A bioactive supramolecular and covalent polymer scaffold for cartilage repair in a sheep model.

Regeneration of hyaline cartilage in human-sized joints remains a clinical challenge, and it is a critical unmet need that would contribute to longer healthspans. Injectable scaffolds for cartilage repair that integrate both bioactivity and sufficiently robust physical properties to withstand joint stresses offer a promising strategy. We report here on a hybrid biomaterial that combines a bioactive peptide amphiphile supramolecular polymer that specifically binds the chondrogenic cytokine transforming growth factor ß-1 (TGFß-1) and crosslinked hyaluronic acid microgels that drive formation of filament bundles, a hierarchical motif common in natural musculoskeletal tissues. The scaffold is an injectable slurry that generates a porous rubbery material when exposed to calcium ions once placed in cartilage defects. The hybrid material was found to support in vitro chondrogenic differentiation of encapsulated stem cells in response to sustained delivery of TGFß-1. Using a sheep model, we implanted the scaffold in shallow osteochondral defects and found it can remain localized in mechanically active joints. Evaluation of resected joints showed significantly improved repair of hyaline cartilage in osteochondral defects injected with the scaffold relative to defects injected with the growth factor alone, including implantation in the load-bearing femoral condyle. These results demonstrate the potential of the hybrid biomimetic scaffold as a niche to favor cartilage repair in mechanically active joints using a clinically relevant large-animal model.

Effect of analgesic therapy on clinical outcome measures in a randomized controlled trial using client-owned dogs with hip osteoarthritis.

BACKGROUND: Pain and impaired mobility because of osteoarthritis (OA) is common in dogs and humans. Efficacy studies of analgesic drug treatment of dogs with naturally occurring OA may be challenging, as a caregiver placebo effect is typically evident. However, little is known about effect sizes of common outcome-measures in canine clinical trials evaluating treatment of OA pain. Forty-nine client-owned dogs with hip OA were enrolled in a randomized, double-blinded placebo-controlled prospective trial. After a 1 week baseline period, dogs were randomly assigned to a treatment (ABT-116 - transient receptor potential vanilloid 1 (TRPV1) antagonist, Carprofen - non-steroidal anti-inflammatory drug (NSAID), Tramadol - synthetic opiate, or Placebo) for 2 weeks. Outcome-measures included physical examination parameters, owner questionnaire, activity monitoring, gait analysis, and use of rescue medication. RESULTS: Acute hyperthermia developed after ABT-116 treatment (P < 0.001). Treatment with carprofen (P ≤ 0.01) and tramadol (P ≤ 0.001) led to improved mobility assessed by owner questionnaire. Nighttime activity was increased after ABT-116 treatment (P = 0.01). Kinetic gait analysis did not reveal significant treatment effects. Use of rescue treatment decreased with treatment in the ABT-116 and Carprofen groups (P < 0.001). Questionnaire score and activity count at the end of treatment were correlated with age, clinical severity at trial entry, and outcome measure baseline status (SR ≥ ±0.40, P ≤ 0.005). Placebo treatment effects were evident with all variables studied. CONCLUSION: Treatment of hip OA in client-owned dogs is associated with a placebo effect for all variables that are commonly used for efficacy studies of analgesic drugs. This likely reflects caregiver bias or the phenomenon of regression to the mean. In the present study, outcome measures with significant effects also varied between groups, highlighting the value of using multiple outcome measures, as well as an a priori analysis of effect size associated with each measure. Effect size data from the present study could be used to inform design of future trials studying analgesic treatment of canine OA. Our results suggest that analgesic treatment with ABT-116 is not as effective as carprofen or tramadol for treatment of hip arthritis pain in client-owned dogs.

Improving the Selectivity of an Osseointegrated Neural Interface: Proof of Concept For Housing Sieve Electrode Arrays in the Medullary Canal of Long Bones.

