The shoulders stability and mobility depends on the synchronization of both musculoskeletal and ligamentous structures, where their tasks become higher in overhead activities (Torres and Gones, 2009, p-1017). An overhead athletes shoulder is placed under extreme demands where sometimes the response is normal and other times pathological (Christoforetti and Caroll, 2005, p-246). Sporting activities such as baseball, swimming, tennis, volleyball and other overhead sports activities are more in risk of causing shoulder injuries than any other sports (Anderson & Alford, 2010, p-1137 ; Alberta et al., 2010, p-903). Thus athletes who take part in over head sports activities are in high risk of both overuse and traumatic shoulder injuries (Brumitt and Dale, 2009, p-132).
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According to Bast et al.,(2010), musculoskeletal and vascular structures are in risk of pathologic and physiologic changes due to overhead throwing activity (pp 461-462). According to Reinold et al.,(2008), an overhead throwing athlete has one of a kind shoulder range of motion( p-523), where it is recorded that the fastest human movement is the shoulders internal rotation while pitching with an excess of 7250 degrees per second, making the pitcher most prone athlete injured among all baseball athletes, where also 75% of time lost in all baseball injuries are the result of overhead shoulder injuries (Wilk et al., 2011, p-329).A baseball athletes shoulder goes trough extreme range of motion subjecting it trough the fastest and most violent maneuvers ever regarding all the other joints in the body (Seroyer et al., 2009, p-108). We can also see that 91 % of injuries in swimming are shoulder injuries (Bak, 2010, p-386).And the most common injury in volleyball athletes is shoulder injury (Taljanovic et al., 2011, p-1).
Both acute and chronic shoulder pain if not treated properly or left untreated can lead to permanent damage of the joint thus reducing the athletes performance (Wu et al., 2010, p-278). According to Brumitt and Dale (2009), sports medicine therapists who fail to correctly identify the injury, or fail to plan specified therapy for each injury will negatively effect on the athletes return to sports (p-132).
Anatomy of the shoulder:
The shoulder is made of four separate articulations which are Sternoclavicular, Acromioclavicular, Glenohumeral and Scapulothoracic. There is less bony stability at the shoulder than any other joint of the body since only the three bones form the shoulder, making it the job of soft tissues to guide and limit motion (DeLee,Drez and Miller, 2009,ch17 section A1). The pectoral or shoulder girdle consist of clavicle anteriorly and scapula posteriorly, anteriorly the medial end of each clavicle joins the sternem whereas their distal ends join the scapula, however the scapula is attached to the thorax and vertebra only by muscles .The shoulder girdle provides the lower limbs with the only attachment with the axial axis further on most of the muscles that move the upper limbs are also attached to the shoulder girdle which gives the shoulder again a one of a kind mobility degree(Marieb, 2004,p228).
Figure 1 Normal function of the shoulder requires the coordinated function of scapulothoracic, sternoclavicular, acromioclavicular, and glenohumeral joints((DeLee, Drez and Miller, 2009,fig 17 A1-1).
The spine projecting laterally forms the acromion where it is articulated with the clavicle forming acromioclavicular joint (Marieb, 2004,p232).The clavicle has a bracing function since it holds both arms and scapula out in the lateral plane, and a compressive function by transmitting force from upper limbs to the axial skeleton( Marieb , 2004,p229).The scapula lies on the dorsal part of the ribcage; it has three borders superior, medial and lateral, the lateral border which is the thickest of all articulates with the humerus by its glenoud cavity forming the glenouhumeral joint(Marieb, 2004,p229).The actions between the humerus and glenoid are translation and rotation, translation is defined by anterior to posterior, superior to inferior and medial to lateral, whereas rotations is internal to external, adduction to abbducation in both scapular and horizontal planes(DeLee,Drez and Miller, 2009,ch17 section A1-2).
