Exploring the muscle architecture effect on the mechanical behaviour of mouse rotator cuff muscles.

Incorporating detailed muscle architecture aspects into computational models can enable researchers to gain deeper insights into the complexity of muscle function, movement, and performance. In this study, we employed histological, multiphoton image processing, and finite element method techniques to characterise the mechanical dependency on the architectural behaviour of supraspinatus and infraspinatus mouse muscles. While mechanical tests revealed a stiffer passive behaviour in the supraspinatus muscle, the collagen content was found to be two times higher in the infraspinatus. This effect was unveiled by analysing the alignment of fibres during muscle stretch with the 3D models and the parameters obtained in the fitting. Therefore, a strong dependence of muscle behaviour, both active and passive, was found on fibre orientation rather than collagen content.

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.

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.

A histoanatomical study of the fiber bundle forming the 'Comma Sign,' a critical marker of the torn edge of the subscapularis tendon.

INTRODUCTION: The "Comma sign" is a well-known indicator of the subscapularis torn edge of the shoulder. We undertook a histoanatomical study of the fiber bundle forming Comma sign (FBCS) to determine why FBCS is maintained even in cuff tear cases. MATERIALS AND METHODS: Part 1: five tissue blocks including the supraspinatus tendon (SSP), rotator interval (RI), and subscapularis tendon (SSC) out of 5 cuff-intact cadavers were histologically observed in serial sections. Part 2: another tissue blocks of 6 cuff-intact cadavers were serially sectioned along the estimated FBCS direction based on the Part 1 findings. Additionally, 5 tissue blocks of cuff-torn cadavers including the three components, SSP, FBCS, and SSC, were serially sectioned along the apparent FBCS. In one slice clearly demonstrating FBCS fibers out of each section series, the components were measured of the sound speed and visualized through a scanning acoustic microscope (SAM). RESULTS: At the lateral portion, RI tissue with the joint capsule became thick and tightly surrounded SSP. Similarly, thicker RI tissue adhered to SSC from the superior and bursal side. More laterally, the borders of SSP/FBCS and FBCS/SSC were unclear with intermingled fibers. At the lateral most portion, RI tissue formed a fiber bundle, FBCS, extending from SSP to the bursal side of SSC. The sound speeds of SSP and SSC were significantly faster than FBCS in both cuff-intact and cuff-torn slices. In SAM images of cuff-torn specimens the FBCS borders were all unclear. CONCLUSIONS: As FBCS extends from the capsule beneath SSP and to the bursal surface of SSC, the FBCS connection to SSP and SSC is hardly lost, even though SSP or SSC detaches from the greater or lesser tubercle, respectively. Additionally, as degeneration make the elasticity difference gradual, the stress concentration at the borders may be diminished, leading to less breakage of FBCS.

A very rare case of an accessory subscapularis muscle and its potential clinical significance.

The subscapularis muscle is the largest muscle of the rotator cuff and its main function is internal rotation. It is morphologically variable in both point of origin and insertion. The presence of an accessory subscapularis muscle can lead to brachial plexus neuropathy. This report presents a very rare accessory subscapularis muscle originating from two distinct bands on the subscapularis and teres major muscles. The insertion was divided among four tendons. The fourth tendon is bifurcated. One of these was connected to the tendon of the subscapularis muscle and the other three inserted into the base of the coracoid process of the scapula. This anomalous muscle has the potential to entrap the nerves of the posterior cord such as the axillary, lower subscapular, and thoracodorsal nerves.

The effect of swimming volume and intensity on changes in supraspinatus tendon thickness.

