Introduction

As the most common type of rotator cuff injury, supraspinatus tendon tears frequently manifest symptoms such as shoulder pain and restricted range of motion, accounting for approximately 90%1,2. After a supraspinatus tendon tear, fat cells are deposited inside and outside the muscle bundle as well as infiltrating the tendon through the rupture, leading to increased brittleness3. Studies have shown that surgical treatment for severe supraspinatus tendon tears can effectively repair these injuries and prevent fat infiltration, thereby reducing the risk of recurrence4,5. However, clinical focus remains on how to efficiently address mild or moderate supraspinatus tendon tears and inhibit fat infiltration in patients undergoing conservative treatment to minimize the risk of recurrence.

As one of the most widely researched biologic therapies, platelet-rich plasma (PRP) is a platelet concentrate derived from autologous whole blood after centrifugation6. PRP can promote the proliferation of tendon tissue and inhibit fat infiltration in torn supraspinatus tendons. Nevertheless, the efficacy of PRP in treating supraspinatus tendon tears varies in different studies, possibly due to the poor fluid absorption of supraspinatus tendon and the easy loss of liquid PRP after injection7,8. PRP gel can adhere stably to the site of tendon tear injury and continuously release growth factors and anti-inflammatory factors. This mechanism facilitates tendon-bone healing and vascular remodeling at the damaged site, thereby accelerating tendon repair. This study aimed to investigate the clinical value of PRP gel in the treatment of supraspinatus tendon tears.

Materials and methods

Study population

This is a retrospective study. A total of 82 patients with supraspinatus tendon tears diagnosed by musculoskeletal ultrasound (MSKUS), MRI, or ultrasound-guided magnetic resonance angiography (USMRA) between October 2022 and February 2023 were recruited. Routine follow-up after treatment was carried out at 1 week and 1, 3 and 6 months. The study was approved by the Medical Ethics Committee of Huzhou Central Hospital (No. 202110024-02) and all patients signed informed consents. We confirmed that all methods were performed in accordance with the relevant guidelines and regulations.

The rotator cuff injuries involved in this study were partial injuries. The supraspinatus tendon tears, as assessed by MSKUS, was classified in accordance with the Ellman Rotator Cuff Injury Classification Method9: (1) bursal-sided tear: The abnormal echogenic area is located on the lateral aspect of the superficial subacromial bursa; (2) articular- sided tear: The abnormal echogenic area is situated on the deep side adjacent to the cartilage surface; (3) intratendinous tear: The echogenic area is found in the central region of the tendon; (4) full-thickness tear: The abnormal echo extends from the superficial acromial subcapsule to the deep cartilage surface, traversing through all layers of the supraspinatus tendon, with or without an “articular cartilage sign.” The severity of supraspinatus tendon tears was classified according to Ellman’s criteria9: Grade I (mild): tear depth < 3 mm; Grade II (moderate): 3 mm ≤ tear depth ≤ 6 mm; Grade III (severe): tear depth > 6 mm. The severity of an injury can be determined based on the depth of supraspinatus tendon tears—ranging from superficial to deep or vice versa. Both musculoskeletal ultrasound and magnetic resonance imaging are effective modalities for assessing tear depth and thereby distinguishing injury severity. Inclusion and exclusion criteria were as follows7,8. Inclusion criteria: (1) History of shoulder pain and active range of motion limitation; (2) Supraspinatus tendon tears diagnosed by MSKUS or MRI or USMRA examination; (3) mild or moderate tears of the supraspinatus tendon confirmed by arthroscopy; (4) Failure of conservative treatment through conventional oral drug.

