Developing Advanced Patient-Specific In Silico Models: A New Era in Biomechanical Analysis of Tooth Autotransplantation.

INTRODUCTION: As personalized medicine advances, there is an escalating need for sophisticated tools to understand complex biomechanical phenomena in clinical research. Recognizing a significant gap, this study pioneers the development of patient-specific in silico models for tooth autotransplantation (TAT), setting a new standard for predictive accuracy and reliability in evaluating TAT outcomes. METHODS: Development of the models relied on 6 consecutive cases of young patients (mean age 11.66 years ± 0.79), all undergoing TAT procedures. The development process involved creating detailed in silico replicas of patient oral structures, focusing on transplanting upper premolars to central incisors. These models underpinned finite element analysis simulations, testing various masticatory and traumatic scenarios. RESULTS: The models highlighted critical biomechanical insights. The finite element models indicated homogeneous stress distribution in control teeth, contrasted by shape-dependent stress patterns in transplanted teeth. The surface deviation in the postoperative year for the transplanted elements showed a mean deviation of 0.33 mm (±0.28), significantly higher than their contralateral counterparts at 0.05 mm (±0.04). CONCLUSIONS: By developing advanced patient-specific in silico models, we are ushering in a transformative era in TAT research and practice. These models are not just analytical tools; they are predictive instruments capturing patient uniqueness, including anatomical, masticatory, and tissue variables, essential for understanding biomechanical responses in TAT. This foundational work paves the way for future studies, where applying these models to larger cohorts will further validate their predictive capabilities and influence on TAT success parameters.

Accuracy of photon-counting computed tomography for the measurement of bone quality in the knee.

Visualization and quantification of bone microarchitecture in the human knee allows gaining insight into normal bone structure, and into the structural changes occurring in the onset and progression of bone diseases such as osteoporosis and osteoarthritis. However, current imaging modalities have limitations in capturing the intricacies of bone microarchitecture. Photon counting computed tomography (PCCT) is a promising imaging modality that presents high-resolution three-dimensional visualization of bone with a large field of view. However, the potential of PCCT in assessing trabecular microstructure has not been investigated yet. Therefore, this study aimed to evaluate the accuracy of PCCT in quantifying bone microstructure and bone mechanics in the knee. Five human cadaveric knees were scanned ex vivo using a PCCT scanner (Naetom alpha, Siemens, Germany) with an in-plane resolution of 146.5 µm and slice thickness of 100 µm. To assess accuracy, the specimens were also scanned with a high-resolution peripheral quantitative computed tomography (HR-pQCT; XtremeCT II, Scanco Medical, Switzerland) with a nominal isotropic voxel size of 60.7 µm as well as with micro-computed tomography (micro-CT; TESCAN UniTOM XL, Czech Republic) with a nominal isotropic voxel size of 25 µm which can be considered gold standards for in vivo and ex vivo scanning, respectively. The thickness and porosity of the subchondral bone and the microstructure of the underlying trabecular bone were assessed in the load bearing regions of the proximal tibia and distal femur. The apparent Young's modulus was determined by micro-finite element (µFE) analysis of subchondral trabecular bone (STB) in the load bearing regions of the proximal tibia using PCCT, HR-pQCT and micro-CT images. The correlation between PCCT measurements and micro-CT and HR-pQCT, respectively, was calculated. The coefficients of determination (R2) between PCCT and micro-CT based parameters, ranged from 0.69 to 0.87. The coefficients of determination between PCCT and HR-pQCT were slightly higher and ranged from 0.71 to 0.91. Apparent Young's modulus, assessed by µFE analysis of PCCT images, correlated well with that of micro-CT (R2 = 0.80, mean relative difference = 19 %). However, PCCT overestimated the apparent Young's modulus by 47 %, but the correlation (R2 = 0.84) remained strong when compared to HR-pQCT. The results of this study suggest that PCCT can be used to quantify bone microstructure in the knee.

Omega-3 PUFAs prevent bone impairment and bone marrow adiposity in mouse model of obesity.

