Advances and Innovations of 3D Bioprinting Skin.

Three-dimensional (3D) bioprinted skin equivalents are highlighted as the new gold standard for alternative models to animal testing, as well as full-thickness wound healing. In this review, we focus on the advances and innovations of 3D bioprinting skin for skin regeneration, within the last five years. After a brief introduction to skin anatomy, 3D bioprinting methods and the remarkable features of recent studies are classified as advances in materials, structures, and functions. We will discuss several ways to improve the clinical potential of 3D bioprinted skin, with state-of-the-art printing technology and novel biomaterials. After the breakthrough in the bottleneck of the current studies, highly developed skin can be fabricated, comprising stratified epidermis, dermis, and hypodermis with blood vessels, nerves, muscles, and skin appendages. We hope that this review will be priming water for future research and clinical applications, that will guide us to break new ground for the next generation of skin regeneration.

Definitions of unfavorable surgical outcomes and their risk factors based on disability score after spine surgery for lumbar spinal stenosis.

BACKGROUND: Risk factors for unfavorable surgical outcomes are dependent on the definitions of the unfavorable surgical outcomes. The aims of this study were to compare risk factors for each unfavorable surgical outcome according to two different definitions of "unfavorable" surgical outcomes after surgery for lumbar spinal stenosis (LSS) as well as compare the clinical course from the preoperative period to 3 years postoperatively between cases with favorable and unfavorable outcomes according to the two different definitions. METHODS: Overall, 295 patients who underwent spine surgery for LSS and a follow-up evaluation at 3 years postoperatively were enrolled and divided into favorable and unfavorable groups, based on two different definitions for unfavorable surgical outcomes, as evaluated at 12 months postoperatively: the patient-reported outcome (PRO) and minimal clinically important difference (MCID) methods. In the PRO method, patients with a postoperative Oswestry Disability Index (ODI) score > 22 were considered as having an "unfavorable" outcome, whereas in the MCID method, those with a postoperative ODI score that changed < 12.8 points from the preoperative value were classified as having an "unfavorable" outcome. As a primary outcome, risk factors for unfavorable surgical outcomes according to each definition were investigated at 12 months postoperatively. RESULTS: In the PRO method, female sex (P = 0.011; odds ratio (OR): 2.340), elementary school attainment (vs. university attainment; P = 0.035; OR: 2.875), and higher preoperative ODI score (P = 0.028; OR: 2.340) were associated with higher odds for an unfavorable surgical outcome. In the MCID method, a higher preoperative ODI score was associated with higher odds (P <  0.001; OR: 0.920) of a favorable surgical outcome. In the PRO method, the favorable outcome group demonstrated significantly lower visual analog scale for back and leg pain and lower ODI scores than the unfavorable outcome group at 3 years postoperatively, whereas in the MCID method, clinical outcomes were not different between the two groups at 3 years postoperatively. CONCLUSION: A higher preoperative ODI score may be a risk factor for postoperative ODI > 22 after surgery for LSS. It may also be associated with higher odds for improvements in the ODI score of > 12.8.

Morphometric study of gender difference in osteoarthritis posterior tibial slope using three-dimensional magnetic resonance imaging.

Posterior tibial slope (PTS) is an important parameter of sagittal alignment associated with postoperative stability and kinematics after total knee arthroplasty (TKA). However, data are limited regarding the innate gender differences in PTS in Koreans. The current study separately measured the PTS of the medial and lateral tibial plateau on magnetic resonance images of 511 patients with knee joint osteoarthritis who had Kellgren and Lawrence grade 3 and 4 (430 women, 81 men) and compared the measurements between and within the genders. The tibia was then rotated to the tibial plateau with the tibial centroid axis and the PTS was evaluated from best-fit planes on the surface of the proximal tibia and individually for the medial, lateral, and overall plateaus. The average overall PTS was 10.0° ± 3.5°. The average overall PTS of the female and male patients was 10.2° ± 3.4° and 8.8° ± 4.0°, respectively. The average medial PTS was 10.4° ± 4.0°, significantly greater than the mean lateral PTS of 8.7° ± 3.9° (P < 0.05). The average medial and lateral tibial slopes for female patients were 10.7° ± 3.8° and 8.8° ± 3.8°, respectively, while the average medial and lateral tibial slopes for male patients were 8.9° ± 4.8° and 7.9° ± 4.7°, respectively. The medial and overall PTS were significantly greater in female patients than in male patients (P < 0.05). The results showed a gender difference in PTS and that medial PTS was greater than lateral PTS. These findings have clinical relevance in knee reconstructive surgery for determining ideal placement of the posterior slope tibial component. Surgeons should be aware of variability and gender differences in the tibial slope of patients undergoing TKA.

