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.

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.

Acute and Chronic Subtalar Joint Instability: Does It Really Exist?

Acute and chronic subtalar instability and commonly coexistent with other hindfoot pathology but can be difficult to diagnose. A high degree of clinical suspicion is required as most imaging modalities and clinical maneuvers are poor at detecting isolated subtalar instability. The initial treatment is similar to ankle instability, and a wide variety of operative interventions have been presented in the literature for persistent instability. Outcomes are variable and limited.

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.

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.

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.

Mortality and Conversion to Transfemoral Amputation After Transtibial Amputation in the Veterans Affairs Health System.

INTRODUCTION: Transtibial below-knee amputation (BKA) is associated with considerable morbidity, particularly in the vasculopathic population. The purpose of this study was to determine the cumulative probability of undergoing transfemoral above-knee amputation (AKA) conversion within 5 years of BKA and associated risk factors while accounting for the competing risk of death. METHODS: This is a retrospective, national database study with structured query of the Veterans Affairs (VA) database for patients who underwent BKA from 1999 to 2020, identified by Current Procedural Terminology codes. Above-knee amputation conversion was identified using Current Procedural Terminology codes in combination with natural language processing to match procedure laterality. After internally validating our patient identification method, risk factors were collected. Competing risk analysis estimated the cumulative incidence rate of AKA conversion and associated risk factors with death as a competing risk. RESULTS: Our query yielded 19,875 patients (19,640 men, 98.8%) who underwent BKA with a median age of 66 years (interquartile range, 60 to 73). The median follow-up was 951 days (interquartile range, 275 to 2,026). The crude cumulative probabilities of AKA conversion and death at 5 years were 15.4% (95% confidence interval [CI], 14.9% to 16.0%) and 47.7% (95% CI, 46.9% to 48.4%), respectively. In the Fine and Gray subdistribution hazard model, peripheral vascular disease had the highest AKA conversion risk (hazard ratio [HR] 2.66; 95% CI, 2.22 to 3.20; P < 0.001). Other factors independently associated with AKA conversion included urgent operation (HR 1.32; 95% CI, 1.23 to 1.42), cerebrovascular disease (HR 1.19; 95% CI, 1.11 to 1.28), chronic obstructive pulmonary disease (HR 1.15; 95% CI, 1.07 to 1.24), and previous myocardial infarction (HR 1.10; 95% CI, 1.02 to 1.19) (All P < 0.02). DISCUSSION: Within this predominantly male, VA population, BKA carries a high risk of conversion to AKA within 5 years, without reaching a steady risk of AKA conversion within 5 years. Peripheral vascular disease, chronic obstructive pulmonary disease, cerebrovascular disease, previous myocardial infarction, and urgent BKA increase the risk of AKA conversion. LEVEL OF EVIDENCE: Level III.

A robotic cadaveric flatfoot analysis of stance phase.

The symptomatic flatfoot deformity (pes planus with peri-talar subluxation) can be a debilitating condition. Cadaveric flatfoot models have been employed to study the etiology of the deformity, as well as invasive and noninvasive surgical treatment strategies, by evaluating bone positions. Prior cadaveric flatfoot simulators, however, have not leveraged industrial robotic technologies, which provide several advantages as compared with the previously developed custom fabricated devices. Utilizing a robotic device allows the researcher to experimentally evaluate the flatfoot model at many static instants in the gait cycle, compared with most studies, which model only one to a maximum of three instances. Furthermore, the cadaveric tibia can be statically positioned with more degrees of freedom and with a greater accuracy, and then a custom device typically allows. We created a six degree of freedom robotic cadaveric simulator and used it with a flatfoot model to quantify static bone positions at ten discrete instants over the stance phase of gait. In vivo tibial gait kinematics and ground reaction forces were averaged from ten flatfoot subjects. A fresh frozen cadaveric lower limb was dissected and mounted in the robotic gait simulator (RGS). Biomechanically realistic extrinsic tendon forces, tibial kinematics, and vertical ground reaction forces were applied to the limb. In vitro bone angular position of the tibia, calcaneus, talus, navicular, medial cuneiform, and first metatarsal were recorded between 0% and 90% of stance phase at discrete 10% increments using a retroreflective six-camera motion analysis system. The foot was conditioned flat through ligament attenuation and axial cyclic loading. Post-flat testing was repeated to study the pes planus deformity. Comparison was then made between the pre-flat and post-flat conditions. The RGS was able to recreate ten gait positions of the in vivo pes planus subjects in static increments. The in vitro vertical ground reaction force was within ± 1 standard deviation (SD) of the in vivo data. The in vitro sagittal, coronal, and transverse plane tibial kinematics were almost entirely within ± 1 SD of the in vivo data. The model showed changes consistent with the flexible flatfoot pathology including the collapse of the medial arch and abduction of the forefoot, despite unexpected hindfoot inversion. Unlike previous static flatfoot models that use simplified tibial degrees of freedom to characterize only the midpoint of the stance phase or at most three gait positions, our simulator represented the stance phase of gait with ten discrete positions and with six tibial degrees of freedom. This system has the potential to replicate foot function to permit both noninvasive and surgical treatment evaluations throughout the stance phase of gait, perhaps eliciting unknown advantages or disadvantages of these treatments at other points in the gait cycle.

