Rehabilitation and surgical reconstruction of the upper limb in tetraplegia: an update

Force-amplifying implant to improve key pinch strength in tendon transfer surgery: Cadaver model proof-of-concept

The brachioradialis (BR) to flexor pollicis longus (FPL) tendon transfer surgery is a common procedure used to restore key pinch grip for incomplete spinal cord injury patients. However, the procedure only restores 22% of the physiological grip strength, which is important for successfully grasping objects and minimizing fatigue. The purpose of this study was to evaluate the efficacy of using a novel force-amplifying pulley implant to modify the standard BR to FPL tendon transfer surgery to improve key pinch grip strength in a human cadaver forearm model. A total of eight cadaveric specimens were mounted onto a custom testbed where a torque-controlled motor actuated the BR tendon to produce key pinch grip. In each cadaver, two experimental groups were examined: a standard and an implant-modified BR to FPL tendon transfer surgery. A force sensor mounted to the thumb recorded isometric key pinch grip forces over a range of input BR forces (2 N-25 N) applied in a ramp-and-hold protocol. Across the range of input BR forces, the average improvement in key pinch grip strength in the implant-modified surgery compared to the standard surgery was 58 ± 7.1% (ranging from 41% to 64% improvement). Throughout the experiments, we observed that the implant did not hinder the movement of the BR or FPL tendons. These results suggest that a BR to FPL tendon transfer surgery utilizing a force-amplifying pulley implant to augment force transmission can provide additional functional strength restoration over the standard procedure that directly sutures two tendons together.

A Comparative Outcome Study of Hamstring Versus Tibialis Anterior and Synthetic Grafts for Deltoid to Triceps Transfers

PURPOSE

To assess elbow extension strength and complications after deltoid-triceps transfers using hamstring tendon graft compared with tibialis anterior and synthetic tendon grafts.

METHODS

A retrospective review of deltoid-triceps transfers in patients with tetraplegia performed between 1983 and 2014.

RESULTS

Seventy-five people (136 arms) had surgery performed, with the majority undergoing simultaneous bilateral surgery (n = 61; 81%). Tibialis anterior tendon grafts were used in 68 arms, synthetic grafts in 23 arms, and hamstring tendon grafts in 45 arms. The average age at surgery was 31 years. Sixty-three arms (46%) were assessed between 12 and 24 months after surgery. Seventy percent of the group (n = 54) were able to extend their elbow against gravity (grade 3 of 5 or greater) following surgery. Seventy-nine percent of those with hamstring grafts achieved grade 3 of 5 or more compared with 77% with tibialis anterior and 33% with synthetic grafts. There was a statistically significant difference in postsurgery elbow extension between the tibialis anterior group and the synthetic graft group and the hamstring and the synthetic graft group but not between the tibialis anterior and the hamstring group. Complications occurred in 19 arms (14%), the majority occurring immediately after surgery and associated with the wounds. The remaining complications were with the synthetic graft group in which dehiscence of the proximal attachment occurred in 30% of the arms.

CONCLUSIONS

Autologous tendon grafting is associated with achievement of antigravity elbow extension in a greater proportion of individuals than with prosthetic grafting.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Functional Priorities in Persons with Spinal Cord Injury: Using Discrete Choice Experiments To Determine Preferences

Major goals of rehabilitation and health interventions in people with spinal cord injury (SCI) are to improve functional independence, increase social participation, and enhance quality of life (QOL). Determining functional areas perceived by consumers as most important can assist in research prioritization, planning for delivery of health services, and policy development. Five high priority areas of functioning for the SCI population (arm/hand use, walking, bladder/bowel control, sexual function, and relief of pain) were chosen to determine the preferences for these five attributes. A discrete choice experiment was conducted involving 151 persons with SCI sampled from Australia and the United States of America. Consistent with prior research, arm/hand function had the highest preference, with odds ratios of subjects being 44-76% more likely to choose arm/hand function over the other four functions. Preference for normal arm/hand function was found to be significantly more preferred by the group with paraplegia compared with those with tetraplegia; that is, retaining and not trading off existing arm/hand function for other improved functions. There were no significant differences found in preferences between bladder/bowel function and walking or elimination of pain, although walking was preferred in earlier (≤ 10) post-injury years and pain amelioration became more important with a longer duration (>10 years) post-injury. Sexual function had the lowest preference when traded against the other four functions. Understanding the functional preferences of persons with SCI will help to inform future research design, as well as enabling successful translation of research into practice and health policy, meeting the needs of people with SCI.

