Rotator Cuff Injury

　　1, Etiology

　　There are four main viewpoints on the etiology of rotator cuff injury: blood supply theory, degeneration theory, impingement theory, and trauma theory.

　　1, Degeneration Theory

　　The histopathological manifestations of tendon degeneration described by Yamanaka through the study of cadaveric specimens include: deformation, necrosis, calcium salt deposition, fibrinoid thickening, glassy degeneration, partial rupture of muscle fibers, the formation of fibrils, and the disappearance of collagen wavy morphology. There is proliferation of small arteries, and chondrocyte-like cells appear within the tendons. The degeneration of the rotator cuff insertion (enthesis) is manifested by the duplication of the tidal line and irregularity, the normal four-layer structure (intrinsic tendon, tidal line, mineralized fibrocartilage, and bone) is irregular or disappears, or granulomatous changes appear. These changes are rarely seen in adults under the age of 40, but show a trend of increasing severity with age.

　　The study by Uhtoff et al. demonstrated the pathological characteristics of enthesopathy: disordered arrangement, rupture, and the formation of osteophytes at the insertion of tendons. The degree of degeneration of the sulcus, which is the distance between the cartilage edge of the humeral head and the insertion of the supraspinatus tendon, is proportional to the width of the sulcus. The degeneration of the insertion of the tendons reduces the tension of the tendons and becomes an important cause of rotator cuff tears.

　　The degeneration and transformation of tendons, partial rupture, and complete rupture of tendons are common causes of injury in elderly patients.

　　2, Blood Supply Theory

　　Codman first described the 'danger zone' located within 1 cm of the distal end of the supraspinatus tendon, which is an avascular area where rotator cuff tears most commonly occur. Perfusion studies of cadaveric specimens have confirmed the existence of the danger zone, that is, the blood supply of the bursal surface is better than that of the joint surface, consistent with the higher incidence of joint surface tears than bursal surface tears. Brooks found that there is also an avascular area within 1.5 cm of the distal end of the infraspinatus tendon. However, the incidence of supraspinatus tears is much higher than that of infraspinatus tendons, so in addition to blood supply factors, there should be other factors.

　　3. Impingement Theory

　　The concept of shoulder impingement syndrome (impingement syndrome of the shoulder) was first proposed by Neer II in 1972, who believed that rotator cuff injury was caused by impingement under the acromion. This impingement usually occurs in the anterior one-third of the acromion and below the coracoid process under the acromioclavicular joint. Neer II divided the impingement syndrome according to the anatomical location of the impingement and named it outlet impingement syndrome and non-outlet impingement syndrome. He believed that 95% of rotator cuff tears were caused by impingement syndrome. The supraspinatus tendon passes through the acromion and greater tuberosity, and the long head of the biceps brachii tendon is located deep to the supraspinatus, crossing over the head of the humerus to terminate at the top or superior rough tubercle of the glenoid. During shoulder movement, these two tendons move back and forth under the coracoid arch. The degeneration or developmental abnormalities of the acromion and subacromial structures, or instability of the glenohumeral joint caused by dynamic reasons, can lead to impingement injuries of the supraspinatus tendon, long head of the biceps brachii tendon, and subacromial tendon. Early stage is bursal lesion, and in the middle and late stages, tendinous degeneration and rupture occur.

　　However, some clinical studies have shown that a considerable number of cases of rotator cuff tears are not related to subacromial impingement, but are solely due to injury or tendon degeneration. In addition, cases with anatomical abnormalities related to subacromial impingement do not always lead to rotator cuff rupture. Therefore, subacromial impingement syndrome is an important etiology of rotator cuff injury, but not the only factor.

　　4. Trauma

　　(1) Overview: Trauma as an important etiology of rotator cuff injury has been widely accepted. Occupational injuries, sports injuries, and traffic accidents are common causes of rotator cuff trauma. Neviaser et al. found in patients over 40 years of age that if the shoulder cannot be abduced after reduction in patients with anterior glenohumeral joint dislocation, the incidence of rotator cuff injury is 100%, while axillary nerve injury accounts for only 7.8%. In the elderly, trauma that does not cause fracture or dislocation can also lead to rotator cuff tears. Any displaced greater tuberosity fracture is associated with rotator cuff avulsion fractures. Trauma can be divided into severe trauma and repetitive minor trauma according to the magnitude of the injury-causing force, with the latter being more important in rotator cuff injuries. Repeated minor injuries in daily activities or sports cause microtears of muscle fibers within the tendons (microtear), which, if not sufficiently repaired, will further develop into partial or full-thickness tendon tears. This pathological process is more common in professional athletes engaged in throwing sports.

