Symmetry analysis of talus bone: A Geometric morphometric approach

Is a keystone Bone Anomaly the Main Cause of Flatfoot (Pes Planus)?

BACKGROUND

Flatfoot (pes planus) is a decrease or loss of longitudinal medial arch height. The cause of symptomatic flatfoot occurring in adolescents is still unclear. In this study, the relationship between adolescent pes planus and foot bone shape was investigated. For this purpose, the volume and superficial area data of the foot bones of adolescent individuals with flatfoot deformity and individuals without any foot deformity were compared.

METHODS

Between September 2022 and June 2023, 30 individuals with adolescent pes planus with a medial arch angle greater than 145 degrees and 30 individuals without any foot deformity were included in the study. Computed tomography (CT) images of the participants' feet were obtained with a General Electric brand IQ model 32 detector CT device with a section thickness of 0.625 mm in accordance with the bone protocol. Using the 3D Slicer program on CT images, foot bones were segmented and the volume and surface area ratios of each foot bone were determined.

RESULTS

Cuneiforme mediale and cuneiforme intermediale volume ratios in individuals with flatfoot deformity decreased by 14% and 24%, respectively, compared with the control group ( P <0.05). Cuneiforme mediale and cuneiforme intermediale superficial area ratios were found to be 10% and 30% lower in the flatfoot group compared with the control group, respectively ( P <0.05). There was no difference in the volume and superficial area ratios of other foot bones between the groups ( P >0.05).

CONCLUSIONS

The study results suggest that symptomatic adolescent flatfoot deformity may be associated with developmental anomalies of the os cuneiforme mediale and os cuneiforme intermedium.

Quantitative analysis of sagittal curvatures of the tibial plafond by computed tomography

Background

Although the talar morphology has been well understood, studies on the corresponding tibial plafond are still lacking. Based on computed tomography (CT) data, this quantitative study divided the tibial plafond into anterior and posterior regions on five sagittal sections. The objectives of this study were (I) to determine whether the sagittal curvatures of the tibial plafond can be quantitatively and accurately described using the double-diameter method; (II) to compare the difference between the anterior and posterior diameters on five sagittal sections.

Methods

In this study, CT data were collected from 100 adult ankles, and the three-dimensional (3D) ankle joint model was reconstructed using CT images. An anatomical coordinate system of the 3D ankle joint model was created to establish the standard coronal and sagittal planes. The measurement outcomes of sagittal curvatures included: the anterior and posterior diameters, the distal tibial arc length (TiAL) and the distal tibial mortise depth (TMD) on five sagittal sections (the most medial, medial 1/4, middle, lateral 1/4 and the most lateral section). Subgroup analysis was performed to compare the differences between males and females.

Results

Analysis of the sagittal curvatures showed that the anterior diameter of tibial plafond was significantly smaller than the posterior diameter on five sagittal sections with a mean difference ranging from 3.9 to 6.8 mm (P<0.001). For the anterior diameters, the anteromedial curve had the smallest diameter (35.3±5.3 mm), and the anterolateral curve had the largest diameter (38.0±5.8 mm). For the posterior diameter, the posteromedial curve had the smallest diameter (39.2±6.4 mm), and the posterolateral 1/4 curve had the largest diameter (43.5±6.9 mm). One-way analysis of variance (ANOVA) revealed significant differences in the anterior and posterior diameters among five groups (P<0.012). Subgroup analysis showed that gender partly affected the results of sagittal curvature measurements.

Conclusions

The sagittal curvatures of the tibial plafond can be described quantitatively and accurately using anterior and posterior diameters. Our study showed that there were significant differences between the anterior and posterior diameters, and gender was an important factor influencing the sagittal curvatures of the tibial plafond.

Symmetry of the left and right tibial plafond; a comparison of 75 distal tibia pairs

PURPOSE

Tibia plafond or pilon fractures present a high level of complexity, making their surgical management challenging. Three-Dimensional Virtual Planning (3DVP) can assist in preoperative planning to achieve optimal fracture reduction. This study aimed to assess the symmetry of the left and right tibial plafond and whether left-right mirroring can reliably be used.

METHODS

Bilateral CT scans of the lower limbs of 75 patients without ankle problems or prior fractures of the lower limb were included. The CT images were segmented to create 3D surface models of the tibia. Subsequently, the left tibial models were mirrored and superimposed onto the right tibia models using a Coherent Point Drift surface matching algorithm. The tibias were then cut to create bone models of the distal tibia with a height of 30 mm, and correspondence points were established. The Euclidean distance was calculated between correspondence points and visualized in a boxplot and heatmaps. The articulating surface was selected as a region of interest.

RESULTS

The median left-right difference was 0.57 mm (IQR, 0.38 - 0.85 mm) of the entire tibial plafond and 0.53 mm (IQR, 0.37 - 0.76 mm) of the articulating surface. The area with the greatest left-right differences were the medial malleoli and the anterior tubercle of the tibial plafond.

CONCLUSION

The tibial plafond exhibits a high degree of bilateral symmetry. Therefore, the mirrored unfractured tibial plafond may be used as a template to optimize preoperative surgical reduction using 3DVP techniques in patients with pilon fractures.

Morphological features of the non-affected side of the hindfoot in patients with unilateral varus ankle osteoarthritis

BACKGROUND

The innate shape characteristics of the hindfoot bones alter the loading conditions of the foot and thus may be associated with an increased risk of developing varus ankle osteoarthritis (OA). This study aimed to clarify the innate morphological patterns of the hindfoot bones that may be associated with ankle OA by analyzing the differences between the bone morphology of the non-affected side of patients with unilateral varus ankle OA and that of healthy participants.

METHODS

In this case-control study, computed tomography images were used to develop three-dimensional models of three hindfoot bones (distal tibia with fibula, talus, and calcaneus) from 23 non-affected sides of patients with radiography-diagnosed unilateral ankle OA and 22 healthy control participants. Anatomical and sliding landmarks were placed on the surface of each bone, and the principal components (PCs) of shape variation among specimens were independently calculated for each bone, preserving homology between individuals. The PC modes representing 5% or more of the overall variation were statistically compared between the ankle OA and control groups.

