Finite element stress analysis of the bearing component and bone resected surfaces for total ankle replacement with different implant material combinations.

BACKGROUND: A proper combination of implant materials for Total Ankle Replacement (TAR) may reduce stress at the bearing component and the resected surfaces of the tibia and talus, thus avoiding implant failure of the bearing component or aseptic loosening at the bone-implant interface. METHODS: A comprehensive finite element foot model implanted with the INBONE II implant system was created and the loading at the second peak of ground reaction force was simulated. Twelve material combinations including four materials for tibial and talar components (Ceramic, CoCrMo, Ti6Al4V, CFR-PEEK) and three materials for bearing components (CFR-PEEK, PEEK, and UHMWPE) were analyzed. Von Mises stress at the top and articular surfaces of the bearing component and the resected surfaces of the tibia and talus were recorded. RESULTS: The stress at both the top and articular surfaces of the bearing component could be greatly reduced with more compliant bearing materials (44.76 to 72.77% difference of peak stress value), and to a lesser extent with more compliant materials for the tibial and talar components (0.94 to 28.09% difference of peak stress value). Peak stresses at both the tibial and talar bone-implant interface could be reduced more strongly by using tibial and talar component materials with smaller material stiffness (7.31 to 66.95% difference of peak stress value) compared with bearing materials with smaller material stiffness (1.11 to 24.77% difference of peak stress value). CONCLUSIONS: Implant components with smaller material stiffness provided a stress reduction at the bearing component and resected surfaces of the tibia and talus. The selection of CFR-PEEK as the material of tibial and talar components and UHMWPE as the material of the bearing component seemed to be a promising material combination for TAR implants. Wear testing and long-term failure analysis of TAR implants with these materials should be included in future studies.

Can Repeated Ponseti Management for Relapsed Clubfeet Produce the Outcome Comparable With the Case Without Relapse? A Clinical Study in Term of Gait Analysis.

BACKGROUND: The prevention and treatment of relapsed clubfoot remained challenging tasks. There were controversies as to treatment options and management, such as complete subtalar release, application of an Ilizarov external frame, or repeated Ponseti method; and different options were available in different treatment centers. This study was designed to evaluate the clinical outcome of relapsed clubfeet treated by repeated Ponseti method in comparison with the cases without relapse in term of gait analysis and to clarify the clinical efficacy of repeated Ponseti method in treating the relapsed clubfeet. METHODS: Thirty-seven patients (53 feet) were retrospectively identified from our database according to the inclusion and exclusion criteria. Among the 37 patients, 17 cases (25 relapsed clubfeet) were assigned to group I, whereas 20 cases (28 clubfeet without relapse) were assigned to group II. Clinical examination, gait analysis, and kinematic gait deviation criteria from Texas Scottish Rite Hospital for Children were used for evaluation. RESULTS: There was statistically significant difference in the parameters of foot length, stride length, and single limb support time (%gait cycle) between the 2 groups (P<0.05). No statistically significant difference was found in the kinematic parameters of total hip, knee, and ankle excursion, peak knee and ankle flexion and extension, and internal foot progression (P>0.05). There was no statistically significant difference in peak hip, knee, and ankle flexion moment, peak knee valgus moment, and peak ankle power (P>0.05). No statistically significant difference was found in equinus and calcaneus gait, increased ankle dorsiflexion, foot drop, and internal foot progression angle (P>0.05). CONCLUSIONS: Repeated Ponseti method for relapsed clubfeet can yield good or excellent clinical results. We recommend repeated Ponseti method as the treatment choice for relapsed clubfeet in the early stage. LEVEL OF EVIDENCE: Level III-retrospective comparative study.

Positive and negative factors for the treatment outcomes following total ankle arthroplasty? A systematic review.