Obesity adversely affects bone and fat metabolism in mice and humans. Omega-3 polyunsaturated fatty acids (omega-3 PUFAs) have been shown to improve glucose metabolism and bone homeostasis in obesity. However, the impact of omega-3 PUFAs on bone marrow adipose tissue (BMAT) and bone marrow stromal cell (BMSC) metabolism has not been intensively studied yet. In the present study we demonstrated that omega-3 PUFA supplementation in high fat diet (HFD + F) improved bone parameters, mechanical properties along with decreased BMAT in obese mice when compared to the HFD group. Primary BMSCs isolated from HFD + F mice showed decreased adipocyte and higher osteoblast differentiation with lower senescent phenotype along with decreased osteoclast formation suggesting improved bone marrow microenvironment promoting bone formation in mice. Thus, our study highlights the beneficial effects of omega-3 PUFA-enriched diet on bone and cellular metabolism and its potential use in the treatment of metabolic bone diseases.

A combined experimental and finite element analysis of the human elbow under loads of daily living.

Elbow trauma is often accompanied by a loss of independence in daily self-care activities, negatively affecting patients' quality of life. Finite element models can help gaining profound knowledge about native human joint mechanics, which is crucial to adequately restore joint functionality after severe injuries. Therefore, a finite element model of the elbow is required that includes both the radio-capitellar and ulno-trochlear joint and is subjected to loads realistic for activities of daily living. Since no such model has been published, we aim to fill this gap. For comparison, 8 intact cadaveric elbows were subjected to loads of up to 1000 N, after they were placed in an extended position. At each load step, the displacement of the proximal humerus relative to the distal base plate was measured with optical tracking markers and the joint pressure was measured with a pressure mapping sensor. Analogously, eight finite element models were created based on subject-specific CT scans of the corresponding elbow specimens. The CT scans were registered to the positions of tantalum beads in the experiment. The optically measured displacements were applied as boundary conditions. We demonstrated that the workflow can predict the experimental contact pressure distribution with a moderate correlation, the experimental peak pressures in the correct joints and the experimental stiffness with moderate to excellent correlation. The predictions of peak pressure magnitude, contact area and load share on the radius require improvement by precise representation of the cartilage geometry and soft tissues in the model, and proper initial contact in the experiment.

Structural and functional heterogeneity of mineralized fibrocartilage at the Achilles tendon-bone insertion.

A demanding task of the musculoskeletal system is the attachment of tendon to bone at entheses. This region often presents a thin layer of fibrocartilage (FC), mineralized close to the bone and unmineralized close to the tendon. Mineralized FC deserves increased attention, owing to its crucial anchoring task and involvement in enthesis pathologies. Here, we analyzed mineralized FC and subchondral bone at the Achilles tendon-bone insertion of rats. This location features enthesis FC anchoring tendon to bone and sustaining tensile loads, and periosteal FC facilitating bone-tendon sliding with accompanying compressive and shear forces. Using a correlative multimodal investigation, we evaluated potential specificities in mineral content, fiber organization and mechanical properties of enthesis and periosteal FC. Both tissues had a lower degree of mineralization than subchondral bone, yet used the available mineral very efficiently: for the same local mineral content, they had higher stiffness and hardness than bone. We found that enthesis FC was characterized by highly aligned mineralized collagen fibers even far away from the attachment region, whereas periosteal FC had a rich variety of fiber arrangements. Except for an initial steep spatial gradient between unmineralized and mineralized FC, local mechanical properties were surprisingly uniform inside enthesis FC while a modulation in stiffness, independent from mineral content, was observed in periosteal FC. We interpreted these different structure-property relationships as a demonstration of the high versatility of FC, providing high strength at the insertion (to resist tensile loading) and a gradual compliance at the periosteal surface (to resist contact stresses). STATEMENT OF SIGNIFICANCE: Mineralized fibrocartilage (FC) at entheses facilitates the integration of tendon in bone, two strongly dissimilar tissues. We focus on the structure-function relationships of two types of mineralized FC, enthesis and periosteal, which have clearly distinct mechanical demands. By investigating them with multiple high-resolution methods in a correlative manner, we demonstrate differences in fiber architecture and mechanical properties between the two tissues, indicative of their mechanical roles. Our results are relevant both from a medical viewpoint, targeting a clinically relevant location, as well as from a material science perspective, identifying FC as high-performance versatile composite.