　　(2) Forms of violence: Common forms of violence in acute injuries include:

　　① The upper arm is directly pulled by violence, resulting in injury to the supraspinatus tendon.

　　② The upper arm is subjected to an external force that causes it to be suddenly and excessively adducted, leading to excessive traction on the supraspinatus tendon.

　　③ The axilla is subjected to a counter-impact injury from below upwards below the glenoid cavity, causing the supraspinatus tendon to be relatively pulled and injured by impact under the acromial arch.

　　④ Direct violence from the outer upper part of the shoulder exerts a downward impact force on the upper end of the humerus, causing the rotator cuff to be pulled and injured.

　　In addition, less common injuries include incised wounds and gunshot wounds, etc.

　　(3) Degenerative factors.

　　In summary, the intrinsic factors of rotator cuff injury are the tissue degeneration of the rotator cuff tendons with aging, as well as the inherent weakness of the avascular area in the anatomical structure. Trauma and impingement accelerate the degeneration of the rotator cuff and contribute to the occurrence of rupture. As Neviaser emphasized, four factors contribute to the degenerative process of the rotator cuff to varying degrees, and no single factor can cause rotator cuff injury alone. The key factor should be determined based on the specific situation.

　　Second, Pathogenesis

　　Rotator cuff injuries can be divided into three types according to the degree of injury: contusion, incomplete rupture, and complete rupture.

　　Rotator cuff contusion causes congestion, edema, and even fibrosis of the tendons, which is a reversible injury. The subacromial bursa on the surface of the tendon has corresponding inflammatory reactions, and the bursa has exudative changes. Partial tears of the rotator cuff tendon fibers can occur on the joint surface side (below) or the bursal surface side (above) of the supraspinatus tendon, as well as within the tendon itself. Incomplete tears often develop into complete tears if not properly treated or repaired. Complete tears refer to a full-thickness tendon rupture, causing a transverse injury between the glenohumeral joint and the subacromial bursa. This type of injury is more common in the supraspinatus tendon, followed by the subscapularis tendon, and less common in the teres minor tendon. It is also not uncommon for both the supraspinatus and subscapularis tendons to be involved simultaneously.

　　When the direction of the tear after a tendon rupture is perpendicular to the direction of the muscle fibers, it is called a transverse rupture; when the direction of the tear is consistent with the direction of the muscle fibers, it is called a longitudinal rupture. The splitting of the rotator cuff gap also belongs to longitudinal rupture and is a special type of injury. According to the range of tendon rupture, it can be divided into three types: small tears, large tears, and extensive tears. According to Lyons' classification method: small tears are less than 3 cm; medium tears are 3-4 cm; large tears are less than 5 cm, and there are 2 tendons involved. The author's classification is as follows: small tears refer to a single tendon rupture with a range less than half of the tendon's transverse diameter; large tears refer to a single tendon rupture with a length greater than half of the tendon's transverse diameter; extensive tears involve 2 or more rotator cuff tendons, with retraction and defect of the rotator cuff tissue.

　　It is generally believed that injuries within 3 weeks are considered fresh injuries, while those over 3 weeks are considered chronic injuries. The ends of fresh tendon ruptures are irregular, the muscle swells, the tissue is friable, and there is effusion in the glenohumeral joint cavity. In chronic ruptures, the ends have formed scars, are smooth and rounded, and are relatively hard. There is a small amount of纤维素-like effusion in the joint cavity, and the bare area of the joint surface near the greater tubercle is covered by vascularized or granulation tissue.

　　1. Dysfunction

　　For patients with large shoulder袖 rupture, the active function of shoulder elevation and abduction is limited. The range of abduction and elevation is both less than 45°. However, there is no obvious limitation in passive activity range.

　　2. Muscle atrophy

　　For patients with a history of more than 3 weeks, there is varying degrees of atrophy of the shoulder muscles, with the deltoid, supraspinatus, and infraspinatus muscles being more common.

　　3. Secondary joint contracture

　　For patients with a course of disease over 3 months, there is a varying degree of limitation in the range of motion of the shoulder joint, with marked limitation in abduction, external rotation, and elevation.

　　Firstly, clinical manifestations

　　1. Trauma history

　　History of acute injury, as well as repetitive or cumulative injury history, is of reference significance for the diagnosis of this disease.

