Knee joint forces: prediction, measurement, and significance

Machine learning for rapid estimation of lower extremity muscle and joint loading during activities of daily living

Joint contact and muscle forces estimated with musculoskeletal modeling techniques offer useful metrics describing movement quality that benefit multiple research and clinical applications. The expensive processing of laboratory data associated with generating these outputs presents challenges to researchers and clinicians, including significant time and expertise requirements that limit the number of subjects typically evaluated. The objective of the current study was to develop and compare machine learning techniques for rapid, data-driven estimation of musculoskeletal metrics from derived gait lab data. OpenSim estimates of patient joint and muscle forces during activities of daily living were simulated using laboratory data from 70 total knee replacement patients and used to develop 4 different machine learning algorithms. Trained machine learning models predicted both trend and magnitude of estimated joint contact (mean correlation coefficients ranging from 0.93 to 0.94 during gait) and muscle forces (mean correlation coefficients ranging from 0.83 to 0.91 during gait) based on anthropometrics, ground reaction forces, and joint angle data. Patient mechanics were accurately predicted by recurrent neural networks, even after removing dependence on key subsets of predictor features. The ability to quickly estimate patient mechanics from derived measurements of movement has the potential to broaden the impact of musculoskeletal modeling by enabling faster assessment in both clinical and research settings.

Evaluation and Validation of a Joint Stress Test to Induce Activity-Related Knee Joint Discomfort - a Prospective Case-Control Study

BACKGROUND

The assessment of improvement or maintenance of joint health in healthy subjects is a great challenge. The aim of the study was the evaluation of a joint stress test to assess joint discomfort in subjects with activity-related knee joint discomfort (ArJD).

RESULTS

Forty-five subjects were recruited to perform the single-leg-step-down (SLSD) test (15 subjects per group). Subjects with ArJD of the knee (age 22-62 years) were compared to healthy subjects (age 24-59 years) with no knee joint discomfort during daily life sporting activity and to subjects with mild-to-moderate osteoarthritis of the knee joint (OA, Kellgren score 2-3, age 42-64 years). The subjects performed the SLSD test with two different protocols: (I) standardization for knee joint discomfort; (II) standardization for load on the knee joint. In addition, range of motion (ROM), reach test, acute pain at rest and after a single-leg squat and knee injury, and osteoarthritis outcome score (KOOS) were assessed. In OA and ArJD subjects, knee joint discomfort could be reproducibly induced in a short time interval of less than 10 min (200 steps). In healthy subjects, no pain was recorded. A clear differentiation between study groups was observed with the SLSD test (maximal step number) as well as KOOS questionnaire, ROM, and reach test. In addition, a moderate to good intra-class correlation was shown for the investigated outcomes.

CONCLUSIONS

These results suggest the SLSD test is a reliable tool for the assessment of knee joint health function in ArJD and OA subjects to study the improvements in their activities. Further, this model can be used as a stress model in intervention studies to study the impact of stress on knee joint health function.

Foot progression angle estimation using a single foot-worn inertial sensor

Background

The foot progression angle is an important measure used to help patients reduce their knee adduction moment. Current measurement systems are either lab-bounded or do not function in all environments (e.g., magnetically distorted). This work proposes a novel approach to estimate foot progression angle using a single foot-worn inertial sensor (accelerometer and gyroscope).

Methods

The approach uses a dynamic step frame that is recalculated for the stance phase of each step to calculate the foot trajectory relative to that frame, to minimize effects of drift and to eliminate the need for a magnetometer. The foot progression angle (FPA) is then calculated as the angle between walking direction and the dynamic step frame. This approach was validated by gait measurements with five subjects walking with three gait types (normal, toe-in and toe-out).

Results

The FPA was estimated with a maximum mean error of ~ 2.6° over all gait conditions. Additionally, the proposed inertial approach can significantly differentiate between the three different gait types.

Conclusion

The proposed approach can effectively estimate differences in FPA without requiring a heading reference (magnetometer). This work enables feedback applications on FPA for patients with gait disorders that function in any environment, i.e. outside of a gait lab or in magnetically distorted environments.

Real-Time Prediction of Joint Forces by Motion Capture and Machine Learning

Conventional biomechanical modelling approaches involve the solution of large systems of equations that encode the complex mathematical representation of human motion and skeletal structure. To improve stability and computational speed, being a common bottleneck in current approaches, we apply machine learning to train surrogate models and to predict in near real-time, previously calculated medial and lateral knee contact forces (KCFs) of 54 young and elderly participants during treadmill walking in a speed range of 3 to 7 km/h. Predictions are obtained by fusing optical motion capture and musculoskeletal modeling-derived kinematic and force variables, into regression models using artificial neural networks (ANNs) and support vector regression (SVR). Training schemes included either data from all subjects (LeaveTrialsOut) or only from a portion of them (LeaveSubjectsOut), in combination with inclusion of ground reaction forces (GRFs) in the dataset or not. Results identify ANNs as the best-performing predictor of KCFs, both in terms of Pearson R (0.89-0.98 for LeaveTrialsOut and 0.45-0.85 for LeaveSubjectsOut) and percentage normalized root mean square error (0.67-2.35 for LeaveTrialsOut and 1.6-5.39 for LeaveSubjectsOut). When GRFs were omitted from the dataset, no substantial decrease in prediction power of both models was observed. Our findings showcase the strength of ANNs to predict simultaneously multi-component KCF during walking at different speeds-even in the absence of GRFs-particularly applicable in real-time applications that make use of knee loading conditions to guide and treat patients.

Development of a specimen-specific in vitro pre-clinical simulation model of the human cadaveric knee with appropriate soft tissue constraints

A human cadaveric specimen-specific knee model with appropriate soft tissue constraints was developed to appropriately simulate the biomechanical environment in the human knee, in order to pre-clinically evaluate the biomechanical and tribological performance of soft tissue interventions. Four human cadaveric knees were studied in a natural knee simulator under force control conditions in the anterior posterior (AP) and tibial rotation (TR) axes, using virtual springs to replicate the function of soft tissues. The most appropriate spring constraints for each knee were determined by comparing the kinematic outputs in terms of AP displacement and TR angle of the human knee with all the soft tissues intact, to the same knee with all the soft tissues resected and replaced with virtual spring constraints (spring rate and free length/degree). The virtual spring conditions that showed the least difference in the AP displacement and TR angle outputs compared to the intact knee were considered to be the most appropriate spring conditions for each knee. The resulting AP displacement and TR angle profiles under the appropriate virtual spring conditions all showed similar shapes to the individual intact knee for each donor. This indicated that the application of the combination of virtual AP and TR springs with appropriate free lengths/degrees was successful in simulating the natural human knee soft tissue function. Each human knee joint had different kinematics as a result of variations in anatomy and soft tissue laxity. The most appropriate AP spring rate for the four human knees varied from 20 to 55 N/mm and the TR spring rate varied from 0.3 to 1.0 Nm/°. Consequently, the most appropriate spring condition for each knee was unique and required specific combinations of spring rate and free length/degree in each of the two axes.

Estimating Knee Joint Load Using Acoustic Emissions During Ambulation

Quantifying joint load in activities of daily life could lead to improvements in mobility for numerous people; however, current methods for assessing joint load are unsuitable for ubiquitous settings. The aim of this study is to demonstrate that joint acoustic emissions contain information to estimate this internal joint load in a potentially wearable implementation. Eleven healthy, able-bodied individuals performed ambulation tasks under varying speed, incline, and loading conditions while joint acoustic emissions and essential gait measures-electromyography, ground reaction forces, and motion capture trajectories-were collected. The gait measures were synthesized using a neuromuscular model to estimate internal joint contact force which was the target variable for subject-specific machine learning models (XGBoost) trained based on spectral, temporal, cepstral, and amplitude-based features of the joint acoustic emissions. The model using joint acoustic emissions significantly outperformed (p < 0.05) the best estimate without the sounds, the subject-specific average load (MAE = 0.31 ± 0.12 BW), for both seen (MAE = 0.08 ± 0.01 BW) and unseen (MAE = 0.21 ± 0.05 BW) conditions. This demonstrates that joint acoustic emissions contain information that correlates to internal joint contact force and that information is consistent such that unique cases can be estimated.

