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Table 2 Exposure and results of each study included in the review that evaluated occupational load

From: The association between occupational loading and spine degeneration on imaging – a systematic review and meta-analysis

Study Type of loading or exposure Outcomes Study results and RevMan analysis
Disc degeneration
 Battie et al. 1995 job code (1–4), total occupational lifting (day), mean time working twisted/bent, mean time sitting at work, occupation driving (hrs lifetime) Disc degeneration (signal intensity) There was an association between job code (0–4), occupational lifting and occupational sitting with disc degeneration. Greater occupational loading/lifting was associated with greater disc degeneration but associations were small (r = 0.18–0.31) Those with sitting had less disc degeneration.
 Biering-Sorensen et al. 1985 work is sedentary, light manual or heavy manual; worker undertakes heavy manual work, amount of physical activity at work Relative disc degeneration (method was unclear) (for each level from L1 to S1) RevMan: there was statistically significantly greater for L4 disc degeneration in daily manual workers compared to seldom manual workers (OR = 2.27; 95% CI 1.21 to 4.25), but no difference in disc degeneration at L5 (OR = 1.21; 95% CI 0.44 to 3.36) for physical activity at work. All other comparisons for disc degeneration were not significant but data was not presented.
 Elfering et al. 2002 Frequent lifting or carrying heavy objects, forward bending, vibration, sedentary activity, working night shifts Disc degeneration (1–5 Pearce score)
(summary score for all levels together)
The association of working night shifts and disc degeneration did not reach statistical significance (OR = 9.58 95% CI 1.00 to 91.62)
 Hangai et al. 2008 Lifting more than 10 kg for more than one third of the working hours. Disc degeneration (signal intensity with modified Pirfmann’s classification) (for each level from L1 to S1) RevMan: Occupational lifting was not significantly associated with degeneration at any of the levels. L1 L2 (OR = 3.16 95% CI 0.37 to 26.75), L2 L3 (OR = 1.92 95% CI 0.20 to 18.61), L3 L4 (OR = 1.34 95% CI 0.05 to 38.91), L4 L5 (OR = 2.23 95% CI 0.21 to 23.84) and L5S1 (OR = 1.48 95% CI 0.09 to 23.88)
 Hartwig et al. 1997 Nurse, construction workers and controls Unclear disc degeneration measure assessed as mono, bi, tri or multi-segmental. Not enough data to calculate an odds ratio. Results suggest that 17% of patients with high workload had mono-segmental degeneration as opposed to 29% of those with no workload, suggesting that those with more workload had degeneration at more levels.
 Hung et al. 2014 Workers that carry heavy loads divided into low, intermediate and moderate lifting loads. Disc dehydration (T2-weigthed signal intensity loss There was a statistically significant difference in disc degeneration (dehydration) between lifting loads for L1 L2 (OR = 2.4 95% CI 1.4 to 4.0), L2 L3 (OR = 3.3 95% CI 1.3 to 3.2), L3 L4 (OR = 3.7 95% CI 2.4 to 3.5), L4 L5 (OR = 4.9 95% CI 3.0 to 8.0) and L5S1 (OR = 3.6 95% CI 2.3 to 5.7) when comparing the high load to the low load groups. There was also a significant difference between the intermediate and low load groups for L2 L3, L3 L4, L4 L5 and L5S1.
 Luoma et al. 1998 Drivers, carpenters and office workers Disc signal intensity (L2 L3-L5S1) RevMan: There were no differences between groups. L2 L3 (OR = 0.55 95% CI 0.16 to 1.96), L3 L4 (OR = 1.50 95% CI 0.66 to 3.42), L4 L5 (OR = 2.04 95% CI 1.35 to 3.08) and L5S1 (OR = 1.30 95% CI 0.70 to 2.43)
 Savage et al. 1997 ambulance workers, hospital porters, car production workers, brewery drayman and office workers Disc degeneration (signal intensity) (all levels together) RevMan: There was no difference between groups in relation to disc degeneration. Car production vs office workers (OR = 1.00 95% CI 0.34 to 2.94); hospital porters vs office workers (OR = 1.63 95% CI 0.45 to 5.91
 Schenk et al. 2006 nurses and office workers Disc degeneration (signal intensity) (1–5) RevMan: Disc degeneration was different between occupational groups for grade 2 with more degeneration in nurses (OR: 1.89; 95% CI 1.34 to 2.66, n = 544 all levels) and grade 4 with more degeneration in office workers (OR = 0.50 95% CI 0.29 to 0.86). There was no difference for grade 3 (OR = 1.14 95% CI 0.80 to 1.64) and grade 5 (OR = 0.75 95% CI 0.37 to 1.52),
 Videman et al. 2007 Job code (1–4)
History of lifting at work (1000 kg)
Disc signal intensity (L1-S1) There was a significant association between history of lifting at work and signal intensity in the opposite direction (better signal with more load (Regression coefficient 0.001, p = 0.002), there was no association of occupational loading scoring and disc degeneration.
