Cartilage injuries in the knee can be a big problem. Healing is very slow, if it happens at all. That's because the cartilage in the knee doesn't have much of a blood supply. Getting athletes with a full-thickness (down to the bone) cartilage tear back on their feet and returned to their sport can be a challenge.

That's why researchers have worked hard to find ways to enhance or speed up cartilage healing. Two techniques developed in the recent past are microfracture and autologous chondrocyte implantation (ACI). Chondrocytes are cartilage cells. In this study from Italy, the results of these two treatment methods are compared.

Microfracture is the drilling of tiny holes in the cartilage to stimulate bleeding and a healing response. Autologous chondrocyte implantation (ACI) is the removal of normal, healthy cartilage cells from the patient. The donor tissue is either removed and expanded (grown) in the lab and then reinjected or it can be harvested from the patient and immediately reinjected directly into the damaged area.

When ACI was first developed, there were some problems. The surgery is complex and the outer layer of the bone (next to the cartilage) often responded by growing too much, a process called periosteal hypertrophy. Some of the results were reportedly controversial.

As a result, surgeons continued to improve the procedure. Now, a second-generation approach has been developed. This means the basic idea stays the same, but scientists have figured out a new and improved way to do it. In this procedure, a manmade scaffold can be placed on top of the defect in the cartilage. This scaffold is three-dimensional (3-D), biodegradable set of polymers. Polymers are plastics or proteins. In this case, the polymers used are proteins. Because it is manmade, it is considered tissue engineered.

Once it is in place, then chondrocytes harvested from the patient's own healthy cartilage were expanded and placed on the scaffold. The cells were able to make more chondrocyte cells. The final result is a bioengineered tissue called Hyalograft C. The question now is whether or not this new second-generation bioengineered approach is superior to microfracture.

This report shares the five-year results of 40 patients who had the second-generation autologous chondrocyte implantation (Hyalograft C) and compares those results to 40 patients who had the microfracture instead. A five-year follow-up is considered medium-term between short-term and long-term. Outcomes were measured by the presence of symptoms (pain, swelling), knee stability (buckling or giving way), change in knee function, and return to sports.

Patients were not randomly placed in one or the other group. They were treated based on health and insurance policies. The chondral lesions were considered moderate to severe (grade III and IV). They measured from 1.0 cm2 up to 5.0 cm2. Anyone with defects larger or smaller was not included. Patients were between the ages of 16 and 60 and were very active. Most (84 per cent) were well-trained athletes.

Patients were fairly well matched between the two groups (same ages, gender, size of defect). Some of the patients in both groups had a previous knee surgery for some other knee injury (e.g., torn meniscus, ligament rupture, damaged cartilage).

The surgery (either microfracture or implantation) was performed arthroscopically. Anyone with a torn anterior cruciate ligament (ACL) had a repair or reconstruction done at the same time as the microfracture or chondrocyte harvesting. Any instability present was corrected during the surgery. Everyone was treated the same postoperatively and during one-full year of rehab.

No one was allowed to put weight on the healing knee for the first four weeks. Range of motion was allowed along with easy strengthening exercises. The exercises did not put much pressure against the healing area of the joint surface. Weight bearing was introduced and gradually progressed from partial weight to full weight on the leg. Most people were able to put their full weight on the knee at the end of six weeks.

Everyone was followed by a physiotherapist who designed and supervised the rehab program. The program was able to help patients regain strength, endurance, and proprioception (joint sense of position). The final goal was to prepare competitive athletes for return to their previous sports activities. No one was allowed to participate in sports any earlier than 10 to 12 months after the surgery.

Patients in both groups had good results with improved symptoms, motion, and function. There was a noted decline in sports activities in the group who had microfracture at the end of five years. The level of sport activity was kept the same from two years to five years after the implantation procedure. Overall, the Hyalograft C group had greater improvements that lasted the full five years compared with the microfracture group. Reoperation and complication rates were equal between the two groups.

The authors concluded that chondrocyte implantation is an effective cartilage repair technique. Any size defect can be repaired this way. The repair site is more stable than with microfracture because of the type of repair tissue that develops. With microfracture, the repair tissue is more likely to be fibrous and unstable.

The second-generation technique is not without its problems. The procedure requires considerable skill on the part of the surgeon. It's a two-step surgical procedure (harvesting then implantation) and rehab takes a long time. Since most of the patients in this study were young with traumatic cartilage lesions, the authors suggest further studies are needed with older groups who have large degenerative lesions before recommending this procedure for all ages.

Elizaveta Kon, MD, et al. Arthroscopic Second-Generation Autologous Chondrocyte Implantation Compared with Microfracture for Chondral Lesions of the Knee. Prospective Nonrandomized Study at 5 Years. In The American Journal of Sports Medicine. January 2009. Vol. 37. No. 1. Pp. 33-41.