Stem cell mobilisation and homing to improve fracture healing

Stem cell homing and migration is regulated through chemokine SDF-1 and its receptor CXCR4. In vitro studies in mice have demonstrated endogenous mobilisation of mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) by administering growth factors and AMD3100, which is an antagonist of CXCR4. The hypothesis of my study was that antagonism of the CXCR4-SDF1 axis would mobilise stem and progenitor cells into the circulation, and by increasing the available pool of cells in early fracture healing, improve bone formation. Peripheral blood MSCs and EPCs were isolated from rats treated with VEGF and AMD3100. Non-mobilised controls did not yield any viable MSC CFUs, whereas mobilised were significantly higher at 2.9±1.8 CFUs/ml blood (p=0.029). The MSCs were CD29 and CD90 positive and CD34 negative, however unlike bone marrow MSCs, they had a mixed CD45 expression. These cells were only able to differentiate down osteogenic lines in vitro. Mobilised EPCs had the typical ‘cobblestone’ morphology, were CD45 and CD34 negative, with low to variable expression of endothelial markers CD31 and VEGFR2, and MSC marker CD29. These cells had variable in vitro tube forming ability and could differentiate down adipogenic and not osteogenic lines. In order to evaluate the potential of endogenous mobilisation on fracture healing, a rat femoral osteotomy model stabilised with an external skeletal fixator was used. Several modifications were made to improve the reliability of the model and are reported in my thesis. The influence of gap size on interfragmentary strain and subsequent healing using this system was evaluated to identify the optimised situation to measure the effect of endogenous mobilisation. Mechanical analysis of the construct stiffness and the interfragmentary strain showed the gap size did not have an influence on the construct stiffness. However, increased gap size significantly reduced day 0 interfragmentary strain (p=0.013), with 1.0mm gap having significantly higher interfragmentary strain than the 2.0mm gap (p=0.029). To evaluate the effect of interfragmentary strain on healing, a femoral osteotomy in 12-14 week old female Wistar rats was stabilised with an osteotomy gap of 1.0mm, 1.5mm and 2.0mm. After five weeks, the 1.0mm gap had the largest callus (0.069um3) and bone volume per microCT slice (0.035um3). As the gap size increased, the bone volume per slice decreased, however significance was not found (p=0.082). Histomorphometry also showed the bone formation deceased as the gap increased. There was an increase in cartilage formation associated with the decrease in bone in the 1.5mm gap, whereas the 2.0mm gap had an increase in fibrous tissue associated with a decrease in cartilage and bone, indicating that the 2.0mm gap was tending towards fibrous non-union. The 1.5mm gap provided a suitable compromise to test endogenous mobilisation, and although the interfragmentary gap strain reduced as the gap enlarged, there was a reduction in osteotomy healing as the gap size increased. VEGF (V), IGF-1 (I) or GCSF (G) combined with AMD3100, or AMD3100 alone (A) were subsequently investigated using the rodent fracture model with a 1.5mm gap. At 5 weeks, groups V, I and A had increased bone formation compared to control animals, however, group A had a significant increase in bone volume (p=0.01) and group I a significant increase in % bone within the callus (p=0.035). Group G on the other hand, showed a decrease in bone volume. Irrespective of whether there was an increased or decreased bone content, all treated groups had an increase in trabecular thickness, or more accurately, thicker segments of woven bone, compared with the controls. Histomorphometric analysis showed decreased cartilage tissue was associated with increased bone in groups with improved healing, and was associated with increased fibrous tissue in poorly performing groups. Overall therefore, AMD3100 given alone significantly increased fracture healing over and above the control level. In conclusion, disruption of SDF1-CXCR4 axis can mobilise stem and progenitor cells, and can boost impaired fracture healing in a rat femoral osteotomy model

Postoperative complications associated with external skeletal fixators in cats

OBJECTIVES: The objective of this study was to quantify complications associated with external skeletal fixators (ESFs) in cats and to identify potential risk factors. METHODS: A retrospective review of medical records and radiographs following ESF placement was performed. RESULTS: Case records of 140 cats were reviewed; fixator-associated complications (FACs) occurred in 19% of cats. The region of ESF placement was significantly associated with complication development. Complications developed most frequently in the femur (50%), tarsus (35%) and radius/ulna (33%). Superficial pin tract infection (SPTI) and implant failure accounted for 45% and 41% of all FACs, respectively. SPTI occurred more frequently in the femur, humerus and tibia, with implant failure more frequent in the tarsus. No association between breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, degree of fracture load sharing, and the incidence or type of FAC was identified. No association between region of placement, breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, fracture load sharing and the time to complication development was identified. CONCLUSIONS AND RELEVANCE: Complication development is not uncommon in cats following ESF placement. The higher complication rate in the femur, tarsus and radius/ulna should be considered when reviewing options for fracture management. However, cats appear to have a lower rate of pin tract infections than dogs

