The Collapse Of Paratenon Affect The Microenvironment Of Intrinsic Achilles Tendon Regeneration In Acute Achilles Tendon Rupture

BackgroundAcute Achilles tendon rupture is a common sports injury.With the aging population,increasing rates of obesity,and growing popularity of ball games,there has been a steady rise in the incidence of acute Achilles tendon ruptures year after year.Achilles tendon ruptures are a huge drain on medical resources.In addition,unlike fractures,Achilles tendon cannot reach the original elastic and tension state even after healing,causing irreversible impact on the patient’s ability to exercise.There is still a lot of debate about the best treatment for Achilles tendon ruptures,and both surgical and non-surgical methods have their pros and cons.How to improve the return to exercise rate and reduce complications of Achilles tendon rupture is a difficult problem to be solved.The paratendon is a highly vascularized,loose membrane-like tissue that surrounds the Achilles tendon and provides nourishment and facilitates lubrication.The paratendon is an important blood supply source of Achilles tendon,which can affect the healing of Achilles tendon.In recent years,microenvironment has become a hot topic in tissue regeneration.Various cytokines,immune cells and stem cells interact with each other to promote tissue repair.It has been shown that stem cells cannot be recruited normally even when growth factors are added after the paratendon is removed.The paratendon may be an important structure to maintain microenvironment homeostasis.Although the paratendon plays an important role in tendon regeneration,the interference of the paratendon on the tendon microenvironment is limited.In clinical work,we have found that the healing and moulding of the broken end of the Achilles tendon is not ideal in patients treated conservatively with plaster fixation.Our analysis of the underlying mechanism may be that,in traditional plaster fixation,wrapping the bandage too tightly or plantar-flexing the ankle joint may lead to the collapse and folding of the local soft tissue of the skin,causing the narrowing of the paratendon at the broken end of the Achilles tendon,interfering with the microenvironment required for the healing of the Achilles tendon and hindering the healing and shaping of the Achilles tendon.ObjectiveTo observe the influence of the collapse of the paratendon on the healing of the Achilles tendon,the animal model of the collapse of the paratendon was established,so as to proved that the collapse of the paratendon could affect the endogenous regeneration of the Achilles tendon by interfering with the microenvironment.Methods1.Preparation of 3D clampTo simulate the narrowing of the paratendon,the diameter of the paratendon was restricted by a fixed diameter clamp attached to the outside of the skin after the Achilles tendon was cut.2.Rabbits grouping24 skeletal mature New Zealand rabbits were randomly divided into 2 groups by random number table method,control group and experimental group,with 12 rabbits in each group.3.Establishment of animal models and intervationThe paratendon and skin were sutured after minimally invasive laceration of the Achilles tendon.In the experimental group,prefabricated 3D clamp.was installed outside the skin of the broken end of Achilles tendon,and external compression was used to simulate paratendon collapse.Plantar flexion 150 degrees after external fixation with plaster tube.The control group received only plaster fixation after suture.After operation,all animals were kept in a single cage with free access to food and water and free movement.After 2 weeks,all animals had their casts,sutures and 3D-printed clamps removed,allowing free ankle movement.2 weeks and 4 weeks after surgery were used as observation points to detect the healing status of Achilles tendon and perform pathological examination,anatomical observation,tissue and immunohistochemical examination.Results1.Anatomical observation and measurement showed that the broken end of the control group was connected by fresh granulation tissue,while the distal end of the Achilles tendon in some experimental groups was not completely fused with granulation tissue 2 weeks after surgery.4 weeks after surgery,the repair site of the control group was in the shape of a spindle,while that of the experimental group was in the shape of a dumbbell.Compared with the control group,the mean length of Achilles tendon in the experimental group was longer(p<0.05),the adhesion grade was more serious(p<0.05).2.Histological analysis showed that the experimental group had more inflammatory cell infiltration,disordered collagen fiber arrangement and more abundant blood vessels.3.Immunofluorescence staining showed that the signal intensity of proliferating cell nuclear antigen(PCNA)was higher and stem cell marker CD 146 was higher in the experimental group than in the control group.4.Immunohistochemistry confirmed that the intensity of vascular endothelial growth factor(VEGF)was stronger and the duration was longer in the experimental group,while the expression intensity of transforming growth factor-β1(TGF-β1)was lower.Conclusion1.Collapse of the paratendon can delay the healing of Achilles tendon,and lead to structural disorders of the cells,fibers and vessels of the healing tissue of the Achilles tendon,and further elongation of the Achilles tendon after the release of plaster fixation.2.paratendon collapse can lead to the disturbance of the expression pattern of growth factors,decreased expression of TGF-1β,increased expression of VEGF and prolonged duration during Achilles tendon repair3.The collapse of the paratendon can lead to the decrease of endogenous repair,the increase of exogenous repair,and the decrease of stem cells involved in repair,dominated by fibroblasts.