Nonunion scaphoid bone shape prediction using iterative kernel principal polynomial shape analysis.

BACKGROUND: The scaphoid is an important mechanical stabilizer for both the proximal and distal carpal columns. The precise estimation of the complete scaphoid bone based on partial bone geometric information is a crucial factor in the effective management of scaphoid nonunion. Statistical shape model (SSM) could be utilized to predict the complete scaphoid shape based on the defective scaphoid. However, traditional principal component analysis (PCA) based SSM is limited by its linearity and the inability to adjust the number of modes used for prediction. PURPOSE: This study proposes an iterative kernel principal polynomial shape analysis (iKPPSA)-based SSM to predict the pre-morbid shape of the scaphoid, aiming at enhancing the accuracy as well as the robustness of the model. METHODS: Sixty-five sets of scaphoid images were used to train SSM and nine sets of scaphoid images were used for validation. For each validation image set, three defect types (tubercle, proximal pole, and avascular necrosis) were virtually created. The predicted shapes of the scaphoid by PCA, PPSA, KPCA, and iKPPSA-based SSM were evaluated against the original shape in terms of mean error, Hausdorff distance error, and Dice coefficient. RESULTS: The proposed iKPPSA-based scaphoid SSM demonstrates significant robustness, with a generality of 0.264 mm and a specificity of 0.260 mm. It accounts for 99% of variability with the first seven principal modes of variation. Compared to the traditional PCA-based model, the iKPPSA-based scaphoid model prediction demonstrated superior performance for the proximal pole type fracture, with significant reductions of 25.2%, 24.7%, and 24.6% in mean error, Hausdorff distance, and root mean square error (RMSE), respectively, and a 0.35% improvement in Dice coefficient. CONCLUSION: This study showed that the iKPPSA-based SSM exploits the nonlinearity of data features and delivers high reconstruction accuracy. It can be effectively integrated into preoperative planning for scaphoid fracture management or morphology-based biomechanical modeling of the scaphoid.

A new mathematical model for evaluating surface changes in the mid-abdominal sagittal plane after two-level pedicle reduction osteotomy in patients with ankylosing spondylitis.

BACKGROUND: The purpose of this study was to create a mathematical model to precalculate the acreage change in the abdominal median sagittal plane (ac-AMSP) of patients with ankylosing spondylitis (AS) for whom two-level pedicle subtraction osteotomy (PSO) was planned. METHODS: A single-centre retrospective review of prospectively collected data was conducted among 11 adults with AS. Acreage of the abdominal median sagittal plane (a-AMSP) was performed. The distances and angles between the osteotomy apexes, anterosuperior edge of T12, xiphoid process, superior edge of the pubis, and anterosuperior corner of the sacrum were measured on preoperative thoracolumbar computed tomography. A mathematical model was created using basic trigonometric functions in accordance with the abdominal parameters. Planned osteotomized vertebra angles (POVAs) were substituted into the mathematical model, and the predictive ac-AMSP (P-AC) was obtained. A paired sample t test was performed to determine the differences between the P-AC and actual ac-AMSP (A-AC) and between the predictive acreage change rate (P-CR) and actual acreage change rate (A-CR). RESULTS: The mean age and GK were 44.4 ± 8.99 years and 102.9° ± 19.17°, respectively. No significant difference exists between A-CR and P-CR via mathematical modeling (p > 0.05). No statistically significant difference existed between POVA and actual osteotomized vertebra angles (AOVA) (p > 0.05). A statistically significant difference was observed between preoperative and postoperative measurements of LL, SVA, and GK variables (p < 0.001). CONCLUSIONS: The novel mathematical model was reliable in predicting the ac-AMSP in AS patients undergoing two-level PSO.

A Cadaveric Study of the Optimal Isometric Region on the Anterolateral Surface of the Knee in Anterolateral Ligament Reconstruction.