Sieve electrodes stand poised to deliver the selectivity required for driving advanced prosthetics but are considered inherently invasive and lack the stability required for a chronic solution. This proof of concept experiment investigates the potential for the housing and engagement of a sieve electrode within the medullary canal as part of an osseointegrated neural interface (ONI) for greater selectivity toward improving prosthetic control. The working hypotheses are that (A) the addition of a sieve interface to a cuff electrode housed within the medullary canal of the femur as part of an ONI would be capable of measuring efferent and afferent compound nerve action potentials (CNAPs) through a greater number of channels; (B) that signaling improves over time; and (C) that stimulation at this interface generates measurable cortical somatosensory evoked potentials through a greater number of channels. The modified ONI was tested in a rabbit (n = 1) amputation model over 12 weeks, comparing the sieve component to the cuff, and subsequently compared to historical data. Efferent CNAPs were successfully recorded from the sieve demonstrating physiological improvements in CNAPs between weeks 3 and 5, and somatosensory cortical responses recorded at 12 weeks postoperatively. This demonstrates that sieve electrodes can be housed and function within the medullary canal, demonstrated by improved nerve engagement and distinct cortical sensory feedback. This data presents the conceptual framework for housing more sophisticated sieve electrodes in bone as part of an ONI for improving selectivity with percutaneous connectivity toward improved prosthetic control.

Guided growth of the proximal femur: a pilot study in the lamb model.

BACKGROUND: The concept of guided growth has been used for decades in the lower extremities of children, but has not been applied to correct varus or valgus deformity in the hip, such as those that occur in children with cerebral palsy or developmental dysplasia of the hip. The purpose of this study is to determine whether guided growth techniques are effective at altering the morphology of the proximal femur in a lamb model. METHODS: Ten, 2-month-old mixed-breed male lambs underwent hemiepiphyseal drilling and screw placement. Drilling occurred eccentrically (inferiorly) in an attempt to close only a portion of the growth plate. In 5 lambs, a sham surgery was performed in which the screw did not cross the proximal femoral physis. Growth was compared between groups and with the opposite hip in which no procedure was performed in both groups. Standardized radiographs were obtained preoperatively and monthly. A 3-dimensional computed tomography scan and standard histology were obtained postnecropsy. Version and neck shaft angle (NSA) was determined and recorded at the time of the index procedure with the aid of fluoroscopy. Radiographs were assessed by measurement of the NSA and the articular trochanteric distance (ATD). Results were compared by using the t test: paired 2 sample for means. RESULTS: The NSA and ATD were compared preoperatively and at a mean of 3.3 months after surgery. They were no significant differences preoperatively between the screw or sham group. Postoperatively, the NSA was 132 versus 143 (P=0.006) and the ATD -0.6 mm versus 10 mm (P=0.033) for the screw and sham hips, respectively. The sham group showed no statistical differences between the operative and nonoperative sides postoperatively, although the ATD trended toward a larger number on the "sham" side, possibly because of a growth stimulation effect. CONCLUSIONS: Screw hemiepiphysiodesis seems to alter the growth of the proximal femur in the lamb model. SIGNIFICANCE: Further studies are ongoing and with more research this technique could be used to correct or prevent proximal femoral deformity in the growing child. LEVEL OF EVIDENCE: Level II.

Experimental Basis for Creating an Osseointegrated Neural Interface for Prosthetic Control: A Pilot Study in Rabbits.

INTRODUCTION: While debate persists over how to best prevent or treat amputation neuromas, the more pressing question of how to best marry residual nerves to state-of-the-art robotic prostheses for naturalistic control of a replacement limb has come to the fore. One potential solution involves the transposition of terminal nerve ends into the medullary canal of long bones, creating the neural interface within the bone. Nerve transposition into bone is a long-practiced, clinically relevant treatment for painful neuromas. Despite neuropathic pain relief, the physiological capacity of transposed nerves to conduct motor and sensory signals required for prosthesis control remains unknown. This pilot study addresses the hypotheses that (1) bone provides stability to transposed nerves and (2) nerves transposed into bone remain physiologically active, as they relate to the creation of an osseointegrated neural interface. METHODS: New Zealand white rabbits received transfemoral amputation, with the sciatic nerve transposed into the femur. RESULTS: Morphological examination demonstrates that nerves remain stable within the medullary canal, while compound nerve action potentials evoked by electrical stimulation of the residual nerve within the bone could be achieved at 12 weeks (p < 0.0005). CONCLUSION: Transposed nerves retain a degree of physiological function suitable for creating an osseointegrated neural interface.

