principles for the evaluation and management of shoulder

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Principles for the Evaluation and Management of Shoulder Instability

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TH E JO U R NA L OF BONE & JOINT SURGER Y · JBJS .ORG

VO LU M E 88-A · NU M B ER 3 · MA RCH 2006PR I NCI PLE S FOR THE EV A LU A T ION AND MANAGEM ENT OF SH O U L DER INSTABILIT Y

Principles for the Evaluation and Management

of Shoulder InstabilityBY FREDERICK A. MATSEN III, MD, CAROLINE CHEBLI, MD, AND STEVEN LIPPITT, MD

An Instructional Course Lecture, American Academy of Orthopaedic Surgeons

During use of the normal shoulder, the humeral head is centered within the glenoid and the coracoacromial arch. When the shoulder cannot main-tain this centered position during use, it is unstable. An unstable shoulder pre-vents normal function of the upper ex-tremity. Shoulder instability is not the same as joint laxity. Joint laxity is a property of normal joints and allows the shoulder to attain its full range of functional positions.

The concavity of the glenoid and the coracoacromial arch along with the passive and active forces that press the humeral head into the glenoid and the coracoacromial arch maintain the head in its centered position. This concavity-compression mechanism is dependent on the integrity of the glenoid and the coracoacromial arch, muscular com-pression, and restraining ligaments of the shoulder. Loss of any of these elements due to developmental, de-generative, traumatic, or iatrogenic factors may compromise the ability of the shoulder to center the humeral head in the glenoid.

The questions to answer during an evaluation of a patient with sus-pected instability are: (1) Is the problem in the glenohumeral joint? (2) Is the problem one of failure to maintain the humeral head in its centered position? (3) What mechanical factors are con-

tributing to this instability? (4) Are the identified mechanical factors amenable to surgical repair or reconstruction? This evaluation is based primarily on a carefully elicited history, a physical examination of the stability mechanics, and plain radiographs. If more com-plex imaging methods are needed to discover subtle or “occult” instability, the condition is often not responsive to surgical correction.

For surgical treatment of gleno-humeral instability to be appropriate, the instability must be attributable to mechanical factors that can be modified by surgery. The causes may be deficien-cies of the glenoid concavity, deficien-cies in the muscles that compress the head into the socket, and/or deficiencies in the capsule and ligaments.

Instability is one of the most commonly diagnosed and treated con-ditions of the shoulder. Diverse and ad-mittedly confusing approaches to this problem have been proposed, making it difficult to understand how best to eval-uate and manage affected patients. This lecture offers a practical foundation to aid in the understanding of clinical shoulder stability and instability1,2.

Glenohumeral stability requires that the humeral head remain centered in the glenoid fossa. When the humeral head does not remain centered, the pa-tient has glenohumeral instability.

The glenohumeral joint is a bal-ance between mobility and stability3. Its mobility is limited by the joint capsule, which prevents the humeral head from rotating into excessive positions. The joint capsule and associated ligaments act as checkreins to rotation and func-tion only at the extremes of motion, when they come under tension. While they also limit translation of the hu-meral head on the glenoid, restraint of translation alone cannot keep the head centered (just as a dog’s leash cannot keep the dog in the center of the yard unless it severely limits the dog’s mo-tion). During the midrange of motion, the capsule and ligaments are lax and, therefore, allow the humeral head to be passively translated during physical as-sessments such as the sulcus and drawer tests. In spite of the capsuloligamen-tous laxity, which is required for normal shoulder mobility, the humeral head remains precisely centered in the glen-oid fossa during active motion of the normal shoulder4. This centering is nec-essary in order for the hand to be pre-cisely and securely positioned in space. If the relative position of the humeral head and glenoid fossa were not secure and precise, the hand could not write, paint, throw, lift, hit, or operate with accuracy. The fact that the humeral head remains precisely centered, even in the shoulders of a gymnast with ex-



649



treme joint laxity who is performing a vault or holding the iron-cross position, demonstrates the remarkable ability of the shoulder to be stabilized by concavity-compression5.

Stability of the glenohumeral joint is critical for precise and strong function of the upper extremity. In the past, the mechanisms providing stabil-ity have been categorized as “static” and “dynamic” or as “active” and “passive.” We now recognize that the entire system functions as an integrated whole. For example, in the past it was stated that the anteroinferior glenohumeral liga-ment is the primary static stabilizer of the shoulder. This is patently not the case because when we sleep or rest in a chair the inferior glenohumeral liga-ment is not under tension (and thus is not functional) and, although the mus-cles around the shoulder are relaxed, the glenohumeral joint is not unstable. Similarly, the rotator cuff muscles have been called “dynamic stabilizers” of the shoulder, but, even in an anesthetized shoulder, the passive tension in these muscles provides sufficient compres-sion to stabilize the ball in the socket (as observed in the operating room when the shoulder muscles are paralyzed).

