Dynamic magnetic resonance imaging of muscle function after surgery.
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Biomedical subjects
Silvia S Blemker
Publications and source records attributed to Silvia S Blemker.
Rectus femoris and vastus intermedius fiber excursions predicted by three-dimensional muscle models.
Computer models of the musculoskeletal system frequently represent the force-length behavior of muscle with a lumped-parameter model. Lumped-parameter models use simple geometric shapes to characterize the arrangement of muscle fibers and tendon; this may inaccurately represent changes in fiber length and the resulting force-length behavior, especially for muscles with complex architecture. The purpose of this study was to determine the extent to which the complex features of the rectus femoris and vastus intermedius architectures affect the fiber changes in length ("fiber excursions"). We created three-dimensional finite-element models of the rectus femoris and vastus intermedius muscles based on magnetic resonance (MR) images, and compared the fiber excursions predicted by the finite-element models with fiber excursions predicted by lumped-parameter models of these muscles. The finite-element models predicted rectus femoris fiber excursions (over a 100 degrees range of knee flexion) that varied from 55% to 70% of the excursion of the muscle-tendon unit and vastus intermedius fiber excursions that varied from 55% to 98% of the excursion muscle-tendon unit. In contrast, the lumped-parameter model of the rectus femoris predicted fiber excursions that were 86% of the excursion of the muscle-tendon unit and vastus intermedius fiber excursions that were 97% of the excursion of the muscle-tendon unit. These results suggest that fiber excursions of many fibers are overestimated in lumped-parameter models of these muscles. These new representations of muscle architecture can improve the accuracy of computer simulations of movement and provide insight into muscle design.
Biomechanical Phenomena↗
Three-dimensional representation of complex muscle architectures and geometries.
Almost all computer models of the musculoskeletal system represent muscle geometry using a series of line segments. This simplification (i) limits the ability of models to accurately represent the paths of muscles with complex geometry and (ii) assumes that moment arms are equivalent for all fibers within a muscle (or muscle compartment). The goal of this work was to develop and evaluate a new method for creating three-dimensional (3D) finite-element models that represent complex muscle geometry and the variation in moment arms across fibers within a muscle. We created 3D models of the psoas, iliacus, gluteus maximus, and gluteus medius muscles from magnetic resonance (MR) images. Peak fiber moment arms varied substantially among fibers within each muscle (e.g., for the psoas the peak fiber hip flexion moment arms varied from 2 to 3 cm, and for the gluteus maximus the peak fiber hip extension moment arms varied from 1 to 7 cm). Moment arms from the literature were generally within the range of fiber moment arms predicted by the 3D models. The models accurately predicted changes in muscle surface geometry over a 55 degrees range of hip flexion, as compared to changes in shape predicted from MR images (average errors between the model and measured surfaces were between 1.7 and 5.2 mm). This new framework for representing muscle will enhance the accuracy of computer models of the musculoskeletal system.
Adult↗
A 3D model of muscle reveals the causes of nonuniform strains in the biceps brachii.
Biomechanical models generally assume that muscle fascicles shorten uniformly. However, dynamic magnetic resonance (MR) images of the biceps brachii have recently shown nonuniform shortening along some muscle fascicles during low-load elbow flexion (J. Appl. Physiol. 92 (2002) 2381). The purpose of this study was to uncover the features of the biceps brachii architecture and material properties that could lead to nonuniform shortening. We created a three-dimensional finite-element model of the biceps brachii and compared the tissue strains predicted by the model with experimentally measured tissue strains. The finite-element model predicted strains that were within one standard deviation of the experimentally measured strains. Analysis of the model revealed that the variation in fascicle lengths within the muscle and the curvature of the fascicles were the primary factors contributing to nonuniform strains. Continuum representations of muscle, combined with in vivo image data, are needed to deepen our understanding of how complex geometric arrangements of muscle fibers affect muscle contraction mechanics.
Biomechanical Phenomena↗
Three-dimensional muscle-tendon geometry after rectus femoris tendon transfer.
