title: Tissue shrinkage with the holmium:yttrium aluminum garnet laser. A postoperative assessment of tissue length, stiffness, and structure.
abstract: The effect of laser energy on the length, stiffness, and structure of connective tissue was examined in a rabbit patellar tendon model. A holmium:yttrium-aluminum-garnet laser was used to deliver a calculated dose of laser energy (300 J/cm2) to one randomly selected patellar tendon in each of 13 adult New Zealand White rabbits. The contralateral patellar tendon was used as a control. Radiopaque markers were placed in the patella and tibial tuberosity to allow for patellar tendon length measurements (via standard lateral radiographs) before and after laser application and at 4 and 8 weeks. Limbs were not immobilized during the postoperative period. The tendons were harvested at 0 weeks (N = 7) and 8 weeks (N = 6) and evaluated for tensile, stiffness, cross-sectional area, histologic changes, and electron microscopic appearance. The results demonstrated significant tendon shrinkage (6.6% +/- 1.4%) after application of the calculated laser energy dose. However, tendon length had increased significantly beyond the immediate postlaser length at 4 weeks and beyond its original length by 8 weeks. At 8 weeks, the lased tendons were significantly less stiff with significantly greater cross-sectional areas than contralateral controls. There was generalized fibroblastic response throughout the entire lased tendon characterized by a marked increase in cellularity. There was also a change from the normal bimodal pattern of large- and small-diameter collagen fibers to a unimodal pattern with predominantly small-diameter fibers in the lased tendons. The tissue alterations seen in this study suggest that the biologic response of connective tissue to laser energy causes a further compromise in tissue integrity, beyond that attributed to the initial physical effects of the laser. These alterations must be taken into consideration when determining postoperative rehabilitation of laser-modified tissues.
authors.affiliation: Laboratory for Comparative Orthopaedic Research, College of Veterinary Medicine, Michigan State University, East Lansing 48824, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Schaefer
authors.forename: M J
authors.initials: MJ
authors.lastname: Ciarelli
authors.forename: S P
authors.initials: SP
authors.lastname: Arnoczky
authors.forename: H E
authors.initials: HE
authors.lastname: Ross
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000818:Animals; D001182:Arthroscopy; D001696:Biomechanical Phenomena; D003094:Collagen; D003238:Connective Tissue / Q000473:pathology; D006801:Humans; D066298:In Vitro Techniques; D017075:Laser Coagulation; D010329:Patella / Q000601:surgery*; D011817:Rabbits; D013710:Tendons / Q000473:pathology / Q000502:physiology / Q000601:surgery*
chemical_list: D003094:Collagen