Ludovic P. Bouré

Augmentation of bone defect healing using a new biocomposite scaffold: an in vivo study in sheep.

Previous studies support resorbable biocomposites made of poly(L-lactic acid) (PLA) and beta-tricalcium phosphate (TCP) produced by supercritical gas foaming as a suitable scaffold for tissue engineering. The present study was undertaken to demonstrate the biocompatibility and osteoconductive properties of such a scaffold in a large animal cancellous bone model. The biocomposite (PLA/TCP) was compared with a currently used beta-TCP bone substitute (ChronOS, Dr. Robert Mathys Foundation), representing a positive control, and empty defects, representing a negative control. Ten defects were created in sheep cancellous bone, three in the distal femur and two in the proximal tibia of each hind limb, with diameters of 5 mm and depths of 15 mm. New bone in-growth (osteoconductivity) and biocompatibility were evaluated using microcomputed tomography and histology at 2, 4 and 12 months after surgery. The in vivo study was validated by the positive control (good bone formation with ChronOS) and the negative control (no healing with the empty defect). A major finding of this study was incorporation of the biocomposite in bone after 12 months. Bone in-growth was observed in the biocomposite scaffold, including its central part. Despite initial fibrous tissue formation observed at 2 and 4 months, but not at 12 months, this initial fibrous tissue does not preclude long-term application of the biocomposite, as demonstrated by its osteointegration after 12 months, as well as the absence of chronic or long-term inflammation at this time point.

Behavioural and cardiorespiratory effects of a constant rate infusion of medetomidine and morphine for sedation during standing laparoscopy in horses

REASONS FOR PERFORMING STUDY Standing surgical procedures are performed commonly in horses under sedation. This approach minimises the morbidity/mortality risks associated with general anaesthesia. The use of a medetomidine and morphine combination has not been investigated in horses despite the usefulness of each drug individually. OBJECTIVE To determine the efficacy of a medetomidine and morphine combination to produce standing sedation with minimal cardiorespiratory changes and adequate analgesia for exploratory laparascopy in mature horses. HYPOTHESIS The combination of medetomidine and morphine will induce reliable sedation with minimal cardiorespiratory changes. METHODS Medetomidine (5 microg/kg bwt i.v.) followed in 10 min by morphine (50 microg/kg bwt i.v.) and 10 min later by a constant rate infusion (CRI) of medetomidine and morphine (5 and 30 microg/kg bwt/h, respectively) was administered in 7 horses undergoing standing exploratory laparoscopy. Quality of sedation and cardiorespiratory function were assessed. RESULTS Sedation was satisfactory after the medetomidine and morphine bolus. The CRI of both drugs enhanced sedation and ataxia. Mean visual analogue scores on a scale of 10 varied between 7.8 and 8.8 and were similar between anaesthesiologists and surgeons. Heart rate, respiratory rate and packed cell volume (PCV) decreased significantly after medetomidine and, at some periods, during the CRI. Blood pressure only increased significantly at 5 min and arterial O2 decreased significantly at 10 min post medetomidine. PCV remained significantly lower and total protein decreased post morphine and CRI administration. Arterial CO2 increased towards the end of the CRI. Cardiac output did not change significantly over time. CONCLUSION AND CLINICAL RELEVANCE The combination of medetomidine and morphine results in reliable sedation and stable cardiorespiratory function in horses undergoing exploratory laparascopy.

Evaluation of a laparoscopic technique for collection of serial full-thickness small intestinal biopsy specimens in standing sedated horses

OBJECTIVE To assess a technique for laparoscopic collection of serial full-thickness small intestinal biopsy specimens in horses. ANIMALS 13 healthy adult horses. PROCEDURES In the ex vivo portion of the study, sections of duodenum and jejunum obtained from 6 horses immediately after euthanasia were divided into 3 segments. Each segment was randomly assigned to the control group, the double-layer hand-sewn closure group, or the endoscopic linear stapler (ELS) group. Bursting strength and bursting wall tension were measured and compared among groups; luminal diameter reduction at the biopsy site was compared between the biopsy groups. In the in vivo portion of the study, serial full-thickness small intestinal biopsy specimens were laparoscopically collected with an ELS from the descending duodenum and distal portion of the jejunum at monthly intervals in 7 sedated, standing horses. Biopsy specimens were evaluated for suitability for histologic examination. RESULTS Mean bursting strength and bursting wall tension were significantly lower in the ELS group than in the hand-sewn and control groups in both the duodenal and jejunal segments. Use of the hand-sewn closure technique at the biopsy site reduced luminal diameter significantly more than use of the stapling technique. In the in vivo part of the study, all 52 biopsy specimens collected during 26 laparoscopic procedures were suitable for histologic examination and no clinically important perioperative complications developed. CONCLUSIONS AND CLINICAL RELEVANCE Laparoscopic collection of serial full-thickness small intestinal biopsy specimens with a 45-mm ELS may be an effective and safe technique for use in healthy adult experimental horses.