OBJECTIVE: Isolated intra-articular anterior cruciate ligament (ACL) reconstruction is not capable of restoring instability in many cases leading some to recommend concomitant anterolateral ligament (ALL) reconstruction. The satisfactory fixation site and graft length change are crucial in ligament reconstruction to restore the ALL function and avoid some unwanted graft behavior. The purpose of this investigation is to determine the optimal isometric region on the anterolateral aspect of the knee for ALL reconstruction using a three-dimensional optical instrument and a suture similar to an intraoperative isometric test. METHODS: Six freshly frozen cadaveric human knees were used in this study. Data regarding the anterolateral surface were obtained using an optical measurement system to create a three-dimensional model. Nine points were selected on the femur (F1-F9) and tibia (Ta-Ti) respectively. The three-dimensional length change between each pair of tibial and femoral points was measured during passive knee flexion from 0° to 90° in 15° increments. Subsequently, five femoral points (A-E) were selected from the lateral femur, located in different areas relative to the lateral femoral epicondyle, and three tibial reference points (T1-T3) were selected in the isometric test. The changes in the length between each pair of reference points were measured using sutures. The 95% confidence interval for the rate of length change was estimated using the mean and standard deviation of the maximum rate of length change at different flexion angles, and the data were expressed as the mean (95% confidence interval) and compared with the maximum acceptable rate of change (10%). RESULTS: The maximum acceptable change rate for ligament reconstruction is 10%, and the mean maximum rates and the 95% confidence interval (CI) of length change for the point combinations were calculated. Among all the combined points measured using the optical measurement system and the suture, the qualified point combination for reconstruction was F3 (8mm posterior and 8mm proximal to the lateral femoral epicondyle)-Tb (8mm proximal to the midpoint between the center of Gerdy's tubercle and the fibula head), A (posterior and proximal to the lateral femoral epicondyle)-T2 (10mm below the joint line)and A-T3 (15 mm below the joint line). The position of F3-Tb and A-T2 are close to each other. CONCLUSION: The most isometric area of the femur for ALL reconstruction was posterior and proximal to the lateral femoral epicondyle. We recommend that the initial location of the femoral point be set at 8 mm posterior and 8 mm proximal to the lateral femoral epicondyle and the tibial point at approximately 10 mm below the joint line, midway between Gerdy's tubercle and fibular head, and subsequently adjusted to the most satisfactory position according to the isometric test.

Finite element study of sagittal fracture location on thoracolumbar fracture treatment.

Background: Posterior internal fixation is the main method used for the treatment of thoracolumbar fractures. Fractures often occur in the upper 1/3 of the vertebral body. However, they can also occur in the middle or lower 1/3 of the vertebral body. At present, there is no report discussing the potential effects of sagittal location on instrument biomechanics or surgical strategy. The object of this study was to investigate the effect of the sagittal location of the fracture region of the vertebral body on the biomechanics of the internal fixation system and surgical strategy. Methods: A finite element model of the T11-L3 thoracolumbar segment was established based on a healthy person's CT scan. Different sagittal fracture location finite element models were created by resection of the upper 1/3, middle 1/3, and lower 1/3 of the L1 vertebral body. Three surgical strategies were utilized in this study, namely, proximal 1 level and distal 1 level (P1-D1), proximal 2 level and distal 1 level (P2-D1), and proximal 1 level and distal 2 levels (P1-D2). Nine fixation finite element models were created by combining fracture location and fixation strategies. Range of motion, von Mises stress, and stress distribution were analyzed to evaluate the effects on the instrument biomechanics and the selection of surgical strategy. Results: In all three different fixation strategies, the maximum von Mises stress location on the screw did not change with the sagittal location of the fracture site; nevertheless, the maximum von Mises stress differed. The maximum rod stress was located at the fracture site, with its value and location changed slightly. In the same fixation strategy, a limited effect of sagittal location on the range of motion was observed. P2D1 resulted in a shorter range of motion and lower screw stress for all sagittal locations of the fracture compared with the other strategies; however, rod stress was similar between strategies. Conclusion: The sagittal location of a fracture may affect the intensity and distribution of stress on the fixation system but does not influence the selection of surgical strategy.

Investigation of the Friction Properties of a New Artificial Imitation Cartilage Material: PHEMA/Glycerol Gel.

