[Histological observation of tendon-bone healing after anterior cruciate ligament reconstruction by platelet-rich plasma combined with deproteinized bone of calf].

OBJECTIVE: The tendon-bone healing is the key point to ensure the success of the anterior cruciate ligament (ACL) reconstruction. To observe the histological change in the tendon-bone healing after ACL reconstruction by different concentrations of platelet-rich plasma (PRP) combined with deproteinized bone (DPB) of calf as bone tunnel infilling and to investigate the active effect of the complex on tendon-bone healing and to define the optimal concentration of PRP.

METHODS: Eight mL blood was drawn from central artery of New Zealand rabbit ears; PRP was prepared by Landesberg method, and liquid supernatant was used as thinner to prepare different concentrations of PRP (30%, 60%, and 100%). Fresh osteoepiphysis spongy bone was harvested from lower end of femur of newborn calf to prepare DPB by way of 30% H2O2 and ether alternating soaking for 24 hours continuous 6 times. DPB was soaked in different concentrations of PRP and mixed with activator to prepare the PRP/DPB complex. A total of 54 New Zealand white rabbits, aging 8-12 months, weighing (2.5 +/- 0.4) kg, were divided randomly into 3 groups: group A (30% PRP/DPB complex, n = 18), group B (60% PRP/DPB complex, n = 18), and group C (100% PRP/DPB complex, n = 18). The legs of the rabbits were randomly divided into experimental side and the control side; ACL was reconstructed by semitendinosus and PRP/DPB complex in bone tunnel in the experimental side, and only by semitendinosus in the control side. The general conditions of the rabbits were observed postoperatively and HE staining was used to observe the tendon-bone healing, then I-IV levels of semi-quantitative analysis of the tendon-bone healing were evaluated according to Demirag standard at 3, 6, and 12 weeks.

RESULTS: General observation: Synovial fluid slightly increased in the specimens and no bony tissue was found in inner of femoral tunnel at 3 weeks; there was no synovial fluid in all the specimens and scar tissue was discovered in inner of femoral tunnel at 6 weeks; and there was no synovial fluid and the tendons became tighter with fibrous tissue at 12 weeks. Histological observation: New granulation tissue formed in the tendon-bone interface of group A experimental sides at 3 weeks; there was various widths of Sharpey type textile fiber in the tendon-bone interface at 6 weeks; Sharpey type textile fiber arranged regularly, which formed an irregular and blur "tidal line" at 12 weeks. Group B experimental sides were better than any other group at 3, 6, and 12 weeks; chondrocyte-like arranged regularly in the tendon-bone interface at 3 weeks; the number of chondrocyte-like per unit area was more than that of the other groups at 6 weeks; and chondrocyte-like proliferated and matured in the tendon-bone interface, Sharpey type textile fiber became tighter and ordered. Group C experimental sides were similar to both sides of group A at 3 weeks, however, the proliferation of relatively mature dense connective tissue was worse than that of other groups at 6 and 12 weeks. According to Demirag grading, there were significant differences in tendon-bone healing between the experimental sides and the control sides of group B at 3 and 6 weeks, and between group B experimental sides and group C experimental sides at 12 weeks (P < 0.05).

CONCLUSION: The mixture of PRP/PRP has good biocompatibility and bone induction, so it can enhance tendon-bone healing after ACL reconstruction when the concentration of PRP is 60%.