Interspecies Variation in the Fibroblast Distribution of the Anterior Cruciate Ligament

Abstract

Background The future of the treatment of a ruptured anterior cruciate ligament is likely to involve cell-based therapies. These therapies are intrinsically dependent on the cellular distributions in the ligament. Thus, when selecting an animal model for testing of these new treatment methods, it is important to select a model that has similar cellular distributions to that of the normal human anterior cruciate ligament. Hypothesis There are interspecies differences in the histology of the anterior cruciate ligament. Study Design A descriptive histological study comparing the cell and vessel distribution of normal human anterior cruciate ligaments with that of 3 animal models and anterior cruciate ligaments from osteoarthritic human knees. Methods The histology of each of the anterior cruciate ligament sources was quantified in terms of cell number density, expression of α-smooth muscle actin, blood vessel density, and cell nuclear morphology using standardized histomorphometric techniques. Results The normal human anterior cruciate ligament was similar to the canine anterior cruciate ligament and the anterior cruciate ligament from patients with osteoarthritis with respect to cell density, blood vessel density, and cell nuclear shape. The normal anterior cruciate ligament had significantly fewer vessels than the bovine anterior cruciate ligament and rounder cells than the bovine and ovine anterior cruciate ligaments. Conclusions There is significant interspecies variation in the histology of the anterior cruciate ligament, with the canine anterior cruciate ligament most similar to the human anterior cruciate ligament. Clinical Relevance This finding may have an effect on the accuracy of testing of new, cell-based treatments for the ruptured anterior cruciate ligament, such as guided tissue regeneration.