Background and objectives: To examine single versus multiple applications of the gallium aluminum arsenide (GaAlAs) laser on the healing of surgically injured medial collateral ligaments (MCLs) in rats.
Study design/materials and methods: Sixteen rats were studied, with 12 receiving surgical transection to their right MCL and 4 receiving a sham injury. Group 1 (n = 4) received a single dose of GaAlAs laser therapy (wavelength 660 nm, average power 8.8 mW, pulse 10 kHz, dosage 31.6 J/cm(2)) directly to their MCL during surgery. Group 2 (n = 4) received 9 doses of GaAlAs laser therapy applied transcutaneously on alternate days (wavelength 660 nm, average power 8.8 mW, pulse 10 kHz, dosage 3.5 J/cm(2)). The controls (Group 3, n = 4) received one session of placebo laser at the time of surgery, with the laser equipment shut down, while the sham injured Group 4 (n = 4) received no treatment. Biomechanical tests for structural stiffness, ultimate tensile strength (UTS), and load-relaxation were done at 3 weeks after injury. The stiffness and UTS data were normalized by expressing as a percentage of the left side of each animal before statistical analysis.
Results: The load-relaxation data did not show any differences between the groups (P = 0.18). The normalized stiffness levels of Groups 2 (81.08+/-11.28%) and 4 (92.66+/-13.19%) were significantly higher (P = 0.025) than that of the control Group 3 (58.99+/-15.91%). The normalized UTS of Groups 2 (81.38+/-5.68%) and 4 (90.18+/-8.82%) were also significantly higher (P = 0.012) than that of the control (64.49+/-9.26%). Although, Group 1 had higher mean stiffness and UTS values than the control, no statistically significant difference was found between these two groups.
Conclusions: Multiple laser therapy improves the normalized strength and stiffness of repairing rat MCLs at 3 weeks after injury. The multiple treatments seem to be superior to a single treatment when the cumulative dosages are comparable between the two modes of application.
Copyright 2004 Wiley-Liss, Inc.