C L I N I C A L C O M M E N T A R Y

Nonoperative Management of Shoulder Impingement Syndrome

Secondary

Abdulazeem Kamkar, MS, PT' lames I. Irrgang, MS, PT, ATC2 Susan 1. Whitney, PhD, PT, A7C3

houlder pain and disability in throwing athletes are common orthopaedic prob- lems seen by physical ther- apists (29). Two common

etiologies of shoulder pain are shoul- der instability and impingement syn- drome. Neer (33) defined impinge- ment syndrome as "impingement of the rotator cuff beneath the coracoa- cromial arch." Conservative and sur- gical management of this syndrome are well described in the literature ( 1 6, 28, 33, 38). Nonoperative man- agement consists of rest, anti-inflam- matory medications, and therapeutic exercises emphasizing the function of the rotator cuff muscles. Recently, electromyographic studies have been performed to analyze the function of shoulder muscles in sport and exer- cise (3, 18, 19, 37, 43). Electromyo- graphic activity of the serratus ante- rior muscle during shoulder function in overhead sports has been docu- mented (19, 37, 43). Nuber et al (37) proposed that fatigue of the ser- ratus anterior muscle from repetitive use may cause impingement because of improper temporal sequencing of the scapulothoracic musculature. The purpose of this paper is to re- view the pertinent anatomy and bio- mechanics of the shoulder, review primary and secondary impingement syndromes, and describe nonopera- tive management of shoulder im- pingement syndromes.

Shoulder pain secondary to impingement of the rotator cuff tendons underneath the coracoa- cromial arch is a common problem seen in athletes who perform repetitive overhead activities. Shoulder impingement has been classified into primary and secondary types. Several factors contrib- ute to impingement, including rotator cuff weakness, posterior capsule tightness, and subacromial crowding. Recently, it has been proposed that scapulothoracic muscle weakness could be a factor that contributes to impingement. Traditional rehabilitation protocols for shoulder impingement syndrome stress individualized rota tor cuff strengthening. The authors propose that individualized scapulothoracic muscle strengthening should be a part of any protocol for nonoperative treatment of secondary shoulder impingement syndrome.

Key Words: scapulothoracic muscles, shoulder impingement syndrome, rehabilitation ' Resident, Orthopedic Manipulative Therapy, laurel Rehabilitation and Sponc Therapy, Uniontown, PA 15401; staff physical therapist, Industrial Rehabilitation, St. Francis Medical Center, 3rd Floor, Medical CMce Building, 4221 Penn Ave., Pittsburgh, PA 15224 ' Assistant professor, Department of Physical Therapy, University of Pittsburgh; director, Outpatient PT and Sports Medicine, University of Pittsburgh Medical Center, Center for Sports Medicine and Rehabilitation, Pittsburgh, PA 'Assistant professor, Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA This paper was submitted by A. Kamkar as partial fulfillment of the requirements of the master of science degree at the University of Pittsburgh.

REVIEW OF LITERATURE

Anatomy

CoracoacromMl Arch and Rotator

Cuff In reviewing the anatomy of the shoulder related to impingement syndrome, the coracoacromial arch and the subacromial elements are the focus of attention. The coracoa- cromial arch, as the name implies, is formed by the coracoid and acro- mion processes and the connecting coracoacromial ligament. Under- neath this arch are the subacromial- subdeltoid bursa, the rotator cuff tendons, the long head of the biceps, the glenohumeral joint capsule, and

the upper surface of the humeral head (Figures 1 and 2). The coracoa- cromial arch protects the humeral head and the subacromial structures from direct trauma. The coracoacro- mial arch also prevents superior d i s location of the humeral head. How- ever, in abnormal states, impinge- ment may occur as the rotator cuff and other subacromial structures be- come encroached between the greater tuberosity and the coracoa- cromial arch (28).

The rotator cuff tendons include the subscapularis tendon anteriorly, the supraspinatus tendon superiorly, and the infraspinatus and teres mi- nor tendons posteriorly. The four

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

Subacro bursa

Acrom ion

Coracoacromial l igament \ I Supras~ ina tus

\ Art icu lar

m i a l -

u l a r i s

cav i ty

FIGURE 1. The coracoacromial arch and underlying subacromial structures of the left shoulder. (Adapted from lobe (1 S), with permission).

FIGURE 2. Cross-sectional view of the coracoacro- mial arch. (Adapted from lobe (IS), with permission).

tendons blend with each other and with the capsule of the glenohumeral joint to attach to the lesser tuberos- ity, the greater tuberosity, and the transverse humeral ligament (Figures 1 and 2). T h e long head of the bi- ceps penetrates the rotator cuff be- tween the supraspinatus and the sub- scapularis tendons and courses over the humeral head. Passage of the ro- tator cuff tendons under the coraco- acromial arch is facilitated by the in- terposition of the subacromial-sub-

deltoid bursa, which acts as a lubricating medium (28, 40).

T h e supraspinatus and infraspi- natus muscles are innervated by the suprascapular nerve (C4, 5. 6). the teres minor is innervated by the axil- lary nerve (C4, 5. 6). and the sub- scapularis is innervated by the upper and lower subscapular nerves (C5, 6, 7) (49).

Muscles of the ScaPulothoracic Ar- ticulation T h e scapulothoracic ar- ticulation lacks the characteristics of a true joint and is regarded as an articulation (27). Lack of ligamen- tous restraints a t this "joint" dele- gates the function of stability fully to the muscles that attach the scapula to the thorax. Hence, the scapulothora- cic articulation is a prime example of dynamic stability in the human body. Several muscles control the motion a t the scapulothoracic articulation, and, therefore, their proper function is vital to the normal biomechanics of the shoulder. These muscles in-

clude the serratus anterior, trape- zius, levator scapulae, rhomboid ma- jor, rhomboid minor, latissimus dorsi, pectoralis major, and pectora- lis minor (40, 44). It has been sug- gested that the serratus anterior and trapezius muscles are the most im- portant muscles acting upon the sca- pulothoracic articulation (6, 16, 23).

T h e muscular digitations of the serratus anterior originate from the upper eight to 10 ribs and fascia over the intercostals. T h e first digit of the serratus anterior originates from the first and second ribs, plus the intercostal fascia. T h e other dig- its of the serratus anterior originate from a single rib. T h e lowest four digits of the serratus anterior inter- digitate with the upper five digits of the obliquus externus abdominis. This broad origin on the thoracic wall runs ventral to the scapula and inserts on the medial border of the scapula. T h e first digit of the serra- tus anterior attaches ventrally and dorsally to a triangular area on the superior scapular angle. T h e next two o r three digitations form a trian- gular sheet and attach to the ventral surface of the medial border of the scapula. T h e lower four o r five digits form a musculotendinous attachment that inserts on a triangular area on the inferior scapular angle. This at- tachment is mostly ventral to the scapula, with a small insertion on the tip of the inferior scapular angle (Figure 3). T h e serratus anterior is innervated by the long thoracic nerve (C5. 6. 7) (49).

