Recently, there are many patients and friends consulting about shoulder joint diseases, in order to enhance the understanding of shoulder joint diseases and achieve early diagnosis and timely treatment, this article is specially written for everyone’s reference, and we hope that it will be helpful to the people’s health care. Rotator cuff injury was firstly discovered and named by Smith in 1834, which did not attract much attention at that time, until Codman and Akerson pointed out in 1931 that this disease is an important cause of shoulder pain, and made a preliminary research on its diagnosis and treatment, many scholars began to carry out a large number of studies on this disease. Rotator cuff injury is one of the most common shoulder joint disorders in middle-aged and elderly people, which can cause shoulder pain and severe shoulder dysfunction, and its incidence accounts for about 17% of shoulder joint lesions, and Nobuhara’s statistics in Japan is 41%, which seriously affects the quality of life of middle-aged and elderly people. In this article, we will review the anatomical biomechanics, etiology, diagnosis and treatment of rotator cuff. I. Anatomy and biomechanics: The rotator cuff is composed of the muscle fibers of the supraspinatus, infraspinatus, subscapularis and teres minor that originate from the scapula and attach around the humeral head, mixed with the shoulder joint capsule to form a cuff-like structure at the anatomical neck of the humeral head, which has a supportive and stabilizing effect on the acromioclavicular joint. When the shoulder is abducted and lifted, the contraction of the rotator cuff muscles fixes the humeral head on the glenoid and prevents the strong contraction of the deltoid muscle from causing direct impingement of the humeral head on the acromion or the rostral shoulder arch. The supraspinatus acts as an overhead stabilizer for the humeral head, the infraspinatus and teres minor act as backward stabilizers and externally rotate the humerus, and the subscapularis has a role in internally rotating the humerus. The supraspinatus is the most important of the rotator cuff muscles in its role and is also the most susceptible to injury. Another role of the rotator cuff is to maintain a so-called airtight joint cavity, which helps maintain synovial fluid to nourish articular cartilage and prevent secondary osteoarthritis. The concept of rotator cuff gap tear was first proposed by Nobuhara, who suggested that the main clinical symptom is shoulder pain during shoulder lifting with force, and the patient has a feeling of instability in the shoulder joint. Anatomically, the rotator cuff space is the space between the supraspinatus tendon and the subscapularis tendon, and it is a triangle-like structure in the coronal plane. The medial side of the triangle is the root of the rostral process, and its upper and lower sides are formed by the supraspinatus tendon and subscapularis tendon, respectively, which terminate laterally at the greater tuberosity of the humerus and overlie the tendon of the long head of the biceps brachii in the intertransverse sulcus of the tuberosity. The rotator cuff space is the structure that bridges the supraspinatus tendon and subscapularis tendon and is actually part of the entire rotator cuff structure and is the structurally weakest part of the rotator cuff, limiting the downward movement of the humeral head and external rotation of the shoulder joint. Once the injury occurs, it will lead to the weakening of the combined force of supraspinatus and subscapularis muscles in the process of abduction of the upper arm, and the decrease of the force of the humeral head fixing on the glenoid, resulting in the laxity of glenohumeral joint and the decrease of the stability of the shoulder joint. Second, etiology pathogenesis: rotator cuff injury has many factors, including trauma, glenohumeral joint instability, shoulder-thoracic joint dysfunction, congenital or developmental deformity and degenerative changes. Among them, the degeneration theory and the impingement theory are the most known. (a) Degeneration theory: Lindblom and Palmer found that there was an obvious lack of blood vessels about lcm away from the end point of supraspinatus muscle by microangiography of rotator cuff, which was called “critical zone” by Codman and Moseley, and was caused by the blood vessels of supraspinatus, subscapularis and subscapularis muscles. Codman and Moseley called this area the “critical zone,” which is the junction of branches of the suprascapular and subscapularis arteries from the muscle belly and branches of the anterior rotator cuff artery from the greater tuberosity. Prior to degeneration of the supraspinatus tendon, there was marked ischemia in the avascular zone. This area of lack of blood supply causes localized ischemia of the tendon, which is an intrinsic factor leading to rotator cuff degeneration and tearing. Since then, some scholars through the study that the supraspinatus muscle vascularity reduction area