A method for measuring joint kinematics designed for accurate registration of kinematic data to models constructed from CT data

Ulnohumeral joint static cartilage compression is affected by radial head implant size

INTRODUCTION

Radiocapitellar joint arthroplasty is a commonly performed procedure, which often leads to early failure or instability. Few studies assess the effect of radiocapitellar joint arthroplasty on the ulnohumeral joint. We hypothesized that static forces of contact (compressing cartilage, or cartilage relaxation contact force) would reveal the effect of varying radial head implant size and elbow position on the ulnohumeral joint.

METHODS

A minimally-invasive method of measuring cartilage relaxation contact force was utilized in 10 fresh-frozen human cadaveric specimens that did not require significant dissection or intraarticular sensor placement. Specimens were rigidly fixed in various positions of elbow flexion and forearm pronosupination with increasing radial head implant lengths. Uniaxial distracting forces were applied and displacement was repeatedly measured with resultant best-fit polynomial curves to determine inflections corresponding to the force required to overcome static cartilage relaxation as in previous work.

FINDINGS

Baseline mean (intra-cadaver) cartilage relaxation contact force was 11.8 N (standard error of the mean = 0.3) at 90° of elbow flexion and neutral rotation. There was little variation within specimens (Intraclass correlation coefficient > 0.94). Cartilage relaxation contact force increased at the ulnohumeral joint with radial head implant overstuffing (> 4 mm, P < 0.05) and elbow flexion (120°, P < 0.001). Pronosupination altered cartilage relaxation contact force in an implant-length independent manner (P < 0.05).

INTERPRETATION

Radiocapitellar joint arthroplasty implant length and elbow joint position independently contribute to increased cartilage relaxation contact force at the ulnohumeral joint. This further supports attempts at anatomic reconstruction of the radiocapitellar joint to prevent pathologic ulnohumeral joint loading.

Validation of a 3D CT imaging method for quantifying implant migration following anatomic total shoulder arthroplasty

Glenoid component loosening remains a common complication following anatomic total shoulder arthroplasty (TSA); however, plain radiographs are unable to accurately detect early implant migration. The purpose of this study was to validate the accuracy of a method of postoperative, three-dimensional (3D) computed tomography (CT) imaging with metal artifact reduction (MAR) to detect glenoid component migration following anatomic TSA. Tantalum bead markers were inserted into polyethylene glenoid components for implant detection on 3D CT. In-vitro validation was performed using a glenoid component placed into a scapula sawbone and incrementally translated and rotated, with MAR 3D CT acquired at each test position. Accuracy was evaluated by root mean square error (RMSE). In-vivo validation was performed on six patients who underwent anatomic TSA, with two postoperative CT scans acquired in each patient and marker-based radiostereometric analysis (RSA) performed on the same days. Glenoid component migration was calculated relative to a scapular coordinate system for both MAR 3D CT and RSA. Accuracy was evaluated by RMSE and paired Student's t-tests. The largest RMSE on in-vitro testing was 0.24 mm in translation and 0.11° in rotation, and on in-vivo testing was 0.47 mm in translation and 1.04° in rotation. There were no significant differences between MAR 3D CT and RSA measurement methods. MAR 3D CT imaging is capable of quantifying glenoid component migration with a high level of accuracy. MAR 3D CT imaging is advantageous over RSA because it is readily available clinically and can also be used to evaluate the implant-bone interface.

Development and validation of a kinematically-driven discrete element model of the patellofemoral joint

Quantifying the complex loads at the patellofemoral joint (PFJ) is vital to understanding the development of PFJ pain and osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses with potential application at the PFJ to better understand PFJ mechanics. The current study validated a DEA modeling framework driven by PFJ kinematics to predict experimentally-measured PFJ contact stress distributions. Two cadaveric knee specimens underwent quadriceps muscle [215 N] and joint compression [350 N] forces at ten discrete knee positions representing PFJ positions during early gait while measured PFJ kinematics were used to drive specimen-specific DEA models. DEA-computed contact stress and area were compared to experimentally-measured data. There was good agreement between computed and measured mean and peak stress across the specimens and positions (r = 0.63-0.85). DEA-computed mean stress was within an average of 12% (range: 1-47%) of the experimentally-measured mean stress while DEA-computed peak stress was within an average of 22% (range: 1-40%). Stress magnitudes were within the ranges measured (0.17-1.26 MPa computationally vs 0.12-1.13 MPa experimentally). DEA-computed areas overestimated measured areas (average error = 60%; range: 4-117%) with magnitudes ranging from 139 to 307 mm² computationally vs 74-194 mm² experimentally. DEA estimates of the ratio of lateral to medial patellofemoral stress distribution predicted the experimental data well (mean error = 15%) with minimal measurement bias. These results indicate that kinematically-driven DEA models can provide good estimates of relative changes in PFJ contact stress.

Specimen-specific predictions of contact stress under physiological loading in the human hip: validation and sensitivity studies

Hip osteoarthritis may be initiated and advanced by abnormal cartilage contact mechanics, and finite element (FE) modeling provides an approach with the potential to allow the study of this process. Previous FE models of the human hip have been limited by single specimen validation and the use of quasi-linear or linear elastic constitutive models of articular cartilage. The effects of the latter assumptions on model predictions are unknown, partially because data for the instantaneous behavior of healthy human hip cartilage are unavailable. The aims of this study were to develop and validate a series of specimen-specific FE models, to characterize the regional instantaneous response of healthy human hip cartilage in compression, and to assess the effects of material nonlinearity, inhomogeneity and specimen-specific material coefficients on FE predictions of cartilage contact stress and contact area. Five cadaveric specimens underwent experimental loading, cartilage material characterization and specimen-specific FE modeling. Cartilage in the FE models was represented by average neo-Hookean, average Veronda Westmann and specimen- and region-specific Veronda Westmann hyperelastic constitutive models. Experimental measurements and FE predictions compared well for all three cartilage representations, which was reflected in average RMS errors in contact stress of less than 25%. The instantaneous material behavior of healthy human hip cartilage varied spatially, with stiffer acetabular cartilage than femoral cartilage and stiffer cartilage in lateral regions than in medial regions. The Veronda Westmann constitutive model with average material coefficients accurately predicted peak contact stress, average contact stress, contact area and contact patterns. The use of subject- and region-specific material coefficients did not increase the accuracy of FE model predictions. The neo-Hookean constitutive model underpredicted peak contact stress in areas of high stress. The results of this study support the use of average cartilage material coefficients in predictions of cartilage contact stress and contact area in the normal hip. The regional characterization of cartilage material behavior provides the necessary inputs for future computational studies, to investigate other mechanical parameters that may be correlated with OA and cartilage damage in the human hip. In the future, the results of this study can be applied to subject-specific models to better understand how abnormal hip contact stress and contact area contribute to OA.

Hemiarthroplasty of hip joint: An experimental validation using porcine acetabulum

Biphasic properties of articular cartilage allow it to be an excellent bearing material and have been studied through several simplified experiments as well as finite element modelling. However, three-dimensional biphasic finite element (FE) models of the whole joint are rare. The current study was carried out to experimentally validate FE methodology for modelling hemiarthroplasty. Material properties such as equilibrium elastic modulus and permeability of porcine acetabular cartilage were initially derived by curve-fitting an experimental deformation curve with that obtained using FE. These properties were then used in the hemiarthroplasty hip joint modelling. Each porcine acetabular cup was loaded with 400N using a 34mm diameter CoCr femoral head. A specimen-specific FE model of each acetabular cup was created using μCT and a series of software processes. Each model was analysed under conditions similar to those tested experimentally. Contact stresses and contact areas predicted by the model, immediately after loading, were then compared with the corresponding experimentally measured values. Very high peak contact stresses (maximum experimental: 14.09MPa) were recorded. A maximum difference of 12.42% was found in peak contact stresses. The corresponding error for contact area was 20.69%. Due to a fairly good agreement in predicted and measured values of contact stresses and contact areas, the integrated methodology developed in this study can be used as a basis for future work. In addition, FE predicted total fluid load support was around 80% immediately after loading. This was lower than that observed in conforming contact problems involving biphasic cartilage and was due to a smaller local contact area and variable clearance making fluid exudation easier.