Fracture risk assessment and evaluation of femoroplasty in metastatic proximal femurs. An in vivo CT-based finite element study.

The goal of this study was twofold. First, we aimed to evaluate the accuracy of a finite element (FE) model to predict bone fracture in cancer patients with proximal femoral bone metastases. Second, we evaluated whether femoroplasty could effectively reduce fracture risk. A total of 89 patients were included, with 101 proximal femurs affected with bone metastases. The accuracy of the model to predict fracture was evaluated by comparing the FE failure load, normalized for body weight, against the actual occurrence of fracture during a 6-month follow-up. Using a critical threshold, the model could identify whether femurs underwent fracture with a sensitivity of 92% and a specificity of 66%. A virtual treatment with femoroplasty was simulated in a subset of 34 out of the 101 femurs; only femurs with one or more well-defined lytic lesions were considered eligible for femoroplasty. We modeled their lesions, as well as the surrounding 4 mm of trabecular bone, to be augmented with bone cement. The simulation of femoroplasty increased the median failure load of the FE model by 57% for lesions located in the head/neck of the femur. At this lesion location, all high risk femurs that had fractured during follow-up effectively moved from a failure load below the critical threshold to a value above. For lesions located in the trochanteric region, no definite improvement in failure load was found. Although additional validation studies are required, our results suggest that femoroplasty can effectively reduce fracture risk for several osteolytic lesions in the femoral head/neck.

The effect of different grasping types on strain distributions in the trapezium of bonobos (Pan paniscus).

The thumb has played a key role in primate evolution due to its involvement in grasping and manipulation. A large component of this wide functionality is by virtue of the uniquely shaped trapeziometacarpal (TMC) joint. This TMC joint allows for a broad range of functional positions, but how its bone structure is adapted to withstand such a large variety of loading regimes is poorly understood. Here, we outline a novel, integrated finite element - micro finite element (FE-µFE) workflow to analyse strain distributions across the internal bony architecture. We have applied this modelling approach to study functional adaptation in the bonobo thumb. More specifically, the approach allows us to evaluate how strain is distributed through the trapezium upon loading of its distal articular facet. As loading conditions, we use pressure distributions for different types of grasping that were estimated in a previous study. Model evaluation shows that the simulated strain values fall within realistic boundaries of the mechanical response of bone. The results show that the strain distributions between the simulated grasps are highly similar, with dissipation towards the proximo-ulnar cluster of trabeculae regardless of trapezial bone architecture. This study presents an innovative FE-µFE approach to simulating strain distributions, and yields insight in the functional adaptation of the TMC joint in bonobos.

Novel thiazolidinedione analog reduces a negative impact on bone and mesenchymal stem cell properties in obese mice compared to classical thiazolidinediones.

OBJECTIVE: The use of thiazolidinediones (TZDs) as insulin sensitizers has been shown to have side effects including increased accumulation of bone marrow adipocytes (BMAds) associated with a higher fracture risk and bone loss. A novel TZD analog MSDC-0602K with low affinity to PPARγ has been developed to reduce adverse effects of TZD therapy. However, the effect of MSDC-0602K on bone phenotype and bone marrow mesenchymal stem cells (BM-MSCs) in relation to obesity has not been intensively studied yet. METHODS: Here, we investigated whether 8-week treatment with MSDC-0602K has a less detrimental effect on bone loss and BM-MSC properties in obese mice in comparison to first generation of TZDs, pioglitazone. Bone parameters (bone microstructure, bone marrow adiposity, bone strength) were examined by µCT and 3-point bending test. Primary BM-MSCs were isolated and measured for osteoblast and adipocyte differentiation. Cellular senescence, bioenergetic profiling, nutrient consumption and insulin signaling were also determined. RESULTS: The findings demonstrate that MSDC-0602K improved bone parameters along with increased proportion of smaller BMAds in tibia of obese mice when compared to pioglitazone. Further, primary BM-MSCs isolated from treated mice and human BM-MSCs revealed decreased adipocyte and higher osteoblast differentiation accompanied with less inflammatory and senescent phenotype induced by MSDC-0602K vs. pioglitazone. These changes were further reflected by increased glycolytic activity differently affecting glutamine and glucose cellular metabolism in MSDC-0602K-treated cells compared to pioglitazone, associated with higher osteogenesis. CONCLUSION: Our study provides novel insights into the action of MSDC-0602K in obese mice, characterized by the absence of detrimental effects on bone quality and BM-MSC metabolism when compared to classical TZDs and thus suggesting a potential therapeutical use of MSDC-0602K in both metabolic and bone diseases.

