Fatigue-related changes in intermuscular electromyographic coherence across rotator cuff and deltoid muscles in individuals with and without subacromial pain.

Neuromuscular fatigue induces superior migration of the humeral head in individuals with subacromial pain. This has been attributed to weakness of rotator cuff muscles and overactive deltoid muscles. Investigation of common inputs to motoneuron pools of the rotator cuff and deltoid muscles offers valuable insight into the underlying mechanisms of neuromuscular control deficits associated with subacromial pain. This study aims to investigate intermuscular coherence across the rotator cuff and deltoid muscles during a sustained submaximal isometric fatiguing contraction in individuals with and without subacromial pain. Twenty symptomatic and 18 asymptomatic young adults participated in this study. Surface EMG was recorded from the middle deltoid (MD) and infraspinatus (IS). Intramuscular EMG was recorded with fine-wire electrodes in the supraspinatus (SS). Participants performed an isometric fatiguing contraction of 30° scaption at 25% MVC until endurance limit. Pooled coherence of muscle pairs (SS-IS, SS-MD, IS-MD) in the 2-5 Hz (delta), 5-15 Hz (alpha) and 15-35 Hz (beta) frequency bands during the initial and final 30s of the fatigue task were compared. SS-IS and SS-MD delta-band coherence increased with fatigue in the asymptomatic group, but not the symptomatic group. In the alpha and beta bands, SS-IS and SS-MD coherence increased with fatigue in both groups. IS-MD beta-band coherence was greater in the symptomatic than the asymptomatic group. Individuals with subacromial pain failed to increase common drive across rotator cuff and deltoid muscles and have altered control strategies during neuromuscular fatigue. This may contribute to glenohumeral joint instability and subacromial pain experienced by these individuals.

Decreased rotator cuff muscle cross-sectional areas in subjects with adhesive capsulitis: a study comparing male and female subjects.

OBJECTIVE: To compare rotator cuff (RC) muscle cross-sectional areas (CSA) in subjects with adhesive capsulitis (AC) to age- and sex-matched controls. MATERIALS AND METHODS: We retrospectively analyzed 97 shoulder MRIs or MR arthrography studies, of which 42 were clinically diagnosed with AC (27 female, 15 male) and 55 were age- and sex-matched controls (38 female, 17 male). All AC subjects underwent imaging ≥ 6 months after symptom onset. All imaging was examined to exclude RC full-thickness tears and prior surgery. A standardized T1 sagittal MR image was segmented in each subject to obtain the CSA of subscapularis (SSC), supraspinatus (SSP), and infraspinatus (ISP) muscles. Differences in CSAs between AC and control subjects were analyzed by sex (females and males separately) and all subjects combined. RESULTS: AC females had significantly decreased SSC (P = 0.002) and total (P = 0.006) CSAs compared to controls. Male AC subjects showed decreased SSC (P = 0.044), SSP (P = 0.001), and total (P = 0.005) CSAs. Across all subjects, male and female, the AC cohort had significantly decreased SSC (P = 0.019) and total (P = 0.029) CSAs compared to controls. CONCLUSION: Decreased RC muscle CSAs were present in AC subjects with ≥ 6 months of symptom duration, with decreased SSC and total CSAs in male and female subjects, and decreased SSP CSA in males.

Subacromial balloon spacer massive rotator cuff tear treatment systematic review and meta-analysis: Patient selection and physical therapy may be keys to outcome success.

