The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 80, Issue 1

Instructional Course Lecture | January 01, 1998

Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Instability of the Shoulder: Complex Problems and Failed Repairs. Part I. Relevant Biomechanics, Multidirectional Instability, and Severe Loss of Glenoid and Humeral Bone*†

EVAN L. FLATOW, M.D.‡, NEW YORK, N.Y.; JON J. P. WARNER, M.D.§, PITTSBURGH, PENNSYLVANIA

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An Instructional Course Lecture, The American Academy of Orthopaedic Surgeons

J Bone Joint Surg Am, 1998 Jan 01;80(1):122-40

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Historically, much of the literature on glenohumeral instability has concerned recurrent locked anterior glenohumeral dislocation. As the standard objective of operative intervention was the elimination of such a dislocation, many operations yielded a high proportion of successful results. However, increased attention to the special needs of active, athletic individuals has led to a higher standard for the success of operative reconstruction: the maintenance of full motion and strength in addition to the restoration of stability. Modern repair procedures avoid overtightening and emphasize restoration of the integrity of the capsular-ligamentous-labral complex. Although there is controversy as to whether an operation for unidirectional anterior instability should include a capsulorrhaphy in addition to repair of a Bankart lesion, most investigators agree that no more than a minor capsular tightening, with no procedure on bone, is needed for this most common type of shoulder instability^60,75,88,100.

Figures in this Article

Introduction

The situation is understandably more complex in the small number of patients in whom the instability of the shoulder is associated with more severe anatomical distortions. The recognition that symptomatic glenohumeral translations could occur in multiple directions in shoulders with global capsular laxity led to the development of more extensive capsular reconstructions. Furthermore, although capsular and ligamentous structures are usually the major sites of abnormality, in unusual instances severe loss of glenoid bone or a large humeral impression fracture may necessitate operative treatment.

Little information is available to guide the clinician in the care of these difficult problems as reports in the literature and discussions at meetings have tended to focus on recurrent anterior glenohumeral instability, especially with regard to the choice between open and arthroscopic techniques. The purpose of the current paper was to review the evaluation and management of patients who have multidirectional instability, major loss of bone from the glenoid, or a large humeral impression fracture, each of which substantially increases the level of complexity of operative reconstruction.

*Printed with permission of The American Academy of Orthopaedic Surgeons. This article will appear in Instructional Course Lectures, Volume 47, The American Academy of Orthopaedic Surgeons, Rosemont, Illinois, March 1998.

†No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

‡The Shoulder Service, New York Orthopaedic Hospital, Columbia-Presbyterian Medical Center, 161 Fort Washington Avenue, New York, N.Y. 10032.

§Shoulder Service, Center for Sports Medicine, Department of Orthopaedic Surgery, University of Pittsburgh, 4601 Baum Boulevard, Pittsburgh, Pennsylvania 15213-1217.

‡The Shoulder Service, New York Orthopaedic Hospital, Columbia-Presbyterian Medical Center, 161 Fort Washington Avenue, New York, N.Y. 10032.

§Shoulder Service, Center for Sports Medicine, Department of Orthopaedic Surgery, University of Pittsburgh, 4601 Baum Boulevard, Pittsburgh, Pennsylvania 15213-1217.

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TABLE I ANATOMICAL FACTORS AFFECTING THE STABILITY OF THE SHOULDER*

*Reprinted, with modifications and permission, from: Warner, J. J. P.; Schulte, K. R.; and Imhoff, A. B.: Current concepts in shoulder instability. Adv. Op. Orthop., 3: 219, 1995.

Factor	Function	Abnormality*
Congruity of articular surface	Concavity-compression effect	Glenoid dysplasia, fracture, Hill-Sachs lesion, and reverse Hill-Sachs lesion
Glenoid labrum	Increased depth of socket and surface area; anchoring point for ligaments and capsule	Bankart lesion
Negative intra-articular pressure	Vacuum effect	Capsular rupture, defect of the rotator interval, capsular laxity, and capsular injury
Coracohumeral ligament/superior glenohumeral ligament	Limits external rotation and inferior translation in adduction and posterior translation in flexion	Lesion of the rotator interval
Middle glenohumeral ligament	Limits external rotation and inferior translation in adduction and anterior translation in mid-abduction	Bankart lesion and capsular injury
Inferior glenohumeral ligament complex	Limits anterior, posterior, and inferior translation in abduction	Bankart lesion and capsular injury
Posterior aspect of the capsule	Limits posterior translation in the flexed, adducted, and internally rotated shoulder	Posterior capsular laxity and injury
Rotator cuff	Dynamic compression of the joint; steering effect	Overuse injury (fatigue) and rupture
Biceps (long head)	Dynamic restraint to anterior and superior translation	Lesion of the superior portion of the labrum, anterior and posterior (SLAP lesion) and rupture

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TABLE I ANATOMICAL FACTORS AFFECTING THE STABILITY OF THE SHOULDER*

*Reprinted, with modifications and permission, from: Warner, J. J. P.; Schulte, K. R.; and Imhoff, A. B.: Current concepts in shoulder instability. Adv. Op. Orthop., 3: 219, 1995.