Experimental validation of a voxel-based finite element model simulating femoroplasty of lytic lesions in the proximal femur.

Femoroplasty is a procedure where bone cement is injected percutaneously into a weakened proximal femur. Uncertainty exists whether femoroplasty provides sufficient mechanical strengthening to prevent fractures in patients with femoral bone metastases. Finite element models are promising tools to evaluate the mechanical effectiveness of femoroplasty, but a thorough validation is required. This study validated a voxel-based finite element model against experimental data from eight pairs of human cadaver femurs with artificial metastatic lesions. One femur from each pair was left untreated, while the contralateral femur was augmented with bone cement. Finite element models accurately predicted the femoral strength in the defect (R2 = 0.96) and augmented (R2 = 0.93) femurs. The modelled surface strain distributions showed a good qualitative match with results from digital image correlation; yet, quantitatively, only moderate correlation coefficients were found for the defect (mean R2 = 0.78) and augmented (mean R2 = 0.76) femurs. This was attributed to the presence of vessel holes in the femurs and the jagged surface representation of our voxel-based models. Despite some inaccuracies in the surface measurements, the FE models accurately predicted the global bone strength and qualitative deformation behavior, both before and after femoroplasty. Hence, they can offer a useful biomechanical tool to assist clinicians in assessing the need for prophylactic augmentation in patients with metastatic bone disease, as well as in identifying suitable patients for femoroplasty.

Adaptive local thresholding can enhance the accuracy of HR-pQCT-based trabecular bone morphology assessment.

High-resolution peripheral quantitative computed tomography (HR-pQCT) devices can scan extremities at bone microstructural level in vivo and are used mainly in research of bone diseases. Two HR-pQCT scanners are commercially available to date: XtremeCT (first generation) and XtremeCT-II (second generation) from Scanco Medical AG (Switzerland). Recently, we have proposed an adaptive local thresholding (AT) technique and showed that it can improve quantification accuracy of bone microstructural parameters, with visually less sharp cone-beam CT (CBCT) images providing a similar accuracy than XtremeCT. The aim of this study was to evaluate whether the AT segmentation technique could enhance the accuracy of HR-pQCT in quantifying bone microstructural images and to assess whether the agreement between XtremeCT and XtremeCT-II could be improved. Nineteen radii were scanned with three scanners from Scanco Medical AG: (1) XtremeCT at 82 µm, (2) XtremeCT-II at 60.7 µm and (3) the small animal microCT scanner VivaCT40 at 19 µm voxel size. The scans were segmented applying two different methods, once following the manufacturer standard technique (ST), and once by means of AT. Three-dimensional (3D) morphological analysis was performed on the trabecular volume of the segmented images using the manufacturer's standard software to calculate bone volume fraction (BV/TV), trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N). The average accuracy of XtremeCT improved from R2 = 0.76 (ST) to 0.85 (AT) and reached the same level of accuracy as XtremeCT-II with ST (R2 = 0.86). The largest improvements were obtained for BV/TV and Tb.Th. For XtremeCT-II, mean accuracy improved slightly from R2 = 0.86 (ST) to 0.89 (AT). For both segmentations and both scanners, the standard section was quantified slightly more accurate than the subchondral section. The agreement between the scanners was enhanced from R2 = 0.89 (ST) to 0.98 (AT). In conclusion, AT can enhance the accuracy of XtremeCT to quantify distal radius bone microstructural parameters close to XtremeCT-II level and increases the agreement between the two HR-pQCT scanners. High-resolution peripheral quantitative computed tomography, segmentation, bone microstructural parameters.

