In vivo axial load-share ratio measurement using a novel hexapod system for safe external fixator removal.

BACKGROUND: External fixation is widely used in the treatment of traumatic fractures; however, orthopedic surgeons encounter challenges in deciding the optimal time for fixator removal. The axial load-share ratio (LS) of the fixator is a quantitative index to evaluate the stiffness of callus healing. This paper introduces an innovative method for measuring the LS and assesses the method's feasibility and efficacy. Based on a novel hexapod LS-measurement system, the proposed method is to improve the convenience and precision of measuring LS in vivo, hence facilitating the safe removal of external fixators. METHODS: A novel hexapod system is introduced, including its composition, theoretical model, and method for LS measurement. We conducted a retrospective study on 82 patients with tibial fractures treated by the Taylor Spatial Frame in our hospital from September 2018 to June 2020, of which 35 took LS measurements with our novel method (Group I), and 47 were with the traditional method (Group II). The external fixator was removed when the measurement outcome (LS < 10%) was consistent with the surgeon's diagnosis based on the clinical and radiological assessment (bone union achieved). RESULTS: No significant difference was found in the fracture healing time (mean 25.3 weeks vs. 24.9 weeks, P > 0.05), frame-wearing duration (mean 25.5 weeks vs. 25.8 weeks, P > 0.05), or LS measurement frequency (mean 1.1 times vs. 1.2 times, P > 0.05). The measurement system installation time in Group I was significantly shorter compared to Group II (mean 14.8 min vs. 81.3 min, P < 0.001). The LS value of the first measurement in Group I was lower than that of Group II (mean 5.1% vs. 6.9%, P = 0.011). In Group I, the refracture rate was 0, but in Group II it was 4.3% (2/47, P > 0.05). CONCLUSION: The novel hexapod LS-measurement system and involved method demonstrated enhanced convenience and precision in measuring the LS of the external fixator in vivo. The LS measurement indicates the callus stiffness of fracture healing, and is applicable to evaluate the safety of removing the fixator. Consequently, it is highly recommended for widespread adoption in clinical practice.

Can axial loading restore in vivo disc geometry, opening pressure, and T2 relaxation time?

Background: Cadaveric intervertebral discs are often studied for a variety of research questions, and outcomes are interpreted in the in vivo context. Unfortunately, the cadaveric disc does not inherently represent the LIVE condition, such that the disc structure (geometry), composition (T2 relaxation time), and mechanical function (opening pressure, OP) measured in the cadaver do not necessarily represent the in vivo disc. Methods: We conducted serial evaluations in the Yucatan minipig of disc geometry, T2 relaxation time, and OP to quantify the changes that occur with progressive dissection and used axial loading to restore the in vivo condition. Results: We found no difference in any parameter from LIVE to TORSO; thus, within 2 h of sacrifice, the TORSO disc can represent the LIVE condition. With serial dissection and sample preparation the disc height increased (SEGMENT height 18% higher than TORSO), OP decreased (POTTED was 67% lower than TORSO), and T2 time was unchanged. With axial loading, an imposed stress of 0.20-0.33 MPa returned the disc to in vivo, LIVE disc geometry and OP, although T2 time was decreased. There was a linear correlation between applied stress and OP, and this was conserved across multiple studies and species. Conclusion: To restore the LIVE disc state in human studies or other animal models, we recommend measuring the OP/stress relationship and using this relationship to select the applied stress necessary to recover the in vivo condition.

Data on the axial response of steel tubes infilled with rubberised alkali-activated concrete.

The presented data cover experimental and numerical axial load-shortening results of steel tubes infilled with rubberised alkali-activated concrete. The experimental data are obtained from 36 concrete filled steel tube specimens with circular and square cross-sections, length-to-diameter/width ratios of 2 and 4, and three different rubber contents in the concrete infill. The data from the numerical assessment cover the axial load-shortening response of over 300 finite element models. These cover a wide range of concrete infill strengths and rubber contents, steel tube grades, specimen widths, and steel tube wall thicknesses. Detailed descriptions of the material and methods, experimental testing, and numerical modelling procedures are also provided. The data reported herein supports the discussion in the research article "Axial compressive behaviour of composite steel elements incorporating rubberised alkali-activated concrete," and in the case of the numerical parametric assessment, give for the first time the full axial load-shortening response of all the models considered.

