Abstract
Objective
Greater tuberosity (GT) fragments were communicated, and additional techniques to increase the GT fragment stability after the locking plate fixation was necessary. This study aimed to analyze the reinforcement effects on the anterior‐avulsion GT fragment in Neer three‐part proximal humeral fractures (PHFs) using transosseous suture and suture anchor techniques.
Methods
Eighteen fresh‐frozen human cadaveric shoulder specimens were used in the study. Standardized fracture of the GT and surgical neck was created in 18 human cadaveric proximal humerus. The GT fragments were reinforced with transosseous suture (TS), suture anchor (SA), and suture in addition to the PHILOS plate fixation. The fixed humerus was tested by applying static loading to the supraspinatus tendon. Load forces and fragment displacement were evaluated by a biomechanical testing machine, and the load to 3‐ and 5‐mm displacements, load to failure, and mode of failure were recorded for all specimens. Nonparametric variables were examined by the Kruskal–Wallis test, and the Bonferroni post hoc test was used to analyze the mean loads to create 3‐ and 5‐mm displacements as well as the failure load.
Results
The age, female proportion, and bone mineral density showed no statistically significant differences between the three groups. The mean loading force to create 3‐mm and 5‐mm displacement in the TS group (254.9 ± 77.4, 309.6 ± 152.7) were significantly higher than those in the suture group (136.1 ± 16.7, 193.4 ± 14.5) (P = 0.024, P = 0.005). For the SA group, the force to create 3‐ and 5‐mm displacement (204.3 ± 60.9, 307.8 ± 73.5) were comparable to those in the TS group (P = 0.236, P = 0.983). Moreover, the loading force to failure in the TS group (508.6 ± 217.7) and SA group (406.6 ± 114.9) was significantly higher than that in the suture group (265.9 ± 52.1) (P = 0.021, P = 0.024). In the TS group, three failed due to tendon‐bone junction rupture; bone tunnel broken occurred in two specimens; suture rupture could also be seen in one specimen. All specimens in the suture group failed because of suture rupture. In the SA group, three specimens failed due to suture rupture; two failed secondary to tendon‐bone junction rupture; and one failed because of shaft fracture.
Conclusions
Transosseous suture is a new type of reinforcement for GT fragment in Neer‐three part PHFs. The transosseous suture was superior to the suture only in the reinforcement of the anterior‐avulsion GT fragment of Neer three‐part PHFs, and it had comparable biomechanical strength to the suture anchor.
Keywords: Greater tuberosity fragment, Proximal humeral fracture, Suture anchor, Transosseous suture
The image shows the mean load to 3 mm, 5 mm of displacement and failure among the suture only, suture anchor, and transosseous suture groups. The transosseous suture was superior to the suture only and had comparable biomechanical strength to the suture anchor in the reinforcement of the anterior‐avulsion GT fragment of Neer three‐part PHFs.
Introduction
Greater tuberosity (GT) fragments are often involved in proximal humeral fractures (PHFs), which commonly occur in elderly people with osteoporosis and young people suffering from high energy. 1 Isolated GT fractures account for approximately 19% of proximal humeral fractures, and 30% of GT fractures are caused by anterior shoulder dislocation. 1
Surgical techniques are different based on the morphology of isolated GT fractures, and clinical outcomes are usually satisfactory, 2 however, the GT fragments in the Neer 3 and 4 part PHFs are often displaced or malunited. 3 Currently, the widely used surgical methods include locking plate fixation, screw, and suture anchor. 4 We previously found that GT fractures of Neer three‐part PHFs were relatively comminuted, and GT fragments could be classified as anterior‐split, posterior‐split, complete‐split, anterior‐avulsion, and posterior‐avulsion types based on their morphology and location. The extent of GT fragment coverage provided by the locking plate differed in various fragment types, and the locking plate alone could not fully cover the anterior‐avulsion and posterior type fragments.
A previous study reported that the additional rotator cuff suture could not enhance the stability of the GT fragment and prevent displacement. 5 It proved that if the GT fragment could not be effectively fixed by the plate, the reinforcement with only the tension‐reducing suture could easily lead to fixation failure. The arthroscopic double‐row suture anchor fixation technique has been widely used in the treatment of comminuted, displaced GT fracture. 6 , 7 Concerning its biomechanical property, it could be used in the GT fragment reinforcement as well. However, the suture anchor technique needed relatively high bone mineral density to hold the anchor. In patients with severe osteoporosis around the humeral head, the anchor would easily be pulled out. In addition, humeral head bone loss was commonly seen in PHFs, in which the suture anchor could not be drilled in. In consequence, the bone tunnel could be used as a promising alternative to the suture anchor to reinforce the GT fragment in cases with severe osteoporosis and obvious humeral head bone loss.
