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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 15  |  Issue : 4  |  Page : 268-275

Comparative evaluation of effect of heavy vehicle driving and other professions as causative factor of osteoarthritis of knee: An observational cross-sectional pilot study


1 Parul Institute of Ayurved and Research, Vadodara, Gujarat, India
2 Department of Kayachikitsa, Parul Institute of Ayurved, Parul University, Vadodara, Gujarat, India
3 Department of Sharir Rachana, J. S. Ayurved Mahavidyalaya, Nadiad, Gujarat, India

Date of Submission04-Sep-2020
Date of Decision18-Jun-2021
Date of Acceptance28-Jul-2021
Date of Web Publication16-Dec-2021

Correspondence Address:
Bhagawan G Kulkarni
Parul Institute of Ayurved and Research, AP Ishwarpura, Tal Waghodia, Vadodara - 391 760, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joa.joa_55_20

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  Abstract 


Background: Knee is subjected to constant stress during everyday activities. In various occupations, position influences its structure and function. Heavy vehicle driving is one such occupation that exerts strain on the musculoskeletal system of the body, especially knees. The objective of this study was to assess the effect of heavy vehicle driving as occupation on the structure of knee. Methodology: It is a comparative, cross-sectional observational study. Twenty-five heavy vehicle drivers and 25 persons of other occupations were included in the study. After history and clinical examination of both knees, range of motion (ROM) was calculated by goniometer. X-ray of both knees (anteroposterior and lateral views) was done. Assessment was done based on findings of X-ray, ROM, knee pain, and inflammation. Results: Pain, stiffness, crepitations, reduced joint space, painful and restricted movements, development of osteophytes, and subchondral sclerosis of knee joint were more in heavy vehicle drivers as compared to subjects of other occupations. Changes suggestive of osteoarthritis of knee changes were more in heavy vehicle drivers when compared with other occupations. Conclusion: Heavy vehicle drivers may suffer from degenerative changes in knee with respect to its anatomical structures and biomechanics when compared to other occupations. Duration of driving and daily driving hours was found to have influence on the health of knee.

Keywords: Ayurveda, goniometry, knee, occupational diseases, osteoarthritis, range of motion, sandhigata vata


How to cite this article:
Kulkarni BG, Deshpande SV, Bedekar SS. Comparative evaluation of effect of heavy vehicle driving and other professions as causative factor of osteoarthritis of knee: An observational cross-sectional pilot study. J Ayurveda 2021;15:268-75

How to cite this URL:
Kulkarni BG, Deshpande SV, Bedekar SS. Comparative evaluation of effect of heavy vehicle driving and other professions as causative factor of osteoarthritis of knee: An observational cross-sectional pilot study. J Ayurveda [serial online] 2021 [cited 2022 Jan 27];15:268-75. Available from: http://www.journayu.in/text.asp?2021/15/4/268/332608




  Introduction Top


Joints play a major role in making a variety of postures a human body may produce. It is well known that a variety of movements of a joint are positively related to complexity of structure and inversely related to its stability. Joints that serve single function are less complex than the joints that serve multiple functions. Knee is the largest joint in the human body. It is continuously subjected to bending, pounding, and twisting in day-to-day activities. As a result of constant movement and impact of trauma, osteoarthritis (OA) is one of the highly prevalent diseases of knee. Multiple risk factors such as age, gender, obesity, occupation, and heredity are also outlined as a causative factor of OA of knee. Among these, occupation is a noteworthy risk factor. As long as knee is in normal position, it sustains the moderate mechanical loading stress. However, in various kinds of occupation, due to change in position of knee, loading stress alters, which results in derangement of internal structures of joint and functional homeostasis as well. Hence, occupation such as driving heavy vehicle may influence health of knee joint.

It also highlights clinical feature of OA explained by Sushruta as hanti sandhi gata (~destructs the joint). Riding on cart or horse, excess walking is also mentioned as a causative factor of various diseases of joints. Vata vitiated in such a way is capable of degenerating anatomy of joints which exactly happens in pathology (samprapti) of OA (sandhigata vata).