T h e trapezius muscle originates from the medial third of the supe- rior nuchal line, the external occipi- tal protuberance, the ligamentum nuchae, the apices of the seventh cervical vertebrae, all the thoracic spinous processes, and the supraspi- nous ligaments of the cervical and thoracic vertebrae. T h e upper fibers descend to attach to the lateral third of the posterior border of the clavi- cle. T h e middle fibers of the trape- zius run horizontally to the medial acromial margin and superior lip of

JOSPT Volume 17 Number 5 May 1993

C L I N I C A L C O M M E N T A R Y

FIGURE 3. Muscular origins and insertions on the anterior scapula. (Adapted from Butters (S), with permission).

major L 8 I \ I S S I r U S

O W 9 1

FIGURE 4. Muscular origins and insertions on the postenor scapula. (Adapted from Butters (S), with permission).

the spine of the scapula. T h e inferior fibers ascend to attach to an aponeu- rosis gliding over a smooth triangu- lar surface a t the medial end of the spine of the scapula to a tubercle a t the scapular lateral apex (Figure 4). T h e trapezius muscle is innervated by the spinal accessory nerve and second, third, and fourth cervical ventral rami (49).

T h e levator scapulae muscle originates by tendinous slips from

the transverse processes of the atlas, axis, C3, and C4 vertebrae and de- scends diagonally to insert on the medial superior angle of the scapula. T h e scapular end of the muscle con- sists of two "folds" o r "flaps" (an an- terior fold and a posterior fold) that partly fuse just above the superior scapular angle. T h e posterior fold at- taches to the dorsal aspect of the me- dial margin of the scapula opposite the supraspinous fossa by way of an aponeurosis. T h e anterior fold has an attachment to the fascia of the serratus anterior. This fold tapers to a narrow tendon attached to the cos- tal surface of the medial border of the scapula at the level of the root of the scapular spine (Figure 4). T h e levator scapulae is innervated by the dorsal scapular nerve (C3, 4, 5) (49).

T h e rhomboid major muscle originates from the second to fifth thoracic spinous processes and the overlying supraspinous ligaments. T h e fibers descend to insert on the medial scapular border between the root of the scapular spine and the inferior angle of the scapula (Figure 4) (49). T h e rhomboid minor muscle originates from the lower ligamen- tum nuchae and the seventh cervical and first thoracic spinous processes to attach to the medial scapular bor- der a t the root of the scapular spine (Figure 4). T h e rhomboids are in- nervated by the dorsal scapular nerve (C4, 5) (49).

T h e latissimus dorsi originates from the spinous processes of the last six thoracic vertebrae. the lower

The scapulohumeral rhythm is the result of

movement at four joints.

three o r four ribs, the lumbar and sacral spinous processes through the thoracolumbar fascia, the posterior one-third of the external lip of the

iliac crest, and a slip from the infe- rior scapular angle (Figure 4). It is the scapular slip that allows the latis- simus dorsi to act a t the scapulothor- acic articulation. T h e latissimus dorsi inserts on the intertubercular sulcus of the humerus (Figure 4). T h e latis- simus dorsi is innervated by the thor- acodorsal nerve (C6, 7, 8) (49).

T h e pectoralis major originates from the sternal half of the clavicle, half of the anterior surface of the sternum to the level of the sixth o r seventh costal cartilages, the sternal end of the sixth rib, and the aponeu- rosis of the obliquus externus ab- dominis. T h e fibers of pectoralis ma- jor converge to form a tendon that inserts on the lateral lip of the inter- tubercular sulcus of the humerus (49). Although the pectoralis major does not insert on the scapula, it acts upon the scapulothoracic articulation through its insertion on the humerus (Figure 6). T h e pectoralis major is innervated by the medial and lateral pectoral nerves (C5, 6, 7, 8; T1) (49).

T h e pectoralis minor originates from the outer surface of the upper margins of the third to fifth ribs near their cartilage. T h e fibers of pectoralis minor ascend laterally, converging to a tendon that inserts on the coracoid process of the scap- ula (Figure 3). T h e pectoralis minor is innervated by the medial and lat- eral pectoral nerves (C6, 7, 8) (49).

Biomechanics

In shoulder movement, glenohu- meral movement is associated with scapulothoracic movement. T h e movements of the scapula are not performed in isolation and are asso- ciated with movements at the sterno- clavicular and acromioclavicular joints (1 4). Movement a t the scapulo- thoracic articulation is important for the normal biomechanics of the shoulder joint. T h e scapulothoracic articulation orients the glenoid fossa so that it can provide a stable base for articulation with the humeral

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

head and maintain optimal contact with the moving humerus (36).

Scapulohumeral Rhythm T h e glenohumeral, scapulothoracic, ster- noclavicular, and acromioclavicular joints have to participate in shoulder movement in a coordinated, con- comitant, and smooth pattern. This complex pattern has been termed scapulohumeral rhythm by Codman (1 4). T h e scapulohumeral rhythm serves two important purposes. First, the distribution of the motion be- tween the glenohumeral and scapu- lothoracic joints maintains the gle- noid fossa in an optimal position to receive the articular surface of the humeral head. Second, the concur- rent motion of the scapula maintains the optimal length/tension relation- ship of the muscles acting on the hu- merus. This minimizes active and passive insufficiency of scapular mus- cles that act upon the humerus (36).

T h e scapulohumeral rhythm is the result of movement a t four joints. T o simplify this pattern, sca- pulohumeral rhythm will be divided into glenohumeral/scapulothoracic and acromioclavicular/sternoclavicu- lar contributions. In reality, scapulo- humeral rhythm is inseparable and occurs a t all four joints concurrently.

Glenohumeral/Scapulothoracic Contribution Normal maximal shoulder elevation is 180". T h e gle- nohumeral contribution to this mo- tion is 120°, and the scapulothoracic contribution is 60" (36, 45). Overall, shoulder elevation could be divided into 2" of glenohumeral motion per 1 " of scapulothoracic motion (45). T h e first 30-60" of arm elevation have been termed the setting phase ( 1 4). T h e setting phase of motion is accounted for primarily by glenohu- meral motion. T h e type and amount of scapulothoracic contribution to the setting phase is inconsistent (14). It is suggested that the scapula is seeking a position of stability in rela- tion to the humerus during the set- ting phase (1 4). Inman et al (1 4) have observed that in the setting phase, the scapula may remain fixed,

protract, retract, o r oscillate between protraction and retraction until sta- bility is achieved. Following the set- ting phase, the contribution of the

Posterior capsule stretching may be

helpful in treatment of impingement

syndrome.

scapulothoracic articulation equals the contribution of the glenohu- meral joint until the end range of shoulder flexion, where the glenohu- meral contribution increases (36).