Exclusion criteria: (1) Presence of other rotator cuff structural injuries; (2) Suffering from adhesive joint capsitis, osteoarthritis, rheumatoid arthritis, gouty arthritis, or other rheumatic immune arthritis; (3) Abnormal coagulation function or blood transfusion; (4) Systems-based hematologic diseases or acute or chronic infectious diseases; (5) Anticoagulant therapy one week before surgery (such as aspirin, warfarin, or heparin); (6) Platelet count < 150 × 109/L; (7) Taking non-steroidal anti-inflammatory drugs within 48 h; (8) Infection at the puncture site; (9) Severe heart, liver, kidney, or other organ dysfunction or intolerance to examination; (10) History of shoulder deformity, trauma, or surgery.

Methods

Instrumentation and parameters

The Mindray DC-80 S and Mindray Resona R7T ultrasound diagnostic devices (Mindray Bio-Medical Electronics Co., Ltd., China) were utilized, employing a probe frequency of 12 MHz in MSKUS examination mode. Color Doppler ultrasound assessment was performed using low-speed blood flow settings. The affected shoulder and supraspinatus fossa underwent routinely scanned, combining transverse and longitudinal scanning. Fat infiltration assessment of the supraspinatus muscle was evaluated using a semi-quantitative grading system10which used the Heckmatt scale for grading the muscle echogenicity within each ROI in the supraspinatus and infraspinatus muscles.

PRP Preparation

Anticoagulant ratio was briefly described below11. Two 20 ml screw-cap syringes were used, with each syringe containing a mixture of 2.0 ml of sodium citrate anticoagulant (10 ml: 0.25 g, Tianjin Jinyao Pharmaceutical Co., Ltd., China) and 18 ml of elbow vein blood in a 9:1 ratio. After blood collection, the syringe tips were sealed with disposable sterile plugs, shaken well, encapsulated in disposable sterile sealing bags, and symmetrically inverted into a low-speed centrifuge with TD5Z model (Changzhou Liangyou Medical Device Co., Ltd., China ). Two-step centrifugation was put to use11,12. Then, a total of 5.0 ml PRP was obtained, of which 1.0 ml was sent for testing, and the remaining 4 ml was used for clinical treatment (Fig. 1A-C).

Fig. 1
figure 1

The process of PRP preparation. (A) Blood stratification after the first centrifugation; (B) the upper layer of platelet-poor plasma and the bottom layer of platelet-rich plasma after the second centrifugation; (C) PRP was successfully prepared.

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Treatment groups

The enrolled patients were assigned to PRP gel group, PRP group and sodium hyaluronate group on account of age, illness duration, and tearing strength. Patients among three groups received ultrasound-guided puncture of glenohumeral joint combined with subacromial bursa and after successful puncture, and 5 mg triamcinolone acetonide (2 ml: 20 mg, Zhejiang Xianju Pharma Co., Ltd., China) were injected respectively13. One week later, the following treatment was administered independently.

PRP gel group14: 500U lyophilizing thrombin powder (500U, Hunan Yige Pharmaceutical Co., Ltd., China) was dissolved in 1.0 ml saline solution. PRP gel was created by simultaneously mixing liquid PRP and liquid thrombin at a specific site, allowing for adsorption to the tear. According to the type of supraspinatus tendon tears, one needle was employed to inject the liquid PRP, while another needle was utilized for the injection of thrombin. Two puncture needles were guided to the site of supraspinatus tendon tear respectively by double-needle method under ultrasound guidance, specifically targeting the tear in the supraspinatus tendon (Supplementary Vedio 1 and 2). One needle was use to inject 3.0 ml of PRP, while the other delivered 0.6 ml of thrombin (containing 300U of thrombin); subsequently, the two needles were withdrawn (Fig. 2).

Fig. 2
figure 2

In PRP gel group, PRP gel was injected into the supraspinatus tendon tear site. Two puncture needles (A,B) were guided to the site of supraspinatus tendon tear respectively by double-needle method (C) under ultrasound guidance (D).

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PRP group: Based on the type of supraspinatus tendon tears, a needle was guided to the supraspinatus tendon tear site under ultrasound guidance, and 3.0 ml of PRP was injected prior to withdrawing the needle (Figure 3).

