Spindle activity of the tenotomized gastrocnemius muscle in the cat

Outcomes of Arthroscopic Nerve Release in Patients Treated for Large or Massive Rotator Cuff Tears and Associated Suprascapular Neuropathy: A Prospective, Randomized, Double-Blinded Clinical Trial

BACKGROUND

Suprascapular neuropathy has been observed in the setting of rotator cuff tears (RCTs), but its association with these tears and their treatment are unclear.

HYPOTHESIS

Arthroscopic suprascapular nerve release during rotator cuff repair will not alter the outcomes of neuropathy.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A total of 42 patients with large/massive reparable RCTs and suprascapular neuropathy were recruited and followed up at 6 and 12 months. Electrophysiological results as well as Disabilities of the Arm, Shoulder and Hand (DASH), American Shoulder and Elbow Surgeons (ASES), and Constant scores were evaluated at selected time periods. Patients were randomly assigned to 2 groups. Patients in the control group underwent arthroscopic repair of the rotator cuff without combined arthroscopic release of the superior transverse scapular ligament; in the second group, the superior transverse ligament was released. The primary outcome was to examine full suprascapular nerve recovery through electrophysiological changes between groups. The secondary/tertiary outcomes were analysis of clinical outcomes and assessment of the relation between RCT size and the degree of suprascapular nerve recovery. Patients, clinical staff members, and the neurologist were blinded to the type of surgical procedure.

RESULTS

Of 42 patients, 37 completed the follow-up at 12 months (median age, 64 years [range, 50-75 years]). Overall, 17 of 19 (89.5%) patients in the control group and 15 of 18 (83.3%) patients in the nerve release group had full nerve recovery, with no significant difference between the 2 groups. Clinically, all patients in both groups showed a significant improvement (P < .001), but no significant difference was observed between the 2 groups in terms of 12-month postoperative scores (control group: DASH: median, 5 [range, 0-21]; ASES: median, 88 [range, 83-98]; Constant: median, 86 [range, 70-98]) (nerve release group: DASH: median, 6 [range, 0-25]; ASES: median, 90 [range, 83-98]; Constant: median, 88 [range, 75-98]). Also, no significant difference was found between the 2 groups regarding other secondary and tertiary outcomes.

CONCLUSION

Combined arthroscopic release of the superior transverse scapular ligament and rotator cuff repair in patients with large/massive RCTs and suprascapular neuropathy did not produce statistically significant improved outcomes compared with repair of the rotator cuff alone.

REGISTRATION

NCT02318381 (ClinicalTrials.gov identifier).

Ankle muscle tenotomy does not alter ankle flexor muscle recruitment bias during locomotor-related repetitive limb movement in late-stage chick embryos

In ovo, late-stage chick embryos repetitively step spontaneously, a locomotor-related behavior also identified as repetitive limb movement (RLM). During RLMs, there is a flexor bias in recruitment and drive of leg muscle activity. The flexor biased activity occurs as embryos assume an extremely flexed posture in a spatially restrictive environment 2-3 days before hatching. We hypothesized that muscle afferent feedback under normal mechanical constraint is a significant input to the flexor bias observed during RLMs on embryonic day (E) 20. To test this hypothesis, muscle afference was altered either by performing a tenotomy of ankle muscles or removing the shell wall restricting leg movement at E20. Results indicated that neither ankle muscle tenotomy nor unilateral release of limb constraint by shell removal altered parameters indicative of flexor bias. We conclude that ankle muscle afference is not essential to ankle flexor bias characteristic of RLMs under normal postural conditions at E20.

Suprascapular neuropathy in the setting of rotator cuff tears: study protocol for a double-blinded randomized controlled trial

Background

It has been indicated that rotator cuff tears, especially large or massive ones, can cause suprascapular neuropathy. When such a diagnosis has been established, it is still unknown whether an arthroscopic release of the superior transverse scapular ligament during cuff repair can change the course of this neuropathy.

