A dynamic model of the knee and lower limb for simulating rising movements

My Top Five Concepts for Selecting Lower Extremity Exercises For Cruciate Ligament and Patellofemoral Rehabilitation

This clinical commentary will address five key concepts that can be used by clinicians as criteria for selecting lower extremity weight bearing exercises (WBE) and non-weight bearing exercises (NWBE) employed for cruciate ligament and patellofemoral rehabilitation. The following will be discussed for both cruciate ligament and patellofemoral rehabilitation: 1) Knee loading varies between WBE and NWBE; 2) Knee loading varies with technique variations within WBE and NWBE; 3) Knee loading varies between different WBE; 4) Knee loading varies as a function of knee angle; and 5) Knee loading increases with increased knee anterior translation beyond toes.

Uncertainty in Muscle–Tendon Parameters can Greatly Influence the Accuracy of Knee Contact Force Estimates of Musculoskeletal Models

Understanding the sources of error is critical before models of the musculoskeletal system can be usefully translated. Using in vivo measured tibiofemoral forces, the impact of uncertainty in muscle–tendon parameters on the accuracy of knee contact force estimates of a generic musculoskeletal model was investigated following a probabilistic approach. Population variability was introduced to the routine musculoskeletal modeling framework by perturbing input parameters of the lower limb muscles around their baseline values. Using ground reaction force and skin marker trajectory data collected from six subjects performing body-weight squat, the knee contact force was calculated for the perturbed models. The combined impact of input uncertainties resulted in a considerable variation in the knee contact force estimates (up to 2.1 BW change in the predicted force), especially at larger knee flexion angles, hence explaining up to 70% of the simulation error. Although individual muscle groups exhibited different contributions to the overall error, variation in the maximum isometric force and pathway of the muscles showed the highest impacts on the model outcomes. Importantly, this study highlights parameters that should be personalized in order to achieve the best possible predictions when using generic musculoskeletal models for activities involving deep knee flexion.

Techniques to determine knee joint contact forces during squatting: A systematic review

This review article provides an overview of techniques used to determine human knee joint contact forces during squatting. The main two approaches are experimental and theoretical. Thigh calf contact has a significant effect on knee forces and should not be neglected. In this study, data were searched electronically and organized by techniques to find knee joint contact force during squatting theoretically and experimentally. There was a large variation in peak tibiofemoral (CV = 0.45) and patellofemoral (CV = 0.38) contact forces predicted theoretically. However, very little variation was observed between peak tibiofemoral contact forces (CV = 0.12) measured in vivo experimentally but measured knee joint force is available up to a limited knee flexion angle. There was a reduction in knee joint contact forces due to thigh calf contact. Literature of knee joint contact force prediction theoretically during squatting incorporating thigh calf contact force is very limited.

Kinematics and kinetics comparison of ultra-congruent versus medial-pivot designs for total knee arthroplasty by multibody analysis

Nowadays, several configurations of total knee arthroplasty (TKA) implants are commercially available whose designs resulted from clinical and biomechanical considerations. Previous research activities led to the development of the so-called medial-pivot (MP) design. However, the actual benefits of the MP, with respect to other prosthesis designs, are still not well understood. The present work compares the impact of two insert geometries, namely the ultra-congruent (UC) and medial-pivot (MP), on the biomechanical behaviour of a bicondylar total knee endoprosthesis. For this purpose, a multibody model of a lower limb was created alternatively integrating the two implants having the insert geometry discretized. Joint dynamics and contact pressure distributions were evaluated by simulating a squat motion. Results showed a similar tibial internal rotation range of about 3.5°, but an early rotation occurs for the MP design. Furthermore, the discretization of the insert geometry allowed to efficiently derive the contact pressure distributions, directly within the multibody simulation framework, reporting peak pressure values of 33 MPa and 20 MPa for the UC and MP, respectively. Clinically, the presented findings confirm the possibility, through a MP design, to achieve a more natural joint kinematics, consequently improving the post-operative patient satisfaction and potentially reducing the occurrence of phenomena leading to the insert loosening.

The effect of modelling parameters in the development and validation of knee joint models on ligament mechanics: A systematic review

BACKGROUND

The ligaments in the knee are prone to injury especially during dynamic activities. The resulting instability can have a profound impact on a patient's daily activities and functional capacity. Musculoskeletal knee modelling provides a non-invasive tool for investigating ligament force-strain behaviour in various dynamic scenarios, as well as potentially complementing existing pre-planning tools to optimise surgical reconstructions. However, despite the development and validation of many musculoskeletal knee models, the effect of modelling parameters on ligament mechanics has not yet been systematically reviewed.

OBJECTIVES

This systematic review aimed to investigate the results of the most recent studies using musculoskeletal modelling techniques to create models of the native knee joint, focusing on ligament mechanics and modelling parameters in various simulated movements.

DATA SOURCES

PubMed, ScienceDirect, Google Scholar, and IEEE Xplore.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Databases were searched for articles containing any numerical ligament strain or force data on the intact, ACL-deficient, PCL-deficient, or lateral extra-articular reconstructed (LER) knee joints. The studies had to derive these results from musculoskeletal modelling methods. The dates of the publications were between 1 January 1995 and 30 November 2021.

METHOD

A customised data extraction form was created to extract each selected study's critical musculoskeletal model development parameters. Specific parameters of the musculoskeletal knee model development used in each eligible study were independently extracted, including the (1) musculoskeletal model definition (i.e., software used for modelling, knee type, source of geometry, the inclusion of cartilage and menisci, and articulating joints and joint boundary conditions (i.e., number of degrees of freedom (DoF), subjects, type of activity, collected data and type of simulation)), (2) specifically ligaments modelling techniques (i.e., ligament bundles, attachment points, pathway, wrapping surfaces and ligament material properties such as stiffness and reference length), (3) sensitivity analysis, (4) validation approaches, (5) predicted ligament mechanics (i.e., force, length or strain) and (6) clinical applications if available. The eligible papers were then discussed quantitatively and qualitatively with respect to the above parameters.

RESULTS AND DISCUSSION

From the 1004 articles retrieved by the initial electronic search, only 25 met all inclusion criteria. The results obtained by aggregating data reported in the eligible studies indicate that considerable variability in the predicted ligament mechanics is caused by differences in geometry, boundary conditions and ligament modelling parameters.

CONCLUSION

This systematic review revealed that there is currently a lack of consensus on knee ligament mechanics. Despite this lack of consensus, some papers highlight the potential of developing translational tools using musculoskeletal modelling. Greater consistency in model design, incorporation of sensitivity assessment of the model outcomes and more rigorous validation methods should lead to better agreement in predictions for ligament mechanics between studies. The resulting confidence in the musculoskeletal model outputs may lead to the development of clinical tools that could be used for patient-specific treatments.

