A new parametric approach for modeling hip forces during gait

Physicomechanical, morphological and tribo-deformation characteristics of lightweight WC/AZ31B Mg-matrix biocomposites for hip joint applications

Exploring high strength materials with a higher concentration of reinforcements in the alloy proves to be a challenging task. This research has explored magnesium-based composites (AZ31B alloy) with tungsten carbide reinforcements, enhancing strength for medical joint replacements via league championship optimisation. The primary objective is to enhance medical joint replacement biomaterials employing magnesium-based composites, emphasising the AZ31B alloy with tungsten carbide reinforcements. The stir casting method is utilised in the manufacture of magnesium matrix composites (MMCs), including varied percentages of tungsten carbide (WC). The mechanical characteristics, such as micro-hardness, tensile strength, and yield strength, have been assessed and compared with computational simulations. The wear studies have been carried out to analyse the tribological behaviour of the composites. Additionally, this study investigates the prediction of stress and the distribution of forces inside bone and joint structures, therefore offering significant contributions to the field of biomedical research. This research contemplates the use of magnesium-based MMCs for the discovery of biomaterials suitable for medical joint replacement. The study focuses on the magnesium alloy AZ31B, with particles ranging in size from 40 to 60 microns used as the matrix material. Moreover, the outcomes have revealed that when combined with MMCs based on AZ31B-magnesium matrix, the WC particle emerges as highly effective reinforcements for the fabrication of lightweight, high-strength biomedical composites. This study uses the league championship optimisation (LCO) approach to identify critical variables impacting the synthesis of Mg MMCs from an AZ31B-based magnesium alloy. The scanning electron microscopy (SEM) images are meticulously analysed to depict the dispersion of WC particulates and the interface among the magnesium (Mg) matrix and WC reinforcement. The SEM analysis has explored the mechanisms underlying particle pull-out, the characteristics of inter-particle zones, and the influence of the AZ31B matrix on the enhancement of the mechanical characteristics of the composites. The application of finite element analysis (FEA) is being used in order to make predictions regarding the distribution of stress and the interactions of forces within the model of the hip joint. This study has compared the physico-mechanical and tribological characteristics of WC to distinct combinations of 0%, 5%, 10% and 15%, and its impact on the performance improvements. SEM analysis has confirmed the findings' improved strength and hardness, particularly when 10%-15% of WC was incorporated. Following the incorporation of 10% of WC particles within Mg-alloy matrix, the outcomes of the study has exhibited enhanced strength and hardness, which furthermore has been evident by utilising SEM analysis. Using ANSYS, structural deformation and stress levels are predicted, along with strength characteristics such as additional hardness of 71 HRC, tensile strength of 140-150 MPa, and yield strength closer to 100-110 MPa. The simulations yield significant insights into the behaviour of the joint under various loading conditions, thus enhancing the study's significance in biomedical environments.

Modeling Human Suboptimal Control: A Review

This review paper provides an overview of the approaches to model neuromuscular control, focusing on methods to identify nonoptimal control strategies typical of populations with neuromuscular disorders or children. Where possible, the authors tightened the description of the methods to the mechanisms behind the underlying biomechanical and physiological rationale. They start by describing the first and most simplified approach, the reductionist approach, which splits the role of the nervous and musculoskeletal systems. Static optimization and dynamic optimization methods and electromyography-based approaches are summarized to highlight their limitations and understand (the need for) their developments over time. Then, the authors look at the more recent stochastic approach, introduced to explore the space of plausible neural solutions, thus implementing the uncontrolled manifold theory, according to which the central nervous system only controls specific motions and tasks to limit energy consumption while allowing for some degree of adaptability to perturbations. Finally, they explore the literature covering the explicit modeling of the coupling between the nervous system (acting as controller) and the musculoskeletal system (the actuator), which may be employed to overcome the split characterizing the reductionist approach.

