By: 25 October 2011

Haris S. Vasiliadis, MD, PhD, et al.
The American Journal of Sports Medicine. May 2010. Vol. 38. No. 5. Pp. 943-949.

The type of cartilage being considered here is the hyaline cartilage, and damage to this layer of cartilage can result in full-thickness lesions. This type of injury can cause knee pain and loss of knee motion and function.

One successful method of repair is called autologous chondrocyte implantation (ACI). In this study, scientists take a look at how well the actual repair tissue holds up over time. Evaluating the quality of tissue after ACI isn’t easy. The surgeon can go back in with an arthroscope and take a look, but this requires another surgery and is invasive. No one knows if this procedure might cause problems later.

MRIs are a noninvasive way to look inside the joint, but standard MRIs don’t show the cellular structure of the cartilage in enough detail to really assess the repair tissue. So the authors of this article conducted a study using a newer MRI technique called dGEMRIC (delayed gadolinium-enhanced MRI of cartilage).

The radiologist puts the gadolinium compound into the knee joint to spread throughout the joint and into the cartilage. The gadolinium seeps in the best wherever there is healthy cartilage tissue with plenty of glycosaminoglycans (GAG). A normal level of gadolinium is around 65 mg/mL in normal cartilage tissue. By comparison, severely damaged cartilage from osteoarthritis only absorbs about 10 mg/mL. After the dye is injected into the joint, the patient walks around for about 15 minutes to help spread the gadolinium into the cartilage. Then MRIs are taken to look at the filling of the defect, the smoothness of the surface, and the presence of bone edema. The dGEMRIC technique measures GAG concentration and gives surgeons an idea of how much degeneration is present in the ACI repair.

In this study, testing was done anywhere from nine to 18 years after the original ACI. What they found was good quality of repair tissue, but there were osteophytes, bone cysts, and bone edema also present in, under, or around the repair tissue. These new lesions did not seem to bother the patients or affect knee function.

Age was a factor, as older patients had more cysts and younger patients had more bone spurs. Areas of damage with an irregular surface had better outcomes than defects with a smooth surface. The reason for this is unknown but will be studied further.

The authors concluded that assessing and predicting the long-term durability of ACI can be difficult. But studying the results of ACI is important in order to find the best way to treat the problem. As this study showed, the dGEMRIC technique can be used as a noninvasive alternative to arthroscopic exam and tissue biopsy.

This newer MRI method provides valuable information about the composition of repair tissue. This is a different way to judge the results of ACI from the usual clinical tests performed on the patient. dGEMRIC may become a universally accepted non-invasive way to evaluate the results of all methods of cartilage lesion repair.