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

Predictions of Anterior Cruciate Ligament Dynamics From Subject-Specific Musculoskeletal Models and Dynamic Biplane Radiography

In vivo knee ligament forces are important to consider for informing rehabilitation or clinical interventions. However, they are difficult to directly measure during functional activities. Musculoskeletal models and simulations have become the primary methods by which to estimate in vivo ligament loading. Previous estimates of anterior cruciate ligament (ACL) forces range widely, suggesting that individualized anatomy may have an impact on these predictions. Using ten subject-specific (SS) lower limb musculoskeletal models, which include individualized musculoskeletal geometry, muscle architecture, and six degree-of-freedom knee joint kinematics from dynamic biplane radiography (DBR), this study provides SS estimates of ACL force (anteromedial-aACL; and posterolateral-pACL bundles) during the full gait cycle of treadmill walking. These forces are compared to estimates from scaled-generic (SG) musculoskeletal models to assess the effect of musculoskeletal knee joint anatomy on predicted forces and the benefit of SS modeling in this context. On average, the SS models demonstrated a double force peak during stance (0.39-0.43 xBW per bundle), while only a single force peak during stance was observed in the SG aACL. No significant differences were observed between continuous SG and SS ACL forces; however, root mean-squared differences between SS and SG predictions ranged from 0.08 xBW to 0.27 xBW, suggesting SG models do not reliably reflect forces predicted by SS models. Force predictions were also found to be highly sensitive to ligament resting length, with ±10% variations resulting in force differences of up to 84%. Overall, this study demonstrates the sensitivity of ACL force predictions to SS anatomy, specifically musculoskeletal joint geometry and ligament resting lengths, as well as the feasibility for generating SS musculoskeletal models for a group of subjects to predict in vivo tissue loading during functional activities.

Viscoelastic and failure properties of two configurations of triple-folded hamstring tendons used for anterior cruciate ligament (ACL) reconstruction

BACKGROUND

Hamstring autografts are commonly used for anterior cruciate ligament (ACL) reconstruction. Different folding techniques exist in tripling the semitendinosus. Few anatomical studies exist in evaluating their viscoelastic properties. The purpose of this study was to characterize and compare the viscoelastic and failure properties of two hamstring graft configurations, the "Z" construct and "2" construct.

METHODS

Ten matched pairs of fresh-frozen cadaveric semitendinosus hamstring grafts were used to create the "2" configuration or "Z" configuration. The biomechanical testing consisted of four phases: preconditioning, where graft dimensions (mm) were measured; stress relaxation, where load, displacement and time data were collected and equilibrium relaxation (%) was calculated; dynamic creep, where the total construct elongation was calculated; and ramp-to-failure, where maximum failure load was recorded.

RESULTS

The "2" configuration demonstrated recorded forces (N) significantly greater at each time point when compared to the "Z" configuration during stress relaxation (p = 0.003). The "2" configuration exhibited significantly less construct elongation (mm) during dynamic creep at 10 cycles (p = 0.008) and 2000 cycles (p = 0.0001). The maximum measured load at failure was significantly greater in the "2" configuration constructs than "Z" configuration (p = 0.013). Moreover, the axial loads at 2, 3 and 4 mm of displacement were, on average, greater in the "2" configuration than "Z" configuration (p = 0.152; p = 0.080; p = 0.012), respectively.

CONCLUSION

The results of this study provide support for folding techniques for tripled grafts to provide higher viscoelastic and failure properties for techniques with less suture interfaces. Future studies can potentially evaluate the clinical significance of these findings.

Biomechanical Study of a Tricompartmental Unloader Brace for Patellofemoral or Multicompartment Knee Osteoarthritis

Objective: Off-loader knee braces have traditionally focused on redistributing loads away from either the medial or lateral tibiofemoral (TF) compartments. In this article, we study the potential of a novel "tricompartment unloader" (TCU) knee brace intended to simultaneously unload both the patellofemoral (PF) and TF joints during knee flexion. Three different models of the TCU brace are evaluated for their potential to unload the knee joint. Methods: A sagittal plane model of the knee was used to compute PF and TF contact forces, patellar and quadriceps tendon forces, and forces in the anterior and posterior cruciate ligaments during a deep knee bend (DKB) test using motion analysis data from eight participants. Forces were computed for the observed (no brace) and simulated braced conditions. A sensitivity and validity analysis was conducted to determine the valid output range for the model, and Statistical Parameter Mapping was used to quantify the effectual region of the different TCU brace models. Results: PF and TF joint force calculations were valid between ~0 and 100 degrees of flexion. All three simulated brace models significantly (p < 0.001) reduced predicted knee joint loads (by 30-50%) across all structures, at knee flexion angles >~30 degrees during DKB. Conclusions: The TCU brace is predicted to reduce PF and TF knee joint contact loads during weight-bearing activity requiring knee flexion angles between 30 and 100 degrees; this effect may be clinically beneficial for pain reduction or rehabilitation from common knee injuries or joint disorders. Future work is needed to assess the range of possible clinical and prophylactic benefits of the TCU brace.

ReadySim: A computational framework for building explicit finite element musculoskeletal simulations directly from motion laboratory data

Musculoskeletal modeling allows researchers insight into joint mechanics which might not otherwise be obtainable through in vivo or in vitro studies. Common musculoskeletal modeling techniques involve rigid body dynamics software which often employ simplified joint representations. These representations have proven useful but are limited in performing single-framework deformable analyzes in structures of interest. Musculoskeletal finite element (MSFE) analysis allows for representation of structures in sufficient detail to obtain accurate solutions of the internal stresses and strains including complex contact conditions and material representations. Studies which performed muscle force optimization directly in a finite element framework were often limited in complexity to minimize computational time. Recent advances in computational efficiency and control schemes for muscle force prediction have made these solutions more practical. Yet, the formulation of subject-specific simulations remains a challenging problem. The objectives of this work were to develop an open-source computational framework to build and run simulations which (a) scale the size of MSFE models and efficiently estimate (b) joint kinematics and (c) muscle forces from human motion data collected in a typical gait laboratory. A computational framework was built using MATLAB and Python to interface with model input and output files. The software uses laboratory marker data to scale model segment lengths and estimate joint kinematics. Concurrent muscle force and tissue strain estimations are performed based on the estimated kinematics and ground reaction forces. This software will improve the usability and consistency of single-framework MSFE simulations. Both software and template model are made freely available on SimTK.Novelty Statement Single framework musculoskeletal modeling directly in a finite element environment for muscle force estimation and tissue strain analysis. Open dissemination of unilateral musculoskeletal finite element model and software used in manuscript.

Mapping Stresses on the Tibial Plateau Cartilage in an Ovine Model Using In-Vivo Gait Kinematics

Understanding stresses within the knee joint is central to understanding knee function, and the etiology and progression of degenerative joint diseases such as post-traumatic osteoarthritis. In this study, in vivo gait kinematics of four ovine subjects were recorded using a highly accurate Instrumented Spatial Linkage (ISL) as each subject walked on a standard treadmill. The subjects were then sacrificed, and the right hind limbs removed. Ten purpose-built Fibre Bragg Grating (FBG) sensors were positioned within each stifle joint and used to measured contact stresses on the articulating surface of the tibial plateau as the recorded gait was replicated using a 6-degrees-of-freedom parallel robotic system. This study provides the first accurate, direct measurement of stress in a joint during in vivo gait replication. It was hypothesized that the results would indicate a direct link between gait kinematics and measured stress values. Contrary to this expectation no direct link was found between individualistic differences in kinematics and differences in stress magnitudes. This finding highlights the complex multifactorial nature of stress magnitudes and distribution patterns across articular joints. The results also indicate that stress magnitudes within the knee joint are highly position dependent with magnitudes varying substantially between points only a few mm apart.