The History and Future of Neuromusculoskeletal Biomechanics

The Executive Council of the International Society of Biomechanics has initiated and overseen the commemorations of the Society's 50th Anniversary in 2023. This included multiple series of lectures at the ninth World Congress of Biomechanics in 2022 and XXIXth Congress of the International Society of Biomechanics in 2023, all linked to special issues of International Society of Biomechanics' affiliated journals. This special issue of the Journal of Applied Biomechanics is dedicated to the biomechanics of the neuromusculoskeletal system. The reader is encouraged to explore this special issue which comprises 6 papers exploring the current state-of the-art, and future directions and roles for neuromusculoskeletal biomechanics. This editorial presents a very brief history of the science of the neuromusculoskeletal system's 4 main components: the central nervous system, musculotendon units, the musculoskeletal system, and joints, and how they biomechanically integrate to enable an understanding of the generation and control of human movement. This also entails a quick exploration of contemporary neuromusculoskeletal biomechanics and its future with new fields of application.

The novel magnesium-titanium hybrid cannulated screws for the treatment of vertical femoral neck fractures: Biomechanical evaluation

Background

Conventional cannulated screws are commonly used for internal fixation in the treatment of vertical femoral neck fractures. However, the noticeably high rates of undesirable outcomes such as nonunion, malunion, avascular necrosis, and fixation failure still troubled the patients and surgeons. It is urgent to develop new cannulated screws to improve the above clinical problems. The purpose of this study was to design a novel magnesium-titanium hybrid cannulated screw and to further evaluate its biomechanical performance for the treatment of vertical femoral neck fractures.

Methods

A novel magnesium-titanium hybrid cannulated screw was designed, and the conventional titanium cannulated screw was also modeled. The finite element models for vertical femoral neck fractures with magnesium-titanium hybrid cannulated screws and conventional cannulated screws were respectively established. The hip joint contact force during walking gait calculated by a subject-specific musculoskeletal multibody dynamics model, was used as loads and boundary conditions for both finite element models. The stress and displacement distributions of the cannulated screws and the femur, the micromotion of the fracture surfaces of the femoral neck, and the overall stiffness were calculated and analyzed using finite element models. The biomechanical performance of the Magnesium-Titanium hybrid cannulated screws was evaluated.

Results

The maximum stresses of the magnesium-titanium hybrid cannulated screws and the conventional cannulated screws were 451.5 ​MPa and 476.8 ​MPa, respectively. The maximum stresses of the femur with the above different cannulated screws were 140.3 ​MPa and 164.8 ​MPa, respectively. The maximum displacement of the femur with the hybrid cannulated screws was 6.260 ​mm, lower than the femur with the conventional cannulated screws, which was 7.125 ​mm. The tangential micromotions in the two orthogonal directions at the fracture surface of the femoral neck with the magnesium-titanium hybrid cannulated screws were comparable to those with the conventional cannulated screws. The overall stiffness of the magnesium-titanium hybrid cannulated screw system was 490.17 ​N/mm, higher than that of the conventional cannulated screw system, which was 433.92 ​N/mm.

Conclusion

The magnesium-titanium hybrid cannulated screw had superior mechanical strength and fixation stability for the treatment of the vertical femoral neck fractures, compared with those of the conventional cannulated screw, indicating that the magnesium-titanium hybrid cannulated screw has great potential as a new fixation strategy in future clinical applications.The translational potential of this article: This study highlights an innovative design of the magnesium-titanium hybrid cannulated screw for the treatment of vertical femoral neck fractures. The novel magnesium-titanium hybrid cannulated screw not only to provide sufficient mechanical strength and fixation stability but also to contribute to the promotion of fracture healing, which could provide a better treatment for the vertical femoral neck fractures, beneficially reducing the incidence of nonunion and reoperation rates.

The effects of pressure biofeedback on hip and trunk muscle activity and lumbopelvic alignment during one-leg standing

