Investigation into the effect of deltoid ligament injury on rotational ankle instability using a three-dimensional ankle finite element model

Background

Injury to the lateral collateral ligament of the ankle may cause ankle instability and, when combined with deltoid ligament (DL) injury, may lead to a more complex situation known as rotational ankle instability (RAI). It is unclear how DL rupture interferes with the mechanical function of an ankle joint with RAI.

Purpose

To study the influence of DL injury on the biomechanical function of the ankle joint.

Methods

A comprehensive finite element model of an ankle joint, incorporating detailed ligaments, was developed from MRI scans of an adult female. A range of ligament injury scenarios were simulated in the ankle joint model, which was then subjected to a static standing load of 300 N and a 1.5 Nm internal and external rotation torque. The analysis focused on comparing the distribution and peak values of von Mises stress in the articular cartilages of both the tibia and talus and measuring the talus rotation angle and contact area of the talocrural joint.

Results

The dimensions and location of insertion points of ligaments in the finite element ankle model were adopted from previous anatomical research and dissection studies. The anterior drawer distance in the finite element model was within 6.5% of the anatomical range, and the talus tilt angle was within 3% of anatomical results. During static standing, a combined rupture of the anterior talofibular ligament (ATFL) and anterior tibiotalar ligament (ATTL) generates new stress concentrations on the talus cartilage, which markedly increases the joint contact area and stress on the cartilage. During static standing with external rotation, the anterior talofibular ligament and anterior tibiotalar ligament ruptured the ankle's rotational angle by 21.8% compared to an intact joint. In contrast, static standing with internal rotation led to a similar increase in stress and a nearly 2.5 times increase in the talus rotational angle.

Conclusion

Injury to the DL altered the stress distribution in the tibiotalar joint and increased the talus rotation angle when subjected to a rotational torque, which may increase the risk of RAI. When treating RAI, it is essential to address not only multi-band DL injuries but also single-band deep DL injuries, especially those affecting the ATTL.

Automatic planning and geometric analysis of the drilling path in core decompression surgery for osteonecrosis of the femoral head

BACKGROUND AND OBJECTIVE

Core decompression surgery is an effective treatment method for patients with pre-collapse osteonecrosis of the femoral head (ONFH). The treatment relies on accurately predrilling the wire into the necrotic lesion. However, the surgical planning of this drilling path remains unclear. This paper aims to develop a framework to automatically plan the drilling path and analyze its geometric parameters.

METHODOLOGY

The proposed system consists of two stages. The first stage is to detect the key points. Besides the entry point and target point for the drilling path, the center of the femoral head (FH) and the boundary points of the necrotic lesion are also detected for the subsequent geometric analysis. In the second stage, the geometric parameters of the drilling path are analyzed, including the size of the necrotic lesion, the length from the entry point to the target point, the relative location between the FH center and the necrosis center, and the angular range of the drilling path in the anterior-posterior (AP) direction and superior-inferior (SI) direction.

RESULTS

All of the drilling paths designed by the proposed system were considered successful, starting from the proximal subtrochanteric region, terminating at the center of the necrotic lesion, and remaining within the femoral neck. The relative coordinates of the centers of the femoral head and necrotic lesion were (-0.89,5.14,2.63) mm for the left femurs and (1.55,5.92,2.63) mm for the right femurs, on average. The angular range of the drilling path was 39.99±29.58 degrees in the SI direction and 46.18±40.73 degrees in the AP direction.

CONCLUSION

This study develops a framework that allows for automatic planning and geometric analysis of the drilling path in core decompression surgery. The target point of the drilling path primarily resides in the lateral-anterior-superior region relative to the femoral head center. Surgeons and researchers can benefit from our unified framework while still maintaining the flexibility to adapt to variations in surgical cases.

The Structure, Biology, and Mechanical Function of Tendon/Ligament-Bone Interfaces

After tendon or ligament reconstruction, the interface between the hard bone and soft connective tissue is considerably weakened and is difficult to restore through healing. The tendon/ligament-bone interface is mechanically the weakest point under tensile loading and is often the source of various postoperative complications, such as bone resorption and graft laxity. A comprehensive understanding of the macro- and microfeatures of the native tendon/ligament-bone interface would be beneficial for developing strategies for regenerating the tissue. This article discusses the structural, biological, and mechanical features of the tendon/ligament-bone interfaces and how these can be affected by aging and loading conditions.

Subtracting-adding strategy for necrotic lesion segmentation in osteonecrosis of the femoral head

PURPOSE

Osteonecrosis of the femoral head (ONFH) is a severe bone disease that can progressively lead to hip dysfunction. Accurately segmenting the necrotic lesion helps in diagnosing and treating ONFH. This paper aims at enhancing deep learning models for necrosis segmentation.

METHODS

Necrotic lesions of ONFH are confined to the femoral head. Considering this domain knowledge, we introduce a preprocessing procedure, termed the "subtracting-adding" strategy, which explicitly incorporates this domain knowledge into the downstream deep neural network input. This strategy first removes the voxels outside the predefined volume of interest to "subtract" irrelevant information, and then it concatenates the bone mask with raw data to "add" anatomical structure information.

RESULTS

Each of the tested off-the-shelf networks performed better with the help of the "subtracting-adding" strategy. The dice similarity coefficients increased by 10.93%, 9.23%, 9.38% and 1.60% for FCN, HRNet, SegNet and UNet, respectively. The improvements in FCN and HRNet were statistically significant.

CONCLUSIONS

The "subtracting-adding" strategy enhances the performance of general-purpose networks in necrotic lesion segmentation. This strategy is compatible with various semantic segmentation networks, alleviating the need to design task-specific models.

Progress and Advances in Porous Silica-based Scaffolds for Enhanced Solid-state Hydrogen Storage: A Systematic Literature Review

Hydrogen plays a crucial role in the future energy landscape owing to its high energy density. However, finding an ideal storage material is the key challenge to the success of the hydrogen economy. Various solid-state hydrogen storage materials, such as metal hydrides, have been developed to realize safe, effective, and compact hydrogen storage. However, low kinetics and thermodynamic stability lead to a high working temperature and a low hydrogen sorption rate of the metal hydrides. Using scaffolds made from porous materials like silica to confine the metal hydrides is necessary for better and improved hydrogen storage. Therefore, this article reviews porous silica-based scaffolds as an ideal material for improved hydrogen storage. The outcome showed that confining the metal hydrides using scaffolds based on porous silica significantly increases their storage capacities. It was also found that the structural modifications of the silica-based scaffold into a hollow structure further improved the storage capacity and increased the affinity and confinement ability of the metal hydrides, which prevents the agglomeration of metal particles during the adsorption/desorption process. Hence, the structural modifications of the silica material into a fibrous and hollow material are recommended to be crucial for further enhancing the metal hydride storage capacity.

A multi-branch network to detect post-operative complications following hip arthroplasty on X-ray images

Background: Postoperative complications following total hip arthroplasty (THA) often require revision surgery. X-rays are usually used to detect such complications, but manually identifying the location of the problem and making an accurate assessment can be subjective and time-consuming. Therefore, in this study, we propose a multi-branch network to automatically detect postoperative complications on X-ray images. Methods: We developed a multi-branch network using ResNet as the backbone and two additional branches with a global feature stream and a channel feature stream for extracting features of interest. Additionally, inspired by our domain knowledge, we designed a multi-coefficient class-specific residual attention block to learn the correlations between different complications to improve the performance of the system. Results: Our proposed method achieved state-of-the-art (SOTA) performance in detecting multiple complications, with mean average precision (mAP) and F1 scores of 0.346 and 0.429, respectively. The network also showed excellent performance at identifying aseptic loosening, with recall and precision rates of 0.929 and 0.897, respectively. Ablation experiments were conducted on detecting multiple complications and single complications, as well as internal and external datasets, demonstrating the effectiveness of our proposed modules. Conclusion: Our deep learning method provides an accurate end-to-end solution for detecting postoperative complications following THA.

