Resorbable porous ceramics derived from chemically converted corals have been used successfully as bone graft substitutes for many years. Converted corals provide a 3D porous architecture that resembles cancellous bone with a pore diameter of 200–700 μm. The success of these corals as a bone graft substitute relies on vascular ingrowth, differentiation of osteoprogenitor cells, remodelling and graft resorption occurring together with host bone ingrowth into the porous microstructure or voids left behind during resorption. The resorption rate of the coral can be controlled by partial conversion to provide a hydroxyapatite (HA) layer via thermal modification. This study examined the resorption rates and bone formation of partially converted corals in a bilateral metaphyseal defect model.

Bilateral defects (5 mm x 15 mm) were created 3 mm below the joint line in the proximal tibia of 41 skeletally mature New Zealand white rabbits following ethical approval. Two variations of a calcium carbonate–HA coral (Pro Osteon 200 R, Interpore-Cross International, Irvine, CA) were examined with different HA thickness (200R; 14% or 200 RT; 28%). Empty defects (negative control) or defects filled with morcellised bone autograft from the defect sites (positive control) were performed. The tibiae were harvested at 6, 12, 24, 36 or 52 weeks, radiographed (standard x-rays and faxitron) in the anteroposterior and lateral planes. Tibias were processed for torsional testing and quantitative histomorphometry using back scattering scanning electron microscopy. Four additional rabbits were killed at time zero to determine the mechanical properties of the intact tibia (n=6 tibias) and 2 for tibias for time zero histomorphometry. Data were analysed using a 3-way analysis of variance.

No clinical complications were encountered in this study. Radiographic assessment revealed a progression in healing, implant resorption and bone infiltration. Cortical closure in the 200 R and 200RT treated defects was noted by 24 weeks. All specimens failed in torsional testing with a spiral fracture initiating at the distal defect site and extending into the distal diaphysis. Torsional properties reached intact control tibia levels by 24 weeks in both groups. No significant differences were noted between 200 R and 200 RT based on torsional data. SEM revealed progressive resorption of the calcium carbonate core of the 200 R and 200 RT with time, infiltration of bone and ingrowth to the HA layers. Time and measurement site (cortical versus cancellous) were significant for implant resorption, bone, and void. The thinner HA layer (200 R) resorbed more quickly compared to the thicker layer (200 RT) in the canal as well as cortical sites. Increased bone and decreased void were noted at the cortex measurement sites in the 200 R group at 24 weeks and in the 200 RT group at 12 and 24 weeks (p< 0.05). Implants were nearly completely resorbed by 52 weeks with only a few percent of implant remaining.

Introduction: The biomechanical properties of tendon and ligament have long been the subject of intense research. The understanding of the ultrastructure as it relates to the biomechanical function and clinical demands have often considered the ultimate properties at failure alone. Tendons and ligaments are predominately loaded in-vivo at subfailure loads and often in the initial toe region. To date, little work has focussed on the viscoelastic properties of the tendon in the initial toe region. The biomechanical behaviour at these low loads may reflect the unique mechanical interactions between the fasciles and collagen fibrils. This study examined stress relaxation of ligaments in the initial non-linear portion of the load vs. displacement curve.

Methods: Six flexor tendons (2.5 mm wide x 1mm thick) were harvested from 18 month cross bred whethers and stored in 0.145 M NaCl until testing. Tensile testing was performed on a MACH 1 Micromechanical Testing Machine (BIOSYNTECH, Laval, Quebec, Canada) in 0.145M phosphate buffered saline at room temperature. Tendons (gauge length 30mm) were displaced to 0.5, 1 and 5% strain at a loading rate of 50 microns/sec and stress relaxation measured over a period of 300 seconds and repeated for 4 sequences. Data was analysed using an analysis of variance.

Results and Discussion: Peak loads at 0.5 % strain ranged from 50 g (sequence 1) to 130 g (sequence 4) while at 5 % strain peak loads reached upwards to 1600 g. These loads are well within the initial toe region of the load-displacement behaviour of the ligament. The MACH 1 testing system provide a reliable and highly accurate system to control micron level displacements and mg load resolution. Recently, Yamamoto and coworkers reported the stress relaxation behavior and strain rate effects of collagen fascicles differed greatly from those of bulk tendons. The differences in tensile and viscoelastic properties between fascicles and bulk tendons may be attributable, in part, to ground substances, mechanical interaction between fascicles, and the difference of crimp structure of collagen fibrils. The present study supports an important role of tissue ultra-structure at low loads with regard to stress relaxation. Subtle changes in ground susbtance, water content or biochemical consituents not evident in testin

Introduction: Various plating devices and screw systems are available for single and multi-level cervical fusions. Recent reports regarding screw migration under torsional load and a “windshield wiper effect” has brought to light the importance of plate and screw design as well as the choice of graft.

Aim: This study examined the relative stability of cervical plating systems under pure bending and axial-torsional fatigue using the Cloward type graft.

Methods: Five fresh-frozen human cervical and 10 porcine spines assessed by dual-energy x-ray absorptiometry (DEXA) scanning and then reconstructed at the C_2–3 and levels using the anterior Cloward technique. C_4–5 Two different plating systems (a solid plate and a hollow plate) were used and alternated between the C2–3 and C4–5 levels. Strain gauges placed on the plates themselves. The systems were subjected to pure bending and torsional loading.. Five kilogram loads were used to apply bending moments to the spine and did not differ between the two systems evaluated. Bending moments and displacement angles were recorded for the pure bending loading regime and torque versus time was recorded for the torsional fatigue loading.

Results: Strain gauge analysis revealed minimal strains on the plates under the loading conditions. Torque versus time was measured, and the decay constant was calculated from the decay curves. The hollow plating system decayed quicker than the solid plating system. Angular displacement under pure bending was minimal. The hollow system plate system resisted greater torque compared with the solid system. The decay curves eventually reached an asymptote for the both systems. This implied that the systems become stable under fatigue loading. The X-rays illustrated no failure at the screw/ bone interface (i.e. No “wiper” effect) after torsional fatigue.

Introduction: The transition from fixed bearing to mobile bearing total replacements represents a recent trend in Australia with the introduction of many new designs. The complex kinematics of mobile bearing designs coupled with the importance of proper surgical techniques including soft tissue balancing presents a number of factors that may influence the short and long-term success of these implants. There have been few reports in the literature on the performance of many of the new mobile bearing design with regards to initial wear of the polyethylene (PE) insert.

Aim: To investigate the patterns of wear on three mobile bearing knee PE inserts that had been retrieved soon after implantation.

Methods: Three mobile bearing knee PE inserts were retrieved at the time of revision surgery and submitted to our laboratory for examination. The proximal and distal articulating surfaces were examined by measuring surface roughness (Ra) using a Surfanalyzer (5400 (Federal Products Co., Providence, RI, USA) following ISO 97. Optical microscopy and scanning electron microscope (SEM) analyses were used to locate and identify patterns of wear.

Results: The average time in service for the PE inserts was 18.6 months. The maximum Ra values were noted on the anterior-lateral side for all implants. Optical and SEM analysis revealed wear mechanisms that included burnishing, scratches, pitting and cold flow. Damage to the distal surface was noted in all samples with extensive wear tracks noted in the LCS and TRAC knees.

Conclusion: The surface roughness analyses showed asymmetrical wear on the distal PE interfaces as well as wear on the proximal PE interfaces. The presence of embedded particles and debris suggests a third-body mechanism. Dislocation and general instability may have exacerbated the early signs of wear in these components.