Hip Joint Reaction Forces Research Articles

Kinematic–kinetic compliant acetabular cup positioning based on preoperative motion tracking and musculoskeletal modeling for total hip arthroplasty

The invention of the surgical robot enabled accurate component implantation during total hip arthroplasty (THA). However, a preoperative surgical planning methodology is still lacking to determine the acetabular cup alignment considering the patient-specific hip functions during daily activities such as walking. To simultaneously avoid implant edgeloading and impingement, this study established a kinematic–kinetic compliant (KKC) acetabular cup positioning method based on preoperative gait kinematics measurement and musculoskeletal modeling. Computed tomography images around the hip joint and their biomechanical data during gait, including motion tracking and foot–ground reaction forces, were collected. Using the reconstructed pelvic and femur geometries, the patient-specific hip muscle insertions were located in the lower limb musculoskeletal model via point cloud registration. The designed cup orientation has to be within the patient-specific safe zone to prevent implant impingement, and the optimized value selected based on the time-dependent hip joint reaction force to minimize the risk of edgeloading. As a validation of the proposed musculoskeletal model, the predicted lower limb muscle activations for seven patients were correlated with their surface electromyographic measurements, and the computed hip contact force was also in quantitative agreement with data from the literature. However, the designed cup orientations were not always within the well-known Lewinnek safe zone, highlighting the importance of KKC surgical planning based on patient-specific biomechanical evaluations.

The Etiology of Neuromuscular Hip Dysplasia and Implications for Management: A Narrative Review.

This study summarizes the current knowledge of the etiology of hip dysplasia in children with neuromuscular disease and the implications for management. This article is based on a review of development of the hip joint from embryology through childhood growth. This knowledge is then applied to selective case reviews to show how the understanding of these developmental principles can be used to plan specific treatments. The development of the hip joint is controlled by genetic shape determination, but the final adult shape is heavily dependent on the mechanical environment experienced by the hip joint during growth and development. Children with neuromuscular conditions show a high incidence of coxa valga, hip dysplasia, and subluxation. The etiology of hip pathology is influenced by factors including functional status, muscular tone, motor control, child's age, and muscle strength. These factors in combination influence the development of high neck-shaft angle and acetabular dysplasia in many children. The hip joint reaction force (HJRF) direction and magnitude determine the location of the femoral head in the acetabulum, the acetabular development, and the shape of the femoral neck. The full range of motion is required to develop a round femoral head. Persistent abnormal direction and/or magnitude of HJRF related to the muscular tone can lead to a deformed femoral head and a dysplastic acetabulum. Predominating thigh position is the primary cause defining the direction of the HJRF, leading to subluxation in nonambulatory children. The magnitude and direction of the HJRF determine the acetabular shape. The age of the child when these pathomechanics occur acts as a factor increasing the risk of hip subluxation. Understanding the risk factors leading to hip pathology can help to define principles for the management of neurologic hip impairment. The type of neurologic impairment as defined by functional severity assessed by Gross Motor Function Classification System and muscle tone can help to predict the risk of hip joint deformity. A good understanding of the biomechanical mechanisms can be valuable for treatment planning.

Influence of obesity on load-transfer mechanism, contact mechanics, and longevity of cemented acetabular cup

ObjectiveThis investigation aimed to assess the impact of obesity on the load-transfer mechanism, longevity, and contact mechanics of cemented acetabular cups. MethodsThree obesity scenarios were considered: obese case-I (100–110 kg), obese case-II (120–130 kg), and obese case-III (140–150 kg). Utilising six finite element models, the effects of different bodyweights on load transfer, contact mechanics, and cup longevity during normal walking conditions were assessed. Muscle forces and hip joint reaction forces were adjusted and linearly calibrated based on obesity cases. ResultsElevated stresses in cortical and cancellous bones, as well as the cement mantle, were observed in obese cases, suggesting a heightened risk of loosening and failure of the cemented fixation of the acetabular cup. Additionally, increased contact pressure and micromotion between articulating surfaces were noted in obese individuals, with a gradual escalation from obese case-I to obese case-III. ConclusionsThese findings highlight the significant negative impact of obesity on the performance of cemented acetabular cups, emphasizing the importance of considering bodyweight variations in the design and assessment of orthopaedic implants for optimal functionality and durability.

A novel computational framework for the estimation of internal musculoskeletal loading and muscle adaptation in hypogravity.

