Torque-ratio-adjustable ankle-foot exoskeleton for resisting perturbation in forward direction within fan-shaped region of pelvis horizontal plane.

Introduction: The ankle-foot exoskeleton has been demonstrated to help users resist anterior perturbation in the horizontal pelvis plane. However, its effects on perturbations in other directions remain unclear. This paper focuses on how the ankle-foot exoskeleton helps people resist perturbations coming from forward directions within the fan-shaped region in the pelvis horizontal plane. Methods: Firstly, we proposed and validated a hypothesis that the human torque ratio of inversion to plantar flexion torque would change with the perturbation directions of anterior (dir0) and 45° deviating from anterior to left (dir45). Subsequently, based on the regulation demand, we developed an ankle-foot exoskeleton that can adjust the torque ratio delivered to the human body by controlling the forces on two cross-arranged cables. Finally, we evaluated and compared the assistance performance of three powered assistive modes (NM, medBD, and latBD) with the unpowered one (UN) by setting different force pairs in two cables. Results: The results showed that, with the assistance, the margin of stability was increased and the standard deviations of ankle-foot segmental movements were decreased. Meanwhile, the biological inversion torque has a significant difference among the three assistive modes. Compared to the UN, the latBD was shown to reduce the biological inversion torque by 15.8 % and 13.7 % in response to the dir0 and dir45 perturbations, respectively, while the reductions for the NM and medBD were smaller. It was also observed that the torque ratios, generated by the human and the exoskeleton in latBD mode, differed by about 0.1 under dir0 and 0.08 under dir45, while the physiologically similarity of the exoskeleton torque ratio in NM and medBD modes were smaller. Based on the above results, we found that the more physiologically similar the exoskeleton torque ratio, the better the assistive performance. Discussion: The findings demonstrated that the torque-ratio-adjustable exoskeleton could support human resistance to perturbations coming from forward directions within a fan-shaped region in the pelvis horizontal plane and indicated that the exoskeleton's torque ratio should be carefully modulated to match the ratio of the human under various environmental conditions for better assistive performance.

Acute traumatic subtalar dislocation: A rare but important clinical entity with 15-year retrospective radiological analysis of 23 cases.

Objectives: The objectives of this study were to contribute to the limited existing knowledge about subtalar dislocations, analyze the computed tomography (CT) findings and advantages over radiography, and report the rate and potential risk factors of post-traumatic peri-talar osteoarthritis (OA). Material and Methods: A total of 23 cases of traumatic subtalar dislocation during a 15-year period at three regional hospitals were retrospectively reviewed. Results: All 23 cases were closed dislocations. Successful close reduction was performed in 17 patients (73.9%) and 6 patients (26.1%) required open reduction and internal fixation. Twenty patients (87%) had associated foot and ankle fractures. Fractures of calcaneal medial tubercle were the most common (75%), followed by talar head (30%), sinus tarsi (25%), and medial malleolus (25%). The radiograph's sensitivity for identifying fractures was 48.1%. The mean follow-up period is 30 months. Symptomatic OA affected 8 patients (36.4%). No post-trauatic talar avascular necrosis was noted. Fractures were present in all of those patients with post-traumatic OA (100%). Three out of five patients who sustained high-energy mechanism injury developed radiographic OA (66.7%). Three out of six patients (50%) treated with open reduction and internal fixation also developed radiographic OA. Conclusion: Subtalar dislocation remains a rare injury. It is strongly associated with foot and ankle fractures. Fractures of the calcaneal medial tubercle were the most common. The risk of post-traumatic symptomatic peritalar OA is high. CT is useful in detecting occult fractures and injured bony subregions. We postulated potential risk factors of post-traumatic OA (fracture, high-energy mechanism of injury, open reduction, and internal fixation); however, this requires further study.

Total Closed Talar Dislocation without Ankle Fracture: A Case Report.

We report a case of a 61-year-old female who presented to the emergency room after a fall from stairs. A total closed talar dislocation without talus or ankle fracture was diagnosed. The treating surgeon indicated an open reduction after an unsuccessful attempt at closed reduction. After six months of follow-up, the patient reported mild pain and partial weight-bearing with no discomfort; however, signs of talar avascular necrosis were present on magnetic resonance images and CT scans.

Parallel versus Angulated Screw Configuration in Subtalar Arthrodesis for Posttraumatic Arthritis.

