A statistical shape analysis for the assessment of the main geometrical features of the distal femoral medullary canal.

Statistical Shape Models (SSMs) are widely used in orthopedics to extract the main shape features from bone regions (e.g., femur). This study aims to develop an SSM of the femoral medullary canal, investigate its anatomical variability, and assess variations depending on canal length. The canals were isolated from 72 CT femur scans, through a threshold-based segmentation. A region of interest (ROI) was selected; sixteen segments were extracted from the ROI, ranging from 25% of the full length down to the most distal segment. An SSM was developed to identify the main modes of variation for each segment. The number of Principal Components (PCs) needed to explain at least 90% of the shape variance were three/four based on the length of the canal segment. The study examined the relationship between the identified PCs and geometric parameters like length, radius of curvature, ellipticity, mean diameter, and conicity, reporting range and percentage variation of these parameters for each segment. The SSMs provide insights into the anatomical variability of the femoral canal, emphasizing the importance of considering different segments to capture shape variations at various canal length. These findings can contribute for the design of personalized orthopedic implants involving the distal femur.

Reliable in vitro method for the evaluation of the primary stability and load transfer of transfemoral prostheses for osseointegrated implantation.

Osseointegrated transfemoral prostheses experience aseptic complications with an incidence between 3% and 30%. The main aseptic risks are implant loosening, adverse bone remodeling, and post-operative periprosthetic fractures. Implant loosening can either be due to a lack of initial (primary) stability of the implant, which hinders bone ingrowth and therefore prevents secondary stability, or, in the long-term, to the progressive resorption of the periprosthetic bone. Post-operative periprosthetic fractures are most often caused by stress concentrations. A method to simultaneously evaluate the primary stability and the load transfer is currently missing. Furthermore, the measurement errors are seldom reported in the literature. In this study a method to reliably quantify the bone implant interaction of osseointegrated transfemoral prostheses in terms of primary stability and load transfer was developed, and its precision was quantified. Micromotions between the prosthesis and the host bone and the strains on the cortical bone were measured on five human cadaveric femurs with a typical commercial osseointegrated implant. To detect the primary stability of the implant and the load transfer, cyclic loads were applied, simulating the peak load during gait. Digital Image Correlation was used to measure displacements and bone strains simultaneously throughout the test. Permanent migrations and inducible micromotions were measured (three translations and three rotations), while, on the same specimen, the full-field strain distribution on the bone surface was measured. The repeatability tests showed that the devised method had an intra-specimen variability smaller than 6 µm for the translation, 0.02 degrees for the rotations, and smaller than 60 microstrain for the strain distribution. The inter-specimen variability was larger than the intra-specimen variability due to the natural differences between femurs. Altogether, the measurement uncertainties (intrinsic measurement errors, intra-specimen repeatability and inter-specimen variability) were smaller than critical levels of biomarkers for adverse remodelling and aseptic loosening, thus allowing to discriminate between stable and unstable implants, and to detect critical strain magnitudes in the host bone. In conclusion, this work showed that it is possible to measure the primary stability and the load transfer of an osseointegrated transfemoral prosthesis in a reliable way using a combination of mechanical testing and DIC.

Full-field strain distribution in hierarchical electrospun nanofibrous poly-L(lactic) acid/collagen scaffolds for tendon and ligament regeneration: A multiscale study.

Regeneration of injured tendons and ligaments (T/L) is a worldwide need. In this study electrospun hierarchical scaffolds made of a poly-L (lactic) acid/collagen blend were developed reproducing all the multiscale levels of aggregation of these tissues. Scanning electron microscopy, microCT and tensile mechanical tests were carried out, including a multiscale digital volume correlation analysis to measure the full-field strain distribution of electrospun structures. The principal strains (εp1 and εp3) described the pattern of strains caused by the nanofibers rearrangement, while the deviatoric strains (εD) revealed the related internal sliding of nanofibers and bundles. The results of this study confirmed the biomimicry of such electrospun hierarchical scaffolds, paving the way to further tissue engineering and clinical applications.

Variability of intervertebral joint stiffness between specimens and spine levels.