Introduction: Spaceflight is associated with substantial and variable musculoskeletal (MSK) adaptations. Characterisation of muscle and joint loading profiles can provide key information to better align exercise prescription to astronaut MSK adaptations upon return-to-Earth. A case-study is presented of single-leg hopping in hypogravity to demonstrate the additional benefit computational MSK modelling has when estimating lower-limb MSK loading. Methods: A single male participant performed single-leg vertical hopping whilst attached to a body weight support system to replicate five gravity conditions (0.17, 0.25, 0.37, 0.50, 1 g). Experimental joint kinematics, joint kinetics and ground reaction forces were tracked in a data-tracking direct collocation simulation framework. Ground reaction forces, sagittal plane hip, knee and ankle net joint moments, quadriceps muscle forces (Rectus Femoris and three Vasti muscles), and hip, knee and ankle joint reaction forces were extracted for analysis. Estimated quadriceps muscle forces were input into a muscle adaptation model to predict a meaningful increase in muscle cross-sectional area, defined in (DeFreitas et al., 2011). Results: Two distinct strategies were observed to cope with the increase in ground reaction forces as gravity increased. Hypogravity was associated with an ankle dominant strategy with increased range of motion and net plantarflexor moment that was not seen at the hip or knee, and the Rectus Femoris being the primary contributor to quadriceps muscle force. At 1 g, all three joints had increased range of motion and net extensor moments relative to 0.50 g, with the Vasti muscles becoming the main muscles contributing to quadriceps muscle force. Additionally, hip joint reaction force did not increase substantially as gravity increased, whereas the other two joints increased monotonically with gravity. The predicted volume of exercise needed to counteract muscle adaptations decreased substantially with gravity. Despite the ankle dominant strategy in hypogravity, the loading on the knee muscles and joint also increased, demonstrating this provided more information about MSK loading. Discussion: This approach, supplemented with muscle-adaptation models, can be used to compare MSK loading between exercises to enhance astronaut exercise prescription.

Intra and inter-rater variability in the construction of patient-specific musculoskeletal model

BackgroundVariations observed in biomechanical studies might be attributed to errors made by operators during the construction of musculoskeletal models, rather than being solely attributed to patient-specific geometry. Research questionWhat is the impact of operator errors on the construction of musculoskeletal models, and how does it affect the estimation of muscle moment arms and hip joint reaction forces? MethodsThirteen independent operators participated in defining the muscle model, while a single operator performed 13 repetitions to define the muscle model based on 3D bone geometry. For each model, the muscle moment arms relative to the hip joint center of rotation was evaluated. Additionally, the hip joint reaction force during one-legged stance was assessed using static inverse optimization. ResultsThe results indicated high levels of consistency, as evidenced by the intra- rater and inter-rater agreement measured by the Intraclass Correlation Coefficient (ICC), which yielded values of 0.95 and 0.99, respectively. However, the estimated muscle moment arms exhibited an error of up to 16 mm compared to the reference musculoskeletal model. It was found that muscles attached to prominent anatomical landmarks were specified with greater accuracy than those attached over larger areas. Furthermore, the variability in estimated moment arms contributed to variations of up to 12% in the hip joint reaction forces. SignificanceBoth moment arm and muscle force demonstrated significantly lower variability when assessed by a single operator, suggesting the preference for employing a single operator in the creation of musculoskeletal models for clinical biomechanical studies.

Mechanical evaluation of revision surgery for femoral shaft nonunion initially treated with intramedullary nailing: Exchange nailing versus augmentation plating

