The subtalar joint: biomechanics and functional representations in the literature

The foot and ankle complex as a four degrees-of-freedom system: Kinematic coupling among the foot bones

Seventy-eight parameters are theoretically needed to describe the relative position and orientation of all the 14 bones in the foot and ankle with respect to a reference bone (foot posture). However, articular contacts and soft tissues introduce kinematic coupling, reducing the number of the foot degrees-of-freedom (DOF). This study aims at providing quantification and definition of these couplings. The foot posture was measured in vitro through a series of computed tomography scans, spanning the whole range of foot dorsi/plantar flexion and pronation/supination, also considering the effect of weightbearing. The envelope of foot postures was investigated by means of principal component analysis. The foot and ankle motion were well described with four principal sets of kinematic couplings, that is, synergies. One synergy covers the independent motion of the ankle, while three synergies describe the foot motion. The first foot synergy shows all the bones rotating approximatively about a common axis, mapping the foot abduction/adduction about the Chopart joint. The second foot synergy results in a spherical motion, whose center is located between lateral cuneiform and navicular bone, mapping the foot pronation/supination. The third foot synergy maps the opening of the foot arches during the load acceptance. The foot and ankle complex can thus be described as a four DOF system, whose motion is the result of the linear combination of four synergies. Significance: Synergies reveal the contribution of each bone to the three-dimensional foot posture, providing a compact representation of the motion of the foot and ankle complex, improving the comprehension of its physiology.

Assistance force-line of exosuit affects ankle multidimensional motion: a theoretical and experimental study

BACKGROUND

The talocrural joint and the subtalar joint are the two major joints of the ankle-joint complex. The position and direction of the exosuit force line relative to these two joint axes can influence ankle motion. We aimed to understand the effects of different force-lines on ankle multidimensional motion.

METHODS

In this article, three assistance force line schemes for ankle exosuits were proposed: perpendicular to the talocrural joint axis (PT), intersecting with the subtalar joint axis (IS), and parallel to the triceps surae (PTS). A theoretical model was proposed to calculate the exosuit's assistance moment. Seven participants completed four experimental tests of ankle plantarflexion, including three passive motions assisted by the PT, PTS and IS schemes, and one active motion without exosuit assistance (Active).

RESULTS

The simulation results demonstrated that all three exosuits were able to produce significant moments of ankle plantarflexion. Among these, the PT scheme exhibited the highest moments in all dimensions, followed by the PTS and IS schemes. The experimental findings confirmed the effectiveness of all three exosuit schemes in assisting ankle plantarflexion. Additionally, as the assistive force lines approached the subtalar joint, there was a decrease in ankle motion assisted by the exosuits in non-plantarflexion directions, along with a reduction in the average distance of ankle angle curves relative to active ankle motion. Furthermore, the linear correlation coefficients between inversion and plantarflexion, adduction and plantarflexion, and adduction and inversion gradually converged toward active ankle plantarflexion motion.

CONCLUSIONS

Our research indicates that the position of the exosuit force line to the subtalar joint has a significant impact on ankle inversion and adduction. Among all three schemes, the IS, which has the closest distance to the subtalar joint axes, has the greatest kinematic similarity to active ankle plantarflexion and might be a better choice for ankle assistance and rehabilitation.

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.

Clinical outcomes following tibiotalocalcaneal arthrodesis with intramedullary nailing combined with partial fibulectomy and onlay bone graft

INTRODUCTION

Although intramedullary nailing is a popular method for tibiotalocalcaneal arthrodesis, nonunion is one of the most commonly reported complications. This study aimed to evaluate the fusion rate, improvement in functional outcomes, and occurrence of complications in tibiotalocalcaneal arthrodesis using retrograde intramedullary nailing with partial fibulectomy and onlay bone graft technique.

MATERIALS AND METHODS

Twenty-six consecutive patients using the proposed technique were retrospectively reviewed. For radiographic outcomes, the union rate, alignment, and any related complications were assessed. Functional outcomes were evaluated using the American Orthopedic Foot and Ankle Society hindfoot scale, Foot and Ankle Outcome Score, and visual analog scale, preoperatively and at the final follow-up.

RESULTS

The mean follow-up period was 38.2 months. The tibiotalar joint achieved complete union in 80.8% at six months postoperatively, while all the cases achieved complete union at 12 months postoperatively. However, the subtalar joint achieved complete union in 26.9% at six months postoperatively, which gradually increased to 73.1% at 12 months postoperatively, and 80.8% at the final follow-up without revision surgery. A subgroup analysis showed there was a trend of higher subtalar fusion rate when an additional screw for the subtalar joint fixation was placed (86.7% vs. 54.5%). The functional outcomes significantly improved at the final follow-up. A few minor complications occurred, including surgical site infection, irritational symptoms, and metal failure; however, they eventually resolved.

