Funding opportunities for applied research that support clinical issues relevant to the veterinary field
From traditional research grants to investigator training
AO VET is working on the development of training grants for young investigators, better opportunities for structured research mentoring of young trainees, and the introduction of new, innovative surgical training courses on best practices in preclinical animal research.
AO VET will also act as a resource across the AO group to facilitate the most ethical appropriate use of animals in research.
Research grant calls will open in spring 2024
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Funded research projects
AO VET–ARI Collaborative Research Grants
An In Vitro Biomechanical Investigation of an Interlocking Nail System and Locking Compression Plate Fixation of Osteotomized Equine Humerus
The humerus is the most commonly fractured proximal bone in Thoroughbred racehorses, with a prevalence of 50% of all proximal limb and pelvic fractures occurring on race-day and during training. Humeral fractures are also common after a traumatic event such as falling, and is the fourth most commonly fractured long bone in a heterogeneous equine population following kick injuries with a prevalence surpassing that of the third metacarpal/tarsal bones. The characteristic complete fracture of the humerus courses from the caudoproximal cortex in a long oblique or soft spiral configuration to the caudodistal cortex. Complete humeral fractures in mature horses (>300 kg body weight) are difficult to treat by internal fixation and the principal decision has to be between euthanasia or extended stall rest. In the largest published case series, only 23% of horses undergoing internal fixation for humeral fractures had a positive outcome. The grave to guarded prognosis is a consequence of unsuitable surgical implants that do not have sufficient strength to achieve adequate stability. Thus, conservative therapy with stall rest is currently the only viable alternative to surgical fixation and only for minimally or not displaced fracture but complications are frequent and include support limb laminitis, ongoing fracture displacement with associated soft tissue injury and/or radial nerve paralysis, malunion, and nonunion.
Fracture stabilization in equine orthopedics is usually achieved with double plate fixation, which is technically challenging in the humerus because of the complex surface topographies and difficulty to engage adequate bone stock, particularly distally. More recently, IIN fixation has been used successfully in veterinary orthopedics and has resulted in successful outcomes in foals with diaphyseal humeral fractures. The IIN veterinary systems are designed for small animals and are too weak to be used in mature horses with the size of the largest nail available (8-mm diameter) limiting its usage to neonatal and young foals. A larger custom IIN prototype with a 12.7-mm diameter has be described for large animal humeral and femoral fracture fixation and showed encouraging results in horses up to 377 kg used in combination with a cranial bone plate in heavier animals. However, this prototype never reached the veterinary market and no IIN systems for use in large animal fracture fixation is currently commercially available. The identification of a IIN system already commercially available from the human market would facilitate and accelerate its implementation in large animal surgery and would limit the research and development investments that would be required to market a new nail only for the large animal veterinary market.
In-vivo characterisation of 3D-printed bone graft substitute material in a rabbit femoral defect model
In orthopaedic, spine and maxillofacial surgery there is a growing, unmet need for biomaterials that can support bone regeneration in the millions of patients who suffer from challenging and non-healing bone defects each year. Although autologous bone grafts ("autograft") is considered the standard of care for replacing bone it has several important limitations, including donor site morbidity and a physical limit as to how much bone can be harvested. Allograft bone, which provides an option for replacing larger bone defects, also has limitations, including cost and the potential disease transmission.
In light of the unmet needs of patients with non-healing bone defects and the limitations (described above) of current "natural" bone graft materials, the market for synthetic bone graft substitutes in humans continues to increase and is expected to top $4 billion by year 2025. However, these commercially available, off-the-shelf bone graft substitutes assume that one size fits all, which is not the case when dealing with complex post trauma, post-cancer resection or congenital anomalies bone reconstruction surgeries where surgeons are facing individually unique bone defects (anatomically, mechanically and functionally). There is an urgent need to a cost-efficient, customizable solution for repairing these bone defects in both humans and animals.