PURPOSE: Subacromial balloon spacer implantation (SBSI) efficacy for massive rotator cuff tear treatment was evaluated based on perceived shoulder function, active shoulder mobility, pain, complications and research study methodological quality. The purpose was to better discern the efficacy of this device from both surgical and rehabilitative perspectives to improve patient outcomes. METHODS: PubMed, EMBASE and Cochrane Library databases were searched (1 January 2010 to 1 June 2024) using 'balloon spacer', 'subacromial spacer', 'subacromial balloon spacer', 'shoulder spacer' and 'inspace' terms. Pre-surgery (baseline), 12-month (12-m) and 24-month (24-m) post-SBSI mean changes were compared using one-way ANOVA and Scheffe post hoc tests, and comparative study effect sizes were calculated (p ≤ 0.05). RESULTS: This review consists of 27 studies with 894 patients (67.8 ± 5 years of age) and 29.4 ± 17-month follow-up. Modified Coleman Methodology Scores (MCMS) revealed fair overall quality (mean = 61.4 ± 11). Constant-Murley scores improved from 34.8 ± 6 (baseline), to 64.2 ± 9 (12-m) and 67.9 ± 8 (24-m) (12-m, 24-m > baseline, p < 0.001). ASES scores improved from 35.1 ± 14 (baseline), to 83.3 ± 7 (12-m) and 81.8 ± 5 (24-m)(12-m, 24-m > baseline, p < 0.001). VAS pain scores improved from 6.6 ± 1 (baseline), to 2.6 ± 1 (12-m) and 2.0 ± 1 (24-m) (12-m, 24-m < baseline, p < 0.001). Flexion increased from 108.5 ± 25° (baseline), to 128.5 ± 30° (12-m) and 151.2 ± 14° (24-m) (24-m > 12-m, baseline, p = 0.01). Abduction increased from 97.7 ± 24° (baseline) to 116.3 ± 23° (12-m) and 142.3 ± 15° (24-m) (24-m > 12-m, baseline, p = 0.02). External rotation (ER) in adduction changed from 33.1 ± 7° (baseline) to 32.5 ± 4° (12-m) and 53.9 ± 9° (24-m)(24-m > 12-m, baseline, p = 0.01). ER at 90° abduction increased from 56.3 ± 3° (baseline) to 83.5 ± 5° (12-m) and 77.1 ± 4° (24-m) (24-m, 12-m > baseline, p = 0.01). Comparison studies, however, displayed insignificant results with small effect sizes. CONCLUSION: Despite overall fair MCMS scores, at 24-m post-SBSI, shoulder function improved and pain decreased. More rigorous comparative studies, however, revealed insignificant findings. Patients with the potential to re-establish the essential glenohumeral joint force couple that depresses the humeral head on the glenoid fossa and who comply with physical therapy may be more likely to achieve success following SBSI. LEVEL OF EVIDENCE: Level IV.

Anatomical analysis of the motor endplate zones of the suprascapular nerve to the infraspinatus muscle and its clinical significance in managing pain disorder.

Myofascial pain syndrome caused by myofascial trigger points is a musculoskeletal disorder commonly encountered in clinical practice. The infraspinatus muscle is the region most frequently involved in the myofascial pain syndrome in the scapular region. The characteristics of the myofascial trigger points are that they can be found constantly in the motor endplate zone. However, localizing myofascial trigger points within the motor endplate zone and establishing an accurate injection site of the infraspinatus muscle has been challenging because the anatomical position of the motor endplate zone of the infraspinatus muscle is yet to be described. Therefore, this cadaveric study aimed to scrutinize the motor endplate zone of the infraspinatus muscle, propose potential myofascial trigger points within the muscle, and recommend therapeutic injection sites. Twenty specimens of the infraspinatus muscle for nerve staining and 10 fresh frozen cadavers for evaluation of the injection were used in this study. The number of nerve branches penetrating the infraspinatus muscle and their entry locations were analyzed and photographed. Modified Sihler's staining was performed to examine the motor endplate regions of the infraspinatus muscle. The nerve entry points were mostly observed in the center of the muscle belly. The motor endplate was distributed equally throughout the infraspinatus muscle, but the motor endplate zone was primarily identified in the B area, which is approximately 20-40% proximal to the infraspinatus muscle. The second-most common occurrence of the motor endplate zone was observed in the center of the muscle. These detailed anatomical data would be very helpful in predicting potential pain sites and establishing safe and effective injection treatment using botulinum neurotoxin, steroids, or lidocaine to alleviate the pain disorder of the infraspinatus muscle.

Predictors of infraspinatus muscle degeneration in individuals with an isolated supraspinatus tendon tear.