Disc height
 Battie et al. 1995 job code (1–4), total occupational lifting (day), mean time working twisted/bent, mean time sitting at work, occupation driving (hr lifetime) Disc height There was an association between job code (0–4), occupational lifting and occupational sitting with disc height but the association was not strong r = −0.22)
 Biering-Sorensen et al. 1985 work is sedentary, light manual or heavy manual; worker undertakes heavy manual work, amount of physical activity at work Disc height (for each level from L1 to S1) There were no significant differences for disc height
 Brinckmann et al. 1998 Different occupations such as mining, steelworkers and normative data of unexposed individuals Disc height (for each level from T12 to S1) Occupational loading was associated with a smaller disc height at a few spinal levels, particularly in those working in underground mines.
 Hung et al. 2014 Workers that carry heavy loads divided into low, intermediate and moderate lifting loads. Disc height narrowing (Farfan method. L4 L5 and L5S1 RevMan: There were significant differences between groups for disc height narrowing at L5S1 (OR = 5.8 (2.7 to 13.6)).
 Riihimaki et al. 1990 Concrete reinforcement workers and house painters Disc space narrowing (0–5 for each level) RevMan: Concrete workers had greater disc height narrowing overall (OR = 2.19; 95% CI 1.34 to 3.58), L3 L4 (OR = 5.34; 95% CI 1.17 to 24.39) and L4 L5 (OR = 2.54; 95% CI 1.26 to 5.11) than painters. There was no difference at L1 L2 (OR = 2.84 95% CI 0.57 to 14.25), L2 L3 (OR = 0.93 95% CI 0.13 to 6.66) and L5S1 (OR = 1.35 95% CI 0.73 to 2.48).
 Videman et al. 2006 Job code (1–4), occupational driving, maximum weight lifted at work (kg) Disc height narrowing There was an association between occupational lifting and changes in degeneration over 5 years. (0.1 points/disc decrease in disc height = 0.021)
 Videman et al. 2007 Job code (1–4) Disc height T12-S1) There was an association between lifetime occupational loading score and disc height (regression coefficient 0.038, p = 0.004) and no association between history of lifting at work and disc height.
Overall measure of degeneration
 Munoz-Gomez et al. 1980 Work load calculated as above or below the general average Degeneration (osteophytes, disc bulge and costotransversal arthrosis) RevMan: Those with occupational load greater than the average had greater degeneration (OR = 1.63; 95% CI 1.03 to 2.57).
Disc Bulge or herniation
 Arevalo et al. 2014 Heavy physical work activities Disc herniation There was an association between heavy physical work and disc herniation (OR = 2.0; 95%CI 1.42 to 2.76)
 Battie et al. 1995 job code (1–4), total occupational lifting (day), mean time working twisted/bent, mean time sitting at work, occupation driving (hr lifetime) Disc bulging
(summary score for upper T12-L4 and lower lumbar spine L4-S1)
There was no association between occupational loading and disc bulging
 Hung et al. 2014 Workers that carry heavy loads divided into low, intermediate and moderate lifting loads. disc bulging, L4 L5 and L5S1 There was a statistically significant difference in disc bulging between lifting categories for L2 L3 (OR = 3.8 (2.3 to 6.3)), L3 L4 (OR = 3.6(2.4 to 5.6)), L4 L5 (OR = 3.1 (2.0 to 4.9) and (L5S1 (OR = 2.6 (1.7 to 4.0) when comparing the high load to the low load groups.