BACKGROUND: Rectus femoris tendon transfer is performed in patients with cerebral palsy to improve knee flexion during walking. This procedure involves detachment of the muscle from its insertion into the quadriceps tendon and reattachment to one of the knee flexor muscles. The purpose of the present study was to evaluate the muscle-tendon geometry and to assess the formation of scar tissue between the rectus femoris and adjacent structures. METHODS: Magnetic resonance images of the lower extremities were acquired from five subjects after bilateral rectus femoris tendon transfer. A three-dimensional computer model of the musculoskeletal geometry of each of the ten limbs was created from these images. RESULTS: The three-dimensional paths of the rectus femoris muscles after transfer demonstrated that the muscle does not follow a straight course from its origin to its new insertion. The typical muscle-tendon path included an angular deviation; this deviation was sharp (>35 degrees ) in seven extremities. In addition, scar tissue between the transferred rectus femoris and the underlying muscles was visible on the magnetic resonance images. CONCLUSIONS: The angular deviations in the rectus femoris muscle-tendon path and the presence of scar tissue between the rectus femoris and the underlying muscles suggest that the beneficial effects of rectus femoris tendon transfer are derived from reducing the effects of the rectus femoris muscle as a knee extensor rather than from converting the muscle to a knee flexor. These findings clarify our understanding of the mechanism by which rectus femoris tendon transfer improves knee flexion.
Adolescent↗
Magnetic resonance imaging findings after rectus femoris transfer surgery.
We describe the magnetic resonance (MR) imaging appearance of the knee flexor and extensor tendons after bilateral rectus femoris transfer and hamstring lengthening surgery in five patients (10 limbs) with cerebral palsy. Three-dimensional models of the path of the transferred tendon were constructed in all cases. MR images of the transferred and lengthened tendons were examined and compared with images from ten non-surgical subjects. The models showed that the path of the transferred rectus femoris tendon had a marked angular deviation near the transfer site in all cases. MR imaging demonstrated irregular areas of low signal intensity near the transferred rectus femoris and around the hamstrings in all subjects. Eight of the ten post-surgical limbs showed evidence of fluid near or around the transferred or lengthened tendons. This was not observed in the non-surgical subjects. Thus, MR imaging of patients with cerebral palsy after rectus femoris transfer and hamstring-lengthening surgery shows evidence of signal intensity and contour changes, even several years after surgery.
Adolescent↗
Real-time imaging of skeletal muscle velocity.
PURPOSE: To test the feasibility of using real-time phase contrast (PC) magnetic resonance imaging (MRI) to track velocities (1-20 cm/second) of skeletal muscle motion. MATERIALS AND METHODS: To do this we modified a fast real-time spiral PC pulse sequence to accommodate through-plane velocity encoding in the range of -20 to +20 cm/second. We successfully imaged motion of the biceps brachii and triceps brachii muscles during elbow flexion and extension in seven unimpaired adult subjects using real-time PC MRI. RESULTS: The velocity data demonstrate that the biceps brachii and the triceps brachii, antagonistic muscles, move in opposite directions during elbow flexion and extension with velocity values in the muscle tissue ranging from -10 to +10 cm/second. CONCLUSION: With further development, real-time PC MRI may provide a means to analyze muscle function in individuals with neurologic or movement disorders who cannot actively complete the repeated motions required for dynamic MRI techniques, such as cine PC MRI, that are more commonly used in musculoskeletal biomechanics applications.
Adult↗
Cine phase-contrast magnetic resonance imaging as a tool for quantification of skeletal muscle motion.
In recent years, biomechanics researchers have increasingly used dynamic magnetic resonance imaging techniques, such as cine phase contrast (cine PC), to study muscle and bone motion in vivo. Magnetic resonance imaging provides a non-invasive tool to visualize the anatomy and measure musculoskeletal tissue velocities during joint motion. Current application of cine PC magnetic resonance imaging in biomechanics includes study of knee joint kinematics, tendon strain, and skeletal muscle displacement and shortening. This paper article reviews the use of cine PC magnetic resonance imaging for quantification of skeletal muscle motion. The imaging studies presented examine the relative motion of the knee flexor and extensor muscles after orthopedic surgery and examine the uniformity of shortening within the biceps brachii muscle. The current challenges and limitations of using cine PC magnetic resonance imaging in biomechanics research are addressed as well as opportunities for future studies of skeletal muscle motion using dynamic magnetic resonance imaging.
