THE EFFECT OF TENOTOMY ON THE STRUCTURE OF FAST AND SLOW MUSCLE IN THE RABBIT

Consequences of ankle joint immobilisation: insights from a morphometric analysis about fibre typification, intramuscular connective tissue, and muscle spindle in rats

Orthosis immobilisations are routinely used in orthopaedic procedures. This intervention is applicable in bone fractures, ligament injuries, and tendonitis, among other disorders of the musculoskeletal system. We aimed to evaluate the effects of ankle joint functional immobilisation on muscle fibre morphology, connective tissue, muscle spindle and fibre typification triggered by a novel metallic orthosis. We developed a rodent-proof experimental orthosis able to hold the tibiotalar joint in a functional position for short and long terms. The tibialis anterior muscles of free and immobilised legs were collected and stained by histology and histochemistry techniques to investigate general muscle morphology, connective tissue and muscle fibre typification. Morphometric analysis of muscle cross-section area, fibre type cross-section area, fibre type density, percentage of intramuscular connective tissue, and thickness of the muscle spindle capsule were obtained to gain insights into the experimental protocol. We found that short- and long-term immobilisation decreased the cross-section area of the muscles and induced centralisation of myonuclei. The connective tissue of immobilised muscle increased after 2 and 4 weeks mainly by deposition of type III and type I collagen fibres in the perimysium and endomysium, respectively, in addition to muscle spindle capsule thickening. Type IIB muscle fibre was severely affected in our study; the profile assumed odd shapes, and our data suggest interconversion of these fibre types within long-term immobilisation. In conclusion, our protocol has produced structural and histochemical changes in muscle biology. This method might be applied to various rodent models that enable genetic manipulation for the investigation of muscle degeneration/regeneration processes.

Muscle Degeneration Induced by Sequential Release and Denervation of the Rotator Cuff Tendon in Sheep

Background

In a sheep rotator cuff model, tenotomy predominantly induces fatty infiltration, and denervation induces mostly muscle atrophy. In clinical practice, myotendinous retraction after tendon tear or lateralization after tendon repair tear may lead to traction injury of the nerve.

Purpose/Hypothesis

To analyze whether an additional nerve lesion during rotator cuff repair leads to further degeneration of the rotator cuff muscle in the clinical setting. We hypothesized that neurectomy after tendon tear would increase atrophy as well as fatty infiltration and that muscle paralysis after neurectomy would prevent myotendinous retraction after secondary tendon release.

Study Design

Controlled laboratory study.

Methods

Twelve Swiss alpine sheep were used for this study. For the 6 sheep in the tenotomy/neurectomy (T/N) group, the infraspinatus tendon was released; 8 weeks later, the suprascapular nerve was transected. For the 6 sheep in the neurectomy/tenotomy (N/T) group, neurectomy was performed, and the infraspinatus was tenotomized 8 weeks later. All sheep were sacrificed after 16 weeks. Magnetic resonance imaging (MRI) was performed before the first surgery (baseline) and then after 8 and 16 weeks. The MRI data were used to assess muscle volume, fat fraction, musculotendinous retraction, pennation angle, and muscle fiber length of the infraspinatus muscle.

Results

Three sheep (2 in the T/N and 1 in the N/T group) had to be excluded because the neurectomy was incomplete. After 8 weeks, muscle volume decreased significantly less in the T/N group (73% ± 2% of initial volume vs 52% ± 7% in the N/T group; P < .001). After 16 weeks, the mean intramuscular fat increase was higher in the T/N group (36% ± 9%) than in the N/T group (23% ± 6%), without reaching significance (P = .060). After 16 weeks, the muscle volumes of the N/T (52% ± 8%) and T/N (49% ± 3%) groups were the same (P = .732).

Conclusion

Secondary neurectomy after tenotomy of a musculotendinous unit increases muscle atrophy. Tenotomy of a denervated muscle is associated with substantial myotendinous retraction but not with an increase of fatty infiltration to the level of the tenotomy first group.

Clinical Relevance

Substantial retraction, which is associated with hitherto irrecoverable fatty infiltration, should be prevented, and additional neurogenic injury during repair should be avoided to limit the development of further atrophy.

