【Disease Overview】 Shoulder instability is a series of disorders including shoulder dislocation, subluxation, pain and laxity after instability. Shoulder instability has a great impact on the training of athletes, especially for those sports with more overhead movements, such as baseball, softball, volleyball and swimming. Its incidence is unknown. In recent years, with the continuous research on the anatomy and pathology of the shoulder joint and the application of new techniques and methods, great progress has been made in the treatment of shoulder instability. The diagnosis of shoulder instability relies on a complete medical history, physical examination and imaging. The type of instability must be evaluated in detail to determine the specific direction of unidirectional or multidirectional dislocation or symptomatic subluxation.
In addition, imaging is helpful in the diagnosis of shoulder instability. various imaging techniques such as X-ray plain film, arthrography, CT and ultrasound have been used to examine shoulder instability, but none of them can comprehensively and effectively evaluate various shoulder pathologies. MRI can show multifaceted tissue structures and can comprehensively evaluate various common shoulder pathologies, and is gradually becoming the method of choice for evaluating shoulder instability. MRI arthrography of the shoulder joint combines the advantages of MRI and arthrography and can further improve the diagnosis of shoulder pathologies.
The following sections describe the treatment of shoulder instability one by one.
[Local anatomy] The glenohumeral joint is the joint with the largest range of motion in the body, with a mobility of nearly 360°, but the bony structure of the joint does not provide firm stability. Its scapular glenoid is a flat, disc-shaped structure that is shallow and small. At all times of shoulder motion, only 1/4 of the humeral bone forms a joint with the glenoid. This small, flattened scapular glenoid does not provide as much reliable intrinsic stability to the humeral head as the acetabulum does to the hip joint. Shoulder joint stability factors include static structures, dynamic structures, and intra-articular negative pressure (Figure 1-6-1).
(1) Bone and cartilage: The shoulder joint is an unstable ball and socket joint. The humeral head is hemispherical with a posterior tilt of 30º. The surface of the scapular glenoid corresponds to only 1/4 of the surface of the humeral head and the two surfaces do not coincide. kvittne found that only 25% to 30% of the articular surface area is in contact. In upper arm abduction of 90º, the average displacement of the shoulder joint in the anterior and posterior directions was 20 mm, and in anterior flexion of 30º the joint displacement was minimal, about 10 mm. and the heterogeneity of articular cartilage thickness increased the stability of the joint.
(2) Joint capsule and ligaments: The shoulder capsule is loose and weak, providing only little resistance or stability by itself. The anterior aspect of the capsule is reinforced by the superior, middle, and inferior glenohumeral ligaments formed by the thickened portions of the three capsules, and these structures in turn are tightly fused to the glenoid lip around the glenoid. The glenohumeral ligament complex consists of the superior glenohumeral ligament (SGHL), the middle glenohumeral ligament (MGHL), and the inferior glenohumeral ligament (LGHL). in 0° external rotation, the inferior glenohumeral ligament is lax, and the superior and middle glenohumeral ligaments prevent inferior instability; in extreme external rotation and 45° external rotation, the middle glenohumeral ligament prevents anterior displacement of the humeral head; in extreme external rotation and external rotation, the inferior glenohumeral ligament prevents anterior displacement of the humeral head.
The superior glenohumeral ligament begins below the long head tendon stop of the biceps tendon of the scapular glenoid and ends above the stop of the subscapularis tendon of the lesser tuberosity of the humerus. The superior glenohumeral ligament is the primary structure that prevents downward subluxation of the humerus in the 0° external compartment. It is also the primary stabilizing factor against forward and backward stresses in the 0° external compartment.
The middle glenohumeral ligament is wider at the attachment of the articular glenoid, beginning with the superior glenohumeral ligament and extending down the anterior border of the articular glenoid to the junction of the middle and lower 1/3 of the articular glenoid border. In the humerus, it also attaches anterior to the anatomic neck of the humerus. The middle glenohumeral ligament limits external rotation during mild and moderate abduction of the upper extremity, but plays little role when the upper extremity is abducted at 90°.
The inferior glenohumeral ligament is divided into anterior and posterior bundles and attaches to the mensural border of the articular glenoid from 2 to 3 points anteriorly to 8 to 9 points posteriorly. Its attachment to the humerus ends below the epiphysis in the horizontal direction below the anatomical and surgical neck of the humerus. The anterosuperior and posterior margins of this ligament are usually thick, and the axillary portion is depressed to form a so-called “sling-basket” type structure. When the shoulder is rotated externally, the basket slides forward and upward, the anterior band is tense and the posterior band fans out; when the shoulder is rotated internally, the opposite change occurs. Thus, the inferior glenohumeral ligament complex is the primary stabilizing structure against forward and backward stresses in shoulder abduction of 45° or more. This ligament provides a limiting force on the limits of motion and assists in the posterior rotation of the humeral head in the articular glenoid. Studies have confirmed that dislocation does not occur if the inferior glenohumeral ligament is intact, so the inferior glenoid labrum complex is the primary static stabilizing structure of the shoulder joint.
(3) Glenoid labrum: The glenoid labrum is composed of dense fibrous connective tissue and continues with the hyaline cartilage of the scapular glenoid. The appearance of the scapular glenoid labrum is similar to the meniscus structure in the knee joint, and the annular glenoid labrum is a static stabilizing structure of the shoulder joint.