Introduction: Musculoskeletal multibody models of the spine can be used to investigate the biomechanical behaviour of the spine. In this context, a correct characterisation of the passive mechanical properties of the intervertebral joint is crucial. The intervertebral joint stiffness, in particular, is typically derived from the literature, and the differences between individuals and spine levels are often disregarded. Methods: This study tested if an optimisation method of personalising the intervertebral joint stiffnesses was able to capture expected stiffness variation between specimens and between spine levels and if the variation between spine levels could be accurately captured using a generic scaling ratio. Multibody models of six T12 to sacrum spine specimens were created from computed tomography data. For each specimen, two models were created: one with uniform stiffnesses across spine levels, and one accounting for level dependency. Three loading conditions were simulated. The initial stiffness values were optimised to minimize the kinematic error. Results: There was a range of optimised stiffnesses across the specimens and the models with level dependent stiffnesses were less accurate than the models without. Using an optimised stiffness substantially reduced prediction errors. Discussion: The optimisation captured the expected variation between specimens, and the prediction errors demonstrated the importance of accounting for level dependency. The inaccuracy of the predicted kinematics for the level-dependent models indicated that a generic scaling ratio is not a suitable method to account for the level dependency. The variation in the optimised stiffnesses for the different loading conditions indicates personalised stiffnesses should also be considered load-specific.

In vitro and in silico methods for the biomechanical assessment of osseointegrated transfemoral prostheses: a systematic review.

The amputee population according to the World-Health-Organization is about 40 million. However, there is a high abandon rate of socket prostheses for the lower limb (25%-57%). The direct connection between the external prosthesis and the patient's bone makes osseointegrated prostheses for transfemoral amputees advantageous (e.g., improvement of the motor control) compared to socket prostheses, which are currently the gold standard. However, similarly to other uncemented prostheses, the osseointegrated ones are at risk of aseptic loosening and adverse bone remodelling caused by stress-shielding. The preclinical assessment of these prostheses has already been evaluated using different methods which did not provide unanimous and comparable evidence. To compare data from different investigations, a clear and detailed overview of the methods used to assess the performance is necessary. In this review 17 studies investigating the primary stability, stress shielding and stress concentration of osseointegrated transfemoral prostheses are examined. Primary stability consists in the biomechanical stability upon implant insertion. Primary stability is assessed measuring extraction force (either with a pull-out or a push-out test) and micromotion at the interface between the implant and the host bone with LVDT (in vitro test) or numerical models. Stress-shielding causes adaptive changes in the bone density around metal implants, and thus in the bone strength and stiffness. Stress-shielding is assessed with strain gauges or numerical models measuring the load transfer and the strain distribution on the surface of the femur, and between the implant and the bone respectively. Stress concentration can lead to the formation of cracks inside the bone, resulting in fractures. The stress concentration is assessed measuring the load transfer and the strain energy density at the interface between the implant and the bone, using numerical models. As a result, a global view and consensus about the methods are missing from all these tests. Indeed, different setup and loading scenario were used in the in vitro test, while different model parameters (e.g., bone properties) were used in the numerical models. Once the preclinical assessment method is established, it would be important to define thresholds and acceptance criteria for each of the possible failure scenarios investigated.

Correlation Between Sagittal Balance and Mechanical Distal Junctional Failure in Degenerative Pathology of the Spine: A Retrospective Analysis.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: This study aimed to investigate the failure of the caudal end of lumbar posterior fixation in terms of pre-operative and post-operative spinopelvic parameters, correction performed, demographic and clinical data. METHODS: The lumbar, thoraco-lumbar and lumbo-sacral posterior fixations performed with pedicle screws and rods in 2017-2019 were retrospectively analyzed. As 81% failures occurred within 4 years, an observational period of 4 years was chosen. The revision surgeries due to the failure in the caudal end were collected in the junctional group. Fixations which have not failed were gathered in the control group. The main spinopelvic parameters were measured for each patient on standing lateral radiographs with the software Surgimap. Demographic and clinical data were extracted for both groups. RESULTS: Among the 457 patients who met the inclusion criteria, the junctional group included 101 patients, who required a revision surgery. The control group collected 356 primary fixations. The two most common causes of revision surgeries were screws pullout (57 cases) and rod breakage (53 cases). SVA, PT, LL, PI-LL and TPA differed significantly between the two groups (P = .021 for LL, P < .0001 for all the others). The interaction between the two groups and the pre-operative and post-operative conditions was significant for PT, SS, LL, TK, PI-LL and TPA (P < .005). Sex and BMI did not affect the failure onset. CONCLUSIONS: Mechanical failure is more likely to occur in patients older than 40 years with a thoraco-lumbar fixation where PT, PI-LL and TPA were not properly restored.

1st EFORT European Consensus "Medical & Scientific Research Requirements for the Clinical Introduction of Artificial Joint Arthroplasty Devices": Background, Delphi Methodology & Consensus process.

