Many people rely economically on occupations involving high loading of the hip or knee joints for lengthy periods, possibly placing them at increased risk of developing chronic pain in these joints. There is a growing body of evidence from large longitudinal cohort studies, case-control studies and population-based surveys that certain occupations, or having work involving considerable heavy lifting, kneeling or squatting, may be associated with increased risk of symptomatic hip or knee osteoarthritis and joint replacement surgery. Only a few studies have evaluated the effectiveness of specific workplace strategies to reduce this risk. Identifying modifiable workplace risk factors and implementing feasible and accessible preventative strategies will be of great public health significance in the next decade.
Worldwide, chronic hip or knee pain is highly prevalent among older people. The large population-based English Longitudinal Study of Ageing has recently shown that 20% of people aged 60 years and over either report moderate to severe hip or knee pain and disability and would be considered in need of joint replacement surgery or have already undergone hip or knee replacement surgery for chronic pain . Many analgesic options are available for people with chronic hip or knee pain; however, the benefits of these treatments for many people are only marginal over placebo, and are often outweighed by their cost or side effects . With the ageing of the population worldwide, the prevalence of chronic hip or knee pain and disability will increase markedly. Many people rely economically on occupations involving high loading of the hip or knee joints for lengthy periods, possibly placing them at increased risk of developing chronic joint pain. Identifying modifiable workplace risk factors and implementing feasible and accessible preventative strategies may be of great public health significance in the next decade.
Possible causes of hip pain
The most common cause of chronic hip pain in older people is osteoarthritis. Other common causes include greater trochanteric pain syndrome, referred pain from lumbar spine impingement and acetabular labral tears. The nature and specific location of the pain can often aid diagnosis. As ‘hip pain’ is difficult to define topographically , a physical examination and imaging are often required to differentiate the likely aetiology.
Hip osteoarthritis typically results in pain localised to the anterior groin region, with pain and stiffness particularly present at the initiation of activity. Pain is activity related at first, becoming chronic with increased loss of articular cartilage and structural disease progression. Typically, the passive range of hip motion is increasingly restricted, particularly internal rotation . In fact, decreased internal rotation is often a precursor to symptomatic disease, indicating subtle abnormalities in the structure of the hip joint that would substantially increase the risk of developing osteoarthritis .
Acetabular labral tears are demonstrated in more than half of patients with mechanical hip pain . The acetabular labrum functions to increase the stability of the hip joint as well as distribute the load passing through the hip joint. Tears in this innervated fibro-cartilage ring attached to the bony rim of the acetabulum increase the risk of damaging loading of the articular cartilage. Labral tears can be caused by direct trauma or sporting injuries, or simply repetitive microtrauma or hip dysplasia. For many people, labral tears may be the primary precipitator for the early development of painful radiographic hip osteoarthritis. Labral tears may play a role similar to meniscal tears in the knee joint, producing a poor biomechanical environment for the joint and increased risk for the early development of osteoarthritis. Similar to osteoarthritis, the pain associated with labral tears is mostly located in the anterior groin region; however, pain can be located lateral or deep in the posterior buttock region. In addition to pain, symptoms of clicking locking or giving way are reported, the most typical being clicking . In contrast to hip osteoarthritis, restriction in hip range of motion is minimal. However, labral tears are associated with ageing and were demonstrated in more than 90% of cadavers studied in people with a mean age of 78 years .
Chronic lateral hip pain is often termed ‘greater trochanteric pain syndrome’ . The differential diagnosis between trochanteric bursitis or gluteus medius pathology and pain referred from the lumbar spine is often difficult, and a combination of all three possible. All can result in aching pain localised in the region of the greater trochanter exacerbated by sleeping on the affected side, going down stairs or standing for long periods of time. A physical examination is usually required to distinguish between mechanical hip pain and pain originating in the lumbar spine. Imaging may be required to identify trochanteric bursitis or gluteus medius pathology as the likely cause of lateral hip pain.
