Abstract
Wire cerclage remains the standard method of care for sternal fixation, following median sternotomy, despite being beset with complications. An emerging treatment option has been to augment the wires with an adhesive. A patented ionomeric glass (mole fraction: SiO2:0.48, ZnO:0.36, CaO:0.12, SrO:0.04) has been used to formulate GPC+, a glass polyalkenoate cement (GPC), by mixing it with poly(acrylic) acid (PAA) and de-ionized water. In a human cadaver study, this material, when applied with wire cerclage, was able to significantly reduce sternal instability. However, the material has yet to be tested in pertinent animal models. Here, after a series of physical and mechanical tests to confirm suitability of the experimental material for implantation, three samples of GPC+ were implanted in either the tibia or femur of three different rabbits, alongside sham defects, for two different time modalities. A further seven samples of GPC+ and one poly(methyl methacrylate) control (PMMA) were implanted in either the tibia or femur of two different sheep. The sheep containing the PMMA was sacrificed at 8 weeks and the other at 16 weeks, to evaluate time dependent biological response. Upon sacrifice, microCT images were acquired and histology slides prepared for analysis. All three GPC+ samples implanted in the rabbit model, for the two time modalities, were characterized by minimal bone resorption along with a mild inflammatory response. Five of the seven GPC+ materials implanted in the sheep model (all three implanted for 8 weeks and two of those implanted for 16 weeks) were associated with mild to moderate immune response, comparable to that observed with PMMA, as well as mild bone resorption. The remaining two GPC + materials (implanted in the sheep model for 16 weeks) exhibited no bone resorption or inflammatory response and appeared to stimulate increased bone density at the implant site. These results suggest that GPC + can be a viable bone adhesive for use in hard tissue applications such as sternal fixation and stabilization.Experiments performed to synthesize & test Sr-doped glass adhesive for sternal fixation. (1) Sr-doped ionomeric glass fired, ground down and mixed with aqueous polyacrylic acid to produce the adhesive. (2) Adhesive characterized and tested by a suite of laboratory-based tests to ensure suitability for implantation. (3) Adhesive implanted into a rabbit model (distal femur, 12 weeks post implantation) where micro-CT images confirmed an excellent bone/cement interface, no evidence of bone resorption and some bone remodelling. (4) Adhesive subsequently implanted into a sheep model; at 16-weeks, a continuous bone—adhesive interface is seen suggesting no bone resorption. There was an increase in the peri-implant radiodensity, suggesting enhanced mineral content of the bone surrounding the GPC+ implant.
Highlights
Median sternotomy, first introduced in 1953 [1], is the standard method of care to gain access to the heart and large vessels with ~700,000 procedures carried out annually in the US alone [2]
The handling properties of this specific batch of glass polyalkenoate cement (GPC)+ were in line with those reported for the same material previously [19, 44, 45] and deemed suitable for sternal augmentation by a cardiac surgeon
There was a slightly more variable response to the GPC+ implants in sheep. This variability could be attributed to difficulties in respect to drilling into the harder sheep bone, which can be twice as dense as human bone [42], thereby increasing the opportunity for thermal bone injury, which could have prompted more remodelling than was observed in the rabbit model
Summary
First introduced in 1953 [1], is the standard method of care to gain access to the heart and large vessels with ~700,000 procedures carried out annually in the US alone [2]. In which stainless steel wires are tightened across the manubrium and in between the rib spaces is the most commonly used method This procedure can result in significant complications [3] including wires cutting through the apposed tissues, infections and postoperative pain; the latter arising from micromotion between the sternal halves, which can be exacerbated by physiological forces such as a cough or a sneeze. Sternal dehiscence can occur in up to 5% of patients, exacerbated by risk factors including obesity, diabetes, smoking, and osteoporosis [6]. Such dehiscence is directly linked to deep sternal wound infection and has been associated with a mortality rate of up to 47% [7]. As a result of these complications, alternative sternal fixation and stabilization methods, such as the use of bone cement, are being investigated
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