Knee and Hip Osteoarthritis and our Occupations
Knee and hip osteoarthritis is so common that they are the most replaced joints in our bodies. Can our occupation influence this process?
This week I am writing about hip and knee osteoarthritis. As we mentioned in my last article before half-term these are the most replaced joints in our bodies. In the UK there are about 70,000 knee replacements each year or approximately 160,000 procedures if we include hip replacements.
This week I am discussing another factor in the evolution of osteoarthritis (OA); this is the influence of what we do day in and day out. People are often defined by their occupation. Apart from the obvious jokes, such as ‘suspicious gardener enjoys a good plot’ or a ‘a lousy lawyer is always appealing’, a job can not only define us in terms of how we see ourselves but it can also directly impact on our physical health.
Your Occupation and Your Body
There is always an element of repetition and/or postural strain in any given occupation. According to anthropologists, the Englishmen who drew the powerful longbows at the Battle of Agincourt had recognisably enlarged left arm bones and osteophytes on their left wrists, left shoulders and right finger bones. Osteophytes by the way are small bony growths that reflect frequent high loading over time. The draw weight of a longbow (in order to pull the string back) was 90kg and this would send an arrow traditionally made from ash about 180-200 metres. These men would discharge an arrow at a rate of roughly 6 per minute and they normally carried a quiver of 60-70 arrows.
Obviously in 1415 under Henry V there was no such thing as Occupational Health. For our longbowmen this was only a warm-up before hand to hand combat. These were hard men for hard times.
The early seeds of Occupational Health were sown in 1832 by the surgeon Charles Turner Thackrah (now known as the ‘Father of Occupational Medicine’) in his book about industrial diseases. Clearly the industrial revolution led to many reforms such as the ‘Factory Act’ passed in 1833. This was in direct response to the dreadful working conditions that children were subjected to.
Meanwhile, as we are now, The Health and Safety at Work Act 1974 is the primary piece of legislation covering occupational health and safety in Great Britain. Unlike previous acts in the UK, the Health and Safety at Work Act encompasses all industries and employees. The act also led to the creation of the UK’s Health and Safety Executive (HSE), which was put in place to regulate and reinforce UK legislation.
Clearly our life expectancy has increased and with this we all desire to maintain a quality of life to match, preferably without chronic pain, so our bodies must last longer. It would still be useful to know what movements and duties contribute most of all to knee and hip deterioration.
The Relationship of Kneeling and Squatting with Knee Osteoarthritis
As you would expect some of these factors are quite general in nature. One of the most common occupational risk factors for knee and hip osteoarthritis is simply heavy repetitive physical workload. In one study published in 2015 in a journal called ‘Work’ it was found that men who worked for 11–30 years in building and construction work had a 3.7-fold greater risk of developing knee OA, after adjustment for various confounding factors. Results from another British study revealed a more than five-fold greater risk of knee osteoarthritis among workers over the age of 55 years who were exposed to a combination of heavy lifting (> 25 kg) and kneeling/squatting or climbing stairs. Those who reported regular knee bending without lifting were only at 2.5 times greater risk. Here we arrive at a common theme, which is any task involving knee bending.
Kneeling or squatting are commonplace in many jobs. One such extreme example is ‘low seam mining’ in the coal-mining industry. Low-seam mines are those mines with a seam height of no more than 42 inches! The working height of the coal mine obviously coincides with the height of the coal seam. Imagine how hard those working conditions would be with a working height of a just one metre. This was very well recognised in the U.S by the mining industry who commissioned a study to examine the impact on the health of these miners. Obviously, these men were obliged to undertake kneeling and squatting postures almost all the time and demonstrated in the image below. The National Institute for Occupational Safety and Health (NIOSH) in the US, analysed musculoskeletal injury data from eight low-seam coal mines in 2009 (Gallagher et al). The data unsurprisingly reflected that the highest frequency of any bodily injury was to the knee joint. In fact, when compared to the low back, the frequency of knee injury was 1.7 times greater!