In Vitro Mechanical Evaluation of a Novel Pin–Sleeve System for External Fixation of Distal Limb Fractures in Horses: A Proof of Concept Study

OBJECTIVE To evaluate the efficacy of a novel pin-sleeve cast (PSC) system for external fixation of distal limb fractures in horses and to compare it with the transfixation pin cast (TPC) system. STUDY DESIGN Experimental. SAMPLE POPULATION One bone substitute each was used for the TPC and PSC systems. The PSC was tested in 4 configurations characterized by different pin preloads. METHODS Specimens were loaded in axial compression in the elastic range. Variables compared statistically were: bone substitute axial displacement and axial strain measured above implants with strain gauges. Pin preload was correlated with the variables investigated. Load to failure and a fatigue tests supplemented the investigation. RESULTS The PSC configuration with the highest pin preload showed a significantly lower axial displacement compared with the TPC. No significant differences were observed between all other PSC configurations and the TPC. All PSC systems had a significant decrease in recorded strain compared with the TPC system. Pin axial preload inversely correlated with axial displacement but had no effect on axial strain. In the failure test, the PSC encountered plastic deformation earlier than the TPC. In the fatigue test, the PSC ran >200,000 cycles. CONCLUSIONS Preliminary in vitro tests showed that the PSC system significantly reduced peri-implant strain while concurrently having comparable axial displacement to the TPC system. CLINICAL RELEVANCE The PSC system has the potential to reduce the risk of pin loosening in horses.

Calcium Phosphate Based Three-Dimensional Cold Plotted Bone Scaffolds for Critical Size Bone Defects

Bone substitutes, like calcium phosphate, are implemented more frequently in orthopaedic surgery to reconstruct critical size defects, since autograft often results in donor site morbidity and allograft can transmit diseases. A novel bone cement, based on β-tricalcium phosphate, polyethylene glycol, and trisodium citrate, was developed to allow the rapid manufacturing of scaffolds, by extrusion freeform fabrication, at room temperature. The cement composition exhibits good resorption properties and serves as a basis for customised (e.g., drug or growth factor loaded) scaffolds for critical size bone defects. In vitro toxicity tests confirmed proliferation and differentiation of ATDC5 cells in scaffold-conditioned culture medium. Implantation of scaffolds in the iliac wing of sheep showed bone remodelling throughout the defects, outperforming the empty defects on both mineral volume and density present in the defect after 12 weeks. Both scaffolds outperformed the autograft filled defects on mineral density, while the mineral volume present in the scaffold treated defects was at least equal to the mineral volume present in the autograft treated defects. We conclude that the formulated bone cement composition is suitable for scaffold production at room temperature and that the established scaffold material can serve as a basis for future bone substitutes to enhance de novo bone formation in critical size defects.

Characterization of an ovine bilateral critical sized bone defect iliac wing model to examine treatment modalities based on bone tissue engineering.

Critical sized bone defect (CSBD) animal models are used to evaluate and confirm efficacy and potency of new treatment modalities based on bone tissue engineering before the latter can be applied in clinical practice. In this study, a bilateral CSBD model in the iliac wings of sheep is described in detail. To demonstrate that this is a large animal CSBD model in sheep, bone healing within the defect left empty (negative control) or filled with autologous corticocancellous bone graft (clinical gold standard, positive control) was assessed using micro-CT, histology, histomorphometric, and fluorochrome analysis. After three months, new bone into the defect site was formed across the whole defect in the positive controls but limited to the edge of the defects in the negative controls. Bone volume in the positive controls was statistically higher than in the negative controls, with the latter having less than 10% new bone growth. There were no intraoperative or postoperative complications. The model described here represents a reliable and reproducible bilateral CSBD in sheep with low morbidity that can be used for in vivo evaluation of new treatment modalities based on bone tissue engineering.

The use of Reamer Irrigator Aspirator (RIA) autograft harvest in the treatment of critical-sized iliac wing defects in sheep: Investigation of dexamethasone and beta-tricalcium phosphate augmentation

Bone grafts are commonly used for the treatment of segmental bone defects and fracture non-unions. Recently, osseous particles obtained during intermedullary canal reaming (using a Reamer-Irrigator-Aspirator (RIA) device) have been evaluated as graft material during in vitro and clinical studies. The aim of this study was to evaluate and quantify new bone formation after implantation of bone graft material obtained after reaming of the tibia in a bilateral critical-sized iliac wing defect in sheep and to investigate the effect of the augmentation of this graft. A reamer bone graft alone, or after short term incubation in a dexamethasone enriched solution, and a reamer graft collected using beta-tricalcium phosphate (β-TCP) granules in the filter of the RIA collection device were compared to autologous iliac wing graft. In addition, reamer graft was combined with the cellular fraction collected from the irrigation fluid with and without short-term incubation in a dexamethasone enriched solution. It was hypothesized that the amount of physical bone in the reamer bone graft groups would be higher than the amount in the autologous iliac wing graft group and that augmentation of a reamer bone graft would increase bone formation. Three months after implantation, the amount of new bone formation (as percentage of the total defect volume) in the defects was evaluated ex-vivo by means of micro-CT and histomorphometry. The mean amount of bone in the autologous iliac wing graft group was 17.7% and 16.8% for micro-CT and histomorphometry, respectively. The mean amount of bone in all reamer graft groups ranged between 20.4-29.2% (micro-CT) and 17.0-25.4% (histomorphometry). Reamer graft collected using β-TCP granules (29.2±1.7%) in the filter produced a significantly higher amount of bone in comparison to an autologous iliac wing graft evaluated by micro-CT. RIA bone grafts added a small increase in bone volume to the 3month graft volume in this preclinical sheep model. The current model does not support the use of short-term high concentration dexamethasone for augmentation of a graft volume. If avoidance of an iliac wing graft is desirable, or a reaming procedure is required, then a RIA graft or RIA graft plus β-TCP granules are as good as the current gold standard for this model.

