Achilles tendon injuries are considered common and have a slow, complex and ineffective natural repair process because of its low intrinsic cellularity and low vascularity (Arnaud-Franco et al. 2022). Rerupture rates after conservative treatment in acute Achilles tendon ruptures (less than 72 hours after the trauma) are similar to the group of patients undergoing surgical treatment, with the advantage of not presenting complications from the surgical wound and running the risk, even if below, from injury to the sural nerve, which is one of the complications of the procedure (Krogh et al. 2016). No significant difference was observed between the Rupture + Suture and Rupture + ADSCs groups in any of the scores used. The choice of method used in this work, which may be the factor responsible for the lack of difference between groups (Webb and Bannister 1999).
The fact of adding cell therapy to conservative treatment would make it possible for patients not to need the surgical procedure when suffering a tendon rupture and still have strength and work capacity similar to individuals without injury. The current literature about regenerative medicine in this condition has proven, even if only in animals, the specific cell differentiation capacity of ADSCs, paracrine and immunomodulatory effect by changing the phenotypic response of macrophages to tendon injury from a standard pro-inflammatory M1 phenotype for a pro-regenerative M2 phenotype in the acute phase of the injury, maintenance of the original architecture of the tendon by the arrangement of collagen fibers in the histological analysis and even in relation to the greater amount of synthesis of collagen I and III which are important components for the function tendon (Arnaud-Franco et al. 2022; Chailakhyan et al. 2021; Krogh et al. 2016; Shen et al. 2020; Vieira et al. 2014).
Correlating the histology with the ultrasound image (used in the present study), it is observed that, at 12 weeks, the tendon is already in the remodeling phase of the healing process, despite still having high cellularity and a fibrous appearance. These characteristics will give rise to aligned collagen fibers and a decrease in the number of cells around one to two years after the rupture. Perhaps for this reason, regarding the ultrasound score, the Rupture group had a lower score, as the cells were beginning to organize themselves without other factors such as the suture thread (which acts as a tutor for directing the collagen fibers) and the ADSCs which participate in tendon repair by directly contributing by differentiating into tissue-specific cell phenotypes and the production of extracellular matrix. Further clarification would have been provided if we had performed histological analysis in our study, but we were not authorized by the ethics committee to perform this procedure.
But, although there is a significant difference between the groups studied in relation to the ultrasound examination, Möller et al (2002) observed in their work with the use of Nuclear Magnetic Resonance and Ultrasound examination after conservative or surgical treatment of acute rupture of the Achilles tendon, that there was no correlation between the exam findings and the clinical parameters found (Möller et al. 2002), that is, the patients had alterations in the exams but clinically they were without symptoms, the same being observed in this work through the results found in the AOFAS and ATRS BrP scores.
The microenvironment in which ADSCs reside in vivo provides signals (secreted receptors and soluble factors for cell-cell communication, extracellular matrix, oxidative stress, and vascularization) that direct them to metabolize, self-renew, differentiate, or remain inactive. Both intrinsic cell deficits and the aging microenvironment, along with the systemic changes associated with age-associated hormonal and metabolic signals, can inhibit or alter the functions of tendon stem cells, resulting in less physical conditioning of these primitive cells and, therefore, more injuries. frequent and poor results of tendon repair (Zabrzyński et al. 2018). In this way, it is important to emphasize that the health of the individual who will receive the ADSCs is an essential factor for the cellular function after being injected.