Activation of brachioradialis muscles transferred to restore lateral pinch in tetraplegia

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.

Early-stage reconstruction of flexor pollicis longus using palmaris longus in a patient with compartment syndrome of forearm: a case report

Background

The flexor pollicis longus is the most vulnerable muscle in acute compartment syndrome of the forearm. Reconstruction of a dysfunctional flexor pollicis longus is occasionally necessary following compartment syndrome of the forearm.

Case presentation

A 42-year-old Japanese man injured his left forearm in a motor vehicle accident. Open radial shaft fracture and acute compartment syndrome of the left forearm was diagnosed. We performed a fascial release of the forearm and debridement of the involved myonecrosis of the flexor pollicis longus. At second-look operation (3 days after the initial release), we performed palmaris longus tendon transfer to the flexor pollicis longus tendon. At 6-month follow-up, the patient had no complaints and returned to his job. At 2-year follow-up, the patient had achieved 88% of pinch strength, compared with the contralateral hand, and scored 11.4 on the QuickDASH score.

Conclusions

Palmaris longus transfer performed immediately after injury is simple and does not require an additional surgical approach. Hence, early palmaris longus tendon transfer, which can provide satisfactory outcomes, could be considered as a potential choice for flexor pollicis longus reconstruction in patients with compartment syndrome of the forearm.

Regional estimates of cortical thickness in brain areas involved in control of surgically restored limb movement in patients with tetraplegia

Context/Objective: Spinal cord injury (SCI) causes atrophy of brain regions linked to motor function. We aimed to estimate cortical thickness in brain regions that control surgically restored limb movement in individuals with tetraplegia. Design: Cross-sectional study. Setting: Sahlgrenska University hospital, Gothenburg, Sweden. Participants: Six individuals with tetraplegia who had undergone surgical restoration of grip function by surgical transfer of one elbow flexor (brachioradialis), to the paralyzed thumb flexor (flexor pollicis longus). All subjects were males, with a SCI at the C6 or C7 level, and a mean age of 40 years (range = 31-48). The average number of years elapsed since the SCI was 13 (range = 6-26). Outcome measures: We used structural magnetic resonance imaging (MRI) to estimate the thickness of selected motor cortices and compared these measurements to those of six matched control subjects. The pinch grip control area was defined in a previous functional MRI study. Results: Compared to controls, the cortical thickness in the functionally defined pinch grip control area was not significantly reduced (P = 0.591), and thickness showed a non-significant but positive correlation with years since surgery in the individuals with tetraplegia. In contrast, the anatomically defined primary motor cortex as a whole exhibited substantial atrophy (P = 0.013), with a weak negative correlation with years since surgery. Conclusion: Individuals with tetraplegia do not seem to have reduced cortical thickness in brain regions involved in control of surgically restored limb movement. However, the studied sample is very small and further studies with larger samples are required to establish these findings.

Arthrodesis Versus Carpometacarpal Preservation in Key-Grip Procedures in Tetraplegic Patients: A Comparative Study of 40 Cases

PURPOSE

Constructing a lateral key pinch (KP) is a universal aim of any functional upper limb surgery program for tetraplegia. Three stages are required: (1) activating the pinch mechanism by flexor pollicis longus tenodesis to the radius or by tendon transfer to the flexor pollicis longus, (2) simplifying the polyarticular chain, and (3) positioning the thumb column. We compared 2 techniques for accomplishing the latter stage, 1 utilizing arthrodesis of the carpometacarpal joint (CMC) and 1 that did not require arthrodesis of the CMC.

MATERIALS AND METHODS

We reviewed 40 cases of KP reconstruction at a mean follow-up of 7.4 years: 17 who had undergone CMC arthrodesis and 23 without CMC arthrodesis. In this group, an abductor pollicis longus tenodesis was necessary to properly position the thumb column in 17 patients.

RESULTS

Active KP cases with CMC arthrodesis were significantly stronger than those without an arthrodesis. For passive KP cases, the difference between those cases with CMC arthrodesis and those without was not significant. Regarding opening, for active KP cases with CMC preservation alone, the mean distance between the thumb pulp and the index finger was 4.0 cm at rest and 5.8 cm when passively grasping large objects; for active KP cases without arthrodesis, these values were 3.4 and 6.8 cm, respectively, with the wrist in flexion. For passive KP cases, these values were 2.2 and 3.5 cm with CMC arthrodesis compared with 2.4 and 6.9 cm without arthrodesis. Overall, 23.5% of patients with CMC arthrodesis could not maintain contact between the thumb and the index finger compared with 30.4% without arthrodesis.

