Effect of suprascapular nerve injury on muscle and regenerated enthesis in a rat rotator cuff tear model

Anti-Leukotriene Receptor Blockers Improve Tendon-Bone Interface Healing in a Rat Model of Acute Rotator Cuff Tear

BACKGROUND

Excessive expression of proinflammatory cytokines after rotator cuff (RC) surgery impairs the quality of tendon-bone interface (TBI) healing. There is evidence that the asthma drug montelukast (MS) inhibits the expression of proinflammatory cytokines. This study was conducted to verify the effect of MS administration on TBI healing after RC repair.

MATERIALS AND METHODS

Thirteen rats in the MS group were intraperitoneally administered 10 mg/kg of the drug daily for 2 weeks after RC surgery, and 13 rats in the control group were administered only 0.9% saline. The healing effect of the TBI was assessed through histologic and biomechanical analysis 4 weeks after tendon repair.

RESULTS

In the MS group, the expression of interleukin-1 beta (IL-1β; P<.01) and interleukin 6 (IL-6; P<.01) was significantly reduced compared with the control group. In the evaluation of supraspinatus fatty infiltration, the MS group showed significant inhibition of fatty infiltration compared with the control group (P<.001). Histologic analysis showed that the MS group had significant improvements in collagen density (P=.035) and alignment (P=.011). Biomechanical analysis after systemic administration of MS showed an increase in the cross-sectional area (P<.001) and elongation (P<.01) of the TBI.

CONCLUSION

The use of MS improved tendon elasticity through suppressing fatty infiltration and improving TBI collagen density and arrangement. The mechanism is down-regulation of IL-1β and IL-6. These results strongly support the use of MS as an anti-inflammatory agent that does not impair tendon healing. [Orthopedics. 2025;48(2):e105-e112.].

Ezetimibe/Atorvastatin, a Treatment for Hyperlipidemia, Inhibits Supraspinatus Fatty Infiltration and Improves Bone-Tendon Interface Healing in a Rotator Cuff Tear Rat Model

BACKGROUND

Multiple factors, such as muscle fatty infiltration (FI), tendon collagen content, and collagen arrangement, determine bone-tendon interface (BTI) healing after rotator cuff (RC) repair.

PURPOSE

To evaluate the effects of systemic administration of ezetimibe-atorvastatin (EZE/ATZ) combination on muscle FI and tendon collagen density and arrangement in an RC repair rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 26 male Sprague-Dawley rats were randomly divided equally into control and EZE/ATZ groups and subjected to RC tendon repair surgery. Postoperatively, the EZE/ATZ group rats received a combination of EZE (10 mg/kg/d) and ATZ (20 mg/kg/d) for 4 weeks, after which they were sacrificed. Oil Red O staining was used to assess FI in the supraspinatus muscle. The expression of biomarkers related to muscle atrophy and FI was measured using quantitative real-time polymerase chain reaction. For the qualitative and quantitative analysis of FI-related biomarkers, immunohistochemical staining was performed. Biomechanical and histological analyses were performed to evaluate the quality of BTI healing after RC repair.

RESULTS

The EZE/ATZ group showed significantly lower FI compared with the control group (P < .001) and significantly downregulated expression of gene markers related to muscle atrophy and FI. On histological analysis, the EZE/ATZ group exhibited increased collagen type I contents, consistent collagen arrangement (P = .005), and significantly higher collagen density (P = .003) compared with the control group. Biomechanical analysis of the BTI healing revealed that the EZE/ATZ group had significantly increased ultimate strength (P = .006) compared with the control group.

CONCLUSION

Systemic EZE/ATZ administration suppressed supraspinatus FI by downregulating muscle atrophy-related and FI-related genes after RC repair. Additionally, EZE/ATZ use improved collagen biosynthesis, density, and arrangement at the BTI and significantly increased tensile strength.

CLINICAL RELEVANCE

The results of the current study strongly advocate the use of EZE/ATZ to improve shoulder function and tendon healing after RC repair.

Effect of Gabapentin on Tendon-to-Bone Healing in a Rat Model of Rotator Cuff Repair

BACKGROUND

Gabapentin is often used as an analgesic after rotator cuff repair surgery and is recommended as an additional analgesic for arthroscopic rotator cuff repairs. However, evidence of its effects on biological healing mechanisms is lacking. The objective of this study was to investigate the potential of gabapentin in improving tendon-to-bone healing after rotator cuff repair using a rat model.

MATERIALS AND METHODS

A total of 20 male rats were randomly allocated to one of two groups: group 1 (repair only, n=10) or group 2 (gabapentin injection, n=10). The rats in the experimental group (group 2) were administered 80 mg/kg of gabapentin subcutaneously 30 minutes before surgery, followed by 80 mg/kg subcutaneously every 24 hours for 48 hours. We used the left shoulder of every rat, while for biomechanical analysis, we used the right shoulder.

RESULTS

There was no significant difference in the load to failure, ultimate stress, or elongation between the groups. Collagen continuity, orientation, and density were better in group 2 than group 1.

CONCLUSION

In a rat model of rotator cuff repair, gabapentin had a positive impact on the quality of collagen organization at the junction between the tendon and bone, while preserving the biomechanical properties. We propose the use of gabapentin as a supplementary analgesic agent for postoperative pain relief after arthroscopic rotator cuff repair; however, further studies of the effect of gabapentin on biological healing mechanisms are required. [Orthopedics. 2024;47(5):e241-e246.].

