Effect of equinus foot placement and intrinsic muscle response on knee extension during stance.

Equinus gait, a common movement abnormality among individuals with stroke and cerebral palsy, is often associated with knee hyperextension during stance. Whether there exists a causal mechanism linking equinus foot placement with knee hyperextension remains unknown. To investigate the response of the musculoskeletal system to equinus foot placement, a forward dynamic simulation of normal walking was perturbed by augmenting ankle plantarflexion by 10 degrees at initial contact. The subsequent effect on knee extension was assessed when the muscle forces were allowed, or not allowed, to change in response to altered kinematics and intrinsic force-length-velocity properties. We found that an increase in ankle plantarflexion at initial contact without concomitant changes in muscle forces caused the knee to hyperextend. The intrinsic force-length-velocity properties of muscle, particularly in gastrocnemius and vastus, diminished the effect of equinus posture alone, causing the abnormal knee extension to be less pronounced. We conclude that the effect of ankle position at initial contact on knee motion should be considered in the analysis of equinus gait.

Development of robots for rehabilitation therapy: the Palo Alto VA/Stanford experience.

For over 25 years, personal assistant robots for severely disabled individuals have been in development. More recently, using robots to deliver rehabilitation therapy has been proposed. This paper summarizes the development and clinical testing of three mechatronic systems for post-stroke therapy conducted at the VA Palo Alto in collaboration with Stanford University. We describe the philosophy and experiences that guided their evolution. Unique to the Palo Alto approach is provision for bimanual, mirror-image, patient-controlled therapeutic exercise. Proof-of-concept was established with a 2-degree-of-freedom (DOF) elbow/forearm manipulator. Tests of a second-generation therapy robot producing planar forearm movements in 19 hemiplegic and control subjects confirmed the validity and reliability of interaction forces during mechanically assisted upper-limb movements. Clinical trials comparing 3-D robot-assisted therapy to traditional therapy in 21 chronic stroke subjects showed significant improvement in the Fugl-Meyer (FM) measure of motor recovery in the robot group, which exceeded improvements in the control group.

Quantification of force abnormalities during passive and active-assisted upper-limb reaching movements in post-stroke hemiparesis.

We evaluated a method for measuring abnormal upper-limb motor performance in post-stroke hemiparetic subjects. A servomechanism (MIME) moved the forearm in simple planar trajectories, directly controlling hand position and forearm orientation. Design specifications are presented, along with system performance data during an initial test of 13 stroke subjects with a wide range of impairment levels. Performance of subjects was quantified by measuring the forces and torques between the paretic limb and the servomechanism as the subjects relaxed (passive), or attempted to generate force in the direction of movement (active). During passive movements, the more severely impaired subjects resisted movement, producing higher levels of negative work than less-impaired subjects and neurologically normal controls. During active movements, the more severely impaired subjects produced forces with larger directional errors, and were less efficient in producing work. These metrics had significant test-retest repeatability. These motor performance metrics can potentially detect smaller within-subject changes than motor function scales. This method could complement currently used measurement tools for the evaluation of subjects during recovery from stroke, or during therapeutic interventions.

Large index-fingertip forces are produced by subject-independent patterns of muscle excitation.

Are fingertip forces produced by subject-independent patterns of muscle excitation? If so, understanding the mechanical basis underlying these muscle coordination strategies would greatly assist surgeons in evaluating options for restoring grasping. With the finger in neutral ad- abduction and flexed 45 degrees at the MCP and PIP, and 10 degrees at DIP joints, eight subjects attempted to produce maximal voluntary forces in four orthogonal directions perpendicular to the distal phalanx (palmar, dorsal, lateral and medial) and in one direction collinear with it (distal). Forces were directed within 4.7 +/- 2.2 degrees (mean +/- S.D.) of target and their magnitudes clustered into three distinct levels (p < 0.05; post hoc pairwise RMANOVA). Palmar (27.9 +/- 4.1 N), distal (24.3 +/- 8.3 N) and medial (22.9 +/- 7.8 N) forces were highest, lateral (14.7 +/- 4.8 N) was intermediate, and dorsal (7.5 +/- 1.5 N) was lowest. Normalized fine-wire EMGs from all seven muscles revealed distinct muscle excitation groups for palmar, dorsal and distal forces (p < 0.05; post hoc pairwise RMANOVA). Palmar force used flexors, extensors and dorsal interosseous; dorsal force used all muscles; distal force used all muscles except for extensors; medial and lateral forces used all muscles including significant co-excitation of interossei. The excitation strategies predicted to achieve maximal force by a 3-D computer model (four pinjoints, inextensible tendons, extensor mechanism and isometric force models for all seven muscles) reproduced the observed use of extensors and absence of palmar interosseous to produce palmar force (to regulate net joint flexion torques), the absence of extensors for distal force, and the use of intrinsics (strong MCP flexors) for dorsal force. The model could not predict the interossei co-excitation seen for medial and lateral forces, which may be a strategy to prevent MCP joint damage. The model predicts distal force to be most sensitive to dorsal interosseous strength, and palmar and distal forces to be very sensitive to MCP and PIP flexor moment arms, and dorsal force to be sensitive to the moment arm of and the tension allocation to the PIP extensor tendon of the extensor mechanism.