Stress response envelopes of intact tibiofemoral joint and knee osteoarthritis

The purpose of this study was to determine stress envelopes for an intact tibiofemoral joint and to study how they vary with knee loading, external–internal rotation, varus–valgus rotation and cartilage degradation (osteoarthritis) using the finite element method. The envelopes were presented in terms of knee flexion angle. The maximum von Mises stress for all tibiofemoral joint components increased with increasing the axial compressive force magnitude. Menisci exhibited the highest magnitude of maximum von Mises stress as compared to the femoral and tibial cartilages. In a range of flexion angles between 0° and 100°, the medial meniscus exhibited the highest maximum von Mises stress than the lateral meniscus and the stress in medial meniscus tended to increase with increasing the flexion angle. External–internal and varus–valgus rotations changed the stress distribution: higher stress on lateral compartment but lower stress on medial compartment, and conversely. The internal rotation provided more extreme effect than the external rotation. For the knee osteoarthritis, cartilage degradation (early stage) caused maximum von Mises stress to increase on the intact menisci revealing that knee osteoarthritis could also cause meniscal tear. The late osteoarthritis caused the maximum von Mises stress to increase on the calcified cartilage and subchondral bone.

Supplemental Fixation of Supracondylar Distal Femur Fractures: A Biomechanical Comparison of Dual-Plate and Plate-Nail Constructs

OBJECTIVES

This biomechanical study compares the effectiveness of dual-plate (DP) and plate-nail (PN) constructs for fixation of supracondylar distal femur fractures in synthetic and cadaveric specimens.

METHODS

Twenty-four synthetic osteoporotic femurs were used to compare 4 constructs in an extra-articular, supracondylar fracture gap model (OTA/AO type 33-A3). Constructs included: (1) distal lateral femoral locking plate (DLFLP), (2) retrograde intramedullary nail (rIMN), (3) DLFLP + medial locking compression plate (DP construct), and (4) DLFLP + rIMN (PN construct). DP and PN constructs were then directly compared using 7 matched pairs of cadaveric femurs. Specimens underwent cyclic loading in torsion and compression. Biomechanical effectiveness was measured by quantifying the load-dependent stiffness of each construct.

RESULTS

In synthetic osteoporotic femurs, the DP construct had the greatest torsional stiffness (1.76 ± 0.33 Nm/deg) followed by the rIMN (1.67 ± 0.14 Nm/deg), PN construct (1.44 ± 0.17 Nm/deg), and DLFLP (0.68 ± 0.10 Nm/deg) (P < 0.01). The DP construct also had the greatest axial stiffness (507.9 ± 83.1 N/mm) followed by the PN construct (371.4 ± 41.9 N/mm), DLFLP (255.0 ± 45.3 N/mm), and rIMN (109.2 ± 47.6 N/mm) (P < 0.05). In cadaveric specimens, the DP construct was nearly twice as stiff as the PN construct in torsion (8.41 ± 0.58 Nm/deg vs. 4.24 ± 0.41 Nm/deg, P < 0.001), and over one-and-a-half times stiffer in compression (2148.1 ± 820.4 vs. 1387.7 ± 467.9 N/mm, P = 0.02).

CONCLUSIONS

DP constructs provided stiffer fixation than PN constructs in this biomechanical study of extra-articular distal femur fractures. In the clinical setting, fracture morphology, desired healing mode, surgical approach, and implant cost should be considered when implementing these fixation strategies.

Gait Adaptation Using a Cable-Driven Active Leg Exoskeleton (C-ALEX) With Post-Stroke Participants

Individuals with chronic hemiparesis post-stroke exhibit gait impairments that require functional rehabilitation through training. Exoskeletal robotic assistive devices can provide a user with continuous assistance but impose movement restrictions. There are currently devices that allow unrestricted movement but provide assistance only intermittently at specific points of the gait cycle. Our design, a cable-driven active leg exoskeleton (C-ALEX), allows the user both unrestricted movement and continuous force assistance throughout the gait cycle to assist the user in new walking patterns. In this study, we assessed the ability of C-ALEX to induce a change in the walking patterns of ten post-stroke participants using a single-session training protocol. The ability of C-ALEX to accurately provide forces and torques in the desired directions was also evaluated to compare its design performance to traditional rigid-link designs. Participants were able to reach 91% ± 12% of their target step length and 89% ± 13% of their target step height. The achieved step parameters differed significantly from participant baselines ( ). To quantify the performance, the forces in each cable's out of the plane movements were evaluated relative to the in-plane desired cable tension magnitudes. This corresponded to an error of under 2Nm in the desired controlled joint torques. This error magnitude is low compared to the system command torques and typical adult biological torques during walking (2-4%). These results point to the utility of using non-restrictive cable-driven architectures in gait retraining, in which future focus can be on rehabilitating gait pathologies seen in stroke survivors.

What type of exercise is most effective for people with knee osteoarthritis and co-morbid obesity?: The TARGET randomized controlled trial

OBJECTIVE

Different exercise types may yield different outcomes in osteoarthritis (OA) subgroups. The objective was to directly compare effectiveness of two exercise programs for people with medial knee OA and co-morbid obesity.

DESIGN

We performed a participant- and assessor-blinded randomized controlled trial. 128 people ≥50 years with medial knee OA and body mass index ≥30 kg/m² were recruited from the community. Interventions were home-based non-weight bearing (NWB) quadriceps strengthening or weight bearing (WB) functional exercise for 12 weeks. Primary outcomes were change in overall knee pain (numeric rating scale, range 0-10) and difficulty with physical function (Western Ontario and McMaster Universities Osteoarthritis Index, 0-68) over 12 weeks. Secondary outcomes included other pain measures, physical function, quality-of-life, global changes, physical performance, and lower-limb muscle strength.

RESULTS

123 (96%) participants were retained. There was no evidence of a between-group difference in change in pain (mean difference 0.73 units (95% confidence intervals (0.05,1.50)) or function (2.80 units (-1.17,6.76)), with both groups reporting improvements. For secondary outcomes, the WB group had greater improvement in quality-of-life (-0.043 units (-0.085,-0.001)) and more participants reporting global improvement (overall: relative risk 1.40 (0.98,2.01); pain 1.47 (0.97,2.24); function 1.43 (1.04,1.98). Although adverse events were minor, more NWB group participants reported ≥1 adverse event (26/66 (39%) vs 14/62 (23%), p = 0.04).

CONCLUSIONS

Both exercise types similarly improved primary outcomes of pain and function and can be recommended for people with knee OA and obesity. WB exercise may be preferred given fewer adverse events and potential additional benefits on some secondary outcomes.

REGISTRATION

Prospectively registered (Australian New Zealand Clinical Trials Registry #12617001013358, 14/7/2017).

Muscle contributions to medial and lateral tibiofemoral compressive loads during sidestep cutting

The tibiofemoral compressive forces experienced during functional activities are believed to be important for maintaining tibiofemoral stability. Previous studies have shown that both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral joint compressive forces during walking. However, healthy individuals typically engage in more vigorous activities (e.g. jumping and cutting) that provide greater challenges to tibiofemoral stability. Despite this, no previous studies have investigated how both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral compressive loading during such tasks. The present study investigated how muscles contributed to the medial and lateral compartment tibiofemoral compressive forces during sidestep cutting. Three-dimensional marker trajectories, ground reaction forces and muscle electromyographic signals were collected from eight healthy males whilst they completed unanticipated sidestep cutting. OpenSim was used to perform musculoskeletal simulations to compute the contribution of each lower-limb muscle to compressive loading of each compartment of the knee. The greatest contributors to medial compartment loading were the vasti, gluteus maximus and medius, and the medial gastrocnemius. The greatest contributors to lateral compartment loading were the vasti, adductors, medial and lateral gastrocnemius, and the soleus. The soleus displayed the greatest potential for unloading the medial compartment, whereas the gluteus maximus and medius displayed the greatest potential for unloading the lateral compartment. These findings may help to inform interventions aiming to modulate compressive loading at the knee.