Possible causes of knee pain
The most common cause of chronic knee pain in people aged ≥50 years is osteoarthritis. The pain associated with osteoarthritis is mostly related to weight-bearing activity, with joint stiffness experienced on initiation of movement after periods of rest. The pain is typically located on the medial or anterior regions of the knee and experienced as a dull ache, exacerbated when negotiating stairs or walking on uneven ground. Pain and giving way typically experienced while going down stairs is often due to chondromalacia patella or marked osteoarthritis in the patellofemoral joint. Apart from acute trauma or systemic inflammatory diseases, such as rheumatoid arthritis or gout, other common causes of knee pain are intra-articular loose bodies or meniscal tears. Pain is typically episodic and occurs in association with episodes of locking or giving way of the knee, at times followed by gradual swelling around the joint. However, systemic inflammatory diseases, intra-articular loose bodies and meniscal damage or tears can occur concomitantly with radiographic evidence of knee osteoarthritis. The pain descriptors used by the patient can often point to the probable aetiology. Less common causes of chronic knee pain are bursitis and tendinitis. Pain felt at the back of the knee is often caused by a Baker’s cyst or referred from lumbar spine impingement. Occasionally, anterior knee pain may be referred pain from hip osteoarthritis.
Possible causes of knee pain
The most common cause of chronic knee pain in people aged ≥50 years is osteoarthritis. The pain associated with osteoarthritis is mostly related to weight-bearing activity, with joint stiffness experienced on initiation of movement after periods of rest. The pain is typically located on the medial or anterior regions of the knee and experienced as a dull ache, exacerbated when negotiating stairs or walking on uneven ground. Pain and giving way typically experienced while going down stairs is often due to chondromalacia patella or marked osteoarthritis in the patellofemoral joint. Apart from acute trauma or systemic inflammatory diseases, such as rheumatoid arthritis or gout, other common causes of knee pain are intra-articular loose bodies or meniscal tears. Pain is typically episodic and occurs in association with episodes of locking or giving way of the knee, at times followed by gradual swelling around the joint. However, systemic inflammatory diseases, intra-articular loose bodies and meniscal damage or tears can occur concomitantly with radiographic evidence of knee osteoarthritis. The pain descriptors used by the patient can often point to the probable aetiology. Less common causes of chronic knee pain are bursitis and tendinitis. Pain felt at the back of the knee is often caused by a Baker’s cyst or referred from lumbar spine impingement. Occasionally, anterior knee pain may be referred pain from hip osteoarthritis.
Descriptive epidemiology
Disease prevalence is best estimated from large population-based surveys with rigorous sampling strategies. However, such large surveys do not generally allow a physical examination by a trained clinician to determine disease status. Disease status is frequently determined by a survey-specific case definition; the reported incidence and prevalence of hip or knee pain are highly associated with the specific case definition used.
Case definitions for the presence of hip or knee pain vary from a simple “current” or “ever” pain through to a more specific “pain in the past 7 days,” “pain on most days of 1 month” or “pain on most days of 1 month in the past year.” The pain descriptor has also been expanded in several studies to also include “aching or stiffness,” descriptors likely to inflate pain prevalence estimates. Variation in the specificity of pain location is demonstrated, from “in and around the knee” to a more specific “knee pain,” “hip pain” vs. the more specific “anterior groin pain.” Furthermore, in contrast to radiographic criteria, there is usually no requirement for a level of pain severity to be reached for case definition. Hip and knee pain prevalence estimates may therefore include cases where pain is referred from other sites as well as those with minimal or occasional pain of no current or future clinical relevance. These differing definitions and descriptors of pain alone could explain much of the large variability in prevalence and risk factor estimates from population-based studies around the world. Importantly, allowing the inclusion of a wide range of pathology is likely to attenuate the magnitude of any detected risk factors for hip or knee pain.
Some prevalence studies require radiographic confirmation of hip or knee osteoarthritis to define cases of hip or knee pain to try to restrict pathology to osteoarthritis. However, a wide range of radiographic criteria for case definition is evident in the literature , making comparisons between prevalence estimates difficult. While radiographic confirmation may lead to the exclusion of many cases of referred pain or clinically insignificant joint pain, radiographic case definition criteria will exclude people with early osteoarthritis and usually, as only one view is taken, the not inconsiderable number of women with isolated patellofemoral disease . Furthermore, even in the presence of radiographic changes, hip and knee pain may be not directly attributable to osteoarthritis, as many people with radiographic changes typical of osteoarthritis remain asymptomatic. While possibly resulting in a more homogeneous sample for risk factor analysis, requiring radiographic evidence of osteoarthritis will markedly underestimate the burden of knee or hip pain in the community.
