Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography

Comparing the predictions of CT-based subject-specific finite element models of human metastatic vertebrae with digital volume correlation measurements

Several conditions can increase the incidence of vertebral fragility fractures, including metastatic bone disease. Computational tools could help clinicians estimate the risk of vertebral fracture in these patients; however, comparison with in vitro data is mandatory before using them in clinical practice. Nine spine segments were tested under compression and imaged with micro-computed tomography (µCT). The displacement field was calculated for each vertebra using a global digital volume correlation (DVC) approach. Subject-specific homogenised finite element models of each vertebra were built from µCT images, applying experimentally matched boundary conditions at the endplates. Numerical and experimental displacements, reaction forces, and locations showing higher strain concentrations were eventually compared. Additionally, given that µCT cannot be performed in clinical settings, the outcomes of a µCT-based model were also compared to those of a model built from clinical CT scans of the same specimen. Good agreement between DVC and µCT-based FE displacements was found, both for healthy (R2 = 0.69 ÷ 0.83, RMSE = 3 ÷ 22%, max error < 45 μm) and metastatic (R2 = 0.64 ÷ 0.93, RMSE = 5 ÷ 18%, max error < 54 μm) vertebrae. Strong correlations were found between µCT-based and clinical CT-based FE model outcomes (R2 = 0.99, RMSE < 1.3%, max difference = 6 μm). Furthermore, the models qualitatively identified the most deformed regions identified with the experiments. In conclusion, the combination of experimental full-field technique and in-silico modelling enabled the development of a promising pipeline to validate bone strength predictors in the elastic range. Further improvements are needed to analyse vertebral post-yield behaviour better.

Toward subtalar joint axis-driven computer-aided design and computer-aided manufacturing foot orthoses: Reliability of a noninvasive clinical scanning protocol

BACKGROUND

The subtalar joint axis (STJA) occupies a key role in the dynamics of the lower limb kinetic chain, and its location has a wide interindividual variability. It has been suggested that considering the STJA location when designing foot orthoses may help to apply the required mechanical dose. However, the evidence is more anecdotal than empirical.

OBJECTIVE

This study aimed to evaluate the reliability of the STJA digitization, a procedure combining the clinical determination of the functional STJA location and its subsequent 3-dimensional (3D) scanning.

STUDY DESIGN

Two examiners identified the posterior and anterior exit points of the functional STJA on the skin of 15 healthy participants using a clinical method in a repeated-measure design.

METHODS

A handheld 3D scanner was used to scan the feet and the skin markers. The 3D coordinates of the skin markers were subsequently quantified and (1) STJA digitization intratester within-session, (2) STJA digitization intratester between-session, and (3) STJA digitization intertester between-session reliabilities were evaluated.

RESULTS

When pooling all skin marker 3D coordinates, intraclass correlation coefficients (ICCs) for the STJA intratester within-session reliability ranged from 0.74 to 0.98. ICCs for the STJA digitization intratester between-session reliability ranged from 0.58 to 0.94. ICCs for the STJA digitization intertester reliability ranged from 0.56 to 0.81. Standard error of measurement for the mediolateral position of the talus marker (anterior exit point of the STJA) was substantially higher than that for the other coordinates.

CONCLUSIONS

Overall, the STJA digitization demonstrated a good intratester between-session reliability and may be used in a computer-aided design and computer-aided manufacturing workflow to create foot orthoses. However, further efforts should be considered to improve the scanning process and intertester reliability.

Radiographic Analysis of Valgus Ankle Deformity With or Without Medial Longitudinal Arch Collapse

BACKGROUND

Establishing a surgical plan for ankle deformities necessitates a comprehensive understanding of the deforming forces involved, and the morphology of the ankle deformity plays an important role as well. Valgus tibiotalar tilt development has mostly been described in patients with a low medial longitudinal arch, as seen in progressive collapsing foot deformity (PCFD). However, some valgus ankles demonstrate no radiographic evidence of a collapsed medial arch. This study aims to investigate whether there are differences in the radiographic morphology of valgus ankle deformities between patients with and without a low medial longitudinal arch to explore if they have different etiologies.

METHODS

We retrospectively reviewed patients who underwent surgical treatment for asymmetric valgus ankle deformity at our institution between 2017 and 2021. Patients with a valgus tibiotalar tilt (TT) greater than 4 degrees and Meary angle greater than 30 degrees (mean: 38.9) were included in the PCFD group (n = 29). The non-PCFD group (n = 24) with TT greater than 4 degrees and Meary angle less than 4 degrees (mean: 0.3) was also established. In the weightbearing ankle anteroposterior view, the TT and medial distal tibial angle were measured. Additionally, to assess the mediolateral position of the talus, the talar center migration (TCM) and lateral talar dome-plafond distance (LTD-P) ratio in the coronal plane were measured. In weightbearing computed tomography (WBCT), the degree of axial plane talocalcaneal subluxation and the prevalence of sinus tarsi bony impingement were assessed. Intergroup comparison was conducted.

