1135 JRRD JRRD Volume 46, Number 9, 2009 Pages 1135–1142 Journal of Rehabilitation Research & Development Effect of He-Ne laser radiation on healing of osteochondral defect in rabbit: A histological study Mohammad Bayat, PhD; 1* Farshad Javadieh; 2 Masoomeh Dadpay, MD 3 1 Cellular and Molecular Biology Research Center, Medical Faculty, Shahid Beheshti University, MC, Tehran, Iran; 2 Medical Faculty, Shahid Beheshti University, MC, Tehran, Iran; 3 Pathology Department, 501 Army Hospital, Tehran, Iran Abstract—This study examined the influence of low-level laser therapy (LLLT) on the healing of a large osteochondral defect in rabbits. An osteochondral defect with 5 mm diameter was surgically induced in the right femoral patellar groove of 48 adult male rabbits. They were divided into a control and an experimental group. The rabbits were treated at 2, 4, 8, and 16 weeks after surgery, with six rabbits in each study period being tested at each biweekly period. The experimental group received LLLT with a helium-neon (He-Ne) laser (632.8 nm, 10 mW) of 148.4 J/cm 2 three times a week, and the control group received placebo LLLT with equipment switched off. The defects were examined macroscopically and microscopi- cally. The results of the histological examination 2 weeks after surgery showed that the osteochondral healing of the control group was significantly accelerated compared with that of the experimental group. However, the osteochondral healing of the experimental group 4 weeks and 16 weeks after surgery showed that healing accelerated significantly compared with that of the control group. The conclusion was that LLLT with an He-Ne laser could not significantly accelerate healing of a large osteochondral defect in rabbits of the experimental group compared with that of the control group throughout the dura- tion of the present study. Key words: articular cartilage, He-Ne laser, histology, histo- morphometry, knee, laser radiation, low-level laser therapy, osteochondral defect, rabbit, wound healing. INTRODUCTION Articular cartilage has a simple architecture composed of a unique type of cell, i.e., the chondrocyte, embedded in a dense extracellular matrix (ECM). Both the chondro- cyte and ECM distribute within successive cartilage lay- ers identified as superficial, transitional, radial, and calcified zones. The subchondral bone is located deep in the calcified zone. Articular chondrocytes in adults do not divide but help maintain the integrity of the cartilage through balanced synthetic and catabolic activities [1]. Cartilage lesions are classified as either full or partial thickness, depending on whether or not they extend to the subchondral bone [2]. Historically, articular cartilage has been considered to have only a weak capacity for repair, as reported by Hunter 250 years ago [3]. Researchers have generally accepted that those defects that penetrate the subchondral bone (full-thickness defects) are repaired with various tissues, from a fibrous tissue to fibrocartilage. However, the reparative tissue, even histologically hyaline-like cartilage, lacks the biomechanical capabili- ties to express some cartilage-specific molecules, and its Abbreviations: AED = architecture within entire defect, ECM = extracellular matrix, FD = filling of the defect, IRT = integration of repaired tissue, He-Ne = helium-neon, LLLT = low-level laser therapy, MS = matrix staining, TEM = transmission elec- tron microscopic, THP = total histological parameter. * Address all correspondence to Dr. Mohammad Bayat, Cellular and Molecular Biology Research Center, Medical Faculty, Shahid Beheshti University, MC, PO Box 19395/ 4719, Tehran, 1985717443, Iran; +98-21-2387-2502; fax: +98- 21-2243-9949. Email: bayat_m@yahoo.com DOI:10.1682/JRRD.2009.03.0035