Methods/design

This is a single-center, double-blinded randomized controlled trial for which 42 patients with large or massive repairable rotator cuff tears and suprascapular neuropathy will be recruited and followed up at 6 and 12 months. Nerve function will be measured by nerve conduction and electromyography studies preoperatively and at the selected follow-up periods. Patients will be randomly divided into equally numbered groups, the first one being the control group. Patients of this group will undergo arthroscopic repair of the rotator cuff without combined arthroscopic release of the superior transverse scapular ligament; in the second group the ligament will be released. The primary objective is to test the null hypothesis that arthroscopic repair of large/massive rotator cuff tears in patients with combined suprascapular neuropathy provides equivalent outcomes to one-stage arthroscopic cuff repair where the superior suprascapular ligament is additionally released. The secondary objective is to search for a relation between rotator cuff tear size and degree of suprascapular nerve recovery. The tertiary objective is to demonstrate any relation between rotator cuff muscle fatty infiltration grade and degree of suprascapular nerve function. Patients, clinicians during follow-up clinics and the neurologist will be blinded to the type of surgery performed.

Discussion

To the best of our knowledge, we are unaware of any prospective, randomized double-blinded studies with similar objectives. So far, the evidence suggests a positive correlation between massive rotator cuff tears and suprascapular neuropathy. However, there is mixed evidence suggesting that neuropathy can be effectively treated with rotator cuff repair with or without release of the superior transverse scapular ligament.

Trial registration

ClinicalTrials.gov registration number NCT02318381; date of initial release: 5 December 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1672-y) contains supplementary material, which is available to authorized users.

The role of the peripheral and central nervous systems in rotator cuff disease

Rotator cuff (RC) disease is an extremely common condition associated with shoulder pain, reduced functional capacities, and impaired quality of life. It primarily involves alterations in tendon health and mechanical properties that can ultimately lead to tendon failure. RC tendon tears induce progressive muscle changes that have a negative impact on surgical reparability of the RC tendons and clinical outcomes. At the same time, a significant base of clinical data suggests a relatively weak relationship between RC integrity and clinical presentation, emphasizing the multifactorial aspects of RC disease. This review aims to summarize the potential contribution of peripheral, spinal, and supraspinal neural factors that may (1) exacerbate structural and functional muscle changes induced by tendon tear, (2) compromise the reversal of these changes during surgery and rehabilitation, (3) contribute to pain generation and persistence of pain, (4) impair shoulder function through reduced proprioception, kinematics, and muscle recruitment, and (5) help explain interindividual differences and response to treatment. Given the current clinical and scientific interest in peripheral nerve injury in the context of RC disease and surgery, we carefully reviewed this body of literature with a particular emphasis on suprascapular neuropathy that has generated a large number of studies in the past decade. Within this process, we highlight the gaps in current knowledge and suggest research avenues for scientists and clinicians.

Neuropathy of the suprascapular nerve and massive rotator cuff tears: a prospective electromyographic study

BACKGROUND

An association between massive rotator cuff tear (RCT) and suprascapular nerve neuropathy has previously been suggested. The anatomic course of the suprascapular nerve is relatively fixed along its passage. Thus, injury to the nerve by trauma, compression, and iatrogenic reasons is well documented. However, the association between retraction of the RCT and development of neuropathy of the suprascapular nerve remains unclear. We aimed to prospectively evaluate the suprascapular nerve for preoperative neurodiagnostic abnormalities in shoulders with massive RCT.

METHODS AND MATERIALS

A prospective study was performed in 2 centers. Fifty patients with retracted tears of both supraspinatus and infraspinatus were evaluated. This was confirmed with preoperative computed tomography arthrography, and the fatty infiltration of the affected muscles was graded. Forty-nine preoperative electromyograms were performed in a standardized fashion and the results analyzed twice.

RESULTS

Of 49 shoulders, 6 (12%) had neurologic lesions noted on electromyography: 1 suprascapular nerve neuropathy, 1 radicular lesion of the C5 root, 1 affected electromyogram in the context of a previous stroke, and 3 cases of partial axillary nerve palsy with a history of shoulder dislocation. No difference or diminution of the latency or amplitude of the electromyographic curve was found in the cases that presented significant fatty infiltration.