The glenohumeral stabilizing sys-tem has a number of key elements. The concavity of the glenoid, the muscles

that compress the humeral head into the glenoid, the coracoacromial arch, the capsuloligamentous restraints, and adhesion-cohesion of the articular sur-faces all contribute to stability. Defi-ciencies or defects in any of these structures can lead to instability.

Glenoid ConcavityA ball sitting on a flat table has no ten-dency to center itself. Even a slight dis-placing force causes it to slide or roll. If the table has a concavity, the ball will sit at the base of the concavity. The deeper the concavity, the more force it takes to move the ball out of it. The stability is increased if a greater force presses the ball into the concavity (Fig. 1). This

mechanism is known as concavity-compression6.

The glenoid concavity has three components: the osseous glenoid, which is slightly concave; the articular cartilage, which is thicker at the periph-ery and thinner in the center and thus makes the concavity deeper; and the glenoid labrum, which further deepens the glenoid concavity7 (Fig. 2). Because of its increased compliance, the glenoid labrum optimizes the surface area of glenohumeral contact and creates a conforming seal with the head of the humerus. This flexible periphery en-ables small deviations from fixed ball-and-socket kinematics without com-promising the intrinsic stability of the articulation. The glenoid center line is perpendicular to the glenoid articular surface and points slightly posterior to the plane of the scapula (Figs. 3-A and 3-B).

The adequacy of the glenoid concavity in different directions can be assessed with use of three related measures. We use the term glenoido-gram to describe the path taken by the center of the humeral head as it is translated over the surface of the glen-oid in a given direction. It normally has a gull-wing shape with a medially pointing apex at the glenoid center line (Figs. 4-A and 4-B). This shape results from the fact that when the humeral head moves away from the center of the glenoid concavity its center dis-places laterally. A glenoid lacking a lip has a flattened glenoidogram: when the head moves toward the flattened part of the glenoid lip, it does not

Fig. 2

Fig. 1

Concavity-compression. The deeper the concavity, the greater the displacing force that can be re-

sisted for a given compressive load. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt

SB. Principles of glenohumeral stability. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder

surgery: principles and procedures. Philadelphia: Saunders; 2004. p 83.)

The glenoid concavity. The socket is deepened by the thicker cartilage on its periphery and by the

glenoid labrum. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of

glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles and

procedures. Philadelphia: Saunders; 2004. p 88.)



650



move laterally. The lateral movement of the humeral head as it is translated across the face of the glenoid can be noted on physical examination of the normal shoulder.

The stability ratio is the force

necessary to displace the head from the glenoid divided by the load com-pressing the head into the concavity (Fig. 5). The stability ratio is greatest when the head is at the center of the glenoid fossa because that is where the

concavity is deepest. The stability ra-tio is lower when the humeral head is not centered in the glenoid. The stabil-ity ratio is calculated from the slope of the glenoidogram. The so-called load-and-shift test is a clinical analogue of the stability ratio. The load-and-shift test is performed by pressing the hu-meral head into the glenoid fossa and, while the compression is maintained, noting the resistance to translation of the head toward the lip in different directions.

The balance stability angle is the maximal angle between the glenoid center line and the net humeral joint-reaction force before the humeral head dislocates from the glenoid (Fig. 6). Experimentally, the contribution of the glenoid shape to glenohumeral sta-bility can be measured by orienting the glenoid with the center line pointing vertically upward and then tipping it until an unconstrained ball rolls out. In this case, the net force on the ball is the vertically oriented force of gravity, so the angle of tip at the moment of dislocation is the balance stability an-gle. The so-called jerk test, in which the humeral head slips out the back of

Fig. 3-B

The glenoid center line is close to perpendicular to the medial border of the scapula (left) and points slightly posterior to the plane of the scapula

(right). (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE.

Shoulder surgery: principles and procedures. Philadelphia: Saunders; 2004. p 89.)

Fig. 3-A

The glenoid center line is perpendicular to the center of the glenoid concavity. (Reproduced, with

permission, from: Matsen FA 3rd, Lippitt SB. Principles of glenoid concavity. In: Matsen FA 3rd,

Lippitt SB, DeBartolo SE. Shoulder surgery: principles and procedures. Philadelphia: Saunders;

2004. p 89.)



651



the glenoid with cross-body adduc-tion, is a clinical analogue of the labo-ratory measurement of the balance stability angle.

Scapular Factors in InstabilityThe GlenoidThe glenoid faces slightly posteriorly. A line perpendicular to the glenoid concavity is the glenoid center line. This line normally is approximately 10° from the plane of the scapula (Figs. 3-A and 3-B). Anterior deviation of this line lat-erally is referred to as anteversion; pos-terior deviation of this line laterally is retroversion. When maximal shoulder stability is needed—for example, when performing a bench press—the scapula and glenoid rotate forward to ensure that all forces remain aligned with the glenoid center line.