Sternoclavicular/Acromioclavicu- lar Contribution T h e involvement of the sternoclavicular and acromio- clavicular joints in the scapulohu- meral rhythm is an unavoidable con- sequence of their involvement in a closed kinematic chain with the sca- pulothoracic articulation. Motion a t the scapulothoracic joint inescapably produces motion a t the sternoclavic- ular and acromioclavicular joints. In full shoulder elevation, the scapula moves in a 60" arc, which is the re- sult of movement a t the acromiocla- vicular and sternoclavicular joints and is produced by the force couple of the serratus anterior and trapezius (36)-

As shoulder elevation takes place, the upper and lower parts of the trapezius and serratus anterior combine to form a force couple that upwardly rotates the scapula. How- ever, the coracoclavicular ligament limits upward rotation of the scapula at the acromioclavicular joint, which leads to the elevation of the clavicle at the sternoclavicular joint. This clavicular elevation leads to 30" of upward scapular rotation around an axis through the base of the scapular spine. After the first 30" of upward rotation, clavicular elevation is stopped by tautness of the costocla-

vicular ligament. T h e force couple of the serratus anterior and trapezius continues to attempt further upward rotation of the scapula, and in- creased tension a t the coracoclavicu- lar ligament leads to forward rota- tion of the superior aspect of the clavicle around its longitudinal axis. This clavicular rotation will lead to elevation of the acromial end of the clavicle without causing further ele- vation at the sternoclavicular joint. At this point, the acromioclavicular joint becomes the instant axis of ro- tation for the scapula. T h e force couple of the serratus anterior and trapezius will lead to further upward scapular rotation and abduction and an additional 30" of rotation (36).

In summary, the first 90" of shoulder flexion involves 60" of gle- nohumeral motion and 30" of scapu- lothoracic motion (36). T h e scapular movement is the result of clavicular elevation a t the sternoclavicular joint. T h e final 90" of shoulder flex- ion involves 60" of glenohumeral motion with lateral rotation and 30" of scapulothoracic motion. T h e s c a p ular motion is the result of clavicular rotation and elevation a t the acro- mioclavicular joint (36).

It becomes clear that a delicate mechanism exists in the performance of shoulder flexion. Disruption of motion at any of the involved joints may affect the total motion pro- duced (36). Also, the contribution of the force couple of the trapezius and serratus anterior muscles should not be ignored. An imbalance, weakness, o r dysfunction of this force couple may disrupt scapulohumeral rhythm.

Function of the Rotator Cuff T h e rotator cuff muscles consist of the supraspinatus, infraspinatus, teres minor, and subscapularis mus- cles. T h e combined forces of the in- fraspinatus, teres minor, and sub- scapularis join the force of the del- toid to form a force couple (36). T h e functions of the subscapularis, teres minor, and infraspinatus are depres- sion of the humeral head and pre- vention of superior impaction of the

JOSPT Volume 17 Number 5 May 1993

C L I N I C A L C O M M E N T A R Y

L a V V U S

00718

FIGURE 5. line of pull of the scapulothoracic muscles, posterior a s m t . (Adapted from Dvir and Berme (8). 0 1978, Pergamon Press ltd., with permission).

humeral head into the acromion. The subscapularis is an internal rota- tor of the shoulder, and the infraspi- natus and teres minor externally ro- tate the shoulder. The supraspinatus muscle assists the deltoid in abduc- tion and helps stabilize the glenohu- meral joint with the force of gravity (36).

The rotator cuff stabilizes the shoulder against the action of the prime movers to prevent excessive anterior, posterior, superior, or infe- rior humeral head translation. Addi- tionally, the rotator cuff adds power to glenohumeral elevation and rota- tion (28).

Function of the Scapulothoracic Muscles The scapulothoracic mus- cles function as synergists and antag- onists and also combine to form force couples. A force couple has been described as divergent pulls of forces creating a pure rotation (36). In addition, a force couple has been defined as the effect of equal. paral- lel forces acting in opposite direc- tions that leads to rotatory move- ment (26).

The trapezius muscle is function- ally divided into upper, middle, and lower portions. The upper trapezius elevates and upwardly rotates the scapula. The middle trapezius re- tracts the scapula. The lower trape- zius upwardly rotates the scapula and depresses it. The levator scapulae el-

evates and downwardly rotates the scapula. The serratus anterior pro- tracts and upwardly rotates the scap ula. The serratus anterior has been divided into upper and lower por- tions. The upper portion of the ser- ratus anterior assists in elevation of the scapula, and the lower part de- presses the scapula (4 1, 49). Accord- ing to Dvir and Berme (8). the upper portion of the serratus anterior stabi- lizes the scapula along with other scapular muscles, while the lower portion of the serratus anterior pro- vides scapular motion. The pectora- lis minor protracts the scapula. The rhomboid major and minor retract. elevate, and downwardly rotate the scapula (Figures 5 and 6) (21).

The upper and lower fibers of the serratus anterior and the trape- zius form one of the force couples that acts upon the scapulothoracic joint. The converging actions of these fibers produce upward rotation of the scapula during elevation of the arm (14. 40, 44, 49). The force couple of the serratus anterior and the trapezius also serves as a stabiliz- ing synergist for the deltoid muscle, which acts on the glenohumeral joint. In humeral elevation, the ac- tion of the deltoid will lead to down- ward rotation of the scapula, subse- quently leading to active insuffi- ciency of the deltoid. Upward rotation of the scapula produced by the serratus anterior and trapezius force couple will prevent this down- ward rotation and maintain an opti- mal length/tension ratio for the del- toid (36). The lower segments of the pectoralis major, pectoralis minor, levator scapulae, rhomboidei major and minor, and latissimus dorsi form a synergistic group of muscles that downwardly rotates the scapula (44). The lower fibers of the pectoralis major, pectoralis minor, latissimus dorsi, and lower trapezius combine to depress the scapula (Figures 5 and 6) (44).

The sternoclavicular joint is the only skeletal attachment of the shoulder-arm complex to the

FIGURE 6. line of pull of the scapulothoracic muscles, anterior aspect.

thorax. This singular attachment does not provide adequate stability for the shoulder-arm complex, and, thus, this responsibility is delegated to the muscles connecting the clavi- cle and scapula to the trunk (45). The proper movement and position- ing of the shoulder comes not only from the muscles that provide the movement or position but also from the action of the antagonistic mus- cles, which provide stability (45). For example, elevation of the acromion by the upper trapezius and serratus anterior is imprecise without the guidance and control of the rhom- boids and pectoralis minor (45). Ac- cording to Steindler (45), loss of any scapulothoracic muscle will affect movement at the glenohumeral joint.

In isolated paralysis of the serra- tus anterior, shoulder flexion and abduction are drastically affected. Shoulder flexion and abduction are weakened, and the range of motion for these movements is decreased. In complete paralysis of the serratus an- terior, 1 10" of shoulder abduction is the maximal range of motion (ROM) that can be achieved (9). Discoordi- nation of the scapulohumeral rhythm and shoulder pain have been observed as well as shoulder pain fol- lowing repeated use of the arm (9, 24). Similar signs and symptoms have been observed following injury to the spinal accessory nerve, result- ing in paralysis of the trapezius (30).

