eMedicine Specialties > Orthopedic Surgery > Shoulder

Multidirectional Glenohumeral Instability

Author: Daniel C Wnorowski, MD, Consulting Surgeon, Orthopedic Surgeon and Assistant Clinical Instructor, Department of Orthopedic Surgery, Crouse Hospital and SUNY Upstate Medical University
Contributor Information and Disclosures

Updated: Mar 16, 2009

Introduction

Background

Multidirectional instability (MDI) is a relatively common, generally bilateral, atraumatic condition affecting shoulder function. MDI is caused by generalized capsular laxity—that is, insufficiency of the static ligament constraints. See image below.

Labral features characteristic of multidirectional instability; normal appearing. Note: although there are only 2 lb of traction, it is very easy to push the arthroscope between the humeral head and glenoid surfaces (ie, drive-through sign). Photo courtesy of Daniel C. Wnorowski, MD.

[ CLOSE WINDOW ]

Labral features characteristic of multidirectional instability; normal appearing. Note: although there are only 2 lb of traction, it is very easy to push the arthroscope between the humeral head and glenoid surfaces (ie, drive-through sign). Photo courtesy of Daniel C. Wnorowski, MD.

There is excessive mobility of the glenohumeral joint in all directions, although there may be a predominance of 1 direction, typically anteroinferior or posteroinferior.¹

History of the Procedure

The history of multidirectional instability (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 Egyptian times, MDI was acknowledged as a real entity only as recently as 1980, when it was first described in detail by Neer and Foster. Although Perthes² and Bankart,³ in 1906 and 1923, respectively, 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.

For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles, Shoulder Dislocation and Shoulder Separation.

Problem

A patient with symptomatic multidirectional instability (MDI) may complain of instability symptoms but often presents only with pain. Initial treatment is conservative, focusing on strengthening the dynamic components of shoulder stability—the rotator cuff and the scapular stabilizers. A conservative approach is often successful; however, when rehabilitation fails, surgical management may be undertaken to enhance static stabilization by tightening the shoulder capsule, historically via an open procedure, but arthroscopic management is evolving rapidly. The prognosis for MDI is generally good.

Frequency

The prevalence of MDI of the shoulder in the general population is not known. Traumatic shoulder instability is a much more common surgical indication.

Etiology

Shoulder instability has been classified by Hawkins and colleagues,⁴ as well as others, in various ways, including direction (eg, anterior, posterior), degree (dislocation vs subluxation), etiology (eg, traumatic, atraumatic, overuse), and chronology (eg, acute, recurrent, fixed). For this article, 2 major categories are especially useful^5,6,4 :

• The mnemonic device TUBS:
  • T raumatic etiology
  • U nidirectional instability
  • B ankart lesion
  • S urgical repair
• When considering the diagnosis of MDI, it is helpful to remember the mnemonic device AMBRII:
  • A traumatic etiology
  • M ultidirectional instability
  • B ilateral involvement
  • R ehabilitative initial management
  • Rotator I nterval tightening with I nferior capsular shift repairs

Pathophysiology

Physicians must thoroughly understand basic shoulder biomechanics to understand multidirectional instability (MDI), to make the diagnosis in appropriate cases, and to prescribe a proper treatment plan. The best written, simple, understandable, concise, and readable summary of shoulder stability is that of Matsen et al.⁵ Review of the text of Matsen et al is encouraged; highlights of this text 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 describe the following concepts, which contribute to the stability of the shoulder joint: balance, concavity compression, superior stability, adhesion-cohesion, glenohumeral suction cup, limited joint volume, and 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 2 bones relative to each other—namely, the rotator cuff and scapular positioners. Factors that affect balance stability include loss of glenoid surface area, scapular malalignment, and 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 (1) the increased thickness of the glenoid articular cartilage at the periphery of the glenoid relative to its center, (2) the glenoid labrum, and (3) the compressive force of an appropriately functioning rotator cuff. Factors that affect this component include deficiencies of glenoid concavity (congenital flatness); labral hypoplasia, attrition, or tearing; and 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 a deficient superior glenoid and the 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 changes in the fluid chemistry (secondary to inflammatory disease), loss of smoothness of the surfaces (secondary to degenerative disease), and 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 glenohumeral joint 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. Joint puncture by any means, increase in joint fluid secondary to trauma or inflammation, and laxity of the capsule (increasing joint volume) all contribute to the loss of this stabilizing mechanism.

Capsuloligamentous restraints

Matsen et al stress that the aforementioned components provide midrange stability. Midrange stability refers to stability in the mid 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.^7,8,9

The value of the dynamic supports of shoulder stability (ie, rotator cuff, scapular stabilizers) cannot be overstated. The proper compressive function 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.¹⁰

Presentation

The diagnosis of multidirectional instability (MDI) is highly clinical. Suggestive history and physical examination findings are the basis of a diagnosis of MDI. Imaging studies, including plain radiographs, magnetic resonance imaging (MRI), and MRI-arthrography, may be of marginal help. Examination under anesthesia (EUA) and arthroscopic findings are highly supportive.