RESULTS

Significant differences were identified between the OA and control groups in the fifth PC mode for the tibia with fibula (proportion of variance, 5.1%; p =.025), fifth PC mode for the talus (6.7%, p =.031), and third PC mode for the calcaneus (7.4%, p =.001). The hindfoot bones of the participants who developed ankle OA had the following innate morphological characteristics: the lateral malleolar articular surface of the fibula was shifted superiorly, tibial plafond was enlarged posteroinferiorly, posterior width of the talar trochlea was narrower, talonavicular articular surface of the talus was oriented more frontally, anterior-middle talocalcaneal articular surfaces of the talus were more medially shifted and those of the calcaneus were flatter, calcaneal sustentaculum tali was less protruding, and lateral plantar process of the calcaneus was more superiorly positioned.

CONCLUSIONS

These distinctive morphological alterations may increase the incidence and progression of varus ankle OA through aberrant anterior translation, internal rotation, and varus tilting of the talus.

Anthropomorphic Characterization of Ankle Joint

Even though total ankle replacement has emerged as an alternative treatment to arthrodesis, the long-term clinical results are unsatisfactory. Proper design of the ankle device is required to achieve successful arthroplasty results. Therefore, a quantitative knowledge of the ankle joint is necessary. In this pilot study, imaging data of 22 subjects (with both females and males and across three age groups) was used to measure the morphological parameters of the ankle joint. A total of 40 measurements were collected by creating sections in the sagittal and coronal planes for the tibia and talus. Statistical analyses were performed to compare genders, age groups, and image acquisition techniques used to generate 3D models. About 13 measurements derived for parameters (TiAL, SRTi, TaAL, SRTa, TiW, TaW, and TTL) that are very critical for the implant design showed significant differences (p-value < 0.05) between males and females. Young adults showed a significant difference (p-value < 0.05) compared to adults for 15 measurements related to critical tibial and talus parameters (TiAL, TiW, TML, TaAL, SRTa, TaW, and TTL), but no significant differences were observed between young adults and older adults, and between adults and older adults for most of the parameters. A positive correlation (r > 0.70) was observed between tibial and talar width values and between the sagittal radius values. When compared with morphological parameters obtained in this study, the sizes of current total ankle replacement devices can only fit a very limited group of people in this study. This pilot study contributes to the comprehensive understanding of the effects of gender and age group on ankle joint morphology and the relationship between tibial and talus parameters that can be used to plan and design ankle devices.

A Novel Approach of Customized Pelvic Implant Design Based on Symmetrical Analysis and 3D Printing

In pelvic trauma patients, the mismatch of complex geometries between the pelvis and fixation implant is a fundamental cause of unstable and displaced pelvic ring disruption, in which secondary intervention is strongly considered. The geometrical matching in the current customized implant design and clinical practice is through the nonfractured hemi-pelvis for the fractured pelvis. This design philosophy overlooks the anatomical difference between the hemipelves, and further, the geometrical asymmetry at local area still remains unknown. This study analyzed the anatomical asymmetry of a patient's 3D pelvic models from 13 patients. The hemipelves of each patient were registered by using an iterative closet algorithm to an optimum position with minimum deviations. The high deviation regions were summarized between the hemipelves in each case, and a color map was drawn on a hemipelvis model that identified the areas that had a high possibility to be symmetrically different. A severe pelvic trauma case was used to comprehend the approach by designing a 3D printed implant. Each fracture was then registered to the mirrored uninjured hemipelvis by using the same algorithm, and customized fixation implants were designed with reference to the fractured model. The customized fixation plates showed that the implants had lower geometrical deviation when attached onto the re-stitched fracture side than onto the mirrored nonfractured bone. These results indicate that the symmetrical analysis of bone anatomy and the deviation color map can assist with implant selection and customized implant design given the geometrical difference between symmetrical bones. The novel approach provides a scientific reference that improves the accuracy and overall standard of 3D printed implants.

Three-dimensional morphological variations in the calcaneus and talus in relation to the hallux valgus angle

BACKGROUND

The present study aimed to clarify the morphological patterns of the calcaneus and talus that are associated with hallux valgus angle (HVA) by quantifying the differences in the hindfoot bone morphology between left and right sides in HV patients with clear bilateral difference of HVA.

METHODS

Three-dimensional (3D) computed tomography scans of 32 feet of 16 patients with HV who had right-to-left HVA differences of more than 5 degrees (68.8 ± 8.6 years) were enrolled, and 3D surface models of the calcaneus and talus were generated. A total of 556 and 430 landmarks were placed on the calcaneal and talar surfaces, respectively, to calculate the principal components (PCs) of shape variations. The PC scores were compared between the small and large HVA sides within an individual.

RESULTS

The calcaneus in patients with a larger HVA (mean, 43.2 degrees) possessed slender calcaneal tuberosity, more medially oriented posterior articular surface in the coronal plane, and narrower and more concave anterior-middle articular surfaces compared to those with a small HVA (mean, 33.7 degrees). The talus with a larger HVA exhibited more medially oriented talar head in the transverse plane and more anteriorly protruded lateral region of the talar head compared to the small HVA.

CONCLUSIONS

The morphological patterns of the calcaneus in patients with a larger HVA allows the hindfoot bones to easily rotate in the everting direction, while those of the talus could induce a larger internal rotation of the first metatarsal. These morphological patterns of the calcaneus and talus could be structural factors affecting the HV.

Total Talus Replacements

Background

Total talus replacements are a surgical treatment for talar avascular necrosis (AVN) replacing the entire talus. The potential for total talus replacements has increased with the advent of patient-specific implants using 3D printing based on computed tomographic scanning of the ipsilateral or contralateral talus. The primary aim of this review is to summarize the literature on total talus replacements, providing a historical survey, indications, controversies, complications, survival, and functional outcomes.

Methods

A systematic review was performed. Articles with survival of total talus replacements were included. Basic percentages and a critical review of the literature was performed.

Results

Nine articles with 115 patients were included. The mean age ranged from 27.6 to 72 years, but with 5 studies having a mean age of <50 years. Mean follow-up ranged from 12.8 to 152 months. The most common indication was avascular necrosis in 67 patients (58%). Five studies used customized implants and 4 studies used 3D printing. Four studies used ceramic prostheses, 3 cobalt chromium, 1 stainless steel, and 1 titanium with ceramic surface. Three studies involved a talus replacement in conjunction with an ankle replacement. Postoperative complications ranged from 0% to 33%. Of 24 functional outcomes scores, 66.7% demonstrated significant improvement.