A scapula that is malaligned be-cause of poor shoulder kinematics may increase the angle between the glenoid

center line and the net humeral joint-reaction force to a point where the centering of the humeral head is com-promised. Clinically, problems of scap-ular misalignment are suggested when the scapulothoracic muscles fail to posi-tion the glenoid to best align it with the net humeral joint-reaction forces.

An anteverted or retroverted glenoid is less effective in centering the humeral head in the glenoid because the glenoid center line is no longer aligned with the forces generated by the scapulohumeral muscles. Glenoid version can be estimated clinically from standardized axillary radiographs or from computed tomography scans.

A flattened glenoid may not pro-vide sufficient concavity for effective concavity-compression. The glenoid may be flattened in a given direction because it is dysplastic, because the glenoid labrum and peripheral carti-lage are excessively small or compliant,

because the glenoid labrum and pe-ripheral cartilage are worn, because the labrum is avulsed from the glenoid lip, or because the glenoid lip is frac-tured8. A flattened glenoid is suggested when the humeral head translates without a feeling of going over a lip, when there is diminished resistance to the load-and-shift test, or when there is a positive jerk test.

The MusclesThe humeral head is compressed into the glenoid by the muscles of the rota-tor cuff and other scapulohumeral and thoracohumeral muscles. The line of action of each of these muscles is not, as is often described, one of “depression” of the humeral head away from the ac-romion; rather, it is one of compression of the humeral head into the glenoid concavity (Fig. 5).

The subscapularis muscle is the primary anterior compressor. Its effec-

Fig. 4-A

Figs. 4-A and 4-B The glenoidogram. Fig. 4-A The glenoidogram is the path taken by the center of the humeral head as it

translates across the face of the glenoid. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of

glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles and procedures. Philadelphia:

Saunders; 2004. p 100.) Fig. 4-B Translation anteriorly and posteriorly across a normally concave glenoid traces a gull-wing-

shaped path. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of glenoid concavity. In: Matsen FA

3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles and procedures. Philadelphia: Saunders; 2004. p 101.)

Fig. 4-B



652



tive strength is assessed by positioning the arm in maximal internal rotation (with the elbow flexed to a right angle and the hand behind the back) to mini-mize the contribution of other internal rotators, such as the pectoralis major, the latissimus dorsi, and the teres ma-jor, and then noting the amount of iso-metric internal rotation torque that can be generated. This is known as the lum-bar push-off test.

The supraspinatus muscle is the primary superior compressor. Its effec-tive strength is assessed by positioning the arm in 90° of elevation in the plane of the scapula and in internal rotation (so that the supraspinatus lies over the top of the humeral head) and then not-ing the amount of isometric elevation torque that can be generated. This is known as the supraspinatus test.

The infraspinatus is the primary posterior compressor (assisted to a de-gree by the teres minor). Its effective strength is assessed by positioning the arm in neutral rotation and slight eleva-tion in the plane of the scapula with the elbow bent to a right angle and then noting the amount of isometric external rotation torque that can be generated. This is known as the infraspinatus test.

The important characteristic of the muscles of the rotator cuff is that they can function as head compressors in almost any position of the gleno-humeral joint. Other muscles, such as the deltoid, long head of the biceps, pectoralis, latissimus, teres major, and pectoralis major, can contribute to hu-meroglenoid compression in certain glenohumeral positions. For example, when the arm is elevated 90° in the plane of the scapula, the deltoid be-comes a strong compressor of the head into the glenoid.

The effectiveness of concavity-compression can be dramatically dem-onstrated by first performing an ante-rior-posterior drawer test on the relaxed shoulder and noting the ability of the head to translate on the glenoid. The same drawer test is then repeated while the arm is held in abduction by the pa-tient, increasing the net humeral joint force vector pressing the humeral head into the glenoid fossa in the normal

shoulder. Even with the minimal com-pressive force generated by gentle active abduction, the humeral head can no longer be translated by the examiner.

Paralysis, detachment, or dysfunc-tion of the subscapularis, supraspinatus, and/or infraspinatus result in loss of hu-meral head compression. Instability in the direction of the affected tendon may result. As an example, supraspinatus de-ficiency is commonly associated with su-perior displacement of the humeral head relative to the glenoid.

The Coracoacromial ArchAs Codman recognized in the 1920s, the glenohumeral joint is not the only im-portant articulation between the hu-merus and the scapula9. Of comparable importance is the articulation between the coracoacromial arch and the proxi-mal humeral convexity (the spherical contour provided by the external surface

of the tuberosities and the rotator cuff).The principle of concavity-com-

pression applies to the ball-and-socket joint between the proximal humeral convexity and the coracohumeral arch. The primary compressor of this arti-culation is the deltoid. Compression into the arch also results when the arm presses down, such as when the arms are used to rise from an armchair, dur-ing walking with a cane or crutches, and when an athlete performs bar dips, ac-tivities in which stability of the shoulder is essential. The marvel of the design of the shoulder is that the centers of rota-tion for the humeral head, the proxi-mal humeral convexity, the glenoid fossa, and the coracoacromial arch are all superimposed in the normal stable shoulder (Fig. 7).