OBJECTIVE: Determine the demographic and clinical factors that predict infraspinatus muscle degeneration in individuals with an isolated supraspinatus tendon tear. MATERIALS AND METHODS: A retrospective analysis was performed using the medical records of patients who had a shoulder MRI interpreted by 1 of 3 fellowship-trained musculoskeletal radiologists since the implementation of a standardized MRI 3 T protocol within our healthcare system. Demographic (e.g., age, sex) and clinical data (e.g., tear size, muscle degeneration, co-morbidities) were collected. Patients with an isolated supraspinatus tendon tear (n = 121) were assigned to one of two groups based on whether any infraspinatus muscle degeneration was present. Logistic regression was used to assess the univariate relationships between infraspinatus muscle degeneration and patient and clinical data, while least absolute shrinkage and selector operator (LASSO) logistic regression was used to assess the multivariable relationship. RESULTS: Of the patients with an isolated supraspinatus tendon tear, 16.5% had evidence of infraspinatus muscle degeneration. The presence of infraspinatus muscle degeneration was independently associated with cardiovascular disease (P = 0.01), supraspinatus muscle degeneration (P < 0.01), and subscapularis muscle degeneration (P = 0.01). When the multivariable relationship is assessed, supraspinatus muscle degeneration emerged as the only variable of significant importance for detecting infraspinatus muscle degeneration (specificity: 87.1%, sensitivity: 80.0%). CONCLUSION: Infraspinatus muscle degeneration is not uncommon in individuals with an isolated supraspinatus tear and is most associated with concomitant supraspinatus muscle degeneration. These findings highlight the need for clinicians to specifically assess the status of each rotator cuff muscle, even when the tendon itself is intact.

A standardized protocol for needle placement in the infraspinatus muscle: an anatomical perspective.

PURPOSE: This study aimed to evaluate the morphology of the three parts of the infraspinatus muscle based on surface landmarks for precise and effective access, and to propose the most effective fine-wire electrode insertion technique and sites. METHODS: Fifteen Asian fresh cadavers were used. We investigated the probability of the presence of the superior, middle, and inferior parts in each infraspinatus muscle based on surface landmarks. Based on the positional characteristics of the muscle, we determined the needle insertion method and confirmed its effectiveness by dissection. RESULTS: The superior part was mostly observed near the spine of the scapula. The middle part was broadly observed within the infraspinous fossa. The inferior part showed variable location within the infraspinous fossa. The injection accuracy of the superior, middle, and inferior parts in the infraspinatus muscle was 95.8%, 100%, and 91.7%, respectively. Targeting the superior and middle parts for injection of the infraspinatus muscle is relatively more straightforward than targeting the inferior part. Targeting the inferior part of the infraspinatus muscle in this study was more challenging than targeting the superior and middle parts. CONCLUSION: Needling for electromyography should be performed with special care to avoid unintended muscle parts, which could lead to inaccurate data acquisition and affect the conclusions about muscle function.

Delamination in rotator cuff tears: Explanation of etiology through anatomical dissection.

The prognostic significance of delaminated rotator cuff tears remains controversial. However, as the surgical goal is to maximize the contact area between layers, the macroscopic appearance of partial delaminated rotator cuff tears is essential. The aim of this anatomical study was to investigate the morphology of delaminated rotator cuff tears. We hypothesized that delamination zones at the intersection of the supraspinatus and infraspinatus tendon fibers are the origin of articular-side degenerative rotator cuff tears. Forty anatomical specimens were evaluated in this study. The supraspinatus and infraspinatus muscles were dissected, the origins were meticulously worked out and followed to their insertions at the humeral head. Fiber exchanges, overlays and delamination zones between the supraspinatus and infraspinatus muscles were photographically documented and measured. Delamination of rotator cuff tears can be classified into articular-side and bursal-side tears. The articular-layer consists of capsuloligamentous tissue, which included the rotator-cable/rotator-crescent complex, the joint capsule and a small part of the supraspinatus tendon. The bursal-side layer represents the tendinous tissue, which consists of the parallel, tendinous parts of the supraspinatus and infraspinatus muscles. Delamination of rotator cuff tears can be classified into articular-side and bursal-side tears. Present model of degenerative tears might explain the high prevalence of articular-side tears, which expand into the rotator-cable/rotator-crescent complex. It may be important for surgeons to incorporate these anatomical findings and considerations into the surgical planning.

