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

The Role of the ScapulaRussell M. Paine PT'Michael Voight, MEd, PT, ATC, SCS2

- -. The scapular musculature is often neglected in designing a rehabilitation protocol for theC shoulder. Weakness of the scapular stabilizers and resultant altered biomechanics could result in: 1 )abnormal stresses to the anterior capsular structures of the shoulder, 2 ) increased possibility ofI rotator cuf~compression, nd 3 ) decreased pedormance This article presents known facts about thebiomechanics of the scapula and surrounding muscles and suggests methods for evaluation of'1 scapular muscle weakness. Exercise techniques to maximally strengthen the scapular musculatureA are also described. As our ability t o document strength of these muscles improves, we wi ll be ableA * to determine the effect of scapular strengthening on improving symptoms related to impingementRussell M. Paine Michael Vo~ght and instability. Scapular strengthening exercises are usually nonstressful to the rotator cuff and areeasily implemented into a rehabilitation program for the shoulder.

T he role o f the scapulahas recently receivedrenewe d interes t asknowl edge of t h eshoul de r and sur -roun ding s t ruc tures has increased.In normal upper-quarte r funct ion,th e scapula provides a stable basefrom which gleno hum era l mobi l ityoccurs. Stabil ity at th e scapulotho ra-c ic joint is dep end ent upon the sur-round i ng m uscula t ure . Th ese scapu-lar muscles dynam ically posi t ion th eglenoid so tha t e ff ic ient g lenohu-mera l movement can occur . Th escapula has been described by sev-era l author s as a vi ta l com pon ent inove rhead t h rowi ng mot i on (4 .7 .8 ) .Kibler has s tudied t he posi t ion o f thescapula and bel ieves that al terat io nof normal posi t ioning can lead to a l -t e red b i omechanic s o f t h e shoul de r(7) . Wh en weakness is present in th escapular musc uI;~turc , orm al scapu-lar posi t ioning and mechanics maybecome al tered. Efficient concentrican d eccent r ic ac tivity of t he muscula-t u re sur rou ndi ng t he shoul de r is de -pendent o n hav i ng s t rong anch ormuscles t o stabi l ize the scapula.

Key Words:scapular musculature, biomechanics, muscle strengthening' Director of Sportsmedicine Research and Associate Clinical Director, Rehabilitation Services of Houston, 6560Fannin #2040, Houston, TX 77030Instructor, University of Miami School of Medicine, D ivision of Physical Therapy, Coral Gables, F1; NationalDirector of Sports Medicine, Sports Physical Therapist, Inc., Bryn Mawr, PA

W ithou t a stron g, stable base posi-t ion, t he scapula may sl ide lateral ly,thereb y al lowing the glenoid fossa tobecome more "antet i l ted," which wil lplace excess ive s t ress on the anter io rs t ruc tures (7 ) . Saha has a l so de-scribed th e antet i l ted posi t ion as apossible com pon ent of the subluxa-t ion/dislocat ion phenomena in pa-t ients who have un derg one repe t i t ivemi c ro t rauma (9).

FUNCTIONAL ANATOMY ANDBIOMECHANICSIt is imp ortan t th at th e cl inicianhave a t horou gh unde rs t anding ofthe muscles tha t cont rol the scapulaan d no rmal scapular mechanics .Onl y t h rough an unde rs t andi ng ofnorm al biomechanics can the pa tho-mechanics o f i~i. ji rry r dysfu nctionbe unders tood. When descr ibing theposi tion of the sc ;~pula , he point ofreference is the glenoid.

Serratus AnteriorT h e se r ra tus an t e r i o r is an i m-

po rtan t scap ular stabil izing muscle.It takes origin from the first eightr i bs and course s a l ong t he r i b cageto inser t a long th e media l aspec t oft he scapula . Th e uppe r por t i on o fthe serra tus an ter ior inser tion i sspread a long t h e media l bo rde r o fthe scapula, while the low er port ioninser ts into the infer ior angle of th escapula . Innerva tion to th e serra tusanter io r is provided by the long tho-racic nerve, which arises from thevent ra l rami of the f i f th an d seventhcrania l nerves . Du e to th e mul t iplea t tachment s ites , the pr imary role ofthe serra tus anter ior is to s tabi lizet he scapula du r i ng e l eva ti on and t opull t h e scapula forward an d a ro undthe thorac ic cage . Advancem ent ofthe scapula to an a nter io r posi tionon t he thorac ic cage is t e rmed pro-t rac t ion o r s capul a r abduc t i on . T h eterm p rot rac t ion is mo re frequent ly

