An anatomic study of the subscapular nerves: A guide for electromyographic analysis of the subscapularis muscle.

Fifty shoulders from 36 human cadavers were examined to identify the nerves innervating the subscapularis muscle and their point of entry into the muscle. Most of the specimens (82%) revealed three independent nerves to the subscapularis, 16% of the specimens demonstrated four nerves, and 2% of the shoulders demonstrated two nerves to the subscapularis. Variability was noted at the level of origin (division or cord) of each primary nerve branch to the muscle. The point of entry of each nerve into the subscapularis was measured from three clinical anatomic landmarks. The entry points were found to closely follow a line running parallel to the vertebral border of the scapula and inferior from the medial surface of the base of the coracoid. Previous electromyogram studies of the subscapularis have used one electrode to study its dynamic function. The anatomic data in this and other series suggest that multiple electrodes may be required for a complete electromyogram study of the subscapularis. The findings of this study facilitate the placement of two intramuscular fine wire electrodes for electromyogrophic analysis, which permits the investigation of the subscapularis muscle as two functional units.

Surgical management of equinovarus deformity in the adult with head injury.

Equinovarus is the most common residual deformity of the lower extremity in patients who have sustained intracranial injury. Appreciation of the pathophysiology of the deformity aids in surgical management of selected cases. Gait analysis is a valuable tool for preoperative management. Three case reports illustrate the principles of surgical treatment.

A kinematic and electromyographic study of shoulder rehabilitation exercises.

The role of shoulder muscles during passive, active, and resistive phases of shoulder rehabilitation exercises was investigated in ten normal subjects with no history of shoulder pathology. Using the scapular plane as a reference, three-dimensional motion of the shoulder was recorded with a computer-aided motion analysis system (VICON) to determine total shoulder elevation. Simultaneously, electromyographic data were acquired on nine shoulder muscles while performing the three phases of shoulder rehabilitation exercises as described by Neer. Fine wire intramuscular electrodes were placed in the following muscles: trapezius, serratus anterior, deltoid (anterior, middle, and posterior separately), supraspinatus, infraspinatus, biceps, and latissimus dorsi. Phase I (passive) exercises performed in the supine position showed the least electromyography (EMG) activity. There was a gradation of EMG activity as one progressed from Phase I (passive) to Phase II (active) to Phase III (resistive) shoulder exercises. Isometric exercises and Phase III resistive exercises showed high levels of activity in the rotator cuff and deltoid muscles. Supine Phase I exercises should be considered in the early postoperative period after shoulder surgery to achieve maximum motion while minimizing shoulder muscle activity. Progression to Phase II and Phase III exercises may proceed as soft tissue and bony healing permit. Phase III exercises performed with an elastic band should provide a satisfactory method to strengthen these muscles.

Intramuscular wire electromyography of the subscapularis.

The action of the subscapularis muscle is an important component in maintaining shoulder stability. Because of its relative inaccessibility, there have been few electromyographic (EMG) studies of its normal patterns of activity. The subscapularis is innervated by two or more distinct nerves, and therefore the upper and lower parts of the muscle may have different functional roles depending on the position of the humerus. The purpose of this study was to develop safe, reproducible insertion paths to the upper and lower parts of the subscapularis. Six subjects with no previous history of shoulder injury were evaluated. The paths of insertion were designed based on previous anatomical studies as well as dissections. Two pairs of intramuscular wire electrodes were inserted: one directed toward the upper subscapularis and one toward the lower subscapularis. Electrode locations were confirmed using posteroanterior and lateral radiographs and through electrical stimulation. EMG data were recorded during isometric internal rotation exercises with the humerus in 0 or 90 degrees abduction. Significant differences were observed in the EMG activity recorded from the two pairs of electrodes. The EMG activity of the upper subscapularis either remained the same or decreased in going from 0 to 90 degrees abduction, while that of the lower subscapularis increased. The observed differential response confirmed that the electrodes were in different parts of the subscapularis. These preliminary results suggest that in future EMG studies, the subscapularis should be considered as at least two independent muscle units.

On the estimation of joint kinematics during gait.