Combined physeal fractures of the distal radius and ulna: complications associated with K-wire fixation and long-term prognosis in six cats

Objectives The objective was to describe the complications and long-term outcome associated with Kirschner (K)-wire fixation of combined distal radial and ulnar physeal fractures in six cats. Methods Medical records (2002-2014) of six referral institutions were searched for cats with combined distal radial and ulnar physeal fractures. Cases with complete clinical files, radiographs and surgical records were retrospectively reviewed. Long-term outcome was assessed via telephone interviews using an owner questionnaire. Results Complete files were available for 6/9 identified cases (cases 1-6). All fractures were classified as Salter-Harris type I or II. Five cases underwent open reduction and internal fixation via cross-pinning of the distal radius and intramedullary pinning of the ulna (cases 1-3); fixation of the distal radial and ulnar physes with one K-wire each (case 4); and K-wire fixation of the radial physis in combination with two transulnoradial K-wires (case 5). One case underwent closed reduction and percutaneous cross-pinning of the distal radius under fluoroscopic guidance (case 6). The complications encountered were: reduced radiocarpal range of motion (ROM) (cases 1, 3, 4, 5); implant loosening/migration (cases 1, 2, 5); and radioulnar synostosis (case 4). None of the cats developed angular limb deformity. Long-term outcome (12 months to 7 years after surgery) was graded as 'excellent' by the owners in all cases. Conclusions and relevance Prognosis is favourable for feline combined distal radial and ulnar physeal fractures following K-wire fixation in cats over 7 months of age. Implant removal after bony union is recommended to minimise reduction in ROM and to prevent implant loosening/migration

Feline head trauma: a CT analysis of skull fractures and their management in 75 cats

The aim of this study was to describe and evaluate the configurations and management of feline skull fractures and concurrent injuries following head trauma

CT characterisation and classification of feline temporomandibular joint trauma : a case series of 79 cats

Research Areas: Veterinary SciencesObjectives The aim of this study was to characterise and describe patterns of temporomandibular joint (TMJ) injuries occurring in cats using CT. Methods A cross-sectional study was carried out in adherence with the STROBE guidelines. Among the medical and CT records of 79 cats, 158 TMJs were reviewed in a collaborative study between six institutions. Results TMJ injuries were most commonly unilateral, representing 70.9% of cases. The mandibular condyle was fractured in 88 cases (55.7%) of the 158 TMJs observed. Of those, 84.0% were intra-articular condyle fractures, with the medial half of the mandibular condyle over-represented. Luxations occurred in 32.9% of cases, which was 19.0% of all evaluated TMJs. Rostrodorsal luxations were most common representing 87.0% of all luxations. Temporal bone fractures were observed in 30.4% of all cases, which was 18.4% of TMJs. The majority of fractures were of an unknown cause. When the cause was determined, road traffic accident (RTA) was the most frequent, followed by animal interaction, other external forces (sharp or blunt force) and high-rise trauma. Bilateral injuries were 13.1 times more likely to occur in high-rise trauma (P=0.01) and temporal bone fracture was significantly associated with RTAs (P=0.016). No other significant associations were observed between cause of injury and the resulting TMJ injury pattern. Conclusions and relevance Various TMJ injury patterns can occur in cats as a result of trauma. Intra-articular fractures of the medial half of the mandibular condyle occur most commonly. Although unilateral injuries are more frequent, high-rise trauma tends to present with bilateral lesions. Further studies with a larger sample size should be performed to better understand TMJ patterns of injury and how they relate to possible causes.info:eu-repo/semantics/publishedVersio

The influence of gap size on the development of fracture union with a micro external fixator