Cardiolipin content, linoleic acid composition, and tafazzin expression in response to skeletal muscle overload and unload stimuli

Cardiolipin (CL) is a unique mitochondrial phospholipid that, in skeletal muscle, is enriched with linoleic acid (18:2n6). Together, CL content and CL 18:2n6 composition are critical determinants of mitochondrial function. Skeletal muscle is comprised of slow and fast fibers that have high and low mitochondrial content, respectively. In response to overloading and unloading stimuli, these muscles undergo a fast-to-slow oxidative fiber type shift and a slow-to-fast glycolytic fiber type shift, respectively, with a concomitant change in mitochondrial content. Here, we examined changes in CL content and CL 18:2n6 composition under these conditions along with tafazzin (Taz) protein, which is a transacylase enzyme that generates CL lipids enriched with 18:2n6. Our results show that CL content, CL 18:2n6 composition, and Taz protein content increased with an overload stimulus in plantaris. Conversely, CL content and CL 18:2n6 composition was reduced with an unloaded stimulus in soleus. Interestingly, Taz protein was increased in the unloaded soleus, suggesting that Taz may provide some form of compensation for decreased CL content and CL 18:2n6 composition. Together, this study highlights the dynamic nature of CL and Taz in skeletal muscle, and future studies will examine the physiological significance behind the changes in CL content, CL 18:2n6 and Taz.

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.

Muscle shortening induced by tenotomy does not reduce activity levels in rat soleus

1. A slow postural muscle was tenotomized to determine the role of muscle stretch on chronic recruitment patterns in freely moving animals. 2. Different amounts of muscle shortening were induced in the soleus muscles of ten rats by severing the tendon of insertion (n = 3), the whole Achilles' tendon (n = 4) or the origins and insertions (n = 3). 3. Bipolar wire electrodes were implanted on each muscle to record the electromyographic activity (EMG) under control and tenotomized conditions. The complex interference pattern was continuously analysed to determine the number and amplitude of peak potentials (called turns). The numbers of these 'turns' and their amplitudes were determined during 4 control and at least 5 experimental days. Sham-operated controls and groups matched according to the type of tenotomy were analysed for length changes and pathological changes 5 and 10 days post-tenotomy. 4. The total activity levels in all three tenotomy conditions were not significantly changed when compared with their own control levels. No differences in total activity level were found between the three tenotomized conditions. 5. The normal diurnal patterns of muscle recruitment were preserved during the tenotomized conditions, with the highest levels consistently occurring during the first 3 h of the dark cycle. 6. Tenotomy of the soleus, whether induced by distal (ST), distal and proximal (DT) or Achilles' tenotomy (AT) resulted in muscle shortening (9-26 %). No muscle pathology was found in the ST or AT groups. Degeneration was found in the DT group after 5 days, with further increases at 10 days. 7. These data suggest that the absence of stretch had no discernible influence on the aggregate activity levels in the slow postural soleus muscle. Whether tenotomy caused changes in recruitment within individual step cycles was not evaluated.

The effects of tenotomy and overload on the postnatal development of muscle fibre histochemistry in the cat triceps surae

Five to seven day-old kittens were subjected to partial tenotomy of the Achilles (triceps surae) tendon. The effects of tenotomy and overload on the development of muscle fibre histochemistry and fibre sizes were investigated when the cats had reached the adult stage. The examined muscles were the uniform soleus and the mixed medial gastrocnemius. Tenotomized muscles of both types had lower weights than their controls. Tenotomized soleus showed a redistribution of succinic dehydrogenase (SDH) activity, together with signs of muscle fibre death. Tenotomized medial gastrocnemius muscles displayed more severe degenerative signs than the soleus, together with signs of fibre death. The fibre death seemed to affect mainly fibres of type IIb. Moreover, a less distinct differentiation in histochemical staining pattern between muscle fibre types was found in these muscles. Overloaded soleus muscles had greater weights than their controls, while no difference could be shown for the overloaded medial gastrocnemius. The overloaded medial gastrocnemius showed a uniform hypertrophy of all fibre types. Also, overloaded soleus showed a uniform hypertrophy. Both types of muscle showed a normal histology as well as normal staining characteristics (SDH and AcATPase). It is concluded that both soleus and medial gastrocnemius are sensitive to loss of muscle tension during development. The basic features of muscle morphology and histochemistry were normal, though, and it is suggested that other factors account for most of the normally occurring development and differentiation.