RESULTS

Both groups demonstrated a similar degree of TT, with a mean of 11.6 degrees in the PCFD group and 13.7 degrees in the non-PCFD group (P = .2330). However, the PCFD group showed a significantly greater TCM and LTD-P ratio compared with those of the non-PCFD group (P < .0001), indicating that PCFD patients have a more medially translated talus in ankle anteroposterior radiographs. WBCT showed that the PCFD group on average had 18 degrees greater axial plane talocalcaneal subluxation (P < .0001) and 52% higher prevalence of sinus tarsi bony impingement (P = .0002) compared with the non-PCFD group.

CONCLUSION

This study suggests that valgus ankles may exhibit different radiographic morphologies depending on the status of the longitudinal arch. Valgus ankles in PCFD patients tend to have a more medially translated talus. This finding may suggest the presence of different deforming forces between the 2 groups and may indicate the need for different treatment strategies to address talar tilt.

LEVEL OF EVIDENCE

Level III, case-control.

Development and validation of a novel ankle joint musculoskeletal model

An improved understanding of contact mechanics in the ankle joint is paramount for implant design and ankle disorder treatment. However, existing models generally simplify the ankle joint as a revolute joint that cannot predict contact characteristics. The current study aimed to develop a novel musculoskeletal ankle joint model that can predict contact in the ankle joint, together with muscle and joint reaction forces. We modelled the ankle joint as a multi-axial joint and simulated contact mechanics between the tibia, fibula and talus bones in OpenSim. The developed model was validated with results from experimental studies through passive stiffness and contact. Through this, we found a similar ankle moment-rotation relationship and contact pattern between our study and experimental studies. Next, the musculoskeletal ankle joint model was incorporated into a lower body model to simulate gait. The ankle joint contact characteristics, kinematics, and muscle forces were predicted and compared to the literature. Our results revealed a comparable peak contact force and the same muscle activation patterns in four major muscles. Good agreement was also found in ankle dorsi/plantar-flexion and inversion/eversion. Thus, the developed model was able to accurately model the ankle joint and can be used to predict contact characteristics in gait.

Talocalcaneal Ligament Reconstruction Kinematic Simulation for Progressive Collapsing Foot Deformity

BACKGROUND

In progressive collapsing foot deformity (PCFD), an internal and plantar rotation of the talus relative to the calcaneus may result in painful peritalar subluxation. Medial soft tissue procedures (eg, spring ligament repair) aim to correct the talar position via the navicular bone if bony correction alone is not sufficient. The effect of the medial soft tissue reconstruction on the talar reposition remains unclear. We hypothesized that a subtalar talocalcaneal ligament reconstruction might be favorable in PCFD to correct talar internal malposition directly. This pilot study aims to evaluate the anatomical feasibility and kinematic behavior of a subtalar ligament reconstruction in PCFD.

METHODS

Three-dimensional surface model from 10 healthy ankles were produced. A total of 1089 different potential ligament courses were evaluated in a standardized manner. A motion of inversion/eversion and talar internal/external in relation to the calcaneus were simulated and the ligament strain, expressed as a positive length variation, for each ligament was analyzed. The optimal combination for the ligament reconstruction with increased length in internal rotation of the talus, isometric kinematic behavior in inversion/eversion, and extraarticular insertion on talus and calcaneus was selected.

RESULTS

A laterodistal orientation of the talar insertion point in respect to the subtalar joint axis and laterodistal deviation of the calcaneal insertion point presents the highest ligament lengthening in internal talar rotation (+0.56 mm [3.8% of total length]) and presented a near-isometric performance in inversion/eversion (+0.01 to -0.01 mm [0.1% of total length]).

CONCLUSION

This kinematic model shows that a ligament reconstruction in the subtalar space presents a pattern of length variation that may stabilize the internal talar rotation without impeding the physiological subtalar motion.

CLINICAL RELEVANCE

This study investigates the optimal location, feasibility, and kinematic behavior of a ligament reconstruction that could help stabilize peritalar subluxation in progressive collapsing foot deformity.

[Formula: see text].

Increased subtalar rotational motion in patients with symptomatic ankle instability under load and stress conditions

PURPOSE

Differentiating subtalar and ankle instability in the clinical setting is challenging. This study aims to analyze the rotational laxity of the subtalar joint bilaterally in patients with asymptomatic and symptomatic ankle instability under simulated load and stress-induced position of the subtalar joint.

METHODS

A case-control study was conducted using an adjustable load device (ALD). Patients with chronic ankle instability and healthy volunteers were included. Each subject underwent a CT scan under mechanical stress and simulated weight-bearing conditions, maintaining maximum eversion and inversion hindfoot positions. The images were obtained in a single model, allowing calculations of the motion vector as well as the helical axis. The helical axis was defined by a rotation angle and a translation distance.

