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PubMed2006

A biomechanical comparison of locking and nonlocking plates for the fixation of calcaneal fractures.

BACKGROUND: Locking plate systems have been developed in an attempt to increase the strength of fracture fixation and, in so doing, allow earlier mobilization and rehabilitation. The purpose of our study was to compare the mechanical integrity of the locking plate and traditional nonlocking plate fixation for calcaneal fractures in a cadaver model. Our hypothesis was that the locking plate construct provides stronger fixation than the nonlocking plate construct. METHODS: We created a Sanders type-IIB fracture in 10 pairs of fresh-frozen cadaver feet (bone mineral density, 0.50 +/- 0.14 g/cm2 age, 69 +/- 16 years). One foot of each pair was fixed with a nonlocking calcaneal plate (Synthes, Paoli, PA), and the contralateral foot was fixed with the Locking Calcaneal Plate (Synthes, Paoli, PA). The specimens then were cyclically loaded through the tibia from 0 to 700 N at 1 Hz on a materials testing machine to simulate weightbearing. Fragment displacement was measured with a three-dimensional kinematic analysis system. Significance was set at p < 0.05. RESULTS: There was no significant difference between the two plating systems with respect to the mean (+/- SD) number of cycles to failure (locking plate, 3261 +/- 2355; nonlocking plate, 2271 +/- 2465). CONCLUSION: In a cadaver model of type-IIB calcaneal fractures, locking plate fixation did not provide a biomechanical advantage over traditional nonlocking plate fixation.

Aged↗

PubMed2004

In vivo comparison of a metal versus a biodegradable suture anchor.

PURPOSE: This protocol compares an absorbable polylactic acid (PLA) anchor to a similarly sized metallic anchor, comparing the load to failure of the suture anchor construct in vivo in a goat model. TYPE OF STUDY: Basic science. METHODS: Thirty-nine goats underwent bilateral implantation of suture anchors at the intra-articular origin of the long digital extensor tendon at the knee (stifle). Each goat randomly received an absorbable anchor in one knee and a metallic anchor in the other. At 0, 6, and 12 weeks after implantation, the suture attached to the implanted anchor was pulled to failure on a materials testing machine, annotating the load at failure and location of failure of the suture anchor construct. RESULTS: At each time period tested, no difference was found in failure load between metal and PLA suture anchor constructs, nor was there degradation in strength over time of implantation of either anchor. Most failures occurred by suture breakage, and the force required for suture breakage did not differ between anchors. Three absorbable PLA anchors failed, one (1 of 13, 7.7%) at 6 weeks, and 2 (15.4%) at 12 weeks. PLA anchor failure occurred when the suture loop eyelet pulled out of the anchor's PLA body. CONCLUSIONS: The absorbable PLA suture anchor construct, tested in an in vivo, intra-articular model, had similar strength over a 12-week period of implantation with a comparable metal anchor construct. These absorbable anchors offer a reasonable alternative to metal anchors, with comparable strength and function and advantages unique to an absorbable anchor. CLINICAL RELEVANCE: This study provides the reader with an evaluation of the in vivo function and holding strength over time of implantation of an absorbable suture anchor in comparison with a metal anchor.

Absorbable Implants↗

PubMed1997

Active compression-decompression resuscitation: the influence of different chest geometries on the force transmission.

Active compression-decompression cardiopulmonary resuscitation (ACD-CPR) is performed using a plunger-like suction device applied onto the chest. Forces are partly transferred through the center of this device as well as through the peripheral ring of the plunger's lip seal. We analysed the load transmission distribution of the Ambu CardioPump; therefore a homemade mechanical model was used for simulating different chest geometries. We applied compression forces up to 750N on the device using a 'material testing machine', and we determined the load transferred through the central part of the device and the peripheral ring respectively. The results show that the deeper the sternum is inbeded in the chest the more force is distributed onto the peripheral ring of the plunger's vacuum cup. For a simulated flat chest, 70 N was transferred through the peripheral ring; at a simulated sternal depression of 20 mm, more than 300 N were transferred peripherally. This study points out that different chest geometries have to be considered when using CardioPump.

