Computational modelling of bone fracture healing under partial weight-bearing exercise

Biomechanical effects of muscle loading on early healing of femoral stem fractures: a combined musculoskeletal dynamics and finite element approach

Femoral stem fractures (FST) are often accompanied by muscle injuries, however, what muscle injuries affect fracture healing and to what extent is unknown. The purpose of this study was to analyze the extent to which different muscles affect FST healing through a combined musculoskeletal dynamics and finite element approach. Modeling the lower extremity musculoskeletal system for 12 different muscle comprehensives. Muscle and joint reaction forces on the femur were calculated and these data were used as boundary conditions input to the FSTs model to predict the degree of muscle influence on fracture healing. Finally, we will investigate the extent to which muscle influences FST healing during knee flexion. Muscle and joint forces are highly dependent on joint motion and have a significant biomechanical influence on interfragmentary strain (IFS) healing. The psoas major (PM), gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles play a major role in standing, with GM > PM > GL, whereas the gluteus medius posterior (GMP), vastus intermedius (VI), vastus medialis (VM), vastus lateralis superior (VLS), and adductor magnus distalis (AMD) muscles play a major role in knee flexion, with VLS > VM > VI > AMD > GMP. Mechanical stimulus-controlled healing can be facilitated when the knee joint is flexed less than 20°. Different muscles exert varying degrees of influence on the healing of fractures. Therefore, comprehending the impact of particular muscles on fracture site tissue FST healing can aid orthopedic surgeons in formulating improved surgical and rehabilitation strategies.

Improved weight bearing during gait at 6 weeks post-surgery with an angle stable locking system after distal tibial fracture

BACKGROUND

Functional recovery after intramedullary nailing of distal tibial fractures can be monitored using ipsilateral vertical ground reaction forces (vGRF), giving insight into recovery of patients' gait symmetry. Previous work compared patient cohorts to healthy controls, but it remains unclear if these metrics can identify treatment-based differences in return to function post-surgery.

RESEARCH QUESTION

Is treatment of a distal tibial fracture with intramedullary nailing with an angle stable locking system (ASLS) associated with higher ipsilateral vGRF and improved symmetry compared to conventional intramedullary nailing at an early time point?

METHODS

Thirty-nine patients treated with ASLS intramedullary nailing were retrospectively compared to thirty-nine patients with conventional locking. vGRFs were collected at 1, 6, 12, 26, and 52 weeks post-surgery during standing and gait. Discrete metrics of ipsilateral vGRF (maximal force, impulse) and asymmetry were compared between treatments at each time point. Time-scale comparisons of ipsilateral vGRF and lower limb asymmetry were additionally performed for gait trials. Mann-Whitney Test or a two-way analysis of variance tested discrete comparisons; statistical non-parametric mapping tested time-scale data between treatment groups.

RESULTS

During gait, ASLS-treated patients applied more load on the operated limb (17-38% stance, p = 0.015) and consequently loaded limbs more symmetrically (8-37% stance, p = 0.008) during the loading response at 6 weeks post-surgery compared to conventional IM treatment. Discrete measures of symmetry at the same time point identified treatment-based differences in maximal force (p = 0.039) and impulse (p = 0.012), with ASLS-treated patients exhibiting more symmetry. No differences were identified in gait trials at later time points nor from all standing trials.

SIGNIFICANCE

During the initial loading response of gait, increased ipsilateral vGRF and improved weightbearing symmetry were identified in ASLS patients at 6 weeks post-surgery compared to conventional IM nailing. Early and objective metrics of dynamic movement are suggested to identify treatment-based differences in functional recovery.

Influence of knee flexion on early femoral fracture healing: A combined analysis of musculoskeletal dynamics and finite elements

BACKGROUND AND OBJECTIVES

Knee flexion causes a certain amount of misalignment and relative movement of the fractured ends of the femur fracture, and if the flexion angle is too large it will affect the stability of the fracture and the healing process, making it challenging to design a safe range of flexion. However, due to a lack of basic understanding of the effect of knee flexion on the mechanical environment at the fracture site, clinicians are often unable to provide an objective and safe range of motion in flexion based on subjective experience. The aim of this study was to evaluate the effect of knee flexion on plate and fracture healing using finite element analysis (FEA).

