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.

Does Coronal Plane Malalignment of the Tibial Insert in Total Ankle Arthroplasty Alter Distal Foot Bone Mechanics? A Cadaveric Gait Study.

BACKGROUND: Total ankle arthroplasty (TAA) is becoming a more prevalent treatment for end-stage ankle arthritis. However, the effects of malalignment on TAA remain poorly understood. QUESTIONS/PURPOSES: The purpose of this study was to quantify the mechanical effects of coronal plane malalignment of the tibial insert in TAA using cadaveric gait simulation. Specifically, we asked, is there a change in (1) ankle joint congruency, (2) kinematic joint position, (3) kinematic ROM, (4) peak plantar pressure, and (5) center of pressure with varus and valgus malalignment? METHODS: A modified TAA was implanted into seven cadaveric foot specimens. Wedges were used to simulate coronal plane malalignment of the tibial insert. The degree of malalignment (tibial insert angle [TIA] and talar component angle [TCA]) was quantified radiographically for neutral and 5°, 10°, and 15° varus and valgus wedges. Dynamic walking at 1/6 of physiological speed was simulated using a robotic gait simulator. A motion capture system was used to measure foot kinematics, and a pressure mat was used to measure plantar pressure. Joint congruency was quantified as the difference between TIA and TCA. Continuous joint position, joint ROM, peak plantar pressure, and center of pressure for varus and valgus malalignment compared with neutral alignment were estimated using linear mixed effects regression. Pairwise comparisons between malalignment conditions and neutral were considered significant if both the omnibus test for the overall association between outcome and malalignment and the individual pairwise comparison (adjusted for multiple comparisons within a given outcome) had p ≤ 0.05. RESULTS: Descriptively, the TIA and TCA were both less pronounced than the wedge angle and component incongruence was seen (R = 0.65; p < 0.001). Varus malalignment of the tibial insert shifted the tibiotalar joint into varus and internally rotated the joint. The tibiotalar joint's ROM slightly increased as the TIA shifted into varus (1.3 ± 0.7° [mean ± SD] [95% confidence interval -0.7 to 3.4]; p = 0.03), and the first metatarsophalangeal joint's ROM decreased as the TIA shifted into varus (-1.9 ± 0.9° [95% CI -5.6 to 1.7]; p = 0.007). In the sagittal plane, the naviculocuneiform joint's ROM slightly decreased as the TIA shifted into varus (-0.9 ± 0.4° [95% CI -2.1 to 0.3]; p = 0.017). Hallux pressure increased as the TIA became more valgus (59 ± 50 kPa [95% CI -88 to 207]; p = 0.006). The peak plantar pressure slightly decreased in the third and fourth metatarsals as the TIA shifted into valgus (-15 ± 17° [95% CI -65 to 37]; p = 0.03 and -8 ± 4° [95% CI -17 to 1]; p = 0.048, respectively). The fifth metatarsal's pressure slightly decreased as the TIA shifted into valgus (-18 ± 12 kPa [95% CI -51 to 15]) or varus (-7 ± 18 kPa [95% CI -58 to 45]; p = 0.002). All comparisons were made to the neutral condition. CONCLUSIONS: In this cadaver study, coronal plane malalignment in TAA altered foot kinematics and plantar pressure. In general, varus TAA malalignment led to varus shift and internal rotation of the tibiotalar joint, a slight increase in the tibiotalar ROM, and a slight decrease in the first metatarsophalangeal ROM, while a valgus TAA malalignment was manifested primarily through increased hallux pressure with a slight off-loading of the third and fourth metatarsals. CLINICAL RELEVANCE: This study may increase our understanding of the biomechanical processes that underlie the unfavorable clinical outcomes (such as, poor patient-reported outcomes or implant loosening) that have been associated with coronal plane malalignment of the tibial component in TAA.

Neuropathy, claw toes, intrinsic muscle volume, and plantar aponeurosis thickness in diabetic feet.