The critically important sta-bilizing effect of the articulation be-tween the coracoacromial arch and

Fig. 5

The stability ratio is the force necessary to displace the humeral head from the glenoid center di-

vided by the load compressing the humeral head into the glenoid. (Reproduced, with permission,

from: Matsen FA 3rd, Lippitt SB. Principles of glenoid concavity. In: Matsen FA 3rd, Lippitt SB, De-

Bartolo SE. Shoulder surgery: principles and procedures. Philadelphia: Saunders; 2004. p 105.)



653



the proximal humeral convexity is demonstrated by the devastating an-terosuperior instability that results when an acromioplasty is performed in the presence of rotator cuff defi-ciency. Even when the rotator cuff is intact, disruption of the coracoac-romial arch may compromise the ability of the joint to remain centered in the presence of a superiorly direc-ted force.

The Glenohumeral Ligaments and CapsuleIn mid-range positions, the gleno-humeral capsule and its associated ligaments are lax and do not exert a centering effect. At the extremes of motion, however, these structures be-come important contributors to hu-meral centering10. First, they prevent humeral rotation beyond the point where the muscles are effective. As is the case for muscles in general, the ro-tator cuff muscles are able to generate

the most force when they are in mid-excursion. They become less effective when they are maximally extended. It is the job of the capsule and liga-ments to prevent the rotator cuff muscles from becoming overstretched. Second, the ligaments come under progressively greater tension at the ex-tremes of motion. This tension creates a compressive force that is essentially collinear with the force that would otherwise be exerted by the muscle overlying it. This force takes over in positions where the muscle force drops off (Fig. 8).

Third, the ligaments substitute for muscle forces in positions where no muscle is present. For example, the co-racohumeral ligament and rotator in-terval capsule that lie between the supraspinatus and the subscapularis tendons provide a compressive force when the arm is in adduction11. An-other example is the inferior gleno-humeral ligament complex that lies

in the tendon-free zone beneath the glenohumeral joint and provides a compressive force when the arm is abducted. These capsuloligamentous

Fig. 6

The balance stability angle is the maximal angle that the net force on the humeral head forms

with the glenoid center line before dislocation occurs. The net humeral joint-reaction force is the

vector sum of the displacing force and the compressive load. The tangent of the balance stability

angle is the stability ratio. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Princi-

ples of glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: princi-

ples and procedures. Philadelphia: Saunders; 2004. p 108.)

Fig. 7

a, b, and c: Centers of rotation. b: In the stable

and normally aligned shoulder, the centers of

rotation of the humeral articular surface and

the glenoid concavity and the proximal hu-

meral convexity and the coracoacromial arch

are all superimposed. c: The difference in the

radius of the humeral head (r) and that of the

proximal humeral convexity (R) is made up by

the rotator cuff and the tuberosities. (Repro-

duced, with permission, from: Matsen FA 3rd,

Lippitt SB. Principles of glenohumeral stability.

In: Matsen FA 3rd, Lippitt SB, DeBartolo SE.

Shoulder surgery: principles and procedures.

Philadelphia: Saunders; 2004. p 82.)



654



effects are energy-efficient. For exam-ple, the compressive effect of the ten-sion in the coracohumeral ligament and the rotator interval capsule centers the humeral head when the arm is at rest by the side without consuming muscular energy. Similarly, the com-

pressive effect of the inferior gleno-humeral ligament helps to center the humeral head when the arm is in the cocking and early acceleration phases of the throw without consuming addi-tional energy.

When the capsuloligamentous

restraints are deficient, the joint can over-rotate into positions in which the muscles are less able to provide adequate compression. As a result, patients with a substantial avulsion of the capsule from the glenoid often de-scribe weakness of the arm when it is abducted and externally rotated. Simi-larly, patients with a deficiency of the inferior glenohumeral ligament have difficulty throwing because muscular contraction cannot substitute for the compressive forces provided by the in-tact ligament.

Adhesion-Cohesion and the Suction CupThere are two other centering mecha-nisms that do not require energy. One is adhesion-cohesion, a process in which the wettable surfaces of the humeral and glenoid cartilage and the wettable surfaces of the coracoacromial arch and the proximal humeral convexity adhere to each other because of the adhesive and cohesive properties of water mole-cules. These properties enable the two sets of surfaces to glide easily on each other while simultaneously preventing them from separating. The power of ad-hesion-cohesion can be demonstrated by placing a drop of water between two microscope slides and noting the ease

Fig. 9

Mechanics of the Bankart lesion. When a 33-lb (147-N) load is applied to the hand of the outstretched arm,

the resulting torque can produce a tension in the inferior glenohumeral ligament (IGHL) of 1000 lb (4448 N).

