More Like this

1. Intervertebral Disc Mechanics With Nucleotomy: Differences Between Simple and Dual Loading

   https://doi.org/10.1115/1.4050538  

   Yang, Bo ; Klineberg, Eric ; O'Connell, Grace D. ( August 2021 , Journal of Biomechanical Engineering)

   null (Ed.)

   Abstract Painful herniated discs are treated surgically by removing extruded nucleus pulposus (NP) material (nucleotomy). NP removal through enzymatic digestion is also commonly performed to initiate degenerative changes to study potential biological repair strategies. Experimental and computational studies have shown a decrease in disc stiffness with nucleotomy under single loading modalities, such as compression-only or bending-only loading. However, studies that apply more physiologically relevant loading conditions, such as compression in combination with bending or torsion, have shown contradicting results. We used a previously validated bone–disc–bone finite element model (Control) to create a Nucleotomy model to evaluate the effect of dual loading conditions (compression with torsion or bending) on intradiscal deformations. While disc joint stiffness decreased with nucleotomy under single loading conditions, as commonly reported in the literature, dual loading resulted in an increase in bending stiffness. More specifically, dual loading resulted in a 40% increase in bending stiffness under flexion and extension and a 25% increase in stiffness under lateral bending. The increase in bending stiffness was due to an increase and shift in compressive stress, where peak stresses migrated from the NP–annulus interface to the outer annulus. In contrast, the decrease in torsional stiffness was due to greater fiber reorientation during compression. In general, large radial strains were observed with nucleotomy, suggesting an increased risk for delamination or degenerative remodeling. In conclusion, the effect of nucleotomy on disc mechanics depends on the type and complexity of applied loads. 

   more » « less
2. Biomechanical Properties of Various Surgical Suture Needles in a Cadaveric Quadriceps Tendon Model

   Diaz, Miguel A. ; Branch, Eric A. ; Dunn, Jake ; Brothers, Anthony ; Jordan, Steve ( February 2023 , Transactions of the annual meeting of the Orthopaedic Research Society)

