Computational study on synovial fluid flow behaviour in cartilage contact gap under osteoarthritic condition

Effect of hand-wrist exercises on distal radius fracture healing based on markerless motion capture system

With the internal volar locking plate (VLP) technique emerging as a preferred surgical approach, early post-surgery therapeutic exercises have shown promise in promoting wrist functionality after distal radial fractures (DRFs). The biomechanical microenvironment, particularly the role of biomechanical stimuli, plays a crucial role in guiding stem tissue formation at the fracture site. However, much less is known about how various hand exercises interact with the microenvironment and influence fracture healing outcomes. This study employed the Leap Motion Controller for markerless hand motion capture and utilised an enhanced OpenSim hand model to simulate these motions. An advanced DRF healing model, integrating angiogenesis and the mechano-regulated maturation of callus tissue, was applied to simulate the MSCs differentiation and predict the healing outcomes. The effects of various rehabilitation exercises on DRFs' healing outcomes were systematically analysed. The results showed rehabilitation exercises, such as wrist extension/flexion and ulnar deviation, generally had a higher contact force on the distal radius compared with the slack state. Also, the relationship between contact force and muscle activations was not always linear, reflecting the intricate dynamics of the kinematic system. Exercise could induce changes in the bony bridge and cartilage formation, while angiogenesis remained unaffected. In the initial weeks, gripping exercises proved most beneficial, but as time progressed, extension and flexion exercises became more advantageous. The study highlights the importance of tailoring rehabilitation exercises to the dynamic healing process of DRFs. As the healing trajectory progresses, the therapeutic efficacy of specific exercises evolves, necessitating adaptive and patient-specific rehabilitation programs.

Tibial and femoral articular cartilage exhibit opposite outcomes for T1ρ and T2* relaxation times in response to acute compressive loading in healthy knees

Abnormal loading is thought to play a key role in the disease progression of cartilage, but our understanding of how cartilage compositional measurements respond to acute compressive loading in-vivo is limited. Ten healthy subjects were scanned at two timepoints (7 ± 3 days apart) with a 3 T magnetic resonance imaging (MRI) scanner. Scanning sessions included T1ρ and T2* acquisitions of each knee in two conditions: unloaded (traditional MRI setup) and loaded in compression at 40 % bodyweight as applied by an MRI-compatible loading device. T1ρ and T2* parameters were quantified for contacting cartilage (tibial and femoral) and non-contacting cartilage (posterior femoral condyle) regions. Significant effects of load were found in contacting regions for both T1ρ and T2*. The effect of load (loaded minus unloaded) in femoral contacting regions ranged from 4.1 to 6.9 ms for T1ρ, and 3.5 to 13.7 ms for T2*, whereas tibial contacting regions ranged from -5.6 to -1.7 ms for T1ρ, and -2.1 to 0.7 ms for T2*. Notably, the responses to load in the femoral and tibial cartilage revealed opposite effects. No significant differences were found in response to load between the two visits. This is the first study that analyzed the effects of acute loading on T1ρ and T2* measurements in human femoral and tibial cartilage separately. The results suggest the effect of acute compressive loading on T1ρ and T2* was: 1) opposite in the femoral and tibial cartilage; 2) larger in contacting regions than in non-contacting regions of the femoral cartilage; and 3) not different visit-to-visit.

Effect of uncertain clinical conditions on the early healing and stability of distal radius fractures

BACKGROUND AND OBJECTIVES

The healing outcomes of distal radius fracture (DRF) treated with the volar locking plate (VLP) depend on surgical strategies and postoperative rehabilitation. However, the accurate prediction of healing outcomes is challenging due to a range of certainties related to the clinical conditions of DRF patients, including fracture geometry, fixation configuration, and physiological loading. The purpose of this study is to investigate the influence of uncertainty and variability in fracture/fixation parameters on the mechano-biology and biomechanical stability of DRF, using a probabilistic numerical approach based on the results from a series of experimental tests performed in this study.

METHODS

Six composite radius sawboneses fitted with titanium VLP (VLP 2.0, Austofix) were loaded to failure at a rate of 2 N/s. The testing results of the elastic and plastic behaviour of the VLP were used as inputs for a probabilistic-based computational model of DRF, which simulated mechano-regulated tissue differentiation and fixation elastic capacity at the fracture site. Finally, the probability of success in early indirect healing and fracture stabilisation was predicted.