The absence of artificial articular cartilage could cause the failure of artificial joints due to excessive material wear. There has been limited research on alternative materials for articular cartilage in joint prostheses, with few reducing the friction coefficient of artificial cartilage prostheses to the range of the natural cartilage friction coefficient (0.001-0.03). This work aimed to obtain and characterize mechanically and tribologically a new gel for potential application in articular replacement. Therefore, poly(hydroxyethyl methacrylate) (PHEMA)/glycerol synthetic gel was developed as a new type of artificial joint cartilage with a low friction coefficient, especially in calf serum. This glycerol material was developed via mixing HEMA and glycerin at a mass ratio of 1:1. The mechanical properties were studied, and it was found that the hardness of the synthetic gel was close to that of natural cartilage. The tribological performance of the synthetic gel was investigated using a reciprocating ball-on-plate rig. The ball samples were made of a cobalt-chromium-molybdenum (Co-Cr-Mo) alloy, and the plates were synthetic glycerol gel and two additional materials for comparison, which were ultra-high molecular polyethylene (UHMWPE) and 316L stainless steel. It was found that synthetic gel exhibited the lowest friction coefficient in both calf serum (0.018) and deionized water (0.039) compared to the other two conventional materials for knee prostheses. The surface roughness of the gel was found to be 4-5 µm through morphological analysis of wear. This newly proposed material provided a possible solution as a type of cartilage composite coating with hardness and tribological performance close to the nature of use in wear couples with artificial joints.

Sol-gel dip-coated TiO2 nanofilms reduce heat production in titanium alloy implants produced by microwave diathermy.

Objective: To verify that the TiO2 nanofilm dip-coated by sol-gel can reduce titanium alloy implants (TAI)'s heat production after microwave diathermy (MD).Methods: The effect of 40 W and 60 W MD on the titanium alloy substrate coated with TiO2 nanofilm (Experimental Group) and the titanium alloy substrate without film (Control Group) were analyzed in vitro and in vivo. Changes in the skeletal muscle around the implant were evaluated in ex vivo by histology.Results: After 20 min of MD, in vitro the temperature rise of the titanium substrate was less in the Experimental Group than in the Control Group (40 W: 1.4 °C vs. 2.6 °C, p < .01, 60 W: 2.5 °C vs. 3.7 °C, p < .01) and in vivo, the temperature rise of the muscle tissue adjacent to TAI was lower in the Experimental Group than in the Control Group (40 W: 3.29 °C vs. 4.8 °C, p < .01, 60 W: 4.16 °C vs. 6.52 °C, p < .01). Skeletal muscle thermal injury can be found in the Control Group but not in the Experimental Group.Conclusion: Sol-gel dip-coated TiO2 nanofilm can reduce the heat production of TAIs under single 40～60 W and continuous 40 W MD and protect the muscle tissue adjacent to the implants against thermal injury caused by irradiation.

Effect of Position on Regional Kyphosis Angle in Patients with Kyphosis Secondary to Symptomatic Old Osteoporotic Thoracolumbar Fracture.

OBJECTIVE: The purpose of this study was to evaluate the effect of position on regional kyphosis angle (RKA) in patients with kyphosis secondary to symptomatic old osteoporotic thoracolumbar fracture (so-OTLF). METHODS: The authors evaluated the radiographic data of patients with kyphosis secondary to so-OTLF who underwent posterior corrective fusion surgery in our hospital. The spine sagittal parameters were evaluated in the standing position preoperatively. RKA was measured under standing radiograph, full-length spine computed tomography image in prone position and intraoperative prone X-ray radiograph, respectively. Changes in RKA were compared between groups. RESULTS: Thirty-three patients were included. The average RKAs in the standing position, preoperative prone position, and intraoperative prone position were 46.2°, 31.1°, and 30.5° respectively. RKA decreased significantly from standing to preoperative prone position or intraoperative prone position (P < 0.001). In 93.9% (31/33) of the patients, the difference between preoperative prone RKA and intraoperative prone RKA was within 5°. The changes in RKA from standing to intraoperative prone position in the moderate to severe kyphosis group were significantly greater than those in the mild kyphosis group (P < 0.001). CONCLUSIONS: The reductive effect of the intraoperative prone position was greater in patients with moderate to severe kyphosis deformities. RKA in the preoperative prone position was almost the same as the RKA in the intraoperative prone position. Therefore, assessing preoperative full-length spine computed tomography in the prone position helped formulate the plan for corrective surgery in patients with kyphosis secondary to so-OTLF.

