Molecular mechanism of fatty degeneration in rotator cuff muscle with tendon rupture

Fatty degeneration often occurs in rotator cuff muscle with tendon rupture. However, the molecular mechanism underlying this change has not been fully clarified yet. We investigated the gene expression of Wnt10b and adipogenic marker gene, PPARγ and C/EBPα in C2C12 myogenic cell line under inhibition of Wnt10b by adipogenic induction medium, isobutylmethylxanthine, dexamethasone, and insulin (MDI). The role of Wnt‐signal was confirmed by adding Lithium chloride (LiCl), which mimics Wnt signaling to the cultured cell with MDI. We also assessed the expression profiles of same genes in the rat rotator cuff tear model in vivo. MDI induced Oil red‐O staining positive adipocytes and upregulated PPARγ and C/EBPα expression. LiCl inhibited adipogenic induction of MDI. Rotator cuff muscle with tendon rupture showed positive staining for Oil red‐O. Real‐time polymerase chain reaction analyses revealed decreased expression of Wnt10b followed by increased PPARγ and C/EBPα gene expression in the supraspinatus muscle. Fatty degeneration and its molecular events were remarkably seen in the distal one‐third of the detached supraspinatus muscle versus control. Wnt signaling may regulate adipogenic differentiation both in the myoblasts in vitro and the muscle in vivo. Our results indicate that the reduction of Wnt10b in muscle with a rotator cuff tear is a key signal in fatty degeneration of the muscle. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:861–866     

Rotator cuff repair using cell sheets derived from human rotator cuff in a rat model

To achieve biological regeneration of tendon‐bone junctions, cell sheets of human rotator‐cuff derived cells were used in a rat rotator cuff injury model. Human rotator‐cuff derived cells were isolated, and cell sheets were made using temperature‐responsive culture plates. Infraspinatus tendons in immunodeficient rats were resected bilaterally at the enthesis. In right shoulders, infraspinatus tendons were repaired by the transosseous method and covered with the cell sheet (sheet group), whereas the left infraspinatus tendons were repaired in the same way without the cell sheet (control group). Histological examinations (safranin‐O and fast green staining, isolectin B4, type II collagen, and human‐specific CD31) and mRNA expression (vascular endothelial growth factor; VEGF, type II collagen; Col2, and tenomodulin; TeM) were analyzed 4 weeks after surgery. Biomechanical tests were performed at 8 weeks. In the sheet group, proteoglycan at the enthesis with more type II collagen and isolectin B4 positive cells were seen compared with in the control group. Human specific CD31‐positive cells were detected only in the sheet group. VEGF and Col2 gene expressions were higher and TeM gene expression was lower in the sheet group than in the control group. In mechanical testing, the sheet group showed a significantly higher ultimate failure load than the control group at 8 weeks. Our results indicated that the rotator‐cuff derived cell sheet could promote cartilage regeneration and angiogenesis at the enthesis, with superior mechanical strength compared with the control. Treatment for rotator cuff injury using cell sheets could be a promising strategy for enthesis of tendon tissue engineering. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:289–296, 2017.

     

Effect of tamoxifen on fatty degeneration and atrophy of rotator cuff muscles in chronic rotator cuff tear: An animal model study

Fatty degeneration of the rotator cuff muscles is an irreversible change resulting from chronic rotator cuff tear and is associated with poor clinical outcomes following rotator cuff repair. We evaluated the effect of Tamoxifen, a competitive estrogen receptor inhibitor, on fatty degeneration using a mouse model for chronic rotator cuff tear. Sixteen adult mice were divided into two diet groups (Tamoxifen vs. Regular) and subjected to surgical creation of a large rotator cuff tear and suprascapular nerve transection in their left shoulder with the right shoulder serving as a control. The rotator cuff muscles were harvested at 16 weeks and subjected to histology and RT‐PCR for adipogenic and myogenic markers. Histology showed substantially decreased atrophy and endomysial inflammation in Tamoxifen group, but no significant differences in the amount of intramuscular adipocytes and lipid droplets compared to the Regular group. With RT‐PCR, the operated shoulders showed significant upregulation of myogenin and PPAR‐γ, and downregulation of myostatin compared to the nonsurgical shoulder. No significant differences of gene expression were found between the two diet groups. Our study demonstrated that tamoxifen diet leads to decreased muscle atrophy and inflammatory changes following chronic rotator cuff tear, but has no apparent effect on adipogenesis. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1846–1853, 2015.     

