David R. Sarver

Bioabsorbable polymer science for the practicing surgeon.

The structure and function relationships of polymers have long been the purview of engineers and polymer chemists. As bioabsorbable polymer implants continue to make inroads in the medical implant armamentarium, surgeons, long familiar with the properties and handling characterisitcs of metal implants, may find it advantageous to become aware of some of the unique characteristics of these types of materials so that an informed decision can be made regarding their usage. In this article, we present, in relatively nontechnical terms, the salient features of polymers in general and absorbable polymers in particular.

Bioabsorbable fixation devices: status for the craniomaxillofacial surgeon.

With time, more and more types of medical devices become available to assist the surgeon in managing patients. Bioabsorbable fixation devices, which have been directed toward the orthopedic surgeon over the past 10 years, are but one example. One aim of this article is to present the current status of bioabsorbable devices in medical practice to the craniomaxillofacial surgeon who may not be aware of the inroads this technology has made. A bioabsorbable fixation system has become available for use by the craniomaxillofacial surgeon, which is described. A further aim of this article is to present concisely the testing rigor required of such devices before their introduction to the U. S. market. This has the added benefit of explaining the important role of the surgeon in developing and helping reduce to standard clinical practice the use of new technologies.

BIORESORBABLE IMPLANTS - PRACTICAL CONSIDERATIONS

Traditional metal implants, primarily used for internal fixation, have been used by the orthopedic surgeon for years. Decades of development have produced such devices for almost every conceivable need. Despite their widespread use, a relatively consistent set of problems or issues have been identified. These include the potential for long term migration, breakage, stress shielding, reaction to the material, interference with standard imaging techniques, and growth restriction in young patients. A number of bioresorbable polymer devices have recently become available to create a viable alternative for some indications. As expected with an evolving technology, solving one set of problems has engendered another. One of the most limiting aspects of bioresorbable polymers is their inherently lower strength compared to metals. Although more of an issue with some materials and applications than others, significant tissue reactions have been observed in some cases as well. This paper discusses the field of synthetic bioresorbable polymers in general, but with specific reference to those materials and devices that can be used in place of metal implants for internal fixation.

Effect of simulated intraoperative Heating and shaping on mechanical properties of a bioabsorbable fracture plate material

Heating bioabsorbable fracture fixation plates to above their glass transition temperature renders them temporarily malleable, thus facilitating their adaptation to the underlying bone geometry, although the consequence of heating is not well understood. Poly (L-lactide-co-glycolide) copolymer specimens were heated under various conditions, and the effects on specimen mechanics were assessed. Heating temporarily increased toughness while slight reducing flexural modulus. No lasting effects on in vitro material degradation were seen.

A comparative biomechanical analysis of resorbable rigid fixation versus titanium rigid fixation of metacarpal fractures.

Linear (two-dimensional) and three-dimensional (3D) plating systems (Poly-Medics) composed of the resorbable copolymer of polyglycolic acid (PGA) and poly-I-lactic acid (PLLA) (Lactosorb) were studied in vitro. The plates were applied to osteotomized fresh frozen human cadaveric metacarpal bones that were then tested for torsional rigidity and three-point bending strength and rigidity. The results were compared to those from another study of two low-profile titanium plating systems (Leibinger and Synthes). Analysis of variance revealed that the linear-flat Lactosorb plate and screws had apex dorsal rigidity and force-to-displacement measurements equal to all but two of the titanium plates (3D). The 3D-flat Lactosorb plate had the highest torsional rigidity of the resorbable system, but it was only moderately rigid compared to the titanium plating systems. This in vitro biomechanical study of the copolymer PGA-PLLA plating system indicates that, in clinical applications, it may be better suited for metacarpal fractures rather than proximal phalangeal fractures due to the lower demands of torsional loading compared to apex bending.