Methodology for creating a chronic osseointegrated neural interface for prosthetic control in rabbits.

BACKGROUND: Chronic stability and high degrees of selectivity are both essential but somewhat juxtaposed components for creating an implantable bi-directional PNI capable of controlling of a prosthetic limb. While the more invasive implantable electrode arrays provide greater specificity, they are less stable over time due to compliance mismatch with the dynamic soft tissue environment in which the interface is created. NEW METHOD: This paper takes the surgical approach of transposing nerves into bone to create neural interface within the medullary canal of long bones, an osseointegrated neural interface, to provide greater stability for implantable electrodes. In this context, we describe the surgical model for transfemoral amputation with transposition of the sciatic nerve into the medullary canal in rabbits. We investigate the capacity to create a neural interface within the medullary canal histolomorphologically. In a separate proof of concept experiment, we quantify the chronic physiological capacity of transposed nerves to conduct compound nerve action potentials evoked via an Osseointegrated Neural Interface. COMPARISON WITH EXISTING METHOD(S): The rabbit serves as an important animal model for both amputation neuroma and osseointegration research, but is underutilized for the exploration neural interfacing in an amputation setting. RESULTS: Our findings demonstrate that transposed nerves remain stable over 12 weeks. Creating a neural interface within the medullary canal is possible and does not impede nerve regeneration or physiological capacity. CONCLUSIONS: This article represents the first evidence that an Osseointegrated Neural Interface can be surgically created, capable of chronic stimulation/recording from amputated nerves required for future prosthetic control.

Influence of hydroxyapatite-coated and growth factor-releasing interference screws on tendon-bone healing in an ovine model.

PURPOSE: Our purpose was to determine whether a bioresorbable interference screw coated with a hydroxyapatite-based mineral layer designed to release an engineered peptide growth factor (linkBMP-2 [where "BMP-2" indicates bone morphogenetic protein 2]) improved tendon-bone healing compared with a screw without coating. METHODS: Tagged linkBMP-2 peptides were used to quantify binding efficiency and release kinetics on 9 mineral-coated BIORCI screws (Smith & Nephew, Andover, MA). Fourteen mature female sheep were used in this study. In each of the 14 sheep, each stifle was randomized to either receive a linkBMP-2-coated or uncoated interference screw (n = 14 per treatment). The sheep were euthanized at 6 weeks after surgery. Eight sheep were subjected to biomechanical testing for peak load at failure and stiffness, and six sheep were used for histologic analysis according to a semiquantitative scoring scale. RESULTS: The linkBMP-2 molecule bound efficiently to the surface of mineral-coated interference screws. Over 80% of the initially bound linkBMP-2 was released during a 6-week time frame in vitro. Peak load at failure in the linkBMP-2-coated interference screw group (mean +/- SD, 449.3 +/- 84.7 N) was not significantly different from that in the uncoated group (421.0 +/- 61.8 N) (P = .22). Stiffness in the linkBMP-2-coated interference screw group (157.3 +/- 39.6 N/mm) was not significantly different from that in the uncoated group (140.6 +/- 20.3 N/mm) (P = .12). Histologic analysis showed that the tendons in the linkBMP-2-coated interference screw group had higher scores (better) than the uncoated group. In the linkBMP-2-coated interference screw group, mesenchymal cells were present at the interface between screw and tendon, whereas these cells were not present in the uncoated group. CONCLUSIONS: We found that linkBMP-2 can be bound onto a mineral-coated BIORCI interference screw surface and subsequently released from the screw surface in a sustained manner. The histologic result of this study showed that the linkBMP-2-coated interference screw significantly improved the histologic scores of early tendon-bone healing in this sheep model. CLINICAL RELEVANCE: This linkBMP-2 coating material may improve early tendon/ligament fixation.

Comparison of a new braid fixation system to an interlocking intramedullary nail for tibial osteotomy repair in an ovine model.