BACKGROUND: Patient selection, surgeon's experience and implant design play an integral role and affect the treatment outcomes of total ankle arthroplasty (TAA). The aims of this study were to investigate the positive and negative attributes that correlate with different clinical and radiographic outcomes. METHODS: Eight-nine studies matched the inclusion criteria: (1) studies of primary TAA with uncemented prosthesis; (2) mean follow-up of no less than 2-year; (3) reports of clinical and radiographic outcomes, and exclusion criteria: (1) non-English study; (2) more than one type of prosthesis without separated data; (3) kin studies with shorter follow-up or smaller cohort. Age, etiology, preoperative deformity, surgeon's experience, follow-up duration and prosthetic type were studied with respect to different outcomes by mixed-effects logistic regression analysis. RESULTS: Patients factor: older patients reported less pain or stiffness and demonstrated less radiographic loosening which did not require additional surgical intervention. More traumatic arthritis experienced adjacent joints degeneration after TAA. Surgeon factor: less experienced surgeons had more intraoperative complications. Lack of experience for complications management without implant retrieval during early period might result in more revisions or fusion was done. Prosthetic factor: updated instrumentation decreased malalignment. If the polyethylene (PE) insert was significantly narrower than the metal components more implant instability and subsequent severe particulate wear was seen. Designs with flat-on-flat articulation and ridge at the center of the talar component associated with more PE fracture. Minimal bone resection reduced postoperative fractures. A flat cut of the tibial component and a flat undersurface with press-fit by two screws or pegs of the talar component demonstrated less postoperative fractures, whereas a syndesmosis fusion and a small triangular shape with one central fin of the talar component experienced more loosening which did not require additional surgery. Anatomic conical shape of the talar component seemed to reduce adjacent joint degeneration. Finally, fewer failures were found in patients who received HINTEGRA and Salto Talaris. CONCLUSIONS: Based on our investigation, some positive and negative factors for different clinical and radiographic outcomes were found, which should be taken into consideration in clinical practice and ankle implant design.

Prognosticating Factors of Relapse in Clubfoot Management by Ponseti Method.

BACKGROUND: It is challenging that some Ponseti method corrected clubfeet have a tendency to relapse. Controversies remain as to the implication of initial severity, representing the deformity degree, as well as number of casts needed, representing the treatment process, in predicting relapse. However, no study has been reported to take these 2 parameters into comprehensive consideration for outcome measurement. The purpose of this study is to investigate the correlation between the initial Pirani score and the number of casts required to correct the deformity in our series; to evaluate noncompliance as a risk factor of the deformity recurrence in Ponseti treatment; to test the validity and predictive value of a new proposed parameter, ratio of correction improvement (RCI) which is indicated by the initial Pirani scores divided by the number of casts. METHODS: A total of 116 consecutive patients with 172 idiopathic clubfeet managed by Ponseti method were followed prospectively for a minimum of 2 years from the start of brace wearing. RCI value and the other clinical parameters were studied in relation to the risk of relapse by using multivariate logistic regression analysis modeling. RESULTS: A positive correlation between the initial Pirani score and the number of casts required to correct the deformity was found in our series (r=0.67, P<0.01). There were 45 patients (39%) with brace noncompliance. The relapse rate was 49% (22/45). The odds ratio of relapse in noncompliant patients was 10 times more that in compliant patients (odds ratio=10.30 and 95% confidence interval, 2.69-39.42; P<0.01). The multivariate logistic regression analysis showed that there was significant association between relapse and RCI value. There were 42 patients (36%) with RCI value <1, among them, the relapse rate was 57% in 24 patients. The odds ratio of relapse in patients with RCI value <1 was 27 times more likely to relapse than those >1 (odds ratio=26.77 and 95% confidence interval, 5.70-125.72; P<0.01). CONCLUSIONS: On the basis of the findings from our study, we propose the RCI to be a new parameter in predicting the risk of relapse in Ponseti method of clubfoot management. Early intervention is recommended to optimize the brace compliance particularly in case with lower RCI value. LEVEL OF EVIDENCE: Level II-prognostic.

Timing for Ponseti clubfoot management: does the age matter? 90 children (131 feet) with a mean follow-up of 5 years.