Study on TiO2 Nanofilm That Reduces the Heat Production of Titanium Alloy Implant in Microwave Irradiation and Does Not Affect Fracture Healing.

Background: Metal implants can produce heat and damage adjacent tissues under microwave irradiation, which makes local metal implants in the body a contraindication for microwave therapy. However, with the wide application of titanium alloy implants which have low permeability and low conductivity, this concept has been challenged. Our team members have confirmed through previous research that continuous low-power microwave irradiation does not cause thermal damage to the surrounding tissues of the titanium alloy. Is there any other way to further increase the dose of microwave irradiation while reducing the heat production of titanium alloy implants? In this study, the effect of TiO2 nanofilm on reducing the heat production of titanium alloy implants in microwave field was verified by animal experiments, and the effect of TiO2 nanofilm on fracture healing was observed. Methods: 30 rabbits were selected. In the experiment of temperature measurement, 10 rabbits were randomly divided into experimental group (n = 5) and control group (n = 5), and the contralateral lower limb of the rabbits in experimental group was set as the sham operation group. The right femurs in the experimental group were implanted with Ti6Al4V plates coated with TiO2 nanofilm, and the right femurs in the control group were implanted with common titanium alloy plates without TiO2 nanofilm. The same surgical procedure was used in the sham operation group, but no plate was implanted. The temperature of the deep tissue above the metal implant was measured with an anti-interference thermocouple thermometer during 20 minutes of microwave irradiation. The other 20 rabbits were randomly divided into two groups, experimental group (n = 10) and control group (n = 10). The femoral shaft fracture models were established again. Ti6Al4V plates coated with TiO2 nanofilm and common titanium alloy plates were implanted in the two groups, respectively, and both groups were exposed to continuous microwave irradiation with a power of 40 W or 60 W for 30 days after operation. The fracture healing was evaluated by X-ray at 0 day, 14 days, and 30 days after microwave irradiation, respectively. The animals were sacrificed at 30 days after operation for histopathological assessment. Results: The temperature in the experimental group, control group, and sham operation group increased significantly after 40 W and 60 W microwave irradiation (2.18 ± 0.15°C~6.02 ± 0.38°C). When exposed to 40 W microwave, the temperature rise of the control group was 4.0 ± 0.34°C, which was significantly higher than that of the experimental group 2.82 ± 0.15°C (P < 0.01) and the sham operation group 2.18 ± 0.33°C (P < 0.01). There was no significant difference in temperature rise between the experimental group and the sham operation group (P = 0.21). When exposed to 60 W microwave, the temperature rise of the control group was 6.02 ± 0.38°C, which was significantly higher than that of the experimental group 3.66 ± 0.14°C (P < 0.01) and sham operation group 2.96 ± 0.22°C (P < 0.01), and there was no significant difference between the experimental group and the sham operation group (P = 0.32). X-ray evaluation showed that there was no significant difference in callus maturity between the experimental group and the control group at 14 days (P = 0.554), but there was significant difference in callus maturity between the two groups at 30 days (P = 0.041). The analysis of bone histologic and histomorphometric data at 30 days was also consistent with this. Conclusion: Under the animal experimental condition, compared with the common titanium alloy implant, the TiO2 nanofilm can reduce the heat production of the titanium alloy implant in the 2450 MHz microwave field and has no adverse effect on fracture healing. This study opens up a promising new idea for the application of microwave therapy to metal implants in human body.

Mechanical mechanism of suture passer needle break in rotator cuff repair.