Internationally, prevalence estimates for hip or knee pain show wide variability depending on the age and sex distribution of the studied cohort, even when largely comparable case definitions are used. However, universally, the prevalence of hip and knee osteoarthritis increases exponentially with ageing, with estimates for population-based cohorts aged 45 years and over ranging from 7% to 17% for symptomatic knee osteoarthritis and from 2% to 10% for symptomatic hip osteoarthritis . For symptomatic knee osteoarthritis, the prevalence in generally higher among women and among people in rural regions of developing countries compared with urban regions or compared with developed countries . In developing countries, a large proportion of the population, while not obese, is engaged in heavy physical occupational activity within informal rural settings for their entire working life. Such exposure has frequently been linked to increased risk of injury and developing chronic musculoskeletal pain and disability .
Risk factors for hip pain due to osteoarthritis
The risk of symptomatic hip osteoarthritis clearly increases with age and similarly in men and women . While many studies have established being overweight or obese as consistent and strong risk factors for symptomatic knee osteoarthritis, results for hip osteoarthritis have been less consistent . Most studies have only found moderate associations between obesity and incident radiographic hip osteoarthritis. However, the association between obesity and hip osteoarthritis is more likely to be significant, if symptomatic disease was the case definition used in the study . It is not surprising, therefore, that a large prospective study demonstrated that being in the highest body mass index (BMI) quartile increased the risk of total hip replacement surgery two- to threefold in men and women, respectively .
Childhood hip disorders, such as hip dysplasia and slipped capital femoral epiphysis, are known to substantially increase the risk of developing symptomatic osteoarthritis in later life. There is increasing evidence that more common subtle osseous deformities of the hip joint, such as an acetabular dysplasia or a pistol grip deformity (‘femoroacetabular impingement syndrome’), also result in a substantially increased risk of early hip osteoarthritis . Overall, the prevalence of these osseous deformities was found to be high, particularly in males . The large population-based Copenhagen Osteoarthritis Substudy, among almost 4000 people aged 21–90 years (mean age 61 years), demonstrated hip malformations in 71% and 37% of men and women, respectively . Specifically, while the overall prevalence of acetabular dysplasia (4%) or a deep acetabular socket (17%) was comparable between men and women, a pistol grip malformation was found in 20% and 5% of men and women, respectively. While having a hip malformation was not significantly associated with groin pain, having a deep acetabular socket or a pistol grip malformation was associated with two- to threefold significantly increased odds of having hip osteoarthritis (defined as joint space width ≤2 mm) after adjusting for age, sex and BMI . Among cohort participants with hip osteoarthritis, 71% and 37% of men and women, respectively, had concomitant malformations. These findings suggest that subtle hip malformations may be important risk factors for the development of hip osteoarthritis, and particularly in men.
Risk factors for knee pain due to osteoarthritis
Apart from ageing and being female, the other most common risk factor for developing painful knee osteoarthritis is being overweight or obese . Gaining weight during adult life has also been found to give a slightly higher risk of developing knee osteoarthritis compared with constantly being overweight . For women, weight loss has been found to decrease the risk of knee osteoarthritis substantially . While the prevalence of symptomatic knee osteoarthritis is higher in women, a significantly increased risk of symptomatic knee osteoarthritis associated with being female appears to only commence after menopausal age . Other important risk factors for developing symptomatic knee osteoarthritis include a history of acute knee trauma or meniscectomy . Of the 16 studies evaluating the association between previous knee injury and knee osteoarthritis in a recent systematic review , all but two studies concluded that knee injury was a significant and important risk factor. Having a history of substantial knee trauma was associated with a sevenfold increased risk of developing knee osteoarthritis in two recent large prospective cohort studies adjusting for age, gender, BMI, smoking and physical activity . A two- to sixfold increased risk has been reported for the development of knee osteoarthritis 15–20 years after meniscectomy, even without concomitant cruciate ligament damage, the higher risk associated with total meniscectomy (compared with partial) or being obese . Events such as substantial knee trauma, with or with surgery, alter the biomechanical environment of the knee joint and likely result in major changes to the load distribution over the articular cartilage and subchondral bone and triggering an ultimately degradative biochemical response.
There are several well-established risk factors for both symptomatic hip and knee osteoarthritis: age, gender, high BMI, history of joint surgery or trauma. These known risk factors will need to be considered in any evaluation of the influence of occupation or the working environment on the development of hip or knee pain.