IntroductionExchange nailing (EN) or augmentation plating (AP) has been employed to treat nonunions after intramedullary nailing for femoral shaft fractures. Although instability is a factor in hypertrophic nonunion, mechanical evaluations have been limited because the contribution of the callus to fracture site stability varies with healing. Our previous study illustrated the potential for evaluation using a finite element analysis (FEA) that incorporates callus material properties. This study aimed to mechanically evaluate revision surgery for nonunions using FEA. Materials and methodsA quantitative computed tomography-based FEA was performed on virtual revision models of a patient with suspected nonunion after intramedullary nailing. In addition to the initial nailing model (IN) with an 11-mm diameter (D) and 360-mm length (L), four EN models with D12mm (EN1), D13mm (EN2), D12mm-L400mm (EN3), and D13mm-L400mm (EN4) nails and three AP models with 5- (AP1), 6- (AP2), and 7-hole (AP3) plates were created. As with bone, callus was assigned inhomogeneous material properties derived from density based on an empirical formula. The hip joint reaction force and muscle forces at maximum load during the gait cycle were applied. The volume ratio of the callus at the fracture site with a tensile failure risk of ≥1 (tensile failure ratio) and bone fragment movement were evaluated. ResultsThe tensile failure ratio was 11.6 % (IN), 10.1 % (EN1), 6.3 % (EN2), 10.9 % (EN3), 6.2 % (EN4), 6.4 % (AP1), 7.2 % (AP2), and 7.7 % (AP3), respectively. The bone fragment movement showed an opening on the lateral side with the initial intramedullary nailing. However, both revision surgeries reduced the opening, leading to compression except in the EN1 model. The proximal bone fragments were internally rotated relative to the distal fragments, and the rotational instability was more suppressed in models with lower tensile failure ratio. ConclusionsFor EN, the increase in diameter, not length, is important to suppress instability. AP reduces instability, comparable to a 2 mm increase in nail diameter, and screw fixation closer to the fracture site reduces instability. This study suggest that AP is mechanically equivalent to EN and could be an option for revision surgery for femoral shaft nonunions.

Effect of stride length on the running biomechanics of healthy women of different statures.

Tibial stress fracture is a debilitating musculoskeletal injury that diminishes the physical performance of individuals who engage in high-volume running, including Service members during basic combat training (BCT) and recreational athletes. While several studies have shown that reducing stride length decreases musculoskeletal loads and the potential risk of tibial injury, we do not know whether stride-length reduction affects individuals of varying stature differently. We investigated the effects of reducing the running stride length on the biomechanics of the lower extremity of young, healthy women of different statures. Using individualized musculoskeletal and finite-element models of women of short (N = 6), medium (N = 7), and tall (N = 7) statures, we computed the joint kinematics and kinetics at the lower extremity and tibial strain for each participant as they ran on a treadmill at 3.0m/s with their preferred stride length and with a stride length reduced by 10%. Using a probabilistic model, we estimated the stress-fracture risk for running regimens representative of U.S. Army Soldiers during BCT and recreational athletes training for a marathon. When study participants reduced their stride length by 10%, the joint kinetics, kinematics, tibial strain, and stress-fracture risk were not significantly different among the three stature groups. Compared to the preferred stride length, a 10% reduction in stride length significantly decreased peak hip (p = 0.002) and knee (p < 0.001) flexion angles during the stance phase. In addition, it significantly decreased the peak hip adduction (p = 0.013), hip internal rotation (p = 0.004), knee extension (p = 0.012), and ankle plantar flexion (p = 0.026) moments, as well as the hip, knee, and ankle joint reaction forces (p < 0.001) and tibial strain (p < 0.001). Finally, for the simulated regimens, reducing the stride length decreased the relative risk of stress fracture by as much as 96%. Our results show that reducing stride length by 10% decreases musculoskeletal loads, tibial strain, and stress-fracture risk, regardless of stature. We also observed large between-subject variability, which supports the development of individualized training strategies to decrease the incidence of stress fracture.

Mechanical upside of PAO mainstream fixations: co-simulation based on early postoperative gait characteristics of DDH patients.

Purpose: To investigate the early postoperative gait characteristics of patients who underwent periacetabular osteotomy (PAO) and predict the biomechanical performance of two commonly used PAO fixation methods: iliac screw (IS) and transverse screw (TS). Methods: A total of 12 patients with unilateral developmental dysplasia of the hip (DDH) (mean age 27.81 ± 4.64years, 42% male) that were scheduled to undergo PAO surgery were included in this study. Their preoperative CT images and pre- and postoperative gait data were used to create subject-specific musculoskeletal models and complete the inverse dynamics analysis (IDA). Two patients with typical gait characteristics were selected using clustering analysis, and their IDA data were incorporated into finite element (FE) models of IS and TS fixations. Failure simulation was performed by applying iterative steps with increasing gait load to predict yield load. Stress results and yield loads were calculated for each FE model at different phases of the gait cycle. Results: Postoperative gait showed improvement compared to preoperative gait but remained inferior to that of healthy individuals. Postoperative gait was characterized by a lower hip range of motion, lower peri-ilium muscle forces, particularly in the abductors, and a sharper initial peak and flatter second peak of hip joint reaction force (HRF). Finite element analysis (FEA) showed a trend of increasing stress during the second-fourth phases of the gait cycle, with lower stress levels in other phases. At high-stress gait phases, the mean stress of maximum differed significantly between IS and TS (p < 0.05) and between coupled and uncoupled muscle forces (p < 0.05). Failure analysis predicted a slightly larger yield load for TS configurations (6.21*BW) than that for IS (6.16*BW), but both were well above the gait load. Coupled and uncoupled groups showed similar results, but uncoupled groups had lower yield loads (5.9*BW). Conclusion: PAO early postoperative gait shows a normalized trend, but abnormalities persist. IS and TS are both capable of resisting mechanical strain failure, with no significant mechanical advantage found for transverse screw fixation during PAO early postoperative gait. Additionally, it is important to note that the TS may have a higher risk of cyclic fatigue failure due to the localized greater stress concentration. Furthermore, the most medial screw is crucial for pelvic stability.