Shoulder muscle activation and coordination in patients with a massive rotator cuff tear: an electromyographic study

Adaptive muscle activation strategies following a massive rotator cuff tear (MRCT) are inadequately understood, and the relationship among muscles during everyday activities has not been considered. Thirteen healthy subjects comprised the control group, and 11 subjects with a MRCT the patient group. Upper limb function was assessed using the Functional Impairment test‐hand, neck, shoulder, and arm (FIT‐HaNSA). Electromyography (EMG) was recorded from 13 shoulder muscles, comprising five muscle groups, during a shelf‐lifting task. Mean FIT‐HaNSA scores were significantly lower in MRCT patients (p ≤ 0.001), reflecting a severe functional deficit. In MRCT patients, EMG signal amplitude was significantly higher for the biceps brachii‐brachioradialis (p < 0.001), upper trapezius‐serratus anterior (p = 0.025), muscle groups and for the latissimus dorsi (p = 0.010), and teres major (p = 0.007) muscles. No significant differences in the correlation among muscle groups were identified, pointing to an unchanged neuromuscular strategy following a tear. In MRCT patients, a reorganization of muscle activation strategy along the upper limb kinetic chain is aimed at reducing demand on the glenohumeral joint. Increased activation of the latissimus dorsi and teres major muscles is an attempt to compensate for the deficient rotator cuff. Re‐education towards an alternate neuromuscular control strategy appears necessary to restore function. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1140–1146, 2012     

Lateral to medial fibro‐adipogenic degeneration are greater in infraspinatus than supraspinatus following nerve and tendon injury of murine rotator cuff

Small animal models of massive tears of the rotator cuff (RC) were introduced a decade ago and have been extensively used to study the pathophysiology of chronically injured RC. Transection of rodent suprascapular nerve and RC tendon results in progressive muscle atrophy, fibrosis and fat accumulation and affect the infraspinatus and supraspinatus muscles similarly to that seen in the setting of massive RC tears in humans. The purpose of this study was to perform a comprehensive and detailed analysis of the kinetics of fibrotic scar and adipose tissue development comparing phenotypic differences between chronically injured infraspinatus and supraspinatus. Automatic mosaic imaging was used to create large image of whole infraspinatus or supraspinatus sectioned area for quantification of spatial heterogeneity of muscle damage. Pathologic changes advanced from the lateral site of transection to the medial region far from the transection site. A prominent, accelerated muscle fibrosis and fat accumulation was measured in injured infraspinatus compared to supraspinatus. Furthermore, adipose tissue occupied significantly larger area than that of fibrotic tissue in both muscles but was greater in infraspinatus within 6 weeks post induction of injury. Our findings confirm that infraspinatus is more susceptible to accelerated chronic degeneration and can be used to identify the physiological functions that distinguish between the response of infraspinatus and supraspinatus in the setting of massive tears. Whether these pathologic differences observed in mice are reflected in humans is one key aspect that awaits clarification.     

Assessment of pain‐related behavior and pro‐inflammatory cytokine levels in the rat rotator cuff tear model

The cause of pain following rotator cuff tear has not been fully elucidated. The purpose of this study was to evaluate behavior and inflammatory cytokines in a rat unstabilized rotator cuff defect (UCD) model. Forty‐five Sprague–Dawley rats were divided into three groups: sham; UCD; and stabilized rotator cuff defect (SCD). Gait analysis was examined using CatWalk. Tumor necrosis factor (TNF)‐α, interleukin(IL)‐1β, and IL‐6 were measured within the subacromial bursa and the glenohumeral joint synovium at 21 and 56 days after surgery using an enzyme‐linked immunosorbent assay (ELISA). Stride length, print area and contact intensity in the UCD group was significantly lower than in the sham group after surgery. Stride length, print area and contact intensity in the SCD group was significantly higher than in the UCD group. In contrast, TNF‐α, IL‐1β, and IL‐6 in the UCD group was significantly higher than in the sham group at days 21 and 56. However, TNF‐α, IL‐1β, and IL‐6 in the SCD group was significantly lower than in the UCD group at days 21 and 56. The present results suggest that SCD is effective not only in improving shoulder function but also in reducing inflammatory cytokines, which may serve as one source of pain due to rotator cuff tear. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:286–290, 2014.     