METHODS

A human musculoskeletal model was constructed based on CT scan data, and the mechanical properties of the fracture site were changed by adjusting the knee flexion angle. The joint forces, muscle forces and moments acting on the femur were obtained by inverse dynamics analysis, and the biomechanical properties of the fracture-plate system were analyzed using finite elements. A finite element model of the fracture-plate system without muscle loading was also constructed. The effect of knee flexion on the safety of plate fixation and fracture healing was evaluated in terms of the biomechanical properties of the plate and the interfragmentary motion of the fracture.

RESULTS

As the knee flexion angle increases, the von Mises stress of the locked compression plate (LCP) first increases, then decreases, then increases again. The deformation from compression bending to tension twisting occurs simultaneously. At 30° of flexion, shear interfragmentary motion (SIM) was dominant and inhibited fracture healing; at more than 45° of flexion, the plate was twisted and deformed to the lateral side of the body, and the fracture site underwent greater misalignment and relative motion, with destructive effects on bone scabs and healing tissues. If muscle loading is not taken into account, the plate will undergo predominantly bending deformation and will overestimate the interfragmentary strain in the far and near cortex.

CONCLUSIONS

Knee flexion causes the plate to deform from compression bending to extension and torsion, which has an important impact on the safety and healing process of the fracture, and this study provides a biomechanical basis to guide the clinician in the post-operative rehabilitation of femoral fractures in the clinical setting.

Influence of muscle loading on early-stage bone fracture healing

Designing weight-bearing exercises for patients with lower-limb bone fractures is challenging and requires a systematic approach that accounts for patient-specific loading conditions. However, 'trial-and-error' approaches are commonplace in clinical settings due to the lack of a fundamental understanding of the effect of weight-bearing exercises on the bone healing process. Whilst computational modelling has the potential to assist clinicians in designing effective patient-specific weight-bearing exercises, current models do not explicitly account for the effects of muscle loading, which could play an important role in mediating the mechanical microenvironment of a fracture site. We combined a fracture healing model involving a tibial fracture stabilised with a locking compression plate (LCP) with a detailed musculoskeletal model of the lower limb to determine interfragmentary strains in the vicinity of the fracture site during both full weight-bearing (100% body weight) and partial weight-bearing (50% body weight) standing. We found that muscle loading significantly altered model predictions of interfragmentary strains. For a fractured bone with a standard LCP configuration (bone-plate distance = 2 mm, working length = 30 mm) subject to full weight-bearing, the predicted strains at the near and far cortices were 23% and 11% higher when muscle loading was included compared to the case when muscle loading was omitted. The knee and ankle muscles accounted for 38% of the contact force exerted at the knee joint during quiet standing and contributed significantly to the strains calculated at the fracture site. Thus, models of bone fracture healing ought to account explicitly for the effects of muscle loading. Furthermore, the study indicated that LCP configuration parameters play a crucial role in influencing the fracture site microenvironment. The results highlighted the dominance of working length over bone-plate distance in controlling the flexibility of fracture sites stabilised with LCP devices.

Bone Ingrowth Around an Uncemented Femoral Implant Using Mechanoregulatory Algorithm: A Multiscale Finite Element Analysis

