3D Femur Model Research Articles

Analysis of Variation in Sagittal Curvature of the Femoral Condyles.

In designing femoral components, which restore native (i.e., healthy) knee kinematics, the flexion-extension (F-E) axis of the tibiofemoral joint should match that of the native knee. Because the F-E axis is governed by the curvature of the femoral condyles in the sagittal plane, the primary objective was to determine the variation in radii of curvature. Eleven high accuracy three-dimensional (3D) femur models were generated from ultrahigh resolution CT scans. The sagittal profile of each condyle was created. The radii of curvature at 15 deg increments of arc length were determined based on segment circles best-fit to ±15 deg of arc at each increment. Results were standardized to the radius of the best-fit overall circle to 15 deg-105 deg for the femoral condyle having a radius closest to the mean radius. Medial and lateral femoral condyles exhibited multiradius of curvature sagittal profiles where the radius decreased at 30 deg flexion by 10 mm and at 15 deg flexion by 8 mm, respectively. On either side of the decrease, radii of segment circles were relatively constant. Beyond the transition angles where the radii decreased, the anterior-posterior (A-P) positions of the centers of curvature varied 4.8 mm and 2.3 mm for the medial and lateral condyles, respectively. A two-radius of curvature profile approximates the radii of curvature of both native femoral condyles, but the transition angles differ with the transition angle of the medial femoral condyle occurring about 15 deg later in flexion. Owing to variation in A-P positions of centers of curvature, the F-E axis is not strictly fixed in the femur.

Optimizing Femoral Tunnel Placement in ACL Reconstruction: Effect of a 70-degree Arthroscope and Portal Position

Purpose: The aim of this study was to assess the accuracy of femoral tunnel placement for anterior cruciate ligament reconstruction (ACLR) using either an accessory medial portal or a 70-degree arthroscope compared with the standard 2-portal technique. Methods: A computerized 3D model of the femur was obtained with 4 reference points marked around the LFC. Using the simulator, 2 surgeons marked 5 consecutive femoral tunnel points with a 30-degree arthroscope in the lateral portal (30AL), then with a 30-degree arthroscope in an accessory medial portal (30AM), and next with a 70-degree arthroscope in the lateral portal (70AL). This was repeated after one week. Subjects then marked their target femoral tunnel positions (T) on the free femur sawbone model. After each episode, the distances from the marked tunnel point to the 4 reference points (d1, d2, d3, d4) were measured. After mapping to the 3D femur model, the co-ordinates of each marked tunnel position were determined. The distance (r) from T was calculated for each episode. Results: The median value of r was 1.27 mm(SE 0.15 mm) using 30AL, 0.54 mm (SE 0.12 mm) using the 30AM portal, and 0.20 mm (SE 0.047 mm) with 70AL. r was significantly smaller with 70AL (P<0.0001). The difference in r between 30AM and 30AL was also statistically significant (P=0.019). Conclusions: A 70-degree arthroscope in the lateral portal allows greater accuracy in femoral tunnel placement compared with a 30-degree arthroscope in either the lateral or an accessory medial portal.

Computed tomography-based automated 3D measurement of femoral version: Validation against standard 2D measurements in symptomatic patients.