Mechanical alignment tolerance of a cruciate-retaining knee prosthesis under gait loading—A finite element analysis

Component alignment is one of the most crucial factors affecting total knee arthroplasty’s clinical outcome and survival. This study aimed to investigate how coronal, sagittal, and transverse malalignment affects the mechanical behavior of the tibial insert and to determine a suitable alignment tolerance on the coronal, sagittal, and transverse planes. A finite element model of a cruciate-retaining knee prosthesis was assembled with different joint alignments (−10°, −7°, −5°, −3°, 0°, 3°, 5°, 7°, 10°) to assess the effect of malalignment under gait loading. The results showed that varus or valgus, extension, internal rotation, and excessive external rotation malalignments increased the maximum Von Mises stress and contact pressure on the tibial insert. The mechanical alignment tolerance of the studied prosthesis on the coronal, sagittal, and transverse planes was 3° varus to 3° valgus, 0°–10° flexion, and 0°–5° external rotation, respectively. This study suggests that each prosthesis should include a tolerance range for the joint alignment angle on the three planes, which may be used during surgical planning.

Correlation between morphological features of the anterior cruciate ligament: A quantitative study using a porcine model

Introduction

Knowledge of the morphological features of the anterior cruciate ligament (ACL) is critical for accurate reconstruction of it. This study aimed to explore the quantitative correlations among different morphological features of the ACL, thus to provide useful information for improving anatomical reconstruction techniques and designing artificial ligaments.

Methods

19 porcine knees were fixed at full extension using 10% formalin and were dissected to expose the ACL. ACL lengths were measured using a caliper. Mid-substances of the ACL were cut and scanned using X-ray microscopy, and the cross-sectional area (CSA) was measured at the isthmus. Margins of direct and indirect bone insertion sites were distinguished and marked. Measurements were performed on digital photographs to obtain the areas of bone insertions. Statistical analysis using nonlinear regression was used to identify potential correlations among the measurements.

Results

The results showed that the CSA at the isthmus was significantly correlated with the total area of the bone insertion sites and the area of tibial insertion. The area of the tibial insertion was significantly correlated with the area of its direct insertion site. In contrast, the area of the femoral insertion was significantly correlated with the area of its indirect insertion site. The area of the indirect tibial insertion showed a weak correlation with the length of ACL, whereas the length of the ACL was not able to predict or be predicted by any other parameters.

Conclusions

The CSA at the ACL isthmus is more representative for assessing the size of the ACL. However, ACL length has little correlation with the CSA of the isthmus or bone insertion sites, and thus should be evaluated independently for ACL reconstruction.

Biomechanical evaluation of a novel intervertebral disc repair technique for large box-shaped ruptures

Objective: The purpose of this study was to analyze the feasibility of repairing a ruptured intervertebral disc using a patch secured to the inner surface of the annulus fibrosus (AF). Different material properties and geometries for the patch were evaluated. Methods: Using finite element analysis, this study created a large box-shaped rupture in the posterior-lateral region of the AF and then repaired it with a circular and square inner patch. The elastic modulus of the patches ranged from 1 to 50 MPa to determine the effect on the nucleus pulposus (NP) pressure, vertical displacement, disc bulge, AF stress, segmental range of motion (ROM), patch stress, and suture stress. The results were compared against the intact spine to determine the most suitable shape and properties for the repair patch. Results: The intervertebral height and ROM of the repaired lumbar spine was similar to the intact spine and was independent of the patch material properties and geometry. The patches with a modulus of 2-3 MPa resulted in an NP pressure and AF stresses closest to the healthy disc, and produced minimal contact pressure on the cleft surfaces and minimal stress on the suture and patch of all models. Circular patches caused lower NP pressure, AF stress and patch stress than the square patch, but also caused greater stress on the suture. Conclusion: A circular patch with an elastic modulus of 2-3 MPa secured to the inner region of the ruptured annulus fibrosus was able to immediately close the rupture and maintain an NP pressure and AF stress similar to the intact intervertebral disc. This patch had the lowest risk of complications and produced the greatest restorative effect of all patches simulated in this study.

Comparison of navigation systems for total knee arthroplasty: A systematic review and meta-analysis

Background

Component alignment is a crucial factor affecting the clinical outcome of total knee arthroplasty (TKA). Accelerometer-based navigation (ABN) systems were developed to improve the accuracy of alignment during surgery. This study aimed to compare differences in component alignment, clinical outcomes, and surgical duration when using conventional instrumentation (CONI), ABN, and computer navigation (CN) systems.

Methods

A comprehensive literature search was carried out using the Web of Science, Embase, PubMed, and Cochrane databases. Articles that met the eligibility criteria were included in the study. Meta-analyses were performed using the Cochrane Collaboration Review Manager based on Cochrane Review Method. The variables used for the analyses were postoperative clinical outcome (PCO), surgical duration, and component alignment, including the hip-knee-ankle (HKA) angle, coronal femoral angle (CFA), coronal tibial angle (CTA), sagittal femoral angle (SFA), sagittal tibial angle (STA), and the outliers for the mentioned angles. The mean difference (MD) was calculated to determine the difference between the surgical techniques for continuous variables and the odds ratio (OR) was used for the dichotomous outcomes.

Results

The meta-analysis of the CONI and ABN system included 18 studies involving 2,070 TKA procedures, while the comparison of the ABN and CN systems included 5 studies involving 478 TKA procedures. The results showed that the ABN system provided more accurate component alignment for HKA, CFA, CTA, and SFA and produced fewer outliers for HKA, CFA, CTA, and STA. However, while the ABN system also required a significantly longer surgical time than the CONI approach, there was no statistical difference in PCO for the two systems. For the ABN and CN systems, there was no statistical difference in all variables except for the ABN system having a significantly shorter surgical duration.

Conclusion

There was no significant difference in the accuracy of component alignment between the ABN and CN systems, but the ABN approach had a shorter surgical duration and at lower cost. The ABN system also significantly improved the accuracy of component alignment when compared to the CONI approach, although the surgery was longer. However, there was no significant difference in PCO between the CONI, ABN, and CN systems.

Hourglass-shaped grafts are superior to conventional grafts for restoring knee stability and graft force at knee flexion angle of 30° following anterior cruciate ligament reconstruction: A finite element analysis

Background: Anterior cruciate ligament reconstruction (ACLR) using a generally columnar graft is considered the gold standard for treating anterior cruciate ligament ruptures, but such grafts cannot replicate the geometry and mechanical properties of the native anterior cruciate ligament. Purpose: To evaluate the effectiveness of an innovative hourglass-shaped graft versus a traditional columnar graft for restoring joint stability and graft force, while avoiding notch impingement following anterior cruciate ligament reconstruction. Methods: Finite element models of a human knee were developed to simulate ① An intact state, ② anterior cruciate ligament reconstruction using columnar grafts with different diameters (7.5-12 mm in 0.5 mm increments), ③ anterior cruciate ligament reconstruction using columnar grafts with different Young's moduli (129.4, 168.0 and 362.2 MPa) and ④ anterior cruciate ligament reconstruction using hourglass-shaped grafts with different Young's moduli. The knee model was flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. The risk of notch impingement, knee stability and graft forces were compared among the different groups. Results: This study found that columnar grafts could not simultaneously restore knee stability in different degree of freedoms (DOFs) and graft force to a level similar to that of the intact knee. The anterior tibial translation and graft force were restored to a near-normal condition when the internal tibial rotation was over-restrained and valgus tibial rotation was lax. A graft diameter of at least 10 mm was needed to restore knee stability and graft force to physiological levels, but such large grafts were found to be at high risk of notch impingement. In contrast, the hourglass-shaped graft was able to simultaneously restore both knee stability and graft force at knee flexion of 30° while also having a much lower risk of impingement. Conclusion: Under knee flexion angle of 30°, an hourglass-shaped graft was better able to restore joint stability and graft force to a near-physiological level than columnar grafts, while also reducing the risk of notch impingement.