CONCLUSIONS

Active KP is stronger with than without CMC arthrodesis; however, the KP reconstruction does not open as far when grasping large objects. For passive KP, CMC arthrodesis significantly limits passive opening, with no gain in strength. Neither technique is superior in terms of KP stability.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Adaptive motor cortex plasticity following grip reconstruction in individuals with tetraplegia

Background:

Tendon transfer is a surgical technique for restoring upper limb motor control in patients with cervical spinal cord injuries (SCI), and offers a rare window into cortical neuroplasticity following regained arm and hand function.

Objective:

Here, we aimed to examine neuroplasticity mechanisms related to re-established voluntary motor control of thumb flexion following tendon transfer.

Methods:

We used functional Magnetic Resonance Imaging (fMRI) to test the hypothesis that restored limb control following tendon transfer is mediated by activation of that limb’s area of the primary motor cortex. We examined six individuals with tetraplegia who underwent right-sided surgical grip reconstruction at Sahlgrenska University Hospital, Sweden. All were right-handed males, with a SCI at the C6 or C7 level, and a mean age of 40 years (range = 31–48). The average number of years elapsed since the SCI was 13 (range = 6–26). Six right-handed gender- and age-matched control subjects were included (mean age 39 years, range = 29–46). Restoration of active thumb flexion in patients was achieved by surgical transfer of one of the functioning elbow flexors (brachioradialis), to the paralyzed thumb flexor (flexor pollicis longus). We studied fMRI responses to isometric right-sided elbow flexion and key pinch, and examined the cortical representations within the left hemisphere somatomotor cortex a minimum of one year after surgery.

Results:

Cortical activations elicited by elbow flexion did not differ in topography between patients and control participants. However, in contrast to control participants, patients’ cortical thumb flexion activations were not topographically distinct from their elbow flexion activations.

Conclusion:

This result speaks against a topographic reorganization in which the thumb region regains thumb control following surgical tendon transfer. Instead, our findings suggest a neuroplastic mechanism in which motor cortex resources previously dedicated to elbow flexion adapt to control the thumb.

Multicenter Survey of the Effects of Rehabilitation Practices on Pinch Force Strength After Tendon Transfer to Restore Pinch in Tetraplegia

OBJECTIVE

To identify key components of conventional therapy after brachioradialis (BR) to flexor pollicis longus (FPL) transfer, a common procedure to restore pinch strength, and evaluate whether any of the key components of therapy were associated with pinch strength outcomes.

DESIGN

Rehabilitation protocols were surveyed in 7 spinal cord injury (SCI) centers after BR to FPL tendon transfer. Key components of therapy, including duration of immobilization, participation, and date of initiating therapy activities (mobilization, strengthening, muscle reeducation, functional activities, and home exercise), were recorded by the patient's therapist. Pinch outcomes were recorded with identical equipment at 1-year follow-up.

SETTING

Seven SCI rehabilitation centers where the BR to FPL surgery is performed on a routine basis.

PARTICIPANTS

Thirty-eight arms from individuals with C5-7 level SCI injury who underwent BR to FPL transfer surgery (N=34).

INTERVENTION

Conventional therapy according to established protocol in each center.

MAIN OUTCOME MEASURES

The frequency of specific activities and their time of initiation (relative to surgery) were expressed as means and 95% confidence intervals. Outcome measures included pinch strength and the Canadian Occupational Performance Measure (COPM). Spearman rank-order correlations determined significant relations between pinch strength and components of therapy.

RESULTS

There was similarity in the key components of therapy and in the progression of activities. Early cast removal was associated with pinch force (Spearman ρ=-.40, P=.0269). Pinch force was associated with improved COPM performance (Spearman ρ=.48, P=.0048) and satisfaction (Spearman ρ=.45, P=.0083) scores.

CONCLUSIONS

Initiating therapy early after surgery is beneficial after BR to FPL surgery. Postoperative therapy protocols have the potential to significantly influence the outcome of tendon transfers after tetraplegia.