Derotational femoral osteotomy locations and their influence on joint reaction forces in dysplastic hips.

Femoral version (FV) deformities are common in patients with developmental dysplasia of the hip (DDH) and may contribute to cartilage damage due to abnormal joint loading. Derotational femoral osteotomy (DFO) surgery corrects FV deformities. However there is little consensus about the femoral transection location for DFO, and its influence on joint loads is unknown. The purpose of this study was to compare the effects of two common DFO locations on muscle forces and hip joint reaction forces (JRFs) in patients with DDH. DFO was simulated in nine patients with DDH and abnormal FV using patient-specific musculoskeletal models. Femoral transection for DFO was separately simulated proximal and distal to the lesser trochanter and FV values were corrected to an idealized 15°. JRFs during early and late stance of gait were compared between the two simulated transection locations. Most changes to JRFs were similar between proximal and distal DFO, however, statistically significant differences were found for the medial JRF component during late stance among patients with femoral anteversion (p = 0.01). Force changes from five hip muscles were significantly different between DFO locations, however, changes were minimal. Most changes after DFO in patients with femoral retroversion were opposite of those with femoral anteversion, with anteroposterior and superior JRFs increasing after retroversion correction. After DFO correction, superior and medial JRFs in DDH patients remained elevated compared to controls. Understanding the influence of DFO location on muscle-generated hip forces can help surgeons justify decisions and potentially standardize surgical correction of FV deformities in patients with DDH.

On the estimation of hip joint loads through musculoskeletal modeling.

Noninvasive estimation of joint loads is still an open challenge in biomechanics. Although musculoskeletal modeling represents a solid resource, multiple improvements are still necessary to obtain accurate predictions of joint loads and to translate such potential into practical utility. The present study, focused on the hip joint, is aimed at reviewing the state-of-the-art literature on the estimation of hip joint reaction forces through musculoskeletal modeling. Our literature inspection, based on well-defined selection criteria, returned seventeen works, which were compared in terms of methods and results. Deviations between predicted and in vivo measured hip joint loads, taken from the OrthoLoad database, were assessed through quantitative deviation indices. Despite the numerous modeling and computational improvements made over the last two decades, predicted hip joint loads still deviate from their experimental counterparts and typically overestimate them. Several critical aspects have emerged that affect muscle force estimation, hence joint loads. Among them, the physical fidelity of the musculoskeletal model, with its parameters and geometry, plays a crucial role. Also, predicted joint loads are markedly affected by the selected muscle recruitment strategy, which reflects the underlying motor control policy. Practical guidelines for researchers interested in noninvasive estimation of hip joint loads are also provided.

Potential of Neuromuscular Electrical Stimulation as a Bone Loss Countermeasure in Microgravity