The objectives of the 1st EFORT European Consensus on 'Medical and Scientific Research Requirements for the Clinical Introduction of Artificial Joint Arthroplasty Devices' were foremost to focus on patient safety by establishing performance requirements for medical devices. The 1st EFORT European Consensus applied an a priori-defined, modified Delphi methodology to produce unbiased, high-quality recommendation statements, confirmed by consensus voting of a European expert panel. Intended key outcomes are practical guidelines justified by the current stage of knowledge and based on a broad European Expert Consensus, to maintain innovation and optimisation of orthopaedic devices within the boundaries of MDR 2017/745. Twenty-one main research areas of relevance were defined relying on input from the EFORT IPSI WG1 'Introduction of Innovation' recommendations and a related survey. A modified Delphi approach with a preparatory literature review and work in small groups were used to prepare answers to the research questions in the form of 32 draft Consensus statements. A Consensus Conference in a hybrid format, on-site in the Carl Gustav Carus University of Dresden was organised to further refine the draft statements and define consensus within the complete group of participants by final voting, intended to further quantify expert opinion knowledge. The modified Delphi approach provides practical guidelines for hands-on orientation for orthopaedic surgeons, research institutes and laboratories, orthopaedic device manufacturers, patient representatives, Notified Bodies, National Institutes and authorities. For the first time, initiated by the EFORT IPSI (WG1 'Introduction of Innovation'), knowledge of all related stakeholders was combined in the 1st EFORT European Consensus to develop guidelines and result in a comprehensive set of recommendations.

Introduction of innovations in joint arthroplasty: Recommendations from the 'EFORT implant and patient safety initiative'.

With the implementation of the new MDR 2017/745 by the European Parliament, more robust clinical and pre-clinical data will be required due to a more stringent approval process. The EFORT Implant and Patient Safety Initiative WG1 'Introduction of Innovation', combined knowledge of orthopaedic surgeons, research institutes, orthopaedic device manufacturers, patient representatives and regulatory authorities to develop a comprehensive set of recommendations for the introduction of innovations in joint arthroplasty within the boundaries of MDR 2017/745. Recommendations have been developed to address key questions about pre-clinical and clinical requirements for the introduction of new implants and implant-related instrumentation with the participation of a steering group, invited by the EFORT Board in dialogue with representatives from European National Societies and Speciality Societies. Different degrees of novelty and innovation were described and agreed on in relation to when surgeons can start, using implants and implant-related instrumentation routinely. Before any clinical phase of a new implant, following the pre-market clinical investigation or the equivalent device PMCF pathway, it is a common understanding that all appropriate pre-clinical testing (regulatory mandatory and evident state of the art) - which has to be considered for a specific device - has been successfully completed. Once manufacturers receive the CE mark for a medical device, it can be used in patients routinely when a clinical investigation has been conducted to demonstrate the conformity of devices according to MDR Article 62 or full equivalence for the technical, biological and clinical characteristics has been demonstrated (MDR, Annex XIV, Part A, 3.) and a PMCF study has been initiated.

Bone metastases do not affect the measurement uncertainties of a global digital volume correlation algorithm.

Introduction: Measurement uncertainties of Digital Volume Correlation (DVC) are influenced by several factors, like input images quality, correlation algorithm, bone type, etc. However, it is still unknown if highly heterogeneous trabecular microstructures, typical of lytic and blastic metastases, affect the precision of DVC measurements. Methods: Fifteen metastatic and nine healthy vertebral bodies were scanned twice in zero-strain conditions with a micro-computed tomography (isotropic voxel size = 39 µm). The bone microstructural parameters (Bone Volume Fraction, Structure Thickness, Structure Separation, Structure Number) were calculated. Displacements and strains were evaluated through a global DVC approach (BoneDVC). The relationship between the standard deviation of the error (SDER) and the microstructural parameters was investigated in the entire vertebrae. To evaluate to what extent the measurement uncertainty is influenced by the microstructure, similar relationships were assessed within sub-regions of interest. Results: Higher variability in the SDER was found for metastatic vertebrae compared to the healthy ones (range 91-1030 µÎµ versus 222-599 µÎµ). A weak correlation was found between the SDER and the Structure Separation in metastatic vertebrae and in the sub-regions of interest, highlighting that the heterogenous trabecular microstructure only weakly affects the measurement uncertainties of BoneDVC. No correlation was found for the other microstructural parameters. The spatial distribution of the strain measurement uncertainties seemed to be associated with regions with reduced greyscale gradient variation in the microCT images. Discussion: Measurement uncertainties cannot be taken for granted but need to be assessed in each single application of the DVC to consider the minimum unavoidable measurement uncertainty when interpreting the results.

mCrutch: A Novel m-Health Approach Supporting Continuity of Care.