Supraspinatus tendon reconstruction using open infraspinatus tendon shift and autologous biceps tendon interposition grafts.

INTRODUCTION: Inferior tendon quality, wide retraction, and tendon stumps that cannot be mobilized define the limits of what is technically feasible for open and arthroscopic rotator cuff reconstruction. The aim of this study was to develop a procedure that enables the open reconstruction of otherwise non-reconstructable rotator cuff tears. METHODS: From 2014 to 2018, 23 operations were performed on 21 patients (mean age 63) using open procedure involving separating the infraspinatus tendon from the point of insertion on the greater tubercle and mobilizing it proximally and ventrally into the defective area. Any remaining defects were augmented using an autologous biceps tendon interposition graft. This augmentation was performed to achieve complete closure of the defect. Furthermore, the augmentation of the rupture zone was intended to strengthen the tendon stumps of the SSP and ISP to better neutralize the initial tensile forces. After a postoperative period of 12 months-4 years, clinical examination and functional tests were carried out, the Constant score was determined, and radiological and magnetic resonance imaging check-up examinations were performed. RESULTS: The technique resulted in a low-tension closure of an otherwise "non-repairable" superior rotator cuff defect. All patients experienced a significant functional improvement, a reduction in pain, and an increase in muscle strength. An improvement in the Constant score from 48 points preoperatively to 87 points postoperatively (p < 0.05) was observed. In 19 patients (90%), the magnetic resonance image showed an intact reconstruction. Re-rupture was seen in three patients (14%). CONCLUSION: The surgical procedure using infraspinatus tendon shift and autologous biceps tendon interposition grafts resulted in the successful reconstruction of otherwise non-reconstructable massive rotator cuff lesions. The complete closure of the defect was observed.

An unreported infraspinatus muscle variation-two-headed infraspinatus minor muscle and three-headed fusion with the teres minor muscle.

The infraspinatus muscle is situated under the scapular spine in the infraspinous fossa and inserts into the greater tuberosity of the humerus. It is a component of a crucial shoulder muscle group, the rotator cuff. There are a few interesting additional muscles in the infraspinal region. In the literature they are called the infraspinatus superficialis, infraspinatus minor and infraspinatus accessory muscles. The infraspinatus minor muscle is described as a superficial muscle bundle running under the scapular spine. During routine anatomical dissection, an unreported variation of the infraspinatus minor muscle was found. It derived from the inferior surface of the scapular spine and the infraspinous fossa. It had two heads. The superior head inserted on the greater tuberosity of the humerus. The inferior head inserted on the tendinous part of the infraspinatus muscle. There was also an unusual fusion of the infraspinatus muscle with the teres minor muscle. In this paper we will discuss the anatomical and physiological relationships of this morphological variation.

The internal structure of the infraspinatus muscle: a magnetic resonance study.

PURPOSE: This study aimed to describe the internal structure of the infraspinatus muscle. A secondary aim was to explore differences in internal structure between genders, sides, and correlations to demographic data. METHODS: In total, 106 shoulder MRI examinations of patients between 18 and 30 years of age seeking care in 2012-2020 at The Sahlgrenska University Hospital in Gothenburg, Sweden were re-reviewed. RESULTS: The number of intramuscular tendons centrally in the infraspinatus muscle varied between 3 and 8 (median = 5). Laterally, the number of intramuscular tendons varied between 1 and 5 (median = 2). There was no difference in the median between the genders or sides. No correlations between the number of intramuscular tendons and demographic data were found. The muscle volume varied between 63 and 249 ml with a median of 188 ml for males and 122 ml for females. There was no significant difference in volume between the sides. The muscle volume correlated with body weight (Pearson's correlation coefficient, r = 0.72, p < 0.001) and height (r = 0.61, p < 0.001). CONCLUSION: The anatomical variations of the infraspinatus muscle are widespread. In the medial part of the muscle belly, the number of intramuscular tendons varied between 3 and 8, while the number of intramuscular tendons laterally varied between 1 and 5. Results of our study may help to understand the internal structure of the infraspinatus muscle and its function in shoulder stabilization.

