Liner orientation change of dual mobility cup determined via 3D ultrasound imaging and motion analysis: A cadaver study.

BACKGROUND: A mobile polyethylene liner enables the dual mobility cup (DMC) to contribute to restoring hip joint range-of-motion, decreasing wear and increasing implant stability. However, more data is required on how liner orientation changes with hip joint movement. As a first step towards better understanding liner orientation change in vivo, this cadaver study focuses on quantifying DMC liner orientation change after different hip passive movements, using ultrasound imaging and motion analysis. HYPOTHESIS: The liner does not always go back to its initial orientation and its final orientation depends mainly on hip movement amplitude. METHODS: 3D ultrasound imaging and motion analysis were used to define liner and hip movements for four fresh post-mortem human subjects with six implanted DMC. Abduction and anteversion angles of the liner plane relative to the pelvis were measured before and after hip flexion, internal rotation, external rotation, abduction, adduction. RESULTS: Liner orientation changes were generally defined by angle variation smaller than 5°, with the liner nearly going back to its initial orientation. However, hip flexion caused liner abduction and anteversion angle variations greater than 15°. Except for hip adduction, only weak or no correlation was found between the final angle of the liner and the maximal hip joint movement amplitude. DISCUSSION: This study is the first attempt to quantify liner orientation change for implanted DMC via ultrasound imaging and constitutes a step forward in the understanding of liner orientation change and its relationship with hip joint movement. The hypothesis that the final liner abduction and anteversion angles depend mainly on hip movement amplitude was not confirmed, even if hip flexion was the movement generating the most liner orientation changes over 15°. This approach should be extended to in vivo clinical investigations, as measured liner angle variation could provide important support for the wear and stability claims made for DMC. LEVEL OF EVIDENCE: IV; cadaveric study.

What is the best fixation method in medial patellofemoral ligament reconstruction? A biomechanical comparison of common methods for femoral graft attachment.

INTRODUCTION: A variety of techniques have been described for femoral fixation in medial patellofemoral ligament reconstruction (MPFLr). The aim of this study was to compare the biomechanical performance of the most used methods for graft fixation in the femur using human cadaveric tissue. We wondered what is the best fixation method for femoral fixation in MPFL reconstruction? HYPOTHESIS: A suspensory fixation device provides the best femoral fixation. MATERIAL AND METHOD: Twenty cadaveric knees were tested. Four femoral fixation methods were compared (5 knees per group): interference fixation with a Biosure© RG 5 mm and a 7 mm, suture anchor (Healicoil Regenesorb 4.75 mm ©) and suspensory fixation with the Ultrabutton©. The testing was divided in preconditioning, cyclic loading and load to failure. Load to failure, elongation, stiffness and mode of failure were recorded and compared. RESULTS: The Ultrabutton© had the highest mean ultimate load (427 ± 215 N (p = 0.5)), followed by Healicoil anchor © (308 ± 44 N (p > 0.05)) and the interference screw of 7 mm (255 ± 170 N (p > 0.05)). Mean stiffness was similar in the Ultrabutton© and 4.75 mm. Healicoil anchor © groups (111 ± 21 N/mm and 119 ± 20 N/mm respectively), and lowest in 7 mm Biosure© screw fixation group (90 ± 5 N/mm). The Biosure© 5 mm RG screw presented 100% of premature rupture because of tendon slippage. The Ultrabutton© presented the lowest premature rupture (40%). DISCUSSION: A suspensory fixation for the femur had the lowest number of graft failures and highest load to failure. This study has implications for surgeons' choice of graft fixation in MPFLr. It is the first study to test the most commonly femoral used fixation methods, allowing direct comparisons between each method.

Accuracy and precision of the measurement of liner orientation of dual mobility cup total hip arthroplasty using ultrasound imaging.

The Dual Mobility Cup (DMC) was created in 1974 to prevent dislocation and decrease wear. However, the movement of the polyethylene liner in vivo remains unclear. The aims of this study were to visualise liner positions and quantify the accuracy of the liner plane orientation for static positions, using ultrasound imaging. DMC reconstruction and angle between cup and liner were evaluated on isolated submerged DMCs by comparing 3D laser scans and ultrasound imaging. Moreover, the abduction and anteversion angles of the liner plane relative to the pelvis orientation were calculated via combined motion analysis and 3D ultrasound imaging on four fresh post-mortem human subjects with implanted DMC. On submerged DMC, the mean angle error between ultrasound imaging and 3D scan was 1.2°. In cadaveric experiments, intra-operator repeatability proved satisfactory, with low range value (lower than 2°) and standard deviation (lower than 1°). The study demonstrates the feasibility of measuring liner orientation on submerged and ex vivo experiments using ultrasound imaging, and is a first step towards in vivo analysis of DMC movement.

Anterior cruciate ligament reconstruction with short hamstring grafts: the choice of femoral fixation device matters in controlling overall lengthening.