Sleep Disturbance in Patients With Lumbar Spinal Stenosis: Association With Disability and Quality of Life.

STUDY DESIGN: This was a cross-sectional cohort study. OBJECTIVE: The objective of this study was to identify the prevalence of sleep disturbance in patients with symptomatic lumbar spinal stenosis (LSS) and to establish the relationship between sleep disturbance and both functional disability and health-related quality of life in patients with symptomatic LSS. SUMMARY OF BACKGROUND DATA: Despite the possible association between LSS and poor sleep quality, there has been no study regarding the relationship between LSS and sleep disturbance. MATERIALS AND METHODS: A total of 148 patients with LSS were divided into the poor sleeper and nonpoor sleeper groups according to Global Pittsburgh Sleep Quality Index (PSQI) score. Demographic data, Visual Analog Scale (VAS) score for back and leg pain, Oswestry Disability Index (ODI), and EuroQol 5-dimension questionnaire (EQ-5D) were compared between both groups. Multiple regression analysis was performed with ODI or ODI without sleep component as the dependent variable and age, sex, PSQI, VAS for back pain, VAS for leg pain as independent variables. RESULTS: Of the 148 patients who participated in this study, 54 (36.5%) and 94 (63.5%) patients were classified into nonpoor sleeper and poor sleeper groups. Although there were no differences in demographic data or VAS for back or leg pain between the nonpoor sleeper and poor sleeper groups, poor sleepers demonstrated significantly higher ODI scores, and lower EQ-5D than nonpoor sleepers (P=0.003 and 0.004, respectively). There were significant correlations between the global PSQI score and both the ODI score and EQ-5D. Although the surgical treatment group showed significantly higher VAS for back pain, VAS for leg pain, ODI scores, and lower EQ-5D than the conservative treatment group, the ratio of poor to nonpoor sleepers was not different between both groups (P=0.733). In the surgical treatment group, the percent of poor sleeper decreased from 65.1% to 47.6% 6 months after surgery (P<0.001). CONCLUSIONS: The present study demonstrated that 'poor sleep quality' is a prevalent condition (63.5%) in patients with symptomatic LSS. Poor sleep quality has an adverse effect on functional disability and health-related quality of life in symptomatic LSS patients.

Analysis of pelvic compensation for dynamic sagittal imbalance using motion analysis.

PURPOSE: To analyze pelvic compensation during walking in patients with severe sagittal plane deformity by using motion analysis. METHODS: A total of 44 patients with sagittal plane deformity who were scheduled to undergo surgery were included. Motion analysis was performed 3 consecutive times during walking to estimate the anterior pelvic tilt (Ant-PT) angle, trunk kyphosis (TK) angle, and distance of the center of gravity (CoG) from the center of mass (CoM) of the pelvic segment, and hip and knee joint angles during gait. The patients were classified into Ant-PT+/Ant-PT-, TK+/TK-, and CoG+/CoG- groups according to the changes in Ant-PT angle, TK angle, and distance of the CoG from the CoM of the pelvic segment. Increases and decreases in the values of the variables from the first trial to the third trial were indicated with "+" and "-" signs, respectively. RESULTS: The mean Ant-PT angle, TK angle, and distance of the CoG from the CoM of the pelvic segment increased progressively, and the differences in the values of these variables from the first to the third trials were statistically significant (P = 0.046, P = 0.004, and P = 0.007 for the Ant-PT angle, TK angle, and distance of the CoG from the CoM of pelvic segment, respectively). Among the 44 patients, 27 and 34 were classified into the Ant-PT+ and CoG+ groups, respectively. Older age and higher body mass index (BMI) were significantly associated with the Ant-PT+ group. The CoG+ group demonstrated a significantly higher height and weight than the CoG- group. CONCLUSIONS: Higher BMI, height, and weight are risk factors for progressive worsening of dynamic sagittal imbalance. These slides can be retrieved under Electronic Supplementary Material.