CONCLUSIONS

Our technique of tibiotalocalcaneal arthrodesis with partial fibulectomy and onlay bone grafting could be a good option where both the tibiotalar and subtalar joints need to be fused.

Automatic anatomical foot and ankle coordinate toolbox

Accurate analysis of bone position and orientation in foot and ankle studies relies on anatomical coordinate systems (ACS). Reliable ACSs are necessary for many biomechanical and clinical studies, especially those including weightbearing computed tomography and biplane fluoroscopy. Existing ACS approaches suffer from limitations such as manual input, oversimplifications, or non-physiological methods. To address these shortcomings, we introduce the Automatic Anatomical Foot and Ankle Coordinate Toolbox (AAFACT), a MATLAB-based toolbox that automates the calculation of ACSs for the major fourteen foot and ankle bones. In this manuscript, we present the development and evaluation of AAFACT, aiming to provide a standardized coordinate system toolbox for foot and ankle studies. The AAFACT was evaluated using a dataset of fifty-six models from seven pathological groups: asymptomatic, osteoarthritis, pilon fracture, progressive collapsing foot deformity, clubfoot, Charcot Marie Tooth, and cavovarus. Three analyses were conducted to assess the reliability of AAFACT. Firstly, ACSs were compared between automatically and manually segmented bone models to assess consistency. Secondly, ACSs were compared between individual bones and group mean bones to assess within-population precision. Lastly, ACSs were compared between the overall mean bone and group mean bones to assess the overall accuracy of anatomical representation. Statistical analyses, including statistical shape modeling, were performed to evaluate the reliability, accuracy, and precision of AAFACT. The comparison between automatically and manually segmented bone models showed consistency between the calculated ACSs. Additionally, the comparison between individual bones and group mean bones, as well as the comparison between the overall mean bone and group mean bones, revealed accurate and precise ACSs calculations. The AAFACT offers a practical and reliable solution for foot and ankle studies in clinical and engineering settings. It accommodates various foot and ankle pathologies while accounting for bone morphology and orientation. The automated calculation of ACSs eliminates the limitations associated with manual input and non-physiological methods. The evaluation results demonstrate the robustness and consistency of AAFACT, making it a valuable tool for researchers and clinicians. The standardized coordinate system provided by AAFACT enhances comparability between studies and facilitates advancements in foot and ankle research.

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

Patellar Dislocation: Workup and Decision-Making

Acute patellar dislocation (PD) is usually a problem of adolescents and young adults. In most cases, it is a sports-related injury. It is the result of an indirect force on the knee joint, which leads to valgus and external rotation of the tibia relative to the femur. PD is unlikely to occur on a knee with normal patellofemoral joint (PFJ) anatomy. Acute PD consists of an acute injury of the ligamentous medial patellar stabilizers in the background of factors predisposing to patellar instability. These factors are classified into three groups. The first group refers to the integrity of the ligamentous medial patellar restraints, particularly, the medial patellofemoral ligament (MPFL). The second group refers to an abnormal PFJ anatomy, which renders the patella inherently unstable inside the trochlea. The third group refers to the overall axial and torsional profile of the lower limb and to systemic factors, such as ligament laxity and neuromuscular coordination of movement. PD at a younger age is associated with an increased number and severity of patellar instability predisposing factors and lower stress to dislocate the patella. Acute primary PD is usually treated conservatively, while surgical treatment is reserved for recurrent PD. The aim of treatment is to restore the stability and function of the PFJ and to reduce the risk of patellar redislocation. Surgical procedures to treat patellar instability are classified into non-anatomic and anatomic procedures. Non-anatomic procedures are extensor mechanism realignment techniques that aim to center the patella into the trochlear groove. Anatomic procedures aim to restore the PFJ anatomy (ruptured ligaments, osteochondral fractures), which has been severed after the first incident of PD. Anatomic procedures, especially MPFL reconstruction, are more effective in preventing recurrent PD, compared with non-anatomic techniques. Theoretically, all factors that affect PFJ stability should be evaluated and, if possible, addressed. This is practically impossible. Considering that the MPFL ruptures in almost all PDs, MPFL reconstruction is the primary procedure, which is currently selected by most surgeons as a first-line treatment for patients with recurrent PD. Restoration of the axial and torsional alignment of the lower limbs is also increasingly implemented by surgeons. Non-anatomic surgical techniques, such as tibial-tuberosity osteotomy, are used as an adjunct to anatomic procedures. In the presence of multiple PFJ instability factors, acute MPFL reconstruction may be the treatment of choice for acute primary PD as well. Skeletal immaturity of the patient precludes osseous procedures to avoid premature physis closure and subsequent limb deformity. Unfortunately, restoration of the patient's previous activity level or participation in more strenuous sports is questionable and not easy to predict. In the case of competitive athletes, PD may prevent participation in elite levels of sports.