Factor	Function	Abnormality*
Congruity of articular surface	Concavity-compression effect	Glenoid dysplasia, fracture, Hill-Sachs lesion, and reverse Hill-Sachs lesion
Glenoid labrum	Increased depth of socket and surface area; anchoring point for ligaments and capsule	Bankart lesion
Negative intra-articular pressure	Vacuum effect	Capsular rupture, defect of the rotator interval, capsular laxity, and capsular injury
Coracohumeral ligament/superior glenohumeral ligament	Limits external rotation and inferior translation in adduction and posterior translation in flexion	Lesion of the rotator interval
Middle glenohumeral ligament	Limits external rotation and inferior translation in adduction and anterior translation in mid-abduction	Bankart lesion and capsular injury
Inferior glenohumeral ligament complex	Limits anterior, posterior, and inferior translation in abduction	Bankart lesion and capsular injury
Posterior aspect of the capsule	Limits posterior translation in the flexed, adducted, and internally rotated shoulder	Posterior capsular laxity and injury
Rotator cuff	Dynamic compression of the joint; steering effect	Overuse injury (fatigue) and rupture
Biceps (long head)	Dynamic restraint to anterior and superior translation	Lesion of the superior portion of the labrum, anterior and posterior (SLAP lesion) and rupture

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Fig. 1 Drawing of the glenohumeral joint. The subchondral bone of the glenoid is less curved than the humerus, but the articular cartilage of the glenoid is thicker peripherally so the true articular surfaces are, in fact, highly conforming. Because the surface area of the glenoid is far smaller than that of the humerus, the articular surfaces provide less stability in the shoulder than do those in the hip, where the socket is larger and contains a large portion of the femoral head.

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Fig. 2 Drawing showing the glenoid labrum, which extends around the perimeter of the glenoid and increases the surface area (arrows) and depth of the glenoid socket. (Reprinted, with permission, from: Warner, J. J. P., and Caborn, D. N. M.: Overview of instability. Crit. Rev. Phys. and Rehab. Med., 4: 149, 1992.)

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Fig. 3 Drawing of the capsuloligamentous anatomy, viewed from the side with the anterior aspect (A) to the right and the posterior aspect (P) to the left. The humeral head has been removed, leaving the glenoid and the superior glenohumeral (SGHL) and middle glenohumeral (MGHL) ligaments. The inferior glenohumeral ligament complex (IGHLC) consists of an anterior band (AB), a posterior band (PB), and the interposed axillary pouch (AP). The posterior portion of the capsule (PC) is the area proximal to the posterior band. B = biceps. (Reprinted, with permission, from: O'Brien, S. J.; Neves, M. C.; Arnoczky, S. P.; Rozbruck, S. R.; Dicarlo, E. F.; Warren, R. F.; Schwartz, R.; and Wickiewicz, T. L.: The anatomy and histology of the inferior glenohumeral ligament complex of the shoulder. Am. J. Sports Med., 18: 451, 1990.)

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Fig. 4-A Drawing of the hammock-like anatomy of the inferior glenohumeral ligament complex, which allows for reciprocal tightening of its anterior and posterior portions when the arm moves from neutral rotation in abduction (a) to external rotation (b) and to internal rotation (c). (Reprinted, with permission, from: Warner, J. J. P., and Caborn, D. N. M.: Overview of instability. Crit. Rev. Phys. and Rehab. Med., 4: 151, 1992.)

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Fig. 4-B Drawing showing changes in the orientation of the anterior band (aa) and the posterior band (pp) during neutral (NR), internal (IR), and external rotation (ER). (Reprinted, with permission, from: Warner, J. J. P.; Caborn, D. N. M.; Berger, R.; Fu, F. H.; and Seel, M.: Dynamic capsuloligamentous anatomy of the glenohumeral joint. J. Shoulder and Elbow Surg., 2: 131, 1993.)

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Figs. 5-A and 5-B: Photographs of patients demonstrating generalized ligamentous laxity. Fig. 5-A: Laxity of the thumb is demonstrated by this patient who can approximate the thumb to the forearm.

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Fig. 5-B Laxity of the elbow is demonstrated by this patient who can hyperextend the elbow.

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Figs. 6-A, 6-B, and 6-C: Preoperative photographs of a twenty-two-year-old woman who had multidirectional instability. Fig. 6-A: The shoulder demonstrated a sulcus sign of 3+ as the arm was pulled distally by the examiner (not shown).

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Fig. 6-B: The shoulder subluxated anteriorly when the arm was extended and externally rotated. The instability was symptomatic and prevented overhead activities.

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Fig. 6-C: The shoulder dislocated posteriorly when the arm was flexed and internally rotated. The patient was unable to reach for objects or to push open doors.

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Figs. 6-D through 6-H: Photographs made seven years after treatment with an inferior capsular shift from a posterior approach. Fig. 6-D: Elevation.

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Fig. 6-E External rotation.

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Fig. 6-F: Slight loss of internal rotation.

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Fig. 6-G: The shoulder had no anterior subluxation when the arm was extended and externally rotated. The shoulder was stable and strong, and the patient was able to use the arm overhead for athletic activities.

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Fig. 6-H: The shoulder did not dislocate posteriorly when the arm was flexed and internally rotated.

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Figs. 7-A, 7-B, and 7-C: Drawings showing an inferior capsular shift performed from an anterior approach. Fig. 7-A: The subscapularis tendon (straight arrow) is detached. Then the capsule is detached laterally, leaving a cuff for repair. As the humerus is externally rotated (curved arrow), the capsule is detached from around the humeral neck. The extent of this release—that is, how far around the neck posteriorly to detach the capsule—is tailored to the size of the pouch and the degree of instability present. (Reprinted, with permission, from: Bigliani, L. U.: Anterior and posterior capsular shift for multidirectional instability. In Operative Techniques in Shoulder Surgery, pp. 138—139. Edited by L. E. Paulos and J. E. Tibone. Gaithersburg, Maryland, Aspen, 1991.)

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Fig. 7-B: The inferior flap of the laterally-based T-capsulorrhaphy is brought anteriorly and superiorly. (Reprinted, with permission, from: Bigliani, L. U.: Anterior and posterior capsular shift for multidirectional instability. In Operative Techniques in Shoulder Surgery, pp. 138—139. Edited by L. E. Paulos and J. E. Tibone. Gaithersburg, Maryland, Aspen, 1991.)