Background: To compare radiographic union and clinical outcomes between parallel and angulated screw configurations (SCs) for patients undergoing subtalar arthrodesis due to posttraumatic subtalar arthritis (PSA) after displaced intra-articular calcaneal fractures. Methods: This study retrospectively reviewed 140 consecutive PSA cases from March 2011 to November 2021 (parallel SC: group 1, n = 80; angulated SC: group 2, n = 60). Radiographic union, Foot and Ankle Outcome Score (FAOS), and visual analog scale (VAS) scores were among the outcome assessments. Six months after surgery, nonunion was confirmed based on plain radiographs, clinical evaluation, and computed tomography. Results: Groups 1 and 2 included 14 (17.5%) and 3 (5.0%) nonunion cases, respectively (p = 0.035). There was no significant difference in preoperative FAOS and VAS scores between the groups. However, group 2 had significantly better clinical outcomes in 2 of the 5 FAOS domains (sports and quality of life), as well as VAS scores at 3 and 6 months postoperatively and at the final follow-up (p < 0.05). Conclusions: Using the angulated SC for PSA had a lower nonunion rate and superior clinical outcomes than the parallel SC. Obtaining better radiological and clinical outcomes when using the angulated SC, rather than the parallel SC, would be advantageous.

Management and classification of the fracture of lateral process of talus: An overview and literature update.

Fracture of the lateral process of the talus (FLPT) is uncommon in clinical practice and can be easily missed or misdiagnosed. In recent years, as researchers from all over the world have further deepened their research on FLPT, there has been a breakthrough in the classification, and the methods and principles of clinical management have changed accordingly; however, there is still no standardized guideline for the diagnosis and management of FLPT, and there have been few relevant literature review articles related to this kind of fracture in the past at least 5 years. In this article, we review the clinical classification, classification-based therapeutic recommendations, and prognosis of FLPT, with the aim of providing a reference for the clinical diagnosis and management of this infrequent fracture.

Clinical outcomes of subtalar arthroereisis for the treatment of stage 1 flexible progressive collapsing foot deformity.

BACKGROUND: The use of subtalar arthroereisis as an adjunct to the surgical treatment of stage 1 flexible progressive collapsing foot deformity (PCFD) is controversial. The aim was to investigate the clinical outcomes and report the implant removal rate of subtalar arthroereisis as an adjunct for stage 1 PCFD. METHODS: A retrospective study of 212 consecutive feet undergoing operative management of stage 1 PCFD with adjunctive subtalar arthroereisis between October 2010 and April 2018. The primary outcome was the Foot and Ankle Outcome Score (FAOS). Secondary outcomes included Foot and Ankle Disability Index (FADI), Euroqol-5D-5L Index and implant removal rate. RESULTS: Post-operative clinical FAOS outcomes were collected for 153 feet (72.2%). At mean 2.5-year follow-up, the mean ± standard deviation FAOS for each domain was as follows; Pain: 81.5 ± 18.5, Symptoms: 79.5 ± 12.9, Activities of Daily Living: 82.5 ± 15.4 and Quality of Life: 64.2 ± 23.7. EQ-5D-5L Index was 0.884 ± 0.152. Pre-operative scores were available for 20 of these feet demonstrating a statistically significant improvement in all FAOS, FADI and EQ-5D-5L domains (p < 0.05). The implant removal rate for persistent sinus tarsi pain was 48.1% (n = 102). CONCLUSION: Use of a subtalar arthroereisis implant as an adjunct to conventional procedures in stage 1 flexible PCFD can result in significant improvement in pain and function. Patients should be counselled as to the relatively frequent rate of subsequent implant removal. LEVEL OF EVIDENCE: IV.

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.

Hindfoot kinematics and kinetics - A combined in vivo and in silico analysis approach.

