Les tendinopathies sont la première cause de maladie professionnelle en France. Elles sont devenues une préoccupation majeure de santé publique. Cependant, leurs mécanismes physiopathologiques restent encore mal définis. Au cours de cette thèse, nous nous sommes intéressés aux phases précoces de la tendinopathie engendrées par une sur-utilisation du tendon supra-épineux (tSE) de la coiffe de rotateurs de l’épaule chez le rat. Nous avons tenté de comprendre les mécanismes à l’origine de cette pathologie afin de pouvoir agir et la traiter en amont de l’apparition des symptômes.Nous montrons que le profil d’évolution moléculaire des collagènes, des protéoglycanes et des glycosaminoglycanes (GAGs) associé aux phases précoces de la sur-utilisation, témoigne d’un profond remaniement matriciel et d’une différenciation chondroïde des fibroblastes tendineux. Nous avons identifié les métalloprotéinases (MMPs) majeures et leurs inhibiteurs (TIMPs) susceptibles d’être impliqués dans ce remaniement. Nos résultats suggèrent que le mécanisme lésionnel initial et les changements matriciels observés sont dus à un processus induit par des médiateurs locaux libérés par les ténocytes et non à une réaction inflammatoire. Enfin, nous avons cherché à établir une corrélation entre les changements moléculaires observés et le degré de sévérité d’une tendinopathie diagnostiquée chez l’Homme. Nous avons montré, sur des échantillons de tendon patellaire humain une relation entre la quantité des GAGs et le score (VISA score) reflétant le degré pathologique du tendon.Cette étude nous a donc permis d’améliorer nos connaissances des phases précoces du processus d’altération du tSE. Cependant, d’importants efforts restent néanmoins à accomplir dans la caractérisation de la pathogenèse précoce notamment pour préciser le contexte biomécanique qui la génère. / Tendinopathies are the first cause of professional diseases in France. They are a major public health concern. However, their physiopathological mechanisms remain poorly understood. This project aimed at investigating the early stages of supraspinatus tendinopathy caused by overuse. Using a rat animal model, we attempted to understand the mechanisms behind this disease in order to act and treat the symptoms upstream of their onset.We have shown that the molecular changes of collagens, proteoglycans and glycosaminoglycans (GAGs) associated with the early events of overuse attest a major matrix remodeling and chondrogenic differentiation of tendon cells. We identified the main metalloproteinases (MMPs) and their inhibitors (TIMPs) that may be involved in this remodeling. Our results further suggest that the initial mechanisms linked to the observed matrix changes are due to local mediators release by tenocytes rather than an inflammatory process. Finally, we attempted to correlate molecular changes observed during overuse with the severity of the tendinopathy diagnosed in humans. We have shown a relationship between the amount of GAGs and the pathological score (VISA score) on human patellar tendons.This study improved our knowledge of the early pathological events of the supraspinatus tendon. However, more remains to be done for characterizing the early stages of tendinopathy especially to clarify the biomechanical context up-stream.

The supraspinatus tendon is an important structure of the rotator cuff. Subacromial impingement is a common reason for shoulder pain. Despite extensive scientific work in this field, the cause of impingement syndrome is still not fully understood. The general aim of the present thesis was to generate new knowledge with respect to pathogenesis and treatment of impingement syndrome. A combination of animal and clinical studies were performed. Different methods were used such as histology, immunohistochemistry, development and assessment of a novel measuring device and clinical and radiological assessment. Thirty rats were injected with triamcinolone or saline into the subacromial bursa. After five corticosteroid injections, we found focal inflammation, degradation and fragmentation of collagen bundles in the supraspinatus tendon, whereas the control specimens were normal (p=0.035). Subacromial bursitis was induced by injections of carrageenan into the subacromial space (n=28). Fibrocartilaginous metaplasia and bony metaplasia were found in the supraspinatus tendon. Even in specimens with no histologic changes of the collagen bundles the staining for fibronectin was significantly increased. The distance between the anterolateral acromion and the supraspinatus tendon was measured in patients with impingement syndrome intraoperatively (n=30) and in controls (instability, n=15). The mean value of the subacromial distance in controls was 16 mm, the 95% mean confidence limits between 14 and 18 mm. The mean value in the group of patients with impingement syndrome was 8 mm before and 16 mm after the decompression. Fifty patients were reviewed after arthroscopic subacromial decompression. Twenty-five showed calcific deposits in the rotator cuff on radiographs preoperatively. In 13 patients the calcific deposits totally disappeared postoperatively. In another six patients the calcifications had decreased in size. Four patients still showed calcifications, which were 5 mm or greater in size. The postoperative results measured by the Constant score were almost identical in the calcific and the non-calcific groups. Tillander 010916 8 Human surgical supraspinatus tendon specimens were studied from patients with impingement (n=16), ruptured supraspinatus tendons (n=7) and controls (n=10). Degradation of tendinous tissue and fibrin were found only in some specimens from ruptures. The difference in fibronectin staining was significant between controls and patients with a rupture (p=0.002). Fibrosis and thinning of fascicles seemed to be a more non-specific finding, appearing in control, impingement and rupture specimens. In conclusion, subacromial corticosteroid injections may cause rupture of the supraspinatus tendon. Metaplasia of the supraspinatus tendon may play a role in the pathogenesis of impingement and rupture of the supraspinatus tendon. The subacromial distance can be measured intraoperatively and was shown to be lower in patients with impingement than in patients with instability. Calcifications disappear or decrease in size after arthroscopic subacromial decompression and do not seem to influence the postoperative outcome in patients with impingement. Degradation of tendon tissue, fibrin and fibronectin appear to be signs of tendon degeneration, whereas fibrosis and thinning of fascicles were found also in controls.