A Numerical and Experimental Analysis of the Mechanical Behavior of the Aluminum Beverage Can with Internal Varnish Layers during Axial Load Force Testing.

This article presents a numerical and experimental investigation into the impact of can wall thickness and the internal varnish layer thickness on the results of an axial load force test. This study also shows the levels of thermal stresses that emerge after the drying of varnish coating, and how they affect the results of the axial load force test. This research involves the development of suitable numerical models and the experimental acquisition of stress-deformation relationships for the both can material, aluminum, and the varnish. The numerical simulation of the axial load force test has been verified through experimental tests, with a resulting difference of 8.9% between the two sets of results. The findings highlight that changes in the can wall thickness have a more pronounced effect on test outcomes compared to variations in the varnish thickness. Specifically, an increase in the can wall thickness from 90 µm to 100 µm results in a substantial 116 N increase in the force required for a can to collapse. Nevertheless, the presence of a 5 µm varnish layer also contributes measurably, increasing the can's collapse force by 21 N. These results offer valuable practical insights for manufacturers, enabling them to effectively optimize can strength characteristics.

Research on Elastic and Elastic-Plastic Buckling Load of Cylindrical Shell with an Inclined through Crack under Axial Compressive Load.

By experimental methods, 26 specimens were designed to conduct elastic and elastic-plastic buckling tests on cylindrical shells containing cracks. This study discusses the influence of factors such as the length-diameter ratio, the diameter-thickness ratio, the crack length, the inclination of the crack, etc., on the buckling load. Additionally, finite element models were established to compare with experimental results. For the PMMA cylindrical shell, the results showed that as the length-diameter ratio of the cylindrical shell increased, the buckling load first decreased and then increased. For the 6063 aluminum alloy cylindrical shell, with increasing length-diameter ratio, diameter-thickness ratio, and crack length of the cylindrical shell, the buckling load decreased accordingly. However, concerning the crack inclination, as the crack inclination increased, the buckling load increased accordingly. This indicates that the larger the crack inclination, the higher the load capacity of the cylindrical shell containing cracks. Through finite element simulations of cylindrical shells with cracks, it was found that through compressive mechanical properties, both elastic and elastic-plastic buckling loads yielded results that are closer to the experimental results. Additionally, the inclusion of contact effects in numerical simulations further improved the agreement with the experimental results, and the variation trend of the buckling load in the finite element simulation was consistent with the experimental results. The research findings provide valuable references for the assessment of load capacity in structures containing cracks.

Mechanical Properties of Full-Scale UHPC-Filled Steel Tube Composite Columns under Axial Load.

In the realm of civil engineering, ultra-high-performance concrete-filled steel tube composite columns (UCFSTCs) constitute a new type of building material and structure, exhibiting high compressive strength and commendable durability. Given their promising characteristics, the prospects of their application are highly promising and are worthy of further exploration. However, current research has primarily focused on scaled-down specimens, thereby limiting a broader understanding of UCFSTCs' full-scale mechanical properties in real-world scenarios. This study aimed to investigate the mechanical properties of full-scale UHPC-filled steel tube composite columns (FUCFSTCs) in practical engineering applications. With the steel tube strength, steel tube thickness, concrete strength, aspect ratio, and steel tube diameter used as design parameters and the finite element software ABAQUS as the analytical tool, a total of 21 FUCFSTCs were designed and analyzed. Through a comparison with experimental curves, the rationality of both the material constitutive model and finite element model was verified, and the maximum error was 6.54%. Furthermore, this study analyzed the influence of different design parameters on FUCFSTCs' ultimate bearing capacity, ductility coefficient, and the stress-strain relationship of their concrete. The ductility coefficient remained around 1.3, and the cross-sectional size had the greatest impact on the bearing capacity of the composite column, with a maximum increase of 145.90%. Additionally, this paper provides an in-depth analysis of FUCFSTCs' mechanical behavior, failure mode, and stress process under an axial load. In conclusion, this research proposes an axial compression limit bearing capacity formula for FUCFSTCs via statistical regression, with a maximum error of 3.04%, meeting engineering accuracy requirements. Consequently, this study lays a strong foundation for the future application of FUCFSTCs in practical engineering.