Chronic Ankle Instability Does Not Influence Tibiofemoral Contact Forces During Drop Landings Using a Musculoskeletal Model

The purpose of the study was to compare the tibiofemoral contact forces of participants with chronic ankle instability versus controls during landings using a computer-simulated musculoskeletal model. A total of 21 female participants with chronic ankle instability and 21 pair-matched controls performed a drop landing task on a tilted force plate. A 7-camera motion capture system and 2 force plates were used to test participants' lower-extremity biomechanics. A musculoskeletal model was used to calculate the tibiofemoral contact forces (femur on tibia). No significant between-group differences were observed for the peak tibiofemoral contact forces (P = .25-.48) during the landing phase based on paired t tests. The group differences ranged from 0.05 to 0.58 body weight (BW). Most participants demonstrated a posterior force (peak, ∼1.1 BW) for most duration of the landing phase and a medial force (peak, ∼0.9 BW) and large compressive force (peak, ∼10 BW) in the landing phase. The authors conclude that chronic ankle instability may not be related to the increased tibiofemoral contact forces or knee injury mechanisms during landings on the tilted surface.

Knee Forces During Landing in Men and Women

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η²=0.452; unilateral: p < 0.001, η² = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η² = 0.001 - 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η² = 0.085) and hamstrings forces (p < 0.001, η² = 0.183), whereas women had greater quadriceps forces (p = 0.004, η² = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

Estimation of Knee Joint Forces in Sport Movements Using Wearable Sensors and Machine Learning

Knee joint forces (KJF) are biomechanical measures used to infer the load on knee joint structures. The purpose of this study is to develop an artificial neural network (ANN) that estimates KJF during sport movements, based on data obtained by wearable sensors. Thirteen participants were equipped with two inertial measurement units (IMUs) located on the right leg. Participants performed a variety of movements, including linear motions, changes of direction, and jumps. Biomechanical modelling was carried out to determine KJF. An ANN was trained to model the association between the IMU signals and the KJF time series. The ANN-predicted KJF yielded correlation coefficients that ranged from 0.60 to 0.94 (vertical KJF), 0.64 to 0.90 (anterior-posterior KJF) and 0.25 to 0.60 (medial-lateral KJF). The vertical KJF for moderate running showed the highest correlation (0.94 ± 0.33). The summed vertical KJF and peak vertical KJF differed between calculated and predicted KJF across all movements by an average of 5.7% ± 5.9% and 17.0% ± 13.6%, respectively. The vertical and anterior-posterior KJF values showed good agreement between ANN-predicted outcomes and reference KJF across most movements. This study supports the use of wearable sensors in combination with ANN for estimating joint reactions in sports applications.

Patients With Medial Knee Osteoarthritis Reduce Medial Knee Contact Forces by Altering Trunk Kinematics, Progression Speed, and Stepping Strategy During Stair Ascent and Descent: A Pilot Study

Medial knee loading during stair negotiation in individuals with medial knee osteoarthritis, has only been reported in terms of joint moments, which may underestimate the knee loading. This study assessed knee contact forces (KCF) and contact pressures during different stair negotiation strategies. Motion analysis was performed in five individuals with medial knee osteoarthritis (52.8±11.0 years) and eight healthy subjects (51.0±13.4 years) while ascending and descending a staircase. KCF and contact pressures were calculated using a multi-body knee model while performing step-over-step at controlled and self-selected speed, and step-by-step strategies. At controlled speed, individuals with osteoarthritis showed decreased peak KCF during stair ascent but not during stair descent. Osteoarthritis patients showed higher trunk rotations in frontal and sagittal planes than controls. At lower self-selected speed, patients also presented reduced medial KCF during stair descent. While performing step-by-step, medial contact pressures decreased in osteoarthritis patients during stair descent. Osteoarthritis patients reduced their speed and increased trunk flexion and lean angles to reduce KCF during stair ascent. These trunk changes were less safe during stair descent where a reduced speed was more effective. Individuals should be recommended to use step-over-step during stair ascent and step-by-step during stair descent to reduce medial KCF.

Quantifying the Effects of Increasing Mechanical Stress on Knee Acoustical Emissions Using Unsupervised Graph Mining

In this paper, we investigate the effects of increasing mechanical stress on the knee joints by recording knee acoustical emissions and analyze them using an unsupervised graph mining algorithm. We placed miniature contact microphones on four different locations: on the lateral and medial sides of the patella and superficial to the lateral and medial meniscus. We extracted audio features in both time and frequency domains from the acoustical signals and calculated the graph community factor (GCF): an index of heterogeneity (variation) in the sounds due to different loading conditions enforced on the knee. To determine the GCF, a k-nearest neighbor graph was constructed and an Infomap community detection algorithm was used to extract all potential clusters within the graph-the number of detected communities were then quantified with GCF. Measurements from 12 healthy subjects showed that the GCF increased monotonically and significantly with vertical loading forces (mean GCF for no load = 30 and mean GCF for maximum load [body weight] = 39). This suggests that the increased complexity of the emitted sounds is related to the increased forces on the joint. In addition, microphones placed on the medial side of the patella and superficial to the lateral meniscus produced the most variation in the joint sounds. This information can be used to determine the optimal location for the microphones to obtain acoustical emissions with greatest sensitivity to loading. In future work, joint loading quantification based on acoustical emissions and derived GCF can be used for assessing cumulative knee usage and loading during activities, for example for patients rehabilitating knee injuries.

Simulating contact using the elastic foundation algorithm in OpenSim

Modeling joint contact in OpenSim is not well understood. This study systematically investigated the variables associated with the elastic foundation contact model within OpenSim by performing a series of controlled benchtop experiment and concomitant simulations. Four metal-on-plastic interactions were modeled, including a model of a total knee replacement (TKR). Load-displacement curves were recorded during cyclic loading between 100 and 750 N. Geometries were imported and into OpenSim and contact mechanics were modeled with the on-board elastic foundation algorithm. A hybrid optimization algorithm determined that stiffness and dissipation coefficients for TKR implants were 1.52 × 10¹⁰ N/m and 57.7 Ns/m, respectively. Estimations of contact forces were 10.2% of blinded experimental data (average root mean square error: 76.82 ± 11.47 N). In the second portion of this study, freely available eTibia TKR renderings were used to test the ubiquity of the tuning parameters. They were also used to perform a sensitivity analysis of material stiffness and mesh density with regard to penetration depth and computational time. When a stiffness of 1 × 10¹⁰ was applied to an eTibia model with 5000 faces, a 100 kg load caused 0.259 mm of penetration. Under the same conditions, the tuned model experienced 0.300 mm of penetration. Material stiffnesses between 1 × 10¹³ and 1 × 10¹⁵ N/m increased computation time by factors of 12-23. This study provides much needed clarity regarding the use of the OpenSim EF algorithm. It also demonstrates the utility of OpenSim to model deformable materials and complex geometries, and this approach can be adapted to make reasonable estimations for both natural and surgically modified joints.

Impact of antagonistic muscle co-contraction on in vivo knee contact forces

Background

The onset and progression of osteoarthritis, but also the wear and loosening of the components of an artificial joint, are commonly associated with mechanical overloading of the structures. Knowledge of the mechanical forces acting at the joints, together with an understanding of the key factors that can alter them, are critical to develop effective treatments for restoring joint function. While static anatomy is usually the clinical focus, less is known about the impact of dynamic factors, such as individual muscle recruitment, on joint contact forces.