BACKGROUND: The objective of this study was to explore the relationships between claw toe deformity, peripheral neuropathy, intrinsic muscle volume, and plantar aponeurosis thickness using computed tomography (CT) images of diabetic feet in a cross-sectional analysis. METHODS: Forty randomly-selected subjects with type 2 diabetes were selected for each of the following four groups (n = 10 per group): 1) peripheral neuropathy with claw toes, 2) peripheral neuropathy without claw toes, 3) non-neuropathic with claw toes, and 4) non-neuropathic without claw toes. The intrinsic muscles of the foot were segmented from processed CT images. Plantar aponeurosis thickness was measured in the reformatted sagittal plane at 20% of the distance from the most inferior point of the calcaneus to the most inferior point of the second metatarsal. Five measurement sites in the medial-lateral direction were utilized to fully characterize the plantar aponeurosis thickness. A linear mixed-effects analysis on the effects of peripheral neuropathy and claw toe deformity on plantar aponeurosis thickness and intrinsic muscle volume was performed. RESULTS: Subjects with concurrent neuropathy and claw toes had thicker mean plantar aponeurosis (p < 0.006) and may have had less mean intrinsic muscle volume (p = 0.083) than the other 3 groups. The effects of neuropathy and claw toes on aponeurosis thickness were synergistic rather than additive. A similar pattern may exist for intrinsic muscle volume, but results were not as conclusive. A negative correlation was observed between plantar aponeurosis thickness and intrinsic muscle volume (R2 = 0.323, p < 0.001). CONCLUSIONS: Subjects with concurrent neuropathy and claw toe deformity were associated with the smallest intrinsic foot muscle volumes and the thickest plantar aponeuroses. Intrinsic muscle atrophy and plantar aponeurosis thickening may be related to the development of claw toes in the presence of neuropathy.

Metatarsal Shape and Foot Type: A Geometric Morphometric Analysis.

Planus and cavus foot types have been associated with an increased risk of pain and disability. Improving our understanding of the geometric differences between bones in different foot types may provide insights into injury risk profiles and have implications for the design of musculoskeletal and finite-element models. In this study, we performed a geometric morphometric analysis on the geometry of metatarsal bones from 65 feet, segmented from computed tomography (CT) scans. These were categorized into four foot types: pes cavus, neutrally aligned, asymptomatic pes planus, and symptomatic pes planus. Generalized procrustes analysis (GPA) followed by permutation tests was used to determine significant shape differences associated with foot type and sex, and principal component analysis was used to find the modes of variation for each metatarsal. Significant shape differences were found between foot types for all the metatarsals (p < 0.01), most notably in the case of the second metatarsal which showed significant pairwise differences across all the foot types. Analysis of the principal components of variation showed pes cavus bones to have reduced cross-sectional areas in the sagittal and frontal planes. The first (p = 0.02) and fourth metatarsals (p = 0.003) were found to have significant sex-based differences, with first metatarsals from females shown to have reduced width, and fourth metatarsals from females shown to have reduced frontal and sagittal plane cross-sectional areas. Overall, these findings suggest that metatarsal bones have distinct morphological characteristics that are associated with foot type and sex, with implications for our understanding of anatomy and numerical modeling of the foot.

Does activity affect residual limb skin temperatures?

BACKGROUND: Many lower limb amputees experience thermal discomfort as a result of wearing a prosthesis. The development of new prosthetic technology to address thermal discomfort requires an understanding of how activity (or inactivity) affects residual limb skin temperatures and how skin temperatures are mapped across the skin-prosthesis interface. QUESTIONS/PURPOSES: We studied skin temperatures inside the socket and suspension system of unilateral transtibial amputees to determine the following: (1) Does residual limb skin temperature change as a function of activity and its cessation? (2) If changes occur, are there regional differences (circumferential or proximal-distal) in temperature? METHODS: Nine unilateral transtibial amputees provided informed consent to participate in this institutional review board-approved study. Residual limb skin temperatures inside their prosthesis were measured at 16 distributed sites using thermistor sensors and a portable data acquisition system. The 150-minute protocol began with a 60-minute seated rest, continued with a 30-minute treadmill walk at a self-selected speed, and concluded after a second 60-minute seated rest. Data from the last minute of each of the three periods were used for analysis. RESULTS: The skin temperature was 31.0° ± 1.5° C (mean ± SD) at the end of the initial rest period. After 30 minutes of treadmill walking, skin temperature increased to 34.1° ± 1.3° C, an increase of 3.1° C (95% confidence interval [CI], 2.4-3.8; p < 0.001). After the final 60 minutes of rest, the skin temperature was 33.2° ± 1.2° C, 0.9° C lower (95% CI, 0.5-1.2; p < 0.001) than at the end of treadmill walking but 2.2° C higher (95% CI, 1.4-2.9; p < 0.001) than the temperature observed at the end of the initial rest period. Skin temperatures were warmest over the tibialis anterior region (p < 0.006) and decreased from the most proximal to the most distal locations on the residual limb (p = 0.001). CONCLUSIONS: Walking causes a dramatic increase in skin temperatures inside the prosthesis and subsequent rest of twice the walking duration fails to return temperatures to their initial condition. Rest alone is likely to be insufficient to provide thermal relief without doffing the prosthesis. New prosthetic technology is needed to address this problem. Skin temperatures also varied by residual limb location, suggesting that the development of location-specific technology would be advantageous.