Anatomy-mimetic design preserves natural kinematics of knee joint in patient-specific mobile-bearing unicompartmental knee arthroplasty.

PURPOSE: This study aims to evaluate whether different tibial-femoral conformities for patient-specific mobile-bearing unicompartmental knee arthroplasties (UKAs) preserve natural knee kinematics, using computational simulations. METHODS: Different designs for patient-specific mobile-bearing UKAs were evaluated using finite element analysis. Three designs for the identical femoral component were considered: flat (non-conforming design), anatomy-mimetic, and conforming for the tibial insert. RESULTS: The conforming design for the patient-specific mobile-bearing UKAs exhibited a 1.2 mm and 0.7° decrease in the translation and rotation, respectively, in the swing phase compared with those of the natural knee. In addition, the femoral rollback and internal rotation were 2.6 mm and 1.2° lower, respectively, than those of the natural knee, for the conforming design under the deep-knee-bend condition. The flat design for the patient-specific mobile-bearing UKAs exhibited a 2.2 mm and 1.4° increase in the femoral rollback and rotation compared with the natural knee under the deep-knee-bend condition. The anatomy-mimetic patient-specific mobile-bearing UKAs best preserved the natural knee kinematics under the gait and deep-knee-bend loading conditions. CONCLUSIONS: The kinematics of the loading conditions in patient-specific mobile-bearing UKAs was determined to closely resemble those of a native knee. In additional, by replacing the anatomy-mimetic design with a mobile-bearing, natural knee kinematics during gait and deep-knee-bend motions is preserved. These results confirm the importance of tibiofemoral conformity in preserving native knee kinematics in patient-specific mobile-bearing UKA.

Effect of insert material on forces on quadriceps, collateral ligament, and patellar tendon after rotating platform mobile-bearing total knee arthroplasty.

BACKGROUND: There is a gradual increase in the number of patients for total knee arthroplasty (TKA), and TKA demonstrates reliable clinical outcomes. The orthopaedic biomaterials community continuously attempted over the past decades to improve the longevity of UHMWPE in TKA by using various improved technologies. Polyetheretherketone (PEEK) and carbon fiber reinforced-PEEK(CFR-PEEK) are suggested as potential tibial insert materials to replace UHMWPE in some applications. The aim of this study involves evaluating the biomechanical effects of UHMWPE and CFR-PEEK tibial materials on mobile-bearing TKA. METHODS: The finite element (FE) model was obtained by conducting computed tomography and magnetic resonance imaging. The FE investigation included three types of loading conditions corresponding to the loads used in the experiments for FE model validation and model predictions under deep-knee bend loading conditions. We investigated forces on quadriceps, collateral ligament and patellar tendon with UHMWPE and CCFR-PEEK tibial insert materials under the deep-knee-bend condition. RESULTS: Quadriceps force decreased with flexion for CFR-PEEK when compared to that for UHMWPE. A similar trend was observed in terms of the patellar tendon force. An opposite trend was observed in the collateral ligament. Medial collateral ligament force in the CFR-PEEK exceeded that in the UHMWPE, and lateral collateral ligament force in the UHMWPE exceeded that in the CFR-PEEK. CONCLUSION: The CFR-PEEK represents an alternative insert material given its superior biomechanical effect after mobile-bearing total knee arthroplasty. However, a balance between the medial and lateral ligaments is considered as an important factor in the CFR-PEEK tibial insert due to its opposite biomechanical effect.