Introduction: Suture passer needle, as one of commonly used instrument in the arthroscopic rotator cuff repair, often breaks at the notch of the needle, which originally was designed to facilitate suture with thread. Our study aimed to evaluate the suture failure rate and stitch success rate between intact suture needle and broken needle and explore the mechanism of the needle breakage and achieving better future designs. Materials and methods: From 2017 to 2021, consecutive 437 shoulders (11 cases were bilateral) underwent arthroscopic repair for full-thickness rotator cuff tear at the authors' institution. The breakage of needles was recorded. Finite elements analysis and mechanical test were utilized to compare stress distribution, puncture performance, and loaded puncture performance between the broken needle and the intact needle. Results: We identified 19 consecutive patients for whom the needle tip of the TruePass™ suture passer was broken in the 437 shoulder surgeries. Based on the finite element analysis of Abaqus, around the tip and the notch of the intact needle was a large stress concentration. The average puncture force required by intact needle tip and the broken tip is 61.78N and 78.23N respectively. While the intact tip with notch is easier to break than the broken tip. Conclusions: The notch of the needle is a weak point in mechanics. The broken needle without the notch still has good tendon piercing and thread passing ability. The notch of needle may be not necessary, and the tip of the needle should be modified.

A 3D-transient elastohydrodynamic lubrication hip implant model to compare ultra high molecular weight polyethylene with more compliant polycarbonate polyurethane acetabular cups.

Wear remains a significant challenge in the design of orthopedic implants such as total hip replacements. Early elastohydrodynamic lubrication modeling has predicted thicker lubrication films in hip replacement designs with compliant polycarbonate polyurethane (PCU) bearing materials compared to stiffer materials like ultra-high molecular weight polyethylene (UHMWPE). The predicted thicker lubrication films suggest improved friction and wear performance. However, when compared to the model predictions, experimental wear studies showed mixed results. The mismatch between the model and experimental results may lie in the simplifying assumptions of the early models such as: steady state conditions, one dimensional rotation and loading, and high viscosities. This study applies a 3D-transient elastohydrodynamic model based on an ISO standard gait cycle to better understand the interaction between material stiffness and film thickness in total hip arthroplasty material couples. Similar to previous, simplified models, we show that the average and central film thickness of PCU (∼0.4µm) is higher than that of UHMWPE (∼0.2µm). However, in the 3D-transient model, the film thickness distribution was largely asymmetric and the minimum film thickness occurred outside of the central axis. Although the overall film thickness of PCU was higher than UHMWPE, the minimum film thickness of PCU was lower than UHMPWE for the majority of the gait cycle. The minimum film thickness of PCU also had a larger range throughout the gait cycle. Both materials were found to be operating between boundary and mixed lubrication regimes. This 3D-transient model reveals a more nuanced interaction between bearing material stiffness and film thickness that supports the mixed results found in experimental wear studies of PCU hip implant designs.

Novel combined shield design for eye and face protection from COVID-19.

The World Health Organization emphasized the importance of goggles and face shields for protection of medical personnel at the outbreak of the COVID-19 pandemic. Unsurprisingly, almost all countries suffered from a critical supply shortage of goggles and face shields, as well as many other types of personal protective equipment (PPE), for a long period, owing to the lack of key medical material supplies and the inefficiency of existing fabrication methods arising from the need to avoid crowds during the outbreak of COVID-19. In this paper, we propose a novel combined shield design for eye and face protection that can be rapidly fabricated using three-dimensional printing technology. The designed prototype eye-face shield is accessible to the general public, offering more possibilities for yield improvement in PPE during emergent infectious disease events such as COVID-19.

Effects of a 3D-printed orthosis compared to a low-temperature thermoplastic plate orthosis on wrist flexor spasticity in chronic hemiparetic stroke patients: a randomized controlled trial.