This paper reports the architecture of a low-cost smart crutches system for mobile health applications. The prototype is based on a set of sensorized crutches connected to a custom Android application. Crutches were instrumented with a 6-axis inertial measurement unit, a uniaxial load cell, WiFi connectivity, and a microcontroller for data collection and processing. Crutch orientation and applied force were calibrated with a motion capture system and a force platform. Data are processed and visualized in real-time on the Android smartphone and are stored on the local memory for further offline analysis. The prototype's architecture is reported along with the post-calibration accuracy for estimating crutch orientation (5° RMSE in dynamic conditions) and applied force (10 N RMSE). The system is a mobile-health platform enabling the design and development of real-time biofeedback applications and continuity of care scenarios, such as telemonitoring and telerehabilitation.

Assessment of foraminal decompression following discoplasty using a combination of ex vivo testing and numerical tools.

Percutaneous Cement Discoplasty (PCD) is a minimally invasive surgical technique to treat degenerated intervertebral discs. When the disc is severely degenerated, the vacuum observed in place of the nucleus pulposus can be filled with bone cement to restore the disc height, open the foramen space, and relieve pain. This study aimed to evaluate the foramen geometry change due to PCD, in the loaded spine. Cadaveric spines (n = 25) were tested in flexion and extension while Digital Image Correlation (DIC) measured displacements and deformations. Tests were performed on simulated pre-operative condition (nucleotomy) and after PCD. Registering DIC images and the 3D specimen geometry from CT scans, a 3D model of the specimens aligned in the experimental pose was obtained for nucleotomy and PCD. Foramen space volume was geometrically measured for both conditions. The volume of cement injected was measured to explore correlation with the change of foramen space. PCD induced a significant overall foraminal decompression in both flexion (foramen space increased by 835 ± 1289 mm3, p = 0.001) and extension (1205 ± 1106 mm3, p < 0.001), confirming that the expected improvements of PCD show also during spine motion. Furthermore, in extension when the foramen is the most challenged, the impact of PCD on the foramen correlated with the injected cement volume.

Stereophotogrammetric approaches to multi-segmental kinematics of the thoracolumbar spine: a systematic review.

BACKGROUND: Spine disorders are becoming more prevalent in today's ageing society. Motion abnormalities have been linked to the prevalence and recurrence of these disorders. Various protocols exist to measure thoracolumbar spine motion, but a standard multi-segmental approach is still missing. This study aims to systematically evaluate the literature on stereophotogrammetric motion analysis approaches to quantify thoracolumbar spine kinematics in terms of measurement reliability, suitability of protocols for clinical application and clinical significance of the resulting functional assessment. METHODS: Electronic databases (PubMed, Scopus and ScienceDirect) were searched until February 2022. Studies published in English, investigating the intersegmental kinematics of the thoracolumbar spine using stereophotogrammetric motion analysis were identified. All information relating to measurement reliability; measurement suitability and clinical significance was extracted from the studies identified. RESULTS: Seventy-four studies met the inclusion criteria. 33% of the studies reported on the repeatability of their measurement. In terms of suitability, only 35% of protocols were deemed suitable for clinical application. The spinous processes of C7, T3, T6, T12, L1, L3 and L5 were the most widely used landmarks. The spine segment definitions were, however, found to be inconsistent among studies. Activities of daily living were the main tasks performed. Comparable results between protocols are however still missing. CONCLUSION: The literature to date offers various stereophotogrammetric protocols to quantify the multi-segmental motion of the thoracolumbar spine, without a standard guideline being followed. From a clinical point of view, the approaches are still limited. Further research is needed to define a precise motion analysis protocol in terms of segment definition and clinical relevance.

Biomechanical consequences of cement discoplasty: An in vitro study on thoraco-lumbar human spines.