Design optimization of high tibial osteotomy plates using finite element analysis for improved biomechanical effect.

BACKGROUND: High tibial osteotomy (HTO) is a common treatment for moderate osteoarthritis of the medial compartment in the knee joint by the translation of the force center toward the lateral compartment. However, the stability of a short plate such as Puddu used in this procedure was not as effective as other long plates such as Tomofix. No previous studies have used a rigorous and systematic design optimization method to determine the optimal shape of short HTO plate. Therefore, the purpose of this study is to evaluate the improved biomechanical stability of a short HTO plate by using design optimization and finite element (FE) analysis. METHODS: A FE model of HTO was subjected to physiological and surgical loads in the tibia. Taguchi-style L27 orthogonal arrays were used to identify the most significant factors for optimizing the design parameters. The optimal design variables were calculated using the nondominated sorting genetic algorithm II. Plate and bone stresses and wedge micromotions in the initial and optimized designs were chosen as the comparison indices. RESULTS: Optimal designed HTO plate showed the decreased micromotions over the initial HTO plate with enhanced plate stability. In addition, increased bone stress and decreased plate stress supported the positive effect on stress shielding compared to initial HTO plate design. The results yielded a new short HTO design while demonstrating the feasibility of design optimization and potential improvements to biomechanical stability in HTO design. The newly developed short HTO plate throughout the optimization and computational simulation showed the improved biomechanical effect as good as the golden standard, TomoFix, does. CONCLUSIONS: This study showed that plate design has a strong influence on the stability after HTO. This study demonstrated that the optimized short plates had low stress shielding effect and less micromotion because of its improvement in biomechanical performances. Our result showed that design optimization is an effective tool for HTO plate design. This information can aid future developments in HTO plate design and can be expanded to other implant designs.

Failure of Pelvic Compensation in Patients With Severe Positive Sagittal Imbalance: Comparison Between Static Radiographs and Gait Analysis of Spinopelvic Parameters in Adult Spinal Deformity and Lumbar Stenosis.

STUDY DESIGN: Case-control study for motion analysis. OBJECTIVE: To compare spinopelvic parameters using static radiographs with the values obtained using motion analysis during gait between adult spinal deformity (ASD) or lumbar spinal stenosis (LSS). SUMMARY OF BACKGROUND DATA: It is still unclear whether measurement of radiological parameters using static radiographs can reflect natural sagittal balance during gait in the patients with severe positive sagittal imbalance. METHODS: In this age- and sex-matched case control study, a total of 40 patients, each 20 subjects with either ASD or LSS who were scheduled to undergo surgery were included. Both clinical outcomes and sagittal spinopelvic parameters, including sagittal vertical axis (SVA), lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI) were measured. In motion analysis during walking, the angle of anterior pelvic tilt and the angles of the pelvis, hip, and knee were estimated. The correlation between variables was analyzed. RESULTS: On standing lateral x-rays, SVA, PT, and PI - LL were significantly higher in the ASD group while SS and LL were significantly lower in the ASD group. However, on motion analysis, the average mean anterior pelvic tilt ±â€ŠSD values in the ASD group were 8.3 ±â€Š10.7 and 8.5 ±â€Š10.7 on the right and left, respectively, and were not different from matched values in the LSS group. A Bland-Altman plot demonstrated a good agreement between the SS in the x-ray and anterior pelvic tilt in the motion analysis. In the ASD group, SS and SVA showed a significant positive correlation with mean anterior pelvic tilt in motion analysis during gait. CONCLUSION: The present study showed that the failure of pelvic compensation would likely occur in patients with severe positive sagittal imbalance during walking. LEVEL OF EVIDENCE: 3.

Gender differences in morphology exist in posterior condylar offsets of the knee in Korean population.