Cardiopulmonary Resuscitation↗

PubMed1993

Effects of thermocycling and occlusal force on the margins of provisional acrylic resin crowns.

Transitional acrylic crowns were examined for changes in axial contour and increases in marginal gap width after simultaneous thermocycling and occlusal loading. Two groups of 10 crowns--one with a shoulder finish line and another with a chamfer finish line--were treated with 3400 thermocycles and 50,000 load cycles simultaneously within an artificial oral environment chamber in an MTS Dental Materials Testing System. The marginal gaps were increased for both groups after treatment. However, the group of crowns with the shoulder finish lines demonstrated a smaller gap width (x = 90 microns) after treatment than the crowns with chamfer finish lines (x = 210 microns). A statistical comparison identified a significant difference in gap width between groups (p < 0.01). Changes in the axial profile of the groups were similar, but one crown with a chamfer finish line exhibited a cracked margin.

Acrylic Resins↗

PubMed2006

The polymethyl methacrylate cervical cage for treatment of cervical disk disease Part III. Biomechanical properties.

BACKGROUND: In a previous article, we used the PMMA cervical cage in the treatment of single-level cervical disk disease and the preliminary clinical results were satisfactory. However, the mechanical properties of the PMMA cage were not clear. Therefore, we designed a comparative in vitro biomechanical study to determine the mechanical properties of the PMMA cage. METHODS: The PMMA cervical cage and the Solis PEEK cervical cage were compressed in a materials testing machine to determine the mechanical properties. RESULTS: The compressive yield strength of the PMMA cage (7030 +/- 637 N) was less than that of the Solis polymer cervical cage (8100 +/- 572 N). The ultimate compressive strength of the PMMA cage (8160 +/- 724 N) was less than that of the Solis cage (9100 +/- 634 N). The stiffness of the PMMA cervical cage (8106 +/- 817 N/mm) was greater than that of the Solis cage (6486 +/- 530 N/mm). The elastic modulus of the PMMA cage (623 +/- 57 MPa) was greater than that of the Solis cage (510 +/- 42 MPa). The elongation of PMMA cage (43.5 +/- 5.7%) was larger than that of the Solis cage (36.1 +/- 4.3%). CONCLUSIONS: Although the compressive yield strength and ultimate compressive strength of the PMMA cervical cage were less than those of the Solis polymer cage, the mechanical properties are better than those of the cervical vertebral body. The PMMA cage is strong and safe for use as a spacer for cervical interbody fusion. Compared with other cage materials, the PMMA cage has many advantages and no obvious failings at present. However, the PMMA cervical cage warrants further long-term clinical study.

Biomechanical Phenomena↗

PubMed2006

Locking plates for corrective osteotomy of malunited dorsally tilted distal radial fractures: a biomechanical study.

The purpose of the study was to compare the biomechanical properties of five different palmar fixation plate designs in a distal radius osteotomy cadaver model. A 1cm metaphyseal osteotomy gap was made to simulate a corrective osteotomy and the osteotomy plated. Axial load was applied to the distal end of each construct by a material testing machine under control of a motion analysis video system. The specimens were arranged into five implant groups of eight specimens each. No test group developed deformity and movement of the fracture gap greater than 2mm with a load of 100N. Increasing the load to 250N revealed statistically significant differences in stiffness and failure load between the different plates. Axial failure strength and stiffness were greater for the radial correction plates than for the other implants. The former may provide enough stability for corrective osteotomy of dorsally angulated distal radial malunions, even when the osteotomy gap is only filled with cancellous bone graft instead of cortical bone graft.

Aged↗

PubMedDate not supplied

Syndesmosis fixation: analysis of shear stress via axial load on 3.5-mm and 4.5-mm quadricortical syndesmotic screws.