Fig. 3
figure 3

In PRP group, PRP was injected to the supraspinatus tendon tear site. A needle (A) was guided to the supraspinatus tendon tear site under ultrasound guidance (B).

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Sodium hyaluronate group: Under ultrasound guidance, sodium hyaluronate (Sofast, 2.0 ml: 20 mg, Shandong Bausch & Lomb Freda Pharmaceutical Co., Ltd., China) was administered into both the glenohumeral joint and subacromial bursa, with an injection volume of 2.0 ml respectively (Fig. 4).

Fig. 4
figure 4

In sodium hyaluronate group, sodium hyaluronate was injected into the subacromial bursa and glenohumeral joint respectively Under ultrasound guidance. (A) subacromial bursa and (B) glenohumeral joint.

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Outcome measures

Before treatment, as well as at 1 week, 1 month, 3 months, and 6 months after the first treatment, pain was assessed using the Visual Analogue Scale (VAS) score, shoulder function was evaluated using the Constant-Murley score, and fat infiltration of the affected supraspinatus muscle was detected by MSKUS15.

Statistical analysis

Statistical Analysis was performed using SPSS 21.0 statistical software. Qualitative data were expressed as rates, quantitative data consistent with normal distribution were expressed as ± s, and skewed distribution data were presented as median (M) and interquartile range (Q). Differences between groups were compared by t-test, x2 test, Fisher’s test, or Analysis of Variance test. Mean comparisons of multiple groups were analyzed with the Analysis of Variance method, and pairwise comparisons between groups were performed by the letter and shape drawing test. P-value < 0.05 was considered statistically significant.

Results

Patient characteristics

Among the 82 patients with supraspinatus tendon tears, 29 patients were in PRP gel group, 26 in PRP group, and 27 in Sodium hyaluronate group (Supplementary Table 1). Arthroscopic evaluation revealed 46 patients with mild supraspinatus tendon tears (15 in PRP gel group, 14 in PRP group and 17 in sodium hyaluronate group) and 36 patients with moderate tears (14 in PRP gel group, 12 in PRP group and 10 in sodium hyaluronate group). Before treatment, there were no statistically significant differences among PRP gel group, PRP group and sodium hyaluronate group in terms of age, gender, illness duration, VAS score, Constant-Murley score, and degree of supraspinatus tendon tear (P > 0.05) ( Table 1).

Table 1 Comparison of basic clinical data among patients with supraspinatus tendon tearsa.
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The preoperative platelet count in PRP gel group was 199.19 ± 36.37 × 109/L, and the PRP specimen had a platelet count of 906.61 ± 78.36 × 109/L. The average concentration multiple of PRP was 4.17 ± 1.26 times, and the white blood cell count in the PRP specimen was 9.61 ± 1.54 × 109/L. In PRP group, the preoperative platelet count was 181.36 ± 42.63 × 109/L, and the PRP specimen had a platelet count of 947.82 ± 81.45 × 109/L. The average concentration multiple of PRP was 4.55 ± 1.32 times, and the white blood cell count in the PRP specimen was 8.61 ± 2.32 × 109/L. There were no statistically significant differences between the PRP gel group and PRP group regarding preoperative platelet count (t = 1.64, P = 0.11), platelet count measured in PRP specimen (t = 1.88, P = 0.07), white blood cell count in PRP specimen (t = 1.92, P = 0.06), and PRP concentration multiple (t = 1.07, P = 0.29).

Changes in VAS scores before and after treatment among patients with supraspinatus tendon tears

Compared to baseline measurements, the VAS pain scores among PRP gel group, PRP group, and sodium hyaluronate group all significantly decreased at 1 week and 1 month after the first triamcinolone acetonide injection treatment (P < 0.05). However, there were no statistically significant differences among the three groups (P > 0.05).

