In Vivo Measurement of the Human Lumbar Spine Using Magnetic Resonance Imaging to Ultrasound Registration.

OBJECTIVE: This study aimed to refine a magnetic resonance imaging (MRI)-ultrasound registration (ie, alignment) technique to make noninvasive, nonionizing, 3-dimensional measurement of the lumbar segmental motion in vivo. METHODS: Five healthy participants participated in this validation study. We scanned the lumbar region of each participant 5 times using an ultrasound probe while he or she kept a prone lying posture on a plinth. Participant-specific models of L1-L5 were constructed from magnetic resonance (MR) images and aligned with the 3-dimensional ultrasound dataset of each scan using 4 variants of MRI-ultrasound registration approach (simplified intensity-based registration [1] with and [2] without including the transverse processes and their surrounding soft tissues [denoted as TP complex]; and hierarchical intensity-based registration [3] with and [4] without including the TP complex). The robustness and precision of these registration approaches were compared. RESULTS: Although all registration approaches converged to a similar solution, excluding the TP complex improved the percentage of successful registration from 92% to 100%. There was no significant difference in the precision among the 4 MRI-ultrasound registration variants. For the simplified intensity-based registration without including the TP complex, average precision at each degree of freedom was 1.33° (flexion-extension), 2.48° (lateral bending), 1.32° (axial rotation), 2.15 mm (left/right), 1.08 mm (anterior-posterior), and 1.16 (superior-inferior), respectively. CONCLUSION: Given that using simplified intensity-based MRI-ultrasound registration can substantially streamline the registration process and excluding the TP complex would improve the robustness of the registration, we conclude that this combination is the method of choice for in vivo human applications.

Actuator-Assisted Calibration of Freehand 3D Ultrasound System.

Freehand three-dimensional (3D) ultrasound has been used independently of other technologies to analyze complex geometries or registered with other imaging modalities to aid surgical and radiotherapy planning. A fundamental requirement for all freehand 3D ultrasound systems is probe calibration. The purpose of this study was to develop an actuator-assisted approach to facilitate freehand 3D ultrasound calibration using point-based phantoms. We modified the mathematical formulation of the calibration problem to eliminate the need of imaging the point targets at different viewing angles and developed an actuator-assisted approach/setup to facilitate quick and consistent collection of point targets spanning the entire image field of view. The actuator-assisted approach was applied to a commonly used cross wire phantom as well as two custom-made point-based phantoms (original and modified), each containing 7 collinear point targets, and compared the results with the traditional freehand cross wire phantom calibration in terms of calibration reproducibility, point reconstruction precision, point reconstruction accuracy, distance reconstruction accuracy, and data acquisition time. Results demonstrated that the actuator-assisted single cross wire phantom calibration significantly improved the calibration reproducibility and offered similar point reconstruction precision, point reconstruction accuracy, distance reconstruction accuracy, and data acquisition time with respect to the freehand cross wire phantom calibration. On the other hand, the actuator-assisted modified "collinear point target" phantom calibration offered similar precision and accuracy when compared to the freehand cross wire phantom calibration, but it reduced the data acquisition time by 57%. It appears that both actuator-assisted cross wire phantom and modified collinear point target phantom calibration approaches are viable options for freehand 3D ultrasound calibration.

A non-ionizing technique for three-dimensional measurement of the lumbar spine.

