Muscular and Tendon Degeneration after Achilles Rupture: New Insights into Future Repair Strategies.

Lara Gil-Melgosa,Juan Pons-Villanueva,Begoña Calvo,Rafael Llombart,Cristina Ederra,Miguel Susaeta Ruiz,Jorge Grasa,Felipe Prosper,Ainhoa Urbiola,Ana Pérez Ruiz,Mikel Ariz,Purificación Ripalda-Cemborain,Carlos Ortiz-De-Solórzano,Verónica Montiel

doi:10.3390/biomedicines10010019

Abstract

Achilles tendon rupture is a frequent injury with an increasing incidence. After clinical surgical repair, aimed at suturing the tendon stumps back into their original position, the repaired Achilles tendon is often plastically deformed and mechanically less strong than the pre-injured tissue, with muscle fatty degeneration contributing to function loss. Despite clinical outcomes, pre-clinical research has mainly focused on tendon structural repair, with a lack of knowledge regarding injury progression from tendon to muscle and its consequences on muscle degenerative/regenerative processes and function. Here, we characterize the morphological changes in the tendon, the myotendinous junction and muscle belly in a mouse model of Achilles tendon complete rupture, finding cellular and fatty infiltration, fibrotic tissue accumulation, muscle stem cell decline and collagen fiber disorganization. We use novel imaging technologies to accurately relate structural alterations in tendon fibers to pathological changes, which further explain the loss of muscle mechanical function after tendon rupture. The treatment of tendon injuries remains a challenge for orthopedics. Thus, the main goal of this study is to bridge the gap between clinicians’ knowledge and research to address the underlying pathophysiology of ruptured Achilles tendon and its consequences in the gastrocnemius. Such studies are necessary if current practices in regenerative medicine for Achilles tendon ruptures are to be improved.

Highlights

Tendon injuries are one of the most frequent musculoskeletal lesions, with four million new cases worldwide each year
The incidence of Achilles tendon rupture has increased in recent decades
Recent investigation of tissue and cells from tendons such as the rotator cuff has demonstrated the importance of inflammation and fatty infiltration in the development of tendon disease, underscoring the consequent injury to muscle

Summary

Introduction

Tendon injuries are one of the most frequent musculoskeletal lesions, with four million new cases worldwide each year. They represent a significant burden for society and health assistance costs [1]. Despite its strength and thickness, the Achilles is one of the most frequently injured tendons. The incidence of Achilles tendon rupture is rising, Biomedicines 2022, 10, 19. Biomedicines 2022, 10, 19 probably due to the increase in the practice of sports [2,3,4]. Achilles tendon rupture is most common in middle age, affecting the general public participating intermittently in sporting activities but is a frequent tendon injury among qualified athletes [5]. Elderly and sedentary population may suffer discrete ruptures, which are usually missed and later become chronic, with a higher health-care cost (~EUR 6500) than treatments aimed to restore acute ruptures (~EUR 6000 and EUR 4500, operative and non-operative treatments, respectively) [6]

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