RESULTS

A total of 72 feet were included in the study. Thirty-one patients with unilateral symptoms and five healthy controls were selected, defining two groups: symptomatic (n = 31) and asymptomatic (n = 41). An absolute difference of 4.6º (95%CI 2-11.1) rotation angle was found on the helical axis of the symptomatic vs. asymptomatic group (p = 0.001). No significant differences were detected in the translation distance (n.s.) between the groups. Additionally, a significant positive correlation was found between the rotation angle and translation distance through the helical axis in the asymptomatic group (r = 0.397, p = 0.027).

CONCLUSION

Patients with chronic ankle instability suspected of having subtalar joint instability showed a wider subtalar range of laxity in terms of rotation about the helical axis. Furthermore, differences in kinematics between symptomatic and asymptomatic hindfeet was demonstrated when both feet were compared.

LEVEL OF EVIDENCE

III.

Ankle and subtalar joint axes of rotation and center of rotation during walking and running in healthy individuals measured using dynamic biplane radiography

The goal of this study was to determine how foot type and activity level affect ankle and hindfoot motion. Dynamic biplane radiography and a validated volumetric registration process was used to measure ankle and hindfoot motion of 20 healthy adults during walking and running. The helical axes of motion (HAM) during stance were calculated at the tibiotalar and subtalar joints. The intersection of each HAM and the rotation plane of interest defined the tibiotalar and subtalar centers of rotation (COR). Correlations between foot type and hindfoot kinematics were calculated using Pearson's correlations. The effect of activity, phase of gait, and dominant vs. non-dominant limb on HAM and COR were evaluated using linear mixed effects models. Activity and phase of gait influenced the superior location of the tibiotalar (p < 0.041) and subtalar (p < 0.044) CORs. Activity and gait phase affected tibiotalar (p < 0.049) and subtalar (p < 0.044) HAM direction during gait. Both HAM orientation and COR location changed with activity and phase of gait. These ankle and hindfoot kinematics have implications for total ankle replacement design and musculoskeletal models that estimate force and moment generating capabilities of muscles.

Hindfoot motion through helical axis image-based on dynamic CT scan using an original simulated weightbearing device

BACKGROUND

Determining the treatment of subtalar joint (STJ) instability requires a better understanding of the biomechanical principles underlying the condition and, a proper diagnosis. This study aimed to analyze "in vivo" the range of motion of the subtalar joint (STJ) measured on two (2D) and three dimensions (3D) image-based on CT Scan using an original device that maintains a simulated weightbearing. The secondary goal was to correlate the 2D and 3D measurement.

METHODS

An observational study was conducted, using an original Dynamic Simulated Weightbearing Device. Asymptomatic ankles were included. Each subject underwent a CT scan under mechanical stress and simulated weightbearing conditions, maintaining maximum eversion and inversion hindfoot positions. The images were obtained, combining both inversion and eversion positions in a single model, which allows for to calculation of the motion vector as well as the helical axis. The helical axis (rotation angle and translation distance), subtalar tilt, anterior drawer, and, subtalar and calcaneocuboid uncoverage were the determinations.

RESULTS

Forty asymptomatic ankles were included. The average range of motion of the STJ amounts to 31.5° ± 9.1° of rotation and 1.56 ± 0.8 mm of translation distance. The anterior drawer and subtalar uncoverage variables were statistically significantly related to each other (r = 0.57; P = 0.00001). However, these 2-D measured variables were not related to kinematic measures of rotation through the helical axis (3D) (p = 0.14; p = 0.19) CONCLUSIONS: The average range of motion of the STJ amounts to 31.5° ± 9.1° of rotation and 1.56 ± 0.8 mm of translation distance. We found no significant correlation between 2D and 3D measurements. In our opinion, the rotation angle and translation distance should be considered the most accurate measurements and should be calculated on every STJ instability for comparison with the asymptomatic population LEVEL OF EVIDENCE: Observational study.

LEVEL OF EVIDENCE III

Decreased Peritalar Subluxation in Progressive Collapsing Foot Deformity with Ankle Valgus Tilting

Background

Middle facet subluxation (MFS) has been established as an early indicator of peritalar subluxation. However, when progressive collapsing foot deformity (PCFD) affects the ankle leading to a valgus talar tilt (Class E), structures and anatomic relationships distal to the ankle joint may be affected. Therefore, this study aimed to assess radiographic parameters of peritalar subluxation in patients with PCFD who either did or did not have a valgus ankle. Our hypothesis was that these parameters would differ in Class E patients, upsetting their capability to quantify deformity.

Methods

We performed a prospective comparative study utilizing weight-bearing computed tomography (WBCT) images of 21 feet with PCFD and with valgus of the ankle and 64 with flexible PCFD without ankle involvement. Parameters including MFS, the medial cuneiform-to-floor distance, the forefoot arch angle, the talonavicular coverage angle, the hindfoot moment arm (HMA), the foot-ankle offset (FAO), and the talar tilt angle (TTA) were measured and compared. Variables that influence the presence of ankle valgus and overall alignment were assessed by multivariable regression models.