Nanofiber Graft Therapy to Prevent Shoulder Stiffness and Adhesions after Rotator Cuff Tendon Repair: A Comprehensive Review

Stiffness and adhesions following rotator cuff tears (RCTs) are common complications that negatively affect surgical outcomes and impede healing, thereby increasing the risk of morbidity and failure of surgical interventions. Tissue engineering, particularly through the use of nanofiber scaffolds, has emerged as a promising regenerative medicine strategy to address these complications. This review critically assesses the efficacy and limitations of nanofiber-based methods in promoting rotator cuff (RC) regeneration and managing postrepair stiffness and adhesions. It also discusses the need for a multidisciplinary approach to advance this field and highlights important considerations for future clinical trials.

Current research trends on the effect of diabetes mellitus on rotator cuff tendon healing/tendinopathy

Rotator cuff tendon tears are a leading cause of shoulder pain. They are challenging to treat, and tendon-bone healing has a high failure rate despite successful surgery. Tendons connect the muscles and bones, which make them important for the body's overall mobility and stability. Metabolic diseases, including diabetes or high blood pressure, can affect the healing process after repair of a damaged tendon. With a global incidence of 9.3%, diabetes is considered as a significant risk factor for rotator cuff tendon healing because it causes structural, inflammatory, and vascular changes in the tendon. However, the mechanisms of how diabetes affects tendon healing remain unknown. Several factors have been suggested, including glycation product accumulation, adipokine dysregulation, increased levels of reactive oxygen species, apoptosis, inflammatory cytokines, imbalanced matrix-metalloproteinase-to-tissue-inhibitor ratio, and impaired angiogenesis and differentiation of the tendon sheath. Despite the effects of diabetes on tendon function and healing, few treatments are available to improve recovery in these patients. This review summarizes the current literature on the pathophysiological changes of the tendon in diabetes and hyperlipidemia. Preclinical and clinical evidence regarding the association between diabetes and tendon healing is presented. Moreover, current approaches to improve tendon healing in patients with diabetes are reviewed.

Biomechanical and histological evaluation of aspirin in rotator cuff tear rat model

Background: Aspirin is a representative non-steroidal anti-inflammatory drug (NSAIDs) and has been commonly used for the treatment of tendinopathy in clinical practice. In this study, we aimed to evaluate the biomechanical and histological healing effects of aspirin on the healing of the tendon-to-bone interface after rotator cuff tear repair. Methods: A total of 20 male Sprague-Dawley rats were randomly divided into two groups of 10 rats each. Group-C performed repaironly, and group-aspirin treated with aspirin after tendon repair. Group-aspirin rat were intraperitoneally injected with aspirin at 10 mg/kg every 24 h for 7 days. Eight weeks after surgery, the left shoulder of each rat was used for histological analysis and the right shoulder for biomechanical analysis. Results: In the biomechanical analysis, there was no significant difference in load-to-failure (group-C: 0.61 ± 0.32 N, group-aspirin: 0.74 ± 0.91 N; p = .697) and ultimate stress (group-C: 0.05 ± 0.01 MPa, group-aspirin: 0.29 ± 0.43 MPa; p = .095). For the elongation (group-C: 222.62 ± 57.98%, group-aspirin: 194.75 ± 75.16%; p = .028), group-aspirin confirmed a lower elongation level than group-C. In the histological evaluation, the Bonar score confirmed significant differences in collagen fiber density (group-C: 1.60 ± 0.52, group-aspirin: 2.60 ± 0.52, p = .001) and vascularity (group-C: 1.00 ± 0.47, group-aspirin: 2.20 ± 0.63, p = .001) between the groups. Conclusions: Aspirin injection after rotator cuff tear repair may enhance the healing effect during the early remodeling phase of tendon healing.

Effects of adipose-derived cell supplementation on tendon-bone healing in a rat model of chronic rotator cuff tear with suprascapular nerve injury

OBJECTIVE

To investigate the effect of adipose-derived cells (ADCs) on tendon-bone healing in a rat model of chronic rotator cuff tear (RCT) with suprascapular nerve (SN) injury.

METHODS

Adult rats underwent right shoulder surgery whereby the supraspinatus was detached, and SN injury was induced. ADCs were cultured from the animals' abdominal fat. At 6 weeks post-surgery, the animals underwent surgical tendon repair; the ADC (+ve) group (n = 18) received an ADC injection, and the ADC (-ve) group (n = 18) received a saline injection. Shoulders were harvested at 10, 14, and 18 weeks and underwent histological, fluorescent, and biomechanical analyses.

RESULTS

In the ADC (+ve) group, a firm enthesis, including dense mature fibrocartilage and well-aligned cells, were observed in the bone-tendon junction and fatty infiltration was less than in the ADC (-ve) group. Mean maximum stress and linear stiffness was greater in the ADC (+ve) compared with the ADC (-ve) group at 18 weeks.

CONCLUSION

ADC supplementation showed a positive effect on tendon-bone healing in a rat model of chronic RCT with accompanying SN injury. Therefore, ADC injection may possibly accelerate recovery in massive RCT injuries.