A newly reported muscle: an accessory infraspinatus or a deep layer of the latissimus dorsi?

The infraspinatus muscle is a component of the rotator cuff; the latissimus dorsi muscle is the largest muscle of the back. These muscles are not considered very morphologically variable. However, the latissimus dorsi has more frequent variations than the infraspinatus. During anatomical dissection, an additional muscle structure was found. It originated on the medial border of the scapula, ran under the scapular spine, and ended on the greater tubercle next to the infraspinatus attachment. We will discuss the anatomical and physiological relationships of this muscle. We believe that our finding underlines the importance of different muscle variants in the rotator cuff region. Level of evidence: II basic science research.

Comparison of clinical outcome of decompression of suprascapular nerve at spinoglenoid notch for patients with posterosuperior massive rotator cuff tears and suprascapular neuropathy.

PURPOSE: In the present study, we aimed to determine whether decompression of suprascapular nerve (SSN) at the spinoglenoid notch could lead to a better functional outcome for the patients who underwent repairment of rotator cuff due to posterosupeior massive rotator cuff tear (MRCT) and suprascapular neuropathy. METHODS: A total of 20 patients with posterosuperior MRCT and suprascapular neuropathy were analyzed in the present work. The preoperative magnetic resonance imaging (MRI) showed rotator cuff tear in supraspinatus and infraspinatus. All patients underwent arthroscopic rotator cuff repair. Patients were divided into two groups (group A: non-releasing, group B: releasing) according to whether the SSN at the spinoglenoid notch was decompressed. The modified University of California at Los Angeles shoulder rating scale (UCLA) and visual analog scale (VAS) questionnaire were adopted to assess the function of the affected shoulder preoperatively and 12 months after the operation. Electromyography (EMG) and nerve conduction study (NCS) were used to evaluate the nerve condition. Patients underwent MRI and EMG/NCS at 6 months after operation and last follow-up. RESULTS: All patients were satisfied with the treatment. MRI showed that it was well-healed in 19 patients at 6 months after the operation. However, the fatty infiltration of supraspinatus and infraspinatus was not reversed. Only one patient in the non-releasing group showed the retear. The retear rate of group A and group B were 30% (3/10) and 20% (2/10) respectively at 12 months after the operation. One patient undergoing SSN decompression complained of discomfort in the infraspinatus area. His follow-up EMG after 6 months showed fibrillation potentials (1+) and positive sharp waves (1+) in the infraspinatus. The other patients' EMG results showed no abnormality. The postoperative UCLA and VAS scores were improved in both groups, and there was no significant difference in the follow-up outcomes between the two groups. CONCLUSIONS: Patients with postersuperior MRCT and suprascapular neuropathy, decompression of suprascapular nerve at spinoglenoid notch didn't lead to a better functional outcome with the repairment of rotator cuff. Arthroscopic rotator cuff repair could reverse the suprascapular neuropathy. LEVEL OF EVIDENCE: Level III.

Reliable diagnosis of posterosuperior rotator cuff tears requires a combination of clinical tests.