Increased industrialization demands carrying heavy loads from one place to another. To cater the need, roads and highways are paved and their length and breadth is increasing day by day. Vehicles with great power and capacity are invented to carry the loads from one place to another. Driving heavy vehicles needs the constant movement of both lower extremities, especially knees, in order to push clutch, brakes, and accelerator paddles. Hence, driving heavy vehicles for some years may be responsible for degenerative changes in knee. According to Ayurveda, position of driver in heavy vehicle is comparable with awkward sitting posture (dukkha asana) and can cause vitiation of vata. Hence, the present cross-sectional observational study focuses to evaluate the impact of this occupation on knee joint in comparison with nondrivers.

Primary objective

To compare structural changes in knee joint of heavy vehicle drivers with subjects in other occupations on the basis of anteroposterior and lateral X-rays of knees.

Secondary objectives

  1. To compare the range of motion (ROM) in knee joint of heavy vehicle drivers with subjects in other occupations on the basis of goniometric measurements
  2. To compare pain in knee joint of heavy vehicle drivers with subjects in other occupations on the basis of Visual Analog Scale (VAS).



  Methodology Top


Study design

This is a comparative, cross-sectional observational study.

Ethical consideration

The study was approved by the Institutional Ethics Committee of SDM College of Ayurveda and Hospital, Hassan, Karnataka (IEC No. SDMCAH/IEC/96/12-13, date: November 10, 2012). All participants underwent an informed consent process before conducting any study-related activity.

Sample size

As this study was the pilot deployment to find the relation between heavy vehicle driving and knee OA (sandhigata vata) in comparison with other professions, the sample size of total 50 participants was considered for the study.

Study participants

Subjects were included in two groups based on their occupation.

Inclusion criteria

  • Subjects of either gender, between the age range of 30 and 40 years (both years inclusive)
  • Subjects having normal body mass index and no health-related complaints at the time of inclusion
  • In Group A, subjects, who used to drive heavy vehicles for a minimum of 8 h/day for at least 5 years, were included
  • In Group B, subjects from other sedentary occupations – clerks, laboratory technicians, and working for a minimum of 8 h/day for at least 5 years, were included.


Exclusion criteria

  • Known cases of rheumatoid arthritis, poliomyelitis, gout, pseudogout, Paget's disease, psoriatic arthritis, fibromyalgia, bursitis, tendonitis, or other diseases related to joints were excluded
  • History of major trauma, accident, fracture, dislocation, or surgery related to knee
  • Known cases of autoimmune disorders – systemic lupus erythematosus
  • Congenital deformity related to lower extremities
  • Subjects who were using systemic corticosteroids for long period
  • Pregnant and lactating women.


Assessment criteria

Assessment of the subjects was done on the basis of X-ray of both knees (anteroposterior and lateral views), ROM of both knee joints measured by goniometer, and local examination of knee. In case if pain in knee was observed, it was assessed with 10-point VAS.

Study procedure

After obtaining informed consent, subjects were categorized into Group A (drivers) and Group B (sedentary jobs). Detailed medical history taking, general physical examination, and examination of knee were conducted. Those who were not fulfilling inclusion criteria were excluded from the study. For all subjects included, X-ray of both knees (anteroposterior and lateral views) was done. Reporting of X-rays was done by a house radiologist.

Statistical analysis

Data obtained during the study were arranged in tables and charts. Analysis of the data was done using IBM SPSS Statistics for Windows, version 21 (IBM Corp., Armonk, N.Y., USA).


  Results Top


Total 52 subjects (in Group A 27 subjects and in Group B 25 subjects) were included in this study. Out of these, two subjects were excluded from the study as they did not meet inclusion criteria. Thus, there were 27 evaluable cases in Group A and 23 cases in Group B.

Incidence of pain in knee joint

Out of 27 subjects in Group A, 17 (34%) complained of knee pain. Among these, ten (20%) subjects had pain in both knees, whereas seven subjects (16%) had unilateral knee pain. On the other hand, ten (20%) subjects in Group B suffered from knee pain – five (10%) subjects had pain in both knees while the remaining (five subjects) pain was present in only one knee. Observation about intensity of pain showed that, in Group A, 12 (24%) subjects had dull aching pain, while four (8%) had deep pain, while one was having pricking pain. In Group B, nine subjects had dull aching pain while one had deep pain.