3D printing has revolutionized our approach to surgery and to the development of customised, biomimetic scaffolds for tissue engineering. A number of research groups are actively exploring the use of these 3D printed matrices as bone replacement scaffolds or as depot systems for delivering antimicrobial or chemotherapeutic agents to skeletal sites. The material that we have developed is relatively inexpensive and easily sourced. There is a long and successful history of bovine tissues being used in surgery, and the chemical processing used in preparing the decellularised matrix dramatically reduces the immunogenicity of the material. The combination of DECM with PCL, a material with a solid track record as a resorbable polymer, offers real potential as a solution for patients with significant bone loss. In contrast with existing 3D-printable composites made of ceramic and polymer, we expect that the use of a decellularised bovine matrix will provide tangible benefits in terms of early healing response by virtue of the residual bone-derived growth factors in the processed material.
In Vivo Biomechanical Evaluation of a Larger Diameter Angle‐Stable Interlocking Nail in a Calf Tibial Fracture Model
Fracture of long bones is one of the major common orthopedic conditions encountered in ruminants and accounts for up to 10% of the caseload at referral centers. Tibial fractures account for 15-41% of long bone fractures in cattle, regardless of age. The majority of neonatal calves sustain a tibial fracture during assisted delivery or trauma from the dam resulting in typical configurations. In older calves, tibial fractures can occur during transport, while in pasture or in cattle sheds.18 The resulting fracture is typically affecting the diaphysis. Proximal and distal physeal tibial fractures are very unstable and result in a significant economic loss when the bone fails to heal or if the fracture develops into an open fracture, both of which can result from the employment of inadequate fixation methods.
While conservative treatment involving stall confinement and/or use of external coaptation has been reported, severe and potentially life-threatening complications and not acceptable bone healing have been frequently described even in newborn calves less than 80kg. Severe angular limb deformity of the fractured limb with persistent lameness despite bone healing is reported. While open reduction and internal fixation using bone plates and screws can be successful in adults, the thin cortices of calves juvenile bone do not provide sufficient physical strength to hold bone screws. Reports detailing other treatments for juvenile bovine tibial fractures include bone intramedullary rods and external skeletal fixator and describe high complication rates and overall poor clinical outcomes. Intramedullary interlocking nail (IIN) fixation has been used in small animals and resulted in successful outcomes in a large number of cases with similar fractures. Recently, a tibial fracture repair technique using an 8-mm angle-stable interlocking nailing system was reported in 2 calves with encouraging results. While such a small diameter INN system may provide an effective alternative for osteosynthesis of tibial fractures in young calves, biomechanical evaluation of such repair is needed before wide implementation of the system in clinical patients. In current recommendations regarding INN in humans, the largest possible nail diameter should be chosen to tailor the narrowest region of the inside of the medullary cavity as it offers the best biomechanical outcomes. While 8-mm diameter INN are available to veterinary surgeons, choosing a larger nail diameter may make more biomechanical sense, since it allows the superior stiffness offered by a larger-diameter, as compared with smaller-diameter, nail to be exploited. The identification of a IIN system already commercially available from the veterinary or human market to optimally exploit the mechanical potential of the implant within the constraint of what is feasible in farm animal clinical practice would facilitate and accelerate its implementation in surgery.
Improved Biomechanical Properties of Large Animals LCP using Larger Core Diameter Locking-Head Screws
The main goal of internal fixation is to maintain fracture stability to encourage bone union while maintaining a functional limb during healing. Therefore, successful fracture fixation results when the various loading forces acting on the fracture fragments are resisted by the mechanical stiffness of the bone-implant construct. Given the extreme forces horse patients can apply to fracture fixation devices, equine surgeons routinely work at mechanical limits of implants during the repair of adult long-bone fractures. Despite improved orthopedic equipment such as the LCP, providing a fixation with adequate strength to protect the fracture from the forces of weight-bearing throughout the healing period in equine fracture repair remains challenging. Taken together, this explains why open reduction and internal fixation in equine surgery is associated with poor survival rates and a high risk of catastrophic failure of the repair or cyclic fatigue failure of the implants.