Development of a model based method for investigating facet articulation

Reported investigations of facet articulation in the human spine have often been conducted through the insertion of pressure sensitive film into the joint space, which requires incision of the facet capsule and may alter the characteristics of interaction between the facet surfaces. Load transmission through the facet has also been measured using strain gauges bonded to the articular processes. While this method allows for preservation of the facet capsule, it requires extensive instrumentation of the spine, as well as strain-gauge calibration, and is highly sensitive to placement and location of the strain gauges. The inherently invasive nature of these techniques makes it difficult to translate them into medical practice. A method has been developed to investigate facet articulation through the application of test kinematics to a specimen-specific rigid-body model of each vertebra within a lumbar spine segment. Rigid-body models of each vertebral body were developed from CT scans of each specimen. The distances between nearest-neighboring points on each facet surface were calculated for specific time frames of each specimen's flexion/extension test. A metric describing the proportion of each facet surface within a distance (2 mm) from the neighboring surface, the contact area ratio (CAR), was calculated at each of these time frames. A statistically significant difference (p<0.037) was found in the CAR between the time frames corresponding to full flexion and full extension in every level of the lumbar spine (L1-L5) using the data obtained from the seven specimens evaluated in this study. The finding that the contact area of the facet is greater in extension than flexion corresponds to other findings in the literature, as well as the generally accepted role of the facets in extension. Thus, a biomechanical method with a sufficiently sensitive metric is presented as a means to evaluate differences in facet articulation between intact and treated or between healthy and pathologic spines.

In vivo 3D kinematics of normal forearms: analysis of dynamic forearm rotation

BACKGROUND

Forearm rotation is an indispensable activity of daily living and comprises complex motions with rotational and translational components. It is thought that changes in these motions with injury or disease may affect diagnostic indices. Several studies have assessed in vivo forearm kinematics with static conditions, but dynamic forearm kinematics have not yet been reported. The purpose of this study was to analyze forearm kinematics during dynamic rotation using radiographic 3D-2D registration methods.

METHODS

Ten forearms of five healthy males with the mean age of 37 years old were enrolled. Lateral fluoroscopic images were taken during forearm rotation from maximum supination to maximum pronation with their elbows flexed to approximately 45°. Geometric bone models were created from CT scans of the humerus, the radius and the ulna. Three-dimensional kinematics were determined using 3D-2D model registration techniques with the images and models, and the arc of axial rotation of the radius, volar/dorsal translation of the ulna at the distal radioulnar joint and rotation axis of forearm were computed.

FINDINGS

The radial rotation arc was 157°. The ulna translated 3.9 mm (SD 1.5mm) dorsally during activity. The rotation axis of the forearm passed through the center of the radial head and the ulnar head at the 1.9 mm (SD 0.7 mm) posterior from its geometric centroid.

INTERPRETATION

The posteriorly deviated rotation axis at the ulnar head may result in the ulnar head translating dorsally during pronation. These data provide a basis for objective assessment of pathological forearm function.

The Impact of Glenoid Labrum Thickness and Modulus on Labrum and Glenohumeral Capsule Function

The glenoid labrum is an integral component of the glenohumeral capsule’s insertion into the glenoid, and changes in labrum geometry and mechanical properties may lead to the development of glenohumeral joint pathology. The objective of this research was to determine the effect that changes in labrum thickness and modulus have on strains in the labrum and glenohumeral capsule during a simulated physical examination for anterior instability. A labrum was incorporated into a validated, subject-specific finite element model of the glenohumeral joint, and experimental kinematics were applied simulating application of an anterior load at 0 deg, 30 deg, and 60 deg of external rotation and 60 deg of glenohumeral abduction. The radial thickness of the labrum was varied to simulate thinning tissue, and the tensile modulus of the labrum was varied to simulate degenerating tissue. At 60 deg of external rotation, a thinning labrum increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 10.5% average strain) and anterior band (increased 7.5% average strain). These results suggest a cause-and-effect relationship between age-related decreases in labrum thickness and increases in labrum pathology. A degenerating labrum also increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 15.5% strain) and anterior band (increased 10.4% strain). This supports the concept that age-related labrum pathology may result from tissue degeneration. This work suggests that a shift in capsule reparative techniques may be needed in order to include the labrum, especially as activity levels in the aging population continue to increase. In the future validated, finite element models of the glenohumeral joint can be used to explore the efficacy of new repair techniques for glenoid labrum pathology.

In-vivo kinematic analysis of forearm rotation using helical axis analysis

BACKGROUND

Controversy still exists regarding the location and nature (static or dynamic) of the forearm joint axis. This might be due to inconsistent results from in-vitro data and less precise methods of analysis. We present the first in-vivo kinematic analysis of normal forearm joint rotation described by helical axis analysis.

METHODS

Data obtained from computed tomography images of both forearms of five healthy volunteers was used to calculate finite helical axis parameters from transformation matrices. Four positions were analyzed: maximum pronation, maximum supination, 60 degrees pronation, and 60 degrees supination. Kinematic analysis focused on the motion of the radius around the ulna.

FINDINGS

The forearm axis as defined by finite helical axis extended from the radial head between its kinematic center and the proximal radioulnar joint, to the dorsal region of the ulnar head at the distal radioulnar joint. The axis was found to be variable.

INTERPRETATIONS

Helical axis analysis has precisely defined the nature and location of the forearm axis. This new information of forearm kinematics defined by finite helical analysis, may be useful in implant design, and in guiding surgeons in their reconstruction of instabilities of the distal and proximal radioulnar joint.

High-speed X-ray video demonstrates significant skin movement errors with standard optical kinematics during rat locomotion

The sophistication of current rodent injury and disease models outpaces that of the most commonly used behavioral assays. The first objective of this study was to measure rat locomotion using high-speed X-ray video to establish an accurate baseline for rat hindlimb kinematics. The second objective was to quantify the kinematics errors due to skin movement artefacts by simultaneously recording and comparing hindlimb kinematics derived from skin markers and from direct visualization of skeletal landmarks. Joint angle calculations from skin-derived kinematics yielded errors as high as 39 degrees in the knee and 31 degrees in the hip around paw contact with respect to the X-ray data. Triangulation of knee position from the ankle and hip skin markers provided closer, albeit still inaccurate, approximations of bone-derived, X-ray kinematics. We found that soft tissue movement errors are the result of multiple factors, the most impressive of which is overall limb posture. Treadmill speed had surprisingly little effect on kinematics errors. These findings illustrate the significance and context of skin movement error in rodent kinematics.

The glenohumeral capsule should be evaluated as a sheet of fibrous tissue: a validated finite element model

The function of the glenohumeral capsule has typically been evaluated by isolating several discrete, ligamentous regions during experimental and computational investigations. However, recent data suggests that the regions of the glenohumeral capsule have significant interactions and function multiaxially. Therefore, examining the function of the inferior glenohumeral ligament as a discrete structure may not be appropriate. The objective of this work was to validate the predicted strain distribution and deformed shape of the inferior glenohumeral ligament using experimental data for two subject-specific finite element models: (1) a continuous model including all capsular regions, and (2) a discrete model including only the inferior glenohumeral ligament. The distribution of maximum principal strain and deformed shape of the glenohumeral capsule was determined for a cadaveric shoulder in a joint position frequently associated with dislocation (60 degrees of glenohumeral abduction, 52 degrees of external rotation, and a 25 N anterior load applied to the humerus). The experimental kinematics were then applied to the two finite element models constructed from the geometry and material properties from the same cadaveric shoulder and the predicted strain distributions and deformed shapes were determined. For the continuous model, the average difference between predicted strains and experimental strains was less than 5%. The predicted deformed shape was also similar to experimental data, with the anterior band of the inferior glenohumeral ligament clearly wrapped around the humeral head. In contrast, large differences existed between the strains predicted by the discrete model when compared to the experimental strains for this joint position (average difference from experimental data was 20%). In addition, the predicted deformed shape of the inferior glenohumeral ligament did not wrap around the humeral head. These differences may be attributed to neglecting the complex interactions between the anterior band of the inferior glenohumeral ligament with the neighboring capsular regions. Thus, the glenohumeral capsule should not be evaluated as several discrete structures. Rather, it should be evaluated as a single sheet of fibrous tissue.

