The effects of laser-induced collagen shortening on the biomechanical properties of the inferior glenohumeral ligament complex.

The purpose of this study was to determine the effects of laser-induced collagen shortening on the biomechanical properties of the inferior glenohumeral ligament complex. Fifty-seven bone-ligament-bone specimens underwent uniaxial tensioning to 10% strain. Approximately half of the specimens then underwent 10% shortening by lasing using a holmium:yttrium-aluminum-garnet laser. Both groups were again tensioned to 10% strain, and then loaded to failure. Ultimate strain and yield strain were significantly higher in the lased specimens than in the nonlased specimens. No significant difference was found for ultimate stress, yield stress, or elastic modulus between the two groups. Failure of the ligament did not appear to occur in the lased areas. The load-to-failure results suggested that the strength of the ligament complex was not significantly compromised by this lasing protocol.

Ablation rates of human meniscal tissue with the Ho:YAG laser: the effects of varying fluences.

To further define the operating parameters for Holmium laser meniscectomy, an in vitro experimental was set up to specifically measure ablation rates and the concomitant thermal injury. Using an experiment set-up with a laser fiber penetrating through meniscal tissue slices, energy levels were varied between 167 and 927 Joules (J)/cm2 per pulse to measure meniscal ablation rates. Following each experiment the adjacent thermal effects were evaluated with hematoxylin and eosin and trichrome staining. The fastest ablation rate was found at 927 J/cm2 per pulse. The increase in ablation rates was directly proportional to the increases in energy levels. Histological examination showed the average lateral thermal change to be 400 to 500 microns, with no demonstrated relation to the pulse level of energy. At these laser parameters the higher levels of energy per pulse showed better ablation of human meniscal tissue without increasing thermal effects in adjacent tissue. Higher energy levels and fluences appeared desirable for more efficient arthroscopic meniscectomy with the Holmium laser.

Collagen shortening. An experimental approach with heat.

Decreasing joint laxity is a clinical goal of ligament reconstructions. This in vitro study examined the structural and histologic effects of heat shrinkage of human collagen. Two preliminary studies were performed to assess the effect of heat on fresh frozen human tendons obtained from a local tissue bank. As heat was applied to tissue in a saline solution, the percent shrinkage was plotted against temperature. A second study used a freebeam Nd:YAG laser to maximally shrink patellar tendons measuring percent shrinkage versus energy applied. Finally, the effects of 10% shrinkage of fresh frozen human patellar tendons were analyzed mechanically and histologically. Consistent tendon shrinkage curves were found with increasing temperatures in a saline solution. A sharp increase in shrinkage to approximately 70% of resting length was noted around 70 degrees C. Tendon shrinkage by laser induced heat was precise and dose related. Tensile testing of the tendons shortened 10% of their resting length showed a decrease in load to failure to approximately 1/3 compared with that of historical control specimens. Histologic sections showed a well demarcated site of diffuse denaturation and degeneration of collagenous elements. Normal collagen was present adjacent to these thermal changes. These experiments showed that collagen tissue can be shortened precisely by the application of heat. Future studies need to examine the in vivo biologic response of shortened collagen tissue with time, especially recollagenization, restoration of length, and the long term biomechanical effects.