Stress distribution in the bonobo (Pan paniscus) trapeziometacarpal joint during grasping.

The primate thumb plays a central role in grasping and the basal trapeziometacarpal (TMC) joint is critical to its function. The TMC joint morphology varies across primates, yet little is known about form-function interaction within in the TMC joint. The purpose of this study was to investigate how stress distributions within the joint differ between five grasping types commonly employed by bonobos (Pan paniscus). Five cadaveric bonobo forearms were CT scanned in five standardized positions of the hand as a basis for the generation of parametric finite element models to compare grasps. We have developed a finite element analysis (FEA) approach to investigate stress distribution patterns in the TMC joint associated with each grasp type. We hypothesized that the simulated stress distributions for each position would correspond with the patterns expected from a saddle-shaped joint. However, we also expected differences in stress patterns arising from instraspecific variations in morphology. The models showed a high agreement between simulated and expected stress patterns for each of the five grasps (86% of successful simulations), while partially (52%) and fully (14%) diverging patterns were also encountered. We identified individual variations of key morphological features in the bonobo TMC joint that account for the diverging stress patterns and emphasized the effect of interindividual morphological variation on joint functioning. This study gives unprecedented insight in the form-function interactions in the TMC joint of the bonobo and provides an innovative FEA approach to modelling intra-articular stress distributions, a valuable tool for the study of the primate thumb biomechanics.

Alterations in osteocyte lacunar morphology affect local bone tissue strains.

Osteocytes are capable of remodeling their perilacunar bone matrix, which causes considerable variations in the shape and size of their lacunae. If these variations in lacunar morphology cause changes in the mechanical environment of the osteocytes, in particular local strains, they would subsequently affect bone mechanotransduction, since osteocytes are likely able to directly sense these strains. The purpose of this study is to quantify the effect of alterations in osteocyte lacunar morphology on peri-lacunar bone tissue strains. To this end, we related the actual lacunar shape in fibulae of six young-adult (5-month) and six old (23-month) mice, quantified by high-resolution micro-computed tomography, to microscopic strains, analyzed by micro-finite element modeling. We showed that peak effective strain increased by 12.6% in osteocyte cell bodies (OCYs), 9.6% in pericellular matrix (PCM), and 5.3% in extra cellular matrix (ECM) as the lacunae volume increased from 100-200 µm3 to 500-600 µm3. Lacunae with a larger deviation (>8°) in orientation from the longitudinal axis of the bone are exposed to 8% higher strains in OCYs, 6.5% in PCM, 4.2% in ECM than lacunae with a deviation in orientation below 8°. Moreover, increased lacuna sphericity from 0 to 0.5 to 0.7-1 led to 25%, 23%, and 13% decrease in maximum effective strains in OCYs, PCM, and ECM, respectively. We further showed that due to the presence of smaller and more round lacunae in old mice, local bone tissue strains are on average 5% lower in the vicinity of lacunae and their osteocytes of old mice compared to young. Understanding how changes in lacunar morphology affect the micromechanical environment of osteocytes presents a first step in unraveling their potential role in impaired bone mechanoresponsiveness with e.g. aging.

Local anisotropy in mineralized fibrocartilage and subchondral bone beneath the tendon-bone interface.