OBJECTIVES: To compare the change in supraspinatus tendon thickness (STT) following a high volume (HV) and high intensity (HI) swimming practice in shoulders of elite swimmers. DESIGN: Cohort Study. SETTING: Non-clinical, state swim team training facility. PARTICIPANTS: A convenience sample of eight non-injured state and national level swimmers from a regional swim team were recruited for this study. MAIN OUTCOME MEASURES: Ultrasound measures of STT were collected in response to the two swimming practice sessions. Measures were taken prior to each swim practice; immediately after practice; 6-hours post practice and 24-hours post practice. RESULTS: A significant increase in STT resulted from both the HI and HV (p < 0.05) practice immediately post practice. For the HI practice, the STT remained significantly thicker than pre-practice measures at the 6-hour post practice test (p < 0.05) however no longer significant 24-hours post practice. The difference in the change in STT between the HI and HV practice was significantly different immediately post practice and 6-hours post practice (p < 0.05) however no longer significant 24-hour post practice. CONCLUSION: Ultrasound measures of STT following different swimming volumes and intensities may provide information on shoulder tendon loads.

Chronic Nicotine Exposure Minimally Affects Rat Supraspinatus Tendon Properties and Bone Microstructure.

Cigarette smoking is the largest cause of preventable deaths, and a known risk factor for musculoskeletal issues including rotator cuff tendon tears. Tendon degeneration is believed to be due in part to changes in tendon cell health and collagen structure. Several studies have demonstrated that exposure to nicotine negatively impacts tendon healing, but surprisingly, nicotine exposure was shown to increase rat supraspinatus tendon stiffness. In order to address this seeming contradiction, the objective of this study was to comprehensively investigate the effects of long-term (18 weeks) exposure of nicotine on tendon-to-bone microstructural properties in a rat model. We hypothesized that long term subcutaneous nicotine delivery would lead to diminished tendon mechanical properties, decreased bone microstructure in the humeral head, and altered tendon cell morphology compared to age-matched control rats receiving saline. Results demonstrated a small decrease in tendon size and stiffness, with decreased cell density in the tendon midsubstance. However, no differences were found in the enthesis fibrocartilage or in the underlying subchondral or trabecular bone. In conclusion, our study revealed limited effects of nicotine on the homeostatic condition of the supraspinatus tendon, enthesis, and underlying bone. Future studies are needed to ascertain effects of other components of tobacco products.

The prevalence of acromial spurs in relation to study type and specimens examined

Advanced cases of subacromial impingement syndrome usually present with acromial spurs. However, previous studies have reported variations in the prevalence of acromial spurs in shoulders with or without subacromial impingement syndrome as well as with age, sex, and side. Therefore, this study is aimed at investigating the prevalence of acromial spurs in cadaveric shoulders and reviewing the factors leading to the reported variable frequencies. The study examined 220 cadaveric shoulders (110 male and 110 female), with a median age of 82 years (with a range of 53 to 102 years). In 155 shoulders, the rotator cuff tendons were evaluated for tears; acromial spurs were observed in 95 shoulders (43%). No significant association was observed between the prevalence of acromial spurs and sex or side. However, a significant prevalence of spurs (57%) was observed in the oldest-old group, aged ≥ 85 years. Those with acromial spurs also tended to be older (84 years) than those without spurs (81 years). A significant difference in the prevalence of acromial spurs was observed in shoulders with rotator cuff tears compared to those without them: 80% compared to 20%, respectively. Analysis showed a significant number of acromial spurs in shoulders with full-thickness tears (46%) and partial tears (34%). A significant prevalence of acromial spurs was found in shoulders with rotator cuff tears, as well as in aged shoulders. In relevant literature, the prevalence of acromial spurs varies with the type of study undertaken, age, prevalence of rotator cuff tears, and type of radiograph examined

No disponible

Quantitative and Qualitative Analyses of the Glenohumeral Ligaments: An Anatomic Study.