Prediction of Axial Compressive Load-Strain Curves of Circular Concrete-Filled Steel Tube Columns Using Long Short-Term Memory Network.

No study has been reported to use machine learning methods to predict the full-range test curves of circular CFST columns. In this paper, the long short-term memory (LSTM) network was introduced to calculate the axially compressive load-strain curves of the circular CFST columns according to an experiment database of limited scale. To improve the feasibility of input data for the recurrent neural network algorithm, data preprocessing methods and data configurations were discussed. The prediction results indicate that the LSTM network provides more accurate estimations compared with the artificial neural networks, random forest and support vector regression. Meanwhile, this method can be used to calculate the mechanical properties including the elastic modulus, ultimate bearing capacity, and the ductility of the columns with acceptable accuracy for engineering practice (the prediction error within 20%). For future research, it is expected that the machine learning method will be applied to predict the structural response of different members under various loading conditions.

Advantages of the Use of Axial Traction Magnetic Resonance Imaging (MRI) of the Shoulder in Patients with Suspected Rota-Tor Cuff Tears: An Exploratory Pilot Study.

Magnetic Resonance Imaging (MRI) with axial traction is a tool for the assessment of musculoskeletal pathology. Previous reports have demonstrated a better distribution of intra-articular contrast material. No investigations were performed to evaluate glenohumeral joint axial traction MRI in patients with suspected rotator cuff tears. This study aims to assess the morphological changes and the potential advantage of glenohumeral joint axial traction MRI without intra-articular contrast administration in patients with suspected rotator cuff tears. Eleven patients with clinical suspicion of rotator cuff tears underwent a shoulder MRI scan with and without axial traction. PD weighted images with SPAIR fat saturation technique and T1 weighted images with TSE technique were acquired in the oblique coronal, oblique sagittal and axial planes. Axial traction allowed a significant widening of the subacromial space (11.1 ± 1.5 mm vs. 11.3 ± 1.8 mm; p = 0.001) and inferior glenohumeral space (8.6 ± 3.8 mm vs. 8.9 ± 2.8 mm; p = 0.029). With axial traction, there was a significant decrease in measurements of the acromial angle (8.3 ± 10.8° vs. 6.4 ± 9.8°; p < 0.001) and gleno-acromial angle (81 ± 12.8° vs. 80.7 ± 11.5°; p = 0.020). Our investigation demonstrates for the first time significant morphological changes in the shoulder of patients with suspected rotator cuff tears who underwent a glenohumeral joint axial traction MRI.

Numerical study on effect of constant and variable axial loads on RC column subjected to blast load.

Explosion is an instant release of potential energy, heat, temperature and sound producing a pressure wave that travels away from the source radially on which the resulting force the blast wave is a blast load. Besides this, column especially external column as a main load bearing compressive structural component in buildings is the most critical structural element vulnerable to explosion and require an in-depth investigation on its performance against blast loads. Despite this, currently there is perceived gap and meagre of researches regarding numerical investigation on effect of presence of constant and variable axial loads on reinforced concrete column when subjected to blast load. In this study, the responses of reinforced concrete column under different scaled distance blast load scenarios accompanied by constant and axial loads were investigated. The finite element method of structural analysis was employed accompanied by nonlinear explicit time integration software LS-DYNA. The numerical analysis result revealed that RC columns subjected to large axial loads accompanied by small scaled distance blast scenario made the reinforced concrete column to suffer severe damages including crushing of concrete especially direct shear failures and breaking of reinforcing steel bars. In addition to this, comparing the nature and behaviour of variable axial loads with constant axial loads, the former loading case revealed larger nodal displacement values along height of column, and a higher displacement-time history curve was traced. On the other hand, the damage propagation nature of RC columns loaded with variable axial load was slow and progressive and different with RC columns with constant axial loads accompanied by small scaled blast scenario which was rendered to have a severely crushed concrete element without bending actions leaving the entire column inadequate for service.