The enthesis allows the insertion of tendon into bone thanks to several remarkable strategies. This complex and clinically relevant location often features a thin layer of fibrocartilage sandwiched between tendon and bone to cope with a highly heterogeneous mechanical environment. The main purpose of this study was to investigate whether mineralized fibrocartilage and bone close to the enthesis show distinctive three-dimensional microstructural features, possibly to enable load transfer from tendon to bone. As a model, the Achilles tendon-calcaneus bone system of adult rats was investigated with histology, backscattered electron imaging and micro-computed tomography. The microstructural porosity of bone and mineralized fibrocartilage in different locations including enthesis fibrocartilage, periosteal fibrocartilage and bone away from the enthesis was characterized. We showed that calcaneus bone presents a dedicated protrusion of low porosity where the tendon inserts. A spatially resolved analysis of the trabecular network suggests that such protrusion may promote force flow from the tendon to the plantar ligament, while partially relieving the trabecular bone from such a task. Focusing on the tuberosity, highly specific microstructural aspects were highlighted. Firstly, the interface between mineralized and unmineralized fibrocartilage showed the highest roughness at the tuberosity, possibly to increase failure resistance of a region carrying large stresses. Secondly, fibrochondrocyte lacunae inside mineralized fibrocartilage, in analogy with osteocyte lacunae in bone, had a predominant alignment at the enthesis and a rather random organization away from it. Finally, the network of subchondral channels inside the tuberosity was highly anisotropic when compared to contiguous regions. This dual anisotropy of subchondral channels and cell lacunae at the insertion may reflect the alignment of the underlying collagen network. Our findings suggest that the microstructure of fibrocartilage may be linked with the loading environment. Future studies should characterize those microstructural aspects in aged and or diseased conditions to elucidate the poorly understood role of bone and fibrocartilage in enthesis-related pathologies.

Homogenized finite element models can accurately predict screw pull-out in continuum materials, but not in porous materials.

BACKGROUND AND OBJECTIVE: Bone screw fixation can be estimated with several test methods such as insertion torque, pull-out, push-in and bending tests. A basic understanding of the relationship between screw fixation and bone microstructure is still lacking. Computational models can help clarify this relationship. The objective of the paper is to evaluate homogenized finite element (hFE) models of bone screw pull-out. METHODS: Experimental pull-out tests were performed on three materials: two polyurethane (PU) foams having a porous microstructure, and a high density polyethylene (HDPE) which is a continuum material. Forty-five titanium pedicle screws were inserted to 10, 20, and 30 mm in equally sized blocks of all three materials (N = 5/group). Pull-out characteristics i.e. stiffness (S), yield force (Fy), peak pull-out force (Fult) and displacement at Fult (dult) were measured. hFE models were created replicating the experiments. The screw was modeled as a rigid body and 5 mm axial displacement was applied to the head of the screw. Simulations were performed evaluating two different conditions at the bone-screw interface; once in which the screw fitted the pilot hole exactly ("free-stressed") and once in which interface stresses resulting from the insertion process were taken into account ("pre-stressed"). RESULTS: The simulations representing the pre-stressed condition in HDPE matched the experimental data well; S, Fy, and Fult differed less than 11%, 2% and 0.5% from the experimental data, respectively, whereas dult differed less than 16%. The free-stressed simulations were less accurate, especially stiffness (158% higher than the pre-stressed condition) and dult (30% lower than pre-stressed condition) were affected. The simulations representing PU did not match the experiments well. For the 20 mm insertion depth, S, Fy and Fult differed by more than 104%, 89% and 66%, respectively from the experimental values. Agreement did not improve for 10 and 30 mm insertion depths. CONCLUSIONS: We found that hFE models can accurately quantify screw pull-out in continuum materials such as HDPE, but not in materials with a porous structure, such as PU. Pre-stresses in the bone induced by the insertion process cannot be neglected and need to be included in the hFE simulations.

High-Resolution Cone-Beam Computed Tomography is a Fast and Promising Technique to Quantify Bone Microstructure and Mechanics of the Distal Radius.

Obtaining high-resolution scans of bones and joints for clinical applications is challenging. HR-pQCT is considered the best technology to acquire high-resolution images of the peripheral skeleton in vivo, but a breakthrough for widespread clinical applications is still lacking. Recently, we showed on trapezia that CBCT is a promising alternative providing a larger FOV at a shorter scanning time. The goals of this study were to evaluate the accuracy of CBCT in quantifying trabecular bone microstructural and predicted mechanical parameters of the distal radius, the most often investigated skeletal site with HR-pQCT, and to compare it with HR-pQCT. Nineteen radii were scanned with four scanners: (1) HR-pQCT (XtremeCT, Scanco Medical AG, @ (voxel size) 82 µm), (2) HR-pQCT (XtremeCT-II, Scanco, @60.7 µm), (3) CBCT (NewTom 5G, Cefla, @75 µm) reconstructed and segmented using in-house developed software and (4) microCT (VivaCT40, Scanco, @19 µm-gold standard). The following parameters were evaluated: predicted stiffness, strength, bone volume fraction (BV/TV) and trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N). The overall accuracy of CBCT with in-house optimized algorithms in quantifying bone microstructural parameters was comparable (R2 = 0.79) to XtremeCT (R2 = 0.76) and slightly worse than XtremeCT-II (R2 = 0.86) which were both processed with the standard manufacturer's technique. CBCT had higher accuracy for BV/TV and Tb.Th but lower for Tb.Sp and Tb.N compared to XtremeCT. Regarding the mechanical parameters, all scanners had high accuracy (R2 [Formula: see text] 0.96). While HR-pQCT is optimized for research, the fast scanning time and good accuracy renders CBCT a promising technique for high-resolution clinical scanning.