Background and purpose - There are still controversies as to the age for beginning treatment with the Ponseti method. We evaluated the clinical outcome with different age at onset of Ponseti management for clubfoot. Patients and methods - 90 included children were divided into 3 groups in terms of age at start of treatment. The difference in treatment-related and prognosis-related variables including presentation age, initial Pirani and Dimeglio score, casts required, relapse rates, final Dimeglio score, and international clubfoot study group score (ICFSG) was analyzed. Results - Age between 28 days and 3 months at start of treatment method was associated with fewer casts required, lower relapse rate, and lower final ICFSG score (p < 0.05). Early treatment before 28 days of age required more casts and had a higher relapse rate (p < 0.05). The highest ICFSG scores were found in the ages between 3 and 6 months (p < 0.05). After propensity score matching, age between 28 days and 3 months was demonstrated to have a lower finial ICFSG score. Linear regression models showed that presentation age was positively correlated with final ICFSG score, and was identified as the only independent prognostic risk factor. Interpretation - There was lower rate of relapse and better clinical outcome when treatment was initiated at age between 28 days and 3 months. With the Ponseti method, clubfeet may not need urgent treatment.

Postoperative Functional Evaluation of Percutaneous Vertebroplasty Compared With Percutaneous Kyphoplasty for Vertebral Compression Fractures.

Both percutaneous vertebroplasty (PVP) and percutaneous kyphoplasty (PKP) have shown their superiorities in the treatment of vertebral compression fractures (VCFs), yet, few studies have compared their postoperative functional outcomes in patients with VCFs; the authors therefore conducted this meta-analysis to explore the postoperative functional recovery efficacies of PVP and PKP in the treatment of VCFs. Computerized bibliographic databases were applied to identify relevant articles comparing the therapeutic effect of PVP and PKP in the treatment of VCFs. Standardized mean difference and its 95% confidence interval were calculated. Statistical analyses were conducted with the STATA statistical software. Postoperative Oswestry Disability Index investigation outcomes revealed a significant difference between the PVP group and PKP group. Subgroup analysis by the 8 dimensions of the SF-36 health survey presented a statistical significance in general health between the PVP group and PKP group. The application of PKP has the superiority in postoperative functional recovery of VCFs as compared with PVP, especially in efficaciously extending kyphosis angle, improving vertebral body height and decreasing complication rate.

Results of clubfoot management using the Ponseti method: do the details matter? A systematic review.

BACKGROUND: Although the Ponseti method is accepted as the best choice for treatment of clubfoot, the treatment protocol is labor intensive and requires strict attention to details. Deviations in strict use of this method are likely responsible for the variations among centers in reported success rates. QUESTIONS/PURPOSES: We wished to determine (1) to what degree the Ponseti method was followed in terms of manipulation, casting, and percutaneous Achilles tenotomy, (2) whether there was variation in the bracing type and protocol used for relapse prevention, and (3) if the same criteria were used to diagnose and manage clubfoot relapse. METHODS: We conducted a systematic review of MEDLINE, EMBASE(TM), and the Cochrane Library. Studies were summarized according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses Statement. Five hundred ninety-one records were identified with 409 remaining after deduplication, in which 278 irrelevant studies and 22 review articles were excluded. Of the remaining 109 papers, 19 met our inclusion criteria. All 19 articles were therapeutic studies of the Ponseti method. RESULTS: The details of manipulation, casting, or percutaneous Achilles tenotomy of the Ponseti method were poorly described in 11 studies, whereas the main principles were not followed in three studies. In three studies, the brace type deviated significantly from that recommended, whereas in another three studies the bracing protocol in terms of hours of recommended use was not followed. Furthermore no unified criteria were used for judgment of compliance with brace use. The indication for recognition and management of relapse varied among studies and was different from the original description of the Ponseti method. CONCLUSIONS: We found that the observed clinically important variation may have been the result of deviations from the details regarding manipulation, casting, percutaneous Achilles tenotomy, use of the bar-connected brace, and indication for relapse recognition and management recommended for the classic Ponseti approach to clubfoot management. We strongly recommend that clinicians follow the Ponseti method as it initially was described without deviation to optimize treatment outcomes.

Correlations of ezrin expression with pathological characteristics and prognosis of osteosarcoma: a meta-analysis.

