Accuracy of biplane videoradiography for quantifying dynamic wrist kinematics

In vivo analysis of ankle joint kinematics and ligament deformation of chronic ankle instability patients during level walking

Introduction: Chronic ankle instability (CAI) carries a high risk of progression to talar osteochondral lesions and post-traumatic osteoarthritis. It has been clinically hypothesized the progression is associated with abnormal joint motion and ligament elongation, but there is a lack of scientific evidence. Methods: A total of 12 patients with CAI were assessed during level walking with the use of dynamic biplane radiography (DBR) which can reproduce the in vivo positions of each bone. We evaluated the uninjured and CAI side of the tibiotalar and subtalar joint for three-dimensional kinematics differences. Elongation of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL) were also calculated bilaterally. Results: For patients with CAI, the dorsiflexion of the tibiotalar joint had reduced (21.73° ± 3.90° to 17.21° ± 4.35°), displacement of the talus increased (2.54 ± 0.64 mm to 3.12 ± 0.55 mm), and the inversion of subtalar joint increased (8.09° ± 2.21° to 11.80° ± 3.41°). Mean ATFL elongation was inversely related to mean dorsiflexion angle (CAI: rho = -0.82, P < 0.001; Control: rho = -0.92, P < 0.001), mean ATFL elongation was related to mean anterior translation (CAI: rho = 0.82, P < 0.001; Control: rho = 0.92, P < 0.001), mean CFL elongation was related to mean dorsiflexion angle (CAI: rho = 0.84, P < 0.001; Control: rho = 0.70, P < 0.001), and mean CFL elongation was inversely related to mean anterior translation (CAI: rho = -0.83, P < 0.001; Control: rho = -0.71, P < 0.001). Furthermore, ATFL elongation was significantly (CAI: rho = -0.82, P < 0.001; Control: rho = -0.78, P < 0.001) inversely correlated with CFL elongation. Discussion: Patients with CAI have significant changes in joint kinematics relative to the contralateral side. Throughout the stance phase of walking, ATFL increases in length during plantarflexion and talar anterior translation whereas the elongation trend of CFL was the opposite. This understanding can inform the development of targeted therapeutic exercises aimed at balancing ligament tension during different phases of gait. The interrelationship between two ligaments is that when one ligament shortens, the other lengthens. The occurrence of CAI didn't change this trend. Surgeons might consider positioning the ankle in a neutral sagittal plane to ensure optimal outcomes during ATFL and CFL repair.

Evaluation of a cadaveric wrist motion simulator using marker-based X-ray reconstruction of moving morphology

Surgical intervention is a common option for the treatment of wrist joint arthritis and traumatic wrist injury. Whether this surgery is arthrodesis or a motion preserving procedure such as arthroplasty, wrist joint biomechanics are inevitably altered. To evaluate effects of surgery on parameters such as range of motion, efficiency and carpal kinematics, repeatable and controlled motion of cadaveric specimens is required. This study describes the development of a device that enables cadaveric wrist motion to be simulated before and after motion preserving surgery in a highly controlled manner. The simulator achieves joint motion through the application of predetermined displacements to the five major tendons of the wrist, and records tendon forces. A pilot experiment using six wrists aimed to evaluate its accuracy and reproducibility. Biplanar X-ray videoradiography (BPVR) and X-Ray Reconstruction of Moving Morphology (XROMM) were used to measure overall wrist angles before and after total wrist arthroplasty. The simulator was able to produce flexion, extension, radioulnar deviation, dart thrower's motion and circumduction within previously reported functional ranges of motion. Pre- and post-surgical wrist angles did not significantly differ. Intra-specimen motion trials were repeatable; root mean square errors between individual trials and average wrist angle and tendon force profiles were below 1° and 2 N respectively. Inter-specimen variation was higher, likely due to anatomical variation and lack of wrist position feedback. In conclusion, combining repeatable intra-specimen cadaveric motion simulation with BPVR and XROMM can be used to determine potential effects of motion preserving surgeries on wrist range of motion and biomechanics.