Chronic painful tendinopathies are common, not only in sports and recreationally active people, but also among people with a sedentary lifestyle. Both the lower and upper limbs are affected. There is lack of knowledge about the etiology and pathogenesis to tendinopathy, and many different treatments options have been presented. Unfortunately, most treatments have not been tested in scientific studies. Conservative (non-surgical) treatment has since long shown unsatisfactory results and surgical treatment is known to give unpredictable results. The aim of this thesis was to evaluate new models of painful eccentric training for the conservative treatment of different chronic tendinopathies. After promising results in a pilot study, using painful eccentric calf muscle training in patients with chronic mid-portion Achilles tendinopathy, we investigated if these results could be reproduced in a larger group of patients with both mid-portion and insertional Achilles tendinopathy (study I). After 12 weeks, 89% of the patients with pain from the mid-portion were satisfied and back in previous activities. In the group with insertional Achilles tendinopathy the results were poor. A new model for eccentric training was designed for patients with insertional Achilles tendinopathy. The eccentric calf muscle training was done from tip-toe to floor level (study II). With this new regimen 67% of the patients were satisfied and back in previous activities. The next step was to investigate the effects of painful eccentric quadriceps training on patients with jumper´s knee/patellar tendinopathy (study III). Two different training protocols were used. Eccentric training performed on a 250 decline board showed promising results with reduced pain and a return to previous activities, while eccentric training without the decline board had poor results. In a following prospective study, patients with jumper´s knee/patellar tendinopathy were randomised to either concentric or eccentric painful quadriceps training on a 250 decline board (study IV). After 12 weeks of training, there were significantly better results in the group that did eccentric training. In a pilot study (study V), we investigated painful eccentric deltoideus and supraspinatus muscle training on a small group of patients on the waiting list for surgical treatment of subacromial impingement syndrome. After 12 weeks of training, 5 out of 9 patients were satisfied with the results of treatment and withdrew from the waiting list for surgery. In conclusion, the present studies showed good clinical results with low risks of side effects and low costs. Thus, we suggest that painful eccentric training should be tried in patients with Achilles and patellar tendinopathy before intratendinous injections and surgery are considered. For patients with chronic painful impingement syndrome, the results of our small pilot study are interesting, and stimulates to randomised studies on larger materials.

To explore the potential mechanisms of tendon degeneration, we investigated the role of c-Jun N-terminal Kinase (JNK) activation and the regulation of matrix metalloproteinase 1 (MMP1) in tendon matrix degradation under oxidative stress. JNK and MMP1 activity in samples from normal and ruptured human supraspinatus tendons were evaluated by immunohistochemistry. Real-time quantitative PCR was utilized to evaluate MMP1 mRNA expression and western blotting for MMP1 and JNK protein detection. JNK activation and increased MMP1 activity were found in the torn human supraspinatus tendon tissue, as well as in human tendon cells under in vitro oxidative stress. Inhibition of JNK prevented MMP1 over-expression in oxidative stressed human tendon cells. Results from the current study indicated that stress activated JNK plays an important role in tendon matrix degradation, possibly through upregulating of MMP1.

Surgical repair of torn rotator cuff tendons have a high rate of failure and does not address the underlying pathophysiology. Tissue engineering strategies, employing the use of multipotent progenitor cells or growth factors, represent potential therapies to improve the outcome of rotator cuff surgery. The use of glycosaminoglycan-based biomaterials in these therapies may enhance the effectiveness of cell and growth factor delivery techniques. Furthermore, understanding the cellular and molecular mediators in tendon overuse can help elucidate the causes of tendon degeneration. Thus the overall goals of this dissertation were to 1) develop heparin-based biomaterials to enhance cell pre-culture and maintain growth factor bioactivity and 2) characterize the histological and enzymatic changes in a supraspinatus tendon overuse model. To investigate the use of heparin in enhancing dynamic signaling, mesenchymal stem cells (MSCs) were encapsulated in heparin-containing hydrogels and evaluated for differentiation markers when cocultured with a small population of differentiated cells. To probe the effect of sulfation of heparin on the interactions with protein, selectively desulfated heparin species were synthesized and evaluated for their ability to bind and protect proteins. Finally, to develop a tendon overuse model that can become a test bed for testing future targeted therapeutics, an animal model was evaluated for tissue damage and protease activity. Together these studies represent a multi-pronged approach to understanding how tendon tissues become degenerative and for developing technologies to improve the biological fixation of tendon to bone in order to reduce the need for revision surgeries.