We conducted a meta-analysis to comprehensively evaluate the correlations of ezrin expression with pathological characteristics and the prognosis of osteosarcoma. The MEDLINE (1966-2013), the Cochrane Library Database, EMBASE, CINAHL, Web of Science (1945-2013), and the Chinese Biomedical Database were searched without language restrictions. Meta-analyses conducted using STATA software were calculated. Ten studies met the inclusion criteria, including 459 patients with osteosarcoma. Meta-analysis results illustrated that ezrin expression may be closely associated with the recurrence of osteosarcoma or metastasis in osteosarcoma. Our findings also demonstrated that patients with grade III-IV osteosarcoma showed a higher frequency of ezrin expression than those with histological grade I-II osteosarcoma. Furthermore, we found that patients with positive expression of ezrin exhibited a shorter overall survival than those with negative ezrin expression. The results also indicated that positive ezrin expression was strongly correlated with poorer metastasis-free survival. Nevertheless, no significant relationships were observed between ezrin expression and clinical variables (age and gender). In the current meta-analysis, our results illustrated significant relationships of ezrin expression with pathological characteristics and prognosis of osteosarcoma. Thus, ezrin expression could be a promising marker in predicting the clinical outcome of patients with osteosarcoma.

Proximal humeral bone density assessment and prediction analysis using machine learning techniques: An innovative approach in medical research.

Background: Patients with fractures of the proximal humerus often local complications and failures attributed to osteoporosis. Currently, there is a lack of straight forward screening methods for assessing the extent of local osteoporosis in the proximal humerus. This study utilizes machine learning techniques to establish a diagnostic approach for evaluating local osteoporosis by analyzing the patient's demographic data, bone density, and X-ray ratio of the proximal humerus. Methods: A cohort comprising a total of 102 hospitalized patients admitted during the period spanning from 2021 to 2023 underwent random selection procedures. Resulting in exclusion of 5 patients while enrolling 97 patients for analysis encompassing patient demographics, shoulder joint anteroposterior radiographs, and bone density information. Using the modified Tingart index methodology involving multiple measurements denoted as M1 through M4 obtained from humeral shafts. Within this cohort comprised 76 females (78.4 %) and 21 males (21.6 %), with an average age of 73.0 years (range: 43-98 years). There were 25 cases with normal bone density, 35 with osteopenia, and 37 with osteoporosis. Machine learning techniques were used to randomly divide the 97 cases into training (n = 59) and validation (n = 38) sets with a ratio of 6:4 using stratified random sampling. A decision tree model was built in the training set, and significant diagnostic indicators were selected, with the performance of the decision tree evaluated using the validation set. Multinomial logistic regression methods were used to verify the strength of the relationship between the selected indicators and osteoporosis. Results: The decision tree identified significant diagnostic indicators as the humeral shaft medullary cavity ratio M2/M4, age, and gender. M2/M4 ≥ 1.13 can be used as an important screening criterion; M2/M4 < 1.13 was predicted as local osteoporosis; M2/M4 ≥ 1.13 and age ≥83 years were also predicted as osteoporosis. M2/M4 ≥ 1.13 and age <64 years or males aged between 64 and 83 years were predicted as the normal population; M2/M4 ≥ 1.13 and females aged between 64 and 83 years were predicted as having osteopenia. The decision tree's accuracy in the training set was 0.7627 (95 % CI (0.6341, 0.8638)), and its accuracy in the test set was 0.7895 (95 % CI (0.6268, 0.9045)). Multinomial logistic regression results showed that humeral shaft medullary cavity ratios M2/M4, age, and gender in X-ray images were significantly associated with the occurrence of osteoporosis. Conclusion: Utilizing X-ray data of the proximal humerus in conjunction with demographic information such as gender and age enable the prediction of localized osteoporosis, facilitating physicians' rapid comprehension of osteoporosis in patients and optimization of clinical treatment plans. Level of evidence: Level IV retrospective case study.

Is it worthwhile to screen the hip in infants born with clubfeet?