The effect of shear stress on a fixated distal syndesmosis of the ankle was evaluated with a servohydraulic materials-testing machine. Eighteen syndesmoses were fixated in a quadricortical technique using 3.5-mm cortical and 4.5-mm cortical stainless steel screws. A shear stress was applied via an axial load in an attempt to simulate weightbearing. The 4.5-mm quadricortical screws produced a higher yield load and peak load (484.3 +/- 93.8 N and 597.7 +/- 81.4 N) when compared with the 3.5-mm quadricortical syndesmotic screws (412.8 +/- 55 N, P = .033 and 511.2 +/- 64.4 N). These findings suggest that a larger diameter screw provides greater resistance to an applied shear stress at the distal syndesmosis.

Ankle Injuries↗

PubMed2006

Characterization of nanofilled compared to universal and microfilled composites.

OBJECTIVES: The purpose of this study was to compare the inorganic fraction and the mechanical properties of three nanofilled composites with four universal hybrid and two microfilled composites. The degrees of conversion of the materials photopolymerized using halogen and LED units were also investigated. METHODS: Three nanofilled (Supreme, Grandio and Grandio Flow), four universal hybrid (Point-4, Tetric Ceram, Venus, Z 100) and two microfilled (A 110, Durafill VS) composites were used in this study. Their filler weight content was measured by thermogravimetric analysis. The morphology of the filler particles was determined using scanning-electron microscopy (SEM). Mechanical properties were measured: dynamic and static elastic moduli, flexural strength and Vickers microhardness. The degree of conversion in relation with the depth of polymerization of every material tested was evaluated using Raman spectrophotometry. RESULTS: Nanofilled resin composites show higher elastic moduli than those of universal and microfilled composites, except for the Z-100. The microfilled composites exhibit by far the lowest mechanical properties. The flexural strength does not appear as a discriminating factor in this study. The degrees of polymerization obtained with the halogen lamp are higher than those obtained with the LED lamp. SIGNIFICANCE: Nanofilled resin composites show mechanical properties at least as good as those of universal hybrids and could thus be used for the same clinical indications as well as for anterior restorations due to their high aesthetic properties.

Composite Resins↗

PubMed2002

Mechanical properties of resin cements with different activation modes.

Dual-cured cements have been studied in terms of the hardness or degree of conversion achieved with different curing modes. However, little emphasis is given to the influence of the curing method on other mechanical properties. This study investigated the flexural strength, flexural modulus and hardness of four proprietary resin cements. Materials tested were: Enforce and Variolink II (light-, self- and dual-cured), RelyX ARC (self- and dual-cured) and C & B (self-cured). Specimens were fractured using a three-point bending test. Pre-failure loads corresponding to specific displacements of the cross-head were used for flexural modulus calculation. Knoop hardness (KHN) was measured on fragments obtained after the flexural test. Tests were performed after 24 h storage at 37 degrees C. RelyX ARC dual-cured showed higher flexural strength than the other groups. RelyX ARC and Variolink II depended upon photo-activation to achieve higher hardness values. Enforce showed similar hardness for dual- and self-curing modes. No correlation was found between flexural strength and hardness, indicating that other factors besides the degree of cure (e.g. filler content and monomer type) affect the flexural strength of composites. No statistical difference was detected in the flexural modulus among the different groups.

Analysis of Variance↗

PubMed2006

The effects of temperature and light intensity on the polymerization shrinkage of light-cured composite filling materials.

UNLABELLED: The aim of this study was to investigate the effect of light intensity on polymerization shrinkage of resin composites. The five materials tested were Lite-Fil (A) (LFA), Lite-Fil (P) (LFP), Z100, Palfique, (PAL) and Tetric (TRC). Two types of measurements were made to determine the effects of environmental temperature and light intensity. Results were analyzed by two-way analysis of variance (ANOVA) and Newman-Keuls procedure at (P<0.05). The changes in temperature and/or light intensity strongly affected composite shrinkage. The amount of shrinkage for LFP at 100% light intensity in room temperature (23 degrees C) was 1.26% and increased up to 2.29% at 60 degrees C. By raising the temperature to 37 degrees C and dropping the light intensity to 42% (459 mW/cm2), the amount of polymerization shrinkage was similar to that with full light intensity, and statistically there were no significant differences between 37 degrees C, 45 degrees C, and 60 degrees C. Lower temperatures and lower light intensities produce lower values of shrinkage. However, if the light intensity is below 28%, higher temperatures (60 degrees C) must be applied to obtain a comparable amount of shrinkage. CLINICAL RELEVANCE: Pre-heating composite resin materials at body temperature (37 degrees C) is likely to improve physical properties and compensate any drop of light intensity.