Voluntary activation of biceps-to-triceps and deltoid-to-triceps transfers in quadriplegia

The biceps or the posterior deltoid can be transferred to improve elbow extension function for many individuals with C5 or C6 quadriplegia. Maximum strength after elbow reconstruction is variable; the patient’s ability to voluntarily activate the transferred muscle to extend the elbow may contribute to the variability. We compared voluntary activation during maximum isometric elbow extension following biceps transfer (n = 5) and deltoid transfer (n = 6) in three functional postures. Voluntary activation was computed as the elbow extension moment generated during maximum voluntary effort divided by the moment generated with full activation, which was estimated via electrical stimulation. Voluntary activation was on average 96% after biceps transfer and not affected by posture. Individuals with deltoid transfer demonstrated deficits in voluntary activation, which differed by posture (80% in horizontal plane, 69% in overhead reach, and 70% in weight-relief), suggesting inadequate motor re-education after deltoid transfer. Overall, individuals with a biceps transfer better activated their transferred muscle than those with a deltoid transfer. This difference in neural control augmented the greater force-generating capacity of the biceps leading to increased elbow extension strength after biceps transfer (average 9.37 N-m across postures) relative to deltoid transfer (average 2.76 N-m across postures) in our study cohort.

Evaluation of a Task-Based Intervention After Tendon Transfer to Restore Lateral Pinch

OBJECTIVE

To quantify changes in pinch force and brachioradialis (BR) activation after a task-based training program designed to improve pinch force after BR to flexor pollicis longus (FPL) transfer.

DESIGN

One-group repeated-measures design compared pinch force and BR activation pre- and posttraining. Significant differences were tested with Wilcoxon signed-rank tests for pairwise comparisons at the P≤.05 level.

SETTING

Testing occurred in a Veterans Affairs Medical Center research laboratory and training was in a home setting.

PARTICIPANTS

Participants with cervical spinal cord injury (SCI) and previous BR to FPL transfer were enrolled in the study (N=8). Six patients completed the training program and posttraining measures.

INTERVENTIONS

The 10-week training was a home program that included novel activities to increase BR activation and practice producing pinch force in a variety of upper limb postures. Participants were provided with the task-based training equipment and instructed to practice 3 times per week.

MAIN OUTCOME MEASURES

Fine-wire electromyography of the transferred BR was recorded in maximum effort pinch force (N). Secondary measures included the strength and activation of the antagonist elbow extensor.

RESULTS

Pinch force increased 3.7N (.38kg) and BR muscle activation increased 10% (P≤.05) after the training. There was no increase in elbow extension strength, but participants with previous posterior deltoid to triceps transfer achieved greater activation of the antagonist elbow extensor.

CONCLUSIONS

The findings from this pilot study suggest that outcomes of tendon transfer and conventional therapy can be improved for patients with chronic cervical SCI.

Corticomotor excitability of arm muscles modulates according to static position and orientation of the upper limb

OBJECTIVE

We investigated how multi-joint changes in static upper limb posture impact the corticomotor excitability of the posterior deltoid (PD) and biceps brachii (BIC), and evaluated whether postural variations in excitability related directly to changes in target muscle length.

METHODS

The amplitude of individual motor evoked potentials (MEPs) was evaluated in each of thirteen different static postures. Four functional postures were investigated that varied in shoulder and elbow angle, while the forearm was positioned in each of three orientations. Posture-related changes in muscle lengths were assessed using a biomechanical arm model. Additionally, M-waves were evoked in the BIC in each of three forearm orientations to assess the impact of posture on recorded signal characteristics.

RESULTS

BIC-MEP amplitudes were altered by shoulder and elbow posture, and demonstrated robust changes according to forearm orientation. Observed changes in BIC-MEP amplitudes exceeded those of the M-waves. PD-MEP amplitudes changed predominantly with shoulder posture, but were not completely independent of influence from forearm orientation.

CONCLUSIONS

Results provide evidence that overall corticomotor excitability can be modulated according to multi-joint upper limb posture.

SIGNIFICANCE

The ability to alter motor pathway excitability using static limb posture suggests the importance of posture selection during rehabilitation aimed at retraining individual muscle recruitment and/or overall coordination patterns.

A synthesis of best evidence for the restoration of upper-extremity function in people with tetraplegia

PURPOSE

Because upper-limb function represents overall function for individuals with tetraplegia, the restoration of upper-extremity function is exceedingly important for this population. The purpose of this review was to identify interventions that optimize upper-limb function after tetraplegia based on best available evidence.