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Fig. 7-C: The rotator interval is closed, and the superior flap is brought down and across the inferior flap. This procedure thickens and reinforces the capsule on the side of the approach, while the shift of the inferior aspect of the capsule tensions (but cannot thicken) the opposite (posterior) side. (Reprinted, with permission, from: Bigliani, L. U.: Anterior and posterior capsular shift for multidirectional instability. In Operative Techniques in Shoulder Surgery, pp. 138—139. Edited by L. E. Paulos and J. E. Tibone. Gaithersburg, Maryland, Aspen, 1991.)

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Fig. 8-A: Radiograph showing a chronic unreduced anterior dislocation in an elderly patient.

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Fig. 8-B: An enormous humeral impression fracture was seen at the open reconstruction. The fracture was treated with a humeral head replacement.

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Figs. 9-A through 9-D: An active young female patient who had recurrent anterior instability of the shoulder. Fig. 9-A: Radiographs showing a large humeral impression defect (arrows).

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Fig. 9-B Computerized tomographic scans showing the large size of the defect (arrows).

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Fig. 9-C Radiographs made after ligament reconstruction, which was accompanied by reconstruction of the humeral head defect with a segment of an allograft humeral head.

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Fig. 9-D Photograph of the patient, showing a good functional result.

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Figs. 10-A through 10-J: A young patient who had recurrent anterior dislocation of the shoulder. Fig. 10-A: Anteroposterior radiograph showing evidence of a Hill-Sachs lesion (white arrows) and loss of the sclerotic line representing the anteroinferior aspect of the glenoid rim (black arrows).

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Fig. 10-B Axillary radiograph showing loss of bone from the anteroinferior aspect of the glenoid, which was confirmed by a computerized tomographic scan (not shown).

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Fig. 10-C Photograph made intraoperatively, showing loss of 30 per cent of the anteroinferior aspect of the glenoid.

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Figs. 10-D, 10-E, and 10-F: Postoperative radiographs. Fig. 10-D: Anteroposterior radiograph showing inferior placement of the graft. The capsule was repaired to the edge of the intact glenoid articular surface, and the coracoid was transferred behind the capsule to reinforce it.

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Fig. 10-E: Lateral radiograph showing anteroinferior placement of the graft.

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Fig. 10-F Axillary radiograph showing placement of the graft to reconstruct the anterior aspect of the glenoid rim.

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Figs. 10-G through 10-J: Photographs made one year postoperatively. Fig. 10-G: Elevation.

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Fig. 10-H Full external rotation.

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Fig. 10-I: Full external rotation at 90 degrees of elevation.

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Fig. 10-J: Full internal rotation.

Biomechanical Considerations

An effective approach to the management of glenohumeral instability, with either a primary or a revision operation, depends on a clear understanding of the normal anatomy and biomechanics of the shoulder. The history of the treatment of shoulder instability is based on an evolving understanding of the unique anatomical aspects of this joint, which allow it to have a huge range of motion but also to remain stable¹⁰⁶. Although some early approaches such as the Bristow-Latarjet procedure³¹ were designed to constrain the motion of this joint or to distort the anatomy in order to substitute for injured structures such as the capsule and the labrum, more contemporary approaches have been directed toward the restoration of normal anatomy and selective correction of the abnormality encountered in each patient. An increased understanding of the contribution of both static and dynamic soft-tissue and osseous factors to the stability of this joint has led to a more accurate appreciation of the spectrum of abnormality that contributes to instability (Table I). With all approaches to the treatment of instability, the surgeon should consider which anatomical factor or factors are abnormal in each patient and then should address each factor systematically.

Static Stabilizers

Articular Anatomy

Although the glenohumeral joint surfaces are congruent (Fig. 1), the surface areas of the larger humeral head and the smaller glenoid fossa do not match^91,94. This congruent articulation allows for a very secure concavity-compression effect, which is created by the rotator cuff as it dynamically compresses the humeral head into the matched concavity of the glenoid⁶⁸. Furthermore, the fibrocartilaginous labrum, which extends around the perimeter of the glenoid, increases the depth and surface area of the articulation⁵³ (Fig. 2) and enhances the stability of the joint.

These joint surfaces are related to one another by the orientation of the proximal part of the humerus and the glenoid. Within a wide range of normal retrotorsion for the humerus and retroversion or anteversion for the glenoid, the joint surfaces maintain contact with one another during active overhead motions in both work and sports activities^3,7,8,10.

Any injury that distorts the relationship of the joint surfaces or their congruity may manifest as instability (Table I)^{14,20,24,61,63,84}. For example, a glenoid fracture that results in a loss of concavity of the glenoid leads to a loss of the normal concavity-compression mechanism. A Bankart lesion^68,88 also can disrupt the normal concavity-compression relationship of the joint in addition to representing a detachment of the origin of the glenohumeral ligaments. Other osseous lesions that can affect the normal articular relationships include a large Hill-Sachs lesion^{18,52,87,88,90} or congenital dysplasia⁷² of the joint surfaces.

Articular and labral injuries may exist alone or in combination with other abnormalities, and all of them must be carefully identified and corrected. The goal of treatment is to reconstruct the normal relationships between the articular surfaces.

Capsuloligamentous Structures

The thin capsular tissue is reinforced by collagenous thickenings, which are termed ligaments and may have the appearance of band-like structures⁷⁷ (Fig. 3). Different regions of the capsule each play an important role in the constraint of the humeral head in the glenoid and the prevention of excessive translations and rotations of the joint^{41,57,78,80,98,104,109}. During rotation of the arm, the glenohumeral ligaments and capsule tighten and loosen reciprocally (Figs. 4-A and 4-B), thus limiting translations and rotations in a load-sharing fashion¹⁰⁶. When the shoulder is in a mid-range of rotation, these capsuloligamentous structures are relatively lax and most stability is maintained by the rotator cuff and the biceps, which create a concavity-compression effect across this articulation^45,46,68. With any operation that tightens the capsule and ligaments with the arm in this mid-range of rotation, there is the risk of constraining the joint and preventing rotation^69,111. The Putti-Platt procedure, for example, may cause loss of external rotation. Furthermore, an overly tight anterior repair can lead to posterior humeral subluxation with the joint load focused on the posterior part of the glenoid^11,37, which may be a factor in the development of arthrosis after tight instability repairs⁹.

