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Biomedical subjects

M W Keith

Publications and source records attributed to M W Keith.

At least 19 recordsLinked to original sources
PubMed2000

Reduction of costs of disability using neuroprostheses.

The lifetime costs associated with spinal cord injury are substantial. Assistive technology that reduces complications, increases independence, or decreases the need for attendant services can provide economic as well as medical or functional benefit. This study describes two approaches for estimating the economic consequences of implanted neuroprostheses utilizing functional electrical stimulation. Life care plan analysis was used to estimate the costs of bladder and bowel care with and without a device restoring bladder and bowel function and to compare these with the costs of implementing the device. For a neuroprosthesis restoring hand grasp, the costs of implementation were compared to the potential savings in attendant care costs that could be achieved by the use of the device. The results indicate that the costs of implementing the bladder and bowel system would be recovered in 5 years, primarily from reduced costs of supplies, medications, and procedures. The costs of the hand grasp neuroprosthesis would be recovered over the lifetime of the user if attendant time was reduced only 2 hours per day and in a shorter time if attendant care was further reduced. Neither analysis includes valuation of the quality of life, which is further enhanced by the neuroprostheses through restoration of greater independence and dignity. Our results demonstrate that implantable neuroprosthetic systems provide good health care value in addition to improved independence for the disabled individual.

Bionics↗
PubMed2000

Pin reduction and fixation of volar fracture fragments of distal radius fractures via the flexor carpi radialis tendon.

BACKGROUND: The objective of this study was to evaluate a technique for reduction and stabilization of residually displaced volar fragments in intraarticular distal radius fractures. METHODS: A consecutive series of patients with AO type C3 distal radius fractures treated by one surgeon were studied. Percutaneously placed pins were placed through the flexor carpi radialis tendon to reduce and stabilize volar fracture fragments of distal radius fractures when closed reduction was unsuccessful. The goal of treatment was to achieve less than 2 mm of articular congruity. Postoperative physiotherapy was protocol-based. A validated outcome measurement was used to evaluate patients. RESULTS: Of 117 patients, 10 met the inclusion criteria. In all patients, a successful reduction of the volar fragment was achieved with less than 2 mm of residual articular step-off. Reduction was maintained in 8 patients. Follow-up averaged 29 months, and there were no complications associated with the technique. All patients were satisfied with the treatment. CONCLUSION: Although the final outcome of patients with this type of fracture depends on many factors, in the small series of patients described, a satisfactory reduction was possible using the describe technique. Transtendinous pinning is a new, undescribed technique that is useful in the treatment of such specific injuries.

Adult↗
PubMed1999

Satisfaction with and usage of a hand neuroprosthesis.

OBJECTIVE: To measure the satisfaction with, clinical impact of, and use of an implantable hand neuroprosthesis. SETTING: Eight different medical centers. PARTICIPANTS: Thirty-four individuals with spinal cord injuries at the C5 or C6 motor level. INTERVENTIONS: Participants were implemented with a hand neuroprosthesis that provides grasp and release. The neuroprosthesis includes a surgically implanted stimulator, implanted electrodes sutured to the hand and forearm muscles, and an externally mounted controller. MAIN OUTCOME MEASURE: A survey was mailed to study participants, who were asked to respond to statements such as "If I had it to do over, I would have the hand system implanted again," using a 5-level Likert scale ("strongly agree" to "strongly disagree"). RESULTS: Eighty-seven percent of participants were very satisfied with the neuroprosthesis, 88% reported a positive impact on their life, 87% reported improvements in activities of daily living, and 81% reported improved independence. Participants reported using the neuroprosthesis a median of 5.5 days per week; 15 participants used the neuroprosthesis 7 days per week, and 5 participants reported not using the device. CONCLUSIONS: The neuroprosthesis was used by most participants. The neuroprosthesis performed satisfactorily, increased users' ability to perform activities of daily living and independence, and improved their quality of life.

Adolescent↗
PubMed1999

Variations in innervation of the flexor digitorum profundus muscle.

The composite flexor digitorum profundus muscle has a dual nerve supply from the ulnar nerve (UN) and the anterior interosseous nerve (AIN) but anatomic data regarding the territories of these 2 nerves are limited. In this study, muscles from 20 cadaver forearms were dissected microscopically. The motor nerves were followed to their terminations on individual muscle bellies and the innervation domains mapped. In 75% of cases the AIN supplied the index and middle fingers and the UN supplied the middle, ring, and little fingers; thus, the middle finger had dual innervation. In 20% of cases the AIN went to the index and middle fingers and the UN went to the ring and little fingers. In 5% of cases the AIN went to the index finger and the UN went to the middle, ring, and little fingers. The motor entry points were normalized to the forearm length. The entry points of the UN and AIN branches were at 15% and 30% of forearm length, respectively, distal to the medial epicondyle.

