Comparison of different rotator cuff repair techniques
Arthroscopic rotator cuff repair is one of the most commonly used methods for the treatment of rotator cuff tears, but the best repair method is still under discussion. The anatomical characteristics of the footprint region of the rotator cuff have been clearly addressed in previous related studies[16–19], As a guideline for surgical repair, adequate footprint coverage reduces gap formation, facilitates tendon-to-bone healing, and allows the repaired rotator cuff to have strong biomechanical properties and reduces the risk of re-tear. Biomechanical analysis: excessive contact pressure can lead to excessive stress in the tendon, affecting the blood supply of the tendon, increasing the failure rate. Therefore, we not only need to restore the footprint area of the rotator cuff as much as possible, but also to reduce the stress in the tendon as much as possible, so that the stress in the tendon is more uniform and avoid the concentration of stress. Compared to the single-row technique, the double-row technique restores a larger footprint area with higher stiffness and ultimate failure load[20, 21] Suture bridge technology, on the other hand, is biomechanically superior to single and double row techniques. However, for larger rotator cuff tears, the suture bridge technique does not cover enough, resulting in the formation of gaps, insufficient footprint coverage, and the production of "dog ears" and "beak-like" deformities. Therefore, we propose a modified "fishnet" suture bridge technique, and the special fishnet suture distribution can provide a wider coverage area, make the tendon and footprint area fully contact, restore the original footprint as much as possible, effectively avoid deformity in the repair of larger rotator cuff tears, and do not increase the number of anchors, but also avoid the selection of more complex surgical methods, which are easy to operate, economical and practical. However, there is no research on the stress distribution characteristics of this surgical method, so this study establishes the finite element models of the classical suture bridge technique and the modified "fishing net" suture bridge technique by finite element analysis, and carries out mechanical analysis on the two surgical methods.
Advantages of Selected Finite Element Analysis
We chose finite element analysis to replace traditional animal or cadaveric experiments because finite element analysis can avoid many limitations caused by traditional laboratory experiments, such as ethical problems, specimen number problems and so on. Finite element method has the advantage of simpler and more economical, and can observe the stress distribution characteristics of the model more intuitively and graphically. Previous reports have also confirmed that finite element analysis is of great value in rotator cuff biomechanical studies and is a practical method[22–25]}。
Discussion on mechanical difference between two surgical methods
The stress distributions of the two procedures have similar characteristics, as shown in Fig. 5. The repaired rotator cuff stresses were mainly concentrated at the junction with the humeral head, i.e., the anterior portion of the supraspinatus. Whereas in the anterior part of the supraspinatus, stress was mainly concentrated around the suture. This has similar results to Matsuhashi et al in studying stress distribution in normal rotator cuff tissues[26], That is, the strongest part of the supraspinatus is located in the anterior third, which plays an important role. For the repaired rotator cuff, the stress is still mainly concentrated in the anterior part, so how to better repair the anterior part of the tendon has become the key to surgery.
According to the mechanical analysis, the stress of supraspinatus increased gradually with the increasing of shoulder abduction angle in both models, which indicated that supraspinatus played an important role in shoulder abduction. By comparing the peak stress, it can be seen that the peak stress of supraspinatus in the "fishing net" suture bridge technique is smaller than that in the classical suture bridge at the same angle of shoulder abduction, with a maximum difference of 36.6%. Similar results were obtained in the comparison of mean stress, where the "fisher-net" suture bridge technique resulted in significantly smaller mean stress than the classic suture bridge technique at shoulder abduction of 20 °, 25 °, and 30 ° (p < 0.05). When shoulder abduction was 5 °, 10 °, and 15 °, the difference was not statistically significant (p > 0.05), but the value of mean stress remained lower in the "fishnet" suture bridge technique. The mean stress difference was highest at 30 ° of abduction, reaching 9.66 MPa.
The results showed that the more extensive suture distribution in the modified "fishing net" suture bridge technique could make the tendon and humeral footprint more fully contact, and the stress distribution of the tendon was more uniform, avoiding local stress concentration. It is shown that the modified "fishing net" suture bridge technique is superior to the classical suture bridge in biomechanical angle. More adequate tendon to bone contact and more dispersed stresses within the tendon may facilitate tendon healing and reduce the risk of re-tearing.
Test Limitations
① Because the mechanical environment of the human body is complex, we only compared the internal stress distribution of the tendons between the two surgical methods by finite element analysis, and then we still need to compare the biomechanical properties such as stiffness and ultimate failure load through laboratory related studies.
② In the next step, it should be combined with clinical practice to compare the shoulder joint function score of patients after the two surgical methods and apply the study to examples in terms of tear rate.