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Turnbull T.L.,University of Notre Dame | Turnbull T.L.,Steadman Philippon Research Institute SPRI | Baumann A.P.,University of Notre Dame | Roeder R.K.,University of Notre Dame
Journal of Biomechanics | Year: 2014

In vivo microcracks in cortical bone are typically observed within more highly mineralized interstitial tissue, but postmortem investigations are inherently limited to cracks that did not lead to fracture which may be misleading with respect to understanding fracture mechanisms. We hypothesized that the one fatigue microcrack which initiates fracture is located spatially adjacent to elevated intracortical porosity but not elevated mineralization. Therefore, the spatial correlation between intracortical porosity, elevated mineralization, and fatigue microdamage was investigated by combining, for the first time, sequential, nondestructive, three-dimensional micro-computed tomography (micro-CT) measurements of each in cortical bone specimens subjected to compressive fatigue loading followed by a tensile overload to fracture. Fatigue loading resulted in significant microdamage accumulation and compromised mechanical properties upon tensile overload compared to control specimens. The microdamage that initiated fracture upon tensile overload was able to be identified in all fatigue-loaded specimens using contrast-enhanced micro-CT and registered images. Two-point (or pair) correlation functions revealed a spatial correlation between microdamage at the fracture initiation site and intracortical porosity, but not highly mineralized tissue, confirming the hypothesis. This difference was unique to the fracture initiation site. Intracortical porosity and highly mineralized tissue exhibited a significantly lower and higher probability, respectively, of being located spatially adjacent to all sites of microdamage compared to the fracture initiation site. Therefore, the results of this study suggest that human cortical bone is tolerant of most microcracks, which are generally compartmentalized within the more highly mineralized interstitial tissue, but a single microcrack of sufficient size located in spatial proximity to intracortical porosity can compromise fracture resistance. © 2014 Elsevier Ltd. Source

Smith S.D.,Steadman Philippon Research Institute SPRI | LaPrade R.F.,Steadman Philippon Research Institute SPRI | Jansson K.S.,Steadman Philippon Research Institute SPRI | Aroen A.,Steadman Philippon Research Institute SPRI | And 2 more authors.
Knee Surgery, Sports Traumatology, Arthroscopy | Year: 2014

Purpose: Functional braces are commonly prescribed to treat anterior cruciate ligament (ACL) injury. The results of the existing literature on functional brace use are mixed. The purpose of this study was to evaluate the history and current state of functional ACL bracing and to identify design criteria that could improve upon current bracing technologies. Methods: A literature search was performed through the PubMed MEDLINE database in April 2013 for the keywords "anterior cruciate ligament" and "brace". Articles published between January 1, 1980, and April 4, 2013, were retrieved and reviewed. Current functional braces used to treat ACL injury were identified. The function of the native ACL was carefully studied to identify design requirements that could improve upon current bracing technologies. Results: Biomechanical evaluations of functional brace effects at time zero have been mixed. Functional brace use reportedly does not improve long-term patient outcomes following ACL reconstruction, but has been shown to reduce subsequent injury rates while skiing in both ACL-deficient and reconstructed skiers. In situ force in the ACL varies with flexion angle and activity. Currently, no brace has been designed and validated to replicate the force-flexion behavior of the native ACL. Conclusions: Biomechanical and clinical evidence suggests current functional bracing technologies do not sufficiently restore normal biomechanics to the ACL-deficient knee, protect the reconstructed ACL, and improve long-term patient outcomes. Further research into a functional brace designed to apply forces to the knee joint similar in magnitude to the native ACL should be pursued. Level of evidence: III. © 2013 Springer-Verlag Berlin Heidelberg. Source

Chandra S.S.,Queensland University of Technology | Surowiec R.,Steadman Philippon Research Institute SPRI | Ho C.,Steadman Philippon Research Institute SPRI | Xia Y.,Queensland University of Technology | And 3 more authors.
Magnetic Resonance in Medicine | Year: 2016

Purpose To validate a fully automated scheme to extract biochemical information from the hip joint cartilages using MR T2 mapping images incorporating segmentation of co-registered three-dimensional Fast-Spin-Echo (3D-SPACE) images. Methods Manual analyses of unilateral hip (3 Tesla) MR images of 24 asymptomatic volunteers were used to validate a 3D deformable model method for automated cartilage segmentation of SPACE scans, partitioning of the individual femoral and acetabular cartilage plates into clinically defined sub-regions and propagating these results to T2 maps to calculate region-wise T2 value statistics. Analyses were completed on a desktop computer (10 min per case). Results The mean voxel overlap between automated A and manual M segmentations of the cartilage volumes in the (clinically based) SPACE images was 73% (100×2|AM|/[|A|+|M|]). The automated and manual analyses demonstrated a relative difference error <10% in the median "T2 average signal" for each cartilage plate. The automated and manual analyses showed consistent patterns between significant differences in T2 data across the hip cartilage sub-regions. Conclusion The good agreement between the manual and automatic analyses of T2 values indicates the use of structural 3D-SPACE MR images with the proposed method provides a promising approach for automated quantitative T2 assessment of hip joint cartilages. © 2015 Wiley Periodicals, Inc. Source

