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Background A new surface architecture for cementless orthopaedic implants (OsteoAnchor), which incorporates a multitude of tiny anchor features for enhancing primary fixation, was tested in an ovine hemi-arthroplasty pilot study. Methods Test animals were implanted with a hip stem component incorporating the OsteoAnchor surface architecture produced using additive layer manufacturing and control animals were implanted with stems containing a standard plasma sprayed titanium coating. Findings Intra-operative surgeon feedback indicated that superior primary fixation was achieved for the OsteoAnchor stems and rapid return to normal gait and load bearing was observed post-operation. Following a 16-week recovery time, histological evaluation of the excised femurs revealed in-growth of healthy bone into the porous structure of the OsteoAnchor stems. Bone in-growth was not achieved for the plasma sprayed stems. Interpretation These results indicate the potential for the OsteoAnchor surface architecture to enhance both the initial stability and long term lifetime of cementless orthopaedic implants. [ABSTRACT FROM AUTHOR]

Purpose: Because tibial fixation of soft-tissue grafts in anterior cruciate ligament (ACL) reconstruction is problematic, this study aimed to develop a means of delivering bone graft evenly around tendon autograft and define any mechanical, radiologic, or histologic benefit using an ovine model. Methods: A device to deliver bone graft evenly throughout the tibial tunnel was developed. Forty mature sheep underwent simulated quadruple hamstring tendon–ACL reconstruction by use of a bioresorbable interference screw, either with or without bone graft augmentation of the tibial tunnel. Endpoint data were derived at time 0 and after 6 weeks in vivo. Radiostereometric analysis provided quantitation of the translational characteristics; computed tomography evaluated tunnel volume, and measures of yield strength and stiffness were obtained. Sequential fluorochrome administration assessed bone formation, and light microscopy surveyed the biological response. Results: Radiostereometric analysis highlighted differences in the translational characteristics of ACL-deficient knees when compared with intact knees. Reconstructed knees (with or without autograft) showed significantly greater translation when compared with unoperated knees at 6 weeks; autograft bone augmentation provided no benefit. Neither tunnel volume nor yield strength nor stiffness was improved with the addition of autograft bone. No untoward histologic responses were observed. Bone apposition rates were similar between treatment groups. An even distribution of bone graft throughout the tunnels was observed. Conclusions: This model has confirmed the ability of the bone graft–delivery system to evenly distribute bone graft throughout the tunnels. However, the study has failed to show improvement in stability or fixation strength after augmentation with autograft bone. Clinical Relevance: The autograft bone–delivery system may provide a means of establishing an osteoconductive/inductive environment. At this early juncture (6 weeks), no benefit could be defined. Its use in combination with bone morphogenetic proteins or stem cells may provide more rapid fixation, rehabilitation, and reconstitution of bone volume within the tunnel. [Copyright &y& Elsevier]

Bone plate design has evolved dramatically in recent years. The Dynamic Compression Plate (DCP) has been superseded by bi- and uni-cortical plates that claim a reduced interface contact between the plate and the underlying bone. It is believed that contact reduction ameliorates the localised ischaemia that develops subsequent to plate application. In this study, the interface characteristics of the Limited Contact-Dynamic Compression Plate (LC-DCP) and the Contour Plus (CP) plating systems have been quantitated using Fuji prescale pressure sensitive film interposed between the plate and the bone. Ten-hole plates were applied to the same aspect of either the humeral, radial or ulnar diaphysis of human cadaveric bone in a reproducible manner. The average pressure, force and interface contact area were calculated using Interactive Data Language (IDL) image analysis software. The CP system was consistently lower, in terms of interface contact, than the LC-DCP in each of the specimen locations tested (P<0.0001). The CP system displayed a ‘point-contact’ configuration along the interface with high pressures recorded at these points, the significance of which is unknown. [Copyright &y& Elsevier]

Selection of an appropriate suture requires a knowledge of many factors. These include its mechanical characteristics, its durability, the period of mechanical effectiveness and the tissue reactivity to the material.Absorbable suture materials were incubated in synovial fluid or phosphate buffered saline, at 37 °C, for periods up to 12 weeks. Mechanical testing was performed to determine the yield strength, percentage elongation and stiffness of each material in response to incubation.Significant differences were observed in response to time of incubation, material size (‘0’ or ‘2–0’), incubation medium and material properties (P<0.001).Based on the results obtained Vicryl and PDS appear ideal for short-term and medium term apposition, respectively. Panacryl has more durable mechanical features and may well be suited to long-term tissue apposition, such as tendon repair or arthroplasty. [Copyright &y& Elsevier]