BACKGROUND: While several studies have qualitatively described the anatomy of the glenohumeral ligaments, there remains a lack of consensus regarding their quantitative humeral and glenoid attachment sites. PURPOSE: To quantitatively and qualitatively describe the anatomic humeral and glenoid attachment sites of the glenohumeral ligaments and their relationship to well-established anatomic landmarks. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 10 nonpaired, fresh-frozen human cadaveric shoulders were included in this study. A 3-dimensional coordinate measuring device was used to quantify the location of pertinent bony landmarks and soft tissue attachment areas. All subcutaneous tissues and musculature were removed, with the exception of the rotator cuff (respective muscle bellies cut at their musculotendinous junctions) and the long head of the biceps tendon. The superior glenohumeral ligament (SGHL), middle glenohumeral ligament (MGHL), anteroinferior glenohumeral ligament (AIGHL), posteroinferior glenohumeral ligament (PIGHL), and coracohumeral ligament (CHL) were then transected. Coordinates of points along the perimeters of attachment sites were used to calculate areas, while coordinates of center points were used to determine distances between surgically relevant attachment sites and pertinent bony landmarks. RESULTS: The mean length of the SGHL humeral attachment along the intra-articular cartilage margin was 9.5 ± 3.2 mm, spanning from 12:55 to 1:40, while the SGHL glenoid attachment to the labrum was 1.9 ± 1.2 mm medial to the most lateral extent of the labral rim, spanning from 12:30 to 12:45. The mean length of the MGHL attachment along the intra-articular cartilage margin was 16.4 ± 3.0 mm, equating to 2:10 to 3:35 on the humeral head clockface, and the glenoid attachment was confluent with the labrum, attaching 1.5 ± 1.0 mm medial to the most lateral extent of the labral rim and thus extending from 1:50 to 2:35 on the glenoid clockface. The mean length of the AIGHL attachment along the intra-articular cartilage margin was 12.0 ± 3.0 mm, spanning from 4:05 to 5:10 on the humeral head clockface. The AIGHL bony footprint on the glenoid neck was 48.4 ± 24.5 mm2. The confluent attachment of the AIGHL to the labrum was 1.2 ± 0.9 mm medial to the most lateral extent of the labral rim, corresponding to 3:30 to 4:05 on the glenoid clockface. The mean length of the PIGHL attachment along the intra-articular cartilage margin was 12.0 ± 1.4 mm, spanning from 7:40 to 8:50 on the humeral head clockface. The PIGHL attachment to the labrum was 1.2 ± 0.5 mm medial to the most lateral extent of the labral rim. This attachment to the labrum was calculated to span from 7:35 to 8:50 on the glenoid clockface. The mean length of the CHL origin from the coracoid was 12.9 mm, with its most anterior point located a mean of 14.1 mm from the tip of the coracoid. The mean length of the CHL attachment along the intra-articular cartilage margin was 10.0 ± 4.0 mm, spanning from 11:55 to 12:40 on the humeral head clockface. CONCLUSION: Glenohumeral ligaments were consistently identified in all specimens with minor anatomic variability for the SGHL, MGHL, AIGHL, and PIGHL. Important landmarks including the cartilage surface of the humerus, the bicipital groove, and the clockface can be utilized intraoperatively when attempting anatomic repair of these structures. CLINICAL RELEVANCE: There are multiple open and arthroscopic shoulder procedures that rely on anatomic restoration of these static stabilizers to provide optimal shoulder function and prevent recurrent instability. The qualitative descriptions are comparable with current literature; however, this study is the first to quantify the glenohumeral capsular and ligamentous attachments. The data provided allow for reliable landmarks to be established from known bony and soft tissue structures.

The Law of Use and Disuse: Critical Shoulder Angle and Rotator Cuff Tears-Association Does Not Imply Causation.

The critical shoulder angle has been associated with the development of rotator cuff lesions. Over time, this association has been interpreted as a cause-effect relation without scientific evidence. Beyond the controversies that exist on the reliability and relevance of this radiographic parameter, the critical shoulder angle per se may not be responsible for rotator cuff tears because patient activities throughout several decades could induce not only cuff lesions but also bone remodeling at the acromial level.