Multi-rigid image segmentation and registration for the analysis of joint motion from three-dimensional magnetic resonance imaging.

We report an image segmentation and registration method for studying joint morphology and kinematics from in vivo magnetic resonance imaging (MRI) scans and its application to the analysis of foot and ankle joint motion. Using an MRI-compatible positioning device, a foot was scanned in a single neutral and seven other positions ranging from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation. A segmentation method combining graph cuts and level set was developed. In the subsequent registration step, a separate rigid body transformation for each bone was obtained by registering the neutral position dataset to each of the other ones, which produced an accurate description of the motion between them. The segmentation algorithm allowed a user to interactively delineate 14 foot bones in the neutral position volume in less than 30 min total (user and computer processing unit [CPU]) time. Registration to the seven other positions took approximately 10 additional minutes of user time and 5.25 h of CPU time. For validation, our results were compared with those obtained from 3DViewnix, a semiautomatic segmentation program. We achieved excellent agreement, with volume overlap ratios greater than 88% for all bones excluding the intermediate cuneiform and the lesser metatarsals. For the registration of the neutral scan to the seven other positions, the average overlap ratio is 94.25%, while the minimum overlap ratio is 89.49% for the tibia between the neutral position and position 1, which might be due to different fields of view (FOV). To process a single foot in eight positions, our tool requires only minimal user interaction time (less than 30 min total), a level of improvement that has the potential to make joint motion analysis from MRI practical in research and clinical applications.

Evaluating foot kinematics using magnetic resonance imaging: from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation.

The foot consists of many small bones with complicated joints that guide and limit motion. A variety of invasive and noninvasive means [mechanical, X-ray stereophotogrammetry, electromagnetic sensors, retro-reflective motion analysis, computer tomography (CT), and magnetic resonance imaging (MRI)] have been used to quantify foot bone motion. In the current study we used a foot plate with an electromagnetic sensor to determine an individual subject's foot end range of motion (ROM) from maximum plantar flexion, internal rotation, and inversion to maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation. We then used a custom built MRI-compatible device to hold each subject's foot during scanning in eight unique positions determined from the end ROM data. The scan data were processed using software that allowed the bones to be segmented with the foot in the neutral position and the bones in the other seven positions to be registered to their base positions with minimal user intervention. Bone to bone motion was quantified using finite helical axes (FHA). FHA for the talocrural, talocalcaneal, and talonavicular joints compared well to published studies, which used a variety of technologies and input motions. This study describes a method for quantifying foot bone motion from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation with relatively little user processing time.

The Impact of Coronal Plane Deformity on Ankle Arthrodesis and Arthroplasty.