The capsuloligamentous structures also may provide afferent feedback that modulates contraction of the rotator cuff during active motion of the shoulder⁶⁷. This feedback may occur through the sensory modality of proprioception.

Although there is substantial variation in the development and robustness of portions of the capsule and ligaments, the ligamentous or band-like components can be seen consistently on arthroscopic inspection. However, it is important to remember that only the synovial surface of the capsule can be observed with the arthroscope. Thin, flimsy synovial tissue can appear robust and impressive if pleated or folded by the rotation of the arm. Conversely, a band of capsular thickening may be indistinguishable from the surrounding capsule. Only recently has information about the structural and material properties of these ligaments been gained.

The material properties of the inferior glenohumeral ligament have been investigated extensively. The strength of the inferior glenohumeral ligament in tension has been found to be far lower than that of the knee ligaments, which is to be expected as the shoulder ligaments share load with the muscles and other stabilizing mechanisms¹⁰. Another interesting finding is that regions of the inferior glenohumeral ligament become stronger and stiffer at higher strain rates¹⁰³, suggesting a functional adaptation that stabilizes the humeral head during high-speed athletic activities, when the muscles may be surprised or fatigued.

When loaded in tension, the inferior glenohumeral ligament was found to fail most commonly at the glenoid insertion, which is analogous to a Bankart avulsion, and in its mid-substance, which might be expected to result in capsular stretching and laxity¹⁰. However, there was substantial strain in the mid-substance before failure even in the ligaments that ultimately tore at the glenoid insertion. Recently, a study of repetitive loading of the inferior glenohumeral ligament at increasing levels of subfailure strain demonstrated dramatic decreases in peak force with unrecovered elongation⁸³. These findings suggest that the capsule may be subject to plastic deformation, especially after repetitive trauma.

Repetitive injuries from athletic activities often stretch out many different parts of the capsule, as each episode stresses only the portion of the capsule that was taut in the particular position in which the arm was injured. The reason that acquired laxity, such as that seen in gymnasts or in swimmers who perform the butterfly stroke, is often multidirectional may be that the cumulative effect of multiple minor injuries with the arm in various positions is a globally lax capsule. Conversely, a single violent traumatic episode would tend to focus the worst damage more to a specific region; for example, a traumatic anterior dislocation would result in a Bankart avulsion with anteroinferior capsular stretch.

Intraoperative determination of the region of injury of the capsule and ligaments is important when deciding on the best method of treatment. Labral detachment (a Bankart lesion), humeral detachment, or intraligamentous rupture can occur. Debate continues about the importance of a Bankart lesion compared with a capsular injury. Some surgeons favor isolated Bankart repair, whereas others believe an associated capsular shift is necessary to treat a concomitant capsular injury^{1,10,76,88,90,95,111,112}.

Laxity Compared with Instability

Laxity is a necessary attribute of the capsule and ligaments of the shoulder and allows for the normal large range of motion of this joint. Instability, however, is abnormal symptomatic motion of the humeral head relative to the glenoid during active shoulder motion. As the parameters of normal laxity are quite variable, confusion may develop if an examiner tries to define instability only on the basis of passive movement of the humeral head relative to the glenoid with the patient under anesthesia^{26,28,45,46,79,105,114}. The surgeon must be very careful to correlate the laxity perceived on examination with the patient under anesthesia with the symptoms and physical findings observed on examination when the patient is awake^1,111. A shoulder that can be subluxated when the patient is under anesthesia may or may not be truly unstable. Certainly, many young athletic individuals have relatively lax shoulders, and the assumption that the pain in such an individual is due to instability that necessitates repair with a capsular shift procedure may be erroneous.

Dynamic Stabilizers

Rotator Cuff

The rotator cuff is a complex of four muscles that encircle the humeral head and are conjoined to regions of the joint capsule. These muscles function primarily to stabilize the humeral head in the glenoid and secondarily to move the joint surfaces relative to one another^38,102. The rotator cuff has two major stabilizing mechanisms: concavity-compression^53,68 and synchronous coordinated contraction of the muscle units that steer the humeral head into the glenoid during motion of the arm^13,17.

Injury of the rotator cuff can occur from a single traumatic event or from cumulative trauma, as with repetitive overhead throwing motions. In either case, instability can result. The goal of treatment with either physical therapy or an operation should be to restore the function of the rotator cuff.

Long Head of the Biceps Brachii

Studies have shown that the long head of the biceps brachii has an important dynamic stabilizing role for both anterior and superior translation of the humeral head^38,54,86,107. Injury of the origin of the tendon (a so-called SLAP lesion; superior portion of the labrum, anterior and posterior) often is observed in association with instability, and it may represent the failure of a dynamic stabilizing mechanism^93,108.

Additional Factors Affecting Stability

Glenohumeral stability also is affected by negative intra-articular pressure and by scapulothoracic motion. Negative intra-articular pressure develops in the sealed compartment of the joint, and it is basically a vacuum effect that prevents the joint surfaces from being displaced away from one another. The magnitude of this stabilizing force is relatively small compared with the force of muscle contraction, and it functions mainly to keep the joint surfaces opposed in the relaxed dependent arm^43,64,113. Any condition that vents the capsule, such as a tear or defect of the rotator interval, reduces this stabilizing effect.