To validate 3D methods for femoral version measurement, we asked: (1) Can a fully automated segmentation of the entire femur and 3D measurement of femoral version using a neck based method and a head-shaft based method be performed? (2) How do automatic 3D-based computed tomography (CT) measurements of femoral version compare to the most commonly used 2D-based measurements utilizing four different landmarks? Retrospective study (May 2017 to June 2018) evaluating 45 symptomatic patients (57 hips, mean age 18.7 ± 5.1 years) undergoing pelvic and femoral CT. Femoral version was assessed using four previously described methods (Lee, Reikeras, Tomczak, and Murphy). Fully-automated segmentation yielded 3D femur models used to measure femoral version via femoral neck- and head-shaft approaches. Mean femoral version with 95% confidence intervals, and intraclass correlation coefficients were calculated, and Bland-Altman analysis was performed. Automatic 3D segmentation was highly accurate, with mean dice coefficients of 0.98 ± 0.03 and 0.97 ± 0.02 for femur/pelvis, respectively. Mean difference between 3D head-shaft- (27.4 ± 16.6°) and 3D neck methods (12.9 ± 13.7°) was 14.5 ± 10.7° (p < 0.001). The 3D neck method was closer to the proximal Lee (-2.4 ± 5.9°, -4.4 to 0.5°, p = 0.009) and Reikeras (2 ± 5.6°, 95% CI: 0.2 to 3.8°, p = 0.03) methods. The 3D head-shaft method was closer to the distal Tomczak (-1.3 ± 7.5°, 95% CI: -3.8 to 1.1°, p = 0.57) and Murphy (1.5 ± 5.4°, -0.3 to 3.3°, p = 0.12) methods. Automatic 3D neck-based-/head-shaft methods yielded femoral version angles comparable to the proximal/distal 2D-based methods, when applying fully-automated segmentations.

Comparative Analysis of Convolutional Neural Network Architectures for Automated Knee Segmentation in Medical Imaging: A Performance Evaluation

Abstract Segmentation of anatomical components is a major step in creating accurate and realistic 3D models of the human body, which are used in many clinical applications, including orthopedics. Recently, many deep learning approaches have been proposed to solve the problem of manual segmentation, which is time-consuming and operator-dependent. In the present study, SegResNet has been adapted from other domains, such as brain tumors, for knee joints, in particular, to segment the femoral bone from magnetic resonance images. This algorithm has been compared to the well-known U-Net in terms of evaluation metrics, such as the Dice similarity coefficient and Hausdorff distance. In the training phase, various combinations of hyperparameters, such as epochs and learning rates, have been tested to determine which combination produced the most accurate results. Based on their comparable results, both U-Net and SegResNet performed well in accurately segmenting the femur. Dice similarity coefficients of 0.94 and Hausdorff distances less than or equal to 1 mm indicate that both models are effective at capturing anatomical boundaries in the femur. According to the results of this study, SegResNet is a viable option for automating the creation of 3D femur models. In the future, the performance and applicability of SegResNet in real-world settings will be further validated and tested using a variety of datasets and clinical scenarios.

Evaluation of the reliability and accuracy of femur measurements acquired from computed tomography images

The biological profile holds notable significance within forensic assessments, as it plays a crucial role in determining biological identity. Moreover, it possesses substantial potential for applications in fields such as medical legal cases and forensic anthropology. Recent advancements in technology, specifically in the field of computed tomography, have enabled the accurate acquisition of detailed anatomical data from CT scans present in extensive medical repositories. The validity of new methods developed through the application of these techniques should therefore be analyzed. The primary intent of this research was to investigate the measurement accuracy obtained from CT-generated 3D femur models. To investigate the accuracy and reliability of measurements obtained from CT-generated 3D femur models, 3 different studies were conducted. A dataset comprising fifteen femurs was employed for analysis and measurement purposes. The obtained images were subsequently compared to twelve measurements acquired from the dry femora, enabling an assessment of the reliability and accuracy of both measurement protocols. To investigate the effect of CT parameters and soft tissue, 4 femurs were used. The analysis of twelve femur measurements obtained from the CT images processed with OsiriX software was carried out using Excel software packages and SPSS 24.0. From the results of this study, it can be observed that there is no discernible pattern regarding the reliability of image acquisition in any particular way. This implies that both dry femur bone and 3D virtual femur models can be used interchangeably for the 12 metric measurements used in this study, and at the same time, different scanning parameters or soft tissue influence for these measurements do not make a statistically significant difference.

Virtual 3D femur model to assess femoral version: comparison to the 2D axial slice approach.