Larger and stronger implants for internal fixation can reduce the incidence of catastrophic implant failure. A stronger plate, the 5.5-mm broad LCP, was specially designed with an increased plate thickness for large animal fracture repair. This modification lead to a superior resistance to static overload and a 31% increase in cyclic fatigue of the 5.5 LCP compared to the 4.5 LCP. However, screw loosening and breakage remain a frequent complication in the clinical application of LCP in horses and occur in almost 20% of LCP stabilization. Screw breakage is influenced by the bending stiffness of the screw which can be evaluated by calculation of the area moment of inertia for the screw core diameter (area moment of inertia (I) = π r4/4). A small increase in the core diameter of a screw such as the introduction of a new locking screw with a 1-mm core diameter increase will have a large effect on its bending stiffness and have the potential to reduce the incidence of implant failure. The increased stability of a locking screw with a larger core diameter would be of significant clinical advantage for long bone fracture repair proximal to the third metacarpus/metatarsus which currently have a poorer prognosis, partly because of the decreased ability to supplement internal fixation with external coaptation. Generally, if greater bending loads are applied during a given cycle of loading, fewer cycles are needed to break the implant as a result of fatigue. Another interesting advantage of a screw with an increased bending stiffness worth noting is its expected decreased displacement under an applied load (deflection) improving fatigue resistance. The increased capability of resisting cyclic fatigue of a locking screw with a larger core diameter could improve fracture healing in all fracture repair allowing placement of 6.0-mm locking screws.
Biomechanical Properties of a New Locking Compression Plate Design for Large Animals to Accommodate Modified 5.5-mm Cortex Screws with Larger Head Size: A Study on an Equine Long-Bone Fracture Model
The main goal of internal fixation is maintaining fracture stability to encourage bone union while maintaining a functional limb during healing. Therefore, successful fracture fixation results when the various loading forces acting on the fracture fragments are resisted by the mechanical stiffness of the bone-implant construct. Given the extreme forces equine patients can apply to fracture fixation devices, surgeons routinely work at mechanical limits of implants during the repair of adult long-bone fractures. Despite improved orthopedic equipment such as the LCP, providing a fixation with adequate strength to protect the fracture from weight-bearing forces throughout the healing period, equine fracture repair remains challenging. Taken together, this explains why open reduction and internal fixation in equine surgery are associated with poor survival rates and a high risk of catastrophic failure of the repair or cyclic fatigue failure of the implants.
Larger and stronger implants for internal fixation can reduce the incidence of catastrophic implant failure. A more robust plate, the 5.5-mm broad LCP, was specially designed with an increased plate thickness for large animal fracture repair. This modification led to superior resistance to static overload and a 31% increase in cyclic fatigue of the 5.5 LCP compared to the 4.5 LCP. A larger cortical screw, the 5.5-mm large animal cortex screw, was also specially created for the large animal veterinary market. This modification in the core diameter led to an increased area moment of inertia (area moment of inertia (I) = π r4/4), leading to an improved bending stiffness of the 5.5-mm cortex screw compared to the 4.5-mm. Nevertheless, screw loosening and breakage remain a frequent complication in the clinical application of LCP in horses and occur in almost 20% of LCP stabilization. The 5.5 LCP and 5.5-mm cortical screw were designed with the same head-related features as the 4.5 LCP and 4.5-mm cortical screw, meaning they have the same Combi hole and screw head diameter, respectively. Hence, the relatively small area of pressure under the screw head in the 5.5 LCP Combi hole and the small head diameter of the 5.5-mm cortex screw could reduce the full potential of this construct by undermining its ability to limit stress rising around the screw heads and to produce plate-to-bone compression. The use of modified LCP to accommodate cortical screws with larger head diameters should improve biomechanical stress distribution around the screw heads and allow better plate-to-bone compression, and therefore have the potential to reduce the incidence of implant failure. Generally, when the stress is better distributed around the implants and bone, more cycles are needed to break the implant due to fatigue. In addition, the ability of a screw to generate a higher insertion torque could increase its ability to obtain a stable construct from decreased micromovements between the LCP and bone in the region of the plate occupied by cortical screws. The increased stability of an LCP construct for hybrid plating would be of significant clinical advantage for long bone fracture repair proximal to the third metacarpus/metatarsus, which currently has a poorer prognosis, partly because of the decreased ability to supplement internal fixation with external coaptation.
