The authors have corrected various craniofacial contour deformities using tissue culture-
expanded autogenous tissue. Their method involves obtaining small cartilage biopsy specimens, expanding the number of cells from the biopsy specimens in tissue culture, and injecting the expanded cells into the defect. The authorsâ€™ initial clinical results using this procedure are impressive. In addition to effectively solving the clinical problem, their method has certain advantages over standard techniques. Starting with small cartilage biopsy specimens virtually eliminates donorsite morbidity. Because the reconstructive material comes from the host, problems related to alloplastic implants are avoided. The surgical technique is minimally invasive, thereby decreasing operative exposure and concomitant morbidity.
The expected shortcoming of this early report of clinical work is the lack of long-term resultsâ€”specifically, the long-term shape of the grafted areas. Not only are there no clinical data, but there are also no published scientific data. This clinical trial precedes the scientific data on a new technique.
In parallel work in the field of joint repair where a similar technique using cultured autologous chondrocytes implanted under a patch of periosteum, animal studies were performed to validate the concept before the clinical attempt.1,2 Whereas placing cells into avascular areas of joint defects can isolate the cells from inflammatory attack, implantation of cells in proximity to the vascular compartments of the cranium may have a different outcome.:i Although this technique is interesting and yet quite simple, there is a paucity of data in immune competent animals to suggest that the results of this technique will persist over the long term. Clearly, the placement of cartilage grafts, autologous or allogeneic, has had discouraging clinical results.4,5 Nonetheless, the approach may be the first clinical step in engineering cartilage for craniofacial augmentation.
One issue mentioned in the article is that the cells are grown in culture and differentiate. This phenomenon has been described by many authors 5â€™6 and by ourselves.7 The authors do not give details as to how they know the cells differentiate other than examining their phenotype in culture. Second, they suggest that the cells re differentiated in the second passage, and possibly the third. It is not clear how the cells would re differentiate in mono layer and how this re differentiation was determined. The concept probably relies on the three-dimensional needs of chondrocytes to produce extracellular matrix. We do know that injecting a bolus of primary swine ear or joint chondrocytes into a confined area under the skin of nude mice will permit the formation of new cartilage matrix.7 However, to our knowledge, this has not been replicated in any large animal.
The next generation of this approach could use an artificial three-dimensional scaffold for the cells.
In our own laboratory, we have been studying the use of polymerizable hydrogels as three-dimensional matrices for cartilage matrix formation. Natural substances, such as fibrinogen, hyaluronic acid, or alginate, have shown favorable results in vitro and in nude mice.8-11 Chang etal. have demonstrated proof of concept in sheep for generating cartilage in a defined shape using alginate as the gel scaffold for chondrocytes.12 Other choices may be synthetic hydrogel materials such as polyethylene oxide) that can be modified to incorporate growth factors or other moieties favorable to cartilage matrix formation and polymerized in situ.13 With the groundwork that these investigators have laid, it is likely that these new approaches will now move swiftly toward clinical application. We congratulate these authors on their ingenuity and excellent clinical results.
Mark A. Randolph, M.A.
Plastic Surgery Research Laboratory Massachusetts General Hospital Boston, Mass. 02114 firstname.lastname@example.org
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