A method for automated masking and plantar pressure analysis using segmented computed tomography scans.

BACKGROUND: Plantar pressure, a common gait and foot biomechanics measurement, is typically analyzed using proprietary commercial software packages. Regional plantar pressure analysis is often reported in terms of underlying bony geometry, and recent advances in image processing and accessibility have made computed tomography, radiographs, magnetic resonance imaging, or other imaging methods more popular for incorporating bone analyses in biomechanics. RESEARCH QUESTION: Can a computed tomography-based regional mask provide comparable regional analysis to commercial plantar pressure software and can the increased flexibility of an in-house method obtain additional insight from common measurements? METHODS: A plantar pressure analysis method was developed based on bony geometry from computed tomography scans to calculate peak pressure, pressure time integral incorporating sub-peak values, force time integral, pressure gradient, and pressure gradient angle. Static and dynamic plantar pressure were acquired for 4 subjects (male, 65 ± 2.4 years). Plantar pressure variables were calculated using commercial and computed tomography-based systems. RESULTS: Dynamic peak pressure, pressure time integral, and force-time integral computed using the bone-based software was 5 % (9kPa), 7 % (0.3kPa-s) and 13 % (0.3 N-s) different than the commercial software on average. Region masks of the metatarsals and toes differed between commercial and computed tomography-based software due to subject-specific bone geometry and toe shape. Pressure time integral values incorporating sub-peak pressure were higher and demonstrated higher relative hindfoot values compared to those without. Removing step-on frames to static pressure analysis decreased forefoot pressures. Regional maps of peak pressure and maximum pressure gradient demonstrate different peak locations. SIGNIFICANCE: Computed tomography-based regional masks are comparable to commercial masks. Inclusion of static step-on frames and sub-peak pressures may change regional plantar pressure patterns. Differences in location of maximum pressure gradient and peak pressure may be useful for assessing subject specific injury risk.

Exploring the mechanical properties of 3D-printed multilayer lattice structures for use in accommodative insoles.

Full-contact insoles fabricated from multilayer foams are the standard of care (SoC) for offloading and redistributing high plantar pressures in individuals with diabetes at risk of plantar ulceration and subsequent lower limb amputation. These devices have regional variations in total thickness and layer thickness to create conformity with a patient's foot. Recent work has demonstrated that metamaterials can be tuned to match the mechanical properties of SoC insole foams. However, for devices fabricated using a multilayer lattice structure, having regional variations in total thickness and layer thickness may result in regional differences in mechanical properties that have yet to be investigated. Three lattices, two dual-layer and one uniform-layer lattice structure, designed to model the mechanical properties of SoC insoles, were 3D-printed at three structure/puck thicknesses representing typical regions seen in accommodative insoles. The pucks underwent cyclic compression testing, and the stiffness profiles were assessed. Three pucks at three structure/puck thicknesses fabricated from SoC foams were also tested. Initial evaluations suggested that for the latticed pucks, structure thickness and density inversely impacted puck stiffness. Behaving most like the SoC pucks, a dual-layer lattice that increased in density as structure thickness increased demonstrated consistent stiffness profiles across puck thicknesses. Identifying a lattice with constant mechanical properties at various structure thicknesses may be important to produce a conforming insole that emulates the standard of care from which patient-specific/regional lattice modulations can be made.

