Difference In Failure Load Research Articles

Reproducibility and Side Differences of Mechanical Tests for Determining the Structural Strength of the Proximal Femur

In this experimental study, we evaluated the reproducibility error of mechanical strength tests of the proximal femur when simulating a fall on the trochanter. Based on side differences in femoral failure loads in 55 pairs of femora, we estimated the upper limit of the precision error to be 15% for the side impact test, whereas the intersubject variability was >40%. Mechanical tests are commonly used as the gold standard for determining one of the main functions of bones, that is, to provide mechanical strength. However, it is unknown what magnitude of error is associated with these tests. Here we investigate the precision error and side difference of a side impact test of the proximal femur. BMC was measured using DXA in 54 pairs of femora from donors 79.0 +/- 10.6 years of age. Bones were tested to failure, simulating a fall on the greater trochanter. Failure loads were 3951 +/- 1659N (CV% = 42%) on the right and 3900 +/- 1652N (CV% = 42%) on the left (no significant side difference). The average random difference of femoral BMC was 7 +/- 7% and that of femoral failure loads was 17 +/- 12%. The correlation between BMC and failure load was 79% (r2), but the association between side differences in failure load with those in BMC was only 4%. When confining the analysis to pairs with less than 5% differences in BMC (n = 31), side differences in failure loads were 15 +/- 13%. When correcting failure loads for side differences of BMC, the difference was 16 +/- 15% These results suggest that the upper limit of the precision error for femoral strength tests is approximately 15% in a side impact configuration. Given the large intersubject variability of failure loads, this test provides an efficient tool for determining the structural strength of the proximal femur in a fall.

Effect of vertebroplasty on the compressive strength of vertebral bodies

Purpose of study: To compare the effect of vertebroplasty on the compressive strength of unfractured vertebral bodies.Methods used: Four cadaveric thoracic spines were used for this experiment, for a total of 40 vertebral bodies. Before testing, each thoracic spine was submitted to bone density testing and a radiographic evaluation to rule out any obvious fractures. Under image intensification, 6 ml of a mixture of polymethylmethacrylate (PMMA) with barium was injected into every other vertebral body of each spine specimen. After vertebroplasty, all soft tissues were dissected from the spine and the vertebral bodies were separated and potted into circular fames to allow for mechanical testing. Testing to failure was performed using a combination of axial compression and anterior flexion movements. Two pneumatic cylinders applied anterior and posterior loads at a distance ratio of 4:3 relative to the anterior vertebral body wall while two additional cylinders applied lateral loads, each at a constant rate of 200 N/second.of findings: Average failure load for nonvertebroplasty specimens was 6,724.02±3,291.70 N, whereas the specimens injected with PMMA failed at an average compressive force of 5,770.50±2,133.72 N. No statistically significant difference in failure loads could be found between intact specimens and those that had undergone vertebroplasty.Relationship between findings and existing knowledge: Vertebroplasty is gaining popularity as a treatment for osteoporosis-related problems. We are not aware of any previous biomechanical studies on the effect of PMMA injection on the vertebral compressive strength.Overall significance of findings: We were surprised to note that under these loading conditions, no significant increase in compressive strength of the vertebral bodies could be documented. This suggests that some caution be applied to the concept of “prophylactic” vertebroplasty in patients at risk for fracture.Disclosures: No disclosures.Conflict of interest: No conflicts.

The effect of strand configuration on the tensile properties of quadrupled tendon grafts

Purpose: To compare selected biomechanical properties of 4 different quadrupled tendon graft preparations applicable for anterior cruciate ligament reconstruction. Type of Study: Biomechanical investigation in a cadaver model. Methods: Graft strands were arranged in parallel, braided, bolo-plait, and twist configurations. Elongation of the graft was monitored during loading with an infrared optical measurement system, which measured the 3-dimensional position of twelve spherical reflective markers mounted within the camera field. Permanent elongation, stiffness, and ultimate strength of each graft configuration were determined. Results: Permanent graft strain after the first incremental loading cycle was 7.2% in braid, 6.6% in twist, 6.5% in bolo-plait, and 3.3% in parallel constructs (P <.0001). Permanent graft strain after a second incremental loading cycle was 1.2% in bolo-plait, 1.1% in braid, 0.7% in twist, and 0.7% in parallel preparations (P =.0012). Braid and bolo-plait grafts were less stiff than twist or parallel grafts (P <.0001). Differences in failure load were not significant (P =.171). Conclusions: Variation in graft configuration from the conventional, parallel strand pattern lead to increased viscoelasticity and permanent elongation of grafts with repetitive loading. This deficit is expected to cause increased laxity of the reconstructed knee.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 2 (February), 2002: pp 194–200