Aga C.,Steadman Philippon Research Institute SPRI | Aga C.,University of Oslo | Rasmussen M.T.,Steadman Philippon Research Institute SPRI | Smith S.D.,Steadman Philippon Research Institute SPRI | And 4 more authors.
American Journal of Sports Medicine | Year: 2013

Background: The tibial fixation site has been reported to be the weakest point in anterior cruciate ligament (ACL) reconstructions. Numerous interference screws and combination screw and sheath devices are available for soft tissue fixation, and a biomechanical comparison of these devices is necessary. Hypothesis: Combination screw and sheath devices would provide superior soft tissue fixation properties compared with interference screws in a porcine model. Study Design: Controlled laboratory study. Methods: Eight different intratunnel tibial soft tissue fixation devices were biomechanically tested in a porcine model with bovine tendons, with 10 specimens per group. The soft tissue fixation devices included 3 interference screws-the Bio-Interference Screw, BIOSURE PK, and RCI Screw-and 5 combination screw and sheath devices (combination devices)-the AperFix II, BIOSURE SYNC, ExoShape, GraftBolt, and INTRAFIX. The specimens were subjected to cyclic (1000 cycles, 50-250 N, 0.5 Hz) and pullto- failure loading (50 mm/min) with a dynamic tensile testing machine. Ultimate failure load (N), cyclic displacement (mm), pullout stiffness (N/mm), displacement at failure (mm), load at 3 mm displacement (N), and mechanism of failure were recorded. Results: The ultimate failure loads were highest for the GraftBolt (1136 ± 115.6 N), followed by the INTRAFIX (1127 ± 155.0 N), Aper- Fix II (1122 ± 182.9 N), BIOSURE PK (990.8 ± 182.1 N), Bio-Interference Screw (973.3 ± 95.82 N), BIOSURE SYNC (829.5 ± 172.4 N), RCI Screw (817.7 ± 113.9 N), and ExoShape (814.7 ± 178.8 N). The AperFix II, GraftBolt, and INTRAFIX devices were significantly stronger than the BIOSURE SYNC, RCI Screw, and ExoShape. Although the 3 strongest devices were combination screw and sheath devices, no significant differences were observed between the ultimate failure strengths of the screw and combination devices when compared as groups. The least amount of cyclic displacement after 1000 cycles was observed for the GraftBolt (1.38 ± 0.27 mm), followed by the AperFix II (1.58 ± 0.21 mm), Bio-Interference Screw (1.61 ± 0.22 mm), INTRAFIX (1.63 ± 0.15 mm), ExoShape (1.68 ± 0.30 mm), BIOSURE PK (1.72 ± 0.29 mm), BIOSURE SYNC (1.92 ± 0.59 mm), and RCI Screw (1.97 ± 0.39 mm). The GraftBolt allowed significantly less displacement than did the BIOSURE SYNC and RCI Screw. Similarly, no significant differences were observed between the cyclic displacements of the screws and combination devices when compared as groups. Conclusion: The combination screw and sheath devices did not provide superior soft tissue fixation properties compared with the interference screws alone in a porcine model. Although the highest ultimate failure loads and least amounts of cyclic displacement were observed for combination devices, group comparisons of screw and combination devices did not result in any significant differences for ultimate failure load and cyclic displacement. Clinical Relevance: It is important to consider that these results represent device performance in an in vitro animal model and are not directly transferrable to an in vivo clinical situation. The combination of a sheath and screw did not consistently result in improved fixation characteristics compared with interference screw fixation. © 2013 The Author(s). Source

Jansson K.S.,Steadman Philippon Research Institute SPRI | Michalski M.P.,Steadman Philippon Research Institute SPRI | Smith S.D.,Steadman Philippon Research Institute SPRI | LaPrade R.F.,Steadman Philippon Research Institute SPRI | Wijdicks C.A.,Steadman Philippon Research Institute SPRI
Journal of Biomechanics | Year: 2013

The purpose of the study was to evaluate the load output of a pressure sensor in the presence of liquid saturation in a controlled environment. We hypothesized that a calibrated pressure sensor would provide diminishing load outputs over time in controlled environments of both humidified air and while submerged in saline and the sensors would reach a steady state output once saturated. A consistent compressive load was repeatedly applied to pressure sensors over time (Model 4000, Tekscan, Inc., South Boston, MA) with a tensile testing machine (Instron ElectroPuls E10000, Norwood, MA). All sensors were initially calibrated in a dry environment and were tested in three groups: humid air, submerged in 0.9% saline solution, and dry. Linear regression of load output over time for the pressure sensors exposed to humidity and submerged showed a 4.6% and 4.7% decline in load output each hour for the initial 6. h, respectively (Β=-0.046, 95% CI: [-0.053 to -0.039]; p<0.001) (Β=-0.047, 95% CI: [-0.053 to -0.042; p<0.001). Tests after 72. h of exposure had linear regression decline in load output over time of 0.40% and 0.47% per hour for humidified and submerged sensors, respectively (Β=-0.004, 95% CI: [-0.006 to -0.003]; p<0.001) (Β=-0.047, 95% CI: [-0.053 to -0.042]; p<0.001). Because outcomes in biomedical research can affect clinical practices and treatments, the diminishing load output of the sensor in the presence of liquids should be accounted for. We recommend soaking sensors for more than 48. h prior to testing in a moist environment. © 2012 Elsevier Ltd. Source

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