PURPOSE: This study aimed to analyze the morphometric data from magnetic resonance images of arthritic knees in Korean adults, and to identify the existence of morphological differences of femoral posterior condylar offset (PCO) between genders. METHODS: The differences in anthropometric PCO data in 975 patients (825 female and 150 male) were evaluated. The distances from the anterior and posterior femoral shaft cortex line to the most posterior femoral condyle tangent line were defined as the anterior-posterior dimension (AP) and the PCO. The PCO ratio (PCOR) was calculated as PCO/AP. RESULTS: The medial PCO was greater than the lateral PCO (26.3 ± 2.2 vs. 24.3 ± 2.3 mm, p < 0.01). This difference was observed in both female patients (medial: 26.2 ± 2.2 mm vs. lateral: 24.2 ± 2.2 mm, p < 0.01) and male patients (medial: 26.8 ± 2.3 mm vs. lateral: 24.8 ± 2.4 mm, p < 0.01). The medial and lateral PCO values were also greater in male patients than in female ones (p < 0.01). In contrast, PCOR was greater in female patients than in male ones, both in the medial and lateral femoral condyles (p < 0.01). CONCLUSIONS: It was shown that medial and lateral PCO and PCOR were asymmetric, and that there was gender difference in Korean population in our study. In addition, our data showed that the PCOR of contemporary TKAs may be small for Asian patients that may not be sufficient to meet the needs of the Korean patient population. These results confirm that a gender-specific femoral component design is necessary to recreate the PCO for male and female Asian populations. LEVEL OF EVIDENCE: Non-consecutive patients, Level III.

Validation and cross-cultural adaptation of the Korean version of the Core Outcome Measures Index in patients with degenerative lumbar disease.

PURPOSE: To translate and cross-culturally adapt the Core Outcome Measures Index (COMI) into the Korean language and to test the psychometric properties of the Korean COMI in patients with degenerative lumbar spine diseases. METHODS: A cross-cultural adaptation of the COMI into Korean was carried out using established guidelines. A total of 117 patients with lumbar spinal diseases were recruited from the spinal center of a tertiary care teaching institution and completed a baseline questionnaire including the newly translated COMI, the visual analog scale for back pain and for leg pain, the Oswestry Disability Index (ODI), and the EuroQOL-5 dimensions (EQ-5D). Within 2 weeks after the first assessment, 83 (71%) completed a second COMI questionnaire and a transition question (no change, slight change, moderate change, a lot of change) by phone to assess reproducibility. RESULTS: COMI summary scores displayed 1.7% floor effects and no ceiling effect. For construct validity, each COMI item and COMI summary score well correlated with its corresponding reference questionnaire. Therefore, the predefined hypotheses for the construct validities of each COMI item (ρ > 0.4 with the corresponding questionnaire) and the COMI summary score (ρ > 0.6 with both ODI and EQ-5D) were confirmed. Intraclass correlation coefficients of each COMI item and summary score ranged from 0.93 to 0.98. Therefore, the hypothesis for reliability (ICC > 0.8) was confirmed. CONCLUSIONS: The present study highlights that the Korean version of the COMI is a reliable and valid outcome tool for use in Korean-speaking patients with degenerative lumbar spinal disease. These slides can be retrieved under Electronic Supplementary Material.

Comparative study of 1-year clinical and radiological outcomes using robot-assisted pedicle screw fixation and freehand technique in posterior lumbar interbody fusion: A prospective, randomized controlled trial.

BACKGROUND: The purpose of this study was to compare the clinical outcome of surgery using robot-assisted posterior interbody fusion with that using freehand posterior interbody fusion in patients with degenerative spinal disease. METHODS: 78 participants with degenerative spinal disease were randomly allocated (1:1) to the minimally invasive (MIS), posterior lumbar interbody fusion (Robot-PLIF) or conventional, freehand, open-approach, posterior lumbar interbody fusion (Freehand-PLIF). RESULTS: The baseline-adjusted scores on the Oswestry Disability Index (ODI) in both groups at 1 year after surgery were not different (P = 0.688). However, the decrease in disc height at the proximal adjacent segment was significantly less in the Robot-PLIF group than in the Freehand-PLIF group (P = 0.039). CONCLUSION: One-year surgical outcomes including Visual Analog Scale, ODI and Short Form-36 did not differ between the two groups. The disc height in the proximal adjacent segment was significantly less decreased in the Robot-PLIF group than in the Freehand-PLIF group.