Methods

In this study, instrumented knee implants provided accurate in vivo tibio-femoral contact forces in a unique cohort of 9 patients, which were used as input for subject specific musculoskeletal models, to quantify the individual muscle forces during walking and stair negotiation.

Results

Even between patients with a very similar self-selected gait speed, the total tibio-femoral peak forces varied 1.7-fold, but had only weak correlation with static alignment (varus/valgus). In some patients, muscle co-contraction of quadriceps and gastrocnemii during walking added up to 1 bodyweight (~ 50%) to the peak tibio-femoral contact force during late stance. The greatest impact of co-contraction was observed in the late stance phase of stair ascent, with an increase of the peak tibio-femoral contact force by up to 1.7 bodyweight (66%).

Conclusions

Treatment of diseased and failed joints should therefore not only be restricted to anatomical reconstruction of static limb axes alignment. The dynamic activation of muscles, as a key modifier of lower limb biomechanics, should also be taken into account and thus also represents a promising target for restoring function, patient mobility, and preventing future joint failure.

Trial registration

German Clinical Trials Register: ID: DRKS00000606, date: 05.11.2010.

Electronic supplementary material

The online version of this article (10.1186/s12984-018-0434-3) contains supplementary material, which is available to authorized users.

Stiffness Matters: Part II-The Effects of Plate Stiffness on Load-Sharing and the Progression of Fusion Following Anterior Cervical Discectomy and Fusion In Vivo

STUDY DESIGN

Real time in vivo measurement of forces in the cervical spine of goats following anterior cervical discectomy and fusion (ACDF).

OBJECTIVE

To measure interbody forces in the cervical spine during the time course of fusion following ACDF with plates of different stiffnesses.

SUMMARY OF BACKGROUND DATA

Following ACDF, the biomechanics of the arthrodesis is largely dictated by the plate. The properties of the plate prescribe the extent of load-sharing through the disc space versus the extent of stress-shielding. Load-sharing promotes interbody bone formation and stress-shielding can inhibit maturation of bone. However, these principles have never been validated in vivo. Measuring in vivo biomechanics of the cervical spine is critical to understanding the complex relationships between implant design, interbody loading, load-sharing, and the progression of fusion.

METHODS

Anterior cervical plates of distinct bending stiffnesses were placed surgically following ACDF in goats. A validated custom force-sensing interbody implant was placed in the disc space to measure load-sharing in the spine. Interbody loads were measured in vivo in real time during the course of fusion for each plate.

RESULTS

Interbody forces during flexion/extension were highly dynamic. In animals that received high stiffness plates, maximum forces were in extension whereas in animals that received lower stiffness plates, maximum forces were in flexion. As fusion progressed, interbody load magnitude decreased.

CONCLUSION

The magnitude of interbody forces in the cervical spine is dynamic and correlates to activity and posture of the head and neck. The magnitude and consistency of forces in the interbody space correlates to plate stiffness with more compliant plates resulting in more consistent load-sharing. The magnitude of interbody forces decreases as fusion matures suggesting that smart interbody implants may be used as a diagnostic tool to indicate the progression of interbody fusion.

LEVEL OF EVIDENCE

N/A.

Intraosseous pressure during loading and with vascular occlusion in an animal model

Objectives

We studied subchondral intraosseous pressure (IOP) in an animal model during loading, and with vascular occlusion. We explored bone compartmentalization by saline injection.

Materials and Methods

Needles were placed in the femoral condyle and proximal tibia of five anaesthetized rabbits and connected to pressure recorders. The limb was loaded with and without proximal vascular occlusion. An additional subject had simultaneous triple recordings at the femoral head, femoral condyle and proximal tibia. In a further subject, saline injections at three sites were carried out in turn.

Results

Loading alone caused a rise in subchondral IOP from 11.7 mmHg (sd 7.1) to 17.9 mmHg (sd 8.1; p < 0.0002). During arterial occlusion, IOP fell to 5.3 mmHg (sd 4.1), then with loading there was a small rise to 7.6 mmHg (sd 4.5; p < 0.002). During venous occlusion, IOP rose to 20.2 mmHg (sd 5.8), and with loading there was a further rise to 26.3 mmHg (sd 6.3; p < 0.003). The effects were present at three different sites along the limb simultaneously. Saline injections showed pressure transmitted throughout the length of the femur but not across the knee joint.

Conclusion

This is the first study to report changes in IOP in vivo during loading and with combinations of vascular occlusion and loading. Intraosseous pressure is not a constant. It is reduced during proximal arterial occlusion and increased with proximal venous occlusion. Whatever the perfusion state, in vivo load is transferred partly by hydraulic pressure. We propose that joints act as hydraulic pressure barriers. An understanding of subchondral physiology may be important in understanding osteoarthritis and other bone diseases.

Cite this article: M. Beverly, S. Mellon, J. A. Kennedy, D. W. Murray. Intraosseous pressure during loading and with vascular occlusion in an animal model. Bone Joint Res 2018;7:511–516. DOI: 10.1302/2046-3758.78.BJR-2017-0343.R2.

Effect of joint mimicking loading system on zonal organization into tissue-engineered cartilage

Cartilage tissue engineering typically involves the combination of a biodegradable polymeric support material with chondrocytes. The culture environment in which cell–material constructs are created and stored is an important factor. The aim of the present study was to investigate the effects of combined stimuli on cartilage zonal organization which is important to maintain cartilage functions such as lubrication and cushion. For that purpose, we developed a joint mimicking loading system which was composed of compression and shear stress. To mimic the joint loading condition, we manufactured a stimuli system that has a device similar to the shape of a femoral condyle in human knee. The fibrin/hyaluronic acid mixture with chondrocytes were dropped into support made of silicon, and placed under the device. The cartilage explants were stimulated with the joint mimicking loading system for 1 hour per day over the course of 4 weeks. The amounts of GAG and collagen in the stimulated tissue were more than that of the static cultured tissue. Cells and collagen were arranged horizontally paralleled to the surface by stimuli, while it did not happen in the control group. The results of this study suggests that mechanical load exerting in the joint play a crucial role in stimulation of extracellular matrix (ECM) production as well as its functional rearrangement.

The relationship of age, activity, and body size on osteoarthritis in weight-bearing skeletal regions

This study examined the simultaneous impact of multiple underlying factors on OA expression in weight-bearing joints of the vertebrae and lower limb of a modern European skeletal sample (Lisbon and Sassari). OA was evaluated using standard ranked categorical scoring; composite OA scores derived through principal component analysis. Body size was calculated from postcranial measurements; torsional strength (J) of the femoral midshaft was calculated from three-dimensional surface models, size standardized and used as a proxy for activity. A standard multiple regression was applied. In all regions, the linear combination of age, body mass, stature, and J was significantly related to differences in OA. Across all joints, age was the strongest predictor; neither body size, nor activity variables demonstrated a statistical relationship with OA at the lumbar or knee; J demonstrated a negative correlation with pelvic OA. Variation in OA can be explained by age, stature, body mass, and structural adaptation related to habitual use. The negative correlation between femoral torsional strength with OA suggests that long-term, repetitive physical work capacity in childhood may be protective against OA development later in life. The multifactorial aetiology of OA requires incorporating multiple lines of evidence to interpret individual or population health from bone samples.

An examination of the relationship between dynamic knee joint stiffness and gait pattern of children with cerebral palsy

Dynamic joint stiffness represents the resistance that a joint opposes to an applied moment. Stiffness arises in conditions of joint laxity, instability and increased co-contraction and is commonly utilized as a means to stabilize the joint. The knee joint seems to be crucial for determining the walking pattern. The aim of this study was to investigate the association between the gait pattern, globally quantified by the Gait Profile Score (GPS), which indicates the 'quality' of a particular walking strategy, and knee dynamic joint stiffness (Kk) in children with diplegia. Kk is expressed by plotting the values of the knee flexion-extension moment versus the knee flexion-extension angle during weight acceptance. In this interval, the linear regression was fitted. The angular coefficient of the linear regression corresponded to the joint stiffness index. Sixty-one children with diplegia and 18 healthy individuals took part in this study. From their gait analysis data, the GPS (with its Gait Variable Scores-GVSs) and the Kk were calculated. Data showed that GPS (p = 2.73 × 10^-21) and GVSs values for the patients with diplegia were higher in comparison to healthy controls. The Kk values for patients were not statistically different from those of controls. The correlation between Kk and GPS did not show the presence of any significant relationship (r = -0.04; p > 0.05). Thus, the functional limitation in diplegic children does not seems to be strictly related to Kk.