Factors influencing successful bone union of isolated subtalar arthrodesis for posttraumatic subtalar arthritis: a multicenter case series

BACKGROUND

The purpose of this study was to find the factors influencing successful bone union for isolated subtalar arthrodesis in posttraumatic subtalar arthritis following calcaneal fracture.

MATERIAL AND METHODS

We retrospectively analyzed the rate of successful bone union of 119 cases of isolated subtalar arthrodesis for posttraumatic subtalar arthritis performed at five university hospitals between January 2010 and December 2019. Multivariate logistic regression analysis was used to find the factors associated with successful bone union. Successful bone union was defined as resolution of hindfoot pain with the presence of osseous trabecular bridging involving more than 50% of the posterior facet within 6 months postoperatively.

RESULTS

There were 77 (64.7%) cases of successful bone union, 11 (9.2%) cases of delayed union, 8 (6.7%) cases of questionable union, and 23 (19.3%) cases of nonunion. Use of fully threaded screws was 5.90 times [odds ratio (OR) = 5.90, 95% confidence interval (CI) = 1.42-24.49, p = 0.02] more likely to achieve successful bone union compared to the use of partially threaded screws. Use of two parallel screws or the two divergent screws were 3.71 times (OR = 3.71, 95% CI = 1.05-13.14, p = 0.04) and 4.65 times (OR = 4.65, 95% CI = 1.23-17.53, p = 0.02) more likely to achieve successful bone union compared to the use of a single screw. Use of cancellous autograft or structural autograft was 4.72 times (OR = 4.72, 95% CI = 1.17-19.06, p = 0.03) and 7.12 times (OR = 7.12, 95% CI = 1.46-34.68, p = 0.02) more likely to achieve successful bone union compared to no graft use.

CONCLUSION

Use of fully threaded screws, autograft, and two screws compared to a single screw were the factors associated with successful bone union within six postoperative months after subtalar arthrodesis for the posttraumatic arthritis.

Intrinsic muscles of the foot: Anatomy, function, rehabilitation

The intrinsic muscles of the foot are underappreciated structures in evaluating and treating lower extremity dysfunction. These muscles play a crucial role in the proper function of the foot during sport activities. The functions of these muscles are not generally well understood. Intrinsic dysfunction can lead to a variety of problems. Therefore, it is important for clinicians to have a good understanding of the anatomy and function of the intrinsic foot muscles in order to properly diagnose and treat foot injuries in patients. Published research on the rehabilitation of the intrinsic muscles provides insight into the function as well as benefits of treatment. The purpose of this review is to summarize the published research on the anatomy, function, contribution to pathology, as well as rehabilitation options for the intrinsic muscles of the foot.

Analysis of Lower Extremity Motor Capacity and Foot Plantar Pressure in Overweight and Obese Elderly Women

BACKGROUND

Overweight, obesity and falls are major public health problems and old people are the biggest group suffering falls.

METHODS

92 females were divided into the overweight or obesity (O) group (68.85 ± 3.85) and regular-weight (R) group (67.90 ± 4.02). Lower extremity motor capacity and plantar pressure were compared between the two groups. The IRB approval number is 20190804.

RESULTS

(1) Functional Movement Screen and Fugl-Meyer Assessment scores in the O group were significantly lower than in the R group. The time to complete the Timed Up and Go test in the O group was significantly longer than in the R group. (2) Foot flat phase, double support distance, and left foot axis angle in the O group were significantly higher than in the R group. Distance and velocity, left-foot minimum subtalar joint angle and right-foot maximum subtalar joint angle in the O group were significantly shorter than in the R group. (3) Peak force, average force and pressure of metatarsal 1-4, mid-foot, heel medial and lateral, peak pressure of metatarsal l, midfoot, heel medial and lateral in the O group were significantly higher than in the R group. (p < 0.05).

CONCLUSIONS

Overweight and obese elderly women have a lower sensorimotor function, flexibility and stability in functional movements, but higher loads on the foot.