A scoping review of human skeletal kinematics research using biplane radiography

Biplane radiography has emerged as the gold standard for accurately measuring in vivo skeletal kinematics during physiological loading. The purpose of this scoping review was to map the extent, range, and nature of biplane radiography research on humans from 2004 through 2022. A literature search was performed using the terms biplane radiography, dual fluoroscopy, dynamic stereo X-ray, and biplane videoradiography. All articles referenced in included publications were also assessed for inclusion. A secondary search was then performed using the names of the most frequently appearing principal investigators among included papers. A total of 379 manuscripts were identified and included. The first studies published in 2004 focused on the native knee, followed by studies of the ankle joint complex in 2006, the shoulder in 2007, and the spine in 2008. Nearly half (180, 47.5%) of all manuscripts investigated knee kinematics. The average number of publications increased from 21.6 per year from 2012 to 2017 to 34.6 per year from 2017 to 2022. The average number of participants per study was 16, with a range from 1 to 101. A total of 90.2% of studies featured cohorts of 30 or less. The most prolific research groups for each joint were: Mass General Hospital (lumbar spine and knee), Henry Ford Hospital (shoulder), the University of Utah (ankle and hip), The University of Pittsburgh (cervical spine), and Brown University (hand/wrist/elbow). Future advancements in biplane radiography research are dependent upon increased availability of these imaging systems, standardization of data collection protocols, and the development of automated approaches to expedite data processing.

Cervical facet capsular ligament mechanics: Estimations based on subject-specific anatomy and kinematics

Background

To understand the facet capsular ligament's (FCL) role in cervical spine mechanics, the interactions between the FCL and other spinal components must be examined. One approach is to develop a subject-specific finite element (FE) model of the lower cervical spine, simulating the motion segments and their components' behaviors under physiological loading conditions. This approach can be particularly attractive when a patient's anatomical and kinematic data are available.

Methods

We developed and demonstrated methodology to create 3D subject-specific models of the lower cervical spine, with a focus on facet capsular ligament biomechanics. Displacement-controlled boundary conditions were applied to the vertebrae using kinematics extracted from biplane videoradiography during planar head motions, including axial rotation, lateral bending, and flexion-extension. The FCL geometries were generated by fitting a surface over the estimated ligament-bone attachment regions. The fiber structure and material characteristics of the ligament tissue were extracted from available human cervical FCL data. The method was demonstrated by application to the cervical geometry and kinematics of a healthy 23-year-old female subject.

Results

FCL strain within the resulting subject-specific model were subsequently compared to models with generic: (1) geometry, (2) kinematics, and (3) material properties to assess the effect of model specificity. Asymmetry in both the kinematics and the anatomy led to asymmetry in strain fields, highlighting the importance of patient-specific models. We also found that the calculated strain field was largely independent of constitutive model and driven by vertebrae morphology and motion, but the stress field showed more constitutive-equation-dependence, as would be expected given the highly constrained motion of cervical FCLs.

Conclusions

The current study provides a methodology to create a subject-specific model of the cervical spine that can be used to investigate various clinical questions by coupling experimental kinematics with multiscale computational models.

Joint mobility as a bridge between form and function

Joints enable nearly all vertebrate animal motion, from feeding to locomotion. However, despite well over a century of arthrological research, we still understand very little about how the structure of joints relates to the kinematics they exhibit in life. This Commentary discusses the value of joint mobility as a lens through which to study articular form and function. By independently exploring form-mobility and mobility-function relationships and integrating the insights gained, we can develop a deep understanding of the strength and causality of articular form-function relationships. In turn, we will better illuminate the basics of 'how joints work' and be well positioned to tackle comparative investigations of the diverse repertoire of vertebrate animal motion.

Automatic landmark detection and mapping for 2D/3D registration with BoneNet

The 3D musculoskeletal motion of animals is of interest for various biological studies and can be derived from X-ray fluoroscopy acquisitions by means of image matching or manual landmark annotation and mapping. While the image matching method requires a robust similarity measure (intensity-based) or an expensive computation (tomographic reconstruction-based), the manual annotation method depends on the experience of operators. In this paper, we tackle these challenges by a strategic approach that consists of two building blocks: an automated 3D landmark extraction technique and a deep neural network for 2D landmarks detection. For 3D landmark extraction, we propose a technique based on the shortest voxel coordinate variance to extract the 3D landmarks from the 3D tomographic reconstruction of an object. For 2D landmark detection, we propose a customized ResNet18-based neural network, BoneNet, to automatically detect geometrical landmarks on X-ray fluoroscopy images. With a deeper network architecture in comparison to the original ResNet18 model, BoneNet can extract and propagate feature vectors for accurate 2D landmark inference. The 3D poses of the animal are then reconstructed by aligning the extracted 2D landmarks from X-ray radiographs and the corresponding 3D landmarks in a 3D object reference model. Our proposed method is validated on X-ray images, simulated from a real piglet hindlimb 3D computed tomography scan and does not require manual annotation of landmark positions. The simulation results show that BoneNet is able to accurately detect the 2D landmarks in simulated, noisy 2D X-ray images, resulting in promising rigid and articulated parameter estimations.