The key of extreme mobility of the glenohumeral joint is its articulation between relatively large hemispherical humeral head with the small glenoid process of the scapula (Marieb, 2004, pp268-269).The glenoid labrum is a fabrocartilage that deepens the glenoid cavity, but it doesn’t help in joint stability because of its small size being almost one-third of the humeral head (Marieb, 2004, pp268-269).The glenohumeral joints freedom of movement is also the result of the thin and loose joint cavity covering it, thus the most protection of the joint is provided by ligaments which are mostly found at the anterior aspect of the joint. The coraco-humeral ligament helps in bearing the weight of the upper limb by providing the capsule with strong thickening, also the three intrinsic gleno-humeral ligaments provide reinforcement to the joint but are relatively week. (Marieb, 2004,p268-269). The superior glenohumeral ligament statically suspense the humeral head, where as the middle glenohumeral ligament prevents the humeral head of anterior translation finally the inferior glenohumeral ligament prevents translation in both internal and external rotation ( Giacomo, 2008, pp120-126).
Secondary stability factors of the shoulder include the rotator cuff muscles and tendons the most important tendon is of the long head of biceps brachii muscle that secures the head of the humerus against the glenoid cavity by attaching to the superior margin of the glenoid labrum and running within the intertubercular groove of the humerus(Marieb, 2004, p268).Generally speaking there are nine muscles crossing the shoulder joint having insertions on the humerus, only pectoralis major, latisimus dorsi and deltoid muscles are the essential movers of the arm where as the supraspiantus,infraspinatus, teres minor and subcsapularis that form the rotator cuff have synergist and fixation role where they prevent shoulder dislocation, the remaining two muscles corachobrachialis and teres major have no role in the shoulders reinforcement. The pectoralis major, coracobrachialis and anterior deltoid flex the arm with the biceps brachii acting as assistant muscle, whereas the latisimus dorsi , posterior deltoid and teres major extend the arm, the arm abduction is done by the middle deltoid and the main adductors are pectoralis major anteriorly and latisimus dorsi posteriorly (Marieb, 2004,p354-355).
The anatomy of the shoulder joint is the main factor of shoulder injury in an overhead athlete, while treating an injured shoulder the purpose of treatment is not only elimination of pain but also restoration of function (DeLee,Drez and Miller, 2009,ch 17 section A1).
The Glenohumeral maintains its stability because of its static and dynamic components, where the static stabilizer are the bony, cartilaginous, capsular and ligamentous structures, whereas the dynamic components are the musculature surrounding the shoulder (Lugo, Kung and MA, 2008, p16).
According to Hsilop and Montgonery(2007), the shoulder joint has 8 major movements: Shoulder flexion has a range of motion(RMO) of 00 to 800, the major muscles responsible to this movement are deltoid and coracobrachialis(p87).Shoulder extension RMO 00 to 450 (up to 600),major muscles are latissimus dorsi,deltoid(posterior)and teres major(p91-92).Shoulder abduction RMO 00 to 1800,major muscles are deltoid middle fibers and supraspinatus(p96).Shoulder horizontal abduction, which starts from a position of 900 and adds up with ROM of 900, the major muscle is the deltoid posterior fiber(p99-100).Shoulder horizontal adduction, RMO 00 to 1300 major muscle is the pectoralis major(p103-104).Shoulder external rotation ,RMO 00 to 600 major muscles are infraspinatus and teres major(p107-109).Shoulder internal rotation RMO 00 to 800 ,major muscles are subscapularis, pectoralis major, latissimus dorsi and teres major(p111-113).Shoulder scaption, RMO 00 to 1700 major muscles are a supraspiantus, detoid anterior and middle(p94).
Figure 2- To describe rotation at the shoulder, only three axes are needed, internal/external, adduction/abduction in the scapular plane, and adduction/abduction in the horizontal plane.(DeLee, Drez and Miller, 2009,ch17 fig A1-25)
The bony anatomy of the glenouhumeral joint is unstable since only 25% to 30% of the humeral head articulates with the glenoid cavity(Lugo et al., 2008, p16). The mean size of the glenoid is about 35 mm in vertical diameter and 25 mm in horizontal diameter(DeLee, Drez and Miller, 2009,ch17 section A1-4).Retroversion of 30% is noted at the humeral head articular surface and an retroversion of 7% of the glenoid in general, and a 2mm of deviation as average is noted between the humeral head and the glenoid cavity in rest, hence they change during motion for insistence they are more equal in abduction where pressure is decreased and the contact area is increased and in adduction, the glenoid curvature is larger of the humeral head leading to an increased area of contact(Lugo et al., 2008, p16-17). According to Lugo et al.(2008), when the glenoid loses 21% of its bone structure an permanent loss of stability will be noted, and bone grafting will be crucial after 25% of bone loss of the humeral head(p17).