Comprehensive assessments of scoliotic deformity and spinal instability require repetitive three-dimensional (3D) measurements of motion segments at different functional postures. However, accurate 3D measurement of the spine is a challenging task. In this paper, we present a novel, non-invasive, non-ionizing technique to quantify 3D poses of lumbar motion segments in terms of clinically meaningful anatomical coordinates. The technique used ultra-short echo time (UTE) magnetic resonance (MR) images to construct subject-specific geometrical models of individual vertebrae and registered them with 3D ultrasound dataset acquired during pose measurements. A hierarchical registration approach was used to minimize the detrimental effects of speckle noise and artifacts within soft tissues on registration accuracy. The technique was validated using a human dry bone specimen as well as a fresh porcine cadaver. Registration errors were determined by comparing with a gold standard fiducial-based registration. Results showed that the technique is accurate and reliable with bias in sub-degree and sub-millimeter level (except for the flexion-extension of the porcine cadaver experiment, which was -1.74°), and average precision of 1.11° in rotation and 0.86mm in position for the human dry bone experiment, and 1.26° and 1.23mm for the porcine cadaver experiment. Given its non-ionizing nature, the UTE MR-ultrasound registration technique is particularly useful for repeated measurements and longitudinal follow-up. With further refinement and validation, it could be a powerful tool for 3D spinal assessment.

A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research.

OBJECTIVE: Intraclass correlation coefficient (ICC) is a widely used reliability index in test-retest, intrarater, and interrater reliability analyses. This article introduces the basic concept of ICC in the content of reliability analysis. DISCUSSION FOR RESEARCHERS: There are 10 forms of ICCs. Because each form involves distinct assumptions in their calculation and will lead to different interpretations, researchers should explicitly specify the ICC form they used in their calculation. A thorough review of the research design is needed in selecting the appropriate form of ICC to evaluate reliability. The best practice of reporting ICC should include software information, "model," "type," and "definition" selections. DISCUSSION FOR READERS: When coming across an article that includes ICC, readers should first check whether information about the ICC form has been reported and if an appropriate ICC form was used. Based on the 95% confident interval of the ICC estimate, values less than 0.5, between 0.5 and 0.75, between 0.75 and 0.9, and greater than 0.90 are indicative of poor, moderate, good, and excellent reliability, respectively. CONCLUSION: This article provides a practical guideline for clinical researchers to choose the correct form of ICC and suggests the best practice of reporting ICC parameters in scientific publications. This article also gives readers an appreciation for what to look for when coming across ICC while reading an article.

Hierarchical CT to Ultrasound Registration of the Lumbar Spine: A Comparison with Other Registration Methods.

Three-dimensional (3D) measurement of the spine can provide important information for functional, developmental, diagnostic, and treatment-effect evaluations. However, existing measurement techniques are either 2-dimensional, highly invasive, or involve a high radiation dose, prohibiting their widespread and repeated use in both research and clinical settings. Non-invasive, non-ionizing, 3D measurement of the spine is still beyond the current state-of-the-art. Towards this goal, we developed an intensity-based hierarchical CT-ultrasound registration approach to quantify the 3D positions and orientations of lumbar vertebrae from 3D freehand ultrasound and one-time computed tomography. The method was validated using a human dry bone specimen (T12-L5) and a porcine cadaver (L2-L6) by comparing the registration results with a gold standard fiducial-based registration. Mean (SD) target registration error and percentage of successful registration were 1.2 (0.6) mm and 100% for the human dry bone specimen, and 2.18 (0.82) mm and 92% for the porcine cadaver, indicating that the method is accurate and robust under clinically realistic conditions. Given that the use of ultrasound eliminates ionizing radiation during pose measurements, we believe that the hierarchical CT-ultrasound registration method is an attractive option for quantifying 3D poses of individual vertebra and motion segment, and thus warrants further investigations.

Factors that influence muscle shear modulus during passive stretch.