PURPOSE: There is some disagreement about whether idiopathic congenital talipes equinovarus (CTEV) increases the risk of neonatal developmental dysplasia of the hip (DDH). This study aimed to investigate the incidence of DDH in our infants with idiopathic CTEV. METHODS: We conducted an observational cohort study over a three-year period to assess the relationship between idiopathic CTEV and DDH. All neonates younger than six weeks with idiopathic CTEV who were treated in our medical centre were admitted to this study. Each subject underwent hip ultrasound examination using the Graf method at the age of six weeks. DDH was diagnosed when a hip was type IIa(-) or worse according to the Graf classification of sonographic hip type. RESULTS: A total of 184 patients were diagnosed with idiopathic CTEV and underwent hip sonography. In total, seven hips of five individuals underwent treatment (four girls and one boy). The results indicated that 2.7% of babies (five of 184) with idiopathic CTEV had DDH. However, we did not find any statistically significant difference (p = 0.5776) in the Pirani scores between the DDH group and group with normal hips. CONCLUSIONS: This study revealed that the idiopathic CTEV group had a greater incidence of DDH in comparison with the general population. It is recommended that hip sonography be undertaken particularly in patients with idiopathic CTEV.

Articular geometry can affect joint kinematics, contact mechanics, and implant-bone micromotion in total ankle arthroplasty.

Implant loosening and bearing surface wear remain the most common failure problems of total ankle arthroplasty (TAA). One of the main factors leading to these problems is the nonphysiologic design of articular surfaces. The goals of this study were to reveal the effects of the anatomical medial-lateral borders height differences, coronal and sagittal radii on the joint kinematics, contact mechanics, and implant-bone micromotion in TAA. A previously developed and validated musculoskeletal (MSK) multibody dynamics (MBD) modeling method of TAA based on AnyBody generic MSK MBD model (five simulations for each implant) was used by combining with a finite element analysis. Five ankle implant models with different articular surface morphologies were created according to the anatomic characteristics of Chinese measurement data, marked as Implant A to E. The total ankle forces and motions during walking simulation were predicted by MSK MBD models and the contact mechanics of the bearing surface and the micromotion of the implant-bone interface of TAA were predicted by FE models. Compared with Implant A, the internal-external rotation in Implant E increased by 12.14%, the maximum of anterior-posterior translation in Implant E increased by 5.62%, the maximum reduction of tibial micromotion in Implant E was 59.98%, and for talar, micromotion was 15.36%. The ankle implant with similar anatomic articular surface has the potential to allow patients to recover better motions and reduce the risk of early loosening. This study would provide design guidance for the development of new ankle implants and further advance the development of TAA. Clinical Significance: This study promoted the improvement of ankle implant design and made contributions to improve the service life of ankle implant and patient satisfaction.

Statistical shape modeling of mean shape and principal variability of the human talar bone in the Chinese population.

PURPOSE: The talar bone plays a crucial role in ankle biomechanics and stability. Understanding the shape variability of the talar bone within specific populations is essential for various clinical applications. In this study, we aimed to investigate the mean shape and principal variability of the human talar bone in the Chinese population using statistical shape modeling (SSM). METHODS: CT scans of 214 tali were included to create SSM models. Principal component analysis was used to describe shape variation among the male, female, and overall groups. RESULTS: The largest amount of variation among three groups ranges from 17.2%-18.8% of each variation. The first seven principal components (modes) captured 62.4%-67.5% of the cumulative variance. No dominant shape of the talus was found. Male tali generally have a larger size than the female tali, with the exception of the articular surface of the anterior subtalar joint. CONCLUSIONS: SSM is an effective method of finding mean shape and principal variability. Considerable variabilities were noticed among these three groups and all principal modes of variation. No dominant talar model was found to represent the majority of tali, regardless the gender. Such information is crucial to improve the current understanding of talar pathologies and their treatment strategies.

In Vivo Evaluation of the Position and Orientation of the Geometric Axis of the Tibiotalar Joint.

