Autologous chondrocyte implantation ACI

In 1994, the publication of early results by the Gotenberg team of Petersen, Lindahl and Brittberg had a catalyzing effect on cell engineering.37 Orthopedics was launched into a new age where it was claimed that "hyaline-like" cartilage could be regenerated. Controversy raged principally because this claim challenged the old mantra that cartilage could not heal. Since then several other reports have duplicated those initial results.38-40

The process involves in vitro clonal expansion of harvested autologous chondrocytes after enzymatic digestion, followed by implantation of these cells in suspension into a cartilage defect which has been sutured over using

Figure 2. Autologous chondrocyte implantation technique.

periosteum. These chondrocytes are later implanted into the defect which has been converted into a contained pouch by a sutured periosteal membrane. The periosteum is harvested with care and speedily transferred to the defect. It is sutured with fine absorbable sutures. This sheet of periosteum is sutured with the bone side downward (Fig. 2). This is contrary to the method of its use by O'Driscoll as discussed above. He is of the opinion that periosteum alone will not be the source of healing of the cartilage when used in this way, and animal studies confirmed that chondrocytes are required for the Gothenburg technique to be successful. It may be the case that without cellular expansion, the numbers of cells from the periosteum alone are insufficient to form hyaline tissue, producing a fibrous repair instead.

Three prospective randomized trials have been reported in 2004. In Norway, a multicentre study comparison of microfracture to ACI was carried out in 80patients.21 After a 2-year analysis, Knutsen etal. favored microfiac-ture, but both groups improved. Histology of the repair tissue type found a range from fibocartilage to hyaline in both groups, with a tendency to better histology in the ACI group. The ACI technique has good reports at 8 years and so it is possible that the results will favor ACI in the long term.

A prospective trial by Horas et al.41 examined 40 patients allocated to either mosaicplasty or ACI and concluded that the results as measured by a surgeon-completed Lysholm score were better with mosaicplasty. That study was, however, not strictly randomized, and the patients treated by ACI had more severe symptoms at the start of the study, and lower initial Lysholm scores. Re-analysis of the results at Oswestry, UK, found little real improvement and also that a previous report by Horas et al.42 in the German literature on the same group of patients was in favor of ACI. It is not a concern that there were these two reports, but on reconsidering the results, Horas came to the conclusion that both techniques were probably of equal benefit.43

A third study in 2003 was again a comparison of mosaicplasty with ACI. Professor Bentley and his groups31 in London studied 100 patients in a mean period of 19 months and found the ACI to be slightly better (p = 0.032), although the Cincinatti knee rating showed no significant difference (p = 0.028).

Limitations of ACI include a failure to improve patients in 10-20% of all cases (37-39); site specific variability in success rates43 and limitation to chondral defects rather than the widespread cartilage loss of ostoarthritis. It also cannot be used in inflammatory arthritis. Harvest sites may heal with fibrocartilage if taken down to bone but can themselves be a source of symptoms. Of a group of 10 patients who underwent autologous chondrocyte implantation to the ankle using ipsilateral knee harvests, 3 had Lysholm scores that returned to preoperative levels at one year but 7 had a decrease in Lysholm score of the knee by 15% at 1 year.44

Furthermore, the repair tissue in biopsy specimens from ACI does not have the architecture of mature articular cartilage. The histology with this treatment does improve with time. The layers of orientation of collagen seen in the adult knee develop over several years in the adolescent and it remains to be seen whether completely normal patterns will develop with time in the ACI treated areas.

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