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

In paralysis of the rhomboids, serra- tus anterior and pectoralis minor functions are unopposed, producing excessive upward rotation and pro- traction of the scapula. The exces- sive protraction of the scapula inter- feres with shoulder abduction due to needed scapular retraction in this movement (45).

Phases of T h r o w i n g M o t i o n Un- derstanding biomechanics of throw- ing leads to better understanding of the mechanisms of injury to the shoulder during throwing. The throwing motion has been divided into five phases, which are summa- rized in Table 1.

Classification

In normal shoulder movement, the rotator cuff mechanism is inti- mately related to the coracoacromial arch and is only separated by the subacromial-subdeltoid bursa (Fig- ures 1 and 2) (28). Several factors minimize impingement of the rota- tor cuff. These factors include ade- quate shape of the coracoacromial arch to allow safe passage of the cuff tendons without encroachment; nor- mal inferior surface of the acromio- clavicular joint; normal subacromial bursa; normal function of the hu- meral head depressor mechanism, in- cluding the rotator cuff muscles and the biceps tendon; normal capsular laxity; a smooth gliding upper sur- face of the cuff tendons (28); and proper function of the scapulothora- cic joint (22).

A number of abnormal processes may influence these mechanisms and

Difierentiating primary impingement from

secondary impingement is

crucial.

cause friction, impingement, and in- creased wear of the cuff tendons. Matsen and Arntz (28) described structural and functional factors that could potentially increase rotator cuff impingement. These factors are summarized in Tables 2 and 3.

Traditionally, impingement of the rotator cuff underneath the cor- acoacromial arch has been attributed to repeated mechanical impingement (33). Currently, this mechanical im- pingement is termed primary im- pingement (1 0). Primary impinge- ment may result from subacromial crowding, posterior capsular tight- ness, or excessive superior migration of the humeral head due to weakness of the humeral head depressors (Fig- ure 7) (1 1, 28, 33, 38). Secondary impingement is defined as a relative decrease of the subacromial space due to instability of the glenohu- meral joint (1 0) or functional scapu- lothoracic instability (Figures 7 and

Phase Definition

Wind-up Preparatory activity that is mostly upper extremity flexion and ends when the ball leaves the glove

Early cocking Begins with ball release from the glove as the shoulder ob- tains abduction and external rotation and ends with contact of the forward foot on the ground

Late cocking Characterized by maximum shoulder external rotation Acceleration Begins with derotation of the maximally externally rotated

shoulder and ends with ball release Follow-through Begins with ball release and ends when the throwing motion

ceases

TABLE 1. Phases of throwing motion (1 7, 19).

JOSPT Volume 17 Number 5 May 1993

8) (22). Differentiating primary impinge-

ment from secondary impingement is crucial in the proper management of these two syndromes (1 0). If sec- ondary impingement is managed as a classical case of primary impinge- ment (ie., repeated subacromial in- jections and acromioplasty), the un- derlying problem may not be cor- rected (1 0). The end result of both syndromes is rotator cuff tendon in- flammation and potential rupture. Similar signs and symptoms may be present in both syndromes, however, the mechanism of injury is different (1 0).

P r i m a r y Impingement Primary mechanical impingement has been described by Neer (33) as "impinge- ment of the rotator cuff beneath the coracoacromial arch." Neer (33) ob- served that shoulder flexion with in- ternal rotation leads to passage of the critical avascular zone of the ro- tator cuff under the coracoacromial arch. Neer (33) also noted bony changes and spur formation on the undersurface of the anterior acro- mion. Neer (33) proposed that these bony changes were due to repeated impingement of the rotator cuff be- tween the coracoacromial ligament and the humeral head.

Impingement lesions have been divided by Neer (34) into three pro- gressive stages. Signs that may assist in differentiating the stages of im- pingement lesions have been de- scribed by Neer (34) and by Hawkins and Abrams (1 2). A summary of these stages is provided in Table 4.

A positive impingement sign is present in primary impingement syn- drome (1 2, 34). The impingement sign, as described by Neer (34), is elicited by performing passive shoul- der flexion while preventing upward scapular rotation, which leads to en- croachment of the greater tuberosity against the acromion. Hawkins and Abrams (1 2) describe a similar im- pingement sign in which the shoul- der is flexed to approximately 90" and is forcibly internally rotated to

C L I N I C A L C O M M E N T A R Y

Structure Abnormal Characteristic

Coracoid

Rotator cuff

Acromioclavicular joint Congenital anomaly Degenerative spur formation

Acromion Unfused acromion Abnormal acromial shape Degenerative spurs on the undersurface of the

acromion Malunion/nonunion of an acromial fracture Congenital anomaly Abnormality of shape following surgery or trauma Thickening of the tendon secondary to calcific

deposits Postoperative/posttraumatic thickening of the tendons Thickening of the tendons due to retraction following

partial tears Irregularities of the upper surface due to partial or

complete tears Humerus Increased prominence of the greater tuberosity due to

congenital anomalies or fracture malunions

TABLE 2. Structural factors that may increase subacromial impingement. (Adapted from Matsen and Arntz (28), with permission).

Structure ~bnonnal Characteristic Scapula Abnormal scapular position due to thoracic ky-

phosis or acromioclavicular joint separation Abnormal scapular motion due to trapezius/serratus

anterior paralysis or limited motion at the sca- pulothoracic joint

Functional scapulothoracic instability due to scapu- lothoracic muscle weakness or fatigue (22)

Disruption of the scapulohumeral rhythm due to serratus anterior fatigue or weakness (37)

Rotator cuff Loss of humeral head depressor mechanism due to: C5-6 radiculopathy Suprascapular nerve palsy Partial/full thickness rotator cuff tears Rupture of the long head of the biceps brachii

Clenohumeral joint Posterior capsular tightness which may lead to in- capsule creased superior migration of the humeral

head in shoulder flexion (1 1) Capsular laxity

TABLE 3. Functional factors that may increase subacrornial impingement. (Adapted from Matsen and Arntz (28). with permission).

produce a similar effect. Pain elicited with these signs may indicate im- pingement (1 2, 34).

Deficits in range of motion (ROM) may exist in patients with shoulder impingement. These in- clude deficits in internal rotation and cross-chest adduction ranges due to tightness of the posterior capsule (28). Tightness of the posterior por- tion of the glenohumeral joint cap- sule has been proposed to contribute to impingement svndrome by caus-

ing abnormal superior translation of the humeral head (28). This has been shown by operative tightening of the posterior capsule in cadavers (1 1). Harryman e t al (1 1) found that operative tightening of the posterior capsule led to increased anterior and posterior translation of the humeral head during shoulder flexion and cross-chest adduction.

