DOI: https://doi.org/10.21203/rs.3.rs-2031714/v1
The classic suture bridge technique is one of the most commonly used techniques for the treatment of rotator cuff tears, but there are still some defects when repairing larger rotator cuff tear
The CT and MRI scan data of the shoulder joint of a healthy adult were imported into Mimics 21.0, 3-matic 11.0, Geomagic studio 2012 and UG NX 9.0 to establish the models of the two surgical methods in turn, and then imported into Hypermesh 2019 to complete the pretreatment operations such as material endowment, meshing, applied load and boundary conditions. Finally, Abaqus 6.14 software was imported to compare the characteristics of stress distribution, peak stress, and mean stress of the two surgical methods at 5 °, 10 °, 15 °, 20 °, 25 °, and 30 ° of simulated shoulder abduction.
At shoulder abduction of 5 °, 10 °, 15 °, 20 °, 25 °, and 30 °, the stress in both surgical models was mainly concentrated around the tendon passed by the suture, but the peak stress in the supraspinatus muscle of the modified "fishing net" suture bridge technique was less than that of the classical suture bridge. And when shoulder abduction was 20 °, 25 °, and 30 °, the mean stress of the modified "fishnet" suture bridge technique was significantly smaller than that of the classical suture bridge technique, and the difference was statistically significant (p < 0.05). At 5 °, 10 °, and 15 ° of abduction, the difference was not statistically significant (p > 0.05), but the values remained lower than in the classic suture-bridge technique.
The special suture distribution in the modified "fishing net" suture bridge technique can provide better anatomical coverage without increasing the number of anchors, effectively avoid the generation of deformity, and has a more uniform stress distribution inside the tendon, which is biomechanically superior to the classical suture bridge technique and can be used as a technical means in the repair of large rotator cuff tears.
Rotator cuff injury is a common disease of the shoulder joint that can lead to pain and dysfunction of the shoulder joint, and shoulder pain is the third most common symptom in the musculoskeletal system of the body after back and neck pain[1]。According to Minagawa et al., health examinations were performed in a group of people with a mean age of 69.5 years and the incidence of rotator cuff tears reached 22.1%[2]。Aging is one of the important factors leading to rotator cuff injury, and the older the age, the more severe the rotator cuff injury[2–5], This is associated with degenerative changes in rotator cuff tissue[6]。Conservative treatment may be preferred for rotator cuff injury, but because the rotator cuff itself does not heal spontaneously, in some cases, symptoms do not improve significantly after conservative treatment and thus continue to affect shoulder joint function, surgical treatment is required at this time, of which arthroscopic rotator cuff repair is one of the main surgical options, including single-row, double-row and suture bridge techniques[7]。The suture bridge technique is biomechanically superior to the other two techniques and restores the native anatomical footprint of the rotator cuff as much as possible[8], Become one of the most commonly used technical tools.
However, suture bridge techniques are still insufficient, such as "dog ear" and "beak-like" deformities often present in the repair of large rotator cuff injuries [9], Results in incomplete tendon coverage over footprint and possible tendon impingement with acromion at deformity[10]。Solutions to this problem include increasing the number of anchors or using other techniques, such as superior capsular reconstruction and mesh techniques. The former increases the financial burden on patients, and the latter increases the difficulty of surgery. Therefore, a modified "fishing net" suture bridge technique is proposed in this paper, which can provide better anatomical coverage through special wiring methods without increasing the number of anchors. In this technique, two double-suture anchors are used in the inner row, leaving eight tails, and the outer row is eight-line crossed to form a "fishing net" coverage through two outer row anchors. In the repair of large rotator cuff injuries, more uniform anatomical coverage can be provided without increasing the financial burden on patients, and "dog ear" deformity can be effectively avoided. And we hypothesized that this technique has superior biomechanical properties and can be a reliable technique in rotator cuff repair. A schematic diagram of the modified "fishing net type" suture bridge is shown in Figs. 1 and 2.
