Four Major Complications After ACI Repair of Knee Cartilage

Cartilage defects in the knee joint that go clear to the bone can be treated these days. The technique developed to repair this problem is called autologous chondrocyte implantation (ACI). The procedure is done by taking normal, healthy cartilage cells from the patient. They use these cells to grow more cells in a laboratory setting and then reimplant the new batch of cells in the damaged area of the knee joint. The new cells usually adapt well to the new environment.

Although this treatment method works well, there can be problems or complications after the procedure. In this study, surgeons from Switzerland and Germany follow a group of over 300 patients who had ACI procedures. Three different ACI techniques were used. They watched to see which patients had the most problems after ACI and what those problems were.

The goal was to find the best way to treat these complications. But in the big picture, researchers hope to find ways to prevent problems from occurring after ACI that require revision (a second) surgery. The three methods used were: 1) periosteum-covered ACI, 2) Chondrogide membrane covered ACI, and 3) a three-dimensional matrix-associated ACI.

Two thirds of the patients had the Chondrogide membrane covered type of ACI. One-fourth had the three-dimensional matrix. The rest (14 per cent) had the periosteum covered ACI procedure. This may be the first large study to report on the problems that can occur with ACI. In the past, ACI failures were only discussed in single reports with a small number of cases. By combining the patients of three surgeons together over a period of five years (2001-2006), they were able to study a much larger group and report specifically on complications.

They found four major problems after ACI: 1) hypertrophy, 2) disturbed or inadequate fusion, 3) delamination, and 4) graft failure. Hypertrophy refers to overgrowth of the transplanted tissue. Insufficient fusion describes patients in whom the transplant just didn't regenerate like it should. The edges between the healthy, normal tissue and the implanted cells didn't meld together to form a solid, smooth surface. Delamination is the separation of the cartilage layer from the bone underneath. Shearing forces can cause these two layers to slide apart before fusion takes place.

In a few cases, there was osteonecrosis alink_delimiter_one_string (death of the bone underneath the cartilage transplant). In all cases, patients were diagnosed on the basis of pain and/or loss of function after the surgery. Symptoms occurred anywhere from the first six months up to three years later. Sometimes MRI scans showed abnormal cartilage or


Philipp Niemeyer, MD, et al. Characteristic Complications After Autologous Chondrocyte Implantation for Cartilage Defects of the Knee Joint. In American Journal of Sports Medicine. November 2008. Vol. 36.No.11.Pp.2091-2099.


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