RESULTS

The titanium VLP is a strong and ductile fixation whose flexibility and elastic capacity are governed by flexion working length and bone-to-plate distance, respectively. A fixation with optimised designs and configurations is critical to mechanically stabilising the early fracture site. Importantly, the uncertainty and variability in fracture/fixation parameters could compromise early DRF healing. The physiological loading uncertainty is the most adverse factor, followed by the negative impact of uncertainty in fracture geometry.

CONCLUSIONS

The VRP 2.0 fixation made of grade II titanium is a desirable fixation that is strong enough to resist irreparable deformation during early recovery and is also ductile to deform plastically without implant failure at late rehabilitation.

Depth camera-based model for studying the effects of muscle loading on distal radius fracture healing

BACKGROUND

Distal radius fractures (DRFs) treated with volar locking plates (VLPs) allows early rehabilitation exercises favourable to fracture recovery. However, the role of rehabilitation exercises induced muscle forces on the biomechanical microenvironment at the fracture site remains to be fully explored. The purpose of this study is to investigate the effects of muscle forces on DRF healing by developing a depth camera-based fracture healing model.

METHOD

First, the rehabilitation-related hand motions were captured by a depth camera system. A macro-musculoskeletal model is then developed to analyse the data captured by the system for estimating hand muscle and joint reaction forces which are used as inputs for our previously developed DRF model to predict the tissue differentiation patterns at the fracture site. Finally, the effect of different wrist motions (e.g., from 60° of extension to 60° of flexion) on the DRF healing outcomes will be studied.

RESULTS

Muscle and joint reaction forces in hands which are highly dependent on hand motions could significantly affect DRF healing through imposed compressive and bending forces at the fracture site. There is an optimal range of wrist motion (i.e., between 40° of extension and 40° of flexion) which could promote mechanical stimuli governed healing while mitigating the risk of bony non-union due to excessive movement at the fracture site.

CONCLUSION

The developed depth camera-based fracture healing model can accurately predict the influence of muscle loading induced by rehabilitation exercises in distal radius fracture healing outcomes. The outcomes from this study could potentially assist osteopathic surgeons in designing effective post-operative rehabilitation strategies for DRF patients.

Development of numerical model-based machine learning algorithms for different healing stages of distal radius fracture healing

BACKGROUND AND OBJECTIVES

Early therapeutic exercises are vital for the healing of distal radius fractures (DRFs) treated with the volar locking plate. However, current development of rehabilitation plans using computational simulation is normally time-consuming and requires high computational power. Thus, there is a clear need for developing machine learning (ML) based algorithms that are easy for end-users to implement in daily clinical practice. The purpose of the present study is to develop optimal ML algorithms for designing effective DRF physiotherapy programs at different stages of healing.

METHOD

First, a three-dimensional computational model for the healing of DRF was developed by integrating mechano-regulated cell differentiation, tissue formation and angiogenesis. The model is capable of predicting time-dependant healing outcomes based on different physiologically relevant loading conditions, fracture geometries, gap sizes, and healing time. After being validated using available clinical data, the developed computational model was implemented to generate a total of 3600 clinical data for training the ML models. Finally, the optimal ML algorithm for each healing stage was identified.

RESULTS

The selection of the optimal ML algorithm depends on the healing stage. The results from this study show that cubic support vector machine (SVM) has the best performance in predicting the healing outcomes at the early stage of healing, while trilayered ANN outperforms other ML algorithms in the late stage of healing. The outcomes from the developed optimal ML algorithms indicate that Smith fractures with medium gap sizes could enhance the healing of DRF by inducing larger cartilaginous callus, while Colles fractures with large gap sizes may lead to delayed healing by bringing excessive fibrous tissues.

CONCLUSIONS

ML represents a promising approach for developing efficient and effective patient-specific rehabilitation strategies. However, ML algorithms at different healing stages need to be carefully chosen before being implemented in clinical applications.