Ulnar Extension Coupling in Functional Wrist Kinematics During Hand Activities of Daily Living

PURPOSE

Wrist circumduction is increasingly used as a functional motion assessment for patients. Thus, increasing our understanding of its relation to the functional motion envelope is valuable. Previous studies have shown that the wrist is preferentially extended during hand activities of daily living (ADLs), with greater ulnar than radial deviation. The purpose of this study was to characterize the functional wrist motions of 22 modern ADLs in healthy subjects. We hypothesized that the subjects would perform ADLs predominantly in ulnar extension.

METHODS

Ten right-handed, healthy subjects performed flexion-extension, radioulnar deviation, maximal circumduction, and 22 modern ADLs. Angular wrist positions were obtained by tracking retroreflective markers on the hand and forearm. Angular motion data were analyzed with a custom program for peak/trough angles in flexion extension and radioulnar deviation, ellipse area of circumduction data, and ellipse area of combined motion data.

RESULTS

The required ranges of motion for ADLs were from 46.6° ± 16.5° of flexion (stirring task) to 63.8° ± 14.2° of extension (combing) in flexion-extension and from 15.6° ± 8.9° of radial deviation (opening a jar) to 32.5° ± 8.3° of ulnar deviation (picking up smartphone) in radioulnar deviation. Ellipse area of combined motion data of the 22 ADLs were, on average, 58.2% ± 14.3% of the ellipse area of maximal circumduction. A motion data quadrantal analysis revealed that 54.9% of all ADL wrist motion occurred in ulnar extension. Among the average wrist positions for 22 ADLs, 16 were located in the ulnar extension quadrant.

CONCLUSIONS

This study revealed a functional wrist motion envelope that was less than 60% of wrist maximal motion capacity on average. Our results also showed that the majority of ADLs are performed in ulnar extension of the wrist.

CLINICAL RELEVANCE

Baseline values for healthy subjects performing 22 wrist ADLs can inform future studies assessing dysfunction, postsurgical changes, and rehabilitation progress.

Finite element analysis of the performance of additively manufactured scaffolds for scapholunate ligament reconstruction

Rupture of the scapholunate interosseous ligament can cause the dissociation of scaphoid and lunate bones, resulting in impaired wrist function. Current treatments (e.g., tendon-based surgical reconstruction, screw-based fixation, fusion, or carpectomy) may restore wrist stability, but do not address regeneration of the ruptured ligament, and may result in wrist functional limitations and osteoarthritis. Recently a novel multiphasic bone-ligament-bone scaffold was proposed, which aims to reconstruct the ruptured ligament, and which can be 3D-printed using medical-grade polycaprolactone. This scaffold is composed of a central ligament-scaffold section and features a bone attachment terminal at either end. Since the ligament-scaffold is the primary load bearing structure during physiological wrist motion, its geometry, mechanical properties, and the surgical placement of the scaffold are critical for performance optimisation. This study presents a patient-specific computational biomechanical evaluation of the effect of scaffold length, and positioning of the bone attachment sites. Through segmentation and image processing of medical image data for natural wrist motion, detailed 3D geometries as well as patient-specific physiological wrist motion could be derived. This data formed the input for detailed finite element analysis, enabling computational of scaffold stress and strain distributions, which are key predictors of scaffold structural integrity. The computational analysis demonstrated that longer scaffolds present reduced peak scaffold stresses and a more homogeneous stress state compared to shorter scaffolds. Furthermore, it was found that scaffolds attached at proximal sites experience lower stresses than those attached at distal sites. However, scaffold length, rather than bone terminal location, most strongly influences peak stress. For each scaffold terminal placement configuration, a basic metric was computed indicative of bone fracture risk. This metric was the minimum distance from the bone surface to the internal scaffold bone terminal. Analysis of this minimum bone thickness data confirmed further optimisation of terminal locations is warranted.