An ovine model of anterior cruciate ligament reconstruction was utilized to evaluate the biomechanical and histological response of a polylactic acid tibial fixation staple (Gunze Ltd., Japan/Zimmer, Japan). This was performed in a comparison with metallic staples, currently utilized for this procedure. The prosthesis consisted of autograft combined with a Leeds–Keio (L–K) ligament. Early post-operative mobilization was followed by retrieval of specimens at 6, 12 and 24 weeks post-reconstruction. Evaluation of the mechanical characteristics of the graft reconstructions (tensile strength) showed no significant differences (P>0.05) between the staple types for each time period. The histological response to the polylactic acid staple was minimal over the time period studied, with no adverse tissue reactions observed. The mode of reconstruction failure was observed to change with time (P<0.05) presumably as the graft characteristics alter. Overall the absorbable staples performed at a comparable level with the metallic staples within the scope of the study. [Copyright &y& Elsevier]

The evolution of bone plate design has been with a view to reducing the interface contact between the plate and the underlying bone thereby limiting the perfusion deficiency that develops. Little consequence, however, has been attributed to the drilling of holes in the steps prior to bone plate application; the work present herein attempts to define the vascular response of bone to the trauma of drilling holes.Anaesthetized sheep underwent the creation of drill holes in both tibiae and metatarsi. Animals were then heparinized and euthanatized. Utilizing femoral cannula, perfusion of the vasculature ensued; spalteholz (India ink), disulphine blue and radiocontrast material (barium sulfate). Decalcified histology was performed and correlated with the perfusion studies.Regions of perfusion deficiency were observed immediately adjacent to, and removed from, the drill hole site. Radiographic images showed substantial haematoma formation and vascular disruption in the vicinity of the drill hole site. Histologically, blood vessels immediately adjacent and distal to the drill hole site, contained a proteinaceous/cellular material occluding the vascular space.Our findings support the proposal of a short-term obstruction in cortical blood flow which may contribute to later adaptational osteopaenia following bone plate application. We have observed an acute vascular insufficiency in cortical bone directly related to the trauma of drilling screw holes. [Copyright &y& Elsevier]

Abstract: A prospective cohort of 30 patients undergoing primary total hip arthroplasty for treatment of osteoarthritis was enrolled in a study to characterize the migration behavior of a clinically successful cementless stem. At 6 years, the mean subsidence of the stem was 0.63 mm (range, −0.33 to 3.68 mm); the mean rotation into retroversion was 1.41° (range, −1.33° to 7.48°). No stems had additional subsidence of more than 0.25 mm between 6 months and 6 years. The resultant mean subsidence between 2 and 6 years was 0.03 mm, which is below the limit measurable by radiostereometric analysis. The data demonstrate that subsidence of this cementless stem occurs within the first 6 months, after which there is persistent stabilization. [Copyright &y& Elsevier]

A single, complete, ovine knee was imaged using conventional MRI then dissected allowing comprehensive dimensional measurement of the intra-articular structures. A three-dimensional (3-D) computer model of the knee was generated from the MR sections. Thirty-two individual structural measures were recorded from the image output for which there was an available surgical measure for direct comparison. The results of Pearson''s correlation testing show a rounded score of 1.00, suggesting an exceptional linear correlation between direct anatomical measurement and the 3-D image output. Further analysis of the data revealed an average error of measurement of 0.2 mm across the 32 measures. The findings of this preliminary study suggest that 3-D reconstruction from MR data may be an appropriate, and accurate, means for making dimensional measurements of the bony and soft tissue structures of the ovine knee. It is unlikely that the measurement error would be of any great clinical significance. There is evidence in the literature to suggest that an ovine knee may be considered an acceptable model for substitution for the human knee in diagnostic assessment studies. Therefore, such findings may be considered clinically relevant in the field of human knee assessment. [Copyright &y& Elsevier]

Abstract: Background: A gamma irradiation dose of 15kGy has been shown to adequately sterilise allograft bone, commonly used in femoral impaction bone grafting to treat bone loss at revision hip replacement, without significantly affecting its mechanical properties. The objective of this study was to evaluate whether use of 15kGy irradiated bone affects the initial mechanical stability of the femoral stem prosthesis, as determined by micromotion in a comprehensive testing apparatus, in a clinically relevant time zero in vitro model of revision hip replacement. Methods: Morselised ovine bone was nonirradiated (control), or irradiated at 15kGy or 60kGy. For each dose, six ovine femurs were implanted with a cemented polished taper stem following femoral impaction bone grafting. Using testing apparatus that reproduces stem loading, stems were cyclically loaded and triaxial micromotion of the stem relative to the bone was measured at the proximal and distal stem regions using non-contact laser transducers and linear variable differential transformers. Findings: There were no significant differences in proximal or distal stem micromotion between groups for all directions (p≤0.80), apart for significantly greater distal stem medial–lateral micromotion in the 60kGy group compared to the 15kGy group (P =0.03), and near-significance in the anterior–posterior direction (P =0.08, power=0.85). Interpretation: Using a clinically relevant model and loading apparatus, irradiation of bone at 15kGy does not affect initial femoral stem stability following femoral impaction bone grafting. [Copyright &y& Elsevier]