The effects of tenotomy and compensatory hypertrophy on the postnatal development of soleus motor units in the cat

Kittens, 5-7 days old, were subjected to tenotomy of either the soleus muscle or all its Achilles tendon synergists. When the cats had reached the adult stage, the physiological properties of the soleus motor units were investigated in both the atrophic and hypertrophic situations. Tenotomy resulted in a marked muscle weight loss and overload due to tenotomy of synergists in a marked gain in muscle weight compared to the contralateral side. The motor units of the tenotomized soleus muscles exhibited a moderate shortening of the twitch contraction time, and also a change in twitch shape, related to the degree of atrophy. In the motor units of the hypertrophic soleus muscles, an increased fatiguability could be demonstrated. Further, in this group, there was a tendency towards differentiation of the normally uniform motor units into two groups with different features. The functional implications of this process are discussed. The development of motor units in both the tenotomized and the hypertrophic muscles were only marginally influenced by the operations, and it is concluded that the basic features of their development are largely unaffected by the functional manipulations imposed in the present study.

Decrease in mass of slow and fast tenotomized muscles of guinea pigs: role of nerve impulses and neurogenic factors

The role of nerve impulses and neurogenic factors in the decrease in muscle mass following tenotomy was investigated in 30 adult (15 males, 15 females) guinea pigs. Unilateral tenotomy, neurectomy and simultaneous tenotomy and neurectomy of slow and fast hindlimb muscles were performed in 3 groups respectively. Each group comprised 10 guinea pigs. The unoperated hindlimb of each animal in each group served as control. The weight loss occurred in both slow and fast muscles but was greater in the slow soleus muscle as compared to the fast gastrocnemius muscle. In each muscle the weight loss was least in the tenotomized group. This was followed by the weight loss in the neurectomized group. The greatest weight loss was observed in the simultaneously tenotomized and neurectomized group. These observations agree with the suggestion of other workers that a possible neurogenic factor flowing from the nerves to the muscles was very significant in maintenance of muscle fibre stability. It indicated also that simultaneous neurectomy and tenotomy did not prevent degenerative changes in slow and fast muscles and that it was not nerve impulses reaching the tenotomized muscles that were responsible for degenerative changes observed but that other factors were responsible.

Duchenne dystrophy viewed as a disturbance of nerve-muscle interactions

The possibility that some features of Duchenne muscular dystrophy (DMD) can be explained as a disturbance of nerve-muscle interaction during development is discussed. It is argued that the initial disturbance in DMD is due to a slower rate of maturation of skeletal muscle fibers. Normally, the maturation of the motor reflexes is closely followed by maturation of the muscle fibers. The possibility is considered that if muscle fibers mature more slowly than normal, they are not able to withstand the type of activity imposed upon them by the mature motoneuron. This applies mainly to the high frequency activity imposed on the fibers of motor units that are destined to become "fast." Experimental evidence suggesting such a mechanism is presented.

Rapid atrophy of mouse soleus muscles after tenotomy depends on an intact innervation

Changes in length and mass of mouse soleus muscles have been determined during the first 14 days after division of the Achilles tendon and/or the tibial nerve. Muscle atrophy and associated histological changes were detectable 24 h after tenotomy, and increased progressively over the first week. These changes were less marked in muscles which had also been denervated, and were rapidly reversed if the tendon became reattached. An attempt is made to distinguish the role of the nerve supply from the effects of reduced longitudinal tension in the production of atrophy after tenotomy.

The response of the rat soleus muscle to tenotomy after dorsal root section

Both soleus muscles of rats were tenotomized 5-10 days after deafferentation of one side which was achieved by section of the 4th and 5th lumbar dorsal roots. When examined 2 weeks after tenotomy, all experimental muscles showed central degenerative changes in slow fatigue-resistant fibers. These changes were absent from muscles that had been only deafferented. Experimental deafferented muscles examined 6 weeks after tenotomy showed a substantial recovery which was comparable to that seen in tenotomized muscles with intact afferent innervation. It is concluded that (1) deafferentation does not inhibit the recovery of tenotomized fibers, and (2) the loss of afferent fibers plays no part in the protection from central degeneration known to be afforded by denervation of tenotomized muscles.

Changes in sarcomere length following tenotomy in the rat

The medial belly of the gastrocnemius and the extensor digitorum longus muscles of rats were tenotomized. One day following tenotomy, the mean sarcomere length of the fast medial gastrocnemius was 1.8 microns, a value comparable to that of tenotomized slow soleus. The mean sarcomere length of the tenotomized extensor digitorum longus, however, was 2.0 microns, a figure which differed significantly from the values obtained for both the soleus and the gastrocnemius. Histological preparations showed the presence of central core degeneration in slow fatigue-resistant fibers of the tenotomized gastrocnemius comparable to that seen in the soleus. No changes were found in the fibers of the tenotomized extensor digitorum longus. The fact that central core lesions were produced in the fibers of soleus and medial gastrocnemius but not in the extensor digitorum longus may be related to the lesser reduction in sarcomere length following tenotomy of the latter muscle.