Correction of severe wrist deformity following physeal arrest of the distal radius with the aid of a three-dimensional computer simulation

Growth arrest following physeal injury may result in severe limb deformity. We report a case of complex wrist deformity caused by injury to the distal radial physis resulting in radial shortening and abnormal inclination of the radial articular surface, which was successfully treated by gradual correction after computer simulation. The simulation enabled us to develop an appropriate operative plan by accurately calculating the axis of the three-dimensional (3D) deformity using computer bone models. In the simulative surgery with a full-size stereolithography bone model, an Ilizarov external fixator was applied to the radius such that its two hinges were located on the virtual axis of the deformity, which was reproduced in the actual surgery. This technique of 3D computer simulation is a useful alternative to plan accurate correction of complex limb deformities following growth arrest.

Mapping ligament insertion sites onto bone surfaces in knee by co-registration of CT and digitization data

This paper describes a new methodology that enables mapping of the ligament insertion sites onto bone surfaces in the knee joint by co-registration of the data acquired using digitization and computed tomography (CT). Local coordinate systems on the distal femur and proximal tibia were established by three spherical fiducial markers rigidly affixed to each bone. The fiducial marker centroid locations were identified by a least-squares sphere-fitting algorithm. An optimization correction procedure was proposed to mitigate the effect of the target registration error (TRE) on the alignment of coordinate systems for co-registration. A test with four cadaveric specimens demonstrated successful mapping of insertion sites for five ligaments. Fiducial registration error (FRE) as measured by the differences in inter-marker distances between the two modalities was smaller than 2%. The optimization procedure corrected the insertion site invisibility or partial visibility problem and improved the overall mapping quality, as indicated by substantial reduction of the mean and dispersion of distances from digitized insertion site points to the bone surfaces.

Validation of finite element predictions of cartilage contact pressure in the human hip joint

Methods to predict contact stresses in the hip can provide an improved understanding of load distribution in the normal and pathologic joint. The objectives of this study were to develop and validate a three-dimensional finite element (FE) model for predicting cartilage contact stresses in the human hip using subject-specific geometry from computed tomography image data, and to assess the sensitivity of model predictions to boundary conditions, cartilage geometry, and cartilage material properties. Loads based on in vivo data were applied to a cadaveric hip joint to simulate walking, descending stairs, and stair-climbing. Contact pressures and areas were measured using pressure sensitive film. CT image data were segmented and discretized into FE meshes of bone and cartilage. FE boundary and loading conditions mimicked the experimental testing. Fair to good qualitative correspondence was obtained between FE predictions and experimental measurements for simulated walking and descending stairs, while excellent agreement was obtained for stair-climbing. Experimental peak pressures, average pressures, and contact areas were 10.0 MPa (limit of film detection), 4.4-5.0 MPa, and 321.9-425.1 mm(2), respectively, while FE-predicted peak pressures, average pressures, and contact areas were 10.8-12.7 MPa, 5.1-6.2 MPa, and 304.2-366.1 mm(2), respectively. Misalignment errors, determined as the difference in root mean squared error before and after alignment of FE results, were less than 10%. Magnitude errors, determined as the residual error following alignment, were approximately 30% but decreased to 10-15% when the regions of highest pressure were compared. Alterations to the cartilage shear modulus, bulk modulus, or thickness resulted in +/-25% change in peak pressures, while changes in average pressures and contact areas were minor (+/-10%). When the pelvis and proximal femur were represented as rigid, there were large changes, but the effect depended on the particular loading scenario. Overall, the subject-specific FE predictions compared favorably with pressure film measurements and were in good agreement with published experimental data. The validated modeling framework provides a foundation for development of patient-specific FE models to investigate the mechanics of normal and pathological hips.

Detection of in vivo dynamic 3-D motion patterns in the wrist joint

We present a method for measurement dynamic in vivo carpal motion patterns. The method consists of a 4-D rotational X-ray (RX) with improved image quality and image processing for accurate detection in vivo wrist motion measurements. Dynamic 3-D imaging yields a number of volume reconstructions of the wrist at different phases of its cyclic motion. Next, the carpal reconstructions are registered to their static acquired and segmented counterpart in all phases. With this information, the relation between the applied motion and carpal kinematic behavior is acquired, i.e., the motion patterns. We investigated the precision of the image acquisition and processing and tested it on three healthy subjects. The precision of the image acquisition and image processing is in the range of submillimeters and subdegrees, respectively, which is better than existing systems and sufficient for clinical investigations. Reproducibility measurements show some more deviation ( > 1 degrees). This method was tested on four human volunteers and agrees for the greater part with previously done invasive and nondynamic measurements. In vivo motion pattern measurement with 4-D-RX imaging and processing is accurate and noninvasive. The motion patterns can reveal disorders that could not have been detected in either video fluoroscopy, computed tomography, or MRI.

Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy

BACKGROUND

Tears of the posterior root of the medial meniscus are becoming increasingly recognized. They can cause rapidly progressive arthritis, yet their biomechanical effects are not understood. The goal of this study was to determine the effects of posterior root tears of the medial meniscus and their repairs on tibiofemoral joint contact pressure and kinematics.

METHODS

Nine fresh-frozen cadaver knees were used. An axial load of 1000 N was applied with a custom testing jig at each of four knee-flexion angles: 0 degrees, 30 degrees, 60 degrees, and 90 degrees. The knees were otherwise unconstrained. Four conditions were tested: (1) intact, (2) a posterior root tear of the medial meniscus, (3) a repaired posterior root tear, and (4) a total medial meniscectomy. Fuji pressure-sensitive film was used to record the contact pressure and area for each testing condition. Kinematic data were obtained by using a robotic arm to record the position of the knees for each loading condition. Three-dimensional knee kinematics were analyzed with custom programs with use of previously described transformations. The measured variables were axial rotation, varus angulation, lateral translation, and anterior translation.

RESULTS

In the medial compartment, a posterior root tear of the medial meniscus caused a 25% increase in peak contact pressure compared with that found in the intact condition (p < 0.001). Repair restored the peak contact pressure to normal. No difference was detected between the peak contact pressure after the total medial meniscectomy and that associated with the root tear. The peak contact pressure in the lateral compartment after the total medial meniscectomy was up to 13% greater than that for all other conditions (p = 0.026). Significant increases in external rotation and lateral tibial translation, compared with the values in the intact knee, were observed in association with the posterior root tear (2.98 degrees and 0.84 mm, respectively) and the meniscectomy (4.45 degrees and 0.80 mm, respectively), and these increases were corrected by the repair.

CONCLUSIONS

This study demonstrated significant changes in contact pressure and knee joint kinematics due to a posterior root tear of the medial meniscus. Root repair was successful in restoring joint biomechanics to within normal conditions.

A subject-specific finite element model of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is commonly injured. The stress distribution in the ACL is the key for understanding its function and injury mechanism, as well as for developing optimal surgical reconstruction protocols. In this study, a three-dimensional subject-specific finite element model of human ACL was developed. Bony geometries were reconstructed from CT scan images, while the geometry of the ACL and the orientation of its fiber bundles were measured via a mechanical digitizer. A transversely isotropic, hyperelastic, and nearly incompressible constitutive model was implemented to describe the mechanical properties of the ACL. A 134N anterior tibial load were applied to a cadaveric knee specimen at full extension, 30 degrees , and 60 degrees of flexion by a 6-DOF Robotic/Universal Force-moment Sensor (UFS) system, which was also used to measure the ACL resultant force. Knee kinematics was collected by digitizing two registration blocks attached to the femur and the tibia, respectively, and was input into the FE model as boundary conditions. The resultant force of the ACL calculated by the FE model was comparable to the experimental data, with the error within 10%, thus validated the model. The FE results showed that the average stress in the ACL was between the range 4.7-5.0MPa, with a peak stress between the range 9.8-10.9MPa, which shifted from the posterior lateral (PL) bundle to the anterior medial (AM) bundle as the knee flexed.

