Multidirectional instability of the shoulder
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Multidirectional instability (MDI) is a common shoulder problem seen in young athletes who specialize in overhead movements in their sports. It is a diagnosis specific to the glenohumeral joint of the shoulder and refers to a general laxity of the glenohumeral joint capsule.
In a healthy shoulder, the head of the humerus is stabilized within the glenoid fossa (glenohumeral joint) through multiple structures including (from the inside out) the labrum, glenohumeral ligaments, joint capsule, and rotator cuff muscles. If there is damage or weakness in any of the stabilizing structures, the integrity of the glenohumeral joint can be compromised.
The purpose of the stabilizing structures is to keep the head of the humerus safely within the boundaries of the glenoid fossa while the arm is in motion. In a healthy joint, the connective tissue structures (labrum, ligament, joint capsule) work to restrict the movement of the head of the humerus while the rotator cuff muscles contract to safely keep the head of the humerus within the fossa.
In an athlete with MDI, the rotator cuff muscles may have weakened over time allowing the head of the humerus to glide further than it should within the fossa. Over time, this may lead to stretching of the joint capsule. With weakened rotator cuff muscles and a stretched joint capsule, the head of the humerus may then exceed its normal limits and move past the boundaries of the glenoid fossa causing pain and laxity of the glenohumeral joint.
How is multidirectional instability diagnosed?
Multidirectional instability can be difficult to diagnose in young athletes with a secondary rotator cuff injury. The MDI can be overlooked with a misdiagnosis instead on a rotator cuff muscle strain.
A thorough medical history is critical to diagnosing MDI. Most multidirectional instabilities occur over time through repetitive overuse and do not have a clinically-significant acute mechanism of injury. The athlete will not have a history of a shoulder dislocation, but the athlete may complain of chronic nonspecific pain after using the shoulder.
The athlete may also present with the symptoms of secondary impingement syndrome (pain when the arm is lifted above 90 degrees) or complain of a “dead-arm” after throwing.
The key to diagnosing MDI is the administration of a comprehensive battery of tests specifically designed to test glenohumeral joint laxity. If there is significant anterior, posterior, and/or inferior movement of the head of the humerus during these stability tests, then MDI may be present.
X-rays may be ordered by the physician to rule out other skeletal injuries and an MRI may be ordered to rule out other soft tissue injuries. According to Bahr and Maehlum (2004), the best method for diagnosing MDI is by “comparing both shoulders under general anesthesia”.
Who gets multidirectional instability of the shoulder?
Athletes susceptible to MDI are those in sports that require repetitive overhead motions as in the sports of baseball, softball, and swimming. The condition is seen in those athletes whose sports demand extreme ranges of motion in the shoulder.
What causes multidirectional instability of the shoulder?
Athletes may be predisposed to MDI if they have a congenital condition of hyperlaxity (loose joints). Some individuals are born with excess range of motion in their joints. This can be easily determined by an assessment of the other joints in the body to see if there is a pattern of hyperlaxity throughout the body (elbow, knee, and wrist).
An individual with hyperlaxity may have a higher risk for developing MDI, but it may be prevented in these individuals with a focus on rotator cuff stabilization exercises. A strong rotator cuff may be able to keep the head of the humerus within the fossa regardless of the integrity of the joint capsule. However, if the rotator cuff muscles become weakened from overuse and the muscles atrophy (get smaller), then the symptoms of MDI may begin to present themselves.
Even in individuals with normal connective tissue structures, repeated overhead types of motions (as seen in overhead throwing and some swimming styles) can gradually stretch the joint capsule. Over time, the posterior capsule is gradually stretched. Throwers often have increased external rotation of the glenohumeral joint brought on by years of overhead throwing.
What are the differences between unidirectional instability and multidirectional instability of the glenohumeral joint?
It is important to differentiate athletes with an acute unidirectional instability from an athlete with chronic multidirectional instability. Unidirectional instability means that the athlete usually has sustained an acute injury (one-time injury) that weakens the stabilizing structures of the glenohumeral joint in one direction.
The most common type of unidirectional instability in the shoulder is anterior instability which is typically caused by an anterior subluxation or dislocation. In this case, the injury to the anterior stabilizing structures stretches the connective tissues in only the front of the shoulder. Hence, the instability of the GH joint is only in one direction.
Multidirectional instability means that the GH joint is unstable in two or more directions (anterior, inferior, and posterior). This means that the head of the humerus may glide outside of its normal range in multiple directions.
What can I do to prevent MDI?
Prevention of MDI should focus on strengthening the individual muscles of the rotator cuff along with the muscles responsible for stabilizing the scapula while the arm is in motion. This is especially important for those athletes who have congenital joint hyperlaxity.
What is the treatment for multidirectional instability of the shoulder?