History

The patient with MDI most often presents with complaints of a generalized painful or sore shoulder, which is usually worse with activity or with certain arm positions. Instability symptoms perceived by the patient, such as dislocation, subluxation, or functional symptoms (eg, catching, locking), are less commonly reported than pain.¹¹ In fact, some patients may not appreciate or describe any actual sense of instability. Symptoms may follow a roller coaster pattern and may be aggravated by overhead activity, carrying objects at the side, overuse, or injury. These symptoms are relieved by rest and support of the arm. Nocturnal pain is variable.

The patient usually denies a history of frank traumatic dislocation but may describe subluxation or looseness, even with activities of daily living (ADL). This history should provoke suspicion of and search for a multidirectional pattern of laxity, particularly if bilateral or posterior. The combination of posterior and inferior laxity is classic, according to Neer and Foster.¹²

An athletic history may be contributory.¹³ Patients with a predisposition to MDI who are engaged in sports that are stressful to the shoulder girdle, such as swimming, throwing, or racquet sports, may have a difficult time with consistent high activity levels.

Perhaps one of the most confusing presentations is that of concomitant impingement. Not uncommonly, a patient with MDI may complain chiefly of pain with overhead use, especially if there is involvement with overhead athletics, such as throwing, volleyball, swimming, or racquet sports. Pain, in this case, may be minimal with the arm at the side. Tibone et al¹⁴ have shown that therapeutic management directed at the diagnosis of impingement and rotator cuff pathology in patients participating in overhead activities may be unsuccessful. Underlying instability always must be considered in those who report a painful shoulder, especially in the younger patient who is involved in vigorous activities above the shoulder.

Impingement symptoms (ie, pain with the arm at 90° or more) may be secondary to glenohumeral hypermobility and superior humeral head translation, regardless of acromial arch architecture.

Physical examination

A notable highlight of MDI on examination is the bilaterality of physical findings. Although active ROM (AROM) may be guarded, there are no passive limits. A good stability examination yields underlying glenohumeral hyperlaxity if adequate relaxation can be achieved. The pathognomonic feature of MDI is demonstration of the sulcus sign—the hallmark of the inferior component of the capsular laxity. Again, with adequate relaxation, a patient examiner demonstrates laxity beyond the normal limits with anterior and posterior testing. Grade may be variable, and anterior and posterior components need not be symmetrical.

If the patient is unable to relax, an EUA may be required to demonstrate increased glenohumeral anterior and posterior translation, as well as inferior translation (ie, sulcus sign). More often than not, these findings are symmetrical.

Examination of the labrum (eg, labral grind test, superior labrum anterior and posterior lesion [SLAP] test) also may reveal positive findings, with or without true labral anatomic abnormalities. Furthermore, apprehension testing also may be positive, usually in the direction of the chief component of instability. For example, anterior apprehension findings in the external rotation and abducted position may suggest a predominant anterior-inferior MDI pattern, with or without positive relocation, crank, or fulcrum tests.

Indications

Indications for surgical treatment of multidirectional instability (MDI) include the presence of persistent symptoms to a disabling degree and failure of conservative management, including a supervised rehabilitation program and a trial of activity modification or restriction.

A reasonable trial of conservative treatment is 3-6 months. Any patient for whom conservative management has failed may be counseled regarding the option of surgical treatment. The following points must be considered:

1. Does the patient have sufficient present disability to make surgery a worthwhile endeavor?
2. Has the patient shown satisfactory effort and dedication to the preoperative rehabilitation program?
3. Is the patient willing to continue postoperative rehabilitation for at least 6 months, and does the patient understand the importance of shoulder rehabilitation and muscle strengthening to the stability of his or her shoulder?
4. Is the patient willing to comply with postoperative limitations with regard to immobilization, activity limits, and work and sports restrictions?
5. Is the patient willing to accept the possibility of lost ROM?
6. Is the patient willing to risk axillary nerve injury and other operative complications?

Relevant Anatomy

A thorough discussion of the relevant anatomy is included in the discussion of surgical techniques available for multidirectional instability (MDI), both open and arthroscopic (see Open surgical technique and Arthroscopic surgical technique in the Treatment, Surgical therapy section). The reader is also urged to read the Complications section, especially with regard to precautions necessary when working close to the axillary nerve.

Contraindications

According to Neer and Foster,¹² contraindications to the surgical management of MDI include willful, habitual, or voluntary shoulder instability; collagen connective tissue disorders (eg, Ehlers-Danlos syndrome, Marfan syndrome); and lack of a trial of, or noncompliance with, a supervised rehabilitation program.

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