with age increases degeneration, muscle fiber tissue necrosis and rupture, can be obvious rupture in case of minor trauma, this is the theory of degenerative trauma. It has been found that the dominant hand side is prone to rotator cuff tears, indicating that excessive wear and tear is a major factor in rotator cuff injury. Although, trauma is an external factor causing rotator cuff tear, however, for non-degenerative rotator cuff, trauma generally causes acute large tear or large nodal avulsion fracture, and only for the already degenerative rotator cuff, trauma will cause partial or complete rupture of the rotator cuff. (ii) Impingement theory: The impingement theory was proposed by Neer in 1972. Due to rotator cuff tendon hypertrophy, subacromial and acromioclavicular joint degeneration or osteochondral formation, low acromion and hook deformity in front and below the acromion, etc., the rotator cuff tendon which is located between the rostral acromial arch and the greater tuberosity of humerus head will be easily affected by the collision of the rostral acromial arch when the shoulder is abducted and uplifted and then becomes congested, edematous, denatured or even ruptured.Neer called this phenomenon as impingement syndrome. Kim examined 376 patients with rotator cuff injury and found that 74% of them had impingement of the acromion, which further confirmed Neer’s impingement theory. Bigliani and Morrison classified the acromion into three types of flattened, curved, and hooked acromion after anatomical study of 140 acromion joints in 71 cadaveric cases, and the acromion morphology of 73% of the specimens with complete rotator cuff injury was found to be flat, curved, and hooked. In these specimens, the morphology of the acromion in complete rotator cuff injuries was hook-shaped in 73% of the specimens, and it was concluded that the morphology of the acromion was closely related to the impingement sign of the shoulder. This autopsy result was also supported by the X-ray examination of 200 shoulder joints. Brooks et al. demonstrated that not only the supraspinatus muscle had lack of blood vessels, but also the infraspinatus muscle had obvious ischemia within 1.5 cm from the end point, and thus concluded that lack of blood vessels was not the main cause of rotator cuff tear.Ozaki et al. found that a lot of lesions of the rotator cuff, such as trabecular structural disorders, osseous sclerosis, osteochondral atrophy, and cystic degeneration, were found in the bursal surface of the rotator cuff, and that the bursal surface was partially broken or fully broken. They found that many acromioclavicular lesions such as trabecular structural disorders, osteosclerosis, osteochondral atrophy and cystic degeneration occurred in the bursa side of the rotator cuff in partial or full-thickness fracture specimens, but not in the rotator cuff below, i.e., on the articular side. Therefore, it is hypothesized that subacromial bony changes are secondary to rotator cuff injury and not due to subacromial bony degeneration causing rotator cuff injury. Other authors have correlated impingement syndrome with rotator cuff tears and found that rotator cuff tears increased with age, whereas subacromial osteochondral changes were not associated with age. Thus, it was hypothesized that impingement syndrome is not a major cause of rotator cuff tears.Harvie [3] and others have recently proposed that genetic factors play an important role in all-over rotator cuff tears through a controlled study of twin siblings versus the general population. It is now believed that rotator cuff tears are in fact the result of a combination of intrinsic and extrinsic factors. Intrinsic factors include the lack of vascularized area of the rotator cuff tendon and the specific location and function of the supraspinatus muscle, while extrinsic factors include repetitive use of the shoulder joint, subacromial impingement and varying degrees of traumatic injury to the shoulder joint. Clinical manifestations and signs: 1. Shoulder pain is the early symptom of rotator cuff rupture: the most typical pain is the pain in neck and shoulder at night and the pain in “over-head position” activity (when the affected limb is lifted higher than the top of one’s head). In the presence of chronic subacromial bursitis, the pain is persistent and recalcitrant. Sometimes accompanied by radiating pain to the neck and upper limbs, the pain is aggravated by lying on the affected side, seriously affecting sleep, and the patient is very painful. Pain has become the main reason for patients to consult the doctor and an important parameter for evaluating the effect of treatment. 2. Weakness of shoulder joint, atrophy of supraspinatus, infraspinatus and deltoid muscles. Depending on the location of rotator cuff injury, shoulder joint weakness can be manifested as abduction weakness, supination weakness or posterior extension weakness. Due to the pain and weakness, the active activity of shoulder joint is limited, and it can not be lifted and abducted, which affects the function of shoulder joint, but the passive activity range of shoulder joint is usually not obviously limited. 