Wear Analysis of Tibial Inserts Made of Highly Cross-Linked Polyethylene Supplemented with Dodecyl Gallate before and after Accelerated Aging

The wear of the tibial insert is one of the primary factors leading to the failure of total knee arthroplasty. As materials age, their wear performance often degrades. Supplementing highly cross-linked polyethylene (HXLPE) with dodecyl gallate (DG) can improve the oxidation stability of tibial inserts for use in total knee arthroplasty (TKA). This study aimed to evaluate the wear resistance of HXLPE supplemented with DG (HXLPE-DG) tibial inserts before and after accelerated aging. HXLPE-DG tibial inserts were subjected to wear testing of up to 5 million loading cycles according to ISO 14243, and the resulting wear particles were analyzed according to ISO 17853. The wear rate, number, size, and shape of the wear particles were analyzed. The average wear rate of the unaged samples was 4.39 ± 0.75 mg/million cycles and was 3.22 ± 1.49 mg/million cycles for the aged samples. The unaged tibial inserts generated about 2.80 × 107 particles/mL following the wear test, but this was considerably lower for the aged samples at about 1.35 × 107 particles/mL. The average equivalent circle diameter (ECD) of the wear particles from the unaged samples was 0.13 μm (max: 0.80 μm; min: 0.04 μm), and it was 0.14 μm (max: 0.66 μm; min: 0.06 μm) from the aged samples. Moreover, 22.1% of the wear particles from the unaged samples had an aspect ratio (AR) of >4 (slender shape), while this was 15.4% for the aged samples. HXLPE-DG improves the wear performance of the material over time. HXLPE-DG is a novel material that has been demonstrated to have antiaging properties and high wear resistance, making it a promising candidate for use in TKA. Nevertheless, the results are preliminary and will be clarified in further studies.

Comparison of the morphology of the anterior cruciate ligament and related bony structures between pigs and humans

INTRODUCTION

Pigs are widely used for clinical research on the anterior cruciate ligament (ACL) because of the similarity of the knee structure to the human knee. But evidence to support the suitability of using porcine samples to guide clinical practices is limited. This study aims to explore the qualitative and quantitative morphological features of the porcine knee and ACL, and to compare these with data on humans reported in literature.

METHODS

Nineteen porcine knees were used for this study. The bone structures were measured on coronal X-ray images. The length of the ACL was measured using a caliper. The ACL bone insertion sites were marked and measured on a digital photograph. The lengths of the long and short axis of the ACL isthmus were measured on the X-ray microscopy reconstructed images. The outcomes were compared with previously reported data on humans using an abstract independent-samples T test.

RESULTS

Qualitative observation indicated a similar location, orientation and general morphology of the porcine ACL to human ACLs. The major difference was the location of the ACL tibial insertion with respect to the anterior horn of the lateral meniscus (AHLM). The porcine ACL was split into AM and PL bundles by the AHLM, while the AHLM was adjacent to the anterolateral border of the ACL tibial insertion in human knees. The quantitative comparison showed no significant difference between the human and porcine ACL in terms of the length of the ACL, the width of the femoral condyle and tibial plateau, and the tibial interspinal width. However, the CSA, the lengths of the long and short axis of the ACL isthmus, and the femoral and tibial insertion areas of the porcine ACL were all significantly larger than the reported features in human knees.

CONCLUSION

The location, orientation and basic morphology of the porcine ACL and knee are similar to humans. However, the two-bundle structure is more distinct in a porcine ACL, and the dimensions of the porcine ACL are generally larger. This study may provide useful information to researchers when assessing the feasibility and limitations of using porcine samples for research on the human ACL and knee.

Correlation between component alignment and short-term clinical outcomes after total knee arthroplasty

OBJECTIVE

This study aimed to investigate the correlation between component alignment and short-term clinical outcomes after total knee arthroplasty (TKA).

METHODS

50 TKA patients from a regional hospital were enrolled in the study. The following component alignments were measured from radiological data acquired within 1 week after surgery: hip-knee-ankle angle (HKA), medial distal femoral angle (MDFA), medial proximal tibial angle (MPTA), femoral flexion-extension angle (FEA), tibial slope angle (TSA), femoral rotational angle (FRA) and tibial rotational angle (TRA). The Hospital for Special Surgery (HSS) knee scoring system was used to assess clinical outcomes after 1 year, with patients being divided into three groups (excellent, good and not good) according to the HSS scores. Difference analysis and linear correlation analysis were used for the statistical analysis.

RESULTS

The results showed significant differences in MDFA (p = 0.050) and FEA (p = 0.001) among the three patient groups. It was also found that the total HSS had only a moderate correlation with FEA (r = 0.572, p < 0.001), but FEA had a positive linear correlation with pain scores (r = 0.347, p = 0.013), function scores (r = 0.535, p = 0.000), ROM scores (r = 0.368, p = 0.009), muscle scores (r = 0.354, p = 0.012) and stability scores (r = 0.312, p = 0.028). A larger MDFA was associated with lower FE deformity scores (r = -0.289, p = 0.042) and the TSA had a positive influence on the ROM (r = 0.436, p = 0.002). Also, changes in FRA produced a consequent change in the FE deformity score (r = 0.312, p = 0.027), and the muscle strength scores increased as TRA increased (r = 0.402, p = 0.004).

CONCLUSION

The results show that the FEA plays a significant role in clinical outcomes after TKA. Surgical techniques and tools may need to be improved to accurately adjust the FEA to improve joint functionality and patient satisfaction.

Graft Diameter Should Reflect the Size of the Native Anterior Cruciate Ligament (ACL) to Improve the Outcome of ACL Reconstruction: A Finite Element Analysis

The size of the anterior cruciate ligament (ACL) often varies between individuals, but such variation is not typically considered during ACL reconstruction (ACLR). This study aimed to explore how the size of the ACL affects the selection of a suitable graft diameter. A finite element model of a human knee was implanted with intact ACLs of different dimensions (0.95, 1 and 1.05 times the size of the original ACL) and with grafts of different diameters, to simulate ACLR (diameter 7.5–12 mm in 0.5 mm increments). The knee models were flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. Knee kinematics (anterior tibial translation (ATT), internal tibial rotation (ITR) and valgus tibial rotation (VTR)) and ligament forces were recorded and compared among the different groups. The results showed that, compared with the intact knee, a graft diameter of 7.5 mm was found to increase the ATT and VTR, but reduce the graft force. Increasing the graft diameter reduced knee laxity and increased the graft force. A 10% increase in the size of the ACL corresponded to a 3 mm larger graft diameter required to restore knee stability and graft force after ACLR. It was concluded that the graft diameter should be selected according to the dimensions of the native ACL, for better restoration of knee functionality. This study may help to improve the clinical treatment of ACL ruptures.

Biomechanical evaluation of a short-rod technique for lumbar fixation surgery

Objective: The purpose of this study was to analyze the stability and instrument-related complications associated with fixation of the lumbar spine using the Short-Rod (SR) technique.

Methods: Using finite element analysis, this study assessed the stability of a bilateral lumbar fixation system when inserting the pedicle screws at angles of 10°, 15°, and 20° to the endplate in the sagittal plane. Using the most stable construct with a screw angle, the model was then assessed with different rod lengths of 25, 30, 35, and 45 mm. The optimal screw inclination angle and rod length were incorporated into the SR model and compared against traditional parallel screw insertion (pedicle screws in parallel to the endplate, PPS) in terms of the stability and risk of instrument-related complications. The following parameters were evaluated using the validated L4–L5 lumbar finite element model: axial stiffness, range of motion (ROM), stress on the endplate and facet joint, von-Mises stress on the contact surface between the screw and rod (CSSR), and screw displacement.