Results

Patients with PCFD and ankle valgus demonstrated a higher mean HMA (20.79 mm [95% confidence interval (CI), 17.56 to 24.02 mm] versus 8.94 mm [95% CI, 7.09 to 10.79 mm]), FAO (14.89% [95% CI, 12.51% to 17.26%] versus 6.32% [95% CI, 4.96% to 7.68%]) and TTA (95% CI, 17.10° [14.75° to 19.46°] versus 2.30° [95% CI, 0.94° to 3.65°]) and lower mean MFS (21.84% [95% CI, 15.04% to 28.63%] versus 38.45% [95% CI, 34.55% to 42.34%]) compared with the group without ankle valgus (p < 0.0001 for all). The FAO was influenced by MFS in the group without ankle valgus (p <0.0001) but not in the group with ankle valgus (p = 0.9161). FAO values of ≥12.14% were a strong predictor (79.2%) of ankle valgus deformity.

Conclusions

Subluxation of the middle facet was not as severe and did not influence the overall alignment in patients with PCFD who had valgus of the ankle (Class E). These findings suggest a distal peritalar reduction in the presence of a proximal deformity, making MFS an imprecise disease parameter in this scenario. An FAO value of ≥12.14% was a strong indicator of ankle deformity in patients with PCFD.

Level of Evidence

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

In vivo evaluation of ankle kinematics and tibiotalar joint contact strains using digital volume correlation and 3 T clinical MRI

BACKGROUND

In vivo evaluation of ankle joint biomechanics is key to investigating the effect of injuries on the mechanics of the joint and evaluating the effectiveness of treatments. The objectives of this study were to 1) investigate the kinematics and contact strains of the ankle joint and 2) to investigate the correlation between the tibiotalar joint contact strains and the prevalence of osteochondral lesions of the talus distribution.

METHODS

Eight healthy human ankle joints were subjected to compressive load and 3 T MRIs were obtained before and after applying load. The MR images in combination with digital volume correlation enabled non-invasive measurement of ankle joint kinematics and tibiotalar joint contact strains in three dimensions.

FINDINGS

The total translation of the calcaneus was smaller (0.48 ± 0.15 mm, p < 0.05) than the distal tibia (0.93 ± 0.16 mm) and the talus (1.03 ± 0.26 mm). These movements can produce compressive and shear joint contact strains (approaching 9%), which can cause development of lesions on joints. 87.5% of peak tensile, compressive, and shear strains in the tibiotalar joint took place in the medial and lateral zones.

INTERPRETATION

The findings suggested that ankle bones translate independently from each other, and in some cases in opposite directions. These findings help explain the distribution of osteochondral lesions of the talus which have previously been observed to be in medial and lateral regions of the talar dome in 90% of cases. They also provide a reason for the central region of talar dome being less susceptible to developing osteochondral lesions.

A Cadaveric Comparison of the Kinematic and Anatomical Axes and Arthrokinematics of the Metatarsosesamoidal and First Metatarsophalangeal Joints

Presently, developments in weightbearing computed tomography and biplanar fluoroscopy technologies offer exciting avenues for investigating normative and pathologic foot function with increasing precision. Still, data quantifying sesamoid bone and proximal phalange motion are currently sparse. To express joint kinematics and compare various clinical cohorts, future studies of first ray motion will necessitate robust coordinate frames that respect the variations in underlying anatomy while also aligning closely with the functional, physiological axes of motion. These activity-dependent functional axes may be represented by a mean helical axis of the joint motion. Our cadaveric study quantified joint kinematics from weightbearing computed tomography scans during simulated toe lift and heel rise tasks. We compared the spatial orientations of the mean finite helical axes of the metatarsosesamoidal and metatarsophalangeal joints to the primary joint axis of two relevant methods for defining metatarsal coordinate frames: inertial axes and fitting of geometric primitives. The resultant kinematics exhibited less crosstalk when using a metatarsal coordinate system based on fitting cylindrical primitives to the bony anatomy compared to using principal component axes. Respective metatarsophalangeal and metatarsosesamoidal arthrokinematic contact paths and instantaneous centers of rotation were similar between activities and agree well with currently published data. This study outlines a methodology for quantitatively assessing the efficacy and utility of various anatomical joint coordinate system definitions. Improvements in our ability to characterize the shape and motion of foot bones in the context of functional tasks will elucidate their biomechanical roles and aid clinicians in refining treatment strategies.