3.Pressure pain in the space between the anterior and inferior part of the acromion and the greater tuberosity. When the arm is lifted or rotated, a popping sound or a gravel rolling sound can be felt. Obvious gravel rolling sound is mostly seen in the third stage of the impingement sign, especially in complete rotator cuff tear injury. 4, the pain arc sign is positive, the affected limb in abduction lifting 600-1200 when the rotator cuff is subjected to the greatest stress and obvious anterior shoulder pain. 5. Positive hanging arm test, some patients can’t lift actively or can’t hold the upper limb after lifting due to pain. 6. Impingement test: there is pain when the humeral tuberosity impinges with the acromion. Imaging diagnosis (a) X-ray examination of rotator cuff injury has no direct diagnostic value, especially for acute tear or early lesions, but with the following X-ray signs, the diagnosis of subacromial impingement has reference value: (1) the acromion is too low in the form of hook or curve acromion; (2) subacromion and the humeral tuberosity is dense or osteochondritis dissecans formation; (3) the front of the acromion or the acromioclavicular joint, humeral tuberosity decalcification, erosion, (4) Rounding of the humeral tuberosity, disappearance of the boundary between the articular surface of the humeral head and the tuberosity, and deformation of the humeral head; (5) Reduction of the distance between the acromion and the humeral head. The range of normal acromion-humeral head distance is 1-1.5cm, less than 1.0cm is narrow, less than 0.5cm suggests extensive rotator cuff tear. Conventional X-ray film shows that rotator cuff injury patients with humeral head displacement and humeral tuberosity deformity, its positive rate is 78%, specificity is 98%, so the measurement of the acromion – humeral head spacing is very important. (ii) Arthrography was introduced in the 1930s and is the traditional imaging method for diagnosing rotator cuff tear injuries. Arthrographic methods include single-contrast contrast and double-contrast contrast, which utilize the principle of diagnosis by utilizing the humeromembranous articular cavity contrast agent to overflow into the subacromial bursa through the ruptured rotator cuff or to fill the biceps tendon sheath, and are able to make a diagnosis of full-thickness tear, partial tear of the articular surface of the rotator cuff, rotator cuff gap splitting, and frozen shoulder, and are especially accurate in diagnosing full-thickness tear. Accuracy rates of 90-100% have been reported by different authors. However, shoulder arthrography is an invasive test that requires X-ray fluoroscopy-guided puncture into the joint cavity, which is not only radiologically harmful, but also prone to misdiagnosis due to technical factors of the puncturer. The injection of contrast into the subacromial bursa can lead to misdiagnosis when the technique is not skillful, and Kelloran et al. pointed out that uneven distribution of contrast in the joint cavity, projection of the biceps tendon sheath to the lateral aspect of the greater tuberosity in external rotation, and injection of contrast into the subacromial bursa can lead to misdiagnosis. In patients with partial rotator cuff tears, shoulder arthrography is less accurate. (ii) Ultrasound diagnosis of rotator cuff tear has been applied in clinic since the early 80’s. Due to the advantages of non-invasiveness, dynamic observation, repeatability, high accuracy, ability to detect rotator cuff tendon tears other than supraspinatus; convenient operation, time-saving, low cost; ability to diagnose biceps tendon disorders at the same time; and unique value for postoperative follow-up of rotator cuff tear, etc., and the accuracy of diagnosis is high, as reported by foreign countries, the accuracy is 90%. The accuracy rate is 90%, and the sensitivity of ultrasound diagnosis of rotator cuff tear is reported to be 75% and the specificity is 92.3% in China. Therefore, it has been emphasized by clinical workers, and now many scholars are happy to accept it, especially it has unique value in epidemiological investigation and postoperative follow-up observation. However, when applying ultrasound to diagnose rotator cuff injury, the operator must be fully familiar with the pathological and anatomical basis of rotator cuff in order to make a reasonable description of the image, the diagnostic standard is not easy to grasp, and the diagnostic accuracy has a great correlation with the individual operation technique and experience, and it is difficult to make a uniform standard due to the difference of instruments, therefore, ultrasound diagnosis is mainly used as a more obvious tear, and it is easy to produce false-positive or false-negative results for the partially torn and the small full-thickness torn. According to Brandt, there are 7 ultrasound diagnostic