The effect of osmolarity on shape retention following laser-mediated cartilage reshaping

Laser reshaping of mechanically deformed cartilage specimens accelerates stress relaxation and results in permanent shape change. The mechanism of laser-mediated cartilage reshaping is still unknown, but clearly depends upon the complex molecular interactions between the physio-chemical environment and matrix proteins (collagen, and proteoglycans). It is well known in articular tissues that the mechanical properties of cartilage are sensitive to changes in tissue pH and osmolarity. The objective of this study was to determine the effect of osmolarity on shape change during laser reshaping in morphologic cartilage tissues. Porcine nasal septal cartilage specimens were cut (20 x 5 x 1.5 mm) and immersed in osmotically graded NaCl (0.2NS, 0.8NS, 1.0NS, 1.2NS and 5NS) or Phosphate buffered (0.2NS, 0.9NS, 1.0NS, 1.1NS, and 5NS) solutions for 12 hours to establish equilibrium. Then, specimens were bent into semicircular shapes, secured with clamps, and irradiated with an Nd:YAG laser (lambda= 1320nm, 5W, 15 secs, 5mm spot size) along the region of maximum curvature. Resultant bend angle was measured. Shape retention was calculated by comparing resultant curvature with pre-irradiation measurements. Non-irradiated, untreated (negative controls) cartilage retained less than 46% of the original bend. There was no difference in shape retention with respect to varying osmolarity (changed tissue water content) in either group. Resultant bend angles varied from 84 degrees to 194 degrees corresponding to shape retention varying from 42% to 72% in specimens which were immersed in either NaCl or Phosphate buffered solutions. While laser heating of deformed specimens does result in significant reshaping, the alterations in osmolarity do not seem to effect this process significantly over the range of values evaluated in this study.