Dynamic electromyographic evaluation of adolescents with traumatic cervical injury after biceps to triceps transfer: the role of phasic contraction

PURPOSE

To characterize the EMG firing pattern of the biceps after transfer to the triceps.

METHODS

Seven subjects (12 arms), 18.0 +/- 1.7 years old, consented to fine wire EMG assessment of the biceps, averaging 23.0 +/- 10.0 months (range: 9 to 45 months) after transfer. Subjects were tested under 3 conditions: (1) single flexion and extension, (2) self-selected alternating elbow flexion and extension, and (3) isometric flexion and extension. A strain gauge electrogoniometer measured elbow movement. Using root-mean-squared values of biceps EMG, ratios of extension/flexion activity were calculated for each muscle. Conventional manual muscle testing grades were obtained before and after surgery.

RESULTS

Median manual muscle testing for elbow extension was 0 before surgery and 4- (range: 3- to 4) following surgery. For each of the 3 conditions tested, the biceps reversed its action to an elbow extensor (p < .05).

CONCLUSIONS

Our findings show that the biceps, after transfer to the triceps in patients with C5 or C6 spinal cord injury, can be trained to activate preferentially during elbow extension, a reversal of its ordinary action as an elbow flexor.

Motor capacities of upper limbs in tetraplegics: a new scale for the assessment of the results of functional surgery on upper limbs

STUDY DESIGN

Metrological investigation.

OBJECTIVES

To study the validity and the reliability of a Motor Capacities Scale (MCS) specifically designed for tetraplegics who undergo a functional surgery of upper limbs.

SETTING

Bouffard-Vercelli Centre, Cerbere, France.

METHODS

From diverse sources (observation of patients, review of literature, discussions with occupational therapists and physicians), we compiled a list of 300 activities relating to daily living tasks. From this list, 80 items of motor capacities were retained. They correspond to the abilities of a patient to perform basic and functional tasks regardless of contextual factors (environmental and personal factors). In a preliminary study, items were reviewed by occupational therapists and by 40 tetraplegics for criticism. An open study and an intermediate study were conducted to assess, respectively, the feasibility and the reliability of the MCS. A prefinal study was focused on construct validity. Convergent and divergent hypotheses were formulated and tested against other measures. Four criteria were identified for the elimination of some of the 36 remaining items: a variance of the item equal to 0, a low reproducibility, a high level of redundancy studied by item-to-item correlation and a low level of comprehension.

RESULTS

In all, 52 tetraplegics were included in the prefinal study. Global inter-rater reproducibility was excellent (intraclass correlation coefficient of 0.99). In accordance with the criteria of elimination, the number of items was reduced to 31. Correlations with the Sollerman test and the Asia Motor Score were, respectively, 0.959 and 0.7444 (P<0.0001). Correlation with the interval since the onset of the tetraplegia and the educational level were, respectively, 0.20 and 0.195 (P=0.163).

CONCLUSION

MCS displays a good apparent and content validity, and excellent reproducibility and construct validity. Metrological properties were good enough to allow the evaluation of sensitivity to change in the final study.

Implantation of the Freehand System during initial rehabilitation using minimally invasive techniques

STUDY DESIGN

Series of four single subjects with and without intervention design.

