Rotator cuff injury is a common condition in shoulder surgery, with a prevalence of 5%-39% depending on the literature. As the pivot of the upper extremity, the shoulder joint determines the range of motion and spatial accuracy of the entire upper extremity. The rotator cuff muscle group, as one of the main dynamic factors for precise control of the spatial position of the shoulder joint, plays a crucial role in the function of the shoulder joint. Therefore, rotator cuff injury can cause different degrees of dysfunction and pain in the shoulder joint, which can seriously affect the patient’s ability to perform daily life and quality of life. However, the understanding of this disease in China is still at a relatively late stage. This article will provide an overview of the anatomy, etiology, diagnosis and treatment of rotator cuff injury.
I. Anatomy and function of rotator cuff
1.Anatomy
The rotator cuff is composed of the subscapularis muscle in front, the supraspinatus muscle above, and the infraspinatus and teres minor muscles in the back. They are fused with the joint capsule at a position close to the stop and form a cuff-like structure that wraps around the glenohumeral joint.
2.Function
Compared to the hip joint, the shoulder joint is more mobile but less intrinsically stable. The presence of the rotator cuff provides the shoulder joint with good intrinsic stability and precise spatial position control. Before we talk further about the function of the rotator cuff, let’s get acquainted with the force-even balance theory proposed by Inman in 1944 and further refined by Burkhart in 1993.
3, Force couple balance consists of two aspects.
(1) Balance on the coronal plane: The rotator cuff muscles located below the rotational center of the shoulder joint, including the lower part of the subscapularis, the lower part of the infraspinatus and all of the teres minor, produce a moment that can balance with the moment produced by the deltoid muscle, so that the direction of the combined force points to the center of the articular glenoid, resisting the upward traction force produced by the contraction of the deltoid muscle and maintaining the stability of the shoulder joint during supination.
(2) Balance on the axis: The moment balance between the subscapularis in the front and the infraspinatus and teres minor muscles in the rear. That is, the direction of the resulting combined force points to the center of the articular glenoid. This allows the shoulder joint to remain stable in any spatial position within the range of motion.
The function of the rotator cuff is to provide a balance of forces in the above two planes to meet the functional requirements of the shoulder joint.
Etiology of rotator cuff injury
1.Impact
The concept of subacromial impingement was introduced by Neer at the JBJS in 1972 and was proposed to be treated by resection of the rostral shoulder ligament and anterior acromioplasty. Between 1965 and 1970, Neer treated 50 shoulders with supraspinatus tendinitis/partial rupture/total rupture by this method. In 1986 Bigliani [4] reported on the relationship between the morphology of the acromion and rotator cuff rupture. He classified the rotator cuff into three types according to its morphology: planar, flexural and hooked. The incidence of rotator cuff injury was higher in hooked rotator cuffs than in the first two. This study seems to further clarify that impingement is the cause of rotator cuff injury. However, several other studies have shown that the composition of rotator cuff morphology varies in proportion to the age group. Therefore, there has been a debate on whether rotator cuff morphology is a cause or a consequence of rotator cuff injury.
2, Local stress environment, blood supply, and degeneration
The 3D finite element analysis by Seki N. et al. showed that the maximum tension on the supraspinatus tendon during shoulder abduction occurs on the articular side of the anterior part of the tendon. The anterior articular side of the supraspinatus tendon is the most common first site of rotator cuff injury. The blood supply to the rotator cuff comes from the lateral ascending branch of the anterior rotator humeral artery, the acromion branch of the thoracic acromion artery, the suprascapular artery, and the posterior rotator humeral artery, and Codman suggested in 1934 that the most distal 10 mm of the supraspinatus tendon was an ischemic zone. Subsequent histologic studies have confirmed the existence of this ischemic zone, where the articular side of the region has only scattered vascular distribution and a significantly weaker blood supply than the bursal side of the same region. The proximal stop of the infraspinatus tendon was also a zone of lack of blood supply. There is also a tendency for the blood supply to decrease in the rotator cuff with age.
All of the above theories support the idea that strain and degenerative changes with age are one of the causes of rotator cuff injury.
3.Trauma
Traumatic injury is rarely a direct cause of rotator cuff injury, but generally occurs when the strength of the rotator cuff decreases on the basis of degeneration, resulting in rotator cuff rupture.
4.Occupational factors
People who are engaged in upper limb overhead work and high intensity upper limb work are prone to rotator cuff injury. A study investigated the incidence of rotator cuff lesions in 733 workers working in 12 different jobs, and the authors found the following occupational risk factors for rotator cuff lesions: upper arm flexion of more than 45 degrees during greater than or equal to 15% of the working time; high intensity upper extremity work greater than or equal to 9% of the working time.