Three months after surgery, statistical differences in VAS pain scores were observed among the three groups when compared to pre-treatment (F = 9.63, P = 0.0002). Pairwise comparisons showed that both PRP gel group (2.07 ± 0.52 vs. 2.80 ± 0.85, t = 3.84, P = 0.0003) and PRP group (2.33 ± 0.55 vs. 2.80 ± 0.85, t = 2.33, P = 0.02) exhibited lower scores than sodium hyaluronate group, with statistically remarkable differences. Nevertheless, there was no statistically significant difference between PRP gel group and PRP group (2.07 ± 0.52 vs. 2.33 ± 0.55, t = 1.77, P = 0.08).

At 6 months postoperatively, there were noteworthy differences in VAS scores among the three groups, with significant differences (F = 12.84, P < 0.0001). Pairwise comparisons demonstrated that the PRP gel group had lower scores than both PRP group (2.13 ± 0.57 vs. 2.67 ± 0.71, t = 3.07, P = 0.003) and sodium hyaluronate group (2.13 ± 0.57 vs. 3.17 ± 1.02, t = 4.67, P < 0.0001). Additionally, PRP group presented lower scores than sodium hyaluronate group (2.67 ± 0.71 vs. 3.17 ± 1.02, t = 2.03, P = 0.04), with all differences being statistically significant (Table 2).

Table 2 Changes in VAS scores before and after treatment among patients with supraspinatus tendon tears (score)a.
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Changes in shoulder function before and after treatment among patients with supraspinatus tendon tears

There were no statistically significant differences in the Constant-Murley scores of the shoulder joint among the three groups before treatment, as well as at 1 week and 1 month postoperatively (P > 0.05). Nonetheless, the Constant-Murley scores of the shoulder joint in all three groups were significantly improved at 1 week and 1 month postoperatively compared to before treatment, with the differences being statistically significant (P < 0.05).

At 3 months postoperatively, the Constant-Murley score for the shoulder joint in PRP gel group was higher than that in both PRP group and sodium hyaluronate group, with a notable difference (F = 9.64, P < 0.05). Nevertheless, there was no statistically significant difference between PRP group and sodium hyaluronate group (t = 1.60, P = 0.10).

At 6 months postoperatively, the Constant-Murley score of the shoulder joint in PRP gel group was significantly higher than that in PRP group and sodium hyaluronate group (F = 12.08, P < 0.05). Furthermore, the score in PRP group was higher than that in sodium hyaluronate group, demonstrating a significant difference (t = 2.61, P = 0.01) (Table 3).

Table 3 Changes in Constant-Murley scores before and after treatment among patients with supraspinatus tendon tearsa.
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Changes in supraspinatus fatty infiltration by MSKUS before and after treatment

No statistically significant differences in supraspinatus fat infiltration by MSKUS were measured among the three groups before surgery, as well as at 1 week, 1 month and 3 months postoperatively (P > 0.05). Simultaneously, at 6 months postoperatively, supraspinatus fat infiltration by MSKUS in PRP gel group and PRP group was notably lower than that in sodium hyaluronate group (1.86 ± 0.52 vs. 1.96 ± 0.64 vs. 2.32 ± 0.55, F = 5.06, P = 0.008). Furthermore, supraspinatus fat infiltration by MSKUS in PRP group was significantly lower than that in sodium hyaluronate group (1.96 ± 0.64 vs. 2.32 ± 0.55, t = 2.16, P = 0.03) ( Table 4). Ultrasound images of the fat infiltration of the supraspinatus muscle before and 6 months after the treatment with PRP gel were shown in Fig. 5.

Table 4 Changes in fatty infiltration degree of supraspinatus muscle by MSKUS before and after treatment for supraspinatus tendon tearsa.
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Fig. 5
figure 5

Ultrasound images of the fat infiltration of the supraspinatus muscle before and 6 months after the treatment with PRP gel. (A) before the treatment with PRP gel; (B) 6 months after the treatment with PRP gel.