Quantifying femoral version is crucial in diagnosing femoral version abnormalities and for accurate pre-surgical planning. There are numerous methods for measuring femoral version, however, reliability studies for most of these methods excluded children with hip deformities. To propose a method of measuring femoral version based on a virtual 3D femur model, and systematically compare its reliability to the widely used Murphy's 2D axial slice technique. We searched our imaging database to identify hip/femur CTs performed on children (<18 years old) with a clinical indication of femoral version measurement (September 2021-August 2022). Exclusion criteria were prior hip surgery, and inadequate image quality or field-of-view. Two blinded radiologists independently measured femoral version using the virtual 3D femur model and Murphy's 2D axial slice method. To assess intrareader variability, we randomly selected 20% of the study sample for re-measurements by the two radiologists >2 weeks later. We analyzed the reliability and correlation of these techniques via intraclass correlation coefficient (ICC), Bland-Altman analysis, and deformity subgroup analysis. Our study sample consisted of 142 femurs from 71 patients (10.6±4.4 years, male=31). Intra- and inter-reader correlations for both techniques were excellent (ICC≥0.91). However, Bland-Altman analysis revealed that the standard deviation (SD) of the absolute difference between the two radiologists for the Murphy method (mean 13.7°) was larger than that of the 3D femur model technique (mean 4.8°), indicating higher reader variability. In femurs with hip flexion deformity, the SD of the absolute difference for the Murphy technique was 17°, compared to 6.5° for the 3D femur model technique. In femurs with apparent coxa valga deformity, the SD of the absolute difference for the Murphy technique was 10.4°, compared to 5.2° for the 3D femur model technique. The 3D femur model technique is more reliable than the Murphy's 2D axial slice technique in measuring femoral version, especially in children with hip flexion and apparent coxa valga deformities.

Femur reconstruction in 3D ultrasound for orthopedic surgery planning.

Derotation varisation osteotomy of the proximal femur in pediatric patients usually relies on 2-dimensional X-ray imaging, as CT and MRI still are disadvantageous when applied in small children either due to a high radiation exposure or the need of anesthesia. This work presents a radiation-free non-invasive tool to 3D-reconstruct the femur surface and measure relevant angles for orthopedic diagnosis and surgery planning from 3D ultrasound scans instead. Multiple tracked ultrasound recordings are segmented, registered and reconstructed to a 3D femur model allowing for manual measurements of caput-collum-diaphyseal (CCD) and femoral anteversion (FA) angles. Novel contributions include the design of a dedicated phantom model to mimic the application ex vivo, an iterative registration scheme to overcome movements of a relative tracker only attached to the skin, and a technique to obtain the angle measurements. We obtained sub-millimetric surface reconstruction accuracy from 3D ultrasound on a custom 3D-printed phantom model. On a pre-clinical pediatric patient cohort, angular measurement errors were [Formula: see text] and eventually [Formula: see text] for CCD and FA angles, respectively, both within the clinically acceptable range. To obtain these results, multiple refinements of the acquisition protocol were necessary, ultimately reaching success rates of up to 67% for achieving sufficient surface coverage and femur reconstructions that allow for geometric measurements. Given sufficient surface coverage of the femur, clinically acceptable characterization of femoral anatomy is feasible from non-invasive 3D ultrasound. The acquisition protocol requires leg repositioning, which can be overcome using the presented algorithm. In the future, improvements of the image processing pipeline and more extensive surface reconstruction error assessments could enable more personalized orthopedic surgery planning using cutting templates.