 Luoma et al. 1998 Drivers, carpenters and office workers Disc bulging RevMan: Carpenters were more likely to have posterior disc bulging at L3 L4 OR = 2.73; 95% CI 1.12 to 6.64) and anterior bulging at L45 (OR = 2.86; 95% CI 1.05 to 7.79) when compared to the sedentary group. There was no difference for anterior disc bulging at L2 L3 (OR = 2.60 95% CI 0.74 to 9.22), L3 L4 (OR = 3.0 95% CI 0.86 to 10.41) and L5S1 (OR = 1.39 95% CI 0.49 to 3.92) or posterior disc bulging at L2 L3 (OR = 2.53 95% CI 0.60 to 10.69), L4 L5 (OR = 1.92 95% CI 0.89 to 4.16) and L5S1 (OR = 1.33 95% CI 0.95 to 1.87)
 Schenk et al. 2006 nurses and office workers Disc abnormalities (bulging, protusion, extrusion, etc) RevMan: There was no significant difference in disc bulging between groups. (OR = 1.33 95% CI 0.95 to 1.97)
 Videman et al. 2006 Job code (1–4), occupational driving, maximum weight lifted at work (kg) Disc bulging There was an association between occupational lifting and disc bulging (0.07 points/disc increase in disc height = 0.065)
Modic changes
 Elfering et al. 2002 Summary score from 0 to 4 combining of lifting or carrying heavy objects, forward bending, vibration and sedentary work Modic changes (summary score for all levels together) Occupational loading was not associated Modic changes
 Han et al. 201 Work was self-reported and rated as light physical (mainly walking, moderate physical work (sitting/walking) and hard physical work (heavy working) Modic changes assessed according to Modic et al. and graded into Type I, II or II. There was a significant difference in the incidence of modic changes according to the level of physical work. In total 8 of 54 (15%) of those with light physical work had modic changes, 16 of 99 (26%) of those with moderate physical load and 23 of 57 (40%) of those with hard physical work had modic changes
 Schenk et al. 2006 nurses and office workers Modic changes RevMan: There was no difference in Modic changes between groups. (OR = 0.91 95% CI 0.52 to 1.58),
Schmorl’s nodes
 Frymoyer et al. 1984 Lifting Schmorl’s nodes There was no association between lifting and the spine outcomes evaluated.
Endplate abnormalities
 Riihimaki et al. 1990 Concrete reinforcement workers and house painters Endplate sclerosis RevMan: There was no difference in endplate sclerosis between groups. Overall (OR = 1.97 95% CI 0.96 to 4.05), L1 L2 (OR = 4.70 95% CI 0.22 to 98.43), L2 L3 (OR = 2.84 95% CI 0.57 to 14.25), L3 L4 (OR = 0.93 95% CI 0.13 to 6.66), L4 L5 (OR = 2.84 95% CI 0.57 to 14.25) and L5S1 (OR = 0.83 95% CI 0.33 to 2.09)
 Videman et al. 2006 Job code (1–4), occupational driving, maximum weight lifted at work (kg) Upper endplate irregularities There was no association between occupational lifting and changes in endplate abnormalities over a 5-year follow-up.
Osteophytes
 Frymoyer et al. 1984 Lifting Osteophytes There was no association between lifting and the spine outcomes evaluated.
 Riihimaki et al. 1990 Concrete reinforcement workers and house painters Anterior and posterior spondylophytes RevMan: Concrete workers had more spondylophytes at L1 L2 (OR = 3.68; 95% CI 1.20 to 11.27), L4 L5 spondylophytes (OR = 3.68; 95% CI 1.20 to 11.27) than painters. There was no difference for overall (OR = 1.68 95% CI 1.05 to 2.69), L2 L3 (OR = 1.84 95% CI 0.84 to 4.06), L3 L4 (OR = 1.97 95% CI 0.96 to 4.05) and L5S1 (OR = 1.43 95% CI 0.63 to 3.25).
 Videman et al. 2006 Job code (1–4), occupational driving, maximum weight lifted at work (kg) Osteophytes There was no association between occupational lifting and changes in osteophytes over time.
High Intensity Zones
 Videman et al. 2006 Job code (1–4), occupational driving, maximum weight lifted at work (kg) High intensity zones (signal intensity) There was no association between occupational lifting and changes in high intensity zones over time.