Occupational risk factors
The highest level of evidence for determining risk factors comes from large population-based longitudinal cohort studies, which allow recording of risk exposure prior to disease incidence. However, longitudinal cohort studies are very costly, needing to be large and with a lengthy follow-up to accumulate sufficient ‘cases’ of incident disease, even in fairly prevalent conditions, such as symptomatic hip or knee osteoarthritis. A case-control design is therefore frequently used as a feasible option, even though accurate retrospective reporting of physical workload exposure over a long period is problematic for most people and is vulnerable to differing recall between cases and controls. Furthermore, identifying and assembling what is considered a valid control group is often an issue of ongoing contention. For symptomatic hip or knee osteoarthritis, it may be argued that it is particularly difficult to establish a causal relationship using a case-control study design given the actual timing of disease incidence is uncertain and likely to have a lengthy non-symptomatic lead time. The evidence from case-control studies is therefore generally considered less convincing, compared with prospective cohort studies. However, it is unlikely that developing chronic hip or knee pain will lead people to choose an occupation requiring increased physical loading of these joints.
Evaluation of risk exposure is mostly conducted through self-report or interview questionnaires. For studies evaluating occupational risk factors for hip or knee pain, questions are usually posed to estimate total exposure to activities demonstrated to increase loading of these joints, for example, heavy lifting, standing, climbing stairs or ladders, squatting or kneeling. Some larger national population-based surveys, however, have used occupational class or job title as a surrogate measure of physical load. Using these surrogate measures, particularly if only a few crude classifications are included, is likely to attenuate risk magnitude as one occupational class can cover a range of physical workload exposures.
Evidence from systematic reviews
Two recent well-conducted systematic reviews evaluated studies published up to May 2007 examining causal relationships between physical workload exposures and risk of hip or knee osteoarthritis . Studies were only included in these systematic reviews, if controlled and if the case definition ‘osteoarthritis’ was confirmed by radiographs, relevant World Health Organization (WHO) International Classification of Diseases codes or presence of a total joint replacement (or on the waiting list).
Hip osteoarthritis
For hip osteoarthritis, 22 studies met the inclusion criteria . Most of the 22 studies had a case-control design, with only a few large longitudinal cohort studies included and rated as well conducted by the reviewer . All studies evaluating work exposure to heavy lifting showed a two- to threefold significantly increased risk of hip osteoarthritis. A dose–response relationship was demonstrated in several studies; 10–25 kg over at least 10–20 years was associated with a clearly increased risk . Only five studies examined the causal relationship between the occupational need to climb stairs or ladders; and three studies demonstrated a twofold significantly increased risk of hip osteoarthritis. However, the only study evaluating the risk associated with stair or ladder climbing, and considered of high methodological quality could not find a significant association in this case-control study of older men . No studies were retrieved that evaluated the influence of heavy lifting combined with kneeling and squatting.
Fourteen studies evaluated the risk of hip osteoarthritis associated with farming. All but one study demonstrated a two- to 12-fold significantly increased risk . This risk estimate is likely to be conservative, as farmers leaving this occupation due to painful hips (healthy worker effect) will not have been included. Six studies evaluated the risk for hip osteoarthritis associated with construction work. While most studies showed significantly increased risk, the magnitude of risk was not as large as that demonstrated for farming. This finding of a smaller risk was attributed to the generally smaller samples in these studies of construction workers, and the anticipated greater heterogeneity of workloads within the classification of ‘construction work’ compared with farming. All studies in the 2008 systematic review found stronger associations between heavy, physical, occupational demands and hip osteoarthritis in men compared with women. This gender bias has mostly been attributed to the relatively small number of women exposed to heavy, physical, occupational demands in the conducted studies, compared with men. However, the demonstrated higher prevalence of subtle osseous deformities of the hip joint among men would also increase their vulnerability for developing hip osteoarthritis. These hip joint structural characteristics have not been evaluated or considered in any multivariate analyses of occupational risk factors for hip osteoarthritis in studies conducted to date. This review concluded that there was moderate to strong evidence for an association between heavy lifting over a 10–20-year period and hip osteoarthritis and a twofold increased risk for farmers after 10 years’ exposure . There was insufficient evidence for other occupational classes or for climbing stairs and ladders, kneeling or squatting.