The treatment for MDI focuses on long-term conservative rehabilitation rather than on surgical repair. If the muscles surrounding the head of the humerus can be strengthened, than the humerus can be effectively stabilized. Surgery is considered a last resort and only if a long-term rehabilitation program is unsuccessful.
The rehabilitation program should focus on stretching structures that may be tight and strengthening those muscles that are weak. Early in the rehabilitation program, the focus should be on strengthening the individual rotator cuff muscles and the muscles that stabilize the scapula while exercising within a pain-free range of motion.
The muscles of the rotator cuff and their actions include:
• Supraspinatus – abduction (lifting arm to the side of the body)
• Subscapularis – internal rotation
• Infraspinatus – external rotation
• Teres Minor – external rotation
Because these muscles are small in comparison to the other muscles in the shoulder, the muscles should be loaded with less than 30% of a one repetition maximum (1RM) lift. With lighter intensity, the number of repetitions can be increased (3 sets of 15 repetitions). This type of exercise will target the small muscles of the rotator cuff.
Along with working the muscles individually, exercises can be added to the rehabilitation program to strengthen the muscles in conjunction with each other. One of the more common exercises to get the muscles of the rotator cuff to co-contract is stabilizing exercises.
The athlete lies on a treatment table with their injured shoulder flexed to 90 degrees in front of their body. The goal of the athlete is to maintain this position of the arm while the therapist gently taps the hand in multiple directions. This exercises forces the muscles of the rotator cuff to quickly contract and stabilize the shoulder. As the athlete improves in the dynamic contraction of their rotator cuff, the force exerted by the physical therapist on the hand can increase.
Exercises to strengthen the muscles that stabilize and move the scapula are also an important component for a MDI rehabilitation program. The movements of the scapula include protraction (movement forward of the scapula), retraction (movement backwards as in the position of standing at attention), upward rotation (movement upwards), and downward rotation (return to anatomical position).
Maybe even more important than strengthening the individual muscles that move the scapula, is to develop good coordination between the muscles of the scapula and the muscles that move the humerus because they need to be able to work effortlessly together.
These types of exercises should be initially performed under the supervision of a trained sports medicine professional to ensure that the athlete is performing them correctly. Cheating movements may be substituted and performed by the athlete. They may not be aware that they are doing them because they may have been substituting movements for years without knowing it due to muscular atrophy and weakness.
As the individual muscles regain their strength and neuromuscular coordination of the muscles improves, the athlete can move to training the muscles eccentrically through advanced shoulder exercises. These exercises do not lift more weight, but they focus on sport-specific lengthening contractions.
One of the critical roles of the posterior muscles of the rotator cuff is to decelerate the arm at the end of an overhead throw. This eccentric contraction slows down the head of the humerus after the arm has accelerated through its range of motion. These muscles need to be trained to perform quick eccentric contractions in order to keep the head of the humerus safely within the joint.
Recovery – Getting back to Sport
Once functional exercises can be performed pain-free, then the athlete is ready to begin sport-specific progressive functional training for the purpose of returning to sport. Once Sport-specific functional exercises are those that mimic the movements that the athlete needs to perform in sport, but are performed at a slower speed and lower intensity.
For the throwing athlete, a gradual progression of overhand throwing exercises can be started. Initially, the athlete should perform the throwing motion at 50% of speed and with no sport implement.
As the athlete becomes more comfortable with the motion, a whiffle ball can be added to the exercises. The athlete can perform multiple repetitions of throwing a whiffle ball while gradually increasing the intensity of the throws from 50% to 65% and so on.
Over time, the athlete gradually progresses to throwing the sport implement of his/her sport. The intensity of the throws is carefully monitored to ensure that the motions continue to be pain-free. Distance and intensity are only increased when multiple repetitions can be performed with pain-free good mechanics.
When Can I Return to Play?
The athlete should only attempt to return to sports when he/she has been released by a qualified sports medicine professional. The athlete should be pain-free in all motions of the shoulder, have full strength of the muscles that move the scapula and of the rotator cuff, and have normal scapulohumeral rhythm between the muscles of the scapula and shoulder.
References
- Anderson, M.K., Hall, S.J., & Martin, M. (2005). Foundations of Athletic Training: Prevention, Assessment, and Management. (3rd Ed.). Lippincott Williams & Wilkins: Philadelphia, PA.
- Bahr, R. & Maehlum, S. (2004). Clinical Guide to Sports Injuries. Human Kinetics: Champaign, IL.
- Irvin, R., Iversen, D., & Roy, S. (1998). Sports Medicine: Prevention, Assessment, Management, and Rehabilitation of Athletic Injuries. (2nd Ed.). Allyn and Bacon: Needham Heights, MA.
- Kibler, W.B., Herring, S.A., Press, J.M.,& Lee, P.A. (1998). Functional Rehabilitation of Sports and Musculoskeletal Injuries. Aspen Publication: Gaithersburg, MA.
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