Diagnosis and treatment of recurrent anterior instability of the shoulder joint
Anatomically and biomechanically, the shoulder joint is one of the most unstable and frequently dislocated joints in the body, accounting for approximately 50% of all joint dislocations. The incidence of anterior dislocation of the shoulder joint ranges from 2% to 8% in the population, and accounts for 1/3 of all shoulder emergencies. while failure to immobilize the shoulder joint for 3 to 4 weeks after the initial dislocation is thought to be the main cause of recurrent dislocation, many scholars believe that other factors are more important, and that the occurrence of recurrent dislocation depends largely on the location and nature of the injury sustained during the first dislocation. Studies have shown that the greater the trauma that caused the first dislocation, the lower the incidence of dislocation recurrence. The age of the patient at the time of the first dislocation is another important factor; Hovelius believes that the recurrence rate is 95% for patients younger than 20 years old, Mclaughlin believes that the recurrence rate is less than 50% for those older than 25 years old, and Kinnett believes that the recurrence rate is less than 15% for those older than 50 years old, but is prone to combined rotator cuff injuries and large nodal fractures. The recurrence rate is 94% between the ages of 10 and 20, 79% between the ages of 20 and 30, and 50% between the ages of 30 and 40. Recurrence of dislocation occurs frequently in young people, especially in athletes. The duration of fixation does not seem to affect the stability of the shoulder joint, while the degree and location of the first trauma is related to the frequency of recurrence.
Shoulder joint stabilizing structures can be divided into two main categories: active stabilizing structures as well as passive stabilizing structures. The former includes the deltoid, biceps and rotator cuff muscles, while the geometric shape of the shoulder glenoid, glenoid labrum, joint capsule and glenohumeral ligament belong to the latter. These structures play a role in stabilizing the shoulder joint during motion, but none of them play a role in the full range of motion of the shoulder joint. It is generally accepted that the glenohumeral ligament is significantly tight at the limit of the shoulder range of motion and plays an important role in shoulder stabilization, whereas in the middle range of maximum shoulder motion, the glenohumeral ligament is more relaxed and the active stabilizing structures, the shape of the shoulder glenoid, the glenoid labrum, and the intra-articular negative pressure play an important role in shoulder stabilization.
Passive stabilizing structures of the shoulder joint
The geometry of the shoulder pelvis and the glenoid labrum are important passive stabilizing structures of the shoulder joint. The glenoid labrum can significantly deepen the shoulder pelvis, but does not change the curvature of the shoulder pelvis articular surface. Repeated shoulder dislocations can erode the articular cartilage beneath the anterior glenoid and destroy the glenoid labrum in the corresponding area. The loss of the cartilage glenoid labrum leads to a reduction in the height of the glenoid rim, which further affects the stability of the shoulder joint. The glenoid labrum can increase the depth of the shoulder glenoid by nearly 50%, and if removed, it can reduce the ability of the shoulder joint to resist humeral head dislocation by 20%. In addition to the glenoid labrum, the bony structure of the shoulder glenoid itself is an important factor in maintaining shoulder stability. Patients with Bankart often have varying degrees of combined glenoid bone loss, which affects the shape and curvature of the glenoid. Tests have shown that if there is a large bony defect in the anterior and inferior portions of the shoulder pelvis, the stability of the shoulder joint in the abductor-external rotation and abductor-neutral positions of the affected limb is significantly reduced even after Bankart repair has repaired the anterior ligamentous capsule tissue back to the edge of the shoulder pelvis. The glenohumeral joint has a very loose capsule with a surface area approximately twice the size of the humeral head, allowing the glenohumeral joint to move freely. However, on the other hand, maintaining a negative intra-articular pressure of nearly 146 N while the capsule remains intact is an important factor in maintaining glenohumeral joint stability.
The glenohumeral ligaments, which include the rostrohumeral, superior, middle and inferior glenohumeral ligaments, are actually formed by the thickening of the shoulder capsule in a specific area, rather than being separate structures like the ligaments around the knee. The glenohumeral ligament is an important passive stabilizing structure of the shoulder joint, but as mentioned earlier no stabilizing structure of the shoulder joint acts as a stabilizer in any position of glenohumeral motion, and the stabilizing effect of the glenohumeral ligament is closely related to the position of the limb. In patients with recurrent anterior instability of the shoulder joint, it was observed that the long head of the biceps tendon significantly reduced the anterior-posterior displacement of the humeral head, especially when the shoulder joint was externally rotated. Thus, when the anterior ligamentous capsule structure of the shoulder joint is damaged, the biceps long head tendon becomes an important structure for maintaining anterior stability of the shoulder joint, even more than any rotator cuff muscle tissue. The superior glenoid labrum is where part of the biceps longissimus tendon stops, and the superior and middle glenohumeral ligaments all originate from this area. When the upper glenoid labrum is torn, it can significantly increase tension in the inferior glenohumeral ligament, resulting in increased displacement of the humeral head in multiple directions. In shoulder abduction of 00, the subscapularis and the middle glenohumeral ligament are the most important structures to maintain anterior stability of the shoulder joint; in abduction of 450, the middle glenohumeral ligament and the anterior bundle of the inferior glenohumeral ligament are the most important structures to maintain anterior stability of the shoulder joint; and in shoulder abduction greater than 450, the axillary and posterior bundles of the inferior glenohumeral ligament are the most important structures to maintain anterior stability of the shoulder joint. Therefore, the inferior glenohumeral ligament complex is the most important passive stabilizing structure in the position that most commonly causes anterior and inferior shoulder dislocation in clinical practice.