Full Regional Creep Displacement Map of Articular Cartilage Based on Nanoindentation Array

The elucidation of the mechanisms underlying articular cartilage lesions poses a formidable challenge in the field of cartilage repair. Despite significant strides in cartilage mechanics research, the region-dependent creep properties of articular cartilage remain elusive. In this study, we employ depth-sensing indentation tests to experimentally determine the creep properties of four distinct regions of articular cartilage, thereby unveiling a region-dependent full map of creep parameters. The measured creep displacement-time response curves indicate that the creep properties of the articular cartilage exhibit a clear regional correlation. Accordingly, the full regional creep map of articular cartilage is experimentally constructed for the first time. The correlation between the microstructures and the creep properties of cartilage in different regions is revealed. A three-parameter model is established to describe the creep velocity-displacement response of cartilage. Raman spectra reveal that the proteoglycan content is positively correlated with creep properties. The Raman shift directly indicates diverse residual stresses in different microregions. The obtained data facilitate a deep understanding of the potential creep dependent damage mechanism of cartilage and the further development of artificial cartilage materials.

Computational Modelling for Managing Pathways to Cartilage Failure

Over several decades the perception and therefore description of articular cartilage changed substantially. It has transitioned from being described as a relatively inert tissue with limited repair capacity, to a tissue undergoing continuous maintenance and even adaption, through a range of complex regulatory processes. Even from the narrower lens of biomechanics, the engagement with articular cartilage has changed from it being an interesting, slippery material found in the hostile mechanical environment between opposing long bones, to an intriguing example of mechanobiology in action. The progress revealing this complexity, where physics, chemistry, material science and biology are merging, has been described with increasingly sophisticated computational models. Here we describe how these computational models of cartilage as an integrated system can be combined with the approach of structural reliability analysis. That is, causal, deterministic models placed in the framework of the probabilistic approach of structural reliability analysis could be used to understand, predict, and mitigate the risk of cartilage failure or pathology. At the heart of this approach is seeing cartilage overuse and disease processes as a 'material failure', resulting in failure to perform its function, which is largely mechanical. One can then describe pathways to failure, for example, how homeostatic repair processes can be overwhelmed leading to a compromised tissue. To illustrate this 'pathways to failure' approach, we use the interplay between cartilage consolidation and lubrication to analyse the increase in expected wear rates associated with cartilage defects or meniscectomy.

Modelling articular cartilage: the relative motion of two adjacent poroviscoelastic layers

In skeletal joints two layers of adjacent cartilage are often in relative motion. The individual cartilage layers are often modelled as a poroviscoelastic material. To model the relative motion, noting the separation of scales between the pore level and the macroscale, a homogenization based on multiple scale asymptotic analysis has been used in this study to derive a macroscale model for the relative translation of two poroviscoelastic layers separated by a very thin layer of fluid. In particular the fluid layer thickness is essentially zero at the macroscale so that the two poroviscoelastic layers are effectively in contact and their interaction is captured in the derived model via a set of interfacial conditions, including a generalization of the Beavers-Joseph condition at the interface between a viscous fluid and a porous medium. In the simplifying context of a uniform geometry, constant fixed charge density, a Newtonian interstitial fluid and a viscoelastic scaffold, modelled via finite deformation theory, we present preliminary simulations that may be used to highlight predictions for how oscillatory relative movement of cartilage under load influences the peak force the cartilage experiences and the extent of the associated deformations. In addition to highlighting such cartilage mechanics, the systematic derivation of the macroscale models will enable the study of how nanoscale cartilage physics, such as the swelling pressure induced by fixed charges, manifests in cartilage mechanics at much higher lengthscales.

Influence of therapeutic grip exercises induced loading rates in distal radius fracture healing with volar locking plate fixation

BACKGROUND AND OBJECTIVE

Therapeutic exercises could potentially enhance the healing of distal radius fractures (DRFs) treated with volar locking plate (VLP). However, the healing outcomes are highly dependant on the patient-specific fracture geometries (e.g., gap size) and the loading conditions at the fracture site (e.g., loading frequency) resulted from different types of therapeutic exercises. The purpose of this study is to investigate the effects of different loading frequencies induced by therapeutic exercises on the biomechanical microenvironment of the fracture site and the transport of cells and growth factors within the fracture callus, ultimately the healing outcomes. This is achieved through numerical modelling and mechanical testing.

METHODS

Five radius sawbones specimens (Pacific Research Laboratories, Vashon, USA) fixed with VLP (VRP2.0+, Austofix) were mechanically tested using dynamic test instrument (INSTRON E3000, Norwood, MA). The loading protocol used in mechanical testing involved a series of cyclic axial compression tests representing hand and finger therapeutic exercises. The relationship between the dynamic loading rate (i.e., loading frequency) and dynamic stiffness of the construct was established and used as inputs to a developed numerical model for studying the dynamic loading induced cells and growth factors in fracture site and biomechanical stimuli required for healing.