Tissue Engineering for the Ovine Rotator Cuff: Surgical Anatomy, Approach, Implantation and Histology Technique, along with Review of Literature.

Aim: Tissue engineering is a contemporary topic, which is widely discussed in shoulder surgery. The preclinical success of tissue engineering has not yet fully translated to clinical studies. In this study, we present our experience in this subject and discuss measurements to analyze the sheep tissue as comparative model. We also present a comprehensive systematic review of the literature in relation to tissue engineering and rotator cuff. Method: We studied the anatomy, histology and surgical approach of 24 infraspinatus tendons specimens in sheep and focused on certain measurements such as: (1) size of the normal tendon; (2) diameter of the normal footprint; and (3) bone hardness of the footprint using a durometer. Blood from six sheep was obtained and processed to produce platelet rich plasma using both the Harvest Smartprep and Cascade kit. We then outlined an approach to the infraspinatus tendon footprint in preparation for implantation of a biological augmentation material, which was repaired using a double row technique. This was followed by a histological analysis. Results: The average measurements of the footprint were 21 mm ×21 mm, the tendon length was 35.1 mm and the width proximal and distal was 21.9 and 14 mm, respectively. The average bone hardness at the 12, 3, 6, and 9 o'clock position was 64.1, 52.3, 50.1, and 37.7 respectively. Central footprint and lateral edge hardness was 44.8 and 43.4. Only the Harvest Smartprep and using a modified method, was able to produce a platelet concentration factor of 4. The Cascade method was unable to concentrate sheep blood. Conclusion: The sheep model is a suitable tissue for studying the rotator cuff. The researcher must be aware of certain interspecies caveats. Clinical tissue engineering and surgical techniques must be modified in order to be suitable when using sheep model.

Macroscopic and microscopic anatomy of the rotator cable in the shoulder.

BACKGROUND: The rotator cable, a semicircular fiber bundle in the lateral portion of the rotator cuff, has been believed to transmit forces among cuff tendons. This study was performed to clarify the functional anatomy of the rotator cable through histoanatomical methods. METHODS: Twenty-two cuff-intact shoulders of fixed cadavers were dissected. The cable was investigated from the cuff surface and articular/bursal sides of the capsule. The width of the cable and distances from the capsule attachment to both of the lateral and medial borders of the cable were measured, and their correlations to the humeral head diameter were calculated. The location of the cable on the humeral head was observed and recorded. In additional five shoulders the cuff/capsule complex and greater tubercle were harvested en block and histologically investigated. RESULTS: The rotator cable was evident in the capsule of 14 shoulders. One specimen demonstrated the cable of double curves. The capsule thickness alteration corresponding to the medial border of the cable with a single curve existed approximately on the so-called 'flexion point' where the humerus started to form a spherical curve from the greater tubercle to the joint surface. The 'flexion point' macroscopically corresponded to the medial boundary of the contact area between the cuff and head. The distance between the cable and capsule attachment showed marked negative correlation to the head diameter. Histologically the cable demonstrated cartilaginous metaplasia and vertical fiber orientation to the supraspinatus. CONCLUSIONS: The rotator cable does not always exist in all the shoulders and its appearances are varied. The location and cartilaginous metaplasia of the cable suggested compression force between the cuff and humeral head, and the force would help cable creation in capsule layer. The vertical fiber orientation of the cable to the supraspinatus would be unlikely to explain force transmission among the cuff tendons.

Biomechanical analysis of the humeral head coverage, glenoid inclination and acromio-glenoidal height as isolated components of the critical shoulder angle in a dynamic cadaveric shoulder model.