Correcting for distal femoral asymmetry is necessary to determine postoperative alignment deviations from planned alignment of the femoral component

BackgroundOne method for assessing the accuracy of manual, patient-specific, navigational, and robotic-assisted total knee arthroplasty (TKA) instrumentation is to use a post-operative computer tomogram and determine the deviation of the femoral component alignment relative to the planned alignment in the native (i.e. healthy) contralateral distal femoral epiphysis. However, side-to-side asymmetry might introduce errors which inflate alignment deviations. This study quantified asymmetry in the distal femoral epiphysis. MethodsHigh resolution CT images (0.5 mm slice thickness) were acquired from bilateral lower limb specimens of 13 skeletally mature subjects with no skeletal abnormalities. Images were segmented to generate 3D femur models. Asymmetry was quantified by differences in positions and orientations required to shape-match the distal epiphysis of the mirror 3D femur model to the distal epiphysis of the contralateral 3D femur model. ResultsAsymmetry was due to random rather than systematic differences. Random differences (i.e. standard deviations) in proximal–distal (P-D) and anterior-posterior (A-P) positions were 1.1 mm and in varus-valgus (V-V) and internal-external (I-E) orientations were 0.9° and 1.3°, respectively. These represented substantial relative errors of up to 50 % in previously reported overall alignment deviations. ConclusionsAlthough small in an absolute sense, asymmetry of the distal femur epiphysis introduced substantial relative errors when assessing accuracy of femoral component alignment in TKA. When post-operative computer tomograms are used to assess the accuracy of manual, patient specific, navigational, and robotic-assisted TKA instrumentation, the overall deviation should be corrected for asymmetry to better indicate the accuracy of the surgical technique.

Clinical three-dimensional anatomy of the femur considering navigation-aided surgery of total knee arthroplasty in Japanese patients

PurposeFew studies exist regarding sagittal alignment describing femur morphology in navigation-aided surgery. This study investigated the three-dimensional (3D) sagittal femoral alignment of the whole femur. MethodsSeventy-three consecutive patients (59 females, 14 males, mean age: 76.1 years), yielding 140 femurs, were included in this study. A computed-tomography-based patient-specific 3D femur model was used to define a mechanical axis-based reference plane. Proximal and distal femoral axis angles (PFA, DFA) to the reference plane were measured in 3D using custom software. PFA and DFA represent the proximal and distal inclination of the femoral anatomical axis in sagittal plane, respectively. ResultsPFA (10.6 ± 1.5°) was greater than DFA (2.6 ± 1.6°; P < 0.0001). DFA in females (2.3 ± 1.4°) was smaller than in males (3.9 ± 1.7°; P < 0.0001). ConclusionThis is the first report of measurement of femoral sagittal alignment related to both 3D anatomy and decision making of femoral flexion angle using navigation surgery for total knee arthroplasty. This report shows a robust DFA measurement that could be used as a template for femoral implants flexion angle when performing both conventional and navigated total knee arthroplasty.

The Impact of Coronal Configuration of the Proximal Femur on its Mechanical Properties and the Validation of a New Theoretical Model: Finite Element Analysis and Biomechanical Examination.

This study aims to establish the coronal configuration of the proximal femur as an independent factor for its mechanical properties and provide validation for the theoretical model "fulcrum-balance-reconstruction." The digital 3D femur model constructed with the lower extremity high-resolution computed tomography of a senior subject was applied with the axial compression of 2100N under 5 different α angles of 10°, 5°, 0°, -5°, -10°. The equivalent stress distribution of the femoral geometric model under each angle were calculated. Under the same five α angles, fatigue test was performed on 15 composite artificial left femurs (three specimens in each angle group) to obtain the failure cycle and fracture site. The statistical analysis was accomplished using One-Way ANOVA. The maximum stress of the entire femur in physiological angle (α=10°) occurred below femoral neck with a value of 63.91 MPa. When the proximal femur is in extreme abducted angle (α=-10°), the maximum stress shift to the lower medial cortex of femoral shaft with a value of 105.2 MPa. As the α angle changed from 10° to -10°, the greater trochanteric region had the largest increment in maximum stress (2.78 times for cortex and 1.67 times for cancellous bone) locally at the proximal femur. The failure cycles of the artificial femurs with a variety of abduction angle were averagely 9126 ± 2453.87 (α=-10°), 58,112.33 ± 1293.84 (α=-5°), 92,879.67 ± 2398.54 (α=0°), 172,045.3 ± 11011.11 (α=5°), and 264,949.3 ± 35,067.26 (α=10°), and the statistical analysis revealed that the α angle of the group of concern is proportional to the P value of the corresponding group compared to the 10° group(α=5° & α=10°, P=0.01; α=0 & α=10°, P=0.001; α=-5°, -10° & α=10°, P < 0.001). In fatigue test, the fracture appeared on femoral neck for the α angles of 10° (three subcapital), 5° (two basal; one transcervical), and 0° (one transcervical). Fracture sites located at trochanteric region were observed with the more abducted angles including 0° (two subtrochanteric) and -5° (two intertrochanteric; one subtrochanteric). The fracture line was only found on femoral shaft in the -10° group. With increasing hip abduction, the proximal femur shows declining mechanical properties, which suggests higher risk of hip fracture and increasement in the fraction of trochanteric fracture subtype. Furthermore, the hypothesis of "fulcrum-balance-reconstruction" was validated by our study to a certain extent.