Active Stabilization Structures of the Shoulder Joint
The active stabilizing mechanism of the shoulder joint is achieved through the muscles surrounding it, which are manifested in the following ways: 1 the volume and tension of the muscles themselves; 2 the effect of the muscle contraction in pressing the humeral head toward the shoulder glenoid; 3 the tension of the above passive stabilizing structures during joint movement; and 4 the restrictive and barrier effect produced by the contracted muscles. Studies have shown that of the active stabilizing structures around the shoulder joint, the subscapularis muscle plays the most important stabilizing role when the shoulder joint is in the external rotation position, while the stabilizing role of the long head tendon of the biceps is most pronounced when the shoulder joint is in the rotational neutral position.
The rotator cuff muscle group itself is an important barrier against shoulder dislocation. A large anterior rotator cuff deficit can significantly affect the stability of the shoulder joint. A deficit extending from the supraspinatus muscle to the infraspinatus muscle can lead to instability below the shoulder joint, and a deficit in the rotator cuff gap can also lead to instability in the anterior shoulder joint. On the other hand, the contraction of the rotator cuff muscles can move the humeral head toward the shoulder glenoid, thus providing a stable fulcrum during shoulder motion. If this mechanism is affected by shoulder muscle paralysis or rotator cuff injury, it can lead to instability of the shoulder joint. The subscapularis muscle is an important construct in maintaining anterior stability of the shoulder joint during upper arm abduction activities. The infraspinatus muscle also contracts simultaneously, creating a synergistic effect with the subscapularis. Electromyography shows that the subscapularis and infraspinatus muscles contract to keep the humeral head relatively stable in the shoulder glenoid during shoulder abduction in the range of 600-1500. Experiments have shown that supraspinatus paralysis alone does not result in significant shoulder instability and that the remaining other rotator cuff muscles still provide a stable fulcrum during shoulder motion. The deltoid muscle is important for shoulder stability, and the deltoid produces compressive and shear stresses relative to the shoulder glenoid. In anterior instability of the shoulder joint, the central and posterior bundles of the deltoid muscle produce greater compressive stresses in favor of shoulder joint stability, while the anterior bundle produces greater shear stresses that are detrimental to joint stability. Therefore, the muscle strength of the middle and posterior deltoid fibers should be strengthened during conservative treatment or postoperative rehabilitation for patients with anterior instability.
Other stabilization mechanisms of the shoulder joint
Recent studies on the stabilization mechanisms of the shoulder joint have shown that the ligamentous tissues of the capsule surrounding the shoulder joint not only have a mechanical limiting effect, but also that the proprioceptors in these tissues play an important role in regulating the activity of the active stabilizing structures of the joint: the proprioceptive information transmitted by these proprioceptors influences the motor and reflex activity of the muscles surrounding the joint, thus helping to maintain the stability of the joint. The damage to the capsular ligament complex that accompanies joint dislocation or subluxation not only affects the mechanical stabilization of the joint but also affects proprioceptive input. The results showed that healthy and post-operative patients had similar perceptual abilities and were significantly better than those with unstable shoulders. Other authors have also found that athletes engaged in overhead sports have reduced proprioceptive sensitivity on the dominant side compared to the contralateral shoulder joint. The explanation for these phenomena is that the laxity of the joint capsule ligaments affects the sensitivity of the proprioceptors therein. This sensitivity can be restored by surgical treatment to re-establish normal tension of the joint capsule.
Pathological changes of shoulder instability
Recurrent dislocation of the shoulder joint, mostly seen in athletes in volleyball, wrestling and gymnastics, has the same mechanism of injury as acute shoulder dislocation: during sports, whenever the shoulder joint is in upper arm abduction during a fall and the hand or elbow is on the ground, there is a risk of dislocation of the shoulder joint. This position moves the head of the humerus to the underside of the scapular glenoid, leaving the lower part of the joint capsule in a state of tension and traction. Once the external force is too great, the humeral head is dislodged from the glenoid. In some cases, the humeral head dislocates through the joint capsule (a minority of cases are called extracapsular dislocations), while in others, the humeral head remains within the joint capsule, called intracapsular dislocations.
Possible pathologic changes leading to recurrent anterior instability of the shoulder joint include.
