The Possible Role of Botulinum Toxin A in the Structural Regeneration of Gastrocnemius Muscle and Achilles Tendon of Albino Rat after Experimental Achilles Tenotomy

Abstract

The present study was aiming to detect the alteration in the Achilles tendon and gastrocnemius muscle after experimental Achilles tenotomy and to evaluate the effect of Botox and also suturingon these alterations. In this study, 30 male albino rats were used. At the beginning of the experiment, the rats were equally divided into five groups: -GroupI: (Control group) -Group II: underwent experimental Achilles tenotomy. -Group III: underwent experimental Achilles tenotomy and repaired with suture. -Group IV: underwent the operation, without repair followed by injection of Botox in the gastrocnemius muscle 6 units/kg body weight. -Group V:underwent the operation, followed by tendon repair and I.M.I. of Botox in the gastrocnemius muscle 6 units/kg body weight.

The animals were sacrificed after 3 weeks. Paraffin sections -stained with Hematoxylin& Eosin and Masson's trichrome- as well as semithin sections –stained with Toluidine blue- were prepared from the obtained specimens. Statistical analysis was also performed. The tendon from the control groups showed parallel aligned collagen fibers with fibrocytes trapped between the fibers. The gastrocnemius muscle specimens showed that the myofibers were uniform in size and shape with visible cross striations and peripherally located nuclei. The endomysium between them contained small blood vessels and few delicate collagen fibers. In the second group, the tendon showed separated irregularly arranged collagen fibers with numerous vaculations and an increase in the number of fibroblasts and fibrocytes. Invasion of the tendon by inflammatory cells and large congested blood vessels was highly significant. The gastrocnemius muscle showed distorted architecture, apparent increase in the number of internal nuclei with highly significant endomysial fibrosis and inflammatory cellular infiltrations. Moreover, mast cells and phagocytic cells were also noticed. In the third group, the Achilles tendon showed irregular collagen fibers with highly significant mononuclear cellular infiltration. Small blood vessels were also present. In the muscle specimens there were disruption of the muscular architecture with highly significant cellular infiltration and endomysial fibrosis that was non-significantly decreased compared to the non-sutured group. Mast cells were also present. In the fourth group, the tendon showed compact and regular arrangement of collagen fibers with significant decrease in mononuclear cellular infiltration as compared to the second group (Botox non-injected group). Mast cells, lipid droplets and congested blood vessels were also seen in this group. Although the architecture of the gastrocnemius muscle was preserved, there were areas of lost cross striations and atrophy of the myofibers. However, significant decrease in mononuclear cellular infiltration within the muscle was noticed as compared to the second group, non-significant muscle fibrosis was observed. In the fifth group, the tendon showed compact and regularly arranged collagen fibers. Significant decrease in mononuclear cellular infiltration as compared to the third group (Botox non-injected) was observed. The muscle showed preserved architecture but with areas of lost cross striations and muscle fibers atrophy. There was significant decrease in cellular infiltration as compared to the third group (Botox non-injected). Also non-significant muscle fibrosis compared to the Botox non-sutured group (group IV) was observed. Mast cells were also noticed. In conclusion,Achilles tendon rupture can affect the histology of the tendon as well as that of the muscle. Suturing of the Achilles tendon is more beneficial than non-suturing of the tendon as it could decrease muscle fibrosis. Botox also could be beneficial in achieving better healing of the tendon and less formation of scar tissue. Giving additional rest to the gastrocnemius muscle and through its anti-inflammatory property, Botox could lead to better healing and less scaring. On the other hand, Botox could weaken the muscle microstructure as detected in the present work. So it is recommended to investigate the effect of different Botox doses on muscle microstructure in further studies.