Table 3 KneeOA and kneeling: details of the studies
ReferenceStudy populationAge (years)Participation rate (%)Exposure measured byDiagnostic criteriaAdjusted for/Matched byComparisonsResults (OR, 95% CI)DesignQuality of the study (+, ++, +++)/Strength/Weakness
Anderson and Felson, 1988122428 men, 2765 women from a population study (HANESI) KneeOA: 105 men210 women35–7475Questionnaire graded in relation to heavy work by experienced occupational professionalsKellgren and Lawrence grade 2–4 TFJSingle AP, non-weight-bearing of both kneesRace, BMI educationKneeling none vs much45–54 yearsMenWomen55–64 yearsMenWomen0.82, 0.32 to 2.112.07, 0.71 to 6.082.45, 1.21 to 4.973.49, 1.22 to 10.5Cross-sectional+++Strength: Well described design and materialsWeakness: Non-weight bearing x-rays may underestimate kneeOAExposure measured by current occupation (risk of misclassification) Use of job titles (risk of misclassification)
Felson et al, 199116Cases: 176 men, 279 women with kneeOAControls: 569 men 807 womenFrom the Framingham Heart StudyMean 7396InterviewPhysical demands scored by trained codersKneeOA, TFJ, grade 2–4Weight-bearing radiographsAgeBMISmokingHistory of knee injuryEducationKnee-bending plus sedentary or light demandsMenWomenMedium, heavy, very heavy demandsMenWomen1.07, 0.53 to 2.171.43, 0.77 to 2.632.22, 1.38 to 3.580.59, 0.16 to 2.15Cohort+++Strength: Longitudinal design; Case-definition: weight-bearing radiographsWeakness: Exposure classified by job title (risk of misclassification). Few subjects with heavy physical work, especially among women
Cooper et al, 199420Cases: 109 (30 men, 79 women grade 3–4 OAControls: 218 age- and sex-matched (without knee pain) From a large general practice55–90Mean: 73QuestionnaireDetails of the main job entailed eight specific physical activitiesSymptomatic kneeOA Kellgren and Lawrence grade 3–4TFJ±PFJWeight-bearing APBMI, Heberden’s nodesKneeling >30 min/day in an average working daySquatting >30 min/day in an average working day3.4, 1.3 to 9.16.9, 1.8 to 26.4Case–control++Strength: Weight-bearing radiographs, inclusion of PFJ OAInclusion of subjects with moderate and severe symptomatic OAWeakness: Exposure measured retrospectively by interviews (risk of recall bias) Small number of male participants and subjects with heavy lifting
Elsner et al, 199636Cases: 115 men, 86 women with kneeOA from an orthopaedic clinicControls: 95 men 87 women from general practice in the same area<45: 27%45–55: 27%>55: 46%61 among casesPhysical demands reported in a diary bookAll degrees of radiological kneeOAAgeKneeling (always/often vs seldom/never) MenWomenSquatting (always/often vs seldom/never) MenWomen2.2, 1.01 to 4.992.2, 0.51 to 10.171.8, 0.92 to 3.732.0, 0.57 to 7.34Case–control++Strength: Well described design and materialsWeakness: Case definition: grade 1–4 OA (risk of misclassification) Exposure: lifting weights (no frequency, no duration) (risk of misclassification), retrospective (risk of recall bias) Low participation rate among casesControls collected over 4 years; selection of the controls not defined (risk of selection bias)
Coggon et al, 200025Cases: 518 (205 men 313 women) Controls: 518 (205 men 313 women) from the same communityFrom three English districts in a 2-year period47–93Mean: 7355InterviewOccupation held for >1 year from school ageSpecified physical activityCases waiting for surgeryBMIHeberden’s nodesPrevious knee injuriesMatched by sex and ageKneeling/squatting >1 h/day1–9.9 yearsMenWomen10–19.9 yearsMenWomen⩾20 yearsMenWomen3.0, 1.4 to 6.12.8, 1.4 to 5.51.3, 0.5 to 3.20.8, 0.3 to 2.01.7, 0.7 to 4.03.2, 0.8 to 13.0Case–control+++Strength: High number of participants, interviews with specification of different physical activities. Weakness: Exposure data collected retrospectively (risk of recall bias). Low participation rate especially among controls. Case-definition: Placed on a waiting list for TKR (risk of selection bias)
Lau et al, 200026Cases: 166 men492 womenControls: 166 age- and sex-matched from general practice in the same regionOver a 3-month periodInterviewPhysical activity in job in which they had work for the longest period before symptoms28% had TKR, 15% waiting for TKR, 57%Grade 3–4 OAMatched by sex and ageKneeling ⩾1 h/dayMenWomenSquatting ⩾1 h/dayMenWomen1.4, 0.7 to 3.00.9, 0.6 to 1.31.2, 0.7 to 2.01.1, 0.8 to 1.5Case–control+++Strength: High number of participantsExposure collected by interviews, specified in different physical activities. Controls with knee complaints excludedWeakness: Exposure collected retrospectively (risk of recall bias). Case-definition: subjects seeking hospitals for kneeOA (risk of selection bias)
