The effect of nonablative laser energy on joint capsular properties. An in vitro mechanical study using a rabbit model.

To evaluate the effect of laser energy at nonablative levels on the mechanical properties of joint capsular tissues, we tested the femoropatellar joint capsules of 12 mature New Zealand White rabbits. Specimens were divided into three treatment groups (5, 10, and 15 watts) and one control group. All specimens were first nondestructively mechanically tested to determine stiffness and viscoelastic properties and then treated with laser energy or served as a control. Shrinkage was recorded and mechanical testing was repeated. The application of laser energy resulted in 9%, 26%, and 38% reduction in capsular tissue length for the 5, 10, and 15 watt groups, respectively. Tissue shrinkage was significantly and strongly correlated with energy density. Laser energy caused a significant decrease in tensile stiffness only in the 10 and 15 watt groups. Laser energy did not change the relaxation properties at any energy density. This study demonstrates that significant capsular shrinkage can be achieved with the application of nonablative laser energy without detrimental effects to the viscoelastic properties of the tissue; although at higher energy densities, laser energy did lessen capsular stiffness properties. The results of this study should be interpreted with caution until in vivo studies are performed.