A method for in-vivo kinematic analysis of the forearm

PURPOSE

To develop a method for in-vivo kinematic study of normal forearm rotation using computed tomographic (CT) images and a custom apparatus which allows for control of amount of forearm rotation.

METHODS

The forearm of one asymptomatic volunteer was CT-scanned in five positions: neutral, 60 degrees pronation, maximal pronation, 60 degrees supination, and maximal supination. Surface registration of the pronated/supinated image datasets with the neutral position was performed. The resulting transformation matrices were decomposed into finite helical axis (FHA) parameters. Kinematics were expressed as motion of the radius relative to the ulna.

RESULTS

The axes of the forearm passed through the volar region of the radial head at the proximal radioulnar joint (PRUJ), extending towards the dorsal region of the ulnar head at the distal radioulnar joint (DRUJ). Distinct FHAs were calculated for each forearm position analyzed relative to neutral rotation. Forearm pronation FHAs were different from forearm supination FHAs.

CONCLUSIONS

Our experimental methodology is capable of describing the in-vivo kinematics of the forearm with good accuracy and reliability. Future in-vivo studies would need to be performed using a larger sample size to further validate our preliminary results. An ideal clinical application of this methodology would be in the comparative study of patients with forearm dysfunction.

In vivo three-dimensional displacement of the distal radioulnar joint during resisted forearm rotation

PURPOSE

The in vivo displacement of the distal radioulnar joint (DRUJ) while under resisted pronation or supination has never been previously quantified. Being a joint with 3 dimensions of motion (dorsopalmar translation, changes in ulnar variance, and radioulnar coaptation), our purpose was to determine its 3-dimensional (3D) displacement during resisted rotational torque.

METHODS

Ten normal subjects (aged 31.8 years+/-7.8; F, 5; M, 5) were recruited. Computed tomography scans of a subjects' distal forearms were obtained while grasping the handles of a custom apparatus to keep the fist and forearm in neutral rotation. Scanning was performed in 3 conditions: no rotational torque (control), maximum isometric supination, and maximum isometric pronation. The 3D displacement of the DRUJ, using the ulnar fovea as the reference point, during isometric rotational torque was determined using markerless bone registration techniques.

RESULTS

The mean 3D displacement of the ulnar fovea during maximum isometric pronation and maximum isometric supination was 3.09 mm+/-0.94 and 2.17 mm+/-1.55, respectively. During maximum isometric pronation, the ulnar fovea displaced a mean of 0.51 mm+/-1.79 dorsally. During maximum isometric supination, the ulnar fovea displaced a mean of 0.13 mm+/-2.07 volarly. In both conditions, ulnar variance increased (0.23 mm+/-2.52 for isometric pronation and 0.44 mm+/-1.57 for isometric supination), and there was increased radioulnar coaptation (0.37 mm+/-0.86 for isometric pronation, 0.039 mm+/-0.66 for isometric supination).

CONCLUSIONS

Resisted rotational torque can be applied to the DRUJ while in neutral rotation during computed tomography imaging, producing measurable displacements in 3D. This technique of studying the DRUJ has the potential to improve our ability to detect and quantify instabilities of the DRUJ.

Carpal kinematics after proximal row carpectomy

PURPOSE

Proximal row carpectomy (PRC) is a clinically useful motion-sparing procedure for the treatment of certain degenerative conditions of the wrist. Clinical outcome studies after PRC have shown that wrist flexion-extension averages approximately 60% of that of the contralateral wrist. The purpose of this study was to determine how the kinematics of the wrist are altered after PRC.

METHODS

Eight fresh-frozen cadaver forearms were scanned with computed tomography before and after PRC. Forearms were scanned in 5 different wrist positions (neutral, extension, flexion, radial deviations, and ulnar deviation). Wrists were positioned dynamically and then held statically in a custom fixture through forces applied to the 4 wrist flexor/extensor tendon groups. Three-dimensional computer models of the radius, lunate, and capitate were generated from the computed tomographic images, and the kinematics of the capitate and lunate were calculated relative to the neutral position. For the intact wrist, the motion of the capitate was calculated relative to both the lunate (midcarpal motion) and the radius (overall wrist motion) and the motion of the lunate was calculated relative to the radius (radiocarpal motion). After PRC, only the movement of the capitate relative to the radius was calculated, which represents radiocapitate and overall wrist motion. All motions were plotted in 3 dimensions for purposes of qualitative visualization.

RESULTS

After PRC, the capitate articulated with the lunate fossa of the radius for all positions in all samples. Overall wrist motion decreased 28%, 30%, 40%, and 12% in flexion, extension, radial deviation, and ulnar deviation, respectively. Motion at the radiocarpal joint after PRC, however, was greater compared with motion at the radiocarpal and midcarpal joints of the intact wrist during flexion and extension. This was not the case in radial deviation because of impingement of the trapezoid on the radial styloid. In radial and ulnar deviation, motion of the capitate head changed from predominantly rotational in the intact wrist (midcarpal joint) to a combination of rotation and translation after PRC (radiocarpal joint).

CONCLUSIONS

Removal of the proximal carpal row decreased normal wrist flexion and extension. Although ulnar deviation was preserved, radial deviation was limited by impingement of the trapezoid on the radial styloid. Radiocapitate range of motion after PRC was greater than capitolunate range of motion in the intact wrists. Compared with previously published requirements, wrist range of motion observed after PRC was sufficient for activities of daily living.

Low-dose computed tomography: a solution for in vivo medical imaging and accurate patient-specific 3D bone modeling?

BACKGROUND

The number of in vivo clinical biomedical experiments based on computed tomography is increasing. International radiation-protection bodies are promoting the use of low-dose computed tomography to reduce radiation absorption by the subject undergoing imaging. On the other hand no data exist in the literature to quantify whether or not low-dose computed tomography would lead to a decrease of result quality when used for three-dimensional bone modeling and related measurements.

METHODS

This paper aimed at finding a consensus between minimal X-ray radiation of the subject, and satisfactory image data quality, especially for accurate three-dimensional bone modeling. Several standard computed tomography and low-dose computed tomography sequences were analyzed in three tests and statistically compared.

FINDINGS

Absence of significant difference between standard and low-dose computed sequences indicated that the low-dose setting would not produce less accurate three-dimensional models, while it decreased the effective X-ray dose up to 90% compared to standard settings.

INTERPRETATION

Low-dose computed tomography seems suitable for accurate three-dimensional bone modeling, while the related effective X-ray radiation is low. Such setting is therefore advised for any in vivo medical imaging aiming to collect bone data.

IMAGE FUSION OF COMPUTED TOMOGRAPHIC AND MAGNETIC RESONANCE IMAGES FOR THE DEVELOPMENT OF A THREE-DIMENSIONAL MUSCULOSKELETAL MODEL OF THE EQUINE FORELIMB

Biomechanical models that compute the lengths and forces of muscle-tendon units are broadly applicable to the study of factors that promote injury and the planning and effects of orthopedic surgical procedures in equine athletes. A three-dimensional (3D) generic musculoskeletal model of the equine forelimb comprised of bony segment, muscle-tendon, and ligament information, was developed based on high-resolution computed tomographic (CT) and T1-weighted magnetic resonance (MR) images from an isolated forelimb of a Thoroughbred racehorse. Image fusion was achieved through coregistration of CT and MR images with an image analysis program (Analyze) by adjustment of the relative position and orientation of fiducial markers visible in both modalities until the mutual information between the images was maximized. 3D surfaces of the bones and origin/insertion sites, centroid paths and volumes of the muscle-tendon and ligamentous structures were obtained from the multimodal (CT/MR) images using semiautomated and manual segmentation combined with sagittal and transverse color-cryosection anatomic images obtained from three other cadaveric equine forelimbs. Once bony and soft-tissue structures were reconstructed in the same coordinate system, data were imported to a software package for interactive musculoskeletal modeling (SIMM). The combination of integrated CT and MR acquisitions and anatomical images provided an accurate and efficient means of generating a 3D model of the musculoskeletal structures of an average-sized equine adult horse.