Results: The results showed that the SR model with a 15° screw inclination angle and 35 mm rod length was superior in terms of construct stability and risk of complications. Compared to the PPS model, the SR model had lower stiffness, lower ROM, less screw displacement, and lower stress on the facet cartilage, the CSSR, and screws. However, the SR model also suffered more stress on the endplate in flexion and lateral bending.

Conclusion: The SR technique with a 15° screw inclination and 35 mm rod length offers good lumbar stability with a low risk of instrument-related complications.

Moderate External Rotation of Tibial Component Generates More Natural Kinematics Than Internal Rotation After Total Knee Arthroplasty

This study aimed to investigate the influence of tibial malrotation on knee kinematics after total knee arthroplasty (TKA). A symmetric fixed-bearing posterior-stabilized prosthesis was implanted in the validated knee model with different rotational alignments of the tibial component (neutral, 3° external rotation, 5° external rotation, 3° internal rotation, and 5° internal rotation). Computational kinematic simulations were used to evaluate the postoperative kinematics of the knee joint including anteroposterior translation femoral condyles and axial rotation of tibial component during 0°–135° knee flexion. The results revealed that the neutral position of the tibial component was not the closest kinematics to the intact knee, the model with 5° external rotation of the tibial component showed the closest lateral condyle translation and tibial axial rotation, and moderate external rotation could improve the kinematics after TKA.

A Strong Correlation Between the Severity of Flatfoot and Symptoms of Knee Osteoarthritis in 95 Patients

Objective

The purpose of this study is to assess the association between the presence and severity of flatfoot and symptoms of knee OA.

Methods

95 participants with knee OA were recruited from a patient cohort at a regional hospital. Symptoms of knee OA, including knee degeneration, femorotibial alignment, pain, stiffness and dysfunction were assessed using the Kellgren-Lawrence (K-L) grading system, femoral-tibial angle (FTA), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Participants were divided into groups with flatfoot (mild, moderate and severe) and without flatfoot based on the Clarke's angle. Linear regression and ordinal logistic regression were used for statistical analysis, as appropriate.

Results

Having flatfoot was associated with a significantly increased risk of having a higher K-L grade (OR: 20.03; 95% CI, 5.88, 68.27; p < 0.001), smaller FTA (Beta: −2.96; 95% CI, −4.41, −1.50; p < 0.001), higher pain score (Beta: 0.47; 95% CI, 0.24, 0.69; p < 0.001) and greater loss of function (Beta: 0.25; 95% CI, 0.02, 0.48; p = 0.03). Severe grades of flat feet were associated with a higher K-L grade (OR: 0.19; 95% CI, 0.08, 0.44; p < 0.001), smaller FTA (Beta: 1.51; 95% CI, 0.66, 2.35; p = 0.001), higher pain score (Beta: −0.25; 95% CI, −0.39, −0.11; p = 0.001), greater stiffness (Beta: −0.24; 95% CI, −0.38, −0.09; p = 0.002) and greater loss of function (Beta: −0.27; 95% CI, −0.41, −0.14; p < 0.001).

Conclusion

The results indicated that the severity of flattening is significantly associated with symptoms of knee OA. For the conservative management of knee OA, both flatfoot and its severity should be carefully considered.

An Efficient Needleless Grasping Suture Technique for Graft Preparation in Anterior Cruciate Ligament Reconstruction

Objective

Several needleless techniques have been developed to outcome the inherent disadvantages of the traditional needle stitching technique for graft preparation, such as tendon damage through the needle, time consumption, and the potential risk of needlestick injury. The purpose of the present study is to compare the graft preparation time and the biomechanical performance between an efficient needleless technique and the traditional needle stitching technique for graft preparation in anterior cruciate ligament reconstruction (ACLR).

Methods

The time required to perform a complete suture on 20 hamstring tendons during ACLRs was measured. The grafts from one side were prepared using the needle stitching technique. The grafts from the other side used the needleless grasping suture technique. For the second part of the study, 12 fresh-frozen porcine flexor tendons were divided into two groups using two techniques and were mounted in an electric tensile test system. Each group was pretensioned to 100 N to simulate the maximum initial graft tension. The suturing state of sutures and graft (intact and damaged) and the load-elongation curve were recorded for each group. A Student’s t-test was used to compare the means of the two groups.

Results

In operation, the needleless grasping suture technique group (19.8 ± 4.8, range: 13.5–32.9 s) was significantly faster (p &lt; 0.05) than the needle stitching technique group (52.7 ± 12.7, range: 36.0–87.5 s). The state of sutures in each group was intact. The mean elongation was 11.75 ± 1.38 (range: 9.47–12.99) mm and 10.59 ± 1.02 (range: 9.12–11.76) mm in the needleless stitching technique group and the needle grasping suture technique group, respectively. There was no statistically significant difference in the elongation between the two groups (p &gt; 0.05).

Conclusion

The needleless grasping suture technique was a convenient and efficient method for graft preparation in ACLR.

Central femoral tunnel placement can reduce stress and strain around bone tunnels and graft more than anteromedial femoral tunnel in anterior cruciate ligament reconstruction

The present study investigated the effects of anteromedial (AM) and central femoral footprint placement on stress and strain distribution around the femoral and tibial tunnel and graft following anterior cruciate ligament reconstruction (ACLR). A three-dimensional (3D) reconstructed knee model was validated and used for simulating ACLR by finite element analysis. A combined loading during normal human walking was applied to the knee models using different anatomic femoral tunnel placement at 20° knee flexion. The results of von Mises stress and principal strain at the entrances of the femoral and tibial tunnel and ACL graft was determined. The peak von Mises stress and the maximum principal strain in the AM footprint group were 8.78 MPa and 8850.89 μ-strain at the entrance of femoral tunnel, and 5.29 MPa and 5553.27 μ-strain at the entrance of tibial tunnel. The results in the AM footprint group were higher than that in the central footprint group. The peak von Mises stress around the ACL graft following AM footprint ACLR was 28.63 MPa, higher than that following the central footprint ACLR. The AM footprint ACLR generated more significant peak von Mises stress and maximum principal strain around the entrances of femoral and tibial tunnel and the graft than the central footprint. The present results are of clinical relevance as they can provide a better understanding of tunnel enlargement and graft failure.

Biomechanical changes at the adjacent segments induced by a lordotic porous interbody fusion cage

Biomechanical changes at the adjacent segments after interbody fusion are common instigators of adjacent segment degeneration (ASD). This study aims to investigate how the presence of a lordotic porous cage affects the biomechanical performance of the adjacent segments. A finite element model (FEM) of a lumbar spine implanted with a lordotic cage at L3-L4 was validated by in-vitro testing. The stress distribution on the cage and range of motion (ROM) of L3-L4 were used to assess the stability of the implant. Three angles of cage (0° = non-restoration, 7° = normal restoration and 11° = over-restoration) were modelled with different porosities (0%, 30% and 60%) and evaluated in the motions of flexion, extension, lateral bending and rotation. The ROM, intervertebral disc pressure (IDP) and facet joint force (FJF) were used to evaluate biomechanical changes at the adjacent segments in each model. The results indicated that porous cages produced more uniform stress distribution, but cage porosity did not influence the ROM, IDP and FJF at L2-L3 and L4-L5. Increasing the cage lordotic angle acted to decrease the ROM and IDP, and increase the FJF of L4-L5, but did not alter the ROM of L2-L3. In conclusion, changes in ROM, IDP and FJF at the adjacent segments were mainly influenced by the lordotic angle of the cage and not by the porosity. A larger angle of lordotic cage was shown to reduce the ROM and IDP, and increase the FJF of the lower segment (L4-L5), but had little effect on the ROM of the upper segment (L2-L3).