Normal scapulothoracic motion is essential for normal glenohumeral function. Patients who have shoulder instability often have abnormal scapulothoracic motion, and sometimes they may have frank winging of the scapula^66,81,115. Whether scapulothoracic dysfunction is primary or secondary in these patients, it has several important biomechanical consequences for the glenohumeral joint. First, failure of the scapula to rotate properly so that the glenoid remains underneath the rotating humeral head increases the tendency for instability because of loss of the stable glenoid platform on which the humeral head can rotate. Second, if the scapula wings, the coracoacromial arch will descend relative to the advancing greater tuberosity and the patient will have functional impingement¹¹⁵. Therefore, it is imperative for the orthopaedic surgeon to assess scapulothoracic function in a patient who has shoulder instability. In shoulders in which instability is treated non-operatively, muscle rehabilitation should include the axioscapular stabilizers (the serratus anterior, trapezius, and rhomboid muscles) as well as the rotator-cuff muscles.

In conclusion, in order to treat shoulder instability successfully, the physician must consider all static and dynamic factors that stabilize the joint. Isolated lesions as well as combined conditions must be identified and treated according to sound principles of anatomy and biomechanics.

Multidirectional Instability

The most common form of shoulder instability is recurrent anterior subluxation or dislocation. When this condition is initiated by a major traumatic event, there is often detachment or stripping of the labrum and the inferior glenohumeral ligament complex from the anteroinferior aspect of the glenoid (a Bankart lesion)^2,15,82. Most investigators^{7,60,75,88,100,112} agree on the need to repair this lesion, but there is debate about whether a concomitant capsulorrhaphy is needed. Thomas and Matsen¹⁰⁰ argued that most patients who have unidirectional anterior instability of traumatic onset need only a repair of the Bankart lesion. However, the translations induced by a Bankart lesion in an experiment were found to be small (inadequate to allow a complete dislocation)⁹⁵. Indeed, Jobe⁵⁸ noted that, geometrically, in order for the labrum to pull away from the glenoid, both the labrum and the attached capsule must deform (for example, the way a turtleneck collar stretches while being pulled off over the head). Early arthroscopic repairs that focused only on the Bankart lesion thus may have had a high rate of failure because, as minimally invasive procedures, they did not cause scarring of the lax capsule. In contrast, open approaches either include an explicit capsulorrhaphy or at least reduce capsular laxity through scarring. In any event, a wide variety of anterior reconstructions have been found to be effective for the treatment of unidirectional anterior glenohumeral instability. Multidirectional instability is more complex. Bankart lesions are less frequent, and capsular laxity becomes the dominant abnormality.

In 1980, Neer and Foster⁷⁶ reviewed the literature on glenohumeral instability^{3,25,29,89,101} and introduced a new type of capsular procedure, which they termed inferior capsular shift, for reconstruction of multidirectional instability. In that and subsequent reports^73-76, Neer emphasized several points.

1. Shoulders may become loose not only because of trauma and inherent ligamentous laxity but also because of repetitive minor injury and stress (as occurs in swimming the butterfly stroke or performing gymnastics). These stresses are often an important factor in the development of multidirectional instability.

2. Not all loose shoulders are painful, and the surgeon must be convinced that the instability is symptomatic before considering repair.

3. Standard anterior repairs may correct multidirectional instability incompletely, resulting in persistent symptomatic inferior and posterior instability.

4. Overly tight anterior repairs may tighten the joint asymmetrically, causing a fixed subluxation to the posterior side, which can result in arthrosis.

5. Rehabilitation of the muscles that stabilize the humerus is important not only in non-operative management but also to protect the repair postoperatively, as "the capsule and ligaments normally function only as a checkrein."⁷⁶

Multidirectional instability is defined as symptomatic glenohumeral instability in more than one direction: anterior, inferior, and posterior^{5,23,34,39,70,73-76}. There has been controversy about whether multidirectional and unidirectional instability are always distinct conditions or just extreme examples from a continuing degree of joint laxity, as has been proposed by Bigliani et al.⁷. The latter approach suggests that varying degrees of capsulorrhaphy may be necessary depending on the lesion that is encountered.

Clinical Presentation

Although extremely hypermobile shoulders can become symptomatic without unusual trauma, there may be a discrete injury that initiates symptoms. Repetitive stress on the shoulder from athletic activities or work-related events often are involved. Patients who have multidirectional instability report recurrent subluxation and a sense of instability more commonly than locked dislocation. When dislocations occur, they often do so without a major injury and spontaneously reduce or can be reduced by the patient. It is important to evaluate the history of each patient carefully for suggestions of voluntary instability⁸⁹.

Symptoms may be vague, but they can suggest the directions of instability involved. Pain in the overhead, abducted, and externally rotated position is associated with anterior instability. Discomfort with the arm in forward elevation and internal rotation (for example, when pushing open heavy doors) suggests posterior instability. Patients who have inferior instability often report pain and paresthesias (traction on the brachial plexus) when carrying heavy objects.

The patient may have a history of laxity of many joints, sometimes involving ankle sprains, patellar dislocations, or other ligament problems. Family members also may have a history of these types of disorders. The role of biochemical abnormalities, generalized laxity syndromes, and defined collagen disorders (for example, Ehlers-Danlos syndrome) in multidirectional instability have been investigated but not well characterized^{4,19,28,30,33,56}.

The physical examination may demonstrate generalized joint laxity with findings such as hyperextension at the elbows or the metacarpophalangeal joints or the ability to approximate the thumbs to the forearms (Figs. 5-A and 5-B). Laxity of the contralateral shoulder may be a clue to the multidirectional nature of the instability. Scapulothoracic instability with scapular mistracking may coexist with glenohumeral instability, and the examiner should look for this disorder⁷⁵.