OBJECTIVES: To compare bone healing of tibial osteotomy repaired with Nitinol wire braid and hardened steel rods (Braid system) and polymethylmethacrylate bone cement with an interlocking intramedullary (IM) nail fixation in an ovine model. STUDY DESIGN: In vitro and in vivo experimental study. ANIMALS: Adult female sheep (n=22). METHODS: Using sheep tibia, a middiaphyseal transverse osteotomy was performed in the right tibia, which were then randomly assigned to the Braid system group or IM nail group (n=5). The left tibia were used as controls. The torsional properties of tibial constructs were compared. The study was repeated in vivo in 12 sheep and mechanical properties and bone healing were evaluated at 12 weeks. RESULTS: In vitro, there was no significant difference in torsional stiffness between the groups. In vivo, operative time for the Braid system group was significantly shorter than the IM nail group. At 12 weeks, there were no significant differences in maximum torque and torsional stiffness between IM nail and Braid system groups nor were there significant radiographic or histologic differences between the groups. CONCLUSIONS: The Braid system might decrease operative time for repair of transverse middiaphyseal tibial fractures and result in similar bone healing at 12 weeks after surgery compared with an interlocking IM nail repair. CLINICAL RELEVANCE: A Nitinol Braid system may be a treatment option for transverse midshaft tibial fractures.

Acceleration of second and fourth metatarsal fracture healing with recombinant human bone morphogenetic protein-2/calcium phosphate cement in horses.

OBJECTIVE: To compare the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2)/calcium phosphate (CP) to autogenous cancellous bone graft (CBG) and to no treatment on bone healing, in surgically induced osteotomies and ostectomies of the accessory metatarsal bones in an equine model. STUDY DESIGN: Experimental. ANIMALS: Adult horses (n=9). METHODS: Segmental ostectomies of the second metatarsal bone (MT2) and osteotomies of the fourth metatarsal bone (MT4) were performed bilaterally in 9 horses. There were a total of 35 defects (1 MT4 was previously fractured) created and supplemented randomly either with no treatment (untreated control), rhBMP-2/CP cement, or matrix (CPC or CPM), or CBG. Radiography was performed every 2 weeks until study endpoint at 12 weeks. After euthanasia, bone healing was evaluated using radiography, mechanical testing, and histology. Data were analyzed with ANOVA followed by the Duncan's Multiple Range Test or nonparametric analyses. RESULTS: At 12 weeks, radiographic scores for union were significantly greater for the rhBMP-2 (P<.0001) and CBG (P=.004) groups compared with the untreated control group, for both MT2 ostectomies and MT4 osteotomies. The rhBMP-2 treated MT2 had greater maximum torque to failure in torsion than CBG and control limbs at 12 weeks (P=.011). Histologic analysis demonstrated increased bone formation and more mature bone at the ostectomy site for MT2 in the rhBMP-2 and CBG groups compared with the untreated control group. CONCLUSION: Injection of rhBMP-2/CP into surgically induced ostectomies and osteotomies of the accessory metatarsal bones might accelerate early bone healing in the horse. CLINICAL RELEVANCE: RhBMP-2/CP may be as effective if not superior to CBG as an adjuvant treatment to accelerate healing of bone defects.

Effect of contact time on variance of ground reaction forces during force platform gait analysis of a heterogeneous sample of clinically normal dogs.

OBJECTIVE To develop contact time (ConT) and withers height-normalized relative ConT (ConT*) for force platform gait analysis of dogs. ANIMALS 29 healthy client-owned dogs. PROCEDURES Height at the most dorsal aspect of the shoulders (withers) was measured with a framing square. Dogs were trotted across a force platform at their preferred velocity with controlled acceleration (± 0.5 m/s2). Ranges of ConT and ConT* centered on the population mean ConT were created. Variance effects on ground reaction forces (GRFs) for 4 thoracic limb and 4 pelvic limb ConT and associated ConT* ranges were examined. Efficiency of trial capture and effects of velocity ranges on GRF variance were determined. RESULTS Individual dogs had the greatest effect on GRF variance for thoracic and pelvic limbs. Narrow ConT and ConT* ranges had few significant effects on GRFs but were inefficient at capturing trials. The ConT ranges of 0.22 to 0.29 seconds and 0.19 to 0.25 seconds for thoracic and pelvic limbs, respectively, provided the most efficient rates of trial capture with the fewest significant effects on GRFs. Compared with ConT and ConT* ranges, relative velocity ranges had higher efficiency and smaller GRF variance effects. CONCLUSIONS AND CLINICAL RELEVANCE Dogs of various morphologies have differing limb velocities. Use of ConT as a surrogate for limb velocity may improve GRF data quality. We identified ConT and ConT* ranges associated with low GRF variance. However, relative velocity ranges captured data more efficiently. Efficient capture of data may help avoid worsening of lameness during gait analysis of dogs.

