Great debates in trauma biomechanics Glatt, Vaida; O'Toole, Robert; Mehta, Samir ...
OTA international : the open access journal of orthopaedic trauma
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At the 2021 annual meeting of the Orthopaedic Trauma Association, the Basic Science Focus Forum hosted its first ever debate-style symposium focused on biomechanics and fracture repair. The 3 ...subjects of debate were "Mechanics versus Biology-Which is 'More Important' to Consider?" "Locked Plate versus Forward Dynamization versus Reverse Dynamization-Which Way Should I Go?" and "Sawbones versus Cadaver Models-What Should I Believe Most?" These debates were held because fracture healing is a highly organized synergistic response between biological factors and the local mechanical environment. Multiple studies have demonstrated that both factors play roles in governing bone healing responses, and the causal relationships between the 2 remain unclear. The lack of clarity in this space has led to a spectrum of research with the common goal of helping surgeons make good decisions. Before reading further, the reader should understand that the questions posed in the debate titles are unanswerable and might represent a false choice. Instead, the reader should appreciate that the debates were held to gain a more thorough understanding of these topics based on the current state of the art of experimental and clinical studies, by using an engaging and thought-provoking format.
Glisson’s capsule is the interstitial connective tissue that surrounds the liver. As part of its normal physiology, it withstands significant daily changes in liver size. The pathophysiology of the ...capsule in disease is not well understood. The aim of this study was to characterise the changes in capsule matrix, cellular composition, and mechanical properties that occur in liver disease and to determine whether these correlate with disease severity or aetiology.
Samples from ten control patients, and six with steatosis, seven with moderate fibrosis, and 37 with cirrhosis were collected from autopsies, intraoperative biopsies, and liver explants. Matrix proteins and cell markers were assessed by staining and second harmonic generation imaging. Mechanical tensile testing was performed on a test frame.
Capsule thickness was significantly increased in cirrhotic samples compared with normal controls irrespective of disease aetiology (70.12 ± 14.16 μm and 231.58 ± 21.82 μm, respectively), whereas steatosis and moderate fibrosis had no effect on thickness (90.91 ± 11.40 μm). Changes in cirrhosis included an increase in cell number (fibroblasts, vascular cells, infiltrating immune cells, and biliary epithelial cells). Key matrix components (collagens 1 and 3, hyaluronan, versican, and elastin) were all deposited in the lower capsule, although only the relative amounts per area of hyaluronan and versican were increased. Organisational features, including crimping and alignment of collagen fibres, were also altered in cirrhosis. Unexpectedly, capsules from cirrhotic livers had decreased resistance to loading compared with controls.
The liver capsule, similar to the parenchyma, is an active site of disease, demonstrating changes in matrix and cell composition as well as mechanical properties.
We assessed the changes in composition and response to stretching of the liver outer sheath, the capsule, in human liver disease. We found an increase in key structural components and numbers of cells as well as a change in matrix organisation of the capsule during the later stages of disease. This allows the diseased capsule to stretch more under any given force, suggesting that it is less stiff than healthy tissue.
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•The capsule is an active site of disease: thickness and cellularity increase markedly in cirrhosis.•Extracellular matrix composition and organisation change in cirrhosis.•The cirrhotic capsule stretches more and is less stiff.
Category:
Sports; Basic Sciences/Biologics
Introduction/Purpose:
Achilles tendon disorders are among the most common conditions observed by sports medicine physicians and among the most difficult to ...diagnose using current clinical tools. While qualitative imaging is a validated method to grade the severity of tendinopathy, predicting the risk of these patients progressing or suffering tendon ruptures remains a major clinical need. Therefore, the purpose of this study was to determine the efficacy of quantitative ultrasound imaging to explain in vitro fatigue-induced degradation of Achilles tendon mechanical properties. We hypothesized that decreases in mean echogenicity would be linked to in vitro tendon fatigue characterized by decreased mechanical properties.
Methods:
In this cadaveric tendon study, we cyclically fatigued 10 cadaveric Achilles tendons (7 donors; sex: 4M, 3F; age: 60+-15 years) and acquired b-mode ultrasound images to determine if stress-imaging biomarkers provide new insight into tendon status. We cut dog-bone shapes to concentrate tendon damage at the mid-substance where we acquired ultrasound images. In a custom- built testing bath, we cyclically applied 10-20 MPa of tendon stress at 1 Hz for 150,00 or until the specimen failed. Every 500th cycle, we applied 2 slow (0.25 Hz) tendon stresses of 10-20 MPa while acquiring ultrasound images using an 18MHz transducer.
