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The first goal of this study was to develop reliable three-dimensional definitions of alignment for the ankle, subtalar, and hindfoot joints. These alignments are based on three-dimensional morphological features derived from renderings of the bones obtained from weightbearing computer tomography. The second goal was to establish a database quantifying the alignment of the ankle, subtalar, and hindfoot joints in a healthy population during weightbearing bilateral standing. This level 1 study was performed on 95 normal subjects in which random subjects were recruited into a control group. Weightbearing computed tomography scans of the leg were collected in neutral, bilateral, standing posture. In 30 of the subjects, both the left and right leg was scanned. Six alignment parameters for each joint were calculated from morphological measurements conducted on three-dimensional renderings of the bones. Intra- and intertester reliability was assessed from repeated measurements by several testers. Analysis of variance statistics of the alignment parameters showed no statistical differences due to age, gender, or foot side. Intraclass correlation coefficient analysis showed excellent inter- and intratester reliability. It was concluded that the alignment process is comprehensive and reliable. Therefore, without classification by gender or age, it may be used as a foundation for quantifying abnormal alignment associated with various ankle deformities. Clinical significance: The alignment methodology and control database may be used to diagnose ankle, subtalar, and hindfoot misalignment. It can also serve as basis for surgical planning designed to restore normal alignment in various hindfoot pathologies, such as ankle realignment in total ankle replacement.

Background: During radial shaft fracture fixation, it is important to contour the plate appropriately to restore the radial bow in order to maintain normal forearm mechanics and motion. The aim of this study was to investigate the fit of precontoured radial shaft plates versus surgeon-contoured plates. Methods: Six 10-hole Acumed® precontoured volar and dorsolateral radius plates and twelve 10-hole Synthes straight titanium 3.5 mm LC-DCP plates were drilled with arrays of 1.5 mm diameter holes to permit measurement of the plate distance off bone. Plates were applied to 6 cadaver radii and secured with a screw on each end. Three plate conditions were tested: precontoured plates, precontoured plates with further surgeon contouring, and straight plates with surgeon contouring. Surgeon contouring time for each plate was recorded. Each plate was divided into 3 equal regions, and the average distance gaps for each region and the entire plate were calculated. Results: For the volar side, precontoured plates had a larger total gap compared to that plate with additional surgeon contouring (1.4 mm difference) and the straight surgeon-contoured plates (1.2 mm difference). On the dorsal side, there was no difference in fit between the 3 plate conditions at any location. No differences were found in plate contouring times. Conclusions: The precontoured dorsal plate fit was as good as the surgeon-contoured plates indicating this plate could potentially be used in fracture surgery without further bending. The precontoured volar plate was under-contoured, on average, and would likely require further bending to restore the radial bow.

Progressive peritalar subluxation (PTS) is part of adult acquired flatfoot deformity (AAFD). We investigated the use of the middle facet as an indicator of PTS using standing, weight-bearing computed tomography (CT) images. We hypothesized that weight-bearing CT would be an accurate method of measuring increased subluxation ("uncoverage") and incongruence of the middle-facet among patients with AAFD.We included 30 patients with stage-II AAFD (20 female and 10 male; mean age, 57.4 years [range, 24 to 78 years]) and 30 matched controls (20 female and 10 male; mean age, 51.8 years [range, 19 to 81 years]) who underwent standing, weight-bearing CT. Two independent and blinded fellowship-trained foot and ankle surgeons measured the amount of subluxation (percentage of uncoverage) and the incongruence angle of the middle facet at the midpoint of its longitudinal length, using coronal-plane, weight-bearing, cone-beam CT images. Intraobserver and interobserver reliabilities were assessed using intraclass correlation coefficients (ICCs). Comparisons were performed using independent t tests or Wilcoxon tests. P values of0.05 were considered significant.Substantial to almost perfect intraobserver and interobserver reliability was observed for both measurements. We found that the middle facet demonstrated significantly increased PTS in patients with AAFD, with a mean value for joint uncoverage of 45.3% (95% confidence interval [CI], 38.5% to 52.1%) compared with 4.8% (95% CI, 3.2% to 6.4%) in controls (p0.0001). A significant difference was also found for the incongruence angle, with a mean value of 17.3° (95% CI, 14.7° to 19.9°) in the AAFD group and 0.3° (95% CI, 0.1° to 0.5°) in controls (p0.0001). A joint incongruence angle of8.4° was found to be diagnostic for symptomatic stage-II AAFD.We investigated the use of the middle facet of the subtalar joint as a marker for PTS in patients with AAFD. We confirmed that standing, weight-bearing CT images allowed accurate measurements and that significant differences were found in the percentage of joint uncoverage and the incongruence angle compared with controls.The assessment of the amount of subluxation and incongruence of the middle facet of the subtalar joint represents an accurate diagnostic tool for symptomatic adult acquired flatfoot deformity.

Radial fractures often require surgical stabilization with fracture fixation plates. Incomplete morphological reconstruction was linked to poor outcome such as limited forearm rotation. Pre-contoured plates are often used, but large inter-subject morphological variations may result in poor fit. Therefore, the goal of this study was to develop a reliable virtual measure of plate-to-bone fit. In addition, the study evaluated the accuracy with which 3D printed bones reproduce the morphology of the physical radius. Virtual models and 3D-printed models of six cadaver radii were produced from bone scans. Level of fit of pre-contoured plates were measured in three ways: directly on pre-contoured physical plates fitted to cadaver bone; pre-contoured physical plates fitted to 3D printed bone; and virtual plate models fitted to virtual bone models. In addition, the study evaluated the accuracy with which 3D printed bone reproduces the physical bone morphology. The results indicate excellent agreement between the physical and virtual level of fit measures as well as excellent geometrical accuracy of the 3D-printed bones. These provide the necessary foundation for guiding the development of better fitted pre-contoured fracture fixation plates as well as for developing pre-surgically patient specific pre-contoured plates.