criteria for rotator cuff tear: 1) interruption of echoes in the rotator cuff; 2) central strong echogenic band; 3) no rotator cuff echoes; 4) strong echogenic spots in the rotator cuff; 5) thinning of localized echogenic areas; 6) flat laminar echoes; and 7) thin hypoechoic shadows. (C) MRI examination is a commonly used clinical method to diagnose rotator cuff injury, which is completely non-invasive, with high soft tissue resolution and multi-plane imaging, which can observe rotator cuff tendon and its damage more intuitively, so its application prospect is significantly better than that of shoulder arthrography. Especially for the diagnosis of partial rotator cuff tear, conventional MRI is better than shoulder arthrography because it can determine whether there is a partial tear on the side of the bursa and within the tendon through the changes of rotator cuff morphology and signal. The accuracy of conventional MRI in the diagnosis of rotator cuff tears has been inconsistently reported by various authors. Evancho et al. reported that the sensitivity of conventional MRI for the diagnosis of total rotator cuff tears was 80%, whereas Singson et al. reported a sensitivity of 100%. o Iannotti et al. classified rotator cuff injuries into the following categories based on the pathologic changes on MRI: (1) Tendinitis: uniform increase in tendon signal intensity without morphological changes, subacromial and deltoid muscles, and (2) Tendonitis: uniform increase in tendon signal intensity without morphological changes. changes, and the fat layer of the subacromial and subdeltoid bursa is intact. (2) Incomplete rupture: a limited increase in tendon signal intensity with morphologic changes and disruption of the continuity of the fat layer of the subacromial and subdeltoid bursa. (3) Complete rupture: Significant increase in tendon signal intensity, obvious abnormal morphology, such as interruption of tendon continuity, retraction of the tendon muscle belly junction, or obvious muscle atrophy, increased signal intensity of the muscle, and interruption or disappearance of the continuity of the fat layer of the subacromial subcapsular bursa of the acromion and deltoid. (D) MRI shoulder arthrography is a new imaging method to diagnose rotator cuff injury in recent years. Zheng Zhuozhao et al. through the comparative study of rotator cuff injury imaging diagnostic methods that whether it is to diagnose rotator cuff tear or rotator cuff tear, MRI shoulder arthrography has high sensitivity, specificity and accuracy, and can be used as the first choice of diagnosis of rotator cuff lesions. Combining the characteristics of shoulder arthrography and conventional MRI scanning, MRI shoulder arthrography can not only visualize the morphology and signals of rotator cuff tendons, but also evaluate rotator cuff injuries relatively accurately. According to the literature, the accuracy of MRI shoulder arthrography in diagnosing rotator cuff tear can reach 100%. (A) Non-surgical treatment Non-surgical treatment of rotator cuff injury includes: rest, application of non-hormonal anti-inflammatory drugs, physical therapy, local closure, suction of calcified deposits, various kinds of exercises that are beneficial to the recovery of muscle strength and comprehensive rehabilitation methods. Most scholars believe that non-surgical treatment is suitable for patients with a short course (within 3 months), small tears, Neer stage I or older patients who do not have high functional requirements for the shoulder. Due to the wide variations in case selection, evaluation criteria, and quality of nonoperative treatment, the excellent rates of nonoperative treatment reported in the literature range from 33% to 82%. Goldberg reported that in 46 patients with full-thickness rotator cuff injuries who were treated conservatively, 59% of the patients had symptomatic improvement. Bokor et al. treated 53 full-thickness rotator cuff tears with comprehensive nonoperative treatment and achieved a pain relief rate of 77%, which increased over time, with 67% of the patients in pain relief at 6 years and 81% of the patients at 9 years of follow-up. Bartolozzi et al. reached similar conclusions after a multifactorial analysis of the follow-up data of 136 patients with rotator cuff injuries treated conservatively: the effectiveness of nonsurgical treatment was closely related to the length of follow-up, with the longer the duration the better the results, and found that poor outcomes were closely associated with rotator cuff tears of >1 cm, persistence of symptoms for >1 year prior to treatment, and significant functional decline. (ii) Surgical treatment (ii) Surgical treatment It has been 100 years since Muller (1898) first reported the use of surgery to repair rotator cuff tears. With the continuous improvement of technology and the introduction of arthroscopic techniques, there are a wide range of invasive treatments for rotator cuff injuries. Anatomically, the rotator cuff plays a role in the three-dimensional movement