Coxa valga and antetorta increases differences among different femoral version measurements : potential implications for derotational femoral osteotomy planning.

To evaluate how abnormal proximal femoral anatomy affects different femoral version measurements in young patients with hip pain. First, femoral version was measured in 50 hips of symptomatic consecutively selected patients with hip pain (mean age 20 years (SD 6), 60% (n = 25) females) on preoperative CT scans using different measurement methods: Lee et al, Reikerås et al, Tomczak et al, and Murphy et al. Neck-shaft angle (NSA) and α angle were measured on coronal and radial CT images. Second, CT scans from three patients with femoral retroversion, normal femoral version, and anteversion were used to create 3D femur models, which were manipulated to generate models with different NSAs and different cam lesions, resulting in eight models per patient. Femoral version measurements were repeated on manipulated femora. Comparing the different measurement methods for femoral version resulted in a maximum mean difference of 18° (95% CI 16 to 20) between the most proximal (Lee et al) and most distal (Murphy et al) methods. Higher differences in proximal and distal femoral version measurement techniques were seen in femora with greater femoral version (r > 0.46; p < 0.001) and greater NSA (r > 0.37; p = 0.008) between all measurement methods. In the parametric 3D manipulation analysis, differences in femoral version increased 11° and 9° in patients with high and normal femoral version, respectively, with increasing NSA (110° to 150°). Measurement of femoral version angles differ depending on the method used to almost 20°, which is in the range of the aimed surgical correction in derotational femoral osteotomy and thus can be considered clinically relevant. Differences between proximal and distal measurement methods further increase by increasing femoral version and NSA. Measurement methods that take the entire proximal femur into account by using distal landmarks may produce more sensitive measurements of these differences.Cite this article: Bone Jt Open2022;3(10):759-766.

3D printed fracture reduction guides planned and printed at the point of care show high accuracy – a porcine feasibility study

PurposeAfter surgical treatment of comminuted diaphyseal femoral and tibial fractures, relevant malalignment, especially rotational errors occur in up to 40–50%. This either results in a poor clinical outcome or requires revision surgery. This study aims to evaluate the accuracy of reduction if surgery is supported by 3D guides planned and printed at the point of care.MethodsTen porcine legs underwent computed tomography (CT) and 3D models of femur and tibia were built. Reduction guides were virtually constructed and fitted to the proximal and distal metaphysis. The guides were 3D printed using medically approved resin. Femoral and tibial comminuted diaphyseal fractures were simulated and subsequently reduced using the 3D guides. Postoperative 3D bone models were reconstructed to compare the accuracy to the preoperative planning.ResultsFemoral reduction showed a mean deviation ± SD from the plan of 1.0 mm ± 0.9 mm for length, 0.9° ± 0.7° for varus/valgus, 1.2° ± 0.9° for procurvatum/recurvatum and 2.0° ± 1.7° for rotation. Analysis of the tibial reduction revealed a mean deviation ± SD of 2.4 mm ± 1.6 mm for length, 1.0° ± 0.6° for varus/valgus, 1.3° ± 1.4° for procurvatum/recurvatum and 2.9° ± 2.2° for rotation.ConclusionsThis study shows high accuracy of reduction with 3D guides planned and printed at the point of care. Applied to a clinical setting, this technique has the potential to avoid malreduction and consecutive revision surgery in comminuted diaphyseal fractures.Level of EvidenceBasic Science.