Ability of a multi-segment foot model to measure kinematic differences in cavus, neutrally aligned, asymptomatic planus, and symptomatic planus foot types.

BACKGROUND: Multi-segment foot models (MFMs) provide a better understanding of the intricate biomechanics of the foot, yet it is unclear if they accurately differentiate foot type function during locomotion. RESEARCH QUESTION: We employed an MFM to detect subtle kinematic differences between foot types, including: pes cavus, neutrally aligned, and asymptomatic and symptomatic pes planus. The study investigates how variable the results of this MFM are and if it can detect kinematic differences between pathologic and non-pathologic foot types during the stance phase of gait. METHODS: Independently, three raters instrumented three subjects on three days to assess variability. In a separate cohort, each foot type was statically quantified for ten subjects per group. Each subject walked while instrumented with a four-segment foot model to assess static alignment and foot motion during the stance phase of gait. Statistical analysis performed with a linear mixed effects regression. RESULTS: Model variability was highest for between-day and lowest for between-rater, with all variability measures being within the true sample variance. Almost all static measures (radiographic, digital scan, and kinematic markers) differed significantly by foot type. Sagittal hindfoot to leg and forefoot to leg kinematics differed between foot types during late stance, as well as coronal hallux to forefoot range of motion. The MFM had low between-rater variability and may be suitable for multiple raters to apply to a single study sample without introducing significant error. The model, however, only detected a few dynamic differences, with the most dramatic being the hallux to forefoot coronal plane range of motion. SIGNIFICANCE: Results only somewhat aligned with previous work. It remains unclear if the MFM is sensitive enough to accurately detect different motion between foot types (pathologic and non-pathologic). A more accurate method of tracking foot bone motion (e.g., biplane fluoroscopy) may be needed to address this question.

Normal and malaligned talonavicular fusion alters cadaveric foot pressure and kinematics.

Talonavicular (TN) fusion is a common treatment for TN arthritis or deformity correction. There is incongruous evidence regarding remaining motion at the talocalcaneal and calcaneocuboid joints after TN fusion. Additionally, the effects of a malaligned TN fusion are not well understood and alignment of the fusion may be important for overall foot integrity. This project assessed the kinematic and kinetic effects of neutral and malaligned TN fusions. Ten cadaveric feet were tested on a gait simulator in four conditions: unfused, fused in neutral, fused in varus, and fused in valgus. The fusions were simulated with external fixation hardware. An eight-camera motion analysis system and a 10-segment foot model generated kinematic data, and a pressure mat captured pressure data. Simulated TN fusion was achieved in eight feet. From unfused to fused-neutral, range of motion (ROM) was not eliminated in the adjacent joints, but the positions of the joints changed significantly throughout stance phase. Furthermore, the ROM increased at the tibiotalar joint. Plantar pressure and center of pressure shifted laterally with neutral fusion. The malalignments marginally affected the ROM but changed joint positions throughout stance phase. Pressure patterns were shifted laterally in varus malalignment and medially in valgus malalignment. The residual motion and the altered kinematics at the joints in the triple joint complex after TN fusion may subsequently increase the incidence of arthritis. Clinical significance: This study quantifies the effects of talonavicular fusion and malalignment on the other joints of the triple joint complex.

Subject-specific material properties of the heel pad: An inverse finite element analysis.

Individuals with diabetes are at a higher risk of developing foot ulcers. To better understand internal soft tissue loading and potential treatment options, subject-specific finite element (FE) foot models have been used. However, existing models typically lack subject-specific soft tissue material properties and only utilize subject-specific anatomy. Therefore, this study determined subject-specific hindfoot soft tissue material properties from one non-diabetic and one diabetic subject using inverse FE analysis. Each subject underwent cyclic MRI experiments to simulate physiological gait and to obtain compressive force and three-dimensional soft tissue imaging data at 16 phases along the loading-unloading cycles. The FE models consisted of rigid bones and nearly-incompressible first-order Ogden hyperelastic skin, fat, and muscle (resulting in six independent material parameters). Then, calcaneus and loading platen kinematics were computed from imaging data and prescribed to the FE model. Two analyses were performed for each subject. First, the skin, fat, and muscle layers were lumped into a single generic soft tissue material and optimized to the platen force. Second, the skin, fat, and muscle material properties were individually determined by simultaneously optimizing for platen force, muscle vertical displacement, and skin mediolateral bulging. Our results indicated that compared to the individual without diabetes, the individual with diabetes had stiffer generic soft tissue behavior at high strain and that the only substantially stiffer multi-material layer was fat tissue. Thus, we suggest that this protocol serves as a guideline for exploring differences in non-diabetic and diabetic soft tissue material properties in a larger population.