Crashworthiness Assessment of Carbon/Glass Epoxy Hybrid Composite Tubes Subjected to Axial Loads.

The crashworthiness of composite tubes is widely examined for various types of FRP composites. However, the use of hybrid composites potentially enhances the material characteristics under impact loading. In this regard, this study used a combination of unidirectional glass-carbon fibre reinforced epoxy resin as the hybrid composite tube fabricated by the pultrusion method. Five tubes with different length aspect ratios were fabricated and tested, in which the results demonstrate "how structural energy absorption affects by increasing the length of tubes". Crash force efficiency was used as the criterion to show that the selected L/D are acceptable of crash resistance with 95% efficiency. Different chamfering shapes as the trigger mechanism were applied to the tubes and the triggering effect was examined to understand the impact capacity of different tubes. A finite element model was developed to evaluate different crashworthiness indicators of the test. The results were validated through a good agreement between experimental and numerical simulations. The experimental and numerical results show that hybrid glass/carbon tubes accomplish an average 25.34 kJ/kg specific energy absorption, average 1.43 kJ energy absorption, average 32.43 kN maximum peak load, and average 96.67% crash force efficiency under quasi-static axial loading. The results show that selecting the optimum trigger mechanism causes progressive collapse and increases the specific energy absorption by more than 35%.

Frontal plane ankle stiffness increases with axial load independent of muscle activity.

Ankle sprains are the most common musculoskeletal injury, typically resulting from excessive inversion of the ankle. One way to prevent excessive inversion and maintain ankle stability is to generate a stiffness that is sufficient to resist externally imposed rotations. Frontal-plane ankle stiffness increases as participants place more weight on their ankle, but whether this effect is due to muscle activation or axial loading of the ankle is unknown. Identifying whether and to what extent axial loading affects ankle stiffness is important in understanding what role the passive mechanics of the ankle joint play in maintaining its stability. The objective of this study was to determine the effect of passive axial load on frontal-plane ankle stiffness. We had subjects seated in a chair as an axial load was applied to the ankle ranging from 10% to 50% body weight. Small rotational perturbations were applied to the ankle in the frontal plane to estimate stiffness. We found a significant, linear, 3-fold increase in ankle stiffness with axial load from the range of 0% body weight to 50% body weight. This increase could not be due to muscle activity as we observed no significant axial-load-dependent change in any of the recorded muscle activations. These results demonstrate that axial loading is a significant contributor to maintaining frontal-plane ankle stability, and that disruptions to the mechanism mediating this sensitivity of stiffness to axial loading may result in pathological cases of ankle instability.

Thinner tuberosity osteotomy is more resistant to axial load in medial open-wedge distal tuberosity proximal tibial osteotomy: A biomechanical study.