Variance associated with walking velocity during force platform gait analysis of a heterogeneous sample of clinically normal dogs.

OBJECTIVE To determine whether walking at specific ranges of absolute and relative (V*) velocity would aid efficient capture of gait trial data with low ground reaction force (GRF) variance in a heterogeneous sample of dogs. ANIMALS 17 clinically normal dogs of various breeds, ages, and sexes. PROCEDURES Each dog was walked across a force platform at its preferred velocity, with controlled acceleration within 0.5 m/s2. Ranges in V* were created for height at the highest point of the shoulders (withers; WHV*). Variance effects from 8 walking absolute velocity ranges and associated WHV* ranges were examined by means of repeated-measures ANCOVA. RESULTS The individual dog effect provided the greatest contribution to variance. Narrow velocity ranges typically resulted in capture of a smaller percentage of valid trials and were not consistently associated with lower variance. The WHV* range of 0.33 to 0.46 allowed capture of valid trials efficiently, with no significant effects on peak vertical force and vertical impulse. CONCLUSIONS AND CLINICAL RELEVANCE Dogs with severe lameness may be unable to trot or may have a decline in mobility with gait trial repetition. Gait analysis involving evaluation of individual dogs at their preferred absolute velocity, such that dogs are evaluated at a similar V*, may facilitate efficient capture of valid trials without significant effects on GRF. Use of individual velocity ranges derived from a WHV* range of 0.33 to 0.46 can account for heterogeneity and appears suitable for use in clinical trials involving dogs at a walking gait.

Influence of trial repetition on lameness during force platform gait analysis in a heterogeneous population of clinically lame dogs each trotting at its preferred velocity.

OBJECTIVE To determine variance effects influencing ground reaction forces (GRFs) in a heterogeneous population of lame dogs during trotting. ANIMALS 30 client-owned dogs with thoracic limb lameness and 31 dogs with pelvic limb lameness. PROCEDURES GRFs, velocity, height at the dorsal aspect of the scapulae (ie, withers), and shoulder height were obtained. Each dog was trotted across a force platform at its preferred velocity. Variance effects for 12 velocity and associated relative velocity (V*) ranges were examined. RESULTS Individual dog, velocity, V*, and limb significantly influenced GRFs. Withers height V* ranges were associated with small variance in GRFs, but all absolute and V* ranges were associated with significant effects for all 4 limbs and both types of lameness. Significant changes in lame limb GRFs and velocity in ipsilateral trials in dogs with thoracic limb and pelvic limb lameness were evident with trial repetition. Withers height V* range of 0.55 to 0.93 captured a large proportion of trials (> 90%) in dogs with thoracic limb or pelvic limb lameness, with limited effects on peak vertical force and vertical impulse. CONCLUSIONS AND CLINICAL RELEVANCE Trial repetition caused alterations to GRFs and subject velocity that may have confounded assessment of lameness, which supported the concept that a priori selection of a velocity or V* range for force platform gait analysis should use a range that captures valid trials efficiently while minimizing GRF variance. These ranges typically would span the preferred velocity of subject dogs, such as withers height V* of 0.55 to 0.93.

Multiscale Porosity Directs Bone Regeneration in Biphasic Calcium Phosphate Scaffolds.