AO VET Seed grants
Translational Medicine: Resorbable bone adhesive for noninvasive mandibular fracture repair in dogs (USA)
There is a need for improved, non-invasive products that can fixate canine mandibular fractures and promote osteosynthesis. Dogs sustaining facial fractures commonly suffer fractures to the mandible (~90%). These jaw fractures typically (~50%) involve the major chewing tooth (mandibular first molar). The large size of this tooth creates an area of weakness that is prone to fracture. Mandibular fracture repair can be particularly challenging in the caudal mandible of dogs. Muscular attachments and neurovascular structures in the caudal mandible complicate surgical exposure compared to rostral fracture repair.
Repairing these fractures are typically approached by either open reduction and rigid internal fixation, or through non-invasive repair techniques where stabilization is applied in the oral cavity. Anatomic structures such as tooth roots and the inferior alveolar neurovascular bundle severely limit locations where pilot screw holes can be created for conventional plate fixation. Noninvasive fracture repair techniques minimize surgical exposure of the fracture site and minimize risk for damaging or disrupting anatomic structures such as tooth roots or vessels. Intraoral repair techniques that spare the health of neighboring teeth include placing wires around teeth (interdental wiring) and the application of composite splints bonded to the tooth crowns. Whilst this may generate enough stabilization to promote healing, it is not as rigid as bone plating techniques and TN may provide additional stabilization for noninvasive fracture repair. Thus far, TN has demonstrated increased load to failure in transverse, osteotomized mandibles. Characterization and quantification of TN’s contribution to composite splint stabilization in spontaneously created fractures will help guide clinical repair recommendations.
Unraveling the mechanism of action of intra articular medications in an explant model for OA (Austria)
Osteoarthritis (OA), a chronic degenerative joint disease characterized by cartilage breakdown, subchondral bone remodeling and synovial inflammation, is the most common musculoskeletal disorder in humans as well as in horses and among the most important causes of pain, disability and health related economic loss. Secondary to a variety of etiologic factors such as mechanical injury, genetics, ageing, gender and obesity, a common molecular pathway linking biochemical and biomechanical processes leads to the typical pathological progression of OA with an imbalance of cartilage matrix synthesis and degradation and a vicious positive feedback loop involving cartilage breakdown and synovial inflammation. All tissues within a joint (cartilage, synovial membrane, subchondral bone and potential auxiliary structures like meniscus) contribute to and simultaneously are affected by the disease process. They release pro-inflammatory cytokines and proteolytic enzymes that trigger a positive feedback loop leading to further destruction of articular cartilage and articular inflammation. Synovial macrophages were found to be key player in promoting this artcular inflammation during OA. The synovial macrophages can be classified as “classically activated” M1 macrophages that have a pro-inflammatory phenotype and “alternatively activated” M2 macrophages with an anti-inflammatory phenotype and involvement in tissue remodeling.
Unfortunately, to date no disease-modifying treatment is available and therapy is largely limited to relieving the symptoms of OA. Several intra articular medications, including ACS, PRP and PAAG have reportedly achieved clinical improvement with reduction in lameness, but the mechanism by which their administration may result in alleviation of OA symptoms is incompletely understood.
Up to now the readout of most reports, testing new treatment approaches for OA, is based on clinical improvement, single molecular markers or diagnostic imaging. Hence, we still know very little about the exact molecular mechanism, signalling pathways and crosstalk between the different joint tissues and even less how these are modulated by intra articular medications. To date only a very limited number of studies exists that describe treatment effects on specific molecular pathways in a joint in the course of OA. Most of these in vitro cultures focus on only one or two articular tissues involved in the onset and/or progression of OA. However, given the complex pathophysiology of OA, it is paramount to study treatment effects in a model system, which account for the intricate interaction of cartilage, synovium and subchondral bone. Evaluating the effect of currently used intra articular treatments on different components of a joint, their crosstalk and their inflammatory response will help understanding pathophysiologic processes of OA and offer valuable information how to optimize application modalities or their composition. The aim of the proposed study is to unravel the modes of action of these treatments on the molecular level and compare their influence on the pathophysiological pathways active during OA using our recently developed in vitro osteochondral-synovial explant model for OA.