Analysis of Variance↗

PubMedDate not supplied

Mechanical characteristics of poly-L-lactic acid absorbable screws and stainless steel screws in basilar osteotomies of the first metatarsal.

The purpose of this study is to evaluate the structural characteristics of 3.5-mm. stainless steel cortical screws and poly-L-lactic acid (PLA) absorbable screws in oblique closing base wedge osteotomies of the first metatarsal. Six pairs of frozen first metatarsal bones were excised from the specimen group. An oblique base wedge osteotomy was performed and fixated with either a 3.5-mm. stainless steel or PLA screw. Specimens were loaded to failure with the Bionix Material Testing System at a constant rate of 0.166 mm./sec. A Student's t test for paired samples with a 95% confidence interval was used to measure differences in ultimate load, ultimate displacement, and structural stiffness. The following results (mean +/- standard deviation) were obtained: Structural stiffness, PLA 12.35 +/- 3.82 N/mm. and stainless steel 10.13 +/- 5.74 N/mm.: ultimate displacement, PLA 7.39 +/- 3.23 mm. and stainless steel 10.89 +/- 7.91 mm.; ultimate load, PLA 57.95 +/- 1.01 N and stainless steel 51.49 +/- 5.22 N. In this fracture model, there were no statistically significant differences in the structural characteristics of PLA 3.5-mm. screws and stainless steel screws in oblique closing base wedge osteotomies of the first metatarsal.

Absorption↗

PubMed1999

Optimization of the arthroscopic indentation instrument for the measurement of thin cartilage stiffness.

Structural alterations associated with early, mostly reversible, degeneration of articular cartilage induce tissue softening, generally preceding fibrillation and, thus, visible changes of the cartilage surface. We have already developed an indentation instrument for measuring arthroscopic stiffness of cartilage with typical thickness >2 mm. The aim of this study was to extend the applicability of the instrument for the measurement of thin (<2 mm) cartilage stiffness. Variations in cartilage thickness, which will not be known during arthroscopy, can nonetheless affect the indentation measurement, and therefore optimization of the indenter dimensions is necessary. First, we used theoretical and finite element models to compare plane-ended and spherical-ended indenters and, then, altered the dimensions to determine the optimal indenter for thin cartilage measurements. Finally, we experimentally validated the optimized indenter using bovine humeral head cartilage. Reference unconfined compression measurements were carried out with a material testing device. The spherical-ended indenter was more insensitive to the alterations in cartilage thickness (20% versus 39% in the thickness range 1.5-5 mm) than the plane-ended indenter. For thin cartilage, the optimal dimensions for the spherical-ended indenter were 0.5 mm for diameter and 0.1 mm for height. The experimental stiffness measurements with this indenter correlated well with the reference measurements (r = 0.811, n = 31, p < 0.0001) in the cartilage thickness range 0.7-1.8 mm. We conclude that the optimized indenter is reliable and well suited for the measurement of thin cartilage stiffness.

Animals↗

PubMed2002

In vitro evaluation of the retention of composite fiber and stainless steel posts.

