Osteochondritis dissecans (OCD) creates a “dead” region of cartilage and growing bone in joints. Conservative treatment often consists of simply resting the affected joint, but sometimes surgeons resort to repairing OCD lesions in horses by removing the damaged areas, hoping fresh cartilage and bone will get stimulated to replace it. That technique has limited success and works best in smaller lesions. For larger lesions, well, athletic careers get put aside as owners wait for nature to do its best—which isn’t always as good as they’d like.
That’s why Irish scientists recently tested a new OCD repair method that’s based on the idea of actually replacing the damaged tissue with healthy tissue. Specifically, they’re replacing OCD lesions with bioengineered tissue, made up of three layers similar to the tissue layers they’re replacing.
“I think what makes this technique successful is that we’re looking at what’s in the joint itself and mimicking those materials,” said Fergal J. O’Brien, PhD, FAS, CEng, FIEI, FEAMBES, MRIA, professor of bioengineering and regenerative medicine at RCSI Anatomy in the Royal College of Surgeons in Ireland, in Dublin.
“It’s quite complex because you’ve got the smooth articular cartilage which allows your joints to move, and that sits on top of the subchondral bone, and in between you’ve got the calcified cartilage that separates the two,” he said. “It required a lot of research and work to get the bioengineering down for this graft material.”
Constructed mostly of collagen prepared from cattle, the three layers build up a sort of “sheet” of tissue that can be cut, at the moment of surgery, to custom fit into the lesion, O’Brien said. First, the surgeons must clear out (debride) the damaged tissue, caving away down to living, bleeding tissue. Then, they can shape the bioengineered graft material and set it in place (fixing it with a kind of bioabsorbable glue, if necessary) before closing up the surgery site.
The replacement material “works like a sponge,” absorbing cells into the structure—which then serves as a matrix for natural cells to grow into, O’Brien said. An added bonus is that some of the absorbed cells are bone marrow cells, and these include stem cells. Stem cells are “embryonic” in nature, in that they can develop into essentially any kind of cell in the body, depending on where they’re located.
“This three-tier structure basically tells the stem cells at the top to form cartilage because there’s cartilage there and those at the bottom to form bone because there’s bone there, and then the intermediate layer serves just to make sure you don’t have bone forming in the cartilage area,” O’Brien said. “So what you’ve got is a structure that effectively directs the body’s own cells to regeneration.”
Over time, the implanted biomaterial resorbs as natural tissue formation takes over, he said.
O’Brien and colleagues tested their technique on a jumping-bred 15-month old Warmblood filly with large OCD lesions in both stifles.
“This was going to end her show career before it even began,” he said.
They implanted the three-layer tissue in each stifle under general anesthesia. The horse underwent 10 weeks of stall rest and six weeks of hand walking.
At her 22-month follow-up, the young mare was working at the “intended level” under saddle in walk, trot, and canter, and jumping, O’Brien said. Although she had mild fluid build-up in one stifle and slight scars on both, the horse showed no signs of lameness.
Ultrasound examinations showed healthy tissue growing at the three layers, consistent with the natural tissue for that area.
“We were pleasantly surprised, because my initial impression was that the lesions were too big for healing to occur,” O’Brien said.
The material was originally developed with human medicine in mind, said O’Brien. But during the initial safety testing phases, opportunities came up to test it on horses. Those opportunities benefited not only human medical knowledge but also the horses themselves by offering an effective therapy.
“It’s lovely to be able to say that we’re not just using animals to test on, but are actually using our knowledge to help animals,” he said.
The study, “Repair of large osteochondritis dissecans lesions using a novel multilayered tissue engineered construct in an equine athlete,” was published in the Journal of Tissue Engineering and Regenerative Medicine.