BACKGROUND: Ankle coronal plane deformity represents a complex 3-dimensional problem, and comparative data are lacking to guide treatment recommendations for optimal treatment of end-stage ankle arthritis with concomitant coronal plane deformity. METHODS: In total, 224 patients treated for end-stage ankle arthritis were enrolled in an observational trial. Of 112 patients followed more than 2 years, 48 patients (19 arthrodesis, 29 arthroplasty) had coronal plane deformity and were compared to 64 patients without coronal plane deformity (18 arthrodesis, 46 arthroplasty) defined as greater than 10 degrees of varus or valgus. The arthroplasty implants used had different internal constraints to intracomponent coronal plane tilting. Patients completed Musculoskeletal Functional Assessment (MFA) and SF-36 preoperatively and at 3, 6, 12, 24, and 36 months postoperatively. Measures included change in SF-36 and MFA, as well as compared reoperation rates and pain scales. RESULTS: For the groups with coronal plane ankle deformity, the median for the arthrodesis group was 19.0 degrees and the median for the arthroplasty group was 16.9 degrees. In the deformity cohort during the follow-up period, we had 7 major reoperations: 2 in the arthrodesis group and 5 in the arthroplasty group, all with the less constrained implant design. MFA, vitality, and social function of the SF-36 improved for all groups. Patients without preoperative deformities had greater improvement with fusion or replacement at both 2 and 3 years. There was no difference in improvement between those patients with coronal deformity who received arthroplasty vs arthrodesis. CONCLUSION: Patients with and without coronal plane deformity may benefit from ankle arthroplasty and arthrodesis, although greater improvements may be expected in those without preoperative deformity. In this study, at final follow-up of 3 years, overall we found no meaningful difference in patient-reported outcomes between the patients with preoperative coronal plane deformities whether they had a fusion or a replacement as treatment for end-stage ankle arthritis. LEVEL OF EVIDENCE: Level II, comparative study.

Ankle fusion and replacement gait similar post-surgery, but still exhibit differences versus controls regardless of footwear.

Persons with ankle osteoarthritis (AOA) often seek surgical intervention to alleviate pain and restore function; however, recent research has yielded no superior choice between the two primary options: fusion and replacement. One factor yet to be considered is the effect of footwear on biomechanical outcomes. Comparisons of AOA biomechanics to a normative population are also sparse. The objectives of this study were to (1) determine how footwear uniquely affected gait in persons with ankle fusion and replacement and (2) provide context for AOA biomechanics via comparisons to a healthy adult sample. Thirty-four persons with AOA performed overground walking trials barefoot and shod before surgical intervention and then received either an ankle fusion (n = 14) or replacement (n = 20). Two and/or three years post-surgery, patients returned for gait analysis. Nineteen controls performed the same gait procedures during a single study visit. Spatiotemporal variables and peak angles, internal moments, powers, and forces were calculated to quantify gait behavior. Overall, the two surgical groups performed similarly to each other but demonstrated marked differences from controls both pre- and post-surgery. No significant differences were detected when examining the effect of footwear. The motion of the midfoot with respect to the hindfoot and forefoot may be instrumental in gait biomechanics following an ankle fusion or replacement and should be considered in future investigations.

Comparing 4-Year Changes in Patient-Reported Outcomes Following Ankle Arthroplasty and Arthrodesis.

BACKGROUND: The rate of total ankle arthroplasty (TAA) is increasing relative to ankle arthrodesis (AA) for patients seeking surgical treatment for end-stage ankle arthritis. Patients and providers would benefit from a more complete understanding of the rate of improvement, the average length of time to achieve maximal function and minimal pain, and whether there is a greater decline in function or an increase in pain over time following TAA compared with AA. The objectives of this study were to compare treatment changes in overall physical and mental function and ankle-specific function, as well as pain intensity at 48 months after TAA or AA in order to determine if the improvements are sustained. METHODS: This was a multisite prospective cohort study that included 517 participants (414 TAA and 103 AA) who presented for surgical treatment. Participants were compared 48 months after surgery using the Foot and Ankle Ability Measure (FAAM) Activities of Daily Living and Sports subscales (0 to 100 points), the Short Form-36 (SF-36) Physical and Mental Component Summary (PCS and MCS) scores (0 to 100 points), and pain scores (0 to 10 points). RESULTS: Both groups achieved significant improvement in the 2 FAAM measures, the SF-36 PCS score, and all of the pain measures at 48 months after surgey (p < 0.001). Mean improvements from baseline in patients undergoing TAA for the FAAM Activities of Daily Living, FAAM Sports, and SF-36 scores were at least 9 points, 8 points, and 3.5 points, respectively, which were higher than in those undergoing AA. Mean improvements in worst and average pain were at least 0.9 point higher in patients undergoing TAA than in those undergoing AA at 12, 24, and 36 months. These differences were attenuated by 48 months. For both treatments, all improvements from baseline to 24 months had been maintained at 48 months. CONCLUSIONS: When both procedures are performed by the same group of surgeons, patients who undergo TAA or AA for end-stage ankle arthritis have significant improvement in overall function, ankle-specific function, and pain at 48 months after surgery, with better functional improvement in the TAA group. LEVEL OF EVIDENCE: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.