Kinematics of the midcarpal and radiocarpal joint in flexion and extension: an in vitro study

PURPOSE

To apply carpal kinematic analysis using noninvasive medical imaging to investigate the midcarpal and radiocarpal contributions to wrist flexion and extension in a quasidynamic in vitro model.

METHODS

Eight fresh-frozen cadaver wrists were scanned with computed tomography in neutral, full flexion, and full extension. Body-mass-based local coordinate systems were used to track motion of the capitate, lunate, and scaphoid with the radius as a fixed reference. Helical axis motion parameters and Euler angles were calculated for flexion and extension.

RESULTS

Minimal out-of-plane carpal motion was noted with the exception of small amounts of ulnar deviation and supination in flexion. Overall wrist flexion was 68 degrees +/- 12 degrees and extension was 50 degrees +/- 12 degrees. In flexion, 75% of wrist motion occurred at the radioscaphoid joint, and 50% occurred at the radiolunate joint. In extension, 92% of wrist motion occurred at the radioscaphoid joint, and 52% occurred at the radiolunate joint. Midcarpal flexion/extension between the capitate and scaphoid was 0 degrees +/- 5 degrees in extension and 10 degrees +/- 13 degrees in flexion. Midcarpal flexion/extension between the capitate and lunate was larger, with 15 degrees +/- 11 degrees in extension and 22 degrees +/- 19 degrees in flexion.

CONCLUSIONS

The capitate and scaphoid tend to move together. This results in greater flexion/extension for the scaphoid than the lunate at the radiocarpal joint. The lunate has greater midcarpal motion between it and the capitate than the scaphoid does with the capitate. The engagement between the scaphoid and capitate is particularly evident during wrist extension. Out-of-plane motion was primarily ulnar deviation at the radiocarpal joint during flexion. These results are clinically useful in understanding the consequences of isolated fusions in the treatment of wrist instability.

The effect of the orientation of the radial head on the kinematics of the ulnohumeral joint and force transmission through the radiocapitellar joint

Background. The treatment of radial head fractures that are not amenable to an open reduction and internal fixation, remains to be a difficult issue. A potential problem with prosthetic replacement of the radial head is the shape of current radial head prostheses. The purpose of this study was to determine the effect of the shape of the radial head on kinematics and load transfer of the elbow. Methods. Kinematics of the elbow and radiocapitellar force transmission were measured in 6 fresh frozen upper extremities. The effect of radial head shape was tested by rotating the head 90 degrees , with a custom-made 'native' radial head prosthesis. 3-D spatial orientation of the ulna showed an average difference in ulnohumeral laxity, between the nominal and 90 degrees conditions, of 0.1 degrees throughout the arc of motion with neutral forearm rotation (maximum: 2 degrees ). Findings. We found an average difference in ulnar axial rotation, of 0.1 degrees (maximum: 1.9 degrees ). No differences showed statistical significance. Radiohumeral joint force was measured and maximally showed a 32 times increase of force in the altered shape conditions. Interpretation. Our results show that the kinematics of the elbow was not affected by altering the shape of the radial head, but it did adversely affect the forces in the radiohumeral joint. This could possibly generate degenerative changes in the elbow.

Analysis of skin movement with respect to flexional bone motion using MR images of a hand

This study describes the methodology for analyzing skin movement with respect to the predefined flexional motion of the hand. The 3D in vivo geometric data were acquired through magnetic resonance (MR) scanning of multiple hands in various postures. Custom software was developed to segment MR images and to generate polygonal isosurfaces. A new bone coordinate system (BCS) was defined to describe the skin movement measured with the skin-surface markers. The BCS was defined by the surface registration technique, which could minimize the distance among the 3D polygonal surfaces of different postures. MR images of six subjects in the 3 postures were captured with skin-surface markers for the experiment. Skin movement on the second metacarpal bone, which was fixed during the flexional motion, ranged from 1.169 to 10.885 mm. While the distance of the skin movement varied from one subject to another, a common skin movement direction was observed among the six subjects. For the repeatability evaluation of the proposed method, the MR images of the same subject were independently processed 10 times by a trained operator. The standard deviation of the skin movement on the second metacarpal of the index finger with respect to the predefined flexional motion ranged from 0.45 to 0.74 mm.

In vivo three-dimensional motion analysis of the forearm with radioulnar synostosis treated by the Kanaya procedure

Attempts to separate congenital radioulnar synostosis and restore forearm rotation had been disappointing until a new mobilization technique was developed by Kanaya and colleagues using free vascularized fascio-fat graft interposition. This technique provides a functional rotation arc, but postoperative forearm motion is difficult to evaluate given the inaccuracies in determining the range of motion and rotational axis using conventional x-rays or computed tomography. This study represents an attempt to analyze in vivo three-dimensional motion of the forearm with radioulnar synostosis treated by Kanaya's operation using a markerless bone registration technique. Six patients with seven postoperative forearms (six with congenital and one with posttraumatic radioulnar synostosis) underwent 3D computed tomography with the forearm in neutral, fully pronated, and fully supinated positions. Range of motion according to this method was 30 +/- 18 degrees, significantly smaller than the 82 +/- 29 degrees from manual examination. Improvements in range of motion were significantly greater in cases without dislocation of the radial head (46 +/- 13 degrees) than in cases with dislocation (19 +/- 10 degrees). Dislocation of the radial head was also significantly correlated with an abnormal axis of rotation of the forearm.

A Model of Stress and Strain in the Interosseous Ligament of the Forearm Based on Fiber Network Theory

Fiber network theory was developed to describe cloth, a thin material with strength in the fiber directions. The interosseous ligament (IOL) of the forearm is a broad, thin ligament with highly aligned fibers. The objectives of this study were to develop a model of the stress and strain distributions in the IOL, based on fiber network theory, to compare the strains from the model with the experimentally measured strains, and to evaluate the force distribution across the ligament fibers from the model. The geometries of the radius, ulna, and IOL were reconstructed from CT scans. Position and orientation of IOL insertion sites and force in the IOL were measured during a forearm compression experiment in pronation, neutral rotation, and supination. An optical image-based technique was used to directly measure strain in two regions of the IOL in neutral rotation. For the network model, the IOL was represented as a parametric ruled three-dimensional surface, with rulings along local fiber directions. Fiber strains were calculated from the deformation field, and fiber stresses were calculated from the strains using average IOL tensile properties from a previous study. The in situ strain in the IOL was assumed uniform and was calculated so that the net force predicted by the network model in neutral rotation matched the experimental result. The net force in the IOL was comparable to experimental results in supination and pronation. The model predicted higher stress and strain in fibers near the elbow in neutral rotation, and higher stresses in fibers near the wrist in supination. Strains in neutral forearm rotation followed the same trends as those measured experimentally. In this study, a model of stress and strain in the IOL utilizing fiber network theory was successfully implemented. The model illustrates variations in the stress and strain distribution in the IOL. This model can be used to show surgeons how different fibers are taut in different forearm rotation positions—this information is important for understanding the biomechanical role of the IOL and for planning an IOL reconstruction.

In Vivo Registration of Both Electrogoniometry and Medical Imaging: Development and Application on the Ankle Joint Complex

An in vivo method for joint kinematics visualization and analysis is described. Low-dose computed tomography allowed three-dimensional joint modeling, and electrogoniometry collected joint kinematic data. Data registration occurred using palpated anatomical landmarks to obtain interactive computer joint simulation. The method was applied on one volunteer's ankle, and reproducibility was tested (maximal discrepancy: 3.6 deg and 5.5 mm for rotation and translation respectively).