In gait analysis, the concepts of Euler and helical (screw) angles are used to define the three-dimensional relative joint angular motion of lower extremities. Reliable estimation of joint angular motion depends on the accurate definition and construction of embedded axes within each body segment. In this paper, using sensitivity analysis, we quantify the effects of uncertainties in the definition and construction of embedded axes on the estimation of joint angular motion during gait. Using representative hip and knee motion data from normal subjects and cerebral palsy patients, the flexion-extension axis is analytically perturbed +/- 15 degrees in 5 degrees steps from a reference position, and the joint angles are recomputed for both Euler and helical angle definitions. For the Euler model, hip and knee flexion angles are relatively unaffected while the ab/adduction and rotation angles are significantly affected throughout the gait cycle. An error of 15 degrees in the definition of flexion-extension axis gives rise to maximum errors of 8 and 12 degrees for the ab/adduction angle, and 10-15 degrees for the rotation angles at the hip and knee, respectively. Furthermore, the magnitude of errors in ab/adduction and rotation angles are a function of the flexion angle. The errors for the ab/adduction angles increase with increasing flexion angle and for the rotation angle, decrease with increasing flexion angle. In cerebral palsy patients with flexed knee pattern of gait, this will result in distorted estimation of ab/adduction and rotation. For the helical model, similar results are obtained for the helical angle and associated direction cosines.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of lower extremity kinematics during level walking.

A simple external marker system and algorithms for computing lower extremity joint angle motion during level walking were developed and implemented on a computer-aided video motion analysis system (VICON). The concept of embedded axes and Euler rotation angles was used to define the three-dimensional joint angle motion based on a set of body surface markers. Gait analysis was performed on 40 normal young adults three times on three different test days at least 1 week apart using the marker system. Angular motion of the hip, knee, and ankle joints and of the pelvis were obtained throughout a gait cycle utilizing the three-dimensional trajectories of markers. The effect of uncertainties in defining the embedded axis on joint angles was demonstrated using sensitivity analysis. The errors in the estimation of joint angle motion were quantified with respect to the degree of error in the construction of embedded axes. The limitations of the model and the marker system in evaluating pathologic gait are discussed. The relatively small number of body surface markers used in the system render it easy to implement for use in routine clinical gait evaluations. Additionally, data presented in this paper should be a useful reference for describing and comparing pathologic gait patterns.

Dynamic electromyography. I. Numerical representation using principal component analysis.

A complete description of human gait requires consideration of linear and temporal gait parameters such as velocity, cadence, and stride length, as well as graphic waveforms such as limb rotations, forces, and moments at the joints and phasic activity of muscles. This results in a large number of interactive parameters, making interpretation of gait data extremely difficult. Statistical pattern recognition techniques can simplify this problem. For this approach to be successful, first it is necessary to reduce the number of interactive parameters to a manageable set. In this study, we present an application of principal component analysis as a means for representing graphic waveforms in a parsimonious manner. In particular, we concentrate on representing the phasic muscle activity recorded using surface electrodes from ten major muscles of the lower extremity of 35 normal subjects during level walking. A 32 point vector is created in which each point of the vector represents the normalized area under the curve of a portion of rectified and smoothed electromyographic signal, expressed as a function of gait cycle. Principal components are computed and the first few weighting coefficients are retained as features to represent the original EMG data. We show that the corresponding basis vectors span parts of the gait cycle where the most variability between individual subjects exists. We also show that the basis vectors can be used to represent the EMG data of subjects not originally used to generate the basis vectors.

Dynamic electromyography. II. Normal patterns during gait.

Human gait is a complex phenomenon. Many descriptors are needed to completely describe gait in terms of the biomechanics involved. The descriptors, when expressed as a function of the gait cycle, are complex waveforms. For each of these variables, a single "normal" pattern with bands of deviation has generally been accepted as a reference in clinical/research use to explain the abnormalities in a patient's walking pattern. In fact, one observes many "normal" patterns, and a body of research has been devoted to explaining the differences between these patterns in terms of walking speed, age, cadence, sex, etc. It would be simpler in one sense to start with the fact that different people walk with different patterns, not one pattern with bands of deviation. Numerical representation of the waveforms simplifies the analysis and interpretation of waveform data and facilitates comparison between subjects or groups of subjects. When combined with pattern recognition techniques, it also is useful for identifying subpatterns within a group. In this article, the numerical representation of electromyographic data by Karhunen-Loeve expansion are combined with cluster analysis to obtain patterns of dynamic phasic activity of 10 muscles of the lower extremity. From the 35 normal subjects walking at self-selected speed, two to four patterns are developed for each of the muscles and the physiological significance of the patterns are discussed.

Gait analysis of patients who have Paget disease.

Eighteen patients who had Paget disease were evaluated in our gait-analysis laboratory. The results were compared with those of ten healthy age-matched control subjects in order to quantitate the biomechanical changes and to describe the specific patterns of walking that occur secondary to bowing of a lower extremity. Kinetic and kinematic data were acquired using infrared video cameras and force platforms; electromyographic data were obtained using surface electrodes. Velocity and cadence were decreased and stride time and double-limb support time were increased in the patients who had Paget disease compared with the control subjects. Frequently, the knee of the limb that was affected by Paget disease was flexed during stance and flexed less during swing. When the involved knee was in varus angulation it also had an increased adduction moment, which may be related to the bowing deformity. Although the patterns of ground-reaction force were similar in the patients and the control subjects, the magnitudes of forces were reduced in the patients. Phasic muscle activity was similar in the two groups.