BACKGROUND: The complex anatomical structure of the foot-ankle imposes challenges to accurately quantify detailed hindfoot kinematics and estimate musculoskeletal loading parameters. Most systems used to capture or estimate dynamic joint function oversimplify the anatomical structure by reducing its complexity. RESEARCH QUESTION: Can four dimensional computed tomography (4D CT) imaging in combination with an innovative foot manipulator capture in vivo hindfoot kinematics during a simulated stance phase of walking and can talocrural and subtalar articular joint mechanics be estimated based on a detailed in silico musculoskeletal foot-ankle model. METHODS: A foot manipulator imposed plantar/dorsiflexion and inversion/eversion representing a healthy stance phase of gait in 12 healthy participants while simultaneously acquiring 4D CT images. Participant-specific 3D hindfoot rotations and translations were calculated based on bone-specific anatomical coordinate systems. Articular cartilage contact area and contact pressure of the talocrural and subtalar joints were estimated using an extended foot-ankle model updated with an elastic foundation contact model upon prescribing the participant-specific rotations measured in the 4D CT measurement. RESULTS: Plantar/dorsiflexion predominantly occurred at the talocrural joint (RoM 15.9±3.9°), while inversion/eversion (RoM 5.9±3.9°) occurred mostly at the subtalar joint, with the contact area being larger at the subtalar than at the talocrural joint. Contact pressure was evenly distributed between the talocrural and subtalar joint at the beginning of the simulated stance phase but was then redistributed from the talocrural to the subtalar joint with increasing dorsiflexion. SIGNIFICANCE: In a clinical case study, the healthy participants were compared with four patients after surgically treaded intra-articular calcaneal fracture. The proposed workflow was able to detect small but meaningful differences in hindfoot kinematics and kinetics, indicative of remaining hindfoot pathomechanics that may influence the onset and progression of degenerative joint diseases.

Closed medial subtalar dislocation: A case report and literature review.

Subtalar dislocation is characterized by simultaneous dislocation of the subtalar (talocalcaneal) and talonavicular joints, hence the name talocalcaneonavicular. These lesions can be grouped into four distinct categories: anterior and posterior, which are exceptional, lateral and medial. Medial subtalar dislocations are more frequent, are due to low-energy trauma and generally have good functional results. Anatomical reduction and stabilization of the subtalar joint and optimal management of all associated foot injuries are the key to good results.

Does the Sagittal Radiographic Morphology of Subtalar Joint Affect the Alignment of Foot?

OBJECTIVES: The etiology of flatfoot and cavus foot is multicausal and controversial. So far, no literature reports the relationship between the sagittal morphology of subtalar joint and the alignment of foot. The purpose of this study was to explore whether the subtalar alignment would influence the configuration of foot. METHODS: From January 2017 to January 2020, we included 109 feet in the flatfoot group, 95 feet in the cavus group, and 104 feet in the control group in this retrospective comparative study. The Gissane angle and calcaneal posterior articular surface inclination angle represented the sagittal morphology of the subtalar joint. Meary's angle, calcaneal pitch angle, and talar pitch angle reflected the alignment of foot. They were measured in the weightbearing foot X-rays. The angles in different groups were compared via Mann-Whitney U test. We calculated the correlation between the sagittal alignment of subtalar joint and the alignment of foot using Spearman's correlation analysis. Interobserver and intraobserver reliability were calculated. RESULTS: The Gissane angle, calcaneal posterior articular surface inclination angle, Meary's angle, talar pitch angle, and calcaneal pitch angle were significantly different in the three groups. The Gissane angle had an excellent correlation with the Meary's angle (r = 0.850, p < 0.0001), and the talar pitch angle (r = -0.825, p < 0.0001), and a good correlation with the calcaneal pitch angle (r = 0.638, p < 0.0001). The calcaneal posterior articular surface inclination angle had an excellent correlation with the Meary's angle (r = -0.902, p < 0.001), and the talar pitch angle (r = 0.887, p < 0.0001), and a good correlation with the calcaneal pitch angle (r = -0.702, p < 0.0001). The interobserver and intraobserver reliability for all radiographic measurements was good to excellent. CONCLUSION: A subtalar joint with a larger Gissane angle and a more horizontal calcaneal posterior articular surface angle tended to have a higher foot arch and vice versa. The inspiration from this study was that the deformities of flatfoot and cavus foot may relate to the subtalar deformity.

Effects of added trunk load on the in vivo kinematics of talocrural and subtalar joints during landing.