The influence of hand grip strength on surgical outcomes after surgery for degenerative lumbar spinal stenosis: a preliminary result.

BACKGROUND CONTEXT: Although a number of prognostic factors have been demonstrated to be associated with surgical outcome of degenerative lumbar spinal stenosis (DLSS), no study has investigated the relation between hand grip strength (HGS) and treatment outcome of DLSS. PURPOSE: The purpose of the present study was to examine the influence of HGS on surgical outcomes after surgery for patients with DLSS. STUDY DESIGN: This is an observational study. PATIENT SAMPLE: Patients who underwent spine surgery for DLSS were included in the study. OUTCOME MEASURES: Oswestry Disability Index (ODI), EuroQOL (EQ-5D), and visual analog scale (VAS) scores for back or leg pain were assessed. MATERIALS AND METHODS: A total of 172 consecutive patients who underwent spine surgery for DLSS were included in the present study. Patients were assigned to either high HGS group (≥26 kg for men and ≥18 kg for women, n=124) or low HGS group (<26 kg for men and <18 kg for women, n=48) based on their preoperative HGS performance. Oswestry Disability Index, EQ-5D, and VAS scores for back and leg pain were assessed and compared between two groups preoperatively, 3 and 6 months after surgery. The primary outcome measure was baseline-adjusted ODI scores 6 months after surgery. The secondary outcome measures, including the overall ODI score, EQ-5D score, VAS score for back and leg pain, were assessed at each time point during the 6-month follow-up period. RESULTS: As primary outcome, baseline-adjusted ODI scores were significantly lower in the high HGS group than in the low HGS group 6 months after surgery. In the secondary outcome measurements, the ODI, EQ-5D, and VAS scores for back and leg pain improved significantly with time after surgery in both groups. The effects of HGS group on the overall changes in the ODI and EQ-5D scores during the 6-month period were significantly different between the two groups; however, they were not significantly different on VAS score for back and leg pain. The pattern of change in the ODI during the follow-up period was significantly different between the two groups. CONCLUSIONS: Patients with preoperative high HGS display better surgical outcome in terms of disability and health status 6 months after spine surgery. Preoperative HGS can act as a predictor of surgical outcome in patients with DLSS.

Change in pain catastrophizing in patients with lumbar spinal surgery.

BACKGROUND CONTEXT: Even though catastrophizing can negatively moderate the outcome of surgery for lumbar spinal stenosis (LSS), it is still unclear whether pain catastrophizing is an enduring stable or a dynamic structure related to pain intensity after spine surgery. PURPOSE: The purpose of this study was to determine whether catastrophizing would change in patients who undergo spinal surgery for LSS. STUDY DESIGN: A prospective observational cohort study was carried out. STUDY SAMPLE: Patients who underwent spine surgery for LSS comprised the study sample. OUTCOME MEASURES: The Visual Analog Pain Scale (VAS) scores for back/leg pain, Oswestry Disability Index (ODI), and Pain Catastrophizing Scale (PCS) were the outcome measures. METHODS: The present observational cohort consisted of 138 patients between the ages of 40 and 80 years who were scheduled to undergo surgery for LSS. Among them, a total of 96 patients underwent a 3-year assessment after surgery. The PCS questionnaire was used for pain catastrophizing assessment before and 3 years after surgery. The VAS for back and leg pain, and ODI were assessed 3 and 6 months, and 1 and 3 years after surgery. The correlations between variables were analyzed before and 3 years after surgery. To clarify the causal relationship, time-series and linear mixed models were also used. RESULTS: At 3 years after surgery, ODI, VAS for back and leg pain, and PCS scores were significantly decreased. The correlation of PCS with VAS and ODI was significant both before and 3 years after surgery. The correlation between change in pain or disability and change in pain catastrophizing from preoperative to 3 years after surgery was also significant. In the causal relationship between pain and catastrophizing, overall changes in pain and disability were significant predictors of overall changes in pain catastrophizing from baseline to 3 year after surgery. CONCLUSION: The present study shows that pain catastrophizing can change in association with the improvement in pain intensity after spine surgery. Therefore, catastrophizing may not be an enduring stable construct, but a dynamic construct.

