Does having an arthritic knee change the way you walk on your good leg?

In 2008 I was approached by a doctor working in Orthopaedics, Andy Metcalfe. Andy was interested in finding out how patients with knee arthritis walk. In particular he was keen to know if the way they were walking might be contributing to their joint damage. His patients were also telling him that being careful with the painful leg was putting extra strain on their good side. Were they right and did that make them more likely to need a knee replacement on that side in the future?

Andy’s questions were interesting to us in ORLAU as we have a dedicated laboratory, a gait lab, for measuring how people walk. Even though measuring walking is one of our main areas of expertise, we hadn’t done much work on arthritis. A new area of research opened up for us and nine years later we have just published the third and final paper from the study which became Andy’s PhD. It feels like a good point to reflect on what we have learned.

We decided to test 20 patients who had painful arthritis in just one joint, a knee joint. It turns out that arthritis in one joint alone is quite unusual and Andy had to wade through 610 sets of patient records to find them. Our volunteer patients walked up and down in our gait lab before going for their knee replacements. We attached shiny markers to their legs to measure how their joints were moving. We used the force measuring equipment in the floor to see how they were loading both legs, and hence their knees.

We also placed electrodes on their skin to pick up the electrical signals from their muscles. So what did we find?

Before their surgery patients did walk with greater than normal loads on their arthritic knee joint. Some had higher peak loads, but for most people the main problem was that the high loads lasted longer. Our volunteers didn’t have a particularly visible limp but it appeared that their slower, stiffer walking pattern might be adding to their problems. We also saw that the muscles on either side of the knee were working against each other for periods of their walking cycle, a phenomenon known as co-contraction. The effect of this was to increase the load on the damaged cartilage. At first sight this approach seems counterproductive. Why make the situation worse? In fact this co-contraction is a natural result of uncertainty. Most people do the same when walking on ice, for example. Were our patients guarding their sore knee against painful trips and stumbles? Once again a walking pattern designed to protect the joint might actually be making the situation worse.

Andy’s patients were also concerned about their good leg, so what changes did we see there? We found that they were right; the loading was increased on that side too. In fact the loads were higher than normal for both the knee and the hip. The knee muscles on the good side were also co-contracting in the same way as those on the arthritic joint. It looks like this could help to explain why so many patients need a second joint replacement.