CONCLUSION

This study did not detect a suprascapular lesion in the majority of cases of massive RCT. With a low association of neuropathy with massive RCT, we find no evidence to support the routine practice of suprascapular nerve release when RCT repair is performed.

Physiologically adaptive changes of the L5 afferent neurogram and of the rat soleus EMG activity during 14 days of hindlimb unloading and recovery

The hindlimb unloading rat model (HU, Morey's model) is usually used to mimic and study neuromuscular changes that develop during spaceflights. This Earth-based model of microgravity induces a muscular atrophy of the slow postural muscle of hindlimbs, such as the soleus, a loss of strength, modifications of contraction kinetics, changes in histochemical and electrophoretical profiles and modifications of the tonic EMG activity. It has been suggested in the literature that some of these neuromuscular effects were due to a reduction of afferent feedback during HU. However, no direct data have confirmed this hypothesis. The aim of this study was to clearly establish if changes of the L5 afferent neurogram are closely related to the soleus EMG activity during and after 14 days of HU. Immediately after HU, the EMG activity of the soleus muscle disappeared and was associated with a decrease in the afferent neurogram. The soleus electromyographic and afferent activities remained lower than the pre-suspension levels until the sixth day of HU and were recovered between the sixth and the ninth day. On the twelfth and fourteenth days, they were increased beyond the pre-suspension levels. During the first recovery day, these activities were significantly higher than those on the fourteenth HU day and returned to the pre-suspension levels between the third and sixth recovery days. To conclude, our study directly demonstrates that the HU conditions cannot be considered as a functional deafferentation, as suggested in the literature, but only as a reduction of afferent information at the beginning of the HU period.

Expression of Myosin heavy chain isoforms in rat soleus muscle spindles after 19 days of hypergravity

The aim of this study was to determine whether a period of 19 days in hypergravity was long enough to induce changes in the expression of myosin heavy chain (MyHC) isoforms in the muscle spindles. The soleus muscle of 10 male Wistar rats (control: CONT, n=5; hypergravity: HG, n=5) was frozen, cut into serial sections, and labeled with antibodies against MyHCs: I, IIA, IIA + IIX + IIB, slow-tonic, and alpha-cardiac. Forty CONT and 45 HG spindles were analyzed. The results from HG spindles compared to CONT showed that there was no change in the cross-sectional area of intrafusal fibers. However, along the entire length of B1 fibers, the expression of both MyHC I and alpha-cardiac was increased significantly, whereas the labeling against MyHC IIA and MyHC slow-tonic was decreased. In B2 fibers, the labeling against MyHC IIA (region A), slow-tonic (region A), and fast myosins (regions A-C) was statistically decreased. In chain fibers, the labeling against both MyHC IIA and fast MyHC was reduced significantly. We conclude that hypergravity has a real impact on the MyHC content in the muscle spindles and induces some inverse changes of those observed in hypogravity for MyHCs I, alpha-cardiac, and slow-tonic.

Expression of myosin heavy chain isoforms along intrafusal fibers of rat soleus muscle spindles after 14 days of hindlimb unloading

Morphological, contractile, histochemical, and electrophoretical characteristics of slow postural muscles are altered after hindlimb unloading (HU). However, very few data on intrafusal fibers (IFs) are available. Our aim was to determine the effects of 14 days of hindlimb unloading on the morphological and immunohistochemical characteristics of IF in rat soleus muscle. Thirty-three control and 32 unloaded spindles were analyzed. The number and distribution of muscle spindles did not appear to be affected after unloading. There was no significant difference in number, cross-sectional area, and histochemical properties of IF between the two groups. However, after unloading, a significant decrease in slow type 1 MHC isoform and a slight increase in slow-tonic MHC expression were observed in the B and C regions of the bag1 fibers. The alpha-cardiac MHC expression was significantly decreased along the entire length of the bag2 fibers and in the B and C regions of the bag1 fibers. In 12 muscle spindles, the chain fibers expressed the slow type 1 and alpha-cardiac MHC isoforms over a short distance of the A region, although these isoforms are not normally expressed. The most striking finding of the study was the relative resistance of muscle spindles to perturbation induced by HU.