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Comparison of adverse effects and efficacy after treatment for patients with supraspinatus tendon tears

Among 82 patients with supraspinatus tendon tears, two patients developed skin bruising after the first ultrasound-guided triamcinolone acetonide injection, and one patient experienced pain at the injection site within 24 h. This resulted in an adverse effects incidence rate of 3.66%. Symptomatic treatment with ice packs effectively relieved these symptoms.

In PRP gel group, 25 out of 29 patients (86.21%) developed shoulder discomfort such as soreness and swelling within 2–3 days post-treatment with PRP gel. Similarly, in PRP group, 20 out of 26 patients (76.92%) experienced comparable symptoms after receiving PRP treatment; however, these symptoms resolved spontaneously over time. No significant adverse effects occurred during sodium hyaluronate injection in sodium hyaluronate group.

There were no statistically significant differences in treatment efficacy among three groups at 1 month and 3 months postoperatively (P > 0.05). However, at 6 months postoperatively, the treatment efficacy in PRP gel group was statistically higher than that in PRP group and sodium hyaluronate group (93.10% vs. 80.77% vs. 66.67%, χ²=6.14, P = 0.01). No statistically significant difference was observed in treatment efficacy between PRP group and sodium hyaluronate group (χ² =1.37, P = 0.24) ( Table 5).

Table 5 Comparison of treatment efficacy for supraspinatus tendon tearsa.
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Discussion

Supraspinatus tendon tear is one of the most prevalent types of rotator cuff injuries, occurring in 25% of people over 50 years old and up to 50% of those over 70 years old2,16. If a supraspinatus tendon tear is not addressed promptly, it is easy to cause fat infiltration resulting in retear, significantly impacting the patient’s quality of life17.

Tendon inflammation and edema are associated with supraspinatus tendon tears18. Steroid hormones possess potent anti-inflammatory properties, which can effectively mitigate the inflammatory response after supraspinatus tendon tears and relieve joint pain19. In this study, the VAS scores for pain decreased significantly in three groups one week after triamcinolone acetonide injection (P < 0.05). As the local inflammation and edema of the tendon subsided, joint function improved. Furthermore, this study demonstrated that the Constant-Murley scores for shoulder joints among three groups changed significantly at one month post-treatment compared to pre-treatment. This improvement may be attributed to the resolution of tendon edema and pain symptoms after supraspinatus tendon tears, which had previously restricted joint motion. However, although injection therapy of steroid hormone can improve pain and joint motion in the short term, it does not effectively repair supraspinatus tendon tears20. Therefore, it is essential to advise patients to take a rest and avoid physical activity after treatment to prevent aggravating tendon injury. In addition, it is of utmost importance to explore an effective treatment to promote the repair of supraspinatus tendon tears.

The region located 1 cm area from the attachment site of the supraspinatus tendon is lacking blood supply. Consequently, once a tear occurs, healing becomes challenging and may easily give rise to chronic tendon inflammation21,22. This particular characteristic contributes to the difficulty in healing supraspinatus tendon injuries and results in a high rate of postoperative retear due to insufficient repair factors at both the tendon-bone interface and within the union itself. PRP releases a substantial amount of growth factors that can effectively promote healing between the tendon and bone. In this study, the Constant-Murley scores of the shoulder joints in PRP gel group and PRP group were higher than those in sodium hyaluronate group at 3 and 6 months postoperatively (P < 0.05). The treatment efficacy in PRP gel group was higher than that in PRP group and sodium hyaluronate group at 6 months postoperatively (93.10% vs. 80.77% vs. 66.67%, χ²=6.14, P = 0.01).

After a supraspinatus tendon tear, local tendon tension decreases, contributing to a brittle texture of the supraspinatus tendon and muscle belly, which increases the risk of retear23,24. In this study, the VAS scores for pain in both PRP gel group and PRP group utilizing PRP were lower than those in sodium hyaluronate group at 3 and 6 months postoperatively; the fat infiltration assessed by MSKUS in PRP gel group and PRP group was statistically lower than that in sodium hyaluronate group at 6 months postoperatively (F = 5.06, P = 0.008). This difference may be attributed to the possibility that some patients in sodium hyaluronate group may develop fat infiltration over time, leading to tendon retear without PRP intervention; in contrast, patients in both PRP gel and PRP groups benefited from PRP, which may promote the healing of local tendon tears, and increase tendon toughness as well as muscle bundle elasticity, thereby reducing the risk of fat infiltration.