PURPOSE: This study compared the tensile retentive strength of composite fiber-reinforced dowels luted with a resin cement to stainless steel dowels luted with zinc phosphate cement. MATERIALS AND METHODS: The crowns of 40 extracted human mandibular premolars were removed with a separating disc 1-mm coronal to the cementoenamel junction. The teeth were randomly divided into 4 groups (n = 10). A post space was prepared in each specimen to a depth of 9 mm, using the drill supplied by the respective manufacturer. For the stainless steel post group, 1.25-mm-diameter posts were cemented with zinc phosphate cement. For the composite fiber reinforced groups, posts with diameters of 1.00, 1.25, and 1.50 mm were luted with a Bisphenol A-Glycidyl Methacrylate (BIS-GMA) resin bonding system (Jeneric/Pentron, Wallingford, CT) according to manufacturer specifications. The specimens were stored in a sealed container with a moist environment for 24 hours, placed in a fixture in an 801 Materials Test Systems (MTS) machine (MTS Systems Corp, Minneapolis, MN), and loaded in tension at a rate of 5.0 mm/min until failure. Differences among the 4 groups were determined using a one-way analysis of variance and Tukey-B post-hoc tests (alpha = 0.05). RESULTS: The mean loads to failure ranged from 43.9 +/- 10.4 kg for the stainless steel dowel group to 19.9 +/- 5.7 kg for the composite fiber-reinforced 1.00-mm-diameter group. The stainless steel post luted with zinc phosphate cement provided significantly greater tensile resistance than all composite fiber dowel groups. The retention of the 1.00-mm composite fiber-reinforced post was significantly less than the remaining groups. CONCLUSIONS: Under the conditions of this study, the stainless steel dowel luted with zinc phosphate cement provided significantly greater retention.

Analysis of Variance↗

PubMed2006

The anisotropy of biological composites studied with ultrasonic technique.

One of the most common biological composites is wood material. This natural orthotropic like material is characterized by a high anisotropy determined by the special disposition of the microstructure elements. The anisotropy of wood can be described in various ways using the values of ultrasonic velocities of bulk waves (longitudinal and shear) observed on the velocity surface deduced from the theoretical relationships given by the Christofel's equation. The simultaneous view into the three symmetry planes of the anisotropic behavior of wood is presented on the velocity surface. The spatial filtering action of wood structure is easily connected with longitudinal and shear velocities. The first step in examining the anisotropy of wood is to relate the velocities to the symmetry axes. The simplest way to describe the anisotropy of wood is to express the ratios of velocities. These ratios can be calculated separately for longitudinal or shear waves or for a combination of both. The birefringence of shear waves have a particular interest for the fine definition of anisotropy. A more global appreciation of wood anisotropy than the values of individual velocities is given with acoustic invariants. The stability of calculation of acoustic invariants versus different propagation angles confirms the validity of the chosen model for the tested material. Wood species having high density and any important organized structure in the millimeter scale exhibit a high ratio of invariants. The acoustic behavior of tropical wood species is less anisotropic than that of species from a temperate zone having low density.

Algorithms↗

PubMed2004

Initial fixation strength of flexible all-inside meniscus suture anchors in comparison to conventional suture technique and rigid anchors: biomechanical evaluation of new meniscus refixation systems.

BACKGROUND: The newest generation of meniscus repair devices is designed to combine the benefits of the all-inside technique with the biomechanical properties of sutures. HYPOTHESIS: New flexible all-inside suture anchors have better fixation strength than rigid anchors, but there is no difference when compared to conventional horizontal and vertical mattress sutures. STUDY DESIGN: Controlled laboratory study. METHODS: In fresh-frozen bovine menisci, initial fixation strength, stiffness, and failure mode of different meniscus fixation techniques (FastT-Fix, RapidLoc, Meniscus Arrow, horizontal and vertical 2.0 Ethibond sutures) were evaluated in a computer-based materials testing machine at a rate of 12.5 mm/sec. RESULTS: The vertical and horizontal FastT-Fix suture anchors were the strongest devices with regard to pullout strength, with no significant difference compared to the vertical 2-0 Ethibond sutures. Horizontal sutures, Meniscus Arrow, and RapidLoc had significantly lower pullout strength. Vertical and horizontal FastT-Fix suture anchors showed significantly higher stiffness than the other devices. CONCLUSIONS: Biomechanical properties of flexible all-inside meniscus anchors (FastT-Fix) are comparable to conventional vertical suture techniques. Characteristics of the flexible RapidLoc are comparable to rigid anchors (Meniscus Arrow). CLINICAL RELEVANCE: From the biomechanical point of view, flexible all-inside meniscus refixation devices are an alternative to conventional suture techniques and rigid meniscus anchors.

Animals↗

PubMed1993

In vitro characterization of visible light-cured glass ionomer liners.