Background: Fitting the surface morphology of the talar trochlea is one of the common methods to define the geometric axis of the tibiotalar joint (GATJ). However, the in vivo motion of such axis during gait has not been fully investigated. Methods: The ankle kinematic data of fifteen volunteers were collected by a dual fluoroscopic imaging system with a model-image registration method. The GATJ was defined by sphere-fitting the medial or lateral part of the trochlear surface of the talus. The position and orientation of this axis during gait were measured. To verify this axis, the distances of the feature points of the talus to the GATJ during gait were also measured. Results: There was no statistically significant difference in the distances of feature points of the talus to the GATJ among the seven key poses of the gait cycle. And the position and orientation of the GATJ during gait also showed no statistically significant difference. Conclusion: The GATJ is the axis about which the talus rotated. And it is one fixed axis during gait. The current finding may help the design of the talar component for total ankle replacement based on the surface morphology of the talar trochlea.

Shape Approximation and Size Difference of the Upper Part of the Talus: Implication for Implant Design of the Talar Component for Total Ankle Replacement.

The implant design of the talar component for total ankle replacement (TAR) should match the surface morphology of the talus so that the replaced ankle can restore the natural motion of the tibiotalar joint and may reduce postoperative complications. The purpose of this study was to introduce a new 3D fitting method (the two-sphere fitting method of the talar trochlea with three fitting resection planes) to approximate the shape of the upper part of the talus for the Chinese population. 90 models of the tali from CT images of healthy volunteers were used in this study. Geometrical fitting and morphological measurements were performed for the surface morphology of the upper part of the talus. The accuracy of the two-sphere fitting method of the talar trochlea was assessed by a comparison of previously reported data. Parameters of the fitting geometries with different sizes were recorded and compared. Results showed that compared with previously reported one-sphere, cylinder, and bitruncated cone fitting methods, the two-sphere fitting method presented the smallest maximum distance difference, indicating that talar trochlea can be approximated well as two spheres. The radius of the medial fitting sphere R M was 20.69 ± 2.19 mm which was significantly smaller than the radius of the lateral fitting sphere R L of 21.32 ± 1.88 mm. After grouping all data by the average radius of fitting spheres, the result showed that different sizes of the upper part of the talus presented significantly different parameters except the orientation of the lateral cutting plane, indicating that the orientation of the lateral cutting plane may keep consistent for all upper part of the talus and have no relationship with the size. The linear regression analyses demonstrated a weak correlation (R 2 < 0.5) between the majority of parameters and the average radius of the fitting spheres. Therefore, different sizes of the upper part of the talus presented unique morphological features, and the design of different sizes of talar components for TAR should consider the size-specific characteristics of the talus. The parameters measured in this study provided a further understanding of the talus and can guide the design of different sizes of the talar components of the TAR implant.

Comparison of joint load, motions and contact stress and bone-implant interface micromotion of three implant designs for total ankle arthroplasty.

BACKGROUND AND OBJECTIVE: Loosening and wear are still the main problems for the failure of total ankle arthroplasty, which are closely related to the micromotion at the bone-implant interface and the contact stress and joint motions at the articular surfaces. Implant design is a key factor to influence the ankle force, motions, contact stress, and bone-implant interface micromotion. The purpose of this study is to evaluate the differences in these parameters of INBONE II, INFINITY, and a new anatomic ankle implant under the physiological walking gait of three patients. METHODS: This was achieved by using an in-silico simulation framework combining patient-specific musculoskeletal multibody dynamics and finite element analysis. Each implant was implanted into the musculoskeletal multibody dynamics model, respectively, which was driven by the gait data to calculate ankle forces and motions. These were then used as the boundary conditions for the finite element model, and the contact stress and the bone-implant interface micromotions were calculated. RESULTS: The total ankle contact forces were not significantly affected by articular surface geometries of ankle implants. The range of motion of the ankle joint implanted with INFINITY was a little larger than that with INBONE II. The anatomic ankle implant design produced a greater range of motion than INBONE II, especially the internal-external rotation. The fixation design of INFINITY achieved lower bone-implant interface micromotion compared with INBONE II. The anatomic ankle implant design produced smaller contact stress with no evident edge contact and a smaller tibia-implant interface micromotion. In addition, significant differences in the magnitudes and tendencies of total ankle contact forces and motions among different patients were found. CONCLUSIONS: The articular surface geometry of ankle implants not only affected the ankle motions and contact stress distribution but also affected the bone-implant interface micromotions. The anatomic ankle implant had good performance in recovering ankle joint motion, equalizing contact stress, and reducing bone-implant interface micromotion. INFINITY's fixation design could achieve smaller bone-implant interface micromotion than INBONE II.