This is due to the difference between the external load lever arm (30 in [76 cm]) and the inferior glenohumeral

ligament lever arm (1 in [2.5 cm]). (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles

of glenohumeral ligaments and capsule. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: princi-

ples and procedures. Philadelphia: Saunders; 2004. p 122.)

Fig. 8

Hypothetical graph showing the interplay between muscular and capsular tension. As the humerus

is passively externally rotated, the force that the subscapularis can generate drops off while the

force generated by the anterior capsular ligaments increases in a complementary manner.



655



with which they slide and the difficulty of distracting them. The second mecha-nism is the glenohumeral suction cup12. The center of a suction cup is noncom-pliant while the periphery is flexible. This is exactly the structure of the glen-oid surface: thin cartilage overlies bone in the center, and compliant capsule, labrum, and thicker cartilage are at the periphery (Fig. 2). As a result, the glen-oid can stick to the humeral head, like a child’s suction-cup arrow can stick to a glass window. The suction-cup mechanism is enhanced by the slightly negative intra-articular pressure within the joint.

Neither the adhesion-cohesion nor the suction-cup mechanism con-sumes energy, and both provide so-called low-cost centering when the arm is at rest. These mechanisms also have the convenient property of working in any position of the shoulder.

When the conforming glenoid lip is lacking or when the joint surfaces are no longer covered with smooth wetta-ble hyaline cartilage, the shoulder will often feel “out of place.” For example, in a total shoulder replacement, the poly-ethylene glenoid component neither conforms to the humeral head, to allow a suction-cup effect, nor is wettable, to allow adhesion-cohesion. As a result, patients treated with total shoulder ar-throplasty may experience less secure centering of the humeral head on the glenoid than do those with a normal shoulder. The adhesion-cohesion and suction-cup mechanisms may also be disrupted when there is a joint effusion or hemarthrosis.

Evaluation of the Shoulder for InstabilityHistoryShoulder stability is the ability to keep the ball centered in the socket. The diagnosis of instability is based on a carefully elicited history and on direct observation of the shoulder’s centering capability13.

When one obtains the patient’s history, it is useful to start with an open-ended question such as “How does your arm bother you?” and then give the patient plenty of opportunity

to reply while one listens for descrip-tions suggestive of mechanical symp-toms, such as “slip,” “goes out,” or “gives way.” The history is more indi-cative of instability if these symptoms are episodic with interspersed periods of relatively normal function. It is help-ful to have the patient describe or show the arm positions in which these epi-sodes of instability occur. Instability in abduction, extension, and external rota-tion is usually anteroinferior, whereas instability in flexion, internal rotation, and adduction is usually posterior. The severity of the instability is indicated by the frequency of these episodes, the functional disruption that they cause, and whether the patient can recenter the humerus without help. A descrip-

tion of the initial episode can also indi-cate the likelihood of traumatic injury to the stabilizing structures. Here, a lit-tle understanding of basic mechanics is helpful (Fig. 9). When a 33-lb (147-N) force is applied to the hand of the ab-ducted, externally rotated upper ex-tremity, its lever arm to the center of the humeral head is about 30 in (76 cm). In opposition to this torque is the tension in the anterior-inferior glenohumeral ligament that works through a lever arm of 1 in (2.5 cm). The torque equi-librium equation indicates that essen-tially 1000 lb (4448 N) of tension in the inferior glenohumeral ligament would result from the 33-lb force exerted on the outstretched arm, clearly enough to avulse the capsulolabral complex

Fig. 10

Radiographic views of the glenohumeral joint. The anteroposterior view in the plane of the scap-

ula shows loss of the glenoid surface line inferiorly (arrow) (a), and the axillary view shows an an-

terior defect of the glenoid rim (arrow) (b). (Reproduced, with permission, from: Matsen FA 3rd,

Lippitt SB. Principles of glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder

surgery: principles and procedures. Philadelphia: Saunders; 2004. p 117.)



656



from the anterior-inferior aspect of the glenoid, producing a Bankart lesion. In contrast, a rear-end motor-vehicle colli-sion, even with a relative velocity of 30 mi/hr (48.2 km/hr), would not be ex-pected to produce a Bankart lesion in the driver whose hands were on the steering wheel. Similarly, a hard fall on the outstretched hand might apply enough force to avulse the posterior aspect of the labrum, whereas lifting a moderately sized box might not. The clinician needs to visualize what the suggested mechanism might produce at the tissue level.

If there is a substantial tissue injury, surgical intervention may be needed to achieve strong anatomic healing. If there is no reason to sus-pect a tissue injury, rehabilitation of the strength and coordination of the stabilizing musculature rather than surgery is likely to be the treatment of first choice.

