Repair Of Avascular Meniscal Injuries Using Meniscal Fragments

Objectives:1. To investigate the bilogical viability of the meniscal fragments with different size under subcutaneous environment.2. To investigate whether the implantation of juvenile and adult minced meniscal fragments could improve the healing of avascular meniscal injuries.Methods:1. Medial menisci were harvested from both knee of rabbits, and the inner two third of which were minced into different size:0.5mm×0.5mm×0.5mm (Group A), and1.0mm×1.0mm×1.0mm (Group B), and2.0mm×2.0mm×2.0mm (Group C). The meniscal fragments were packed into the fascia sheath and then implanted into the subcutaneous pockets. At1,2,3weeks after implantation, the meniscal fragments were harvested and cell migration was investigated by confocal laser scanning microscope and hematoxylin and eosin staining. At3weeks after implantation, aggrecan was detected using Safranin O and Fast Green staining, Collagen Ⅰ and Collagen Ⅱ and PCNA were evaluated by immunohistochemistry.2. Cylindrical explants (diameter:8mm, height:3mm) were excised from the inner two-thirds of adult swine menisci, and a4-mm-diameter inner cylinder was removed from the center. The inner cylinder was cut horizontally into three equal parts, forming a sandwich structure that was reinserted with the middle part substituted by minced juvenile meniscal fragments (0.5mm×0.5mm×0.5mm)(Group A), juvenile meniscal columns (Group B), minced mature meniscal fragments (0.5mm×0.5mm×0.5mm)(Group C), or mature meniscal columns (Group D). Explants were cultured for2,4, or6weeks. At each time point, explants were evaluated by confocal laser scanning microscope, and assessed by histological evaluation. At6weeks, repair tissue were analyzed by Safranin O/fast green staining, picosirius red staining&polarized light microscopy and type Ⅰ and Ⅱ collagen immunohistochemistry.3. Avascular meniscal defect was made in the inner two-thirds of the body of medial meniscus in adult rabbits. They are randomly divided into four groups, in Group A, juvenile meniscal fragments (0.5mm×0.5mm×0.5mm) were implanted into the defects; Group B, juvenile meniscal colmns; Group C:the adult meniscal fragments (0.5mm×0.5mm×0.5mm); Group D:the adult meniscal column. At4weeks,8weeks after implantation, meniscal repair was assessed by gross evaluation and histology.Results:1. Confocal laser scanning microscope results showed cell migration to surface of the rabbit meniscal fragments increased along with the time (P<0.05) and was highest in Group A, followed by Group B, then Group C (P<0.05). HE staing confirmed the cell migration. At3weeks after implantation, immunohistochemistry results showed that level of Collagen Ⅰ and Collagen Ⅱ and expression of PCNA was highest in Group A, followed by Group B, then Group C (P<0.05), but aggrecan content remained at the same level.2. In swine meniscus in vitro organ culture model, Confocal laser scanning microscopy results showed that cells clearly had accumulated at the surface of both parts and increased along with the culture time (P <0.05). Cell accumulation was highest in Group A, followed by Groups B, C, and D (P<0.05). In HE stained sections, The interfaces of periphery and between the fragments were evaluated respectively. In the interfaces of periphery, there were significant differences at each time point among all groups (P<0.05). Healing increased over time. There were significant differences in groups A, B, C and D among all time points (P<0.05). At the interface between the fragments in Group A and Group C, there were significant differences among all time points (P<0.05), and the scores in Group A were higher than Group C at all time point (P<0.05). At6weeks, Safranin O/fast green staining, picosirius red staining&polarized light microscopy and type Ⅰ and Ⅱ collagen immunohistochemistry showed the coexistence of type Ⅰ and Ⅱ collagens in the extracellular matrix (ECM) of the peripheral interface in Groups A, B, and C but not in Group D.3. In rabbits, meniscal repair was assessed by gross evaluation and histology. The semi-quantitative score of gross evaluation and histology was best in Group A, followed by Groups B, C, and D at all time point (P<0.05). There were significant differences at each time point among all groups (P<0.05).Conclusion:1. Meniscal fragments were viable after short term percutaneous implantation. There was an inverse relationship between the biological viability of the fibrochondrocytes and meniscal fragment size.2. Implantation of minced meniscal fragments could increase the healing of avascular meniscal injury in vitro and in vivo. Implantation of juvenile meniscal fragments showed better healing than adult meniscal fragments.