Sagittal knee kinematics in relation with the posterior tibia slope during jump landing after an anterior cruciate ligament reconstruction

Purpose

An increased posterior tibia plateau angle is associated with increased risk for anterior cruciate ligament injury and re-rupture after reconstruction. The aims of this study were to determine whether the tibia plateau angle correlates with dynamic anterior tibia translation (ATT) after an anterior cruciate ligament reconstruction and whether the tibia plateau angle correlates with aspects of knee kinematics and kinetics during jump landing.

Methods

Thirty-seven patients after anterior cruciate ligament reconstruction with autograft hamstring tendon were included. Knee flexion angle and knee extension moment during single leg hops for distance were determined using a motion capture system and the dynamic ATT with its embedded method. The medial and lateral posterior tibia plateau angle were measured using MRI. Moreover, passive ATT was measured using the KT-1000 arthrometer.

Results

A weak negative correlation was found between the maximal dynamic ATT and the medial tibia plateau angle (p = 0.028, r = − 0.36) and between the maximal knee flexion angle and the lateral tibia plateau angle (p = 0.025, r = − 0.37) during landing. Patients with a smaller lateral tibia plateau angle show larger maximal knee flexion angle during landing than the patients with larger lateral tibia plateau angle. Also, the lateral tibia plateau angle is associated the amount of with muscle activity.

Conclusion

The posterior medical tibia plateau angle is associated with dynamic ATT. The maximal knee flexion angle and muscle activity are associated with the posterior lateral tibia plateau angle.

Level of evidence

III

Biomechanical testing of fixed and adjustable femoral cortical suspension devices for ACL reconstruction under high loads and extended cyclic loading

Purpose

To compare loop elongation after 5000 cycles, loop-elongation at failure, and load at failure of the fixed-loop G-Lok device and three adjustable-loop devices (UltraButton, RigidLoop Adjustable and ProCinch RT), during testing over extended cycles under high loading.

Methods

Five devices of each type were tested on a custom-built rig fixed to an Instron machine. The testing protocol had four stages: preloading, cyclic preconditioning, incremental cyclic loading and pull-to-failure. Outcome measures were loop elongation after 5000 cycles, loop-elongation at failure, and load at failure.

Results

The loop elongation after 5000 cycles for G-Lok was 1.46 ± 0.25 mm, which was comparable to that of RigidLoop (1.51 ± 0.16 mm, p = 1.000) and ProCinch (1.60 ± 0.09 mm, p = 1.000). In comparison, the loop elongation for UltraButton was 2.66 ± 0.28 mm, which was significantly larger than all other devices (p = 0.048). The failure load for all devices ranged between 1455 and 2178 N. G-Lok was significantly stronger than all adjustable-loop devices (p = 0.048). The elongation at failure was largest for UltraButton (4.20 ± 0.33 mm), which was significantly greater than G-Lok (3.17 ± 0.33 mm, p = 0.048), RigidLoop (2.88 ± 0.20 mm, p = 0.048) and ProCinch (2.78 ± 0.08 mm, p = 0.048). There was no significant difference in elongation at failure for the rest of the devices.

Conclusions

Our study has shown that the G-Lok fixed-loop device and the three adjustable-loop devices (UltraButton, RigidLoop Adjustable and ProCinch RT) all elongated less than 3 mm during testing over an extended number of cycles at high loads, nonetheless, the fixed loop device performed best in terms of least elongation and highest load at failure.

Treatment of Acute Proximal Anterior Cruciate Ligament Tears-Part 1: Gap Formation and Stabilization Potential of Repair Techniques

Background:

Recently, there has been a resurgence of interest in primary repair of the anterior cruciate ligament (ACL), with fixation techniques evolving. However, to date, there have been no biomechanical studies comparing fixed to adjustable fixation repair techniques.

Hypothesis:

Adjustable ACL repair provides for improved stabilization compared with fixed techniques with respect to both gap formation and residual load-bearing capability.

Study Design:

Controlled laboratory study.

Methods:

A total of 4 different ACL repair techniques (n = 5 per group), including single– and double–cinch loop (CL) cortical button fixation as well as knotless single–suture anchor fixation, were tested using a porcine model. For adjustable single-CL loop fixation, additional preconditioning (10 cycles at 0.5 Hz) was performed. The force after fixation and the actuator displacement to achieve a time-zero preload of 10 N were measured for fixed techniques. Incrementally increasing cycling (1 mm/500 cycles) from 1 to 8 mm was performed for 4000 cycles at 0.75 Hz before pull to failure (50 mm/min). The final residual peak load and gap formation for each test block were analyzed as well as ultimate strength.

Results:

Knot tying of a single-CL over a button (mean ± SD, 0.66 ± 0.23 mm) and knotless anchor fixation (0.20 ± 0.12 mm) resulted in significant time-zero gaps (P < .001) and significantly higher overall gap formation at reduced residual loading (analysis of covariance, P < .001) compared with both the double-CL loop and adjustable fixation techniques. The adjustable group showed the highest failure load and stiffness, at 305.7 N and 117.1 N/mm, respectively. The failure load of the knotted single-CL group was significantly reduced compared with all other groups (P < .001).

Conclusion:

Adjustable single-CL cortical button fixation with intraoperative preconditioning optimized time-zero ACL tension and led to significantly improved stabilization and reduced gap formation, with the highest ultimate strength. Single-CL loop knot tying over the button and knotless anchor fixation resulted in time-zero gaps to achieve slight tension on the ACL and significantly higher gap formation at reduced load-bearing capability.

Clinical Relevance:

Although the clinical relevance of gap formation is uncertain, a biomechanical understanding of the stabilization potential of current ACL repair techniques is pertinent to the continued evolution of surgical approaches to enable better clinical outcomes.

Fixed- Versus Adjustable-Loop Devices for Femoral Fixation in Anterior Cruciate Ligament Reconstruction: A Systematic Review

PURPOSE

To compare biomechanical and clinical outcomes between adjustable-loop devices (ALDs) and fixed-loop devices (FLDs) in the femoral fixation component of anterior cruciate ligament reconstruction (ACLR) using a hamstring autograft or allograft.

METHODS

A multi-database search was performed on July 18, 2018, according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. All articles directly comparing ALDs and FLDs in ACLR using hamstring grafts were included. Non-English-language articles were excluded.

RESULTS

We included 13 biomechanical, 2 prospective, and 6 retrospective studies in this review. Retensioning of ALDs was performed in 4 of 13 biomechanical studies and in all clinical studies. Biomechanically, 11 studies showed a statistically significantly larger maximum irreversible displacement of the graft in the ALD group. Two studies showed no statistically significant difference with retensioning of the TightRope ALD, whereas all 3 studies that examined knotting of ALDs showed no statistically significant difference between the FLD and ALD groups. Five studies reported statistically significantly higher graft stiffness for FLDs than ALDs. Retensioning or knotting did not produce any significant change in construct stiffness. Nine studies reported a statistically significantly higher ultimate load to failure for FLDs. With knotting of ALDs, this difference was no longer statistically significant in only 1 study. Clinical studies showed no statistically significant differences in clinical, functional, radiologic, and complication outcomes between both groups.