While there are many other criti-cal elements of the history, three key questions need to be answered: (1) Is the humeral head really becoming un-centered during the symptomatic epi-sodes or is something else going on? (2) In which direction is the head moving when it leaves the glenoid center? (3) Is the instability the result of a substan-tial tear or detachment and, if so, what tissues are likely to be involved? It is often easier to sort out these questions by carefully obtaining a history than by any other means.

Physical ExaminationThe physical examination should try to answer these same three questions. An easy way to start is to have the patient demonstrate the position of the shoulder when the initial injury occurred and the mechanism of the initial injury as well as the subsequent episodes. It is most useful if the patient can say, “My shoul-

der goes out when I do this.” Close ob-servation prevents one from making a misdiagnosis of glenohumeral instabil-ity when, in fact, the problem is scapu-lothoracic snapping, for example. This “no touch” part of the examination is non-threatening for the patient and in-formative for the physician.

When the “no touch” examina-tion is inconclusive, the examiner can then look for apprehension and state-ments of recognition when the shoulder is placed in positions characteristic of common instability patterns. The exam-iner should start with the contralateral shoulder so that the patient will know what to expect during the examination of the involved shoulder. The anterior apprehension test is conducted by plac-ing the arm in abduction, extension, and external rotation. The posterior apprehension test is conducted by plac-ing the arm in adduction, midflexion, and internal rotation. Instability or a

Fig. 11-B

Avulsed labrum. (Reproduced, with permis-

sion, from: Matsen FA 3rd, Lippitt SB. Princi-

ples of glenoid concavity. In: Matsen FA 3rd,

Lippitt SB, DeBartolo SE. Shoulder surgery:

principles and procedures. Philadelphia:

Saunders; 2004. p 109-11.)

Fig. 11-A

Figs. 11-A through 11-D Deficiencies of the glenoid rim. Fig. 11-A Compressible labrum. (Repro-

duced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of glenoid concavity. In: Mat-

sen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles and procedures. Philadelphia:

Saunders; 2004. p 109-11.)



657



sensation of impending instability in one of these positions can help confirm whether the instability is anterior or posterior. Tests for instability are most conclusive when the patient volunteers, “That’s how my shoulder feels when it’s ready to go out.” Pain alone on these tests is insufficient evidence of instability.

A second important element of the physical examination for stability is to determine the status of the glenoid concavity, particularly in the direction of the instability. This is conveniently ac-complished by having the seated patient relax with the forearm resting on the thigh. First, the anterior and posterior translatability of the humeral head is de-termined as a measure of joint laxity. Next, the humeral head is pressed into the glenoid fossa while anterior and then posterior translation is attempted (the load-and-shift test). Easy translation of the head while it is being pressed into the glenoid center suggests that the lip of the glenoid concavity is deficient in that di-rection. Anterior deficiency of the glen-oid lip is most commonly the result of a Bankart lesion or a glenoid lip fracture.

Posterior lip deficiency may result from deficiency or detachment of the poste-rior aspect of the labrum or a posterior glenoid fracture. In traumatic instabil-ity, translation of the humeral head over the edge of the glenoid lip may be ac-companied by a grinding sensation as the head moves over the area from which the labrum has been avulsed or the os-seous lip has been fractured. If the pa-tient recognizes this sensation as what he or she feels when the shoulder goes out of place, the diagnosis is reinforced.

A third important element of the physical examination for stability is the assessment of the muscles that compress the humeral head into the glenoid. These evaluations include tests for the isomet-ric strength of the subscapularis, supra-spinatus, and infraspinatus.

Other elements of the physical examination may include tests of lax-ity, such as assessments for the drawer and sulcus signs. It must be recognized, however, that the ability of the examiner to demonstrate that the joint is translat-able (lax) does not mean that the shoul-

Fig. 11-D

Glenoid dysplasia. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles of

glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles and

procedures. Philadelphia: Saunders; 2004. p 109-11.)

Fig. 11-C

Fractured glenoid lip. (Reproduced, with permission, from: Matsen FA 3rd, Lippitt SB. Principles

of glenoid concavity. In: Matsen FA 3rd, Lippitt SB, DeBartolo SE. Shoulder surgery: principles

and procedures. Philadelphia: Saunders; 2004. p 109-11.)



658



der is unstable. It is important to recall that lax yet stable joints are essential for gymnasts.

Imaging of the ShoulderThe primary purpose of the radio-graphic examination is to determine, on standardized views, (1) whether the hu-meral head is seated well in the glenoid, (2) if there is a major glenoid osseous defect inferiorly or posteriorly, and (3) if there is a major humeral head defect posteriorly or anteriorly (Fig. 10).

It is tempting to perform a computed tomography scan for every patient with an unstable shoulder. However, often the relevant osseous anatomy can be assessed adequately on a plain anteroposterior radiograph in the plane of the scapula, which shows humeral head centering and the integrity of the anterior glenoid-lip line; an apical oblique radiograph, which shows defects in the posterolat-eral aspect of the humeral head and

anteroinferior aspect of the glenoid lip; and a true axillary radiograph, which shows humeral centering along with anterior humeral head defects and an-terior or posterior glenoid bone de-fects. If these studies do not show the bone anatomy adequately, a computed tomography scan is indicated.

