Compensatory hypertrophy of the teres minor muscle after large rotator cuff tear model in adult male rat

Vascular photobiomodulation increases muscle fiber diameter and improves the gait during compensatory hypertrophy of plantar muscle in rats

The local photobiomodulation (LPBM) has demonstrated positive effects during compensatory hypertrophy (CH) in skeletal muscle as a response to an overload. The aim was to compare the effects of the transcutaneous vascular photobiomodulation (VPBM) and the LPBM on muscle fiber size, gait functionality, and on mechanical sensitivity during the CH model in rats. VPBM was administered over the rat's main tail vein and LPBM was applied over the plantar muscle region. VPBM induced an increase in muscle fiber diameter and cross-sectional area (CSA) after 7 days. At 14 days, an increase in the fiber diameter was found in both irradiated groups. The VPBM and LPBM promoted the reestablishment of normal gait evaluated by the sciatic functional index after 14 days. No changes were found in the mechanical (nociceptive) sensitivity in VPBM and LPBM groups in comparison to the CH group but there was an increase in the nociceptive sensitivity in the CH groups in comparison to the control after 7 and 14 days. In conclusion, both PBM, vascular and local, were able to improve the muscle size and gait during the CH process with more pronounced effects when irradiation was performed systemically (VPBM).

Roles of Oxidative Stress in Acute Tendon Injury and Degenerative Tendinopathy-A Target for Intervention

Both acute and chronic tendon injuries are disabling sports medicine problems with no effective treatment at present. Sustained oxidative stress has been suggested as the major factor contributing to fibrosis and adhesion after acute tendon injury as well as pathological changes of degenerative tendinopathy. Numerous in vitro and in vivo studies have shown that the inhibition of oxidative stress can promote the tenogenic differentiation of tendon stem/progenitor cells, reduce tissue fibrosis and augment tendon repair. This review aims to systematically review the literature and summarize the clinical and pre-clinical evidence about the potential relationship of oxidative stress and tendon disorders. The literature in PubMed was searched using appropriate keywords. A total of 81 original pre-clinical and clinical articles directly related to the effects of oxidative stress and the activators or inhibitors of oxidative stress on the tendon were reviewed and included in this review article. The potential sources and mechanisms of oxidative stress in these debilitating tendon disorders is summarized. The anti-oxidative therapies that have been examined in the clinical and pre-clinical settings to reduce tendon fibrosis and adhesion or promote healing in tendinopathy are reviewed. The future research direction is also discussed.

Quantitative magnetic resonance imaging assessment of the infraspinatus and teres minor in massive rotator cuff tear and its significance in clinical outcome after rotator cuff repair

BACKGROUND

Teres minor (TM) muscle hypertrophy in large to massive rotator cuff tears (RCTs) has been considered a compensatory change to atrophy of the infraspinatus (ISP). However, few reports have assessed its relation to the prognosis after rotator cuff repair.

METHODS

A total of 139 patients who underwent arthroscopic repair of large to massive RCTs involving the ISP between January 2013 and December 2015 were retrospectively investigated. Occupational ratios of the ISP (OR_ISP) and TM (OR_TM) were measured by sagittal magnetic resonance imaging (MRI). Rotator cuff healing was evaluated by MRI 1 year postoperatively, and functional outcomes using the Simple Shoulder Test (SST) and Constant score and external rotator (ER) strength by isokinetic muscle performance test (IMPT) were measured.

RESULTS

A total of 116 patients completed the MRI and IMPT at 1 year postoperatively, and functional scores were measured at least 2 years postoperatively. Of these, the repaired tendon had not healed in 34 patients (29%). There was a highly negative correlation between OR_ISP and OR_TM both pre- and postoperatively (Pearson correlation = -0.52 and -0.54, respectively). Preoperative OR_ISP was significantly higher in the healed than in the healing failure group (0.47 ± 0.10 vs. 0.41 ± 0.12, P = .02); however, postoperative OR_ISP and pre- and postoperative OR_TM were not. The preoperative OR_ISP cutoff value for healing was 0.46. For functional outcomes, only postoperative OR_ISP showed a statistical correlation with SST, Constant score (P = .04 and .03, respectively), and ER strength (P = .02).

CONCLUSION

TM muscle hypertrophy in large to massive RCT appears to be a compensatory change in the progression of atrophy of the ISP muscle and was not a significant indicator of either better healing of the repaired rotator cuff tendon or better function. Only preoperative OR_ISP was an independent prognostic factor affecting rotator cuff healing after repair of large to massive RCTs.