The effect of prior compression tests on the plantar soft tissue compressive and shear properties.

Changes in the shear plantar soft tissue properties with diabetes are believed to play a role in plantar ulceration, yet little is known about these properties. Our group recently conducted shear tests on specimens previously tested in compression to fully characterize the tissue under both these loading modes. However, previously tested specimens may not necessarily provide representative mechanical properties as prior testing may have altered the tissue to an unknown extent. Thus, the purpose of this study was to test the effect of prior compression testing on both the plantar soft tissue shear and compressive properties using paired specimens. First, one specimen from each pair was subject to compression using our standard protocol with modifications to compare compressive properties before and after the protocol while the other specimen from each pair was left untested. Then, both specimens (i.e., one previously compression tested and one previously untested) were subject to shear testing. The results indicate that prior compression testing may affect the tissue compressive properties by reducing peak stress and modulus; however, additional testing is needed since these results were likely confounded by stress softening effects. In contrast, neither the elastic nor the viscoelastic plantar soft tissue shear properties were affected by prior testing in compression, indicating that previously compression tested specimens should be viable for use in future shear tests. However, these results are limited given the small sample size of the study and the fact that only nondiabetic specimens were examined.

Role of Robotic Gait Simulators in Elucidating Foot and Ankle Pathomechanics.

Testing with cadaveric foot and ankle specimens began as mechanical techniques to study foot function and then evolved into static simulations of specific instances of gait, before technologies were eventually developed to fully replicate the gait cycle. This article summarizes the clinical applications of dynamic cadaveric gait simulation, including foot bone kinematics and joint function, muscle function, ligament function, orthopaedic foot and ankle pathologies, and total ankle replacements. The literature was reviewed and an in-depth summary was written in each section to highlight one of the more sophisticated simulators. The limitations of dynamic cadaveric simulation were also reviewed.

Regional differences in the mechanical properties of the plantar aponeurosis.

The plantar aponeurosis functions to support the foot arch during weight bearing. Accurate anatomy and material properties are critical in developing analytical and computational models of this tissue. We determined the cross-sectional areas and material properties of four regions of the plantar aponeurosis: the proximal middle and distal middle portions of the tissue and the medial (to the first ray) and lateral (to the fifth ray) regions. Bone-plantar aponeurosis-bone specimens were harvested from fifteen cadaveric feet. Cross-sectional areas were measured using molding, casting, and sectioning methods. Mechanical testing was performed using displacement control triangle waves (0.5, 1, 2, 5, and 10 Hz) loaded to physiologic tension by estimating from body weight and area ratio of the region. Five specimens were tested for each region. Regional deformations were recorded by a high-speed video camera. There were overall differences in cross-sectional areas and biomechanical behavior across regions. The stress-strain responses are non-linear and mainly elastic (energy loss 3.6% to 7.2%). Moduli at the proximal middle and distal middle regions (400 and 522 MPa) were significantly higher than the medial and lateral regions (225 and 242 MPa). The effect of frequency on biomechanical outcomes was small (e.g., 3.5% change in modulus), except for energy loss (107% increase as frequency increased from 0.5 to 10 Hz). These results indicate that the plantar aponeurosis tensile response is non-linear, nearly elastic, and frequency independent. The cross-sectional area and material properties differ by region, and we suggest that such differences be included to accurately model this structure.

The effect of diabetes and tissue depth on adipose chamber size and plantar soft tissue features.