Biomechanical Phenomena↗
In vivo motion of the rectus femoris muscle after tendon transfer surgery.
Rectus femoris transfer surgery is performed to convert the rectus femoris muscle from a knee extensor to a knee flexor. In this surgery, the distal tendon of the rectus femoris is detached from the patella and reattached to one of the knee flexor tendons. The outcomes of this procedure are variable, and it is not known if the surgery successfully converts the muscle to a knee flexor. We measured the motion of muscle tissue within the rectus femoris and vastus intermedius during knee extension in 10 unimpaired control subjects (10 limbs) and 6 subjects (10 limbs) after rectus femoris transfer using cine phase-contrast magnetic resonance imaging. Displacements of the vastus intermedius during knee extension were similar between control and tendon transfer subjects. In the control subjects, the rectus femoris muscle consistently moved in the direction of the knee extensors and displaced more than the vastus intermedius. The rectus femoris also moved in the direction of the knee extensors in the tendon transfer subjects; however, the transferred rectus femoris displaced less than the vastus intermedius. These results suggest that the rectus femoris is not converted to a knee flexor after its distal tendon is transferred to the posterior side of the knee, but its capacity for knee extension is diminished by the surgery.
Adolescent↗
In vivo anatomy of the Neer and Hawkins sign positions for shoulder impingement.
The Neer and Hawkins impingement signs are commonly used to diagnose subacromial pathology, but the anatomy of these maneuvers has not been well elucidated in vivo. This 3-dimensional open magnetic resonance imaging study characterized shoulder anatomy and rotator cuff impingement in 8 normal volunteers placed in the Neer and Hawkins positions. Subacromial and intraarticular contact of the rotator cuff was graded, and minimum distances were computed between the tendon insertion sites and the glenoid, acromion, and coracoid. Both the Neer and Hawkins maneuvers significantly decreased the distance from the supraspinatus insertion to the acromion and posterior glenoid and from the subscapularis insertion to the anterior glenoid. However, the Hawkins position resulted in significantly greater subacromial space narrowing and subacromial rotator cuff contact than the Neer position. In the Hawkins position, subacromial contact of the supraspinatus and infraspinatus was observed in 7 of 8 and 5 of 8 subjects, respectively. In contrast, rotator cuff contact with the acromion did not occur in any subject in the Neer position. Intraarticular contact of the supraspinatus with the posterosuperior glenoid was observed in all subjects in both positions. Subscapularis contact with the anterior glenoid was also seen in 7 of 8 subjects in the Neer position and in all subjects in the Hawkins position. This extensive intraarticular contact suggests that internal impingement may play a role in the Neer and Hawkins signs.
Adult↗
Creating and simulating skeletal muscle from the visible human data set.
Simulation of the musculoskeletal system has important applications in biomechanics, biomedical engineering, surgery simulation, and computer graphics. The accuracy of the muscle, bone, and tendon geometry as well as the accuracy of muscle and tendon dynamic deformation are of paramount importance in all these applications. We present a framework for extracting and simulating high resolution musculoskeletal geometry from the segmented visible human data set. We simulate 30 contact/collision coupled muscles in the upper limb and describe a computationally tractable implementation using an embedded mesh framework. Muscle geometry is embedded in a nonmanifold, connectivity preserving simulation mesh molded out of a lower resolution BCC lattice containing identical, well-shaped elements, leading to a relaxed time step restriction for stability and, thus, reduced computational cost. The muscles are endowed with a transversely isotropic, quasi-incompressible constitutive model that incorporates muscle fiber fields as well as passive and active components. The simulation takes advantage of a new robust finite element technique that handles both degenerate and inverted tetrahedra.
Algorithms↗