Secondary Impingement Second- ary impingement is a relative de- crease in the subacromial space due

---- 0- IhMlmCdl- -Wavy mpnpemsnt

FIGURE 7. Factors involved in shoulder impingement.

to glenohumeral instability o r func- tional scapulothoracic instability (Figure 8) (1 0. 16, 17, 22). Second- ary shoulder impingement due to glenohumeral instability may be trig- gered by weakness of the rotator cuff mechanism and the biceps ten- don. This weakness leads to overload of the passive restraints of the gleno- humeral joint during throwing activ- ities, which results in glenohumeral laxity. T h e active restraints of the glenohumeral joint (ie., the rotator cuff and biceps tendon) attempt to stabilize the humeral head; however, fatigue and weakness of this mecha- nism result in abnormal translation of the humeral head with secondary mechanical impingement of the rota- tor cuff by the coracoacromial arch. T h e result of secondary impinge- ment is inflammation of the rotator cuff tendons (Figure 8) (1 0, 16, 17). An overlap has been observed be- tween the impingement syndrome and glenohumeral instability (48). Warner et al (48) have found that 68% of the patients with anterior shoulder instability studied showed signs of impingement. In addition to a positive impingement sign, a posi- tive apprehension sign and reloca-

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

SECONDARY SUBACROHAL IUPlffiEYENT

FIGURE 8. Secondary shoulder impingement

tion sign may be present in this group, indicating anterior glenohu- meral instability (1 6, 17).

Subacromial impingement sec- ondary to functional scapular insta- bility is another proposed mecha- nism of secondary impingement in throwing athletes (Figure 8) ( 1 0, 22). In this case, weakness of the scapulo- thoracic muscles leads to abnormal positioning of the scapula. Disrup- tion of scapulohumeral rhythm may occur, leading to impingement of the rotator cuff underneath the coracoa- cromial arch if humeral elevation is not synchronized with scapular ele- vation and upward rotation. With disruption of the scapulohumeral rhythm, the acromion may not be el- evated sufficiently to allow passage of the rotator cuff underneath the coracoacromial arch, leading to im- pingement (22). If weakness o r fa- tigue of the serratus anterior muscle is present, the scapula may not be held against the thorax and mav show excessive winging of the verte- bral border and tipping of the infe- rior angle of the scapula (47). This excessive winging and tipping of the scapula will lead to a relative de- crease in the subacromial space, causing impingement (47). A positive impingement sign will also be pres-

JOSPT Volume 17 Number 5 Mav 1993

ent in patients with secondary shoul- der impingement (10, 22).

An electromyography (EMG) study showed that the serratus ante- rior shows high levels of activity dur- ing the late cocking, acceleration, and follow-through phases of pitch- ing (19). T h e activation of the serra- tus anterior during late cocking is needed to eccentrically decelerate the retracting scapula. During accel- eration, the serratus anterior con- centrically protracts the scapula as the arm is adducted and internally rotated. In addition to controlling protraction and retraction of the scapula, the serratus anterior is a component of a force couple that u p wardly rotates the scapula during el- evation of the arm. This upward ro-

tation is vital to clear the abducting humeral head from impinging against the acromion. T h e serratus anterior, along with the other scapu- lothoracic muscles, also contributes to stabilization of the scapula. Posi- tioning of the scapula keeps the gle- noid fossa underneath the humerus, which leads to improved glenohu- meral stability (19). Thus, scapulo- thoracic stability contributes to dy- namic glenohumeral stability. T h e scapular stabilization provided by the serratus anterior and other scapulo- thoracic muscles provides a stable base for scapulohumeral muscles to act upon the humerus, which im- proves efficiency of the muscles and dynamic glenohumeral stability.

In an effort to identify patients

Stage I: Edema and Inflammation Typical age: < 25 years, but may occur at any age Clinical course: Reversible lesion Physical signs: 1. Tenderness to palpation over the

greater tuberosity of the humerus 2. Tenderness along the anterior ridge of

the acromion 3. Painful arc of abduction between 60-

120°, which is increased with resist- ance at 90'

4. Positive impingement sign 5. Restriction of shoulder range of mo-

tion (ROM) may be present with sig- nificant subacromial inflammation

Stage 11: Fibrosis and Tendinitis Typical age: Clinical course:

Physical signs:

Stage Ilk Bone Spurs and Tendon Ruptures

Typical Age: Clinical course: Physical signs:

25-40 years of age Not reversible by modifying activities

and time In addition to Stage I signs: 1. Greater degree of sott tissue crepitus

may be felt due to scarring in the sub- acromial space

2. Catching sensation with lowering of the arm at approximately 100"

3. Limitation of active and passive shoul- der ROM

>40 years Not reversible In addition to Stage I, II signs: 1. Limitation of shoulder ROM, which is

more pronounced with active motion 2. lnfraspinatus atrophy 3. Weakness of shoulder abduction and

external rotation 4. Biceps tendon involvement 5. Acromioclavicular ioint tenderness

TABLE 4. Progressive stages of impingement as described by Neer and Hawkins (12, 34).

219

C L I N I C A L C O M M E N T A R Y

with functional scapular instability, Kibler (22) has described a lateral scapular slide test. In this test, the distance between the inferior scapu- lar angle and the spinous process of the closest vertebral body is meas- ured in three positions. T h e meas- urements are taken with the subject in a relaxed position with the arms at the sides, with the hands on their il- iac crests with the thumbs pointed posteriorly, and with the arm ab- ducted to 90" with maximal internal rotation and elbow extension. Meas- urements are taken bilaterally, and side-to-side comparisons are made. It is suggested that with weakness of the trapezius, serratus anterior, and rhomboids, the scapula will slide lat- erally, leading to an increase in the distance measured in the involved limb (22). In a study of symptomatic throwing athletes and an activity- matched control group, Kibler (22) found that the symptomatic group showed a significant increase (> 1 cm side-to-side difference) in the lat- eral scapular slide distance in the sec- ond and third positions compared with the control group. Kibler (22) concluded that the increased lateral scapular slide distance in the throw- ing athletes indicated functional sca- pulothoracic instability.

Traditional Nonoperative Treatment of Shoulder Impingement Syndrome

Several protocols have been de- signed for the rehabilitation of the injured shoulder (Table 5). Most of these protocols focus on strengthen- ing the rotator cuff muscles (1 3, 18, 28, 32) in addition to the restoration of normal ROM, endurance, and pain control (13, 16, 28, 32, 35, 38, 42). Physical modalities such as ultra- sound, heat, and cold have been sug- gested for control of pain and in- flammation (1 3, 35, 42). Jobe and Bradley (1 6) described a program of kinesiologic repair, which involves a specific training program for the ro- tator cuff and the scapular rotators to establish proper scapulohumeral

Authors Suggested Treatment Protocol

Pappas et al (38) Return of normal passive and active ROM, synchrony of motion, strength, endurance, and integrated muscle action, and progressive return to pitching.

Hawkins and Kennedy (13) Rest, icelheat, ultrasound, anti-inflammatov medica- tions, stretching and strengthening program for the rotator cuff and large shoulder girdle muscles.

Moynes (32) Relative rest, stretching and strengthening exercises with emphasis on the rotator cuff muscles, and gradual return to sports.