　　2. Pain and tenderness

　　Commonly located in the anterior shoulder pain, located in the front and lateral side of the deltoid muscle, acute pain is severe and persistent; chronic pain is spontaneous dull pain, symptoms worsen after shoulder movement or increased load, passive external rotation of the shoulder joint also increases pain, and worsening at night is one of the common clinical manifestations. Tenderness is often seen near the greater tubercle of the humerus or in the subacromial interspace.

　　3. Dysfunction

　　For patients with large shoulder袖 rupture, the active function of shoulder elevation and abduction is limited. The range of abduction and elevation is both less than 45°. However, there is no obvious limitation in passive activity range.

　　4. Muscle atrophy

　　For patients with a history of more than 3 weeks, there is varying degrees of atrophy of the shoulder muscles, with the deltoid, supraspinatus, and infraspinatus muscles being more common.

　　5. Secondary joint contracture

　　For patients with a course of disease over 3 months, there is a varying degree of limitation in the range of motion of the shoulder joint, with marked limitation in abduction, external rotation, and elevation.

　　Secondly, special signs

　　1. Shoulder drop test

　　Passively raise the affected arm to the range of 90° to 120°, remove the support, and the affected arm cannot support itself, causing arm drop and pain, which is positive.

　　2. Impingement test

　　Press down on the acromion, and at the same time, raise the affected arm passively. If there is pain or inability to raise the arm under the acromial interspace, it is positive.

　　3. Pain arc sign

　　When there is pain in the anterior or subacromial area of the shoulder when the affected arm is raised within the range of 60° to 120°, it is positive, which has certain diagnostic significance for shoulder袖 contusion and partial tearing.

　　4. Glenohumeral joint friction sound

　　That is, the glenohumeral joint produces a grinding sound or grinding sound during active movement or passive activity, often caused by scar tissue at the end of the shoulder袖.

　　This disease is caused by direct trauma to the shoulder, such as falls, accidents, or sudden braking while driving. Therefore, attention should be paid to lifestyle habits, high-risk workers such as construction workers, miners, and machinery operators are prone to injury, and protection should be taken during work. Stay calm when facing things, avoid emotional excitement leading to conflict and causing this disease. In addition, early detection, early diagnosis, and early treatment are also of great significance in preventing this disease.

　　1. X-ray Photography

　　X-ray plain film examination is not specific for the diagnosis of this disease. When the shoulder acromion and the top of the humeral head are photographed at a horizontal distance of 1.5m, the distance between them should not be less than 12mm. If it is less than 10mm, it generally suggests the presence of a large rotator cuff tear. Under the traction of the deltoid muscle, it can promote the upward movement of the humeral head, and the X-ray plain film shows that the subacromial space is narrow. In some cases, the surface of the greater tuberosity is irregularly ossified or osteophytes are formed, and the cancellous bone shows bone atrophy and porosity. In addition, if there are X-ray manifestations such as a low acromion, a hook-shaped acromion, and hardening and irregularity of the subacromial joint surface, it provides evidence of the presence of impingement factors. The dynamic observation of the elevated arm movement can observe the relative relationship between the greater tuberosity and the acromion and whether there is an impingement phenomenon under the subacromial area. X-ray plain film examination also helps to differentiate and exclude shoulder joint fractures, dislocations, and other bone and joint diseases.

　　2. Joint Arthrography

　　In normal anatomical conditions, the glenohumeral joint communicates with the subscapular bursa and the sheath of the long head of the biceps brachii muscle, but does not communicate with the subacromial bursa or the infraspinatus bursa. If the subacromial bursa or the infraspinatus bursa appears in the glenohumeral joint arthrography, it indicates that the interposed structure - the rotator cuff has ruptured, causing the contrast agent in the glenohumeral joint cavity to leak out through the rupture and enter the subacromial bursa or the infraspinatus bursa. Arthrography of the glenohumeral joint is a very reliable diagnostic method for complete rotator cuff tears, but it cannot make an accurate diagnosis for partial rotator cuff tears.

　　The method of glenohumeral joint arthrography is: the patient lies on his back, a mark is made at the tip of the coracoid process of the affected arm, the skin is disinfected, and sterile gauze is placed. Local skin infiltration anesthesia is performed 1cm laterally and below the tip of the coracoid process, followed by a vertical puncture with a thin, long needle into the joint cavity, or the needle tip is introduced into the glenohumeral interval under X-ray guidance. First, 1ml of a pre-prepared mixed contrast agent (60% diatrizoate meglumine 20ml, plus 2% lidocaine 10ml and injection water 10ml, prepared into a mixed solution containing 30% diatrizoate meglumine and 0.5% lidocaine 40ml) is injected, and the distribution of the contrast agent on the humeral head and glenohumeral joint surface is observed. If the contrast agent is evenly distributed along the humeral head or glenohumeral joint, it indicates successful puncture. The remaining contrast agent is slowly injected to fill the glenohumeral joint cavity completely. Generally, the capacity of the glenohumeral joint cavity is within the range of 15-25ml. The capacity and shape of the glenohumeral joint, as well as whether the contrast agent leaks out, are observed in the internal and external rotation positions of the hanging arm, and in the internal and external rotation positions of the elevated arm, as well as in the internal and external rotation lateral positions at the 90° abduction position, and the film is taken at the clearest position for recording.