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used in describing this an terio rniovement in o rd er to avoid confi r-s ion wi th s l io r~lde r bduct ion. T h emovement of protract ion is involvedwi th pushing and p unching typeactivities.Rhomboids

T h e rhomboi ds (n i q j or and n ii-nor ) funct ion to s tabi lize the media lh o r d e r o f t h e s ca pu la . T h e r h o m -boids a re verv ac t ive in scapular ad-duct ion o r re t rac tion. which can bede f i ned a s backward ro t a t i on o f t hescapula toward the ver tebra l column .T h e rhomboi d m i nor t akes o r ig i nfrom the spinous process of th e sev-en th cervical and f i rs t thorac ic ver te -brae an d inser t s into the media l bor-de r o f t he scapul a nea r t h e ba se o ft he scapula r sp i ne . T h e rhomboi dmqjor or igina tes f rom th e secondthrou gh f i f th thorac ic ver tebrae andinser t s into the media l ho rde r of thescapula just below t he insert ion o ft he mi nor . Inne rva t i on t o bo th t h erhomboi d ma j or and m i nor i s p ro-vided by the dorsa l scapular nerve .If rhomboid weakness is present , thescapula will be unable to achiev e ful lretract io n. Full retrac t ion is essentialno t on l y fo r ove rhead t h rowi ng mo-t ion but a l so for swimm ing s trokessuch as the c rawl . T h e inabil ity toachieve th e ful ly retr acted posi t iond u r i n g t h e t h r o w in g o r o v e r h ea dmotion can lead to increased stresson t h e an t e r i o r s t ruc ture s o f t heshoul de r (7). Activities that involve apul l ing mot ion may be affec ted bylack of rhomboid strength. Electro-myographic ana lys is has d em on-strated a high level of rhomboid ac-t ivi ty d ur i ng t he acce lera t ion phaseof pi tching (4) . Th is suggests tha t th erhomboi ds a r e con t rac ti ng eccen t r i-cally to prov ide stabi l izat ion t o th emedia l bor de r o f t he scapul a dur i ngacce lera t ion (4) . T h er e i s a l so highrhom boid e lec t romvo graphic ac t ivi tvd u r i n g t h e f o l l o w t h r o u g h p h as e o ft h rowi ng a s t he muscl e con t i n t ~ es ocont rac t eccentr ica l ly to "brake" th eenergy re leased du ring acce lera tion

(4). The re for c~ , he s t r eng t h o f thcrhomboids is vi tal in throwing andove rhead ;mil niovenient . St reng t h-en i ng t h is m~rsc l e ro up shoul d beenipl iasi7ed when rehi~hil i tat ingpatients with ant erio r instabili ty.Upper Trapezius/Levator Scapulae

T h e uppe r t rapei rius an d leva torscapulae muscles ar e suspensorvmusc le s o f t h e scapula . T h e u ppe rt rape7ius or igina tes f rom the supe-rio r nuchal l ine, the exter nal occipi-tal p rotub eran ce of th e skull , andth e seventh cervica l ver tebra . T h eupper t rape7ius f ibers course dow n-ward t o inser t into the di sta l thi rd o ft he scapul a. Inne rva t ion t o t he u pp er t r a p e 7 i ~s provide d bv the spi-na l accessory nerve . T h e leva torscapula o r igina tes f rom th e poster iortuberc les of th e t ransverse processesof cervica l ver teb rae 1-4. T h e inser-t ion of th e levator scapula is alongthe media l bo rde r of the scapula a tth e level of th e scapular spine. In-nervation is provided bv the cervicalplexus wi th f requ ent cont r ibut ion bythe dorsa l scapular nerve . M inimumupper t rapez ius e lec t romvographicact ivi tv has been reported in quiets tanding (10). Add ing a weight tot he hand o r e levat ion of t he sc i ~pul ainit ia tes a s t ro ng co nt rac t ion of boththe upp er t rapez ius and leva tor scap-ula (11). T h e up per t rape7i irs has a lsobeen shown t o be constant ly ac tivedur i n g an ibu l a ti on t o pe r fo rm itssuspensorv role ( I ) . In ad di t ion to i tss l lspensorv funct ion, the upp ertrape7ius assists in upward rotationof th e scapula. wh ich is criticill in th en i ove rnent o f t he a rm ove rhe i d . I ft he l rpward ro t a ti on of t he sc ap t ~ l i ~snot effective, sirhi~crom ial mp inge-men t niav occur .Pectoralis Minor