BACKGROUND: Plantar ulceration is a serious complication of diabetes. However, the mechanism of injury initiating ulceration remains unclear. The unique structure of the plantar soft tissue includes superficial and deep layers of adipocytes contained in septal chambers, however, the size of these chambers has not been quantified in diabetic or non-diabetic tissue. Computer-aided methods can be leveraged to guide microstructural measurements and differences with disease status. METHODS: Adipose chambers in whole slide images of diabetic and non-diabetic plantar soft tissue were segmented with a pre-trained U-Net and area, perimeter, and minimum and maximum diameter of adipose chambers were measured. Whole slide images were classified as diabetic or non-diabetic using the Axial-DeepLab network, and the attention layer was overlaid on the input image for interpretation. RESULTS: Non-diabetic deep chambers were 90 %, 41 %, 34 %, and 39 % larger in area (26,954 ± 2428 µm2 vs 14,157 ± 1153 µm2), maximum (277 ± 13 µm vs 197 ± 8 µm) and minimum (140 ± 6 µm vs 104 ± 4 µm) diameter, and perimeter (405 ± 19 µm vs 291 ± 12 µm), respectively, than the superficial (p < 0.001). However, there was no significant difference in these parameters in diabetic specimens (area 18,695 ± 2576 µm2 vs 16627 ± 130 µm2, maximum diameter 221 ± 16 µm vs 210 ± 14 µm, minimum diameter 121 ± 8 µm vs 114 ± 7 µm, perimeter 341 ± 24 µm vs 320 ± 21 µm). Between diabetic and non-diabetic chambers, only the maximum diameter of the deep chambers differed (221 ± 16 µm vs 277 ± 13 µm). The attention network achieved 82 % accuracy on validation, but the attention resolution was too coarse to identify meaningful additional measurements. CONCLUSIONS: Adipose chamber size differences may provide a basis for plantar soft tissue mechanical changes with diabetes. Attention networks are promising tools for classification, but additional care is required when designing networks for identifying novel features. DATA AVAILABILITY: All images, analysis code, data, and/or other resources required to replicate this work are available from the corresponding author upon reasonable request.

Prospective Multicenter Study of Salto Talaris Ankle Arthroplasty With Minimum 4-Year Follow-Up.

BACKGROUND: Total ankle arthroplasty (TAA) continues to be investigated as a primary treatment for end-stage ankle arthritis. The objective of this study is to report mid- to long-term results of the Salto Talaris TAA using prospectively collected patient-reported outcomes and implant survival rates with 4- to 13-year follow-up. METHODS: This was a retrospective study of prospectively collected data from 2 multicenter cohort studies from 3 centers. Three hundred fourteen subjects who received a Salto Talaris TAA from 2005 to 2015 were included in the study. Follow-up ranged 4-13 years following index procedure. Outcomes included 36-Item Short Form Health Survey (SF-36) mental and physical component summary scores, pain scores, and adverse events including additional surgeries, revision, or removal of components. RESULTS: Significant improvements were seen in pain and physical function scores at 2-year follow-up and were generally maintained through most recent follow-up. The survival rate of the prosthesis was >95% (n = 30/32 at >10 years, n = 272/282 at 4.5-10 years). Thirteen patients (4.1%) underwent revision or removal of their prosthesis. Time to revision ranged from 2 months to 6.5 years following the index procedure. Twenty-two patients (7.0%) had additional surgery that did not involve revision or removal of components. CONCLUSION: Treatment of end-stage ankle arthritis with this implant provided patients with improved pain and functional outcome scores at mid- to long-term follow-up. The significant improvements reported at 2-4 years appeared to endure through the extended follow-up period. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Second metatarsal length is positively correlated with increased pressure and medial deviation of the second toe in a robotic cadaveric simulation of gait.