　　Glenohumeral joint arthrography can not only show rotator cuff tears but also can judge the size of the tear according to the location and extent of contrast agent leakage. In addition, it can identify pathologic changes such as rotator cuff interval splitting, glenohumeral joint contracture, 'frozen shoulder', and instability of the glenohumeral joint. If a double-contrast arthrography with diatrizoate meglumine and gas is performed (the former 4-5ml, the latter 20-25ml), the anatomical shape of the labrum and joint capsule can be clearly displayed in the axial view when the shoulder is abducted 90°. This is undoubtedly a useful auxiliary diagnostic method when CT examination is not available.

　　Before performing a glenohumeral joint arthrography, an iodine allergy test should be performed first.

　　3. CT examination

　　The use of CT alone is of little significance for the diagnosis of rotator cuff lesions. The combined use of CT and arthrography is meaningful for detecting tears of the subscapularis and infraspinatus muscles and for identifying coexisting pathological changes. In cases of widespread rotator cuff tears accompanied by instability of the glenohumeral joint, CT examination can help to detect abnormal anatomical relationships between the glenoid and the humeral head as well as manifestations of instability.

　　4. Magnetic resonance imaging

　　Magnetic resonance imaging (MRI) is an important method for diagnosing rotator cuff injuries, which can display pathological changes of the tendon tissue based on different signals of the injured tendons in terms of edema, congestion, rupture, and calcium salt deposition. The advantages of MRI are that it is a non-invasive examination method with reproducibility and high sensitivity to soft tissue injuries, with a sensitivity of over 95%. However, the high sensitivity leads to a higher rate of false positives, and further improvement of the specificity of diagnosis requires in-depth imaging and pathological comparative studies as well as the accumulation of case numbers and practical experience.

　　5. Ultrasound diagnostic method

　　Ultrasound diagnosis is also a non-invasive diagnostic method, which is simple, reliable, and can be repeated, making it an advantage. Ultrasound diagnosis can clearly distinguish rotator cuff injuries, with high-resolution probes able to show pathological changes such as edema and thickening of the rotator cuff. In cases of partial rotator cuff rupture, it shows defects or atrophy, thinning; in complete rupture, it shows the ends and fissures, as well as the extent of the tendon defect. Ultrasound diagnosis is superior to arthrography in the diagnosis of incomplete tendon rupture.

　　6. Arthroscopic diagnosis

　　Shoulder arthroscopy is a minimally invasive examination method, generally used for cases suspected of having rotator cuff injury, labral lesions, long head of the biceps brachii tendon detachment (SLAP) lesions, and instability of the glenohumeral joint. The arthroscopic diagnosis of rotator cuff injury usually adopts a lateral decubitus position with the upper limb abducted 70° or a semi-recumbent position (beach chair position), with an entry point 2 to 3 cm below the posterior-lateral angle of the acromion, with the acromial tip as a landmark, inserting the arthroscope between the infraspinatus and teres minor muscles, and inserting a drainage guide wire from the front under the guidance of the arthroscope. The order of observation within the joint cavity is as follows: anteriorly: including the glenoid, anterior labrum, anterior inferior margin, glenohumeral ligament, subscapularis tendon, and supraspinatus tendon, as well as the rotator cuff interval; superiorly: the supraspinatus tendon and its proximal insertion of the greater tubercle, the long head of the biceps brachii tendon and its origin on the superior glenoid with surrounding labrum (for subscapularis injuries, arthroscopy should be performed via the anterior approach); posteriorly: the articular surface of the humeral head and the posterior superior aspect, as well as the posterior inferior aspect of the glenoid and labrum. In case of necessity, an endoscope can be inserted through the subacromial space to observe whether there is any injury or partial tendon rupture on the rotator cuff bursal surface, and at the same time, it can observe the presence of osteophytes or other impinging factors below the acromion. While observing under the arthroscope, different directions of push-pull, traction, can be performed on the glenohumeral joint to understand the stability of the joint.