Conclusion

Total talus replacements are a promising alternative to tibiotalocalcaneal fusion for patients with avascular necrosis of the talus; however, further studies are required to ensure reliable outcomes prior to widespread adoption of this technology.

Level of Evidence

Level IV, review of case series.

Human talar ontogeny: Insights from morphological and trabecular changes during postnatal growth

Objectives

The study of the development of human bipedalism can provide a unique perspective on the evolution of morphology and behavior across species. To generate new knowledge of these mechanisms, we analyze changes in both internal and external morphology of the growing human talus in a sample of modern human juveniles using an innovative approach.

Materials and Methods

The sample consists of high‐resolution microCT scans of 70 modern juvenile tali, aged between 8 postnatal weeks and 10 years old, from a broad chronological range from Middle/Late Neolithic, that is, between 4800 and 4500 BCE, to the 20th century. We applied geometric morphometric and whole‐bone trabecular analysis (bone volume fraction, degree of anisotropy, trabecular number, thickness, and spacing) to all specimens to identify changes in the external and internal morphology during growth. Morphometric maps were also generated.

Results

During the first year of life, the talus has an immature and globular shape, with a dense, compact, and rather isotropic trabecular architecture, with numerous trabeculae packed closely together. This pattern changes while children acquire a more mature gait, and the talus tends to have a lower bone volume fraction, a higher anisotropy, and a more mature shape.

Discussion

The changes in talar internal and external morphologies reflect the different loading patterns experienced during growth, gradually shifting from an “unspecialized” morphology to a more complex one, following the development of bipedal gait. Our research shows that talar plasticity, even though genetically driven, may show mechanical influences and contribute to tracking the main locomotor milestones.

Assessment of the Root Canal Similarity in Contralateral Mandibular Incisors

INTRODUCTION

The purpose of this study was to determine the degree of similarity between contralateral mandibular incisors utilising 3-dimensional (3D) models obtained from micro-computed tomographic (micro-CT) scans of extracted human teeth. The null hypothesis was that contralateral mandibular incisors do not exhibit matching symmetry.

METHODS

Sixty pairs (n = 120) of extracted mandibular incisors were obtained from 30 patients and scanned with micro-CT with a voxel size of 15.0 μm. 3D virtual models of the pulpal cavities were rendered. Geometric morphometric deviation analysis was performed after mirroring, automatic alignment, and co-registration of the models of contralateral teeth root mean square (RMS) errors were calculated. The quantitative analysis of the 3D models included 6 different geometric parameters. Data sets were examined with a 2-sample Kolmogorov-Smirnov test. Post hoc retrospective power analysis was performed to find statistical power (α = 0.05).

RESULTS

Contralateral pairs had a narrower distribution in deviation than random pairs. Also, contralateral pairs showed a statistically higher similarity coefficient (5 out of 6 geometric parameters) compared to random pairs (P < .001); no difference was found when comparing central to lateral pairs or between Vertucci type I configurations compared to non-type I. RMS errors had significantly lower Contralateral premolars (CPs) values than random pairs (P < .001).

CONCLUSIONS

A high degree of similarity was demonstrated for pairing contralateral mandibular incisors using 3D models. The similarity between contralateral central and lateral incisors suggests that when screened and matched, these 4 teeth might be used in endodontic research where similar root canal anatomy is crucial.

Morphological Asymmetry of Pelvic Rings: A Study Based on Three-Dimensional Deviation Analysis

OBJECTIVE

To evaluate the morphological asymmetry of pelvic rings existing in healthy individuals in terms of three-dimensional (3D) geometric shapes.

METHODS

This study was a retrospective self-control study. CT images of healthy pelvises, scanned from Jan 2014 to Jan 2019, were taken from 159 subjects (88 males and 71 females) aged 20 to 59 years (39.1 ± 8.7 years). Digital pelvic ring models were reconstructed from CT images and then flipped over the corresponding sagittal planes to obtain their mirrored models. A 3D deviation analysis of a pelvic ring was conducted between the original model and its mirrored model via model registration and quantification of the geometric differences. Next, the pelvic rings were split to the left and right hipbones. The same flipping procedures as done by pelvic rings were performed for left hipbones to obtain their mirrored models. A 3D deviation analysis was also performed between the left and right hip bones. Quantitative variables representing deviation mainly included the average deviation (AD) and the maximum deviation (MD). MDs over 4 mm and 10 mm were deemed as critical levels for evaluating the severity of asymmetry as per Matta's scoring system. The quantitative assessments of the asymmetry covered pelvic rings, bilateral hip bones and the specific anatomic regions of a hip bone.

RESULTS

157 out of 159 pelvic rings (98.74%) had more than 4 mm of the MD and 27 (16.98%) of them exceeded 10 mm of the MD. The MD of pelvic rings was 1.23 times as high as that for the bilateral hip bones (7.46 mm vs. 6.08 mm, P < 0.05). The ADs of pelvic rings and bilateral hip bones were 1.28 mm and 0.94 mm, respectively (P < 0.05); 2.27% of the surface points of a pelvic ring had more than 4 mm geometric deviations compared with its mirrored model, while 0.59% (P < 0.05) of bilateral hip bones were on the same level of deviation. 119 out of 159 pelvic iliac crests (74.8%) had MDs more than 4 mm, and 15 (9.4%) reached 10 mm or more. Only 15 (9.4%) pelvises presented asymmetric features in the area of obturator foramen where the MDs exceeded 4 mm.

CONCLUSIONS

Pelvic asymmetry exists in the general population, but 3D geometric symmetry is present in specific anatomic regions. It implies that restoring the 3D symmetry of specific anatomic regions is more reliable than "restoring the symmetry of pelvic ring" in pelvic ring reduction or pelvic fixation design.

Morphometric measurement of the proximal tibia to design the tibial component of total knee arthroplasty for the Thai population

Purpose

This study evaluates the morphology of the Thai proximal tibia based on three-dimensional (3D) models to design the tibial component.