Split-Depressed Lateral Tibial Plateau Fractures: A Comparison of Augmented Percutaneous Screws Versus Augmented Plate and Screw Construct in a Cadaveric Model

OBJECTIVES

To compare the strength of fixation of percutaneous screw versus plate/screw fixation in a paired cadaver model of OTA 41-B3 (Schatzker type II) split-depression fractures of the lateral tibial plateau.

METHODS

Six matched pairs of cadaveric knees were acquired. An OTA 41-B3 (Schatzker type II) split-depression fracture was created in all specimens using a standardized method. One specimen from each matched pair of knees was fixed with percutaneous screws, and the other was fixed with a plate/screw construct. All specimens underwent augmentation of the central metaphyseal defect with calcium phosphate. Mean residual displacement (depression) was measured on thin-slice high-resolution computed tomography using a standardized methodology following 3 experimental conditions: (1) after they were fixed, before loading; (2) unloaded cycling (simulating postoperative range of motion exercises); and (3) loaded cycling (simulating postoperative weight-bearing). Load to failure was also compared.

RESULTS

After adjustment for baseline measurements, there was no significant difference in mean residual depression of the lateral tibial plateau between treatments groups after unloaded or loaded cyclic testing. Mean residual depression was less than 1 mm in both the treatment groups. Load to failure was statistically equivalent between treatment groups.

CONCLUSIONS

In our cadaveric study, in combination with calcium phosphate augmentation for both methods, percutaneous screw fixation conferred comparable strength of fixation compared with plate/screw constructs for treatment of OTA 41-B3 (Schatzker type II) tibial plateau fractures.

Shape-memory-alloy-based smart knee spacer for total knee arthroplasty: 3D CAD modelling and a computational study

This study introduced a shape memory alloy (SMA)-based smart knee spacer for total knee arthroplasty (TKA). Subsequently, a 3D CAD model of a smart tibial component of TKA was designed in Solidworks software, and verified using a finite element analysis in ANSYS Workbench. The two major properties of the SMA (NiTi), the pseudoelasticity (PE) and shape memory effect (SME), were exploited, modelled, and analysed for a TKA application. The effectiveness of the proposed model was verified in ANSYS Workbench through the finite element analysis (FEA) of the maximum deformation and equivalent (von Mises) stress distribution. The proposed model was also compared with a polymethylmethacrylate (PMMA)-based spacer for the upper portion of the tibial component for three subjects with body mass index (BMI) of 23.88, 31.09, and 38.39. The proposed SMA -based smart knee spacer contained 96.66978% less deformation with a standard deviation of 0.01738 than that of the corresponding PMMA based counterpart for the same load and flexion angle. Based on the maximum deformation analysis, the PMMA-based spacer had 30 times more permanent deformation than that of the proposed SMA-based spacer for the same load and flexion angle. The SME property of the lower portion of the tibial component for fixation of the spacer at its position was verified by an FEA in ANSYS. Wherein, a strain life-based fatigue analysis was performed and tested for the PE and SME built spacers through the FEA. Therefore, the SMA-based smart knee spacer eliminated the drawbacks of the PMMA-based spacer, including spacer fracture, loosening, dislocation, tilting or translation, and knee subluxation.

Knee Joint Loading in Healthy Adults During Functional Exercises: Implications for Rehabilitation Guidelines

Study Design Controlled laboratory study. Background The inclusion of specific exercises in rehabilitation after knee injury is currently expert based, as a thorough description of the knee contact forces during different exercises is lacking. Objective To quantify knee loading during frequently used activities such as squats, lunges, single-leg hops, walking stairs, standing up, and gait, and to grade knee joint loading during these activities. Methods Three-dimensional motion-analysis data of 15 healthy adults were acquired during 9 standardized activities used in rehabilitation. Experimental motion data were processed using musculoskeletal modeling to calculate contact and shear forces on the different knee compartments (tibiofemoral and patellofemoral). Using repeated-measures analyses of variance, contact and shear forces were compared between compartments and exercises, whereas muscle and average maximum femoral forces were compared only between exercises. Results With the exception of squats, all therapeutic exercises imposed higher forces to the tibiofemoral joint compared to gait. Likewise, patellofemoral forces were greater during all exercises when compared to gait. Greater compartmental contact forces were accompanied by greater compartmental shear forces. Furthermore, force distribution over the medial and lateral compartments varied between exercises. With increased knee flexion, more force was imposed on the posterior portion of the condyles. Conclusion These results suggest that with careful selection of exercises, forces on an injured zone of the joint can be reduced, as the force distribution differs strongly between exercises. Based on the results, a graded exercise program for progressive knee joint loading during rehabilitation can be conceptualized. J Orthop Sports Phys Ther 2018;48(3):162-173. Epub 6 Jan 2018. doi:10.2519/jospt.2018.7459.

Editorial Commentary: Obese and Overweight: Should They Be Concerned About the Long-Term Consequences of a Partial Meniscectomy?

Is obesity associated with inferior outcomes after partial meniscectomies? Recent research using data from the Chondral Lesions and Meniscus Procedures trial could not demonstrate any differences in obese and overweight patients compared with individuals with a normal body mass index. However, the inclusion of multiple confounders, and a short follow-up of only 1 year limit the validity of their study and the results must be viewed with great caution.

A pilot biomechanical assessment of curling deliveries: is toe sliding more likely to cause knee injury than flatfoot sliding?

BACKGROUND

The aim of this study was to determine whether toe sliding is more likely to cause knee injuries than flatfoot sliding in curling.

METHODS

Twelve curlers participated in the study, each delivering 12 stones. Six stones per volunteer were delivered using a flatfoot slide and six were delivered using a toe slide. The Pedar-X in-shoe pressure system recorded the plantar pressure during each of the slides, while a sagittal plane digital video recorded the body position of the curler. Measurements were taken from the video recordings using a software overlay program (MB Ruler), and this, combined with the Pedar-X data, gave the overall joint force in the tuck knee.

RESULTS

The knee joint force for toe sliding was more than double that of flatfoot sliding (p<0.05). There was a strong correlation between the increase in knee joint force and the increase in the moment arm of the ground reaction force. Images produced using the three-dimensional Vicon system confirm that toe sliding produces a larger moment arm than flatfoot sliding.

CONCLUSION

Injuries are more likely to occur in toe sliding, compared with flatfoot sliding, due to the increase in force and moment, pushing the weight of the curler forward over the knee, which could make the adopted position less stable. Curlers might consider avoiding toe sliding to reduce the risk of knee injuries if the two types of delivery could be performed equally well.

Knee function after limb salvage surgery for malignant bone tumor: comparison of megaprosthesis and distal femur allograft with epiphysis sparing

PURPOSE

Limb salvage surgery is increasingly used for the treatment of distal femur bone sarcomas. Total knee replacement using megaprosthesis and epiphysis-sparing biologic reconstruction using an allograft are widely used in order to preserve joint motion. We aimed to compare the results of these procedures using gait analysis in patients undergoing limb salvage surgery.

METHODS

Fifteen patients were included, nine undergoing allograft with epiphysis sparing (Allograft group) and six undergoing megaprosthesis (Megaprosthesis group). Every patient underwent a gait analysis using the Plug-in-Gait protocol. Spatiotemporal parameters, knee kinematics, and kinetics were compared between the two groups and a cohort of ten asymptomatic subjects. Knee function was assessed by the Gait Deviation Index (GDI) and the Gilette Gait Index (GGI).