OBJECTIVES

To describe a minimally invasive surgical technique used to implant the Freehand System during initial spinal cord injury (SCI) rehabilitation and to report rehabilitation outcomes of four recently injured adolescents using the Freehand System.

SETTING

Nonprofit children's hospital specializing in orthopedic and SCI care.

METHODS

Four subjects with C5 tetraplegia between 13 and 16 years of age and between 9 and 16 weeks following traumatic SCI underwent implantation of the Freehand System using minimally invasive surgical techniques. Outcomes on muscle strength, pinch force, hand function, performance of activities of daily living and satisfaction with and without the Freehand System were collected.

RESULTS

Each subject was successfully implanted with the Freehand System without perioperative complications and employed the Freehand System during therapy services and ad lib on the rehabilitation floor. At the last follow-up, every subject remained a motor candidate for the Freehand System. With the Freehand System, average lateral and palmar pinch force was 1.8 and 1.6 kg respectively; average pinch force without functional electrical stimulation (FES) was 0.29 kg. With the Freehand System, three subjects improved their rate of performance on The Upper Extremity Capabilities Questionnaire. All subjects increased their level of independence on The Quadriplegia Index of Function. On the Canadian Occupational Performance Measure (COPM) with the Freehand System, average performance and satisfaction scores improved for every patient. Three of the four subjects continued to use the system at home.

CONCLUSION

This case series demonstrates that the Freehand System can vastly improve hand function and performance of rehabilitation activities within days after a minimally invasive implant procedure during initial SCI rehabilitation. Satisfaction with the Freehand System beyond initial rehabilitation is evidenced by continued use at home.

Analyse critique des modalités d’évaluation des résultats de la chirurgie fonctionnelle du membre supérieur tétraplégique. Revue de la littérature sur les 50 dernières années

OBJECTIVE

To study the methods of assessment of upper limb functional surgery in the literature.

METHODS

The literature review relating to the years 1950-2002 was carried out with three data bases: Medline, Pascal, Embase. This review also involved a thorough study of non-indexed references.

RESULTS

Although many instruments or tests are used to assess outcome after surgery, their reliability, validity and responsiveness have not been adequately proven. Methodology appears to be the major failing of the various scales used to assess these patients. The conceptual models underlying the evaluation are all too often unspecified. There is a lack of pertinence of the selected tasks for tetraplegics. There is limited documentation of the guiding framework or conceptualisation. Furthermore, the process of item selection is often unknown. Scales or instruments are also deemed to be too insensitive to document the small but meaningful functional gains made by tetraplegics after functional surgery.

CONCLUSION

To answer the need for a specific assessment tool for tetraplegics who undergo functional surgery, we have developed a national, multicenter, prospective and longitudinal study based on two concepts: the first concept is related to Life Habits that are the activities of daily living and social roles recognised by the socio-cultural context of a person according to age, sex and social and personal identity. They include activities that should be accomplished on a daily basis (nutrition, fitness, personal care, communication, mobility, etc.). Life Habits presenting a significant level of disruption can create handicap situations. The second concept is in relation with Motor Capacities that correspond to the abilities of a patient to perform basic and functional tasks regardless of contextual factors (environmental and personal factors).

Prospective evaluation of biceps to triceps and deltoid to triceps for elbow extension in tetraplegia

PURPOSE

The purpose of this study was to evaluate and compare the deltoid to triceps and biceps to triceps transfers for restoration of elbow extension in young persons with tetraplegia.

METHODS

This was a prospective randomized study. Sixteen arms of 9 subjects between 8 and 20 years of age with cervical-level spinal cord injuries were assigned randomly to undergo either a deltoid to triceps transfer or a biceps to triceps transfer. All arms were followed-up prospectively for at least 2 years after surgery.