Sandmark et al, 200027Cases: 325 men, 300 women with TKRControls: 264 men, 284 womenFrom 14 counties in Sweden between 1991 and 199555–7080Interviews questionnaireOccupational historySpecified physical activity including lifts at work (kg)TKR between 1991–1993BMI, smoking, sports activity, Age-matchedSquatting/knee bending (number) MediumMenWomenHighMenWomenKneeling (min) MediumMenWomenHighMenWomen1.3, 0.8 to 2.21.2, 0.7 to 1.92.9, 1.7 to 4.91.1, 0.6 to 1.91.4, 0.9 to 2.21.5, 1.0 to 2.32.1, 1.4 to 3.31.5, 0.9 to 2.4Case–control+++Strength: High participation rate, good description of material and methods. Adjustment for relevant confoundersWeakness: Case-definition: TKR (risk of selection bias) Exposure assessment retrospective (risk of recall bias). Use of job titles (risk of misclassification)
Jensen 2005750 floor-layers, 50 carpenters, 49 controls without knee demands selected from responders in a questionnaire study of workers in Copenhagen area26–7278 in questionnaire studyJob titleVideo-recordings for kneelingNo low-moderate, high and very high exposure to kneelingKellgren and Lawrence grade 2–4 TFJNot weight-bearingKneeling/squatting vs no kneeling or squattingLow-moderateHighVery high2.96, 0.5 to 17.24.20, 0.6 to 27.64.92, 1.1 to–21.9Cross-sectional++Strength: Description of material and designs, video-taped exposure measurements. Blinded assessment of the radiographs. Clinical investigationWeakness: Few participants (underestimation). Selection of participants for the radiological study: stratified sample– only restrictive statistical analysisRadiographs non-weight-bearing (non-differential risk of misclassification) Exposure to lifting not video-recorded
Seidler et al, 200128Cases with kneeOA: 105 men90 womenControls without OA: 105 men90 women from an orthopaedic clinic108 from general practiceCasesMean: 53ControlsMean: 3564QuestionnaireSpecified physical demands, lifted (kg/day) and durationTFJGrade 1–4PFJ excludedAge, BMI, sports activitiesNo kneeling vs kneeling daily >10 yearsMenWomen2.2, 0.8 to 6.1NSCase–control++Strength: Well described design and materials, exposure collected by interviews and specified in different physical activities. Controls without radiological kneeOA and subjects with meniscal lesions excludedWeakness: Case definition: OA grade 1–4. 66% of cases had grade 1 OA, only 10% grade 3–4 OA (risk of misclassification). Retrospective exposure assessment (risk of recall bias). Only few with high exposure (n = 15)
Dawson et al, 200329Cases: 29 women placed on waiting list for TKR during past 12 monthsControls: 82 women age-matched from general practice50–7045InterviewedOccupational risk factors in jobWaiting for TKRAgeGeneral practitionerKneeling at least 2 days per week <15 years vs: 15 to <26 years⩾26 years2.7, 0.76 to 9.584.18, 1.26 to 13.8Case–control++Strength: Well-described design and materialsWeakness: Participation rate low, high exclusion rate. Retrospective exposure assessment (risk of recall bias). Exposure defined as kneeling two times per week (weight, period not defined) (risk of misclassification). Housewives included. Duration of exposure divided in three categories; lowest category = exposure <24 years (risk of misclassification)
Manninen et al, 200230Cases: 55 men226 womenControls: 524 age- and sex-matched from same population55–75Cases: 78.5Controls: 65.6Telephone interviewPhysical demands before the age of 49 yearsFirst surgery for kneeOABMIKnee injuryKneeling or squatting vs none<2 h/dayMenWomen⩾2 h/dayMenWomenTotal0.58, 0.21 to 1.640.97, 0.59 to 1.591.68, 0.66 to 4.281.81, 1.11 to 2.951.73, 1.13 to 2.66Case–control+++Strength: High number of female participants, interviews with specification of different physical activitiesWeakness: Retrospective exposure assessment: (risk of recall bias). Few men (n = 55). Cases defined as TKR (risk of selection bias)
Yoshimura et al, 200431Cases: 101 women with kneeOA from six hospitals in three cities of JapanControls: 101 women, random sample from the local populationAverage 73–3Cases: 84Controls: 59QuestionnaireSpecific physical demandsRadiological grade 3–4 kneeOAAge-matchedAdjusted for potential risk factors (not further defined)Kneeling ⩾1 h/day vs no kneeling on an average dayFirst jobMain jobSquatting ⩾1 h/day vs no squatting on an average dayFirst jobMain job0.95, 0.52 to 1.760.87, 0.48 to 1.581.05, 0.57 to 1.941.20, 0.66 to 2.17Case–control++Strength: Well-described design and materialsWeakness: Small number of participants. Differences in participation rate among cases and controls. 50% of cases had a previous knee injury compared with 14% controls. Few exposed. Cases defined as TKR (risk of selection bias) Retrospective exposure assessment: (risk of recall bias)
  • AP, anterior-posterior; TFJ tibio-femoral joint.

  • +, Poor quality score 1–5; ++, medium quality score 6–10; +++, high quality score >10.