The purpose of this study was to characterize the in vitro performance of three visible light-cured glass ionomer liners. The liners containing 2-HEMA showed significantly higher compressive strength, diametral tensile strength and Vickers hardness than the liner without 2-HEMA. Statistically significant differences were found in the optical properties of the materials tested. The liners containing 2-HEMA manifested higher shear strength at liner/composite than at dentin/liner interfaces. The acid-base reaction was significantly delayed after light exposure in all the liners tested. The liner without 2-HEMA presented the greatest maximum gap at the liner/dentin interface. Significant correlations were detected between the optical properties of the liners and the top-bottom differences in the extent of conversion, as well as between the maximum marginal gap at the dentin/liner interface and the bond strength with dentin and composite. These correlations suggest the following areas for further developments: incorporation of low molecular weight polyalkenoic acids or accelerating agents to increase the initial carboxylate yield, increase in total transmittance and reduction in diffuse reflectance to improve the in-depth conversion, and reinforcement of the dentin liner interface to prevent gap formation.

Analysis of Variance↗

PubMedDate not supplied

Stability of a cannulated screw versus a Kirschner wire for the proximal crescentic osteotomy of the first metatarsal: a biomechanical study.

The purpose of this study was to compare the stability of a Kirschner wire (K-wire) versus a single cannulated screw for fixation of the proximal crescentic first metatarsal osteotomy. Seven matched pairs of fresh-frozen human cadaver first metatarsal specimens were dissected out en bloc at the first metatarsal-medial cuneiform complex; right and left specimens were randomized as to fixation. In screw specimens, a cannulated screw was mounted from the proximal medial side of the metatarsal, traversing osteotomy and engaging the lateral diaphyseal cortical bone. In the corresponding specimen, a K-wire was placed from the distal medial metatarsal cortex oriented as close to the longitudinal metatarsal axis as possible. Using a materials testing machine, a continuous load was applied to the plantar aspect of the metatarsal head at a rate of 5 mm/min until a displacement of 10 mm was reached. The following parameters were measured: initial stiffness of the entire specimen, stiffness of the osteotomy, the force required to create a 1-mm displacement, the force required to create a 0.15-mm gap across the osteotomy, and the ultimate force to create the 10-mm displacement. Both specimen and osteotomy stiffness were found to be significantly higher for screw fixation versus the K-wire (P <.05). Although there was also a difference in the force-to-failure load in favor of screw fixation, this result was found not found to be statistically significant.

Biomechanical Phenomena↗

PubMed1999

Occipital screw pullout strength. A biomechanical investigation of occipital morphology.

STUDY DESIGN: A three-group design with consistent pullout strength measures. OBJECTIVES: To determine pullout strength of three fixation types (unicortical screws, bicortical screws, wires) and to investigate their correlation with respect to occipital morphology. SUMMARY OF BACKGROUND DATA: A secured, multidirectional occipitocervical fusion requires internal fixation. Devices secured at occipital protuberance were suggested to offer the greatest pullout strength because of this region's thickness. METHODS: Twelve fresh human cadaveric occiputs were sketched with a grid delineating 21 fixation sites. Each site was drilled and hand-tapped. Four specimens were instrumented with unicortical screws on one side of the midline and bicortical screws on the other. Another four were instrumented with bicortical screws and wires, and the remaining four were instrumented with unicortical screws and wires. Two points on each specimen were secured with identical fixation to examine side-to-side symmetry. An MTS materials testing apparatus (MTS Systems Corporation, Eden Prairie, MN) was used to displace the fixators. Pullout strengths at different anatomic locations were recorded. RESULTS: The greatest pullout strength was at the occipital protuberance for all fixation types. The bicortical pullout strength was 50% greater than unicortical. The wire pullout strength was not significantly different from that of the unicortical screw (P > 0.05). Seventy-eight percent of wires broke at 1100 N. Unicortical pullout strength at occipital protuberance was comparable with that of the bicortical screw at other locations. CONCLUSIONS: Unicortical screw fixation at occipital protuberance offers acceptable pullout strength without the potential complications of bicortical screws or wire fixation.

Biomechanical Phenomena↗