A novel methodology to reproduce previously recorded six-degree of freedom kinematics on the same diarthrodial joint

The objective of this study was to develop a novel method to more accurately reproduce previously recorded 6-DOF kinematics of the tibia with respect to the femur using robotic technology. Furthermore, the effect of performing only a single or multiple registrations and the effect of robot joint configuration were investigated. A single registration consisted of registering the tibia and femur with respect to the robot at full extension and reproducing all kinematics while multiple registrations consisted of registering the bones at each flexion angle and reproducing only the kinematics of the corresponding flexion angle. Kinematics of the knee in response to an anterior (134 N) and combined internal/external (+/-10 N m) and varus/valgus (+/-5 N m) loads were collected at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. A six axes, serial-articulated robotic manipulator (PUMA Model 762) was calibrated and the working volume was reduced to improve the robot's accuracy. The effect of the robot joint configuration was determined by performing single and multiple registrations for three selected configurations. For each robot joint configuration, the accuracy in position of the reproduced kinematics improved after multiple registrations (0.7+/-0.3, 1.2+/-0.5, and 0.9+/-0.2 mm, respectively) when compared to only a single registration (1.3+/-0.9, 2.0+/-1.0, and 1.5+/-0.7 mm, respectively) (p<0.05). The accuracy in position of each robot joint configuration was unique as significant differences were detected between each of the configurations. These data demonstrate that the number of registrations and the robot joint configuration both affect the accuracy of the reproduced kinematics. Therefore, when using robotic technology to reproduce previously recorded kinematics, it may be necessary to perform these analyses for each individual robotic system and for each diarthrodial joint, as different joints will require the robot to be placed in different robot joint configurations.

Subject-specific finite element model of the pelvis: development, validation and sensitivity studies

A better understanding of the three-dimensional mechanics of the pelvis, at the patient-specific level, may lead to improved treatment modalities. Although finite element (FE) models of the pelvis have been developed, validation by direct comparison with subject-specific strains has not been performed, and previous models used simplifying assumptions regarding geometry and material properties. The objectives of this study were to develop and validate a realistic FE model of the pelvis using subject-specific estimates of bone geometry, location-dependent cortical thickness and trabecular bone elastic modulus, and to assess the sensitivity of FE strain predictions to assumptions regarding cortical bone thickness as well as bone and cartilage material properties. A FE model of a cadaveric pelvis was created using subject-specific computed tomography image data. Acetabular loading was applied to the same pelvis using a prosthetic femoral stem in a fashion that could be easily duplicated in the computational model. Cortical bone strains were monitored with rosette strain gauges in ten locations on the left hemipelvis. FE strain predictions were compared directly with experimental results for validation. Overall, baseline FE predictions were strongly correlated with experimental results (r2=0.824), with a best-fit line that was not statistically different than the line y=x (experimental strains = FE predicted strains). Changes to cortical bone thickness and elastic modulus had the largest effect on cortical bone strains. The FE model was less sensitive to changes in all other parameters. The methods developed and validated in this study will be useful for creating and analyzing patient-specific FE models to better understand the biomechanics of the pelvis.

Kinematics of the midcarpal and radiocarpal joints in radioulnar deviation: an in vitro study

PURPOSE

Carpal kinematics have been studied widely yet remain difficult to understand fully. The noninvasive measurement of carpal kinematics through medical imaging has become popular. Studies have shown that with radial deviation the scaphoid and lunate flex whereas the capitate moves radiodorsally relative to the lunate. This study investigated the midcarpal and radiocarpal contributions to radial and ulnar deviation of the wrist. This was accomplished through noninvasive characterization of the scaphoid, lunate, and capitate using 3-dimensional medical imaging of the wrist in radial and ulnar deviation.

METHODS

Eight fresh-frozen and thawed cadaveric wrists were used in an experimental set-up that positioned the wrist through spring-scale actuation of the 4 wrist flexor and extensor tendon groups. The wrists were scanned by computed tomography in neutral and full radial and ulnar deviation. Body mass-based local coordinate systems were used to track the motion of the capitate, lunate, and scaphoid with the radius as a fixed reference. Helical axis motion and Euler angles were calculated from neutral to radial and ulnar deviation for the capitate relative to the radius, lunate, and scaphoid and for the lunate and scaphoid relative to the radius.

RESULTS

The capitate, scaphoid, and lunate moved in a characteristic manner relative to the radius and to one another. Radial and ulnar deviation occurred primarily in the midcarpal joint. Midcarpal motion accounted for 60% of radial deviation and 86% of ulnar deviation. In radial deviation the proximal row flexed and the capitate extended; the converse was true in ulnar deviation.

CONCLUSIONS

Radioulnar deviation (in-plane motion) occurred mostly through the midcarpal joint, with a lesser contribution from the radiocarpal joint. The results of our study agree with previous investigations that found the scaphoid and lunate flex in radial deviation (out-of-plane motion) relative to the radius whereas the capitate extends (out-of-plane motion) relative to the scaphoid/lunate (with the converse occurring in ulnar deviation). Our study shows how these out-of-plane motions combine to produce in-plane wrist radioulnar deviation. The use of 3-dimensional visualization greatly aids in the understanding of these motions. The results of our study may be useful clinically in understanding the consequences of isolated midcarpal fusions in the treatment of wrist instability.

4D rotational x-ray imaging of wrist joint dynamic motion

Current methods for imaging joint motion are limited to either two-dimensional (2D) video fluoroscopy, or to animated motions from a series of static three-dimensional (3D) images. 3D movement patterns can be detected from biplane fluoroscopy images matched with computed tomography images. This involves several x-ray modalities and sophisticated 2D to 3D matching for the complex wrist joint. We present a method for the acquisition of dynamic 3D images of a moving joint. In our method a 3D-rotational x-ray (3D-RX) system is used to image a cyclically moving joint. The cyclic motion is synchronized to the x-ray acquisition to yield multiple sets of projection images, which are reconstructed to a series of time resolved 3D images, i.e., four-dimensional rotational x ray (4D-RX). To investigate the obtained image quality parameters the full width at half maximum (FWHM) of the point spread function (PSF) via the edge spread function and the contrast to noise ratio between air and phantom were determined on reconstructions of a bullet and rod phantom, using 4D-RX as well as stationary 3D-RX images. The CNR in volume reconstructions based on 251 projection images in the static situation and on 41 and 34 projection images of a moving phantom were 6.9, 3.0, and 2.9, respectively. The average FWHM of the PSF of these same images was, respectively, 1.1, 1.7, and 2.2 mm orthogonal to the motion and parallel to direction of motion 0.6, 0.7, and 1.0 mm. The main deterioration of 4D-RX images compared to 3D-RX images is due to the low number of projection images used and not to the motion of the object. Using 41 projection images seems the best setting for the current system. Experiments on a postmortem wrist show the feasibility of the method for imaging 3D dynamic joint motion. We expect that 4D-RX will pave the way to improved assessment of joint disorders by detection of 3D dynamic motion patterns in joints.

Three-dimensional finite element modeling of ligaments: technical aspects

The objective of this paper is to describe strategies for addressing technical aspects of the computational modeling of ligaments with the finite element (FE) method. Strategies for FE modeling of ligament mechanics are described, differentiating between whole-joint models and models of individual ligaments. Common approaches to obtain three-dimensional ligament geometry are reviewed, with an emphasis on techniques that rely on volumetric medical image data. Considerations for the three-dimensional constitutive modeling of ligaments are reviewed in the context of ligament composition and structure. A novel approach to apply in situ strain to FE models of ligaments is described, and test problems are presented that demonstrate the efficacy of the approach. Approaches for the verification and validation of ligament FE models are outlined. The paper concludes with a discussion of future research directions.

