Biomechanical Measurement Error Can Be Caused by Fujifilm Thickness: A Theoretical, Experimental, and Computational Analysis

© 2017 Ahmed Sarwar et al. This is the first study to quantify the measurement error due to the physical thickness of Fujifilm for several material combinations relevant to orthopaedics. Theoretical and experimental analyses were conducted for cylinder-on-flat indentation over a series of forces (750 and 3000 N), cylinder diameters (0 to 80 mm), and material combinations (metal-on-metal, MOM; metal-on-polymer, MOP; metal-on-bone, MOB). For the scenario without Fujifilm, classic Hertzian theory predicted the true line-type contact width as WO={(8FDcyl)/(πLcyl)[(1-cyl2)/Ecyl+(1-flat2)/Eflat]}1/2, where F is compressive force, Dcyl is cylinder diameter, Lcyl is cylinder length, cyl and flat are cylinder and flat Poisson\u27s ratios, and Ecyl and Eflat are cylinder and flat elastic moduli. For the scenario with Fujifilm, experimental measurements resulted in contact widths of WF=0.1778×F0.2273×D0.2936 for MOM tests, WF=0.0449×F0.4664×D0.4201 for MOP tests, and WF=0.1647×F0.2397×D0.3394 for MOB tests, where F is compressive force and D is cylinder diameter. Fujifilm thickness error ratio WF/WO showed a nonlinear decrease versus cylinder diameter, whilst error graphs shifted down as force increased. Computational finite element analysis for several test cases agreed with theoretical and experimental data, respectively, to within 3.3% and 1.4%. Despite its wide use, Fujifilm\u27s measurement errors must be kept in mind when employed in orthopaedic biomechanics research

Biomechanical analysis using FEA and experiments of metal plate and bone strut repair of a femur midshaft segmental defect

© 2018 Jason Coquim et al. This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional “high stiffness” femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern “low stiffness” femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone

Fretting Corrosion Testing of Total Hip Replacements with Modular Heads and Stems

© 2017 Elsevier Inc. All rights reserved. Human hip joints with diseased cartilage and bone are commonly replaced using total hip replacements (THRs), which often have modular head and neck components that connect via matching taper, much like nested cones. Fretting corrosion occurs when subtle relative motion (i.e., micromotion) causes abrasion at the head-neck taper connection (i.e., fretting), thus allowing surrounding biofluids to degrade the material (i.e., corrosion). Corrosion then releases toxic metallic debris that causes local tissue lysis and painful inflammation, ultimately leading to revision surgery. However, concern with long-term systemic effects remains as the toxic debris diffuses throughout the body. Modular THRs are susceptible to fretting corrosion; however, they are important to allow intraoperative flexibility to reconstruct the joint with optimized biomechanics. Therefore, this chapter describes a procedure for investigating fretting corrosion of THRs, as well as how to analyze, present, and interpret results

Biomechanical Testing of the Intact and Surgically Treated Pelvis

© 2017 Elsevier Inc. All rights reserved. Pelvic fractures account for over one-tenth of all human bone fractures, but acetabular fractures account for about half of all pelvic fractures. Acetabular fractures can be simple (or elementary) and complex (or associated), being caused by a low-energy fall in the elderly and high-energy impact in the young. No gold standard exists for surgical repair of these injuries; however, surgeons most often use plate-and-screw fixation, although cable fixation may be used when osteoporosis prevents good screw fixation into bone. Acetabular fracture repair is often accompanied by simultaneous total hip arthroplasty for elderly patients who eventually require a hip prosthesis due to osteoarthritis. The goal of surgical repair is perfect anatomical reduction of the hip to minimize pain, improve strength, and restore function. A key element is the biomechanical stability provided by various acetabular fracture fixation methods. Therefore, this chapter shows how to surgically repair a pelvic acetabular fracture and perform biomechanical testing, as well as how to analyze, report, and interpret data

Biomechanical Response under Stress-Controlled Tension-Tension Fatigue of a Novel Carbon Fiber/Epoxy Intramedullary Nail for Femur Fractures