Repeatability of kinematic, kinetic, and electromyographic data in normal adult gait.

The repeatability of gait variables is an important consideration in the clinical use of results of quantitative gait analysis. Statistical measures were used to evaluate repeatability of kinematic, kinetic, and electromyographic data waveforms and spatiotemporal parameters of 40 normal subjects. Subjects were evaluated three times on each test day and on three different test days while walking at their preferred or natural speed. Intrasubject repeatability was excellent for kinematic data in the sagittal plane both within a test day as well as between test days. For joint angle motion in the frontal and transverse planes, the repeatability was good within a test day and poor between test days. Poor between-day repeatability of joint angle motion in the frontal and transverse planes was noted to be partly due to variabilities in the alignment of markers. Vertical reaction and fore-aft shear forces were more repeatable than the mediolateral shear force. Sagittal plane joint moments were more repeatable than frontal or transverse plane moments. For electromyographic data, repeatability within a day was slightly better than between test days. In general, the results demonstrate that with the subjects walking at their natural or preferred speed, the gait variables are quite repeatable. These observations suggest that it may be reasonable to base significant clinical decisions on the results of a single gait evaluation.

An improved design of electrodes for measurement of streaming potentials on wet bone in vitro and in vivo.

Streaming potentials are generated by mechanical stress in wet bone and may constitute a control mechanism for bone remodeling. Measurement of streaming potentials in bone has attracted considerable effort in past years but quantitative studies have been hampered by relatively poor repeatability when using Ag.AgCl electrodes which contact bone via a wick moistened with electrolyte. Improvement now has been achieved with an electrode design that limits the specific area of contact of an agar/salt bridge by means of a silastic seal, thus permitting the same equipotential surface to be contacted for each set of measurements. This reduces variations caused by bone structure and impedance, and facilitates quantitative comparisons of the response of bone samples to selected variables. The new design also permits considerable qualitative improvement in recordings made from bone during locomotor function in experimental animals in vivo.

External ultrasound can generate microampere direct currents in vivo from implanted piezoelectric materials.

Under development is an internal fixation plate that incorporates a piezoelectric element to generate current when excited mechanically by either weight bearing or external application of ultrasound. The intent is to deliver this current to electrodes at a fracture or osteotomy site to aid in prevention or treatment of nonunion. The present study examines quantitatively the ability of external ultrasound to generate current from small piezoelectric ceramic elements implanted in tissue. An ultrasonic transducer (2.25 MHz, 10-20 V input, less than 10 mW/cm2 output) was employed to excite small test coupons of a piezoelectric ceramic in vitro and in vivo with various materials, including water, PVC gel, cortical bone, and living soft tissues, interposed. In all instances, it was possible to generate currents of up to 20 microA after rectification; currents up to 1 mA were achieved in some cases. The work indicates that external ultrasonic energy could effectively power small internal devices designed to stimulate bone healing, without the need for implanted batteries or percutaneous leads.

Design considerations in development of a prototype, piezoelectric internal fixation plate: a preliminary report.

The piezoelectric internal fixation plate represents a new concept in orthopaedic implants. The purpose of this device is to provide stable bone fixation while delivering internally generated, microampere direct currents to prevent or treat nonunion of a fracture or osteotomy. Clinically, currents of this type have been effective in treatment of nonunion, but application has required separate, implanted, or external battery or radiofrequency powered circuits. The "piezoplate" being developed contains an integral piezoelectric element that generates current in response to either physiological loading such as weightbearing or to externally applied ultrasound. Currents are processed by a rectifying circuit for delivery to bone by electrodes. Specially designed series/parallel piezoelectric elements and dual processing circuits are required to generate optimum rectified currents from the low-frequency, high-voltage signals generated by weightbearing, as well as the high-frequency, low-voltage signals produced by ultrasound. This paper reports on the current status of development and describes design parameters of this device which combines the modalities of mechanical fixation and electrical stimulation in a single implant.

Repeatability of phasic muscle activity: performance of surface and intramuscular wire electrodes in gait analysis.

Repeatability is an important consideration for gait analysis data that are being used as an adjunct to clinical decision making. An index of repeatability may be based on a statistical criterion (variance ratio) that reflects similarity of wave forms over a number of identical cycles. The purpose of this study was to use the variance ratio to assess the repeatability of phasic muscle activity recorded with surface and bipolar intramuscular wire electrodes during gait on 10 normal subjects. Variance ratios were calculated using rectified and smoothed electromyographic data recorded simultaneously from the two types of electrodes. Three measures of repeatability (reproducibility, reliability, and constancy--defined as the cycle-to-cycle, run-to-run, and day-to-day repeatability of phasic muscle activity) were used to compare the performance of the two electrode techniques. Results show that the reproducibility and reliability were better for surface electrodes than for intramuscular wire electrodes, and constancy was good for surface electrodes and poor for intramuscular wire electrodes. Repeatability improved with increasing smoothing window lengths but was better for surface electrodes than wire electrodes, irrespective of the smoothing window. This study indicates that surface electrode data represent a more consistent measure of activity of superficial muscles, if comparisons are to be made between gait data from different test days.