Photobiomodulation modulates the expression of inflammatory cytokines during the compensatory hypertrophy process in skeletal muscle

Compensatory hypertrophy (CH) occurs due to excessive mechanical load on a muscle, promoting an increase in the size of muscle fibers. In clinical practice, situations such as partial nerve injuries, denervation, and muscle imbalance caused by trauma to muscles and nerves or diseases that promote the loss of nerve conduction can induce CH in muscle fibers. Photobiomodulation (PBM) has demonstrated beneficial effects on muscle tissue during CH. The aim of the present study was to evaluate the effect of PBM on the inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) as well as type 2 metalloproteinases (MMP-2) during the process of CH due to excessive load on the plantaris muscle in rats. Forty-five Wistar rats weighing 250 g were divided into three groups: control group (n = 10), hypertrophy (H) group (n = 40), and H + PBM group (n = 40). CH was induced through the ablation of synergist muscles of the plantaris muscle. The tendons of the gastrocnemius and soleus muscles were isolated and sectioned to enable the partial removal of each of muscle. The preserved plantaris muscle below the removed muscles was submitted to excessive functional load. PBM was performed with low-level laser (AsGaAl, λ = 780 nm; 40 mW; energy density: 10 J/cm²; 10 s on each point, 8 points; 3.2 J). Animals from each group were euthanized after 7 and 14 days. The plantaris muscles were carefully removed and sent for analysis of the gene and protein expression of IL-6 and TNF-α using qPCR and ELISA, respectively. MMP-2 activity was analyzed using zymography. The results were submitted to statistical analysis (ANOVA + Tukey's test, p < 0.05). The protein expression analysis revealed an increase in IL-6 levels in the H + PBM group compared to the H group and a reduction in the H group compared to the control group. A reduction in TNF-α was found in the H and H + PBM groups compared to the control group at 7 days. The gene expression analysis revealed an increase in IL-6 in the H + PBM group compared to the H group at 14 days as well as an increase in TNF-α in the H + PBM group compared to the H group at 7 days. Increases in MMP-2 were found in the H and H + PBM groups compared to the control group at both 7 and 14 days. Based on findings in the present study, it is concluded that PBM was able to modulate pro-inflammatory cytokines that are essential for the compensatory hypertrophy process. However, it has not shown a modulation effect directly in MMP-2 activity during the same period evaluated.

Effect of preoperative teres minor hypertrophy on reverse total shoulder arthroplasty

BACKGROUND

The preoperative status of the teres minor (Tm) can affect the outcome of reverse total shoulder arthroplasty (RTSA). The effect of preoperative Tm hypertrophy on the outcome of RTSA is unclear.

METHODS

A total of 86 shoulders that underwent RTSA were retrospectively enrolled. Of these, 48 cases with a Tm occupation ratio (OR) of >0.288 in the preoperative magnetic resonance image were assigned to the hypertrophic group, and 38 cases to the control group. The two groups were compared with respect to preoperative rotator cuff tear involvement, fatty infiltration, pre- and postoperative rotator cuff ORs, pain scores, functional scores, range of motion, and muscle strength. Postoperative Tm ORs in 1-year follow-up multidetector computed tomography were compared with preoperative Tm ORs.

RESULTS

Preoperatively, integrities of infraspinatus (ISP) and supraspinatus were significantly different between the 2 groups (P = .001, 0.009, each). Preoperative ISP ORs were significantly related to preoperative Tm ORs (r = -0.534, P < .001). The mean pre- to postoperative change of Tm ORs in the hypertrophic group decreased (-0.029 ± 0.068), whereas that of the control group increased (+0.047 ± 0.092). Postoperative pain scores, functional scores, range of motion, and muscle strength were not different between groups.

CONCLUSIONS

In cases of advanced rotator cuff tear requiring RTSA, Tm hypertrophy is found to be related to tear and atrophy of the ISP, suggesting that Tm hypertrophy is a compensatory change for ISP dysfunction. However, Tm hypertrophy was observed to diminish after RTSA. Preoperative Tm hypertrophy appears to have no beneficial effect on the outcomes of RTSA.