BACKGROUND: The purpose of this study was to investigate axial load resistance of the tibia depending on the thickness of tibial tuberosity osteotomy in medial open-wedge distal tuberosity proximal tibial osteotomy (OWDTO). The hypothesis is that a thin tibial tuberosity osteotomy shows high axial load resistance of the tibia. METHODS: The OWDTO model was constructed from imitation bones of the tibia. Distal tibial tuberosity osteotomy was performed with thicknesses of 7, 14, and 21 mm (n = 5 for each group). Cyclic axial-load fatigue tests were performed to investigate the strain at five measurement points on the OWDTO model. An axial-load failure test was also performed to investigate the maximum strain for failure. RESULTS: The 7-mm OWDTO model showed a significantly lower stain range than the 14-mm model at the middle part of the lateral hinge (P = 0.0263, mean difference: -852.6 µÎµ), posterior part (P = 0.0465, mean difference: -1040.0 µÎµ), posterior tibial cortex (P < 0.0001, mean difference: -583.4 µÎµ), and plate (P = 0.0029, mean difference: -121.6 µÎµ). There were no significant differences in the strain at the tibial tuberosity between the groups. The axial load for complete failure was significantly higher in the 7-mm model than in the 21-mm model (P = 0.0010, mean difference: 2577.0 N). The failure points were at the lateral hinges. CONCLUSIONS: Thinner distal tibial tuberosity osteotomy is more resistant to axial load and may be recommended for the prevention of tibial and lateral hinge fractures after OWDTO.

Experimental Investigation of Special-Shaped Concrete-Filled Square Steel Tube Composite Columns with Steel Hoops under Axial Loads.

Special-shaped concrete-filled steel tube (SS-CFST) columns can be embedded in the wall, thus preventing the columns from protruding. This feature makes it popular in steel residential buildings. This paper proposes a new special-shaped concrete-filled square steel tube (SS-CFSST) composite column composed of multiple square steel tubes connected by steel hoops to form L-, T- or cross-shaped sections. Eight specimens were tested under axial loads with section shape, construction method, slenderness ratio, steel tube thickness, and steel strength as variation parameters. The structural performance, such as failure modes, peak load, load-displacement curves, load-strain curves, and Poisson's ratio of the steel tubes, were analyzed. The tests illustrated that the failure modes of hoop-type specimens and weld-type stub columns were mainly the local buckling of steel tubes and bending failure, and those of the weld-type slender columns were mainly overall bending failure. The load-carrying capacity of the hoop-type specimen was higher than that of the weld-type specimen with the same cross-sectional dimensions and slenderness ratio. Next, the stress-strain relationship model of core concrete in the SS-CFSST composite column was established by considering the restraint effect of the connection coincidence area of steel tubes and steel hoops on concrete. Additionally, the finite element model (FEM) of the column was established using this constitutive model. By comparing the failure modes, load-strain curves and bearing capacities obtained from the tests and FEM, the established FEM can accurately evaluate the mechanical properties of SS-CFSST composite columns with steel hoops under axial compression.

Experimental Investigation on the Vertical Ductility of Rectangular CFST Columns Loaded Axially.

A total of 5 steel and 21 rectangular composite concrete-filled steel tube (CFST) columns of moderate slenderness were tested to investigate their ductility under axial compression. The importance of the vertical ductility of columns was discussed, and a novel ductility measure was proposed and utilized to examine the ductility of tested specimens. The analyses showed that the ductility of axially compressed CFST columns highly depends on their failure mode. The key feature influencing the ductility is their ability to dissipate the energy of imposed loads. The larger the volume of a material that may permanently deform and consequently dissipate the energy, the greater this ability. In consequence, the ductility of specimens exhibiting local failure mode was higher in comparison to the columns that underwent global or mixed global-local failure. It was found that both steel and composite columns were able to carry axial loads in the post-critical state; but due to the limitations of local buckling of the steel cross-section in the concrete core and concrete confinement, all tested composite columns showed greater ductility than their steel counterparts.

Seismic Behavior of Existing Reinforced Concrete Columns with Non-Seismic Details under Low Axial Loads.