This study aimed to compare the reinforcement effects on the anterior‐avulsion GT fragment in Neer three‐part PHFs using: (i) suture and suture anchor techniques; (ii) suture and transosseous suture techniques; and (iii) suture anchor and transosseous suture techniques. Therefore, a biomechanical human cadaveric model that applied forces of the superior rotator cuff on the GT fragment was established. The hypothesis for this study was that the transosseous suture was comparable to the suture anchor technique.
Materials and Methods
Ethical Approval
This bio‐mechanical study using cadaveric specimens was exempted from ethical approval by the Peking University People's Hospital Ethical Committee.
Specimen Preparation
Testing was performed using 18 fresh‐frozen human cadaveric shoulder specimens without obvious rotator cuff injury or GT fracture. The humerus was dissected from the specimens with preserved rotator cuff muscle, and all soft tissues were resected from the humerus. The infraspinatus remained intact and attached to humerus. Specimens were thawed at room temperature 24 h before testing.
Bone mineral density (BMD) measurement (dual‐energy X‐ray absorptiometry) was performed for each specimen to assess bone quality at the site of the GT area. According to our previous study, a standardized anterior‐avulsion GT fragment with 1 × 1 cm around the supraspinatus footprint was created. Another fracture line oriented 90o to the humeral shaft was created around the surgical neck. Specimens were randomly assigned to the transosseous suture (TS) group (n = 6), suture anchor (SA) group (n = 6), and suture group (n = 6). All fixation constructs were completed by a single orthopedic surgeon.
Fixation Configurations
Suture Group
Two sutures (Orthocord No. 2) were passed through the tendon‐bone junction. The plate was fixed at 8 mm below the GT superior edge and 4 mm behind the bicipital groove. Sutures were knotted through the designated holes in the plate (Fig. 1).
Fig. 1.
Suture fixation configuration
Suture Anchor (SA) Group
One double‐loaded suture anchor (Mitek 5.0 Titanium, Orthocord No. 2) was inserted at the angle of 45 o on the articular edge of the humeral head. Two sutures were passed through the rotator cuff attached to the GT fragments and were tied. Two suture limbs from the anchor were threaded through the suture hole of the PHILOS locking plate and were knotted (Fig. 2).
Fig. 2.
Suture anchor fixation configuration
Transosseous Suture (TS) Group
Three bone tunnels, 5 mm apart, were drilled from the fracture site to the edge of the humeral head with 45o in the coronal plane. Two sutures (Orthocord No. 2) were passed through the bone tunnels and the tendon‐bone junction. Sutures were knotted through the designated holes in the PHILOS locking plate (Fig. 3).
Fig. 3.
Transosseous suture fixation configuration
Biomechanical Testing
The shaft was positioned in the custom‐made jig, which was fixed horizontally on the table of the testing machine (AG‐X; Shimadzu Corp., Tokyo, Japan) (Fig. 4). The supraspinatus tendon was sutured to a nylon cord connected to the testing system. Each fixation construct was measured in 6 specimens. The loading pattern followed the previous protocol, 8 for which a 50 N preload was set, then followed with a load speed of 5 mm/s until construct failure. Two aligned markers were made above and below the GT fracture line to measure displacement. A digital camera recorded the test until construct failure, and an independent researcher blinded measured GT displacements. Load to 3‐ and 5‐mm displacements, load to failure, and mode of failure were recorded for all specimens. Failure was considered as a sudden decrease in the load–displacement curve, fracture of the humeral neck or shaft, anchor loosening, suture rupture, fracture of the bone tunnel, or 20‐mm displacements of the GT.
Fig. 4.
Biomechanical testing setup
Statistical Analysis
Statistical analysis was performed with SPSS (IBM Corp, Armonk, NY, USA). Nonparametric variables were examined by the Kruskal–Wallis test, and the Bonferroni post hoc test was used to analyze the mean loads to create 3‐ and 5‐mm displacements as well as the failure load. Statistical significance was set as P < 0.05.
Results
The age, female proportion, and bone mineral density showed no statistically significant differences between the three groups (P = 0.24, P = 1.00, P = 0.31) (Table 1).
TABLE 1.