We calculated the change in tendon echogenicity caused by the applied stress to determine if this stress-imaging biomarker was associated with tendon failure. We compared these stress-imaging biomarkers from the tendons that failed (N=6) and the tendons that survived (N=4) cyclic fatigue damage using an unpaired t-test (p < 0.05).
Results:
Quantitative analysis of the ultrasound images indicated 2 key differences between tendons that failed during the cyclic loading protocol and those that did not (Figure 1 shows representative data of tendons with similar demographics but one tendon exhibited increased change in echogenicity before failing while the other tendon exhibited smaller changes in echogenicity and did not rupture). First, mean echogenicity decreased before failure. Second, the average change in mean echogenicity was significantly greater in tendons that failed (p = 0.031). For most tendons that did fail, mean echogenicity decreased during the third phase of fatigue life. For the tendons that did not fail, mean echogenicity plateaued along with strain during the second phase of fatigue.
Conclusion:
This study found detectable differences in image echogenicity during a stress test between tendons that fail during cyclic loading and those that do not. While preliminary, our findings indicate that B-mode ultrasound has potential as a clinically viable tool to predict severe tendon injuries. Our future work is focused on developing computer-based predictive tools to assess Achilles tendon fatigue in patients with tendinopathy following prolonged tendon loading to establish quantitative imaging thresholds that can serve as clinical benchmarks.
Abstract Introduction Lower patient satisfaction and high rates of plate prominence has led to the use of lower profile, smaller plates in the treatment of midshaft clavicle fractures. Specifically ...regarding the use of 2.7 mm reconstruction plates, there lacks biomechanical comparison to its more robust 3.5 mm counterpart. This study was designed to compare the mechanical properties of anteroinferior plate fixation on a clavicle fracture model using either 2.7 mm or 3.5 mm reconstruction plates. Methods Forty-eight synthetic left clavicles were divided into two groups based on the type of fixation: 3.5 mm or 2.7 mm pelvic reconstruction plate fixed in the anteroinferior position. Fixation was tested on AO/OTA 15B1.3 transverse midshaft fractures. Each specimen underwent the following three mechanical tests: axial compression, torsion, and four-point bending. Results Significant differences were observed in axial (p = 0.016) and torsional (p = 0.00097) stiffness between the two groups. The average bending rigidity (EI) was found to be significantly lower for the 2.7-mm plates as compared to the 3.5-mm plates (p = 0.03). The loading scenarios performed in the mechanical tests did not lead to failure of any implants. Conclusion While our results show clear mechanical superiority of 3.5-mm reconstruction plates over 2.7-mm plates, superior results in the clinical setting may not necessarily translate. With exceptional mechanical strength also noted for the 2.7 mm plate, well above the biomechanical properties of an intact clavicle, these results may obviate the need for robust plates in general.
•In sagittal plane bending, plates were less stiff than two-screw constructs.•In torsion and transverse plane bending, both constructs behaved similarly.•Lateral gaps at the joint occurred more ...readily with plates during cyclic loading.•Talonavicular fusion constructs must maintain contact across the articular surface.
This study compared stiffness between two constructs for talonavicular arthrodesis: a dorsomedial plating system and two partially threaded cannulated cancellous screws. We hypothesized that the plate would exhibit greater stiffness and resistance to deformation during cyclic loading.
The constructs were implanted in eight matched pairs of cadaveric feet and subjected to axial torsion, cantilever bending in two directions, and cyclic loading to failure.
The two-screw constructs were significantly stiffer in plantar-dorsal bending (p = .025) and trended towards a higher number of cycles before failure than the plate group (p = .087). No significant differences were observed in internal torsion (p = .620), external torsion (p = .165), or medial-lateral bending (p = .686).
This study provided the first biomechanical assessment of a plating system with an integrated compression screw, which was significantly less stiff than a two-screw construct when loaded from plantar to dorsal.
Current surgical fracture treatment paradigms, which use rigid metallic constructs to heal bones, provide reasonable clinical outcomes; however, they do not leverage recent advances in our ...understanding of bone healing and mechanotransduction throughout bone healing. The objective of this review was to investigate the efficacy and potential clinical applicability of surgical techniques and implants that deliberately introduce interfragmentary motion throughout the healing process.
The authors searched PubMed and Google Scholar databases for articles reporting on fracture repair using dynamic locking plates, dynamized surgical techniques, and reverse dynamization. Data collection also included assessment of additively manufactured (AM) implants that provide dynamic mechanical behaviors.