Anatomic ankle implant can provide better tibiotalar joint kinematics and loading.

Restoration of ankle kinematic functions is the major objective following total ankle arthroplasty (TAA). However, the clinical results of traditional ankle implants are still unsatisfactory. Anatomic ankle implant may provide better ankle kinematic functions and load distribution. In this study, the biomechanical performances between two potential anatomic ankle implants and a commercial INBONE II implant were compared using a previously developed patient-specific musculoskeletal multibody dynamics model during walking. Furthermore, the effects of the different height differences between the medial and lateral borders on the ankle biomechanics and kinematics were also investigated. Significant improvements in kinematic functions especially in internal-external rotation and inversion-eversion, and in load balance between the medial and lateral contacts of the two anatomic ankle implants were observed, as compared to the INBONE II ankle implant. The design of anatomic ankle implant with the medial peak higher than the lateral peak had better performance in restoring the internal-external rotation and balancing the medial and lateral contact forces. The kinematics and loads were not sensitive to the height difference for the anatomic ankle implant with medial border higher than lateral border. The anatomic articular surface design of artificial ankle implant can provide better tibiotalar joint kinematics and loading, therefore, anatomic ankle implant should be considered in the future implant design and surgical procedures.

Investigation on the contour and bone mineral density of the distal tibial cutting surface used for total ankle arthroplasty.

PURPOSE: This study was designed to investigate (1) the contour of the distal tibial cutting surface, and (2) the bone mineral density (BMD) of the distal tibial cutting surface used during total ankle arthroplasty (TAA). METHODS: Eight-four distal tibial models were created using foot and ankle computerized tomographic (CT) images taken from normal people. The distal tibial cutting surface for TAA was determined to be 10 mm proximal to the tibial plafond. The bony contour and BMD values were determined from the CT image at that level. A bounding box was made on the contour and the width and length of the contour was measured. Regional BMD was evaluated by Hounsfield units (HU) value measurement, with 7 regions of interest (ROI) on 8 different directions for all the 84 CT images. Two different observers made independent measurements and mean HU values for all the 56 ROIs were calculated. RESULTS: Great variations were found among the contours of the cutting surface especially in term of the shape of the anterior and posterior tibial tubercle, and the fibular notch. These variations could be grouped into six categories. For the BMD of the cutting surface, the medial border of the cutting surface did not included cortical bone. The HU value of seven ROIs, which included cortical bone, were significantly greater than all the other ROIs. Few statistical differences were found by multiple comparisons among HU value of all the 49 ROIs without cortex. CONCLUSIONS: Great variability existed in the shape and the BMD of the distal tibial cutting surface.

Finite element analysis of the initial stability of arthroscopic ankle arthrodesis with three-screw fixation: posteromedial versus posterolateral home-run screw.