Although elastography has been increasingly used for evaluating muscle shear modulus associated with age, sex, musculoskeletal, and neurological conditions, its physiological meaning is largely unknown. This knowledge gap may hinder data interpretation, limiting the potential of using elastography to gain insights into muscle biomechanics in health and disease. We derived a mathematical model from a widely-accepted Hill-type passive force-length relationship to gain insight about the physiological meaning of resting shear modulus of skeletal muscles under passive stretching, and validated the model by comparing against the ex-vivo animal data reported in our recent work (Koo et al. 2013). The model suggested that resting shear modulus of a slack muscle is a function of specific tension and parameters that govern the normalized passive muscle force-length relationship as well as the degree of muscle anisotropy. The model also suggested that although the slope of the linear shear modulus-passive force relationship is primarily related to muscle anatomical cross-sectional area (i.e. the smaller the muscle cross-sectional area, the more the increase in shear modulus to result in the same passive muscle force), it is also governed by the normalized passive muscle force-length relationship and the degree of muscle anisotropy. Taken together, although muscle shear modulus under passive stretching has a strong linear relationship with passive muscle force, its actual value appears to be affected by muscle's mechanical, material, and architectural properties. This should be taken into consideration when interpreting the muscle shear modulus values.

Assessment of scoliotic deformity using spinous processes: comparison of different analysis methods of an ultrasonographic system.

OBJECTIVE: The purpose of this study was to evaluate the performance of 5 analysis methods in quantifying scoliotic deformity, using the spatial positions of SP tips acquired by a custom-developed ultrasound-based system, with different curve fitting methods and angle metrics in terms of their correlation with Cobb angle, test-retest reliability, vulnerability to digitization errors, and accuracy of identifying end vertebrae and convexity direction. METHODS: Three spinal column dry bone specimens were randomly configured to 30 different scoliotic deformities. Raw spatial data of the SP tips were processed by the following 3 methods: (1) fifth-order polynomial fitting, (2) locally weighted polynomial regression (LOESS) with smoothing parameter (α) = .25, and (3) LOESS with α = .4. Angle between the 2 tangents along the spinal curve with the most positive and negative slopes (ie, posterior deformity angle) and summation of the angles formed by every 2 lines joining 3 neighboring SPs between the end vertebrae (ie, accumulating angle) were computed to quantify scoliotic deformity. Their performances were compared in terms of their correlation with Cobb angle, test-retest reliability, vulnerability to digitization errors, and accuracy of identifying end vertebrae. RESULTS: Posterior deformity angle calculated from the spinal curve constructed by LOESS with α = .4 excelled in every aspect of the comparison (ie, Cobb angle, test-retest reliability, vulnerability to digitization errors, and accuracy of identifying end vertebrae and convexity direction), making it the method of choice of those tested for processing the spatial data of the SP tips in this ultrasonography study using dry bone specimens. CONCLUSIONS: The ultrasound-based system and the LOESS (0.4)-posterior deformity angle method developed for this study offer a viable technology for quantifying scoliotic deformity in a reliable and radiation-free manner. However, further validation using scoliosis subjects is needed before they can be used to quantify spinal deformity in the clinical setting.

Quantifying the passive stretching response of human tibialis anterior muscle using shear wave elastography.

BACKGROUND: Quantifying passive stretching responses of individual muscles helps the diagnosis of muscle disorders and aids the evaluation of surgical/rehabilitation treatments. Utilizing an animal model, we demonstrated that shear elastic modulus measured by supersonic shear wave elastography increases linearly with passive muscle force. This study aimed to use this state-of-the-art technology to study the relationship between shear elastic modulus and ankle dorsi-plantarflexion angle of resting tibialis anterior muscles and extract physiologically meaningful parameters from the elasticity-angle curve to better quantify passive stretching responses. METHODS: Elasticity measurements were made at resting tibialis anterior of 20 healthy subjects with the ankle positioned from 50° plantarflexion to up to 15° dorsiflexion at every 5° for two cycles. Elasticity-angle data was curve-fitted by optimizing slack angle, slack elasticity, and rate of increase in elasticity within a piecewise exponential model. FINDINGS: Elasticity-angle data of all subjects were well fitted by the piecewise exponential model with coefficients of determination ranging between 0.973 and 0.995. Mean (SD) of slack angle, slack elasticity, and rate of increase in elasticity were 10.9° (6.3°), 5.8 (1.9) kPa, and 0.0347 (0.0082) respectively. Intraclass correlation coefficients of each parameter were 0.852, 0.942, and 0.936 respectively, indicating excellent test-retest reliability. INTERPRETATION: This study demonstrated the feasibility of using supersonic shear wave elastography to quantify passive stretching characteristics of individual muscle and provided preliminary normative values of slack angle, slack elasticity, and rate of increase in elasticity for human tibialis anterior muscles. Future studies will investigate diagnostic values of these parameters in clinical applications.