BACKGROUND: Landing from heights is a common movement for active-duty military personnel during training. And the additional load they carry while performing these tasks can affect the kinetics and ankle kinematic of the landing. Traditional motion capture techniques are limited in accurately capturing the in vivo kinematics of the talus. This study aims to investigate the effect of additional trunk load on the kinematics of the talocrural and subtalar joints during landing, using a dual fluoroscopic imaging system (DFIS). METHODS: Fourteen healthy male participants were recruited. Magnetic resonance imaging was performed on the right ankle of each participant to create three-dimensional (3D) models of the talus, tibia, and calcaneus. High-speed DFIS was used to capture the images of participants performing single-leg landing jumps from a height of 40 cm. A weighted vest was used to apply additional load, with a weight of 16 kg. Fluoroscopic images were acquired with or without additional loading condition. Kinematic data were obtained by importing the DFIS data and the 3D models in virtual environment software for 2D-3D registration. The kinematics and kinetics were compared between with or without additional loading conditions. RESULTS: During added trunk loading condition, the medial-lateral translation range of motion (ROM) at the talocrural joint significantly increased (p < 0.05). The subtalar joint showed more extension at 44-56 ms (p < 0.05) after contact. The subtalar joint was more eversion at 40-48 ms (p < 0.05) after contact under the added trunk load condition. The peak vertical ground reaction force (vGRF) significantly increased (p < 0.05). CONCLUSIONS: With the added trunk load, there is a significant increase in peak vGRF during landing. The medial-lateral translation ROM of the talocrural joint increases. And the kinematics of the subtalar joint are affected. The observed biomechanical changes may be associated with the high incidence of stress fractures in training with added load.

Subtalar Osteochondral Lesions: Diagnosis, Indications, and Prognosis.

Although most commonly found in the knee, elbow, and talar dome, osteochondral lesions can also be found in the subtalar joint and can occur due to either high or low energy trauma. Diagnosis of these lesions in the subtalar joint is typically confirmed with advanced imaging such as computerized tomography and MRI. Although there are a few published case reports, there is otherwise very limited literature on the prevalence, treatment options, prognosis, or outcomes for patients with osteochondral lesions of the subtalar joint, and thus further research is required in this area.

The Relationship Between Calcaneofibular Ligament Injury and Ankle Osteoarthritis Progression: A Comprehensive Analysis of Stress Distribution and Osteophyte Formation in the Subtalar Joint.

BACKGROUND: Ankle osteoarthritis (OA) mainly arises from trauma, particularly lateral ligament injuries. Among lateral ligament injuries, ankles with calcaneofibular ligament (CFL) injuries exhibit increased instability and can be a risk factor ankle OA progression. However, the relationship between CFL injury and OA progression remains unclear. Therefore, this study aims to assess the relationship between CFL injuries and ankle OA by investigating stress changes and osteophyte formation in subtalar joint. METHODS: We retrospectively reviewed the magnetic resonance imaging (MRI) and plain radiographic evaluations of 100 ankles of 91 patients presenting with chronic ankle instability (CAI), ankle OA, or other ankle conditions. The association between CFL injuries on the oblique view of MRI and the severity of ankle OA (based on Takakura-Tanaka classification) was statistically evaluated. Additionally, 71 ankles were further subjected to CT evaluation to determine the association between the CFL injuries and the Hounsfield unit (HU) ratios of the subtalar joint and medial gutter, and the correlation between the subtalar HU ratios and osteophyte severity were statistically evaluated. RESULTS: CFL injury was observed in 35.9% (14/39) of patients with stage 0, 42.9% (9/21) with stage 1, 50.0% (10/20) with stage 2, 100% (9/9) with stage 3a, and 90.9% (10/11) with stage 3b. CFL-injured ankles exhibited higher HU ratios in the medial gutter and lower ratios in the medial posterior subtalar joint compared to uninjured ankles. A negative correlation was observed between medial osteophyte severity and the medial subtalar joint HU ratio. CONCLUSION: Our findings suggest that CFL injuries are common in severe ankle OA impairing the compensatory function of the subtalar joint through abnormal stress distribution and osteophyte formation. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Hindfoot joint kinematics analysis after the resection of talocalcaneal coalition.

BACKGROUND: The subtalar joint movement between the talus and calcaneus is restricted in patients with talocalcaneal coalition (TCC). When the motion of the subtalar joint is restricted, shock absorption in the foot decreases, leading to pain during walking. Resection methods to maintain subtalar motion by removing abnormal unions have been proposed. The purpose of this study was to analyze the joint kinematics of patients who underwent TCC resection and to quantitatively evaluate the results of the surgery based on the measured kinematics. METHODS: Joint kinematics of five patients with TCC were obtained using a biplane fluoroscopic imaging system and an intensity-based two-/three-dimensional registration method. The joint kinematics of the tibiotalar and subtalar joints and the tibiocalcaneal motion during the stance phase of walking were obtained. From the kinematics of the hindfoot joints, the inversion/eversion range of motion (ROM) of the patients before and after resection was statistically analyzed using the Wilcoxon signed-rank test to test whether TCC resection improved the ROM. RESULTS: During the loading response period, the eversion ROM of the subtalar joint and tibiocalcaneal motion significantly increased postoperatively. In addition, a significant postoperative increase was observed in the subtalar and tibiocalcaneal inversion ROM during the pre-swing period. SIGNIFICANCE: TCC resection surgery increased the ROM of the subtalar joint, which in turn contributed to the increase in tibiocalcaneal ROM. Increased subtalar and tibiocalcaneal ROM could result in increased shock attenuation and may be a contributing factor to pain relief during walking.