Large and load-bearing bone defects are challenging to treat and cause pain and disfigurement. The design of efficacious bone scaffolds for the repair of such defects involves a range of length scales from the centimeter down to the micrometer-scale. Here, we assess the influence on bone regeneration of scaffold rod spacing (>300 µm) and microporosity (<50 µm), as well as the combination of different structures and materials in the same scaffold, i.e., at the millimeter scale. We use four single-domain scaffolds, microporous (MP) or nonmicroporous (NMP) and with either a "small" or "large" rod spacing. Multidomain scaffolds combine four regions corresponding to the macro- and microarchitectures of the single-domain scaffolds. The scaffolds are implanted in pig mandibles for 3 weeks and bone regeneration is assessed by measuring the average bone volume fraction, BVF̅, the bone distribution and the trabecular thickness from micro-CT data. For the single-domain scaffolds, BVF̅ was 45 ± 3% for MP-small, 39 ± 2% for MP-large, 25 ± 2% for NMP-small, and 25 ± 2% for NMP-large. MP scaffolds have significantly higher BVF̅ and a more uniform bone distribution compared to NMP, regardless of rod spacing. The average trabecular thickness is significantly larger in MP compared to NMP, and in "large" compared to "small" scaffolds. Microporosity affects trabecular thickness throughout the scaffold, while rod spacing affects it only at the scaffold periphery. In multidomain scaffolds, MP-large and NMP-large domains have similar BVF̅ as compared to their respective single-domain counterparts. These results suggest that combining different architectures into one scaffold conserves the properties of each domain. Hence, bone growth and morphology can be tailored by controlling scaffold architecture from the millimeter down to the micrometer level. This will allow the customization of scaffold designs for the treatment of large and load-bearing bone defects.

Variance associated with the use of relative velocity for force platform gait analysis in a heterogeneous population of clinically normal dogs.

Factors that contribute to variance in ground reaction forces (GRFs) include dog morphology, velocity, and trial repetition. Narrow velocity ranges are recommended to minimize variance. In a heterogeneous population, it may be preferable to minimize data variance and efficiently perform force platform gait analysis by evaluation of each individual dog at its preferred velocity, such that dogs are studied at a similar relative velocity (V*). Data from 27 normal dogs were obtained including withers and shoulder height. Each dog was trotted across a force platform at its preferred velocity, with controlled acceleration (±0.5 m/s(2)). V* ranges were created for withers and shoulder height. Variance effects from 12 trotting velocity ranges and associated V* ranges were examined using repeated-measures analysis-of-covariance. Mean bodyweight was 24.4 ± 7.4 kg. Individual dog, velocity, and V* significantly influenced GRF (P <0.001). Trial number significantly influenced thoracic limb peak vertical force (PVF) (P <0.001). Limb effects were not significant. The magnitude of variance effects was greatest for the dog effect. Withers height V* was associated with small GRF variance. Narrow velocity ranges typically captured a smaller percentage of trials and were not consistently associated with lower variance. The withers height V* range of 0.6-1.05 captured the largest proportion of trials (95.9 ± 5.9%) with no significant effects on PVF and vertical impulse. The use of individual velocity ranges derived from a withers height V* range of 0.6-1.05 will account for population heterogeneity while minimizing exacerbation of lameness in clinical trials studying lame dogs by efficient capture of valid trials.

In vitro biomechanical evaluation of four surgical techniques for fusion of equine centrodistal and tarsometatarsal joints.

OBJECTIVE To evaluate the biomechanical properties of 4 methods for fusion of the centrodistal and tarsometatarsal joints in horses and compare them among each other and with control tarsi. SAMPLE 24 sets of paired tarsi without substantial signs of osteoarthritis harvested from equine cadavers. PROCEDURES Test constructs (n = 6/type) were prepared from 1 tarsus from each pair to represent surgical drilling; 2 medially to laterally placed kerf-cut cylinders (MLKCs); a single large, dorsally applied kerf-cut cylinder (DKC); and a dorsomedially applied locking compression plate (DMLCP). Constructs and their contralateral control tarsi were evaluated in 4-point bending in the dorsoplantar, lateromedial, and mediolateral directions; internal and external rotation; and axial compression. Bending, torsional, and axial stiffness values were calculated. RESULTS Mean stiffness values were consistently lower for surgical drilling constructs than for contralateral control tarsi. Over all biomechanical testing, surgical drilling significantly reduced joint stability. The MLKC constructs had superior biomechanical properties to those of control tarsi for 4-point bending but inferior properties for external and internal rotation. The DMLCP and DKC constructs were superior to control tarsi in dorsoplantar, rotational, and axial compression directions only; DMLCP constructs had no superior stiffness in lateromedial or mediolateral directions. Only the DKC constructs had greater stiffness in the mediolateral direction than did control tarsi. Over all biomechanical testing, DMLCP and DKC constructs were superior to the other constructs. CONCLUSIONS AND CLINICAL RELEVANCE These biomechanical results suggested that a surgical drilling approach to joint fusion may reduce tarsal stability in horses without clinical osteoarthritis, compared with stability with no intervention, whereas the DMLCP and DKC approaches may significantly enhance stability.