Reinforced concrete (RC) columns of old existing buildings are vulnerable to earthquakes because the hoops comprising their transverse reinforcement are widely spaced and anchored using 90° hooks. This study extensively evaluated the seismic behavior of RC columns with such non-seismic details. Experiments were conducted by applying lateral cyclic loads to five full-scale column specimens with various transverse reinforcement details subjected to low axial loads. The experimental results demonstrated that the internal transverse crosstie had a significant confinement effect in the non-seismic detailed columns with 90° hoop anchor hooks. In addition, the lateral load-drift relationships, ductilities, and energy dissipation capabilities of the columns were not significantly affected by the hoop spacing or anchor hook angle when a low axial load was applied up to a drift ratio of 3.5% before failure. The evaluation model based on ASCE/SEI 41-17 was then shown to approximate the initial stiffness, maximum strength, and post-peak strength reduction behavior of the non-seismically reinforced column. This study was based on the experimental behavior of single column members, and it needs to be extended to research on frame structures in which columns are connected to beams and slabs.

Deformation and Failure Properties of High-Ni Lithium-Ion Battery under Axial Loads.

To explore the failure modes of high-Ni batteries under different axial loads, quasi-static compression and dynamic impact tests were carried out. The characteristics of voltage, load, and temperature of a battery cell with different states of charge (SOCs) were investigated in quasi-static tests. The mechanical response and safety performance of lithium-ion batteries subjected to axial shock wave impact load were also investigated by using a split Hopkinson pressure bar (SHPB) system. Different failure modes of the battery were identified. Under quasi-static axial compression, the intensity of thermal runaway becomes more severe with the increase in SOC and loading speed, and the time for lithium-ion batteries to reach complete failure decreases with the increase in SOC. In comparison, under dynamic SHPB experiments, an internal short circuit occurred after impact, but no violent thermal runaway was observed.

Artificial Neural Network (ANN) and Finite Element (FEM) Models for GFRP-Reinforced Concrete Columns under Axial Compression.

In reinforced concrete structures, the fiber-reinforced polymer (FRP) as reinforcing rebars have been widely used. The use of GFRP (glass fiber-reinforced polymer) bars to solve the steel reinforcement corrosion problem in various concrete structures is now well documented in many research studies. Hollow concrete-core columns (HCCs) are used to make a lightweight structure and reduce its cost. However, the use of FRP bars in HCCs has not yet gained an adequate level of confidence due to the lack of laboratory tests and standard design guidelines. Therefore, the present paper numerically and empirically explores the axial compressive behavior of GFRP-reinforced hollow concrete-core columns (HCCs). A total of 60 HCCs were simulated in the current version of Finite Element Analysis (FEA) ABAQUS. The reference finite element model (FEM) was built for a wide range of test variables of HCCs based on 17 specimens experimentally tested by the same group of researchers. All columns of 250 mm outer diameter, 0, 40, 45, 65, 90, 120 mm circular inner-hole diameter, and a height of 1000 mm were built and simulated. The effects of other parameters cover unconfined concrete strength from 21.2 to 44 MPa, the internal confinement (center to center spiral spacing = 50, 100, and 150 mm), and the amount of longitudinal GFRP bars (ρv = 1.78-4.02%). The complex column response was defined by the concrete damaged plastic model (CDPM) and the behavior of the GFRP reinforcement was modeled as a linear-elastic behavior up to failure. The proposed FEM showed an excellent agreement with the tested load-strain responses. Based on the database obtained from the ABAQUS and the laboratory test, different empirical formulas and artificial neural network (ANN) models were further proposed for predicting the softening and hardening behavior of GFRP-RC HCCs.

Compatibility Optimal Design of Axially Loaded Circular Concrete-Filled Steel Tube Stub Columns.

Numerous studies have been carried out on the axially loaded circular concrete-filled steel tube (CCFST) stub columns. However, to date, no clear evaluation criterion for the compatibility of its design parameters has been established. In the present study, the compatibility of the design parameters (concrete compressive strength fc, steel yield strength fy, diameter D and thickness of steel tube t) of axially loaded CCFST stub columns was quantitatively investigated in terms of the contribution of the composite actions to the axial bearing capacity of the columns. The composite ratio λ was proposed as an indicator to represent the effectiveness of the composite actions. A numerical framework of the determination of λ was established, making use of a series of existing widely recognized constitutive models of structural steel and concrete. Some modifications were carried out on these models to ensure the numerical stability of the presented analysis. Moreover, the rationality of the combined use of these models was verified. The analytical results show that excessive or very small D/t ratio should be avoided in design. Meanwhile, the combined use of low-strength steel and high-strength concrete should be avoided. A table of optimal D/t ratios corresponding to different material strength matches was provided for designers. Finally, an optimization of the design parameters using the proposed method and the existing design specification was performed.

