Rotator Cuff Tendon Repair after Injury in Hyperlipidemic Swine Decreases Biomechanical Properties

Understanding Fibrous Tissue in the Effective Healing of Rotator Cuff Injury

The rotator cuff is a crucial group of muscles and tendons in the shoulder complex that plays a significant role in the stabilization of the glenohumeral joint and enabling a wide range of motion. Rotator cuff tendon tears can occur due to sudden injuries or degenerative processes that develop gradually over time, whether they are partial or full thickness. These injuries are common causes of shoulder pain and functional impairment, and their complex nature highlights the essential role of the rotator cuff in shoulder function. Scar formation is a crucial aspect of the healing process initiated following a rotator cuff tendon tear, but excessive fibrous tissue development can potentially lead to stiffness, discomfort, and movement limitations. Age is a critical risk factor, with the prevalence of these tears increasing among older individuals. This comprehensive review aims to delve deeper into the anatomy and injury mechanisms of the rotator cuff. Furthermore, it will inspect the signaling pathways involved in fibrous tissue development, evaluate the various factors affecting the healing environment, and discuss proactive measures aimed at reducing excessive fibrous tissue formation. Lastly, this review identifed gaps within existing knowledge to advance methods for better management of rotator cuff tendon injuries.

Chronic Adaptation of Achilles Tendon Tissues upon Injury to Rotator Cuff Tendon in Hyperlipidemic Swine

The biomechanical properties of the tendon are affected due to the changes in composition of the tendon extracellular matrix (ECM). Age, overuse, trauma and metabolic disorders are a few associated conditions that contribute to tendon abnormalities. Hyperlipidemia is one of the leading factors that contribute to the compromised biomechanical. Injury was made on infraspinatus tendon of hyperlipidemic swines. After 8 weeks (i) infraspinatus tendon from the injury site, (ii) infraspinatus tendon from the contralateral side and (iii) Achilles tendon, were collected and analyzed for ECM components that form the major part in biomechanical properties. Immunostaining of infraspinatus tendon on the injury site had higher staining collagen type-1 (COL1A1), biglycan, prolyl 4-hydroxylase and mohawk but lower staining for decorin than the control group. The Achilles tendon of the swines that had injury on infraspinatus tendon showed a chronic adaptation towards load which was evident from a more organized ECM with increased decorin, mohawk and decreased biglycan, scleraxis. The mechanism behind the collagen turnover and chronic adaptation to load need to be studied in detail with the biomechanical properties.

Hyperlipidemia Induced Pathological Changes with no Effect in Biomechanical Properties in the Achilles Tendon of Young Swine

Hyperlipidemia is linked to atherosclerosis and various diseases. Its strong association with Achilles tendinopathies and xanthomas affects tendon properties through lipid deposition in tendon tissue. We examined the impact of hyperlipidemia on the biomechanical properties of the swine Achilles tendons. Swines were fed a high-cholesterol-high-fat diet to induce hyperlipidemia, and their Achilles tendons were collected and examined for biomechanical properties. The ultimate tensile strength, modulus of elasticity and viscoelastic properties did not exhibit significant differences between hyperlipidemic and control swines. H&E and pentachrome staining revealed extracellular matrix (ECM) disorganization and cellular infiltration in the hyperlipidemic swines, highlighting a marked difference between the control and hyperlipidemic groups. These results suggest hyperlipidemia in young swines alters the tendon composition and may contribute to weak biomechanical properties with time.

Mitochondrial Biogenesis as a Therapeutic Target for Rotator Cuff Tendon Tears

Rotator Cuff Injuries (RCI) are highly prevalent and characterized by shoulder pain, restricted shoulder movement, and difficulty with overhead activity, radiating pain in the deltoid muscle, and atrophy of the rotator cuff muscles. Increasing age, hand dominance, smoking, hypertension, hyperlipidemia, and obesity are common risk factors. Chronic inflammation plays a critical role in the underlying pathogenesis. RCI accounts for massive healthcare expenditure costing about $15,000 per repair, and over 4.5 million physician visits per year, however, there is still no therapeutic target to improve clinical outcomes. Mitochondrial biogenesis in response to inflammatory stimuli supports increased cellular energy requirements, cell proliferation, and differentiation. This suggests that mitochondrial biogenesis may play a role in healing RCI by serving as a protective factor against free oxygen species and promoting homeostasis within the rotator cuff. There is evidence highlighting the potential therapeutic benefits of mitochondrial biogenesis in various inflammatory diseases, but no study explored the role of mitochondrial biogenesis in rotator cuff tears. Since hypercholesterolemia is a risk factor for RCI, we investigated the effects of hypercholesterolemia on the expression of PGC-1α, a marker of mitochondrial biogenesis, in rotator cuff muscle. The findings revealed an increased gene and protein expression of inflammatory mediators and PGC-1α, suggesting enhanced inflammation and increased mitochondrial biogenesis due to hypercholesterolemia. Additional studies are warranted to further investigate the chronic effect of hyperlipidemia induced RCI to elucidate the cause of insufficient mitochondrial biogenesis unable to protect the rotator cuff and the therapeutic effect of promoting mitochondrial biogenesis.