Practice Essentials
Multidirectional instability (MDI) is a relatively common, generally bilateral, typically atraumatic condition affecting shoulder function. MDI is caused by generalized capsular laxity—that is, insufficiency of the static ligament constraints of the glenohumeral joint (GHJ). There is excessive mobility of the GHJ in all directions: anterior, posterior, and inferior. However, there may be a predominance of one direction, typically anteroinferior or posteroinferior. [1]
The history of MDI of the shoulder is neither as colorful nor as ancient as that of traumatic shoulder instability. Whereas traumatic shoulder dislocation and its treatment can be traced back to ancient Egypt, MDI was acknowledged as a real entity only in 1980, when it was first described in detail by Neer and Foster. [2]
Although Perthes [3] in 1906 and Bankart [4] in 1923 described the essential lesion of recurrent traumatic glenohumeral dislocations (ie, detachment of the labrum and inferior glenohumeral ligament from the glenoid), the role of generalized capsular laxity in glenohumeral instability was not appreciated until 1980.
A patient with symptomatic MDI may complain of instability symptoms but often presents only with pain; accordingly, a high index of suspicion is required. The diagnosis is highly clinical. Suggestive history and physical examination findings are the basis of a diagnosis of MDI (see Presentation). Imaging studies, including plain radiography, magnetic resonance imaging (MRI), and magnetic resonance (MR) arthrography, may be of marginal help (see Workup). Examination under anesthesia (EUA) and arthroscopic findings are highly supportive.
Sometimes, the patient may describe an injury or traumatic event. Often, adolescent athletes may report indistinct trauma. However, it is important to perform a thorough physical examination in these patients because MDI may present with muscular or myofascial pain when the underlying pathology is capsular laxity.
Initial treatment is conservative, focusing on strengthening the dynamic components of shoulder stability—the rotator cuff and the scapular stabilizers. A conservative approach is most often successful; however, when a period of prolonged rehabilitation (6-9 months) fails, surgical management may be undertaken to enhance static stabilization by tightening the shoulder capsule. (See Treatment.) Historically, this was typically accomplished with an open procedure, but arthroscopic management is evolving rapidly. The prognosis for MDI is generally good.
For patient education resources, see the First Aid and Injuries Center, as well as Shoulder Dislocation and Shoulder Separation.
Anatomy
The GHJ is a relatively nonconstrained joint, and in MDI, this joint has increased laxity. Typical characteristics of MDI are that of a loose capsule, with poorly developed glenohumeral ligaments, and a variable labral anatomy. The labrum may be normal and unimpressive for an unstable joint, or attenuated or hypoplastic, or even sometimes torn or abraded. Anterior or posterior labral tears or separation (Bankart lesions) may be present. [4]
Capsular tissue is typically thin and redundant, especially inferiorly, with small anterior and posterior bands of the inferior glenohumeral ligaments, and superiorly, at the cuff interval. The axillary recess or pouch is impressively patulous. The articular surfaces are most often normal or show minimal chondromalacia, and Hill-Sachs impaction type lesions are quite atypical. For more anatomic details, see Treatment.
Pathophysiology
Physicians must have a thorough knowledge of basic shoulder biomechanics in order to understand MDI, to make the diagnosis in appropriate cases, and to prescribe a proper treatment plan. Review of Matsen's text on evaluation and management of the shoulder [5] is encouraged; highlights are summarized in this section.
The shoulder is unlike other joints in the body in that for it to meet the demands for extreme motion, osseous- and ligamentous-based stability is sacrificed. Matsen et al [5] described the following concepts, which contribute to the stability of the shoulder joint:
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Balance
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Concavity compression
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Superior stability
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Adhesion-cohesion
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Glenohumeral suction cup
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Limited joint volume
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Capsuloligamentous constraints
Balance
Balance refers to the passage of the net joint-reaction forces on the humeral head through the center of the glenoid fossa. An analogy is made to a golf ball on a tee. The key components of balance include alignment of the humerus with the glenoid center line, facilitated by the surface arcs and areas of the glenoid and humeral head and by the muscles that position these two bones relative to each other—namely, the rotator cuff and scapular positioners.
