Osteoarthritis is a disease that is millions of years old. Researchers have even found evidence for osteoarthritis in dinosaurs. It's also one of the most prevalent diseases to impact our bones - and its rates will only grow with an ageing population worldwide.
As our joints wear and tear, the protective cartilage around them gradually breaks down. This leads to pain, stiffness and swelling. Age, sex, weight and genes can all play a role in whether you develop osteoarthritis. But it's difficult to assess how much repetitive use of a joint can affect whether and where osteoarthritis develops.
Of course, most studies about the disease are very much grounded in the present. But some, like my most recent research, step way back into the past to uncover the disease's history. Archaeologists have found evidence for osteoarthritis in populations across the world - particularly where individuals would have engaged in harder physical labour for a longer time and from an earlier onset.
My recent research on osteoarthritis from the ancient Egyptian village of Deir el-Medina is an example of looking into the past to help modern clinical studies. Bones and texts showed how decades of strenuous hikes led to higher levels of osteoarthritis in workers' knees and ankles.
The village of the King's artisans
Deir el-Medina is the village of the workmen who constructed and decorated the pharaohs' tombs during Egypt's New Kingdom period (1550-1070 BCE). The workers at Deir el-Medina were highly literate. Fortunately for us, they dug an enormous pit next to the village and ultimately filled it with thousands of ostraca - pieces of pottery or stone with writing on them.
This archaeological trove included amazing records of daily life: letters, receipts, court cases, drawings and more. These reveal that the artisans were highly valued for their skills. The Egyptian state provided them with many benefits as a result.
They had servants to help with daily tasks; housing, rations, and even healthcare. These perks ensured that they could continue their work on the royal tomb efficiently.
But the workforce still suffered from osteoarthritis. There's evidence for osteoarthritis at the site in the joints of skeleton buried at Deir el-Medina. The workmen's knees and ankles especially exhibited higher levels of osteoarthritis than women from Deir el-Medina or other comparative populations in Egypt.
So what might account for these higher levels of osteoarthritis despite all the benefits afforded to these artisans?
The dreaded commute
In Egypt's New Kingdom, kings were buried in a deep valley in the Theban mountains, their tombs cut into the rock and hidden from view. The workers' village at Deir el-Medina was established in a neighbouring valley so that the king's tomb was simultaneously accessible and secluded.
During the week workers stayed in huts that overlooked the Valley of the Kings. The distance between these sites is relatively short - less than two kilometres, but the workmen's daily and weekly hikes required steep climbs.
Each day, workers descended 93 metres into the Valley of the Kings, then made the return journey to their huts at night: the equivalent of climbing up a 28-story building after a day at work.
These hikes help to explain the higher rates of osteoarthritis in their legs. The next question was how frequently they made this commute. After all, even tomb builders got days off or fell ill.
Here, Deir el-Medina's extensive texts were a huge help. Absence records and scribal journals recorded the work week and the days different workers were absent. These combined records showed that workers were not expected to work - or were absent - 44% of the year. They were consequently hiking 161 days of the year in a career that lasted between 25 and 35 years. Despite their days off, the strenuous commute took its toll on workmen's joints.
Perhaps surprisingly, the workers' skeletons demonstrated very few examples of more extreme forms of osteoarthritis. As joints break down, bone can eventually rub directly against bone, leaving a polished appearance called eburnation.
Only a couple of joints from Deir el-Medina showed evidence for eburnation. These were more frequently from women rather than the workmen. This suggests that the workmen's regular hikes didn't provide the level or kind of stress necessary to result in more extreme cases of osteoarthritis.
These findings offer a benchmark to consider how much repetitive joint use contributes to developing osteoarthritis in both moderate and severe forms.
Anne Austin received funding from the American Research Center in Egypt (ARCE) and the University of California Humanities Research Institute while conducting her research.