   INTRODUCTION: Quadriceps tendon autografts have experienced a rapid rise in popularity for anterior cruciate ligament (ACL) reconstruction due to advantages in graft sizing and potential improvement in biomechanics. While there is a growing body of literature on use of quadriceps tendon grafts, deeper investigation into the biomechanical properties of stitch techniques in this construct has been limited. The purpose of this study was to evaluate the performance of a novel suture needle against different conventional suture needles by comparing the biomechanical properties of two commonly used stitch methods, a whip stitch, and a locking stitch in quadriceps tendon. It was hypothesized that the new device would be capable of creating both whip stitches and locking stitches that are biomechanically equivalent to similar stitch techniques performed with conventional needle products. METHODS: This was a controlled biomechanical study. A total of 24 matched pair cadaveric knees were dissected and a total of 48 quadriceps tendons were harvested and tested. All tendon grafts were standardized to the same size. Samples were then randomized into the following groups, keeping the matched pairs together: (Group 1, n=16) consisted of Company W’s novel two-part suture needle design, (Group 2, n=16) consisted of Company A suture, and (Group 3, n=16) consisted of Company B suture. For each group, the matched pairs were categorized into subgroups to be instrumented with either a whip stitch or a locking stitch. Two fellowship-trained surgeons performed all stitching, where they each instrumented 8 tendon grafts per group. For instrumentation, the grafts were clamped to a preparation stand in accordance with the manufacturer’s recommendations for passing each suture needle. A skin marker was used to identify and mark five evenly spaced points, 0.5 cm apart, as a guide to create a 5-stitch series. For Group 1, the whip stitch as well as the locking whip stitch were performed with a novel 2-part needle. For Group 2, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle. Similarly, for Group 3, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle (Figure 1). Cyclical testing was performed using a servohydraulic testing machine (MTS Bionix) equipped with a 5kN load cell. A standardized length of tendon, 7 cm, was coupled to the MTS actuator by passing it through a cryoclamp cooled by dry ice to a temperature of -5°C (Figure 2). All testing samples were then pre-conditioned to normalize viscoelastic effects and testing variability through application of cyclical loading to 25-100 N for three cycles. The samples were then held at 89 N for 15 minutes. Thereafter, the samples were loaded to 50-200 N for 500 cycles at 1 Hz. If samples survived, they were ramped to failure at 20 mm/min. Displacement and force data was collected throughout testing. Metrics of interest were total elongation (mm), stiffness (N/mm), ultimate failure load (N) and failure mode. Data are presented as averages plus/minus standard deviation. A one-way analysis of variance (ANOVA) with a Tukey pairwise comparison post hoc analysis was used to evaluate differences between the various stitching methods. Statistical significance was set at P = .05. RESULTS SECTION: For the whip stitch methods, the total elongation was found to be equivalent across all methods (W: 36 ± 10 mm; A: 32 ± 18 mm; B: 33 ± 8 mm). The stiffness of Company A (103 ± 11 N/mm) method was significantly larger than Company W (64 ± 8 N/mm; p=.001), whereas stiffness of whip stitch by Company W was equivalent to Company B (80 ± 32 N/mm). The ultimate failure load was equivalent across all whip stitch methods (W: 379 ± 31 mm; A: 412 ± 103 mm; B: 438 ± 63 mm). For the locking stitch method, the total elongation (W: 26 ± 10 mm; A: 14 ± 2 mm; B: 29 ± 5 mm), stiffness (W: 75 ± 11 N/mm; A: 104 ± 23 N/mm; B: 79 ± 10 N/mm) and ultimate load (W: 343 ± 22 N; A: 369 ± 30 N; B: 438 ± 63 N) were found to be equivalent across all methods. The failure mode for all groups is in Table 1. The common mode of failure across study groups and stitch configuration was suture breakage. However, the whip stitch from Company A and Company B had varied failure modes. DISCUSSION: Products from the three manufacturers were found to produce biomechanically equivalent whip stitches and locking stitches with respect to elongation and ultimate failure load. The only significant difference observed was that the whip stitch created with Company A’s product had a higher stiffness than Company W’s product, which could have been due to differences in the suture material. In this cadaveric quadriceps tendon model, it was shown that when using Company W’s novel two-part suture needle, users were capable of creating whip stitches and locking stitches that achieved equivalent biomechanical performance compared to similar stitch techniques performed with conventional needle products. A failure mode limited solely to suture breakage for methods completed with Company W’s needle product suggest a reliable suture construct with limited tissue damage. SIGNIFICANCE/CLINICAL RELEVANCE: Having a suture needle device with the versatility to easily perform different stitching constructs may provide surgeons an advantage needed to improve clinical outcomes. The data presented illustrates a strong new suture technique that has equivalent performance when compared to conventional needle devices and has promising applications in graft preparation for ligament and tendon reconstruction. 

   more » « less
3. Age and Sex Differences in Load‐Induced Tibial Cortical Bone Surface Strain Maps

   https://doi.org/10.1002/jbm4.10467  

   Carriero, Alessandra ; Javaheri, Behzad ; Bassir Kazeruni, Neda ; Pitsillides, Andrew A. ; Shefelbine, Sandra J. ( February 2021 , JBMR Plus)

   Bone adapts its architecture to the applied load; however, it is still unclear how bone mechano‐adaptation is coordinated and why potential for adaptation adjusts during the life course. Previous animal models have suggested strain as the mechanical stimulus for bone adaptation, but yet it is unknown how mouse cortical bone load‐related strains vary with age and sex. In this study, full‐field strain maps (at 1 N increments up to 12 N) on the bone surface were measured in young, adult, and old (aged 10, 22 weeks, and 20 months, respectively), male and female C57BL/6J mice with load applied using a noninvasive murine tibial model. Strain maps indicate a nonuniform strain field across the tibial surface, with axial compressive loads resulting in tension on the medial side of the tibia because of its curved shape. The load‐induced surface strain patterns and magnitudes show sexually dimorphic changes with aging. A comparison of the average and peak tensile strains indicates that the magnitude of strain at a given load generally increases during maturation, with tibias in female mice having higher strains than in males. The data further reveal that postmaturation aging is linked to sexually dimorphic changes in average and maximum strains. The strain maps reported here allow for loading male and female C57BL/6J mouse legs in vivo at the observed ages to create similar increases in bone surface average or peak strain to more accurately explore bone mechano‐adaptation differences with age and sex. © 2021 The Authors.JBMR Pluspublished by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