INTRODUCTION: For future long-duration spaceflight missions, additional methods of loading the skeleton may be required to supplement exercise to minimize bone loss. Neuromuscular electrical stimulation (NMES) can elicit muscular contractions that create strain on bone. However, the potential effectiveness of NMES on the proximal femur during disuse is not known.METHODS: We measured the maximum isometric force of NMES-induced contractions of the rectus femoris and the hamstrings of 10 subjects (5 male, 5 female), sitting with the hips and knees at 90 degrees of flexion. We employed 2-D biomechanical models of the knee and hip to estimate the hip joint reaction forces, applied these forces to a generic femur finite element analysis model, and qualitatively compared the peak principal strains of the proximal femoral neck to the peak strains modeled in previous studies for other forms of exercise.RESULTS: The average peak tensile/compressive strains were 1380 ± 719 µε/-2179 ± 1130 µε and 573 ± 345 µε/-900 ± 543 µε for the male and female subjects, respectively. While results varied between studies, the strains achieved during NMES generally were comparable to those achieved during walking or stairs, with some individuals matching higher intensity activities.DISCUSSION: This study demonstrated that isometric NMES contractions of the thigh muscles can create strain in the proximal femoral neck similar to that achieved during low impact activities. While NMES alone will unlikely create a sufficient daily strain stimulus to prevent bone loss, it will likely improve the current spaceflight countermeasures by adding more frequent loading throughout the day.Abitante TJ, Bouxsein ML, Duda KR, Newman DJ. Potential of neuromuscular electrical stimulation as a bone loss countermeasure in microgravity. Aerosp Med Hum Perform. 2022; 93(11):774-782.

Characteristics of hip joint reaction forces during a range of activities.

The paper reports the characteristics of joint forces for 9 activities in 18 normal healthy subjects. Activities included Walk, Walk Turn, Stand to Sit, Sit to Stand, Squat, Stand Reach, Kneel Reach, Lunge, and Golf Swing. Within the cohort ∼30% variability occurred in the manner in which each activity was completed. Within the activities the average maximum load characteristics varied in magnitude (0.5-6.4 ρBWT) and also in duration (0.96-5.89s.) when compared to walking (3.1 ρBWT,1.1s.). The corresponding impulse ranged from 1.6 during the Walk to 6.7 ρ.BWT.s for the Golf Swing . As high loads with low sliding velocities have been shown in the literature to be damaging to the tribology of compliant contact surfaces the findings are postulated by the authors to be specifically important for the pre-clinical testing of cartilage substitutional materials. Note: Force was normalized to body weight (ρBWT) throughout the study.

Three dimensional analysis of hip joint reaction force using Q Hip Force (AQHF) software: Implication as a diagnostic tool.

Assessment of hip joint reaction force (JRF) is one of the analytical methods that can enable an understanding of the healthy walking index and the propensity towards disease. In this study, we have designed software, Analysis Q Hip Force (AQHF), to analyze the data retrieved from the mathematical equations for calculating the JRF and ground reaction force (GRF) that act on the hip joint during the early part of the stance phase. The stance phase is considered the least stable sub-phase during walking on level ground, and the gait stability is sequentially minimized during walking on elevated ramps. We have calculated the JRF and GRF values of walking stances on varied inclinations. The data obtained from these calculations during walking on elevated ramps were exported from mathematical equations to Q Hip Force software as two separate values, namely the JRF data and GRF data of the hip joint. The Q Hip Force software stores the two reaction force data in a text file, which allows the import and easy readability of the analyzed data with the AQHF application. The input and output data from the AQHF software were used to investigate the effect of different walking ramps on the magnitude of the hip JRF and GRF. The result of this study demonstrates a significant correlation between the JRF/GRF values and healthy walking indices till a ramp elevation of 70°. The software is designed to calculate and extrapolate data to analyze the possibility of stress in the hip joint. The framework developed in this study shows promise for preclinical and clinical applications. Studies are underway to use the results of JRF and GRF values as a diagnostic and prognostic tools in different diseases.

Changes in hip joint contact stress during a gait cycle based on the individualized modeling method of “gait-musculoskeletal system-finite element”