The Mine Safety and Health Administration (MSHA) database in the US recorded that on average 41 days were lost for each knee injury as opposed to 22 days for back injuries! They estimated that the average cost was $13,121 per knee injury! Using this average cost per knee injury and the 227 knee injuries reported to MSHA in 2007 the estimated financial burden of knee injuries in underground low-seam mining was calculated at nearly three million dollars. These injuries are likely clearly attributed to the low working heights, confining workers to sustained knee-straining activities like kneeling and squatting postures. The study concluded that novel knee pad designs were required to redistribute the stresses at the knee across a greater surface area and to other regions of the leg away from key structures of the knee.
As I mentioned this is an unusual extreme example, but it does demonstrate how much impact knee straining has. Knee-strain postures do vary over a broad spectrum of occupations. There was a study in 2015 on ‘Occupational Kneeling and Squatting’ (Ditchin et al) which was published in the International Archives of Occupational and Environmental Health. This study looked at a huge range of jobs and tasks. Overall, it investigated 20 different occupations including floor installers and carpet fitters, shipyard workers, plumbers, roofers, screed floors, stone masons, tilers, welders and paving. These occupations were then examined to assess the different tasks that they involved relative to the knee joint stress. The most employed overall knee straining activity was kneeling (75% of the time) followed by other postures (making up the other 25%) such as sitting on our heels, squatting, and crawling. They didn’t correlate which of these postures were resulted in knee joint deterioration. This was also purely an estimate as even the same occupation has very different work content day to day. Equally there are specific characteristics to all construction sites and workplaces, and individual preferences of working postures, so daily exposure within a single job is hard to estimate accurately.
Hip Osteoarthritis and Farming
Compared to knee osteoarthritis, there are relatively few studies that have focused on occupational osteoarthritis in the hip. Many of the aggravating factors for hip OA also closely correlate with knee OA. In fact, according to one investigation from Scandinavia that looked at male workers employed in the Swedish construction industry, the incidence rates for OA in hip and knee were positively correlated. Obviously, just like knee OA, heavy physical workload or manual labour have been identified as a key common occupational risk factor. Occupational groups that have been identified as having are at increased risks include farmers and other agricultural workers, construction workers, firefighters, food processing workers, female cleaners and healthcare workers to name but a few.
One occupation that has been studied for hip OA is farming. This might be of interest as we all live in a rural area. An investigation published in 1992 in the British Medical Journal in even suggested that hip OA should be viewed as a key industrial disease in farming. This study concluded that the risk had a direct association with how long you had farmed for. Risk increased somewhat following 1–5 years of farming and by a further threefold after 10 years of farming. Meanwhile female farmers had an approximate two-fold increased risk if they had spent more than 10 years in agriculture.
Another study was also published in 2004 entitled ‘Osteoarthritis of the Hip Joint and Farm Work’ in the Journal of American Industrial Medicine. Livestock based farming systems showed a significant positive relationship to the risk of developing hip joint osteoarthritis. They concluded that working on larger dairy and pig farms appeared to have a much stronger correlation with OA of the hip. Unfortunately, in terms of cow numbers, it is true that dairy farms have been getting bigger over the years due to economies of scale. Pig production also appears to have followed the same pattern. Dairy herds in Britain for instance have increased from 75 cows in 2000 to 113 in 2010. The data for 2016 shows the average herd size in the UK is now 143 cows (148 in England; 142 in Wales and 180 in Scotland). The 2004 study did also demonstrate that arable farmers had a significantly lower risk of incurring osteoarthritis than other farmers in general.
We all need to make a living. It is worth pointing out that even my profession suffers from degeneration to our hands (especially thumbs) wrists and elbows because of the soft tissue work we do. We perform of course what is quite literally ‘manual therapy’. However, it is quite useful to know what movements or tasks contribute to aches and pains in other professions even if some it is relatively obvious.