Methods

The 3D models of 480 tibias were created using reverse engineering techniques from computed tomography imaging data obtained from 240 volunteers (120 males, 120 females; range 20–50 years). Based on 3D measurements, a digital ruler was used to measure the distance between the triangular points of the models. The morphometric parameters consisted of mediolateral length (ML), anteroposterior width (AP), medial anteroposterior width (MAP), lateral anteroposterior width (LAP), central to a medial length (CM), central to a lateral length (CL), medial anterior radius (MAR), lateral anterior radius (LAR), and tibial aspect ratio (AR). An independent t-test was performed for gender differences, and K-means clustering was used to find the optimum sizes of the tibial component with a correlation between ML length and AP width in Thai people.

Results

The average morphometric parameters of Thai proximal tibia, namely ML, AP, MAP, LAP, CM, and CL, were as follows: 72.52 ± 5.94 mm, 46.36 ± 3.84 mm, 49.22 ± 3.62 mm, 43.59 ± 4.05 mm, 14.29 ± 2.72 mm, and 15.28 ± 2.99 mm, respectively. The average of MAR, LAR, and AR was 24.43 ± 2.11 mm, 21.52 ± 2.00 mm, and 1.57 ± 0.08, respectively. All morphometric parameters in males were significantly higher than those of females. There was a difference between the Thai proximal tibia and other nationalities and a mismatch between the size of the commercial tibial component and the Thai knee. Using K-means clustering analysis, the recommended number of ML and AP is seven sizes for the practical design of tibial components to cover the Thai anatomy.

Conclusion

The design of the tibial component should be recommended to cover the anatomy of the Thai population. These data provide essential information for the specific design of Thai knee prostheses.

Visualization and quantification of the degenerative pattern of the distal tibia and fibula in unilateral varus ankle osteoarthritis

The present study aimed to quantify and visualize the degenerative patterns of the distal tibia and fibula due to ankle osteoarthritis (OA). We analyzed differences in tibial and fibular surface deviation between sides of patients with unilateral varus ankle OA (medial talar tilt > 4°) by registering each surface model to the mirror image of corresponding bone. Computed tomography images of both feet of 33 patients (OA: 22, control: 11) were examined. Statistically significant surface depression of approximately 2.5 mm on the anterior articular surface of the medial malleolus, and surface elevation of approximately 1 mm on the anterodistal edge of the tibiofibular joint and the lateral malleolus were observed in OA patients. These bone degenerations were found to be correlated with those on the other side of the ankle joint, the medial margin of the talar trochlea and the lateral articular surface of the talus, respectively. In contrast, the amount of bone depression on the plafond was smaller than previously anticipated. Such quantitative information about stereotypical patterns of bone degeneration in ankle OA would contribute to better understanding of the development of ankle OA and possible therapeutic interventions.

Polycarbonate-urethane coating can significantly improve talus implant contact characteristics

Talus implants can be utilized in cases of talus avascular necrosis and has been regarded as a promising treatment method. However, existing implants are made of stiff materials that directly oppose natural cartilage. The risk of long-term cartilage wear and bone fracture from the interaction between the cartilage and stiff implant surfaces has been documented in post-hemiarthroplasty of the hip, knee and ankle joints. The aim is to explore the effects of adding a layer of compliant material (polycarbonate-urethane; PCU) over a stiff material (cobalt chromium) in talus implants. To do so, we obtained initial ankle geometry from four cadaveric subjects in neutral standing to create the finite element models. We simulated seven models for each subject: three different types of talus implants, each coated with and without PCU, and a biological model. In total, we constructed 28 finite element models. By comparing the contact characteristics of the implant models with their respective biological model counterparts, our results showed that PCU coated implants have comparable contact area and contact pressure to the biological models, whereas stiff material implants without the PCU coating all have relatively higher contact pressure and smaller contact areas. These results confirmed that adding a layer of compliant material coating reduces the contact pressure and increases the contact area which in turn reduces the risk of cartilage wear and bone fracture. The results also suggest that there can be clinical benefits of adding a layer of compliant material coating on existing stiff material implants, and can provide valuable information towards the design of more biofidelic implants in the future.

Clinical Use of Talar Prostheses

»

The blood supply to the talus is vulnerable to damage, making the talus susceptible to osteonecrosis, with limited treatment options.

»

Talar bone replacement has been investigated as a treatment option to preserve ankle function and maintain limb length.

»

Successful talar bone replacements have been performed for the past >35 years, with variations in design, methods of fixation, materials, and manufacturing techniques.

»

The designs of talar prostheses range from custom-made partial (talar body) or total prostheses to prefabricated universal (non-custom-made) prostheses.

»

Total talar prostheses have been demonstrated to function better than partial talar prostheses; however, there is a need for long-term studies regarding custom-made total talar prostheses and prefabricated universal talar prostheses in order to determine their long-term effectiveness.

Quantitative analysis of regional specific pelvic symmetry

Understanding bilateral pelvic symmetry can be useful for analyzing complex pelvis anatomy and simplifying difficult procedures for pelvic fractures. This paper aims to quantify the degree of regional pelvic symmetry using computer-based methods. CT scans of 30 intact pelvises were digitized into 3D models and regions were defined: the ilium, acetabulum, pubis, and ischium. The right hemipelvis was aligned with the left, and deviations between the two models were quantified using method 1 (global registration) and method 2 (local registration). Symmetry was evaluated using the root mean square (RMS) of the deviations and the percentage of points within preset thresholds of ± 2 mm and ± 1 mm. The results showed that > 86% of points are within the ± 2 mm deviation threshold and average RMS are < 1.33 mm. For all regions, method 2 showed lower deviations than method 1. The pubis and ischium regions showed a large difference in symmetry between the two methods indicating high local symmetry, but a degree of global asymmetry. Conversely, the acetabular and iliac regions showed similar levels of symmetry with the two methods. When evaluated locally, the pelvic regions can be considered highly symmetric; the acetabulum is highly symmetric globally as well. These findings can be used in future studies to assess the feasibility of patient-specific implants using the mirrored contralateral hemipelvis as a template for unilateral pelvic fracture fixation. The left image shows the "cut planes" used to define four pelvic regions: the ilium, acetabulum, pubis, and ischium. The right image shows a deviation color map (DCM) used to quantify bilateral pelvic symmetry. The scale and color illustrate the degree of deviation of the left hemipelvis with the right hemipelvis with the units in millimeters (mm).