A novel tool to quantify in vivo lumbar spine kinematics and 3D intervertebral disc strains using clinical MRI

Medical imaging modalities that calculate tissue morphology alone cannot provide direct information regarding the mechanical behaviour of load-bearing musculoskeletal organs. Accurate in vivo measurement of spine kinematics and intervertebral disc (IVD) strains can provide important information regarding the mechanical behaviour of the spine, help to investigate the effects of injuries on the mechanics of the spine, and assess the effectiveness of treatments. Additionally, strains can serve as a functional biomechanical marker for detecting normal and pathologic tissues. We hypothesised that combining digital volume correlation (DVC) with 3T clinical MRI can provide direct information regarding the mechanics of the spine. Here, we have developed a novel non-invasive tool for in vivo displacement and strain measurement within the human lumbar spine and we used this tool to calculate lumbar kinematics and IVD strains in six healthy subjects during lumbar extension. The proposed tool enabled spine kinematics and IVD strains to be measured with errors that did not exceed 0.17 mm and 0.5%, respectively. The findings of the kinematics study identified that during extension the lumbar spine of healthy subjects experiences total 3D translations ranging from 1 mm to 4.5 mm for different vertebral levels. The findings of strain analysis identified that the average of the maximum tensile, compressive, and shear strains for different lumbar levels during extension ranged from 3.5% to 7.2%. This tool can provide base-line data that can be used to describe the mechanical environment of healthy lumbar spine, which can help clinicians manage preventative treatments, define patient-specific treatments, and to monitor the effectiveness of surgical and non-surgical interventions.

Role of the intrinsic subtalar ligaments in subtalar instability and consequences for clinical practice

Subtalar instability (STI) is a disabling complication after an acute lateral ankle sprain and remains a challenging problem. The pathophysiology is difficult to understand. Especially the relative contribution of the intrinsic subtalar ligaments in the stability of the subtalar joint is still controversial. Diagnosis is difficult because of the overlapping clinical signs with talocrural instability and the absence of a reliable diagnostic reference test. This often results in misdiagnosis and inappropriate treatment. Recent research offers new insights in the pathophysiology of subtalar instability and the importance of the intrinsic subtalar ligaments. Recent publications clarify the local anatomical and biomechanical characteristics of the subtalar ligaments. The cervical ligament and interosseous talocalcaneal ligament seem to play an important function in the normal kinematics and stability of the subtalar joint. In addition to the calcaneofibular ligament (CFL), these ligaments seem to have an important role in the pathomechanics of subtalar instability (STI). These new insights have an impact on the approach to STI in clinical practice. Diagnosis of STI can be performed be performed by a step-by-step approach to raise the suspicion to STI. This approach consists of clinical signs, abnormalities of the subtalar ligaments on MRI and intraoperative evaluation. Surgical treatment should address all the aspects of the instability and focus on a restoration of the normal anatomical and biomechanical properties. Besides a low threshold to reconstruct the CFL, a reconstruction of the subtalar ligaments should be considered in complex cases of instability. The purpose of this review is to provide a comprehensive update of the current literature focused on the contribution of the different ligaments in the stability of the subtalar joint. This review aims to introduce the more recent findings in the earlier hypotheses on normal kinesiology, pathophysiology and relation with talocrural instability. The consequences of this improved understanding of pathophysiology on patient identification, treatment and future research are described.

Diagnostic accuracy of measurements in progressive collapsing foot deformity using weight bearing computed tomography: A matched case-control study

BACKGROUND

We aimed to investigate the diagnostic accuracy of known two-dimensional (2D) and three-dimensional (3D) measurements for Progressive Collapsing Foot Deformity (PCFD) in weight-bearing computed tomography (WBCT). We hypothesized that 3D biometrics would have better specificity and sensitivity for PCFD diagnosis than 2D measurements.

METHODS

This was a retrospective case-control study, including 28 PCFD feet and 28 controls matched for age, sex and Body Mass Index. Two-dimensional measurements included: axial and sagittal talus-first metatarsal angles (TM1A and TM1S), talonavicular coverage angle (TNCA), forefoot arch angle (FFAA), middle facet incongruence angle (MF°) and uncoverage percentage (MF%). The 3D Foot Ankle Offset (FAO) was obtained using dedicated semi-automatic software. Intra and interobserver reliabilities were assessed. Receiver Operating Characteristic (ROC) curves were calculated to determine diagnostic accuracy (Area Under the Curve (AUC)), sensitivity and specificity.

RESULTS

In PCFD, mean MF% and MF° were respectively 47.2% ± 15.4 and 13.3° ± 5.3 compared with 13.5% ± 8.7 and 5.6° ± 2.9 in controls (p < 0.001). The FAO was 8.1% ± 3.8 in PCFD and 1.4% ± 1.7 in controls (p < 0.001). AUCs were 0.99 (95%CI, 0.98-1) for MF%, 0.96 (95%CI, 0.9-1) for FAO, 0.90 (95%CI, 0.81-0.98) for MF°. For MF%, a threshold value equal or greater than 28.7% had a sensitivity of 100% and specificity of 92.8%. Conversely, a FAO value equal or greater than 4.6% had a specificity of 100% and a sensitivity of 89.2%. All other 2D measurements were significantly different in PCFD and controls (p < 0.001).