Introduction The goal of this study was to characterize the abnormal joint surface interaction at the ankle, hindfoot and midfoot joints of the cavovarus foot using distance mapping on weightbearing computed tomography (WBCT) images by comparing a series of cavovarus feet to a series of normally-aligned feet. Methods In this case-control study, ten feet (10 patients) with asymptomatic cavovarus shape (cases; N = 10) were compared to 10 matched-paired (by age, gender and body mass index) normally-aligned feet (10 patients) (controls; N = 10). Three-dimensional models were produced from the images and distance maps representing joint surface configuration were generated for the ankle, hindfoot and midfoot joints. The distance maps for each joint were then compared between the two groups and between regions in the same group. Results In the cavovarus group there was a significant increase in surface-to-surface distance at the posterior tibiotalar joint and a reduced distance at the anterior part, together with a greater distance at the posterior half of the medial gutter. Also, a decrease in surface-to-surface distance on the anterior half of the anterior facet and an increased distance on the posterior quadrants of the posterior facet of the subtalar joint were found. At the sinus tarsi, the lateral aspect of the talonavicular joint, the naviculocuneiform and the tarsometatarsal joints there was a statistically significant increase in surface-to-surface distance in cavovarus patients as compared to controls. Conclusion Distance mapping analysis on WBCT images identified significant differences in surface-to-surface interaction at the foot and ankle joints between cavovarus and normally-aligned feet. Level of evidence Level III, case-control study.

Category: Ankle; Hindfoot; Midfoot/Forefoot Introduction/Purpose: The cavovarus configuration sets the grounds for various pathological conditions, often involving the arthritic degeneration of the medial column. The objective of this study was to analyze the joint surface interaction at the ankle, hindfoot and midfoot joints using distance mapping on WBCT images in a series of cavovarus feet and compare them to normally aligned feet. Methods: In this case-control study, a database containing WBCT datasets from 370 feet (189 patients) obtained in a specialized foot and ankle unit from July 2016 to October 2018 was used. Ten feet (10 patients) with asymptomatic cavovarus shape were extracted (cases group; N= 10) and compared to 10 matched-paired (by age, gender and body mass index) normally aligned feet (10 patients) (controls group; N=10). Colored distance maps were generated for the ankle, hindfoot and midfoot joints and divided in zones, therefore differences were assessed between the two groups. Results: In the cavovarus group there was a significant increase in surface-to-surface distance at the posterior tibiotalar joint and a reduced distance at the anterior part, together with a greater distance at the posterior half of the medial gutter. Also, a decrease in surface-to-surface distance on the anterior half of the anterior facet and an increased distance on the posterior quadrants of the posterior facet of the subtalar joint were found. At the sinus tarsi, the lateral aspect of the talonavicular joint, the naviculocuneiform and the tarsometatarsal joints there was a statistically significant increase in surface-to-surface distance in cavovarus patients as compared to controls. Conclusion: In this study, the use of distance mapping analysis on WBCT images enabled to identify significant differences in surface-to-surface interaction at the foot and ankle joints between cavovarus and normally-aligned feet.

Category: Hindfoot; Ankle; Other Introduction/Purpose: The goal of this study was to describe the abnormal joint surface interaction at the ankle, hindfoot and midfoot joints in patients presenting with Pes Planovalgus (PP) using three-dimensional (3D) distance mapping on weightbearing computed tomography (WBCT) images by comparing a series of PPs to a series of normally-aligned feet. We hypothesized that in PPs joint interactions would reveal significantly increased spaces in the medial side of the ankle, hindfoot and midfoot joints. Methods: In this case-control study, ten feet (10 patients) with asymptomatic PP (cases; N=10) were compared to 10 matched- paired (by age, gender and body mass index) normally-aligned feet (10 patients) (controls; N=10). Three-dimensional models were produced from the images and distance maps representing joint surface configuration were generated for the ankle, hindfoot and midfoot joints. The distance maps for each joint were then compared between the two groups and between regions in the same group. Results: In PP patients there was a significantly increased surface-to-surface distance anteromedially at the ankle joint (+46.3%, pConclusion: We found significant differences in surface-to-surface interaction at the foot and ankle joints between Pes Planovalgus and normally-aligned controls. Distance mapping on WBCT images could be used in clinical practice as a diagnostic support to gauge the morphological changes of articular spaces occurring in Pes Planovalgus.

Head and neck injuries are common in contact sports such as American football. Different mechanisms can produce such injuries, including compressive impact forces on the crown of the helmet with th...

Joint surface interaction and ligament constraints determine the kinematic characteristics of the ankle and subtalar joints. Joint surface interaction is characterized by joint contact mechanics and by relative joint surface position potentially characterized by distance mapping. While ankle contact mechanics was investigated, limited information is available on joint distance mapping and its changes during motion. The purpose of this study was to use image-based distance mapping to quantify this interaction at the ankle and subtalar joints during tri-planar rotations of the ankle complex. Five cadaveric legs were scanned using Computed Tomography and the images were processed to produce 3D bone models of the tibia, fibula, talus and calcaneus. Each leg was tested on a special linkage through which the ankle complex was loaded in dorsiflexion/plantarflexion, inversion/eversion, and internal/external rotation and the resulting bone movements were recorded. Fiduciary bone markers data and 3D bone models were combined to generate color-coded distance maps for the ankle and subtalar joints. The results were processed focusing on the changes in surface-to-surface distance maps between the extremes of the range of motion and neutral. The results provided detailed insight into the three-dimensional highly coupled nature of these joints showing significant and unique changes in distance mapping from neutral to extremes of the range of motion. The non-invasive nature of the image-based distance mapping technique could result, after proper modifications, in an effective diagnostic and clinical evaluation technique for application such as ligament injuries and quantifying the effect of arthrodesis or total ankle replacement surgery.

Kinematics and flexibility properties of both natural and replaced ankle joints are affected by the geometry of the articulating surfaces. Recent studies proposed an original saddle-shaped, skewed, truncated cone with laterally oriented apex, as tibiotalar contact surfaces for ankle prosthesis. The goal of this study was to compare in vitro this novel design with traditional cylindrical or medially centered conic geometries in terms of their ability to replicate the natural ankle joint mechanics. Ten lower limb cadaver specimens underwent a validated process of custom design for the replacement of the natural ankle joint. The process included medical imaging, 3D modeling and printing of implantable sets of artificial articular surfaces based on these three geometries. Kinematics and flexibility of the overall ankle complex, along with the separate ankle and subtalar joints, were measured under cyclic loading. In the neutral and in maximum plantarflexion positions, the range of motion under torques in the three anatomical planes of the three custom artificial surfaces was not significantly different from that of the natural surfaces. In maximum dorsiflexion the difference was significant for all three artificial surfaces at the ankle complex, and only for the cylindrical and medially centered conic geometries at the tibiotalar joint. Natural joint flexibility was restored by the artificial surfaces nearly in all positions. The present study provides experimental support for designing articular surfaces matching the specific morphology of the ankle to be replace, and lays the foundations of the overall process for designing and manufacturing patient-specific total ankle replacements.