Cadaver↗
PubMed1999

The function of the finger intrinsic muscles in response to electrical stimulation.

The actions of the dorsal interosseous, volar interosseous, and lumbrical muscles were investigated using applied electrical stimulation and recording the moments that were generated across the metacarpophalangeal joint in flexion/extension and abduction/adduction, the proximal interphalangeal joint in flexion/extension, and the distal interphalangeal joint in flexion/extension. These measurements were made isometrically at various joint angles and levels of stimulation with both able bodied subjects and persons who had sustained tetraplegia. It was determined that the dorsal interossei, including the first, were strong abductors of the fingers and generated a significant moment in metacarpophalangeal (MP) joint flexion and interphalangeal (IP) joint extension. The volar interossei were the primary adductors of the fingers, as well as providing a significant moment in MP joint flexion and IP joint extension. The lumbrical muscles were found to be MP joint flexors and IP joint extensors, although the moments that were generated were on average 70% lower than the interossei. The role of the lumbricals as finger abductors or adductors could not be determined from the data. This information on the actions and moment generating capabilities of the intrinsic muscles led to the incorporation of the interossei into electrically induced hand grasp provided by an implanted neuroprosthesis. The evaluation of the intrinsic muscles in the neuroprosthesis was accomplished by recording the moment generating capabilities of these muscles across each of the joints of the finger. These muscles were capable of generating moments that were 80-90% of the average attained by the able bodied subjects, and have provided a substantial improvement to the electrically induced hand grasp.

Adult↗
PubMed1999

Implantable transducer for two-degree of freedom joint angle sensing.

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.

Animals↗
PubMed1998

An elbow extension neuroprosthesis for individuals with tetraplegia.

Functional electrical stimulation (FES) of the triceps to restore control of elbow extension was integrated into a portable hand grasp neuroprosthesis for use by people with cervical level spinal cord injury. An accelerometer mounted on the upper arm activated triceps stimulation when the arm was raised above a predetermined threshold angle. Elbow posture was controlled by the subjects voluntarily flexing to counteract the stimulated elbow extension. The elbow moments created by the stimulated triceps were at least 4 N.m, which was sufficient to extend the arm against gravity. Electrical stimulation of the triceps increased the range of locations and orientations in the workspace over which subjects could grasp and move objects. In addition, object acquisition speed was increased. Thus elbow extension enhances a person's ability to grasp and manipulate objects in an unstructured environment.

Biomechanical Phenomena↗
PubMed1997

Tissue response to chronically stimulated implanted epimysial and intramuscular electrodes.

Twenty-four epimysial and 16 intramuscular electrodes were implanted in five adult dogs for periods ranging from 11 to 50 months. Chronic stimulation was applied to half of the electrodes for eight weeks near the end of the implantation period. The tissue response was rated by the amount and appearance of the fibrous tissue and inflammatory cells seen in the capsule lining the region of the electrode. The encapsulation tissues were composed primarily of collagen and fibroblasts and some macrophages and few other inflammatory cells. The epimysial electrodes exhibited more variation between and within electrodes, but had more of the better scores than the intramuscular electrodes. No difference in the distribution of scores was measured between the control and stimulated groups for the epimysial electrodes. While the scores for the intra-muscular electrodes varied very little, variance was sufficient to indicate a trend for poorer ratings with the application of chronic stimulation. Fibrous capsules were generally thinner under the epimysial electrodes than around the intramuscular electrodes. For both electrode types, the thickness was not correlated with the application or level of chronic stimulation. Thickness was shown to be positively correlated to the degree of loss of the sutures used to anchor the epimysial electrodes.

Animals↗
PubMed1997

An implanted upper-extremity neuroprosthesis. Follow-up of five patients.