Total Wrist Arthroplasty Alignment and Its Potential Association with Clinical Outcomes

Purpose  There is a lack of quantitative research that describes the alignment and, more importantly, the effects of malalignment on total wrist arthroplasty (TWA). The main goal of this pilot study was to assess the alignment of TWA components in radiographic images and compare them with measures computed by three-dimensional analysis. Using these measures, we then determined if malalignment is associated with range of motion (ROM) or clinical outcomes (PRWHE, PROMIS, QuickDash, and grip strength). Methods  Six osteoarthritic patients with a single type of TWA were recruited. Radiographic images, computed tomography images, and clinical outcomes of the wrists were recorded. Using posteroanterior and lateral radiographs, alignment measurements were defined for the radial and carpal components. Radiographic measurements were validated with models reconstructed from computed tomography images using Bland-Altman analysis. Biplanar videoradiography (<1mm and <1 degree accuracy) was used to capture and compute ROM of the TWA components. Linear regression assessed the associations between alignment and outcomes. Results  Radiographic measures had a 95% limit-of-agreement (mean difference ±  1.96 × SD) of 3 degrees and 3mm with three-dimensional values, except for the measures of the carpal component in the lateral view. In our small cohort, wrist flexion-extension and radial-ulnar deviation were correlated with volar-dorsal tilt and volar-dorsal offset of the radial component and demonstrated a ROM increase of 3.7 and 1.6 degrees per degree increase in volar tilt, and 10.8 and 4.2 degrees per every millimeter increase in volar offset. The carpal component's higher volar tilt was also associated with improvements in patient-reported pain. Conclusions  We determined metrics describing the alignment of TWA, and found the volar tilt and volar offset of the radial component could potentially influence the replaced wrist's ROM. Clinical Relevance  TWA component alignment can be measured reliably in radiographs, and may be associated with clinical outcomes. Future studies must evaluate its role in a larger cohort.

Biomechanics of the Distal Radioulnar Joint During In Vivo Forearm Pronosupination

Background  Ulnar variance (UV) and center of rotation (COR) location at the level of the distal radioulnar joint (DRUJ) change with forearm rotation. Nevertheless, these parameters have not been assessed dynamically during active in vivo pronosupination. This assessment could help us to improve our diagnosis and treatment strategies. Questions/purposes  We sought to (1) mathematically model the UV change, and (2) determine the dynamic COR's location during active pronosupination. Methods  We used biplanar videoradiography to study DRUJ during in vivo pronation and supination in nine healthy subjects. UV was defined as the proximal-distal distance of ulnar fovea with respect to the radial sigmoid notch, and COR was calculated using helical axis of motion parameters. The continuous change of UV was evaluated using a generalized linear regression model. Results  A second-degree polynomial with R 2 of 0.85 was able to model the UV changes. Maximum negative UV occurred at 38.0 degrees supination and maximum positive UV occurred at maximum pronation. At maximum pronation, the COR was located 0.5 ± 1.8 mm ulnarly and 0.6 ± 0.8 mm volarly from the center of the ulnar fovea, while at maximum supination, the COR was located 0.2 ± 0.6 mm radially and 2.0 ± 0.5 mm volarly. Conclusion  Changes in UV and volar translation of the COR are nonlinear at the DRUJ during pronosupination. Clinical Relevance  Understanding the dynamic nature of UV as a function of pronosupination can help guide accurate evaluation and treatment of wrist pathology where the UV is an important consideration. The dynamic behavior of COR might be useful in designing DRUJ replacement implants to match the anatomical motion.

Optical motion capture accuracy is task-dependent in assessing wrist motion

Optical motion capture (OMC) systems are commonly used to capture in-vivo three-dimensional joint kinematics. However, the skin-based markers may not reflect the underlying bone movement, a source of error known as soft tissue artifact (STA). This study examined STA during wrist motion by evaluating the agreement between OMC and biplanar videoradiography (BVR). Nine subjects completed 7 different wrist motion tasks: doorknob rotation to capture supination and pronation, radial-ulnar deviation, flexion-extension, circumduction, hammering, and pitcher pouring. BVR and OMC captured the motion simultaneously. Wrist kinematics were quantified using helical motion parameters of rotation and translation, and Bland-Altman analysis quantified the mean difference (bias) and 95% limit of agreement (LOA). The rotational bias of doorknob pronation, a median bias of -4.9°, was significantly larger than the flexion-extension (0.7°, p < 0.05) and radial-ulnar deviation (1.8°, p < 0.01) tasks. The rotational LOA range was significantly smaller in the flexion-extension task (5.9°) compared to pitcher (11.6°, p < 0.05) and doorknob pronation (17.9°, p < 0.05) tasks. The translation bias did not differ between tasks. The translation LOA range was significantly larger in circumduction (9.8°) compared to the radial-ulnar deviation (6.3°, p < 0.05) and pitcher (3.4°, p < 0.05) tasks. While OMC technology has a wide-range of successful applications, we demonstrated it has relatively poor agreement with BVR in tracking wrist motion, and that the agreement depends on the nature and direction of wrist motion.