Factors that affect balance stability include the following:
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Loss of glenoid surface area
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Scapular malalignment
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Muscle imbalance or weakness (eg, rotator-cuff dysfunction)
Concavity and compression
The concept of concavity compression refers to the stabilizing effect of the depth of the concave glenoid fossa on translation of the convex humeral head. This is augmented by the following:
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Increased thickness of the glenoid articular cartilage at the periphery of the glenoid relative to its center
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Glenoid labrum
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Compressive force of an appropriately functioning rotator cuff
Factors that affect this component include the following:
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Deficiencies of glenoid concavity (congenital flatness)
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Labral hypoplasia, attrition, or tearing
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Rotator-cuff dysfunction
Superior stability
Superior stability refers specifically to the superior-inferior component of glenoid concavity, which resists proximal migration of the humeral head within the glenoid. Coupled with the compressive function of the rotator cuff, even with a torn supraspinatus, this component can resist the upward pull of the deltoid. Factors that affect such superior stability include the following:
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Deficient superior glenoid
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Biceps-labral anchorage
Adhesion-cohesion
Adhesion-cohesion is a mechanism by which fluid on coated surfaces provides an intrinsic adherence between the surfaces. This may be affected by the following:
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Changes in the fluid chemistry (secondary to inflammatory disease)
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Loss of smoothness of the surfaces (secondary to degenerative disease)
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Alterations in the contact areas
Glenohumeral suction cup
The glenohumeral suction-cup effect depends upon the tendency for matched concave and convex surfaces with a flexible periphery to center and stabilize after expressing any intervening air and fluid, thereby forming a seal. Deficiencies of the glenoid labrum or of the margin of the glenoid can adversely affect this stabilizing mechanism.
Limited joint volume
The limited joint volume mechanism reflects the fact that the normal GHJ is really a potential space, contains minimal fluid, and has an inherent negative pressure. A sealed joint ensures an increase in this negative pressure with attempted distraction, thus increasing the joint reactive force independent of other muscular forces. Factors contributing to the loss of this stabilizing mechanism include the following:
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Joint puncture by any means
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Increase in joint fluid secondary to trauma or inflammation
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Laxity of the capsule (increasing joint volume)
Capsuloligamentous restraints
Matsen et al [5] stressed that the aforementioned components provide midrange stability—that is, stability in the middle of the range of motion (ROM), where the ligaments and capsule provide little tension-dependent static stability. These factors act independently of the capsuloligamentous restraints.
The capsule serves as a passive leash that can restrain glenohumeral motion within a given ROM. The insertion of the capsule upon the glenoid labrum provides continuity for the concavity mechanisms described above. The glenohumeral ligaments are ideally positioned thickenings within the capsule that serve to check large forces encountered within the capsule during specific arm positions and activities.
Numerous studies have elucidated the role of the capsuloligamentous complex in the static stabilization of the shoulder, and it has been shown that the inferior glenohumeral ligament is clearly the most crucial component. [6, 7, 8] This includes both an anterior and a posterior component, which create a sling that functions to hold the shoulder in the appropriate anatomic position.
The value of the dynamic supports of shoulder stability (ie, rotator cuff and scapular stabilizers) cannot be overstated. Proper compressive functioning of the rotator cuff is essential for glenohumeral stability and remains the primary focus of rehabilitative management for this problem. Deficits of shoulder proprioceptive function have been reported in MDI. [9]
Etiology
Shoulder instability has been classified on the basis of a number of different variables, [5, 10, 11] including the following:
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Degree ( dislocation vs subluxation)
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Etiology (eg, traumatic, atraumatic, overuse)
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Chronology (eg, acute, recurrent, fixed)
It may be helpful to keep in mind the mnemonic device TUBS, defined as follows:
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Traumatic etiology
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Unidirectional instability
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Bankart lesion
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Surgical repair
When the diagnosis of MDI is under consideration, it is helpful to remember the mnemonic device AMBRII, defined as follows:
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Atraumatic etiology
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Multidirectional instability
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Bilateral involvement
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Rehabilitative initial management
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Rotator Interval tightening with Inferior capsular shift repairs
Epidemiology
The prevalence of MDI (atraumatic shoulder instability) in the general population is not known. Traumatic shoulder instability is a much more common surgical indication. A study in Japanese military cadets (N = 5402) found that the overall overall incidence of traumatic shoulder instability events was 10.3 per 1000 person-years. [12]
Prognosis
In general, patients who have had open capsular shifts do reasonably well. Published studies indicate that the recurrence rate for MDI after surgery is about 10%. Loss of ROM after open capsular shift repair was greater in the early case series than in the later series, particularly for external rotation and abduction. Reported complications are rare.
Good results tend to persist with time as well. Stability does not seem to be lost at later follow-up on individuals with conventional open shift repair.
The long-term follow-up of arthroscopic management of MDI remains to be definitvely assessed. Advocates of both suture techniques reported results that were somewhat less favorable in some cases than those of open surgery at follow-ups of up to 2 years, with recurrence rates of approximately 20-30% [13, 14] vs 10% for open repairs. [2, 15, 16] However, others reported similar results 4 years or longer after treatment. [17]
Thermal repairs have generally shown poorer outcomes, with failure rates of 60%. [18, 19] Because of these poorer outcomes, the unacceptable risks, and the reported complications, thermal capsulorrhaphy is no longer recommended.