BACKGROUND: The term `crossover second toe' has been used to describe a deformity of the second metatarsophalangeal joint (MTPJ) that includes a progressive migration of the second toe in a dorsal and medial direction. The long onset and complex anatomy of the deformity has led to uncertainty about its etiology and treatment. The purpose of this study was to investigate the relationship between second metatarsal length and second MTPJ plantar pressure and joint angles during gait. We hypothesized that elongation of the second metatarsal would increase the plantar pressure underneath the second MTPJ and be associated with a deviation of the MTPJ angles in a dorsal and medial direction. METHODS: Incremental surgical elongation of the second metatarsal was performed on six cadaveric feet. A robotic gait simulator (RGS) simulated physiologic tibial motion, tendon loading, and ground reaction forces (GRF) on the cadaveric feet. We determined the peak pressure and pressure-time integral under the second MTPJ during gait, as well as the transverse and sagittal MTPJ angles. RESULTS: Second metatarsal peak pressure and pressure-time integral were positively correlated with an increase in second metatarsal length. First metatarsal peak pressure and pressure-time integral were significantly negatively associated with second metatarsal length. MTPJ transverse plane angle was positively associated with second metatarsal length but sagittal angle was not. CONCLUSION: Our results support the hypothesis that second metatarsal length is positively associated with medial deviation of the second toe and increased plantar pressure underneath the second MTPJ. CLINICAL RELEVANCE: It is biomechanically plausible that this association could lead to the joint instability seen in crossover toe patients.

Comparative gait analysis of ankle arthrodesis and arthroplasty: initial findings of a prospective study.

BACKGROUND: Little is known about functional outcomes of ankle arthroplasty compared with arthrodesis. This study compared pre-surgical and post-surgical gait measures in both patient groups. METHODS: Eighteen patients with end-stage ankle arthritis participated in an ongoing longitudinal study (pre-surgery, 12 months post-surgery) involving gait analysis, assessment of pain and physical function. Outcome measures included temporal-distance, kinematic and kinetic data, the Short Form 36 (SF-36) body pain score, and average daily step count. A mixed effects linear model was used to detect effects of surgical group (arthrodesis and arthroplasty, n = 9 each) with walking speed as a covariate (α = 0.05). RESULTS: Both groups were similar in demographics and anthropometrics. Followup time was the same for each group. There were no complications in either group. Pain decreased (p < 0.001) and gait function improved (gait velocity, p = 0.02; stride length, p = 0.035) in both groups. Neither group increased average daily step count. Joint range of motion (ROM) differences were observed between groups after surgery (increased hip ROM in arthrodesis, p = 0.001; increased ankle ROM in arthroplasty, p = 0.036). Peak plantar flexor moment increased in arthrodesis patients and decreased in arthroplasty patients (p = 0.042). CONCLUSION: Initial findings of this ongoing clinical study indicate pain reduction and improved gait function 12 months after surgery for both treatments. Arthroplasty appears to regain more natural ankle joint function, with increased ROM. Long-term follow up should may reveal more clinically meaningful differences.

Foot radiographic angle variation as a function of weightbearing magnitude.

Weightbearing radiographs are widely used to investigate foot disorders. However, it is unclear how imaging during partial weightbearing affects foot alignment measurements. This study aimed to determine a partial weightbearing threshold that yields consistent measurements of various radiographic angles. Eighteen normal fresh-frozen cadaveric foot specimens were dissected and prepared for mechanical testing using a custom-designed, computed tomography-compatible loading frame. Specimens were placed in a neutral ankle position and scanned in five axial loading conditions (0%, 12.5%, 25%, 37.5%, and 50% bodyweight) using weightbearing computed tomography. (Note 50% bodyweight per foot represents full bodyweight in quiet stance.) The lateral first talometatarsal and calcaneal pitch angles were measured on lateral radiographic projections, and the hallux valgus angle and first-second, fourth-fifth, and first-fifth intermetatarsal angles were measured on axial projection images. The lateral first talometatarsal angle decreased significantly with increased bodyweight loading (p < 0.01). Mean significant decreases in the lateral first talometatarsal angle compared to 0% were 6.6° for 12.5%, 7.6° for 25%, 8.8° for 37.5%, and 10.0° for 50% bodyweight loading; 12.5% to 50% was also significant. There was no significant differences between other loading condition pairings or with increased axial load at other angles. The medial longitudinal arch flattened with increasing axial load, resulting in a decreased lateral first talometatarsal angle. However, this radiographic parameter did not change between the 25% and 50% bodyweight conditions, indicating that partial weightbearing imaging (between 12.5% and 25% bodyweight) might be enough to reproduce the sagittal foot alignments observed under full weightbearing conditions in normal feet.

