Human biologist, vets and engineer work jointly
on cartilage grafting technique
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"
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
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."