The Femoral Tunnel Drilling Angle at 45° Coronal and 45° Sagittal Provided the Lowest Peak Stress and Strain on the Bone Tunnels and Anterior Cruciate Ligament Graft

Purpose: The aims of this study were to 1) investigate the effects of femoral drilling angle in coronal and sagittal planes on the stress and strain distribution around the femoral and tibial tunnel entrance and the stress distribution on the graft, following anterior cruciate ligament reconstruction (ACLR), 2) identify the optimal femoral drilling angle to reduce the risk of the tunnel enlargement and graft failure.

Methods: A validated three-dimensional (3D) finite element model of a healthy right cadaveric knee was used to simulate an anatomic ACLR with the anteromedial (AM) portal technique. Combined loading of 103.0 N anterior tibial load, 7.5 Nm internal rotation moment, and 6.9 Nm valgus moment during normal human walking at joint flexion of 20° was applied to the ACLR knee models using different tunnel angles (30°/45°/60° and 45°/60° in the coronal and sagittal planes, respectively). The distribution of von Mises stress and strain around the tunnel entrances and the graft was calculated and compared among the different finite element ACLR models with varying femoral drilling angles.

Results: With an increasing coronal obliquity drilling angle (30° to 60°), the peak stress and maximum strain on the femoral and tibial tunnel decreased from 30° to 45° and increased from 45° to 60°, respectively. With an increasing sagittal obliquity drilling angle (45° to 60°), the peak stress and the maximum strain on the bone tunnels increased. The lowest peak stress and maximum strain at the ACL tunnels were observed at 45° coronal/45° sagittal drilling angle (7.5 MPa and 7,568.3 μ-strain at the femoral tunnel entrance, and 4.0 MPa and 4,128.7 μ-strain at the tibial tunnel entrance). The lowest peak stress on the ACL graft occurred at 45° coronal/45° sagittal (27.8 MPa) drilling angle.

Conclusions: The femoral tunnel drilling angle could affect both the stress and strain distribution on the femoral tunnel, tibial tunnel, and graft. A femoral tunnel drilling angle of 45° coronal/ 45° sagittal demonstrated the lowest peak stress, maximum strain on the femoral and tibial tunnel entrance, and the lowest peak stress on the ACL graft.

Femoral Stems With Porous Lattice Structures: A Review

Cementless femoral stems are prone to stress shielding of the femoral bone, which is caused by a mismatch in stiffness between the femoral stem and femur. This can cause bone resorption and resultant loosening of the implant. It is possible to reduce the stress shielding by using a femoral stem with porous structures and lower stiffness. A porous structure also provides a secondary function of allowing bone ingrowth, thus improving the long-term stability of the prosthesis. Furthermore, due to the advent of additive manufacturing (AM) technology, it is possible to fabricate femoral stems with internal porous lattices. Several review articles have discussed porous structures, mainly focusing on the geometric design, mechanical properties and influence on bone ingrowth. However, the safety and effectiveness of porous femoral stems depend not only on the characteristic of porous structure but also on the macro design of the femoral stem; for example, the distribution of the porous structure, the stem geometric shape, the material, and the manufacturing process. This review focuses on porous femoral stems, including the porous structure, macro geometric design of the stem, performance evaluation, research methods used for designing and evaluating the femoral stems, materials and manufacturing techniques. In addition, this review will evaluate whether porous femoral stems can reduce stress shielding and increase bone ingrowth, in addition to analyzing their shortcomings and related risks and providing ideas for potential design improvements.

The Three-Dimensional Morphology of Femoral Medullary Cavity in the Developmental Dysplasia of the Hip

OBJECTIVE

This study aimed to assess the morphology of the femoral medullary canal in subjects with developmental dysplasia of the hip (DDH) with the intent of improving the design of femoral stems in total hip arthroplasty.

METHODS

Computed tomography images of 56 DDH hips, which were classified into Crowe I to Crowe IV, and 30 normal hips were collected and used to reconstruct three-dimensional morphology of the femoral medullary cavity. Images of twenty-one cross sections were taken from 20 mm above the apex of the lesser trochanter to the isthmus. The morphology of femoral cavity was evaluated on each cross section for the longest canal diameter, the femoral medullary torsion angle (FMTA), and the femoral medullary roundness index (FMRI).

RESULTS

The Crowe IV group displayed the narrowest medullary canal in the region superior to the end of the lesser trochanter, but then gradually aligned with the medullary diameter of the other groups down to the isthmus. The FMTA along the femoral cavity increased with the severity of DDH, but the rate of variation of FMTA along the femoral canal was consistent in the DDH groups. The DDH hips generally showed a larger FMRI than the normal hips, indicating more elliptical shapes.

CONCLUSION

A femoral stem with a cone shape in the proximal femur and a cylindrical shape for the remainder down to the isthmus may benefit the subjects with severe DDH. This design could protect bone, recover excessive femoral anteversion and facilitate the implantation in the narrow medullary canal.

Restoration of Joint Inclination in Total Knee Arthroplasty Offers Little Improvement in Joint Kinematics in Neutrally Aligned Extremities

Kinematically aligned total knee replacements have been shown to better restore physiological kinematics than mechanical alignment and also offer good postoperative satisfaction. The purpose of this study is to evaluate the extent to which an inclined joint line in a kinematically aligned knee can alter the postoperative kinematics. A multi-body dynamic simulation was used to identify kinematic changes in the joint. To accurately compare mechanical alignment, kinematic alignment and a natural knee, a “standard” patient with neutral alignment of the lower extremities was selected for modeling from a joint database. The arthroplasty models in this study were implanted with a single conventional cruciate-retaining prosthesis. Each model was subjected to a flexion movement and the anteroposterior translation of the femoral condyles was collected for kinematic analysis. The results showed that the mechanical alignment model underwent typical paradoxical anterior translation of the femoral condyles. Incorporating an inclined joint line in the model did not prevent the paradoxical anterior translation, but a 3° varus joint line in the kinematic alignment model could reduce the peak value of this motion by about 1 mm. Moreover, the inclined joint line did not restore the motion curve back to within the range of the kinematic curve of the natural knee. The results of this study suggest that an inclined joint line, as in the kinematic alignment model, can slightly suppress paradoxical anterior translation of the femoral condyles, but cannot restore kinematic motions similar to the physiological knee. This finding implies that prostheses intended to be used for kinematic alignment should be designed to optimize knee kinematics with the intention of restoring a physiological motion curve.

Changing the Diameter of the Bone Tunnel Is More Effective Than Changing the Tunnel Shape for Restoring Joint Functionality After ACL Reconstruction

The clinical implications of changing the shape of the bone tunnel for Anterior cruciate ligament reconstruction (ACLR) is controversial and few studies have reported on the long-term prevalence for osteoarthritis. As such, this study aims to evaluate the effect of tunnel shape on joint biomechanics. Finite element models of an ACLR were constructed with different shapes (circular, oval, rounded rectangular, rectangular, and gourd-shaped) and diameters (7.5, 8.5, and 9.5 mm) for the bone tunnel. A combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment and 6.9 Nm valgus tibial moment was applied at a joint flexion angle of 20°. Joint kinematics and the strain energy density (SED) on the articular cartilage were compared among the different groups. The results showed that conventional ACLR (circular tunnel) lead to an increase in joint kinematics over the intact joint, a lower ligament force and a higher SED on the lateral tibial cartilage. ACLR using the other tunnel shapes resulted in even greater joint kinematics, lower graft force and greater SED on the lateral tibial cartilage. Increasing the tunnel diameter better restored joint kinematics, graft force and articular SED, bringing these values closer to those from the intact knee. In conclusion, increasing the tunnel diameter may be more effective than changing the tunnel shape for restoring joint functionality after ACLR.