CONCLUSIONS

Despite the superior biomechanical properties of FLDs, ALDs and FLDs yielded similar clinical outcome scores and graft rerupture rates. Biomechanical outcomes were improved with retensioning of ALDs after tibial fixation, as per manufacturer recommendations.

LEVEL OF EVIDENCE

Level III, systematic review of Level III and IV studies.

A lower extremity model for muscle-driven simulation of activity using explicit finite element modeling

A key strength of computational modeling is that it can provide estimates of muscle, ligament, and joint loads, stresses, and strains through non-invasive means. However, simulations that can predict the forces in the muscles during activity while maintaining sufficient complexity to realistically represent the muscles and joint structures can be computationally challenging. For this reason, the current state of the art is to apply separate rigid-body dynamic and finite-element (FE) analyses in series. However, the use of two or more disconnected models often fails to capture key interactions between the joint-level and whole-body scales. Single framework MSFE models have the potential to overcome the limitations associated with disconnected models in series. The objectives of the current study were to create a multi-scale FE model of the human lower extremity that combines optimization, dynamic muscle modeling, and structural FE analysis in a single framework and to apply this framework to evaluate the mechanics of healthy knee specimens during two activities. Two subject-specific FE models (Model 1, Model 2) of the lower extremity were developed in ABAQUS/Explicit including detailed representations of the muscles. Muscle forces, knee joint loading, and articular contact were calculated for two activities using an inverse dynamics approach and static optimization. Quadriceps muscle forces peaked at the onset of chair rise (2174 N, 1962 N) and in early stance phase (510 N, 525 N), while gait saw peak forces in the hamstrings (851 N, 868 N) in midstance. Joint forces were similar in magnitude to available telemetric patient data. This study demonstrates the feasibility of detailed quasi-static, muscle-driven simulations in an FE framework.

A computationally efficient strategy to estimate muscle forces in a finite element musculoskeletal model of the lower limb

Concurrent multiscale simulation strategies are required in computational biomechanics to study the interdependence between body scales. However, detailed finite element models rarely include muscle recruitment due to the computational burden of both the finite element method and the optimization strategies widely used to estimate muscle forces. The aim of this study was twofold: first, to develop a computationally efficient muscle force prediction strategy based on proportional-integral-derivative (PID) controllers to track gait and chair rise experimental joint motion with a finite element musculoskeletal model of the lower limb, including a deformable knee representation with 12 degrees of freedom; and, second, to demonstrate that the inclusion of joint-level deformability affects muscle force estimation by using two different knee models and comparing muscle forces between the two solutions. The PID control strategy tracked experimental hip, knee, and ankle flexion/extension with root mean square errors below 1°, and estimated muscle, contact and ligament forces in good agreement with previous results and electromyography signals. Differences up to 11% and 20% in the vasti and biceps femoris forces, respectively, were observed between the two knee models, which might be attributed to a combination of differing joint contact geometry, ligament behavior, joint kinematics, and muscle moment arms. The tracking strategy developed in this study addressed the inevitable tradeoff between computational cost and model detail in musculoskeletal simulations and can be used with finite element musculoskeletal models to efficiently estimate the interdependence between muscle forces and tissue deformation.

Effect of hip joint angle at seat-off on hip joint contact force during sit-to-stand movement: a computer simulation study

Background

Sit-to-stand movements are a necessary part of daily life, and excessive mechanical stress on the articular cartilage has been reported to encourage the progression of osteoarthritis. Although a change in hip joint angle at seat-off may affect hip joint contact force during a sit-to-stand movement, the effect is unclear. This study aimed to examine the effect of the hip joint angle at seat-off on the hip joint contact force during a sit-to-stand movement by using a computer simulation.

Methods

A musculoskeletal model was created for the computer simulation, and eight muscles were attached to each lower limb. Various sit-to-stand movements were generated using parameters (e.g., seat height and time from seat-off to standing posture) reported by previous studies. The hip joint contact force for each sit-to-stand movement was calculated. Furthermore, the effect of the hip joint angle at seat-off on the hip joint contact force during the sit-to-stand movement was examined. In this study, as the changes to the musculoskeletal model parameters affect the hip joint contact force, a sensitivity analysis was conducted.

Results and conclusions

The hip joint contact force during the sit-to-stand movement increased approximately linearly as the hip flexion angle at the seat-off increased. Moreover, the normal sit-to-stand movement and the sit-to-stand movement yielding a minimum hip joint contact force were approximately equivalent. The effect of the changes to the musculoskeletal model parameters on the main findings of this study was minimal. Thus, the main findings are robust and may help prevent the progression of hip osteoarthritis by decreasing mechanical stress, which will be explored in future studies.

Electronic supplementary material

The online version of this article (10.1186/s12938-018-0610-5) contains supplementary material, which is available to authorized users.

Mechanical assessment of tripled hamstring tendon graft when using suspensory fixation for cruciate ligament reconstruction

BACKGROUND

Tripling semitendinosus tendon for ACL graft preparation facilitates creation of longer and thicker grafts. Our objective was to evaluate the mechanical difference between tripled tendon grafts, prepared by three methods, by comparing with quadrupled tendon graft.

METHODS

Bovine hind-foot hoof extensors were allocated to four groups. Group I had quadrupled graft construct. Tripled graft constructs were prepared by passing the tendon to the Endobutton CL loop and stitching the third strand to (i) the loop (in Group II) or (ii) to one strand(in Group III) or (iii)to loop and both tendon strands (in Group IV). The constructs were preloaded from 10 to 50 N at 0.1 Hz for 10 cycles, followed by 1000 cycles of sinusoidal loading between 50 and 250 N at a frequency of 0.5 Hz. The specimens were then subjected to load to failure test at the rate of 50 mm/min. Displacement with cyclic loading, load at failure and the mode of failure were noted.

RESULTS

The load at failure was 957 ± 23.30 N (Mean ± Standard Deviation) in Group I, 590.8 ± 24.40 N in Group II, 682.6 ± 59.28 N in Group III and 963.4 ± 21.72 N in Group IV. The displacement with cyclic loading was 1.13 ± 0.11 mm in Group I, 4.908 ± 0.55 mm in Group II, 1.822 ± 0.55 mm in Group III and 1. 126 ± .018 mm in Group IV. There was no significant difference between the Groups I and IV with respect to the load at failure and displacement (p > 0.05). The values were significantly different in Group II and Group III (p < 0.01), when compared to groups I and IV.

CONCLUSIONS

Tripled grafts have mechanical properties equivalent to quadrupled grafts only when the three strands are sutured together. Caution may be warranted when using suspensory fixation device with tripled tendons and the third strand must be securely attached to the loop of fixation device and to the other two strands.

Fixed- Versus Adjustable-Loop Femoral Cortical Suspension Devices for Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis of Biomechanical Studies

Background:

Fixed- and adjustable-loop femoral cortical suspension devices are commonly used for femoral graft fixation during anterior cruciate ligament reconstruction (ACLR).

Purpose:

To compare the biomechanical results of fixed- versus adjustable-loop femoral cortical suspension devices in studies simulating ACLR with an isolated device and/or specimen setup using porcine femora and bovine flexor tendons.

Study Design:

Systematic review.