Skeletal muscle response to tenotomy

Tenotomy is a commonly encountered clinical entity, whether traumatic or iatrogenic. This article reviews the response of skeletal muscle to tenotomy. The changes are subdivided into molecular, architectural, and functional categories. Architectural disruption of the muscle includes myofiber disorganization, central core necrosis, Z-line streaming, fibrosis of fibers and Golgi tendon organs, changes in sarcomere number, and alterations in the number of membrane particles. Molecular changes include transient changes in myosin heavy chain composition and expression of neural cell adhesion molecule (NCAM). Functionally, tenotomized muscle produces decreased maximum tetanic and twitch tension. Alterations in normal skeletal muscle structure and function are clinically applicable to the understanding of pathological states that follow tendon rupture and iatrogenic tenotomy.

Partial transformation from fast to slow muscle fibers induced by deafferentation of capsaicin-sensitive muscle afferents

Mechanical and histochemical characteristics of the lateral gastrocnemius (LG) muscle of the rat were examined 21 days after capsaicin injection into the LG muscle. The capsaicin caused a decrease in generation rate of twitch and tetanic tension and an increase in fatigue resistance of LG muscle. The histochemical muscle fiber profile evaluated by myosin adenosine triphosphatase and reduced nicotinamide adenine dinucleotide tetrazolium reductase methods showed an increase of type I and IIC fibers and a decrease of the type IIB in whole muscle, and a decrease of the IIA, IIX fibers in the red part accompanied by their increase in the white part. Therefore the capsaicin treatment, which selectively eliminated fibers belonging to the III and IV groups of muscle afferents, induced muscle fiber transformation from fast contracting fatiguing fibers to slowly contracting nonfatiguing ones.

The effect of tenotomy and immobilization on muscle spindles and tendon organs of the rat calf muscles. A histochemical and morphometrical study

The morphological and histochemical alterations in the muscle spindles and Golgi tendon organs of tenotomized or immobilized calf muscles of rats (m. soleus, m. gastrocnemius) were studied in 54 animals. The intact contralateral feet served as controls. There was no change in the number of mechanoreceptors in either the tenotomized or the immobilized muscles. The diameter of the intrafusal fibers was increased somewhat after 1 week, but decreased by 14% to 40% in 3 weeks. The periaxial space of muscle spindle had diminished or disappeared by 2 weeks from the beginning of the procedures. The thickness of the outer capsule of the spindles had markedly increased, especially in the polar region. In the Golgi tendon organs the capsule had also thickened significantly and the internal space diminished. The alterations were similar following tenotomy or immobilization, but more marked after tenotomy than after immobilization.

Degeneration and alteration of axons and intrafusal muscle fibers in spindles following tenotomy

The effect of tenotomy (cutting of distal and proximal tendons) on the spindles in soleus muscle of adult rats was examined by light and electron microscopy in tissue obtained 1, 2, 3, 4, 5, 6, 7, and 14 days after surgery. Degenerative changes in the spindles progressed with time; also, the degree of alteration observed in a spindle varied with its position in the muscle, i.e., the earliest and most extensive changes occurred in spindles situated near the tendons. The disorganization and breakdown of myofibrils in the intrafusal muscle fibers were observed 3 days after tenotomy and continued with longer periods after surgery. The progression of morphological changes included alteration in fiber outline and the external lamina of the intrafusal muscle fibers and changes in the extracellular environment within the spindle capsule. The intrafusal muscle fibers of some spindles were shortened, apparently due to the loss of their polar ends, and degenerated axons which apparently supplied the intrafusal muscle fibers were also observed. Completely necrotic intrafusal fibers were absent. A possible relationship between the observed morphologic alterations and an adjustment of the spindle to muscle shortening is discussed.