PURPOSE: Clinical diagnosis of posterosuperior rotator cuff tears remains uncertain due to a lack of evidence-based consensus. This review aimed to compare the diagnostic accuracy of commonly used clinical tests for posterosuperior rotator cuff tears. METHODS: The authors conducted an electronic literature search using Medline, Embase and the Cochrane library/Central, to identify original clinical studies reporting diagnostic accuracy of clinical tests to diagnose the presence of posterosuperior rotator cuff tears involving the infraspinatus, supraspinatus and/or teres minor. RESULTS: The electronic literature search returned 1981 records, of which 14 articles were eligible. Among 17 tests included in the systematic review, 6 tests were eligible for meta-analysis: drop arm sign, Jobe test, external rotation lag sign, Hawkins-Kennedy test, Neer test and painful arc abduction test. According to QUADAS-2 criteria, risk of bias was low in 1 study, moderate in 2 and high in 4. The highest pooled sensitivity was 0.77 (CI 0.67-0.85), for the Jobe test, while the lowest pooled sensitivity was 0.38 (CI 0.01-0.98), for the drop arm sign. CONCLUSIONS: The Jobe test had the best pooled sensitivity, while the drop arm sign had the best pooled specificity. As no single clinical test is sufficiently reliable to diagnose posterosuperior rotator cuff tears, clinicians should consider various combinations of patient characteristics and clinical tests, as well as imaging modalities, to confirm diagnosis and select the appropriate treatment option. More reliable clinical diagnosis of posterosuperior rotator cuff tears could reduce the reliance on magnetic resonance imaging or arthrography and their associated costs and waiting times. LEVEL OF EVIDENCE: Level II.

Infraspinatus and deltoid length and patient height: implications for lateralization and distalization in reverse total shoulder arthroplasty.

BACKGROUND: Restoration of muscular strength is predicated on restoration of muscle length. The purpose of this study was to describe infraspinatus and deltoid length preoperative to reverse total shoulder arthroplasty (RTSA) to guide distalization and lateralization to restore preoperative muscle length. METHODS: This was a retrospective radiographic study. We measured the infraspinatus length on preoperative computed tomographic images and the deltoid length on preoperative radiographs. For all measurements, reliability was first established by comparing measurements between 2 observers, and intraclass correlation coefficients (ICCs) were calculated. We then calculated descriptive statistics for these muscle lengths and developed a formula to predict these muscle lengths from patient demographics. RESULTS: We measured infraspinatus length in 97 patients and deltoid length in 108 patients. Inter-rater reliability was excellent, with all ICCs >0.886. The mean infraspinatus length was 15.5 cm (standard deviation 1.3) and ranged from 12.6-18.9 cm, whereas the deltoid length was 16.2±1.7 cm and ranged from 12.5-20.2 cm. Both infraspinatus (r = 0.775, P < .001) and deltoid length (r = 0.717, P < .001) were highly correlated with patient height but did not differ between diagnoses. Formulae developed through linear regression allowed prediction of muscle length to within 1 cm in 78% and within 2 cm in 100% for the infraspinatus and 60% and 88% for the deltoid. CONCLUSION: Deltoid and infraspinatus length are variable but highly correlated with patient height. To maintain tension, 2 mm of lateralization and distalization should be added for every 6 inches (∼15 cm) of height above average for a Grammont-style RTSA.

Strategies for controlling axial shoulder rotation change shoulder muscle activity during external rotation exercises.

BACKGROUND: The infraspinatus muscle has a crucial role in shoulder stability. Although axial shoulder rotation is useful for selective activation of the infraspinatus, no study has examined the influence of exercise position on axial shoulder rotation during shoulder external rotation (ER) exercises. Thus, this study investigated the muscle activity in the infraspinatus, posterior deltoid, and middle trapezius during shoulder ER exercises performed with and without controlled axial shoulder rotation in 2 different positions. METHODS: Twenty healthy subjects performed prone external rotation (PER) exercises with and without pressure biofeedback and seated external rotation (SITER) exercises with and without posterior humeral head gliding. Muscle activity during each ER exercise was measured using surface electromyography. RESULTS: Exercise strategy (P < .001) and position (P < .001) had a significant main effect on muscle activity in the infraspinatus and posterior deltoid. However, no significant interaction between strategy and position was observed. For muscle activity in the middle trapezius, strategy and position had a significant interaction effect (P = .014). Muscle activity in the infraspinatus increased significantly with the use of strategies to control axial shoulder rotation, whereas muscle activity in the posterior deltoid and middle trapezius decreased significantly. For all 3 muscles, greater activity was observed in the prone position than the seated position. CONCLUSION: We suggest that PER with pressure biofeedback can be useful to improve selective activation of the infraspinatus muscle while further eliciting infraspinatus muscle activity.