Effect of Simulated Bone Resorption on the Biomechanical Performance of Intramedullary Devices for Foot and Ankle Arthrodesis

Midfoot and subtalar arthrodesis surgeries are performed to correct foot deformities and relieve arthritic pain. These procedures often employ intramedullary (IM) devices. The aim of the present study was to evaluate the biomechanical performance of a sustained dynamic compression (SDC) IM device compared to mechanically static devices in withstanding the effects of simulated bone resorption. Mechanically static and SDC IM devices were implanted in simulated bone blocks (n = 5/device). Compressive loads were measured with a custom-made mechanism to simulate bone resorption. The construct bending stiffness was determined from a 4-point bend test. Resorption was simulated by cutting a 1 mm or 2 mm gap in the midpoint of each construct and repeating the loading (n = 6/device). Initial compressive loads after device insertion were greater in the SDC IM devices when compared to the static devices (p < .01). The SDC device was able to sustain compression from 2 mm to 5.5 mm of simulated resorption depending upon device length, while the static devices lost compression within 1 mm of simulated resorption regardless of implant length (p < .001). In the 4-point bend test, the SDC device maintained its bending stiffness during simulated resorption whereas the static device displayed a significant loss in bending stiffness after 1 mm of simulated resorption (p < .001). The SDC device exhibited a significantly higher bending stiffness than the static device (p < .001). The SDC IM device demonstrated superior biomechanical performance during simulated resorption compared to static devices (p < .001). In conclusion, the ability of SDC IM devices to maintain construct stability and sustain compression across the fusion site while adapting to bone resorption may lead to greater fusion rates and overall quicker times to fusion than static IM devices. Surgeons who perform midfoot and subtalar arthrodesis procedures should be aware of a device's ability to sustain compression, especially in cases where bone resorption and joint settling are prevalent postoperatively.

Turmell-Meter: A Device for Estimating the Subtalar and Talocrural Axes of the Human Ankle Joint by Applying the Product of Exponentials Formula

The human ankle is a complex joint, most commonly represented as the talocrural and subtalar axes. It is troublesome to take in vivo measurements of the ankle joint. There are no instruments for patients lying on flat surfaces; employed in outdoor or remote sites. We have developed a "Turmell-meter" to address these issues. It started with the study of ankle anatomy and anthropometry. We also use the product of exponentials' formula to visualize the movements. We built a prototype using human proportions and statistics. For pose estimation, we used a trilateration method by applying tetrahedral geometry. We computed the axis direction by fitting circles in 3D, plotting the manifold and chart as an ankle joint model. We presented the results of simulations, a prototype comprising 45 parts, specifically designed draw-wire sensors, and electronics. Finally, we tested the device by capturing positions and fitting them into the bi-axial ankle model as a Riemannian manifold. The Turmell-meter is a hardware platform for human ankle joint axes estimation. The measurement accuracy and precision depend on the sensor quality; we address this issue by designing an electronics capture circuit, measuring the real measurement with a Vernier caliper. Then, we adjust the analog voltages and filter the 10-bit digital value. The Technology Readiness Level is 2. The proposed ankle joint model has the properties of a chart in a geometric manifold, and we provided the details.

Monitoring the Role of Physical Activity in Children with Flat Feet by Assessing Subtalar Flexibility and Plantar Arch Index

Flat foot is a common pediatric foot deformity which involves subtalar flexibility; it can affect the plantar arch. This study analyzes the evolution of two parameters, i.e., plantar index arch and subtalar flexibility, before and after physiotherapy and orthoses interventions, and examines the correlation between these two parameters. Methods: The study included 30 participants (17 boys, 12 girls, average age 9.37 ± 1.42 years) with bilateral flat foot. We made two groups, each with 15 subjects. Assessments of the subtalar flexibility and plantar arch index used RSScan the platform, and were undertaken at two time points. Therapeutic interventions: Group 1—short foot exercises (SFE); Group 2—SFE and insoles. Statistical analyses included Student’s t-test, Cohen’s D coefficient, Pearson and Sperman correlation. Results: Group 1—subtalar flexibility decreased for the left and right feet by 28.6% and 15.9% respectively, indicating good evolution for the left foot. For both feet, a decrease of the plantar index arch was observed. Group 2—subtalar flexibility decreased for the right and left feet by 43.4% and 37.7% respectively, indicating a good evolution for the right foot. For both feet, a decrease of plantar index arch was observed. Between groups, subtalar flexibility evolved well for Group 2; this was attributed to mixt intervention, physical therapy and orthosis. For plantar arch index, differences were not significant between the two groups. We observed an inverse correlation between subtalar flexibility and plantar arch index. Conclusions: Improvement of plantar index arch in static and dynamic situations creates the premise of a good therapeutic intervention and increases foot balance and postural control. The parameter which showed the most beneficial influence was the evolution is subtalar flexibility.

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.

