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.

Biomechanical considerations of fracture treatment and bone quality maintenance in elderly patients and patients with osteoporosis.

Osteoporosis is a major public health problem that is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures of the hip, spine, and wrist. Poor bone quality in patients with osteoporosis presents the surgeon with difficult treatment decisions. Bone fracture repair has more pathways with combinations of bone formation mechanisms, which depend on the type of fracture fixation to be applied to achieve the desirable immobilization. There only may be one remodeling principle and in less than ideal conditions, mechanical and biophysical stimuli may provide effective augmentation of fracture healing in elderly patients. A different stimulus may limit its association to a specific healing mechanism. However, no matter which fixation method is used, an accurate reduction is a requisite for bone healing. Failure to realign the fracture site would result in delayed union, malunion, or nonunion. Therefore, a basic understanding of the biomechanics of osteoporotic bone and its treatment is necessary for clinicians to establish appropriate clinical treatment principles to minimize complications and enhance the patient's quality of life. We describe the biomechanical considerations of osteoporosis and fracture treatment from various aspects. First, bone structure and strength characterization are discussed using a hierarchical approach, followed by an innovative knowledge-based approach for fracture reduction planning and execution, which particularly is beneficial to osteoporotic fracture. Finally, a brief review of the results of several experimental animal models under different fracture types, gap morphologic features, rigidity of fixation devices, subsequent loading conditions, and biophysical stimulation is given to elucidate adverse mechanical conditions associated with different bone immobilization techniques that can compromise normal bone fracture healing significantly.

In vivo determination of subject-specific musculotendon parameters: applications to the prime elbow flexors in normal and hemiparetic subjects.

OBJECTIVE: This study aimed at estimating the musculotendon parameters of the prime elbow flexors in vivo for both normal and hemiparetic subjects. DESIGN: A neuromusculoskeletal model of the elbow joint was developed incorporating detailed musculotendon modeling and geometrical modeling. BACKGROUND: Neuromusculoskeletal modeling is a valuable tool in orthopedic biomechanics and motor control research. However, its reliability depends on reasonable estimation of the musculotendon parameters. Parameter estimation is one of the most challenging aspects of neuromusculoskeletal modeling. METHODS: Five normal and five hemiparetic subjects performed maximum isometric voluntary flexion at nine elbow positions (0 degrees -120 degrees of flexion with an increment of 15 degrees ). Maximum flexion torques were measured at each position. Computational optimization was used to search for the musculotendon parameters of four prime elbow flexors by minimizing the root mean square difference between the predicted and the experimentally measured torque-angle curves. RESULTS: The normal group seemed to have larger maximum muscle stress values as compared to the hemiparetic group. Although the functional ranges of each selected muscle were different, they were all located at the ascending limb of the force-length relationship. The muscle optimal lengths and tendon slack lengths found in this study were comparable to other cadaver studies reported in the literature. CONCLUSION: Subject-specific musculotendon parameters could be properly estimated in vivo. RELEVANCE: Estimation of subject-specific musculotendon parameters for both normal and hemiparetic subjects would help clinicians better understand some of the effects of this pathological condition on the musculoskeletal system.