Biplanar Videoradiography to Study the Wrist and Distal Radioulnar Joints

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, and the effects of treatments. Measurement systems that use skin surface markers to infer skeletal motion have provided important insight into normal and pathological kinematics, however, accurate arthrokinematics cannot be attained using these systems, especially during dynamic activities. In the past two decades, biplanar videoradiography (BVR) systems have enabled many researchers to directly study the skeletal kinematics of the joints during activities of daily living. To implement BVR systems for the distal upper extremity, videoradiographs of the distal radius and the hand are acquired from two calibrated X-ray sources while a subject performs a designated task. Three-dimensional (3D) rigid-body positions are computed from the videoradiographs via a best-fit registrations of 3D model projections onto to each BVR view. The 3D models are density-based image volumes of the specific bone derived from independently acquired computed-tomography data. Utilizing graphics processor units and high-performance computing systems, this model-based tracking approach is shown to be fast and accurate in evaluating the wrist and distal radioulnar joint biomechanics. In this study, we first summarized the previous studies that have established the submillimeter and subdegree agreement of BVR with an in vitro optical motion capture system in evaluating the wrist and distal radioulnar joint kinematics. Furthermore, we used BVR to compute the center of rotation behavior of the wrist joint, to evaluate the articulation pattern of the components of the implant upon one another, and to assess the dynamic change of ulnar variance during pronosupination of the forearm. In the future, carpal bones may be captured in greater detail with the addition of flat panel X-ray detectors, more X-ray sources (i.e., multiplanar videoradiography), or advanced computer vision algorithms.

A Practical Guide to Measuring Ex vivo Joint Mobility Using XROMM

X-Ray Reconstruction of Moving Morphology (XROMM), though traditionally used for studies of in vivo skeletal kinematics, can also be used to precisely and accurately measure ex vivo range of motion from cadaveric manipulations. The workflow for these studies is holistically similar to the in vivo XROMM workflow but presents several unique challenges. This paper aims to serve as a practical guide by walking through each step of the ex vivo XROMM process: how to acquire and prepare cadaveric specimens, how to manipulate specimens to collect X-ray data, and how to use these data to compute joint rotational mobility. Along the way, it offers recommendations for best practices and for avoiding common pitfalls to ensure a successful study.

Biomechanical function requirements of the wrist. Circumduction versus flexion/abduction range of motion

The biomechanical function of the wrist is widely assessed by measuring the range of motion (RoM) in two separate orthogonal planes: flexion-extension (FE) and radioulnar deviation (RUD). However, the two motions are coupled. The aim of this study is to compare wrist circumduction with FE and RUD RoM in terms of representativeness of the kinematic requirements for performing activities of daily living (ADL). To this end, the wrist motion of healthy participants was measured while performing maximum RoM in FE and in RUD, circumduction, and thirty-two representative ADL. Active and functional RoM (ARoM and FRoM) were computed in each plane, the evolving circumduction curves were adjusted to ellipses, and intensity maps representing the frequency of the coupling angles in ADL were plotted, both per ADL and globally for both hands. Ellipses representing different percentages of coupling angles in ADL were also plotted. Wrist circumduction fits the coupling angles measured in ADL better than ARoM or FRoM. As a novelty, quantitative data for both circumduction and the coupling angles required in ADL are provided, shedding light on the real biomechanical function requirements of the wrist. Results might be used to quantify mobility reduction and its impact on the performance of ADL, globally and per ADL, to enhance rehabilitation strategies, as well as in clinical decision-making, robotics, and prostheses.