    The diet of patients with rotator cuff injury should be light and easy to digest, with more fruits and vegetables, reasonable dietary搭配, and attention to adequate nutrition. In addition, patients need to pay attention to avoid spicy, greasy, and cold foods.

　　First, treatment

　　The choice of treatment method depends on the type and time of rotator cuff injury. The acute phase of rotator cuff contusion, partial rupture, or complete rupture generally adopts non-surgical therapy.

　　1, Treatment of rotator cuff contusion

　　Including rest, triangular bandage suspension, immobilization for 2 to 3 weeks, and at the same time, local physical therapy is applied to eliminate swelling and relieve pain. For those with severe pain, 1% lidocaine combined with corticosteroid injection into the subacromial bursa or glenohumeral joint cavity can be used. After pain relief, shoulder joint functional rehabilitation training begins.

　　2, Acute phase of rotator cuff rupture

　　Lying on the back, the upper limb in zero position (zeroposition) traction, that is, skin traction is performed at 155° of abduction and 155° of upward elevation of the upper limb, with a duration of 3 weeks. At the same time, bedside physical therapy is performed. After 2 weeks, traction is intermittently released 2 to 3 times a day, and shoulder and elbow functional exercises are performed to prevent joint stiffness. It is also possible to change to zero position figure-of-eight plaster or zero position brace fixation after 1 week of bed traction, which is convenient for activities on the ground. Zero position traction is conducive to the repair and healing of the rotator cuff tendons under low tension, and it is also beneficial to utilize limb gravity to promote the recovery of glenohumeral joint function after traction is removed.

　　3, Indications for surgical treatment

　　Large rotator cuff tears, rotator cuff tears that are ineffective with non-surgical treatment, and cases with subacromial impingement factors. Large rotator cuff tears generally cannot heal spontaneously. Factors affecting spontaneous healing include:

　　(1) Separation and defect at the distal end.

　　(2) Ischemia at the residual end.

　　(3) Joint fluid leakage.

　　(4) There are factors of subacromial impingement.

　　After 4 to 6 weeks of non-surgical treatment, the acute inflammation and edema of the rotator cuff have subsided, and the non-healing tendon ends have formed a relatively hard scar tissue, which is conducive to tendon repair and insertion reconstruction.

　　There are many methods for shoulder cuff repair, and the commonly used method is the Mclaughlin method, which is to make a bone groove near the original insertion site of the shoulder cuff on the proximal side of the greater tuberosity, and implant the proximal end of the shoulder cuff into the bone groove when the affected arm is in the abduction position.

　　This method has a wide range of indications and is suitable for large and extensive shoulder cuff tears. To prevent postoperative adhesions and impacts in the subacromial space, the coracohumeral ligament should be cut and the anterior and lateral part of the acromion should be excised and shaped at the same time as the shoulder cuff repair. For patients with subacromial impingement syndrome, acromial shaping is its indication.

　　For shoulder cuff defects caused by widespread tears of the supraspinatus tendon and infraspinatus tendon, the upper 2/3 of the subscapularis muscle from the attachment site of the glenoid can also be freed, forming a subscapularis muscle flap that is transferred upwards and fixed on the combined defect site of the supraspinatus and infraspinatus tendons. In addition, Debeyre's method of shifting the supraspinatus muscle for repair is also a surgical treatment method for large defects of the supraspinatus tendon. That is, free the supraspinatus muscle in the suprascapular fossa, retain the suprascapular nerve branch to the supraspinatus muscle and the accompanying vascular bundle, shift the entire supraspinatus muscle laterally, cover the defect site of the tendon, and re-fix the supraspinatus muscle in the suprascapular fossa. For large shoulder cuff defects, synthetic fabric grafts can also be used for repair. After postoperative physical therapy and rehabilitation training, the function of the shoulder joint can be largely restored, pain can be relieved, and daily life activities can be met.

　　II. Prognosis

　　The Japanese Shinohara Hospital reported the largest group of shoulder cuff repair surgery cases in the international community, with a total of 1148 cases, 1235 shoulders, with an average follow-up of 6.73 years. 70.1% of the patients had complete pain relief, and 79.4% of the patients had muscle strength recovery to grade 5. 94% of the patients could meet the needs of daily life activities. Correct diagnosis, early treatment, and systematic rehabilitation treatment after surgery are the basic conditions for achieving satisfactory therapeutic effects. If the shoulder cuff injury is not repaired and develops naturally, it will eventually lead to shoulder cuff arthritis, joint instability, or secondary joint contracture, leading to the dysfunction of joint function.