RESULTS

Both treatment groups showed decreased knee flexion during the loading response phase. Megaprosthesis patients showed a decreased knee flexion all along stance phase. There was no difference in gait pattern between the treatment groups. GDI was significantly lower in Megaprosthesis and Allograft patients when compared to controls (86.4 and 84.3 vs 94, all p < 0.05). This difference was not clinically relevant.

CONCLUSION

Our study reveals that Megaprosthesis and Allograft patients did not show differences in gait patterns and global function. Even though Allograft and Megaprosthesis patients have significant changes in gait pattern, knee function is acceptable with effective gait mechanisms. Changes occur during stance phase and are due to the quadriceps weakness. The particular pattern of gait in Megaprosthesis patients could be a concern for prosthesis wear and should be investigated on this specific aspect.

LEVEL OF EVIDENCE

4.

Evaluation of a Surrogate Contact Model in Force-Dependent Kinematic Simulations of Total Knee Replacement

Knowing the forces in the human body is of great clinical interest and musculoskeletal (MS) models are the most commonly used tool to estimate them in vivo. Unfortunately, the process of computing muscle, joint contact, and ligament forces simultaneously is computationally highly demanding. The goal of this study was to develop a fast surrogate model of the tibiofemoral (TF) contact in a total knee replacement (TKR) model and apply it to force-dependent kinematic (FDK) simulations of activities of daily living (ADLs). Multiple domains were populated with sample points from the reference TKR contact model, based on reference simulations and design-of-experiments. Artificial neural networks (ANN) learned the relationship between TF pose and loads from the medial and lateral sides of the TKR implant. Normal and right-turn gait, rising-from-a-chair, and a squat were simulated using both surrogate and reference contact models. Compared to the reference contact model, the surrogate contact model predicted TF forces with a root-mean-square error (RMSE) lower than 10 N and TF moments lower than 0.3 N·m over all simulated activities. Secondary knee kinematics were predicted with RMSE lower than 0.2 mm and 0.2 deg. Simulations that used the surrogate contact model ran on average three times faster than those using the reference model, allowing the simulation of a full gait cycle in 4.5 min. This modeling approach proved fast and accurate enough to perform extensive parametric analyses, such as simulating subject-specific variations and surgical-related factors in TKR.

The analysis of knee joint loading during drop landing from different heights and under different instruction sets in healthy males

Background

Mechanical loading during exercise has been shown to promote tissue remodeling. Safe and accessible exercise may be beneficial to populations at risk of diminished bone and joint health. We examined the effect of drop height and instruction on knee loading during a drop-landing task and proposed a task that makes use of drop heights that may be appropriate for rehabilitation purposes and functional in daily life to examine transient knee joint loads.

Methods

Twenty males (22.0 ± 2.8 years) performed drop landings from 22 cm (low) and 44 cm (high) heights, each under three instructions: “land naturally” (natural), “softly” (soft), and “stiffly” (stiff). Knee compression force and external flexion moment were estimated using three-dimensional inverse dynamics and normalized to body mass.

Results

Peak knee compression force was larger (p < 0.001) for high (17.8 ± 0.63 N/kg) than low (14.8 ± 0.61 N/kg) heights. There was an increase (p < 0.001) in the knee compression force across soft (11.8 ± 0.40 N/kg), natural (17.0 ± 0.62 N/kg), and stiff (20.2 ± 0.67 N/kg) instructions. Peak knee flexion moment in high-natural (2.12 ± 0.08 Nm/kg) was larger (p < 0.001) than in high-soft (1.88 ± 0.08 Nm/kg), but lower than in high-stiff (2.23 ± 0.08 Nm/kg). No differences in peak knee flexion moment were observed across instructions for the low height.

Conclusions

We propose a drop-landing task that creates a scalable increase in knee compression loading. The absence of increased knee flexion moment with drop from the low height, compared to high, suggests that individuals could perform the task without incremental risk of knee injury. This task could be used in future studies to examine the effect of acute bouts of mechanical loading on bone and cartilage metabolism.

Enhanced mechanical properties of photo-clickable thiol-ene PEG hydrogels through repeated photopolymerization of in-swollen macromer

Current hydrogels used for tissue engineering are limited to a single range of mechanical properties within the replicated tissue construct. We show that repeated in-swelling by a single hydrogel pre-cursor solution into an existing polymerized hydrogel followed by photo-exposure increases hydrogel mechanical properties. The process is demonstrated with a photo-clickable thiol-ene hydrogel using a biocompatible precursor solution of poly(ethylene glycol) dithiol and 8-arm poly(ethylene glycol) functionalized with norbornene. The polymer fraction in the precursor solution was varied by 5, 10, and 20 percent by weight and an off-stoichiometric ratio of thiol : ene was used, leaving free enes available for subsequent reaction. Multiple swelling and exposure cycles for the same precursor solution were performed. The compressive modulus increased by a factor between three and ten (formulation dependent), while volume swelling ratio decreased by a factor of two, consistent with increased crosslink density. The modified hydrogels also demonstrate increased toughness by fracturing at compressive forces five times greater than the initial hydrogel. We attribute the increased toughness to subsequent increases in crosslink density created by the repeated photopolymerization of in-swollen macromer. This technique demonstrates the ability to significantly modify hydrogel network properties by exploiting swelling and polymerization processes that can be applied to traditional three-dimensional printing systems to spatially control local mechanical properties.

Soldier-relevant body borne loads increase knee joint contact force during a run-to-stop maneuver

The purpose of this study was to understand the effects of load carriage on human performance, specifically during a run-to-stop (RTS) task. Using OpenSim analysis tools, knee joint contact force, grounds reaction force, leg stiffness and lower extremity joint angles and moments were determined for nine male military personnel performing a RTS under three load configurations (light, ~6kg, medium, ~20kg, and heavy, ~40kg). Subject-based means for each biomechanical variable were submitted to repeated measures ANOVA to test the effects of load. During the RTS, body borne load significantly increased peak knee joint contact force by 1.2 BW (p<0.001) and peak vertical (p<0.001) and anterior-posterior (p=0.002) ground reaction forces by 0.6 BW and 0.3 BW, respectively. Body borne load also had a significant effect on hip (p=0.026) posture with the medium load and knee (p=0.046) posture with the heavy load. With the heavy load, participants exhibited a substantial, albeit non-significant increase in leg stiffness (p=0.073 and d=0.615). Increases in joint contact force exhibited during the RTS were primarily due to greater GRFs that impact the soldier with each incremental addition of body borne load. The stiff leg, extended knee and large braking force the soldiers exhibited with the heavy load suggests their injury risk may be greatest with that specific load configuration. Further work is needed to determine if the biomechanical profile exhibited with the heavy load configuration translates to unsafe shear forces at the knee joint and consequently, a higher likelihood of injury.

Damage in total knee replacements from mechanical overload

The mechanical loads acting across the knee joint following total knee replacements (TKR) during activities of daily living have recently been measured using instrumented TKRs. Using a series of postmortem retrieved TKR constructs we investigated whether these mechanical loads could result in damage to the implant bone interface or supporting bone in the tibia. Eighteen cemented en bloc tibial components (0 to 22 years in service) were loaded under axial compression in increments from 1 to 10 times body weight and digital image correlation was used to measure bone strain and interface micromotion during loading and unloading. Failure was considered to occur when micromotion exceeded 150µm or compressive bone strain exceeded 7300με. The results show that all retrieved specimens had sufficient bone strength to support most activities of daily living, but ~40% would be at risk under larger physiologic loads that might occur secondary to a higher impacts such as jogging or a stumble. The tray-bone micromotion (regression model R(2)=0.48, p=0.025) was greater for donors with lower age at implantation (p=0.0092). Proximal bone strain (model R(2)=0.46, p=0.03) was greater for donors with longer time in service (p=0.021). Distal bone strain (model R(2)=0.58, p=0.005) was greater for donors with more time in service (p=0.0054) and lower peri-implant BMD (p=0.049). High mechanical overload of a single or repetitive nature may be an initiating factor in aseptic loosening of total joint arthroplasties and should be avoided in order to prolong the life of the implant.

