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Safety, Effectiveness, and Durability of Second-Line Cartilage Implantation
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Posted on: 01/22/2009
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Patients with severe damage to the knee cartilage are not without treatment options. One of those is reserved for the repair of full-thickness (down to the bone) chondral (cartilage) injuries caused by acute or repetitive trauma. It is called autologous chondrocyte implantation (ACI) and it was originally designed for patients who had a failed primary (first) procedure.
In autologous chondrocyte implantation (ACI), healthy cartilage cells are harvested from the patient and used to grow more healthy cells to fill in the defect. Most of these patients have had prior treatment with one of the other methods to treat damage to the articular (joint) cartilage. Such surgical repair procedures include debridement, microfracture, drilling or abrasion, or osteochondral grafting.
In this study, 154 patients with failed results from their first treatment for articular cartilage defects received an autologous chondrocyte implantation (ACI). The work was done by dozens of surgeons at multiple different centers around the United States and Canada. The goal was to examine three things: effectiveness, safety, and durability of ACI for these patients.
A previous failedsurgery meant that the patient still had significant pain and loss of function. Patients were eligible for this rescue procedure if they were: 1) at least 18 years old, 2) had a previous (now failed) surgery within the last three years, and 3) fair-to-poor score on a knee rating scale (the Modified Cincinnati Knee Rating System). The knee rating scale was an indication of overall knee condition.
There were certain restrictions on who could be chosen for the implantation procedure. They could not have had 1) a previous ACI treatment on the same knee, 2) removal of the meniscus (meniscectomy), or 3) knee arthritis (osteoarthritis or rheumatoid arthritis).
Results of the ACI treatment were measured in two ways: benefit to the patient and differences in the patients. Benefit to the patient included knee pain, knee function, quality of life, and overall health. It was also noted how long the benefits lasted (duration).
At the same time, the researchers were looking for differences in patients. Were there reasons why the first procedure failed in this group of patients? Was there some characteristic that could explain the failures? Would it be possible to screen patients ahead of time looking for a particular factor or group of factors that might predict failure, and thus prevent it from happening?
A two-stage chondrocyte implantation method was used. In the first procedure, the normal, healthy cells were removed from the patient. They were sent to a lab where scientists used them to grow even more cells. This process is called expansion. Once there were enough cells and they had been tested for viability (meaning they are alive and have the potential to stimulate cartilage growth in the defect), then they were placed in the cartilage lesion.
After that, everyone was followed for at least four years. Patient characteristics compared between the failed ACI group and the successful group included age, gender, body mass index (BMI), and level of knee pain and function. They also looked at overall knee condition, number of cartilage lesions, lesion size, and lesion location.
Three-fourths of the patients had a successful outcome. One-fourth experienced failure defined as no improvement in symptoms after three months of rehab and/or the need for retreatment of the cartilage defect after ACI. Using data collected from the patients with a failed ACI procedure, they were able to calculate the time to failure, which could be used as part of the prognosis (i.e., what to expect after surgery).
In the statistical analysis of the data collected, the authors were able to predict the probability of ACI success after the first (non-ACI) procedure failed. From this information, they were also able to make predictions about the expected durability of the ACI as second-line therapy. This type of information helps the surgeon give the patient a reasonable prognosis.
All of that was geared toward evaluating the effectiveness of the procedure. Then they turned their attention to the safety of ACI. Of course, a failed surgery was considered a serious adverse event. Other complications such as infection, delayed healing, hypertrophy (graft overgrowth), and joint adhesions were assessed as mild, moderate, or severe.
About half of the group had at least one problem following the ACI procedure. Usually, this was overgrowth of the bone around the implant. Most adverse effects occurred within the first two years. The presence of adverse events after ACI did NOT necessarily mean the patient would have a failed response eventually.
And in the last analysis performed, the time to failure (TTF) or durability was reviewed. They found that when failure occurred, it didn't happen until after the study ended at 48 months (four years). Comparing these results with non-ACI treatment, the ACI procedure outlasted the non-ACI approach by at least 31 months.
Looking back at the patient records, they checked to see if having one type of first (non-ACI) procedure over another made any difference. In other words, did the patients who had a marrow-stimulating procedure do better than patients who had debridement (removing fragments of tissue)? The answer was no. Both groups had an equal number of failures and successes.
The authors concluded that the results of their study agree with other studies done on the same topic. Patients with moderate-to-large chondral lesions who did not improve with non-ACI treatment can go on to have a good result with an ACI as a second procedure. This opens up the treatment possibilities for patients with poor knee function after a failed cartilage first procedure for full-thickness chondral injuries.
The improvements in this group of patients were significant and long lasting. Most of the patients had no problems with daily activities and could even participate in sports with no (or very few) limitations. The true durability of ACI repair isn't really known, since this study ended at 48 months. The authors suggest further studies to gain a better understanding of the long-term durability of ACI repairs.
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References:
Kenneth Zaslav, MD, et al. A Prospective Study of Autologous Chondrocyte Implantation in Patients with Failed Prior Treatment for Articular Cartilage Defect of the Knee. In The American Journal of Sports Medicine. January 2009. Vol. 37. No. 1. Pp. 42-55.
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