Knee osteoarthritis
For knee osteoarthritis, the 2008 review retrieved 25 observational studies that met the inclusion criteria . Again, apart from five longitudinal cohort studies, all other risk evaluations were derived from either case-control studies (difficulty of recalling past activity accurately and recall bias) or cross-sectional surveys (difficulty establishing a causal relationship). The results for the 17 studies evaluating the risk associated with heavy lifting were inconsistent, with only nine studies demonstrating a significant association. Restricting analysis to the six studies considered to be of high methodological quality by the reviewer demonstrated a significant odds ratio (OR) for developing knee osteoarthritis ranging from 1.9 to 7.1 associated with heavy lifting . For kneeling or squatting (usually defined in studies as >1 h per day), eight out of 12 studies demonstrated a significant two- to sevenfold increased odds of developing knee osteoarthritis . When the analysis was restricted to the six studies considered to be of high methodological quality, an OR for incident knee osteoarthritis from 1.1 to 3.0 was demonstrated . Furthermore, a dose–response relationship was detected by several studies. Four studies evaluating the combination of heavy lifting and kneeling/squatting demonstrated significantly increased ORs in the range of 2.2–5.4 . Two studies compared heavy lifting alone with the combination of heavy lifting with kneeling, both demonstrating a marked increase in risk associated with the combination of activities . Only a few case-control studies with marked methodological limitations examined the association between climbing stairs or ladders and knee osteoarthritis; hence, the review considered the evidence of ORs ranging from 1.7 to 6.1 to still be inconclusive.
Twelve studies evaluated the risk of knee osteoarthritis according to occupational class, with highly significant associations demonstrated in most studies for miners, floor layers (patella-femoral disease), farmers and certain professions within the construction industry. The most highly rated study in this group, a case-control study conducted among more than 1000 workers in Sweden, found a two- to threefold significantly increased prevalence of total knee replacement surgery among male construction workers, male forestry workers and farmers (male or female) .
Overall, due to the reliance on relatively small case-control studies, the strength of evidence for a causal relationship between occupational workload and hip or knee pain was considered moderate by the author of the reviews.
Review update
The studies
A literature search was conducted in July 2010 to update the evidence provided by the above two systematic reviews. Studies were identified by the keywords (knee or hip), (osteoarthritis or osteoarthrosis or knee pain or hip pain) and (work or occupation). The search was limited to English language full-text articles. Only controlled studies evaluating occupational risk factors for symptomatic disease were included. In total, 10 studies were identified, two evaluating symptomatic hip and knee osteoarthritis, two assessing symptomatic hip osteoarthritis ( Table 1 ) and six restricted to symptomatic knee osteoarthritis ( Table 2 ).
| Ref | Size | Age (yrs) | Exposure measure | Diagnostic Criteria | Adjusted/Matched | Significant findings (OR, 95% CI) or (RR, 95% CI) | Design | Strengths/Weakness |
|---|---|---|---|---|---|---|---|---|
| Allen 2010 | 2729 | ≥45 | Occupational group Occupational activity Longest held job: Walking, lifting/carrying, sitting, standing, bending/twisting, squatting, climbing stairs, crawling, crouching/kneeling, heavy work while standing. Lifetime exposures: heavy work while standing, sitting/kneeling/walking >50% job; lifting>10x/week. | Symptoms. K/L ≥2. | Age Gender Race BMI Smoking Knee/hip injury Household tasks | Lifting: 1.67 (1.26–2.23) Bend, twist reach: 1.60 (1.18–2.17) Crawling: 2.28 (1.43–3.65) Heavy work standing: 1.75 (1.17–2.61) Lifting 10 kg ≥ 10/week: 1.71 (1.28–2.29) | Cross-sectional | Strengths: Large community-based cohort, detailed exposure information, adjustment for most other important risk factors. Weakness: Recall bias, high prevalence heavy occupational activity, rural community – may limit generalisability |