BACKGROUND: During one-leg standing (OLS), optimum activity of the gluteus medius (Gmed), multifidus (MF), and quadratus lumborum (QL) muscles relies upon maintaining neutral lumbopelvic alignment. However, no studies have examined how using pressure biofeedback during OLS affects the activity of these muscles and the concomitant alignment of the pelvis and trunk. OBJECTIVES: The purpose of this study was to investigate the effect of pressure biofeedback on the activity of the Gmed, MF, and QL and the femoropelvic and trunk lean angles during OLS. METHODS: Twenty-four healthy males performed OLS with (PB+) and without (PB-) pressure biofeedback. For all OLS conditions, a pressure sensor was placed between the lateral surface of the humerus on the non-supporting side and the wall. Under the PB- condition, participants performed preferred OLS while the examiner measured the maximum pressure caused by trunk lean. Under the PB+ condition, participants were asked to perform at a threshold of 50% of the maximal pressure (PB+ 1 condition) and with minimal change in pressure (PB+ 2 condition). Muscle activities of MF, QL, and Gmed as well as the femoropelvic and trunk lean angles were measured under various OLS conditions. RESULTS: The activity of the Gmed, MF, and QL was greater under both PB+ conditions than under the PB- condition (p< 0.05). Also, both PB+ conditions resulted in a greater femoropelvic angle and reduced trunk lean angle. There were no significant differences in muscle activity, femoropelvic angle, or trunk lean angle between PB+ 1 and PB+ 2 (p> 0.05). CONCLUSIONS: These results suggest that pressure biofeedback is a useful modality for increasing the activity of the Gmed and trunk muscles, especially the MF muscle on the non-supporting leg side, and for preventing compensatory movements such as trunk deviation and pelvic lateral deviation during OLS.

Chronic hip pain in adults: Current knowledge and future prospective

Chronic hip pain is distressing to the patient as it not only impairs the daily activities of life but also affects the quality of life. Chronic hip pain is difficult to diagnose as patients often present with associated chronic lumbar spine and/or knee joint pain. Moreover, nonorthopaedic causes may also present as chronic hip pain. The accurate diagnosis of chronic hip pain starts with a detailed history of the patient and thorough knowledge of anatomy of the hip joint. Various physical tests are performed to look for the causes of hip pain and investigations to confirm the diagnosis. Management of chronic hip pain should be mechanistic-based multimodal therapy targeting the pain pathway. This narrative review will describe relevant anatomy, causes, assessment, investigation, and management of chronic hip pain. The focus will be on current evidence-based management of hip osteoarthritis, greater trochanteric pain syndrome, meralgia paresthetica, and piriformis syndrome. Recently, there is emphasis on the role of ultrasound in interventional pain procedures. The use of fluoroscopic-guided radiofrequency in periarticular branches of hip joint has reported to provide pain relief of up to 36 months. However, the current evidence for use of platelet-rich plasma in chronic hip osteoarthritis pain is inconclusive. Further research is required in the management of chronic hip pain regarding comparison of fluoroscopic- and ultrasound-guided procedures, role of platelet-rich plasma, and radiofrequency procedures with long-term follow-up of patients.

The Effect of Intensive Abductor Strengthening on Postoperative Muscle Efficiency and Functional Ability of Hip-Fractured Patients: A Randomized Controlled Trial

BACKGROUND

Hip fractures are common in the elderly and many patients fail to regain prefracture hip abductor strength or functional status. The purpose of this clinical trial was to compare the effects of an intensive abductor muscle exercise program versus a standard physiotherapy intervention in hip-fractured patients.

MATERIALS AND METHODS

Ninety six femoral neck-fractured patients were randomized into equal-sized groups. A 12-week standard physiotherapy program was implemented in the control group(S-PT) whereas an intensive exercise program, emphasizing on abductors' strengthening, was implemented in the research group(I-PT). Abductors' isometric strength of the fractured hip, abductor ratio% in the fractured compared to contralateral hip, and functional level were assessed at the 3^rd (postintervention) and 6^th (followup) months.

RESULTS

Postintervention, abductors' isometric strength was 35.7% greater (P < 0.0005) and abductor ratio% was 2.5% higher (P < 0.0005) in I-PT group, compared to S-PT group. With regard to functional assessments, I-PT group was 29.1% faster during Timed Up and Go (TUG) test and achieved a 26.7% higher Lower Extremity Functional Scale Greek version's (LEFS-Greek) total score, compared to S-PT group (P < 0.0005). At followup, abductors' isometric strength was 37.0% greater (P < 0.0005) and abductor ratio% was 7.1% higher (P < 0.0005) in I-PT group, compared to S-PT group. In addition, I-PT group was 45.9% faster during TUG test (P < 0.0005) and achieved an 11.2% higher LEFS-Greek total score, compared to S-PT group (P = 0.013).

CONCLUSIONS

Compared to the standard physiotherapy intervention, the intensive abductor-strengthening program significantly increased both abductors' isometric strength of the fractured hip and abductor ratio% and resulted in patients' enhanced functional level.

