Early clinical and radiographic outcomes of trabecular metal total ankle using transfibular approach

Abstract

Musculoskeletal conditions are the most commonly occurring medical conditions, and they have a considerable influence on the quality of health and living standard of the millions of people across the world. Annually, around the globe, approximately 2.3 million bone-tissue graft transplants are performed. The bone fracture, osteoporosis, osteoarthritis, and various neoplastic disorders are the common clinical problems related with bone and skeletal system. The common approaches to these bone problems are autografts or allografts. These protocols have certain limitations such as resorption, donor site morbidity, compromised supply, rejection rate up to 50% at some sites, and the risk of inducing transmissible diseases. Consequently, considerable attention has been directed toward the use of bioactive materials as synthetic grafts for bone regeneration. These include hydroxyapatite (HAP), tricalcium phosphate, bioactive glass, and glass ceramics. More significantly, calcium phosphates are the major constituent of bone mineral. The most extensively used synthetic calcium phosphate ceramic for bone replacement is HAP with a chemical formula of Ca10(PO4)6(OH)2. It has Ca:P molar ratio of 1.667 and is regarded as the most stable composition compared to other calcium phosphate ceramic within a pH range of 4.2–8.0. Calcium phosphate cement is one of the most important types of bioceramic material. In combination with various calcium phosphates, an injectable paste can be formed, which is cured over a period of time, in which resultant product is a carbonate apatite. The cements cure in situ and are gradually resorbed and replaced by a newly formed bone. The concept of a bioactive glass was pioneered by Hench and colleagues. The composition of Bioglass is a series of special designed glasses, consisting of a Na2O–CaO–SiO2 glass with the addition of P2O5, B2O3, and CaF2. A biologically active hydroxycarbonate apatite layer is formed on the surface of bioactive glasses in vitro and in vivo. The chemical properties could be controlled in bioactive glasses and eventually its bonding to tissue. Certain specialized compositions of Bioglass (e.g., 45S5) can bond to soft tissue as well as bone, in either bulk or particulate form. Moreover, apatite-wollastonite glass-ceramic, with an assembly of small apatite particles effectively reinforced by β-wollastonite exhibit not only bioactivity, but also a fairly high mechanical strength. Mechanical properties like the bending strength, toughness against fracture, and Young’s modulus of A-W glass-ceramic are the highest among bioactive glasses and glass-ceramics enabling it to be used in some compression load-bearing applications. Overall, the advantages of bioactive glasses are the magnitude of their surface reactivity and the ability to change the chemical composition, thus facilitating bonding with variety of tissues. Mechanical properties are the drawback as these materials have relatively low bending strength in comparison to other ceramic materials. The bioactive calcium phosphate ceramics, bioglasses, and glass-ceramics form a mechanically strong interfacial bond with bone. The strength of the bond is normally equivalent to or greater than the strength of the host bone, depending on test conditions. Therefore, all of these materials have excellent bioactivity. Nevertheless, bioactive ceramics have a flexural strength, strain-to-failure, and fracture toughness, which is less than the bone and the elastic modulus is greater than the bone. In other words, most bioactive materials have a less-than-optimal biomechanical compatibility when used in load-bearing applications. An approach to mitigate this problem involves designing and structural tailoring of bioactive composites. The concept of matching the mechanical behavior of an implant, with the tissue to be replaced in order to solve the problem of stress shielding of conventional biomaterials, was proposed by Bonfield et al. Thus, the composite approach can significantly meet the challenge of a long life, as a demand for the new-generation implant materials. Calcium phosphate ceramics, bioglasses, and glass ceramics are generally considered to be bone bioactive ceramics. These materials generally get bonded to the surrounding osseous tissue and enhance further bone-tissue formation. The direct bone bonding to bioactive glasses was first observed and reported by Hench et al., since then considerable progress has been made in understanding the basic mechanism of the formation of bone and biomaterial bond and its effect on bone formation.