RESULTS

There is a strong positive linear relationship between the loading rate and axial stiffness of the construct fixed with VLP. The loading rates induced by the moderate frequencies (i.e., 1-2 Hz) could promote endochondral ossification, whereas relatively high loading frequencies (i.e., over 3 Hz) may hinder the healing outcomes or lead to non-union. In addition, a dynamic loading frequency of 2 Hz in combination of a fracture gap size of 3 mm could produce a better healing outcome by enhancing the transport of cells and growth factors at the fracture site in comparison to free diffusion (i.e. without loading), and thereby produces a biomechanical microenvironment which is favourable for healing.

CONCLUSION

The experimentally validated numerical model presented in this study could potentially contribute to the design of effective patient-specific therapeutic exercises for better healing outcomes. Importantly, the model results demonstrate that therapeutic grip exercises induced dynamic loading could produce a better biomechanical microenvironment for healing without compromising the mechanical stability of the overall volar locking plate fixation construct.

The modes and competing rates of cartilage fluid loss and recovery

Cartilage loses, recovers, and maintains its thickness, hydration, and biomechanical functions based on competing rates of fluid loss and recovery under varying joint-use conditions. While the mechanics and implications of load-induced fluid loss have been studied extensively, those of fluid recovery have not. This study isolates, quantifies, and compares rates of cartilage recovery from three known modes: (1) passive swelling - fluid recovery within a static unloaded contact area; (2) free swelling - unrestricted fluid recovery by an exposed surface; (3) tribological rehydration - fluid recovery within a loaded contact area during sliding. Following static loading of adult bovine articular cartilage to between 100 and 500 μm of compression, passive swelling, free swelling, and tribological rehydration exhibited average rates of 0.11 ± 0.04, 0.71 ± 0.15, and 0.63 ± 0.22 μm/s, respectively, over the first 100 s of recovery; for comparison, the mean exudation rate just prior to sliding was 0.06 ± 0.04 μm/s. For this range of compressions, we detected no significant difference between free swelling and tribological rehydration rates. However, free swelling and tribological rehydration rates, those associated with joint articulation, were ∼7-fold faster than passive swelling rates. While previous studies show how joint articulation prevents fluid loss indefinitely, this study shows that joint articulation reverses fluid loss following static loading at >10-fold the preceding exudation rate. These competitive recovery rates suggest that joint space and function may be best maintained throughout an otherwise sedentary day using brief but regular physical activity. STATEMENT OF SIGNIFICANCE: Cartilage loses, recovers, and maintains its thickness, hydration, and biomechanical functions based on competing rates of fluid loss and recovery under varying joint-use conditions. While load-induced fluid loss is extremely well studied, this is the first to define the competing modes of fluid recovery and to quantify their rates. The results show that the fluid recovery modes associated with joint articulation are 10-fold faster than exudation during static loading and passive swelling during static unloading. The results suggest that joint space and function are best maintained throughout an otherwise sedentary day using brief but regular physical activities.

Post-traumatic Osteoarthritis in Rabbits Following Traumatic Injury and Surgical Reconstruction of the Knee

Post-traumatic osteoarthritis (PTOA) of the knee is often attributed to anterior cruciate ligament (ACL) and meniscus injury. The development of PTOA, however, does not seem to depend on whether or not the damaged ACL is reconstructed. There has been a need to develop animal models to study the mechanisms of PTOA following reconstruction of a traumatized knee. Eighteen rabbits underwent closed-joint trauma to produce ACL rupture and meniscus damage. Then, for the first time, the traumatized knee was surgically repaired in this animal model. Upon euthanasia at 1-, 3- or 6-month post-trauma, joint stability, cartilage morphology and mechanical properties, as well as histology of the cartilage and subchondral bone were evaluated. Trauma-induced knee injury involved 72% mid-substance ACL rupture, 28% partial ACL tear and 56% concurrent medial meniscal damage. ACL reconstruction effectively restored joint stability by reducing joint laxity to a level similar to that in the contralateral intact knee. Compared to their contralateral controls, reconstructed limbs showed osteoarthritic changes to the cartilage and subchondral bone as early as 1-month post-trauma. The degeneration progressed over time up to 6-month. Overall, the medial compartments had more tissue damage than their corresponding lateral counterparts. Damage patterns to the ACL, the frequency of observed concurrent meniscal injury, and reductions in cartilage integrity and health were consistent with clinical observations of human patients who undergo ACL injury and reconstruction. Thus, we believe the combined closed-joint injury and surgical repair lapine model of PTOA, being first-ever and clinically relevant, shows promise to evaluate well-targeted therapeutics and other interventions for this chronic disease.

