What is shoulder joint ?
The shoulder joint is called a ball-and-socket joint. The ball is the rounded top of the bone in the upper arm (humerus), which fits into the socket — the cup-shaped (glenoid) outer part of the shoulder blade. The shoulder joint is held in place and supported by the rotator cuff, a complex of muscles and tendons; the labrum, a rim of cartilage that surrounds the glenoid; and capsule & ligaments that surrounds the joint. Failure in any or all of these structures can lead to the looseness that is diagnosed as shoulder instability.
What is shoulder dislocation ?
When the top (ball or head) of the humerus moves out of its usual location in the shoulder joint, the shoulder is said to be dislocated.
What is subluxation ?
When the top (ball or head) of the humerus is only partially displaced and not totally out of its socket is called subluxation.
Shoulder dislocations are the most common joint dislocation, accounting for more than 50% of all dislocations treated in hospitals. Young adult men and older women tend to be the groups with the highest rate of shoulder dislocations.
Mechanism of dislocation
A shoulder is dislocated when the arm is pulled or twisted with extreme force in an anterior, upward, downward or backward direction. This extreme force literally pops the top (ball) of the humerus out of its socket.
Almost all shoulder dislocations are related to trauma. Occasionally, the dislocation occurs after ordinarily motions, such as raising an arm or rolling over in bed. In these cases, the real cause may be that the shoulder ligaments are abnormally loose. Loose ligaments are sometimes due to an inherited condition that can increase the risk of dislocation toward all sides of the joint. It is called multidirectional instability (MDI).
Types of dislocation
Shoulder dislocations into three types, depending on the direction of the dislocation:
Anterior dislocation — The top (ball) of the humerus is displaced forward, toward the front of the body. This is the most common type of shoulder dislocation, accounting for more than 95% of cases. In young people, the cause is typically sports and accident related. In older people, it usually is caused by a fall on an outstretched arm.
Posterior dislocation — The top of the humerus is displaced toward the back of the body. Posterior dislocations account for 2% to 4% of all shoulder dislocations and are the type most likely to be related to seizures and electric shock. Posterior dislocations also can happen because of a fall on an outstretched arm or a blow to the front of the shoulder.
Inferior dislocation — The top of the humerus is displaced downward. This type of shoulder dislocation is the rarest, occurring in only one out of every 200 cases. It can be caused by various types of trauma in which the arm is pushed violently downward.
Recurrent dislocation - When dislocation more than two times it is called recurrent dislocation.
Symptoms of a dislocated shoulder include:
X-rays and MRI.
For acute dislocation, close reduction under anaesthesia and immobilization for 3 weeks in young age group and 2 weeks for old followed by rehabilitation.
In case of recurrent dislocation, subluxation and chronic instability arthroscopic repair of labrum, ligament and capsule is treatment of choice.
Recurrent dislocation with glenoid rim fracture and hill-sachs lesion, Latarjet procedure is appropriate treatment option.
For old or missed dislocation, open relocation and different bony procedures for stability is good option.
Complication and recurrence
Surgical treatment for shoulder instability is generally considered quite safe. Performed by an experienced orthopaedic surgeon, the risk of infection, nerve or vascular injury, is minimal.
Following surgery and throughout rehabilitation the patient is monitored for stiffness. Occasionally arthroscopic release of the capsule is necessary to restore motion.
Individuals with a prior high number of dislocations are likely to develop some degree of arthritis in the joint, secondary to the trauma of the dislocation and reduction.
The incidence of recurrence of either a partial or complete dislocation that is treated non-surgically is largely dependent on the patient's age. In patients under 20 years old who experience a traumatic dislocation, the recurrence rate is as high as 95 percent – a phenomenon that is probably related to natural looseness in the joint and return to activities that place stress on the joint. Among patients age 40 and older the recurrence rate drops dramatically, to about 15 percent, owing to a natural tightness in the joints that develops with age and changes in activity level.
Recurrence rates in patients who undergo surgery vary depending on the patient's level of activity. However, overall the results are quite good, with a general recurrence rate of less than 5 percent for those with surgical treatment of traumatic dislocation. Among patients with multidimensional, loose-jointed lax shoulders, the rate is closer to 10 percent.