Surgical Outcomes of Articular Surface Crush Injury of Hawkins Ⅲ Talus Neck and Medial Malleolus Fracture

The present study was performed to evaluate the effects of the medial and anterolateral approach combined with internal fixation by double head compression screws and countersunk K-wires for Hawkins Ⅲ talus neck and medial malleolus fracture. Eleven patients with articular surface crush injury resulting in Hawkins Ⅲ talus neck fractures accompanied by medial malleolus fractures were reviewed. All patients underwent emergency operations. The fractures were fixed using double head compression screws and countersunk K-wires through combined medial and anterolateral approaches. FAOS, AOFAS ankle-hindfoot scale, and VAS questionnaire scores were recorded. In addition, ROM of the ankle and postoperative complications were assessed. All patients were followed up for a median of 52.45 ± 5.15 months. The multiple scales data of FAOS on the affected side were: pain score 89.14 ± 7.08; activities of daily living score 89.57 ± 8.88; quality-of-life score 89.20 ± 7.44; sports score 75.00 ± 15.49; and other symptoms score 84.74 ± 7.51. The mean overall AOFAS ankle-hindfoot score was 88.36 ± 6.39. The VAS score was 0.72 ± 0.65. Ankle motion included dorsiflexion (13.18° ± 9.02°) and plantar flexion (32.27° ± 12.34°). Subtalar joint motion included eversion (10.91° ± 7.01°) and inversion (11.36° ± 7.45°). All scores of the healthy side were higher than those of the affected side (p < .05). In addition to ROM of the ankle and subtalar joint and sports score, various indicators of recovery rate had scores > 80%. One patient developed skin necrosis, which healed after debridement and wound dressing. Late complications included subtalar and/or ankle traumatic arthritis in six patients, four of whom showed no obvious clinical symptoms. In conclusion, the method of emergency surgery and medial and anterolateral approach combined with countersunk K-wires to fix small bone fragments to restore the integrity of the articular surface is acceptable for Hawkins Ⅲ talus neck with medial malleolus fracture.

Do Patient Positioning and Portal Placement for Arthroscopic Subtalar Arthrodesis Matter?

Background

Arthroscopic subtalar arthrodesis was first described over 2 decades ago and originally performed in the lateral decubitus or supine position using anterolateral and posterolateral portals situated about the fibula. More recently, several authors have advocated for prone positioning utilizing posteromedial and posterolateral portals with an optional accessory lateral portal. To date, a comparison of these techniques has been limited.

Purpose

To determine the effect of patient positioning and portal placement on complication rates after arthroscopic subtalar arthrodesis.

Study Design

Systematic review; Level of evidence, 4.

Methods

A systematic review was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Patients were placed into 1 of 3 groups: the lateral group if they were positioned lateral or supine with lateral-based portals; the 2-portal prone group if they were positioned prone with posteromedial and posterolateral portals; or the 3-portal prone group if posteromedial, posterolateral, and accessory lateral portals were utilized in the prone position. Inverse variance-weighted fixed-effects models were used to evaluate pooled estimates.

Results

A total of 20 studies examining 484 feet in 468 patients with a mean follow-up of 36.1 months were included for analysis. Overall, 8 studies examined patients in the prone position with 2 posterior portals (n = 111; 22.9%), 7 articles evaluated lateral portals (n = 182; 37.6%), and 5 studies examined patients in the prone position with 3 portals (n = 191; 39.5%). The total complication rate was similar (P = .620) between the 2-portal prone (18.9%), 3-portal prone (17.8%), and lateral (17.6%) groups. There was no difference observed in the rate of complications secondary to portal placement (P ≥ .334), rate of painful hardware (P ≥ .497), and rate of repeat surgery (P ≥ .304). The 2-portal prone group had a significantly higher rate of nonunion than the lateral group (8.1% vs 1.1%, respectively; P = .020) but not the 3-portal prone group (5.8%; P = .198).

Conclusion

The current study demonstrated a higher rate of nonunion following arthroscopic subtalar arthrodesis with prone patient positioning using posteromedial and posterolateral portals without an accessory lateral portal.

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

Accurate in vivo quantification of subtalar joint kinematics can provide important information for the clinical evaluation of subtalar joint function; the analysis of outcome of surgical procedures of the hindfoot; and the design of a replacement subtalar joint prosthesis. The objective of the current study was to explore the potential of full weight-bearing clinical computed tomography (CT) to evaluate the helical axis and centre of rotation of the subtalar joint during inversion and eversion motion. A subject specific methodology was proposed for the definition of the subtalar joint motion combining three-dimensional (3D) weight-bearing imaging at different joint positions with digital volume correlation (DVC). The computed subtalar joint helical axis parameters showed consistency across all healthy subjects and in line with previous data under simulated loads. A sphere fitting approach was introduced for the computation of subtalar joint centre of rotation, which allows to demonstrate that this centre of rotation is located in the middle facet of the subtalar joint. Some translation along the helical axis was also observed, reflecting the elasticity of the soft-tissue restraints. This study showed a novel technique for non-invasive quantitative analysis of bone-to-bone motion under full weight-bearing of the hindfoot. Identifying different joint kinematics in patients with ligamentous laxity and instability, or in the presence of stiffness and arthritis, could help clinicians to define optimal patient-specific treatments.