Background The clinical outcomes of total ankle replacement are limited by prosthesis component malpositioning during surgery. The goal of this study is to assess the mechanical impact of this malpositioning in a validated computer model. Methods In a previously developed multi-body dynamic model of the human ankle complex three different artificial implants were designed, each one presenting a different approximation of the natural articular surfaces of the corresponding specimen. The most common implant translational and rotational malpositionings were defined and mimicked. Dynamic simulations of joint motion were run for the various surfaces and malpositionings. The same input loading conditions derived from a previous in-vitro experiment on the corresponding natural specimen were applied. Findings From load-displacement graphs it was observed that all three artificial surfaces reproduced well physiological motion between the calcaneus and the tibia/fibula, with a maximum difference of 2°. It was found that antero-posterior translation of either the tibial or the talar component and inclination of the tibial component in the sagittal plane led to considerable increases in the range of motion. Antero-posterior and dorsiflexion of the tibial component resulted in an increased internal-external rotation by up to 3.5° and 4.0°, respectively. The corresponding increase of inversion-eversion was 5.0° and 6.5°. Interpretation This study showed that relatively small surgical errors have great consequences in replaced joint mechanics. The present model can be used in future studies to analyse the effect of malpositioning with any specific current total ankle prosthesis.

Background: The purpose of this study was to compare the mechanical properties of metacarpal neck fracture fixation by headless compression screw (HCS) with that of Kirschner wire (KW) cross-pinning and locking plate (LP) fixation. Methods: A metacarpal neck fracture was created in 30 fourth-generation composite Sawbones metacarpal models. A volar-based wedge was removed using a custom jig to simulate a typical apex dorsal fracture, unstable in flexion. The models were divided into 3 equal groups based on the method of fixation: retrograde cross-pinning with two 1.2-mm KWs, 2.0-mm dorsal T-plate with six 2.0-mm locking screws (LP), and a 3.0-mm retrograde HCS. Models were fixed at the proximal end, mounted in a material testing machine, and loaded through a cable tensioned over the metacarpal head, simulating grip loading. Cyclic loading from 0 to 40 N was performed, followed by loading to failure. Load, displacement, and failure mode were recorded. Results: Stiffness of the HCS (7.3 ± 0.7 N/m) was significantly greater than the KW (5.8 ± 0.5 N/m) but significantly less than the LP (9.5 ± 1.9 N/m). With cyclic loading to 40 N, the LP exhibited significantly less displacement (0.2 ± 1.3 mm) compared with the HCS (2.5 ± 2.3 mm) and KW (2.8 ± 1.0 mm). Load to failure for the HCS (215.5 ±3 9.0 N) was lower than that of the KW (279.7 ± 100.3 N) and of the LP (267.9 ± 44.1 N), but these differences were not statistically significant. Conclusions: The HCS provided mechanical fracture fixation properties comparable with KW fixation. The LP construct allowed significantly less displacement and had the highest strength of the 3 fixation methods.

Many failures in total joint replacement are associated to prosthesis-to-bone mismatch. With recent additive-manufacturing, that is, 3D-printing, custom-made prosthesis can be created by laser-melting metal powders layer-by-layer. Ankle replacement is particularly suitable for this progress because of the limited number of sizes and the poor bone stock. In this study a novel procedure is presented for subject-specific ankle replacements, including medical-imaging, joint modelling, prosthesis design, and 3D-printing. Three shank-foot specimens were CT-scanned, and corresponding 3D bone models of the tibia, fibula, talus, and calcaneus were obtained. From these models, specimen-specific implant sets were designed according to three different concepts, and 3D-printed from cobalt-chromium-molybdenum powder. Accuracy of the overall procedure was assessed via distance map comparisons between original anatomical and final metal implants. Restoration of natural ankle joint mechanics was check after implantation of each of the three sets. In a special rig, a manually-driven dorsi/plantar-flexion was applied throughout the passive arc. Additionally, at three different joint positions, joint torques were imposed in the frontal and axial anatomical planes. Mean manufacturing errors were found to be smaller than 0.08 mm. Consistent motion patterns were observed over repetitions, with the mean standard deviation smaller than 1.0 degree. In each ankle specimen, mobility, and stability at the replaced joints compared well with the original natural condition. For the first time, custom-made implants for total ankle replacements were designed, manufactured with additive technology and tested. This procedure is a first fundamental step toward the development of completely personalized prostheses. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

none 7 si A study of Cobalt-Chromium-Molybdenum endoprosthetic ankle implant fabrication by means of SLM is presented, including process characterization and kinematic considerations. Process optimization is first performed on samples with simple geometry to maximize density and mechanical strength using Co-Cr-Mo powders. Parameters such as laser scanning velocity, laser power and scanning strategy are varied, amongst others. Mechanical tests and microstructural analyses are performed to define process parameter windows for fabrication of near full density prostheses with negligible microstructural defects. Prosthetic ankles, based on medical imaging and biomechanical modeling, are then manufactured and kinematically tested to confirm their functional integrity and performance. mixed Liverani, E.; Fortunato, A; Leardini, A.; Belvedere, C.; Siegler, S.; Ceschini, L.; Ascari, A. Liverani, E.; Fortunato, A; Leardini, A.; Belvedere, C.; Siegler, S.; Ceschini, L.; Ascari, A.