T h e pectoral is m inor is an ante-r ior m uscle tha t t akes or igin f romthe axia l ske le ton (second throu ghsixth r ibs) and inser ts into the media laspec t of the coracoid process on th e

s c i ~ p u l ; ~ .h e pectoral is min or is in-ne rv ; ~ t ed v t lie medial-lateral pecto-ra l ncrves . l ' h e pec tor-I I '1s minorfunct ions to pe rh rn i severa l niove-ments : abduct ion, depress ion, dow n-ward rota t ion, and upward t il t of thescapula.With normal physiologic move-me nt, th e scapular muscles act inconcer t wi th o n e ano ther . Recauseeach muscle is made up o f mul t iplefibers that co urse in differen t direc-t ions, each mu scle mav have mu lt iplef imctions. T h e t rapez ius re t rac t s andelevates the scapula . Th e rhom boidsand levator scapulae primari ly re-t rac t and ro ta te the scapula down-ward . T h e se r rat us an t e r i o r ro t a te sthe scapula upward and p rot rac t s thescapula.An importan t force couple exist sto a llow forward rota t ion of th escapula. A forc e coup le is the act ionof two forces act ing in opposi te di-rec t ions to impose rota tion ab out theaxis (6) . T h e lower f ibers of th e ser-ra t us d raw t he l ower ang l e o f t hescapr~la orward to cou ple with th et rapez ius and leva tor scapr ~laen for-ward rotat ion (6). Inman et al alsodescr ibe the ro le of th e leva tor scap-ulae and up pe r t rapezius in assistingwith upward rotat ion of the scapula(5).Th ev descr ibe the leva tor scapu-l ae a s t he ~ rpw ard orce un it r a t he rthan the lower f iber of the serra tus .T h e lower force uni t i s descr ibed asconsistent activity of the fo urt h an dfif th digi tat ions of th e serra tus ante-r i o r . T h e seven th an d e i gh t h d ig it a-tions display less activitv in th e lastdegrees of abduction. which al lowst he ang l e t o r ema i n in t he corona lplane . As the serra tus anter io r andupp er t rape7i11sprov i de upward ro -t at io n i ~ n dti1hili7;1tion of tlic scap-rrla, th e deltoid is able to assert itsac ti on on t he hum erus and no t t hescapula (2). Th is coupl ing effec t wascon firm ed by Mosely et al . who per-form ed e lec t romyographic ana lvsesdu ring sever i~l capular exerc ises (8)(Tabl e 1 ). T h e fo rce co i ~p l e rov idesan ext remelv importan t funct ionwi th upw ard rota t ion of the acro-

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Muscle Exercise % of MMT FunctionUpper trapeziusMidd le trapezius'Lower trapeziusLevator scapulaeRhomboidsMidd le serratus anteriorLower serratus anterio rPectoralis minor

RowingHorizontal ABD(neutral)RowingABDRowingRowingHorizontal ABDFlexionPush-ups with aplusPress-up

RetractionRetractionRetractionUpward rotationRetractionRetractionRetractionUpward rotation andprotractionUpward rotation andprotractionDepression

MMT = manual muscle test.Mosely (8) periormedan EMC analysis during several rehabilitationexercises. The values reported were expressedas a percentage o i a maximum isometric muscle test that was performed for each muscle.TABLE 1. Most efficient exercises for specific muscles.

mion away f rom the h um erus in for-ward elevation of the shoulder ,thereby prevent ing impingement .

EVALUATION OF SCAPULARSTABILITY

T h e imp or tant s tabi li7at ion func-t ion o f the ser ratus anter ior is dra-matically prese nted in patients withe x t r e m e w e a kn es s o r d a m a g e t o t h elong thoracic nerve. W hen car ryingobjects in f ron t of th e body, thesepatients will dem ons trate severewinging of th e scapula, which pro-duces a s t rong contract ion of th e ser -ra tus anter ior to prevent backwardrotat ion of the scapula.Scapular winging has been tradi-t ionally demonstrated by having thepatient push against th e wall with hishand s just below t he waist (Figurela) . I f the ser ratus anter ior a ndoth er stabil izers a re weak, t he scap-ula will rota te backward o r wing.Another me thod to demons t r a t escapular winging is to ask the p atientto forward f lex the shou lder to 90(Figure 1b). I f the ser ratus anter ioris not per form ing i ts stabil izing func-tion, the m ost dram atic effect will beobserved in th e f irst 45 ' of elevationas the scapula seeks the optimal posi-t ion to allow f or eff icient glenoh u-

meral rotation. I t is impo rtant t oconduct a bilateral examination,since sl ight winging may be n orma lin individuals with normal hyper-mobility.Current t reatment techniques toincrease scapular stabil ity have beendevelo ped, an d positive clinical re-sults have been observed. T h e mostdram atic effects have been seen inpatients with significant scapularwinging. T h e l imiting factor in ob-