Fine-wire electromyographic recording during force generation. Application to index finger kinesiologic studies.

When accurately placed, fine-wire electrodes (FWEs) permit selective electromyographic recording during kinesiologic studies; however, their potential to limit contraction of the index finger muscles has not previously been evaluated. Given that these electrodes cannot be reinserted, reliable techniques are necessary to achieve proper placement while minimizing subject discomfort and electrode waste. The small size, close arrangement, and anatomic variability of hand and forearm muscles create challenges to achieving these goals. In this study, we simultaneously measured maximal fingertip forces and fine-wire electromyographic signals from all seven muscles of the index finger. Forces in five directions, with and without FWEs in place, were not statistically different (repeated-measures analysis of variance, P < 0.46) in five healthy adult subjects. To guide electrode placement, we identified skin penetration landmarks, direction of needle advancement, and depth of muscle fibers. Fibers of flexor digitorum superficialis and flexor digitorum profundus to the index finger were more distal than depicted in textbooks, requiring electrode placement at or distal to the midpoint of the forearm. For these muscles and the extensor digitorum, locating the desired fibers first with a monopolar needle electrode facilitated subsequent FWE placement. For the dorsal and palmar interossei, lumbrical, and extensor indicis proprius, insertion was aided by concurrent monitoring of the electromyographic signals. We achieved a 93% success rate during FWE placement in a total of 60 muscles. Techniques for recording from each of the seven index finger muscles are described.

Anatomical and electrophysiological determinants of the human thenar compound muscle action potential.

Clinical interpretation of the compound muscle action potential (CMAP) requires a precise understanding of its underlying mechanisms. We recorded normal thenar CMAP5 and motor unit action potentials using different electrode configurations and different thumb positions. Computer simulations show that the CMAP has four parts: rising edge, negative phase, positive phase, and tail which correspond to four distinct stages of electrical activity in the muscle: initiation at the end-plate, propagation, termination at the muscle/tendon junctions, and slow repolarization. The shapes of volume-conducted signals recorded beyond the muscle are also explained by these four stages. Changes in CMAP shape associated with thumb abduction are due to changes in termination times resulting from changes in muscle-fiber lengths. These findings demonstrate that the negative and positive phases of the CMAP are due to different mechanisms, and that anatomical factors, particularly muscle-fiber lengths, play an important role in determining CMAP shape.

Drop-counting flow computer.

An inexpensive microcomputer (VIC-20) was adapted to count drops of fluid and calculate flow. To minimize both the expense and the bench space occupied by the flow computer, we eliminated the need for a video monitor by employing a liquid crystal alphanumeric display. Neither tape recorders nor disk drives are needed because the flow-computing program resides in a "game cartridge." Furthermore, the power supply of the computer powers the interface and display. The computer's real-time clock is utilized to time intervals between drops falling through an infrared beam. The computed flow values are then shown on the liquid crystal display, and they are sent to an external recorder via a digital-to-analog converter. A second digital-to-analog converter can be used to trigger a fraction collector. When compared with timed manual collections, the flow computer was shown to yield highly accurate, linear measurements of water and blood flow. Although the drops-per-milliliter constant varied with orifice size and hematocrit, the hematocrit fluctuations observed in typical isolated organ experiments would not appreciably affect the blood flow determinations.

A solid-state arteriovenous oxygen difference analyzer for flowing whole blood.

This communication describes a spectrophotometric device which determines the arteriovenous oxygen difference (a-v O2) on whole blood flowing through optical cuvettes. The instrument consists entirely of commercially available solid-state components, including the light sources, light-emitting diodes. When calibrated against conventional determinations of blood oxygen content, the output of the a-v O2 analyzer was shown to be highly linear and to be independent of total hemoglobin concentration. The electronic circuit, the theory of the measurement, and sources of error are described in detail.