CLINICAL TRIAL IDENTIFIER

ISRCTN30713542.

Contact between the acetabulum and dome of a Kerboull-type plate influences the stress on the plate and screw

We used a three-dimensional finite element method to investigate the conditions behind the Kerboull-type (KT) dome. The KT plate dome was divided into five areas, and 14 models were created to examine different conditions of dome contact with the acetabulum. The maximum stress on the KT plate and screws was estimated for each model. Furthermore, to investigate the impact of the contact area with the acetabulum on the KT plate, a multiple regression analysis was conducted using the analysis results. The dome-acetabulum contact area affected the maximum equivalent stress on the KT plate; good contact with two specific areas of the vertical and horizontal beams (Areas 3 and 5) reduced the maximum equivalent stress. The maximum equivalent stress on the hook increased when the hardness of the bone representing the acetabulum varied. Thus, we confirmed the technical importance of providing a plate with a broad area of appropriate support from the bone and cement in the posterior portion of the dome and also proved the importance of supporting the area of the plate in the direction of the load at the center of the cross-plate and near the hook.

Fine tuning total knee replacement contact force prediction algorithms using blinded model validation

The purpose of this study was to perform a blinded comparison of model predictions of total knee replacement contact forces to in vivo forces from an instrumented prosthesis during normal walking and medial thrust gait by participating in the "Third Grand Challenge Competition to Predict in vivo Knee Loads." We also evaluated model assumptions that were critical for accurate force predictions. Medial, lateral, and total axial forces through the knee were calculated using a previously developed and validated parametric numerical model. The model uses equilibrium equations between internal and external moments and forces to obtain knee joint contact forces and calculates a range of forces at instances during the gait cycle through parametric variation of muscle activity levels. For 100 instances during a normal over-ground gait cycle, model root mean square differences from eTibia data were 292, 248, and 281 for medial, lateral, and total contact forces, respectively. For 100 instances during a medial thrust gait cycle, model root mean square differences from eTibia data were 332, 234, and 470 for medial, lateral, and total contact forces, respectively. The percent difference between measured and predicted peak total axial force was 2.89% at the first peak and 9.36% at the second peak contact force for normal walking and 3.94% at the first peak and 14.86% at the second peak contact force for medial thrust gait. After unblinding, changes to model assumptions improved medial and lateral force predictions for both gait styles but did not improve total force predictions. Axial forces computed with the model compared well to the eTibia data under blinded and unblinded conditions. Knowledge of detailed knee kinematics, namely anterior-posterior translation, appears to be critical in obtaining accurate force predictions.

Finite element analysis of different repair methods of Vancouver B1 periprosthetic fractures after total hip arthroplasty

OBJECTIVE

To use finite element analysis to study the stability of different fixation methods used to repair Vancouver type B1 periprosthetic fractures occurring after total hip arthroplasty (THA).

METHODS

An artificial femur was used as the basis for the solid model; U2 series femoral stem (United Orthopedic Corporation, Hsinchu, Taiwan) was used for modelling of the prosthesis; and the modelling of the cable plate, wires and screws was based on information given in the manufacturer's catalogue (Zimmer, Warsaw, IN, USA). The analysis model was constructed using the ANSYS software, and all material settings were based on literature values. A six-orifice cable plate, unicortical screws (20mm long and 4.5mm in diameter) and bicortical screws (50mm long and 4.5mm in diameter) were constructed. Four analysis models were defined. The basic model had a plate and three cable wires above the fracture line and two bicortical screws below the fracture line. In the second model, two unicortical screws were added above the fracture line. In the third model, three wires were added below the fracture line. In the fourth model, both the proximal screws of the second model and the distal wires of the third model were added to the basic model. To ensure that the numerical values produced by analysis reached convergence, mesh convergence was tested.

RESULTS

Adding two proximal unicortical screws to the basic Ogden construct (plate, proximal wires and distal screws) lessened displacement of the fracture and decreased the von Mises stress on the repair. Adding three distal wires to the basic construct had no noticeable effect.

CONCLUSION

Better fixation power is achieved by using both proximal and distal screws (the locking-plate concept) in treating Vancouver type B1 periprosthetic fracture after THA.