Design, Characterization, and Preliminary Assessment of a Two-Degree-of-Freedom Powered Ankle-Foot Prosthesis.

Powered ankle prostheses have been proven to improve the walking economy of people with transtibial amputation. All commercial powered ankle prostheses that are currently available can only perform one-degree-of-freedom motion in a limited range. However, studies have shown that the frontal plane motion during ambulation is associated with balancing. In addition, as more advanced neural interfaces have become available for people with amputation, it is possible to fully recover ankle function by combining neural signals and a robotic ankle. Accordingly, there is a need for a powered ankle prosthesis that can have active control on not only plantarflexion and dorsiflexion but also eversion and inversion. We designed, built, and evaluated a two-degree-of-freedom (2-DoF) powered ankle-foot prosthesis that is untethered and can support level-ground walking. Benchtop tests were conducted to characterize the dynamics of the system. Walking trials were performed with a 77 kg subject that has unilateral transtibial amputation to evaluate system performance under realistic conditions. Benchtop tests demonstrated a step response rise time of less than 50 milliseconds for a torque of 40 N·m on each actuator. The closed-loop torque bandwidth of the actuator is 9.74 Hz. Walking trials demonstrated torque tracking errors (root mean square) of less than 7 N·m. These results suggested that the device can perform adequate torque control and support level-ground walking. This prosthesis can serve as a platform for studying biomechanics related to balance and has the possibility of further recovering the biological function of the ankle-subtalar-foot complex beyond the existing powered ankles.

Enhancing Post-Surgical Rehabilitation Outcomes in Patients with Chronic Ankle Instability: Impact of Subtalar Joint Axis Balance Exercises Following Arthroscopic Modified Broström Operation.

Background and Objectives: This study aimed to evaluate the effects of subtalar joint axis-based balance exercises on the anterior talofibular ligament (ATFL) thickness, ankle strength, and ankle stability after an arthroscopic modified Broström operation (AMBO) for chronic ankle instability (CAI). Materials and Methods: The study included 47 patients diagnosed with CAI who underwent AMBO and were randomly divided into three groups: control (n = 11), general balance exercise (n = 17), and subtalar joint axis balance exercise (n = 19), regardless of the affected area. Participants in the exercise rehabilitation group performed exercises for 60 min twice a week for six weeks, starting six weeks after AMBO. ATFL thickness, ankle strength, and ankle dynamic stability were measured using musculoskeletal ultrasonography, Biodex, and Y-balance test, respectively, before and after treatment. Results: Compared with the remaining groups, the subtalar joint axis balance exercise group had reduced ATFL thickness (p = 0.000), improved ankle strength for eversion (p = 0.000) and inversion (p = 0.000), and enhanced ankle stability (p = 0.000). Conclusions: The study results suggest that subtalar joint axis-based balance exercises may contribute to the early recovery of the ankle joint after AMBO.

Biomechanical Effects of Subtalar Joint Fusion and Medial Ligament Reconstruction in Simulated Progressive Collapsing Foot Deformity.