Relationships between individual isometric muscle forces, EMG activity and joint torque in monkeys

The aim of the present work was to determine the EMG activity and the moment of force developed by the main elbow flexor muscles, and to establish on this basis the degree of their participation in isometric contractions performed at various positions of the elbow. This was achieved by recording the following biomechanical parameters: EMG and tensile stress (or force) from biceps brachii (BB) and brachioradialis (BR); EMG from brachialis; external resultant force (FE). There was: a linear or quadratic relationship between the integrated EMG from each muscle and FE; a linear relationship between the force produced by BB or BR and FE. The slope of these relationships depended on the elbow angle, except for that between BB force and FE. It is proposed that iEMG changes compensate for those of the force lever arm. It has been calculated that the contribution of BR to external torque decreased from the extension to flexion while that of BB increased from 70 degrees to 90 degrees and then decreased. How far these data can be extrapolated to man is a matter of discussion based on iEMG and anthropometrical data.

Effects of short-term denervation on avian muscle spindle structure

The role of the nerve in maintaining the ultrastructural integrity of avian muscle spindles was investigated by denervating the pigeon's extensor digitorum communis for periods of 10, 19, and 28 days. The equatorial region of control intrafusal fibers had a reduced density of myofilaments. Sensory endings contained mitochondria and structures resembling synaptic vesicles, and were associated with satellite cells. In the polar region, fibers had a high concentration of myofilaments; small motor endings, unlike sensory endings, lay outside of the fiber's basal lamina. The outer capsule consisted of thin, tightly layered cells which gradually became reduced in number distal to the equatorial region. In both equatorial and polar regions the capsule became more disrupted with longer denervation periods, and lysosomes and phagocytes became more abundant. The equatorial region of denervated fibers contained many myofibrils and some had peripherally-located nuclei, unlike the controls; sensory terminals were absent. The polar region of some fibers had disorganized myofilaments and others had a reduced myofilament density. Fiber diameters increased significantly in both regions. Thus, denervated intrafusal fibers lost some characteristics which distinguish them from extrafusal fibers.

Atrophic effects of proximal tendon transection with and without denervation on mouse soleus muscles

The response of mouse soleus muscles to transection of the proximal tendon was examined at both gross and microscopic levels. Changes in length and mass of the muscle, and in the dimensions, number, and ATPase staining characteristics of the muscle fibers, were determined at various times to 4 to 6 weeks after tenotomy. Muscles shortened by more than 50% and lost about 60% of their mass. Fiber cross-sectional area increased, and then decreased and stabilized below control after 7 days, and degenerative lesions appeared in some fibers. Fiber numbers decreased by nearly 20% and then remained constant, apparently by regeneration of new fibers replacing atrophied ones. The proportion of muscle fibers of the slow-twitch type was reduced. No structural or functional changes in motor nerve terminals could be detected, except for detachment from severely atrophied fibers. Concurrent denervation decreased both shortening and the loss of mass after tenotomy. Fiber diameter decreased but no significant degenerative lesions or loss of fibers could be detected. Fiber-type composition was unchanged. These experiments provide quantitative information about the degenerative changes in tenotomized muscles without the variable complications arising from tendon reattachment. Comparison of the responses with those that follow transection of the Achilles tendon shows that the degree of atrophy is independent of the extent of active muscle shortening after tenotomy.

Rapid adjustment of sarcomere length in tenotomized muscles depends on an intact innervation

Mean sarcomere length has been determined by laser diffraction in fibres of mouse soleus muscle at various times after division of the proximal tendon. Sarcomere length was initially reduced by 27% but was normal from 7 days after tenotomy. Initial shortening was less but recovery slower if the muscle was also denervated. Sarcomere length did not recover by 14 days if the tendon was cut soon after the muscle fibres became reinnervated after nerve section. It is suggested that afferent nervous pathways are involved in the short-term adjustment of sarcomere length to fibre length.

