Recapillarization of tenotomized skeletal muscles after delayed tendon suture. I. Experimental study

Local inhibition of nitrergic activity in tenotomized rats accelerates muscle regeneration by increasing fiber area and decreasing central core lesions

Muscular atrophy is a progressive degeneration characterized by muscular proteolysis, loss of mass and decrease in fiber area. Tendon rupture induces muscular atrophy due to an intrinsic functional connection. Local inhibition of nitric oxide synthase (NOS) by Nω-nitro-L-arginine methyl ester (L-NAME) accelerates tendon histological recovery and induces functional improvement. Here we evaluate the effects of such local nitrergic inhibition on the pattern of soleus muscle regeneration after tenotomy. Adult male Wistar rats (240 to 280 g) were divided into four experimental groups: control (n=4), tenotomized (n=6), vehicle (n=6), and L-NAME (n=6). Muscular atrophy was induced by calcaneal tendon rupture in rats. Changes in muscle wet weight and total protein levels were determined by the Bradford method, and muscle fiber area and central core lesion (CCL) occurrence were evaluated by histochemical assays. Compared to tenotomized (69.3±22%) and vehicle groups (68.1%±17%), L-NAME treatment induced an increase in total protein level (108.3±21%) after 21 days post-injury. A reduction in fiber areas was observed in tenotomized (56.3±1.3%) and vehicle groups (53.9±3.9%). However, L-NAME treatment caused an increase in this parameter (69.3±1.6%). Such events were preceded by a remarkable reduction in the number of fibers with CCL in L-NAME-treated animals (12±2%), but not in tenotomized (21±2.5%) and vehicle groups (19.6±2.8%). Altogether, our data reveal that inhibition of tendon NOS contributed to the attenuation of atrophy and acceleration of muscle regeneration.

Passive skeletal muscle excursion after tendon rupture correlates with increased collagen content in muscle

PURPOSE

This study was designed to measure time-dependent changes in muscle excursion and collagen content after tenotomy, and to analyze the correlation between muscle excursion and collagen content in a rabbit model.

MATERIALS AND METHODS

Twenty-four rabbits underwent tenotomy of the second extensor digitorum longus (EDL) muscles on the right legs and were randomly assigned to three groups based on the period of time after tenotomy (2, 4, and 6 weeks). The second EDL muscles on left legs were used as controls. At each time after tenotomy, passive muscle excursion and collagen content, determined by hydroxyproline content, were measured bilaterally, and the ratio of each value to the normal one was used.

RESULTS

The mean ratio of muscle excursion after tenotomy to the value of the control decreased in a time-dependent fashion: 92.5% at 2 weeks, 78.6% at 4 weeks, and 55.1% at 6 weeks. The mean ratio of hydroxyproline content in muscle to the value of the control increased in a time-dependent fashion: 119.5% at 2 weeks, 157.3% at 4 weeks, and 166.6% at 6 weeks. There was a significant negative correlation between the ratio of hydroxyproline content in muscle after tenotomy to the control values and the ratio of muscle excursion after tenotomy to the control values (r=-0.602, p=0.002).

CONCLUSION

The decrease in muscle excursion seems to correlate with the increase in collagen content in the muscle in a time-dependent fashion following tenotomy.

The effect of muscle excursion on muscle recovery after tendon repair in a neglected tendon injury: a study in rabbit soleus muscles

We attempted to determine whether muscle excursion observed during operation can be a prognostic indicator of muscle recovery after delayed tendon repair in a rabbit soleus model. Eighteen rabbits underwent tenotomy of the soleus muscles bilaterally and were divided into three groups according to the period from tenotomy to repair. The tendons of each group were repaired 2, 4, and 6 weeks after tenotomy. The excursion of each soleus muscle was measured at the time of tenotomy (baseline), at 2, 4, 6 weeks after tenotomy, and 8 weeks after tendon repair. The amount of muscle recovery after tendon repair in terms of muscle excursion independently depended on the timing of repair and on the muscle excursion observed during repair. The regression model predicted that the muscle excursion recovered on average by 0.6% as the muscle excursion at the time of repair increased by 1% after adjusting for the timing of repair. This study suggests that measuring the muscle excursion during tendon repair may help physicians estimate the potential of muscle recovery in cases of delayed tendon repair.

Effects of rotator cuff ruptures on the cellular and intracellular composition of the human supraspinatus muscle

Ruptures of the rotator cuff tendons of the human shoulder are a common incidence and lead to functional impairment of the four muscles connected to the cuff, entailing profound changes of their cellular tissue composition. Most importantly, such tendon tears lead to atrophy, fatty degeneration and fibrosis of the corresponding muscles. The muscle most commonly affected with such changes is the M. supraspinatus. The present study uses biopsy samples from the supraspinatus muscle of 12 elderly patients and 6 controls to examine the rupture-induced muscle change at both the cellular and the intracellular (ultrastructural) levels. Amounts of fatty tissue, connective tissue and muscle were assessed by light microscopy-based morphometry and stereology. Stereology of electron micrographs was employed to determine volume densities of muscle fibre mitochondria, myofibrils and intracellular lipid. Results demonstrate that the supraspinatus muscles of patients with a massive rupture contain significantly higher amounts not only of fatty tissue but also of intracellular lipid than those of control subjects. These patients further exhibit a major decrease in relative amounts of myofibrils, thus confirming that change of intracellular composition is a major component of the observed muscle degeneration. The results contribute to establish the true spectrum of supraspinatus muscle damage in humans induced by tendon rupture.

Quantitative alterations in intramuscular connective tissue following immobilization: an experimental study in the rat calf muscles

The purpose of the present investigation was to study the effect of immobilization in two different positions, shortened or lengthened, on the connective tissue and capillarization of the rat calf muscles. In 18 rats the left hind limb was immobilized so that the soleus and gastrocnemius muscles were in a lengthened position and tibialis anterior was in a shortened position, and in 18 rats vice versa. The right hind limbs were kept free to serve as controls. After 1, 2, and 3 weeks of immobilization, an equal number of rats were killed and the muscles were analyzed. The connective tissue muscle ratio was measured from histological sections by automatic image analyzer and the number of capillaries per 1000 muscle fibers was also recorded. In the intact muscles the proportions of intramuscular connective tissue in the soleus, gastrocnemius, and tibialis anterior were 2, 3, and 5%, respectively. During the immobilization period of 3 weeks the proportion of connective tissue increased significantly in all muscles, but the only significant difference between the positions was in the soleus muscle in which more connective tissue was found in the lengthened position, 54% vs 30% in the shortened position. The amount of capillaries decreased significantly during immobilization in all muscles to about 65% of normal capillar density, but the position of immobilization seemed to have no effect on this phenomenon. The increase in intramuscular connective tissue during immobilization seems to occur simultaneously with muscle atrophy and loss of muscle capillarity. The stretched position of immobilization seems to have an additional fibrotic effect if the immobilized muscle, such as soleus, consists mainly of type I fibers generally known to be more vulnerable to disuse atrophy than type II fibers.