Abstract
Aim
A gentamicin-eluting biocomposite consisting of hydroxyapatite (HA) and calcium sulphate (CaS)*1 can provide effective dead space management and bone formation in chronic osteomyelitis. However, radiographic follow-up after implantation of this biomaterial has shown imaging features previously not described with other comparable bone graft substitutes. Last year we presented preliminary results with a follow-up of 6 months. Now we present the radiographic, µCT and histological one-year follow-up of the critical-size bone defect model in sheep. The aim of this study was to simulate the clinical situation in a large animal model to correlate different imaging techniques used in the clinic (Radiography, CT and MRI scans) with histological finding.
Methods
Standardised bone defects were created in ten Merino-wool sheep (age two to four years). Large drill holes (diameter 2.5cm, depth 2cm, volume approx. 10ml) were placed in the medial femoral condyles of both hind legs and filled with gentamicin-eluting biocomposite. Initially surgery was carried out on the right hind leg.
Three months later, an identical intervention was performed on the contralateral side. Animals were sacrificed at three and six weeks and 4.5, six and twelve months. Radiographs and MRI scans were taken immediately after sacrifice. Filled bone voids were harvested en-block and analysed using µCT, and histology.
Results
We present our radiographic, µCT and histological results after a follow-up of twelve months. The bio-composite was clearly visible on all post-operative radiographs and resorbed over the next four months following the before described pattern of “halo sign” and “marble sign”. µCT images of the “halo sign” show degradation of the biocomposite starting at its surface, with the degradation products CaS and HA carried into the periphery of the bone void. µCT images of the “marble sign” showed the further degradation of the biocomposite from the surface to its core, leaving a “marble shaped” remnant of the biocomposite behind. These remnants are completely resorbed at 4.5 months. µCT scans at twelve and six months' reveal progression of trabecula bone formation. The histological results confirm the µCT findings.
Conclusion
We have established a large animal model, which mimics the clinical situation and reproduces comparable radiographic post implantation features previously observed in clinical cases (including the “halo” and the “marble” sign). Using µCT imaging and histology we can describe and understand the biodegradation process and the bone formation capacity of the biocomposite in detail.
*1 CERAMENTTM|G, BONESUPPORT, Lund, Sweden
*2 CERAMENTTM|G