Muscle activations to stabilize the knee following arthroscopic partial meniscectomy

BACKGROUND

Arthroscopic partial meniscectomy patients are at increased risk of developing knee osteoarthritis. This population, particularly those with weaker quadriceps, have larger-than-normal knee adduction moments, which tend to load the medial tibiofemoral joint. Larger knee adduction moments predict progression of knee osteoarthritis and may contribute to the increased risk in meniscectomy patients. Increased muscle activity to support these large moments may further elevate articular loads. We examined a) the muscle activity while walking in a meniscectomy and control population, and b) the relationship between knee strength and muscle activity.

METHODS

Gait patterns and knee extension strength were assessed in 89 male arthroscopic partial meniscectomy patients and 30 age-matched healthy controls. Surface electromyography was recorded during walking from ten muscles that cross the knee.

FINDINGS

Compared to controls, the meniscectomy group displayed greater muscle activity while walking, with increased hamstrings activation, yet no difference in directed co-contraction. While controlling for age, no differences were found between meniscectomy subjects with weak and normal knee extension strength, in hamstrings activity, quadriceps activity or directed co-contraction.

INTERPRETATION

The generalised increase in non-directed muscle activity in the meniscectomy group may provide enhanced muscular support of larger-than-normal knee adduction moments. Higher levels of antagonist co-contraction may increase muscle forces and, subsequently, joint articular loads, contributing to the increased risk of developing knee osteoarthritis following arthroscopic partial meniscectomy.

Kinesiology of the hip: a focus on muscular actions

The 21 muscles that cross the hip provide both triplanar movement and stability between the femur and acetabulum. The primary intent of this clinical commentary is to review and discuss the current understanding of the specific actions of the hip muscles. Analysis of their actions is based primarily on the spatial orientation of the muscles relative to the axes of rotation at the hip. The discussion of muscle actions is organized according to the 3 cardinal planes of motion. Actions are considered from both femoral-on-pelvic and pelvic-on-femoral perspectives, with particular attention to the role of coactivation of trunk muscles. Additional attention is paid to the biomechanical variables that alter the effectiveness, force, and torque of a given muscle action. The role of certain muscles in generating compression force at the hip is also presented. Throughout the commentary, the kinesiology of the muscles of the hip are considered primarily from normal but also pathological perspectives, supplemented with several clinically relevant scenarios. This overview should serve as a foundation for understanding the assessment and treatment of musculoskeletal impairments that involve not only the hip, but also the adjacent low back and knee regions.

Relative importance of gait vs. joint positioning on hip contact forces after total hip replacement

Implant loosening is a common indication for total hip replacement (THR) revision. High contact forces and implant twisting moments are thought to be associated with implant loosening. Relationships between joint positioning and hip forces, or outcomes, have been investigated through in vivo and in vitro modalities. Relationships between hip forces and gait are less understood, despite repeated findings that gait following a THR does not fully return to normal. We tested the hypothesis that gait parameters would be better predictors of implant force (peak contact forces and peak twisting moment during walking) than joint positioning parameters. Subjects underwent gait analysis, hip force modeling, and measurement of clinical radiographs 1 year after successful THR surgery. Gait parameters were consistently more influential in determining hip forces. Alone, gait explained as much as 67% of the variation in force, compared to a maximum of 33% by joint geometry. Combinations of gait and joint positioning parameters together explained up to 86% of the variation in hip force parameters. Results suggest that gait may provide a valuable postoperatively modifiable target to improve hip loads and potentially reduce the risk for implant loosening.

Video analysis of trunk and knee motion during non-contact anterior cruciate ligament injury in female athletes: lateral trunk and knee abduction motion are combined components of the injury mechanism

BACKGROUND

The combined positioning of the trunk and knee in the coronal and sagittal planes during non-contact anterior cruciate ligament (ACL) injury has not been previously reported.

HYPOTHESIS

During ACL injury female athletes demonstrate greater lateral trunk and knee abduction angles than ACL-injured male athletes and uninjured female athletes.

DESIGN

Cross-section control-cohort design.

METHODS

Analyses of still captures from 23 coronal (10 female and 7 male ACL-injured players and 6 female controls) or 28 sagittal plane videos performing similar landing and cutting tasks. Significance was set at p < or = 0.05.