The most dramaticeffecfs have been seenin patients with

significant scapularwinging.

jectively identifying the significanceof these clinical results has been th einabi li ty t o accurately docu men t def -ici ts and improvements in s t re ngthof the scapular musculature. Kiblerhas described th e lateral scapularslide measurement, which measuresthe abil ity o f th e scapular stabil izers

FIGURE 1. A) This posit ion demonstrates winging othe scapula by having the patient push into the wawith the hands below the waist. The serratusanterior contracts to prevent backward rotation ofthe scapula. Iiweakness is present unilaterally,winging wil l be observed. B) This technique allowsthe clinician to view scapular winging duringdynamic elevation of the arm. Resistance from therubber tubing iorces maximum contraction o i heserratus anterior to stabilize the scapula. Weaknesswi ll be observed unilaterally as scapular winging.We have found this technique to be more effectivein demonstrating lack o i scapular stabilization.

to control the medial bord er of thescapula (7). An increase of 1 cm o rmo re in side-to-side me asurem entswas repor ted to cor rela te d i rect lywith symptoms of pain an d de-creased shoulder function. Repro-ducibility and reliability of determining the point of reference on theVolume 18 Number I July I993 JOSP

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C 1 , I N I C A I . C O M M E N T A R Y

scapula t o measu re m ovem ent i s di f-ficul t to achieve. lsokinet ic test ing o fprot rac t ion an d re t rac t ion as ameans to quant i fy scapular s t rengthis current ly u nderway. T h e early re -sul ts of day-to-day rel iabi li ty hav ebeen promis ing.SCAPULAR STRENGTHENINGEXERCISESSerratus Anterior

Mosely has descr ibed th e push-u p wi th a plus as an effec tive methodt o s t rengthen t he se r ra t us an t e r i o r(8).Th is exerc i se is perform ed byhaving the pa t ient per form a prrsh-U D w ith fu ll s c a ~ u l a r r o t r a c t i o n tt he t o p of a push-up (F i gure 2). Ifpa t ien t s a re e i t he r unable t o com-ple te o r tole ra te thi s exerc i se , theymay begin th e push -up with a plus inthe s tand ing posi tion wi th the i rhan ds aga ins t the wall (Figure Ja ) .T h e s t andi ng push-of f p rogre s si onallows the therapist to gen tly "push"

FIGURES 2A and B. Push-ups with a plus. Thisexercice was shown by Mosely et a1 to have thehighest electromyographic activity for the serratusanterior. The exercise is performed by executing anormal push-up, followed by an extra "push" to theceiling to allow full protraction. The digitations ofthe serratus can be observed in the "plus" position.

FIGURES 3A an d B. Push-niic allo\v the patient toperinrrn a c l o d krnetic chain exercise. This exercisewill strengthen all shoulder girdle muscles, withemphasis on the pectoralis major and minor.Progression to a therapist-assisted wall push brcesthe patient to perform both concentric and eccentriccontractions.

th e pa t ient in to the wall (Figure Jb) .An efficient eccentric contrac t ion isprodu ced as the pa t ient ca tches him-self and decelerates.Quadruped stabil isat ion is an-ot he r closed kinet ic chain exercisethat st im ulates pr op er stabi lizat ion ofth e scapula (Figure 4). T h e g oa l o fthis exercise is for the p at ient t o t ryto cont rol scapular winging tha t maybe present w hi le the therapis t pro-vides manual resistance t o the un in-volved arm .T h e p u n c h i n g ( s ta n d in g o r s u -pine) motion is another effect ive ex-e rci se for s t rengt heni ng t h e se r ra t usanter io r . Pa t ients e leva te the i r shoul-d e r s t o 00' with th e e lbow extend ed

and pe r form a punchi ng m ot ion t oal low maximal protract ion. Manualres is tance can be provided to th e an-t er io r s h o ~ ~ l d e rF i gure 5). Resist-ance may a l so be appl ied throu ght he l ong ax is o f t he a rm. Addi ti onalforms of res i s tance can be providedt hrough t he use of dumbbe ll s , t hebody blade (Hymanson, Inc. , PlayaDel Rey, CA) , an d surgica l tubing(F i gure 6). As previously mentioned,isokinetic devices th at al low scap ularpro tract ion /retract io n p rov ide ;In aggress ive means of s t rengthe ning th escapular muscu la ture (Figure 7).Middle Trapezius/Rhomboids