of the shoulder joint. In the coronal plane, there is a force couple between the deltoid muscle and the lower part of the rotator cuff (infraspinatus, teres minor, and infraspinatus); in the horizontal plane, there is another force couple between the anterior part of the rotator cuff (infraspinatus) and the posterior part (infraspinatus, teres minor). The purpose of rotator cuff tear repair is to rebalance these two pairs of force couples and restore shoulder joint stability, not just to repair the tear. However, due to the varied pathology of rotator cuff injuries, depending on the selected cases, the surgical methods and the evaluation criteria, the total effective rate is reported to be between 70% and 95%. The surgical treatment of rotator cuff injury can be divided into open surgery and arthroscopic surgery. Open surgery: McLuohling repair method This method is to fix the tendon and bone at the anatomical neck above the anterior aspect of the greater tuberosity of the humerus or to bury the proximal end of the rotator cuff into the bone groove at the anatomical neck and fix it, which is suitable for the patients with very few distal end stubs or those who can not be directly anastomosed. The advantage of this method is that the contact area between the proximal end of the tendon and the bone heals close to the structure of the normal rotator cuff stopping point, avoiding the scar formation of conventional side-to-side sutures.Neer (1972) concluded that rotator cuff injuries are closely related to rotator cuff impingement, and therefore an acromioplasty should be performed at the same time as the rotator cuff repair. Acromioplasty consists of excision of the rostrocapillary ligament, thickening of the subacromial bursa, and wedge resection of the anterior and inferior portions of the acromion until the arm is free of impingement in supination and abduction. Fokter used open surgery to treat 51 patients with full rotator cuff injuries with a mean follow-up of 4 years and a satisfaction rate of 88.2%. It was concluded that the treatment outcome was significantly related to the size of the tear and the duration of surgical treatment after the injury, independent of the mode of surgery, the mode of postoperative rehabilitation, and age. The combined application of subacromial decompression and rotator cuff repair acromioplasty in open surgery is the most commonly used method to treat rotator cuff injuries. For patients with large tears that cannot be repaired by conventional methods, many scholars have obtained better results by applying muscle transposition.Karas et al. applied the transposition of subscapularis muscle to the posterior superior in 20 cases of large tears (> 5cm) to treat large supraspinatus muscle tears with myasthenia gravis.The results showed that 85% of the patients were satisfied, but 2 cases had lost their shoulder elevation and 9 cases felt weak and uncomfortable during prolonged and repetitive over-exercise. Tiredness and discomfort during exercise, it pointed out that subscapularis transposition application for the treatment of large rotator cuff defects is effective, but caution should be exercised in patients who require too much supraspinatus horizontal motion. In addition, like Debeyre’s supraspinatus muscle lift, the supraspinatus muscle is stripped of part of its supraspinatus fossa attachment point and the muscle is pushed outward for defect repair while preserving the supraspinatus blood supply. It is mainly used for patients with large supraspinatus tendon defects. (ii) Advances in arthroscopic techniques have provided new treatment methods for rotator cuff injuries. Under arthroscopic surveillance, the type of tear can be diagnosed and evaluated, and the injury can be treated. The clear visualization of the structures involved makes the surgery safer than ever before, avoiding the potentially dangerous complications associated with open surgery, especially for triceps injuries. Since the early 1990s, many scholars have performed arthroscopic treatment of rotator cuff injuries, reporting excellent rates of 80%-92%. There are three methods of arthroscopic surgery for rotator cuff injury, namely subacromial decompression molding and rotator cuff repair; rotator cuff repair assisted by shoulder joint lesion debridement and small incision; and simple shoulder arthroscopic debridement. Wolf [8] and others applied arthroscopic treatment of rotator cuff injuries followed up for 4-10 years with a satisfaction rate of 94%.Severud [9] compared the efficacy of arthroscopic treatment of rotator cuff injuries with that of small incision treatment of rotator cuff injuries and found that there was no significant difference in the long term efficacy of the two, and that surgical efficacy was independent of the surgical method and depended more on the type of injury, while the arthroscopic group had a lower incidence of shoulder stiffness at 6-12 weeks and were able to achieve better range of motion. Hata [10] compared the use of small incision