Static stretch sensitivity of Ia and II afferents in the cat's gastrocnemius

The static discharge characteristics of deefferented Ia and II spindle afferents in the cat medial gastrocnemius muscle have been compared with respect to incidence and firing rate of spontaneously firing units, length threshold of nonspontaneous units, linearity of the response to stretch, and position sensitivity. Measurements of the stretch response were taken 20s after each step increase in length so as to obtain the nearly fully adapted rate. Under this condition the frequency-length relationship was quite linear, especially for group II units. The mean position sensitivity of group II fibers exceeded that of Ia fibers in the ratio of 1.5: 1.0. The incidence of spontaneously discharging units was about 20% for both types of unit. The relationships between some of these measures and axonal conduction rate were examined. No correlation of position sensitivity with axonal conduction velocity was detected for either afferent type, but the length thresholds of the group II afferents showed a significant trend for slower conducting, that is, smaller fibers to be less sensitive. There was some indication of a direct relationship between conduction velocity and length threshold for Ia fibers. The contradiction to the "size principle" and mechanisms contributing to the static discharge behavior of the spindle are discussed.

Tenotomy of the avian anterior latissimus dorsi muscle. I. Effect of age on fiber-type transformation and regeneration from the stump in chicks

The chick's anterior latissimus dorsi muscle (ALD) was tenotomized at its origin at either 1 day or 4 weeks of age, and investigated histochemically and ultrastructurally at intervals thereafter to determine whether muscle fiber-type transformation from a slow to a twitch type is greater in young birds than older birds. No transformation of fiber type occurred in either procedure, but a new muscular connection regenerated between the scar tissue at the end of the original tenotomized stump and the former origin. This regenerated muscle had a mosaic pattern of fiber types, as demonstrated by myofibrillar ATPase activity, and contained predominantly fast fibers, as contrasted with controls or the tenotomized portion, which contained predominantly slow tonic muscle fibers. The regenerated portion contained muscle spindles. The original portion of the tenotomized muscle was indistinguishable from the control muscle. These responses of the chick ALD to tenotomy are quite different from those in the pigeon, which are reported in the following study.

Motor nerve terminal defect following tenotomy

Post-tetanic potentiation and the underlying post-tetanic repetition in cat soleus muscle require normal motor nerve terminals. These indices of nerve terminal viability are depressed 10 days and absent 15 days after tenotomy of the soleus muscle.

Spectral analysis of the electromyogram of the temporal muscle in the rhesus monkey (Macaca mulatta)

Spontaneous EMG activity of one mandibular elevator and postural muscle, the anterior temporalis, was recorded from 20 unanesthetized rhesus monkeys subjected to 4 experimental protocols. The EMG activity was analyzed with a spectral analyzer to determine changes in particular frequency bandwidths after (1) administering a dissociative drug, (2) placing weights on the mandible, (3) detaching the muscle, and (4) adaptation of the muscle to oral respiration. The mean distribution of frequency components indicated that ketamine--HCl increased the power of all frequencies below 400 c/sec, particularly those at 20--40 c/sec. A period of hyperactivity and increased recruitment and discharge of motor units occurred within the first 30 min following administration of the drug. Passive and sustained lowering of the jaw with increased weights indicated that increasing the front incisor distance 2--4 cm significantly decreased the frequency components below 400 c/sec accompanying a decrease in active motor units. Comparison of frequency components of the temporalis EMG before and within 40 days after detachment suggested some subtle variations in the mean distributions predominantly around 200 c/sec but without significant changes. Comparison of the mean spectral distribution between 8 nasal-breathing and 8 oral-breathing monkeys indicated a significant loss of power in the normal dominant frequency range of 20--100 c/sec in the oral respiratory group except for enhancement of the 20 c/sec bandwidth. The results suggest that the anterior temporalis alters its EMG activity during both short (i.e., min, h) and long-term (i.e., months, year) adaptations of the muscle.

The bilateral response of the temporal muscle in the rhesus monkey (Macaca mulatta) to short-term detachment of the muscle and increased loading of the mandible

The electromyographic background activity of the temporal muscle was observed after short-term detachment of the muscle and with increased loads on the mandible. Detachment of the muscle increased its mean spike discharge within the first 24 days but without significant changes in the spectral components. Loading the mandible decreased both the spike discharge and spectral components.