Reconstruction of the interosseous ligament restores normal forearm compressive load transfer in cadavers

PURPOSE

Longitudinal radioulnar dissociation may result when compressive load to the hand causes excessive proximal migration of the radius with interosseous ligament (IOL) disruption and radial head fracture. Although radial head salvage or arthroplasty and temporary distal radioulnar joint pinning constitute the current treatment for this injury IOL reconstruction has been proposed to restore normal forearm mechanics. To help provide a biomechanical basis for IOL reconstruction we measured load transfer and proximal migration of the radius with the IOL intact, cut, and reconstructed while leaving the radial head intact.

METHODS

We dissected the central third of 12 normal cadaveric forearms to bone-IOL-bone. We applied 136 N of compressive load to the hand and measured proximal radial migration and 3-dimensional force vectors acting in the distal radius, distal ulna, IOL, proximal radius, and proximal ulna. Experiments were performed in neutral forearm rotation and neutral elbow varus-valgus. The protocol was repeated with the IOL intact, cut, and reconstructed with single and double flexor carpi radialis allografts.

RESULTS

With the IOL intact 94% +/- 3 % of hand load was in the distal radius with 75% +/- 2% was transmitted to the proximal radius. With the IOL cut 92% +/- 2% of hand load was in the distal radius and this was unchanged at the proximal radius. With single flexor carpi radialis reconstruction 94% +/- 3% of hand load was in the distal radius and 80% +/- 2% was in the proximal radius; with double flexor carpi radialis reconstruction these numbers changed to 95% +/- 3% and 74% +/- 2%, respectively. Forces in the forearm were mainly in the longitudinal and transverse directions with negligible components in the dorsal-volar direction. Transverse force in the IOL was about half that of the longitudinal force in the intact and reconstructed states.

CONCLUSIONS

When the IOL is cut and load is applied to the hand the unloading of the proximal radius and the transversely directed force that compresses normally across the proximal and distalradioulnar joints is lost. Reconstruction of the IOL can restore the normal load transfer characteristics. These data help provide a biomechanical basis for IOL reconstruction. Further research on the biomechanics of IOL reconstruction in the setting of radial head replacement along with clinical evaluation is needed.

Development and Validation of a Computed Tomography-Based Methodology to Measure Carpal Kinematics

Motion of the wrist bones is complicated and difficult to measure. Noninvasive measurement of carpal kinematics using medical images has become popular. This technique is difficult and most investigators employ custom software. The objective of this paper is to describe a validated methodology for measuring carpal kinematics from computed tomography (CT) scans using commercial software. Four cadaveric wrists were CT imaged in neutral, full flexion, and full extension. A registration block was attached to the distal radius and used to align the data sets from each position. From the CT data, triangulated surface models of the radius, lunate, and capitate bones were generated using commercial software. The surface models from each wrist position were read into engineering design software that was used to calculate the centroid (position) and principal mass moments of inertia (orientation) of (1) the capitate and lunate relative to the fixed radius and (2) the capitate relative to the lunate. These data were used to calculate the helical axis kinematics for the motions from neutral to extension and neutral to flexion. The kinematics were plotted in three dimensions using a data visualization software package. The accuracy of the method was quantified in a separate set of experiments in which an isolated capitate bone was subjected to two different known rotation/translation motions for ten trials each. For comparison to in vivo techniques, the error in distal radius surface matching was determined using the block technique as a gold standard. The motion that the lunate and capitate underwent was half that of the overall wrist flexion-extension range of motion. Individually, the capitate relative to the lunate and the lunate relative to the radius generally flexed or extended about 30 deg, while the entire wrist (capitate relative to radius) typically flexed or extended about 60 deg. Helical axis translations were small, ranging from 0.6 mm to 1.8 mm across all motions. The accuracy of the method was found to be within 1.4 mm and 0.5 deg (95% confidence intervals). The mean error in distal radius surface matching was 2.4 mm and 1.2 deg compared to the use of a registration block. Carpal kinematics measured using the described methodology were accurate, reproducible, and similar to findings of previous investigators. The use of commercially available software should broaden the access of researchers interested in measuring carpal kinematics using medical imaging.

Stress and strain in the anterior band of the inferior glenohumeral ligament during a simulated clinical examination

The objective of this research was to predict, with a finite-element model, the stress and strain fields in the anterior band of the inferior glenohumeral ligament (AB-IGHL) during application of an anterior load with the humerus abducted. The stress and strain in the AB-IGHL were determined during a simulated simple translation test of a single intact shoulder. A 6-degree-of-freedom magnetic tracking system was used to measure the kinematics of the humerus with respect to the scapula. A clinician applied an anterior load to the humerus until a manual maximum was achieved at 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension and external rotation. For the computational analysis, the experimentally measured joint kinematics were used to prescribe the motion of the humerus with respect to the scapula, whereas the material properties of the AB-IGHL were based on published experimental data. The geometry of the AB-IGHL, humerus, and scapula was acquired by use of a volumetric computed tomography scan, which was used to define the reference configuration of the AB-IGHL. Strains reached 12% along the inferior edge and 15% near the scapular insertion site at the position of maximum anterior translation. During this motion, the AB-IGHL wrapped around the humerus and transferred load to the bone via contact. Predicted values for von Mises stress in the ligament reached 4.3 MPa at the point of contact with the humeral head and 6.4 MPa near the scapular insertion site. A comparison of these results to the literature suggests that the computational approach provided reasonable predictions of fiber strain in the AB-IGHL when specimen-specific geometry and kinematics with average material properties were used. The complex stress and strain distribution throughout the AB-IGHL suggests that the continuous nature of the glenohumeral capsule should be considered in biomechanical analyses. In the future, this combined experimental and computational approach will be used for subject-specific studies of capsular function and could provide quantitative data to help surgeons improve methods for the diagnosis and treatment of glenohumeral instability.

Three-dimensional modeling and animation of two carpal bones: a technique

The objectives of this study were to (a). create 3D reconstructions of two carpal bones from single CT data sets and animate these bones with experimental in vitro motion data collected during dynamic loading of the wrist joint, (b). develop a technique to calculate the minimum interbone distance between the two carpal bones, and (c). validate the interbone distance calculation process. This method utilized commercial software to create the animations and an in-house program to interface with three-dimensional CAD software to calculate the minimum distance between the irregular geometries of the bones. This interbone minimum distance provides quantitative information regarding the motion of the bones studied and may help to understand and quantify the effects of ligamentous injury.

Calibration and validation of 6 DOFs instrumented spatial linkage for biomechanical applications. A practical approach

A method for both calibration and validation of a 6 DOF electrogoniometer is presented. A 6 Revolute Instrumented Spatial Linkage (6R-ISL) and a three-dimensional digitizer (3DD) were used simultaneously to collect both static and continuous poses of unconstrained or constrained motions. Validation occurred using a calibrated ball-and-socket joint. A parametrical model of the 6R-ISL (i.e. Virtual Goniometer or VG) was designed using a standard multibody system geometry. Two approaches were used to adjust the VG parameters: a parametrical adjustment of the VG linkage geometry, and a functional adjustment of the potentiometer calibration curves (angle-voltage) in a predefined range of motion. After calibration, 6R-ISL accuracy was better than 1 mm and 1 degrees for translation and orientation, respectively. The functional method presented in this paper can be suggested as a practical approach, which allows on-line checking and calibration of 6R-ISL within the specific range of interest of a particular anatomical joint. In addition, improving the potentiometer calibration curves was less time consuming than the parametrical adjustment.

Passive strain distribution in the interosseous ligament of the forearm: implications for injury reconstruction

PURPOSE

For severe forearm injuries such as an Essex-Lopresti fracture-dislocation, functional reconstruction necessitates repair of the interosseous ligament (IOL) to restore normal load sharing between the radius and ulna. Locating or tensioning such a reconstruction improperly can lead to abnormal load sharing and/or restriction of forearm rotation. The normal IOL strains should indicate the proper location of reconstruction grafts and the proper forearm rotation for tensioning the grafts. The objective of this study was to quantify the passive strain distribution of the IOL of the forearm with passive rotation of the forearm throughout the range of motion.