and conventional open surgery for rotator cuff injuries, the small incision approach did not lead to postoperative deltoid muscle atrophy, and at 3-month postoperative follow-up, shoulder scores were significantly higher than those of the conventional open group, which allowed for earlier recovery. Massoud performed arthroscopic acromioplasty and debridement for 114 chronic small and medium-sized rotator cuff injuries, and 74.6% of the patients were satisfied with the results, of which the satisfaction rates of patients under 60 years old and patients over 60 years old were 59.3% and 87.5%, respectively, which were significantly different. Early arthroscopic rotator cuff repairs were often performed with single-row rivet suture fixation, which gradually revealed some defects over time.Apreleva et al. recently showed that the attachment of the rotator cuff to the humerus is a complex three-dimensional structure, and the single-row reconstruction technique is not capable of completely reconstructing the normal rotator cuff due to the point-contact fixation of the rivets. Single-row rivet suture reconstruction of rotator cuff injuries can only reconstruct 67% of the rotator cuff, whereas conventional open perforator suture rotator cuff surgery can reconstruct 85% of the rotator cuff stopping point, and it is believed that the increase in the reconstructed area can promote healing and enhance the strength of the repaired tendon.Ian proposed the use of a double-row reconstruction technique for rotator cuff repairs. The double-row technique fixes the rotator cuff stump in two layers: the inner layer is fixed to the humeral head close to the outer edge of the articular surface, and the outer layer is fixed to the outer side of the bone bed at the inner edge of the trapping point of the greater tuberosity, which allows reconstruction of the entire rotator cuff, increases the contact area, and improves the healing process. The double-row reconstruction has an increased number of fixation points due to the addition of a second row of fixation, which increases the initial strength of the reconstructed tissue, reduces the load carried by each rivet, and improves the mechanical strength and function of the repaired rotator cuff, allowing for better healing at the anatomic point. De Beer et al. treated 58 patients with rotator cuff injuries using a modified double-row reconstruction method with an excellent rate of 90% at an average follow-up of 15 months, and more importantly, ultrasound showed an intact rotator cuff in 89% of the patients at postoperative follow-up. This may indicate that the double-row reconstruction technique may reduce postoperative rotator cuff retears and improve postoperative outcomes. Millett devised an alternative “mattress-type double-rivet fixation” that also increases the area of the rotator cuff to be reconstructed. This method consists of two separate suture rivets that are fixed independently of each other and then connected by a suture loop so that the load is distributed over the two rivets, which reduces the failure rate of the fixation. Compared with other double-row fixation methods, it has similar strength and requires fewer sutures to pass through the rotator cuff, making it a simple method. The treatment of massive rotator cuff tears has been controversial since today, and the management of this condition has included conservative treatment, arthroscopic debridement and or biceps tendon resection, partial repair and tendon transposition. Previously, it was thought that rotator cuff injuries of 10-30 mm could be operated arthroscopically, and large and giant rotator cuff tears should be repaired by open surgery due to supraspinatus tendon retraction, adhesion, and bursa fatigue scarring, and that open surgery was preferred to arthroscopic surgery for large and giant tear injuries. However, with the development of arthroscopic techniques, these views have changed, and Lo and Burkhart initially reported the use of arthroscopic repair of large rotator cuff injuries. The procedure was performed by anteriorly dissecting the rostro-humeral ligament and posteriorly isolating the supraspinatus and infraspinatus muscles to release the supraspinatus tendon. A significant improvement in pain scores was found at 18 months of follow-up. Bennett reported a 95% patient satisfaction rate in arthroscopic repair of giant rotator cuff injuries using the “convergence of margins method” and the “gap shift method”, and Jones and Savoie reported an 88% satisfaction rate in the repair of giant rotator cuff injuries using the same method. Jones and Savoie used the same method to repair large rotator cuff injuries, with a satisfaction rate of 88%. With the maturity of arthroscopic technology, it can be predicted that it will be the future development direction for the treatment of rotator cuff injury, which not only has a wide field of vision, but also can clarify the etiology of rotator cuff injuries, and is less traumatizing and quicker to recover after surgery.