To investigate biomechanical differences between this technique and the classic suture bridge technique. In this study, three-dimensional finite element (FE) analysis was used to compare the biomechanical differences between the two suture techniques in a supraspinatus repair model. We hypothesized that the modified "fishing net" suture bridge technique would have a more uniform stress distribution, avoid stress concentration in the tendon, and would be expected to reduce the risk of re-tear。
Model development
A 45-year-old healthy adult male volunteer, 175 cm in height and 70 kg in weight, with no previous history of shoulder trauma surgery was selected. Volunteer left shoulder joints were scanned using 64-slice spiral CT (slice thickness 0.625 mm) and 3.0T nuclear magnetic resonance (slice thickness 2.5 mm), and the data obtained from the scans were exported in DICOM format.
Establishment of shoulder joint bony structure: Import the CT data obtained above into Mimics 21.0 software in DICOM format, use the function of threshold segmentation, set the threshold range of bony structure, with the minimum of 226 HU and the maximum of 1676 HU, obtain the bony structure of shoulder joint and its surrounding, and then use the function of region growth to extract the scapula, humerus and clavicle we want, so that the shoulder joint bony structure is extracted
Establishment of rotator cuff soft tissue: Generally, the acquisition of rotator cuff soft tissue depends on MRI data. Since the soft tissue cannot be directly obtained through the threshold setting, it is necessary to manually adjust and edit the mask to separate the target soft tissue, and perform the unified coordinate axis assembly for the bony structure obtained by CT and the soft tissue structure obtained by MRI.[11, 12](Fig. 3).
The whole shoulder joint model was imported into the reverse engineering software Geomagic studio 2012 in STL format, and the model was optimized for noise reduction, repair, and removal of nails using multiple functions under the "polygon" toolbar to generate NURBS surfaces, which were finally exported in STEP format. Two surgical models were designed using UG NX 9.0 software and the suture anchors were simplified to cylinders. As shown in Fig. 4. Preprocessing of the analysis was done using Hypermesh 2019 software and finally solved with quasi-static analysis of Abaqus/Explicit.
Material properties and meshing
Two sets of models were imported into Hypermesh 2019 in STEP format to assign material properties to the models. Because bone stiffness is much greater than soft tissue, bony structures were assumed as rigid bodies in this study for simplifying calculations[13], The remaining parts are assigned different moduli of elasticity and Poisson 's ratios depending on the material[14, 15], See Table 1 for details.
|
Material |
Elastic Modulus |
Poisson 's ratio |
|---|---|---|
|
Tendon |
168 |
0.49 |
|
Suture |
591 |
0.45 |
|
Anchor |
3850 |
0.38 |
Because the bones were simplified to rigid bodies, mesh types R3D3 and R3D4 were chosen with a mesh size of 1.5 mm. The remaining construct mesh type was C3D4 with tendon mesh size of 1 mm, anchor 0.1 mm and suture 0.05 mm. The classic suture bridge technique model yielded a total of 146,091 nodes and 531,258 elements. The fishnet model yielded a total of 207,697 nodes and 635,713 units.
Boundary Conditions and Load Application
Set the distal end of each muscle of the rotator cuff to the skeletal junction for a "tie" binding and all remaining external surfaces for a "General Contact" universal contact with a coefficient of friction of 0.2. The humeral head is treated as a sphere, and the center of the sphere is found to rotate the humerus around the center of the sphere to complete the abduction movement of the shoulder joint. Constraint the scapula and clavicle with all degrees of freedom, constrain the humerus 1–4 and 6th degrees of freedom, rotate the humerus around the Y-axis at the 5th degree of freedom, and set the rotation angle to 30 °, so as to complete the movement of shoulder joint abduction 0–30 °. At this point, the pre-processing of the finite element model is completed, and the two finite element models are shown in Fig. 5. The inp files generated by Hypermesh were imported into Abaqus 6.14 to analyze the biomechanical properties of both surgical models。
Evaluation indicators
① Distribution of stress cloud pattern of supraspinatus muscle and comparison of peak stress and mean stress of supraspinatus muscle in two surgical models at shoulder abduction of 5 °, 10 °, 15 °, 20 °, 25 ° and 30 °
② Ten representative nodes of supraspinatus muscle in the above cloud pattern were selected, and the mean values of nodes in each group were calculated by spss26.0 software for comparison
Statistical analysis
Statistical analysis was performed using SPSS 26.0 software for statistical analysis of the data. The results were expressed as mean ± standard deviation (x ± s) and independent sample t-test was used; P < 0.05 was considered statistically significant.
