The effect of the combination of locking screws and non-locking screws on the torsional properties of a locking-plate construct
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.
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ABSTRACT: There are several factors that can affect the fatigue life of a bone plate, including the mechanical properties of the plate and the complexity of the fracture, position of the screws can influence construct stiffness, plate strain and cyclic fatigue of the plate. No studies have investigated these variables in implants utilized for long bone fracture fixation in dogs and cats. The purpose of the present study was to evaluate the effect of plate working length on construct stiffness, gap motion and resistance to cyclic fatigue of dog femora with a simulated fracture gap stabilized using a 12-hole 2.4 mm LCP. Femora were plated with 12-hole 2.4 mm locking compression plates (LCP) using 2 screws per fracture segment or with 12-hole 2.4 mm LCP using 5 screws per fracture segment resulting in a short working length. Construct stiffness did not differ significantly between stabilization techniques. Implant failure did not occur in any of the plated femora during cycling. Mean +/- SD yield load at failure in the short plate working length stabilization technique were significantly higher than in the long plate working length stabilization technique. In a femoral fracture gap model stabilized with a 2.4 mm LCP applied in contact with the bone, plate working length had no effect on stiffness, gap motion and resistance to fatigue. The short plate working length constructs failed at higher loading amount; however, yield loads for both short and long plate working length stabilization techniques were within physiologic range.BMC Veterinary Research 06/2013; 9(1):125. DOI:10.1186/1746-6148-9-125 · 1.74 Impact Factor
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ABSTRACT: OBJECTIVE: To compare the screw push-out strength and resistance to cantilever bending of 5 different angle-stable systems using 4 different insertion torque values to tighten locking screws. STUDY DESIGN: In vitro mechanical testing of 5 screw-plate constructs. SAMPLE POPULATION: Screw plate constructs (n = 60) were tested; 12 of each design, 3 for each torque value. METHODS: To compare push-out strength, screws were loaded in axial direction on the screw tip until loosening of the locking mechanism was recorded. For cantilever bending test, screws were loaded perpendicularly to their longitudinal axis at 2 mm of distance from the under surface of the plate. Load was applied in displacement control at 1 mm/min. RESULTS: There was a significant difference between the 5 different angle-stable systems regarding both push-out and cantilever bending strength. There was an influence of insertion torque value on push-out strength for 2 systems and insertion torque value influenced cantilever bending behavior only in 1 locking system. CONCLUSIONS: Locking mechanisms using "thread in thread" principle provided a stronger screw push-out behavior. Screws materials and core diameter of the different screws were directly related to cantilever bending strength.Veterinary Surgery 02/2013; 42(3). DOI:10.1111/j.1532-950X.2013.01088.x · 0.99 Impact Factor
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ABSTRACT: The case report of a 14-month-old Thoroughbred filly with acute onset of severe right hindlimb lameness is presented. The horse had a severe and sudden abduction of the hindlimbs due to a side effect of an overdose of lidocaine, which had been administered in a constant rate infusion after a colic surgery. Transcutaneous ultrasonography and standing radiography of the pelvis revealed proximal and cranial displacement of the greater trochanter and free bone fragments consistent with an apophyseal avulsion fracture of the greater trochanter. The complete diagnosis was obtained with the horse in a standing position. The filly was euthanatized because of deterioration resulting from the colic condition and of the poor prognosis of the fracture of the greater trochanter. Postmortem evaluation confirmed an apophyseal avulsion fracture of the right greater trochanter. To the authors' knowledge, ultrasonographic and radiographic findings of this fracture have not been described in the standing horse. The diagnosis was reached quite easily with the horse in a normal standing position when the characteristic ultrasonographic and radiographic findings were detected.Veterinary and Comparative Orthopaedics and Traumatology 06/2012; 25(4):342-7. DOI:10.3415/VCOT-11-11-0164 · 1.03 Impact Factor