Characteristics of specimen in three testing groups
| Suture group (n = 6) | Suture anchor group (n = 6) | Transosseous suture group (n = 6) | P | |
|---|---|---|---|---|
| Age, mean (SD) | 76.1 (10.3) | 75.5 (12.4) | 78.2 (8.2) | 0.24 |
| Female, n (%) | 5 (83.3%) | 5 (83.3%) | 5 (83.3%) | 1.00 |
| BMD, g/cm2 mean (SD) | 0.58 (0.2) | 0.56 (0.3) | 0.58 (0.2) | 0.31 |
Load to 3‐, 5‐mm Displacement
The mean loading force to create 3‐mm and 5‐mm displacement in the TS group (254.9 ± 77.4 and 309.6 ± 152.7) were significantly higher than those in the suture group (136.1 ± 16.7, 193.4 ± 14.5) (P = 0.004, P = 0.009). They were 204.3 ± 60.9 and 307.8 ± 73.5 in the SA group, significantly higher than those in the suture group (P = 0.024, P = 0.005). The differences between the SA and TS group were not statistically significant (Table 2, Fig. 5).
TABLE 2.
Loading forces to 3‐, 5‐mm GT displacement and fixation failure (N)
| Suture group | Suture anchor group | Transosseous suture group | |
|---|---|---|---|
| Load to 3 mm displacement (mean ± SD) | 136.1 ± 16.7 | 204.3 ± 60.9 a | 254.9 ± 77.4 b |
| Load to 5 mm displacement (mean ± SD) | 193.4 ± 14.5 | 307.8 ± 73.5 a | 309.6 ± 152.7 b |
| Load to failure (mean ± SD) | 265.9 ± 52.1 | 406.6 ± 114.9 a | 508.6 ± 217.7 b |
The difference between the suture technique and suture anchor group was statistically significant
The difference between the suture technique and suture on bone group was statistically significant.
Fig. 5.
Comparison of mean load to 3, 5 mm of displacement and failure among the 3 fixation constructs. DISP, displacement. *: The difference between the suture technique and suture anchor group was statistically significant. **: The difference between the suture technique and transosseous suture group was statistically significant
Load to Failure
Moreover, for the load to failure, the force in the TS group (508.6 ± 217.7) and SA group (406.6 ± 114.9) were significantly higher than that in the suture group (265.9 ± 52.1) (P = 0.021, P = 0.024). The difference between the SA and TS was not statistically significant (Table 2, Fig. 5).
Failure Mode
In the TS group, three failed due to tendon‐bone junction rupture; bone tunnel broken occurred in two specimens; suture rupture could also be seen in one specimen. All specimens in the suture group failed because of suture rupture (Fig. S1). In the SA group, three specimens failed due to suture rupture; two failed secondary to tendon‐bone junction rupture (Fig. S2); one failed because of shaft fracture.
Discussion
Increasing the biomechanical strength of anterior‐avulsion GT fragment in the Neer three‐part PHFs is pivotal to avoiding postoperative displacement and improving shoulder joint function. This study aimed to compare the biomechanical effect on reinforcement of the anterior‐avulsion GT fragment of Neer three‐part PHFs using the transosseous suture and suture anchor techniques. The results showed the transosseous suture had the highest loading force of 3‐mm displacement, 5‐mm displacement, and failure load, and it had comparable biomechanical strength to the suture anchor.
Strengths of the Suture Anchor Technique in Reinforcement of GT Fragment
In a previous study, we found the fracture line morphology of GT fragments of Neer three‐part PHFs was in a fan shape. GT fragments could be classified based on their location and morphology. The extent of GT fragment coverage provided by the locking plate differed in various fragment types. The anterior‐avulsion, posterior‐avulsion, and posterior‐split types were defined as “risky types” for postoperative displacement due to insufficient plate coverage. Deforming forces from the rotator cuff muscles could lead the GT fragment displaced and malunited. In a biomechanical study, Bono et al. 9 showed that displaced GT broke the balance of force couple required to elevate the arm. Insufficient mechanical stability of the tuberosities may generate poor clinical outcomes. Therefore, we should pay more attention to the GT fragment fixation to pursue a better shoulder function.
The GT fragments were usually reinforced with non‐absorbable sutures passing through the rotator cuff tendon and the suture hole at the tip of the plate in clinical practice. Although the rotator cuff was strengthened by the non‐absorbable suture based on the parachute theory, it provided the stress along the direction of the rotator cuff to resist the traction of the rotator cuff muscles and could not compress the GT fragment to the footprint area. In the rehabilitation exercises, the deforming forces from the rotator cuff could cause the secondary displacement of the GT fragment. Like the double row suture anchor in rotator cuff repair surgery, the suture anchors could also be used to reinforce the superior or posterior GT fragment of Neer three‐part PHFs that could not be covered by the plate. The anchor suture technology could provide forces perpendicular to the direction of deforming forces and compress the GT fragment to the footprint area to avoid secondary displacement.
