynaud's phenomenon, vibration induced white finger, and difficulties in hearing.

BACKGROUND: An association has previously been reported between finger blanching and hearing difficulties, but only in workers with exposure to noise and hand transmitted vibration (HTV). AIMS: To explore the association in a community sample, including cases who lacked occupational exposure to noise or HTV. METHOD: A questionnaire was mailed to 12 606 subjects aged 35-64 years, chosen at random from the age-sex registers of 34 British general practices. Inquiry was made about years of employment in noisy jobs, lifetime exposure to HTV, hearing difficulties and tinnitus, and lifetime history of cold induced finger blanching. Subjects were classed as having severe hearing difficulty if they used a hearing aid or found it difficult or impossible to hear conversation in a quiet room. Associations of finger blanching with hearing difficulties and tinnitus were analysed by logistic regression. RESULTS: Among 8193 respondents were 185 who reported severe hearing difficulty and 1151 who reported finger blanching. After adjustment for age and years of work in noisy jobs, hearing difficulty was about twice as common in men and women who reported finger blanching, including those who had never been importantly exposed to noise and in those never exposed to HTV. CONCLUSIONS: These data support an association between finger blanching and hearing loss, which is not explained by confounding occupational exposure to noise, and suggest that it may extend to causes of blanching other than vibration induced white finger. Further investigations are warranted to confirm the association and explore possible mechanisms, such as sympathetic vasoconstriction in the cochlea.

Adult↗

PubMed2001

Risk of hand-arm vibration syndrome according to occupation and sources of exposure to hand-transmitted vibration: A national survey.

BACKGROUND: Although some occupational sources of hand-transmitted vibration (HTV) have been extensively investigated, the risks associated with others are poorly characterized. METHODS: A questionnaire was mailed to a community sample of 12,240 men aged 16- 64 years and 906 men from the armed forces. Questions covered current occupation, sources of HTV, numbness or tingling in the fingers in the past week, and finger blanching. In the 5,364 respondents who had been at work in the past week, associations between symptoms and exposures were examined by logistic regression, with odds ratios converted into prevalence ratios (PRs). RESULTS: Altogether, 513 men (10%) reported cold-induced finger blanching and 769 (14%) sensory symptoms in the fingers. The risk of blanching was increased in builders (PR 2.4, 95% CI 1.0-5.2), carpenters and joiners (PR 1.9, 95% CI 1.0-3.4), motor mechanics (PR 2.3, 95% CI 1.1-4.6), and laborers (PR 2.8, 95% CI 1.3-6.0); while the risk of sensory symptoms was elevated in laborers (PR 4.0, 95% CI 2.3-6.6) and plant operatives (PR 3.5, 95% CI 1.9-5.9). Use of hand-guided mowers, concrete breakers, chain saws, and jig saws was significantly associated with symptoms. CONCLUSIONS: Little attention has been paid to the risks of vibration injury in construction workers, woodworkers, motor mechanics, and laborers, or to the risks from mowers, jig saws and several other common vibratory tools. These should be a focus for further investigation and preventive measures.

Adolescent↗

PubMed2001

Use of keyboards and symptoms in the neck and arm: evidence from a national survey.

The objective of this study was to examine the relationship between upper limb symptoms and keyboard use in a population survey. A questionnaire was mailed to 21,201 subjects aged 16-64 years, selected at random from the registers of 34 British general practices. Information was collected on occupation and on regular use of keyboards (for >4 h in an average working day), pain in the upper limbs and neck, numbness or tingling in the upper limbs, headaches, and feelings of tiredness or stress. Associations were explored by logistic regression, with the resultant odds ratios converted into prevalence ratios (PRs). Among 12,262 respondents, 4899 held non-manual occupations. These included 1871 regular users of keyboards (e.g. computer operators, data processors, clerks, administrators, secretaries and typists). Pain in the neck or upper limbs and sensory symptoms were common in the non-manual workers overall (with 1 week period prevalences of 30 and 15%, respectively), and were associated with older age, smoking, headaches and tiredness or stress. After adjustment for these factors, regular keyboard use was significantly associated with pain in the past week in the shoulders (PRs 1.2-1.4) and the wrists or hands (PR 1.4), but not with elbow pain or sensory symptoms over the same period, or with neck or upper limb pain that prevented normal activities in the past year. Disabling symptoms were somewhat less prevalent among symptomatic keyboard users than among other symptomatic workers. We conclude that use of keyboards was associated with discomfort at the shoulder and wrist or hand, but risk estimates were lower than generally reported in workplace surveys. Previous estimates of risk in the occupational setting may have been biased by shared expectations, concerns, or other aspects of illness behaviour.

Adolescent↗

PubMed2001

Exposure to hand-transmitted vibration and pain in the neck and upper limbs.

Workers exposed to hand-transmitted vibration (HTV) often experience aches and pains in the upper limbs, but there have been few studies of the pattern and severity of symptoms, or their relationship to the estimated dose of vibration. As part of a wider survey of vibration, we mailed a questionnaire about exposures to HTV and pain in the neck and upper limbs to a sample of men selected at random from the registration lists of 34 British general practices and the pay records of the armed services. Analysis was confined to the 1856 male respondents who had been employed in manual occupations for a year or more and who reported the last week as being representative of their job. Inquiry was made about pain in the neck, shoulder, elbow and wrist/hand over the past week and past year (including pains that limited normal activity). Subjects were classed according to their lifetime exposure to HTV and their estimated average daily vibration dose [A(8) r.m.s.] in the previous week. A total of 283 men had a minimum estimated A(8) greater than a proposed action level of 2.8 m/s(2), and in this group symptoms were about twice as prevalent as in manual workers who had never used vibratory tools. The excess risk was somewhat higher for distal sites than for proximal ones (e.g. the prevalence ratio for hand/wrist pain in the past week was 2.7 versus 1.8 for neck pain). This accords with the pattern of transmission of HTV to the upper limb, although a confounding effect from other ergonomic risk factors cannot be discounted.

Adolescent↗