5. Other risk factors
Smoking, genetic factors, etc. Some studies have shown that the relative risk of developing the lesion in siblings of patients with clinically diagnosed rotator cuff rupture is 2.42 compared to the control population.
Diagnosis of rotator cuff injury
1. Symptoms
(1) Pain: pain during exercise and nocturnal pain are common. Pain is evaluated using the VAS score. The quantification of pain facilitates the evaluation of changes in condition and treatment effect.
(2) Decreased muscle strength: mainly the decrease of abduction, external rotation and internal rotation strength. This is manifested by difficulties in daily activities such as washing, combing hair, dressing, holding and placing objects in high places, and driving.
(3) Decrease in mobility: The decrease in mobility is mainly in supination, external rotation and internal rotation. The distinctive feature of reduced mobility is the difference between active and passive mobility, which indicates that reduced muscle strength is the cause of reduced mobility. However, it is generally believed that patients with a complete rotator cuff rupture are less likely to develop periacetabular adhesions because the glenohumeral cavity is already in communication with the subacromial bursa and the synovial fluid will organize the adhesions.
2.Physical examination
(1) Visual examination: atrophy of the supraspinatus and infraspinatus muscles, fullness of the subacromial bursa, etc.
(2) Palpation: The “Tent test” is performed by placing the upper arm on the side of the body with the shoulder joint slightly posteriorly extended, rotating the shoulder joint internally and externally with one hand, and placing the other hand on the lateral side of the anterior angle of the acromion, and the depression of the deep surface of the deltoid muscle can be palpated in the shoulder joint with a ruptured supraspinatus tendon. This test has a high sensitivity and specificity for diagnosing rotator cuff injury. Tenderness: tenderness in large nodes, small nodes, and the inter-nodal groove.
(3) Mobility testing: The American Academy of Shoulder and Elbow Surgeons recommends the steps of flexion, abduction, posterior extension, internal rotation, external rotation, and external and internal rotation in the 90 degree position of abduction.
(4) Muscle strength examination: abduction muscle strength in the scapular plane; external rotation muscle strength in the neutral and abduction 90° positions of the shoulder joint; internal rotation muscle strength examination: liftoff test and belly press test.
(5) Impingement test: the pain arc sign is the pain in the shoulder joint during the abduction of the shoulder joint in the coronal plane from 60° to 100°; the Neer impingement test is the pain in the shoulder joint during the flexion of the shoulder joint in the sagittal plane; the Hawkins impingement test is the pain in the shoulder joint during the flexion of the shoulder joint at 90° and the flexion of the elbow joint at 90°, and the pain in the shoulder joint during the internal and external rotation of the shoulder joint in this position. The pain in the shoulder joint is positive.
(6) Neurological function examination: to differentiate from the muscle strength disorder caused by cervical spondylosis and brachial plexus nerve injury, and to clarify the functional status of the suprascapular nerve.
2.X-ray film
Standard radiographs include: a true anterior-posterior view of the shoulder joint, a standard lateral scapular view and an axillary view. Indirect signs of the presence of rotator cuff injury are: superior displacement of the humeral head, reduction of the AHI; osteosclerosis of the greater tuberosity and acromion. Arthrography can reveal the entry of contrast into the subacromial bursa. It can be used to differentiate rotator cuff injury from frozen shoulder, which shows a reduction in the volume of the joint cavity without spillage of contrast agent.
3. Ultrasonography
Many controlled studies have shown that the sensitivity and specificity of ultrasound for the diagnosis of rotator cuff rupture is comparable to that of MRI for experienced operators. Ultrasound is also inexpensive and allows for real-time dynamic examination. A rotator cuff rupture appears as a localized depression and low signal in the rotator cuff on ultrasound images.
3.Magnetic resonance imaging
It is the main diagnostic tool for rotator cuff injury and has high sensitivity and specificity. The diagnosis of rotator cuff rupture is based on the interruption of the normal signal in the rotator cuff in the oblique coronal, oblique sagittal and axial planes on T2-weighted images and its replacement by a liquid high signal. MRI arthrography: Compared with conventional MRI, MRI arthrography can improve the sensitivity and specificity of the diagnosis of rotator cuff injury, especially in the diagnosis of partial rotator cuff rupture.
IV. Classification of rotator cuff injury
The first thing that needs to be clarified is whether the rotator cuff rupture is a partial rupture or a total rupture. In partial ruptures, the rupture is first classified according to the site of the rupture: articular side rupture and bursal side rupture; and then further classified according to the depth of the rupture: Grade 1. In total ruptures, the rupture is generally classified according to the size of the rupture: small rupture small.
