Biomechanical comparison of inside?outside screws, cables, and regular screws, using a sawbone model

Abstract

Our aim was to conduct a biomechanical comparison of the pull-out strengths of inside-outside (I/O) screws, cables, and bone screws to determine whether I/O screws provide greater pull-out resistance than cables or bone screws, and their effectiveness with the screw diameter. There is no remarkable biomechanical experimental study comparing the I/O technique with conventional spinal techniques. The diameter of the screw heads were also biomechanically tested to determine the optimal size that can be used. In this study, 45 blocks of 50x50x5 mm of "sawbone" (synthetic bone, model 1137, Pacific Research Laboratories, Vashon, WA, USA) were used as bone substitutes. Fifteen sets of 14-mm inside-outside Dynalok screws and nuts, 15 wire cables, and 15 bone screws were inserted into a separate sawbone block. An MTS Bionx materials testing machine was used to measure the load to failure of each implant. The mean values and standard deviations of each group were calculated and Student's t-test was used for comparison. The load to failure of the inside-outside screws was significantly greater than that of the cables (p<0.0000004) and the regular bone screws (p<0.000002). The results also revealed that increasing the diameter of the head of the screw also increases the resistance against the pull-out strengths. Thus, using a larger screw in occipitocervical stabilization provides safe and stable fixation of the occipital bone to the cervical spine. This study also proved that sawbone is a useful and reliable alternative to allogenic fresh cadaveric bone grafts or animal bones for certain biomechanical testing.

Failure analysis of C-5 after total disc replacement with ProDisc-C at 1 and 2 levels and in combination with a fusion cage: finite-element and biomechanical models

“…The use of synthetic fixation media for the mechanical evaluation of spinal instrumentation has been documented in a number of studies. 2,6,8,14,20,23,30 The standard deviation of the measured load at failure was 8%, which is in the range of previous studies that used similar test materials. 2,6,8,14,20,23,30 For the intact construct, as expected, no vertebral body failure occurred for any of the vertebral body heights tested.…”

“…2,6,8,14,20,23,30 The standard deviation of the measured load at failure was 8%, which is in the range of previous studies that used similar test materials. 2,6,8,14,20,23,30 For the intact construct, as expected, no vertebral body failure occurred for any of the vertebral body heights tested. In all implanted tests, independent of the vertebral body height, the C-5 vertebra fracture occurred before the maximum test load was reached through a vertical split line that passed always through the keel cut, associating the keel cut with a geometrical defect that can act as stress raiser, promoting the vertebral body fracture.…”

Correction of clivoaxial angle deformity in the setting of suboccipital craniectomy: technical note

“…Caglar et al compared the biomechanical pullout strength of inside-out bolts with cables and standard screws. 5 Using a saw-bone model, they tested each group for pullout strength. They showed an average resistance of 1383 N for the 14-mm inside-out bolt, 636 N for multifilament cables, and 457 N for a 10-mm traditional screw system.…”

Use of Polyurethane Foam in Orthopaedic Biomechanical Experimentation and Simulation

“…Calgar et al (Caglar et al, 2005) performed biomechanical comparative studies of different types of screws and cables using Sawbone models and found out that the load to failure of screws was significantly greater than that of the cables. Farshad et al (Farshad et al, 2011)used PU foam blocks to test bone tunnels drilled during anterior cruciate ligament reconstruction.…”