Sex- and age-related variations in the three-dimensional orientations and curvatures of the articular surfaces of the human talus

The high prevalence of foot pathologies in women and the elderly could be associated with gender and age difference in the morphology of the foot, particularly the morphology of the keystone of the foot, the talus. The present study investigated the orientation and curvature of the three articular surfaces of the talus in relation to sex and age based on computer tomography (CT), to identify possible morphological factors of the higher prevalence of foot disorders in women and elderly. Fifty-six participants were included in this study. The orientations of the talocrural, subtalar, and talonavicular joints were quantified three-dimensionally by calculating normal and principal axes of the articular surfaces defined by planar approximation. The curvature radii of the articular surfaces were quantified by cylindrical and spherical approximations. The talonavicular surface was significantly more twisted in the frontal plane and less adducted in the transverse plane in females than in males. With aging, the subtalar articular surface was significantly facing more posteriorly. Moreover, it was found that the curvature radii of the trochlea and navicular articular surfaces significantly increased with aging, indicating a flattening of these surfaces. The identified changes in the talar morphology with aging could potentially lead to a higher prevalence of foot disorders in the elderly.

Morphometric geometric differences between right and left human tali: A cadaveric study of fluctuating asymmetry via systematic measurement and three-dimensional scanning

Background

Little is known about differences in the size and morphology of the right and left human tali. The present study demonstrates differences between right and left talar morphometric geometric profiles as fluctuating asymmetry in matched pairs of cadaveric specimens.

Methods

In total, 24 tali were collected in this study. All eligible tali were systematically measured with a Vernier caliper and three-dimensional laser scanner, which provided data for further analysis regarding the talar morphometric geometric profiles. Data were calculated to demonstrate differences between the right and left talar profiles using a matched-pair method, including the general size of the talus.

Results

The average talar length was 53.5 mm, the average talar dome height was 31.2 mm, and the average talar body width was 41.3 mm. The average anterior trochlear width, middle trochlear width, posterior trochlear width, and trochlear length were 31.8, 31.2, 28.3, and 30.7 mm, respectively. Eleven matched pairs of intact tali were eligible for the matched-pair study. Paired t-tests showed significant differences in the talar dome height (P = 0.019), middle trochlear width (P = 0.027), and posterior trochlear width (P = 0.016) between the right and left tali. However, there were no significant differences in the surface area or volume between the right and left tali.

Conclusion

Significant differences in the morphometric profile were found between the right and left matched pairs of tali. This basic information indicates that the profile of the contralateral talus may not be used as a single reference to reconstruct or duplicate the talus of interest in certain conditions such as talar prosthesis implantation or customized total ankle replacement.

Virtual reconstruction of unilateral pelvic fractures by using pelvic symmetry

PURPOSE

Pelvic fractures are known to be one of the most difficult injuries to treat. The objective of this study is to introduce a novel technique for virtual unilateral pelvic fracture reconstruction. Since the pelvis exhibits remarkable left-right symmetry, the contralateral hemipelvis can be used as a template for rebuilding the fractured hemipelvis.

METHODS

CT scan data of the pelvic region of eight subjects with acute unilateral pelvic fractures were involved in this study. Computer-aided design software was used to create 3D models of these pelvises. The contralateral hemipelvis of each subject was then reflected across the sagittal plane, and the fractured hemipelvis was rebuilt by aligning the bone fragments with their equivalent location on the reflected side. To evaluate the quality of this reduction process, a 3D deviation analysis was conducted to calculate the differences between the reflected intact hemipelvis and the reconstructed hemipelvis.

RESULTS

Results showed that the average root mean square (RMS) of deviations and average percentage of points within a ± 2 mm predefined threshold was 1.32 ± 0.22 mm and 88.4 ± 3.78%, respectively. The deviation color maps obtained indicated that the largest differences were along the fracture lines and on the non-articular surfaces of the pelvises.

CONCLUSION

These results allowed us to conclude the validity of this procedure, since the average RMS difference was below 2 mm and the average percentage of points within ± 2 mm was high. The proposed technique will allow surgeons to provide their patients with more accurate reconstruction procedures which can potentially improve surgical outcomes.

Exploring sexual dimorphism of the modern human talus through geometric morphometric methods

Sex determination is a pivotal step in forensic and bioarchaeological fields. Generally, scholars focus on metric or qualitative morphological features, but in the last few years several contributions have applied geometric-morphometric (GM) techniques to overcome limitations of traditional approaches. In this study, we explore sexual dimorphism in modern human tali from three early 20th century populations (Sassari and Bologna, Italy; New York, USA) at intra- and interspecific population levels using geometric morphometric (GM) methods. Statistical analyses were performed using shape, form, and size variables. Our results do not show significant differences in shape between males and females, either considering the pooled sample or the individual populations. Differences in talar morphology due to sexual dimorphism are mainly related to allometry, i.e. size-related changes of morphological traits. Discriminant function analysis using form space Principal Components and centroid size correctly classify between 87.7% and 97.2% of the individuals. The result is similar using the pooled sample or the individual population, except for a diminished outcome for the New York group (from 73.9% to 78.2%). Finally, a talus from the Bologna sample (not included in the previous analysis) with known sex was selected to run a virtual resection, followed by two digital reconstructions based on the mean shape of both the pooled sample and the Bologna sample, respectively. The reconstructed talus was correctly classified with a Ppost between 99.9% and 100%, demonstrating that GM is a valuable tool to cope with fragmentary tali, which is a common occurrence in forensic and bioarchaeological contexts.

Bilateral Symmetry, Sex Differences, and Primary Shape Factors in Ankle and Hindfoot Bone Morphology

Background:

Ankle injuries and joint degeneration may be related to ankle bone morphology. Little data exist to characterize healthy hindfoot bone morphology. The purpose of this study was to characterize side-to-side symmetry and sex differences in ankle and hindfoot bone morphology, and to identify the primary shape factors that differentiate ankle and hindfoot bone morphology among individuals.