Axial and para-axial loading response evaluation on human cadaver-harvested lumbar vertebral blocks: In vitro experiment with possible clinical implications for clinical practice.

The aim of the present study conducted on the lumbar spine was to confirm that the pronounced decrease in resistance in the system is a phenomenon that can be eminently affected by the adaptive changes that occur at the level of the intervertebral disc at axial mechanical stresses. The biomechanical trial was carried out on 11 lumbar segments L1-L5, gathered from adult human cadavers. The dissection considered the complete keeping of all bone, disc, articulated and ligamentous components in their anatomical position. All 11 samples were frozen 24 h prior to the performance of the biomechanical measurement. The specimens were placed in the testing device, their placement being conditioned by the estimated dimensional values. Thus, to calculate the load and axial resistance, the models were placed vertically, central between the test machine ferries. The testing was carried out by applying variable forces and displacement supervision. The displacement interval was represented by a segment of 0-10 mm with surveillance every 2 mm. Mobility in the sagittal plane (flexion earlier in our case) was much higher than that in the frontal plane, obviously limiting mobility via the intervertebral disc and articular complex through the presence of arches. Statistical analysis demonstrated the lack of any correlation values between the two types of movements (R2=0.005507), underlining the absence of any prediction elements. A noteworthy aspect is that the correlations appeared low, statistically insignificant, even within the same movement in the sagittal plane between the two levels, L1-L3 and L3-L5 (R2=0.610427), which may lead to the possibility of the emergence of significant differences in mobility between respective levels. The behavior type of the monitored specimens and the results obtained allowed the mapping of objective parallelism between the values obtained and the behavior in vivo of the lumbar vertebral segment.

Bony callus stiffness indirectly evaluated by the axial load-share ratio in vivo as a guide to removing a monolateral external fixator safely.

PURPOSE: As the monolateral external fixator is increasingly used in trauma-control and definitive management for high-energy long bone fractures, timing the fixator removal remains a challenge for surgeons. The purpose of this study was to determine the feasibility and effectiveness of the bony callus stiffness indirectly evaluated by the axial load-share ratio in vivo as a guide to removing a monolateral external fixator safely. METHODS: A total of 131 patients with tibial shaft fractures treated by the monolateral external fixator in our institution were collected from January 2013 to July 2019. In group I, the fixators were removed based on the clinical and radiological assessment only by the treating surgeon. As for group II, the axial load-share (LS) ratio test was accomplished by another medical team without the knowledge of the clinical results. The external fixator was removed when the mechanical test outcome (LS ratio < 10%) was consistent with the conclusion drawn from the clinical and radiological assessment (bone union achieved) by the treating surgeon. RESULTS: There was no statistical significance in demographic data between the two groups (P > 0.05). In group I, four patients suffered refracture (the refracture rate was 7.7%) after fixator removal and were successfully treated by an intramedullary nail. In group II, 71 patients underwent fixator removal after the first mechanical test, and another eight patients terminated the external fixation after the second test. None of the 79 patients in group II suffered refracture (the refracture rate was 0%). There was statistical significance in the refracture rate between the two groups (P < 0.05). CONCLUSION: The bony callus stiffness indirectly evaluated by the axial load-share ratio in vivo using the additional circular frame components is an effectively quantitative indicator to complement the clinical assessment of fracture healing in a monolateral external fixation treatment. Removal of the monolateral external fixator is safe when the axial load-share ratio dropped below 10%.