RESULTS

Elbow extension was restored in 8 arms via the deltoid and in 8 arms via the biceps transfers. At the 24-month follow-up evaluation 7 of the 8 biceps transfers produced antigravity strength (grade 3 or better); in contrast only one arm with the deltoid transfer was able to extend against gravity. There was a considerable but subclinical loss (no subject appreciated any functional deficit) of elbow flexion torque after both transfers. Three months after surgery the deltoid group showed a 51% loss of elbow flexion torque and the biceps group showed a 52% loss of elbow flexion torque. By 24 months after surgery both groups improved but still showed a loss of flexion torque (deltoid 32%, biceps 47%). After gaining elbow extension the subjects in both groups rated the performance of most activities of daily living (ADL) and all self-selected activities as better, as measured on the Modified University of Minnesota Tendon Transfer Functional Improvement Questionnaire and the Canadian Occupational Performance Measure, respectively. Likewise all subjects were more satisfied with performance of their goals after undergoing elbow extension reconstruction.

CONCLUSIONS

This study showed the benefits of restoring elbow extension in persons with tetraplegia and provided support for the biceps transfer as an alternative to the deltoid to triceps transfer in individuals with good brachialis and supinator strength.

Satisfaction with upper-extremity surgery in individuals with tetraplegia

OBJECTIVE

To measure the satisfaction of individuals with tetraplegia with their upper-extremity reconstructive surgery.

DESIGN

Survey.

SETTING

Two Spinal Cord Injury Model Systems centers.

PARTICIPANTS

Sixty-seven individuals with spinal cord injury at the C4 through C8 motor level (107 arms).

INTERVENTIONS

Participants had upper-extremity surgery to improve function. The surgical procedures included tendon transfers for elbow extension, wrist extension, hand grasp, and pinch or hand grasp neuroprosthesis.

MAIN OUTCOME MEASURE

A survey was mailed to participants, who were asked to respond to statements such as, "If I had it to do over, I would have the hand/arm surgery again," using a 5-level Likert scale (ranging from strongly agree to strongly disagree).

RESULTS

Seventy percent of the participants were generally satisfied with the results of their upper-extremity surgery, 77% reported a positive impact on their lives, 68% reported improvements in activities of daily living (ADLs), 66% reported improved independence, 69% reported improvement in occupation, 71% reported improved appearance or neutral, 78% reported their hand worked as well (or neutral) as it did when surgery was first performed, and 86% reported postoperative therapy as being beneficial.

CONCLUSIONS

Upper-extremity surgery had a positive impact on life, increased ability to perform ADLs and to be independent, and improved quality of life.

Towards a realistic biomechanical model of the thumb: the choice of kinematic description may be more critical than the solution method or the variability/uncertainty of musculoskeletal parameters

A biomechanical model of the thumb can help researchers and clinicians understand the clinical problem of how anatomical variability contributes to the variability of outcomes of surgeries to restore thumb function. We lack a realistic biomechanical model of the thumb because of the variability/uncertainty of musculoskeletal parameters, the multiple proposed kinematic descriptions and methods to solve the muscle redundancy problem, and the paucity of data to validate the model with in vivo coordination patterns and force output. We performed a multi-stage validation of a biomechanical computer model against our measurements of maximal static thumbtip force and fine-wire electromyograms (EMG) from 8 thumb muscles in each of five orthogonal directions in key and opposition pinch postures. A low-friction point-contact at the thumbtip ensured that subjects did not produce thumbtip torques during force production. The 3-D, 8-muscle biomechanical thumb model uses a 5-axis kinematic description with orthogonal and intersecting axes of rotation at the carpometacarpal and metacarpophalangeal joints. We represented the 50 musculoskeletal parameters of the model as stochastic variables based on experimental data, and ran Monte Carlo simulations in the "inverse" and "forward" directions for 5000 random instantiations of the model. Two inverse simulations (predicting the distribution of maximal static thumbtip forces and the muscle activations that maximized force) showed that: the model reproduces at most 50% of the 80 EMG distributions recorded (eight muscle excitations in 5 force directions in two postures); and well-directed thumbtip forces of adequate magnitude are predicted only if accompanied by unrealistically large thumbtip torques (0.64+/-0.28Nm). The forward simulation (which fed the experimental distributions of EMG through random instantiations of the model) resulted in misdirected thumbtip force vectors (within 74.3+/-24.5 degrees from the desired direction) accompanied by doubly large thumbtip torques (1.32+/-0.95Nm). Taken together, our results suggest that the variability and uncertainty of musculoskeletal parameters and the choice of solution method are not the likely reason for the unrealistic predictions obtained. Rather, the kinematic description of the thumb we used is not representative of the transformation of net joint torques into thumbtip forces/torques in the human thumb. Future efforts should focus on validating alternative kinematic descriptions of the thumb.

