Autologous Chondrocyte Implantation or Microfracture?

The current issue of AJSM has two great articles regarding articular cartilage repair  procedures that go very well together.  I think this is an amazing aspect of orthopedics as we are making ground on developing ways to restore normal cartilage.  The Cartilage Defectimplications of this are staggering.  If you share an interest in articular cartilage repair, I recommend you read the special issue of JOSPT on articular cartilage and meniscal repair procedures that I guest edited, specifically my guest editorial and my article on postoperative rehabilitation following articular cartilage repair procedures.


Autologous Chondrocyte Implantation Compared to Microfracture

The first study is a comparison of outcomes between microfracture and second-generation autologous chondrocyte implantation (ACI).  80 patients with grade III-IV cartilage defects of the femoral condyle or trochlea were enrolled in the study and split evenly between groups.  The second-generation ACI procedure used Hyalograft C. 

microfracture pickingBoth groups showed significantly greater results at the 5 year post-op mark, however, the ACI group showed greater improvements in the International Knee Documentation Committee objective and subjective scores.  Even more interestingly, the return to sports rate between groups was similar at the 2-year mark and remained stable for the ACI group, but decreased for the microfracture group.


Results of Autologous Chondrocyte Implantation in Patients with Failed Prior Treatment

The second study prospectively assess the results of 126 patients undergoing ACI after a failure of a previous articular cartilage repair procedure.  This is a very large and prestigious study by the STAR group (Study of the Treatment of Articular Repair), which consists of all the best cartilage repair surgeons in the country.  The past procedures included predominantly debridement (48%) and microfracture (27%), as well as subchondral drilling, abrasion arthroscopy, and osteochondral autograft.

Results of the study were good with 76% of subjects showing successful results for a long duration.  All measurements showed a statistically significant and clinically meaningful improvements after ACI.  However, these results are lower than many of the previously reported outcomes following ACI when used as the first surgical procedure.  Here are photos of before (top) and after (bottom) of ACI for a femoral condyle defect (left) and patella defect (right):

ACI implant on condyle and patella


Clinical Implications

Putting the results of these two studies together leads to a very interesting and meaningful result.  While ACI and microfracture may yield similar post-op results at the 2-year follow-up, the ACI procedure continues to show durable results while the microfracture group slowly deteriorates over time.  This is significant when looking at these two studies together.  Although ACI appears to be a valuable surgical procedure for failed articular cartilage repair procedures, results of ACI used as the primary procedure are better than when used secondary after another procedure (such as microfracture) fails.  Based on these results, it may be better to have the ACI in the first place rather than try a microfracture.

These results make sense, as the ACI procedure has been shown to result in Type II collagen tissue similar to native articular cartilage while the microfracture is predominantly Type I collagen.  Think of the ACI procedure as restoring cartilage while the microfracture just creates a “scab” of a fibrin clot that simply covers the defect.  Because this tissue is inferior to Type II collagen, it does not hold up as well to weightbearing and functional loading.  Unfortunately the negative of the ACI procedure is a long rehab course and longer time to return to full activities, but based on these studies the slight delay may be worth it to prevent future complications.

Have you seen these results in your clinic?  Would you agree or disagree?  There are a lot of pros and cons with both procedures.  Hopefully as we continue to improve our knowledge and techniques all repair procedures will show better results.

E. Kon, A. Gobbi, G. Filardo, M. Delcogliano, S. Zaffagnini, M. Marcacci (2008). Arthroscopic Second-Generation Autologous Chondrocyte Implantation Compared With Microfracture for Chondral Lesions of the Knee: Prospective Nonrandomized Study at 5 Years The American Journal of Sports Medicine, 37 (1), 33-41 DOI: 10.1177/0363546508323256

K. Zaslav, B. Cole, R. Brewster, T. DeBerardino, J. Farr, P. Fowler, C. Nissen (2008). A Prospective Study of Autologous Chondrocyte Implantation in Patients With Failed Prior Treatment for Articular Cartilage Defect of the Knee: Results of the Study of the Treatment of Articular Repair (STAR) Clinical Trial The American Journal of Sports Medicine, 37 (1), 42-55 DOI: 10.1177/0363546508322897