Relationship between shear elastic modulus and passive muscle force: an ex-vivo study.

As muscle is stretched, it reacts with increasing passive resistance. This passive force component is important for normal muscle function. Unfortunately, direct measurement of passive muscle force is still beyond the current state-of-the-art. This study aimed to investigate the feasibility of using Supersonic shear wave elastography (SSWE) to indirectly measure passive muscle force. Sixteen gastronomies pars externus and 16 tibialis anterior muscles were dissected from 10 fresh roaster chickens. For each muscle specimen, the proximal bone-tendon junction was kept intact with its tibia or femur clamped in a fixture. Calibration weights (0-400 g in 25 g per increment) were applied to the distal tendon via a pulley system and muscle elasticity was measured simultaneously using SSWE. The measurements were repeated for 3 cycles. The elasticity-load relationship of each tested muscle for each loading cycle was analyzed by fitting a least-squares regression line to the data. Test-retest reliability was evaluated using intraclass correlation coefficient (ICC). Results demonstrated that the relationships between SSWE elasticity and passive muscle force were highly linear for all the tested muscles with coefficients of determination ranging between 0.971 and 0.999. ICCs were 0.996 and 0.985, respectively, for the slope and y-intercept parameters of the regression lines, indicating excellent reliability. These findings indicate that SSWE, when carefully applied, can be a highly reliable technique for muscle elasticity measurements. The linear relationship between SSWE elasticity and passive muscle force identified in the present study demonstrated that SSWE may be used as an indirect measure of passive muscle force.

Test-retest reliability, repeatability, and sensitivity of an automated deformation-controlled indentation on pressure pain threshold measurement.

OBJECTIVE: The purpose of this study was to construct a computerized deformation-controlled indentation system and compare its test-retest reliability, repeatability, and sensitivity with a manual algometer for pressure pain threshold (PPT) measurements. METHODS: Pressure pain threshold measurements were made on 16 healthy subjects for 2 sessions on bilateral erector spinae muscles at L1, L3, and L5 spinal levels, consisting of 5 repeated trials each using computerized algometry on one side and manual algometry on the other side. Mean, SD, coefficient of variation, standard error of measurement, minimal detectable change, and intraclass correlation coefficient were calculated for both manual and computerized PPT measurements. Effects of session, level, method, and side on PPT measurements were evaluated using analysis of variance. RESULTS: Manual PPT measurements were significantly larger than computerized PPT measurements (P = .017), and session 2 was significantly larger than session 1 (P = .021). Coefficient of variation, intraclass correlation coefficient, standard error of measurement, and minimal detectable change of the manual and computerized PPT measurements were 10.3%, 0.91, 0.19 kg/cm(2), and 0.54 kg/cm(2) and 15.6%, 0.87, 0.26 kg/cm(2), and 0.73 kg/cm(2), respectively. CONCLUSIONS: Although computerized algometry offers the benefits of eliminating the effects of operator reaction time, operator anticipation, alignment error, and variation in indentation rate on PPT measurements, these results indicate that manual algometry using load-controlled strategy may be better than computerized deformation-controlled algometry in terms of test-retest reliability, repeatability, and sensitivity. Constant load-controlled indentation protocol may be more favorable for PPT measurements. Future computerized instrumentation for PPT measurements should adopt a load-controlled mechanism.

Towards the application of one-dimensional sonomyography for powered upper-limb prosthetic control using machine learning models.

