Abstract
We evaluated the mechanical behavior of the repaired surfaces of defective articular cartilage in the intercondylar region of the rat femur after a hydrogel graft implant. The results were compared to those for the adjacent normal articular cartilage and for control surfaces where the defects remained empty. Hydrogel synthesized by blending poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate-co-acrylic acid) was implanted in male Wistar rats. The animals were divided into five groups with postoperative follow-up periods of 3, 5, 8, 12 and 16 weeks. Indentation tests were performed on the neoformed surfaces in the knee joint (with or without a hydrogel implant) and on adjacent articular cartilage in order to assess the mechanical properties of the newly formed surface. Kruskal-Wallis analysis indicated that the mechanical behavior of the neoformed surfaces was significantly different from that of normal cartilage. Histological analysis of the repaired defects showed that the hydrogel implant filled the defect with no signs of inflammation as it was well anchored to the surrounding tissues, resulting in a newly formed articular surface. In the case of empty control defects, osseous tissue grew inside the defects and fibrous tissue formed on the articular surface of the defects. The repaired surface of the hydrogel implant was more compliant than normal articular cartilage throughout the 16 weeks following the operation, whereas the fibrous tissue that formed postoperatively over the empty defect was stiffer than normal articular cartilage after 5 weeks. This stiffness started to decrease 16 weeks after the operation, probably due to tissue degeneration. Thus, from the biomechanical and histological point of view, the hydrogel implant improved the articular surface repair.
Highlights
Different synthetic and biological materials have been studied for use in the repair of osteochondral defects [1,2,3,4,5,6], but to date no method has been reliable in restoring a functional articular surface
The repaired surface of the hydrogel implant was more compliant than normal articular cartilage throughout the 16 weeks following the operation, whereas the fibrous tissue that formed postoperatively over the empty defect was stiffer than normal articular cartilage after 5 weeks
In the present study we chose to use the model used by Kempson et al [12] and the results obtained showed that the mechanical performance of the repaired surfaces of control and hydrogel graft implants differed from that of hyaline cartilage
Summary
Different synthetic and biological materials have been studied for use in the repair of osteochondral defects [1,2,3,4,5,6], but to date no method has been reliable in restoring a functional articular surface. In addition to being compliant, when implanted hydrogels allow the normal flow of body fluids responsible for cell maintenance. Since they are physically similar to soft tissues, especially articular cartilage, these gels have appropriate mechanical properties and may be used as a graft for the repair of articular cartilage defects. Their surface and functional properties should provide the necessary mechanical support for the joint [10]
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