Piezoelectric internal fixation devices: a new approach to electrical augmentation of osteogenesis.

Prototype testing has been accomplished on a piezoelectric, internal fixation plate. This device combines a piezoelectric material with an internal fixation device as an integrated structure that provides mechanical stability, together with self-generated electrical stimulation, for treating fractures and nonunion. In bench and animal tests we have demonstrated that cyclical loading can cause a device of this type to generate electrical charge while attached to bone. After rectification, direct currents within the range known to stimulate osteogenesis can be produced by weight-bearing loads. Furthermore, electrical output of the implants can be increased by externally applied ultrasonic energy. These twin developments add significantly to the potential armamentarium of devices to enhance bone healing.

Ultrasound mapping of the buttock-cushion interface contour.

For patients susceptible to decubitus ulcers, wheelchair cushions and other body support surfaces must be prescribed with a view to providing a uniform distribution of buttock-cushion interface pressures. The capacity to distribute pressure uniformly at the support interface depends on the shape of the bony prominences, and the amount and mechanical compliance of the overlying soft tissue: an indication of this capability may be given by the indentation contour of the buttock-cushion interface. Using normal subjects, we devised a method for measuring this contour using ultrasonic dimension gauging techniques. Because the technique can describe the geometry of soft tissues deformed under load, it could make an important contribution to successful employment of analytical modeling to predict internal tissue stresses during sitting.

Acoustic properties of polyvinyl chloride gelatin for use in ultrasonography.

Visualization of superficial structures with conventional rapid scanners has been difficult. A solid flexible polyvinyl chloride (PVC) gelatin slab used as a stand-off material can provide a constant scan distance and thus overcome the problem of poor near field resolution. PVC gelatin expands the capability of the 3-4 MHz transducer to delineate superficial structures. We report on the acoustic properties of the PCV gelatin, including the values of velocity and attenuation as a function of both frequency and temperature, and the comparison of data with published values of velocity and attenuation for water, soft tissue, and a phantom material.

Oxygen consumption of elderly persons with bilateral below knee amputations: ambulation vs wheelchair propulsion.

Elderly bilateral below knee (BK) amputees were tested for oxygen consumption (VO2), heart rate (HR) and velocity (V) during ambulation on a 40m walkway and a stationary wheelchair ergometer. Values obtained from amputees were compared to values obtained from a control population of the same age group. On test day 1 bilateral amputees and normal subjects ambulated at their natural pace on a walkway for approximately 5 minutes. On test day 2 each subject propelled a stationary wheelchair ergometer at their natural rate for the same distance that they ambulated. Measurements of VO2 (ml/m/kg), HR (beats/min), and V (m/min) were obtained during both sessions. Results show that the bilateral BK group required significantly more VO2 (ml/m/kg) (123%), had higher HR (26%), and slower V (36%) than the normal group during ambulation. The energy cost in terms of ml/min/kg during ambulation was similar, suggesting that the amputees ambulated at the same power cost as normals but at lower velocities. During wheelchair propulsion the BK group and normal group showed no significant difference in the 2 criteria. Results suggest that wheelchair propulsion is a more energy efficient mode of mobility for elderly bilateral BK amputees than ambulation. Energy cost and heart rate determinations may be valuable in choosing the course of mobility training and recommended activity levels. Cosmetic, psychosocial, and other clinical factors must be considered in prescribing rehabilitation.

Microprocessor-base system for ultrasonic tissue characterization.

A microprocessor-based ultrasonic data acquisiton and analysis system has been developed for measuring acoustic parameters of biologic media in a controlled environment. The system consists of commercially available pulse-echo electronics and both minicomputers and microcomputers. Measurements were made on various biologic tissues, both freshly excised and formalin fixed. Propagation velocity measurements were made using the substitution technique. Peak amplitude and log power spectra difference methods were used for attenuation measurements. Measured results indicate that propagation velocity in the soft tissues was in the range of 1530-1580 m/sec at 20 degrees C. Velocity variation among tissues at any given frequency was less than 2%; dispersion in the frequency range 1-10 MHz was approximately 1.5%. Attenuation coefficients showed a marked dependence on frequency increasing in a linear fashion. The slope of the attenuation frequency curve varied with tissue type and could be used for tissue characterization.