History of onset of pain revealed that in Group A, 3 subjects (6%) were experiencing progressive intensity of pain, 11 (22%) had intermittent pain, while 3 (6%) had continuous pain in knee. While, in Group B, 1 (2%) subject had progressive intensity of pain, 8 (16%) had intermittent knee pain, while 1 (2%) subject was undecided about onset of pain. Comparison of both the groups was statistically insignificant (P > 0.05), however, it can be observed that incidence of knee pain was found more in subjects of Group A as compared to subjects of Group B. Furthermore, intensity of pain was observed more in Group A as compared to Group B [Table 1] and [Graph 1].
Table 1: Analysis of pain in both groups

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Joint stiffness and crepitus

Joint stiffness and crepitus are important early signs of arthritis. In Group A, 11 (22%) subjects had stiffness, while only 4 (8%) subjects in Group B suffered from stiffness in knee. Out of 11 subjects in Group A, 10 (20%) subjects had morning stiffness for 10–15 min while 1 subject had stiffness after activities related to knee, whereas in Group B, all the 4 subjects had morning stiffness.

In Group A, out of 27 subjects, crepitus was observed in 11 (22%) subjects, while in Group B, it was observed in 7 (14%) subjects. It indicates that a greater number of subjects in Group A were suffering from joint stiffness and crepitus. Joint stiffness and crepitus are important attributes seen in cases of OA of knee. Continuous repetitions of the same movements such as vibrations in vehicles or machines are important biomechanical stresses influencing the OA knee [Table 2] and [Graph 2], [Graph 3].
Table 2: Analysis of joint stiffness and crepitus

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Movements of joints

Movement of joint was observed during physical examination for occurrence of pain, while ROM was observed by using goniometer. In Group A, 7 (14%) subjects had painful extension and 2 (4%) subjects had restricted extension, while 12 (24%) subjects had painful flexion of knee. On the contrary in Group B, one subject had pain in extension and flexion of knee. Observation about ROM shows that in Group A, 25 subjects reduced ROM – between 100° and 135° during flexion. On the other hand, only three (6%) subjects have the same ROM in Group B. The difference observed in both the groups is statistically insignificant (P > 0.05). However, based on difference in number of subjects in both the groups, it can be observed that in the group of drivers, painful flexion and reduced ROM were seen, while in the other group, movements of joints are not much affected [Table 3] and [Graph 4].
Table 3: Analysis of range of motion

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Analysis of X-ray of knee (anteroposterior and lateral views)

Analysis of joint space

Out of 27 subjects in Group A, 7 (14%, expected count is 4.8) and 2 (4%) were showing reduced space in medial and lateral compartments, respectively, in both knees. While, out of 23 subjects in Group B, 1 (2%, expected count 4.1) subject showed reduced space in both, medial as well as lateral, compartments, 2 (4%) subjects showed reduced space in medial compartment, and 2 (4%) showed reduced lateral compartment. Comparison of both the groups showed significant phi and Cramer's value (0.013 < 0.05).

Observations about patellofemoral compartment showed that, in Group A, 9 (18%) subjects showed reduced space. In Group B, 5 (6%) showed reduced space. However, the difference was seen as statistically insignificant (P > 0.05).

Analysis of osteophytes and subchondral sclerosis

The presence of osteophytes and subchondral sclerosis is an important indication of OA. Analysis of X-ray of knee showed that seven (14%) subjects in Group A and three (6%) subjects in Group B had peripheral osteophytes. Central osteophytes were seen in four (8%) subjects from Group A. Subchondral cyst was not found in X-ray of any subject. Subchondral sclerosis was observed in five (10%) subjects in Group A, however, it was absent in Group B. Based on these observations, it can be claimed that subjects in the drivers' group (A) showed presence of more osteophytes and subchondral sclerosis as compared to the other occupation group (B) [Table 4] and [Figure 1], [Figure 2]
Table 4: Analysis of X ray of knee in both groups

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Figure 1: X-ray of left knee anteroposterior and lateral views (Patient T-G, id 030710, heavy vehicle drivers' group) showing reduced joint space in medial component and osteophytes

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Figure 2: X-ray of left knee anteroposterior and lateral views (Patient BGT, id 030707, heavy vehicle drivers' group) showing reduced joint space in medial and lateral component and gross osteophytes

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Analysis of pain in other joints

In Group A, pain associated with other joints was also seen. Elbow pain was present in eight (16.3%), backache in seven (14.3%), and cervical pain in two (4.1%) subjects. On the other hand, in Group B, there was no complaint related to any other joint.