Sex- and age-related morphological variations in the talar articular surfaces of the calcaneus

BACKGROUND

The prevalence of foot pathologies, such as flatfoot deformity and hallux valgus, is higher in women and increases with age. It has been reported that these types of foot disorders may also be linked to excessive mobility of the subtalar joint to the eversion direction during weight bearing. Given that the mobility of the joint is determined by its articular morphology, sex- and age-related variations in the subtalar articular surface morphology are possible. The purpose of this study was to investigate the orientation and the curvature radii of the talar articular facets of the calcaneus in relation to age and sex using three-dimensional computer tomography.

METHODS

Fifty-six feet without subtalar injuries or disorders were included in this study. The orientations of the talar articular surfaces of the calcaneus were quantified in the sagittal and coronal planes. The curvature radii of the articular surfaces of the calcaneus were also assessed based on the approximations of the sphere surfaces.

RESULTS

The talar articular surface was oriented more anteriorly and medially in the females than in the males. The curvature radius of the calcaneal posterior facet in the females exhibited a positive correlation with age, indicative of increased articular surface flattening.

CONCLUSIONS

The morphological features of the female calcaneus could induce excessive eversion and could lead to a higher prevalence of foot disorders, including flatfoot and hallux valgus, in elderly females. This study contributes to an understanding of the sexual dimorphism of the articular surfaces of the calcaneus and provides insight into the mechanisms that underline various foot disorders.

The Ankle-Joint Complex: A Kinesiologic Approach to Lateral Ankle Sprains

Copious research exists regarding ankle instability, yet lateral ankle sprains (LASs) persist in being among the most common recurrent musculoskeletal injuries. Key anatomical structures of the ankle include a triform articulating structure that includes the inferior tibiofibular, talocrural, and subtalar joints. Functionally, force absorption and propulsion through the ankle complex are necessary for any task that occurs in weight bearing. For optimal ankle performance and avoidance of injury, an intricate balance between stability and mobility is necessary to ensure that appropriate force transfer occurs during sports and activities of daily living. Consideration for the many structures that may be directly or indirectly involved in LASs will likely translate into advancements in clinical care. In this clinical review, we present the structure, function, and relevant pathologic states of the ankle complex to stimulate a better understanding of the prevention, evaluation, and treatment of LASs.

Adverse Events and Their Risk Factors Following Intra-articular Corticosteroid Injections of the Ankle or Subtalar Joint

BACKGROUND

Little data exists regarding the incidence of adverse events and their associated risk factors following intra-articular corticosteroid injection of the ankle and subtalar joint. The aim of this study was to determine the complication rate associated with such injections and to identify any predictive risk factors.

METHODS

Adult patients who had received an intra-articular ankle or subtalar joint injection between January 2000 and April 2016 at one of 3 regional hospitals (2 level 1 trauma centers and 1 community hospital) were included. Patients with prior intra-articular injection of corticosteroid into the ankle or subtalar joint were excluded. Explanatory variables were sex, age, race, body mass index, diabetes status, tobacco use, presence of fluoroscopic guidance, location of intra-articular injection, and administering physician's years of experience.

RESULTS

Of the 1708 patients included in the final cohort, 99 patients (5.8%) had a total of 104 adverse events within 90 days postinjection. The most prevalent types of adverse events were postinjection flare in 78 patients (4.6% of total cohort, 75% of adverse events) followed by skin reaction in 10 patients (0.6% of total cohort, 9% of adverse events). No infections were noted. Multivariable logistic regression analysis found that intra-articular injection in the subtalar ( P = .004) was independently associated with development of an adverse event. Fluoroscopic guidance was not found to be protective of an adverse event compared to nonguided injections ( P = .476).