Increasingly, the rat femoral fracture model is being used for preclinical investigations of fracture healing, however, the effect of gap size and its influence on mechanobiology is not well understood. We aimed to evaluate the influence of osteotomy gap on osteotomy healing between the previously published extremes of guaranteed union (0.5 mm) and non-union (3 mm) using this model. A femoral osteotomy in 12–14 week old female Wistar rats was stabilised with a micro fixator (titanium blocks, carbon fiber bars) with an osteotomy gap of 1.0 mm (n = 5), 1.5 mm (n = 7), 2.0 mm (n = 6). After five weeks, the left femur was retrieved. The osteotomy gap was scanned using X-ray microtomography and then histologically evaluated. The radiographic union rate (complete mineralised bone bridging across the osteotomy) was three times higher for the 1.0 mm than the 2.0 mm gap. The 1.0 mm gap had the largest callus (0.069μm3) and bone volume (0.035μm3). Callus and bone volume were approximately 50% smaller within the 2.0 mm gap. Using cadaveric rat femurs stabilised with the external fixator, day 0 mechanical assessment of construct stiffness was calculated on materials testing machine displacement vs load output. The construct stiffness for the 1.0, 1.5 and 2.0 mm gaps was 32.6 ± 5.4, 32.5 ± 2.4, and 32.4 ± 8.3 N/mm (p = 0.779). Interfragmentary strain (IFS) was calculated using the change in osteotomy gap displacement as measured using microstrain miniature differential reluctance transducer spanning the osteotomy gap. Increasing the gap size significantly reduced the IFS (p = 0.013). The mean ‘day 0’ IFS for the 1.0, 1.5 and 2.0 mm gaps were 11.2 ± 1.3, 8.4 ± 1.5 and 6.1 ± 1.2% respectively. A 1.5 mm gap resulted in a delayed fracture healing by 5 weeks and may represent a useful test environment for fracture healing therapy. Increasing gap size did not affect construct stiffness, but did reduce the ‘day 0’ IFS, with a doubling of non-union and halving of bone volume measured between 1.0 and 2.0 mm gaps

Multiligament stifle injury, a multicenter retrospective study in 26 dogs

Objectives: To describe multiligament stifle injury in dogs and report complications and long-term outcomes. Methods: Medical records of dogs surgically treated for multiligament stifle injury were reviewed from six veterinary hospitals. Long-term follow-up was collected from referring veterinarians. Results: Twenty-six client-owned dogs and 26 stifles were included. Road traffic accidents and limb entrapment were the most common causes of injury. Cranial cruciate and lateral collateral ligament rupture was the most common combination of injury (10 cases). The caudal cruciate ligament was damaged in 12/23 cases but was surgically addressed in only 2 cases. Cranial cruciate ligament rupture was present in all cases and was managed using TPLO (6 cases), extracapsular suture (15 cases) and TTA (2 cases). Postoperative immobilisation with a transarticular external skeletal fixator was used in 4/26 cases. Intraoperative complications were reported in 2/23 cases, short-term complications in 17/25 cases, of which eight were major, and long-term complications in 7/18, of which two were major. Patella luxation was seen in one case and is a previously unreported complication. The overall outcome was excellent in 9/24 cases, good in 5/24 cases, fair in 7/24 cases and poor in 3/24 cases. Follow-up time ranged from 1.5 months to 9 years with the median (IQR) of 9.5 (4.0 to 28.5) months. Conclusions: Multiligament stifle injury in dogs is associated with a high rate of major complications. The overall outcome was good to excellent in just over half of the dogs

The Extracellular Domain of Myelin Oligodendrocyte Glycoprotein Elicits Atypical Experimental Autoimmune Encephalomyelitis in Rat and Species

Atypical models of experimental autoimmune encephalomyelitis (EAE) are advantageous in that the heterogeneity of clinical signs appears more reflective of those in multiple sclerosis (MS). Conversely, models of classical EAE feature stereotypic progression of an ascending flaccid paralysis that is not a characteristic of MS. The study of atypical EAE however has been limited due to the relative lack of suitable models that feature reliable disease incidence and severity, excepting mice deficient in gamma-interferon signaling pathways. In this study, atypical EAE was induced in Lewis rats, and a related approach was effective for induction of an unusual neurologic syndrome in a cynomolgus macaque. Lewis rats were immunized with the rat immunoglobulin variable (IgV)-related extracellular domain of myelin oligodendrocyte glycoprotein (IgV-MOG) in complete Freund’s adjuvant (CFA) followed by one or more injections of rat IgV-MOG in incomplete Freund’s adjuvant (IFA). The resulting disease was marked by torticollis, unilateral rigid paralysis, forelimb weakness, and high titers of anti-MOG antibody against conformational epitopes of MOG, as well as other signs of atypical EAE. A similar strategy elicited a distinct atypical form of EAE in a cynomolgus macaque. By day 36 in the monkey, titers of IgG against conformational epitopes of extracellular MOG were evident, and on day 201, the macaque had an abrupt onset of an unusual form of EAE that included a pronounced arousal-dependent, transient myotonia. The disease persisted for 6–7 weeks and was marked by a gradual, consistent improvement and an eventual full recovery without recurrence. These data indicate that one or more boosters of IgV-MOG in IFA represent a key variable for induction of atypical or unusual forms of EAE in rat and Macaca species. These studies also reveal a close correlation between humoral immunity against conformational epitopes of MOG, extended confluent demyelinating plaques in spinal cord and brainstem, and atypical disease induction