| Jarvholm 2008 | 204,741 Males | 15–67 | Job title | Surgically treated primary hip OA. | Age BMI | None significant. | Cohort | Strengths: Prospective cohort design, surgery incidence collected from national registry. Weakness: Use of job title as proxy measure of occupational workload exposure, no adjustment history of injury or sporting activities. |
| Juhakoski 2009 | 840 | 30–72 | Questionnaire Occupational activity : Physical workload (six categories): light sedentary, other sedentary work, light standing/movements, fairly light or medium heavy, heavy manual or very heavy manual. | Clinical examination of those reporting hip pain in past month. | Sex Age BMI Education Smoking Alcohol Leisure time physical activity Injury | (Compared with light sedentary) Fairly light or medium heavy: 3.1 (1.2–8.0) Heavy manual labour: 6.7 (2.3–19.5) | Cohort | Strengths: Population based prospective study with long follow-up period, symptomatic hip OA diagnosed by physicians. Weakness: Limited number of very heavy manual labour subjects ( n = 12), wide CI’s. |
| Thelin 2007 | 3437 Males | 40–60 | Occupational class : Farmer ( n = 1220). Rural non-farmer ( n = 1130). Urban ( n = 1087). | Hospitalised: Any OA. Hip OA. Hip joint surgery. | Age Residence | (Compared to urban controls) Farming men Any OA: 2.1 (1.4–3.2) Hip OA: 3.0 (1.7–5.3) Non-farming men No significance findings. | Cohort | Strengths: Large longitudinal cohort, case definition by national registry. Weakness: Limited information on hospital care for hip OA (Prior 1997 not available), no adjustments for BMI, hip/joint injury, smoking. |
| Ref | Size | Age (yrs) | Exposure measure | Diagnostic Criteria | Adjusted/Matched | Significant findings (OR, 95% CI) or (RR, 95% CI) | Design | Strengths/Weakness |
|---|---|---|---|---|---|---|---|---|
| Allen 2010 | 2729 | ≥45 | Occupational group Occupational activity Longest held job: Walking, lifting/carrying, sitting, standing, bending/twisting, squatting, climbing stairs, crawling, crouching/kneeling, heavy work while standing. Lifetime exposures: heavy work while standing, sitting/kneeling/walking >50% job; lifting>10x/week. | Symptoms K/L ≥2. | Age Gender Race BMI Smoking Knee/hip injury Household tasks | Walking: 1.46 (1.12–1.90) Lifting: 1.42 (1.13–1.80) Standing: 1.38 (1.08–1.77) Sitting: 0.72 (0.57–0.90) Crawling: 1.59 (1.05–2.41) Heavy work standing: 1.44 (1.03–2.02) | Cross-sectional | Strengths: Large community-based cohort, detailed exposure information, adjustment for most other important risk factors. Weakness: Recall bias, high prevalence heavy occupational activity, rural community – may limit generalisability. |
| Jarvholm 2008 | 204,741 | 15–67 | Job title . | Surgically treated primary knee OA. | Age BMI | (Compared with white collar workers) Asphalt workers: 2.81 (1.11–7.13) Brick layers: 2.14 (1.08–4.25) Floor layers: 4.72 (1.80–12.33) Plumbers: 2.29 (1.19–4.43) Rock workers: 2.59 (1.18–5.69) Sheet-metal workers: 2.60 (1.06–6.37) Wood workers: 2.02 (1.11–3.69) | Cohort | Strengths: Prospective cohort design, surgery incidence collected from national registry. Weakness: Use of job title as proxy measure of occupational workload exposure, no adjustment history of injury or sporting activities. |
| Dahaghin 2009 | 970 (Cases: 480 Controls: 490) | 17–88 | Occupational class : Sedentary, laborious or housekeeping. Occupational activity : >1 h/day: Standing, walking, sitting. >30 min/day: Walking up/downhill, squatting, knee bending, cycling. Lifting >2 kg/day. Climbing stairs >3/day. | ACR clinical criteria. | Age Sex BMI Knee injury | Occupational class None significant. Occupational activity Walking 1–2 h/day: 0.60 (0.42–0.85) Sitting 1–2 h/day: 0.54 (0.36–0.80) Squatting >30 min/day: 1.51 (1.12–2.04) Cycling >30 min/day: 2.06 (1.23–3.45) | Case-Control | Strengths: Community-based, life grid to help participant plot work activities, adjustment for most other important risk factors. Weakness: Recall bias, controls younger, differential response (80% cases, 47% controls). |