Probabilistic evaluation of the material properties of the in vivo subject-specific articular surface using a computational model.

This article used probabilistic analysis to evaluate material properties of the in vivo subject-specific tibiofemoral (TF) joint model. Sensitivity analysis, based on a Monte Carlo (MC) method, was performed using a subject-specific finite element (FE) model generated from in vivo computed tomography (CT) and magnetic resonance imaging (MRI) data, subjected to two different loading conditions. Specifically, the effects of inherent uncertainty in ligament stiffness, horn attachment stiffness, and articular surface material properties were assessed using multifactorial global sensitivity analysis. The MRI images were taken before and after axial compression, and when the flexion condition had been maintained at up to 90 degree flexion in the subject-specific knee joint. The loading conditions of the probabilistic subject-specific FE model (axial compression and 90 degree flexion) were similar to the MRI acquisition setup. We were able to detect the influence of material parameters while maintaining the potential effect of parametric interactions. Throughout the in silico property optimization, a subject-specific FE model was used and less sensitive parameters were eliminated in the global sensitivity method. Soft tissue material properties were estimated using an optimization procedure that involved the minimization of the differences between the kinematics predicted by the subject-specific model and those obtained through in vivo subject-specific data. The results of this approach suggest that the articular surface mechanical properties could be found by using in vivo measurements, which clarifies the valuable tool for future subject-specific studies related to TF joint scaffolds, allografts and biologics. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1390-1400, 2017.

Computational model-based probabilistic analysis of in vivo material properties for ligament stiffness using the laxity test and computed tomography.

The objective of this paper was to evaluate in vivo material properties in order to address technical aspects of computational modeling of ligaments in the tibiofemoral joint using a probabilistic method. The laxity test was applied to the anterior-posterior drawer under 30° and 90° of flexion with a series of stress radiographs, a Telos device, and computed tomography. Ligament stiffness was investigated using sensitivity analysis based on the Monte-Carlo method with a subject-specific finite element model generated from in vivo computed tomography and magnetic resonance imaging data, subjected to laxity test conditions. The material properties of ligament stiffness and initial ligament strain in a subject-specific finite element model were optimized to minimize the differences between the movements of the tibia and femur in the finite element model and the computed tomography images in the laxity test. The posterior cruciate ligament was the most significant factor in flexion and posterior drawer, while the anterior cruciate ligament primarily was the most significant factor for the anterior drawer. The optimized material properties model predictions in simulation and the laxity test were more accurate than predictions based on the initial material properties in subject-specific computed tomography measurement. Thus, this study establishes a standard for future designs in allograft, xenograft, and artificial ligaments for anterior cruciate ligament and posterior cruciate ligament injuries.

Influence of Dentoalveolar Ankylosis on the Biomechanical Response of a Single-rooted Tooth and Surrounding Alveolar Bone: A 3-dimensional Finite Element Analysis.

