Orthopaedic fixations

Polylactides have a high modulus that makes them more suitable for load bearing applications such as in orthopaedic fixation and sutures. 

The homopolymer of the L-lactide (PLLA) exhibits high tensile strength (50-70 MPa) and low elongation ( 4%), and consequently has a high modulus (3 GPa)," which makes it suitable for load-bearing applications such as orthopaedic fixation and sutures. PLLA is partially crystallisable with a melting temperature of 175-178 °C and a glass transition temperature... 

Biodegradable synthetic polymers such as poly(glycolic acid), poly(lactic acid) and their copolymers, and copolymers of trimethylene carbonate and glycolide have been used in a number of clinical applications [26-30]. The major applications include resorbable sutures, drug delivery systems and orthopaedic fixation devices such as pins, rods and screws [31, 32]. 

PLA can be processed by extrusion, thermoforming, injection, blow moulding, fibre spinning or stretehing. It is printable and heat sealable. The actual or potential applications are found in the crop and food sectors (films, food packaging, soft drinks) and for non-woven materials in hygienic products. The properties of biocompatibility and of bioresorption of PLA permits the development of suture threads and ehps, orthopaedic fixations (screws, pins) and of resorbable implants (Clarinval, 2002). Some of the main products are given below. 

In 2003, an up-to-date summary of studies was edited by Epinette and Manley (2003), describing the state-of-the-art of hydroxyapatite coatings in orthopaedics as this stood at the close of 2002. This compilation of results was designed to help to answer the still somewhat hotly debated question of whether the favourable results achieved in the short term with this method of biologic fixation of total joint implants has withstood the test of time. The goal of Epinette and Manley s book was mainly to determine if the use of hydroxyapatite coatings for the fixation of orthopaedic implants to bone has been proven by the survivorship and satisfaction of those patients who had received hip and knee implants. 

Bostman, O. and PMajamaki, H. Clinical biocompatibUity of biodegradable orthopaedic implants for internal fixation a review. Biomater 2000,21(24), 2615-2621. 

Jacob, E., et al., 1993. Evaluation of biodegradable cefazolin sodium microspheres for the prevention of infection in rabbits with experimental open tibial fractures stabilized with internal-fixation. Journal of Orthopaedic Research 11 (3), 404—411. 

Ducheyne, P. 1984. Biological fixation of implants, in Functional Behavior of Orthopaedic Biomaterials, G.W Hastings and P. Ducheyne, Eds. CRC Press, Boca Raton, FL. 

Friedman, R.F., Black, J., Galante, J.O. et al., 1994. Current concepts in orthopaedic biomaterials and implant fixation. In Instructional Course Lectures, J.M. Schafer (Ed.), pp. 233-255. The American Academy of Orthopaedic Surgeons. 

Perren, S.M., 1989. The biomechnics and biology of internal fixation using plates and nails. Orthopaedics 12 21. 

Key words orthopaedic, implant fixation, fracture healing, viscosupplementation, bone morphogenic protein. 

Majola, A., Vainionpaa, S., Vihtonen, K. et a/. (1991) Absorption, biocompatibility, and fixation properties of polylactic add in bone tissue An experimental study in rats. Clinical Orthopaedics and Related Research 268, 260-269. 

Clearly, a need exists to develop an optimum polymer/bone interface which will provide a direct, stable, permanent fixation in hard tissue for both present and future polymeric components in orthopaedic prostheses. This need provided a strong incentive to pursue the present study on surface activation and to investigate the development of methods of creating hydroxyapatite-like surfaces on polyethylene, the currently used orthopaedic polymer. The surface activation entailed the selective surface phosphonylation of polymeric films made of polyethylene and nylon-12. Nylon-12 was chosen as a representative heterochain polymer whose chain structure closely resembles polyethylene and yet contains hydrolyzable functionalities similar to those of nylon-6, a widely used biomaterial. To study the biocompatibility of a typical new surface, the current study also involved the interaction of a modified polyethylene film with fibroblasts and hydroxyapatite salt solution. 

Greene, AH., Bumgardner, JD., Yang, Y, Moseley, J., Haggard, WO. 2008. Chitosan-coated stainless steel screws for fixation in contaminated fractures. Clinical Orthopaedics and Related Research 466 1699-1704. 

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