Knowledge of the stabilizing role of the ankle and subtalar ligaments is important for improving clinical techniques such as ligament repair and reconstruction. However, this knowledge is incomplete. The goal of this study was to expand this knowledge by investigating the stabilizing function of the ligaments using multiple morphologically subject-specific computational models. Nine models were created from the lower extremities of nine donors. Each model consisted of the articulating bones, articular cartilage, and ligaments. Simulations were conducted in ADAMS™ - a dynamic simulation program. During simulation, tibia and fibula were fixed while cyclic moments in all three anatomical planes were applied to the calcaneus one-at-a-time. The resulting displacements between the bones and the forces in each ligament were computed. Simulations were conducted with all ligaments intact and after simulated ligament serial sectioning. Each model was validated by comparing the simulation results to experimental data obtained from the specimen used to construct the model. From the results the stabilizing role of each ligament was established and the effect of ligament sectioning on Range of Motion and Overall Laxity was identified. On the lateral side, ATFL provided stabilization in supination, CFL restrained inversion, external rotation and dorsiflexion and PTFL limited dorsiflexion and external rotation. On the medial side, PTTL restrained dorsiflexion and internal rotation, ATTL limited plantarflexion and external rotation, and TCL limited dorsiflexion, eversion and external rotation. At the subtalar joint, ITCL limited plantarflexion and its posterior-lateral bundle restrained subtalar inversion. CL restrained plantarflexion/dorsiflexion, and internal and external rotation. The large inter-model variability observed in the results indicate the importance of using multiple subject-specific models rather than relying on one "representative" model.

Background Ankle passive kinematics is determined primarily by articular surface morphology and ligament constraints. Previous morphological studies concluded that the talar dome can be approximated by a truncated cone, whose apex is directed medially and whose major axis is the axis of rotation of the ankle. This and other functional morphology concepts were evaluated in this study whose goal was to describe and quantify the 3D morphology of the talus using 3D image-based bone models and engineering software tools. Methods CT data from 26 healthy adults were processed to produce 3D renderings of the talus and were followed by morphological measurements including the radii of curvature of circles fitted to the medial and lateral borders of the trochlea and radii of curvature of coronal sections. Findings The surfaces containing the medial and lateral borders of the trochlea are not parallel and the radius of curvature of the medial border is larger than the lateral border. In the coronal plane the trochlear surface was mostly concave. Interpretation The trochlear surface can be modeled as a skewed truncated conic saddle shape with its apex oriented laterally rather than medially as postulated by Inman. Such shape is compatible, as opposed to Inman's cone postulate, with the observed pronation/supination and provides stable congruency in movements of inversion/eversion. The results challenge the fundamental theories of functional morphology of the ankle and suggest that these new findings should be considered in future biomechanical research and in clinical applications such as design of total ankle replacements.

Category: Hindfoot Introduction/Purpose: Peritalar subluxation comprises part of the three-dimensional and complex distortion that occurs in patients with adult-acquired flatfoot deformity (AAFD) and is characterized by subluxation of the hindfoot through the triple joint complex. It is traditionally graded on weightbearing computed tomography (WBCT) coronal plane images, depending upon the degree of angulation and subluxation of the posterior facet of the subtalar joint. In this case-control study, we describe a new marker of peritalar subluxation represented by the amount of subluxation and joint incongruence of the middle facet of the subtalar joint. We hypothesized that the amount of joint subluxation and incongruence at the middle facet would be significantly increased in patients with AAFD when compared to controls. Methods: Case-control study, we included 30 patients with stage II AAFD (19 females/11 males), mean age 52.2 (range, 29 to 81) years, and 30 controls (18 females/12 males), mean age 49.3 (range, 28 to 83) years, that underwent WBCT as part of the evaluation of their foot condition. Age and gender were statistically similar in both groups. The amount of subluxation of the subtalar joint at the middle facet (% of uncoverage) and angle of joint incongruence, both measured at the midpoint of its longitudinal length, was measured in coronal WB CBCT images by two independent and blinded fellowship-trained foot and ankle surgeons. A second set of measurements was performed after one month (wash-out period). Intra- and interobserver reliability were assessed by Pearson/Spearman’s and Intraclass Correlation Coefficient (ICC), respectively. Comparison was performed using Paired Student T-Test or each pair Wilcoxon rank sum test. P-values lower than 0.05 were considered significant. Results: We found overall good to excellent intra- (range, 0.90-0.95) and interobserver reliability (range, 0.75-0.93) for the measurements. We found significantly increased subluxation of the subtalar joint at the middle facet in patients with AAFD, with a mean value for middle facet uncoverage of 45.3% (95% CI, 40.5% to 50.1%), when compared to 4.8% (95% CI, 0% to 9.6%) in controls (pConclusion: We described the use of the subtalar joint middle facet as a marker for peritalar subluxation in patients with AAFD. We found significant and marked differences in the percentage of joint uncoverage and incongruence when compared to controls. Hopefully, the use of the middle facet as an indicator for peritalar subluxation can potentially help in the early detection of high- risk AAFD patients for progressive collapse and development of sinus tarsi and subfibular impingement, as well as arthritic degeneration of the subtalar joint. Future longitudinal and prospective studies are needed.

For some patients with radiculopathy a source of nerve root compression cannot be identified despite positive electromyography (EMG) evidence. This discrepancy hampers the effective clinical management for these individuals. Although it has been well-established that tissues in the cervical spine move in a three-dimensional (3D) manner, the 3D motions of the neural elements and their relationship to the bones surrounding them are largely unknown even for asymptomatic normal subjects. We hypothesize that abnormal mechanical loading of cervical nerve roots during pain-provoking head positioning may be responsible for radicular pain in those cases in which there is no evidence of nerve root compression on conventional cervical magnetic resonance imaging (MRI) with the neck in the neutral position. This biomechanical imaging proof-of-concept study focused on quantitatively defining the architectural relationships between the neural and bony structures in the cervical spine using measurements derived from 3D MR images acquired in neutral and pain-provoking neck positions for subjects: (1) with radicular symptoms and evidence of root compression by conventional MRI and positive EMG, (2) with radicular symptoms and no evidence of root compression by MRI but positive EMG, and (3) asymptomatic age-matched controls. Function and pain scores were measured, along with neck range of motion, for all subjects. MR imaging was performed in both a neutral position and a pain-provoking position. Anatomical architectural data derived from analysis of the 3D MR images were compared between symptomatic and asymptomatic groups, and the symptomatic groups with and without imaging evidence of root compression. Several differences in the architectural relationships between the bone and neural tissues were identified between the asymptomatic and symptomatic groups. In addition, changes in architectural relationships were also detected between the symptomatic groups with and without imaging evidence of nerve root compression. As demonstrated in the data and a case study the 3D stress MR imaging approach provides utility to identify biomechanical relationships between hard and soft tissues that are otherwise undetected by standard clinical imaging methods. This technique offers a promising approach to detect the source of radiculopathy to inform clinical management for this pathology.