An implanted neuroprosthesis supplying functional neuromuscular stimulation was used to provide grasp and release to tetraplegic individuals. This article describes the results, at a minimum of three years, for the first five patients to have operative implantation of an eight-channel stimulator-receiver. All of the patients had a clinically complete spinal cord injury with motor function remaining at the level of the fifth or sixth cervical nerve root. In addition to implantation of the stimulator system, each patient had augmentative operations on the hand to improve function. The procedures included tendon transfers, side-to-side tendon anastomoses, arthrodesis of the interphalangeal joint of the thumb, and rotational osteotomy of the radius. The neuroprosthesis provides two grasp patterns controlled by voluntary motion of the shoulder or wrist. Functional evaluations included measurement of pinch force, a grasp-release test, evaluation of the level of functional independence, and usage surveys. Pinch force ranged from eight to twenty-five newtons. All five patients demonstrated functional grasp patterns, had increased independence, and were able to use the neuroprosthesis at home on a regular basis. The implanted stimulator has proved to be safe and reliable, with seven years as the longest time in situ at the time of writing.

Activities of Daily Living↗
PubMed1996

Restoration of pronosupination control by FNS in tetraplegia--experimental and biomechanical evaluation of feasibility.

Individuals with C5/C6 tetraplegia lack voluntary control of the forearm pronators. We evaluated the feasibility of restoring forearm pronation/supination control using an electrically activated pronator opposed by voluntary supination. To this end, we measured the electrically produced pronation moments of subjects with tetraplegia. The maximal pronation moment achieved by stimulating the pronator quadratus ranged from 30 to 100 N cm in three forearms of two subjects. These moments were sufficient to produce forearm pronation in all three forearms. Voluntary control of pronosupination during constant pronator stimulation was achieved by having the subject voluntarily supinate or relax to change the balance of rotational torques acting on the forearm. In all cases, the subjects were able to supinate voluntarily against the continuously stimulated pronator, producing intermediate angles between full pronation and full supination. We also observed under some conditions that subjects could voluntarily pronate and supinate even without pronator stimulation. Using a biomechanical model, we show how pronation can be initiated from a supinated position using the brachioradialis, with gravity completing the pronation. This method of pronation without stimulation is extremely sensitive to the orientation of the forearm in the gravitational field, and thus is not a widely applicable technique. We conclude that forearm pronosupination via Functional Neuromuscular Stimulation is feasible, and would provide subjects the ability to pronate without the assistance of gravity.

Biomechanical Phenomena↗
PubMed1996

Tendon transfers and functional electrical stimulation for restoration of hand function in spinal cord injury.

Spinal cord injury at the C5 and C6 level results in loss of hand function. Electrical stimulation of paralyzed muscles is one approach that has demonstrated significant capacity for restoring grasp and release function. One potential limitation of this approach is that key muscles for stimulation may have lower motor neuron damage, rendering the muscles unexcitable. We have used surgical modification of the biomechanics of the hand to overcome this limitation. Tendon transfer of paralyzed but lower motor neuron intact muscles can compensate for potential function lost owing to muscles with lower motor neuron damage. Such procedures have been performed to provide finger extension, thumb extension, finger flexion, and wrist extension. Additional surgical procedures have been performed to enhance the function provided with electrical stimulation. These are side-to-side synchronization of the finger flexor and extensor tendons, the flexor digitorium superficialis Zancolli-lasso procedure, and thumb interphalangeal joint arthrodesis. These procedures have been performed in 11 patients with C5 and C6 level spinal injuries and functional electrical stimulation neuroprostheses. In these patients, 41 different functional electrical stimulation-related procedures were performed and 38 gave the desired result after surgery. One procedure resulted in no increase or decrease in function or muscle output, and two procedures resulted in a decrease in muscle force or joint range of motion. The issues that must be considered in performing functional electrical stimulation-related tendon transfers are discussed.

Electric Stimulation Therapy↗
PubMed1996

Measurement of isometric elbow and shoulder moments: position-dependent strength of posterior deltoid-to-triceps muscle tendon transfer in tetraplegia.