ObjectiveTo construct a comprehensive simulation method of “gait-musculoskeletal system (MS)-finite element (FE)” for analysis of hip joint dynamics characteristics and the changes in the contact stress in the hip throughout a gait cycle.MethodsTwo healthy volunteers (male and female) were recruited. The 3D gait trajectories during normal walking and the CT images including the hip and femur of the volunteers were obtained. CT imaging data in the DICOM format were extracted for subjected 3D hip joint reconstruction. The reconstructed 3D model files were used to realize the subject-specific registration of the pelvis and thigh segment of general musculoskeletal model. The captured marker trajectory data were used to drive subject-specific musculoskeletal model to complete inverse dynamic analysis. Results of inverse dynamic analysis were exported and applied as boundary and load settings of the hip joint finite element in ABAQUS. Finally, the finite element analysis (FEA) was performed to analyze contact stress of hip joint during a gait cycle of left foot.ResultsIn the inverse dynamic analysis, the dynamic changes of the main hip-femoral muscle force with respect to each phase of a single gait cycle were plotted. The hip joint reaction force reached a maximum value of 2.9%BW (body weight) and appeared at the end of the terminal stance phase. Twin peaks appeared at the initial contact phase and the end of the terminal stance phase, respectively. FEA showed the temporal changes in contact stress in the acetabulum. In the visual stress cloud chart, the acetabular contact stress was mainly distributed in the dome of the acetabulum and in the anterolateral area at the top of the femoral head during a single gait cycle. The acetabular contact area was between 293.8 and 998.4 mm2, and the maximum contact area appear at the mid-stance phase or the loading response phase of gait. The maximum contact stress of the acetabulum reached 6.91 MPa for the model 1 and 6.92 MPa for the model 2 at the terminal stance phase.ConclusionsThe “Gait-MS-FE” technology is integrated to construct a comprehensive simulation framework. Based on human gait trajectories and their CT images, individualized simulation modeling can be achieved. Subject-specific gait in combination with an inverse dynamic analysis of the MS provides pre-processing parameters for FE simulation for more accurate biomechanical analysis of hip joint.Graphical abstract

Comparison of Hip and Low Back Loads between Normal Gait, Axillary Crutch Ambulation and Walking with a Hands-free Crutch in a Healthy Population.

BackgroundInstead of using axillary crutches, using a hands-free crutch (HFC) has been associated with higher functional outcome scores. However, hip and back pain have been reported as side effects.Purpose/HypothesisThe purpose of this study was to compare range of motion and joint reaction forces at the hip and low back between HFC walking, normal walking, and standard crutch walking. It was hypothesized that hip joint reaction forces and low back joint reaction forces would be higher with HFC walking compared with normal walking and axillary crutch walking.Study DesignControlled Laboratory StudyMethodsUsing 3D motion analysis and force plates, kinematics and ground reaction forces were measured in 12 healthy subjects during gait, crutch ambulation and HFC walking. Gait speed, hip and trunk range of motion, and hip and low back reaction forces, were compared using repeated-measures ANOVA.ResultsGait speed during HFC ambulation was reduced 33% compared to crutch ambulation (P<0.001) and 44% compared to normal gait (p<0.001). Hip range of motion was reduced during both crutch conditions compared to gait (p<0.001). Trunk range of motion was greatest during HFC walking compared to both gait and crutch ambulation (p<0.001). Peak hip joint reaction force during HFC walking was 11% lower than during gait (p=0.026) and 30% lower than during crutch walking (p<0.001). Peak low back reaction force during HFC walking was 18% higher than during gait (p=0.032) but not different than during crutch walking.ConclusionHip joint reaction forces during HFC walking did not exceed those during gait or axillary crutch ambulation. However, a reduction in hip motion using the HFC was associated with increases in trunk motion and low-back loading. These could be a cause for reports of low-back pain accompanying HFC usage.Level of EvidenceLevel 3

Finite Element Analysis of Customized Acetabular Implant and Bone after Pelvic Tumour Resection throughout the Gait Cycle

The aim of this paper is to investigate and compare the stress distribution of a reconstructed pelvis under different screw forces in a typical walking pattern. Computer-aided design models of the pelvic bones and sacrum made based on computer tomography images and individually designed implants are the basis for creating finite element models, which are imported into ABAQUS software. The screws provide compression loading and bring the implant and pelvic bones together. The sacrum is fixed at the level of the L5 vertebrae. The variants of strength analyses are carried out with four different screw pretension forces. The loads equivalent to the hip joint reaction forces arising during moderate walking are applied to reference points based on the centres of the acetabulum. According to the results of the performed analyses, the optimal and critical values of screw forces are estimated for the current model. The highest stresses among all the models occurred in the screws and implant. As soon as the screw force increases up to the ultimate value, the bone tissue might be locally destroyed. The results prove that the developed implant design with optimal screw pretension forces should have good biomechanical characteristics.

Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading

AimsIn the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading.MethodsTorque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule.ResultsThe medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading.ConclusionThe capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability.Cite this article: Bone Joint Res 2021;10(9):594–601.