    

   more » « less
4. Relations Between Bone Quantity, Microarchitecture, and Collagen Cross‐links on Mechanics Following In Vivo Irradiation in Mice

   https://doi.org/10.1002/jbm4.10545  

   Pendleton, Megan M. ; Emerzian, Shannon R. ; Sadoughi, Saghi ; Li, Alfred ; Liu, Jennifer W. ; Tang, Simon Y. ; O'Connell, Grace D. ; Sibonga, Jean D. ; Alwood, Joshua S. ; Keaveny, Tony M. ( September 2021 , JBMR Plus)

   Humans are exposed to ionizing radiation via spaceflight or cancer radiotherapy, and exposure from radiotherapy is known to increase risk of skeletal fractures. Although irradiation can reduce trabecular bone mass, alter trabecular microarchitecture, and increase collagen cross‐linking, the relative contributions of these effects to any loss of mechanical integrity remain unclear. To provide insight, while addressing both the monotonic strength and cyclic‐loading fatigue life, we conducted total‐body, acute, gamma‐irradiation experiments on skeletally mature (17‐week‐old) C57BL/6J male mice (n = 84). Mice were administered doses of either 0 Gy (sham), 1 Gy (motivated by cumulative exposures from a Mars mission), or 5 Gy (motivated by clinical therapy regimens) with retrieval of the lumbar vertebrae at either a short‐term (11‐day) or long‐term (12‐week) time point after exposure. Micro‐computed tomography was used to assess trabecular and cortical quantity and architecture, biochemical composition assays were used to assess collagen quality, and mechanical testing was performed to evaluate vertebral compressive strength and fatigue life. At 11 days post‐exposure, 5 Gy irradiation significantly reduced trabecular mass (p < 0.001), altered microarchitecture (eg, connectivity densityp < 0.001), and increased collagen cross‐links (p < 0.001). Despite these changes, vertebral strength (p = 0.745) and fatigue life (p = 0.332) remained unaltered. At 12 weeks after 5 Gy exposure, the trends in trabecular bone persisted; in addition, regardless of irradiation, cortical thickness (p < 0.01) and fatigue life (p < 0.01) decreased. These results demonstrate that the highly significant effects of 5 Gy total‐body irradiation on the trabecular bone morphology and collagen cross‐links did not translate into detectable effects on vertebral mechanics. The only mechanical deficits observed were associated with aging. Together, these vertebral results suggest that for spaceflight, irradiation alone will likely not alter failure properties, and for radiotherapy, more investigations that include post‐exposure time as a positive control and testing of both failure modalities are needed to determine the cause of increased fracture risk. © 2021 The Authors.JBMR Pluspublished by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

    

   more » « less
5. Quasi-static cyclic loading tests on steel gravity framing with concrete slab

   https://doi.org/10.17603/ds2-xa1b-ac84  

   Park, Sangwook ; Clayton, Patricia ; Helwig, Todd ; Engelhardt, Michael ; Williamson, Eric ( January 2023 , Designsafe-CI)

   This research investigated experimentally the seismic performance of steel gravity framing with a concrete slab at the system level. Two half-story, two-by-three bay steel gravity frame specimens were tested under cyclic loading. Bolted-bolted double-angle connections were used for a beam-to-column gravity connection. Primary design variables and construction details include the orientation of the metal deck to the loading direction, the presence or absence of metal deck seams on secondary beams, and the contribution of additional reinforcement bars in the concrete slab. Concrete blocks were positioned at the midpoint of each bay to simulate gravity loads, and a quasi-static displacement-controlled cyclic loading protocol was applied to the specimen using three hydraulic actuators. These investigations confirmed general observations from previous subassembly testing programs that the composite steel gravity framing system can provide substantial flexural stiffness, strength, and ductility under cyclic loading. Further, the test findings showed that the primary design variables and construction details significantly affected the cyclic behavior of composite gravity connections. Comparing the test results from a multi-bay setup and a subassembly testing setup, the cyclic behavior showed remarkable differences, especially for cases with weak axis decking or strong axis decking with a seam. These large differences are attributed to a significant separation of the girder from the column in the subassembly testing setup, which may not be present in a real building. Virtually all previous cyclic loading tests on gravity connections have been conducted in subassembly test setups. These subassembly tests are therefore the basis for the models that are currently used to include gravity frame connections in the seismic performance assessment of buildings, and these models may be quite inaccurate in some cases. The data generated in this system-level testing program is intended to support efforts to develop improved models of gravity connections subject to seismic loading. 

   more » « less