Matsen and Arntz (28) Avoidance of repeated injury, restoration of normal flexibility, restoration of normal strength, aerobic conditioning, and gradual return to work or sports.

Neviaser et al (35) Anti-inflammatory medications, moist heat, 're- stricted exercises," and avoidance of overhead activities.

Richardson et a1 (42) Stretching, anti-inflammatory medications, ice, rest, and injectable steroids.

TABLE 5. Nonoperative treatment of shoulder impingement syndrome.

rhythm. T h e emphasis placed on re- storing scapulohumeral rhythm and strengthening the rotator cuff and the scapular rotators is crucial. T h e proper scapulohumeral rhythm acts to lessen the risk of impingement by synchronizing scapulothoracic mo- tion with glenohumeral motion. Ad- equate strength of the rotator cuff decreases impingement by depress- ing the humeral head and prevent- ing excessive superior migration of the humeral head during elevation of the arm. Additionally, strengthen- ing the rotator cuff provides dv- namic stability to the glenohumeral joint by controlling excessive hu- meral head migration. Proper strengthening of the scapular rota- tors assures that the scapula follows the humerus, providing dynamic sta- bility and assuring synchrony of sca- pulohumeral rhythm.

DISCUSSION

After reviewing the biomechan- ics of shoulder elevation, it becomes apparent that this complex move- ment is carried out by a delicate mechanism. Scapulohumeral rhythm is critical for normal arm elevation. T h e force couple of the deltoid and the rotator cuff and the force couple of the serratus anterior and the tra- pezius are of great importance dur-

ing elevation of the arm. T h e func- tions of these force couples are to achieve smooth arm elevation with- out impinging the humeral head against the coracoacromial arch and to enhance dynamic stability of the glenohumeral joint. T h e force cou- ple of the trapezius and serratus an- terior achieves upward rotation of the scapula by acting concentrically during humeral elevation. During lowering of the arm, this force cou- ple acts eccentrically to control downward rotation of the scapula. If strong downward rotation of the scapula is needed (eg., forced lower- ing of the arm), it will be performed by concentric contraction of the lower segment of the pectoralis ma- jor, pectoralis minor, levator scapu- lae, rhomboids, and latissimus dorsi (44).

Weakness of the scapulothoracic muscles may cause o r aggravate im- pingement. If humeral elevation is not synchronized with upward scapu- lar rotation o r lowering of the arm is not synchronized with downward scapular rotation, impingement may occur.

T h e throwing athlete performs repetitive overhead movements a t high velocities and with explosive forces (39). Weakness o r fatigue of the scapular muscles after repeated use mav lead to impingement due to

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

Muscle Suggested Exercises . . . . . -

Serratus anterior

Upper trapezius Middle trapezius

Lower trapezius

Levator scapulae

Rhomboids

Latissirnus dorsi Pectoralis major Pectoralis minor

Scapular plane abduction5 (31), push up5 (31), end range shoulder flexion in prone5 (141, serratus anterior puncht (21)

Shoulder shrug5 (1, 4, SO), scapular plane abduction5 (31) Rowing5 (31), shoulder elevation and hyperextension in

standings (1, SO), shoulder abduction and flexion in prone5 (1, SO), scapular retraction with horizontal ab- duction of the externallv rotated shoulder in pronet (21)

Scapular plane abduction and rowing5 (31), shoulder depression and retraction in sittings (SO), elevation of the externally rotated arm which is positioned diago- nally between flexion and abductiont (21)

Shoulder elevation, abduction, flexion5 (2, 71, rowing5 (31)

Rowing5 (31), shoulder retraction, elevation, and abduc- tion§ (7), scapular retraction with horizontal abduction of the internally rotated shoulder in pronet (21)

Press ups5 (46), lat pull downt (16) Press ups5 (46) Press ups5 (3 1)

5 Exercises based upon E,MC studres. t Exercises based upon anatomomechanical studies.

TABLE 6. Suggested exercises for the scapulothoracic muscles.

failure of the scapular rotators to achieve the required scapular rota- tion with humeral elevation. Also, shoulder pain from impingement may lead to inhibition of the scapu- lar muscles, causing further impinge- ment (Figure 8). If the scapulothora- cic muscles are not properly re- trained following acute shoulder injury, these muscles may suffer disuse atrophy o r may not function in proper sequence.

T h e validity of the lateral scapu- lar slide test (22). which was de- signed to identify patients with func- tional scapulothoracic instability, is yet to be proven and should be viewed cautiously. Hypertrophy of the upper back and medial scapular musculature of the dominant arm of throwers may introduce error to the measurement. In addition, func- tional scapular instability is a dy- namic deficiency, which may not be apparent in static conditions that this test utilizes (arm held isometrically in different degrees of abduction).

Several rehabilitation protocols have been designed for the treat- ment of impingement syndrome and rotator cuff injuries. T h e shoulder

rehabilitation protocols seem to fo- cus on the proper function of the rotator cuff, with little emphasis on function of the scapulothoracic mus- culature. Jobe and Bradley (1 6) have included strengthening of the scapu- lar rotators in their protocol for treatment of shoulder injuries and stress the upper trapezius, serratus anterior, and latissimus dorsi. Elec- tromyography has been used to study the activity of various shoulder muscles in different sports activities. Jobe et al (1 9), Nuber et al (37). and Ryu e t al (43) emphasize the func- tion of the serratus anterior in pro- viding a stable base for articulation of the humeral head and stress that the strength and endurance of the serratus anterior should be ad- dressed as part of treatment of shoulder impingement syndrome. Although the researchers are com- mended for their efforts, these stud- ies have not included all of the s c a p ular muscles responsible for scapular motion and stabilization. In addition to the serratus anterior, the trape- zius, levator scapulae, rhomboids, pectoralis minor, latissimus dorsi, and pectoralis major muscles control

FIGURE 9. Wall push with ernphacrc on protracting the scapula.

FIGURE 10. End range shoulder flexion in prone.

FIGURE 11. Serratus anterm punch r c performed by lyrng supine on a bench, maintaining the shoulder at 90"f flexion with the elbow fully extended, and protracting the scapula to its end range.

scapular motion and contribute to its stabilization during movement of the arm. Stability of the scapulothoracic joint could not be achieved by one muscle alone. Proper function of all of the scapulothoracic muscles is nec-

JOSPT Volume 17 Number 5 May 1993

C L I N I C A L C O M M E N T A R Y

essary to achieve dynamic stability of the scapula. Isolated strengthening of one of the scapulothoracic mus- cles will create a muscular imbal- ance, which could aggravate the con- dition. T h e authors believe that a comprehensive protocol for treat- ment of secondary shoulder impinge- ment should take into consideration the proper function of all of the sca- pulothoracic musculature as well as the rotator cuff muscles. Proper function includes strength, endur- ance, and synchrony of activation during movement. Proper function of the scapulothoracic muscles pro- motes synchrony of the scapulohu- meral rhythm and may lessen the risk of impingement.