Comparative biomechanical performance of two configurations of screw constructs and types used to stabilize different sites of unstable Pauwels type II femoral neck fractures: A finite element analysis

A smaller dimension of the femoral neck in the Asian population may have difficulty placing inverted triangle multiple screws configuration for treatment. Posterior triangle configuration, which is suitable in limited space of the femoral neck, is a promising alternative treatment approach. This study aimed to investigate the biomechanical performance of inverted and posterior triangles of multiple screws fixation configuration for both cannulated and standard solid-core screws in stabilizing Pauwels type II femoral neck fracture sub-capital, mid-cervical, and basilar regions using Finite Element (FE) method. A 3D femur model was created for Pauwels type II femoral neck fractures. The fracture sites were in the mid-cervical, sub-capital, and basilar regions, with a spacing of 7 mm between adjacent fracture lines. Both cannulated and solid-core screws were configured in the inverted and posterior triangle patterns. The applied physiological loads to the FE models included muscle and hip contact forces. Equivalent von Mises (EQV) stresses were used to monitor fixation strength whereas elastic strain of each configuration indicated the degree of stability of a fracture site. EQV stress on the screws for posterior and inverted triangle configuration ranged from 212.1 to 290.2MPa, and 224.4-314.8MPa, respectively. The EQV stress the posterior triangle configuration was lower than the inverted triangle configuration by 5.5-10.8%. The stress exhibited on the screw was greatest when the fracture site was at basilar regions, 1.1-1.3 times greater than fracture in sub-capital region. Elastic strain at fractures retained by cannulated screw was greater than solid-core screw with maximum difference of 68 microstrains. Cannulated screw provided less stability than the solid-core screw. The screws used in the posterior triangle configuration exhibits lower screw stress in all fracture regions of the femoral neck. The solid-core screw shows superior biomechanical properties compared with cannulated screw with lower EQV stress and better fracture stability. Posterior triangle configuration is considered an alternative treatment of choice for the patient with a small dimension of the femoral neck.

Computational simulation of cephalomedullary nailing in the osteoporotic Asian femur and clinical implications

PurposeTo assess the conformity of PFNA-II® and introduce clinical implications of new cephalomedullary nail (CMN) by analyzing three-dimensional (3D) modeling with virtual implantation at the actual size. Materials and methodsThirty-four patients (average age; 79 years, range 68–94 years) who sustained the intertrochanteric fracture of the femur were enrolled in the present study. After importing into Mimics® software, the intact femurs on the opposite side were selected as cropping areas to reconstruct the 3D femur model with the medullary canal. PFNA-II® and new CMNs (lateral angle 0° and 2°, CCD angle 130°; CMN0° and CMN2°) were processed at the actual size and ideally placed in the proximal femur using Mimics® software. The virtual entry point (EP), nail conformity, and anatomical relationships with the adjacent structures were assessed. ResultsThe virtual EP of PFNA-II® was placed along the cervico-trochanteric (CT) junction in the posterior half around trochanteric fossa and always medial to the tip of greater trochanter (GT). There were six abutments in PFNA-II® models, one impingement in CMN 0°, and no impingement in CMN 2°. All the models with cortical abutment showed increased anterior and lateral bowing of the proximal shaft owing to age-dependent changes. Compared with PFNA-II®, with a decreasing tendency on the mediolateral angle of new CMNs, the virtual EP shifted to the medial and anterior side towards the CT junction. By simulating the intentional positioning in the media-to-lateral direction, the abutments in the PFNA-II® model could not be avoided. Furthermore, the lag screw of CMN 0° was placed ideally at the center or inferior side of the femoral head < 10 mm in any direction without a cortical abutment. ConclusionTo avoid cortical abutment of CMN in the Asian geriatric femur, the virtual EP would be technically placed in the medial to the GT tip, and the implant design should be changed to decrease the mediolateral angle.