Muscle architectural changes after massive human rotator cuff tear

Rotator cuff (RC) tendon tears lead to negative structural and functional changes in the associated musculature. The structural features of muscle that predict function are termed “muscle architecture.” Although the architectural features of “normal” rotator cuff muscles are known, they are poorly understood in the context of cuff pathology. The purpose of this study was to investigate the effects of tear and repair on RC muscle architecture. To this end thirty cadaveric shoulders were grouped into one of four categories based on tear magnitude: Intact, Full‐thickness tear (FTT), Massive tear (MT), or Intervention if sutures or hardware were present, and key parameters of muscle architecture were measured. We found that muscle mass and fiber length decreased proportionally with tear size, with significant differences between all groups. Conversely, sarcomere number was reduced in both FTT and MT with no significant difference between these two groups, in large part because sarcomere length was significantly reduced in MT but not FTT. The loss of muscle mass in FTT is due, in part, to subtraction of serial sarcomeres, which may help preserve sarcomere length. This indicates that function in FTT may be impaired, but there is some remaining mechanical loading to maintain “normal” sarcomere length‐tension relationships. However, the changes resulting from MT suggest more severe limitations in force‐generating capacity because sarcomere length‐tension relationships are no longer normal. The architectural deficits observed in MT muscles may indicate deeper deficiencies in muscle adaptability to length change, which could negatively impact RC function despite successful anatomical repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2089–2095, 2016.     

关节镜下治疗大型肩袖撕裂

目的探讨肩关节镜下治疗大型肩袖撕裂的方法和疗效。方法对34例大型肩袖撕裂患者在关节镜下行单排或双排FastTakII锚钉止点重建术。应用美国肩肘外科医师协会评价系统（ASES）和加利福尼亚大学洛杉矶分校（UCLA）肩关节标准评分。结果34例均获随访,时间4．5～40（7．7±2．4）个月。术后患肩在主动上举、内收、后伸、外展、外旋和内旋6个方向的活动度较术前均有改善（P〈0．05）;患肩完成10项13常活动能力：术前为8．45分±O．97分,术后提高至24．60分±1．21分（P〈0．05）;ASES和UCLA评分：术前分别为24．64分±2．44分和8．06分±1．47分,术后分别提高至71．15分±1．28分和21．77分±1．16分（P〈0．05）;VAS评分：术前为7．18分±2．33分,术后为3．43分±1．75分（P〈0．05）。结论肩关节镜下肩袖重建手术微创治疗优势显著,3～5个作业通道和专业化手术器械的合理交替配合操作能满足大型肩袖撕裂止点重建需求,经镜下双排或单排锚钉重建后的大型损伤肩袖稳定性良好,肩关节功能改善明显。     

Neurohistology of the subacromial bursa in rotator cuff tear

This study was undertaken to identify and quantitate neural elements in the human subacromial bursa. Biopsy specimens of subacromial bursae were obtained from patients with rotator cuff tears and from cadavers of patients with no history of shoulder disorder (controls). We used a modified gold chloride method to characterize neural elements within the subacromial bursa. The population of intrabursal neural elements was calculated by computerized image analysis. The subacromial bursa demonstrated an extensive neural network: four morphological types of mechanoreceptors and many free nerve endings were identified. In general, there was an inverse relationship between the population density of neural elements and the extent of cuff tear. The population density of neural elements of the subacromial bursa associated with massive cuff tear was significantly lower than that observed in control shoulders. With regard to clinical symptoms, a significant correlation was established between the population density of neural elements in the subacromial bursa and shoulder pain at rest. Our investigation strongly suggests that the subacromial bursa is intimately involved in the perception of shoulder pain, providing an anatomical basis for afferent neural input in proprioceptive reflex ares.     

Botulinum toxin is detrimental to repair of a chronic rotator cuff tear in a rabbit model

Re‐tear continues to be a problem after rotator cuff repair. Intramuscular botulinum toxin (Botox) injection can help optimize tension at the repair site to promote healing but could have an adverse effect on the degenerated muscle in a chronic tear. We hypothesized that Botox injection would improve repair characteristics without adverse effect on the muscle in a chronic rotator cuff tear model. The supraspinatus tendon of both shoulders in 14 rabbits underwent delayed repair 12 weeks after transection. One shoulder was treated with intramuscular Botox injection and the other with a saline control injection. Six weeks after repair, outcomes were based on biomechanics, histology, and magnetic resonance imaging. Botox‐treated repairs were significantly weaker (2.64 N) than control repairs (5.51 N, p = 0.03). Eighty percent of Botox‐treated repairs and 40% of control repairs healed with some partial defect. Fatty infiltration of the supraspinatus was present in all shoulders (Goutallier Grade 3 or 4) but was increased in the setting of Botox. This study provides additional support for the rabbit supraspinatus model of chronic cuff tear, showing consistent fatty infiltration. Contrary to our hypothesis, Botox had a negative effect on repair strength and might increase fatty infiltration. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1152–1157, 2015.