PURPOSE: The purpose was to conduct an independent biomechanical study comparing the main types of femoral fixation adapted to short hamstring grafts in anterior cruciate ligament (ACL) reconstruction surgery and to validate their performance. METHODS: The ACLip® Femoral, ToggleLoc™ Ziploop (TLZ), and Tape Locking Screw (TLS®) implants were tested in tension in the following three different configurations: implant alone, implant fixed on the femur without graft, and implant fixed on the femur with graft. Grafts alone were also tested. The femurs and the 4-strand semi-tendinosus grafts were derived from porcine and human models, respectively. Each set-up was subjected to the same protocol of creep (50 N for 30 s), cycling (1000 cycles between 50 and 250 N, 1 Hz), and load to failure (50 mm/min). RESULTS: A total of 93 tests were performed (30 ACLip®, 30 TLZ, 20 TLS®, and 13 ST4 alone). For the implants tested with femur and graft, the mean ± standard deviation (SD) overall elongation at 250 N after cycling was 5.2 ± 0.2 mm, 8.4 ± 2.1 mm, and 5.3 ± 0.8 mm, the mean ± SD ultimate load to failure was 736 ± 116 N, 830 ± 204 N, and 640 ± 242 N, and the mean ± SD stiffness at the 1000th cycle was 185 ± 15 N/mm, 172 ± 19 N/mm, and 178 ± 21 N/mm for ACLip®, ToggleLoc™, and TLS® devices, respectively. There was no significant difference between the implants except for post-cycling elongation between TLZ and the other two implants (p < 0.05). CONCLUSION: The choice of femoral fixation device plays a decisive role in controlling the overall lengthening of an ACL reconstruction using a short hamstring graft. All implants validated the specifications in terms of ultimate load to failure, the TLS® system had, however, a low performance limit. ToggleLoc™ with adjustable loop should no longer be used on the femur side; instead the other types of fixation should be used to improve the overall elongation control.

Distal biceps tendon repair via new knotless endobutton fixation: A biomechanical study.

BACKGROUND: Distal biceps tendon repair using endobutton fixation has shown the best biomechanical results in terms of pullout strength. Here, we compared Sethi's enhanced tension adjustable endobutton technique known as the "tension slide technique" to a new knotless endobutton fixation technique without a post-fixation screw. Our new approach is as effective as the tension slide technique in terms of pullout strength and gapping after early mobilization. METHODS: A biomechanical cadaveric study with 16 paired arms was performed. With the radius held in place, the distal biceps tendon was loaded at 100 N for 500 cycles and the load was then increased until failure. Gapping after loading cycles and maximum load to failure were recorded and compared. RESULTS: Median bone-tendon gapping was 5.77 mm (interquartile range (IQR) 4.84-9.11) for tension slide technique and 4.72 mm (IQR 1.77-6.16) for the knotless fixation (p = 0.047). Median load to failure was 257.87 N (IQR 222.07-325.35) in the tension slide technique group and 407.78 N (IQR 358.54-485.20) in the knotless group (p = 0.047). DISCUSSION: The knotless endobutton provides better pullout strength and elongation results compared to the tension slide technique without the use of an interference screw, allowing early mobilization in order to faster return to daily living activities.Level of evidence: Basic science study.

Corrigendum: Strain Assessment of Deep Fascia of the Thigh During Leg Movement: An in situ Study.

[This corrects the article DOI: 10.3389/fbioe.2020.00750.].

Strain Assessment of Deep Fascia of the Thigh During Leg Movement: An in situ Study.

Fascia is a fibrous connective tissue present all over the body. At the lower limb level, the deep fascia that is overlying muscles of the outer thigh and sheathing them (fascia lata) is involved in various pathologies. However, the understanding and quantification of the mechanisms involved in these sheathing effects are still unclear. The aim of this study is to observe and quantify the strain field of the fascia lata, including the iliotibial tract (ITT), during a passive movement of the knee. Three fresh postmortem human subjects were studied. To measure hip and knee angles during knee flexion-extension, passive movements from 0° to around 120° were recorded with a motion analysis system and strain fields of the fascia were acquired using digital image correlation. Strains were computed for three areas of the fascia lata: anterior fascia, lateral fascia, and ITT. Mean principal strains showed different strain mechanisms depending on location on the fascia and knee angle. For anterior and lateral fascia, a tension mechanism was mainly observed with major strain greater than minor strain in absolute value. While for the ITT, two strain mechanisms were observed depending on knee movement: tension is observed when the knee is extended relatively to reference position of 47°, however, pure shear can be observed when the knee is flexed. In some cases, minor strain can also be higher than major strain in absolute value, suggesting high tissue compression probably due to microstructural fiber rearrangements. This in situ study is the first attempt to quantify the superficial strain field of fascia lata during passive leg movement. The study presents some limitations but provides a step in understanding strain mechanism of the fascia lata during passive knee movement.

Ilio-psoas impingement with a dual-mobility liner: an original case report and review of literature.

Ilio-psoas impingement after total hip arthroplasty often occurs with the metallic rim of the acetabular cup. The main causes are poor cup anteversion or anterior wall defect. We firstly report here the case of a patient complaining of iliopsoas impingement due to contact with the liner of a dual-mobility device. Ultrasonography and Computed Tomographic scan clearly showed the direct mechanical contact of the dual-mobility liner with the iliopsoas tendon.

