A prospective randomised study of laser reshaping of cartilage in vivo.

Laser reshaping using low laser energy levels was performed on the cartilage of ten porcine ears. The ears were examined up to 4 months after laser reshaping and the stability of the reshaping was assessed by photography and casts obtained from alginate impressions of the ears. The cartilage was also studied histologically in three animals at 3 weeks, 8 weeks, and 4 months using haematoxylin and eosin (H&E), periodic-acid-Schiff (PAS) and alcian blue stains as well as Mib-1 antibody stain to detect cells in cycle. These ears were compared with the other control or non-irradiated ear. All the treated ears initially demonstrated a controlled alteration in their shape. Four were exposed to a pulse energy of 2 J/cm2 at 20 Hz with a spot diameter of 1.1 mm for 7 s and retained their shape for up to 14 days. However, the three exposed to the same levels of energy for 9 s showed tissue necrosis whereas the three which were treated for less than 4 s returned to their original shape after 24 h. Histological examination revealed that there was a dramatic eccentric proliferation of perichondrium away from the centre of irradiation with a noticeable absence of any inflammation. In all laser-irradiated areas there was a loss of staining with PAS and a dramatic increase in staining with alcian blue within the cartilage matrix. Viable chondrocytes were absent from the irradiated cartilage. Staining with a Mib-1 antibody that detects cells in cycle showed positive staining in a small fraction of proliferated perichondrial cells where new cartilage had been produced.