Suggested Exercises for the Scapulothoracic Muscles

Several exercises used to strengthen the scapulothoracic mus- cles are summarized in Table 6. Fig- ures 9- 16 illustrate some suggested exercises for the scapulothoracic muscles. Most of these exercises are based upon anatomomechanical o r electrophvsiological studies and should be viewed cautiously. Several EMG studies have been performed to examine the activity of different scapulothoracic muscles (1 , 2, 4, 7, 14, 3 1, 46, 50). T h e results of these studies should be viewed carefully due to the presence of methodologi- cal flaws, including the use of surface electrodes (which may introduce er- ror to the study due to "cross-talk") (50). the use of active motion only (4), and the lack of utilization of standardized resistance (3 1, 46, 50). A need exists to verify these posi- tions electromyographicall~ in well- controlled randomized studies.

T h e function of the scapulothor- acic muscles is to provide mobility as well as stability for the scapula. S c a p ular positioning (mobility) synchro- nizes scapulothoracic joint motion with glenohumeral joint motion and decreases risk of impingement. Scap- ular stabilization by the scapulothor-

FIGURE 12. Rowing.

FIGURE 13. Scapular retraction with horizontal abductton of the externally rotated shoulder in prone.

FIGURE 15. Scapular retraction with horizontal abductron of the internally rotated shoulder in prone.

FIGURE 14. Elevatron of the externally rotated arm, whtth is positioned diagonally between flexion and abduction.

acic muscles offers a stable base for the glenohumeral muscles and allows them to function properly. T h e sca- pulothoracic muscles a re not re- quired to contract powerfully in short periods of time nor are they required to produce large amounts of force. Thus, it could be hypothe-

FIGURE 16. Press up

sized that the scapulothoracic mus- cles serve as primarily a postural function. Postural muscles should contain a larger proportion of type I fibers. Autopsy studies have shown that the lower and middle portions of the trapezius contain predomi- nantly type I fibers (80 and 76%. re- spectivelv) (25). T h e upper portion of the trapezius also contains a higher percentage of type I tibers (67%) (25). These data would s u p port the above hypothesis regarding the postural function of the scapulo- thoracic muscles. Thus, in rehabilita- tion of the scapulothoracic muscles, their postural function should be ad-

Volume 17 Number 5 May 1993 JOSPT

C L I N I C A L C O M M E N T A R Y

dressed and retrained (ie., endur- ance exercises). This i s done by training the muscles with low weights and high repetitions. Al- though return o f endurance o f the scapulothoracic muscles should be emphasized, return o f their strength should also be a goal.

Deficits in ROM, if present, should be addressed. Posterior c a p sule stretching may be helpful in treatment o f impingement syndrome (16, 28, 38, 48). Posterior capsular tightness could be examined by as- sessing posterior glenohumeral mo- tion as part o f the accessory motion testing (dorsal glide o f the humeral head) (20) as well as assessing inter- nal rotation and cross-chest adduc- t ion o f the shoulder (28). I f posterior capsular tightness is present, i t should be addressed by passive stretching techniques (16, 28, 38) and by dorsal glenohumeral jo int mobilization techniques (20). Deficits o f scapulothoracic jo int motion, if present, should be addressed.

T h e patient's shoulder examina- t ion will dictate whether o r not the above exercises are needed. In addi- t ion to strength and endurance o f the scapulothoracic muscles, flexibil- i ty o f the scapulothoracic muscles should be assessed and maintained. T h e authors believe that a protocol should serve only as a guide in plan- ning a specific program that is indi- vidualized to meet the patient's needs. A comprehensive nonopera- tive management protocol for shoul- der impingement syndrome should emphasize endurance and strength o f the scapulothoracic musculature in addition to the traditional treat- ment goals o f restoring normal range o f motion, strength, and en- durance o f the rotator cu f f muscles. Further research uti l izing EMG is needed to find optimum testing and exercise positions for the scapulo- thoracic muscles.

CONCLUSION

Weakness o f the scapulothoracic musculature could lead to secondary

subacromial impingement through disruption o f the scapulohumeral rhythm, abnormal scapular position- ing, and functional scapulothoracic instability. T h e authors suggest that a comprehensive protocol for treat- ment o f secondary shoulder impinge- ment should include restoration o f normal active and passive mobility o f the shoulder, with special emphasis on restoring normal scapulohumeral rhythm. Additionally, exercises to develop strength and endurance o f the shoulder muscles, with special emphasis on the rotator cuf f and sca- pulothoracic muscles, should be in- cluded. Further research is needed to determine the function o f the sca- pulothoracic muscles and to verify exercise positions traditionally em- ployed for strengthening the scapu- lothoracic muscles. JOSPT

ACKNOWLEDGMENTS

T h e authors wish to acknowl- edge Lat i f Almulla; A l Caprara, CSCS, and David Pezzullo, PT, for their assistance with preparation o f the illustrations.

REFERENCES Basmajian /V, DeLuca Cj: Muscles Alive: Their Function Revealed by Elec- tromyography, pp 265-268. Balti- more: Williams & Wilkins, 1985 Behrsin lF, Maguire K: Levator scapulae action during shoulder movement: A possible mechanism for shoulder pain of cervical origin. Aust 1 Physiother 32(2):101-106, 1986 Blackburn TA, McLeod WD, White B, Wofford L: EMC analysis of posterior rotator cuff exercises. Athl Train 25(1):40-45, 1990 Bull ML, Vitti M, DeFreitas V: Electro- myographic study of the trapezius (pars superior) and serratus anterior (pars inferior) muscles in free move- ment of the arm. Electromyogr Clin Neurophysiol29: 1 19- 125, 1989 Butters KP: The scapula. In: Rockwood CA, Matsen FA (eds), The Shoulder No1 I), pp 335-336. Philadelphia: WB Saunders Company, 1990 Comtet 11, Herzberg C, A1 Nassan I: Biomechanical basis of transfers for shoulder paralysis. Hand Clin 5(1): 1- 14, 1989 DeFreitas V, Vitti M, Furlani 1: Electro-

myographic study of levator scapulae and rhomboideus major muscles in movements of the shoulder and arm. Electromyogr Clin Neurophysiol 20:205-2 16, 1980

8. Dvir Z, Berme N: The shoulder com- plex in arm elevation: A mechanism approach. 1 Biomech 1 1:2 19-225, 1978

9. Cregg /R, Labosky D, Harty M, Lotke P, Ecker M, DiStefano V, Das M: Ser- ratus anterior paralysis in the young athlete. 1 Bone loint Surg 6 1A(6):8 15- 832, 1979

10. Harner CD, Fu FH, Klein AH: Shoulder impingement syndrome: New con- cepts. Presented at the Fourth Annual Panther Sports Medicine Symposium (Current Concepts of the Shoulder in Throwing and Racquet Sports), Pitts- burgh, PA, November 29-December 1, 1990

1 1. Harryman DT, Sidles /A, Clarck lM, McQuade Kl, Cibb TD, Matsen FA: Translation of the humeral head on the glenoid with passive glenohumer- a1 motion. 1 Bone loint Surg 72A@): 1334- 1343, 1990