Sodium hyaluronate-g-2-((N-(6-aminohexyl)-4-methoxyphenyl)sulfonamido)-N-hydroxyacetamide with enhanced affinity towards MMP12 catalytic domain to be used as visco-supplement with increased degradation resistance

The present paper describes the functionalization of sodium hyaluronate (NaHA) with a small molecule (2-((N-(6-aminohexyl)-4-methoxyphenyl)sulfonamido)-N-hydroxyacetamide) (MMPI) having proven inhibitory activity against membrane metalloproteins involved in inflammatory processes (i.e. MMP12). The obtained derivative (HA-MMPI) demonstrated an increased resistance to the in-vitro degradation by hyaluronidase, viscoelastic properties close to those of healthy human synovial fluid, cytocompatibility towards human chondrocytes and nanomolar affinity towards MMP 12. Thus, HA-MMPI can be considered a good candidate as viscosupplement in the treatment of knee osteoarticular disease.

Rheological Properties and Its Effect on the Lubrication Mechanism of PVP K30 and PVP 40-50 G as Artificial Synovial Fluids

The effect of polyvinylpyrrolidone (PVP) on the rheological properties of joint prostheses is still unclear, despite its good lubricity and biocompatibility. In the present work, PVP K30 and PVP 40-50 G solutions at different concentrations were analyzed for rheological and lubrication properties. The rheological properties of the samples were measured at a shear rate range of 0–1800 s−1 (advanced air bearing rheometer Bohlin Gemini 2 and Plate MCR 72/92 rheometer for PVP30 and PVP 40-50 G, respectively). It was found that both the viscosity and shear stress of the samples reduced with a shear rate increase. PVP 40-50 G/sterile water showed higher viscosity as compared to the PVP K30/sterile water sample at a lower shear rate. However, at a higher shear rate, the PVP K30 sample produced better results. Further numerical study results showed the pressure and molecular viscosity distributions. The inclusion of PVP improved the load caring capacity and hence, it is a promising lubrication additive for artificial joints.

A Probabilistic Failure Risk Approach to The Problem of Articular Cartilage Lubrication

BACKGROUND AND OBJECTIVE

The geometrical and mechanical properties that characterise the cartilage contact gap are uncertain and spatially varied. To date the effects of such uncertainties on cartilage lubrication have not been explored. Using a probabilistic approach, the purpose of this study is to numerically investigate the influence of surficial cartilage glycoaminoglycan (GAG) content on joint lubrication behaviour. Gap asperity stiffness and polymer brush border (PBB) thickness are affected by the uncertainty of surficial GAG concentration, and so their correlated effects in maintaining hydrodynamic joint lubrication are investigated.

METHODS

Correlated sampling data are first generated by Monte Carlo simulation. These data are used as inputs for the cartilage contact model, which includes three distinctive features of cartilage tissue (tension-compression nonlinearity, aggrecan dependent permeability and compressive modulus) and fluid flow resistance effects of PBB on cartilage surface. The degree of hydrodynamic lubrication after thirty minutes of constant loading is used as an indicator for assessing the lubrication performance at the contact interface.

RESULTS

The increase of PBB thickness with GAG concentration enhances the hydrodynamic lubrication component in the cartilage contact gap, whereas increasing the asperity stiffness with GAG concentration impairs hydrodynamic lubrication. GAG loss rate increases with the rise of GAG concentration. More aggrecan shedding through the surface could result in a thicker and denser PBB, and therefore enhance the lubrication performance in mixed-mode regime. On the other hand, higher GAG content makes the asperities stiffer, which may impede contact gap closure, and thus encourage gap fluid loss and impair the lubrication performance of cartilage.

CONCLUSION

The lubrication performance of cartilage varies with the physiological conditions of the joint. Since a range of variables are internally related, the outcomes on joint lubrication are difficult to predict. A probabilistic approach accounting for the uncertainties can potentially result in more accurate evaluations of joint lubrication performance.