In vitro Evaluation of the Torsional Strength Reduction of Neonate Calf Metatarsal Bones with Bicortical Defects Resulting from the Removal of External Fixation Implants

OBJECTIVE To compare the torsional strength of calf metatarsal bones with defects produced by removal of 2 different implants. STUDY DESIGN In vitro mechanical comparison of paired bones with bicortical defects resulting from the implantation of 2 different external fixation systems: the transfixation pin (TP) and the pin sleeve system (PS). SAMPLE POPULATION Neonatal calf metatarsal bones (n = 6 pairs). METHODS From each pair, 1 bone was surgically instrumented with 2 PS implants and the contralateral bone with 2 TP implants. Implants were removed immediately leaving bicortical defects at identical locations between paired metatarsi. Each bone was tested in torque until failure. The mechanical variables statistically compared were the torsional stiffness, the torque and angle at failure, and work to failure. RESULTS For TP and PS constructs, respectively, there were no significant differences between construct types for any of the variables tested. Mean ± SD torsional stiffness: 5.50 ± 2.68 and 5.35 ± 1.79 (Nm/°), P = .75; torque: 57.42 ± 14.84 and 53.43 ± 10.16 (Nm); P = .34; angle at failure: 14.76 ± 4.33 and 15.45 ± 4.84 (°), P = .69; and work to failure 7.45 ± 3.19 and 8.89 ± 3.79 (J), P = .17). CONCLUSIONS Bicortical defects resulting from the removal of PS and TP implants equally affect the investigated mechanical properties of neonate calf metatarsal bones.Objective To compare the torsional strength of calf metatarsal bones with defects produced by removal of 2 different implants. Study Design In vitro mechanical comparison of paired bones with bicortical defects resulting from the implantation of 2 different external fixation systems: the transfixation pin (TP) and the pin sleeve system (PS). Sample Population Neonatal calf metatarsal bones (n = 6 pairs). Methods From each pair, 1 bone was surgically instrumented with 2 PS implants and the contralateral bone with 2 TP implants. Implants were removed immediately leaving bicortical defects at identical locations between paired metatarsi. Each bone was tested in torque until failure. The mechanical variables statistically compared were the torsional stiffness, the torque and angle at failure, and work to failure. Results For TP and PS constructs, respectively, there were no significant differences between construct types for any of the variables tested. Mean ± SD torsional stiffness: 5.50 ± 2.68 and 5.35 ± 1.79 (Nm/°), P = .75; torque: 57.42 ± 14.84 and 53.43 ± 10.16 (Nm); P = .34; angle at failure: 14.76 ± 4.33 and 15.45 ± 4.84 (°), P = .69; and work to failure 7.45 ± 3.19 and 8.89 ± 3.79 (J), P = .17). Conclusions Bicortical defects resulting from the removal of PS and TP implants equally affect the investigated mechanical properties of neonate calf metatarsal bones.

Biomechanical and computational evaluation of two loading transfer concepts for pancarpal arthrodesis in dogs

OBJECTIVE To evaluate 2 plate designs for pancarpal arthrodesis and their effects on load transfer to the respective bones as well as to develop a computational model with directed input from the biomechanical testing of the 2 constructs. SAMPLE Both forelimbs from the cadaver of an adult castrated male Golden Retriever. PROCEDURES CT imaging was performed on the forelimb pair. Each forelimb was subsequently instrumented with a hybrid dynamic compression plate or a castless pancarpal arthrodesis plate. Biomechanical testing was performed. The forelimbs were statically loaded in the elastic range and then cyclically loaded to failure. Finite element (FE) modeling was used to compare the 2 plate designs with respect to bone and implant stress distribution and magnitude when loaded. RESULTS Cyclic loading to failure elicited failure patterns similar to those observed clinically. The mean ± SD error between computational and experimental strain was < 15% ± 13% at the maximum loads applied during static elastic loading. The highest bone stresses were at the distal extent of the metacarpal bones at the level of the screw holes with both plates; however, the compression plate resulted in slightly greater stresses than did the arthrodesis plate. Both models also revealed an increase in bone stress at the proximal screw position in the radius. The highest plate stress was identified at the level of the radiocarpal bone, and an increased screw stress (junction of screw head with shaft) was identified at both the most proximal and distal ends of the plates. CONCLUSIONS AND CLINICAL RELEVANCE The FE model successfully approximated the biomechanical characteristics of an ex vivo pancarpal plate construct for comparison of the effects of application of different plate designs.