The primary fixation and long-term stability of a cementless femoral implant depend on bone ingrowth within the porous coating. Although attempts were made to quantify the peri-implant bone ingrowth using the finite element (FE) analysis and mechanoregulatory principles, the tissue differentiation patterns on a porous-coated hip stem have scarcely been investigated. The objective of this study is to predict the spatial distribution of evolutionary bone ingrowth around an uncemented hip stem, using a three-dimensional (3D) multiscale mechanobiology-based numerical framework. Multiple load cases representing a variety of daily living activities, including walking, stair climbing, sitting down, and standing up from a chair, were used as applied loading conditions. The study accounted for the local variations in host bone material properties and implant-bone relative displacements of the macroscale implanted FE model, in order to predict bone ingrowth in microscale representative volume elements (RVEs) of 12 interfacial regions. In majority RVEs, 20-70% bone tissue (immature and mature) was predicted after 2 months, contributing toward a progressive increase in average Young's modulus (1200-3000 MPa) of the interbead tissue layer. Higher bone ingrowth (mostly greater than 60%) was predicted in the anterolateral regions of the implant, as compared to the posteromedial side (20-50%). New bone tissue was formed deeper inside the interbead spacing, adhering to the implant surface. The study helps to gain an insight into the degree of osseointegration of a porous-coated femoral implant.

Numerical Modeling of Shockwave Treatment of Knee Joint

Arthritis is a degenerative disease that primarily affects the cartilage and meniscus of the knee joint. External acoustic stimulation is used to treat this disease. This article presents a numerical model of the knee joint aimed at the computer-aided study of the regenerative effects of shockwave treatment. The presented model was verified and validated. A numerical analysis of the conditions for the regeneration of the tissues of the knee joint under shockwave action was conducted. The results allow us to conclude that to obtain the conditions required for the regeneration of cartilage tissues and meniscus (compressive stresses above the threshold value of 0.15 MPa to start the process of chondrogenesis; distortional strains above the threshold value of 0.05% characterized by the beginning of the differentiation of the tissues in large volumes; fluid pressure corresponding to the optimal level of 68 kPa to transfer tissue cells in large volumes), the energy flux density of therapeutic shockwave loading should exceed 0.3 mJ/mm².

Balance Between Mechanical Stability and Mechano-Biology of Fracture Healing Under Volar Locking Plate

The application of volar locking plate (VLP) is promising in the treatment of dorsally comminuted and displaced fracture. However, the optimal balance between the mechanical stability of VLP and the mechanobiology at the fracture site is still unclear. The purpose of this study is to develop numerical models in conjunction with experimental studies to identify the favourable mechanical microenvironment for indirect healing, by optimizing VLP configuration and post-operative loadings for different fracture geometries. The simulation results show that the mechanical behaviour of VLP is mainly governed by the axial compression. In addition, the model shows that, under relatively large gap size (i.e., 3-5 mm), the increase of FWL could enhance chondrocyte differentiation while a large BPD could compromise the mechanical stability of VLP. Importantly, bending moment produced by wrist flexion/extension and torsion moment produced from forearm rotation could potentially hinder endochondral ossification at early stage of healing. The developed model could potentially assist orthopaedic surgeons in surgical pre-planning and designing post-operation physical therapy for treatment of distal radius fractures.

Optimal time-dependent levels of weight-bearing for bone fracture healing under Ilizarov circular fixators

It is known that weight-bearing exercises under Ilizarov circular fixators (ICF) could enhance bone fracture healing by mechano-regulation. However, interfragmentary movements at the fracture site induced by weight-bearing may inhibit angiogenesis and ultimately delay the healing process. To tackle this challenge, a computational model is presented in this study which considers the spatial and temporal changes in mechanical properties of fracture callus to predict optimal levels of weight-bearing during fracture healing under ICF. The study takes sheep fractures as example and shows that the developed model has the capability of predicting patient specific, time-dependent optimal levels of weight-bearing which enhances mechano-regulation mediated healing without hindering the angiogenesis process. The results demonstrate that allowable level of weight-bearing and timings depend on fracture gap size. For normal body weights (BW) and moderate fracture gap sizes (e.g. 3 mm), weight-bearing with 30% BW could start by week 4 post-operation and gradually increase to 100% BW by week 11. In contrast, for relatively large fracture gap sizes (i.e. 6 mm), weight-bearing is recommended to commence in later stages of healing (e.g. week 11 post-operation). Furthermore, increasing ICF stiffness (e.g. using half pins instead of pretension wires) can increase the level of weight-bearing significantly in the early stages up to a certain time point (e.g. week 8 post-operation) beyond which no noticeable benefits could be achieved. The findings of this study have potential applications in designing post-operative weight bearing exercises.