Arthrodesis of the equine centrodistal and tarsometatarsal joints using a single modified kerf-cut cylinder.

OBJECTIVES: To describe a technique for surgical placement of a modified kerf-cut cylinder for the purpose of arthrodesis across the equine centrodistal and tarsometatarsal joints. METHODS: Each horse (n = 4) underwent unilateral placement of a single kerf-cut cylinder spanning the centrodistal and tarsometatarsal joints with the placement of an autologous cancellous bone graft. Horses were evaluated via lameness examination and radiography postoperatively and euthanatization of each horse was performed at four different time points up to 12 weeks post-surgery to evaluate for lameness, implant stability and success with integration in the surrounding bone. RESULTS: Implants were placed successfully in three of four horses. In one horse, due to technical error, the implant was misaligned with the joint spaces. Although the horse exhibited minimal pain, it was euthanatized at the two week follow-up. Implant placement in the remaining three horses was successfully achieved. At eight weeks, radiographically there was evidence of osseous union across the joint spaces. No change in lameness was detected at any point after surgery. At 12 weeks post-surgery, histologically the implants were filled with mineralized osteoid and demonstrated integration with the surrounding tissue. CLINICAL SIGNIFICANCE: The surgical approach and placement of modified kerf-cut cylinders for arthrodesis of the centrodistal and tarsometatarsal joints were successfully achieved with minimal signs of postoperative pain and a short rehabilitation time period in normal horses.

Micropore-induced capillarity enhances bone distribution in vivo in biphasic calcium phosphate scaffolds.

UNLABELLED: The increasing demand for bone repair solutions calls for the development of efficacious bone scaffolds. Biphasic calcium phosphate (BCP) scaffolds with both macropores and micropores (MP) have improved healing compared to those with macropores and no micropores (NMP), but the role of micropores is unclear. Here, we evaluate capillarity induced by micropores as a mechanism that can affect bone growth in vivo. Three groups of cylindrical scaffolds were implanted in pig mandibles for three weeks: MP were implanted either dry (MP-Dry), or after submersion in phosphate buffered saline, which fills pores with fluid and therefore suppresses micropore-induced capillarity (MP-Wet); NMP were implanted dry. The amount and distribution of bone in the scaffolds were quantified using micro-computed tomography. MP-Dry had a more homogeneous bone distribution than MP-Wet, although the average bone volume fraction, BVF‾, was not significantly different for these two groups (0.45±0.03 and 0.37±0.03, respectively). There was no significant difference in the radial bone distribution of NMP and MP-Wet, but the BVF‾, of NMP was significantly lower among the three groups (0.25±0.02). These results suggest that micropore-induced capillarity enhances bone regeneration by improving the homogeneity of bone distribution in BCP scaffolds. The explicit design and use of capillarity in bone scaffolds may lead to more effective treatments of large and complex bone defects. STATEMENT OF SIGNIFICANCE: The increasing demand for bone repair calls for more efficacious bone scaffolds and calcium phosphate-based materials are considered suitable for this application. Macropores (>100µm) are necessary for bone ingrowth and vascularization. However, studies have shown that microporosity (<20µm) also enhances growth, but there is no consensus on the controlling mechanisms. In previous in vitro work, we suggested that micropore-induced capillarity had the potential to enhance bone growth in vivo. This work illustrates the positive effects of capillarity on bone regeneration in vivo; it demonstrates that micropore-induced capillarity significantly enhances the bone distribution in the scaffold. The results will impact the design of scaffolds to better exploit capillarity and improve treatments for large and load-bearing bone defects.

Effect of inhaled endotoxin on cardiopulmonary function and E-selectin expression in pigs.