  Discussion Top


According to Ayurveda, knee is a joint with movements (cheshtavanta) and kora type of joint. It is also a marma (vital point) which can cause limping (khanjata) up on injury.[1] In the context of etiological factors of vata vyadhi, Charaka has referred dukkha shayyasan (abnormal sleeping and sitting arrangements) as a major causative factor for diseases caused due to vata. Vata is closely related to asthi (~bones). Hence, vitiation of vata can affect structure and functions of a joint. In pathology of sandhigata vata (~degenerative OA), the joint is damaged.[2]

Modern anatomy also tells that knee is the largest joint. It has a hinge-like structure and is subjected to constant twisting, pounding, bending, etc., because of everyday activities. It can also suffer from the impact of falls. It results in high incidence of knee arthritis. It is also the most complex joint. Since knee is bearing entire weight of the body and also has high mobility, it is the most susceptible to injuries.[3] Complexity of this joint is that knee is fusion of three joints in one, namely lateral and medial femorotibial joints and patellofemoral joint. In the knee, the menisci divide the joint cavity incompletely.[4] It is also a compound joint as there is more than a pair of articular surfaces – articular surfaces of femur, tibia, and patella came together. Movements at knee are flexion, extension, and internal (medial) and external (lateral) rotation. The range of extension is 5°–10° beyond straight. Active flexion is 120° with the hip extended, 140° when it is flexed, and 160° when aided by a passive element, for example, sitting on the heels posture (vajrasana). Voluntary rotation is 60°–70° but conjunct rotation only 20.°

The weight-bearing joints of lower extremity, particularly the knee, are designed in such a way that they can absorb and distribute the forces, which are applied to the body – 1–1.5 times body weight with walking and six times body weight during the descending phase of stair climbing.[5] Homeostasis of the joint is dependent on moderate mechanical loading that is necessary to maintain healthy articular cartilage.[6] This loading may become catabolic if appropriate intensity and duration exceed or abnormal joint mechanics is observed. In a previous study, examining deep knee flexion, a common occupational task, forces on the tibiofemoral joint were estimated to be 4.7–5.6 times body weight in the vertical direction as compared to 2.9–3.5 times body weight in the horizontal direction.[7] Zelle et al. reported that average thigh-calf contact forces of 34.2% of body weight and 30.9% of body weight for squatting and kneeling near full flexion, respectively.[8] Foot posture has been shown to significantly affect varus knee moments during gait,[9] and it is possible that the differences in foot posture across subjects may have increased internal rotation of the tibia and thereby the varus moments.[10]

Activities that involve constant kneeling, squatting, lifting, carrying, and standing work are associated with OA knee. Miners, carpenters, construction workers, dairy farm workers, etc., are engaged in constant bending, squatting, and lifting heavy weights. According to published studies, occupations which require combination of squatting or kneeling and lifting heavy weight have a high rate of OA knee. It is increasingly recognized that for activity, such as squatting, the tibiofemoral and patellofemoral joints are exposed to different loads and constant stress. It is observed that people who need to perform repeated squatting or kneeling and lifting heavy weight as a part of job have increased risk for worsening of cartilage morphology scores at patellofemoral joint and medial tibiofemoral joint. These findings highlight the importance of biomechanical loading on the pathogenesis of OA knee, precisely patellofemoral OA.[11]

Quality of life is directly affected by structural and functional integrity of joint. Charaka has referred awkward sleeping and sitting postures (dukkha shayyaasana) as etiological factors of vata vyadhi. Vata has intimate relation with the asthi (~bones), hence vitiated vata influences structure and functions of the joints. If vitiated vata gets lodged in joints, it causes destruction of joint and loss of function, pain, and crackling sound. This observation clearly indicates symptoms of OA knee. Sushruta mentions knee as a vital point (marma), and any injury due to trauma or occupation can cause irreversible deformity in knee. Therefore, people involved in occupations that involve awkward sleeping and sitting postures (dukkha shayyaasana), are prone for degenerative changes in knee.