On the Effect of Friction on Tibiofemoral Joint Kinematics

The effect of friction on nonlinear dynamics and vibration of total knee arthroplasties is yet to be investigated and understood. This research work aims at studying the influence of friction on nonlinear dynamics, friction-induced vibration, and damage of tibiofemoral joints. For this purpose, a spatial dynamic knee model is developed using an asymmetric nonlinear elastic model accounting for knee joint ligaments and a penalty contact model to compute normal contact stresses in the joint while contact detection is treated such that the associated computational time is reduced. Several friction models are considered and embedded in the dynamic model to estimate tangential friction forces in the knee joint. External loads and moments, due to the presence of all soft tissues, e.g., muscles and hip-joint reaction forces, applied to the femoral bone are determined using a musculoskeletal approach. In the post-processing stage, damage, i.e., wear and creep, are estimated using three wear models and an empirical creep formulation, respectively. In addition, a FFT analysis is performed to evaluate likely friction-induced vibration of tibiofemoral joints. Mesh density analysis is performed and the methodology is assessed against outcomes available in the literature. It can be concluded that friction influences not only the tribology, but also dynamics of the knee joint, and friction-induced vibration is likely to take place when the friction coefficient increases.

Acetabular Edge Loading During Gait Is Elevated by the Anatomical Deformities of Hip Dysplasia.

Developmental dysplasia of the hip (DDH) is a known risk factor for articular tissue damage and secondary hip osteoarthritis. Acetabular labral tears are prevalent in hips with DDH and may result from excessive loading at the edge of the shallow acetabulum. Location-specific risks for labral tears may also depend on neuromuscular factors such as movement patterns and muscle-induced hip joint reaction forces (JRFs). To evaluate such mechanically-induced risks, we used subject-specific musculoskeletal models to compare acetabular edge loading (AEL) during gait between individuals with DDH (N = 15) and healthy controls (N = 15), and determined the associations between AEL and radiographic measures of DDH acetabular anatomy. The three-dimensional pelvis and femur anatomy of each DDH and control subject were reconstructed from magnetic resonance images and used to personalize hip joint center locations and muscle paths in each model. Model-estimated hip JRFs were projected onto the three-dimensional acetabular rim to predict instantaneous AEL forces and their accumulative impulses throughout a gait cycle. Compared to controls, subjects with DDH demonstrated significantly higher AEL in the antero-superior acetabulum during early stance (3.6 vs. 2.8 × BW, p ≤ 0.01), late stance (4.3 vs. 3.3 × BW, p ≤ 0.05), and throughout the gait cycle (1.8 vs. 1.4 × BW*s, p ≤ 0.02), despite having similar hip movement patterns. Elevated AEL primarily occurred in regions where the shallow acetabular edge was in close proximity to the hip JRF direction, and was strongly correlated with the radiographic severity of acetabular deformities. The results suggest AEL is highly dependent on movement and muscle-induced joint loading, and significantly elevated by the DDH acetabular deformities.

Effect of simulated rehabilitation on hip joint loading during single limb squat in patients with hip dysplasia

Rehabilitation for patients with developmental dysplasia of the hip (DDH) addresses modifiable factors in an effort to reduce symptoms and prevent or delay the development of osteoarthritis, yet its effect on joint mechanics remains unknown. Our objective was to establish how rehabilitation (muscle strengthening and movement training), simulated with a musculoskeletal model and probabilistic analyses, alters hip joint reaction forces (JRF) in patients with DDH during a single limb squat. In four patients with DDH, hip abductor strengthening was simulated by increasing the maximum isometric force value between 0 and 32.6% and movement training was simulated by decreasing the hip adduction angle between 0 and 10° relative to baseline. 2,000 Monte Carlo simulations were performed separately to simulate strengthening and movement training, from which 99% confidence bounds and sensitivity factors were calculated. Our results indicated that simulated movement training aimed at decreasing hip adduction had a substantially larger influence on hip JRF than strengthening, as indicated by 99% confidence bounds of the resultant JRF (0.88 ± 0.55 xBW vs. 0.31 ± 0.12 xBW, respectively). Relative to baseline, movement training that resulted in a 10° decrease in hip adduction decreased the resultant JRF by 0.78 ± 0.65 xBW, while strengthening the abductors by 17.6% increased resultant JRF by 0.18 ± 0.06 xBW. To our knowledge, these results are the first to provide evidence pertaining to the effect of rehabilitation on joint mechanics in patients with DDH and can be used to inform more targeted interventions.