According to Lugo et al.(2008), the glenohumeral joint alone lets the shoulder to move 1200 but the contribution of the scapulothoratic articulation gives it an significant increase, this contribution is called scapulothoratic rhythm where an proportional equation 2 to 1 is given between the glenohumeral motion and scapulothoeratic motion respectively, disruption of this ratio leads to glenohumeral joint pathology(p18).The scapula is internally rotated by 300, abducted 30 and anteriorly rotated by 200, shoulder is proven to lose its limitations in extension and internal rotation when the scapula is fused (Lugo et al., 2008, p17).
The shoulder musculature also plays an effective role in positioning the arm and producing torque and force for accelerating a load and moving it(Lugo et al., 2008,p17).Scapulothoracic muscles generate large torques towards the glenohumeral joint due to their cross shaped anatomy and their distance from joint center of rotation, the most important of these muscles are trapezius, levator scapulae, rhomboids, serratus anterior, pectoralis minor and subclavius; the seratus anterior helps for maintaining the medial angle against the chest whereas the trapezius helps to rotate and elevate the scapula with synchronization of the glenohumeral motion (Lugo et al., 2008, p17).Where as the rotator cuff muscules are generally responsible for the dynamic stability of the glenohumeral joint in both mid and end range of motions, since they are located closer to the joints center of rotation, dynamically muscles contraction contributes to stability by causing a compression force of the humeral head into the glenoid and contraction causing a tightening of the capsular insertions of the rotator cuff (Lugo et al., 2008, p18).As a summary of the rotator cuff muscles, the supraspiantus intiates in humeral abducton to900, the infraspinatus resists posterior and superior translation and generates 60% of external rotation, the teres minor also resists posterior and superior translation and generates 45% of the external forces, finally the subscapularis resists anterior and inferior translation and is a strong internal rotator( Lugo et al., 2008, p19).
Ligamentous and labral stability
Figure 3- The thin redundant joint capsule has almost twice the surface area of the humeral head, allowing a tremendous range of joint motion(DeLee, Drez and Miller, 2009,ch17 figA1-6).
The relatively constant capsule volume and ligament tension are another key points of the shoulder instability, where excessive translation is prevented because of the constant negative intra articular pressure(DeLee, Drez and Miller, 2009,ch17 section A1-5).The shoulders restraints are provided by the glenohumeral ligaments, coracohumeral ligaments and the posterior capsule, which result in tension on the capsule both statically and dynamically,due to their positioning and insertions of the rotator cuff musculature, the coracohumeral ligament restricts and protects flexion and extension of the shoulder where as internal rotation stresses the middle and inferior sections of the posterior capsule while superior glenohumeral ligament resists inferior translation with the adducted arm in neutral position and helps the coracohumeral ligament in limiting external rotation while adduction, the middle glenohumeral ligament acts as an anterior stabilizer while adduction and 30 to 40 degrees of abduction, finally the inferior glenohumeral ligament complex resist anterior translation of the humeral head while the arm is in rotation, extension and abduction(Lugo et al., 2008,p19-20). The Rotator interval which is an structure associated with the rotator cuff muscles consists of the superior glenohumeral ligament and the coracohumeral ligament(DeLee, Drez and Miller, 2009,ch17 section A1-6).When the rotator interval is in deficit it will result in a decrease of intra-articular pressure in internal rotation that will lead to inferior instability of the joint(Lugo et al., 2008,p18).The glenoid labrum also adds stability to the glenohumeral joint, by deepening the socket and generating a suction effect, the labrum has two mechanical functions the primer one is to serve as an attachment go the glenohumeral ligaments, the second function is shock absorbing(Lugo et al., 2008,p20-21).