12. Hawkins Rl, Abrams 1s: Impingement syndrome in the absence of rotator cuff tear (Stages I and 2). Orthop Clin North Am 18(3):373-382, 1987

13. Hawkins R/, Kennedy /C: Impinge- ment syndrome in athletes. Am / Sports Med 8(3): 15 1 - 158, 1980

14. lnman Vl, Saunders /B deCM, Abbott LC: Observations on the function of the shoulder joint. 1 Bone loint Surg 26(l)A: 1-30, 1944

15. lobe CM: Cross anatomy of the shoul- der. In: Rockwood CA, Matsen FA (eds), The Shoulder (Vol I), p 89. Phil- adelphia: WB Saunders Company, 1990

16. lobe FW, Bradley /P: The diagnosis and nonoperative treatment of shoulder in- juries in athletes. Clin Sports Med 8:4 19-439, 1989

17. lobe FW, Kvitne RS: Shoulder pain in the overheador throwing athletes: The relationship of anterior instability and rotator cuff impingement. Orthop Rev 18:963-975, 1989

18. lobe FW, Moynes DR: Delineation of diagnostic criteria and a rehabilitation program for rotator cuff injuries. Am 1 Sports Med 10:336-339, 1982

19. lobe FW, Moynes DR, Tibone /E, Perry I: An EMC analysis of the shoulder in pitching: A second report. Am 1 Sports Med 12:2 18-220, 1984

20. Kaltenborn FM: Manual Mobilization of the Extremity loints: Basic Examina- tion and Treatment Techniques, Oslo, Norway: Olaf Norlis Bokhandel, 1989

21. Kendall PF, McCreary EK: Muscles:

JOSPT Volume 17 Number 5 May 1993

C L I N I C A L C O M M E N T A R Y

Testing and Function (3rd Ed), pp 102- 120. Baltimore: Williams & Wilkins, 1983

22. Kibler WB, Chandler TI: Functional scapular instability in throwing ath- letes. Presented at the American Or- thopaedic Society for Sports Medi- cine's 15th Annual Meeting, Traverse City, MI, lune 19-22, 1989

23. Laumann U: Kinesiology of the shoul- der-Electromyographic and stereo- photogrammetric studies. In: Bateman IE, Welsh RP (eds), Surgery of the Shoulder, St. Louis: CV Mosby Com- pany, 1984

24. Leffert RD: Neurological problems. In: Rockwood CA, Matsen FA (eds), The Shoulder (Vol 2), ch 18, Philadelphia: WB Saunders Company, 1990

25. Lindman R, Eriksson A, Thornell LE: Fiber type composition of the human male trapezius muscle: Enzyme-histo- chemical characteristics. Am I Anat 189:236-244, 1990

26. Luttgens K, Wells KF: Kinesiology: Sci- entiiic Basis of Human Motion (7th Ed). Philadelphia: Saunders College, 1982

27. Matsen FA: Biomechanics of the shoul- der. In: Frankel VH, Nordin M (eds), Biomechanics of the Skeletal System, ch 8, Philadelphia: Lea & Febiger, 1980

28. Matsen FA, Arntz CT: Subacromial im- pingement. In: Rockwood CA, Matsen FA (eds), The Shoulder (Vol 2), ch 15, Philadelphia: WB Saunders Company, 1990

29. McLeod WD, Andrews lR: Mecha- nisms of shoulder injuries. Phys Ther 66(lZ): 190 1 - 1904, 1986

30. Morrell S, Roberson lR, Rooks MD: Accessory nerve palsy following tho-

racotomy. Clin Orthop 238:237-240, 1989

3 1. Moseley IS, lobe FW, Pink M, Perry 1, Tibone I: EMC analysis of the scapular muscles during a shoulder rehabilita- tion program. Am I Sports Med 20(2): 128- 134, 1992

32. Moynes DR: Prevention of injury to the shoulder through exercises and ther- apy. Clin Sports Med 2(2):4 13-422, 1983

33. Neer CS 11: Anterior acromioplasty for the chronic impingement syndrome in the shoulder. A preliminary report. I Bone joint Surg 54A(l):4 1-50, 1972

34. Neer CS 11: Impingement lesions. Clin Orthop 173:70-77, 1983

35. Neviaser TI, Neviaser Rl, Neviaser IS, Neviaser IS: The four-in-one arthro- plasty for the painful arc syndrome. Clin Orthop 163: 107- 1 12, 1982

36. Norkin CC, Levangie PK: joint Struc- ture and Function: A Comprehensive Analysis. The Shoulder Complex, ch 5, Philadelphia: FA Davis Company, 1983

37. Nuber CW, lobe FW, Perry I, Moynes DR, Antonelli D: Fine wire electro- myography analysis of the shoulder during swimming. Am I Sports Med 14(1):7-11, 1986

38. Pappas AM, Zawacki RM, McCarthy CF: Rehabilitation of the pitching shoulder. Am I Sports Med 13(4):223- 235, 1985

39. Pappas AM, Zawacki RM, Sullivan TI: Biomechanics of baseball pitching: A preliminary report. Am / Sports Med l3(4):2 16-22,?, 1985

40. Peat M: Functional anatomy of the shoulder complex. Phys Ther 66(lZ): 1855- 1865, 1986

4 1. Radin LE: Biomechanics and functional anatomy. In: Post M fed), The Shoul- der: Surgical and Nonsurgical Manage- ment, Philadelphia: Lea & Febiger, 1988

42. Richardson AB, lobe FW, Collins HR: The shoulder in competitive swim- ming. Am I Sports Med 8(3): 159- 163, 1980

43. Ryu RK, McCormick I, lobe FW, Moynes DR, Antonelli Dl: An electro- myographic analysis of shoulder func- tion in tennis players. Am I Sports Med 16(5):48 1-485, 1 988

44. Sarrafian SK: Cross anatomy and kine- siology. In: Post M (ed), The Shoulder: Surgical and Nonsurgical Manage- ment, Philadelphia: Lea & Febiger, 1988

45. Steindler A: Kinesiology of the Human Body, Springfield, IL: Charles C Thomas, 1955

46. Townsend H, lobe FW, Pink M, Perry I: Electromyographic analysis of the glenohumeral muscles during a base- ball rehabilitation program. Am I Sports Med 19(3):264-272, 199 1

47. Warner lP: Pittsburgh, PA (personal communication)

48. Warner lP, Micheli Ll, Arslanian LE, Kennedy I, Kennedy R: Patterns of flex- ibility laxity, and strength in normal shoulders and shoulders with instabil- ity and impingement. Am Sports Med 18(4):366-375, 1990

49. Williams PL, Warwick R (eds): Gray's Anatomy (37th Ed), New York: Churchill Livingstone, 1989

50. Yamshon L, Bierman W: Kinesiologic electromyography: 11. The trapezius. Arch Phys Med Rehabil 29:647-651, 1948

JOSPT Volume 17 Number 5 May 1993