Prophylactic efficacy of TPLO for the CrCL in canine stifle joint of experimentally eTPA model (Japan)
Cranial cruciate ligament rupture (CrCLR) is an orthopedics disease that occurs with high frequency in dogs. While anterior cruciate ligament rupture in humans occurs with trauma, CrCLR in dogs occurs as a result of chronic degenerative changes of the ligament. The chronic progression is called “cruciate disease.” Cruciate disease is characterized by cartilage metaplasia, weakening by microfracture, and partial tearing followed by complete rupture of the cranial cruciate ligament (CrCL). Although the pathological condition has not yet been clarified, excessive tibial plateau angle (eTPA) is known to be one of the factors of cruciate disease. When a vertical compressive force is applied at the tibiofemoral joint as during weight bearing, cranial tibial thrust (CrTT) is generated and displaces the tibia forward under the CrCLR. It is considered that the greater the tibial plateau angle (TPA), the greater the CrTT, and consequently the greater the load on CrCL. Therefore, Macias and colleagues suggested that caudal deformities of the proximal tibia resulting in excessive TPA(eTPA) were thought to be responsible for CrCL failure in dogs. Our group has previously shown by experiments that increasing TPA can induce CrCL degeneration including cartilage metaplasia.
CrCL is composed of cells and extracellular matrix (ECM), and most of the dry weight is collagens. Up to 90% of ligamentous collagens are type I collagen (COL1) which is the most resistant to tensile force among collagens. Vasseur and colleagues reported that histological findings on hematoxylin eosin staining (HE) as cartilage metaplasia showed reduced mechanical property. Then, Ichinohe and colleagues reported ECM of ruptured CrCL has changed such as decreased COL1, increased type 2 (COL2) and 3 (COL3) collagens, and enhanced expression of the sry-type HMG box 9 (SOX9).
The clinical efficacy of tibial plateau leveling osteotomy (TPLO) is widely recognized. TPLO is a functional stabilization method that was first described by Slocum and Slocum. This surgical method involves an osteotomy and rotation of the proximal tibia to correct the TPA. The goal of TPLO is to neutralize CrTT and prevent cranial displacement of the tibia during the stance phase. Krotscheck and colleagues compared the peak vertical force (PVF) as the weight bearing function between normal dogs versus dogs with CrCLR treated by TPLO, and found that the PVF in the TPLO group had recovered to the level of the normal dogs during both walking and trotting by 6 months postoperatively. However, Rayward and colleagues reported a significant increase in the osteoarthritis (OA) score from preoperatively to 6 months postoperatively. We consider that one of the factors of OA progression is instability that cannot be limited by TPLO. We reported TPLO provided affective craniocaudal stabilization during vertical compression in stifle joint with a transected CrCL. However, TPLO promote instability under drawer movement and internal-external movement in stifle joint with transected CrCL. In clinical cases, the instabilities also may be related to the pivot-shift phenomenon postoperatively. Hulse and colleagues reported that the extent of injury of the articular cartilage after TPLO depends on the degree of CrCL damage. They evaluated the articular cartilage by arthroscopy after TPLO and found that when the CrCL function was preserved, the articular cartilage became normal or nearly normal and the further damage of the CrCL was suppressed, whereas when the CrCL function was not preserved, the degree of damage of the articular cartilage was worsened. Against this background, the focus is also on the treatment of partial CrCL tear. An ex vivo study showed that the smaller the TPA created by TPLO, the lesser the CrCL strain during compression in the stifle. The results of these biomechanical studies suggest that TPLO also reduces the mechanical load on CrCL in vivo, and it is expected that such effects may lead to better CrCL macroscopic findings of partial tears.
However, it is unclear whether this degenerative change has been restored or has been slowed down and healed at the organizational level. So, the purpose of this study is to clarify the prophylactic effects of TPLO on CrCL degeneration in the stifle joints with the eTPA.