[Functional surgery of upper limb in tetraplegics since 50 years]

OBJECTIVE

Development of upper limb functional surgery in tetraplegics in the last 50 years.

METHODS

The literature review relating to the years 1950-2002 was carried out with 3 data bases: Medline, Pascal, Embase. This review also involved a thorough study of non-indexed references.

RESULTS

A large number of surgical procedures are described. Two priorities are stressed by the authors: safety of these procedures and duration of postoperative immobilization.

CONCLUSION

This review of literature shows that the prospects for restoring upper limb function in tetraplegics are greater than ever, offering a larger number of patients the possibility to increase their independence in daily life. Functional surgery remains, nevertheless, demanding in terms of length of immobilization and presupposes requiring a multidisciplinary approach requiring rehabilitation teams to be up to date with surgical procedures.

Releasing the A3 pulley and leaving flexor superficialis intact increases pinch force following the Zancolli lasso procedures to prevent claw deformity in the intrinsic palsied finger

Objective estimates of fingertip force magnitude following surgery to prevent digital metacarpophalangeal (MCP) hyperextension (clawing) in cases of paralysis of the hand's intrinsic muscles will assist clinicians in setting realistic expectations for post-operative pinch strength. We used a cadaveric/optimization approach to predict and confirm the maximal biomechanically possible fingertip force in the intrinsic palsied hand before and after two popular tendon transfer methods to the volar plate of the MCP joint. Both surgeries were also evaluated after release of the A3 pulley-a modification predicted by our published computer model of the forefinger to increase fingertip force magnitude. We predicted maximal static fingertip force by mounting eight fresh cadaveric hands on a frame, placing their forefinger in a functional posture (neutral abduction, 45 degrees of flexion at the MCP and proximal interphalangeal joints, and 10 degrees at the distal interphalangeal joint) and pinning the distal phalanx to a 3D dynamometer. We pulled on individual tendons with tensions up to 25% of maximal isometric force of their associated muscle and measured fingertip force and torque output. Using these measurements, we predicted the optimal combination of tendon tensions that maximized palmar force (analogous to pinch force, directed perpendicularly from the midpoint of the distal phalanx, and in the plane of finger flexion-extension) for four cases: (i) the non-paretic case (all muscles available), (ii) intrinsic palsied hand (no intrinsic muscles functioning), (iii) transfer of flexor superficialis tendon to the volar plate of the MCP (Zancolli lasso) in the intrinsic palsied hand, and (iv) leaving flexor superficialis intact and transferring a tendon of comparable strength to the volar plate of the MCP in the intrinsic palsied hand. Lastly, we applied these optimal combinations of tension to the cadaveric tendons and measured fingertip output. With the A3 pulley intact, the maximal palmar force in cases (ii)-(iv) averaged 48 +/- 23% SD (non-paretic = 100%; case (iv) (61 +/- 25%) > cases (ii) and (iii) (43 +/- 23% and 39 +/- 19%, respectively), p < 0.05). Releasing the A3 pulley significantly increased the average palmar force in cases (ii)-(iv) (73 +/- 42%, p < 0.05), with no significant differences among them. Thus, releasing the A3 pulley may improve palmar force magnitude when it is necessary to transfer the digit's own flexor superficialis tendon to the volar plate of the MCP to prevent clawing in the intrinsic palsied hand.