The mechanical characteristics of the ankle such as its kinematics and load transfer properties are influenced by the geometry of the articulating surfaces. A recent, image-based study found that these surfaces can be approximated by a saddle-shaped, skewed, truncated cone with its apex oriented laterally. The goal of this study was to establish a reliable experimental technique to study the relationship between the geometry of the articular surfaces of the ankle and its mobility and stability characteristics and to use this technique to determine if morphological approximations of the ankle surfaces based on recent discoveries, produce close to normal behavior. The study was performed on ten cadavers. For each specimen, a process based on medical imaging, modeling and 3D printing was used to produce two subject specific artificial implantable sets of the ankle surfaces. One set was a replica of the natural surfaces. The second approximated the ankle surfaces as an original saddle-shaped truncated cone with apex oriented laterally. Testing under cyclic loading conditions was then performed on each specimen following a previously established technique to determine its mobility and stability characteristics under three different conditions: natural surfaces; artificial surfaces replicating the natural surface morphology; and artificial approximation based on the saddle-shaped truncated cone concept. A repeated measure analysis of variance was then used to compare between the three conditions. The results show that (1): the artificial surfaces replicating natural morphology produce close to natural mobility and stability behavior thus establishing the reliability of the technique; and (2): the approximated surfaces based on saddle-shaped truncated cone concept produce mobility and stability behavior close to the ankle with natural surfaces.

Summary Objective Fetal cartilage anlage provides a framework for endochondral ossification and organization into articular cartilage. We previously reported differences between mechanical properties of talar cartilage anlagen and adult articular cartilage. However, the underlying development-associated changes remain to be established. Delineation of the normal evolvement of mechanical properties and its associated compositional basis provides insight into the natural mechanisms of cartilage maturation. Our goal was to address this issue. Materials and methods Human fetal cartilage anlagen were harvested from the tali of normal stillborn fetuses from 20 to 36weeks of gestational age. Data obtained from stress relaxation experiments conducted under confined and unconfined compression configurations were processed to derive the compressive mechanical properties. The compressive mechanical properties were extracted from a linear fit to the equilibrium response in unconfined compression, and by using the nonlinear biphasic theory to fit to the experimental data from the confined compression experiment, both in stress–relaxation. The molecular composition was obtained using Fourier transform infrared (FTIR), and spatial maps of tissue contents per dry weight were created using FTIR imaging. Correlative and regression analyses were performed to identify relationships between the mechanical properties and age, compositional properties and age, and mechanical vs compositional parameters. Results All of the compositional quantities and the mechanical properties excluding the Poisson's ratio changed with maturation. Stiffness increased by a factor of ∼2.5 and permeability decreased by 20% over the period studied. Collagen content and degree of collagen integrity increased with age by ∼3-fold, while the proteoglycan content decreased by 18%. Significant relations were found between the mechanical and compositional properties. Conclusion The mechanics of fetal talar cartilage is related to its composition, where the collagen and proteoglycan network play a prominent role. An understanding of the mechanisms of early cartilage maturation could provide a framework to guide tissue-engineering strategies.

Mechanical characterization of human cartilage anlagen is required to effectively model congenital musculoskeletal deformities. Such modeling can effectively explore the effect of treatment procedures and potentially suggest enhanced treatment methods. Using serial MRI, we have noted shape changes of the cartilaginous hindfoot anlagen in patients with clubfoot, suggesting they are soft and deformable. We therefore determined the stress relaxation behavior of cartilage plugs obtained from third-trimester stillborn fetuses in unconfined and confined compression geometries. The material parameters determined were the aggregate modulus H(A) = 0.15 +/- 0.07 MPa, Poisson's ratio nu = 0.4 +/- 0.06, Young's modulus E(s) = 0.06 +/- 0.03 MPa, and permeability coefficients k(0) = 2.01 +/- 0.8 x 10(-14) m(4) N(-1) s(-1) and M = 4.6 +/- 1.0. As compared with adult articular cartilage, stiffness was an order of magnitude lower than the values reported in the literature, suggesting the relative softness of the tissue, and the permeability was an order of magnitude higher, indicating relative ease of flow in the tissue. Poisson's ratio also was close to the higher end of the range reported in previous studies. Such material is expected to deform and relax to larger extents. These findings are consistent with the deformability of the cartilage anlagen during manipulation and casting for treatment of clubfoot.

BackgroundThe modified Jobe and Docking techniques are commonly used to reconstruct the elbow's ulnar collateral ligament.HypothesisValgus laxity and kinematic coupling after these reconstructive procedures are similar to those of the native ulnar collateral ligament.Study DesignControlled laboratory study.MethodsTesting was conducted on 10 pairs of cadaver elbows using a 4 degrees of freedom loading system. Subfailure valgus loads were applied to the native elbows at different flexion angles; motion and ligament elongation were measured. The elbows were then loaded to failure in valgus at 90° of flexion. The reconstructive techniques were then applied and testing was repeated.ResultsOnly the resting length of the anterior portion of the ulnar collateral ligament anterior bundle remained isometric throughout range of motion. Valgus laxity was nearly equal for the native and reconstructed ligaments at flexion angles of 90° or higher. However, both reconstructions provided less valgus stability than the native ulnar collateral ligament at low flexion angles. Kinematic coupling decreased with increased flexion for both native and reconstructed ligaments.ConclusionThe modified Jobe and Docking techniques reconstruct restraint of the native ulnar collateral ligament to valgus laxity and kinematic coupling at 90° of flexion and higher angles where peak valgus torque is experienced in the throwing elbow.Clinical RelevanceBoth reconstructions provide valgus stability comparable to that of the native ulnar collateral ligament at 90° and higher, helping to explain their success in treating throwing athletes. Both reconstructions provide less valgus stability than the native ulnar collateral ligament at low flexion angles, suggesting that patients undergoing ulnar collateral ligament reconstruction should be cautioned against activities that provide valgus stress at low elbow flexion angles, such as side-arm throwing. This study suggests caution against overtightening the reconstructions at the common 30° of flexion.