Methods:

Computed tomography was used to create 3D surface models of the distal tibia, talus, and calcaneus for 40 ankle and hindfoot bones from 20 healthy individuals. Morphologic differences between left and right bones of the same individual and between males and females were determined. Statistical shape modeling was performed to identify primary shape variations among individuals.

Results:

Side-to-side differences in bone morphology averaged 0.79 mm or less. The average distal tibia in males was larger overall than in females. No significant sex difference was noted in the tali. The average female calcaneus was longer and thinner than the average male calcaneus. Variability in ankle and hindfoot bone morphology is primarily associated with articulating surface shape, overall length and width, and tendon/ligament attachment points.

Conclusion:

In general, the contralateral ankle can serve as an accurate guide for operative restoration of native ankle morphology; however, specific regions demonstrate higher asymmetry.

Clinical Relevance:

Knowledge of regions of high and low bilateral symmetry can improve hindfoot and ankle reconstruction. Design of ankle prostheses can be improved by accounting for differences in bone morphology associated with sex and shape differences among individuals.

Analysis of congruence for talar dome geometry among tali of different sizes

Traumatic injury and idiopathic avascular necrosis of the talus bone can result in osteochondral lesions of the talus leading to pain, motion loss, and disability. Treatment with osteochondral allografting currently requires the donor talus to be size matched to the recipient talus to ensure precise fits. Eliminating or reducing the need for size matching would lessen costs and the delay between diagnosis and treatment. 3D models of 12 tali of varying sizes were used to analyze curvatures and profiles of select areas on the talar dome. The allograft procedure was mimicked to compare the results between using 20mm and 30mm osteochondral allografts with, and without, donor size matching. The observed curvatures and profiles on the talar dome were found to be consistent between tali of different sizes. Size matching was not required to have acceptable levels of deviation between donor and recipient tali when using 20mm length segments. Deviations without size matching were found to be very similar to the deviations with size matching with only 14.8% of the fits without size matching having larger deviations (although less than 1.5mm) than those with size matching. Using the 30mm segments, there was a significant difference between the small female tali and the largest male tali. Thus, donor size matching is not necessary when treating large osteochondral lesions of the talus with an osteochondral allograft taken from the central 20mm of the donor talar dome, and only sex matching may be necessary for 30mm grafts.

Visualization and quantification of the degenerative pattern of the talus in unilateral varus ankle osteoarthritis

The aim of this study was to quantify and visualize the degenerative patterns of the talus in ankle osteoarthritis (OA). The differences in talar morphology between sides of patients with unilateral varus ankle OA (medial talar tilt > 4°) were compared. Computed tomography images of both feet of 35 patients (OA: 22 patients, control: 13 patients) were analyzed. Each surface model of the right and left tali was registered to the opposite talus via a mirror-image technique and an iterative closest point algorithm. The surface deviation between the two models was quantified and visualized by deviation color maps. The results quantitatively demonstrated that osteophytes are generated in the area under the antero-medial margin of the trochlea in OA tali. In severe OA tali, bone resorption of more than 2 mm in the medial portion of the trochlea, as well as a similar degree of osteophyte formation on the lateral surface, was also seen. Stereotypical patterns of degeneration occurring in OA tali were successfully visualized and quantified by left-right comparison of patients with unilateral ankle OA. Such information would contribute to better understanding of the development of ankle OA and preoperative planning of total ankle arthroplasty and arthrodesis.

Bilateral symmetry of the subtalar joint facets and the relationship between the morphology and osteoarthritic changes

There is a paucity in the literature regarding bilateral symmetry between the facets of the subtalar joint. Often surgeons use the contralateral side as a reference when dealing with a fracture or other joint pathology. Moreover, the presence of osteoarthritic (OA) changes in the subtalar joint is suggested to have a relation with its morphology. In this study, we addressed both these issues. Forty pairs of cadaveric tali and calcanei were analyzed by dissection and measurement. Twenty pairs of asymptomatic calcanei were morphologically analyzed by computer tomography imaging. In the cadaveric feet, the length and width of the facets, the number and interfacet connections, the intersection angle, and the presence of OA changes were registered. In the healthy feet, the orientation and curvature of the posterior facet were analyzed based on cylinder fittings. Bilateral symmetry was tested with paired Student's t tests. Significant associations between morphometric parameters and the presence of OA changes were tested with generalized estimating equation logistic regression models. The morphometric data demonstrated a high degree of bilateral symmetry. The types of tali and calcanei between left and right differed in about one-fifth of the individuals. No significant interactions were found between morphological parameters and the presence of OA changes. Only age had a significant association. There was a high degree of symmetry in the subtalar joints facets. No significant associations were found between OA changes and morphological features, whereas other studies did. Further research is needed to explore this relationship in further detail. Clin. Anat., 33:997-1006, 2020. © 2019 Wiley Periodicals, Inc.

Development and Implantation of a Universal Talar Prosthesis

Talar avascular necrosis (AVN) can result in bone collapse with subsequent ankle and subtalar osteoarthritis ending in significant pain and disability. Custom talar body prostheses have been implanted with good results but these are difficult to design, costly and require extensive planning. In the past few years, we have investigated the feasibility of a universal talar replacement prosthesis through multiple studies. This report documents that development and the results from the first patient to receive a universal talar replacement prosthesis. A patient with bilateral talar AVN with collapse had implantation of two universal talar prostheses with final evaluations at 34 months (right) and 12 months (left) post-implantation using visual analog scale, range of motion, SF-36 questionnaire, and personal reflection. The patient had decreased pain, increase range of motion, improvement (or no change) on all domains of the SF-36 and expressed great appreciation for having the procedures done. This report demonstrates the effectiveness and feasibility of a universal talar prosthesis. Continued development of this type of implant can decrease costs, improve access, and provide an acceptable alternative when a custom prosthesis is not possible.