The key part of the examination is to elicit unwanted glenohumeral translations that reliably reproduce the symptoms (Figs. 6-A, 6-B, 6-C, 6-D, 6-E, 6-F, 6-G and 6-H). This is not always easy because laxity may be dramatic but asymptomatic, and symptomatic instability may be impossible to demonstrate if pain, muscle spasm, and guarding prevent subluxation. There are many maneuvers to demonstrate instability, including the anterior and posterior apprehension tests, the anterior and posterior load and shift tests, the fulcrum test, the relocation test, the Fukuda test, and the push-pull or stress test with the patient supine^49,75,76,92. The sulcus sign (inferior sag of the humerus with the arm at the side) and inferior translation of the abducted humerus are especially helpful for elucidating inferior laxity⁷⁶.

Plain radiographs of a shoulder with multidirectional glenohumeral instability generally demonstrate normal findings, but they should be evaluated for the presence of humeral head defects or glenoid lesions (such as osseous Bankart fragments), or both, and for reactive bone or wear. Regular or computerized tomographic arthrograms may demonstrate an increased capsular volume and, less commonly, labral detachments. Magnetic resonance imaging may demonstrate labral lesions and chondral wear. It also may reveal capsular laxity, although it does so somewhat less reliably than arthrography because of the lack of joint distention. Evaluation of multidirectional glenohumeral instability with stress radiographs and cine magnetic resonance imaging has been described, but these studies generally are not used^40,55.

Non-Operative Treatment

Multidirectional instability usually can be treated non-operatively, and this approach is tried in all patients initially. Rehabilitation is designed to strengthen the deltoid, rotator cuff, and scapular stabilizers^16,85. Studies of patients who had generalized laxity and instability of the shoulder have demonstrated imbalances in muscle coordination⁶² and deficits in shoulder joint proprioception⁶⁷. The aim of treatment is to improve muscle tone and coordination and generally to increase the patient's functional adaptation.

Activities are modified to avoid movements that cause symptoms in the shoulder. A brief course of non-steroidal, anti-inflammatory medication may be helpful when chronic joint discomfort results from secondary inflammation. Occasionally, secondary bursitis or rotator-cuff tendinitis may develop, causing shoulder pain that prevents the patient from performing the indicated exercises. In this rare situation, a subacromial injection of a steroid preparation may provide sufficient relief for the patient to resume the exercise regimen.

Operative reconstruction is considered only if the patient does not respond to a lengthy program of conservative treatment (usually a minimum of six months). Most surgeons try to refrain from operating on a patient who is less than sixteen years old because glenohumeral instability may decrease as the normal laxity of adolescence diminishes with age and because non-operative treatment avoids injury to the important proximal humeral physeal plate.

It is important not to operate on a patient who is voluntarily dislocating the shoulder⁸⁹. Patients who have this syndrome may have underlying psychiatric problems and are able to use asymmetrical muscle pull to dislocate the shoulder, often maintaining the position despite attempted manipulations by perplexed physicians in front of distraught parents^35,119. However, overt psychiatric disturbance often is difficult to identify, and patients may have more subtle types of secondary gain or just may have a habitually improper pattern of muscle coordination that results in subluxation. Whatever the cause, individuals who voluntarily dislocate the shoulder with use of their own muscles (so-called muscular dislocators) are poor candidates for stabilization procedures. These patients should be managed with skillful neglect of the shoulder in conjunction with strengthening and retraining of the muscles as well as treatment of any underlying psychological disorder.

Not all patients who can demonstrate shoulder instability to the examiner are voluntary dislocators. Even if the instability is involuntary or began after substantial trauma, many patients learn which positions to avoid (for example, forward elevation and internal rotation in a patient prone to posterior subluxation). Such individuals, described as positional dislocators, may demonstrate dislocation for the examiner, if requested, but otherwise do their best to avoid it. These patients generally are good candidates for operative reconstruction.

Operative Technique

The most widely used reconstruction is the one described by Neer and Foster⁷⁶ or a modification of it. The procedure is designed to reduce capsular volume on all sides of the capsule by thickening and overlapping the anterior aspect of the capsule, if the procedure is carried out through an anterior approach, after completely detaching the inferior aspect of the capsule around the neck of the humerus to reduce the capsular pouch. The inferior portion of the capsule is then shifted anteriorly to increase the tension on the posterior aspect of the capsule so that it equals the tension on the anterior aspect. Neer termed the procedure the inferior capsular shift because of the novel feature of tensioning both the anterior and the posterior aspect of the capsule through one approach by shifting the inferior aspect of the capsule. The procedure occasionally has been misinterpreted as an operation performed primarily or exclusively on the inferior aspect of the capsule. When done through a posterior approach, the procedure on the anterior and posterior aspects of the capsule is reversed.

Examination with the patient under anesthesia can be very helpful with regard to confirming the components of instability. The shoulder is tested for anterior, inferior, and posterior translations in a variety of positions to bring different portions of the capsule and ligament system into play. Although it is rare to change the approach that was determined by preoperative clinical assessment, a surprising finding should not be ignored. Examination with the patient under anesthesia is most helpful when preoperative pain and spasm have precluded a revealing examination in the office.

The goal of treatment is to balance the capsular tension on all sides, and usually this can be accomplished through one operative approach—anterior or posterior. Although Cooper and Brems²² reported that they always performed an anterior approach, many surgeons use an approach on the side of the greatest instability as it is the side that will be best reinforced and strengthened by the overlap of flaps and the scar from the operative approach^5,8,75. Shoulders that dislocate both anteriorly and posteriorly usually are approached from the anterior side.

Anterior Approach for Inferior Capsular Shift

The details of the operative technique have been previously described^5,76,119. The patient is anesthetized with either regional (scalene block) or general anesthesia, and a concealed axillary skin incision leading to a deltopectoral approach is used. Subscapularis-splitting approaches have been helpful for discrete anterior capsular repairs of unidirectional anterior subluxation⁶⁰. However, anatomical detachment and repair of the subscapularis is preferred as part of the approach for capsular shift repairs of multidirectional instability for two major reasons. First, these repairs necessitate the detachment of the capsule around the inferior part of the humeral neck, which generally requires external rotation of the humerus. However, external rotation of the humerus tends to tension the subscapularis and to close any attempted subscapularis-splitting approach. Second, a large portion of the capsule must be freed from adhesions and attachments to surrounding tendons in order to be shifted and therefore must be freed from the overlying subscapularis tendon in particular.