There are several medical application areas that require the segmentation and separation of the component bones of joints in a sequence of images of the joint acquired under various loading conditions, our own target area being joint motion analysis. This is a challenging problem due to the proximity of bones at the joint, partial volume effects, and other imaging modality-specific factors that confound boundary contrast. In this article, a two-step model-based segmentation strategy is proposed that utilizes the unique context of the current application wherein the shape of each individual bone is preserved in all scans of a particular joint while the spatial arrangement of the bones alters significantly among bones and scans. In the first step, a rigid deterministic model of the bone is generated from a segmentation of the bone in the image corresponding to one position of the joint by using the live wire method. Subsequently, in other images of the same joint, this model is used to search for the same bone by minimizing an energy function that utilizes both boundary- and region-based information. An evaluation of the method by utilizing a total of 60 data sets on MR and CT images of the ankle complex and cervical spine indicates that the segmentations agree very closely with the live wire segmentations, yielding true positive and false positive volume fractions in the range 89%-97% and 0.2%-0.7%. The method requires 1-2 minutes of operator time and 6-7 min of computer time per data set, which makes it significantly more efficient than live wire-the method currently available for the task that can be used routinely.

The morphology of the bones, articular surfaces and ligaments and the passive mechanical characteristics of the ankle complex were reported to vary greatly among individuals. The goal of this study was to test the hypothesis that the variations observed in the passive mechanical properties of the healthy ankle complex are strongly influenced by morphological variations. To evaluate this hypothesis six numerical models of the ankle joint complex were developed from morphological data obtained from MRI of six cadaveric lower limbs, and from average reported data on the mechanical properties of ligaments and articular cartilage. The passive mechanical behavior of each model, under a variety of loading conditions, was found to closely match the experimental data obtained from each corresponding specimen. Since all models used identical material properties and were subjected to identical loads and boundary conditions, it was concluded that the observed variations in passive mechanical characteristics were due to variations in morphology, thus confirming the hypothesis. In addition, the average and large variations in passive mechanical behavior observed between the models were similar to those observed experimentally between cadaveric specimens. The results suggest that individualized subject-specific treatment procedures for ankle complex disorders are potentially superior to a one-size-fits-all approach.

The posture of the head and neck is critical for predicting and assessing the risk of injury during high accelerations, such as those arising during motor accidents or in collision sports. Current knowledge suggests that the head's range-of-motion (ROM) and the torque-generating capability of neck muscles are both dependent and affected by head posture. A deeper understanding of the relationship between head posture, ROM and maximum torque-generating capability of neck muscles may help assess the risk of injury and develop means to reduce such risks. The aim of this study was to use a previously-validated device, known as Neck Flexibility Tester, to quantify the effects of head's posture on the available ROM and torque-generating capability of neck muscles. Ten young asymptomatic volunteers were enrolled in the study. The tri-axial orientation of the subjects' head was controlled via the Neck Flexibility Tester device. The head ROM was measured for each flexed, extended, axially rotated, and laterally bent head's orientation and compared to that in unconstrained neutral posture. Similarly, the torque applied about the three anatomical axes during Isometric Maximum Voluntary Contraction (IMVC) of the neck muscles was measured in six head's postures and compared to that in fully-constrained neutral posture. The further from neutral the neck posture was the larger the decrease in ROM and IMVC. Head extension and combined two-plane rotations postures, such as extension with lateral bending, produced the largest decreases in ROM and IMVC, thus suggesting that these postures pose the highest potential risk for injury.

Connective tissue adaptation, including the development of cartilaginous anlagen into bones, is widely believed to be related to dynamic, intermittent load and stress histories. Static stresses, on the other hand, are generally believed deleterious in tissue adaptation. Using serial MRI in a natural human experiment (manipulation and corrective casting of infant clubfoot), we have observed casting produces two effects: (1) the well recognized change in relative positions of the hindfoot anlagen; (2) a newly recognized immediate shape change in the anlagen. These changes seemingly enhance the rate of growth of the anlagen and of the ossific nucleus. The shape change or deformation in the anlagen would occur as a result of alterations in the magnitudes and directions of loading from soft tissue attachments and muscle activity and would necessarily be associated with changes in the stress states within the anlagen and, when present, the ossific nuclei. Given the known role of load and stress history in tissue adaptation, we presume the reduced stress histories influence the enhanced growth rates. These observations contradict some current theories of tissue adaptation since static, rather than dynamic stresses play a crucial role in accelerating the growth and development of anlagen in the infant clubfoot.

A technique to study the three-dimensional (3D) mechanical characteristics of the ankle and of the subtalar joints in vivo and in vitro is described. The technique uses an MR scanner compatible 3D positioning and loading linkage to load the hindfoot with precise loads while the foot is being scanned. 3D image processing algorithms are used to derive from the acquired MR images bone morphology, hindfoot architecture, and joint kinematics. The technique was employed to study these properties both in vitro and in vivo. The ankle and subtler joint motion and the changes in architecture produced in response to an inversion load and an anterior drawer load were evaluated. The technique was shown to provide reliable measures of bone morphology. The left-to-right variations in bone morphology were less than 5%. The left-to-right variations in unloaded hindfoot architecture parameters were less than 10%, and these properties were only slightly affected by inversion and anterior drawer loads. Inversion and anterior drawer loads produced motion both at the ankle and at the subtalar joint. In addition, high degree of coupling, primarily of internal rotation with inversion, was observed both at the ankle and at the subtalar joint. The in vitro motion produced in response to inversion and anterior drawer load was greater than the in vivo motion. Finally, external motion, measured directly across the ankle complex, produced in response to load was much greater than the bone movements measured through the 3D stress MRI technique indicating the significant effect of soft tissue and skin interference.