Association Between the Morphology of Proximal Tibiofibular Joint and the Presence of Knee OA

Objective: The aim of this study was to evaluate the association between the morphology of the proximal tibiofibular joint (PTFJ) and the presence of knee osteoarthritis (OA).

Methods: Twenty-eight OA subjects and 30 healthy subjects were enrolled in this study. A 3D model of the lower limb of each subject was constructed from CT scans and used to measure the characteristics of the PTFJ, including the shape of the articular facets, articular surface area, joint inclination, relative articular height, and joint declination. The association between the characteristics of the PTFJ and presence of knee OA was assessed using binomial logistic regression analysis.

Results: There was a significant difference between the OA and healthy groups in terms of the inclination (p = 0.028) and declination (p = 0.020) of the PTFJ and relative articular height (p = 0.011). A greater inclination angle (OR: 1.463, 95% CI: 1.124–1.582, p = 0.021), greater declination angle (OR: 1.832, 95% CI: 1.691–2.187, p = 0.009), and lower relative articular height (OR: 0.951, 95% CI: 0.826–0.992, p = 0.008) were found to be associated with an increased likelihood of knee OA being present.

Conclusion: The results of this study suggest that abnormal PTFJ morphology is associated with the presence of knee OA.

Impact of scapular notching on glenoid fixation in reverse total shoulder arthroplasty: an in vitro and finite element study

BACKGROUND

The high incidence of scapular notching in reverse total shoulder arthroplasty (RTSA) has spurred several methods to minimize bone loss. However, up to 93% of RTSAs accompanying scapular notching have been reported to maintain good implant stability for over 10 years. This study was conducted to investigate the relationship between scapular notching and glenoid fixation in RTSA.

METHODS

Cadaveric testing was performed to measure the notch-induced variations in strain on the scapular surface and micromotion at the bone-prosthesis interface during arm abductions of 30°, 60°, and 90°. Finite element analysis was used to further study the bone and screw stresses as well as the bone-prosthesis micromotion in cases with a grade 4 notch during complicated arm motions.

RESULTS

The notch resulted in an apparent increase in inferior screw stress in the root of the screw cap and at the notch-screw conjunction. However, the maximum stress (172 MPa) along the screw after notching is still much less than the fatigue strength of the titanium screw (600 MPa) under cyclic loading. The bone-prosthesis micromotion results did not present significant notch-induced variations.

CONCLUSIONS

Scapular notching will lead to few impacts on the stability of an RTSA on the glenoid side. This finding may explain the long-term longevity of RTSA in cases of severe scapular notching. The relationship between scapular notching and weak regions along the inferior screw may explain why fractures of the inferior screw are sometimes reported in patients with RTSA clinically.

Effect of stress-shielding-induced bone resorption on glenoid loosening in reverse total shoulder arthroplasty

Aseptic loosening of the glenoid component is one of the main reasons for the high revision rates of reverse total shoulder arthroplasty (RTSA). It has been reported that the bulky implant designs may lead to stress shielding. However, it is uncertain whether the shielding effect is severe enough to lead to bone resorption and glenoid loosening. The purpose of this study was to evaluate the level of stress-shielding and assess whether bone resorption plays a role in aseptic glenoid loosening following RTSA. A cadaveric in vitro test model was used to validate a finite element model (FEM) of the scapula. The FEM of the scapula, incorporating adaptive bone remodeling algorithms, was used to predict changes in postoperative bone density after RTSA. Changes in bone strength after implantation were also analyzed. The strain values predicted from the FEM of the scapula were in agreement with the in vitro measurements. Analysis of postoperative bone adaptation revealed that strain-induced bone resorption began at the peg of the implant and around the resected bone surface and then gradually expended to the peripheral regions. The bone strength also reduced postoperatively and appeared particularly around the implant peg. Strain-induced bone resorption is a likely source of the bone loss commonly observed in RTSA. The finite element glenoid bone remodeling simulation may be used as a tool to evaluate glenoid implant design.

Stiffness and shape of the ACL graft affects tunnel enlargement and graft wear

PURPOSE

Tunnel enlargement and graft rupture are common complications associated with ACL reconstruction (ACLR). This study aims to explore how variations in graft stiffness and shape affect the strain energy density (SED) around bone tunnel entrances and stress on the graft and subsequently influencing the level of tunnel enlargement and graft wear.

METHODS

Finite element ACLR models were developed using different graft stiffnesses (323 N/mm, 545 N/mm and 776 N/mm) and shapes (circular and elliptical). The models were subjected to a combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment, and 6.9 Nm valgus tibial moment at joint flexion of 30°. SED at tunnel entrances and stresses on the graft was recorded and compared among the different models.

RESULTS

Increasing the graft stiffness resulted in greater stress on the graft (17.2, 24.4 and 31.7 MPa for graft stiffnesses of 323 N/mm, 545 N/mm and 776 N/mm), but had little effect on the SED reduction around the tunnel entrances. Changing the cross section of the graft from circular to elliptical caused an additional reduction in SED (56.8 vs 2.8 kJ/m³) at the posterior zone of the femoral tunnel entrance and increased the stress on the graft (31.7 MPa vs 38.9 MPa).

CONCLUSIONS

This study recommends using ACL grafts with lower stiffness and a circular cross section to reduce tunnel enlargement and graft wear following ACLR.

A novel protection liner to improve graft-tunnel interaction following anterior cruciate ligament reconstruction: a finite element analysis

Background

Deteriorated bone-graft interaction at the tunnel entrance following ACL reconstruction (ACLR) is considered one of the primary causes of long-term tunnel enlargement and graft wear. Methods have been introduced to improve the long-term outcome, such as novel graft materials or alternative fixation methods, but have been met with varying degrees of success. This study aims to design a protection liner to improve the bone-graft interaction at the tunnel entrances.

Methods

A finite element model of a human cadaveric knee was used to simulate traditional ACLR and ACLR using the protection liner. Stress distribution around the tunnel entrances and on the ACL graft were calculated under a combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment, and 6.9 Nm valgus tibial moment at a joint flexion angle of 20°. Results were compared between the traditional ACLR and ACLR using a double liner (femoral and tibial) setup, as well as between the ACLR using a double liner setup and a single liner (femoral side) setup. Different materials (PEEK, Ti-6Al-4V, CoCrMo) for the liner were also evaluated.

Results

The traditional ACLR resulted in concentrated stress on the graft where it contacted the tunnel entrance. Correspondingly, there were stress concentrations at the distal posterior zone of the femoral tunnel entrance and medial posterior zone of the tibial tunnel entrance, while the other zones suffered from a stress reduction. Use of the protection liner reduced the stress concentration around the tunnel entrances by up to 89% and increased the stress at the unloaded zones by up to 106%. Also, stress concentration on the graft was slightly decreased (15.4 vs 15.1 MPa) after using the liner. The single liner setup increased the stress concentration around the tibial tunnel entrance. Stiffer materials improved the stress distribution around tunnel entrances but had little effect on the stress on the graft.

Conclusions

The novel protection liner can improve the stress distribution on the graft and at the tunnel entrances, which may be beneficial for improving the clinical outcome of ACLR.