© 2020 IPEM Metallic intramedullary nails are the “gold standard” implant for repairing femur shaft fractures. However, their rigidity may eliminate axial micromotion at the fracture (causing delayed healing) and they may carry too much load relative to the femur (causing “stress shielding”). Consequently, some researchers have proposed fiber-reinforced composite nails, but only one evaluated cyclic fatigue performance. Therefore, this study assessed the cyclic fatigue response of a carbon fiber/epoxy nail with a novel ply stacking sequence of [02/-45/452/-45/0/-45/452/-452/452/-45/902] previously developed by the present authors. Nails were cyclically loaded in tension-tension at 5 Hz with a stress ratio of R=0.1 from 30% - 85% of the material\u27s ultimate tensile strength (UTS). Thermographic stress analysis, rather than conventional fatigue testing, was used to obtain high cycle fatigue strength (HCFS), below which the nail can be cyclically loaded indefinitely without damage. Also, the mechanical test machine\u27s built-in load cell and an extensometer were used to create stress-strain curves, from which the change in static EO and dynamic E* moduli were obtained. Results showed that HCFS was 70.3% of UTS (or about 283 MPa), while EO and E* remained at 42 GPa without any dRegradation during testing. The current nail shows potential for clinical use

Biomechanical analysis of transverse acetabular fracture fixation in the elderly via the posterior versus the anterior approach with and without a total hip arthroplasty

© IMechE 2020. This study provides the first biomechanical comparison of the fixation constructs that can be created to treat transverse acetabular fractures when using the “gold-standard” posterior versus the anterior approach with and without a total hip arthroplasty in the elderly. Synthetic hemipelvises partially simulating osteoporosis (n = 24) were osteotomized to create a transverse acetabular fracture and then repaired using plates/screws, lag screws, and total hip arthroplasty acetabular components in one of four ways: posterior approach (n = 6), posterior approach plus a total hip arthroplasty acetabular component (n = 6), anterior approach (n = 6), and anterior approach plus a total hip arthroplasty acetabular component (n = 6). All specimens were biomechanically tested. No differences existed between groups for stiffness (range, 324.6–387.3 N/mm, p = 0.629), clinical failure load at 5 mm of femoral head displacement (range, 1630.1–2203.9 N, p = 0.072), or interfragmentary gapping (range, 0.67–1.33 mm, p = 0.359). Adding a total hip arthroplasty acetabular component increased ultimate mechanical failure load for posterior (2904.4 vs. 3652.3 N, p = 0.005) and anterior (3204.9 vs. 4396.0 N, p = 0.000) approaches. Adding a total hip arthroplasty acetabular component also substantially reduced interfragmentary sliding for posterior (3.08 vs. 0.50 mm, p = 0.002) and anterior (2.17 vs. 0.29 mm, p = 0.024) approaches. Consequently, the anterior approach with a total hip arthroplasty may provide the best biomechanical stability for elderly patients, since this fixation group had the highest mechanical failure load and least interfragmentary sliding, while providing equivalent stiffness, clinical failure load, and gapping compared to other surgical options

Mechanical Stress Promotes Cisplatin-Induced Hepatocellular Carcinoma Cell Death

Cisplatin (CisPt) is a commonly used platinum-based chemotherapeutic agent. Its efficacy is limited due to drug resistance and multiple side effects, thereby warranting a new approach to improving the pharmacological effect of CisPt. A newly developed mathematical hypothesis suggested that mechanical loading, when coupled with a chemotherapeutic drug such as CisPt and immune cells, would boost tumor cell death. The current study investigated the aforementioned mathematical hypothesis by exposing human hepatocellular liver carcinoma (HepG2) cells to CisPt, peripheral blood mononuclear cells, and mechanical stress individually and in combination. HepG2 cells were also treated with a mixture of CisPt and carnosine with and without mechanical stress to examine one possible mechanism employed by mechanical stress to enhance CisPt effects. Carnosine is a dipeptide that reportedly sequesters platinum-based drugs away from their pharmacological target-site. Mechanical stress was achieved using an orbital shaker that produced 300 rpm with a horizontal circular motion. Our results demonstrated that mechanical stress promoted CisPt-induced death of HepG2 cells (~35% more cell death). Moreover, results showed that CisPt-induced death was compromised when CisPt was left to mix with carnosine 24 hours preceding treatment. Mechanical stress, however, ameliorated cell death (20% more cell death).Peer Reviewe

Biomechanical impact testing of synthetic versus human cadaveric tibias for predicting injury risk during pedestrian-vehicle collisions

