Georgiev et al. BMC Musculoskeletal Disorders 2010, 11:117 http://www.biomedcentral.com/1471-2474/11/117 Open Access RESEARCH ARTICLE © 2010 Georgiev et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Research article Histological and ultrastructural evaluation of the early healing of the lateral collateral ligament epiligament tissue in a rat knee model Georgi P Georgiev* 1 , Nikolai K Vidinov 1 and Plamen S Kinov 2 Abstract Background: In this study, we evaluated the changes which occurred in the epiligament, an enveloping tissue of the ligament, during the ligament healing. We assessed the association of epiligament elements that could be involved in ligament healing. Methods: Thirty-two 8-month old male Wistar rats were used in this study. In twenty-four of them the lateral collateral ligament of the knee joint was surgically transected and was allowed to heal spontaneously. The evaluation of the epiligament healing included light microscopy and transmission electron microscopy. Results: At the eight, sixteenth and thirtieth day after injury, the animals were sacrificed and the ligaments were examined. Our results revealed that on the eight and sixteenth day post-injury the epiligament tissue is not completely regenerated. Till the thirtieth day after injury the epiligament is similar to normal, but not fully restored. Conclusion: Our study offered a more complete description of the epiligament healing process and defined its important role in ligament healing. Thus, we provided a base for new strategies in ligament treatment. Background The incidence of knee ligament injuries has increased in recent years due to the general public's increase in sports activities [1-4]. Ligaments have been defined as dense bands of connective tissue that stabilize joints and guide joint motion [5,6]. After injury, ligaments do not heal by regeneration but by a formation of scar tissue similar to other wound healing models [6]. The normal and healing ligaments are composed of two major components: the extracellular matrix composed commonly of type I colla- gen and ligament cells [6,7]. Most studies investigated an insufficient repair process and tested different treatments regimes, including tissue engineering approaches, non- steroidal anti-inflammatory drugs, local corticosteroids, hyperbaric oxygen, growth factors, ultrasonic or electri- cal stimulation, laser therapy and also gene therapy [2,5,8,9]. However, mainly the animal models have gone into characterizing the extracellular matrix in both nor- mal and injured ligaments [4,6,11-14], and only few of them have examined the ligament cells composed the enveloping tissue of the ligament, termed epiligament (EL) [6,8]. According to our opinion, the understanding of the healing process in the EL tissue could be essential in understanding the normal recovery in ligament and provide a basis for new treatment strategies. Therefore, we aimed to investigate both with light microscopy and transmission electron microscopy (TEM) the EL changes from the midsubstance of the lateral collateral ligament (LCL), which occurred through the early ligament healing and their possible role in restoration of the ligament. Methods Thirty-two 8-month old male Wistar rats, with weight ranges of 350 - 400 g at the time of surgery, were used for this study after approval was obtained from the Univer- sity Committee on Animal Resources. These rats were divided in four groups, each group including eight ani- mals. The last group of animals underwent no transec- tion and served as intact controls. Twenty-four rats were anesthetized by intraperitoneal injection using a mixture of 5 mg/kg b.w. Xylasine (Bio- * Correspondence: georgievgp@yahoo.com 1 Department of Anatomy, Histology and Embryology, Medical University Sofia, Bulgaria Full list of author information is available at the end of the article