Bent On Success

By Corie Lok
Office of Research

Joint cartilage repairs are taking a step ahead with a novel process that grafts healthy cartilage on to a joint with damaged or missing cartilage.

Called mosaic arthroplasty (MA), the procedure can repair knees, hips, shoulders, ankles or elbows. MA is being optimized for human use by a team of U of G researchers that includes Prof. John Runciman, Engineering; Prof. Mark Hurtig, Clinical Studies; OVC post-doctoral fellow Simon Pearce; and Prof. Jim Dickey, Human Biology and Nutritional Sciences.

Joint injury, where cartilage is torn and destroyed, is a common problem caused mostly by trauma such as sporting or car accidents, says Hurtig, a large-animal surgeon who's been studying the use of MA in racehorses, dogs and sheep. Cartilage provides cushioning between bones, and without it, pain and swelling can result.

If left untreated, cartilage injury can lead to arthritis later in life. The most common treatments are anti-inflammatory drugs, physiotherapy and surgical removal of debris from the joint. But these methods don't repair cartilage damage like MA does, says Hurtig.

Although MA is still in the development stages and not yet commonly used in humans, it's becoming more popular. It boasts improvements over other grafting techniques because it's a one-step process. It's based on using a patient's own fully formed cartilage from an uninjured area of the joint to repair a damaged part.

Here's how it works. Cylinders of bone topped by normal cartilage, measuring just a few millimetres in diameter, are cut out from a non-load-bearing part of the joint and placed like dowels into holes drilled into the part of the joint that's missing cartilage. The bottom bony parts of the dowels eventually grow into the joint, and the tops of the cylinders form the weight-bearing surface of the joint. This eventually forms a continuous cartilage layer on the joint surface.

Because the replacement tissue comes from the actual patient, MA avoids the risk of an immune response against foreign tissue or of developing an infection from donor tissue.

Runciman is helping the research team to better understand the forces at work among cartilage, bone and the grafts (to optimize implant parameters) and to improve the instruments used by surgeons. He says repairing the joint is like repairing a machine. To effectively fix the joint, surgeons need to understand how all its parts fit and work together. But good tools are also needed to fix "mechanical" joint problems.

The instruments used in MA need to be more surgeon-friendly, says Runciman. For example, they should be weighted and balanced so that they feel comfortable and almost unnoticeable in the surgeon's hand.

"You want to make the instruments at one with the surgeon's hand," he says. "This will enhance the surgeon's performance."
There are still problems with the procedure, however. The cylinders sometimes move in their holes - a painful process that can lead to further cartilage damage. The size and shape of the holes need to be optimized to minimize graft movement. Optimizing the size and distance between cylinders could help maximize coverage of the bone with cartilage while maintaining the strength of the cylinders.

To do this, mechanical parameters - such as strength and elasticity - of the joint's components are being entered into a computer. This information will be used to design software capable of building a virtual model of the joint and simulating what happens during MA. This model can test different graft sizes and shapes.

"With modelling software, there don't have to be as many clinical tests on animals in the operating room," says Runciman. "It gives us direction for future testing."