Tendon transfers as applied to tetraplegia

The techniques of the tendon transfers that are used primarily for the functional rehabilitation of upper limbs in tetraplegia are described in this article. The restoration of active elbow extension can be obtained either by biceps-to-triceps or by deltoid-to-triceps transfers. Grasp and key grip can be restored either by active or by passive tendon transfers. The usual motors of active transfer are the BR and ECRL. The usual tenodesis involve the FDS (via lassos), EDC, EPL, FPL, and APL.

Neuroprostheses for the upper extremity

Functional electrical stimulation (FES) neuroprostheses can be used to replace lost motor and sensory function in persons with neurological disorders. FES technology has subsequently been shown effective and safe in restoring hand function in adults with spinal cord injury. The freehand system consists of an implanted receiver-stimulator, an external shoulder position sensor, and an external control unit. Commands are originated by voluntary movement of the contralateral shoulder and are measured by the sensor. There are several types of electrodes: epimysial, intramuscular, nerve cuff, and intraneural. Neuroprostheses are recommended within the context of all available reconstructive options for the upper limbs. Voluntary tendon transfers are the first choice. The clinical outcomes as measured by improvement on scales of impairment, activities of daily living, and satisfaction are rewarding. The next step in improvement of the motor function of person with spinal cord injury will be the addition of a controllable second upper extremity and the elimination of additional external hardware.

Activation patterns of the thumb muscles during stable and unstable pinch tasks

The ability to direct forces between the thumb and fingers is important to secure objects in the hand. We compared the coordination of thumb musculature in key and opposition pinch postures between stable and unstable tasks. The unstable task (producing thumb-tip force wearing a beaded thimble) required well-directed forces; the stable task (producing thumb-tip force against a pinch meter) did not. Fine-wire electromyography of thumb muscles and thumb-tip force magnitudes were recorded. We found no statistical differences in thumb-tip force between postures or stable versus unstable tasks, indicating that the highest magnitudes of force can be accurately directed. Abductor pollicis brevis and extensor pollicis longus were significantly more activated in the unstable tasks, suggesting their importance in directing thumb-tip force. Understanding how pinch forces are directed might influence the choice of muscle-tendon transfers performed to restore function to the severely paralyzed thumb. We introduce a device to quantify the ability to control pinch force magnitude and direction simultaneously.

Effectiveness of supplemental grasp-force feedback in the presence of vision

Previous studies have shown that supplemental grasp-force feedback can improve control for users of a hand prosthesis or neuroprosthesis under conditions where vision provides little force information. Visual cues of force are widely available in everyday use, however, and may obviate the utility of supplemental force information. The purpose of the present study was to use a video-based hand neuroprosthesis simulator to determine whether grasp-force feedback can improve control in the presence of realistic visual information. Seven able-bodied subjects used the simulator to complete a simple grasp-and-hold task while controlling and viewing pre-recorded, digitised video clips of a neuroprosthesis user's hand squeezing a compliant object. The task was performed with and without supplemental force feedback presented via electrocutaneous stimulation. Subjects had to achieve and maintain the (simulated) grasp force within a target window of variable size (+/- 10-40% of full scale). Force feedback improved the success rate significantly for all target window sizes (8-16%, on average), and improved the success rate at all window sizes for six of the seven subjects. Overall, the improvement was equivalent functionally to a 35% increase in the window size. Feedback also allowed subjects to identify the direction of grasp errors more accurately, on average by 10-15%. In some cases, feedback improved the failure identification rate even if success rates were unchanged. It is thus concluded that supplemental grasp-force feedback can improve grasp control even with access to rich visual information from the hand and object.

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.

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.