Investigation of pelvic symmetry using CAD software

Severe pelvic fractures often prove difficult for surgeons as they require patient-specific surgical treatment plans and customized equipment. Developing virtual patient-specific 3D pelvis models would ease the surgical planning process and enable development of custom fixation plates. This paper aims to examine pelvic symmetry to conclude whether the contralateral side may be used as a reference model for the fractured side of the pelvis. Fourteen subjects with intact pelvises were involved in this study. CT scans of the pelvises were converted to 3D models and the right sides of the pelvises were reflected and aligned with the left sides. A deviation analysis was then performed for each set of models and results showed that the average root mean square (RMS) of values was 1.14 ± 0.26 mm and the average percentage of points below a deviation threshold of ± 2 mm was 91.9 ± 5.55%. The deviation color maps (DCMs) showed that the largest deviations were on the non-articular surfaces. The volume and surface area of each model were also examined and showed no significant differences between left and right sides. These results indicate that the pelvis displays bilateral symmetry and this concept can be used to develop fully intact patient-specific 3D pelvis models for fracture reconstruction using the unfractured contralateral side. Graphical Abstract.

Sex determination from talus in Chinese population by three-dimensional measurement approach

OBJECTIVE

The determination of sex is an essential part of building the biological profile for unknown human remains. Sex determination from talus in Chinese population has been rarely reported. The aim of this study was to determine sex by discriminant function analysis through talus measurement in Chinese population.

METHODS

48 male and 47 female Chinese northeast subjects were taken in this research. The ankle joints of these subjects were scanned by CT. In total, thirteen indexes were measured through Mimics and Magics software. Length and breadth indexes of total talus, trochlea, talar head, medial and lateral malleolus articular surface were mainly selected. Nine of them were measured through Mimics software. The other four indexes were measured through Magics software. All data were analyzed by independent-samples t-test in SPSS and Stata software. Discriminant function equations were generated for sex determination.

RESULTS

All the indexes were normally distributed. No significant difference between left and right talus in either males or females was identified (P > 0.05). All results showed significant sexual difference (P < 0.05) except posterior breadth of trochlea. The average accuracy of sex determination ranged from 95.85% to 98.45% in the direct method and 98.95% in the stepwise method.

CONCLUSIONS

Length indexes showed higher accuracy rate than breadth ones. Length of lateral malleolus articular surface was the best discriminator of sexual dimorphism. Talus was proved effective for sex determination in Chinese population. This study provided a remarkable reference for sex determination in forensic science.

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.

Measurement of talar morphology in northeast Chinese population based on three-dimensional computed tomography

Morphological data of talus are important for the design of talar prostheses. The talar morphology of Chinese population has been rarely reported. This study adopted a three-dimensional (3D) measurement approach to provide accurate data for the anatomical morphology of talus in Northeast Chinese population and compared it with that of foreigners.One hundred forty-six healthy subjects form Northeast China underwent computed tomography (CT) arthrography. 3D digital talar model was reconstructed and thirteen morphological parameters were measured through Mimics and Magics software. Length and breadth indexes of total talus, trochlea, medial and lateral malleolus articular surface were mainly selected. Statistical analysis was conducted by independent-samples and paired-samples t test through SPSS software.All the indexes were normally distributed. No significant difference between left and right talus was identified in either males or females (P > .05). Most of the indexes showed significant sexual differences except the radian of lateral malleolus articular surface and the posterior breadth of trochlea (P < .05). The talar anatomy of Chinese subjects is different from the published data in other populations.The promising approach adopted in this study addresses some inconvenience with previous conventional methods on cadaver specimens. The geometric parameters of talus in Chinese population differ from those in other populations. The talar measurements and morphology analysis in this study suggest that population characteristics should be taken into account. This study will provide references for the design of talar prostheses in Chinese population.

New comprehensive procedure for custom-made total ankle replacements: Medical imaging, joint modeling, prosthesis design, and 3D printing

Many failures in total joint replacement are associated to prosthesis-to-bone mismatch. With recent additive-manufacturing, that is, 3D-printing, custom-made prosthesis can be created by laser-melting metal powders layer-by-layer. Ankle replacement is particularly suitable for this progress because of the limited number of sizes and the poor bone stock. In this study a novel procedure is presented for subject-specific ankle replacements, including medical-imaging, joint modelling, prosthesis design, and 3D-printing. Three shank-foot specimens were CT-scanned, and corresponding 3D bone models of the tibia, fibula, talus, and calcaneus were obtained. From these models, specimen-specific implant sets were designed according to three different concepts, and 3D-printed from cobalt-chromium-molybdenum powder. Accuracy of the overall procedure was assessed via distance map comparisons between original anatomical and final metal implants. Restoration of natural ankle joint mechanics was check after implantation of each of the three sets. In a special rig, a manually-driven dorsi/plantar-flexion was applied throughout the passive arc. Additionally, at three different joint positions, joint torques were imposed in the frontal and axial anatomical planes. Mean manufacturing errors were found to be smaller than 0.08 mm. Consistent motion patterns were observed over repetitions, with the mean standard deviation smaller than 1.0 degree. In each ankle specimen, mobility, and stability at the replaced joints compared well with the original natural condition. For the first time, custom-made implants for total ankle replacements were designed, manufactured with additive technology and tested. This procedure is a first fundamental step toward the development of completely personalized prostheses. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Three-dimensional analysis of shape variations and symmetry of the fibula, tibia, calcaneus and talus

The bones forming the talocrural joint (TCJ) and subtalar joint (STJ) are often assumed to be bilaterally symmetric. Therefore, the contralateral limb (i.e. the fibula, tibia, calcaneus and talus) is used as a template or an intra‐subject control in clinical and research practice. However, the validity of the symmetry assumption is controversial, because insufficient information is available on the shape variations and bilateral (a)symmetry of the fibula, tibia, calcaneus and talus. Using three‐dimensional spatially dense sampled representations of bone shapes extracted from bilateral computed tomography scans of 66 individuals (55 male, mean age: 61 ± 10 years; 11 female, mean age: 53 ± 15 years), we analyzed whether: (i) similar shape patterns exist in the left and right bones of the same type; (ii) gender has an effect on bone shape variations; (iii) intra‐subject shape variation is smaller than that of inter‐subject for a given shape variance direction. For the first set of analyses, all left and right instances of the same type of bone were considered as two separate groups, and statistically compared with each other on multiple aspects including group location (central tendency), variance‐covariance scale (dispersion) and orientation (covariance structure) using distance‐based permutational tests. For the second and third sets of analyses, all left and right bones of the same type were pooled into one group, and shape variations in the TCJ and STJ bones were extracted using principal component analysis. The effects of gender on age‐adjusted bone shape differences were assessed using an analysis of covariance. Moreover, intra‐class correlation was employed to evaluate intra‐ and inter‐subject bone shape variations. For each bone type, both sides had similar shape patterns (P_{permutational}‐values > 0.05). After Bonferroni adjustment, gender led to shape differences, which were mainly in the lateral and medial condyles of the tibia (P = 0.003), the length and height of the calcaneus (P < 0.001), the posterior and anterior talar articular surfaces of the calcaneus (P = 0.001), and in the posterior aspect of the talus (P = 0.001). Intra‐subject shape variations in the tibial tuberosity together with the diameter of the tibia, and the curvature of the fibula shaft and the diameter of the fibula were as high as those of inter‐subject. This result suggests that the shape symmetry assumption could be violated for some specific shape variations in the fibula and tibia.