Due to the limited liquid adsorption of tendon tissue, conventional liquid PRP is susceptible to loss after injection, resulting in a short duration of growth factor released from PRP and diminishing its therapeutic effect. In contrast, PRP gel can adhere to the damaged and torn areas for a prolonged period, facilitating the continuous release of a substantial quantity of growth factors. In this study, the results showed that at 6 months postoperatively, the VAS scores for pain were lower in PRP gel group compared to PRP group (2.13 ± 0.57 vs. 2.67 ± 0.71, t = 3.07, P = 0.003) and sodium hyaluronate group (2.13 ± 0.57 vs. 3.17 ± 1.02, t = 4.67, P < 0.0001). Additionally, PRP group revealed lower scores than sodium hyaluronate group (2.67 ± 0.71 vs. 3.17 ± 1.02, t = 2.03, P = 0.04). The Constant-Murley scores for shoulder joint motion were higher in PRP gel group compared to other two groups (F = 12.08, P < 0.05), with PRP group also scoring higher than sodium hyaluronate group (t = 2.61, P = 0.01). These findings may be owing to that the PRP gel group received precise ultrasound-guided injection of PRP gel directly into the torn supraspinatus tendon. Compared to liquid PRP, which tends to disperse quickly after injection, PRP gel adheres effectively at tear sites and stably provides a stable supply of biologically active α-granules and growth factors at high concentrations over time. This mechanism promotes tear repair, enhances tendon strength, restores local tendon tension, prevents infiltration by activated fat cells, induces vascular remodeling, facilitates tendon-bone healing, and effectively promotes tendon tissue regeneration and repair25. In this study, the treatment efficacy in PRP gel group was higher than that in PRP group and in sodium hyaluronate group at 6 months postoperatively (93.10% vs. 80.77% vs. 66.67%, x2 = 6.14, P = 0.01).

For patients with a prolonged disease course, secondary adhesive capsulitis involving the subacromial bursa may occur due to pain from supraspinatus tendon tears that limit shoulder joint movement. Additionally, chronic adhesive bursitis can arise from friction within the subacromial bursa during activities such as shoulder abduction. Although frozen shoulder patients were excluded from our inclusion and exclusion criteria, a small subset of patients with joint capsular adhesions may present with false-negative imaging results. In our treatment protocol, we initially employed visual ultrasound technology to facilitate drug injection into both the glenohumeral joint and the acromial glide capsule. Through ultrasound-guided puncture, these medications were accurately delivered into the glenohumeral glide capsule and glenohumeral joint, thereby achieving a therapeutic effect aimed at alleviating adhesions.

There are also some limitations in this study. (1) The sample size was small, and needs to be expanded for further research in the future. (2) Due to the large individual difference in platelet base, the absolute platelet value of PRP with the same multiple was different, which may affect treatment outcomes. (3) Differences in blood cell proportions among patients may lead to subtle variations in the specific components of PRP prepared under the same centrifugal force and centrifugal time. (4) Theoretically, once platelets exit the human body, their activity may vary under different conditions; although a two-step method for preparing PRP effectively preserved platelet activity, this study did not detect platelet activity in either the PRP gel group or PRP group. (5) upon entering the human body, PRP released significant quantities of growth factors and anti-inflammatory agents; however, this study did not identify these released factors in either group following injection into the lesion site. In the future, we will conduct a large-scale prospective study to explore the preparation and clinical application of PRP.

Conclusions

In conclusion, ultrasound-guided PRP gel treatment can not only alleviate pain and improve joint motion in patients with supraspinatus tendon tears, but also inhibit fat infiltration and enhance treatment efficacy.