Prediction of medial and lateral contact force of the knee joint during normal and turning gait after total knee replacement

The computational modeling approach has commonly been used to predict knee joint contact forces, muscle forces, and ligament loads during activities of daily living. Knowledge of these forces has several potential applications, for example, within design of equipment to protect the knee joint from injury and to plan adequate rehabilitation protocols, although clinical applications of computational models are still evolving and one of the limiting factors is model validation. The objective of this study was to extend previous modeling technique and to improve the validity of the model prediction using publicly available data set of the fifth "Grand Challenge Competition to Predict In Vivo Knee Loads." A two-stage modeling approach, which combines conventional inverse dynamic analysis (the first stage) with a multi-body subject-specific lower limb model (the second stage), was used to calculate medial and lateral compartment contact forces. The validation was performed by direct comparison of model predictions and experimental measurement of medial and lateral compartment contact forces during normal and turning gait. The model predictions of both medial and lateral contact forces showed strong correlations with experimental measurements in normal gait (r = 0.75 and 0.71) and in turning gait trials (r = 0.86 and 0.72), even though the current technique over-estimated medial compartment contact forces in swing phase. The correlation coefficient, Sprague and Geers metrics, and root mean squared error indicated that the lateral contact forces were predicted better than medial contact forces in comparison with the experimental measurements during both normal and turning gait trials.

Metatarsal Loading During Gait—A Musculoskeletal Analysis

Detailed knowledge of the loading conditions within the human body is essential for the development and optimization of treatments for disorders and injuries of the musculoskeletal system. While loads in the major joints of the lower limb have been the subject of extensive study, relatively little is known about the forces applied to the individual bones of the foot. The objective of this study was to use a detailed musculoskeletal model to compute the loads applied to the metatarsal bones during gait across several healthy subjects. Motion-captured gait trials and computed tomography (CT) foot scans from four healthy subjects were used as the inputs to inverse dynamic simulations that allowed the computation of loads at the metatarsal joints. Low loads in the metatarsophalangeal (MTP) joint were predicted before terminal stance, however, increased to an average peak of 1.9 times body weight (BW) before toe-off in the first metatarsal. At the first tarsometatarsal (TMT) joint, loads of up to 1.0 times BW were seen during the early part of stance, reflecting tension in the ligaments and muscles. These loads subsequently increased to an average peak of 3.0 times BW. Loads in the first ray were higher compared to rays 2–5. The joints were primarily loaded in the longitudinal direction of the bone.

Obesity is associated with higher absolute tibiofemoral contact and muscle forces during gait with and without knee osteoarthritis

BACKGROUND

Obesity is an important risk factor for knee osteoarthritis initiation and progression. However, it is unclear how obesity may directly affect the mechanical loading environment of the knee joint, initiating or progressing joint degeneration. The objective of this study was to investigate the interacting role of obesity and moderate knee osteoarthritis presence on tibiofemoral contact forces and muscle forces within the knee joint during walking gait.

METHODS

Three-dimensional gait analysis was performed on 80 asymptomatic participants and 115 individuals diagnosed with moderate knee osteoarthritis. Each group was divided into three body mass index categories: healthy weight (body mass index<25), overweight (25≤body mass index≤30), and obese (body mass index>30). Tibiofemoral anterior-posterior shear and compressive forces, as well as quadriceps, hamstrings and gastrocnemius muscle forces, were estimated based on a sagittal plane contact force model. Peak contact and muscle forces during gait were compared between groups, as well as the interaction between disease presence and body mass index category, using a two-factor analysis of variance.

FINDINGS

There were significant osteoarthritis effects in peak shear, gastrocnemius and quadriceps forces only when they were normalized to body mass, and there were significant BMI effects in peak shear, compression, gastrocnemius and hamstrings forces only in absolute, non-normalized forces. There was a significant interaction effect in peak quadriceps muscle forces, with higher forces in overweight and obese groups compared to asymptomatic healthy weight participants.

INTERPRETATION

Body mass index was associated with higher absolute tibiofemoral compression and shear forces as well as posterior muscle forces during gait, regardless of moderate osteoarthritis presence or absence. The differences found may contribute to accelerated joint damage with obesity, but with the osteoarthritic knees less able to accommodate the high loads.

Monitoring Healing Progression and Characterizing the Mechanical Environment in Preclinical Models for Bone Tissue Engineering

The treatment of large segmental bone defects remains a significant clinical challenge. Due to limitations surrounding the use of bone grafts, tissue-engineered constructs for the repair of large bone defects could offer an alternative. Before translation of any newly developed tissue engineering (TE) approach to the clinic, efficacy of the treatment must be shown in a validated preclinical large animal model. Currently, biomechanical testing, histology, and microcomputed tomography are performed to assess the quality and quantity of the regenerated bone. However, in vivo monitoring of the progression of healing is seldom performed, which could reveal important information regarding time to restoration of mechanical function and acceleration of regeneration. Furthermore, since the mechanical environment is known to influence bone regeneration, and limb loading of the animals can poorly be controlled, characterizing activity and load history could provide the ability to explain variability in the acquired data sets and potentially outliers based on abnormal loading. Many approaches have been devised to monitor the progression of healing and characterize the mechanical environment in fracture healing studies. In this article, we review previous methods and share results of recent work of our group toward developing and implementing a comprehensive biomechanical monitoring system to study bone regeneration in preclinical TE studies.

Selecting boundary conditions in physiological strain analysis of the femur: Balanced loads, inertia relief method and follower load

Selection of boundary constraints may influence amount and distribution of loads. The purpose of this study is to analyze the potential of inertia relief and follower load to maintain the effects of musculoskeletal loads even under large deflections in patient specific finite element models of intact or fractured bone compared to empiric boundary constraints which have been shown to lead to physiological displacements and surface strains. The goal is to elucidate the use of boundary conditions in strain analyses of bones. Finite element models of the intact femur and a model of clinically relevant fracture stabilization by locking plate fixation were analyzed with normal walking loading conditions for different boundary conditions, specifically re-balanced loading, inertia relief and follower load. Peak principal cortex surface strains for different boundary conditions are consistent (maximum deviation 13.7%) except for inertia relief without force balancing (maximum deviation 108.4%). Influence of follower load on displacements increases with higher deflection in fracture model (from 3% to 7% for force balanced model). For load balanced models, follower load had only minor influence, though the effect increases strongly with higher deflection. Conventional constraints of fixed nodes in space should be carefully reconsidered because their type and position are challenging to justify and for their potential to introduce relevant non-physiological reaction forces. Inertia relief provides an alternative method which yields physiological strain results.

Surrogate modeling of deformable joint contact using artificial neural networks

Deformable joint contact models can be used to estimate loading conditions for cartilage-cartilage, implant-implant, human-orthotic, and foot-ground interactions. However, contact evaluations are often so expensive computationally that they can be prohibitive for simulations or optimizations requiring thousands or even millions of contact evaluations. To overcome this limitation, we developed a novel surrogate contact modeling method based on artificial neural networks (ANNs). The method uses special sampling techniques to gather input-output data points from an original (slow) contact model in multiple domains of input space, where each domain represents a different physical situation likely to be encountered. For each contact force and torque output by the original contact model, a multi-layer feed-forward ANN is defined, trained, and incorporated into a surrogate contact model. As an evaluation problem, we created an ANN-based surrogate contact model of an artificial tibiofemoral joint using over 75,000 evaluations of a fine-grid elastic foundation (EF) contact model. The surrogate contact model computed contact forces and torques about 1000 times faster than a less accurate coarse grid EF contact model. Furthermore, the surrogate contact model was seven times more accurate than the coarse grid EF contact model within the input domain of a walking motion. For larger input domains, the surrogate contact model showed the expected trend of increasing error with increasing domain size. In addition, the surrogate contact model was able to identify out-of-contact situations with high accuracy. Computational contact models created using our proposed ANN approach may remove an important computational bottleneck from musculoskeletal simulations or optimizations incorporating deformable joint contact models.