OBJECTIVE: The aim of this study was to compare the effects of two kinds of wrist-hand orthosis on wrist flexor spasticity in chronic stroke patients. DESIGN: This is a randomized controlled trial. SETTING: The study was conducted in a rehabilitation center. PARTICIPANTS: A total of 40 chronic hemiparetic stroke patients with wrist flexor spasticity were involved in the study. INTERVENTIONS: Patients were randomly assigned to either an experimental group (conventional rehabilitation therapy + 3D-printed orthosis, 20 patients) or a control group (conventional rehabilitation therapy + low-temperature thermoplastic plate orthosis, 20 patients). The time of wearing orthosis was about 4-8 hours per day for six weeks. MAIN MEASURES: Primary outcome measure: Modified Ashworth Scale was assessed three times (at baseline, three weeks, and six weeks). Secondary outcome measures: passive range of motion, Fugl-Meyer Assessment score, visual analogue scale score, and the swelling score were assessed twice (at baseline and six weeks). The subjective feeling score was assessed at six weeks. RESULTS: No significant difference was found between the two groups in the change of Modified Ashworth Scale scores at three weeks (15% versus 25%, P = 0.496). At six weeks, the Modified Ashworth Scale scores (65% versus 30%, P = 0.02), passive range of wrist extension (P < 0.001), ulnar deviation (P = 0.028), Fugl-Meyer Assessment scores (P < 0.001), and swelling scores (P < 0.001) showed significant changes between the experimental group and the control group. No significant difference was found between the two groups in the change of visual analogue scale scores (P = 0.637) and the subjective feeling scores (P = 0.243). CONCLUSION: 3D-printed orthosis showed greater changes than low-temperature thermoplastic plate orthosis in reducing spasticity and swelling, improving motor function of the wrist and passive range of wrist extension for stroke patients.

In vitro experimental and numerical study on biomechanics and stability of a novel adjustable hemipelvic prosthesis.

Hemipelvic prostheses are used to reconstruct the damaged pelvis due to bone tumors and traumas. However, biomechanical properties of the reconstructed pelvis remain unclear, causing difficulties to implant development and prediction of surgical outcome. In this study, a novel adjustable hemipelvic prosthesis for the Type 1-3 pelvis resection was used to reconstruct the intact pelvic ring. Two types of Pedicle Screw Rod Systems were proposed to improve the stability of fixation between the prosthesis and the bone. Finite Element models of the reconstructed pelvis were built to analyze the performance of the prosthesis and PSRS. Moreover, an in vitro experimental study was performed to measure the deformation of the human reconstructed pelvis. Numerical results agree well with the experimental data. It was found that displacements and stresses bilaterally transferred more evenly in the reconstructed pelvis enhanced by bilateral Pedicle Screw Rod System. The load-transfer function of the pelvis under double-leg standing stance could be recovered. The bilateral pedicle system has better biomechanical performance than the unilateral pedicle system.

Study on biocompatibility, tribological property and wear debris characterization of ultra-low-wear polyethylene as artificial joint materials.

Ultra-low-wear polyethylene (ULWPE) is a new type polyethylene made by experts who are from China petrochemical research institute, which is easy to process and implant. Preliminary test showed it was more resistant to wear than that of Ultra-high-molecular weight polyethylene (UHMWPE). The purpose of the research is to study biocompatibility, bio-tribological properties and debris characterization of ULWPE. Cytotoxicity test, hemolysis test, acute/chronic toxicity and muscular implantation test were conducted according to national standard GB/T-16886/ISO-10993 for evaluation requirements of medical surgical implants. We obtained that this novel material had good biocompatibility and biological safety. The wear performance of ULWPE and UHMWPE was evaluated in a pin-on-disc (POD) wear tester within two million cycles and a knee wear simulator within six million cycles. We found that the ULWPE was higher abrasion resistance than the UHMWPE, the wear rate of ULWPE by POD test and knee wear simulator was 0.4 mg/106cycles and (16.9 ±â€¯1.8)mg/106cycles respectively, while that of UHMWPE was 1.8 mg/106cycles and (24.6 ±â€¯2.4)mg/106cycles. The morphology of wear debris is also an important factor to evaluate artificial joint materials, this study showed that the ULWPE wear debris gotten from the simulator had various different shapes, including spherical, block, tear, etc. The morphology of worn surface and wear debris analysis showed that wear mechanisms of ULWPE were adhesion wear, abrasive wear and fatigue wear and other wear forms, which were consistent with that of UHMWPE. Thus we conclude that ULWPE is expected to be a lifetime implantation of artificial joint.

The effect of screw tunnels on the biomechanical stability of vertebral body after pedicle screws removal: a finite element analysis.