With the ageing of the population, there is an increasing need for minimally invasive spine surgeries to relieve pain and improve quality of life. Percutaneous Cement Discoplasty is a minimally invasive technique to treat advanced disc degeneration, including vacuum phenomenon. The present study aimed to develop an in vitro model of percutaneous cement discoplasty to investigate its consequences on the spine biomechanics in comparison with the degenerated condition. Human spinal segments (n = 27) were tested at 50% body weight in flexion and extension. Posterior disc height, range of motion, segment stiffness, and strains were measured using Digital Image Correlation. The cement distribution was also studied on CT scans. As main result, percutaneous cement discoplasty restored the posterior disc height by 41% for flexion and 35% for extension. Range of motion was significantly reduced only in flexion by 27%, and stiffness increased accordingly. The injected cement volume was 4.56 ± 1.78 ml (mean ± SD). Some specimens (n = 7) exhibited cement perforation of one endplate. The thickness of the cement mass moderately correlated with the posterior disc height and range of motion with different trends for flexions vs. extension. Finally, extreme strains on the discs were reduced by percutaneous cement discoplasty, with modified patterns of the distribution. To conclude, this study supported clinical observations in term of recovered disc height close to the foramen, while percutaneous cement discoplasty helped stabilize the spine in flexion and did not increase the risk of tissue damage in the annulus.

Experimental validation of a subject-specific finite element model of lumbar spine segment using digital image correlation.

Pathologies such as cancer metastasis and osteoporosis strongly affect the mechanical properties of the vertebral bone and increase the risk of fragility fractures. The prediction of the fracture risk with a patient-specific model, directly generated from the diagnostic images of the patient, could help the clinician in the choice of the correct therapy to follow. But before such models can be used to support any clinical decision, their credibility must be demonstrated through verification, validation, and uncertainty quantification. In this study we describe a procedure for the generation of such patient-specific finite element models and present a first validation of the kinematics of the spine segment. Quantitative computed tomography images of a cadaveric lumbar spine segment presenting vertebral metastatic lesions were used to generate the model. The applied boundary conditions replicated a specific experimental test where the spine segment was loaded in compression-flexion. Model predictions in terms of vertebral surface displacements were compared against the full-field experimental displacements measured with Digital Image Correlation. A good agreement was obtained from the local comparison between experimental data and simulation results (R2 > 0.9 and RMSE% <8%). In conclusion, this work demonstrates the possibility to apply the developed modelling pipeline to predict the displacement field of human spine segment under physiological loading conditions, which is a first fundamental step in the credibility assessment of these clinical decision-support technology.

Critical Review of the State-of-the-Art on Lumbar Percutaneous Cement Discoplasty.

Interbody fusion is the gold standard surgery to treat lumbar disc degeneration disease but can be a high-risk procedure in elderly and polymorbid patients. Percutaneous Cement Discoplasty (PCD) is a minimally invasive technique developed to treat advanced stage of disc degeneration exhibiting a vacuum phenomenon. A patient-specific stand-alone spacer is created by filling the disc with polymethylmethacrylate cement, allowing to recover the disc height and improve the patient's conditions. As it has recently been introduced in the lumbar spine, this review aims to present a transversal state-of-the-art of the surgery from its clinical practice and outcome to biomechanical and engineering topics. The literature was searched across multiple databases using predefined keywords over no limited period of time. Papers about vertebroplasty were excluded. Among 466 identified papers, the relevant ones included twelve clinical papers reporting the variations of the surgical technique, follow-up and complications, four papers reporting biomechanical ex vivo and numerical tests, and four letters related to published clinical papers. Papers presenting the operative practice are reported, as well as follow-ups up to four years. The papers found, consistently reported that PCD significantly improved the clinical status of the patients and maintained it after two years. Spine alignment was impacted by PCD: the sacral slope was significantly reduced, and disc height increased. The foramen opening correlated to the volume of injected cement. Substitutes to the acrylic cement exhibited better osteointegration and mechanical properties closer to bone tissue. Finally, limitations and risks of the surgery are discussed as well as potential improvements such as the development of new filling materials with better mechanical properties and biological integration or the investigation of the inner disc.

Global and local characterization explains the different mechanisms of failure of the human ribs.

Knowledge of the mechanics and mechanistic reasons inducing rib fracture is fundamental for forensic investigations and for the design of implants and cardiopulmonary resuscitation devices. A mechanical rationale to explain the different rib mechanisms of failure is still a challenge. The aim of this work was to experimentally characterize human ribs to test the hypothesis that a correlation exists between the ribs properties and the mechanism of failure. 89 ribs were tested in antero-posterior compression. The full-field strain distribution was measured through Digital Image Correlation. The fracture load ranged 7-132 N. Two main different mechanisms of failure were observed: brittle and buckling. The strain analysis showed that the direction of principal strains was either aligned with the ribs, or oblique, around 45°, with a rather uniform direction in the most strained area. The maximum principal strains were in the range between 1000 and 30000 microstrain and the minimum principal strain between -30000 and -800 microstrain. The ribs undergoing brittle fracture had significantly thicker cortical bone than those undergoing buckling. Also, larger tensile strains were observed in the specimens with brittle fracture than in the buckling ones. These findings support the focus of cortical thickness modelling which could help in sharpening computational models for the aforesaid purposes.