Under certain circumstances, ad-ditional information may be desired re-garding the capsular and labral tissues, the bone, the rotator cuff, or the neuro-logical status of the muscles. In such cases, additional tests such as mag-netic resonance imaging, computed tomography, electromyography, or di-agnostic arthroscopy may be helpful. These additional examinations are not commonly needed because most of the information required for clinical deci-sion-making when glenohumeral insta-bility is suspected can be acquired by carefully obtaining a history, perform-ing a physical examination, and mak-ing plain radiographs.

Treatment of InstabilityDefining the ProblemBefore considering a surgical solution, the surgeon needs to be confident that (1) the problem is glenohumeral insta-bility (i.e., the humeral head is not re-maining centered in the glenoid) and (2) a mechanical problem that can be best treated by surgical intervention (rather than by rehabilitation or activity modification) has been clearly identi-fied. We recognize that anteroposterior drawer tests, sulcus signs, magnetic resonance images of labral and capsu-lar abnormalities, translatability on examination of the patient under anes-thesia, and “drive-through” signs on arthroscopy are not diagnostic of gleno-humeral instability or predictive of the success of surgical management. It is also apparent that recurrent instability associated with uncontrolled epilepsy, inferior subluxation of the humeral head in a patient who has had a stroke, multidirectional instability associated with generalized ligament laxity, and voluntary instability may not be best treated with shoulder surgery.

The primary decision regarding whether to perform the surgical pro-cedure in an open fashion or arthro-scopically depends on whether the treatment is directed at deepening the fossa, reorienting a maloriented fossa, repairing or tightening the ligaments, reattaching torn tendons, or restoring osseous defects. Until the anatomic/mechanical objective is determined, discussion of the surgical approach is secondary.

Treatment PrinciplesRather than describing the surgical techniques in detail, which we have done elsewhere14, we will conclude by outlining the principles that can be ap-plied to the treatment of specific me-chanical problems.

When the concavity is deficient, many of the stabilizing mechanisms are compromised (Figs. 11-A through 11-D). When the instability is secon-dary to glenoid deficiency, this defi-ciency must be addressed. Soft-tissue repairs or reconstructions may be suf-ficient when the soft-tissue elements

Fig. 12

Typical pathology of traumatic anterior

glenohumeral instability. Top: A trau-

matic dislocation. Bottom: Anatomic

defects persisting after reduction.

(Reproduced, with permission, from:

Matsen FA 3rd, Lippitt SB. Principles of

glenohumeral ligaments and capsule.

In: Matsen FA 3rd, Lippitt SB, DeBar-

tolo SE. Shoulder surgery: principles

and procedures. Philadelphia: Saun-

ders; 2004. p 121.)



659



of the concavity are compromised. However, it is difficult to compensate for a substantial osseous defect with a soft-tissue repair because soft tissue cannot withstand the compressive loads as well as bone can. When the osseous lip of the glenoid is flat but ample, it can be built up with use of a glenoid osteoplasty in which the bone beneath the lip is cut, lifted up, and held up with a wedge-shaped bone graft15. Major bone loss at the glenoid periphery can be addressed with a bone graft placed so that the graft reestab-lishes the extent of the glenoid fossa16. When the acromion and the coraco-acromial ligament have been sacri-ficed, allowing anterosuperior escape of the proximal part of the humerus, no anatomic reconstruction has proved satisfactory, and a reverse shoulder prosthesis needs to be considered.

When the cartilage of the glenoid lip is eroded, the resulting loss of depth of the glenoid can be restored by repair-ing the labrum and capsule up on the surface of the glenoid at its lip. A labrum that is intact but not as high and stabiliz-ing as desired can be augmented with capsulolabral plication and/or injection

augmentation. When the glenoid la-brum is avulsed from the osseous glen-oid lip, the fossa-deepening effect of the labrum can be restored by securely reat-taching it to the face of the glenoid (not the neck)17. When the capsule and the glenohumeral ligaments have been torn or avulsed from the glenoid, their integ-rity can be restored with a direct repair (Fig. 12). Reconstruction to address cap-sular or ligamentous deficiencies result-ing from previous surgery or from chronic or recurrent injury may require the use of a tendon graft from the hu-merus to the glenoid.

When the tendon of an otherwise intact subscapularis is deficient, a ham-string tendon graft may enable secure reattachment of the muscle to the bone. In selected circumstances, muscle trans-fers such as a pectoralis major transfer to the lesser tuberosity or other more complex procedures may be considered.

When instability is due to dener-vation or irreparable detachment of the muscles that normally compress the humeral head into the glenoid fossa, surgical treatment other than glenohumeral arthrodesis may not be effective.