INTRODUCTION: Dentoalveolar ankylosis necessarily accompanies the loss of periodontal ligament (PDL), which might alter the biomechanical response of the tooth. The purpose of this study was to investigate the influence of dentoalveolar ankylosis on a single-rooted tooth and the surrounding alveolar bone structures in the biomechanical standpoint. METHODS: A basic model of an intact maxillary central incisor and the surrounding bone structures was chosen for the numeric analysis. From this basic model, 6 different models were further developed by combining 3 types of endodontic status (an intact model, a nonsurgically treated model, and a surgically treated model) and 2 types of periodontal attachment condition (models with or without PDL). For each condition, maximum von Mises stress (σ max) in dentin and bone and maximum tooth displacement (ΔR max) were calculated. RESULTS: In models with dentoalveolar ankylosis, stress was concentrated on the cervical dentin around the cementoenamel junction and the alveolar bone crest, whereas the stress was more evenly distributed along the entire length of the root in models with normal PDL. The models with dentoalveolar ankylosis showed higher stress values in dentin (44.72%-80.56% of σ max increase) and bone (24.23%-80.68% of σ max increase) and lower tooth displacement (59.22%-63.97% of ΔR max decrease) compared with the models with normal PDL. CONCLUSIONS: Dentoalveolar ankylosis exerts significant changes on the biomechanical response of a single-rooted tooth and the surrounding bone structures. The dentoalveolar complex with ankylosis showed characteristic stress concentrations, increased stress values, and decreased tooth displacement compared with that with normal PDL.

Probabilistic Approach for Determining the Material Properties of Meniscal Attachments In Vivo Using Magnetic Resonance Imaging and a Finite Element Model.

The material properties of in vivo meniscal attachments were evaluated using a probabilistic finite element (FE) model and magnetic resonance imaging (MRI). MRI scans of five subjects were collected at full extension and 30°, 60°, and 90° flexion. One subject with radiographic evidence of no knee injury and four subjects with Kellgren-Lawrence score of 1 or 2 (two each) were recruited. Isovoxel sagittal three-dimensional cube sequences of the knee were acquired in extension and flexion. Menisci movement in flexion was investigated using sensitivity analysis based on the Monte Carlo method in order to generate a subject-specific FE model to evaluate significant factors. The material properties of horn attachment in the five-subject FE model were optimized to minimize the differences between meniscal movements in the FE model and MR images in flexion. We found no significant difference between normal and patient knees in flexion with regard to movement of anterior, posterior, medial, and lateral menisci or changes in height morphology. At 90° flexion, menisci movement was primarily influenced by posterior horn stiffness, followed by anterior horn stiffness, the transverse ligament, and posterior cruciate ligament. The optimized material properties model predictions for menisci motion were more accurate than the initial material properties model. The results of this approach suggest that the material properties of horn attachment, which affects the mobile characteristics of menisci, could be determined in vivo. Thus, this study establishes a basis for a future design method of attachment for tissue-engineered replacement menisci.

Influence of apical root resection on the biomechanical response of a single-rooted tooth-part 2: apical root resection combined with periodontal bone loss.

INTRODUCTION: In a clinical situation, an apically resected tooth is often accompanied by a varying degree of periodontal bone loss. The purpose of this study was to assess the influence of apical root resection combined with periodontal bone loss on the biomechanical response of a single-rooted tooth. METHODS: A basic intact model and a basic apically resected model of the upper central incisor were selected for the numerical analysis. From each basic model, 6 models were developed assuming different amounts of periodontal bone loss (0, 0.5, 1, 1.5, 2, and 3 mm). Maximum von Mises stress (σ max), maximum tooth displacement (ΔR max), and effective crown-to-root ratio (α) were calculated for each condition. RESULTS: There were only marginal differences (a 2.1% difference in σ max and a 16.9% difference in ΔR max) between the biomechanical responses of the intact model and the apically resected model when the tooth was supported by a normal periodontium. However, when destruction of the periodontium was assumed, the intact model and the apically resected model responded differently. The difference increased as the periodontal bone loss progressed, resulting in a 68.7% difference in σ max and a 56.3% difference in ΔR max when the periodontal bone loss increased to 3 mm (α = 0.48). CONCLUSIONS: Although the biomechanical response of an apically resected tooth was relatively stable when the tooth was supported by a normal periodontium, the apically resected tooth showed a more deteriorated response compared with the intact tooth as the periodontal bone loss progressed.