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Robots Offer Humans Help on Bended Knee

The human knee can bend up to 160 degrees. This much motion allows us to easily do activities like getting in and out of the bathtub. It also makes it possible to squat down to check the line for a putt on the green while playing golf. Others use this amount of flexion to kneel or to squat while gardening, praying, or doing work tasks.

The knee rarely bends this far again after a knee joint replacement. The average patient has between 100 and 115 degrees of knee bend. Knee flexion after total knee replacement (TKR) rarely goes beyond 120 degrees. The reasons for this limit in motion are many and varied. Researchers report factors present before, during, and after the operation that can affect knee flexion. In this article, doctors from Harvard Medical School outline each of those factors and discuss them.

The doctors say that to increase knee flexion, we must first know how the healthy human knee works. Then limiting factors can be changed to mimic the normal knee. Three TKR implants on the market are designed to increase knee flexion. A total knee system is proposed as one solution. Every surface shape, angle, space is studied. So is how each of these factors changes as the knee flexes. The results are then put to use in these new and improved knee implants.

One way to test how well these new knee systems work is through the use of robots. The first such robotic studies are underway at the Massachusetts Institute of Technology (MIT). Engineers from MIT and doctors from Harvard Medical School are teaming up on this. They are studying all three implants. The results of this ongoing study will help guide future implant designs. Increasing knee flexion is the goal. The outcomes of this study will be reported here as the information is published.

References: Peter G. Sultan, MD, et al. Optimizing Flexion after Total Knee Arthroplasty. In Clinical Orthopaedics and Related Research. November 2003. Volume 416. Pp. 167-173.

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