CONCLUSIONS

MF% and FAO were both accurate measurements for PCFD. MF% demonstrated slightly better specificity. FAO better sensitivity. A combination of threshold values of 28.7% for MF% and 4.6% for FAO yielded 100% sensitivity and specificity.

Significance of the anatomical relationship between the flexor digitorum longus and sustentaculum tali for reconsideration of the talocalcaneonavicular joint stability mechanism

The talocalcaneonavicular joint (TCN-j) is supported by the spring ligament, which has recently been revealed to be part of the joint capsule complex, along with the tendinous sheath of the tibialis posterior and flexor digitorum longus (FDL). Nonetheless, the FDL's role in TCN-j stability has received limited attention. This study aimed to elucidate the positional relationships between the FDL and sustentaculum tali, which comprises the TCN-j. We hypothesized that the FDL runs medial to the sustentaculum tali, and its course significantly changes from the sitting to the standing position. Six ankles from six body donors were investigated, and seven ankles from seven volunteers were assessed using ultrasonography. The FDL was three-dimensionally located inferomedial to the sustentaculum tali. The FDL tendinous sheath was attached to the sustentaculum tali or connected by the tibialis posterior via the tendinous sheath. Based on the in vivo ultrasound image, the FDL location relative to the sustentaculum tali was maintained; however, the curvature of the FDL course was significantly more prominent in standing than in sitting. The FDL force against the bending moment may prevent the excessive eversion of the foot and aid the conventional spring ligament's contribution to TCN-j stability for maintaining the longitudinal arch.

Interaction of loading and ligament injuries in subtalar joint instability quantified by 3D weightbearing computed tomography

Despite decades of research since its first description, subtalar joint instability remains a diagnostic enigma within the concept of hindfoot instability. This could be attributed to current imaging techniques, which are impeded by two-dimensional measurements. Therefore, we used weightbearing computed tomography imaging to quantify three-dimensional displacement associated with subtalar joint instability. Three-dimensional models were generated in seven paired cadaver specimens to compute talocalcaneal displacement after different patterns of axial load (85 kg) combined with torque in internal and external rotation (10 Nm). Sequential imaging was repeated in the subtalar joint containing intact ligaments to determine reference displacement. Afterward, the interosseus talocalcaneal ligament (ITCL) or calcaneofibular ligament (CFL) was sectioned, then the ITCL with CFL and after the ITCL, CFL with the deltoid ligament (DL). The highest translation could be detected in the dorsal direction and the highest rotation occurred in the internal direction when external torque was applied to the foot without load. These displacements differed significantly from the condition containing intact ligaments, with a mean difference of 1.6 mm (95% CI, 1.3 to 1.9) for dorsal translation and a mean of 12.4° (95% CI, 10.1 to 14.8) for internal rotation. Clinical relevance: Our study provides a novel and noninvasive analysis to quantify subtalar joint instability based on three-dimensional WBCT imaging. This approach overcomes former studies using trans-osseous fixation to determine three-dimensional subtalar joint displacement and implements an imaging device and software modalities that are readily available. Based on our findings, we recommend applying torque in external rotation to the foot to optimize the detection of subtalar joint instability.

Difference in orientation of the talar articular facets between healthy ankle joints and ankle joints with chronic instability

Since both the talocrural and subtalar joints can be involved in chronic ankle instability, the present study assessed the talar morphology as this bone is the key player between both joint levels. The 3D orientation and curvature of the superior and the posteroinferior facet between subjects with chronic ankle instability and healthy controls were compared. Hereto, the talus was segmented in the computed tomography images of a control group and a chronic ankle instability group, after which they were reconstructed to 3D surface models. A cylinder was fitted to the subchondral articulating surfaces. The axis of a cylinder represented the facet orientation, which was expressed by an inclination and deviation angle in a coordinate system based on the cylinder of the superior talar facet and the geometric principal axes of the subject's talus. The curvature of the surface was expressed as the radius of the cylinder. The results demonstrated no significant differences in the radius or deviation angle. However, the inclination angle of the posteroinferior talar facet was significantly more plantarly orientated (by 3.5°) in the chronic instability group (14.7 ± 3.1°) compared to the control group (11.2 ± 4.9°) (p < 0.05). In the coronal plane this corresponds to a valgus orientation of the posteroinferior talar facet relative to the talar dome. In conclusion, a more plantarly and valgus orientated posteroinferior talar facet may be associated to chronic ankle instability.

Subtalar axis determined by combining digital twins and artificial intelligence: influence of the orientation of this axis for hindfoot compensation of varus and valgus knees

PURPOSE

Previous studies evaluating hindfoot and knee alignment have suggested compensation between the knee and the hindfoot deformities. However, these studies did not investigate the influence of the orientation of the subtalar axis on the results.