Proximal-distal shift of the center of rotation in a total wrist arthroplasty is more than twice of the healthy wrist

Reproduction of healthy wrist biomechanics should minimize the abnormal joint forces that could potentially result in the failure of a total wrist arthroplasty (TWA). To date, the in vivo kinematics of TWA have not been measured and it is unknown if TWA preserves healthy wrist kinematics. Therefore, the purpose of this in vivo study was to determine the center of rotation (COR) for a current TWA design and to compare its location to the healthy wrist. The wrist COR for six patients with TWA and 10 healthy subjects were calculated using biplane videoradiography as the subjects performed various range-of-motion and functional tasks that included coupled wrist motions. An open-source registration software, Autoscoper, was used for model-based tracking and kinematics analysis. It was demonstrated that the COR was located near the centers of curvatures of the carpal component for the anatomical motions of flexion-extension and radial-ulnar deviation. When compared to healthy wrists, the COR of TWAs was located more distal in both pure radial deviation (P < .0001) and pure ulnar deviation (P = .07), while there was no difference in its location in pure flexion or extension (P = .99). Across all coupled motions, the TWA's COR shifted more than two times that of the healthy wrists in the proximal-distal direction (17.1 vs 7.2 mm). We postulate that the mismatch in the COR location and behavior may be associated with increased loading of the TWA components, leading to an increase in the risk of component and/or interface failure.

The Reliability of Foot and Ankle Bone and Joint Kinematics Measured With Biplanar Videoradiography and Manual Scientific Rotoscoping

The intricate motion of the small bones of the feet are critical for its diverse function. Accurately measuring the 3-dimensional (3D) motion of these bones has attracted much attention over the years and until recently, was limited to invasive techniques or quantification of functional segments using multi-segment foot models. Biplanar videoradiography and model-based scientific rotoscoping offers an exciting alternative that allows us to focus on the intricate motion of individual bones in the foot. However, scientific rotoscoping, the process of rotating and translating a 3D bone model so that it aligns with the captured x-ray images, is either semi- or completely manual and it is unknown how much human error affects tracking results. Thus, the aim of this study was to quantify the inter- and intra-operator reliability of manually rotoscoping in vivo bone motion of the tibia, talus, and calcaneus during running. Three-dimensional CT bone volumes and high-speed biplanar videoradiography images of the foot were acquired on six participants. The six-degree-of-freedom motions of the tibia, talus, and calcaneus were determined using a manual markerless registration algorithm. Two operators performed the tracking, and additionally, the first operator re-tracked all bones, to test for intra-operator effects. Mean RMS errors were 1.86 mm and 1.90° for intra-operator comparisons and 2.30 mm and 2.60° for inter-operator comparisons across all bones and planes. The moderate to strong similarity values indicate that tracking bones and joint kinematics between sessions and operators is reliable for running. These errors are likely acceptable for defining gross joint angles. However, this magnitude of error may limit the capacity to perform advanced analyses of joint interactions, particularly those that require precise (sub-millimeter) estimates of bone position and orientation. Optimizing the view and image quality of the biplanar videoradiography system as well as the automated tracking algorithms for rotoscoping bones in the foot are required to reduce these errors and the time burden associated with the manual processing.

Characterization of Ankle Kinematics and Constraint Following Ligament Rupture in a Cadaveric Model

Ankle sprains are a common injury that may need reconstruction and extensive physical therapy. The purpose of this study was to provide a description of the biomechanics of the ankle joint complex after anterior talofibular (ATFL) and calcaneofibular (CFL) ligament rupture to better understand severe ankle injuries. Envelope of motion of ten cadaveric ankles was examined by manual manipulations that served as training data for a radial basis function used to interpolate ankle mobility at flexion angles under load and torque combinations. Moreover, ankle kinematics were examined while tendons were loaded to identify how their performance is altered by ligament rupture. The force required to plantarflex the ankle following ligament rupture was measured by calculating the load through the Achilles. Following ATFL injury, the largest changes were to internal rotation (5°) in deep plantarflexion and anterior translation (1.5mm) in early plantarflexion. The combined ATFL and CFL rupture changed the internal/external rotation (3°), anterior/posterior translation (1mm), and inversion (5°) throughout flexion relative to the isolated ATFL rupture. The Achilles' load increased by 24% after the rupture of ligaments indicating a reduction in its efficiency. This study suggests that if patients demonstrate a primarily an increased laxity in internal rotation, the damage has solely occurred to the ATFL; however, if the constraint is reduced across multiple motions, there is likely damage to both ligaments. Higher loads in the Achilles suggest that it is overloaded after the injury; hence, targeting the calf muscles in rehabilitation exercises may reduce patients' pain.