This report describes an apparatus which has been developed to measure several isometric elbow and shoulder forces and moments simultaneously and also allows this characterization to be performed across a range of shoulder and elbow joint angles in a horizontal plane. This apparatus was used to characterize the elbow extension strength in individuals with tetraplegia resulting from cervical level spinal cord injury. In all of these individuals, voluntary elbow extension was provided exclusively by the posterior deltoid muscle, which had previously been surgically transferred to the tendon of the paralyzed triceps muscle. Elbow extension is essential for many daily activities, such as reaching above shoulder level and pushing objects away from the body; the widely used posterior deltoid-to-triceps muscle tendon transfer surgery restores some degree of voluntary control to this important function. The apparatus contained a six-axis force-moment transducer to which the arm of each subject was attached. The six outputs of the transducer were transformed to correspond to physiological elbow and shoulder moments and forces. A customized table allowed the shoulder and elbow angles of the subject to be varied over a wide range in a horizontal plane so that the effects of posterior deltoid muscle length could be characterized over the likely functional range of the subject within this plane. It was found that elbow extension strength varied widely across subjects with C5 or C6 tetraplegia, from quite weak to strong enough to propel a manual wheelchair. Furthermore, the elbow extension strength of most subjects showed a strong dependence on both elbow and shoulder angles. Elbow extension was typically weak when the upper arm was elevated to shoulder level at the side, which unfortunately corresponds to the position often adopted by these individuals due to shoulder weakness.

Elbow Joint↗
PubMed1996

Carpal instability in the weight-bearing upper extremity.

The prevalence of carpal instability in a paraplegic population was investigated to establish an association between chronic repetitive stress on the wrist and the development of such instability. Nine of 162 paraplegic patients had static carpal instability and no history of an acute injury of the wrist. The predominant pattern of instability, found in eleven wrists (six patients), was non-dissociative volar intercalated segmental instability. The prevalence of carpal instability increased with the duration of weight-bearing on the upper extremity. Eighteen per cent of the patients in whom the spinal cord injury had occurred more than twenty years before the study had carpal instability. Carpal instability in these weight-bearing upper extremities and the increase in its prevalence with the duration of the forces across the wrist demonstrate an association between chronic repetitive stress on the wrist and carpal instability.

Adult↗
PubMed1995

Functional range of motion of the elbow.

One hundred normal upper extremities in 50 adults were sequentially studied in a Bledsoe brace, which limited elbow motion. The amount of flexion and extension of the elbow was serially limited by 15 degree increments. At each setting, the subjects were asked to perform 12 activities of daily living. The percentage of subjects who completed each task with the specified range of motion was determined. Overall, 49 of the subjects performed all of the tasks with extension limited at 75 degrees and flexion limited at 120 degrees. By isolating the allowable range of motion of the elbow and allowing for compensatory motions and strategies of the normal adjacent joints, the functional elbow range of motion is established as 75 degrees-120 degrees flexion. Thus, the functional status of a patient with a specific elbow range of motion can be predicted more accurately.

Activities of Daily Living↗
PubMed1994

Development of a quantitative hand grasp and release test for patients with tetraplegia using a hand neuroprosthesis.

We developed a quantitative grasp and release test for assessing a hand neuroprosthesis in C5 and C6 level tetraplegic patients. The objectives were (1) to determine if a patient's hand performance with the neuroprosthesis exceeded a defined, clinically acceptable baseline, (2) to compare performance with and without the neuroprosthesis, (3) to measure the consistency of performance over time, and (4) to compare performance among patients. In the test, patients grasped, moved, and released one of six different objects as many times as possible in five 30-second trials for each object, with and without the neuroprosthesis. Unlike earlier tests, the objects and the task were chosen to span a range of difficulties appropriate for C5 and C6 tetraplegic patients using a hand neuroprosthesis. Data from five patients showed that performance with the neuroprosthesis was above the baseline; performance improved with the neuroprosthesis, although it was not generally consistent across sessions; and the neuroprosthesis helped C5 patients manipulate most objects and helped C6 patients primarily with more difficult objects.

Adult↗
PubMed1992

Bipolar latissimus dorsi transposition and functional neuromuscular stimulation to restore elbow flexion in an individual with C4 quadriplegia and C5 denervation.

A bipolar latissimus dorsi transposition was performed on a 17-year-old male patient with a C4 spinal cord injury and complete peripheral denervation at C5. Electrical stimulation of the paralyzed but excitable latissimus dorsi provided elbow flexion that could not be achieved with the paralyzed and denervated elbow flexors. The muscle was attached from the coracoid to the ulna allowing the elbow to be flexed with the forearm and wrist maintained in the neutral position. Following a 6-week immobilization period, the transposed muscle was exercised daily with intramuscular stimulation to increase both strength and endurance. By the fourth month after surgery, the subject could control elbow flexion proportionally with contralateral shoulder elevation using a shoulder position transducer. Functionally, the subject was able to use the neuroprosthetic system to bring his hand to his mouth and feed himself with the aid of a universal cuff and a support to stabilize the shoulder.

Adolescent↗