Surgical rotator cuff muscle biopsies: are they representative of overall muscle quality?

BACKGROUND: Current research on human rotator cuff pathology relies on superficial biopsy specimens. It is unclear whether these biopsies are representative of overall muscle quality. The purpose of this study is to use magnetic resonance imaging with iterative decomposition of echoes of asymmetric length sequencing to investigate variability of fatty infiltration within the supraspinatus and infraspinatus muscle. METHODS: We retrospectively identified 45 patients who underwent arthroscopic rotator cuff repair with preoperative iterative decomposition of echoes of asymmetric length imaging completed. The supraspinatus and infraspinatus were segmented on 4 consecutive slices, including the scapular Y, 2 slices medial, and 1 slice lateral. Intramuscular fat was measured in multiple regions for both supraspinatus (whole muscle, anterior, posterior, superficial band, anterior band, and posterior band) and infraspinatus (whole muscle, superior, inferior, superficial band, superior band, and inferior band). Comparisons of intramuscular fat were determined with Wilcoxon sign-rank tests. Analysis of variance was used to compare between the 4 consecutive slices. Significance was defined as P < .05. RESULTS: Magnetic resonance imaging showed 31 full-thickness supraspinatus tears, 10 partial-thickness supraspinatus tears, and 4 intact supraspinatus tendons and 3 full-thickness infraspinatus tears, 2 partial-thickness infraspinatus tears, and 40 intact infraspinatus tendons. The anterior supraspinatus contained significantly higher fat content than the posterior supraspinatus (7.4% ± 7.4% vs. 5.4% ± 5.7%, P = .003). The superior and inferior halves of the infraspinatus were not different from each other (P = .11). The superficial band did not differ from the whole muscle in both supraspinatus (P = .14) and infraspinatus (P = .20). However, the anterior band of the supraspinatus had significantly more fat than the posterior band (8.2% ± 9.3% vs. 5.0% ± 5.7%, respectively, P < .0001), and the superior band of the infraspinatus had significantly more fat than the inferior band (5.2% ± 4.8% vs. 4.2% ± 5.3%, respectively, P = .03). There was no difference between all 4 medial and lateral slices in the supraspinatus (P = .92) and infraspinatus (P = .90). CONCLUSION: Fat fractions within the supraspinatus and infraspinatus demonstrate significant spatial variability that may influence interpretation of local biopsy samples. Future biopsy studies may benefit from multiple samples between different specific locations.

Relationship between glenohumeral internal rotation deficit and shoulder conditions in professional baseball pitchers.

BACKGROUND: Previous studies have reported that glenohumeral internal rotation deficit (GIRD) may increase the risk of throwing-shoulder injuries. The purpose of this study was to analyze the conditions of the throwing shoulder in professional baseball pitchers with GIRD by comparing with those in pitchers without GIRD. METHODS: In total, 26 male professional baseball pitchers participated in this study. We evaluated passive range of motion (ROM) and isometric muscle strength at internal rotation (IR) and external rotation (ER) at 90° of abduction, as well as the muscle thickness of the supraspinatus (SSP) and infraspinatus (ISP) by ultrasound. The pitchers were divided into 2 groups: those who exhibited a loss of IR of ≥20° in the throwing shoulder (GIRD group) and those who did not (non-GIRD group). RESULTS: In the GIRD group, the total ROM deficit (throwing side - non-throwing side) (P < .001), the muscle thickness ratio (throwing to non-throwing) of the SSP and ISP (P = .017 and P = .014, respectively), and the muscle strength ratio (throwing to non-throwing) of ER (P = .028) were significantly lower than those in the non-GIRD group. In contrast, the muscle strength ratio (throwing to non-throwing) of IR was significantly higher in the GIRD group than in the non-GIRD group (P = .0064). CONCLUSIONS: We have shown that GIRD has significant correlations with several conditions, such as atrophy of the SSP and ISP, weakness of ER strength, enhancement of IR strength, limitation of total ROM, and throwing side, all of which could be important factors for throwing-shoulder injuries.