BACKGROUND: The inherent properties of surface electromyography limit its potential for multi-degrees of freedom control. Our previous studies demonstrated that wrist angle could be predicted by muscle thickness measured from B-mode ultrasound, and hence, it could be an alternative signal for prosthetic control. However, an ultrasound imaging machine is too bulky and expensive. OBJECTIVE: We aim to utilize a portable A-mode ultrasound system to examine the feasibility of using one-dimensional sonomyography (i.e. muscle thickness signals detected by A-mode ultrasound) to predict wrist angle with three different machine learning models - (1) support vector machine (SVM), (2) radial basis function artificial neural network (RBF ANN), and (3) back-propagation artificial neural network (BP ANN). STUDY DESIGN: Feasibility study using nine healthy subjects. METHODS: Each subject performed wrist extension guided at 15, 22.5, and 30 cycles/minute, respectively. Data obtained from 22.5 cycles/minute trials was used to train the models and the remaining trials were used for cross-validation. Prediction accuracy was quantified by relative root mean square error (RMSE) and correlation coefficients (CC). RESULTS: Excellent prediction was noted using SVM (RMSE = 13%, CC = 0.975), which outperformed the other methods. CONCLUSION: It appears that one-dimensional sonomyography could be an alternative signal for prosthetic control. Clinical relevance Surface electromyography has inherent limitations that prohibit its full functional use for prosthetic control. Research that explores alternative signals to improve prosthetic control (such as the one-dimensional sonomyography signals evaluated in this study) may revolutionize powered prosthesis design and ultimately benefit amputee patients.

Immediate effect of nimmo receptor tonus technique on muscle elasticity, pain perception, and disability in subjects with chronic low back pain.

OBJECTIVE: Objectives of this study were to (1) quantify the immediate effect of Nimmo technique on muscle elasticity, pain perception, and disability and (2) evaluate comparative effectiveness of treating all primary and secondary trigger points (TrPs) vs primary TrP only. METHODS: Fourteen chronic low back pain subjects recruited from a chiropractic college were tested in this within-day repeated-measures design study. Gluteus medius containing a prominent TrP was indented for 4 sessions using a mechanoacoustic indentor system. A finite element optimization method extracted hyperelastic material constants of the gluteus medius. Load-deformation response on a standardized block was simulated. Area under the load-deformation curve from 0% to 25% deformation (A(FE)) and force at 25% deformation (F(FE)) were determined. No treatment was applied between the first and second sessions. Only the primary TrP in gluteus medius was treated between the second and third sessions. Full Nimmo treatment was used between the third and fourth sessions requiring treatment of all primary and secondary TrPs. The A(FE), F(FE), tissue thickness, subjective pain, and Oswestry Disability Index were compared between sessions. RESULTS: After full Nimmo treatment, A(FE) and F(FE) were significantly smaller than baseline (P = .021 and .027, respectively) and focal TrP treatment only (P = .003 and .001, respectively). The changes accompanied concomitant improvement in subjective pain and disability. It appears that focal TrP treatment resolves TrP, but full Nimmo treatment further reduces electrogenic spasm. CONCLUSIONS: Immediate effect of a single full Nimmo treatment appears to reduce muscle tone, subjective pain, and disability and be more beneficial than focal TrP treatment.

A mechano-acoustic indentor system for in vivo measurement of nonlinear elastic properties of soft tissue.

