I had some surgery on my left foot. The surgeon told me to put 20 per cent of my body weight on that foot and leg until my follow-up visit in two weeks. Maybe this is a dumb question, but how do I know how to do that? At 180 pounds, I know that I shouldn't put more than 36 pounds on my foot. But how do I know what that feels like?

You are asking a very good question. There are commercially available products such as limb-load monitors, pressure insoles, and force monitoring platforms. But these are expensive and usually only available in a research facility or physical therapy department.

Many therapists don't even have these materials. They often use a simple bathroom scale to give patients a feel for weight load. This is not a perfect solution, but it's a start. Studies show that even with practice, patients aren't able to replicate the required force within five per cent accuracy.

Researchers have found that lower levels of weight-bearing are more difficult to gauge than higher levels. So for example, it's easier to stay on target when you are allowed to put 80 per cent of your body weight compared with only 20 per cent.

Depending on the surgery, extreme accuracy may not be important. For example, weight-bearing on an ankle fusion with instrumentation (plates and/or screws) may be able to tolerate more weight than a cartilage implantation. The fixation devices used in the fusion will help hold the joint in place while bone healing takes place. Cartilage implantation is more delicate. Too much load can disrupt the healing cells leading to graft failure.