In the current study, it was observed that subjects suffering from knee pain were more in the heavy vehicle drivers' group. If a vehicle is not moving, then sitting in a driving seat or sitting in chair is not different from each other. However, in a moving vehicle, the driver is subjected to various forces because of acceleration and deceleration, lateral swaying, and vibrations. While driving, feet are being used actively, managing clutch, brake, and accelerator. In sitting position, if feet are active, they do not support and stabilize lower body which is contrary to usual sitting in a chair. Furthermore, the driver needs to be altered for traffic all times, which requires a fairly stable head-and-neck posture. Muscles of back, neck, shoulder, and arm help in maintaining static muscle tension over a prolonged period. A steady low-level contraction of muscles usually leads to localized muscle fatigue (Konz et al. 1998), which can produce muscle aches and pains.[12] In a survey of drivers aged 55 years or above in the United States, it was found that 35% of participants were having arthritis, out of which 9% required a vehicle with power steering due to same.[13] Rossignol et al. have observed that OA knee is manifested in 56.1% of subjects and OA hip in 51.5% of subjects which are having occupation in which the same movements are repeated continuously, out of which 35.5% of subjects suffering from OA knee and 38.5% of subjects suffering from OA hip were working in vibrating vehicles.[14] It indicates that driving occupation influences the structures and functions of joints. Wear and tear of cartilages due to constant awkward position is one of the reasons for pain. It has also been observed that articular pain may produce an inhibitory effect on muscle reflexes.[15] This observation reveals that the role of pain and functional impairment of muscles leads to fatigability. The muscles around the knee are in continuous action during driving. Energy produced during action is absorbed by the cartilages. This may be the reason for impairment of cartilages. When the cartilage starts degeneration, the bones do not have a smooth surface with which to articulate during motion. As tissues surrounding the joint are constantly irritated and/or stretched, symptoms such as pain and stiffness develop.[13] Anderson and Raanaas concluded that the 1-year prevalence of knee pain among 703 subjects who were full-time taxi drivers was higher than that among the reference group from the local community.[16]

Observations about X-ray of knee revealed that a greater number of subjects in driving profession are showing reduced space in medial compartment of both tibiofemoral joints than the lateral compartment. Findings of Cyrus Cooper et al. support the hypothesis that prolonged or repetitive bending of the knee is a cause of OA in the joint.[17] In 25 subjects from the drivers' group, osteophytes were seen as compared to one in other professionals' group. It indicates the influence of driving as occupation on the structural integrity of knee.

A recent study by Coggon et al. has demonstrated an association between long driving times (more than 4 h/day) and knee cartilage injuries.[18] Several survey results indicate that the knee is one of the joints that are most frequently injured in vehicle accidents.

Occupations which were not previously described at risk of OA such as housekeepers and truck drivers are now at increased risk of developing the same. It indicate a need for redefining the categories of risk. Finally, the disability and economic impact of OA is great. In this context, OA can be etiologically linked to occupation in a sizeable segment of the population, the change of paradigm that OA should not be considered only a disease of aging needs to be considered. OA and occupation must be included in current and future longitudinal population studies of degenerative diseases in order to clarify the etiological relation and preventive measures in such occupations.[19]

Thus, clinical observation by Charaka with reference to awkward sleeping and sitting postures (dukkha shayyaasana) that leads to vitiation of vata and leads to OA (sandhigata vata) is relevant. Awkward sitting posture (dukkha asana) in drivers has close association with osteoarthritic changes in knee joint when compared with the other occupation group. It also highlights clinical feature of OA explained by Sushruta as hanti sandhi gata (~destructs the joint).

Some limitations of the study include small sample size and single centric study. Advanced investigations such as magnetic resonance imaging could not be added due to budgetary constraints.


  Conclusion Top


It can be concluded from the study that there is an influence of driving occupation in causing changes in structures and biomechanics of knee as compared to other occupations. Severity of changes is directly proportional to the number of working years and working hours per day. Radiological changes supporting OA knee are more in the drivers' group. Thus, clinical observation of made by Charaka about relation of awkward sitting posture and OA is also substantiated.

Acknowledgment

The authors are thankful to Rajiv Gandhi University of Health Sciences, Karnataka, for providing research grant for conducting this study. The authors are also thankful to Dr. Prasanna N Rao, Principal, Shri Dharmasthala Manjunatheshwara (SDM) College of Ayurveda and Hospital, and Dr. Girish K. J., Professor, Shri Dharmasthala Manjunatheshwara (SDM) College of Ayurveda and Hospital, for their motivation and support in conducting the study.

Financial support and sponsorship

This study was financially supported by Rajiv Gandhi University of Health Sciences, Karnataka.

Conflicts of interest

There are no conflicts of interest.