OBJECTIVES: Soft tissue exhibits nonlinear stress-strain behavior under compression. Characterizing its nonlinear elasticity may aid detection, diagnosis, and treatment of soft tissue abnormality. The purposes of this study were to develop a rate-controlled Mechano-Acoustic Indentor System and a corresponding finite element optimization method to extract nonlinear elastic parameters of soft tissue and evaluate its test-retest reliability. METHODS: An indentor system using a linear actuator to drive a force-sensitive probe with a tip-mounted ultrasound transducer was developed. Twenty independent sites at the upper lateral quadrant of the buttock from 11 asymptomatic subjects (7 men and 4 women from a chiropractic college) were indented at 6% per second for 3 sessions, each consisting of 5 trials. Tissue thickness, force at 25% deformation, and area under the load-deformation curve from 0% to 25% deformation were calculated. Optimized hyperelastic parameters of the soft tissue were calculated with a finite element model using a first-order Ogden material model. Load-deformation response on a standardized block was then simulated, and the corresponding area and force parameters were calculated. Between-trials repeatability and test-retest reliability of each parameter were evaluated using coefficients of variation and intraclass correlation coefficients, respectively. RESULTS: Load-deformation responses were highly reproducible under repeated measurements. Coefficients of variation of tissue thickness, area under the load-deformation curve from 0% to 25% deformation, and force at 25% deformation averaged 0.51%, 2.31%, and 2.23%, respectively. Intraclass correlation coefficients ranged between 0.959 and 0.999, indicating excellent test-retest reliability. CONCLUSIONS: The automated Mechano-Acoustic Indentor System and its corresponding optimization technique offers a viable technology to make in vivo measurement of the nonlinear elastic properties of soft tissue. This technology showed excellent between-trials repeatability and test-retest reliability with potential to quantify the effects of a wide variety of manual therapy techniques on the soft tissue elastic properties.

Reliability of sonomyography for pectoralis major thickness measurement.

OBJECTIVE: Muscle thickness is a widely used parameter for quantifying muscle function in ultrasound imaging. However, current measurement techniques generally rely on manual digitization, which is subjective, time consuming, and prone to error. The primary purposes of this study were to develop an automated muscle boundary tracking algorithm to overcome these limitations and to report its intraexaminer reliability on pectoralis major muscle. METHODS: Real-time B-mode ultrasound images of the pectoralis major muscles were acquired by an integrated data acquisition system. A transducer placement protocol was developed to facilitate better repositioning of an ultrasound transducer. Intraexaminer reliability of the tracking algorithm for static measurements was studied using intraclass correlation coefficient based on the thickness data from 11 healthy subjects recruited from a chiropractic college measured at 3 independent sessions. Standard error of measurement and minimal detectable change were calculated. Feasibility of using the tracking algorithm for dynamic measurements was also evaluated. RESULTS: All calculated intraclass correlation coefficients were larger than 0.96, indicating excellent reliability of the sonomyographic measurements. Minimal detectable changes were 9.7%, 6.7%, and 6.8% of the muscle thickness at the lateral, central, and medial aspects, respectively. For a 400-frame image stack with 3 pairs of 40 x 40 pixels tracking windows, the tracking took about 80 seconds to complete. CONCLUSIONS: The tracking algorithm offers precise and reliable measurements of muscle thickness changes in clinical settings with potential to quantify the effects of a wide variety of chiropractic techniques on muscle function.

A computer aided method for closed reduction of diaphyseal tibial fracture using projection images: A feasibility study.

A computer aided method for closed tibial shaft fracture reduction based on measurements of 12 projection parameters (6 angulations and 6 translations) from an anteroposterior radiograph, a lateral radiograph, and a transverse projection photograph is examined. The development, validation and reliability of the computer aided method are presented. A custom-made unilateral external fixation device consisting of 7 calibrated one-degree-of-freedom joints was employed to execute the reduction. Five tibial fracture phantoms with initial deformities that covered a wide range of misalignments were tested. The mean (standard deviation) resultant rotational and translational errors after the reduction were 3.32° (0.96°) and 1.65 (0.86) mm, respectively, which indicates good reduction accuracy. Three independent raters made the measurements of the projection parameters to test inter-rater reliability. The intra-class correlation coefficients were found to range between 0.935 and 1, indicating good reliability. Since ideal patient positioning for AP, lateral and transverse image acquisition is not easily attainable, the effect of patient positioning errors on the measurement of projection parameters was explored using a tibial phantom. The preliminary results revealed that 10° deviations in positioning do not greatly affect the measurement of AP and lateral angulation parameters (<1.7°). However, a 10° positioning error about the long bone axis may result in a change of as much as 10.7° in the measurements of transverse projection angulation parameters. In addition, a 10° positioning error about an arbitrary anatomical axis may result in translational projection parameter changes of up to 6.8 mm. For these reasons, a previously validated method that allows for accurate positioning of the tibia about its long axis and a two-step reduction strategy to achieve the best possible deformity reduction are proposed. Procedures to facilitate reliable measurement of tibial torsion are also discussed. It appears that the projection-based reduction method exposes the patient to less radiation and allows for simple, quick and accurate reductions, making it an attractive choice for acute clinical applications.