V. Differential diagnosis of rotator cuff injury
1.Frozen shoulder
Both rotator cuff injury and frozen shoulder may have limited movement of the shoulder joint. However, in the former, the passive range of motion is generally greater than the active range of motion; in the latter, the active and passive ranges of motion are approximately the same.
2.Shoulder lock joint lesion
Acromioclavicular joint pathology is another major cause of shoulder pain and dysfunction. The pain of acromioclavicular joint pathology occurs mostly during maximum shoulder supination, horizontal internal retraction and flexion and internal rotation. Pain in the acromioclavicular joint during supination occurs at maximal supination, whereas pain in subacromial impingement during supination occurs in the range of 60 to 100 degrees of supination. The Hawkins test for shoulder impingement is performed by internally rotating the shoulder in the flexed position, whereas acromioclavicular pain can sometimes occur in this internal position, as identified by the O’Brien’s test. This test is positive for acromioclavicular joint pathology and negative for rotator cuff pathology/acromioclavicular impingement because the latter is a static test and usually does not induce impingement.
3. Lesions of the long head of the biceps
The pain of rotator cuff lesions usually occurs on the lateral aspect of the shoulder joint, while the pain of biceps longus lesions usually occurs on the anterior aspect of the shoulder joint. Further differentiation can be made by the Speed test and Yergason’s test.
6.Treatment of rotator cuff injury
1.Conservative treatment
The two main problems of rotator cuff injury are pain and functional impairment. Therefore, the content of conservative treatment is also aimed at these two aspects. First of all, you can take oral non-steroidal anti-inflammatory drugs for pain. Local injections in the subacromial space can be performed, applying local anesthetics, adrenocorticosteroids and sodium glutamate. Local anesthetics provide immediate pain relief. Adrenocorticosteroids can reduce the inflammatory response of the subacromial bursa, but the number of hormone applications is usually not more than 3-5 times. Some studies have shown that local application of hormones more than 5 times decreases the mechanical strength of the tendon and increases the risk of tendon rupture; moreover, the effect of hormone application reaches its maximum at 3 times, and the effect of further application is no longer significant [12]. Sodium glacialate has both a lubricating effect and an anti-inflammatory effect, and is therefore effective in the treatment of rotator cuff injury/subacromial impingement pain.
2. Surgical treatment
Patients who have received systematic conservative treatment for three to six months without significant relief or even aggravation need to be treated surgically. The selection of specific surgical indications should also be based on the patient’s age, activity requirements and other factors such as the rupture site. Although many patients with rotator cuff ruptures maintain good mobility after systematic conservative treatment, long-term follow-up reveals that the size of the rotator cuff rupture gradually increases and that some of the originally repairable ruptures become irreparable; this is accompanied by a reduction in the acromion/humeral head gap and an increase in the manifestations of osteoarthritis. Therefore, the indications for surgery are stronger in younger patients and those with high activity requirements.
(1) Open surgery
Traditional open surgery includes open anterior acromioplasty and repair of rotator cuff ruptures. Anterior acromioplasty is performed as described in the previous literature. The rotator cuff is repaired by slotting the rotator cuff in the area of the original stop and fixing it with a transosseous suture. There are many methods of tendon suturing, as shown in the figure, of which the suture with the highest strength proven by biomechanical experiments is the modified Mason Allen suture [14].
(2) Arthroscopic surgery
Subacromial decompression and rotator cuff repair is performed through standard anterior, posterior and lateral access with insertion of arthroscope and instruments. The rotator cuff suture is closed using a suture anchor. Compared to traditional open surgery, arthroscopic repair is less invasive, especially for the deltoid at the beginning of the anterior rotator cuff. The sutures are single-row and double-row sutures. The latter gives a greater contact area between the broken end of the rotator cuff and the footprint, which will increase the chance of rotator cuff healing and strength.
(3) Mini-open
combines the advantages of both of these. Arthroscopic subacromial decompression is used to avoid damage to the deltoid starting point. The rotator cuff is then repaired using a small incision from the anterior angle of the acromion, which is generally less time consuming than arthroscopic surgery.
(4) Treatment of some irreparable rotator cuff injuries
(4) Pure debridement: In cases where a huge rotator cuff rupture cannot be repaired directly, and the patient’s shoulder joint is well preserved in the axial and coronal planes. In these patients whose main symptom is pain with still satisfactory mobility, pain can be relieved by removing the hyperplastic synovial and inflammatory tissue. Tendon transfer surgery: In patients with large rotator cuff ruptures that cannot be repaired directly and who have severely reduced external rotation strength, muscle transfers can be used to enhance the coverage of the rotator cuff defect while allowing the patient to regain some external rotation strength. The muscles commonly used for transposition include the latissimus dorsi and the vastus lateralis.