CONCLUSION

The adverse event rate following intra-articular ankle or subtalar joint corticosteroid injection was 5.8%, with postinjection flare being the most common complication. Infections following injection were not reported. Injection into the subtalar joint was independently associated with the development of an adverse event after intra-articular corticosteroid injection, and this was not mitigated by the use of fluoroscopic guidance.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Anatomy of the Subtalar Joint

The subtalar joint is divided into the talocalcaneonavicular and the talocalcaneal joint, separated by a conical interosseous tunnel (canalis and sinus tarsi). The talocalcaneonavicular joint is a ball-and-socket articulation (coxa pedis). An important part of the coxa pedis is the spring ligament. The canalis and sinus tarsi are occupied by the roots of the inferior extensor retinaculum, cervical ligament, interosseous talocalcaneal ligament, and anterior talocalcaneal ligament. Three-dimensional motion in the subtalar joint complex (eversion/inversion) is guided by the axial alignment of the talus, calcaneus, and navicular; the ligaments; and the shape of the articular surfaces.

The subtalar joint: A complex mechanism

Subtalar joint anatomy is complex and can vary significantly between individuals.

Movement is affected by several adjacent joints, ligaments and periarticular tendons.

The subtalar joint has gained interest from foot and ankle surgeons in recent years, but its importance in hindfoot disorders is still under debate.

The purpose of this article is to give a general overview of the anatomy, biomechanics and radiographic assessment of the subtalar joint.

The influence of the subtalar joint on the evolution of ankle joint osteoarthritis is additionally discussed.

Cite this article: EFORT Open Rev 2017;2:309-316. DOI: 10.1302/2058-5241.2.160050

The dimensions of the tarsal sinus and canal in different foot positions and its clinical implications

This study presents a reference for the dimensions of the tarsal sinus and canal in healthy adults in different foot positions to facilitate understanding of the kinematics of the subtalar joint, the effect of an implant, and other clinical issues. In a 3D CT stress test on 20 subjects, the right foot was forced into a neutral and eight different extreme foot positions while CT scans were obtained. The bones were segmented in the neutral foot position. The kinematics of the bones in the extreme positions were determined relative to the neutral position. The dimensions of the tarsal sinus and canal were calculated by determining the radii of the maximal inscribed spheres at 20 equidistant locations along an axis in 3D surface models of the tali and calcanei in each foot position. The radii were small on the medial side and increased laterally. Medial from the middle, the radii were small and not significantly different among the various foot positions. At the lateral side, the dimensions were affected mainly by eversion or inversion and less by dorsiflexion or plantarflexion. The pattern was reproducible among subjects, but there were between-subject differences. The dimensions are mostly determined by rotation in the frontal plane. A pivot point was found medial from the middle. These data serve as a reference and model for predicting the effect of sinus implants and understanding such clinical problems as sinus tarsi syndrome. Between-subjects differences have to be taken into account. Clin. Anat. 30:1049-1057, 2017. © 2017 Wiley Periodicals, Inc.

Differences in Pes Planus and Pes Cavus subtalar eversion/inversion before and after prolonged running, using a two-dimensional digital analysis

In sports, there is a constant discussion about the hyper-pronation and supination of the foot during loading and its relation to injuries or discomfort. The purpose of the present study was to investigate the possible differences in the subtalar joint in the midstance phase of running, between individuals with Pes Planus and Pes Cavus, after 5 min and 45 min of running. Thirty-four subjects, meeting the requirements for Pes Planus (30 feet) and Pes Cavus (35 feet), according to the criteria for Medial Longitudinal Arch-angle, were included in the study. The calcaneal vertical angle, representing the eversion/inversion of the subtalar joint, was measured using with two-dimensional digital analysis and Dartfish Software with the subjects running barefoot on a treadmill, before and after 45 min of outside running wearing shoes. Both individuals with Pes Cavus and Pes Planus showed a significant increase in the calcaneal eversion (P<0.05) after 45 min of running. Between the groups, there was a significantly greater eversion of the Pes Planus, on the right foot, after 45 min of running (P<0.05) compared to the Pes Cavus. The effect of fatigue evident in the present study suggests that further biomechanical research should be considered when exposing the foot to the repetitive nature of running, conditions most likely responsible for the overrepresented overuse injuries among runners.

Gastrocnemius Contracture in Patients With and Without Foot Pathology

BACKGROUND

Several studies report performing a recession of the gastrocnemius tendon as surgical treatment of foot and ankle pain related to an isolated gastrocnemius contracture. Few report ankle range of motion using a validated measurement device or report a control group. All previous studies reporting measurements using a validated device have been small in number.

METHODS

Using a previously validated device, 66 patients presenting with foot or ankle pain and 66 controls were measured for ankle range of motion and isolated gastrocnemius contractures. Clinical and goniometer measurement of ankle range of motion was also performed.

RESULTS

The foot and ankle pain group had a mean dorsiflexion of 11.6 degrees compared with a mean of 17.2 degrees in the control group (P < .0001). No patients in either group had less than 15 degrees of motion with the knee flexed. The difference in dorsiflexion was less using a goniometer than using the validated device, which may be due to measurement technique and external landmarks.