The glenoid labrum has three surfaces: the base is attached to the glenoid rim; the lateral (peripheral) surface is where the capsular ligaments attach and continues with the scapular neck; and the medial (free) surface, crowned with fibrocartilage, continues with the articular surface of the glenoid and meets the humeral head. The glenoid labrum is not completely fixed to the bone, and some of its inner edge is free in the fossa. The shape of the glenoid labrum is meniscal with variations, and Detrisac and Johnson classified the labrum into five types: type A: meniscal, superior only; B: meniscal, posterior only; C: meniscal, anterior only; D: meniscal, A+C posterior superior to anterior inferior; E: all meniscal.
The anterior, anterosuperior portion of the glenoid labrum is loosely attached to the scapula. The anterior upper part of the glenoid labrum is mostly attached to the middle glenohumeral or inferior glenohumeral ligament rather than ending at the glenoid rim, and the attached thin layer of connective tissue is easily propped open. The lower part of the glenoid labrum contains nonelastic fibrous tissue that resembles a continuation of articular cartilage. Histologically, there is a zone of transitional cartilage fibers between the hyaline cartilage and the fibrous glenoid lip, which appears as a narrow band of hyaline cartilage mixed with reticulated collagen fibers. The inferior glenohumeral ligament complex is tightly attached to the anterior and inferior portions of the glenoid labrum and the glenoid rim. The upper fibers of the glenoid labrum are intertwined with the long head of biceps tendon and firmly attached to the scapular glenoid rim, forming the glenoid labrum complex of the biceps tendon. There is a certain bond between the glenoid labrum and the glenoid that is age dependent: Perry measured this bond at 13 kg at birth in males, reaching a maximum of 64 kg at age 30, and 30% lower in females.
The variation of this value can explain the younger the dislocation occurs, the smaller the bonding force and the tendency to develop glenoid labral injury; the older the age, the greater the bonding force and the damage to the joint capsule and ligaments.
The main effects of the glenoid labrum are: increase the depth of the scapular glenoid (50%) and increase the joint contact area; increase the compliance of the scapular glenoid; after removal of the glenoid labrum, the compliance decreases by 50%. Increase the stability of the glenohumeral joint.
2.Dynamic structures Include muscles, tendons.
The muscles around the glenohumeral joint confine the humeral head to the socket of the scapular glenoid and glenoid labrum, playing the role of stabilizing the joint.
The rotator cuff and biceps tendon play a major role. In addition, the deltoid muscle produces the main vertical shear force, the long head tendon of the triceps strengthens the glenoid labrum from posteriorly, and the rostral shoulder ligament starts at the lateral edge of the rostral process and ends just below the lateral edge of the acromion, forming a rostral shoulder arch with the anterior edge of the acromion, providing stability over the shoulder joint.
(1) Rotator cuff: The rotator cuff, composed of the subscapularis, supraspinatus, infraspinatus and teres minor muscles, covers the anterior, posterior and superior glenohumeral joints and acts as a power ligament to strengthen the stability of the shoulder joint. Under the mild external booth, the subscapularis tendon covers the anterior aspect of the humerus with 90ºno tendinous tissue covers the lower part of the humeral head anteriorly; the extreme external booth glenohumeral inferior ligament provides stability of the anterior aspect of the shoulder joint.
(2) Biceps longus tendon: The biceps longus tendon is located in the intersegmental groove, starting from the supraglenoid tuberosity, covered by the thickened transverse humeral ligament extending from the superior glenohumeral ligament, surrounded by synovial membrane, with the synovial membrane reflexed to form a supporting band (lumbo tether) hanging from the joint capsule, and the tendon is still outside the synovial membrane, although it is within the joint. The biceps longus tendon can stabilize the humeral head, and Pagnani found that after cutting the stop of the biceps longus tendon, the movement of the humeral head up and down, as well as anterior and posterior, increased significantly.
3.Intra-articular negative pressure Similar to the hip joint, there is a certain amount of negative pressure in the shoulder joint, which increases its stability. habermeyer study concluded that the negative pressure in the shoulder joint of cadaveric specimens was 34mmHg; in normal people, the negative pressure in the shoulder joint was 32mmHg; and in patients with shoulder dislocation injury, the negative pressure in the joint was reduced or disappeared.
[Classification
1.Classification according to the direction of instability is divided into anterior, posterior, inferior and multidirectional instability. This classification is useful for understanding the causes of instability, the positive findings of physical examination, and the treatment methods.
2.Classification according to the degree of stability is divided into episodic instability posterior shoulder pain, semi-dislocation, and total dislocation.
Dislocation refers to the complete separation of the humeral head from the scapular glenoid joint structure after acute trauma. Partial dislocation is a partial separation of the glenohumeral joint structure due to repeated minor trauma, and can produce corresponding symptoms of instability. Subluxations are usually transient and can reset on their own. It is sometimes difficult to distinguish between subluxation and subluxation, which is not important because the pathology of injury is similar in both. In episodic, undetected instability posterior shoulder pain, the patient has no sensation of instability and no significant history of subluxation or subluxation. Pain is the most obvious symptom and is evident during overhead activities. Typical injuries will be found with the aid of imaging and arthroscopy to clarify the diagnosis.
3. Internationally, the Matsen simplified staging system is commonly used.
(1) TUBS (Traumatic Unidirectional Bankart Lesion Surgery): mostly caused by trauma, unidirectional instability, Bankart injury is common and requires surgical treatment.
(2) AMBRI (Atraumatic Multidirectional Bilateral Rehabilitation Inferior capsular shift): non-traumatic, multidirectional instability, bilateral onset, mostly requiring rehabilitation, and inferior capsular shift surgery if conservative treatment is not effective.