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ABSTRACT: 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.
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.
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.
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.
Veterinary and Comparative Orthopaedics and Traumatology 01/2011; 24(6):426-34. · 0.81 Impact Factor
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ABSTRACT: Little is known about the torsional properties of bone-plate constructs when a combination of locking and non-locking screws have been used. Sixty cadaveric canine femurs were divided into three groups. In the first group, the plate was affixed using three non-locking screws. In the second group, only locking screws were used while a combination of one locking and two non-locking screws were used in the third group. All constructs were subjected to torsion until failure. Torque, angle of torsion, and work were all calculated at the maximum failure point, as well as at five degrees of plastic deformation, which was thought to be more representative of clinical failure. At the maximum failure point, the locking group had significantly higher torque, angle, and work values than the non-locking group. The combination group was intermediate to the two other groups, and significantly differed from the non-locking group in torque, and from the locking group in work. At five degrees of plastic deformation, the locking group required significantly higher torque and work than the non-locking group. The combination group required a significantly higher torque than the non-locking group. This study suggests that a construct composed of all locking screws will fail at a greater torque value, and sustain greater work to failure in torsion compared to a construct composed of all non-locking screws. The addition of a single locking screw to an otherwise non-locking construct will increase the torque at the offset failure point and may be of clinical value in constructs subjected to high torsional loads.
Veterinary and Comparative Orthopaedics and Traumatology 12/2009; 23(1):7-13. · 0.81 Impact Factor
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ABSTRACT: 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.
Veterinary and Comparative Orthopaedics and Traumatology 02/2008; 21(4):312-7. · 0.81 Impact Factor
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ABSTRACT: 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.
Veterinary and Comparative Orthopaedics and Traumatology 02/2008; 21(3):195-201. · 0.81 Impact Factor
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ABSTRACT: The objective was to compare mean peak vertical force (PVF) obtained with a treadmill with two integrated force plates (TM) with the piezoelectric force platform (FP) for sound and lame dogs at a trot. The aim was also to report the inter-step variability (ISV) for both systems and the effect of lameness on these values. Six sound dogs (20.0-25.5 kg) and six dogs with a grade 2/5 forelimb lameness (17.0-36.1 kg) were used in the study. Dogs were acclimatized and assigned an individual target velocity (1.8-2.2 m/s). Mean PVF measurements were obtained for both TM and FP. Subject velocity was controlled by belt speed on TM and restricted to 0.25 M/s above or below the assigned target velocity for FP. Acceleration was limited to +/- 0.3 M/s2. For the sound dogs, concordance and correlation coefficients of the mean PVF for the front limbs was 0.79 and 0.76, respectively. Concordance and correlation for the rear limbs was 0.90 and 0.81, respectively. For the lame dogs, concordance and correlation for the front limbs was 0.73 and 0.59, respectively. Concordance and correlation for the rear limbs was 0.89 and 0.95, respectively. ISV was 0.94 with TM and 0.84 with FP for the sound dogs and 0.96 with TM and 0.87 with FP for the lame dogs. In conclusion, TM provided rapid PVF measurements, good concordance for the hind limbs, and substantial concordance for the forelimbs in both sound and lame dogs at a trot as compared to FP. Both systems demonstrated excellent ISV for both lame and sound dogs.
Veterinary and Comparative Orthopaedics and Traumatology 02/2006; 19(4):205-12. · 0.81 Impact Factor
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Journal of Small Animal Practice 09/2003; 44(8):345, 378, xiii. · 1.00 Impact Factor