OBJECTIVE: Arthroscopic ankle arthrodesis (AAA) is a standard surgical method for the treatment of advanced traumatic ankle arthritis and has become more popular due to its advantages. To fix the tibiotalar joint, the use of three percutaneous screws is considered to have better mechanical stability than the use of two screws. However, it is sometimes difficult to insert three screws because they might block each other due to the small area of the tibiotalar joint surface and the large diameter of the screws; few articles illustrate how to insert three screws without the screws disturbing each other. The purpose of this study is to explore possible screw configurations of tripod fixation in arthroscopic ankle arthrodesis that avoid the collision of screws and yield better biomechanical performance. METHODS: We used the finite element method to examine the impact of different screw positions and orientations on the biomechanical characteristics of a three-dimensional (3D) ankle model. Maximum and average micromotion, pressure on the articular surface, and von Mises stress values of the tibia and the talus were used to evaluate the initial stability of the ankle. RESULTS: Five kinds of three-screw configurations were identified, and finite element analysis results suggested that configurations with the posteromedial home-run screw presented lower micromotion (maximum, 17.96 ± 7.49 µm versus 22.52 ± 12.8 µm; mean, 4.88 ± 1.89 µm versus 5.19 ± 1.92 µm) (especially configuration 3) and better screw distributions on the articular surface than those with the posterolateral home-run screw. CONCLUSION: Screw configurations with the posteromedial home-run screw avoid collision and are more biomechanically stable than those with the posterolateral home-run screw. Thus, inserting the home-run screw through the posteromedial approach is recommended for clinical practice.

Finite-element analysis of the influence of tibial implant fixation design of total ankle replacement on bone-implant interfacial biomechanical performance.

PURPOSE: Implant loosening in tibia after primary total ankle replacement (TAR) is one of the common postoperative problems in TAR. Innovations in implant structure design may ideally reduce micromotion at the bone-implant interface and enhance the bone-implant fixation and initial stability, thus eventually prevents long-term implant loosening. This study aimed to investigate (1) biomechanical characteristics at the bone-implant interface and (2) the influence of design features, such as radius, height, and length. METHODS: A total of 101 finite-element models were created based on four commercially available implants. The models predicted micromotion at the bone-implant interface, and we investigated the impact of structural parameters, such as radius, length, and height. RESULTS: Our results suggested that stem-type implants generally required the highest volume of bone resection before implantation, while peg-type implants required the lowest. Compared with central fixation features (stem and keel), peripherally distributed geometries (bar and peg) were associated with lower initial micromotions. The initial stability of all types of implant design can be optimized by decreasing fixation size, such as reducing the radius of the bars and pegs and lowering the height. CONCLUSION: Peg-type tibial implant design may be a promising fixation method, which is required with a minimum bone resection volume and yielded minimum micromotion under an extreme axial loading scenario. Present models can serve as a useful platform to build upon to help physicians or engineers when making incremental improvements related to implant design.

Talar Dome Investigation and Talocrural Joint Axis Analysis Based on Three-Dimensional (3D) Models: Implications for Prosthetic Design.

Ankle joint kinematics is mainly stabilized by the morphology of the talar dome and the articular surface of tibiofibular mortise as well as the medial and lateral ligament complexes. Because of this the bicondylar geometry of talus dome is believed to be crucial for ankle implant design. However, little data exist describing the precise anatomy of the talar dome and the talocrural joint axis. The aim of this study is to document the anatomy of the talar dome and the axis of the talocrural joint using three-dimensional (3D) computed tomographic (CT) modeling. Seventy-one participants enrolled for CT scanning and 3D talar model reconstruction. All the ankles were held in a neutral position during the CT scanning. Six points on the lateral and medial crest of the talar dome were defined. The coordinate of the six points; radii of lateral-anterior (R-LA), lateral-posterior (R-LP), medial-anterior (R-MA), and medial-posterior (R-MP) sections; and inclination angle of the talar dome were measured, and the inclination and deviation angles of the talocrural joint axis were determined. The mean values of R-LA, R-LP, R-MA, and R-MP were 19.23 ± 2.47 mm, 18.76 ± 2.90 mm, 17.02 ± 3.49 mm, and 22.75 ± 3.04 mm. The mean inclination angle of the talar dome was 9.86 ± 3.30 degrees. Gender variation was found in this parameter. The mean inclination and deviation angles were 8.60 ± 0.07 and 0.76 ± 0.69 degrees for the dorsiflexion axis and -7.34 ± 0.07 and 0.09 ± 0.18 degrees for the plantarflexion axis. Bilateral asymmetries between the medial and lateral crest of the talar dome were found, which resulted in different dorsiflexion and plantarflexion axes of the talocrural joint. Currently, no ankle implants replicate this talar anatomy, and these findings should be considered in future implant designs.