Objective. To study posterior tibialis tendon dysfunction using an in vitro model of the foot and ankle during the heel-off instant of gait. Background. Previous studies have concentrated primarily on the effect of posterior tibialis tendon dysfunction on the kinematics of the hindfoot and the arch. Methods. The specimens were loaded using a custom designed axial and tendon loading system and the location of the center of pressure was used to validate heel-off. Arch position, hindfoot position and plantar pressure data were recorded before and after the posterior tibialis tendon was unloaded. These data were recorded with the ligaments intact and after creating a flatfoot deformity. Results. Unloading the posterior tibialis tendon caused significant posterior movement in the center of pressure for the intact and flatfoot conditions. This also resulted in a medial shift in the force acting on the forefoot. The forefoot loads shifted medially after a flatfoot was created even when the posterior tibialis tendon remained loaded. The spatial relationships of the bones of the arch and the bones of the hindfoot also changed significantly for the intact specimen, and to a lesser extent after a flatfoot. Conclusions. The posterior tibialis tendon plays a fundamental role in shifting the center of pressure anteriorly at heel-off. Posterior tibialis tendon dysfunction causes posterior shift in the center of pressure and abnormal loading of the foot’s medial structures. This may be the reason that posterior tibialis tendon dysfunction leads to an acquired flatfoot deformity. Conversely, flatfoot deformity may be a predisposing factor in the onset of posterior tibialis tendon dysfunction. This tendon also acts to lock the bones of the arch and the hindfoot in a stable configuration at heel-off, but a flatfoot deformity compromises this ability. Relevance Use of plantar pressure characteristics, combined with arch and hindfoot kinematics, can lead to a better understanding of posterior tibialis tendon dysfunction.

This study quantified and compared the efficacy of in-shoe orthoses and ankle braces in stabilizing the hindfoot and medial longitudinal arch in a cadaveric model of acquired flexible flatfoot deformity. This was addressed by combining measurement of hindfoot and arch kinematics with plantar pressure distribution, produced in response to axial loads simulating quiet standing. Experiments were conducted on six fresh-frozen cadaveric lower limbs. Three conditions were tested: intact-unbraced; flatfoot-unbraced; and flatfoot-braced. Flatfoot deformity was created by sectioning the main support structures of the medial longitudinal arch. Six different braces were tested including two in-shoe orthoses, three ankle braces and one molded ankle-foot orthosis.Our model of flexible flatfoot deformity caused the calcaneus to evert, the talus to plantarflex and the height of the talus and medial cuneiform to decrease. Flexible flatfoot deformity caused a pattern of medial shift in plantar pressure distribution, but minimal change in the location of the center of pressure. Furthermore, in-shoe orthoses stabilized both the hindfoot and the medial longitudinal arch, while ankle braces did not. Semi-rigid foot and ankle orthoses acted to stabilize the medial longitudinal arch. Based on these results, it was concluded that treatment of flatfoot deformity should at least include use of in-shoe orthoses to partially restore the arch and stabilize the hindfoot.

We investigate automation and control options for the neck flexibility tester (NFT) (P. McClure et al., 1998), a device originally used to measure the flexibility of the human cervical spine. The motivation is to lay the foundations for design and implementation of investigative devices that would allow studies of mechanical properties of the spine under repetitive dynamic loading. We derive the equations of motion for an automated NFT (ANFT) using a Lagrangian formulation. These equations, which represent a simplified first-order model of the dynamics, are used to simulate the ANFT using the software package Simulink. Two control schemes are examined: proportional plus integral plus derivative (PID) control and dynamic inversion. Both are simulated for setpoint and tracking control. It appears that PID control is preferred due to its simplicity of design and relative insensitivity to the dynamic model of the ANFT.

The Standardization and Terminology Committee (STC) of the International Society of Biomechanics (ISB) proposes a general reporting standard for joint kinematics based on the Joint Coordinate System (JCS), first proposed by Grood and Suntay for the knee joint in 1983 (J. Biomech. Eng. 105 (1983) 136). There is currently a lack of standard for reporting joint motion in the field of biomechanics for human movement, and the JCS as proposed by Grood and Suntay has the advantage of reporting joint motions in clinically relevant terms. In this communication, the STC proposes definitions of JCS for the ankle, hip, and spine. Definitions for other joints (such as shoulder, elbow, hand and wrist, temporomandibular joint (TMJ), and whole body) will be reported in later parts of the series. The STC is publishing these recommendations so as to encourage their use, to stimulate feedback and discussion, and to facilitate further revisions. For each joint, a standard for the local axis system in each articulating bone is generated. These axes then standardize the JCS. Adopting these standards will lead to better communication among researchers and clinicians.

Background Ulnar collateral ligament (UCL) injuries have been successfully treated by the docking reconstruction. Although fixation of the graft has been suggested at 30° of elbow flexion, no quantitative biomechanical data exist to provide guidelines for the optimal elbow flexion angle for graft fixation. Methods Testing was conducted on 10 matched pairs of cadaver elbows with use of a loading system and optoelectric tracking device. After biomechanical data on the native UCL were obtained, reconstruction by the docking technique was performed with use of palmaris longus autograft with one elbow fixated at 30° and the contralateral elbow at 90° of elbow flexion. Biomechanical testing was undertaken on these specimens. Results The load to failure of the native UCL (mean, 20.1 N-m) was significantly higher ( P = .004) than that of the reconstructed UCL (mean, 4.6 N-m). There was no statistically significant difference in load to failure of the UCL reconstructions fixated at 30° of elbow flexion (average, 4.86 N-m) compared with those at 90° (average, 4.35 N-m). Elbows reconstructed at 30° and 90° of elbow flexion produced similar kinematic coupling and valgus laxity characteristics compared with each other and with the intact UCL. Although not statistically significant, the reconstructions fixated at 30° more closely resembled the biomechanical characteristics of the intact elbow than did reconstructions fixated at 90°. Conclusion No statistically significant difference was found in comparing the docking technique of UCL reconstruction with graft fixation at 30° vs. 90° of elbow flexion.