Biohybrid Bovine Bone Matrix for Controlled Release of Mesenchymal Stem/Stromal Cell Lyosecretome: A Device for Bone Regeneration

SmartBone® (SB) is a biohybrid bone substitute advantageously proposed as a class III medical device for bone regeneration in reconstructive surgeries (oral, maxillofacial, orthopedic, and oncology). In the present study, a new strategy to improve SB osteoinductivity was developed. SB scaffolds were loaded with lyosecretome, a freeze-dried formulation of mesenchymal stem cell (MSC)-secretome, containing proteins and extracellular vesicles (EVs). Lyosecretome-loaded SB scaffolds (SBlyo) were prepared using an absorption method. A burst release of proteins and EVs (38% and 50% after 30 min, respectively) was observed, and then proteins were released more slowly with respect to EVs, most likely because they more strongly adsorbed onto the SB surface. In vitro tests were conducted using adipose tissue-derived stromal vascular fraction (SVF) plated on SB or SBlyo. After 14 days, significant cell proliferation improvement was observed on SBlyo with respect to SB, where cells filled the cavities between the native trabeculae. On SB, on the other hand, the process was still present, but tissue formation was less organized at 60 days. On both scaffolds, cells differentiated into osteoblasts and were able to mineralize after 60 days. Nonetheless, SBlyo showed a higher expression of osteoblast markers and a higher quantity of newly formed trabeculae than SB alone. The quantification analysis of the newly formed mineralized tissue and the immunohistochemical studies demonstrated that SBlyo induces bone formation more effectively. This osteoinductive effect is likely due to the osteogenic factors present in the lyosecretome, such as fibronectin, alpha-2-macroglobulin, apolipoprotein A, and TGF-β.

The Effect of High-Intensity Intermittent Training on the Acute Gait Plantar Pressure in Healthy Young Adults

High-intensity intermittent training (HIIT) has been successfully applied in various sports activities, as HIIT was considered as one of the most efficient training methods of exercise for improving physical performance and reducing the weight of overweight individuals. However, its acute effects of HIIT on gait and balance performance were not addressed. Thus, in this study we examined the acute effects of HIIT on dynamic postural control compared with steady-state training (SST) by analyzing plantar pressure parameters. In this study, sixteen healthy male adults were examined in 3 days. After exhaustive ramp-like cycle ergometer testing, the maximal heart rate (HRmax) of each participant was determined on the first day, then either a 20 minutes HIIT at 80–90% of HRmax or a 20 minutes SST at 60% of HRmax was randomly performed on the second and third day, respectively. Plantar pressure parameters were collected at comfortable walking velocity immediately after HIIT and SST respectively, and compared with the baseline data of plantar pressure gathered before maximal ramp test on the first day. The results showed significant differences in the plantar pressure in these three conditions of gait. Compared to pre-intervention and pre-SST, peak pressure and maximum force in the middle and lateral metatarsal increased significantly in post-HIIT. Meanwhile, the foot balance data indicate that post-HIIT exhibits more foot pronation than baseline. The center of pressure (COP) trajectory was medially shifted during the stance phase in post-SST, and noticeably in post-HIIT. The displacement and velocity of medial-lateral COP in the initial contact phase were greater in post-HIIT; while during the forefoot contact phase, post-HIIT showed fewer time percentages and greater velocity of medial-lateral COP. In conclusion, a single high-intensity intermittent training session adversely affected the acute dynamic postural control than steady-state training in healthy male adults.