Effect of tenotomy on self-reinnervated and randomly reinnervated soleus muscle of rat

The time course and degree of atrophic changes caused by tenotomy were compared in normal, self-reinnervated and randomly reinnervated soleus muscle 6 months after transsection and reunion of the nerve at different distances from the muscle. Comparison was made between the behaviour of Type I and Type II fibers, distinguished on the basis of histochemical myofibrillar ATPase and succinic dehydrogenase reactions. Cross-sectional areas of individual muscle fibers were measured using Quantimet 720 image analyser. Selective atrophy of Type I muscle fibers as determined by structural and histochemical changes was observed after tenotomy of normal, self-reinnervated and randomly reinnervated soleus muscles after transsection of the muscular branch of the tibial nerve, Type II muscle fibers in randomly reinnervated muscles were found to be relatively insensitive to tenotomy, as in normal muscle. In randomly reinnervated muscles after transsection and reunion of the sciatic nerve, tenotomy did not cause any visible structural and histochemical abnormalities although a decrease of muscle weight and cross-sectional surface area of fibers was noted. Since in these muscles Type II fibers increased to about 70% of the muscle fiber population, it is suggested that the increased percentage of Type II fibers seemed to prevent the atrophic changes in Type I fibers after tenotomy.

Changes in length of sarcomeres following tenotomy of the rat soleus muscle

Tenotomy of the proximal and distal tendons of the soleus muscle of female Wistar rats was performed and sarcomeric length and muscle fascicle length measured. On the first postoperative day muscle bellies were found shortened and their sarcomeric length considerably reduced. Four weeks following tenotomy, although the muscle bellies remained shortened, sarcomeric length was comparable with that of control muscles. Measurement of muscle fascicle lengths at this time showed that those of experimental muscles were nearly 50% less than those of control muscles. It was concluded from these experiments that a reduction of the number of sarcomeres in series had occurred, thus compensating for the reduced length of the muscle belly.

Differential effects of disuse preceding denervation on the onset and development of fibrillation in fast and slow muscles

Section of the sciatic nerve, performed after a week of muscular disuse, is followed by fibrillation earlier in the soleus (S) than in the anterior tibialis (AT) muscle of the rat. The subsequent development of fibrillation, which is different in the control denervated S as compared with the control denervated AT, tends to become similar in the disused-denervated muscles.

Changes in contractile properties of disused soleus muscles

1. The hypothesis that the pattern of activity of muscle can determine its contractile properties was tested in the case of the rat soleus subjected to chronic disuse.2. In order to characterize the pattern of motor activity over long periods of time, a method of chronic EMG recording with indwelling electrodes was developed. Some characteristics of the EMG recorded from unrestrained animals are described.3. Immobilization of the knee and ankle joints reduced aggregate EMG activity in the soleus to 5-15% of control and resulted in a shift from tonic to a more phasic pattern of firing.4. After 4 weeks of immobilization, speeding of the soleus mechanical properties was indicated by: shortened contraction time; decreased tetanus/twitch ratio; increased maximum rate of development of tetanic tension; and decreased fusion during a 5/sec tetanus.5. Because the contractile properties of the soleus can be altered by a period of disuse with no change in innervation, neuronal control of the contractile mechanism depends in part on impulse activity.

The importance of peripheral changes in determining the sensitivity of striated muscle to depolarizing drugs

1. The sensitivity of the flexor digitorum longus and soleus muscles to depolarizing drugs was tested after cross-union of their respective motor nerves.2. The alien innervation did not affect the sensitivity of either the flexor digitorum longus (FDL) or soleus muscles, which retained their normal characteristic responses to decamethonium and suxamethonium. The time course of muscle contractions was, however, altered by the cross-union operation.3. A considerable increase in sensitivity to depolarizing drugs was shown after de-afferentation and after tenotomy of the soleus muscles. Both these conditions are associated with muscle atrophy.4. It is suggested that hypersensitivity to depolarizing drugs can be expected in any situation where the muscle is undergoing atrophy.