The majority of those participating in the study were male (90.4% of the total participants in the study; 93% in the cases group and 88% in the control group); the mean age is 47. 5 years among the cases and 38.4 years in the control group. The most frequent CNO was 7323 (adjuster and operator of machinery and tools), accounting for 50.9 % of all participants, and the second most common code was 7401 (motor vehicle mechanic and fitter), accounting for 21%; in relation with this variable there are no significative differences between groups.
As for time employed at the company, there are some differences between groups, almost 80% of cases worked more than 10 years in the company but only 27 % of the participants in the control group worked so long in the company; a similar result was obtained when focusing on the time spent doing the same job.
In relation to risk factors, awkward postures were the most frequent when performing work activities. In 98.6% of cases, awkward postures meant keeping one’s arms above shoulder level, and almost 99% of cases were related to repetitive forced flexion-extension movements of the shoulders. These percentages are similar to the results obtained in the control group. Furthermore, 99% of participants with a diagnose of chronic tendinous pathology of the shoulder were exposed to mechanical pressure, and 77.2% engaged in manual handling of loads.
When using standardised sources of information, the INSS shows as one of the main risk factors involved, the manual handling of loads. Physical workload was present in 65.8% of the cases at level 3, which means an intense activity equivalent to 9-12 METS, and biomechanical loading was found in 63.1% of cases (once again at level 3, meaning that it occurs during almost 60% of their working time); although physical and biomechanical workload are present in the 80% of participants that belong to the control group. Mental workload was frequently present in different ways, with lack of autonomy being present in 83 % of cases and a high level of task complexity present in 98% of all participants in the study.
The O*Net network describes the manual handling of loads as the main risk factor involved in the different job descriptions reviewed along with the presence of awkward postures. The second most common risk factor was the use of handheld tools that was found in 79% of the work task descriptions. Similarly, to the Spanish INSS, the American network also explored mental workload, with the most important risk factor being lack of autonomy at work, present in 100% of job descriptions. A high level of precision tasks was present in 76.7% of job descriptions, being the second most frequent risk factor in this area. Percentages are similar in both groups.
The analysis of the association between risk factors and pathology revealed that time in job or at the company were the personal risk factors that most impacted the risk of developing an occupational disease. Thus, workers employed at the same company for between 13 and 60 months had a higher risk of developing an occupational disease, as did those who had been doing the same job for less than 3 months. A previous history of pathology and engagement in physical exercise outside work were not found to be risk factors (Table 1).
Table 1. Odds ratio for participants’ individual characteristics and occupational risk factors
Risk factor
|
OD
(n:73)
|
CG
(n:94)
|
OR
|
95% C.I.
|
p
|
Previous History (yes/no)
|
14/59
|
14/80
|
0.73
|
0.32-1,66
|
0.46
|
Physical Activity
|
31/42
|
43/51
|
1.14
|
0.61-2.11
|
0.67
|
Time at the company
|
|
|
|
|
|
<3 months
|
0/73
|
11/83
|
Not calculated
|
Not calculated
|
|
3-6 months
|
0/73
|
1/93
|
Not calculated
|
Not calculated
|
|
7-12 months
|
0/73
|
2/92
|
Not calculated
|
Not calculated
|
|
13-60 months
|
5/68
|
35/59
|
8.06
|
2.96-21.92
|
0.00**
|
61-120 months
|
9/64
|
19/75
|
1.80
|
0.76-4.25
|
0.17
|
>121 months
|
60/13
|
26/68
|
0.08
|
0.03-0.17
|
0.00**
|
Time in current job
|
|
|
|
|
|
<3 months
|
1/72
|
11/83
|
9.54
|
1.20-75.71
|
0.01*
|
3-6 months
|
5/68
|
3/91
|
0.44
|
0.10-1.94
|
0.27
|
7-12 months
|
3/70
|
3/91
|
0.76
|
0.15-3.92
|
0.75
|
13-60 months
|
16/57
|
30/64
|
1.67
|
0.82-3.37
|
0.15
|
61-120 months
|
16/57
|
17/77
|
0.78
|
0.36-1.68
|
0.53
|
>121 months
|
32/41
|
31/63
|
0.63
|
0.33-1.18
|
0.15
|
[OD = occupational disease; CG = control group; n = number of cases; OR = odds ratio; 95% CI = 95% confidence interval; p = p value].