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Labral features characteristic of multidirectional instability; normal appearing. Note: Although there is only 2 lb of traction, it is very easy to push arthroscope between humeral head and glenoid surfaces (ie, drive-through sign). Courtesy of Daniel C Wnorowski, MD.
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Hypoplastic labrum. Courtesy of Daniel C Wnorowski, MD.
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Posterior and superior aspects of humeral head of shoulder with multidirectional instability are pristine. Typically, there is no Hill-Sachs lesion, even if there has been subluxation. Courtesy of Daniel C Wnorowski, MD.
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Posterior aspect of humeral head of shoulder with multidirectional instability is without Hill-Sachs lesion. Also note patulous capsule. Courtesy of Daniel C Wnorowski, MD.
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Multidirectional instability of right shoulder from posterior portal. Patient is in lateral position with minimal arm traction (2 lb). Note glenohumeral inferior subluxation, with humeral head perched on normal-appearing anterior-inferior labrum. Courtesy of Daniel C Wnorowski, MD.
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Normal subacromial space in patient with multidirectional instability and history of secondary impingement. Courtesy of Daniel C Wnorowski, MD.
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Cosmetically ideal modified axillary incision for open inferior capsular shift. Incision will be made in apex of axillary crease. Courtesy of Daniel C Wnorowski, MD.
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Open approach via axillary incision. Self-retaining retractor is shifted cephalad after mobilization of skin flaps. Courtesy of Daniel C Wnorowski, MD.
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Rotator cuff interval is closed with nonabsorbable suture. T-capsulotomy incision is planned with dotted lines.
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Superomedial (SM) and inferomedial (IM) flaps are created by T-capsulotomy incision. First, IM flap will be advanced superiorly and laterally; then, SM flap will be advanced inferiorly over top of IM flap.
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Finished repair with superomedial (SM) flap advanced inferiorly, overlapping previous inferomedial (IM) flap advancement. Note how axillary pouch has been eliminated.
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Suture passer device (Spectrum; ConMed Linvatec, Largo, FL) is placed through working cannula, then through "pinch" of posterior capsule, and also through posterior labrum. Courtesy of Daniel C Wnorowski, MD.
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Next, with monofilament suture and all-arthroscopic knot-tying technique, knot is tied, thus plicating capsular "pinch" to labrum. Courtesy of Daniel C Wnorowski, MD.
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Process in image above is repeated, placing second, slightly more superior suture and knot. Courtesy of Daniel C Wnorowski, MD.
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Close-up of third "pinch." Courtesy of Daniel C Wnorowski, MD.
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Close-up of third labral pass. Courtesy of Daniel C Wnorowski, MD.
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Third suture is placed. Courtesy of Daniel C Wnorowski, MD.
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Completed third knot. Courtesy of Daniel C Wnorowski, MD.
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Depending on degree of capsular laxity, one may take "double tuck" to achieve additional plication and tightening, at risk of added range-of-motion restriction. Courtesy of Daniel C Wnorowski, MD.
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View from posterior portal of "interval closure"; with suture passer device, monofilament suture is placed at margins of cuff interval. Courtesy of Daniel C Wnorowski, MD.
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Knot is tied through anterosuperior portal, thus closing rotator-cuff interval. Courtesy of Daniel C Wnorowski, MD.
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Second of two anchors placed for posterior plication, given hypoplastic posterior labrum, prior to suture passage. Note anchor placement on posterior margin of articular surface, not on neck of glenoid. This allows for "capsulolabral reconstruction" (see next image). Courtesy of Daniel C Wnorowski, MD.
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After passage of anchor-based suture and completion of plication and "capsulolabral reconstruction," augmenting hypoplastic labrum with capsular fold. Note that these are permanent sutures and therefore are tied off glenoid to avoid knot-articular surface impingement. Courtesy of Daniel C Wnorowski, MD.
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Monopolar radiofrequency probe applied to posterior capsule with grid technique after treatment to 65°C. Ellipses indicate areas of linear application (grid lines). Rectangle indicates untreated island between lines. Courtesy of Daniel C Wnorowski, MD.
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Patient is in beach-chair position; anterior portal. Note capsular laxity with probe and blunted labrum. Photo courtesy of Bradley S Raphael, MD.
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Suture passer device (Suturelasso; Arthrex, Naples, FL) is placed through working cannula, then through "pinch" of posterior capsule and also through posterior labrum; it is threaded with nonabsorbable suture that is tied with knot away from articular cartilage. Photo courtesy of Bradley S Raphael, MD.
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Next, with monofilament sutures and all-arthroscopic knot-tying technique, knots are tied, thus plicating capsular "pinch" to labrum. Photo courtesy of Bradley S Raphael, MD.