A time-dependent mechanobiology-based topology optimization to enhance bone growth in tissue scaffolds

Scaffold-based bone tissue engineering has been extensively developed as a potential means to treatment of large bone defects. To enhance the biomechanical performance of porous tissue scaffolds, computational design techniques have gained growing popularity attributable to their compelling efficiency and strong predictive features compared with time-consuming trial-and-error experiments. Nevertheless, the mechanical stimulus necessary for bone regeneration, which characterizes dynamic nature due to continuous variation in the bone-scaffold construct system as a result of bone-ingrowth and scaffold biodegradation, is often neglected. Thus, this study proposes a time-dependent mechanobiology-based topology optimization framework for design of tissue scaffolds, thereby developing an ongoing favorable microenvironment and ensuring a long-term outcome for bone regeneration. For the first time, a level-set based topology optimization algorithm and a time-dependent shape derivative are developed to optimize the scaffold architecture. In this study, a large bone defect in a simulated 2D femur model and a partial defect in a 3D femur model are considered to demonstrate the effectiveness of the proposed design method. The results are compared with those obtained from stiffness-based topology optimization, time-independent design and typical scaffold constructs, showing significant advantages in continuing bone ingrowth outcomes.

3D Finite Element Analysis of the Modular Prosthesis with Tooth Mechanism of the Femoral Shaft.

ObjectivesTo evaluate the mechanical properties and provide a theoretical basis of a diaphyseal prosthesis with tooth mechanism using the finite element analysis method from the point of view of biomechanics.MethodsA 3D digital femur model was generated based on a 28‐year‐old healthy man's femoral computed tomography (CT) data in Mimics 17.0 and the customized diaphyseal prostheses with/without tooth mechanism were designed in SolidWorks 2016. The 3D femur model after 8 cm osteotomy in the middle of its shaft and the prostheses with/without tooth mechanism was imported into Abaqus 2016 and the finite element analysis models were established. Three biomechanical tests (compression test, torsion test, and 3P‐bending test) under broken load were simulated in FEA to evaluate the performance of the prostheses.ResultsThe stress distributions of the two prostheses were similar and the maximum von Mises stresses placed on them were very close in each test. The maximum von Mises stresses on the prosthesis with tooth mechanism were 31.55, 319.7, and 447.4 MPa, respectively, and those on the prosthesis without tooth mechanism were 26.26, 300.4, and 455.2 MPa, respectively, in the compression, torsion, and 3P‐bending tests. The maximum von Mises stresses on them were far below the ultimate tensile strength or ultimate compressive strength of the titanium alloy.ConclusionsThe diaphyseal prosthesis with tooth mechanism is helpful to adjust the rotation of the long bone during operation. Compared with the conventional diaphyseal prosthesis (without tooth mechanism), the diaphyseal prosthesis with tooth mechanism also has a good biomechanical performance and does not increase the risk of prosthetic failure.

Implant placement accuracy in total knee arthroplasty: validation of a CT-based measurement technique.