METHODS

The 3-dimensional motions of the radius with respect to the ulna were measured throughout forearm rotation in 10 cadaveric forearms by using an instrumented spatial linkage. From the bone motions and ligament insertion site geometry from dissection and computed tomographic scanning, insertion site motions were determined and used to calculate changes in ligament fiber lengths.

RESULTS

The measured strain distribution in the IOL was nonuniform and varied with forearm rotation. The overall magnitude of IOL strain was found to be greatest in supination and smallest in pronation. In supination the strains varied across fibers with strains being greatest in the distal fibers and lowest in the proximal fibers. Strains in neutral rotation were uniform across fibers. Although fibers were generally slack in pronation proximal fibers were less slack than distal fibers.

CONCLUSIONS

The results of this study indicate that fiber strains in the IOL vary from proximal to distal and depend on forearm rotation. Our data suggest that to prevent restriction of forearm rotation all grafts should be tensioned in supination, where measured strains were generally highest. Our data also suggest that a 2-bundle IOL reconstruction may be necessary for proper load transfer between the radius and ulna in both supination and pronation.

Subject-specific finite element analysis of the human medial collateral ligament during valgus knee loading

The objectives of this study were (1) to develop subject-specific experimental and finite element (FE) techniques to study the three-dimensional stress-strain behavior of ligaments, with application to the human medial collateral ligament (MCL), and (2) to determine the importance of subject-specific material properties and initial (in situ) strain distribution for prediction of the strain distribution in the MCL under valgus loading. Eight male knees were subjected to varus-valgus loading at flexion angles of 0 degrees, 30 degrees, and 60 degrees. Three-dimensional joint kinematics and MCL strains were recorded during kinematic testing. Following testing, the MCL of each knee was removed to allow measurement of the in situ strain distribution and to perform material testing. A FE model of the femur-MCL-tibia complex was constructed for each knee to simulate valgus loading at each flexion angle, using subject-specific bone and ligament geometry, material properties, and joint kinematics. A transversely isotropic hyperelastic material model was used to represent the MCL. The MCL in situ strain distribution at full extension was used to apply in situ strain to each MCL FE model. FE predicted MCL strains during valgus loading were compared to experimental measurements using regression analysis. The subject-specific FE predictions of strain correlated reasonably well with experimentally measured MCL strains (R(2)=0.83, 0.72, and 0.66 at 0 degrees, 30 degrees, and 60 degrees, respectively). Despite large inter-subject variation in MCL material properties, MCL strain distributions predicted by individual FE models that used average MCL material properties were strongly correlated with subject-specific FE strain predictions (R(2)=0.99 at all flexion angles). However, predictions by FE models that used average in situ strain distributions yielded relatively poor correlations with subject-specific FE predictions (R(2)=0.44, 0.35, and 0.33 at flexion angles of 0 degrees, 30 degrees, and 60 degrees, respectively). The strain distribution within the MCL was nonuniform and changed with flexion angle. The highest MCL strains occurred at full extension in the posterior region of the MCL proximal to the joint line during valgus loading, suggesting this region may be most vulnerable to injury under these loading conditions. This work demonstrates that subject-specific FE models can predict the complex, nonuniform strain fields that occur in ligaments due to external loading of the joint.

In-vivo measurement of dynamic joint motion using high speed biplane radiography and CT: application to canine ACL deficiency

Dynamic assessment of three-dimensional (3D) skeletal kinematics is essential for understanding normal joint function as well as the effects of injury or disease. This paper presents a novel technique for measuring in-vivo skeletal kinematics that combines data collected from high-speed biplane radiography and static computed tomography (CT). The goals of the present study were to demonstrate that highly precise measurements can be obtained during dynamic movement studies employing high frame-rate biplane video-radiography, to develop a method for expressing joint kinematics in an anatomically relevant coordinate system and to demonstrate the application of this technique by calculating canine tibio-femoral kinematics during dynamic motion. The method consists of four components: the generation and acquisition of high frame rate biplane radiographs, identification and 3D tracking of implanted bone markers, CT-based coordinate system determination, and kinematic analysis routines for determining joint motion in anatomically based coordinates. Results from dynamic tracking of markers inserted in a phantom object showed the system bias was insignificant (-0.02 mm). The average precision in tracking implanted markers in-vivo was 0.064 mm for the distance between markers and 0.31 degree for the angles between markers. Across-trial standard deviations for tibio-femoral translations were similar for all three motion directions, averaging 0.14 mm (range 0.08 to 0.20 mm). Variability in tibio-femoral rotations was more dependent on rotation axis, with across-trial standard deviations averaging 1.71 degrees for flexion/extension, 0.90 degree for internal/external rotation, and 0.40 degree for varus/valgus rotation. Advantages of this technique over traditional motion analysis methods include the elimination of skin motion artifacts, improved tracking precision and the ability to present results in a consistent anatomical reference frame.

Registration of 6-DOFs electrogoniometry and CT medical imaging for 3D joint modeling

The paper describes a method in which two data-collecting systems, medical imaging and electrogoniometry, are combined to allow the accurate and simultaneous modeling of both the spatial kinematics and the morphological surface of a particular joint. The joint of interest (JOI) is attached to a Plexiglas jig that includes four metallic markers defining a local reference system (R(GONIO)) for the kinematics data. Volumetric data of the JOI and the R(GONIO) markers are collected from medical imaging. The spatial location and orientation of the markers in the global reference system (R(CT)) of the medical-imaging environment are obtained by applying object-recognition and classification methods on the image dataset. Segmentation and 3D isosurfacing of the JOI are performed to produce a 3D model including two anatomical objects-the proximal and distal JOI segments. After imaging, one end of a custom-made 3D electrogoniometer is attached to the distal segment of the JOI, and the other end is placed at the R(GONIO) origin; the JOI is displaced and the spatial kinematics data is recorded by the goniometer. After recording, data registration from R(GONIO) to R(CT) occurred prior to simulation. Data analysis was performed using both joint coordinate system (JCS) and instantaneous helical axis (IHA).Finally, the 3D joint model is simulated in real time using the experimental kinematics data. The system is integrated into a computer graphics interface, allowing free manipulation of the 3D scene. The overall accuracy of the method has been validated with two other kinematics data collection methods including a 3D digitizer and interpolation of the kinematics data from discrete positions obtained from medical imaging. Validation has been performed on both superior and inferior radio-ulna joints (i.e. prono-supination motion). Maximal RMS error was 1 degrees and 1.2mm on the helical axis rotation and translation, respectively. Prono-supination of the forearm showed a total rotation of 132 degrees for 0.8mm of translation. The method reproducibility using JCS parameters was in average 1 degrees (maximal deviation=2 degrees ) for rotation, and 1mm (maximal deviation=2mm) for translation. In vitro experiments have been performed on both knee joint and ankle joint. Averaged JCS parameters for the knee were 109 degrees, 17 degrees and 4 degrees for flexion, internal rotation and abduction, respectively. Averaged maximal translation values for the knee were 12, 3 and 4mm posteriorly, medially and proximally, respectively. Averaged JCS parameters for the ankle were 43 degrees, 9 degrees and 3 degrees for plantarflexion, adduction and internal rotation, respectively. Averaged maximal translation values for the ankle were 4, 2 and 1mm anteriorly, medially and proximally, respectively.

The Essex-Lopresti fracture-dislocation factors in early management and salvage alternatives

Treatment recommendations for the Essex-Lopresti lesion have not come very far in 50 years. Although there have been multiple biomechanical studies, the biomechanics of forearm loading and stability remain somewhat elusive. Clinical studies have yielded some insight, but predictable outcomes are exceptional. More studies are needed to further understand the biomechanics of the forearm and provide a basis for reconstruction of the IOL. Although current clinical studies regarding IOL reconstruction and radial head replacement seem promising, long-term results with substantial patient numbers are needed. In the short term, the Essex-Lopresti lesion continues to challenge clinicians.