Evaluation of 6 and 10 Year-Old Child Human Body Models in Emergency Events.

Emergency events can influence a child's kinematics prior to a car-crash, and thus its interaction with the restraint system. Numerical Human Body Models (HBMs) can help understand the behaviour of children in emergency events. The kinematic responses of two child HBMs-MADYMO 6 and 10 year-old models-were evaluated and compared with child volunteers' data during emergency events-braking and steering-with a focus on the forehead and sternum displacements. The response of the 6 year-old HBM was similar to the response of the 10 year-old HBM, however both models had a different response compared with the volunteers. The forward and lateral displacements were within the range of volunteer data up to approximately 0.3 s; but then, the HBMs head and sternum moved significantly downwards, while the volunteers experienced smaller displacement and tended to come back to their initial posture. Therefore, these HBMs, originally intended for crash simulations, are not too stiff and could be able to reproduce properly emergency events thanks, for instance, to postural control.

Experimental characterization of post rigor mortis human muscle subjected to small tensile strains and application of a simple hyper-viscoelastic model.

In models developed for impact biomechanics, muscles are usually represented with one-dimensional elements having active and passive properties. The passive properties of muscles are most often obtained from experiments performed on animal muscles, because limited data on human muscle are available. The aim of this study is thus to characterize the passive response of a human muscle in tension. Tensile tests at different strain rates (0.0045, 0.045, and 0.45 s⁻¹) were performed on 10 extensor carpi ulnaris muscles. A model composed of a nonlinear element defined with an exponential law in parallel with one or two Maxwell elements and considering basic geometrical features was proposed. The experimental results were used to identify the parameters of the model. The results for the first- and second-order model were similar. For the first-order model, the mean parameters of the exponential law are as follows: Young's modulus E (6.8 MPa) and curvature parameter α (31.6). The Maxwell element mean values are as follows: viscosity parameter η (1.2 MPa s) and relaxation time τ (0.25 s). Our results provide new data on a human muscle tested in vitro and a simple model with basic geometrical features that represent its behavior in tension under three different strain rates. This approach could be used to assess the behavior of other human muscles.

Viscoelastic properties of the human sternocleidomastoideus muscle of aged women in relaxation.

Improving the numerical models of the head and neck complex requires understanding the mechanical properties of the muscles; however, most of the data in existing literature have been obtained from studies on animal muscles. Muscle is hyper-elastic, but also viscoelastic. The hyper-elastic behaviour of the human sternocleidomastoideus muscle has been previously studied. The aim of this study is to propose a characterization of the viscoelastic properties of the same human muscle in relaxation. Ten muscles were tested in vitro. The viscoelastic behaviour was modelled with a generalized Maxwell's model studied at the first and second order, using an inverse approach with a subject-specific, finite-element model of each muscle. Based on these models, relaxation times τ (first order: 103s; second order: 18s and 395s) and ratio moduli γ (first order: 0.33; second order: 0.20 and 0.19) were identified. The first-order model provided a good estimate of the relaxation curve (R(2): 0.82), but the second-order model was more representative of the experimental response (R(2): 0.97). Our results provide evidence that the viscoelastic behaviour of the human sternocleidomastoideus muscle can be described using a second-order Maxwell's model and that - combined with the previously identified hyper-elastic properties - the response of the muscle in tension and relaxation is fully characterized.

Hyper-elastic properties of the human sternocleidomastoideus muscle in tension.

Numerical models of the human body require realistic mechanical properties of the muscles as input, but, generally, such data are available only for animals' muscles. As a consequence, the aim of this study was to identify the hyper-elastic behavior of the human sternocleidomastoideus muscle in tension using different constitutive laws. Ten sternocleidomastoideus muscles were tested in vitro. The hyper-elastic behavior was modeled with an exponential law and a hyper-elastic constitutive law studied analytically. The latter was also studied with an inverse approach using a subject-specific, finite-element model of each muscle. The three approaches were compared statistically. From these laws and methods, the shear modulus µ (4 to 98 kPa) and the curvature parameter α (17 to 52) were identified. Both the analytical and finite-element approaches gave parameters of the same order of magnitude. The parameters of the exponential and hyper-elastic laws were linked thanks to simple linear equations. Our results evidence that the hyper-elastic tension behavior of human sternocleidomastoideus muscle can be described using a simple model (exponential) considering basic geometric features (initial length and cross-sectional area).

The non-linear response of a muscle in transverse compression: assessment of geometry influence using a finite element model.

Most recent finite element models that represent muscles are generic or subject-specific models that use complex, constitutive laws. Identification of the parameters of such complex, constitutive laws could be an important limit for subject-specific approaches. The aim of this study was to assess the possibility of modelling muscle behaviour in compression with a parametric model and a simple, constitutive law. A quasi-static compression test was performed on the muscles of dogs. A parametric finite element model was designed using a linear, elastic, constitutive law. A multi-variate analysis was performed to assess the effects of geometry on muscle response. An inverse method was used to define Young's modulus. The non-linear response of the muscles was obtained using a subject-specific geometry and a linear elastic law. Thus, a simple muscle model can be used to have a bio-faithful, biomechanical response.