 
  References Top

1.
Sushruta. Sushruta Samhita with Nibanda Sangraha Commentary of Dalhana. Edited by Vaidya Jadavji Trikamji Acharya. 7th ed. Varanasi: Chaukhambha Orientalia; 2002. p. 824.  Back to cited text no. 1
    
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Madhavakar. Madhavanidana. 2nd ed. Varanasi: Chaukambha Orientalia; 1995.  Back to cited text no. 2
    
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Moore K, Dalley A. Clinically Orientated Anatomy. 4th ed. New York: Lippincott Williams and Wilkins; 1999.  Back to cited text no. 3
    
4.
Singh I. Text Book of Anatomy with Colour Atlas. Volume 1. 3rd ed. New Delhi: Jaypee Brothers Medical Publishers (P) Ltd; 2003. p. 448.  Back to cited text no. 4
    
5.
Andriacchi TP, Andersson GB, Fermier RW, Stern D, Galante JO. A study of lower-limb mechanics during stair-climbing. J Bone Joint Surg Am 1980;62:749-57.  Back to cited text no. 5
    
6.
Griffin TM, Guilak F. The role of mechanical loading in the onset and progression of osteoarthritis. Exerc Sport Sci Rev 2005;33:195-200.  Back to cited text no. 6
    
7.
Dahlkvist NJ, Mayo P, Seedhom BB. Forces during squatting and rising from a deep squat. Eng Med 1982;11:69-76.  Back to cited text no. 7
    
8.
Zelle J, Barink M, Loeffen R, De Waal Malefijt M, Verdonschotm N. Thigh-calf contact force measurements in deep knee flexion. Clin Biomech (Bristol, Avon) 2007;22:821-6.  Back to cited text no. 8
    
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Teichtahl AJ, Morris ME, Wluka AE, Baker R, Wolfe R, Davis SR, et al. Foot rotation--a potential target to modify the knee adduction moment. J Sci Med Sport 2006;9:67-71.  Back to cited text no. 9
    
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Pollard JP, Porter WL, Redfern MS. Forces and moments on the knee during kneeling and squatting. J Appl Biomech 2011;27:233-41.  Back to cited text no. 10
    
11.
Amin S, Goggins J, Niu J, Guermazi A, Grigoryan M, Hunter DJ, et al. Occupation-related squatting, kneeling, and heavy lifting and the knee joint: A magnetic resonance imaging-based study in men. J Rheumatol 2008;35:1645-9.  Back to cited text no. 11
    
12.
Bestowed SJ. Long Driving Hours and Health of Truck Drivers. A Thesis Submitted to the Faculty of New Jersey Institute of Technology, Newark, NJ; 2008.  Back to cited text no. 12
    
13.
Tiller M, Reston J, Fontanorosa J, Price N, Tregear S. Evidence report- musculoskeletal disorders and commercial motor vehicle driver safety presented to the federal motor Carrier safety administration April 30, 2008.  Back to cited text no. 13
    
14.
Rossignol M, Leclerc A, Allaert FA, Rozenberg S, Valat JP, Avouac B, et al. Primary osteoarthritis of hip, knee, and hand inrelation to occupational exposure. Occup Environ Med 2005;62:772-7.  Back to cited text no. 14
    
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Hofmann UK, Jordan M, Rondak I, Wolf P, Kluba T, Ipach I. Osteoarthritis of the knee or hip significantly impairs driving ability (cross-sectional survey). BMC Musculoskelet Disord 2014;15:20.  Back to cited text no. 15
    
16.
Anderson D, Raanaas R. Psychosocial and physical factors and musculoskeletal illness in taxi drivers. In: McCabe PT, Hanson MA, Robertson SA, editors. Contemporary Ergonomics 2000. London, England: Taylor and Francis; 2000. p. 322-7.  Back to cited text no. 16
    
17.
Cooper C, McAlindon T, Coggon D, Egger P, Dieppe P. Occupational activity and osteoarthritis of the knee. Ann Rheum Dis 1994;53:90-3.  Back to cited text no. 17
    
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Chen JC, Dennerlein JT, Shih TS, Chen CJ, Cheng Y, Chang WP, et al. Knee Pain and Driving Duration: A Secondary Analysis of the Taxi Drivers' Health Study. Research and Practice 2004;94:575–81.  Back to cited text no. 18
    
19.
Rossignol M, Leclerc A, Hilliquin P, Allaert FA, Rozenberg S, Valat JP, et al. Primary osteoarthritis and occupations: A national cross-sectional survey of 10 412 symptomatic patients. Occup Environ Med 2003;60:882-6.  Back to cited text no. 19
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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