| BackgroundAnterior cruciate ligament (ACL) is the important ligament of the knee, which maintains the anterior-posterior and lateral stability of the knee, however, ACL is the most easily injured ligament of the knee. Arthroscopic ACL reconstruction is the standard mini-invasive treatment for ACL injury, however, the ratio of ACL revision is as high as 10%?20%. Magnesium is a degradable implanted material. When magnesium degrades, it will form abundant Mg2+ surrounding environment, which could regulate the bone derived cell signal transduction pathway, stimulate osteoblast cells, improve the adhesion rate of osteoblast cells, restrain the activity of the osteoclast cells. However, on one hand, magnesium and its alloy degrade rapidly in the cell culture fluid and have large PH value change, which is potentially harmful to the cells growth surrounding the material. On the other, magnesium and its alloy will produce hydrogen after they are implanted into the body. If magnesium is implanted into the bone tissue and lead to osteolysis,due to the produced hydrogen. Thus, it will affect the tendon-bone healing.AimsThe aim of this study was to induce the bone growth between the surrounding bone and the transplanted tendon graft trough accommodating BMP-2 into the porous section of the ZK60 magnesium alloy Rigid-fix nail, which could accomplish the early tendon-bone healing. Thus, this study would provide the reliable experimental and theoretical support the magnesium metal applied in the sports medicine.Material and MethodThree female healthy beagle dogs were chonsen and performed with ACL recostructio,whicn was harvested right ACL tunnel and nailtunnel with the standard ACL reconstruction process. Thus, the size of the ZK60 magnesium alloy Rigid-fix nail was determined as ?2* 12mm, which was fabricated to be porous with the laser drilling method. The porous Rigid-fix nail was then performed with three point bending test. Eighteen female healthy beagle dogs were chonsen. The ACL reconstruction was done with the flexor digitorum longus tendon autograft and was classified to be three groups according to the different infixations as follows:porous ZK60 magnesium alloy Rigid-fix nail compounded with BMP-2 (BMP-2 group) as the experimental group; porous ZK60 magnesium alloy Rigid-fix nail group (porous group); and no porous ZK60 magnesium alloy Rigid-fix nail group (no porous group) as control groups. X-ray, CT scan and MRI examination performed on every animal at the post fourth day, the fourth week, the eighth week and the twelfth week, which was to observe the dynamic bone growth surrounding the implantation. All the animals were killed and the knee joints were harvested, which were done with pull-out test, hard tissue histology, Giemsa and toluidine blue dyeing and energy spectrum analysis to further detennine the element of the new growth bone surrounding the implantation.ResultThe position of the Rigid-fix nail was perfect at on the fourth day postoperatively. There is significant new bone growth surrounding the Rigid-fix nail on the eighth week postoperatively and the new growth bone has been almost full with the bone tunnel, while the Rigid-fix nail has almost degraded. With the degradation of the Rigid-fix nail, the surrounding new bone was gradually formed and finally two new growth bone nail was formed around the implantation. The CT value of the BMP-2 group is significantly higher than that of the other two groups on the eighth week postoperatively, which has become to be comparable on the twelfth week postoperatively. The result of the pull-out test demonstrated that BMP-2 group was significantly higher than that of the other two groups. The result of pull-out test demonstrated that the contact strength between the implantation and the surrounding bone in the BMP-2 group is significantly higher than that in the porous group and no porous group. At the 12thW postoperatively, the histology demonstrated that the implantation in the porous group and no porous group has already degraded completely. However, the new growth bone was found between the implantation and the surrounding bone in the BMP-2 group. SEM demonstrated that the implantation has almost degraded in the BMP-2 group and the surrounding new growth bone was found. The implantation in the other two groups has already degraded completely and the hole was generated. EDS demonstrated that the element of the new tissue was Ca and P, which was supposed to be new growth bone.ConclusionThe porous ZK60 magnesium alloy Rigid-fix nail was used to infix the graft during the ACL reconstruction. With the new growth bone nails formed, the single Rigid-fix nail infixation was transferred into two new growth bone nails infixation which was belonged to the biological infixation. In the porous Rigid-fix nail compounded with BMP-2 group, the new bone growth was significantly found surrounding the implantation on the eighth week postoperatively and accomplished the early tendon-bone healing. Therefore, the novel porous ZK60 magnesium alloy Rigid-fix nail could be used as an infixation during the ACL reconstruction surgery, which was supposed to promote tendon-bone healing. |
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