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

Relative preservation of triceps over biceps strength in upper limb-onset ALS: the 'split elbow'

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of the motor system. The split hand sign in ALS refers to observed preferential weakness of the lateral hand muscles, which is unexplained. One possibility is larger cortical representation of the lateral hand compared with the medial. Biceps strength is usually preserved relative to triceps in neurological conditions, but biceps has a larger cortical representation and might be expected to show preferential weakness in ALS.

METHODS

Using the South-East England Register for Amyotrophic Lateral Sclerosis, we performed a retrospective longitudinal cohort study and extracted the modified Medical Research Council (MRC) muscle strength score for biceps and triceps in patients with a diagnosis of upper limb-onset ALS in the 19-year period 1996-2015. A Wilcoxon signed-rank test was used to assess the relative strength of the muscles within the total sum of the upper limbs involved in the study.

RESULTS

There were 659 people with upper limb onset of weakness. In 215 there were insufficient data to perform the analysis, and a further 33 were excluded for other reasons, leaving 411 for analysis. Biceps was stronger than triceps in 87 limbs, and triceps was stronger than biceps in 258 limbs, with no difference seen in the remaining 477. Triceps strength scores (mean rank=186.1) were higher than ipsilateral biceps strength scores (mean rank=134.2), Z=-10.1, p<0.001 (two-tailed).

CONCLUSION

Triceps strength is relatively preserved compared with biceps in ALS. This is consistent with a broadly corticofugal hypothesis of selective vulnerability, in which susceptibility might be associated with larger cortical representation.

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.

Sensory-motor equivalence: manual aiming in C6 tetraplegics following musculotendinous transfer surgery at the elbow

Cervical spinal lesions at C6 result in paralysis of the triceps brachii while leaving deltoid and elbow flexor function intact. We examined the spatial-temporal characteristics of goal-directed aiming movements performed by C6 tetraplegics who had undergone musculotendinous transfer surgery in which the posterior deltoid replaces the triceps as the elbow extensor. On some trials, liquid crystal goggles were used to eliminate vision of the limb and target upon movement initiation. Although tetraplegic participants achieved the same degree of movement accuracy/consistency as control participants, their movement times were longer regardless of whether the movements were made away from (elbow extension) or towards the body (elbow flexion). Longer movement times were related to lower peak velocities, and not the symmetry of the aiming profiles. The tetraplegic participants were no more dependent on visual feedback for limb regulation than control participants. Although the characteristics of the movement trajectories were surprisingly similar, in both vision conditions, tetraplegics required more real and proportional time to reduce spatial variability in the limb's trajectory for elbow extensions. Our results indicate that the sensorimotor system is adaptable and that the representations governing limb control are not muscle specific.

How to extend the elbow with a weak or paralyzed triceps: control of arm kinematics for aiming in C6-C7 quadriplegic patients

This study aims to investigate how quadriplegic patients with a C6-C7 spinal lesion coordinate their upper limb to extend the elbow despite the paralysis or weakness of the triceps brachii, and what is the effect of a surgical musculotendinous transfer. For this purpose, aiming movements in a wide workspace were recorded in seven healthy subjects and in patients with incomplete (five cases) or complete (eight cases) triceps paralysis and after musculotendinous transfer (eight cases). We used four electromagnetic field sensors to quantify hand trajectory and to compute the angles describing the rotations at the scapula, glenohumeral joint, elbow and wrist (10 degrees of freedom). Extent and smoothness of the hand trajectories and hand velocity profiles were surprisingly similar between healthy subjects and quadriplegic patients. The reduction of elbow extension observed in patients was compensated by rotations distributed across several degrees of freedom including the scapula. Principal components analysis showed that the joint rotations could be summarized by an additive combination of two synergies, respectively orientating and stretching out the limb, which explained similar amounts of variance in healthy subjects and in patients. The participations of degrees of freedom in the synergies were roughly similar in the different groups of subjects, the main difference concerning scapular medial-lateral rotation, which seems to be critical in patients with a complete triceps paralysis. This demonstrates that elbow extension in quadriplegic patients is due to anticipated mechanical interaction coupling between upper limb segments. We propose that the persisting (incomplete paralysis) or restored (musculotendinous transfer) elbow extensor strength may act by stabilizing the elbow. This counterintuitive preservation of limb kinematics for horizontal aiming movements in quadriplegic patients despite the drastic changes in muscle action provoked by paralysis and/or by surgery strongly suggests that the motor system does not primarily control forces but the morphological aspects of movement, via joint rotation synergies.

Improved kinematics of unrestrained arm raising in C5-C6 tetraplegic subjects after deltoid-to-triceps transfer

STUDY DESIGN

Prospective comparative study.

OBJECTIVE

To determine whether control of upper limb joint synergy during unrestrained arm raising involving shoulder and elbow flexion is modified by deltoid-to-triceps transfer.

SETTING

Rehabilitation unit for spinal cord injury patients, France.

