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Background: Various muscle contraction modalities have differing effects on the musculoskeletal system. To understand the magnitude of these effects, the authors investigated the effects of eccentric and concentric contractions on the bone-tendon interface after rotator cuff repair in mice. Hypothesis: Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns. Study Design: Controlled laboratory study. Methods: The authors performed acute supraspinatus tendon repair of the right shoulder in 104 C57BL/6 mice. Animals were randomized into 4 groups postoperatively: control group (Con group), horizontal running group (Horz group), +15° uphill running group (Up group), and −15° downhill running group (Down group), with 26 animals in each group. At 4 and 8 weeks postoperatively, the authors removed the eyeball, collected blood samples, and extracted the supraspinatus tendon–humerus complex for histological, immunological, bone morphological, and biomechanical tests. Results: At 4 and 8 weeks postoperatively, the Down group exhibited a better collagen cell arrangement and fibrocartilage layer than the other 3 groups. At 4 weeks postoperatively, anti-inflammatory macrophages (M2 macrophages) were observed at the repair site in all groups except for the Con group. At 8 weeks postoperatively, M2 macrophages were withdrawn from the tendon site in all groups. The transforming growth factor β1 concentration in the Down group was greater than that in the other 3 groups at 4 weeks postoperatively, and it was higher than that in the Con group at 8 weeks postoperatively. The bone volume fraction, number of trabeculae, and thickness of trabeculae at the repair site in the Down group, as well as the ultimate strength and failure load in the biomechanical tests, were greater than those in the other 3 groups at 8 weeks postoperatively. Conclusion: Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns. Clinical Relevance: After clinical rotator cuff repair, patients can be rehabilitated by eccentric training to speed up the functional recovery of the shoulder joint. [ABSTRACT FROM AUTHOR]

To systematically review of randomized controlled trials (RCTs) to compared the effects of leukocyte-rich and leukocyte-poor platelet-rich plasma in arthroscopic rotator cuff repair. Two independent reviewers comprehensively searched PubMed, Embase, and Cochrane library databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Comparison of leukocyte-rich platelet-rich plasma or leukocyte-poor platelet-rich plasma in rotator cuff repair in a level I RCTs. Methodological quality assessment was carried out using Cochrane Review Manager 5.3 software. P<0.05 was considered statistically significant. Nine RCTs with 540 patients were included in this review. Meta-analysis showed that leukocyte-poor platelet-rich plasma in significantly reduced retear rate in rotator cuff repair [RR=0.56 95% CI (0.42, 0.75); P<0.05), and in clinical results, the constant score [MD=3.67, 95% CI (1.62, 5.73); P=0.0005], UCLA score [MD=1.60, 95% CI (0.79, 2.42); P=0.0001], ASES score [MD=2.16, 95% CI (0.12, 4.20); P=0.04] were significantly improved. There was a significant result in favor of PRP for the Constant score [MD=−1.24, 95% CI (−1.50, −0.99); P<0.00001], while SST scores were not significantly different among all groups [MD=0.21, 95% CI (−0.21, 0.64); P=0.32]. In conclusion, leukocyte-poor platelet-rich plasma can improved the clinical function and reduced retear rate in arthroscopic rotator cuff repair. In contrast, the efficacy of leukocyte-rich platelet-rich plasma was not significantly improved with the exception of VAS score. [ABSTRACT FROM AUTHOR]

Platelet-rich plasma (PRP) is widely used clinically to treat tendon injuries, and often contains leukocytes. However, the debate regarding the concentration of leukocytes in PRP is still ongoing. This study aimed to evaluate the therapeutic effects of leukocyte-rich platelet-rich plasma (LR-PRP) and leukocyte-poor platelet-rich plasma (LP-PRP) on the healing of the bone-tendon interface (BTI) of the rotator cuff. A total of 102 C57BL/6 mice were used. Thirty mice were used to prepare the PRP, while 72 underwent acute supraspinatus tendon injury repair. The animals were then randomly assigned to three groups: LR-PRP, LP-PRP and control groups. The mice were euthanized at 4 and 8 weeks postoperatively, and histological, immunological and biomechanical analyses were performed. The histological results showed that the fusion effect at the bone-tendon interface at 4 and 8 weeks after surgery was greater in the PRP groups and significantly increased at 4 weeks; however, at 8 weeks, the area of the fibrocartilage layer in the LP-PRP group increased significantly. M2 macrophages were observed at the repaired insertion for all the groups at 4 weeks. At 8 weeks, M2 macrophages withdrew back to the tendon in the control group, but some M2 macrophages were retained at the repaired site in the LR-PRP and LP-PRP groups. Enzyme-linked immunoassay results showed that the concentrations of IL-1β and TNF-α in the LR-PRP group were significantly higher than those in the other groups at 4 and 8 weeks, while the concentrations of IL-1β and TNF-α in the LP-PRP group were significantly lower than those in the control group. The biomechanical properties of the BTI were significantly improved in the PRP group. Significantly higher failure load and ultimate strength were seen in the LR-PRP and LP-PRP groups than in the control group at 4 and 8 weeks postoperatively. Thus, LR-RPR can effectively enhance the early stage of bone-tendon interface healing after rotator cuff repair, and LP-PRP could enhance the later stages of healing after rotator cuff injury. [ABSTRACT FROM AUTHOR]

Background: Mechanical stimulation and platelet-rich plasma (PRP) have been shown to be beneficial for healing of the bone-tendon interface (BTI), but few studies have explored the efficacy of a combination of these applications. We investigated the effect of mechanical stimulation combined with PRP on rotator cuff repair in mice. Hypothesis: Mechanical stimulation combined with PRP can enhance BTI healing in a murine model of rotator cuff repair. Study Design: Controlled laboratory study. Methods: A total of 160 C57BL/6 mice were used. Overall, 40 mice were used to prepare PRP, while 120 mice underwent acute supraspinatus tendon (SST) repair. The animals were randomly assigned to 4 groups: control group, mechanical stimulation group, PRP group, and mechanical stimulation combined with PRP group (combination group). At 4 and 8 weeks postoperatively, animals were sacrificed, the eyeballs were removed to collect blood, and the SST–humeral complexes were collected. Histological, biomechanical, immunological, and bone morphometric tests were performed. Results: Histologically, at 4 and 8 weeks after surgery, the area of the fibrocartilage layer at the BTI in the combination group was larger than in the other groups. The content and distribution of proteoglycans in this layer in the combination group were significantly greater than in the other groups. At 8 weeks postoperatively, trabecular number, and trabecular bone thickness of the subchondral bone area of interest at the BTI of the combination group were greater than those of the other groups, bone volume fraction of the combination group was greater than the control group. On biomechanical testing at 4 and 8 weeks after surgery, the failure load and ultimate strength of the SST–humeral complex in the combination group were higher than in the other groups. Enzyme-linked immunosorbent assay results showed that, at 4 weeks postoperatively, the serum concentrations of transforming growth factor beta 1 and platelet-derived growth factor (PDGF) in the combination group were significantly higher than in the other groups; at 8 weeks, the PDGF-AB concentration in the combination group was higher than in the control and mechanical stimulation groups. Conclusion: Mechanical stimulation combined with PRP can effectively promote the early stage of healing after a rotator cuff injury. Clinical Relevance: These findings imply that mechanical stimulation combined with PRP can serve as a potential therapeutic strategy for rotator cuff healing. [ABSTRACT FROM AUTHOR]