Impaired contractile function of the supraspinatus in the acute period following a rotator cuff tear

Background

Rotator cuff (RTC) tears are a common clinical problem resulting in adverse changes to the muscle, but there is limited information comparing histopathology to contractile function. This study assessed supraspinatus force and susceptibility to injury in the rat model of RTC tear, and compared these functional changes to histopathology of the muscle.

Methods

Unilateral RTC tears were induced in male rats via tenotomy of the supraspinatus and infraspinatus. Maximal tetanic force and susceptibility to injury of the supraspinatus muscle were measured in vivo at day 2 and day 15 after tenotomy. Supraspinatus muscles were weighed and harvested for histologic analysis of the neuromuscular junction (NMJ), intramuscular lipid, and collagen.

Results

Tenotomy resulted in eventual atrophy and weakness. Despite no loss in muscle mass at day 2 there was a 30% reduction in contractile force, and a decrease in NMJ continuity and size. Reduced force persisted at day 15, a time point when muscle atrophy was evident but NMJ morphology was restored. At day 15, torn muscles had decreased collagen-packing density and were also more susceptible to contraction-induced injury.

Conclusion

Muscle size and histopathology are not direct indicators of overall RTC contractile health. Changes in NMJ morphology and collagen organization were associated with changes in contractile function and thus may play a role in response to injury. Although our findings are limited to the acute phase after a RTC tear, the most salient finding is that RTC tenotomy results in increased susceptibility to injury of the supraspinatus.

Hypertrophic teres minor restores shoulder strength and range of external rotation in posterosuperior rotator cuff tears

BACKGROUND

In posterosuperior rotator cuff tears (PS-RCT), the progression of infraspinatus (ISP) muscle atrophy seems to induce compensatory hypertrophy of the teres minor (TM) muscles. However, the effect of these changes on shoulder strength and range of external rotation (ER) remains unclear. This study determined the strength and range of ER in patients with PS-RCT with atrophic ISP and hypertrophic TM and compared this with patients with PS-RCT and normal or deficient TM.

METHODS

We investigated 35 patients with PS-RCT and atrophic ISP. TM muscles were classified as hypertrophic (type A) in 17, normal (type B) in 10, or deficient (type C) in 8. The strength ratio of the affected shoulder to the healthy contralateral shoulder was calculated, and the active range of motion was measured for both shoulders.

RESULTS

The strength ratios of ER in types A, B, and C were 60%, 33%, and 7% (P < .01) with the patient's arm at the side and were 60%, 35%, and 5% (P < .001) at 90° abduction, respectively. The average ranges of ER in types A, B, and C were 22.6°, 15.0°, and -12.5° (P < .001) with the patient's arm at the side and were 71.6°, 44.5°, and 21.9° at 90° abduction (P < .01), respectively. The differences between shoulder types in other measures of strength or ER range were not significant.

CONCLUSIONS

In patients with PS-RCT and atrophic ISP, shoulders with compensatory hypertrophy of the TM had greater strength and range of ER than shoulders with normal or atrophic TM.

An age- and gender-related three-dimensional analysis of rotator cuff transverse force couple volume ratio in 304 shoulders

PURPOSE

The rotator cuff transverse force couple (RCTFC) is fundamental in the shoulder biomechanics, as the balance of its muscle components (the subscapularis relative to the infraspinatus and teres minor) provides stability to the joint. The chronic progression of rotator cuff tears usually present alterations in muscle volume, along with atrophy and compensatory hypertrophy, which can be determined using imaging techniques. The aim of this study was to quantify RCTFC muscle volume in a large sample taking into account the age and gender of the participants involved.

METHODS

An observational, retrospective, cross-sectional, descriptive and comparative study was conducted, evaluating thoracic computed tomography scans from 152 patients (304 shoulders) of indistinct gender, with ages ranging between 18 and 85 years. The RCTFC muscle volume was quantified with an oblique/multiplanar segmentation technique. Measuring time was also documented.

RESULTS

We observed that muscle volume decreases among the different age (p < 0.04) and gender (p < 0.001) groups. However, the RCTFC volume ratio remained constant at 1.02 ± 0.18 without significant differences throughout all age and gender groups evaluated (p > 0.298).

CONCLUSION

The decrease in the RCTFC muscle volume is proportional during the different stages of life, maintaining a constant ratio between its components (physiological RCTFC muscle atrophy). The time-saving segmentation method and volume ratio formula proposed in this study contribute to the management and understanding of rotator cuff tear/pathology.