Neer and Foster⁷⁶ referred to the gap between the supraspinatus and subscapularis as the rotator interval and termed the deeper layer at the same location the cleft between the superior and middle glenohumeral ligaments. They believed that this cleft was generally enlarged in patients who had multidirectional instability. Neer and Foster described closing the cleft and drawing the superior flap tight to cause the middle glenohumeral ligament (and the attached superior glenohumeral ligament) to "act as a sling against inferior subluxation."⁷⁶ Recent biomechanical studies have confirmed this view by showing the anterosuperior (rotator-interval) aspect of the capsule to be important for inferior stability of the adducted arm¹⁰⁹. Indeed, some surgeons have found that, in certain patients, the major lesion is in this region and isolated closure of rotator-interval defects may be all that is needed operatively³². However, in shoulders with multidirectional instability, closure of the rotator interval is just one part of a global capsular tensioning.

Standard anterior capsulorrhaphies may be done in a variety of fashions. When a capacious capsule in a shoulder with multidirectional instability needs reconstruction, many investigators have preferred the lateral T-capsulorrhaphy described by Neer and Foster⁷⁶. The capsule can be shifted most effectively to reduce capsular volume where the capsular circumference is largest, which is in the lateral aspect. Nevertheless, medial T-capsulorrhaphies or even H-capsulorrhaphies (reconstruction in which the vertical limbs of the incision are made both medially and laterally) have been used¹.

Stay sutures are placed in the free edge of the capsule as it is detached (Figs. 7-A, 7-B, and 7-C). As the humerus is externally rotated and flexed, the capsule is incised around the neck of the humerus. A finger may be placed in the inferior pouch to assess how large it is and how much redundant capsule needs to be released from the humerus before repair. The inferior portion of the capsule has been shown to be important for inferior stability of the abducted arm¹⁰⁹. In an anterior approach to a shoulder with classic multidirectional instability, the capsule is detached all the way down to its posterior aspect, which then can be tensioned as the detached inferior aspect of the capsule is shifted anteriorly.

If there is detachment of the glenohumeral ligament complex (a Broca-Perthes-Bankart lesion), it is repaired through an inside-out approach in conjunction with the capsular procedure. Ligament detachments occur in shoulders with multidirectional instability, although less frequently. As patients who have multidirectional instability frequently have symptoms in the mid-range, where the ligaments often are lax, it has been suggested that containment of the humeral head by the glenoid and labrum may also be impaired⁴⁴. Bigliani⁶ has used a so-called barrel stitch (a superior-inferior imbricating stitch just lateral to the labrum) during open reconstruction, and others^44,118 have used arthroscopic pleating of the capsule adjacent to the labrum (sewing a fold of capsule side-to-side to the labrum) to remove capsular stretch medially and to build up the height of the glenoid rim, deepening the socket to help to contain the head.

The capsular flaps are overlapped and repaired with the arm in a balanced position of slight external rotation and slight flexion. Warner et al.¹¹⁰ suggested that it might be desirable to repair the superior flap with the arm adducted and the inferior flap with the arm abducted, as these are the positions that tension those areas, according to basic-science studies.

Arthroscopic capsular tensioning²⁷ and arthroscopic laser contraction of the capsule⁹⁹ have both been described for the treatment of multidirectional instability. However, because stiffness is a less frequent problem than recurrent instability after repairs for multidirectional instability and because most surgeons place the upper extremity in a brace or cast for six weeks after the operation in an attempt to achieve stability, the value of a minimally invasive operation is less obvious.

The upper extremity is immobilized in neutral rotation (to allow symmetrical healing of the anterior and posterior aspects of the capsule) for six weeks, and only gentle isometric exercises and supervised motion of the elbow are permitted during that time. At six weeks, use of the brace is discontinued and range-of-motion exercises are gradually introduced. At twelve weeks, progressive strengthening is instituted on an individualized basis. When repetitive microtrauma is the dominant etiology and excessive generalized laxity is not present, the rehabilitation program may be accelerated. However, when there are multiple loose joints, the major mode of failure usually is recurrent instability from stretching of the repair rather than stiffness; in this situation, the aim of rehabilitation should be to regain shoulder motion slowly over a period of six months or more.

When a capsular shift approach is used for intermediate degrees of instability (for example, so-called bidirectional [anterior and inferior] instability), without a substantial posterior component, the upper extremity is protected in a sling for six weeks. However, after ten days, the upper extremity is removed from the sling and exercises, including isometrics and external rotation to 10 degrees as well as forward elevation to 90 degrees, are begun. At two to four weeks, external rotation is increased to 30 degrees, forward elevation is increased to 140 degrees, and isometric strengthening is added. At four to six weeks, external rotation is increased to 40 degrees, forward elevation is increased to approximately 160 degrees, and resistive exercises are begun. After six weeks, external rotation is increased to 50 degrees and forward elevation, to 180 degrees. After three months, external rotation may be progressed. Strengthening begins with the arm in neutral below 90 degrees. Careful and frequent postoperative follow-up is necessary, as patients who are not progressing quickly enough may need an accelerated program and those who are regaining motion too quickly may need to be slowed down. Return to contact sports generally is restricted until nine to twelve months have elapsed.

Posterior Approach for Inferior Capsular Shift

A variety of skin incisions have been used for a posterior approach. Although oblique or vertical incisions generally leave less prominent scars than transverse incisions, an anterior axillary scar is best from a cosmetic standpoint. For isolated posterior instability, a deltoid split and an infraspinatus-splitting approach to the capsule may allow adequate exposure⁵⁹. An approach under the deltoid also has been used⁹⁶. However, for an extensive capsular mobilization, many surgeons prefer to detach a small portion of the origin of the posterior part of the deltoid and to detach the infraspinatus⁵.