Cemented short-stem total hip arthroplasty: Characteristics of line-to-line versus undersized cementing techniques using a validated CT-based finite element analysis.

Short stems are becoming increasingly popular in total hip arthroplasty as they preserve the bone stock and simplify the implantation process. Short stems are advised mainly for patients with good bone stock. The clinical use of short stems could be enlarged to patients with poor bone stock if a cemented alternative would be available. Therefore, this study aimed to quantify the mechanical performance of a cemented short stem and to compare the "undersized" cementing strategy (stem one size smaller than the rasp) with the "line-to-line" technique (stem and rasp with identical size). A prototype cemented short stem was implanted in eight pairs of human cadaveric femora using the two cementing strategies. Four pairs were experimentally tested in a single-legged stance condition; stiffness, strength, and bone surface displacements were measured. Subject-specific nonlinear finite element models of all the implanted femora were developed, validated against the experimental data, and used to evaluate the behavior of cemented short stems under physiological loading conditions resembling level walking. The two cementing techniques resulted in nonsignificant differences in stiffness and strength. Strength and stiffness as calculated from finite element were 8.7 ± 16% and 9.9 ± 15.0% higher than experimentally measured. Displacements as calculated from finite element analyses corresponded strongly (R 2 ≥ .97) with those measured by digital image correlation. Stresses during level walking were far below the fatigue limit for bone and bone cement. The present study suggests that cemented short stems are a promising solution in osteoporotic bone, and that the line-to-line and undersized cementing techniques provide similar outcomes.

Quantification of 3D microstructural parameters of trabecular bone is affected by the analysis software.

Over the last decades, the use of high-resolution imaging systems to assess bone microstructural parameters has grown immensely. Yet, no standard defining the quantification of these parameters exists. It has been reported that different voxel size and/or segmentation techniques lead to different results. However, the effect of the evaluation software has not been investigated so far. Therefore, the aim of this study was to compare the bone microstructural parameters obtained with two commonly used commercial software packages, namely IPL (Scanco, Switzerland) and CTan (Bruker, Belgium). We hypothesized that even when starting from the same segmented scans, different software packages will report different results. Nineteen trapezia and nineteen distal radii were scanned at two resolutions (20 µm voxel size with microCT and HR-pQCT 60 µm). The scans were segmented using the scanners' default protocol. The segmented images were analyzed twice, once with IPL and once with CTan, to quantify bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N) and specific bone surface (BS/BV). Only small differences between IPL and CTan were found for BV/TV. For Tb.Th, Tb.Sp and BS/BV high correlations (R2 ≥ 0.99) were observed between the two software packages, but important relative offsets were observed. For microCT scans, the offsets were relative constant, e.g., around 15% for Tb.Th. However, for the HR-pQCT scans the mean relative offsets ranged over the different bone samples (e.g., for Tb.Th from 14.5% to 19.8%). For Tb.N, poor correlations (0.43 ≤ R2 ≤ 0.81) for all tested cases were observed. We conclude that trabecular bone microstructural parameters obtained with IPL and CTan cannot be directly compared except for BV/TV. For Tb.Th, Tb.Sp and BS/BV, correction factors can be determined, but these depend on both the image voxel size and specific anatomic location. The two software packages did not produce consistent data on Tb.N. The development of a universal standard seems desirable.