Forty articles were included for final review. It was found that accelerated rates of fracture healing can be achieved with staged 2-part surgeries or dynamic implant designs. Temporal dynamization, where static fixation of bones is followed by the introduction of micromotion and controlled loading, has been shown to improve callus volume and accelerate the healing response. Reverse dynamization, where micromotion is encouraged during early callus formation and arrested later, may represent a significant advance for the treatment of critical defect injuries. Advances in AM techniques will likely provide the ability to create high-resolution implants capable of dynamized and reverse dynamized modalities.
There is no one-size-fits-all approach to optimization of fracture healing. However, it has been clearly demonstrated that fracture treatment can be enhanced by systematically altering the construct stiffness throughout the different phases of healing, which may be achieved with AM implant designs.
The purpose of this study was to systematically quantify distal radioulnar joint stability with a cadaveric model, using radiographic and joint contact force measurements. Six fresh-frozen cadavers ...underwent sequential ulnar styloid osteotomies. Posteroanterior and lateral stress radiographs were obtained and joint contact forces and areas were measured.
Posteroanterior radiographs showed a significant increase in the distal radioulnar joint gap after osteotomy of the base of the ulnar styloid. Contact force and contact area measurements were not significantly different. We conclude that fractures that involve the ulnar styloid base should be considered for operative fixation when carrying out open reduction and internal fixation of fractures of the distal radius.
Tendon mechanical properties respond to altered load in adults, but how load history during growth affects adult tendon properties remains unclear. To address this question, we adopted an avian model ...in which we altered the mechanical load environment across the growth span. Animals were divided at 2 weeks of age into three groups: (1) an exercise control group given the opportunity to perform high-acceleration movements (EXE,
n
= 8); (2) a sedentary group restricted from high-intensity exercise (RES,
n
= 8); and (3) a sedentary group also restricted from high-intensity exercise and in which the gastrocnemius muscles were partially paralyzed using repeated bouts of botulinum toxin-A injections (RES-BTX,
n
= 8). Video analysis of bird movement confirmed the restrictions eliminated high-intensity exercise and did not alter time spent walking and sitting between groups. At skeletal maturity (33–35 weeks) animals were sacrificed for analysis, consisting of high-field MRI and material load testing, of both the entire free Achilles tendon and the tendon at the bone-tendon junction. Free tendon stiffness, modulus, and hysteresis were unaffected by variation in load environment. Further, the bone-tendon junction cross-sectional area, stress, and strain were also unaffected by variations in load environment. These results suggest that: (a) a baseline level of low-intensity activity (standing and walking) may be sufficient to maintain tendon growth; and (b) if this lower threshold of tendon load is met, non-mechanical mediated tendon growth may override the load-induced mechanotransduction signal attributed to tendon remodeling in adults of the same species. These results are important for understanding of musculoskeletal function and tendon health in growing individuals.
Biomechanical models: key considerations in study design Augat, Peter; Hast, Michael W.; Schemitsch, Geoffrey ...
OTA international : the open access journal of orthopaedic trauma,
04/2021, Letnik:
4, Številka:
2S
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Abstract
This manuscript summarizes presentations of a symposium on key considerations in design of biomechanical models at the 2019 Basic Science Focus Forum of the Orthopaedic Trauma Association. ...The first section outlines the most important characteristics of a high-quality biomechanical study. The second section considers choices associated with designing experiments using finite element modeling versus synthetic bones versus human specimens. The third section discusses appropriate selection of experimental protocols and finite element analyses. The fourth section considers the pros and cons of use of biomechanical research for implant design. Finally, the fifth section examines how results from biomechanical studies can be used when clinical evidence is lacking or contradictory. When taken together, these presentations emphasize the critical importance of biomechanical research and the need to carefully consider and optimize models when designing a biomechanical study.
Computational simulation of the behavior of orthopaedic implants in a realistic
in vivo environment is rapidly growing in importance as a test applied to prospective designs as younger patients place ...greater functional demands on their new joints. In addition to muscle and ligament forces, forces caused by implant contact must be computed and applied in an accurate and efficient manner during these simulations. A method is presented by which implant contact forces are computed from the contact nodes on one implant as the nodes penetrate into NURBS surface patches that comprise a second implant using a rigid-body-spring-model (RBSM). A scheme for placing evenly-distributed contact nodes is described, as well as methods for unambiguously interpreting whether a node is in contact with a specific surface. The ability to represent the surface properly was then evaluated using various spring-spacings. Spacing contact nodes 3
mm apart using this scheme appears to produce simulated implant motions that are similar to those obtained using smaller spacings, and results in simulations that are more stable than those possible when a similar number of spring nodes are placed using triangulation.
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