Capsular mobilization and repair is performed in a manner that is similar to that used for the anterior approach. Again, several methods have been described^5,73,75, with the classic procedure being a laterally based T-capsulorrhaphy.

After the operation, all patients wear a brace with the shoulder in neutral or slight extension and in slight external rotation for six weeks. Thereafter, the pace of mobilization is determined by the degree of generalized laxity, the pace of healing, and other factors as have been described for repairs from an anterior approach.

Results of Operative Treatment

Treatment of multidirectional instability with a capsular shift reconstruction has been successful in several studies^{7,22,65,71,73,117}. Altchek et al.¹ reported good results with use of a T-plasty modification of the Bankart procedure for repair of multidirectional instability. Hawkins et al.⁵⁰ reported less favorable results in a series of thirty-one patients who were followed for two to five years postoperatively; twelve (39 per cent) had an unsatisfactory result.

In a study by Cooper and Brems²², thirty-nine (91 per cent) of forty-three shoulders that had been followed for at least two years after an inferior capsular shift were rated by the patient as satisfactory with no recurrent instability. Bigliani et al.⁸ reviewed a series of fifty-two shoulders with classic multidirectional instability that had been treated with an inferior capsular shift. An anterior approach was used in thirty-six shoulders and a posterior approach, in sixteen. All were completely immobilized in a brace for six weeks postoperatively. Forty-six (94 per cent) of the forty-nine shoulders that had been followed for an average of five years (range, two to eleven years) had a satisfactory result.

Major Loss of Humeral or Glenoid Bone

Although glenoid wear or fracture and humeral impression fractures are common in unstable shoulders, only rarely are they large enough to warrant specific treatment. When they are, the reconstruction is made considerably more complex.

Humeral Impression Fractures

Chronic locked anterior and posterior dislocations, especially in older patients who have soft bone, often result in large humeral impression fractures. However, the chronic dislocations are not the same as recurrent dislocations or subluxations, and their treatment has been discussed elsewhere^36,47,51.

Recurrent posterior instability rarely involves large humeral impression fractures, and little information is available on such cases.

When reconstruction for recurrent anterior dislocation is being done in a shoulder with an unusually large Hill-Sachs lesion, several options may be considered. A slightly tighter anterior repair may prevent the extreme of rotation that would allow the edge of the defect to engage the glenoid rim⁷⁵. However, given the risk of late arthrosis after an overly tight anterior repair^9,11,48, this option is rarely advocated. A derotational humeral osteotomy¹¹⁶ may shift the functional range of the arm so that it is rarely externally rotated enough to approximate the defect to the glenoid rim, but this procedure generally is not used in North America. Filling the defect with the infraspinatus tendon also has been described but has been infrequently performed²¹.

Prosthetic replacement is always an option if more than 40 per cent of the humeral head is involved. However, the procedure is used more readily in elderly patients who have a locked unreduced dislocation than in young patients who have recurrent instability (Figs. 8-A and 8-B).

Bone-grafting of the defect may appear to be the most logical and direct approach. Neer⁷⁵ described use of local autogenous bone graft from the surgical neck of the humerus to fill in an unusually large humeral head defect. Gerber⁴² used an allograft consisting of a segment of a humeral head, with some early success (Figs. 9-A, 9-B, 9-C and 9-D). As far as we know, no long-term studies of the procedures are available to help the surgeon to select among these options.

Loss of Glenoid Bone

The glenoid rim may be flattened either by a fracture or by wear from repeated dislocations. Despite frequent discussion of this problem in the literature and at courses, very little information is available regarding how large a defect must be before it needs specific treatment. Steinman et al.⁹⁷ believed that if the defect involved at least 25 per cent of the surface area of the glenoid, then some type of bone reconstruction was necessary.

Defects involving less than 20 per cent of the surface area of the glenoid may be rendered extra-articular by repairing the detached labrum and capsule back to the edge of the remaining intact glenoid articular cartilage. If a chip of bone has been avulsed with the capsule and ligaments attached, then it is repaired with sutures as is done in a standard repair. If the fragment is large enough and can be mobilized, a screw may be used, with the surgeon taking care that the screw head does not contact the humeral articular surface.

Defects involving at least 25 per cent of the glenoid surface usually are reconstructed. If a large single fragment is still present, then it is freshened and repaired¹². If no fragment is available, then the coracoid tip with attached muscle is transferred into the defect behind the repaired capsule in an extra-articular fashion (Figs. 10-A, 10-B, 10-C, 10-D, 10-E, 10-F, 10-G, 10-H, 10-I and 10-J). A screw and washer generally are used. The aim of the procedure is to deepen the socket and to support the capsule, not to act as a bone block.

Overview

Most patients who have glenohumeral instability can be managed successfully without an operation. When operative treatment is necessary, most patients who have post-traumatic unidirectional anterior instability do well after any of several anatomical capsular reconstructions and repair of an associated Bankart avulsion, if one is present. When a patient has severe capsular redundancy or marked loss of glenoid or humeral bone, a more complex reconstruction is needed. An understanding of the biomechanics of the shoulder, careful and appropriate operative technique, and individualized postoperative rehabilitation usually lead to a gratifying result, even in these challenging and complex situations.

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Topics

biomechanics ; humerus ; ligaments ; reconstructive surgical procedures ; rotator cuff ; arm ; shoulder region ; impression fracture ; humerus head

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EVAN L. FLATOW, JON J. P. WARNER; Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Instability of the Shoulder: Complex Problems and Failed Repairs. Part I. Relevant Biomechanics, Multidirectional Instability, and Severe Loss of Glenoid and Humeral Bone*†. The Journal of Bone & Joint Surgery. 1998 Jan;80(1):122-40.

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