CONCLUSION

Patients with foot and ankle pain had less ankle dorsiflexion than the control group. This is the largest study to date using a validated measurement device as well as a control group and supports the findings of previous authors.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Kinematic analysis of subtalar eversion during gait in women with fibromyalgia

OBJECTIVE

To analyse the subtalar eversion range of motion during walking in women with fibromyalgia.

METHOD

Twenty women diagnosed with fibromyalgia were directed to walk barefoot at comfortable and self-paced speed on a 7m walkway. Subtalar eversion range of motion was measured using the difference between the maximum and minimum values of subtalar eversion in stance phase. A range of motion between 4°-6° was considered as reference values for subtalar eversion during gait. Descriptive statistics were performed.

RESULTS

In both right and left lower limb analysis of subtalar eversion range of motion, five women showed joint hypomobility, and twelve showed hypermobility. Only one patient performed unaltered subtalar eversion range of motion in both lower limbs. Both joints expressed high variability, and there were no significant differences between the right and left sides.

CONCLUSIONS

The findings suggest that biomechanical function of the subtalar joint eversion during the loading response phase of gait in women with fibromyalgia, by excessive rigidity or complacency joint, tends to be impaired. This finding suggests that the indication of walking as an auxiliary strategy in the treatment of women with fibromyalgia should be preceded by thorough examination of the mechanical conditions of the subtalar joint of the patient.

Forefoot ulcer risk is associated with foot type in patients with diabetes and neuropathy

AIMS

To stratify the ulceration risk according to the foot morphology in people with diabetes and a history of forefoot neuropathic ulceration.

METHODS

A cross-sectional study was performed on 139 neuropathic individuals with diabetes and previous forefoot ulcers between January 2012 and February 2014. Foot position of the participants was evaluated by using the foot-posture index. A multivariate analysis adjusted for confounding variables was performed with the ulceration risk factors that were found in the univariate analysis.

RESULTS

Two hundred and fifty-eight feet were analysed, 104 (40.3%) feet had a history of ulceration on the forefoot and 154 (59.7%) feet had no previous ulceration. Two positive tests of neuropathy (p<0.001; CI[1.961-6.249] OR 3.500), presence of deformities (p=0.043; CI[1.020-3.599] OR 1.916) and foot type (p=0.039) showed an association with ulceration risk in multivariate analyses. Pronated feet showed a higher risk of ulceration than supinated feet (p=0.011; CI[1.253-5.708] OR 2.675), while significant differences between neutral and supinated feet were not found (p=0.221; CI[0.719-2.753] OR 1.476).

CONCLUSIONS

A pronated foot has a higher risk of ulceration on the forefoot in neuropathic people with deformities and diabetes mellitus. Foot type should be evaluated in people at risk of ulceration.

Biomechanical Evaluation of Strength and Stiffness of Subtalar Joint Arthrodesis Screw Constructs

BACKGROUND

Subtalar arthrodesis is a common treatment for end-stage subtalar joint arthritis as well as many other clinical problems. The best method of subtalar arthrodesis fixation is unknown. The purpose of this study was to compare the strength of subtalar arthrodesis fixation methods including a single posterior screw (SP), 2 posterior minimally divergent screws (MD) and a 2 screw highly divergent screw (HD) construct for subtalar arthrodesis.

METHODS

A biomechanical study was performed including the three different screw configurations (SP, MD, HD). These surrogate bone specimens were subjected to applied inversion and eversion torques about the subtalar joint axis on a servo-hydraulic load frame. Torsional stiffness of the construct and the maximum torque for each configuration were measured. Additionally, a cadaver study was performed using 5 fresh-frozen cadaver specimens. The perpendicular distance from the divergent screw guide-wire placement was measured from anatomic structures.

RESULTS

The HD screw configuration was found to have the highest torsional stiffness in both inversion and eversion, followed by the MD construct and then the SP construct. Similarly, the HD construct had the highest maximum torque versus the MD and SP constructs. All between-group differences were statistically significant (P < .05). The mean distance from key structures to the divergent screw included the sural nerve (13 mm), peroneus brevis tendon (18 mm), tibialis anterior tendon (8 mm), and tibialis posterior tendon (21 mm).

CONCLUSION

This biomechanical and cadaver study supports the use of 2 screws for fixation of subtalar arthrodesis over a single posterior screw. Additionally, we describe a biomechanically superior and potentially safe, alternative 2-screw divergent construct.

CLINICAL RELEVANCE

This study gives biomechanical support for 2 screw, divergent fixation of subtalar arthrodesis or a single over a single screw or two screw minimally divergent construct.