Fixation strength of meniscal repair devices

The aim of this study was to measure and compare the ultimate failure strengths and cyclic fatigue strengths of currently available meniscal suturing devices. No statistically significant difference in failure load was found between a vertical loop suture (mean 46.3 N), a horizontal mattress suture (52.5 N), the T-fix Device® (47.5 N), and the 16-mm (39.2 N) and 13-mm (32.8 N) Bionix Arrow®. Statistically inferior results were seen with the 10-mm Bionix Arrow® (18.8 N), the S.D. Sorb Stapler® (4.3 N), and the 12-mm Arthrex Meniscal Dart® (10.5 N) ( P<0.01). The Mitek Meniscal Repair System® (28.1 N) performed intermediate, with significantly better results than the S.D. Sorb Stapler® and the 12-mm Arthrex Dart®, but significantly worse than the vertical and horizontal sutures, the T-fix® and Bionix 16-mm Device® ( P<0.01). Cyclic fatigue strength was significantly less for the 10-mm Bionix Arrow®, the S.D. Sorb Stapler®, and the 12-mm Arthrex Meniscal Dart® ( P<0.01) compared to all other devices. We conclude that the 13- and 16-mm Bionix Arrow® and the T-fix Device® have comparable ultimate failure strengths and cyclic fatigue strengths to conventional meniscal suturing techniques. The 10-mm Bionix Arrow®, S.D. Sorb Stapler®, and the 12-mm Arthrex Meniscal Dart®, however, have far inferior failure and cyclic fatigue strengths and their clinical application should be questioned.

Failure strength of a new meniscus arrow repair technique: Biomechanical comparison with horizontal suture

A new method for arthroscopic all-inside repair of vertical meniscus lesions by use of a biodegradable fixation device (“meniscus arrow”) has been developed, including a set of cannulas for easy insertion via standard arthroscopic portals. The technique is described. A study to test the fixation properties was performed in the laboratory. Twenty-four fresh frozen bovine medial menisci were defreezed and devided into three groups. In all menisci an artificial vertical lesion was created with a scalpel 3 mm from the peripheral rim. Repair in group I was done with a single horizontal Maxon-0 suture using an Acufex double-barrel cannula (Acufex Meniscal Stitcher; Acufex Microsurgical, Norwood, MA). A knot was tied on the capsular side. Repair in group II was made with one 13 mm Biofix Meniscus arrow (Bioscience Ltd, Tampere, Finland). In group III repair was performed like in group II but the menisci were incubated in isotonic saline at 21°C for 24 hours before testing. Menisci in group I and II were tested within 3 hours after defreezing. Prior to testing total separation of central and peripheral part of meniscus was performed. Thus only the repair site was tested. Pull-out tests to failure were made in a computer-based Nene M5 testing maschine with a cross-head speed of 5 mm/min. Median failure load in group I: 49 N (range 43 to 77 N), in group II: 53 N (range 42 to 65 N) and in group III: 54 N (range 35 to 74 N). No statistically significant difference in failure load was found between the groups. Thus initial failure strength for arrow-repaired bovine menisci is comparable to that of a horizontal suture

New means in spinal pedicle hook fixation. A biomechanical evaluation.

Pedicle hooks which are used as an anchorage for posterior spinal instrumentation may be subjected to considerable three-dimensional forces. In order to achieve stronger attachment to the implantation site, hooks using screws for additional fixation have been developed. The failure loads and mechanisms of three such devices have been experimentally determined on human thoracic vertebrae: the Universal Spine System (USS) pedicle hook with one screw, a prototype pedicle hook with two screws and the Cotrel-Dubousset (CD) pedicle hook with screw. The USS hooks use 3.2-mm self-tapping fixation screws which pass into the pedicle, whereas the CD hook is stabilised with a 3-mm set screw pressing against the superior part of the facet joint. A clinically established 5-mm pedicle screw was tested for comparison. A matched pair experimental design was implemented to evaluate these implants in constrained (series I) and rotationally unconstrained (series II) posterior pull-out tests. In the constrained tests the pedicle screw was the strongest implant, with an average pull-out force of 1650 N (SD 623 N). The prototype hook was comparable, with an average failure load of 1530 N (SD 414 N). The average pull-out force of the USS hook with one screw was 910 N (SD 243 N), not significantly different to the CD hook's average failure load of 740 N (SD 189 N). The result of the unconstrained tests were similar, with the prototype hook being the strongest device (average 1617 N, SD 652 N). However, in this series the difference in failure load between the USS hook with one screw and the CD hook was significant. Average failure loads of 792 N (SD 184 N) for the USS hook and 464 N (SD 279 N) for the CD hook were measured. A pedicular fracture in the plane of the fixation screw was the most common failure mode for USS hooks.(ABSTRACT TRUNCATED AT 250 WORDS)

Increasing Strength of Graphite/Epoxy Bolted Joints by Introducing an Adhesively Bonded Metallic Insert

In this paper a method to increase the failure load in graphite/epoxy bolted joints where the failure mode is bearing strength is proposed by bonding a metallic insert in the hole. In order to design test specimens with significantly reduced compressive stresses at the hole boundary, finite element (FE) analysis was performed. The FE analysis revealed the possibility to reduce the compressive stresses at the hole boundary in quasi-isotropic laminate by approximately 50%, if a 10 mm hole is enlarged to 14 mm and a 2 mm thick metallic insert is adhesively bonded in the hole. Experimental results showed an increased failure load of up to 55% when using an aluminum insert and 30% when using steel insert, the steel insert also giving a 13 % stiffer joint. The adhesively bonded insert altered the failure mode to failure in the adhesive combined with net tension of the composite member. Further studies of FE-results explained the difference in failure load when using a steel or aluminum insert respectively by the fact that the stiffer steel insert causes higher tension stresses in the adhesive, which apperently leads to a primary tension failure in the adhe sive.