If you build it, will they grow?
More specifically, if you build a scaffold to just the right specifications and "seed" it with just the right cells, will they grow into a replacement for a torn anterior cruciate ligament, an important stabilizer of the knee?
A new study suggests the answer might be yes. And there may not even be a need to seed.
The anterior cruciate (ACL) connects the thigh bone to the shin bone and helps hold them in place. One of four ligaments in the knee, the ACL is big and strong and performs well under pressure -- up to 500 pounds. Still, about 200,000 people in the United States tear one every year.
It happened just the other day to the Clippers' Shaun Livingston when he went up for a shot and came down for a catastrophic landing.
Once it's been torn, the ACL is unlikely to heal itself. And putting it back together again presents a problem of Humpty Dumpty-like proportions. Conventional treatment involves reconstruction -- with a piece of another ligament from the patient's own leg (autograft), a ligament from a cadaver (allograft), or a synthetic ligament (prosthesis).
None of these methods is ideal. An autograft can cause problems for the previously healthy ligament used in the graft. An allograft could lead to infection or disease. Prostheses break down sooner or later.
"My hope is to design a synthetic scaffold that will regenerate and form a neo-ligament," says Dr. Cato Laurencin, chairman of the department of orthopaedic surgery at the University of Virginia in Charlottesville.
That's just what seems to happen, Laurencin adds -- although so far, only in rabbits. He led a team that designed a "bio-mimetic scaffold" from a biodegradable polymer called polyL-lactide that has the mechanics of a rabbit's ACL and the same braided structure.
When the scaffold was "seeded" with cells from a rabbit's own ACL, the team found regenerated "ligament-like tissue" 12 weeks after surgery. The ligament was about 30% as strong as an uninjured ACL. That's better than other reconstructions using different techniques: For example, an autograft measured after 30 weeks and a prosthesis after 20 weeks were no more than 15% as strong as the real thing.
The team, which reported its findings in the Feb. 27 issue of the journal Proceedings of the National Academy of Sciences, also found some regeneration, though not as much, when an unseeded scaffold was implanted.
Laurencin believes that result may improve in larger animals -- perhaps even including humans some day -- when the time frame for study can be longer and the patients can undergo some serious rehab. After all, it's hard to get rabbits to do knee lifts.