Mises Stress Distribution and Peak Stress Comparison
The distribution of Mises stress in the supraspinatus muscle at 5 °, 10 °, 15 °, 20 °, 25 °, and 30 ° of shoulder abduction in the two surgical models is shown in Fig. 6. During shoulder abduction from 0 to 30 degrees, the stress was mainly concentrated at the junction of supraspinatus and humeral head, that is, the stress was the largest in the footprint area, and with the increase of shoulder abduction angle, the stress of supraspinatus gradually increased in the two models, and reached the maximum when the abduction angle was 30 °, and the maximum stress occurred around the position where the suture passed through the tendon. At shoulder abduction 5 °, 10 °, 15 °, 20 °, 25 ° and 30 °, the peak stress of the modified "fishing net" suture bridge model was less than that of the classical suture bridge model. Taking 30 ° as an example, the peak stress of the modified "fishnet" suture bridge model is 112.10 MPa, which is smaller than the peak stress value of 136.80 MPa of the classical suture bridge model as shown in Table 2。
|
Shoulder abduction angle |
Classic Suture Bridge |
modified “fishing net” suture bridge |
|---|---|---|
|
5° |
43.33 |
37.98 |
|
10° |
68.08 |
50.00 |
|
15° |
91.60 |
77.01 |
|
20° |
105.10 |
94.07 |
|
25° |
129.00 |
105.70 |
|
30° |
136.80 |
112.10 |
Mean stress measurements in two surgical models at different angles
Ten representative nodes in each cloud map were taken, and the mean values of nodes in each group were calculated by spss26.0 software for comparison. A comparison of the mean stress between the two surgical models at different shoulder abduction angles is shown in Table 3. As can be seen, the mean stress of the supraspinatus muscle gradually increased in both groups of models as the shoulder abduction angle increased. However, the average stress of "fishing net t" suture bridge technique is smaller than that of classical suture bridge at all angles. And when the shoulder abduction angle was 20 °, 25 °, and 30 °, the mean stress of the "fishing net" suture bridge technique was significantly smaller than that of the classical suture bridge, and the difference was statistically significant (p < 0.05). It is evident that the "fishing net" suture bridge technique resulted in significantly lower mean stresses at all angles, with the largest difference in mean stresses at 30 degrees shoulder abduction, 9.66 MPa.
|
Abduction angle |
Mean stress |
T |
P |
|
|---|---|---|---|---|
|
Classic Suture Bridge |
modified “fishing net” suture bridge |
|||
|
5° |
21.34 ± 5.69 |
16.80 ± 5.73 |
1.78 |
P＞0.05 |
|
10° |
24.98 ± 7.30 |
24.39 ± 5.26 |
0.21 |
P＞0.05 |
|
15° |
35.93 ± 6.60 |
32.45 ± 5.39 |
1.29 |
P＞0.05 |
|
20° |
49.87 ± 5.97 |
44.24 ± 2.02 |
2.83 |
P＜0.05 |
|
25° |
55.88 ± 7.07 |
48.13 ± 3.56 |
3.09 |
P＜0.05 |
|
30° |
65.95 ± 10.28 |
56.29 ± 4.36 |
2.74 |
P＜0.05 |
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.
The special suture distribution in the modified "fishing net" suture bridge technique, without increasing the number of anchors, can provide better anatomical coverage, effectively avoid the generation of deformity, and has a more uniform stress distribution inside the tendon, which is biomechanically superior to the classical suture bridge technique and can be used as a technical means in the repair of large rotator cuff tears.
1.Ethical Approval
This declaration is “not applicable”
2.Competing interests
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3.Authors' contributions
Wang completed the conception and design, writing and submission of the article as the first author.
Gao completed the design of figures and tables and suggested modifications to the article
Pan, as the corresponding author, provided guidance and funding throughout the study
4.Funding
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5.Availability of data and materials
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