Displacement of the Metatarsal Sesamoids in Relation to First Metatarsophalangeal Joint Extension.

Background: Quantifying normal sesamoid movement in relation to first metatarsophalangeal joint (MTPJ1) motion is essential to identifying aberrant kinematics and understanding how they may contribute to forefoot pain and dysfunction. The present study aims to report sesamoid displacement in relation to MTPJ1 extension and to compare sesamoid displacement with MTPJ1 range of motion (ROM) from several imaging modalities. Methods: Using 10 fresh frozen cadaveric feet, sesamoid displacement was evaluated during simulated MTPJ1 extension. The ability of 3 MTPJ1 measurement techniques (goniometry, fluoroscopy, and unloaded cone beam computed tomography [CBCT]) in predicting sesamoid displacement were compared. Kinematics were expressed in a coordinate frame based on the specimen-specific first metatarsal anatomy, and descriptive statistics are reported. Results: In the sagittal plane in both neutral and maximally extended positions, the tibial sesamoid was located on average more anteriorly than the fibular sesamoid. The angular displacement of the tibial and fibular sesamoids in the sagittal plane were 30.2 ± 14.3 degrees and 35.8 ± 10.6 degrees, respectively. In the transverse plane, both sesamoids trended toward the body midline from neutral to maximum extension. The intersesamoidal distance remained constant throughout ROM. Of the 3 measurement techniques, MTPJ1 ROM from CBCT correlated best (R 2 = 0.62 and 0.81 [P < .05] for the tibial and fibular sesamoid, respectively) with sagittal plane sesamoid ROM. Conclusion: The sesamoids were displaced anteriorly and medially in relation to increasing MTPJ1 extension. CBCT was the most correlated clinical imaging technique in relating MTPJ1 extension with sesamoid displacement. Clinical Significance: This study advances our understanding of the biomechanical function of the sesamoids, which is required for both MTPJ1 pathology interventions and implant design. These findings support the use of low-dose CBCT as the information gathered provides more accurate detail about bone position compared with other imaging methods.

Evaluation of the Foot Arch in Partial Weightbearing Conditions.

BACKGROUND: Weightbearing plain radiography or computed tomography (CT) is used for diagnosis or treatment selection in foot disorders. This study compared foot alignment between full weightbearing (50% body weight [BW] per foot) plain radiography and nonweightbearing (0% BW) or partial weightbearing (10% BW per foot) CT scans. METHODS: Subjects had both full (50% BW per foot) weightbearing plain radiographs and either a nonweightbearing (0% BW) or a partial weightbearing (20% BW or 10% BW per foot) CT scan. Feet (n = 89) had been previously classified as pes cavus (n = 14/17 [subjects/feet]), neutrally aligned (NA; 20/30), asymptomatic pes planus (APP; 18/24), and symptomatic pes planus (SPP; 15/18). Lateral talometatarsal angle (LTMA) and calcaneal pitch angle were compared between weightbearing radiography and maximum-intensity projection images generated from CT. RESULTS: Significant differences in LTMA were found between nonweightbearing CT scans and full (50% BW per foot) weightbearing plain radiographs: the mean difference was 6.6 degrees in NA, 9.2 degrees in APP, and 11.3 degrees in SPP (P < .0001); no significant difference in LTMA was found for pes cavus. Although the interaction of foot type (P = .084) approached statistical significance, pairwise differences between 10% weightbearing and 50% weightbearing images by foot type were significant but small. The 50% weightbearing condition resulted in calcaneal pitch angles the same or slightly lower or higher than those of the 10% weightbearing and nonweightbearing images. LTMA and calcaneal pitch angle measurements made on full (50% BW per foot) weightbearing plain radiographs and non- (0%) or partial (10% BW per foot) weightbearing angles from CT scans were strongly correlated. CONCLUSION: Different foot types have similar 2-dimensional sagittal plane morphologies with partial weightbearing (10% BW per foot) CT scans and, to a lesser degree, nonweightbearing (0%) neutral-position CT scans when compared to full weightbearing (50% BW per foot) plain radiographs. LEVEL OF EVIDENCE: Level III, retrospective case control study.