The Posterolateral Corner-Locked Technique Is Applicable in a Chinese Population Regarding the Tibial Component Rotation Alignment in Total Knee Arthroplasty

Rotational malalignment between the femoral and tibial components in total knee arthroplasty (TKA) can affect clinical outcomes, but there is no consensus on how to best determine tibia tray orientation. The posterolateral corner-locked (PLCL) technique may be a new method. This study aims to assess the applicability of this technique in a Chinese population. Forty normal Chinese volunteers were recruited and underwent computed tomography (CT) of the lower limbs. Knee model reconstructions and simulated standard tibial osteotomy were conducted digitally. The transepicondylar axis (TEA), the Akagi line, and the line connecting the medial third of the tibial tubercle with the midpoint of the posterior cruciate ligament (PCL) were projected to the tibial cross-section and marked. The PLCL technique was applied using either symmetrical or asymmetrical tibial tray templates, and the anteroposterior (AP) axis of the tibial tray was marked. The angles between the TEA and these lines were calculated, and the statistical differences were analyzed. The angle between the TEA and the Akagi line and between the TEA and the line connecting the medial third of the tibial tubercle with the midpoint of the PCL were 96.90 ± 5.57 and 107.31 ± 5.95 degrees, respectively. The angles between the TEA and the AP axis of the symmetrical and the asymmetrical design tibial trays were 94.01 ± 4.21 and 96.65 ± 4.70 degrees, respectively. Except for the Akagi line and AP axis of the asymmetrical tibial tray, statistical differences were found between all lines (p < 0.05). The PLCL technique is principally suitable for Chinese patients requiring TKA when using the tibial component referred to in this study, although it may result in slight external rotation.

Long-term study on the osteogenetic capability and mechanical behavior of a new resorbable biocomposite anchor in a canine model

Background

Biodegradable suture anchors are commonly used for repairing torn rotator cuffs, but these biodegradable materials still suffer from low mechanical strength, poor osteointegration, and the generation of acidic degradation byproducts.

Method

The purpose of this study was to evaluate the long-term mechanical behavior and osteogenetic capabilities of a biocomposite anchor injection molded with 30% β-tricalcium phosphate microparticles blended with 70% poly (L-lactide-co-glycolide) (85/15). This study investigated in vitro degradation and in vivo bone formation in a canine model. The initial mechanical behavior, mechanical strength retention with degradation time, and degradation features were investigated.

Results

The results showed that the biocomposite anchor had sufficient initial mechanical stability confirmed by comparing the initial shear load on the anchor with the minimum shear load borne by an ankle fracture fixation screw, which is considered a worst-case implantation site for mechanical loading. The maximum shear load retention of the biocomposite anchor was 83% at 12 weeks, which is desirable, as it aligns with the rate of bone healing. The β-tricalcium phosphate fillers were evenly dispersed in the polymeric matrix and acted to slow the degradation rate and improve the mechanical strength of the anchor. The interface characteristics between the β-tricalcium phosphate particles and the polymeric matrix changed the degradation behavior of the biocomposite. Phosphate buffer saline was shown to diffuse through the interface into the biocomposite to inhibit the core accelerated degradation rate. In vivo, the addition of β-tricalcium phosphate induced new bone formation. The biocomposite material developed in this study demonstrated improved osteogenesis in comparison to a plain poly (L-lactide-co-glycolide) material. Neither anchor produced adverse tissue reactions, indicating that the biocomposite had favorable biocompatibility following long-term implantation.

Conclusion

In summary, the new biocomposite anchor presented in this study had favorable osteogenetic capability, mechanical property, and controlled degradation rate for bone fixation.

Translational potential of this article

The new biocomposite anchor had sufficient initial and long-term fixation stability and bone formation capability in the canine model. It is indicated that the new biocomposite anchor has a ​potential for orthopedic application.

Evaluation of a magnesium ring device for mechanical augmentation of a ruptured ACL: Finite element analysis

BACKGROUND

Recently, a ring device was used for mechanical augmentation to aid the healing of ACL. In-vivo study using goat showed improved joint stability after ring repair in comparison to using biological augmentation alone. Objective of this study was to quantify the load and stress levels in the ACL and its femoral insertion site following ring repair.

METHODS

A three dimensional finite element model of a goat stifle joint was developed to find the load and stress level in the ACL and at its femoral insertion site following ring repair.

FINDINGS

Ring repair led to approximately a 50% reduction in anterior-posterior tibial translation over the model with a deficient ACL: 5.2 mm vs 10.6 mm, 4.4 mm vs 9.0 mm, and 2.9 mm vs 5.2 mm at joint flexion angles of 37°, 60° and 90° respectively. After ring repair, the in situ force in the ACL was restored to be nearly 60% of the intact ACL. The maximum Von Mises stress at the femoral insertion site was up to 71% of those for the intact ACL.

INTERPRETATION

This study offers new knowledge on the function of a ring device to mechanically augment ACL repair in order to improve its healing. Quantitative data on loading levels in the repaired ACL and its insertion site that led to its healing could be used as basis for developing novel devices to mechanically augment the healing of ACL in humans.

Polylactide Composite Pins Reinforced with Bioresorbable Continuous Glass Fibers Demonstrating Bone-like Apatite Formation and Spiral Delamination Degradation

The emergence of polylactide composites reinforced with bioresorbable silicate glass fibers has allowed for the long-term success of biodegradable polymers in load-bearing orthopedic applications. However, few studies have reported on the degradation behavior and bioactivity of such biocomposites. The aim of this work was to investigate the degradation behavior and in vitro bioactivity of a novel biocomposite pin composed of bioresorbable continuous glass fibers and poly-L-D-lactide in simulated body fluid for 78 weeks. As the materials degraded, periodic spiral delamination formed microtubes and funnel-shaped structures in the biocomposite pins. It was speculated that the direction of degradation, from both ends towards the middle of the fibers and from the surface through to the bulk of the polymer matrix, could facilitate bone healing. Following immersion in simulated body fluid, a bone-like apatite layer formed on the biocomposite pins which had a similar composition and structure to natural bone. The sheet- and needle-like apatite nanostructure was doped with sodium, magnesium, and carbonate ions, which acted to lower the Ca/P atomic ratio to less than the stoichiometric apatite and presented a calcium-deficient apatite with low crystallinity. These findings demonstrated the bioactivity of the new biocomposite pins in vitro and their excellent potential for load-bearing applications.

A preclinical method for evaluating the kinematics of knee prostheses

The primary intent of anatomical knee implants is to replicate the motions of a normal knee joint. In developing such designs, a preclinical evaluation of kinematic behavior is needed. This study introduces an in vitro testing method for recording movements of the knee joint. A novel testing jig was developed and incorporated into a knee simulator setup alongside a motion capture system to directly track the medial and lateral movements of a knee prosthesis. The test system developed in this study required a number of factors to be validated; (i) gait inputs to the knee simulator (result: 0.37-1.575% error), (ii) validity of global coordinate system in the motion capture system, (iii) the position of flexion facet centers (FFCs) detected by the motion capture system (result: a maximum error of 0.08 mm in AP direction and 0.3 mm in SI direction), (iv) local coordinate system in the motion capture system (result: 1.09% error for the measurement of flexion angle), (v) that FFC results were in good agreement with inputs. In conclusion, the system developed in this study for recording FFC is a direct and reliable in vitro test method for analyzing the kinematics of a knee prosthesis.

Comparison of ISO 14243-1 to ASTM F3141 in terms of wearing of knee prostheses

BACKGROUND

The wear properties of knee implants need to be thoroughly evaluated prior to clinical use to ensure implant longevity. ISO 14243-1:2009 and ASTM F3141-17 are the two standards typically used for evaluating wear, with the ISO standard being more common; ASTM F3141-17 was first released in 2015. The aim of this study is to compare differences between these two standards in terms of wearing on a knee prosthesis.

METHODS

Using finite element analysis based on Archard's law, this study evaluated anterior-posterior and internal-external motion, contact area, contact force, contact stress, volumetric wear rate, wear depth, and wear distribution on the knee prosthesis.