The investigation of bone fracture healing under intramembranous and endochondral ossification

After trauma, fractured bone starts healing directly through bone union or indirectly through callus formation process. Intramembranous and endochondral ossification are two commonly known mechanisms of indirect healing. The present study investigated the bone fracture healing under intramembranous and endochondral ossification by developing theoretical models in conjunction with performing a series of animal experiments. Using experimentally determined mean bone densities in sheep tibia stabilized by the Locking Compression Plate (LCP) fixation system, the research outcomes showed that intramembranous and endochondral ossification can be described by Hill Function with two unique sets of function parameters in mechanical stimuli mediated fracture healing. Two different thresholds exist within the range of mechanical simulation index which could trigger significant intramembranous and endochondral ossification, with a relatively higher bone formation rate of endochondral ossification than that of intramembranous ossification. Furthermore, the increase of flexibility of the LCP system and the use of titanium LCP could potentially promote uniform bone formation across the fracture gap, ultimately better healing outcomes.

Variable Fixation Technology Provides Rigid as Well as Progressive Dynamic Fixation: A Biomechanical Investigation

BACKGROUND

A new locking-screw technology, the Variable Fixation Locking Screw (VFLS; Biomech Innovations), was developed with the aim of promoting secondary fracture-healing. The VFLS features a resorbable sleeve that progressively decreases its mechanical properties and mass during the fracture-healing time. In this study, we investigated whether the VFLS can provide rigid as well as progressive dynamic fixation.

METHODS

The interfragmentary stability provided by the VFLS was tested in a simulated fracture-gap model and compared with that provided by standard locking or by a combination of both technologies under compression and torsional loading. Tests were performed with an intact sleeve (initial condition) and after its chemical dissolution. An optical measurement system was used to characterize interfragmentary movements.

RESULTS

The axial stiffness did not differ significantly among groups in the initial condition. Sleeve resorption significantly decreased construct stiffness. The torsional stiffness of the samples instrumented with the VFLS was lower than that of the control group. The degradation of the sleeve resulted in a significant increase in axial displacement recorded at both the cis and trans cortices. In samples featuring combined technologies, this increase was about 12% to 20% at the trans cortex and about 50% to 60% at the cis cortex. In samples featuring VFLS technology only, this increase was about 20% to 37% at the trans cortex and about 70% to 125% at the cis cortex.

CONCLUSIONS

The initial stability offered by the VFLS is equivalent to that of standard locking-screw technology. The resorption of the degradable sleeve leads to effective and reproducible fracture-gap dynamization, progressively varying the way the fracture gap is strained and the magnitude of the strain.

CLINICAL RELEVANCE

The VFLS provides rigid and progressive dynamic fixation in vitro. Such variable stability might have beneficial effects in terms of triggering and boosting secondary fracture-healing.

The status and challenges of replicating the mechanical properties of connective tissues using additive manufacturing

The ability to fabricate complex structures via precise and heterogeneous deposition of biomaterials makes additive manufacturing (AM) a leading technology in the creation of implants and tissue engineered scaffolds. Connective tissues (CTs) remain attractive targets for manufacturing due to their "simple" tissue compositions that, in theory, are replicable through choice of biomaterial(s) and implant microarchitecture. Nevertheless, characterisation of the mechanical and biological functions of 3D printed constructs with respect to their host tissues is often limited and remains a restriction towards their translation into clinical practice. This review aims to provide an update on the current status of AM to mimic the mechanical properties of CTs, with focus on arterial tissue, articular cartilage and bone, from the perspective of printing platforms, biomaterial properties, and topological design. Furthermore, the grand challenges associated with the AM of CT replacements and their subsequent regulatory requirements are discussed to aid further development of reliable and effective implants.

Therapeutic effects of whole-body vibration on fracture healing in ovariectomized rats: a systematic review and meta-analysis

OBJECTIVE

Whole-body vibration (WBV), providing cyclic mechanical stimulation, has been used to accelerate fracture healing in preclinical studies. This study aimed to summarize and evaluate the effects of WBV on bone healing in ovariectomized rat models and then analyze its potential effects on fractures in human postmenopausal osteoporosis.

METHODS

PubMed, EMBASE, Web of Science, China National Knowledge Infrastructure, VIP, SinoMed, and WanFang databases were searched from their inception date to September 2017, and an updated search was conducted in January 2018. Studies that evaluated the effects of WBV on bone healing compared with control groups in ovariectomized rats were included. Two authors selected studies, extracted data, and assessed the methodological quality. Meta-analyses were performed when the same outcomes were reported in two or more studies.