OBJECTIVE: To evaluate the effect of controlled exposure to inhaled lipopolysaccharides (LPS) on the pulmonary inflammatory response of anesthetized pigs. ANIMALS: Forty-seven 8- to 12-week-old domestic pigs. PROCEDURE: Pigs were anesthetized with pentobarbital, instrumented for measurement of cardiopulmonary function, and randomly assigned to receive saline (0.9% NaCI) solution or 0.25, 0.5, or 1.0 microg of LPS/kg/h for 2 or 6 hours via nebulization through the endotracheal tube. Cardiopulmonary variables were measured, ex vivo neutrophil superoxide production determined, and postmortem assessment for pulmonary neutrophil influx and modulation of adhesion molecule (E-selectin) expression was done. RESULTS: Mild changes in cardiopulmonary function were observed in response to inhaled LPS in the 2-and 6-hour groups. In pigs inhaling LPS (0.5 or 1.0 microg/kg/h) for 6 hours, there was significant pulmonary neutrophil influx observed postmortem. An increase in expression of E-selectin on pulmonary endothelial cells after 6 hours of LPS inhalation (0.5 microg/kg/h) was also observed. In contrast, there was no significant influx of neutrophils or expression of E-selectin in lungs from pigs inhaling LPS for 2 hours. CONCLUSIONS AND CLINICAL RELEVANCE: inhalation of LPS resulted in localized pulmonary inflammation characterized by neutrophil influx and increased expression of the endothelial cell adhesion molecule, E-selectin. It may be possible to relate our experimental findings to the clinical consequences of airborne LPS exposure in swine confinement facilities.

Variance associated with subject velocity and trial repetition during force platform gait analysis in a heterogeneous population of clinically normal dogs.

Factors that contribute to variance in ground reaction forces (GRF) include dog morphology, velocity, and trial repetition. Narrow velocity ranges are recommended to minimize variance. In a heterogeneous population of clinically normal dogs, it was hypothesized that the dog subject effect would account for the majority of variance in peak vertical force (PVF) and vertical impulse (VI) at a trotting gait, and that narrow velocity ranges would be associated with less variance. Data from 20 normal dogs were obtained. Each dog was trotted across a force platform at its habitual velocity, with controlled acceleration (±0.5 m/s(2)). Variance effects from 12 trotting velocity ranges were examined using repeated-measures analysis-of-covariance. Significance was set at P <0.05. Mean dog bodyweight was 28.4 ± 7.4 kg. Individual dog and velocity significantly affected PVF and VI for thoracic and pelvic limbs (P <0.001). Trial number significantly affected thoracic limb PVF (P <0.001). Limb (left or right) significantly affected thoracic limb VI (P = 0.02). The magnitude of variance effects from largest to smallest was dog, velocity, trial repetition, and limb. Velocity ranges of 1.5-2.0 m/s, 1.8-2.2 m/s, and 1.9-2.2 m/s were associated with low variance and no significant effects on thoracic or pelvic limb PVF and VI. A combination of these ranges, 1.5-2.2 m/s, captured a large percentage of trials per dog (84.2 ± 21.4%) with no significant effects on thoracic or pelvic limb PVF or VI. It was concluded that wider velocity ranges facilitate capture of valid trials with little to no effect on GRF in normal trotting dogs. This concept is important for clinical trial design.

Percutaneous lovastatin accelerates bone healing but is associated with periosseous soft tissue inflammation in a canine tibial osteotomy model.

Experimental studies have shown the ability of statins to stimulate bone formation when delivered locally or in large oral doses, however most have been studied in rodents. This anabolic effect is through the selective activation of BMP-2. Our purpose was to determine the effects of local treatment with lovastatin on bone healing in mammals as a preclinical animal model. We administered lovastatin (6 mg/kg) by percutaneous injection to a canine tibial osteotomy stabilized with external fixation. We found that lovastatin improved bone healing after a single injection into the fracture site assessed by serial radiography and histology at bone union. However, lovastatin treatment resulted in adverse local soft tissue inflammation. These results suggest that percutaneous lovastatin injection may be a useful adjuvant treatment over the course of bone healing to augment fracture repair, although further investigation into the mechanism of soft tissue adverse effects is warranted.