Equine allogeneic umbilical cord blood derived mesenchymal stromal cells reduce synovial fluid nucleated cell count and induce mild self-limiting inflammation when evaluated in an lipopolysaccharide induced synovitis model.

REASONS FOR PERFORMING STUDY: Improvement has been reported following intra-articular (i.a.) injection of mesenchymal stromal cells (MSCs) in several species. These observations have led to the use of i.a. MSCs in equine practice with little understanding of the mechanisms by which perceived improvement occurs. OBJECTIVES: To evaluate the effect of i.a. allogeneic umbilical cord blood (CB-) derived MSCs using a lipopolysaccharide (LPS) induced synovitis model. We hypothesised that i.a. CB-MSCs would reduce the inflammatory response associated with LPS injection. STUDY DESIGN: Randomised, blinded experimental study. METHODS: Feasibility studies evaluated i.a. LPS or CB-MSCs alone into the tarsocrural joint. In the principal study, middle carpal joint synovitis was induced bilaterally with LPS and then CB-MSCs were injected into one middle carpal joint. Lameness, routine synovial fluid analysis, and synovial fluid biomarkers were evaluated at 0, 8, 24, 48 and 72 h. RESULTS: LPS injection alone resulted in transient lameness and signs of inflammation. In joints untreated with LPS, injection of 30 million CB-MSCs resulted in mild synovitis that resolved without treatment. Mild (grade 1-2) lameness in the CB-MSC-treated limb was observed in 2 horses and severe lameness (grade 4) in the 3rd, 24 h post injection. Lameness did not correlate with synovitis induced by CB-MSC injection. Simultaneous injection of LPS and CB-MSCs resulted in significant reduction in synovial fluid total nucleated, neutrophil and mononuclear cell numbers compared with contralateral LPS-only joints. No difference was detected in other parameters associated with synovial fluid analysis or in synovial fluid biomarkers. The incidence of lameness was only different from baseline at 8 h, where horses were lame in CB-MSC limbs. CONCLUSIONS: Allogeneic CB-MSCs reduced synovial fluid cell populations and stimulated mild self-limiting inflammation in the synovitis model. Continued evaluation of the effects of i.a. CB-MSC therapy on synovitis in horses is needed to evaluate anti- and proinflammatory properties of CB-MSCs. Immediate interests are dose, timing of treatment, and treatment frequency.

A comparison of conventional compression plates and locking compression plates using cantilever bending in an ilial fracture model.

OBJECTIVES: The purpose of this study was to compare the stiffness, yield load, ultimate load at failure, displacement at failure, and mode of failure in cantilever bending of locking compression plates (LCP) and dynamic compression plates (DCP) in an acute failure ilial fracture model. Our hypothesis was that the LCP would be superior to the DCP for all of these biomechanical properties. METHODS: Ten pelves were harvested from healthy dogs euthanatized for reasons unrelated to this study and divided into two groups. A transverse osteotomy was performed and stabilized with either a 6-hole DCP applied in compression or a 6-hole LCP. Pelves were tested in cantilever bending at 20 mm/min to failure and construct stiffness, yield load, ultimate load at failure, displacement at failure, and mode of failure were compared. RESULTS: The mean stiffness of DCP constructs (193 N/mm [95% CI 121 - 264]) and of LCP constructs (224 N/mm [95% CI 152 - 295]) was not significantly different. Mean yield load of DCP constructs (900 N [95% CI 649 -1151]) and of LCP constructs (984 N [95% CI 733 -1235]) was not significantly different. No significant differences were found between the DCP and LCP constructs with respect to mode of failure, displacement at failure, or ultimate load at failure. CLINICAL SIGNIFICANCE: Our study did not demonstrate any differences between DCP and LCP construct performance in acute failure testing in vitro.

Effect of the length of the superficial plate on bending stiffness, bending strength and strain distribution in stacked 2.0-2.7 veterinary cuttable plate constructs. An in vitro study.