Study design In vitro comparison of three different screws for unicortical fixation in lateral masses of the cervical spine. Objectives To compare the axial load-to-failure of cervical lateral mass screws and their revision screws in a cadaveric model. Summary of background data Lateral mass screws are used for posterior fixation of the cervical spine. Risks to neurovascular structures have led many surgeons to advocate unicortical application of these screws, although fixation strength may vary with screw design. Methods Screws from three posterior cervical fixation systems were used: Axis, Starlock/Cervifix, and Summit. Tested were 3.5-mm cancellous screws, along with revision screws for each system. The C3-C6 vertebrae from three cadaveric specimens were fixed with screws inserted into the lateral masses at a depth of 10 mm with 30 degrees cephalad and 20 degrees lateral angulation. Coaxial pullout force was recorded for each primary and revision screw. Results Axial load-to-failure (mean +/- SD) of the screws was 459 +/- 60 N for Axis screws, 423 +/- 78 N for Starlock screws, and 319 +/- 97 N for Summit screws. The Axis and Starlock screws were significantly stronger than Summit screws (P = 0.017 and P = 0.067, respectively). The load-to-failure of revision screws was much lower than that of primary screws (Axis 54%, Starlock 56%, Summit 63% of the primary screw), without significant difference between screw types. Conclusions The Axis and Starlock screws resisted significantly greater axial load-to-failure than did the Summit screws. For all three systems, the revision screws could not restore the load-to-failure of the primary screw in this model. The tested unicortical screws had a consistently higher load-to-failure than those previously tested under similar conditions, suggesting that currently available screws may be superior to those previously tested.

Objective. The purpose of this study was to quantitatively examine the flexibility of sprained ankles using an arthrometer device and compare the differences in flexibility between ankles following the first sprains and ankles with repeated severe sprains and chronic symptoms. Design. A retrospective in vivo study was used. Background. Many in vitro studies have demonstrated a significant role of joint flexibility in determining mechanical laxity of human cadaveric ankles after sectioning of the lateral ligaments, but few in vivo studies have used the technique to provide objective measurement on the sprained ankles. Furthermore, there is a lack of extensive studies that compared the difference in the ankle flexibility between ankles following the first sprain and ankles with multiple repeated severe sprains and chronic symptoms. Methods. A total of 27 subjects with unilateral ankle sprains participated in this study. The subjects were divided into a first injury group (group A, n=12) and a chronic symptom group (group B, n=15) based on the history of their ankle injuries. The ankle flexibility in anterior drawer and inversion/eversion tests was measured in both ankles of the subjects using an arthrometer device, the ankle flexibility tester – a six-degree-of-freedom instrumented linkage used for measurements of applied forces/moments and resultant rotations and/or translations of the ankle joint complex. The difference in ankle flexibility between the injured ankle and the contralateral intact side was analyzed. Results. The flexibility in anterior drawer test of the injured ankles significantly increased compared to the intact ankles of the same individual in group B, but the same difference was not significant in group A. There were more subjects in group B (46.6%) than in group A (33.3%) who showed a sign of mechanical laxity in their injured ankles. Conclusions. The results indicated that the approach with measurement of ankle flexibility may be a potential tool used to detect the mechanical laxity in the sprained ankles. A tendency was found that patients with multiple ankle sprains and chronic symptoms had a higher occurrence rate of mechanical laxity. The result of the present study may also be interpreted that the ankles with mechanical laxity had higher risk of re-injury and leading to chronic symptoms. Relevance A non-invasive and objective measurement of ankle flexibility has potential to be developed into a diagnostic tool for the mechanical laxity of sprained ankles. The finding of this study may help clinicians in the plan of patient treatment.

This study represents a natural extension of our previous efforts in the design and development of a new class of swellable bone anchors, which absorb body fluids and achieve fixation by an expansion-fit mechanism. Specifically, this study investigates (i) correlations between the optimal swelling strain for highest fixation strength and the foam (or bone) density, and (ii) the influence of a threaded surface on the fixation strength of the swellable implant. For this purpose, the immediate and the final (after swelling) fixation strengths of two variations of the swellable bone anchor designs (a smooth anchor and a screw anchor) were measured in two different foams (used to simulate bone) with different densities. The amount of swelling was varied systematically for each foam and anchor design combinations. This study indicates that the screw swellable anchors have higher initial fixation strength than smooth swellable anchors, but the final fixation strengths of both anchors are quite similar. Further, it is observed that the optimal swelling strain decreased with increasing foam density. Both the smooth and screw swellable anchors were also found to exhibit higher fixation strengths than the metallic screws of similar geometry.

This study was part of a long-term effort to develop a reliable diagnostic procedure for ankle ligament injuries. Earlier efforts led to the development and validation of a six-degrees-of-freedom instrumented linkage capable of measuring the flexibility characteristics of the ankle complex in vitro and in vivo. The major goal of the present study was to determine if these flexibility measurements are sufficiently sensitive to detect the presence of damage to the lateral collateral ligaments of the ankle joint both in vitro and in vivo. The in vitro testing was conducted on the legs from six fresh cadavers before and after serial sectioning of the anterior talofibular ligament and the calcaneofibular ligament. The flexibility in inversion-eversion, anterior drawer, and internal-external rotation was measured before and after resection of the ligaments. The in vivo testing was conducted on five patients with unilateral injuries to the ankle ligament. The flexibility evaluation used for in vitro specimens was also performed on both the injured and the intact ankles. For the in vitro testing, the data analysis was based on comparison of flexibility values before and after resection of the ligaments, whereas the data analysis for the in vivo testing was based on comparison of the flexibility of the injured joint with that of the intact contralateral joint. The results of the in vitro study indicated that both an isolated rupture of the anterior talofibular ligament and combined damage of the anterior talofibular and calcaneofibular ligaments produce statistically significant changes in flexibility. Furthermore, the most sensitive parameters to the presence of ligament injuries were found to be early flexibility in anterior drawer, early flexibility in inversion, and the amount of coupling between internal rotation and inversion. These parameters provided a basis for differentiating between an isolated injury to the anterior talofibular ligament and a combined anterior talofibular and calcaneofibular ligament injury. For an isolated anterior talofibular ligament injury, a significant increase in flexibility in anterior drawer was present, whereas the increase in inversion flexibility or in the amount of coupling was insignificant. However, the increases in inversion flexibility and the amount of coupling became significant when both ligaments were involved. The results of the in vivo study indicated that significant changes in flexibility can be detected in patients with lateral ankle injuries. Finally, both the in vitro and in vivo results suggest that development of a reliable diagnostic test for ankle ligament injury based on changes in passive flexibility may be possible.