BACKGROUND: The Critical Shoulder Angle was introduced as a combined radiographic surrogate parameter reflecting the influence of the morphological characteristics of the scapula on the development of degenerative shoulder disease such as rotator cuff tears and osteoarthritis. Although, glenoid inclination and lateral extension of the acromion were studied in biomechanical models separately, no investigation included all three individual parameters that determine the Critical Shoulder Angle: glenoid inclination, acromial coverage and acromial height in one cadaveric study protocol. METHODS: Three proximal humerus cadavers were attached to a robotic shoulder simulator which allowed for independent change of either lateral acromial coverage, glenoid inclination or acromial height. Combined dynamic scapula-thoracic and glenohumeral abduction up to 60° with different Critical Shoulder Angle configurations was performed and muscle forces as well as joint reaction forces were recorded. FINDINGS: All three components had an effect on either muscle forces and or joint reaction forces. While glenoid inclination showed the highest impact on joint stability with increasing upward-tilting causing cranial subluxation, changing of the lateral acromial coverage or acromial height had less influence on stability but showed significant alteration of joint reaction forces. INTERPRETATION: All three components of the Critical Shoulder Angle, glenoid inclination, lateral acromial extension and acromial height showed independent biomechanical effects when changed isolated. However, glenoid inclination seems to have the largest impact regarding joint stability.

New predictors for subscapularis tear: Coraco-lesser tuberosity angle, lesser tuberosity angle, and lesser tuberosity height.

BACKGROUND: The pathogenesis of degenerative subscapularis (SC) tear is not clear, several mechanisms are involved: intrinsic tendon degeneration or subcoracoid impingement. The aim of this study was to propose new radiographic markers, the coraco-lesser tuberosity angle (CLA), lesser tuberosity angle (LTA) and lesser tuberosity height (LTH). The hypothesis was that higher values of CLA, LTA, and LTH would be associated with a higher likelihood in detecting a SC tear. METHOD: A total of 114 patients who classified as SC tears through arthroscopic evaluation were retrospectively enrolled in the study from 2016 to 2018. Fifty-seven patients with impingement syndrome were also enrolled as the control group for normal-population comparison. The CLA was measured on an anteroposterior shoulder x-ray image with the arm in neutral rotation, the LTA and LTH were measured on magnetic resonance imaging. Multivariable analyses were used to clarify the potential risks for SC tears. All measurements were calculated by two shoulder surgeons independently measured at 2 different times, 1 month apart. RESULTS: The intra- and inter-observer reliabilities for radiologic measurements and the interobserver reliability of SC tear classification were almost perfect. The mean CLA value of SC tear group (41.4±4.2°) was significantly larger than that of the control group (38.7±4.0°, p<0.001). The mean LTA value of SC tear group (33.4±4.3°) was significantly larger than that of the control group (31.0±3.9°, p=0.001). Mean LTH value was 9.5±1.9mm in patients and 8.9±1.5mm for controls, there was no statistically significant difference (p=0.054). Multivariable analysis showed that larger CLAs significantly increased the risk of SC tears, with odds ratios of 1.17 per degree. Moreover, larger LTAs also significantly increased the risk of SC tears, with odds ratios of 1.14 per degree. CONCLUSION: Our findings confirmed associations between new predictors (CLA and LTA) and SC tears. CLA and LTA values were greater in patients with SC tears than in controls, suggesting that they may be independent risk factors for SC tear onset. LEVEL OF EVIDENCE: IV, retrospective study.

Ultrasound of the normal canine supraspinatus tendon: comparison with gross anatomy and histology.

BACKGROUND: This study aimed to compare the ultrasonographic and histological features of the supraspinatus tendon (ST) and its peculiar appearance in contrast with the biceps brachii tendon. METHODS: For this purpose, 19 non-lame dog cadavers were subjected to an ultrasonographic and histologic evaluation of both shoulders after postmortem examination. RESULTS: Close to their insertion on the greater tubercle, all STs displayed a widened portion with a deep central hypoechoic area lacking a fibrillar pattern, when compared with its more proximal aspect and adjacent biceps brachii. Histologically this deep portion corresponded to poorly organised collagen bundles interspersed within a myxoid substance mainly composed of mucopolysaccharides. This central myxoid area with collagen disarray was responsible for the reduced echogenicity on ultrasound. CONCLUSION: The focal widening of the ST insertion and its central mucopolysaccharidic composition could be an anatomical adaptation to marked forces specifically applied to this tendon. However, the ultrasound and histological appearances are very similar to those described in tendinosis, which represents a confounding factor in diagnosing tendonitis at the insertion of the supraspinatus. In the absence of other ultrasonographic criteria of tendinopathy, a hypoechoic central area in the ST near its insertion should be considered normal.