Automated muscle elongation measurement during reverse shoulder arthroplasty planning.

BACKGROUND: Adequate deltoid and rotator cuff elongation in reverse shoulder arthroplasty is crucial to maximize postoperative functional outcomes and to avoid complications. Measurements of deltoid and rotator cuff elongation during preoperative planning can support surgeons in selecting a suitable implant design and position. Therefore, this study presented and evaluated a fully automated method for measuring deltoid and rotator cuff elongation. METHODS: Complete scapular and humeral models were extracted from computed tomography scans of 40 subjects. First, a statistical shape model of the complete humerus was created and evaluated to identify the muscle attachment points. Next, a muscle wrapping algorithm was developed to identify the muscle paths and to compute muscle lengths and elongations after reverse shoulder arthroplasty implantation. The accuracy of the muscle attachment points and the muscle elongation measurements was evaluated for the 40 subjects by use of both complete and artificially created partial humeral models. Additionally, the muscle elongation measurements were evaluated for a set of 50 arthritic shoulder joints. Finally, a sensitivity analysis was performed to evaluate the impact of implant positioning on deltoid and rotator cuff elongation. RESULTS: For the complete humeral models, all muscle attachment points were identified with a median error < 3.5 mm. For the partial humeral models, the errors on the deltoid attachment point largely increased. Furthermore, all muscle elongation measurements showed an error < 1 mm for 75% of the subjects for both the complete and partial humeral models. For the arthritic shoulder joints, the errors on the muscle elongation measurements were <2 mm for 75% of the subjects. Finally, the sensitivity analysis showed that muscle elongations were affected by implant positioning. DISCUSSION: This study presents an automated method for accurately measuring muscle elongations during preoperative planning of shoulder arthroplasty. The results show that the accuracy in measuring muscle elongations is higher than the accuracy in indicating the muscle attachment points. Hence, muscle elongation measurements are insensitive to the observed errors on the muscle attachment points. Related to this finding, muscle elongations can be accurately measured for both a complete humeral model and a partial humeral model. Because the presented method also showed accurate results for arthritic shoulder joints, it can be used during preoperative shoulder arthroplasty planning, in which typically only the proximal humerus is present in the scan and in which bone arthropathy can be present. As the muscle elongations are sensitive to implant positioning, surgeons can use the muscle elongation measurements to refine their surgical plan.

Mechanical and morphological characterization of PMMA/bone composites in human femoral heads.

PMMA bone cement has gained an important place in a variety of orthopaedic applications in the femur. However, appropriate data on the mechanical properties of bone-cement composites from the human femur are lacking. Therefore, the goal of this study was to determine the morphological and quasi-static compressive properties of proximal femoral bone-cement composites. Thirty trabecular bone specimens were extracted from fifteen pairs of human femoral heads using specimen-specific cutting guides to ensure an accurate alignment with the main trabecular direction (MTD). One specimen from each pair was augmented with PMMA bone cement, while the other one was left untreated. Specimens were scanned with µCT to determine morphological parameters and tested in quasi-static compression until failure. We found that the long axis of the specimens was highly aligned with the MTD (mean error < 5°). A higher compressive modulus and ultimate strength were observed for the bone-cement composite specimens (E = 5.7 ± 0.4 GPa; σu = 77.9 ± 5.1 MPa) compared to the bone only specimens (E = 2.9 ± 0.7 GPa; σu = 19.0 ± 5.8 MPa). Furthermore, the composites had a higher modulus, but lower strength than cement itself (E = 5.0 ± 0.3 GPa; σu = 85.9 ± 2.7 MPa) and the composite modulus was significantly correlated with the bone volume fraction (BV/TV). These results are in contrast to previous findings on human vertebral bone, where the composite was more compliant than cement and no correlation was found between BV/TV and the composite modulus. Thus, properties of bone-cement composites cannot simply be applied across different anatomical sites; the site-specific differences in bone density and trabecular alignment should be taken into account. Collectively, the present results suggest that at low BV/TV, cement dominates the composite properties, while at high BV/TV, the contribution of bone becomes apparent, revealing a positive relationship between BV/TV and the on-axis modulus.