St rengt heni ng t he mi ddl e t r ape-zius and rhomboids begins with s/m-

FIGURE4. Quadruped stabilization. Th~s xercise isanother closed chain activity. The patient focuses oncontrolling the scapula oi the we ight-bearing limbwhile the therapist manually resists elbow flexionand extension m the opposite extremity.

FIGURE 5. Manual resisted protraction andretraction allow isolation of the proximal musclesHand placements are the anterior aspect of theshoulder and the distal spine of the scapula.

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FIGURES 6A and B. A punching motion in thestandrng position will strengthen the serratusanterior muscle. This device is a home exerciseproduct (scapular strengthening kit-Breg, Inc.,Carlsbad, CA) that assists in developing scapularstrength. The patient is instructed to fully protractthe scapula by reaching forward. The patient thenslowly returns the hand to the starting position as hefocuses on controll ing the scapula.

ple pinching together of the shoul-de r blades. Th is is a relatively pain-f ree exercise that may be incorpo-rated in to the ear ly s tages of mostshoulder rehabili tat ion programs.Isolation of th e middle trapezius an drhomboids may be accompl ishedthrough the use of man ual resis tance(Figure 5). Resistance may also beprovided wi th dum bbel ls , machinecable columns, an d rub ber tubing.Moselv demo nstr ated a high level ofelectrom yograp hic activity with th eseated row (8).An ef fect ive meth odof per formin g the seated row is theuse of the scapular s t rengthening de-vice (Br eg, Inc., Vista, CA ) . Proper

rhom boids is the bent-over lateralraise.Upper Trapezius/Levator Scapula

T h e upper t rapezius and l eva torscapula can be exercised by perform -

FIGURE 7. lcokrnetrc protactron and retraction areperiormed w ith a new closed cham attachment(Biodex, Shirley, NY).This instrument will help todocument weakness of the serratus and rhomboidmusculature.

ing shoulder sh rugs with tubing.Th is exercise may also be pe r formedusing hand-held dum bbells for resistance. W e p re f e r rubber tub ing overdum bbells in patients suspected ofhaving an inferior t o multidirec-tional instabil ity a t the gle nohu merajoint. Lo ng axis distraction, when using heavy dumbbells, may exag ger-ate th e infer ior g lide of the humeralhead an d should be avoided. An al -

Long axis distraction,when using heavydumbbells, mayexaggerafe the inferiorglide of the humeralheadand should beavoided.

ternat ive method o f s t rengthen ing ithe use of manual resis tance on thetop o f th e scapula an d clavicle . Th ismetho d removes th e s t ress appl ied tthe infer ior capsule of th e glenohu-meral joint .Lower Trapezius/Pedoralis Minor

Mosely showed a high level ofelectromyographic activity in thelower trapezius an d pectoralis mino rwhile perform ing t he press-upexercise (8).CONCLUSION

T h e s h o u ld e r m u s t be consid-ered a kinet ic chain ma de u p of sev-techniq ue is impo rtant to allow full FIGURES 8A and B. The seated row erercice i e era1 oints . T h e function of ;he s c a pscapular prot ract ion a nd ret ract ion excelirnt t o r aggrecsive strengthen~ngo i the ula and sur roun ding mu sculature is(Figure 8).T h e e lbows mus t r emain rhomboids. Proper technique is important. Using the vital t o th e overall norm al functiontuc&ed to the side during scapular strengthening kit, the subject reaches of the shoulder . Ro tator cuffforward to allow full protraction, followed by full st rengthening has been an obviousto the retraction of the shoulder blades. The elbows mustAno ther h igh-level s t ren gthenin g ex- ,ma;n tucked as the hand le is pulled ;,,to [he chest trea tme nt for various pathologies.ercise for the middle t rapezius and whil e the shoulder blades are pinched. Since the or igins of the ro tator cuf f390 Volume 18 Numbe r 1 July 1993 J O S P

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