Shoulder problems are common with a wide range of symptoms and treatments. One diagnosis that continues to challenge orthopedic surgeons is called multidirectional instability. This diagnosis is defined by instability of the shoulder in two (or more) directions. That sounds simple enough but there are shades of instability. And instability must be separated out from laxity (natural looseness of the ligaments).
In this article, three surgeons from three separate educational programs combine their expertise to review the problem and management of multidirectional instability (MDI). They define MDI as instability in two or more directions that presents with bothersome symptoms. There may or may not be hyperlaxity present.
The shoulder is a very complex structure. Stability depends on many different soft tissues including muscles, ligaments, tendons, joint capsule, and the labrum. The labrum is a special rim of fibrous tissue around the shoulder socket to give it greater depth.
Some structures function to dynamically stabilize (hold) the shoulder in place. Muscles and tendons are dynamic stabilizers. Other soft tissues are more static, providing a steady holding power instead. Ligaments, capsule, bone, and labrum are more static in their function.
When any of the stabilizing soft tissues are torn, damaged, or not functioning properly, other structures try to compensate. Now they must do their own job as well as the work of the deficient soft tissues. They can’t keep this up forever. Eventually the compensatory mechanisms fail and problems develop. Multidirectional instability is often one of those resultant problems.
Treatment of any orthopedic problem is best approached using a classification system. For example, in the case of shoulder instability, if the surgeon can identify the direction of instability, severity of instability, and presence of hyperlaxity, then a specific plan of treatment can be developed.
Having a classification system that includes whether there is dynamic versus static instability would be helpful in determining the most optimal treatment plan for each patient. But such a guiding classification system for multidirectional instability (MDI) is not available yet.
The authors suggest different classifications of MDI would respond differently to conservative (nonoperative) versus surgical intervention. For example, someone with a shallow glenoid cavity (shoulder socket) may benefit from rehab to strengthen the muscles around the shoulder.
Rotator cuff strengthening often increases the ability of the humeral head to stay compressed inside the socket. A strong rotator cuff also helps the shoulder resist translational (shear) forces. Restoring normal proprioception (joint sense of its own position) has been shown to improve motor control, thus increasing dynamic stabilization.
In recent years, the important role of the scapula (shoulder blade) in shoulder motion has been recognized. The scapula and shoulder must move together in harmony and with just the right rhythm and flow. Without this dynamic dance, a condition called scapular dyskinesia can develop resulting in shoulder problems and contributing to the instability.
The rehab program must address strength, endurance, proprioception, motor control, and coordination of the entire shoulder complex (including the scapula). Such a program is directed and supervised by a physical therapist. Patients must be advised to plan on at least a six month trial of concentrated efforts in rehab with a lifelong maintenance plan urged.
Some patients with shoulder instability may also do well with a rehab program while others will eventually require surgery. Sometimes recovery of stabilizing motor activity isn’t possible without shifting the capsule or repairing the rotator cuff. Other reconstructive techniques may be needed to fix the anatomic cause of shoulder instability.
The authors offer a detailed discussion of the various surgical interventions that can be used to halt debilitating symptoms of shoulder instability. They include techniques such as open inferior capsular repair, thermal capsulorrhaphy, arthroscopic capsular plication, and rotator interval closure procedures. Drawings, arthroscopic photos, and verbal descriptions of each are provided.
Each of these procedures must be followed by postoperative rehabilitation. The surgeon and physical therapist work closely to develop a specific program for each patient. The therapist works with the patient prescribing exercises based on the direction of the primary (main) instability and type of surgical repair performed. The ultimate goal is to restore normal shoulder motion, preventing stiffness, and helping the patient regain full activity.
Despite all that is known about multidirectional instability (MDI) of the shoulder, there remains much yet to be discovered. For example, the authors point out the need for a classification system to direct and guide treatment. Having a way to identify patients who would have the best outcomes with rehab versus surgery would be helpful.
Likewise, research is needed to develop some criteria for determining who should have each one of the possible surgical options based on best outcomes. There may be other (better) reconstructive techniques waiting to be discovered. Studies comparing results among all the various treatment options are helping surgeons make decisions but the authors say that more information is still needed.