Introduction
Stability of the shoulder (gleno-humeral) joint
Stability is determined by the bony anatomy and the soft tissue supports (capsule, ligaments and muscles).
- Bone anatomy: The gleno-humeral joint is a ball-and socket type of joint. However the ball is four times larger than the socket. Hence, the shape of the bones, by itself, is not enough to stabilize the shoulder.
- Soft tissues: These are very important for the stability of the shoulder.:
- The glenoid labrum: this is a tough structure made of fibro-cartilaginous tissue that is present all around the edge of the socket. It deepens the socket and provides a bumper-like effect against the humeral head.
- Joint capsule: This is a fibrous layer that encloses the joint. It merges with the tendons of the rotator cuff superiorly and anteriorly. It is deficient where the tendon of the long head of biceps passes through it. In addition it is lax inferiorly.
- Ligaments: These are fibrous band-like thickenings of the capsule. They are very important in stabilizing the shoulder. There are three major ligaments – the superior gleno-humeral, the middle gleno-humeral and the inferior gleno-humeral ligament. Of these the inferior gleno-humeral ligament is the most important. In addition there are some minor ligaments like the coraco-humeral ligament.
- Muscles: These provide indirect stability to the shoulder by centering the humeral head and pulling it to the glenoid – called concavity compression effect.
Shoulder Instability
The gleno-humeral joint is the most mobile joint in the body. Any damage to the supporting structures can result in abnormal movements at the joint.
Degrees of instability:
- Micro-instability: In this condition, there is laxity at the shoulder but the humeral head does not slip out of the socket. This places excessive stress on the supporting structures and the rotator cuff leading to their fraying and degeneration. The patient gets pain in the shoulder which is worsened by activities, especially sports.
- Subluxation: In this condition, the humeral head comes to the edge of the glenoid but does not slip out of the joint. In addition to pain, the patient complains of popping of the joint and does not have confidence in performing heavy activities or participating in sports.
- Dislocation: In this condition, the humeral head slips out of the socket. This is a very painful event and needs prompt treatment to reduce the shoulder. Dislocation is usually caused by an injury like a fall, sports collision or motor vehicle accident. The glenoid labrum is torn from the edge of the socket. In addition, there is a tear or peeling off of the capsule and ligaments of the shoulder. It can also be associated with damage to the bones – fracture of glenoid rim or depression in the humeral head.
- Voluntary dislocation: Some patients have excessive laxity of their body and can voluntarily dislocate their shoulder – typically, on both sides. This is a non-traumatic condition and is associated with generalized hypermobility of the body tissues.
Direction of instability:
- Antero-inferior instability: This is the most common pattern of instability. In this condition, the humeral head slips forwards and downwards from the socket.
- Posterior instability: Here, the humeral head slips backwards out of the socket. This occurs during epileptic fits, electric shock or road traffic accidents.
- Multi-directional (or global) instability: In this condition, the humeral head is lax in multiple directions.
What happens after a dislocation?
- After the shoulder is reduced, the arm is rested for a few weeks. This allows healing of the damaged tissues. The capsule and ligaments heal and the joint becomes stable and regains its movements.
- However, in about fifty percent of the cases, the healing is not complete or strong enough; or there is associated injury to the bony socket or humeral head. In these cases the joint dislocates again – sometimes repeatedly. This condition is called recurrent dislocation.
Recurrent dislocation:
- When the healing is not complete or there is associated bony injury, the joint dislocates repeatedly.
- Recurrence of dislocation is more likely in certain age groups. Patients under twenty and those over sixty are very likely to get recurrent dislocation.
- The anatomical abnormalities that occur in recurrent dislocation include:
- Detachment of the glenoid labrum from the socket along with detachment of the capsule – Bankart Lesion
- Stretching and thinning of the capsule
- Depression in the bone of the humeral head – Hill-Sach Lesion
- Erosion of the antero-inferior rim of the glenoid
- Sometimes the capsule is detached from its humeral insertion
Treatment of instability:
First-time dislocation:
- Traumatic antero-inferior dislocation of the shoulder needs prompt reduction. Most often, this can be done in the casualty under intravenous sedation. Sometimes this is not possible and reduction has to be done under anaesthesia in the operation theatre. Very rarely, open surgical reduction may be necessary. Surgical reduction will also be required if there is a delay of more than a few days.
- Posterior dislocations are more difficult to reduce. A large percentage of these need anaesthesia and surgical reduction.
- After reduction, the arm is immobilized in a sling for three weeks to allow the soft tissues to heal. After three weeks the sling is discontinued and exercises begun. Physiotherapy may be necessary to regain the movements and strength.
- Sometimes there is a fracture of the humeral head along with the dislocation. Usually the fragment is small and reduces when the shoulder is relocated. These cases are treated in the usual way. Surgical treatment is required if the fragment is large, or does not relocate, or the fracture involves both the tuberosities, the humeral head or the humeral shaft.
- Fracture of the glenoid rim gives rise to a very unstable situation and needs surgical repair as the primary mode of treatment.
Recurrent dislocation:
- Recurrent dislocation needs surgical stablilzation. It does not heal by immobilization. The surgical procedure is undertaken to address the various anatomical deficiencies that lead to instability:
- Bankart Lesion: The glenoid labrum is re-attached using suture anchors.
- Capsular detachment: Detachment from the glenoid is addressed along with repair of the Bankart defect. Detachment from humerus needs separate repair using suture anchors.
- Capsular laxity: Some degree of laxity can be addressed during Bankart repair. Greater degrees of laxity need additional procedures for stabilization.
- Glenoid defects: Minor defects can be left alone. Significant defects need a bone grafting or bone transfer for reconstruction.
- Hill Sach Lesion: Small defects are left alone. Larger defects are treated by transfer of muscle into the defect (remplissage or open transfer). Very large defects need bony procedure to re-align the defect away from the joint (rotational osteotomy).
Arthroscopic Surgery (keyhole surgery):
- In this technique, surgery is performed using a telescope through tiny incisions. Special equipment is used for imaging the structures. Surgery is performed using special equipment: miniaturized instruments, electrothermal devices and powered devices (shaver), etc.
- The advantages are: better visualization, access to difficult areas, smaller incisions and early recovery.
- The disadvantage is increase in the cost of the surgery.
Open Surgery:
- In this method, surgery is performed using traditional surgical techniques. Although arthroscopic surgery is becoming popular, open surgery still has a role in some situations like severe bone defects, extreme capsular laxity, revision surgery, etc. Some operations that are very difficult to perform by arthroscopy are easily done using open techniques.
- Most often, arthroscopic assessment is carried out before proceeding to open surgery. Now-a-days, even open surgery is done with smaller incisions which allows a faster recovery.
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