Synchronization of calcium sulphate cement degradation and new bone formation is improved by external mechanical regulation

A major challenge faced in the bone materials of weight-bearing without internal fixture support is the mismatch of material degradation and new bone formation, leading to weakening or even failure of the overall bony structure. This study demonstrated in the rat femur model that calcium sulphate cement degradation and new bone formation could be better synchronized by external mechanical force. An ascending force in line with calcium sulphate cement degradation could achieve bone healing in 37 days with ultimate load to failure of 87.00 ± 7.30 N, similar to that of intact femur (80.46 ± 2.79 N, p = 0.369). In contrast, the healing process under either a constant force or no force illustrated significant residual defect volumes of 1.47 ± 0.44 and 4.08 ± 0.89 mm(3) (p < 0.001), and weaker ultimate loads to failure of 69.56 ± 4.74 and 59.17 ± 7.48 N, respectively (p < 0.001). Our results suggest that the mechanical regulation approach deserves further investigation and may potentially offer a clinical strategy to improve synchronization.

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.

A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty

Musculoskeletal (MS) models should be able to integrate patient-specific MS architecture and undergo thorough validation prior to their introduction into clinical practice. We present a methodology to develop subject-specific models able to simultaneously predict muscle, ligament, and knee joint contact forces along with secondary knee kinematics. The MS architecture of a generic cadaver-based model was scaled using an advanced morphing technique to the subject-specific morphology of a patient implanted with an instrumented total knee arthroplasty (TKA) available in the fifth “grand challenge competition to predict in vivo knee loads” dataset. We implemented two separate knee models, one employing traditional hinge constraints, which was solved using an inverse dynamics technique, and another one using an 11-degree-of-freedom (DOF) representation of the tibiofemoral (TF) and patellofemoral (PF) joints, which was solved using a combined inverse dynamic and quasi-static analysis, called force-dependent kinematics (FDK). TF joint forces for one gait and one right-turn trial and secondary knee kinematics for one unloaded leg-swing trial were predicted and evaluated using experimental data available in the grand challenge dataset. Total compressive TF contact forces were predicted by both hinge and FDK knee models with a root-mean-square error (RMSE) and a coefficient of determination (R2) smaller than 0.3 body weight (BW) and equal to 0.9 in the gait trial simulation and smaller than 0.4 BW and larger than 0.8 in the right-turn trial simulation, respectively. Total, medial, and lateral TF joint contact force predictions were highly similar, regardless of the type of knee model used. Medial (respectively lateral) TF forces were over- (respectively, under-) predicted with a magnitude error of M < 0.2 (respectively > −0.4) in the gait trial, and under- (respectively, over-) predicted with a magnitude error of M > −0.4 (respectively < 0.3) in the right-turn trial. Secondary knee kinematics from the unloaded leg-swing trial were overall better approximated using the FDK model (average Sprague and Geers' combined error C = 0.06) than when using a hinged knee model (C = 0.34). The proposed modeling approach allows detailed subject-specific scaling and personalization and does not contain any nonphysiological parameters. This modeling framework has potential applications in aiding the clinical decision-making in orthopedics procedures and as a tool for virtual implant design.

Efeitos do método pilates no torque isocinético dos extensores e flexores do joelho: estudo piloto

INTRODUÇÃO: apesar da popularização do método Pilates como forma de exercício físico, os estudos com a técnica ainda não têm explorado os seus efeitos sobre o torque isocinético dos músculos extensores e flexores do joelho.OBJETIVO: verificar os efeitos do método Pilates no torque isocinético dos extensores e flexores do joelho em mulheres jovens.MÉTODOS: 10 voluntárias foram submetidas à avaliação isocinética (60°/s e 300°/s) dos extensores e flexores do joelho, do membro inferior dominante, pré e pós-intervenção com o método Pilates, considerando-se o pico de torque (PT) e o trabalho total (TT). Oito intervenções foram realizadas ao longo de quatro semanas, constando de 28 exercícios de alongamento e fortalecimento para os principais grupos musculares. A análise estatística, utilizando os testes tde Student ou Wilcoxonpara amostras dependentes, foi utilizada (p<0,05).RESULTADOS: os resultados mostraram melhora significativa para a maioria das variáveis observadas, tanto na extensão do joelho (TT 60°/s - 8,98%, p = 0,0166; PT 300°/s - 11,80%, p = 0,0077; TT 300°/s - 19,68%, p = 0,0051), quanto na flexão (PT 60°/s - 11,44%, p = 0,0171; TT 60°/s - 11,55%, p = 0,0395; TT 300°/s - 12,86%, p = 0,0145), com exceção para duas variáveis, uma referente ao movimento de extensão do joelho (PT 60°/s - 3,04%, p = 0,4413) e outra ao movimento de flexão (PT 300°/s - 2,30%, p = 0,3873).CONCLUSÃO: foi possível verificar que oito sessões de Pilates, realizadas ao longo de quatro semanas, proporcionaram melhora significativa do torque isocinético dos músculos extensores e flexores do joelho em mulheres jovens, em relação ao PT e TT (60°/s e 300°/s) para a maioria das variáveis analisadas.

Estimating total knee replacement joint load ratios from kinematics

Accurate prediction of loads acting at the joint in total knee replacement (TKR) patients is key to developing experimental or computational simulations which evaluate implant designs under physiological loading conditions. In vivo joint loads have been measured for a small number of telemetric TKR patients, but in order to assess device performance across the entire patient population, a larger patient cohort is necessary. This study investigates the accuracy of predicting joint loads from joint kinematics. Specifically, the objective of the study was to assess the accuracy of internal-external (I-E) and anterior-posterior (A-P) joint load predictions from I-E and A-P motions under a given compressive load, and to evaluate the repeatability of joint load ratios (I-E torque to compressive force (I-E:C), and A-P force to compressive force (A-P:C)) for a range of compressive loading profiles. A tibiofemoral finite element model was developed and used to simulate deep knee bend, chair-rise and step-up activities for five patients. Root-mean-square (RMS) differences in I-E:C and A-P:C load ratios between telemetric measurements and model predictions were less than 1.10e-3 Nm/N and 0.035 N/N for all activities. I-E:C and A-P:C load ratios were consistently reproduced regardless of the compressive force profile applied (RMS differences less than 0.53e-3 Nm/N and 0.010 N/N, respectively). When error in kinematic measurement was introduced to the model, joint load predictions were forgiving to kinematic measurement error when conformity between femoral and tibial components was low. The prevalence of kinematic data, in conjunction with the analysis presented here, facilitates determining the scope of A-P and I-E joint loading ratios experienced by the TKR population.

Integrating dynamic stereo-radiography and surface-based motion data for subject-specific musculoskeletal dynamic modeling

This manuscript presents a new subject-specific musculoskeletal dynamic modeling approach that integrates high-accuracy dynamic stereo-radiography (DSX) joint kinematics and surface-based full-body motion data. We illustrate this approach by building a model in OpenSim for a patient who participated in a meniscus transplantation efficacy study, incorporating DSX data of the tibiofemoral joint kinematics. We compared this DSX-incorporated (DSXI) model to a default OpenSim model built using surface-measured data alone. The architectures and parameters of the two models were identical, while the differences in (time-averaged) tibiofemoral kinematics were of the order of magnitude of 10° in rotation and 10mm in translation. Model-predicted tibiofemoral compressive forces and knee muscle activations were compared against literature data acquired from instrumented total knee replacement components (Fregly et al., 2012) and the patient's EMG recording. The comparison demonstrated that the incorporation of DSX data improves the veracity of musculoskeletal dynamic modeling.