MATERIAL AND METHODS

Using computed tomography data of patients without osteoarthritis, digital twins, and artificial intelligence, we identified the orientation of the axis of the subtalar joint. Compensation was evaluated in the subtalar joint according to angular knee deformity and subtalar axis direction.

RESULTS

With the inclination angle defined as the angle between the axis and the XY plane (horizontal) and the deviation angle defined as the angle between the projection of axis on the XZ plane, the inclination angle of the subtalar helical axis showed an average angle of 35.3° (range 5° to 48°). The mean deviation angle for the helical axis was 6.4° (range - 4° to + 12°). Our findings indicated that an increase of the inclination angle of the subtalar axis tends to limit adjustment in the hindfoot alignment toward re-balance of the whole lower limb toward a neutral weight-bearing axis when malalignment of the knee occurs.

CONCLUSION

Malalignment of the knee and different compensations in the hindfoot contribute to various combined deformities in the population: associated valgus or varus deformities and inverse associations of varus/valgus deformities.

Three-Dimensional Innate Mobility of the Human Foot on Coronally-Wedged Surfaces Using a Biplane X-Ray Fluoroscopy

Improving our understanding on how the foot and ankle joints kinematically adapt to coronally wedged surfaces is important for clarifying the pathogenetic mechanism and possible interventions for the treatment and prevention of foot and lower leg injuries. It is also crucial to interpret the basic biomechanics and functions of the human foot that evolved as an adaptation to obligatory bipedal locomotion. Therefore, we investigated the three-dimensional (3D) bone kinematics of human cadaver feet on level (0°, LS), medially wedged (−10°, MWS), and laterally wedged (+10°, LWS) surfaces under axial loading using a biplanar X-ray fluoroscopy system. Five healthy cadaver feet were axially loaded up to 60 kg (588N) and biplanar fluoroscopic images of the foot and ankle were acquired during axial loading. For the 3D visualization and quantification of detailed foot bony movements, a model-based registration method was employed. The results indicated that the human foot was more largely deformed from the natural posture when the foot was placed on the MWS than on the LWS. During the process of human evolution, the human foot may have retained the ability to more flexibly invert as in African apes to better conform to MWS, possibly because this ability was more adaptive even for terrestrial locomotion on uneven terrains. Moreover, the talus and tibia were externally rotated when the foot was placed on the MWS due to the inversion of the calcaneus, and they were internally rotated when the foot was placed on the LWS due to the eversion of the calcaneus, owing to the structurally embedded mobility of the human talocalcaneal joint. Deformation of the foot during axial loading was relatively smaller on the MWS due to restricted eversion of the calcaneus. The present study provided new insights about kinematic adaptation of the human foot to coronally wedged surfaces that is inherently embedded and prescribed in its anatomical structure. Such detailed descriptions may increase our understanding of the pathogenetic mechanism and possible interventions for the treatment and prevention of foot and lower leg injuries, as well as the evolution of the human foot.

Digital volume correlation for the characterization of musculoskeletal tissues: Current challenges and future developments

Biological tissues are complex hierarchical materials, difficult to characterise due to the challenges associated to the separation of scale and heterogeneity of the mechanical properties at different dimensional levels. The Digital Volume Correlation approach is the only image-based experimental approach that can accurately measure internal strain field within biological tissues under complex loading scenarios. In this minireview examples of DVC applications to study the deformation of musculoskeletal tissues at different dimensional scales are reported, highlighting the potential and challenges of this relatively new technique. The manuscript aims at reporting the wide breath of DVC applications in the past 2 decades and discuss future perspective for this unique technique, including fast analysis, applications on soft tissues, high precision approaches, and clinical applications.

Subtalar joint middle facet agenesis: a case report and literature review

Articular facet morphology plays a fundamental role in subtalar joint biomechanics and stability, and likely influences the development of hindfoot osteoarthritis. While multiple anatomical studies have shown wide variation in articular facet configuration, the clinico-radiological findings are rarely presented. We illustrate a case of bilateral subtalar joint middle facet agenesis in a 45-year-old woman, which was missed despite several presentations. We demonstrate the imaging findings to enable clinicians to distinguish this from the more common middle facet coalition. We summarise the developmental anatomy and discuss the potential implications on biomechanical function. Recognition of middle facet agenesis within the complex subtalar joint is important to prevent misdiagnosis and unnecessary surgery.

Modelling the complexity of the foot and ankle during human locomotion: the development and validation of a multi-segment foot model using biplanar videoradiography

We developed and validated a multi-segment foot and ankle model for human walking and running. The model has 6-segments, and 7 degrees of freedom; motion between foot segments were constrained with a single oblique axis to enable triplanar motion [Joint Constrained (JC) model]. The accuracy of the JC model and that of a conventional model using a 6 degrees of freedom approach were assessed by comparison to segment motion determined with biplanar videoradiography. Compared to the 6-DoF model, our JC model demonstrated significantly smaller RMS differences [JC: 2.19° (1.43-2.73); 6-DoF: 3.25° (1.37-5.89)] across walking and running. The JC model is thus capable of more accurate musculoskeletal analyses and is also well suited for predictive simulations.