Methods:

Two independent reviewers searched PubMed, Embase, and the Cochrane Library databases to find studies comparing the biomechanical strength of fixed- and adjustable-loop cortical suspension devices for ACLR with isolated device and/or specimen setups using porcine femora and bovine flexor tendons. Studies that compared both devices with similar biomechanical methods were included. Data extracted included displacement during cyclic loading, ultimate load to failure, and mode of failure of the different cortical suspension devices for ACLR.

Results:

Six studies were identified that met the inclusion criteria, including a total of 76 fixed-loop devices and 120 adjustable-loop devices. Load to failure was significantly different (P < .0001), with the strongest fixation device being the ToggleLoc with ZipLoop adjustable-loop device (1443.9 ± 512.3 N), compared with the Endobutton CL fixed-loop device (1312.9 ± 258.1 N; P = .04) and the TightRope RT adjustable-loop device (863.8 ± 64.7 N; P = .01). Cyclic displacement was significantly different, with Endobutton CL (3.7 ± 3.9 mm) showing the least displacement, followed by ToggleLoc with ZipLoop (4.9 ± 2.3 mm) and TightRope RT (7.7 ± 11.1 mm) (P < .0001). Mode of failure was statistically different between the 3 groups (P = .01), with suture failure accounting for 83.8% of TightRope RT devices, 69.4% of ToggleLoc with ZipLoop devices, and 60.3% of Endobutton CL devices.

Conclusion:

Current biomechanical data suggest that the ToggleLoc with ZipLoop device is the strongest fixation device at “time zero” in terms of ultimate load to mechanical failure. However, the Endobutton CL device demonstrated the least cyclic displacement, which may be a more clinically applicable measure of device superiority.

Evaluation of the accuracy of musculoskeletal simulation during squats by means of instrumented knee prostheses

Standard musculoskeletal simulation tools now offer widespread access to internal loading conditions for use in improving rehabilitation concepts or training programmes. However, despite broad reliance on their outcome, the accuracy of such loading estimations, specifically in deep knee flexion, remains generally unknown. The aim of this study was to evaluate the error of tibio-femoral joint contact force (JCF) calculations using musculoskeletal simulation compared to in vivo measured JCFs in subjects with instrumented total knee endoprostheses during squat exercises. Using the early but common "Gait2392_simbody" (OpenSim) scaled musculoskeletal models, tibio-femoral JCFs were calculated in 6 subjects for 5 repetitions of squats. Tibio-femoral JCFs of 0.8-3.2 times bodyweight (BW) were measured. While the musculoskeletal simulations underestimated the measured knee JCFs at low flexion angles, an average error of less than 20% was achieved between approximately 25°-60° knee flexion. With an average error that behaved almost linearly with knee flexion angle, an overestimation of approximately 60% was observed at deep flexion (ca. 80°), with an absolute maximum error of ca. 1.9BW. Our data indicate that loading estimations from early musculoskeletal gait models at both high and low knee joint flexion angles should be interpreted carefully.

Intraoperative Workflow for All-Inside Anterior Cruciate Ligament Reconstruction: An In Vitro Biomechanical Evaluation of Preconditioning and Knot Tying

PURPOSE

To evaluate and compare the effect of preconditioning according to intraoperative workflow on the elongation behavior of single-side and fully knotted all-inside anterior cruciate ligament (ACL) reconstruction configurations in a biomechanical in vitro study.

METHODS

Four full construct all-inside ACL reconstruction groups (n = 8 per group) were tested using porcine tibias and bovine tendons. Groups included both an all-inside configuration with one- (group 1) and both-side knotted adjustable loop-length devices (group 2), without and with performing intraoperative preconditioning (group 1-intraoperative preconditioned [IPC], group 2-IPC). Adjustable loop-length devices for control groups were knotted according to test configurations. Intraoperative preconditioning specimens were further precycled for 10 times at 0.5 Hz and manually retensioned before knotting. All groups underwent dynamic cycling in position and force control mode each for 1,000 cycles at 0.75 Hz according to in vitro loading parameters replicating the in vivo ACL environment. Finally, a load-to-failure test at 50 mm/min was performed.

RESULTS

Intraoperative preconditioning increases initial graft tension for single- (242 ± 22 N vs 174 ± 13 N; P < .0001) and both-side knotted configurations (225 ± 15 N vs 159 ± 10 N; P < .0001) compared with controls and allows maintained graft tension at higher levels until reaching the end of position-controlled cyclic loading. Furthermore, dynamic elongation is reduced for one- (1.93 ± 0.28 vs 0.76 ± 0.12; P < .0001) and both-side knotted (1.84 ± 0.20 vs 0.96 ± 0.32; P < .0001) configurations by 61% and 47%, respectively. No intergroup (group 1 vs group 2 and group 1-IPC vs group 2-IPC) statistically significant differences could be found between one- and both-side knotted configurations.

CONCLUSIONS

All-inside ACL reconstruction with preconditioning according to intraoperative workflow leads to a statistically significant improved mechanical behavior and may allow for optimizing initial graft tension and elongation for all-inside ACL reconstruction to reduce knee laxity. A single-side knotted configuration achieves similar stabilization strength to fully knotted constructs.

CLINICAL RELEVANCE

Graft insertion until tunnel docking increases the intratunnel graft portion that may optimize graft incorporation. Eliminating a suture knot stack may improve intraoperative workflow and reduce postoperative knot irritation.

Biomechanical comparison of four coupled fixation systems for ACL reconstruction with bone socket or full-tunnel on the tibial side

BACKGROUND

To compare in an animal model the biomechanical properties of four coupled fixation devices currently used in ACL reconstruction. Three out of four devices used a full tibial tunnel with an interference screw, while the other one system used a tibial socket and an adjustable loop suspension device. The null hypothesis is that there are no biomechanical differences between all the techniques tested.

METHODS

Thirty two femur-graft-tibia complexes were mounted on a tensile machine using bovine digital extensor tendons, porcine knees and four different fixation device combinations: After a preconditioning with a tensile load of 90N for five minutes, 1000cycles between 0 and 150N were applied to the complex before the final pulled to failure. Stiffness and strength were evaluated at the final pullout, as was the displacement (slippage) at one, 100, 500, and 1000cycles.

RESULTS

The multiple mean comparison led to a significant difference for the case of stiffness, with worse results in group C compared to group A (p=0.037). Conversely, no differences were found in UFL and slippage between all groups (p>0.05).

CONCLUSION

All the tested systems demonstrated in an animal model sufficient properties for a safe postoperative rehabilitation both for strength and for stiffness and slippage under cyclic loading.

Dynamic simulation of knee-joint loading during gait using force-feedback control and surrogate contact modelling

The aim of this study was to perform multi-body, muscle-driven, forward-dynamics simulations of human gait using a 6-degree-of-freedom (6-DOF) model of the knee in tandem with a surrogate model of articular contact and force control. A forward-dynamics simulation incorporating position, velocity and contact force-feedback control (FFC) was used to track full-body motion capture data recorded for multiple trials of level walking and stair descent performed by two individuals with instrumented knee implants. Tibiofemoral contact force errors for FFC were compared against those obtained from a standard computed muscle control algorithm (CMC) with a 6-DOF knee contact model (CMC6); CMC with a 1-DOF translating hinge-knee model (CMC1); and static optimization with a 1-DOF translating hinge-knee model (SO). Tibiofemoral joint loads predicted by FFC and CMC6 were comparable for level walking, however FFC produced more accurate results for stair descent. SO yielded reasonable predictions of joint contact loading for level walking but significant differences between model and experiment were observed for stair descent. CMC1 produced the least accurate predictions of tibiofemoral contact loads for both tasks. Our findings suggest that reliable estimates of knee-joint loading may be obtained by incorporating position, velocity and force-feedback control with a multi-DOF model of joint contact in a forward-dynamics simulation of gait.