RESULTS

Nine eligible studies were selected. In treatment groups, callus areas were significantly improved in the first 3 weeks, normalized total bone volume and total tissue volume values increased dramatically at 8 weeks, and the mechanical tests showed a significant difference at the end point of the study.

CONCLUSIONS

This study suggested that WBV could accelerate callus formation in the early phase of bone healing, promote callus mineralization and maturity in the later phase, and restore mechanical properties of bones.

A probabilistic-based approach for computational simulation of bone fracture healing

BACKGROUND AND OBJECTIVE

It is widely known that bone fracture healing is affected by mechanical factors such as fracture geometry, fixation configuration and post-operative weight bearing loading. However, there are several uncertainties associated with the magnitude of the mechanical factors affecting bone healing as it is challenging to adjust and control them in clinical practice. The current bone fracture healing investigations mainly adopt a deterministic approach for identifying the optimal mechanical conditions for a favourable bone healing outcome. However, a probabilistic approach should be used in the analysis to incorporate such uncertainties for prediction of bone healing.

METHODS

In this study we developed a probabilistic-based computational model to predict the probability of delayed healing or non-union under different fracture treatment mechanical conditions for fractures stabilised by locking plates.

RESULTS

The results show that there is a strong positive linear correlation between the mechanical stimulations (S) in the fracture gap and the magnitude of weight bearing, the bone-plate distance (BPD) and the plate working length (WL), whereas the fracture gap size has a highly negative and nonlinear correlation with S. While the results show that fracture mechanical microenvironment is more sensitive to the uncertainties in WL compared to BPD, the uncertainty associated with the magnitude of WL is very low and can be resulted from implant manufacturing tolerance. However, there is a high uncertainty associated with the magnitude of BPD as it cannot be accurately adjusted during the surgery. The results show that the tissue differentiation at the far cortex of fracture gap is more sensitive to the variation of BPD compared with that at the near cortex. The probability of delayed healing (fibrous tissue formation) at far cortex is increased from 0% to 40% when coefficient of variation (COV) of BPD rises from 0.1 to 0.9 (for average BPD = 2 mm, WL = 65 mm, fracture gap size = 3 mm and Weight bearing = 150 N). Further, both near and far cortex of fracture site are sensitive to the variation in weight bearing loading.

CONCLUSIONS

The developed probabilistic model may lead to useful guidelines that could help orthopaedic surgeons identify how reliable a specific fracture treatment strategy is.

Bone fracture healing under Ilizarov fixator: Influence of fixator configuration, fracture geometry, and loading

This study aims to enhance the understanding of the relationship between Ilizarov fixator configuration and its effects on bone fracture healing. Using Taylor spatial frame (TSF) as an example, the roles of critical parameters (ie, TSF ring diameter, wire pre-tension, fracture gap size, and axial load) that govern fracture healing during the early stages were investigated by using computational modelling in conjunction with mechanical testing involving an advanced 3D optical measurement system. The computational model was first validated using the mechanical test results and then used to simulate mesenchymal stem cell (MSC) differentiations within different regions of the fracture site under various combinations of TSF ring diameter, wire pre-tension, fracture gap size, and axial load values. Predicted spatially dependent MSC differentiation patterns and the influence of each parameter on differentiations were compared with in vivo results, and good agreement was seen between the two. Gap size was identified as the most influential parameter in MSC differentiation, and the influence of axial loading and TSF configuration (ie, ring diameter and wire pre-tension) on cell differentiation was seen to be gap size dependent. Most changes in cell differentiation were predicted in the external callus (periosteal), which is the crucial region of the callus in the early stages. However, for small gap sizes (eg, 1 mm), significant changes were predicted in the endosteal callus as well. The study exhibits the potential of computational models in assessing the performance of Ilizarov fixators as well as assisting surgeons in patient-specific clinical treatment planning.