RESULTS

Lateral trunk and knee abduction angles were higher in female compared to male athletes during ACL injury (p < or = 0.05) and trended toward being greater than female controls (p = 0.16, 0.13, respectively). Female ACL-injured athletes showed less forward trunk lean than female controls (mean (SD) initial contact (IC): 1.6 (9.3) degrees vs 14.0 (7.3) degrees, p < or = 0.01).

CONCLUSION

Female athletes landed with greater lateral trunk motion and knee abduction during ACL injury than did male athletes or control females during similar landing and cutting tasks.

CLINICAL RELEVANCE

Lateral trunk and knee abduction motion are important components of the ACL injury mechanism in female athletes as observed from video evidence of ACL injury.

A parametric approach to numerical modeling of TKR contact forces

In vivo knee contact forces are difficult to determine using numerical methods because there are more unknown forces than equilibrium equations available. We developed parametric methods for computing contact forces across the knee joint during the stance phase of level walking. Three-dimensional contact forces were calculated at two points of contact between the tibia and the femur, one on the lateral aspect of the tibial plateau, and one on the medial side. Muscle activations were parametrically varied over their physiologic range resulting in a solution space of contact forces. The obtained solution space was reasonably small and the resulting force pattern compared well to a previous model from the literature for kinematics and external kinetics from the same patient. Peak forces of the parametric model and the previous model were similar for the first half of the stance phase, but differed for the second half. The previous model did not take into account the transverse external moment about the knee and could not calculate muscle activation levels. Ultimately, the parametric model will result in more accurate contact force inputs for total knee simulators, as current inputs are not generally based on kinematics and kinetics inputs from TKR patients.

Do gait adaptations during stair climbing result in changes in implant forces in subjects with total hip replacements compared to normal subjects?

BACKGROUND

The study objective was to identify gait abnormalities and their relationships to hip loading during stair climbing after total hip replacement.

HYPOTHESES

(1) total hip replacement subjects would have significantly lower dynamic hip range of motion and peak external moments during stair climbing compared to normal subjects and (2) the peak twisting moment about the long axis of the implant and peak hip forces would be significantly reduced in subjects with total hip replacements compared to normal subjects.

METHODS

Gait parameters during a stair climbing task were measured for 15 total hip replacement subjects and 15 matched normal subjects. Forces were predicted using an analytical model.

FINDINGS

The peak external adduction moment for the total hip replacement subjects was 25% less than normal (P=0.001). The external rotation moment was 26% less than normal (P=0.029) but the extension moment was 77.5% higher in the total hip subjects than in normal subjects (P=0.004). The peak twisting moment and first peak contact force were 18% and 14% lower in the total hip group compared to normal (P=0.090 and P=0.055, respectively). The second peak force was nearly equal (P=0.424) between the two groups.

INTERPRETATION

Stair climbing biomechanics differ from normal in subjects with total hip replacements, however these unconscious alterations do not abnormally increase the hip loads during this activity. More work is necessary to determine exactly what constitutes optimal stair climbing biomechanics for patients with total hip replacements.

Contact mechanics analysis of metal-on-metal hip resurfacing prostheses

Finite-element method was employed to study the contact mechanics in metal-on-metal hip resurfacing prostheses, with particular reference to the effects of bone quality, the fixation condition between the acetabular cup and bone, and the clearance between the femoral head and the acetabular cup. Simple finite-element bone models were developed to simulate the contact between the articulating surfaces of the femoral head and the acetabular cup. The stresses within the bone structure were also studied. It was shown that a decrease in the clearance between the acetabular cup and femoral head had the largest effect on reducing the predicted contact-pressure distribution among all the factors considered in this study. It was found that as the clearance was reduced, the influence of the underlying materials, such as bone and cement, became increasingly important. Stress shielding was determined to occur in the bone tissue surrounding the hip resurfacing prosthesis considered in this study. However, the stress-shielding effects predicted were less than those observed in conventional total hip replacements. Both the effects of bone quality (reduction in elastic modulus) and the fixation condition between the cup and the bone were found to have a negligible effect on the predicted contact mechanics at the bearing surface. The loading was found to have a relatively small effect on the predicted maximum contact pressure at the bearing surface; this was attributed to an increase in contact area as the load was increased.