Biomechanical Comparison of Fixed-Loop and Adjustable-Loop Cortical Suspensory Devices for Metaphyseal Femoral-Sided Soft Tissue Graft Fixation in Anatomic Anterior Cruciate Ligament Reconstruction Using a Porcine Model

PURPOSE

To compare the displacement, stiffness, and ultimate failure load of a fixed-loop cortical suspensory device with 2 adjustable-loop devices when positioned on metaphyseal bone.

METHODS

Thirty devices (10 of each device) were positioned on the metaphyseal cortex of 30 porcine femora simulating anatomic anterior cruciate ligament femoral tunnel placement. Bovine tendons were used for soft tissue grafts, and the constructs were then cycled 1,000 times and pulled to failure, measuring displacement, stiffness, and failure load.

RESULTS

Initial displacement, cyclic displacement, and total displacement were 2.98 mm, 2.09 mm, and 5.08 mm for the Endobutton CL (ECL), 2.82 mm, 2.27 mm, and 5.09 mm for the Tightrope (TRT), and 4.25 mm, 3.19 mm, and 7.44 mm for the adjustable-loop ToggleLoc Inline with Ziploop (TLZ), respectively. There was no difference between the ECL and the TRT on any measured outcome. Differences between the TLZ and ECL were statistically significant (initial displacement P = .024, cyclic displacement P < .001, and total displacement P < .001), as were those between the TLZ and TRT (initial displacement P = .010, cyclic displacement P = .001, and total displacement P < .001). Failure loads were 804 N, 801 N, and 682 N for the TRT, ECL, and TLZ, respectively, with no statistically significant difference.

CONCLUSIONS

When positioned on the metaphyseal cortex, there was no difference in the biomechanical performance of the fixed-loop ECL and adjustable-loop TRT, and no lengthening of the TRTs was observed during cycling. However, the TLZ showed statistically significantly lower stiffness and more displacement during cycling with lengthening of the adjustable loop, the clinical significance of which is unknown.

CLINICAL RELEVANCE

When used for femoral-sided soft tissue graft fixation in an anatomically placed femoral tunnel, the adjustable-loop TRT was biomechanically equivalent to the fixed-loop ECL. However, the adjustable-loop TLZ showed displacement during biomechanical testing that could potentially contribute to clinical failure after anterior cruciate ligament reconstruction. However, the clinical significance was not directly tested.

Suspensory Versus Interference Screw Fixation for Arthroscopic Anterior Cruciate Ligament Reconstruction in a Translational Large-Animal Model

PURPOSE

To compare all-inside cortical-button suspensory fixation in sockets versus interference screw fixation in tunnels with respect to clinical, histologic, and biomechanical assessments of all-soft tissue (AST) tendon autografts used for anterior cruciate ligament (ACL) reconstruction in a canine model.

METHODS

By use of a validated "hybrid" double-bundle ACL reconstruction technique (reconstruction of the anteromedial bundle with preservation of the native posterolateral bundle), dogs were randomly assigned to undergo either suspensory fixation in sockets (n = 6) or interference screw fixation in tunnels (n = 6). Contralateral knees were used as nonoperated controls (n = 12). Quadrupled extensor tendon autografts were used for both ACL reconstruction groups. Dogs were assessed radiographically and functionally and humanely euthanized at 12 weeks after surgery for arthroscopic, gross, biomechanical, and histologic assessments.

RESULTS

Histologic assessments showed significantly (P = .018) better graft incorporation with 4-zone direct healing to bone for the grafts using suspensory fixation in sockets (16.3 ± 1.5) compared with the grafts using interference screw fixation in tunnels (14.2 ± 2.1). Furthermore, graft healing to bone was significantly better at the aperture (P = .05) and mid-socket (P = .01) location for the group that underwent suspensory fixation in sockets (16.1 ± 1.8 and 16.4 ± 1.9, respectively).

CONCLUSIONS

Suspensory fixation of AST grafts in sockets was associated with superior tendon-to-bone healing compared with interference screw fixation in tunnels, with 4-zone direct graft healing to bone seen for femoral and tibial sockets only in the suspensory-fixation group. Biomechanical properties were similar between groups.

CLINICAL RELEVANCE

These data provide evidence suggesting that an all-inside ACL reconstruction technique using adjustable-loop cortical-button suspensory fixation in bone sockets has potential clinical advantages for ACL reconstruction using AST grafts.

In Vivo Knee Contact Force Prediction Using Patient-Specific Musculoskeletal Geometry in a Segment-Based Computational Model

Segment-based musculoskeletal models allow the prediction of muscle, ligament, and joint forces without making assumptions regarding joint degrees-of-freedom (DOF). The dataset published for the “Grand Challenge Competition to Predict in vivo Knee Loads” provides directly measured tibiofemoral contact forces for activities of daily living (ADL). For the Sixth Grand Challenge Competition to Predict in vivo Knee Loads, blinded results for “smooth” and “bouncy” gait trials were predicted using a customized patient-specific musculoskeletal model. For an unblinded comparison, the following modifications were made to improve the predictions: further customizations, including modifications to the knee center of rotation; reductions to the maximum allowable muscle forces to represent known loss of strength in knee arthroplasty patients; and a kinematic constraint to the hip joint to address the sensitivity of the segment-based approach to motion tracking artifact. For validation, the improved model was applied to normal gait, squat, and sit-to-stand for three subjects. Comparisons of the predictions with measured contact forces showed that segment-based musculoskeletal models using patient-specific input data can estimate tibiofemoral contact forces with root mean square errors (RMSEs) of 0.48–0.65 times body weight (BW) for normal gait trials. Comparisons between measured and predicted tibiofemoral contact forces yielded an average coefficient of determination of 0.81 and RMSEs of 0.46–1.01 times BW for squatting and 0.70–0.99 times BW for sit-to-stand tasks. This is comparable to the best validations in the literature using alternative models.

Contribution of tibiofemoral joint contact to net loads at the knee in gait

Inverse dynamics analysis is commonly used to estimate the net loads at a joint during human motion. Most lower-limb models of movement represent the knee as a simple hinge joint when calculating muscle forces. This approach is limited because it neglects the contributions from tibiofemoral joint contact forces and may therefore lead to errors in estimated muscle forces. The aim of this study was to quantify the contributions of tibiofemoral joint contact loads to the net knee loads calculated from inverse dynamics for multiple subjects and multiple gait patterns. Tibiofemoral joint contact loads were measured in four subjects with instrumented implants as each subject walked at their preferred speed (normal gait) and performed prescribed gait modifications designed to treat medial knee osteoarthritis. Tibiofemoral contact loads contributed substantially to the net knee extension and knee adduction moments in normal gait with mean values of 16% and 54%, respectively. These findings suggest that knee-contact kinematics and loads should be included in lower-limb models of movement for more accurate determination of muscle forces. The results of this study may be used to guide the development of more realistic lower-limb models that account for the effects of tibiofemoral joint contact at the knee.