Previous studies had tested various techniques to enhance the biomechanical stability of the isolated GT fragment. A biomechanical study, comparing the single versus double‐row suture anchor fixation for isolated GT fracture, showed that the load to failure was 649 N ± 176 in the double‐row group versus 490 N ± 145 in the single row group. 10 The load to failure in the single row group was similar to the suture anchor and the transosseous suture group in our study.
Failure Mode
Suture rupture was the main failure mode in the suture technique group. In this study, we used the Orthocord No. 2 suture, which has enough biomechanical strength and is widely used in rotator cuff repair surgery. 11 , 12 In the suture technique group, we assumed that the stress concentration was mainly located in the plate suture hole, which not only stretched the suture, but also cut the suture, accelerating the suture failure. In the suture anchor and transosseous suture, we made a hypothesis that the stress mainly concentrated in the tendon‐bone junction conferred by the anchor and the bone tunnel, which explained that tendon‐bone junction tear was one of the main failure modes.
Transosseous Suture Is a Good Candidate to the Suture Anchor
In our study, the transosseous suture had comparable biomechanical strength to the suture anchor, and they were both superior to the suture. For patients with severe osteoporosis, the suture anchor could be easily pulled out by the deforming forces due to insufficient bone mineral density and could not be applied in patients with great bone loss in the humeral head area. For the transosseous suture, a relatively abundant fracture bed was a prerequisite to drilling bone tunnels to strengthen the GT fragment. Besides, the transosseous suture was more suitable in obviously displaced GT fragment, in that case, the superior capsule and cuff were torn, and it was easy to create the bone tunnel. For patients with intact superior capsule and cuff, the GT fragment usually displaced a little and the only suture could support enough mechanical stability. In addition, from a cost‐effectiveness perspective, the transosseous suture technique could save the expenses of an implant.
Porcine models were commonly used in the biomechanical studies of the GT fracture, which would have different bone anatomy and properties. 8 In our study, we used frozen human cadaveric models. Although the mean age of those shoulder specimens was 76 years old, their BMD (0.56 g/cm2) was comparable to that (0.68 g/cm2) reported in a previous study. 13
Strengths and Limitations
Our study compared the reinforcement of three different suture techniques for GT fragment, and concluded that transosseous suture had comparable effect to the suture anchor. The study still had some limitations. We used the human cadaveric model rather than the sawbones, which had uniform bone and rotator cuff properties. Also, it showed that shoulder abduction affected the biomechanical strength of the fixation constructs for isolated GT fragments in a biomechanical study. The mean forces to create 3‐ and 5‐mm displacements at 45° were greater than those at 0° using the suture bridge technique. 14 In our study, we only tested the biomechanical property of the suture anchor and transosseous suture at 0°, and data about various shoulder abductions was lacking. Also, finite element analysis, showing stress distribution of suture anchor and transosseous suture in GT fragment fixation, could be used in future study.
Conclusion
The suture anchor showed superior biomechanical stability to the suture techniques in GT fragment fixation. The suture rupture was the common reason for fixation failure. Also, the transosseous suture had comparable performance in loading force of 3‐mm displacement, 5‐mm displacement, and failure load compared with the suture anchor, and is a good candidate to the suture anchor in clinical practice.
Author Contributions
Model establishment, biomechanical test and data record: Jiabao Ju, Mingtai Ma, Yichong Zhang, Zhentao Ding; Study design and interpretation of the data: Zhongguo Fu and Jianhai Chen. All authors discussed the results and contributed to the final manuscript.
Informed Consent to Participate
The informed consent form was exempted in this bio‐mechanical study.
Supporting information
Supplementary Figure 1. Suture rupture in the suture group.
Supplementary Figure 2. Tendon‐bone junction rupture in the SA group.
Acknowledgment
We gratefully acknowledged Zixiao Zhang and Sizheng Zhan for specimens collection and restoration.
Grant Sources: This work was financially supported by the Peking University People's Hospital Scientific Research Development Funds (RDL2021‐08, PTU2021‐06).
Disclosure: The authors have no relevant financial or non‐financial interests to disclose.
Jiabao Ju and Mingtai Ma contributed equally to this study.
Data Availability Statement
The data will be available upon request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supplementary Figure 1. Suture rupture in the suture group.
Supplementary Figure 2. Tendon‐bone junction rupture in the SA group.
Data Availability Statement
The data will be available upon request.