Effects Induced by Osteophytes on the Strain Distribution in the Vertebral Body Under Different Loading Configurations.

The mechanical consequences of osteophytes are not completely clear. We aimed to understand whether and how the presence of an osteophyte perturbs strain distribution in the neighboring bone. The scope of this study was to evaluate the mechanical behavior induced by the osteophytes using full-field surface strain analysis in different loading configurations. Eight thoracolumbar segments, containing a vertebra with an osteophyte and an adjacent vertebra without an osteophyte (control), were harvested from six human spines. The position and size of the osteophytes were evaluated using clinical computed tomography imaging. The spine segments were biomechanically tested in the elastic regime in different loading configurations while the strains over the frontal and lateral surface of vertebral bodies were measured using digital image correlation. The strain fields in the vertebrae with and without osteophytes were compared. The correlation between osteophyte size and strain alteration was explored. The strain fields measured in the vertebrae with osteophytes were different from the control ones. In pure compression, we observed a mild trend between the size of the osteophyte and the strain distribution (R 2 = 0.32, p = 0.15). A slightly stronger trend was found for bending (R 2 = 0.44, p = 0.075). This study suggests that the osteophytes visibly perturb the strain field in the nearby vertebral area. However, the effect on the surrounding bone is not consistent. Indeed, in some cases the osteophyte shielded the neighboring bone, and in other cases, the osteophyte increased the strains.

Computational modelling of the scoliotic spine: A literature review.

Scoliosis is a deformity of the spine that in severe cases requires surgical treatment. There is still disagreement among clinicians as to what the aim of such treatment is as well as the optimal surgical technique. Numerical models can aid clinical decision-making by estimating the outcome of a given surgical intervention. This paper provided some background information on the modelling of the healthy spine and a review of the literature on scoliotic spine models, their validation, and their application. An overview of the methods and techniques used to construct scoliotic finite element and multibody models was given as well as the boundary conditions used in the simulations. The current limitations of the models were discussed as well as how such limitations are addressed in non-scoliotic spine models. Finally, future directions for the numerical modelling of scoliosis were addressed.

Type, size, and position of metastatic lesions explain the deformation of the vertebrae under complex loading conditions.

BACKGROUND: Bone metastases may lead to spine instability and increase the risk of fracture. Scoring systems are available to assess critical metastases, but they lack specificity, and provide uncertain indications over a wide range, where most cases fall. The aim of this work was to use a novel biomechanical approach to evaluate the effect of lesion type, size, and location on the deformation of the metastatic vertebra. METHOD: Vertebrae with metastases were identified from 16 human spines from a donation programme. The size and position of the metastases, and the Spine Instability Neoplastic Score (SINS) were evaluated from clinical Quantitative Computed Tomography images. Thirty-five spine segments consisting of metastatic vertebrae and adjacent healthy controls were biomechanically tested in four different loading conditions. The strain distribution over the entire vertebral bodies was measured with Digital Image Correlation. Correlations between the features of the metastasis (type, size, position and SINS) and the deformation of the metastatic vertebrae were statistically explored. RESULTS: The metastatic type (lytic, blastic, mixed) characterizes the vertebral behaviour (Kruskal-Wallis, p = 0.04). In fact, the lytic metastases showed more critical deformation compared to the control vertebrae (average: 2-fold increase, with peaks of 14-fold increase). By contrast, the vertebrae with mixed or blastic metastases did not show a clear trend, with deformations similar or lower than the controls. Once the position of the lytic lesion with respect to the loading direction was taken into account, the size of the lesion was significantly correlated with the perturbation to the strain distribution (r2 = 0.72, p < 0.001). Conversely, the SINS poorly correlated with the mechanical evidence, and only in case of lytic lesions (r2 = 0.25, p < 0.0001). CONCLUSION: These results highlight the relevance of the size and location of the lytic lesion, which are marginally considered in the current clinical scoring systems, in driving the spinal biomechanical instability. The strong correlation with the biomechanical evidence indicates that these parameters are representative of the mechanical competence of the vertebra. The improved explanatory power compared to the SINS suggests including them in future guidelines for the clinical practice.