Analysis of a generic talar prosthetic with a biological talus: A cadaver study

Treatment for talar avascular necrosis is challenging. This study evaluates the feasibility of a generic talar implant by cadaveric assessment. Ten cadaveric ankles were CT-scanned to determine talar implant size. The opposite ankles were CT-scanned with the biological talus and then with the implant. 3D ankle geometry was reconstructed and implant position was compared to the biological talus position. The averages among specimens' positive and negative average-deviations were 0.91 mm and 0.70 mm. Seventy percent of talar dome deviations between the biological talus and implant were within an acceptable range. This study yields promising results to support a generic talus bone prosthetic.

Application of 3D-printed and patient-specific cast for the treatment of distal radius fractures: initial experience

BACKGROUND

Distal radius fracture is common in the general population. Fracture management includes a plaster cast, splint and synthetic material cast to immobilise the injured arm. Casting complications are common in those conventional casting technologies. 3D printing technology is a rapidly increasing application in rehabilitation. However, there is no clinical study investigating the application of a 3D-printed orthopaedic cast for the treatment of bone fractures. We have developed a patient-specific casting technology fabricated by 3D printing. This pioneering study aims to use 3D-printed casts we developed for the treatment of distal radius fractures, to provide the foundation for conducting additional clinical trials, and to perform clinical assessments.

METHOD

Ten patients with ages between 5 and 78 years are involved in the clinical trial. Patients are applied 3D-printed casts we developed. Orthopaedic surgeons carried out a six-week follow-up to examine clinical outcomes. Two questionnaires were developed for the assessment of clinical efficacy and patients' satisfaction. These questionnaires are completed by physicians and participating patients.

RESULTS

A 3D-printed cast creates a custom-fitted design to maintain the fractured bone alignment. No loss of reduction is found in all patients. Compartment syndrome and pressure sores are not present. Patient comfort gets positive scores on the questionnaire. All (100%) of the patients opt for the 3D-printed cast instead of the conventional plaster cast.

DISCUSSION

A patient-specific, 3D-printed cast offers a proper fit to immobilise an injured arm and holds the fracture reduction appropriately. A custom-fitted structure reduces the risk of pressure-related complications due to the high and concentrated local stress. The ventilated and lightweight design minimises interference with a patient's daily activities and reduces the risk of cutaneous complications. Patients express a strong preference for using a 3D-printed cast instead of a plaster cast. Limitations of the novel cast include a slight odour after heavy sweating and the relatively high cost due to the limitations of current 3D printing technologies.

CONCLUSIONS

This pioneering study is the first clinical trial on the application of a 3D-printed cast for the treatment of forearm fractures. The novel casting technology heals the fracture effectively without casting complications. The 3D-printed cast is patient-specific and ventilated as well as lightweight, and it features both increased patient comfort and satisfaction.

Three-dimensional Computer-assisted Modeling of Talus Morphology in Chinese Patients

OBJECTIVE

To provide more accurate reference data for the assessment and treatment of talar injuries by constructing 3-D computer-assisted models of the talus and comparing them with reference data obtained from measurements on cadaver specimens.

METHODS

Three-dimensional talus models were constructed from CT data recorded for healthy Chinese volunteers using SuperImage Orthopedics software. Structural variables such as length, width, height and volume of talus were compared using the Fisher least significant difference test to determine the significance of bilateral or sex-specific differences in the study cohort.

RESULTS

Measurement data were normally distributed. No significant difference between the left and right talus in either men or women was identified for any measurement (P > 0.05). The bilateral mean volume of the talus in men (37.87 ± 6.69 mm) was significantly larger than that in women (26.95 ± 5.73 mm; P < 0.05). Although the dimensions of most of the structural features and articular surfaces of the talus were significantly larger in men than in women (P < 0.05), no significant differences in the angles of the talar neck and head were observed between men and women in our cohort (P > 0.05).

CONCLUSION

Our method of 3-D model construction provided precise measurements of the structural features of the talus. The talar dimensions in our Chinese study cohort differ from those previously reported for people of different ethnic groups. Our models should provide accurate reference data for constructing models based on CT images for the assessment and treatment of talar injuries in Chinese patients.

Bone shape difference between control and osteochondral defect groups of the ankle joint

OBJECTIVE

The etiology of osteochondral defects (OCDs), for which the ankle (talocrural) joint is one of the common sites, is not yet fully understood. In this study, we hypothesized that bone shape plays a role in development of OCDs. Therefore, we quantitatively compared the morphology of the talus and the distal tibia between an OCD group and a control group.

METHODS

The shape variations of the talus and distal tibia were described separately by constructing two statistical shape models (SSMs) based on the segmentation of the bones from ankle computed tomography (CT) scans obtained from control (i.e., 35 CT scans) and OCD (i.e., 37 CT scans) groups. The first five modes of shape variation for the SSM corresponding to each bone were statistically compared between control and OCD groups using an analysis of variance (ANOVA) corrected with the Bonferroni for multiple comparisons.

RESULTS

The first five modes of variation in the SSMs respectively represented 49% and 40% of the total variance of talus and tibia. Less than 5% of the variance per mode was described by the higher modes. Mode 5 of the talus (P = 0.004) primarily describing changes in the vertical neck angle and Mode 1 of the tibia (P < 0.0001) representing variations at the medial malleolus, showed statistically significant difference between the control and OCD groups.

CONCLUSION

Shape differences exist between control and OCD groups. This indicates that a geometry modulated biomechanical behavior of the talocrural joint may be a risk factor for OCD.