1. bony injury
(1) Hill-Sachs injury: first proposed in 1940, a bone or cartilage defect on the posterior humeral head, caused by the posterior lateral impact of the humeral head with the anterior inferior glenoid during anterior subluxation of the shoulder. the depth of Hill-Sachs injury is related to the size of the impact violence, shallow or cartilaginous Hill-Sachs injury has small impact violence, i.e. the violence causing dislocation is relatively small. in 1989 Calandra divided Hill-Sachs injury into three degrees: first degree, cartilaginous; second degree, osteochondral; and third degree, bony. the incidence of Hill-Sachs injury is about 31% to 80%. This injury is most often seen in recurrent dislocations, and Pavlov believes that 86% of recurrent dislocations have this injury. It is less common in patients with multidirectional instability, and Obrien believes that 25% of those with multidirectional instability have this injury.
(2) Bony Bankart injury: In 2000, Itoi concluded from a cadaveric study that a bony defect of the anterior inferior glenoid labrum exceeding 21% of the glenoid length in width would cause instability. Some have suggested that if the defect area exceeds 30% of the glenoid, bone grafting is required.
2. glenoid labral injury Rowe proposed a type of glenoid labral injury: separation of the glenoid labrum from the glenoid rim, tearing of the glenoid labrum parenchyma, and severe wear until it disappears. both Perthes and Bankart described anterior inferior glenoid labral injury as closely related to shoulder dislocation, and referred to anterior inferior glenoid labral injury collectively as Bankart injury. The incidence of anterior inferior glenoid labral injury in patients with recurrent shoulder dislocation has been reported in the literature to be 53% to 100%. Most of the anterior inferior glenoid labral injuries are classified as Bankart injury, ALPSA injury, GLAD injury, etc.
Bankart injury: anterior inferior glenoid labrum avulsion of the shoulder joint with or without avulsion or detachment of the glenoid membrane in the corresponding area. It has been found that Bankart injury is present in 85% of traumatic recurrent dislocations, 64% of recurrent transient subluxations, and 84% of failed previous surgical procedures.
ALPSA injury (anterior labroligamentous periosteal sleeve avulsion): ALPSA injury was proposed and named by Neviaser in 1993, with a sleeve tear of the anterior inferior glenoid labrum along with the corresponding localized osteochondral sleeve. The difference from Bankart injury is that the periosteum in the corresponding region of the glenoid labrum is intact and unbroken, and the glenoid labrum and periosteum are retracted and fixed in a low position toward the glenoid neck. Injured glenoid labral complexes tend to retract, and surgery requires freeing the glenoid labrum from under the periosteum and repositioning followed by suture fixation.
GLAD injury (gleno-labral articular disruption): GLAD injury was proposed by Uris in 1995 as a simple intra-articular injury of the anterior inferior glenoid labrum without periosteal injury, and the stop of the inferior glenohumeral ligament is often intact. Most injuries are due to compression of the glenoid labrum during shoulder abduction and external rotation, which may or may not be associated with instability of the shoulder joint.
Perthes injury: Proposed by German physician Perthes in 1906, it refers to the detachment of the anterior inferior glenoid labrum of the shoulder joint and the corresponding area of the glenoid periosteum from the scapular glenoid. The connection between the glenoid labrum and periosteum is intact.
SLAP injury (superior labram injury from anterior to posterior): injury to the superior glenoid labrum from anterior to posterior of the shoulder joint, with or without biceps tendon injury.
3, joint capsule, ligament injury HAGL injury (humeral avulsion of inferior glenohumeral ligament) was proposed by Wolf et al. in 1995. The literature reports that the incidence of HAGL injury is 9%-39%, and HAGL injury is an avulsion injury of the inferior glenohumeral ligament at the humeral head stop of the shoulder joint. The glenohumeral ligament is an important static stabilizing structure of the shoulder joint, of which the strongest is the inferior glenohumeral ligament. The inferior glenohumeral ligament is divided into two bundles, anterior and posterior, forming a hammock-like stabilizing structure. When the shoulder is abducted and externally rotated, the anterior bundle of the inferior glenohumeral ligament becomes the only anterior stabilizing factor. Injury to the glenoid labrum alone does not significantly increase the anterior instability of the shoulder joint; only when the inferior glenohumeral ligament is ruptured does shoulder instability occur. Injuries to the inferior glenohumeral ligament are commonly seen at the glenohumeral junction, but also at the parenchyma and humeral stop. Injuries that occur at the humeral stop are called HAGL injuries. After the inferior glenohumeral ligament humeral stop is ruptured, it must be fixed with in situ sutures to avoid affecting the stability of the shoulder joint.
4. Combined rotator cuff injury Arthroscopic observation of a large number of shoulder dislocation cases shows that the probability of rotator cuff injury is 30%, of which 16% are total rotator cuff tears and 14% are partial rotator cuff tears. Moreover, the incidence of rotator cuff tears increases with age. At the age of 40 years or younger, rotator cuff tears are rarely combined. Sometimes it is combined with a large nodal fracture, etc.
Therefore, for each recurrent dislocation of the shoulder joint. There does not seem to be a single “underlying” injury. The stability of this inherently unstable joint depends on a constant balance between the static and dynamic stabilizing mechanisms that influence motion and stability. In addition to the various primary deficits that can produce instability, secondary deficits can also occur with recurrent dislocations.