FINDINGS

The results show that simulations performed according to ASTM F3141 produced knee kinematics that were more similar to human gait. The maximum wear depth occurred on the medial side of the tibia. However, the region of peak contact stress did not always correspond with the region of the maximum wear depth, indicating that considering the contact stress alone is not sufficient for evaluating wear as the sliding distance also plays an important role. The resulting wear region from the ASTM F3141 simulation was smaller but deeper than the wear region from the simulation per ISO 14243-1. However, the volumetric wear rates were very similar, with 13.48-55.26 mm³/million for ASTM F3141 and 13.64-54.9 mm³/million for ISO 14243-1.

INTERPRETATION

The resulting rate of wear is almost identical between ISO 14243-1 and ASTM F3141. However, there are differences in wear contours and wear depth.

Effect of baseplate positioning on fixation of reverse total shoulder arthroplasty

BACKGROUND

The glenoid component in reverse total shoulder arthroplasty is recommended to be positioned inferiorly or with a downward tilt with the intention of reducing scapular notching. However, it is still unclear whether modifying the position of the glenoid prosthesis affects implant stability. The aim of this study was to determine the association between implant positioning and glenoid prosthesis fixation using Grammont reverse total shoulder arthroplasty.

METHODS

Four positions for the glenoid prosthesis were studied using the finite element method. The glenosphere was positioned as follows: 1) in the middle of the glenoid fossa, 2) flush with the inferior glenoid rim, 3) with an inferior overhang, 4) with a 15° inferior inclination. Bone-prosthesis micromotions and strain-induced bone adaptations were quantified during five daily activities.

FINDINGS

When the glenoid component was tilted inferiorly, the activities producing anterior-posterior shear forces (e.g. standing up from an armchair) caused an increase in peak micromotions. In the lateral-middle glenoid, inferior positioning caused a 64.6% reduction in bone apparent density. In the lateral-inferior glenoid, central positioning led to the most severe bone resorption, reaching 43.9%.

INTERPRETATION

Reducing activities which generate anterior-posterior shear forces on the shoulder joint will increase bone formation and may improve the primary stability of the implant when fixed in the position with an inferior tilt. Postoperative bone resorption is highly dependent on implant positioning. Understanding the relationship between bone resorption and implant positioning will help surgeons improve the long-term stability of reverse total shoulder arthroplasty.

A single-component and hemi-hip prosthesis followed up for 43 years: A case report

RATIONALE

Giant cell tumor (GCT) is a locally aggressive bone tumor with a high recurrence rate if not completely excised. And reconstructive hip surgery using an artificial prosthesis in a young active patient is controversial because of problems related to the durability of the artificial joint.

PATIENT CONCERNS

A 30-year-old man presented with right hip pain and other more severe symptoms, but without fever or night sweats. After 4 months, he experienced intense pain at the root of the right leg and limitation of motion after falling from a bicycle.

DIAGNOSES

Giant cell tumor.

INTERVENTIONS

The patient was treated with surgical resection of the total tumor, and hemiarthroplasty of the hip joint using a custom-made titanium femoral prosthesis.

OUTCOMES

The patient could perform activities of daily living, even walking long distance without pain. He continued to work as a teacher for 30 years and retired 11 years after the surgery.

LESSONS

A well-designed, custom-fitted, single-component, wear-resistant joint prosthesis should be the brand-new direction of development of artificial joints.

The impact of variations in input directions according to ISO 14243 on wearing of knee prostheses

ISO 14243 is the governing standard for wear testing of knee prostheses, but there is controversy over the correct direction of anterior-posterior (AP) displacement and loading and the correct direction of tibial rotation (TR) angles and torque. This study aimed to analyze how altering the direction of AP and TR affected wear on the tibial insert. Modifications to the conditions specified in ISO 14243–1 and ISO 14243–3 were also proposed. As such, five loading conditions were applied to FEA models of a knee prosthesis: (1) Modified ISO 14243–3 with positive AP displacement and TR angle, (2) ISO 14243–3:2004 with negative AP displacement and positive TR angle, (3) ISO 14243–3:2014 with positive AP displacement and negative TR angle, (4) Modified ISO 14243–1 with positive AP load and TR torque, and (5) ISO 14243–1:2009 with negative AP load and positive TR torque. This study found that changing the input directions for AP and TR according to ISO 14243–1 and 14243–3 had an influence on the wear rate and wear contours on the tibial insert model. However, the extent of wear varies depending on the design features of the tibial insert and shape of the input curves. For displacement control according to ISO 14243–3, changing the direction of AP displacement had a marked influence on the wear rate (272.77%), but changing the direction of TR angle had a much lower impact (2.17%). For load control according to ISO 14243–1, reversing the AP load (ISO 14243–1:2009) only increased the wear rate by 6.73% in comparison to the modified ISO 14243–1 conditions. The clinical relevance of this study is that the results demonstrate that tibial wear is affected by the direction of application of AP and TR. Incorrect application of the loading conditions during the design stage may lead to an ineffective preclinical evaluation and could subsequently influence implant longevity in clinical use.

High-quality thulium iron garnet films with tunable perpendicular magnetic anisotropy by off-axis sputtering - correlation between magnetic properties and film strain

Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (Ms) and the coercive field (Hc) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (jc) of 2.5 × 106 A/cm2, an order of magnitude smaller than the previously reported value. We were able to tune Ms, Hc and H⊥ to obtain an ultra-low jc of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.

Metallic Nanoislands on Graphene for Monitoring Swallowing Activity in Head and Neck Cancer Patients

There is a need to monitor patients with cancer of the head and neck postradiation therapy, as diminished swallowing activity can result in disuse atrophy and fibrosis of the swallowing muscles. This paper describes a flexible strain sensor comprising palladium nanoislands on single-layer graphene. These piezoresistive sensors were tested on 14 disease-free head and neck cancer patients with various levels of swallowing function: from nondysphagic to severely dysphagic. The patch-like devices detected differences in (1) the consistencies of food boluses when swallowed and (2) dysphagic and nondysphagic swallows. When surface electromyography (sEMG) is obtained simultaneously with strain data, it is also possible to differentiate swallowing vs nonswallowing events. The plots of resistance vs time are correlated to specific events recorded by video X-ray fluoroscopy. Finally, we developed a machine-learning algorithm to automate the identification of bolus type being swallowed by a healthy subject (86.4%. accuracy). The algorithm was also able to discriminate between swallows of the same bolus from either the healthy subject or a dysphagic patient (94.7% accuracy). Taken together, these results may lead to noninvasive and home-based systems for monitoring of swallowing function and improved quality of life.

Optimization of the Conical Angle Design in Conical Implant–Abutment Connections: A Pilot Study Based on the Finite Element Method

Conical implant–abutment connections are popular for their excellent connection stability, which is attributable to frictional resistance in the connection. However, conical angles, the inherent design parameter of conical connections, exert opposing effects on 2 influencing factors of the connection stability: frictional resistance and abutment rigidity. This pilot study employed an optimization approach through the finite element method to obtain an optimal conical angle for the highest connection stability in an Ankylos-based conical connection system. A nonlinear 3-dimensional finite element parametric model was developed according to the geometry of the Ankylos system (conical half angle = 5.7°) by using the ANSYS 11.0 software. Optimization algorithms were conducted to obtain the optimal conical half angle and achieve the minimal value of maximum von Mises stress in the abutment, which represents the highest connection stability. The optimal conical half angle obtained was 10.1°. Compared with the original design (5.7°), the optimal design demonstrated an increased rigidity of abutment (36.4%) and implant (25.5%), a decreased microgap at the implant–abutment interface (62.3%), a decreased contact pressure (37.9%) with a more uniform stress distribution in the connection, and a decreased stress in the cortical bone (4.5%). In conclusion, the methodology of design optimization to determine the optimal conical angle of the Ankylos-based system is feasible. Because of the heterogeneity of different systems, more studies should be conducted to define the optimal conical angle in various conical connection designs.