Is maximum isometric muscle stress the same among prime elbow flexors?

BACKGROUND: Previous musculoskeletal modeling studies have adopted the assumption of the same maximum isometric muscle stress among the prime elbow flexors. This study aimed at estimating the maximum isometric muscle stress based on subject-specific modeling parameters measured in vivo and validating that assumption. METHODS: Subject-specific musculoskeletal models of the upper limbs of five normal subjects were developed, which incorporated anthropometrically scaled graphics-based geometrical models and Hill-type musculotendon models of the prime elbow flexors. B-mode ultrasound technique was employed to measure the muscle optimal length and pennation angle of each prime elbow flexor, and these architectural parameters were inputted into the model to reduce the number of unknown parameters to be optimized. To allow changes of individual maximum isometric muscle force of the prime elbow flexors, optimizations were conducted by minimizing the root mean square difference between the predicted and measured isometric torque-angle curves. Maximum isometric muscle stress of each prime elbow flexor was estimated by dividing the maximum isometric muscle force with the corresponding physiological cross-sectional area. FINDINGS: Our findings showed that maximum isometric muscle stress among the prime elbow flexors was not significantly different from each other. Thus it appears that it is reasonable to assume the same value for maximum isometric muscle stress for all prime elbow flexors in musculoskeletal modeling studies. INTERPRETATION: Latest medical imaging techniques such as ultrasound for the estimation of musculotendon parameters would provide an alterative method to obtain the muscle architecture parameters noninvasively. The subject-specific musculotendon parameters estimated in this study could be used for developing the neuromusculoskeletal model to predict muscle force and evaluate muscle functions.

A knowledge-based computer-aided system for closed diaphyseal fracture reduction.

BACKGROUND: We recently developed an algorithm to perform closed fracture reduction using unilateral external fixator. Although its validity has been verified experimentally, the whole reduction process was not evaluated owing to the lack of a device that could facilitate its implementation in clinical practice. The objective of this study is to develop a prototype of such a system, and quantify its reduction accuracy. METHODS: The system consists of a custom-made unilateral external device and a self-contained software package. The device features 7 one degree of freedom joints, each allows for continuous adjustments and is equipped with measurement components to facilitate accurate positioning. A CT-based method was developed, which facilitates virtual reduction and calculates the adjustment requirements that reduce a fracture deformity. The device was adjusted off-the-site and reattached back in place to guide the reduction of the fracture fragments. Reduction accuracy was evaluated using eight phantoms of different types, sides and fracture patterns by calculating the rotation about a screw axis and the displacement between the origins of the distal and proximal local coordinate systems after the reduction. FINDINGS: The mean (SD) of the translational and rotational reduction errors were 1.73 (0.97)mm and 2.57 degrees (1.36 degrees), respectively, which demonstrated the accuracy and reliability of the system. INTERPRETATION: The system allows surgeons to perform fracture reduction in an objective, efficient, and accurate manner yet minimize the radiation exposure and lessens the extent of tissue disruption around the fracture site during the reduction process.

A neuromusculoskeletal model to simulate the constant angular velocity elbow extension test of spasticity.

