Elsevier

Biomaterials

Volume 29, Issue 3, January 2008, Pages 266-271
Biomaterials

β-TCP bone graft substitutes in a bilateral rabbit tibial defect model

https://doi.org/10.1016/j.biomaterials.2007.09.035Get rights and content

Abstract

The use of artificial bone graft substitutes has increased as the surgical applications widen and the availability of allograft bone decreases. The ideal graft substitute should reabsorb with time to allow and encourage new bone formation whilst maintaining its properties as an osteoconductive scaffold until it is no longer required. A potential disadvantage of some synthetic substitutes is their long dissolution time. Beta-tricalcium phosphates (β-TCPs) have some advantages when compared to hydroxyapatite (HA), when used as a filler, in that it is more rapidly reabsorbed.

Three commercially available and clinically used β-TCP bone graft substitutes with the same chemistry (Vitoss, Osferion, Chronos) but with varying macro and microscopic characteristics were investigated using a bilateral tibial metaphyseal defect model in New Zealand white rabbits. When placed into tibial defects all three materials performed similarly in terms of mechanical properties of the healing defects. A decrease in properties was found at 12 weeks where implant resorption was nearly achieved while remodelling of the anteromedial cortex had yet to be completed. All materials were osteoconductive and supported new bone formation while implant resorption with time differed between materials. Vitoss resorbed faster than the other materials and is likely to differences in particle geometry, pore structure and interconnectivity.

Introduction

Bone grafting is a vital component in many surgical procedures to facilitate the repair of bone defects or fusions [1], [2], [3]. Autogenous bone remains the “gold standard” when available. Calcium-based bone graft substitutes, however, provide surgeons with an alternative or an additional material to graft the site and participate in the healing process. A potential limitation of hydroxyapatite (HA) bone graft substitutes is their low solubility [4], [5] and slow in vivo resorption profiles [6], [7], [8], [9]. While these materials provide an osteoconductive matrix for bone ingrowth and ongrowth, long-term presence can potentially limit bone formation and make accurate radiological assessments of new bone or healing difficult.

The ideal bone void filler should provide a three-dimensional matrix to support osteoblasts and pre-cursor cells and ultimately bone ingrowth or ongrowth during resorption and healing. A number of beta-tricalcium phosphates (β-TCP) bone graft substitutes have been reported in animal [9], [10], [11], [12], [13] as well as human studies [14], [15], [16], [17]. The in vivo performance of these materials is related, in part, to the chemistry, porosity and density [18], [19], [20], [21], [22], [23], [24], [25]. While the chemistry of β-TCP is similar or nearly identical amongst manufacturers, differences in particle geometry, porosity and pore distribution may influence the in vivo response. Direct comparisons of β-TCPs in granular have not been well reported. This study evaluated bone formation and implant resorption of three β-TCP bone graft substitutes of similar chemistry but different porosity in granular form in a standardized bilateral tibial defect model in New Zealand white rabbits [9], [10].

Section snippets

Methods

Bilateral defects (5 mm wide and 15 mm long) spanning the metaphyseal and diaphyseal region were created 3 mm below the joint line in the anteromedial cortex of the proximal tibia in 66 skeletally mature (3.0 kg) New Zealand white rabbits following ethical approval as previously reported [9], [10]. Defects were created using a micro burr (Linvatec, Key Largo, FL) with a 3 mm diameter tip under saline irrigation. The defects were flushed with sterile saline prior to being filled with the three β-TCP

Results

Faxitron radiographs (Fig. 1), micro CT (Fig. 2) and back scattering electron imaging (Fig. 3) of the materials alone at time zero revealed marked differences between Osferion, Vitoss and Chronos. Vitoss had the most open structure followed by Osferion and Chronos. The Chronos was the most radioopaque followed by Osferion and Vitoss. FTIR spectra however presented similar patterns for all three materials consistent with pure β-TCP (Fig. 4).

Surgical handling of the materials was found to be

Discussion

Bone graft substitutes provide surgeons with alternatives for grafting of bony defects and fusions. This is becoming increasingly important given the scarcity of allograft material and the perceived risks of infection transmission. The surgeon should be concerned with the mechanical and biological properties of the material as well as the handling and ability to assess healing of the grafted site. Osferion and Chronos had similar handling characteristics and were applied to the defect site

Conclusion

This study examined the in vivo response of the β-TCPs alone, without the addition of any growth factor or local autograft. The performance of these materials in such combinations represents another clinical use. β-TCPs could also be used as carriers for bioactive molecules. We chose to examine each material alone to allow a direct comparison of the materials themselves. All three β-TCPs demonstrated osteoconductive behavior and resulted in successful defect healing. There were differences in

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