CT findings in a dog with subacute myopathy and later fibrotic contracture of the infraspinatus muscle.

A 5-year-old Norwegian elkhound was referred due to an acute onset of lameness and persistent shoulder pain over a period of 3 weeks. Computed tomography demonstrated an enlarged, hypoattenuating right infraspinatus muscle with peripheral contrast enhancement and a nonenhancing center, without concurrent lesions in superficial structures or bones. The right infraspinatus muscle showed progressive atrophy on consecutive CT studies. The dog developed clinical symptoms compatible with fibrotic infraspinatus contracture 2 months after the initial presentation, and was treated with infraspinatus tenotomy. Histopathological diagnoses based on intraoperative biopsy samples were fibrotic muscle atrophy and muscle hypertrophy with regeneration.

Shoulder scaption is dependent on the behavior of the different partitions of the infraspinatus muscle.

PURPOSE: The purpose of this study was to investigate if the three partitions (superior, middle, and inferior partitions) of the infraspinatus muscle previously described in anatomical studies will present different behavior during scapular plane abduction (scaption) as described using shear-wave elastography, especially during initial range of motion. METHODS: Eight volunteers held their arm against gravity 15° intervals from 30° to 150° in scaption. Shear-wave elastography was implemented at each position to measure shear modulus at rest and during muscle contraction, as a surrogate for muscle stiffness, of each partition. Muscle activity was defined as the difference in stiffness values between the resting positions and those during muscle contraction (ΔE = stiffness at contraction-stiffness at rest). RESULTS: The activity value for the middle partition was 25.1 ± 10.8 kPa at 30° and increased up to 105° (52.2 ± 10.8 kPa), with a subsequent decrease at larger angle positions (p < .001). The superior partition showed a flatter and constant behavior with smaller activity values except at higher angles (p < .001). Peak activity values for the superior partition were observed at 135° (23.0 ± 12.0 kPa). Increase activity for inferior partition began at 60° and showed a peak at 135° (p < .001; 32.9 ± 13.8 kPa). CONCLUSION: Stiffness measured using shear-wave elastography in each partition of the infraspinatus muscle demonstrated different behavior between these partitions during scaption. The middle partition generated force throughout scaption, while the superior and inferior partitions exerted force at end range.

Feasibility of lower trapezius transfer extended by the infraspinatus fascia for restoration of external rotation in irreparable posterosuperior rotator cuff tears: an anatomical study.

PURPOSE: Lower trapezius (LT) transfer using Achilles tendon allograft or semitendinosus autograft is effective in restoring external rotation in massive irreparable posterosuperior rotator cuff tears (RCT). The purpose of this study was to evaluate if the infraspinatus fascia (IF) could be used in LT transfer to extend the LT tendon. METHODS: Eight fresh-frozen whole-body cadavers were dissected using both shoulders, beach chair position. A 2.5-3 cm wide bundle of the IF was dissected, from the inferior angle of the scapula up to the insertion of the LT which was then detached subperiosteally in continuity with the fascia. The extended tendon was reinforced with sutures and brought to the center of the footprint of the supraspinatus on the humerus. We measured: (a) the distance between the insertion of the LT on the scapula and the inferior angle of the scapula, estimating the length of the IF that can be harvested, (b) the distance between the insertion of the LT on the scapula and the center of footprint of the infrastinatus on the humerus, estimating the distance needed to be covered by the graft (c) the length of the extended tendon between the center of footprint of the infrastinatus on the humerus (fixation point) and its free end, estimating the length available for fixation. RESULTS: The mean length of the fascia that can be harvested is 125.56 mm. The mean distance that needs to be covered by the graft is 100 mm. The extended tendon is long enough leaving 24.69 mm for fixation. CONCLUSIONS: The transfer of the LT extended with the IF on the footprint of the infraspinatus is feasible. It could be a viable alternative to the currently used grafts in LT transfer in irreparable posterosuperior RCT.