BACKGROUND: The purpose of this study is to investigate the biomechanical effect of medial displacement calcaneal osteotomy (MDCO), subtalar joint fusion (SF), and medial ligament reconstruction (MLR: deltoid-spring ligament) in a severe flatfoot model. We hypothesized that (1) combination of MDCO and SF improves the tibiotalar and foot alignment in severe progressive collapsing foot deformity (PCFD) cadaver model. (2) However, if a residual valgus heel alignment remains after MCDO and SF, it can lead to increased medial ligament strain, foot malalignment, and tibiotalar valgus tilt, which will be mitigated by the addition of MLR. METHODS: Ten fresh-frozen cadaveric foot specimens were used to create a severe flatfoot model. The foot alignment changes, including the talo-first metatarsal angle in the axial and sagittal planes, subtalar angle, and tibiotalar angle in the coronal plane, were measured. The angles were measured at the initial condition, after creating the severe flatfoot model, and after each successive reconstructive procedure in the following order: (1) MDCO, (2) SF, and (3) MLR. RESULTS: Tibiotalar valgus tilt was decreased with the MDCO procedure: 4.4 vs 1.0 degrees (P = .04). Adding in situ SF to the MDCO led to increased tibiotalar tilt to 2.5 degrees was different from the initial condition (P = .01). Although the tibiotalar valgus tilt was significantly decreased after adding the MLR to the MDCO/SF procedure compared with the severe flatfoot model (0.8 vs 4.4 degrees, P = .03), no significant difference in the tibiotalar valgus tilt was observed between MDCO/SF and MDCO/SF with MLR. CONCLUSION: Our results demonstrated that MDCO significantly improved forefoot abduction and medial arch alignment, with no significant additional improvement observed with addition of SF. Following SF, a residual valgus heel alignment can contribute to subsequent tibiotalar valgus tilt. The addition of MLR did not show significantly decreased tibiotalar valgus tilt following SF. CLINICAL RELEVANCE: Residual valgus heel alignment after subtalar joint fusion in the surgical treatment of PCFD can lead to increased medial ligament strain. Although MLR might be considered for providing medial stability, it may not necessarily prevent the development of tibiotalar valgus tilt.

The morphology of osseous structure in subtalar joint with chronic ankle instability.

BACKGROUND: Osseous structures have been demonstrated as risk factors for chronic ankle instability (CAI). Previously, the researchers only focused on the osseous structures of ankle, but ignored the osseous structures of subtalar joint(STJ). Accordingly, the aim of our study was to investigate the morphological characteristics of STJ osseous structures in CAI. METHODS: 52 patients with CAI and 52 sex- and age- matched control subjects were enrolled from The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University. The lateral radiographs of ankle in weight-bearing were used to compare the diversity of the two groups. Specifically, The Length of calcaneus, Calcaneal facet height and Absolute foot height, Böhler's angle, Gissane's angle, Calcaneal inclination angle, Talocalcaneal angle, Tibiotalar angle, Tibiocalcaneal angle, Talar-horizontal angle, talar declination angle, facet inclination angle were gauged in the two groups. RESULTS: The Böhler's angle, Calcaneal inclination, Talocalcaneal angle, Tibiotalar angle, Talar-horizontal angle, Talar declination angle, Facet inclination angle and Absolute foot height of CAI group were significantly higher than normal control group (P < 0.05). There were no significant differences in Gissane's angle, Tibiocalcaneal angle, Length of calcaneus and Calcaneal facet height between patients with CAI and normal controls (P > 0.05). CONCLUSIONS: The osseous structures of STJ in CAI patients are different from normal people in morphology. Therefore, we should pay more attention to the changes of STJ anatomical parameters in the diagnosis and prevention of CAI. LEVEL OF EVIDENCE: Ⅲ.

Defining the Structures at Risk and an Anatomical Safe Zone for Percutaneous Antegrade Subtalar Joint Fixation With a Single Screw: A Cadaveric Study.

Percutaneous antegrade (anterior to posterior) fixation for subtalar joint (STJ) arthrodesis offers various intraoperative and biomechanical advantages. Currently, the entry point for percutaneous antegrade STJ screw fixation is not clearly described and variable. To our knowledge, there are no publications that evaluate anatomic structures at risk or define an anatomically safe entry point for this fixation. The aim of this investigation was to define an anatomically safe and reproducible entry point for percutaneous antegrade STJ arthrodesis fixation, while also describing anatomic structures at risk when undertaking this method of fixation. We hypothesized that percutaneous single screw antegrade STJ fixation would encroach upon named anatomic structures in more than one cadaveric specimen. Ten cadaver limbs were used in this investigation. A percutaneous guidewire was inserted 5 mm lateral to the tibialis anterior tendon. The midpoint of the talar neck served as the sagittal plane starting point, as seen on the lateral fluoroscopic view. A cannulated 6.5-mm headed screw was inserted antegrade through the STJ into the calcaneus. Each specimen was dissected to assess the distance from the screw to nearby anatomic structures and distance from the tibialis anterior tendon to named structures. Our hypothesis was found to be incorrect, as 0/10 screws invaded neurovascular or tendinous structures. The dorsalis pedis artery and deep peroneal nerve were on average 12.1 ± 2.79 mm and 12.2 ± 2.82 mm lateral to the screw, respectively. These findings are clinically relevant and ultimately allow us to define an anatomic safe starting point for percutaneous antegrade STJ single screw fixation.

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].