Zimmerman M, Parsons J R, Alexander H
University of Medicine and Dentistry of New Jersey, Newark.
J Biomed Mater Res. 1987 Dec;21(A3 Suppl):345-61.
During the early stages of fracture healing, rigid internal fixation maintains alignment and promotes primary osseous union. Unfortunately, as healing progresses rigid fixation from bone plating can cause bone in the region of the plate to undergo stress protection atrophy. This can result in significant loss of bone mass and osteoporosis. Refracture of the bone upon device removal is a widely reported complication. In an effort to minimize or eliminate stress protection atrophy, we have designed a partially absorbable, fiber-reinforced bone plate. Ideally, such a plate gradually loses rigidity as the fracture heals, increasingly transferring stress to the bone. Stress protection may be avoided and removal of the device after healing may be unnecessary. Composite theory was used to determine an optimum fiber layup for a composite bone plate. Composite analysis suggested the mechanical superiority of a 0 degree/ +/ -45 degree laminae layup. Given this laminated design, a thermoplastic absorbable polymer (polylactic acid polymer) was reinforced with high-modulus carbon fiber to produce a semiabsorbable composite. Implant evaluation included optimizing fabrication techniques, thorough mechanical device testing, and implantation on canine femurs to determine biocompatibility and efficacy. The composite design proved to have superior static and fatigue properties to laminated or random fiber designs used previously. Two techniques for hole fabrication were tested. The production of screw holes during the molding process rather than machining postmolding, improved the mechanical integrity of the finished plate. Although the 0 degree/ +/- 45 degree carbon/polylactic acid composite possessed superior mechanical properties, it was unsuccessful in the in vivo environment. Water absorption and subsequent delamination made the plate flexible. Hypertrophic nonunions developed. Further development to prevent water intrusion and premature loss of mechanical properties is necessary.
在骨折愈合的早期阶段，坚强内固定可维持骨折对线并促进一期骨愈合。不幸的是，随着愈合过程的推进，接骨板的坚强固定会导致接骨板区域的骨质发生应力遮挡性萎缩。这会导致大量骨质丢失和骨质疏松。取出内固定装置后骨再骨折是一种广泛报道的并发症。为了尽量减少或消除应力遮挡性萎缩，我们设计了一种部分可吸收的纤维增强接骨板。理想情况下，随着骨折愈合，这种接骨板的刚度会逐渐降低，越来越多地将应力传递至骨骼。这样可以避免应力遮挡，愈合后可能无需取出内固定装置。采用复合材料理论来确定复合接骨板的最佳纤维铺层。复合材料分析表明，0度/±45度层合铺层具有力学优势。基于这种层压设计，用高模量碳纤维增强热塑性可吸收聚合物（聚乳酸聚合物）以制成半可吸收复合材料。植入物评估包括优化制造技术、全面的力学性能测试以及植入犬股骨以确定生物相容性和有效性。结果证明，这种复合设计在静态和疲劳性能方面优于先前使用的层压或随机纤维设计。测试了两种制孔技术。在成型过程中而非成型后加工制造螺孔，提高了成品接骨板的机械完整性。尽管0度/±45度碳/聚乳酸复合材料具有优异的力学性能，但在体内环境中并不成功。吸水及随后的分层使接骨板变软。出现了肥大性骨不连。有必要进一步改进以防止水侵入和过早丧失力学性能。