The primary goal of many computer-assisted surgical systems like robotics for total knee arthroplasty (TKA) is to accurately execute a preoperative plan. To assess whether the preoperative plan was executed accurately in 3D, one option is to compare the planned and postoperative implant placement using a preoperative and postoperative CT scan of the patient's limb. This comparison requires a 3D-to-3D surface registration between the preoperative and postoperative 3D bone models and between the planned and postoperative 3D implants. Hence, the present study aimed at validating this measurement technique by determining (I) the anatomical regions that result in the lowest 6-degree of freedom (DoF) errors for 3D-to-3D surface registration of bone models, (II) the 6-DoF errors for 3D-to-3D surface registration of the implant models, and (III) the 6-DoF of the complete measurement technique. Four different regions of the femur were tested to determine which one would result in the most accurate 3D-to-3D registration of the bone models using 12 cadaveric lower limb specimens. Next, total knee arthroplasties were performed on six specimens, and the accuracy of the 3D-to-3D implant registration was evaluated against a gold standard registration performed using fiducial markers. The most accurate 3D-to-3D bone registration was obtained when using the largest anatomical regions available after TKA, being the full 3D femur model or the femur model without the distal femur which resulted in root mean square errors within 0.2 mm for translations and 0.2° for rotation. The accuracy of the 3D-to-3D femoral and tibial implant registration was within 0.7 mm for translations and 0.4°-0.6° for rotations, respectively. The accuracy for the overall procedure was within 0.9 mm and 0.6° for both femur and tibia when using femoral regions resulting in accurate 3D-to-3D bone registration. In conclusion, this measurement technique can be used in applications where measurement errors up to 0.9 mm in translations and up to 0.6° in rotations in component placement are acceptable.

Stress Distribution of a New Type of Perforated Implants in Femur Neck Fracture: Finite Element Model

Osteosynthesis of femoral neck fractures (FNF) is accompanied by a large percentage of various complications. The aim of this research was to study biomechanical implications arising from the stress and strain distributions by use of new device –perforated H-beam implant. A reference 3D femur model has been developed using digital femur geometry. The stress and deformity characteristics after the application of force were determined by ANSYS, which entails the finite element analysis (FEA) method. This method was used for both the perforated and non-perforated implant models and compared the application of constant strength. Three types of FNF were realized according to the Pauwell classification system.We concluded that, the perforations in the implants make the distribution of strength and pressure homogenous along the whole implant functioning as wave breaker to reduce the pressure on the bone. This contributes to implant stability and the minimization of bone destruction.

How does the material variation of dynamic hip screw affect the cut-out risk in the treatment of intertrochanteric femoral fractures?

The material selection of dynamic hip screw (DHS) is not usually considered from the point of mechanical effects. In this study, the effects of the titanium alloy and stainless steel DHS was investigated in the cut-out risk of femur using finite element analysis (FEA). Intertrochanteric femur fracture (IFF) (31-A2 type according to AO classification) was created in the 3D femur model obtained from computer tomography images. The DHS model was inserted to the fractured femur model in two different positions (inferior and middle). The material properties of DHS were defined for the FEA. The force applied to the femoral head was determined according to the maximum value that is observed during walking. The results show that the safest model was obtained in the middle placement of titanium alloy DHS according to the safety factor. Consequently, the use of stainless steel DHS for IFF could cause higher failure risk of DHS than the use of titanium alloy DHS.

How does the material variation of dynamic hip screw affect the cut-out risk in the treatment of intertrochanteric femoral fractures?

The material selection of dynamic hip screw (DHS) is not usually considered from the point of mechanical effects. In this study, the effects of the titanium alloy and stainless steel DHS was investigated in the cut-out risk of femur using finite element analysis (FEA). Intertrochanteric femur fracture (IFF) (31-A2 type according to AO classification) was created in the 3D femur model obtained from computer tomography images. The DHS model was inserted to the fractured femur model in two different positions (inferior and middle). The material properties of DHS were defined for the FEA. The force applied to the femoral head was determined according to the maximum value that is observed during walking. The results show that the safest model was obtained in the middle placement of titanium alloy DHS according to the safety factor. Consequently, the use of stainless steel DHS for IFF could cause higher failure risk of DHS than the use of titanium alloy DHS.