*: p<0.05; **: p<0.01
The analysis of the work-related risk factors revealed that awkward postures and repetitive movements were not associated with the onset of the chronic tendinous pathology of the shoulder. However, the manual handling of loads at the second weight level (between 3 and 15 kg) did emerge as a risk factor, as did the use of light hand tools, which was found to significantly increase the risk of overuse injury.
The same result was observed in relation to exposure to mechanical pressure on the arm. When focusing specifically on concrete areas of the arm, mechanical pressure on the palm of the hand was found to pose the highest risk, followed by exertion of mechanical pressure on the fingers.
Impact by a hand tool on the heel of the hand was found to significantly increase risk, and exposure to vibrations increased the risk nearly twofold (see Table 2).
Table 2. Odds Ratio for occupational risk factors rom job cases
Risk Factor
|
OD
(n:73)
|
CG
(n:94)
|
OR
|
95% C.I.
|
p
|
Awkward Postures(yes/no)
|
|
|
|
|
|
Shoulder
|
|
|
|
|
|
Flex/Abd
|
72/1
|
88/6
|
0.20
|
0.02-1.73
|
0.10
|
High Position
|
72/1
|
88/6
|
0.20
|
0.02-1.73
|
0.10
|
Elbow
|
|
|
|
|
|
Pronation/supination
|
64/9
|
93/1
|
13.07
|
1.60-105.7
|
0.02
|
Repetitive Movements(yes/no)
|
43/30
|
28/66
|
0.29
|
0.15-0.56
|
0.00
|
Manual Handling of Loads (yes/no)
|
35/38
|
94/0
|
3.68***
|
2.77-4.89
|
0.00**
|
< 3Kg
|
3/70
|
0/94
|
0.42***
|
1.66-43.14
|
0.00**
|
3-15 Kg
|
20/53
|
40/54
|
1.96
|
1.01-3.78
|
0.04*
|
>15 Kg
|
9/64
|
54/40
|
9.6
|
4.27-21.55
|
0.00**
|
Use of Hand Tools (yes/no)
|
38/35
|
88/6
|
13.50
|
5.24-34.78
|
0.00**
|
< 1Kg
|
4/69
|
0/94
|
0.42
|
0.35-0.56***
|
0.02*
|
1-3 Kg
|
26/47
|
42/52
|
1.46
|
0.77-2.73
|
0.23
|
> 3Kg
|
7/66
|
46/48
|
9.03
|
3.75-21.73
|
0.00**
|
Mechanical Pressure (yes/no)
|
60/13
|
93/1
|
20.15
|
2.56-158.04
|
0.00**
|
Pressure on fingers
|
13/60
|
13/81
|
0.74
|
0.32-1.71
|
0.48
|
Pressure on palm of hand
|
1/72
|
93/1
|
6696
|
411,75-108892
|
0.00
|
Pressure on hand
|
57/16
|
94/0
|
2.64***
|
2.15-3.25
|
0.00**
|
Vibrations
Impact on Heel of Hand
|
33/40
27/46
|
54/40
68/26
|
1.63
4.45
|
0.88-3.03
2.31-8.58
|
0.11
0.00**
|
[OD = occupational disease; CG= control group; n = number of cases; OR = odds ratio; 95% CI = 95% confidence interval; p= p value]. *: p<0.05; **: p<0.01,*** OR calculated for case group.
According to the Spanish INSS Guide, the risk factors that most increased the risk of overuse injuries were biomechanical and physical workload, and lack of autonomy was found to be the most statistically significant psychosocial risk factor (see Table 3).