| D’Souza 2008 | 1970 | ≥60 | Occupational exposure : (longest held job ≥ 5 years) sitting, standing, walking, lifting >10 kg, kneeling/squatting, working in cramped space. Rated according to job title by ergonomic experts. | K/L ≥2. Pain. TKR. | Age Gender BMI Smoking Sport activities | Occupational activity Females Standing: 2.28 (1.09–4.77) Males Sitting: 0.42 (0.18–0.96) Kneeling: 3.08 (1.31–7.21) Heavy lifting: 2.72 (1.14–6.50) All Standing: 1.96 (1.06–3.46) Kneeling: 2.37 (1.27–4.45) Heavy lifting: 2.00 (1.02–3.93) | Cross-sectional | Strengths: National population-based survey (NHANESIII), expert ratings for occupational exposures. Weakness: No adjustment for history of knee injury, housework or other jobs held other than longest job. |
| Jones 2007 | 859 | 20–27 | Occupational exposure : Manual handling activities during the last working day (estimate of weights lifted, time spent squatting, standing, kneeling). Psychosocial factors. | Knee pain past month. | Age Sex BMI Physical activity | (Compared to not carrying/lifting weights) Carrying weights <20: 2.1 (1.3–3.2) Carrying weight >20: 1.7 (1.03–2.8) Lift weights shoulder levelor above <28: 1.8 (1.1–2.9) Psychosocial factors: None significant. | Cohort | Strengths: Prospective cohort, newly employed workers, diverse range of occupations, psychosocial factors included, participation rate 80%. Weakness: Only 2 year follow-up, no adjustment for history of knee pain/injury. |
| Klussmann 2010 | 1310 (Cases: 739 Controls: 571) | 25–75 | Questionnaire and Telephone interview | Cases: K/L ≥2. Knee OA <10 years. No knee injury. Controls: Recruited at accident clinics | Sex BMI Age Smoking Leisure activities Sports risk | Females (Highest tertile compared with 0) Kneeling/squatting: 2.5 (1.35–4.68) Lifting and carrying: 2.13 (1.14–3.98) Males (Highest tertile compared with 0) Kneeling/squatting: 2.47 (1.41–4.32) | Case-Control | Strengths: Wide range occupational exposure, response rate – moderate, adjustment for most other risk factors. Weakness: Uses of clinical controls, cases/controls not matched for age/sex, recall bias. |
| Seidler 2008 | 622 males (Cases: 295 Controls: 327) | 25–70 | Personal interview Occupational class : Occupational groups. Occupational activity : Work time physical workload: kneeling/squatting, cumulative lifting/carrying, kneeling/squatting and lifting/carrying combined. Calculated cumulative exposures up to date diagnosed of OA. | K/L scale ≥2. Chronic complaints. | Age Region BMI Jogging/athletics | Occupations class Chemical/Plastics: 16.1 (3.1–84.8) Plaster, insulators, glaziers, terrazzo workers, construction carpenters, roofers, upholsterers: 4.5 (1.1–19.4) Painters, varnishers: 6.4 (1.5–27.1) Quality inspectors: 6.4 (1.5–27.1) Service workers): 4.3 (1.6–11.7) Kneeling / squatting combined Highest quartile: 2.2 (1.1–5.0) Lifting / carrying combined 2 nd quartile: 2.0 (1.1–3.6) 3 rd quartile: 2.0 (1.1–3.9) Highest quartile: 2.6 (1.1–6.1) Kneeling or squatting Highest quartile: 3.4 (1.8–6.3) Both kneeling / squatting Highest quartile: 7.9 (2.0–31.5) | Case-Control | Strengths: use of pictures for work activities postures in questionnaire, evaluates dose–response relationship. Weakness: Low response rate (61% cases, 55% controls, recall bias, unknown diagnosis among controls, males only. |
| Vrezas 2010 | 622 males (Cases: 295 Controls: 327) | 25–70 | Questionnaire and Telephone interview Occupational activity : Evaluating the influence of a high BMI. | K/L ≥2 Chronic complaints. | Age Region BMI Kneeling/Squatting Lifting/carrying Jogging/athletics | BMI ≤25 kg/m 2 and kneeling/squatting: 1.8 (0.8–3.9) BMI of ≥25 kg/m 2 and kneeling/squatting: 5.3 (2.4–11.5) BMI of ≤25 kg/m 2 and lifting/carrying: 2.4 (1.1–5.4) BMI of ≥25 kg/m 2 and lifting/carrying: 5.0 (2.4–10.5) | Case-Control | Strengths: Evaluates the dose response rate. Weakness: Low response rate (61% cases, 55% controls), recall bias, unknown diagnosis among controls, males only. |
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Factors that affect the occurrence and chronicity of occupation-related musculoskeletal disorders
Epidemiological aspects of studying work-related musculoskeletal disorders
Management of occupation-related musculoskeletal disorders
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