Frederick A. Matsen III, MDCaroline Chebli, MDDepartment of Orthopaedics and Sports Med-icine, University of Washington Medical Cen-ter, 1959 N.E. Pacific Street, Box 356500, Seattle, WA 98195. E-mail address for F.A. Matsen III: [email protected]

Steven Lippitt, MDAkron General Medical Center, 224 West Ex-change Street, Suite 440, Akron, OH 44302

The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a com-mitment or agreement to provide such bene-fits from a commercial entity. A commercial entity paid or directed, or agreed to pay or di-rect, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the au-thors are affiliated or associated (DePuy en-dowed chair.)

Printed with permission of the American Academy of Orthopaedic Surgeons. This arti-cle, as well as other lectures presented at the Academy’s Annual Meeting, will be available in February 2007 in Instructional Course Lectures, Volume 56. The complete volume can be or-dered online at www.aaos.org, or by calling 800-626-6726 (8 A.M.-5 P.M., Central time).

References

1. Lippitt SB, Matsen FA 3rd. Mechanisms of glenohumeral joint stability. Clin Orthop Relat Res. 1993;291:20-8.

2. Matsen FA 3rd, Titelman RM, Lippitt SB, Rock-wood CA Jr, Wirth MA. Glenohumeral instability. In: Rockwood CA Jr, Matsen FA 3rd, Wirth MA, Lippitt SB, editors. The shoulder. Volume 2. 3rd ed. Phila-delphia: Saunders; 2004. p 655-794.

3. Matsen FA 3rd, Fu FH, Hawkins RJ, editors. The shoulder: a balance of mobility and stability. Rose-mont, IL: American Academy of Orthopaedic Sur-geons; 1993.

4. Schiffern SC, Rozencwaig R, Antoniou J, Richard-son ML, Matsen FA 3rd. Anteroposterior centering of the humeral head on the glenoid in vivo. Am J Sports Med. 2002;30:382-7.

5. Lippitt SB, Harris SL, Harryman DT 2nd, Sidles J, Matsen FA 3rd. In vivo quantification of the laxity of normal and unstable glenohumeral joints. J Shoul-der Elbow Surg. 1994;3:215-23.

6. Lippitt SB, Vanderhooft EP, Harris SL, Sidles JA, Harryman DT 2nd, Matsen FA 3rd. Glenohumeral stability from concavity-compression: a quantitative

analysis. J Shoulder Elbow Surg. 1993;2:27-35.

7. Fehringer EV, Schmidt GR, Boorman RS, Churchill S, Smith KL, Norman AG, Sidles JA, Matsen FA 3rd. The anteroinferior labrum helps center the humeral head on the glenoid. J Shoulder Elbow Surg. 2003;12:53-8.

8. Lazarus MD, Sidles JA, Harryman DT 2nd, Matsen FA 3rd. Effect of a chondral-labral defect on glenoid concavity and glenohumeral stability. A cadaveric model. J Bone Joint Surg Am. 1996;78:94-102.

9. Codman EA. The shoulder: rupture of the su-praspinatus tendon and other lesions in or about the subacromial bursa. Malabar, FL: Robert E Kreiger; 1984.

10. Harryman DT 2nd, Sidles JA, Clark JM, Mc-Quade KJ, Gibb TD, Matsen FA 3rd. Translation of the humeral head on the glenoid with passive glenohumeral motion. J Bone Joint Surg Am. 1990;72:1334-43.

11. Harryman DT 2nd, Sidles JA, Harris SL, Matsen FA 3rd. The role of the rotator interval capsule in passive motion and stability of the shoulder. J Bone Joint Surg Am. 1992;74:53-66.

12. Gibb TD, Sidles JA, Harryman DT 2nd, Mc-Quade KJ, Matsen FA 3rd. The effect of capsular venting on glenohumeral laxity. Clin Orthop Relat Res. 1991;268:120-7.

13. Matsen FA 3rd, Lippitt SB, Sidles JA, Harryman DT 2nd. Practical evaluation and management of the shoulder. Philadelphia: WB Saunders; 1994.

14. Matsen FA 3rd, Lippitt SB, De Bartolo SE, edi-tors. Shoulder surgery: principles and procedures. Philadelphia: WB Saunders; 2004.

15. Metcalf MH, Duckworth DG, Lee SB, Sidles JA, Smith KL, Harryman DT 2nd, Matsen FA 3rd. Poster-oinferior glenoplasty can change glenoid shape and increase the mechanical stability of the shoulder. J Shoulder Elbow Surg. 1999;8:205-13.

16. Churchill SR, Moskal M, Lippitt SB, Matsen FA 3rd. Extracapsular anatomically contoured anterior glenoid bone grafting for complex glenohumeral in-stability. Tech Shoulder Elbow Surg. 2001;2:210-8.

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