Table 3. Odds ratio for occupational risk according to the INSS and the O*Net network
Risk Factor
|
|
OD 2D0101 (n:73)
|
CG
(n:94)
|
INSS OR
|
95% C.I.
|
p
|
O*Net OR
|
95% C.I.
|
p
|
Biomechanical Workload (yes/no)
|
Level 2
Level 3
|
24/49
49/24
|
18/76
76/18
|
2.06
0.48
|
1.01-4.2
0.23-0.98
|
0.04
0.04
|
-
|
-
|
-
|
Physical Workload
|
Level 2
Level 3
|
25/48
48/25
|
18/76
76/18
|
2.19
0.45
|
1.08-4.45
0.22-0.92
|
0.02
0.02
|
0.62
|
0.18-2.14
|
0.45
|
Manual Handling of loads
|
Level 2
Level 3
|
59/14
14/59
|
81/13
13/81
|
1.47
0.67
|
0.64-3.37
0.29-1.54
|
0.35
0.35
|
0.55
|
0.48-0.63
|
0.21
|
Mental Workload
|
Level 2
Level 3
|
35/38
38/35
|
46/48
48/46
|
0.96
1.04
|
0.52-1.77
0.56-1.91
|
0.89
0.89
|
0.82
|
0.40-1.70
|
0.60
|
Precision Tasks
|
Level 2
Level 3
|
2/71
70/3
|
2/92
92/2
|
1.29
0.50
|
0.17-9.42
0.08-3.11
|
0.79
0.45
|
0.89
|
0.42-1.85
|
0.75
|
Autonomy
|
Level 2
Level 3
|
12/61
61/12
|
28/66
66/28
|
0.46
2.15
|
0.21-0.99
1.00-4.61
|
0.04
0,04
|
-
|
-
|
-
|
[OD = occupational disease; CG: control group; n = number of cases; OR = odds ratio; 95% CI = 95% confidence interval; p= p value].
According to the data provided by the American Occupational Information Network (O*Net), exposure to precision tasks was the most important risk factor, followed by a heavy mental workload.
Factorial analysis of principal component revealed two main dimensions. The accumulated variance explained by these two factors corresponded to 36.60%. The first one dimension was in relation to load management (19.65%). The included variables and factor loading were manual handling of load [3-15 kg and > 15 kg] (0.61 and -0.81, respectively), vibrations (0.31), physical activity (0.30) and load management (0.75). The second one dimension corresponded to awkward postures (16.95%). (i.e., shoulder Flex/Abd (0.52), high positions (0.54), elbow pronation/supination (0.52), use of hand tools (0.80), impact on heel of hand (0.47). Finally, multiple logistic regression model revealed a positive relationship between probability of shoulder injury with age, factor 1 (i.e., load management) and negative relationship with factor 2 (i.e., awkward postures). (Table 4).
Table 4. Summary of multiple logistical model.
|
Estimate
|
Standard Error
|
Z-value
|
p-value
|
Intercept
|
-5.972
|
1.235
|
-4.836
|
0.0001***
|
Age
|
0.124
|
0.026
|
4.658
|
0.0001***
|
Factor 1 (i.e., load handling)
|
1.638
|
0.329
|
4.965
|
0.0001***
|
Factor 2 (i.e., awkward postures)
|
-0.898
|
0.223
|
-4.030
|
0.0001***
|
***significant differences p < 0.0001.
Deviance of null model was 228.86 on 166 degrees of freedom meanwhile deviance of residual model corresponded to 130.75 with a Chi2 value of 98.11 that correspond to a p-value < 0.0001. R2L model was 0.43.
Odds ratio and confident interval at 95% of covariates variables were 1.13 [1.07, 1.20] for age, 5.14 [2.87, 10.66] for factor 1 (i.e., load management) and 0.41 [0.25, 0.61] for factor 2 (i.e., awkward postures).