Tuning of a nonanalytical hierarchical control system for reaching with FES

Point-to-point functional movements involve simultaneous shoulder and elbow joint rotations. In able-bodied subjects these movements are fully automatic, and feed-forward control ensures the synergistic activity of many muscles. Synergy between joint rotations was defined and described as a scaling between joint angular velocities [19]. Similarly, subjects who can control their shoulder movements may be assisted in reaching tasks by functional electrical stimulation (FES) of elbow extensor muscles. The synergistic control paradigm can be implemented in real-time by employing a hierarchically structured production-rules method. The use of production-rules necessitates the acquisition of knowledge and the assembly of a rule-base. A nonparametric technique was designed for the identification of the rules. The identification process was divided into two phases: determination of the scaling parameters, and determination of the stimulation parameters. The scaling parameters, needed for the coordination of movements, were determined in able-bodied subjects. Those depend exclusively on the initial and target positions of the hand. The number of scalings could be reduced by dividing the workspace into 12 zones. The stimulation parameters, needed for the execution of movements, were determined in subjects with paralyzed elbow extensor muscles by identifying triplets: elbow angular velocity, elbow angular acceleration (velocity increments), and the corresponding pulse durations for various classes of movements and loads attached to the hand.

Implanted functional electrical stimulation hand system in adolescents with spinal injuries: an evaluation

OBJECTIVE

To study the utility and functional benefits of an implanted functional electrical stimulation (FES) system for hand grasp and release in adolescents with tetraplegia secondary to spinal cord injuries.

DESIGN

Intervention study with before-after trial measurement with each subject as his or her own control.

SETTING

Nonprofit pediatric orthopedic rehabilitation facility specializing in spinal cord injury.

PARTICIPANTS

A convenience sample of five adolescents between 16 and 18 years of age with C5 or C6 level tetraplegia at least 1 year after traumatic spinal cord injury. Key muscles for palmar and lateral grasp and release were excitable by electrical stimulation.

INTERVENTIONS

A multichannel stimulator/receiver and eight electrodes were surgically implanted to provide stimulated palmar and lateral grasp and release. In conjunction with implantation of the FES hand system, surgical reconstruction in the form of tendon transfers, tendon lengthenings and releases, and joint arthrodeses was performed to augment stimulated hand function. Rehabilitation of the tendon transfers and training in the use of the FES hand system were provided.

MAIN OUTCOME MEASURES

Measurements of pinch and grasp force, the Grasp and Release Test (GRT), and an assessment of six activities of daily living (ADL) were administered before implantation of the FES hand system and at regular follow-up intervals. Results of the stimulated response of individual muscles and surgical reconstruction were evaluated using standard and stimulated muscle testing techniques and standard assessment of joint range of motion. All subjects completed followup testing.

RESULTS

Lateral and palmar forces were significantly greater than baseline forces (p = .043). Heavy objects on the GRT could only be manipulated with FES, and FES increased the level of independence in 25 of 30 ADL comparisons (5 subjects, 6 activities) as compared to baseline. After training, FES was preferred in 21 of 30 comparisons over the typical means of task completion. Of the 40 electrodes implanted, 37 continue to provide excellent stimulated responses and all of the implanted stimulators have functioned without problems. The surgical reconstruction procedures greatly enhanced FES hand function by either expanding the workspace in which to utilize FES (deltoid to triceps transfer), stabilizing the wrist (brachioradialis to wrist extensor transfer), or stabilizing joints (intrinsic tenodesis transfer, FPL split transfer).

CONCLUSION

For five adolescents with tetraplegia, the combination of FES and surgical reconstruction provided active palmar and lateral grasp and release. Laboratory-based assessments demonstrated that the FES system increased pinch force, improved the manipulation of objects, and typically increased independence in six standard ADL as compared to pre-FES hand function. The study also showed that the five adolescents generally preferred FES for most of the ADL tested. Data on the benefits of the implanted FES hand system outside of the laboratory are needed to understand the full potential of FES.