Localized Rotator Cuff Tendon Degeneration for Cadaveric Shoulders with and Without Tears Isolated to the Supraspinatus Tendon.

Localized differences in tissue degeneration throughout intact and torn rotator cuff tendons have not been well quantified. The objective of this study was to investigate histological differences in localized degeneration in tendons with and without rotator cuff tears isolated to the supraspinatus tendon. Four intact shoulders and four shoulders with rotator cuff tears isolated to the supraspinatus tendon were dissected down to the infraspinatus and supraspinatus tendons. Biopsies were taken throughout the tendon insertion, mid-substance, myotendinous junction, and around the tear if present. Samples were stained with hematoxylin and eosin and tendon degeneration was graded based on collagen fiber organization, nuclei shape, cellularity, and lipoid degeneration. Comparisons in degeneration parameters were made based on the tendon type (supraspinatus vs. infraspinatus), location within the tendon, and presence of a tear. Supraspinatus tendons exhibited more degeneration than the infraspinatus tendon (P < 0.05). Significant increases in lipoid degeneration were found near the myotendinous junction compared to the rest of the tendon (P < 0.001). Tendons with rotator cuff tears showed greater amounts of lipoid degeneration compared to intact tendons (P = 0.03). A strong negative correlation was found between lipoid degeneration and collagen fiber organization (r = -0.922, P = 0.001). No differences in degeneration were found between medial, anterior, and posterior edges of the tear. The study highlights specific factors of tendon degeneration contributing to the local differences in tendon degeneration. By understanding local differences in tendon degeneration, surgical protocols for repair can be improved. Clin. Anat., 33:1007-1013, 2020. © 2019 Wiley Periodicals, Inc.

Is Bony Morphology and Morphometry Associated With Degenerative Full-Thickness Rotator Cuff Tears? A Systematic Review and Meta-analysis.

PURPOSE: To scope the scientific literature and analyze the influence of bony risk factors for degenerative full-thickness primary rotator cuff tear. METHODS: A systematic review of databases PubMed, Scopus, EMBASE, and Cochrane Library was performed up to June 30, 2018. Meta-analysis was performed with mean difference (MD) or risk ratio for degenerative full-thickness rotator cuff injury, and when there were ≥3 studies for the considered potential risk factor. Methodologic quality was assessed using the Newcastle-Ottawa scale. RESULTS: We analyzed 34 studies comprising 5,916 shoulders (3,369 shoulders with rotator cuff tear and 2,546 controls) and identified 19 potential risk factors for degenerative full-thickness rotator cuff tears. There was moderate evidence that a higher critical shoulder angle (MD = 4.41, 95% confidence interval [CI] 3.43 to 5.39), higher acromion index (MD = 0.06, 95% CI 0.04 to 0.09), and lower lateral acromion angles (MD = -7.11, 95% CI -8.32 to -5.90) were associated with degenerative full-thickness rotator cuff tears compared with controls. Moderate evidence showed that a type III acromion significantly increases the risk for full-thickness degenerative rotator cuff tear (risk ratio = 2.26, 95% CI 1.38 to 3.70). CONCLUSION: There is moderate evidence that larger critical shoulder angle, higher acromion index, lower lateral acromion angles, and a type III acromion are significantly associated with degenerative full-thickness rotator cuff tears. Other potential risk factors identified showed insufficient evidence. LEVEL OF EVIDENCE: Level IV, systematic review of level II to IV studies.