© 2020, © 2020 Taylor & Francis Group, LLC. Objective: The tibia is the most commonly fractured long bone in a pedestrian-vehicle collision. The standard injury assessment tool is the “legform,” a device that mimics the human lower limb under impact loads. These devices are designed to identify the impact load that will cause the onset of injury, rather than replicate the type and severity of fracture. Thus, this study is the first to determine if composite tibias made by Sawbones (Pacific Research Labs, Vashon, WA, USA) designed for orthopedic biomechanics research, could also potentially be used for traffic safety research by simulating both the damage tolerance of human cadaveric tibias for peak force and bending moment and the fracture patterns themselves, thereby more accurately predicting injury type during real-world pedestrian-vehicle collisions. Methods: Synthetic tibias (n = 6) and human cadaveric tibias (n = 6) were impacted at midshaft at 8.3 m/s (i.e., 30 km/h) under 3-point bending using a pneumatic impacting apparatus. Fracture force, bending moment, and fracture patterns were compared between the two groups, and Weibull survivability curves generated for force and moment results, to identify injury risk thresholds. Results: There was no difference for synthetic vs. cadaveric tibias regarding impact force (4271+/-938 N vs. 4889+/-993 N, p = 0.44) or bending moment at fracture (275+/-64 Nm vs. 302+/-107 Nm, p = 0.69). Force-time curves for all tibias were similar in shape based on the first three Principal Components (p \u3e 0.14). Weibull survivability curves had differences in shape and in the 10% risk of fracture limits, with force thresholds of 2873 N for the synthetic vs. 3386 N for the cadaveric, and bending moment limits of 180 Nm for the synthetic compared to 157 Nm for the cadaveric. All fracture patterns were clinically realistic, but not consistent between groups. The coefficient of variation for synthetic tibias was \u3e0.2 for both peak force and bending moment, which precludes their use as a reproducible test surrogate for injury prediction. Conclusions: Synthetic composite tibias offer the potential for developing a frangible test surrogate, and matched cadaveric response in several respects. However, the repeatability was not high enough for them to be used in their present form for injury prediction

Mechanical Stress Promotes Cisplatin-Induced Hepatocellular Carcinoma Cell Death

Cisplatin (CisPt) is a commonly used platinum-based chemotherapeutic agent. Its efficacy is limited due to drug resistance and multiple side effects, thereby warranting a new approach to improving the pharmacological effect of CisPt. A newly developed mathematical hypothesis suggested that mechanical loading, when coupled with a chemotherapeutic drug such as CisPt and immune cells, would boost tumor cell death. The current study investigated the aforementioned mathematical hypothesis by exposing human hepatocellular liver carcinoma (HepG2) cells to CisPt, peripheral blood mononuclear cells, and mechanical stress individually and in combination. HepG2 cells were also treated with a mixture of CisPt and carnosine with and without mechanical stress to examine one possible mechanism employed by mechanical stress to enhance CisPt effects. Carnosine is a dipeptide that reportedly sequesters platinum-based drugs away from their pharmacological target-site. Mechanical stress was achieved using an orbital shaker that produced 300 rpm with a horizontal circular motion. Our results demonstrated that mechanical stress promoted CisPt-induced death of HepG2 cells (~35% more cell death). Moreover, results showed that CisPt-induced death was compromised when CisPt was left to mix with carnosine 24 hours preceding treatment. Mechanical stress, however, ameliorated cell death (20% more cell death)

The biomechanical effect of anteversion and modular neck offset on stress shielding for short-stem versus conventional long-stem hip implants

© 2015 IPEM. Short-stem hip implants are increasingly common since they preserve host bone stock and presumably reduce stress shielding by improving load distribution in the proximal femur. Stress shielding may lead to decreased bone density, implant loosening, and fracture. However, few biomechanical studies have examined short-stem hip implants. The purpose of this study was to compare short-stem vs. standard length stemmed implants for stress shielding effects due to anteversion-retroversion, anterior-posterior position, and modular neck offset. Twelve artificial femurs were implanted with either a short-stem modular-neck implant or a conventional length monolithic implant in 0° or 15° of anteversion. Three modular neck options were tested in the short-stem implants. Three control femurs remained intact. Femurs were mounted in adduction and subjected to axial loading. Strain gauge values were collected to validate a Finite Element (FE) model, which was used to simulate the full range of physiologically possible anteversion and anterior-posterior combinations (n = 25 combinations per implant). Calcar stress was compared between implants and across each implant\u27s range of anteversion using one and two-way ANOVA. Stress shielding was defined as the overall change in stress compared to an intact femur.The FE model compared well with experimental strains (intact: slope = 0.898, R = 0.943; short-stem: slope = 0.731, R = 0.948; standard-stem: slope = 0.743, R = 0.859); correction factors were used to adjust slopes to unity. No implant anteversion showed significant reduction in stress shielding (α = 0.05, p \u3e 0.05). Stress shielding was significantly higher in the standard-stem implant (63% change from intact femur, p \u3c 0.001) than in short-stem implants (29-39% change, p \u3c 0.001).Short-stem implants reduce stress shielding compared to standard length stemmed implants, while implant anteversion and anterior-posterior position had no effect. Therefore, short-stem implants have a greater likelihood of maintaining calcar bone strength in the long term