Patient-specific computer model of dynamic squatting after total knee arthroplasty

Knee forces are highly relevant to performance after total knee arthroplasty especially during high flexion activities such as squatting. We constructed subject-specific models of two patients implanted with instrumented knee prostheses that measured knee forces in vivo. In vivo peak forces ranged from 2.2 to 2.3 times bodyweight but peaked at different flexion angles based on the type of squatting activity. Our model predicted tibiofemoral contact force with reasonable accuracy in both subjects. This model can be a very useful tool to predict the effect of surgical techniques and component alignment on contact forces. In addition, this model could be used for implant design development, to enhance knee function, to predict forces generated during other activities, and for predicting clinical outcomes.

Functional bracing of ACL injuries: current state and future directions

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.

The application of musculoskeletal modeling to investigate gender bias in non-contact ACL injury rate during single-leg landings

The central tenet of this study was to develop, validate and apply various individualised 3D musculoskeletal models of the human body for application to single-leg landings over increasing vertical heights and horizontal distances. While contributing to an understanding of whether gender differences explain the higher rate of non-contact anterior cruciate ligament (ACL) injuries among females, this study also correlated various musculoskeletal variables significantly impacted by gender, height and/or distance and their interactions with two ACL injury-risk predictor variables; peak vertical ground reaction force (VGRF) and peak proximal tibia anterior shear force (PTASF). Kinematic, kinetic and electromyography data of three male and three female subjects were measured. Results revealed no significant gender differences in the musculoskeletal variables tested except peak VGRF (p = 0.039) and hip axial compressive force (p = 0.032). The quadriceps and the gastrocnemius muscle forces had significant correlations with peak PTASF (r = 0.85, p < 0.05 and r = - 0.88, p < 0.05, respectively). Furthermore, hamstring muscle force was significantly correlated with peak VGRF (r = - 0.90, p < 0.05). The ankle flexion angle was significantly correlated with peak PTASF (r = - 0.82, p < 0.05). Our findings indicate that compared to males, females did not exhibit significantly different muscle forces, or ankle, knee and hip flexion angles during single-leg landings that would explain the gender bias in non-contact ACL injury rate. Our results also suggest that higher quadriceps muscle force increases the risk, while higher hamstring and gastrocnemius muscle forces as well as ankle flexion angle reduce the risk of non-contact ACL injury.

Femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction: a comparative biomechanical study

BACKGROUND

Optimization of anterior cruciate ligament (ACL) fixation is desired to improve graft healing. New soft tissue cortical suspension devices for femoral tunnel fixation should be biomechanically evaluated.

HYPOTHESIS

All femoral fixation devices would prevent a clinically significant amount of displacement and support loads significantly larger than in situ forces experienced by the ACL during early rehabilitation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four cortical soft tissue ACL graft suspension devices were tested under cyclic and pull-to-failure loading conditions in both an isolated device-only setup and as a complete bone-device-tendon construct in porcine femurs using a tensile testing machine.

RESULTS

There were significant differences in the ultimate failure loads among the devices. The highest ultimate failure loads when tested as a construct were observed for the XO Button (1748 N), followed by the Endobutton CL (1456 N), ToggleLoc with ZipLoop (1334 N), and TightRope RT (859 N). Cyclic displacement after 1000 cycles during isolated device testing was less than 1 mm for all devices. Cyclic displacements after 1000 cycles in the porcine construct were 1.88 mm, 2.74 mm, 3.34 mm, and 1.82 mm for the Endobutton, TightRope, ToggleLoc, and XO Button, respectively; all were significantly different from each other except when the Endobutton was compared with the XO Button. The ToggleLoc exceeded the 3.0-mm displacement threshold defined as a clinical failure. The most displacement occurred during the first cycle, especially for the adjustable-length loop devices. Stiffness reapproximated the native ACL stiffness for all constructs.

CONCLUSION

The Endobutton, TightRope, and XO Button have the necessary biomechanical properties with regard to ultimate failure strength, displacement, and stiffness for initial fixation of soft tissue grafts in the femoral tunnel for ACL reconstruction. The ToggleLoc had sufficient ultimate failure strength but crossed our 3.0-mm clinical failure threshold for cyclic displacement. Although this study was not designed to compare fixed and adjustable-length loop devices, it was noted that both fixed-loop devices allowed less cyclic displacement and initial displacement.

CLINICAL RELEVANCE

Adjustable-length loop devices may need to be retensioned after cycling the knee and fixing the tibial side to account for the increased initial displacement seen with these devices.

Hip and knee joint loading during vertical jumping and push jerking

BACKGROUND

The internal joint contact forces experienced at the lower limb have been frequently studied in activities of daily living and rehabilitation activities. In contrast, the forces experienced during more dynamic activities are not well understood, and those studies that do exist suggest very high degrees of joint loading.

METHODS

In this study a biomechanical model of the right lower limb was used to calculate the internal joint forces experienced by the lower limb during vertical jumping, landing and push jerking (an explosive exercise derived from the sport of Olympic weightlifting), with a particular emphasis on the forces experienced by the knee.

FINDINGS

The knee experienced mean peak loadings of 2.4-4.6×body weight at the patellofemoral joint, 6.9-9.0×body weight at the tibiofemoral joint, 0.3-1.4×body weight anterior tibial shear and 1.0-3.1×body weight posterior tibial shear. The hip experienced a mean peak loading of 5.5-8.4×body weight and the ankle 8.9-10.0×body weight.

INTERPRETATION

The magnitudes of the total (resultant) joint contact forces at the patellofemoral joint, tibiofemoral joint and hip are greater than those reported in activities of daily living and less dynamic rehabilitation exercises. The information in this study is of importance for medical professionals, coaches and biomedical researchers in improving the understanding of acute and chronic injuries, understanding the performance of prosthetic implants and materials, evaluating the appropriateness of jumping and weightlifting for patient populations and informing the training programmes of healthy populations.

Cruciate ligament loading during common knee rehabilitation exercises

Cruciate ligament injuries are common and may lead to dysfunction if not rehabilitated. Understanding how to progress anterior cruciate ligament and posterior cruciate ligament loading, early after injury or reconstruction, helps clinicians prescribe rehabilitation exercises in a safe manner to enhance recovery. Commonly prescribed therapeutic exercises include both weight-bearing exercise and non-weight-bearing exercise. This review was written to summarize and provide an update on the available literature on cruciate ligament loading during commonly used therapeutic exercises. In general, weight-bearing exercise produces smaller loads on the anterior cruciate ligament and posterior cruciate ligament compared with non-weight-bearing exercise. The anterior cruciate ligament is loaded less at higher knee angles (i.e. 50-100 degrees). Squatting and lunging with a more forward trunk tilt and moving the resistance pad proximally on the leg during the seated knee extension unloads the anterior cruciate ligament. The posterior cruciate ligament is less loaded at lower knee angles (i.e. 0-50 degrees), and may be progressed from level ground walking to a one-leg squat, lunges, wall squat, leg press, and the two-leg squat (from smallest to greatest). Exercise type and technique variation affect cruciate ligament loading, such that the clinician may prescribe therapeutic exercises to progress ligament loading safely, while ensuring optimal recovery of the musculoskeletal system.

