Researchers identify potential factors for successful ACI-C

Study cautions against performing the procedure after mosaicplasty or previous autologous chondrocyte implantation.

Selecting the ideal patient for collagen-covered autologous chondrocyte implantation can prove difficult, but British surgeons recently cited variables that may help surgeons more accurately predict clinical outcomes.

In a prospective study of 199 patients, researchers from the Royal National Orthopaedic Hospital in Stanmore, England, led by Professor George Bentley, found that the following characteristics correlated with favorable results in patients who underwent collagen-covered autologous chondrocyte implantation (ACI-C). Patients did best when:

they were young and presented high preop Cincinnati knee scores;
experienced symptoms for less than two years;
had fewer than two previous knee surgeries;
presented with trochlear or lateral femoral condyle defects; and
formed new hyaline-like tissue within three years postop.

The researchers also discovered that patients undergoing the ACI-C procedure after unsuccessful mosaicplasty or ACI surgery had “significantly inferior” results, they wrote in their abstract.

Factors may predict outcome

“This study identified significant factors which could predict the outcome of ACI-C,” said researcher S.P. Krishnan, MRCS, during his presentation at the 6th Symposium of the International Cartilage Repair Society. “However, this should act as an aid to the surgeon in collecting the ideal candidate for ACI-C.” The research constitutes one of the first studies identifying prognostic indications for the procedure, he said.

The study consisted of 108 men and 91 women with a mean preoperative Cincinnati knee score of 41. Researchers included patients between 15-55 years old with defects more than 1 cm². The investigators followed patients for up to four years. They performed arthroscopic evaluations on 137 patients and biopsy on 92 participants.

Age, number of surgeries

Participants showed the greatest mean improvement in knee scores during one-year postop. Of the 137 patients, 122 showed excellent or good results according to the International Cartilage Repair Society grading system, Krishnan said.

In a comparison of age and outcomes, the researchers found that younger patients with higher preoperative scores had significantly better results. “This means that those who had a higher Cincinnati score — function score — from the beginning, showed a higher rate of improvement,” Krishnan said.

Patients with a shorter duration of symptoms and fewer surgeries also demonstrated greater clinical gains. “Those who had less than two years of previous knee symptoms showed significantly superior clinical results,” he said. “Those who had fewer than two previous procedures also showed significant clinical outcomes ... both in terms of excellent/good results and knee Cincinnati scores.”

While the researchers noted that most defects (45%) occurred on the medial femoral condyle, “the lateral femoral condyle and the trochlea group showed significantly superior clinical outcomes when compared to the patella,” Krishnan said.

Histological findings also suggest that, “patients who develop hyaline-like repair tissue within the first three years after surgery are more likely to show durable clinical results,” the researchers wrote. They also found no significant difference between clinical outcome, defect size or patient gender, Krishnan said.

The study sheds light on the optimal ACI-C patient, while cautioning against its use as a revision procedure for others. “ACI-C following previously failed mosaicplasty or ACIs is less likely to give favorable clinical results and should be discouraged,” the researchers wrote.

For more information:
Krishnan SP. Who is the ideal candidate for autologous chondrocyte implantation? #2-5. Presented at the 6th Symposium of the International Cartilage Repair Society. Jan. 8-11, 2006. San Diego.