OBJECTIVES: Use of stacked veterinary cuttable plates (VCP) increases the construct stiffness, but it also increases the stress protection and concentrates the stress at the extremities of the implants. We hypothesized that by shortening the superficial plate, it would not reduce the stiffness of the construct, but that it would reduce the stress concentration at the plate ends. METHODS: A 3 mm fracture gap model was created with copolymer acetal rods, stacked 2.0-2.7 VCP and 2.7 screws. The constructs consisted of an 11-hole VCP bottom plate and a 5-, 7-, 9- or 11-hole VCP superficial plate. Five of each construct were randomly tested for failure in four-point bending and axial loading. Stiffness, load at yield, and area under the curve until contact (AUC) were measured. Strains were recorded during elastic deformation for each configuration. RESULTS: During both testing methods, stiffness, load at yield and AUC progressively decreased when decreasing the length of the superficial plate. No statistically significant differences were obtained for load at yield in four-point bending and AUC in axial loading. The strain within the implant over the gap increased as the length of the superficial plate decreased. CLINICAL SIGNIFICANCE: Shortening the superficial plate reduces the stiffness and strength of the construct, and decreases stress concentration at the implants ends. As the cross section of the implant covering the gap remained constant, friction between the plates may play a role in the mechanical properties of stacked VCP.

The biomechanical properties of the feline femur.

The purpose of this study was to determine the biomechanical properties of feline long bone by testing cadaver bone from mature cats in compression, three-point bending, notch sensitivity and screw pull-out strength. The determination of these properties is of clinical relevance with regard to the forces resulting in long bone fractures in cats as well as the behaviour and failure mode of surgical implants utilized for fracture stabilization and repair in the cat. Cadaveric cat femurs were tested in compression, three-point bending and in three-point bending after the addition of a 2.0 mm screw hole. Cortical screws, 2.7 mm in diameter, were inserted in cadaveric cat femur samples for screw pull-out testing. The mean maximum load to failure of mid diaphyseal feline femurs tested in compression was 4201+/-1218 N. Statistical analysis of the parameter of maximum load tested in compression revealed a statistical difference between sides (p=0.02), but not location (p=0.07), or location by side (p=0.12). The maximum strength of mid diaphyseal feline femurs tested in compression was 110.6+/-26.6 MPa. The modulus of elasticity of mid-diaphyseal cat femurs tested in compression was determined to be 5.004+/-0.970 GPa. The mean maximum load to failure of feline femurs tested in three-point bending was 443+/-98 N. The mean maximum load to failure of feline femurs tested in three-point bending after a 2.0 mm diameter hole was drilled in the mid-diaphyseal region of each sample through both cortices was 471+/-52 N. The mean maximum load required for screw pull-out of 2.7 mm cortical screws placed in feline femurs tested in tension was 886+/-221 N. This data should be suitable for investigating fracture biomechanics and the testing of orthopaedic constructs commonly used for fracture stabilization in the feline patient.

Evaluation of a short glass fibre-reinforced tube as a model for cat femur for biomechanical testing of orthopaedic implants.

The biomechanical testing of tubes made of third generation short glass fibre-reinforced (SGFR) material approximating cat femurs was performed in order to determine their suitability as cat femur surrogates for the biomechanical testing of orthopaedic implants. The tubes were tested in compression, three-point bending, notch testing, and screw pullout. Thin walled (B1-tubes) had a 13% lower maximum load to failure, a 19% higher maximum strength and a 13% lower elastic modulus compared to cat femurs tested in compression. B1-tubes maximum load to failure in three-point bending and screw pullout strength were considerably lower compared to cat femurs (29% and 63%, respectively). Notch testing was not performed on B1-tubes due to low bending strength. Thicker walled (B2-tubes) had a 23% higher maximum load to failure, a 10% higher maximum strength and a 21% lower elastic modulus compared to cat femurs tested in compression. The comparison of B2-tubes and cat femurs in three-point bending revealed a 7% increase in maximum load to failure for the B2-tubes. Drilled B2-tubes (notch testing) were weaker with a 30% lower load to failure compared to cat femurs. A screw pullout comparison of B2-tubes and cat femurs revealed a 2% increase in maximum load to failure for the B2-tubes. These tubes were intended to provide a model as a suitable surrogate for cat femurs for testing the bending strength of various orthopaedic constructs involving plates and screws. Testing revealed that third generation SGFR tubes were not suitable for these purposes and emphasizes the need to carefully evaluate the suitability of any model.