Evaluating knee replacement mechanics during ADL with PID-controlled dynamic finite element analysis

Validated computational knee simulations are valuable tools for design phase development of knee replacement devices. Recently, a dynamic finite element (FE) model of the Kansas knee simulator was kinematically validated during gait and deep flexion cycles. In order to operate the computational simulator in the same manner as the experiment, a proportional-integral-derivative (PID) controller was interfaced with the FE model to control the quadriceps actuator excursion and produce a target flexion profile regardless of implant geometry or alignment conditions. The controller was also expanded to operate multiple actuators simultaneously in order to produce in vivo loading conditions at the joint during dynamic activities. Subsequently, the fidelity of the computational model was improved through additional muscle representation and inclusion of relative hip-ankle anterior-posterior (A-P) motion. The PID-controlled model was able to successfully recreate in vivo loading conditions (flexion angle, compressive joint load, medial-lateral load distribution or varus-valgus torque, internal-external torque, A-P force) for deep knee bend, chair rise, stance-phase gait and step-down activities.

Anterior cruciate ligament strain and tensile forces for weight-bearing and non-weight-bearing exercises: a guide to exercise selection

There is a growing body of evidence documenting loads applied to the anterior cruciate ligament (ACL) for weight-bearing and non-weight-bearing exercises. ACL loading has been quantified by inverse dynamics techniques that measure anterior shear force at the tibiofemoral joint (net force primarily restrained by the ACL), ACL strain (defined as change in ACL length with respect to original length and expressed as a percentage) measured directly in vivo, and ACL tensile force estimated through mathematical modeling and computer optimization techniques. A review of the biomechanical literature indicates the following: ACL loading is generally greater with non-weight-bearing compared to weight-bearing exercises; with both types of exercises, the ACL is loaded to a greater extent between 10° to 50° of knee flexion (generally peaking between 10° and 30°) compared to 50° to 100° of knee flexion; and loads on the ACL change according to exercise technique (such as trunk position). Squatting with excessive forward movement of the knees beyond the toes and with the heels off the ground tends to increase ACL loading. Squatting and lunging with a forward trunk tilt tend to decrease ACL loading, likely due to increased hamstrings activity. During seated knee extension, ACL force decreases when the resistance pad is positioned more proximal on the anterior aspect of the lower leg, away from the ankle. The evidence reviewed as part of this manuscript provides objective data by which to rank exercises based on loading applied to the ACL. The biggest challenge in exercise selection post-ACL reconstruction is the limited knowledge of the optimal amount of stress that should be applied to the ACL graft as it goes through its initial incorporation and eventual maturation process. Clinicians may utilize this review as a guide to exercise selection and rehabilitation progression for patients post-ACL reconstruction.

Knee joint forces: prediction, measurement, and significance

Knee forces are highly significant in osteoarthritis and in the survival and function of knee arthroplasty. A large number of studies have attempted to estimate forces around the knee during various activities. Several approaches have been used to relate knee kinematics and external forces to internal joint contact forces, the most popular being inverse dynamics, forward dynamics, and static body analyses. Knee forces have also been measured in vivo after knee arthroplasty, which serves as valuable validation of computational predictions. This review summarizes the results of published studies that measured knee forces for various activities. The efficacy of various methods to alter knee force distribution, such as gait modification, orthotics, walking aids, and custom treadmills are analyzed. Current gaps in our knowledge are identified and directions for future research in this area are outlined.

The minimum required muscle force for a sit-to-stand task

The purpose of this study was to reveal the minimum required muscle force for a sit-to-stand task. Combining experimental procedures and computational processing, movements of various sit-to-stand patterns were obtained. Muscle forces and activations during a movement were calculated with an inverse dynamics method and a static numerical optimization method. The required muscle force for each movement was calculated with peak muscle activation, muscle physiological cross sectional area and specific tension. The robustness of the results was quantitatively evaluated with sensitivity analyses. From the results, a distinct threshold was found for the total required muscle force of the hip and knee extensors. Specifically, two findings were revealed: (1) the total force of hip and knee extensors is appropriate as the index of minimum required muscle force for a sit-to-stand task and (2) the minimum required total force is within the range of 35.3-49.2 N/kg. A muscle is not mechanically independent from other muscles, since each muscle has some synergetic or antagonistic muscles. This means that the mechanical threshold of one muscle varies with the force exertion abilities of other muscles and cannot be evaluated independently. At the same time, some kinds of mechanical threshold necessarily exist in the sit-to-stand task, since a muscle force is an only force to drive the body and people cannot stand up from a chair without muscles. These indicate that the existence of the distinct threshold in the result of the total required muscle force is reasonable.

Cruciate ligament tensile forces during the forward and side lunge

BACKGROUND

Although weight bearing lunge exercises are frequently employed during anterior cruciate ligament and posterior cruciate ligament rehabilitation, cruciate ligament tensile forces are currently unknown while performing forward and side lunge exercises with and without a stride.

METHODS

Eighteen subjects used their 12 repetition maximum weight while performing a forward lunge and side lunge with and without a stride. A motion analysis system and biomechanical model were used to estimate cruciate ligament forces during lunging as a function of 0-90 degrees knee angles.

FINDINGS

Comparing the forward lunge to the side lunge across stride variations, mean posterior cruciate ligament forces ranged between 205 and 765N and were significantly greater (P<0.0025) in the forward lunge long at 40 degrees , 50 degrees , 60 degrees , 70 degrees , and 80 degrees knee angles of the descent phase and at 80 degrees , 70 degrees , 60 degrees knee angles of the ascent phase. There were no significant differences (P<0.0025) in mean posterior cruciate ligament forces between with and without stride differences across lunging variations. There were no anterior cruciate ligament forces quantified while performing forward and side lunge exercises.

INTERPRETATION

Clinicians should be cautious in prescribing forward and side lunge exercises during early phases of posterior cruciate ligament rehabilitation due to relatively high posterior cruciate ligament forces that are generated, especially during the forward lunge at knee angles between 40 degrees and 90 degrees knee angles. Both the forward and side lunges appear appropriate during all phases of anterior cruciate ligament rehabilitation. Understanding how forward and side lunging affect cruciate ligament loading over varying knee angles may help clinicians better prescribe lunging exercises in a safe manner during anterior cruciate ligament and posterior cruciate ligament rehabilitation.

A novel two-stage framework for musculoskeletal dynamic modeling: an application to multifingered hand movement

In this paper, we present a new computational framework for biodynamic modeling of human movement. The framework decouples the conventional dynamic modeling process into two stages: in the first stage, two-component "agonist-antagonist" torque actuators under hypothesized and testable parametric control drive the forward dynamics, and parameters are identified by tracking both kinematics and kinetics; the second stage completes the mapping from the muscle-tendon forces to the predicted joint torques. An empirical test using multifinger grasping movement data was conducted to illustrate the application of the proposed framework and showed that the model reproduced the measurement accurately in both kinematics and kinetics. The torque components exhibited consistent spatial-temporal patterns across joints, digits, and subjects. The muscle-tendon forces computed based on the model-predicted kinematics and kinetics had the peak values within the same order of magnitude as in vivo data reported in the literature. The potential to predict was also demonstrated as we applied the control parameters of one subject to another and achieved close matches.