Is Advanced Imaging a Must in the Assessment of Progressive Collapsing Foot Deformity?

Advanced imaging modalities have, in very recent years, enabled a considerable leap in understanding progressive collapsing foot deformity, evolving from a simple confirmation of clinical diagnostic using basic measurements to minute understanding of soft tissue and bone involvements. MRI and weight-bearing cone-beam computed tomography are enabling the development of new 3-dimensional measurement modalities. The identification of key articular and joint markers of advanced collapse will allow surgeons to better indicate treatments and assess chances of success with conservative therapies and less invasive surgical procedures, with the hope of improving patient outcomes.

Evaluating lower limb kinematics and pathology with dynamic CT

Evaluating musculoskeletal conditions of the lower limb and understanding the pathophysiology of complex bone kinematics is challenging. Static images do not take into account the dynamic component of relative bone motion and muscle activation. Fluoroscopy and dynamic MRI have important limitations. Dynamic CT (4D-CT) is an emerging alternative that combines high spatial and temporal resolution, with an increased availability in clinical practice. 4D-CT allows simultaneous visualization of bone morphology and joint kinematics. This unique combination makes it an ideal tool to evaluate functional disorders of the musculoskeletal system. In the lower limb, 4D-CT has been used to diagnose femoroacetabular impingement, patellofemoral, ankle and subtalar joint instability, or reduced range of motion. 4D-CT has also been used to demonstrate the effect of surgery, mainly on patellar instability. 4D-CT will need further research and validation before it can be widely used in clinical practice. We believe, however, it is here to stay, and will become a reference in the diagnosis of lower limb conditions and the evaluation of treatment options. Cite this article: Bone Joint J 2021;103-B(5):822-827.

Effect of Lateral Column Lengthening on Subtalar Motion in a Cadaveric Model

BACKGROUND

Although lengthening of the lateral column through a calcaneal neck osteotomy is an integral component of flatfoot reconstruction in younger patients with flexible planovalgus deformities, concern exists as to the effect of this intra-articular osteotomy on subtalar motion. The purpose of this study was to quantify the alterations in subtalar motion following lateral column lengthening (LCL).

METHODS

The subtalar motion of 14 fresh-frozen cadaveric feet was assessed using a 3-dimensional motion capture system and materials testing system (MTS). Following potting of the tibia and calcaneus, optic markers were placed into the tibia, calcaneus, and talus. The MTS was used to apply a rotational force across the subtalar joint to a torque of 5 Nm. Abduction/adduction, supination/pronation, and plantarflexion/dorsiflexion about the talus were recorded. Specimens then underwent LCL via a calcaneal neck osteotomy, which was maintained with a 12-mm porous titanium wedge. Repeat subtalar motion analysis was performed and compared to pre-LCL motion using a paired t test.

RESULTS

No statistically significant differences in subtalar abduction/adduction (10.9 vs 11.8 degrees, P = .48), supination/pronation (3.5 vs 2.7 degrees, P = .31), or plantarflexion/dorsiflexion (1.6 vs 1.0 degrees, P = .10) were identified following LCL.

CONCLUSION

No significant changes in subtalar motion were observed following lateral column lengthening in this biomechanical cadaveric study.

CLINICAL RELEVANCE

Although these findings do not obviate concerns of clinical subtalar stiffness following lateral column lengthening for planovalgus deformity correction, they suggest that diminished postoperative subtalar motion, when it occurs, may be due to soft tissue scarring rather than alterations of joint anatomy.

In Vivo Deformation and Strain Measurements in Human Bone Using Digital Volume Correlation (DVC) and 3T Clinical MRI

Strains within bone play an important role in the remodelling process and the mechanisms of fracture. The ability to assess these strains in vivo can provide clinically relevant information regarding bone health, injury risk, and can also be used to optimise treatments. In vivo bone strains have been investigated using multiple experimental techniques, but none have quantified 3D strains using non-invasive techniques. Digital volume correlation based on clinical MRI (DVC-MRI) is a non-invasive technique that has the potential to achieve this. However, before it can be implemented, uncertainties associated with the measurements must be quantified. Here, DVC-MRI was evaluated to assess its potential to measure in vivo strains in the talus. A zero-strain test (two repeated unloaded scans) was conducted using three MRI sequences, and three DVC approaches to quantify errors and to establish optimal settings. With optimal settings, strains could be measured with a precision of 200 με and accuracy of 480 με for a spatial resolution of 7.5 mm, and a precision of 133 με and accuracy of 251 με for a spatial resolution of 10 mm. These results demonstrate that this technique has the potential to measure relevant levels of in vivo bone strain and to be used for a range of clinical applications.