We developed a neuromusculoskeletal model to simulate the stretch reflex torque induced during a constant angular velocity elbow extension by tuning a set of physiologically-based parameters. Our model extended past modeling efforts in the investigation of elbow spasticity by incorporating explicit musculotendon, muscle spindle, and motoneuron pool models in each prime elbow flexor. We analyzed the effects of changes in motoneuron pool and muscle spindle properties as well as muscle mechanical properties on the biomechanical behavior of the elbow joint observed during a constant angular velocity elbow extension. Results indicated that both motoneuron pool thresholds and gains could be substantially different among muscles. In addition, sensitivity analysis revealed that spindle static gain and motoneuron pool threshold were the most sensitive parameters that could affect the stretch reflex responses of the elbow flexors during a constant angular velocity elbow extension, followed by motoneuron pool gain, and spindle dynamic gain. It is hoped that the model will contribute to the understanding of the underlying mechanisms of spasticity after validation by more elaborate experiments, and will facilitate the future development of more specific treatment of spasticity.

Feasibility of using EMG driven neuromusculoskeletal model for prediction of dynamic movement of the elbow.

Neuromusculoskeletal (NMS) modeling is a valuable tool in orthopaedic biomechanics and motor control research. To evaluate the feasibility of using electromyographic (EMG) signals with NMS modeling to estimate individual muscle force during dynamic movement, an EMG driven NMS model of the elbow was developed. The model incorporates dynamical equation of motion of the forearm, musculoskeletal geometry and musculotendon modeling of four prime elbow flexors and three prime elbow extensors. It was first calibrated to two normal subjects by determining the subject-specific musculotendon parameters using computational optimization to minimize the root mean square difference between the predicted and measured maximum isometric flexion and extension torque at nine elbow positions (0-120 degrees of flexion with an increment of 15 degrees ). Once calibrated, the model was used to predict the elbow joint trajectories for three flexion/extension tasks by processing the EMG signals picked up by both surface and fine electrodes using two different EMG-to-activation processing schemes reported in the literature without involving any trajectory fitting procedures. It appeared that both schemes interpreted the EMG somewhat consistently but their prediction accuracy varied among testing protocols. In general, the model succeeded in predicting the elbow flexion trajectory in the moderate loading condition but over-drove the flexion trajectory under unloaded condition. The predicted trajectories of the elbow extension were noted to be continuous but the general shape did not fit very well with the measured one. Estimation of muscle activation based on EMG was believed to be the major source of uncertainty within the EMG driven model. It was especially so apparently when fine wire EMG signal is involved primarily. In spite of such limitation, we demonstrated the potential of using EMG driven neuromusculoskeletal modeling for non-invasive prediction of individual muscle forces during dynamic movement under certain conditions.

Computational simulation of axial dynamization on long bone fractures.

BACKGROUND: Axial dynamization has been shown in previous studies to promote callus formation, improve bone healing at fracture sites, and enhance bone remodeling. However, the possibility of non-axial movements or uniform fracture site compression during dynamization, and the appropriate relaxation of fixator joints to achieve such function, have not been investigated. METHODS: This study used previously developed computational models based on two commercially available unilateral external fixators (Dynafix and Orthofix) to analyze the fixator joint adjustments used and the fracture site movements generated during dynamization. FINDINGS: When none of the fixator's sliding joints were parallel to the long bone axis, significant non-axial movements occurred during dynamization. The dual sliding joint design of the Dynafix fixator was beneficial in reducing these non-axial movements. When all of the fixator joints were allowed to adjust simultaneously during dynamization, exact axial movement or uniform compression at a complicated fracture site was achievable. INTERPRETATION: This study revealed that significant non-axial movements may occur during dynamization, and that such a deficiency can be corrected by relaxing certain fixator joints in addition to the sliding mechanism. The same modeling technique can also be applied in bone lengthening application to assure desirable limb alignment during the distraction process. These analysis results can aid the performance assessment of an external fixator and facilitate appropriate application of such a device to achieve either active or controlled axial movement.