PURPOSE: Posterior reduction and pedicle screw fixation is a widely used procedure for thoracic and lumbar vertebrae fractures. Usually, the pedicle screws would be removed after the fracture healing and screw tunnels would be left. The aim of this study is to evaluate the effect of screw tunnels on the biomechanical stability of the lumbar vertebral body after pedicle screws removal by finite element analysis (FEA). METHODS: First, the CT values of the screw tunnels wall in the fractured vertebral bodies were measured in patients whose pedicle screws were removed, and they were then compared with the values of vertebral cortical bone. Second, an adult patient was included and the CT images of the lumbar spine were harvested. Three dimensional finite element models of the L1 vertebra with unilateral or bilateral screw tunnels were created based on the CT images. Different compressive loads were vertically acted on the models. The maximum loads which the models sustained and the distribution of the force in the different parts of the models were recorded and compared with each other. RESULTS: The CT values of the tunnels wall and vertebral cortical bone were 387.126±62.342 and 399.204±53.612, which were not statistically different (P=0.149). The models of three dimensional tetrahedral mesh finite element of normal lumbar 1 vertebra were established with good geometric similarity and realistic appearance. After given the compressive loads, the cortical bone was the first one to reach its ultimate stress. The maximum loads which the bilateral screw tunnels model, unilateral screw tunnel model, and normal vertebral model can sustain were 3.97 Mpa, 3.83 Mpa, and 3.78 Mpa, respectively. For the diameter of the screw tunnels, the model with a diameter of 6.5 mm could sustain the largest load. In addition, the stress distributing on the outside of the cortical bone gradually decreased as the thickness of the tunnel wall increased. CONCLUSIONS: Based on the FEA, pedicle screw tunnels would not decrease the biomechanical stability and strength of the vertebral body. A large diameter of screw tunnel and thick tunnel wall were helpful for the biomechanical stability of the vertebral body.

Design and biomechanical study of a novel adjustable hemipelvic prosthesis.

A pelvic endoprosthesis is commonly used in orthopedic surgeries to reconstruct the pelvis after internal hemipelvectomy. This study presents the detailed design of a novel type I+II+III adjustable hemipelvic prosthesis based on the geometrical features of massive human pelvises. Finite element analysis is conducted to estimate the biomechanical performance of the newly designed adjustable hemipelvic prosthesis. Detailed numerical models of the natural and reconstructed pelvises including related soft tissues are developed. Hip contact forces during normal walking, which is one of the most frequent dynamic activities in daily living, are imposed on the pelvis. Results show that the peak stress observed in the reconstructed pelvis model is still within a low and elastic range below the yielding strength of the cortical bone and Ti6Al4V. No significant difference of the stress transferring route, displacement distributions and principal stress vectors is observed between the reconstructed and natural pelvises. The results indicate that the load transferring function of the partially resected pelvis is able to be reliably recovered by the adjustable hemipelvic prosthesis. The principal stress vectors in both pelvis models predict that bone absorption may not apparently occur in the long run. Long-term biomechanical performance of this newly designed prosthesis may be stability.

Biomechanical analysis of a novel hemipelvic endoprosthesis during ascending and descending stairs.

In this study, the biomechanical characteristic of a newly developed adjustable hemipelvic prosthesis under dynamic loading conditions was investigated using explicit finite element method. Both intact and reconstructed pelvis models, including pelvis, femur and soft tissues, were established referring to human anatomic data using a solid geometry of a human pelvic bone. Hip contact forces during ascending stairs and descending stairs were imposed on pelvic models. Results showed that maximum von Mises stresses in reconstructed pelvis were 421.85 MPa for prostheses and 109.12 MPa for cortical bone, which were still within a low and elastic range below the yielding strength of Ti-6Al-4V and cortical bone, respectively. Besides, no significant difference of load transferring paths along pelvic rings was observed between the reconstructed pelvis and natural pelvis models. And good agreement was found between the overall distribution of maximum principal stresses in trabecular bones of reconstructed pelvis and natural pelvis, while at limited stances, principal stresses in trabecular bone of reconstructed pelvis were slightly lower than natural pelvis. The results indicated that the load transferring function of pelvis could be restored by this adjustable hemipelvic prosthesis. Moreover, the prosthesis was predicted to have a reliable short- and long-term performance. However, due to the occurrence of slightly lower principal stresses at a few stances, a porous structure applied on the interface between the prosthesis and bone would be studied in future work to obtain better long-term stability.