Biomechanical and histological effects of intra-articular hyaluronic acid on anterior cruciate ligament in rats

BackgroundThe histologic and biomechanical effects of intra-articular hyaluronic acid on the anterior cruciate ligaments of rats were investigated.MethodsThirty rats were divided into three groups, i.e., the hyaluronic acid group, saline group, and control group. The hyaluronic acid and saline groups received a total of four intra-articular injections, whereas no injection was administered to the control group. The hyaluronic acid group was injected with 50 μg (0.05 cc) hyaluronic acid, and the saline group was injected with 50 μl (0.05 cc) of 0.9% sodium chloride solution. All of the rats were sacrificed on day 29 and the femur-anterior cruciate ligament–tibia complexes from the right knees were prepared, tested mechanically, and evaluated histologically.FindingsThe mode of failure involved the midsubstance of the anterior cruciate ligament in all the specimens. There were no statistically significant differences in the stiffness and ultimate load to failure values between the three groups (P > 0.05). The energy to failure values were evaluated and there was no statistically significant difference between the groups (P = 0.064, chi-square = 3.43). In the histologic analyses, there was a significant difference in the hyalinization values between the hyaluronic acid and saline groups (P = 0.029) and between the hyaluronic acid group and control groups (P = 0.029).InterpretationThe present study shows that intra-articularly delivered hyaluronic acid has no statistically significant effect on the tensile strength of the rat anterior cruciate ligament. Although hyalinization was increased, no difference was found on the other markers for degenerative changes. We conclude that intra-articular hyaluronic acid injections can be performed safely, although the use of a precise injection technique is recommended.