METHODS

Five C6 subjects with C5-C6 tetraplegia sustained posterior deltoid-to-triceps transfer and were compared to a control group of 11 subjects. Kinematics of shoulder and elbow joints before, 6 month and 1 year after surgery, during straight-arm raising (SAR) in the plane of the scapula and hand-to-nape-of-neck movements (HNNMs) were explored. Motion was recorded with a six-camera Vicon motion analysis system and the data used to assess the coupling of elbow and shoulder flexion velocities (EFVs and SFVs) and extension velocities.

RESULTS

All subjects were initially assessed at 6.9 months (mean) postsurgery. Three of the upper limbs were assessed a second time (mean 17.9 months). The first assessment showed an increase in shoulder flexion amplitudes in tetraplegic subjects with presurgery shoulder flexion deficits. Peak SFVs and EFVs and extension velocities were slightly modified at the first postsurgery assessment and dramatically improved at the second assessment during both SAR and HNNM. Despite these increased velocities, joint coordination was only partially restored.

CONCLUSION

A restored elbow active extension improves the speed of elbow flexion. The additional improvement of shoulder motion emphasises the relation between joints in the control of arm movement.

Analysis of posterior deltoid function one year after surgical restoration of elbow extension

PURPOSE

The purpose of this study was to measure the extent and timing of elbow extension torque recovery after posterior deltoid-to-triceps tendon transfer.

METHODS

Elbow extension moment was measured in 40 limbs from 23 patients who underwent surgical restoration using the posterior deltoid-to-triceps tendon transfer at times ranging from 8 weeks to 1 year after surgery. For comparison purposes, elbow extension moment also was measured in healthy controls and persons with C7 spinal cord injuries.

RESULTS

Maximum extension moment was 5.89 +/- 0.24 Nm (mean +/- standard error of mean, n = 40), which corresponds to approximately 65% of the predicted posterior deltoid force and provided an adequate moment to oppose gravity. Based on the shape of the moment-joint angle curve and using a biomechanical model, it was predicted that posterior deltoid was inserted at a relatively short muscle length of 123.1 mm and thus operated exclusively on the ascending limb of the length-tension relationship.

CONCLUSIONS

These observations support an evolving model of muscle architecture in which connective tissue septa restrict muscle fiber elongation during surgical tensioning of the tendon transfer. This relatively short length would result in a significant force loss should any of the repair sites slip or stretch during rehabilitation. These data have implications for the reconstruction and rehabilitation of this patient population.

Indications and future directions for upper limb neuroprostheses in tetraplegic patients: a review

The development of the upper extremity neuroprosthesis has been a challenging and rewarding contribution to the management of the SCI patient. The authors' experience and that of their clinical trial teams has verified that this technology is a strong alternative to conventional reconstruction and conservative management. In the future, even more powerful tools will emerge from the laboratory as these devices and collaborative surgical procedures evolve.

Validation of a Three-Dimensional Baseball Pitching Model

A simulation and optimization procedure was constructed to investigate the relationships between optimal movement and muscular strength for baseball pitching. Four segments (torso, upper arms, lower arms, hands) and six torque generators (shoulders, elbows, wrists) are modeled. The torque generators have torque-angle and torque-angular velocity characteristics of Hill-type muscle function. The optimization objective function includes release velocity and negative terms penalizing joint loading and inaccuracy. The weighting coefficient for joint loads has a strong influence on the results. As this coefficient increases, the motion becomes more similar to actual measured pitches. Combining active state patterns optimized for different weighting coefficients gives larger joint loads in the simulated motion. This supports the hypothesis that well-coordinated active states are important for controlling the relationships of the different torque generators in order to create a reasonable and effective pitching motion. The model proposed here is superior to previous simulations for throwing, from the viewpoint of modeling with characteristics of Hill-type muscle function, and can be used to explore realistic baseball pitching.

Protection of the deltoid to triceps tendon transfer repair sites

The posterior deltoid muscle was used to replace lost elbow extension in 11 patients with C5 or C6 level tetraplegia. During surgery stainless steel sutures were inserted into the donor muscle, graft, and tendon insertion sites. Over the succeeding time periods (1 month to 2 years) the distances between the various markers were measured. Significant tendon elongation of 23.1 +/- 4.8 mm (mean +/- SEM; n = 6) was observed in patients receiving traditional postoperative care. To reduce the tendon elongation observed, a specially designed armrest was developed and applied the first postoperative day. The armrest was designed to maintain the elbow in 20 degrees flexion and to prevent shoulder adduction. The addition of this armrest to the traditional postoperative protocol resulted in a dramatic decrease of tendon elongation to only 8.4 +/- 3.0 mm (n = 5). Elongation occurred within the first 6 postoperative weeks in the armrest group; in the nonprotected group, elongation continued for several additional months. The majority of the elongation in both groups occurred in the proximal portion of the tendon-graft-tendon unit. Although this study did not explicitly measure strength, we conclude that preventing excessive muscle length change is required to protect repair sites in posterior deltoid to triceps transfer. (J Hand Surg 2000; 25A:144-149.

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.