METHODS

A search of MEDLINE, AMED, and PubMed with the search terms "hand function AND tetraplegia" and "upper limb function AND tetraplegia" found 384 articles. After elimination of duplicates and review of titles and abstracts, 43 studies were found to be applicable. Study quality of all applicable studies was assessed with a modified version of the Scottish Intercollegiate Guidelines Network for Cohort Studies methodology.

RESULTS

The applicable studies were organized into three categories: conventional therapies (CT), electrical stimulation therapies (ES), and surgical interventions (SI). The proportion of papers in each category that presented with sufficient methodological quality to contribute to best evidence was as follows: CT: 0/2; ES: 10/21; SI: 6/20.

CONCLUSIONS

ES therapies are beneficial as assistive technologies and as therapeutic intervention in the subacute phase of recovery. SIs are suitable for individuals who meet very specific criteria for tendon-transfer surgery. Further clinical trials are warranted for ES and SI therapies to substantiate prescription of therapeutics.

Comparison of wrist and elbow stabilization following pinch reconstruction in tetraplegia

PURPOSE

Individuals with spinal cord injuries resulting in tetraplegia may receive tendon transfer surgery to restore grasp and pinch function. These procedures often involve rerouting the brachioradialis (Br) and the extensor carpi radialis longus tendons volar to the flexion-extension axis of the wrist, leaving the extensor carpi radialis brevis (ECRB) muscle to provide wrist extension strength. The purpose of this study was to determine whether externally stabilizing the wrist after transfer procedures would improve the ability to activate the transferred Br and resulting pinch force, similar to the effect observed when the elbow is externally stabilized.

METHODS

We used a one-way repeated-measures study design to determine the effect of 3 support conditions on muscle activation and lateral pinch force magnitude in 8 individuals with tetraplegia and previous tendon transfer surgeries. Muscle activation was recorded from Br and ECRB with intramuscular electrodes and from biceps and triceps muscles with surface electrodes. We quantified pinch strength with a 6-axis force sensor and custom grip. We recorded measurements in 3 support conditions: with the arm self-stabilized, with elbow stabilization, and with elbow and wrist stabilization. Pairwise differences were tested using Wilcoxon signed-rank tests.

RESULTS

Maximum effort pinch force magnitude and Br activation were significantly increased in both supported conditions compared with the self-supported trials. The addition of wrist stabilization had no significant effect compared with elbow stabilization alone.

CONCLUSIONS

A strong ECRB has adequate strength to extend the wrist, even after multiple transfers that contribute an additional flexion moment from strong activation of donor muscles. Anatomical and functional differences between the wrist and elbow musculature are important determinants for self-stabilizing joints proximal to the tendon transfer. The ability to increase Br activation and resulting pinch force may be determined, in part, by the individual's ability to develop new coordination strategies.

A simulation analysis of the combined effects of muscle strength and surgical tensioning on lateral pinch force following brachioradialis to flexor pollicis longus transfer

Biomechanical simulations of tendon transfers performed following tetraplegia suggest that surgical tensioning influences clinical outcomes. However, previous studies have focused on the biomechanical properties of only the transferred muscle. We developed simulations of the tetraplegic upper limb following transfer of the brachioradialis (BR) to the flexor pollicis longus (FPL) to examine the influence of residual upper limb strength on predictions of post-operative transferred muscle function. Our simulations included the transfer, ECRB, ECRL, the three heads of the triceps, brachialis, and both heads of the biceps. Simulations were integrated with experimental data, including EMG and joint posture data collected from five individuals with tetraplegia and BR-FPL tendon transfers during maximal lateral pinch force exertions. Given a measured co-activation pattern for the non-paralyzed muscles in the tetraplegic upper limb, we computed the highest activation for the transferred BR for which neither the elbow nor the wrist flexor moment was larger than the respective joint extensor moment. In this context, the effects of surgical tensioning were evaluated by comparing the resulting pinch force produced at different muscle strength levels, including patient-specific scaling. Our simulations suggest that extensor muscle weakness in the tetraplegic limb limits the potential to augment total pinch force through surgical tensioning. Incorporating patient-specific muscle volume, EMG activity, joint posture, and strength measurements generated simulation results that were comparable to experimental results. Our study suggests that scaling models to the population of interest facilitates accurate simulation of post-operative outcomes, and carries utility for guiding and developing rehabilitation training protocols.

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.