Patterns of overhead shoulder injuries
Patterns of injury in shoulder may vary in different overhead sport activities, to study the true aspect of the injury it is a must to give a highlight on the activity itself within each position(Linter, Noonan and Kibler, 2008, p527).Most of the overhead shoulder injuries occur during baseball, swimming, tennis and volleyball(Anderson & Alford, 2010, p-1137 ; Alberta et al., 2010, p-903).Most of the patterns and movements of shoulder injuries occurring in tennis and swimming are similar to baseball pitching(Escamilla and Andrews,2009,p570).According to Chrisotoforetti and Caroll(2005), it is crucial to know the incidence of injury between overhead athletes for proper diagnosis and rehab guiding(p247).
The Baseball is an sports where large amounts of overhead shoulder injuries occur, pitching is divided into six phases: Wind-up, stride, arm cocking, arm acceleration, arm deceleration and follow-through(Houglum,2010, p589).The six phases of this throwing motion have direct impact on the musculoskeletal system of the shoulder that lead to injuries(Linter et al.,2008,p528).
Figure4- key events and phases of baseball pitching (Escamilla and Andrews,2008,p572).
Escamilla and Andrews(2009) examined the results of Jobe’s who tested 56 professional healthy pitchers shoulder muscle activity using an Electromyogram(EMG) measuring maximum voluntary contraction of all shoulder muscles and then tabled the results(table 1), where 0-20% is considered low muscle activity, 21-40% is considered moderate muscle activity, 41-60% is considered high muscle activity and more than 60% is considered very high muscle activity(p-571-572).
Table 1-Shoulder activity by muscle and phase(Escamilla and Andrews,2009,p571).
The windup is the phase where the athlete prepares his body parts in a well synchronized way where the knee of the stride leg is maximum lifted and the two hands are beside each other near the center of the body(Linter et al.,2008,p590).Shoulder activity in this phase is relatively very low since the movements that occur are relatively slow, thus very few and mostly non shoulder injuries occur at this phase(Escamilla and Andrews,2009,p572).
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The stride phase starts when the hands are separated from each other and ends when the stride leg contacts the ground, at this stage the body’s center of gravity lowered(Honuglum,2010,p590).A sudden increase of shoulder activity is noted in stride phase where the scapula is retracted and the humerus abducted to an 900 at least, externally rotated and extended(Houglum,2010,p590 ; Escamilla and Andrews,2008,p572). The supraspiantus has the highest activity during the stride phase where it abducts the shoulder and stabilizes the glenohumeral joint; the deltoids maintain the shoulder in abduction, the risk of injury in this stage is impingement due to abduction(Escamilla and Andrews,2008,p572-573).
The arm cocking phase starts when the stride foot or leading food contacts the ground and ends at maximum shoulder external rotation(Escamilla and Andrews,2009,p573 ; Houglum,2010,p590). The transition phase from cocking to acceleration is the most dangerous phase where most of overhead shoulder injuries occur(Lintner et al.,2008,p528).High shoulder muscular activity is needed in this phase to provide movement to the shoulder in contrast to the rapidly rotating trunk, and to control the high shoulder external rotation that reaches to an 1800(Escamilla and Andrews,2009,p573).The supraspiantus and infraspiantus are highly active in cocking phase to resist glenohumeral distraction and stabilize it(Houglum,2010,p590).Both pectoralis major and deltoid anterior are in huge stress to horizontally adduct the shoulder with an angular velocity reaching 600 degrees per second from the position of 200 abduction to 200 of adduction in a fragment of second, high risk of rotator cuff injuries and impingement are seen during cocking phase (Escamilla and Andrews,2009,p573).
Acceleration phase starts with maximum shoulder external rotation with abduction and ends with the ball release(Escamilla and An drews,2009,p574 ; Houglum,2010,p590). According to Lintner et al.,(2008)glenohumeral and scapular muscles are stressed to their maximum in order to accelerate the arm forwardly ,the glenohumeral joint capsule is wound tight to provide an elastic force. An 900 to 1000 degrees of shoulder abduction is provided by the deltoids, the glenouhumeral internal rotators contract concentrically to generate an internal rotation of 800 with an angular velocity of approximately reaching 70000/second in less than 50msec(p574-575). During this high speed motion the subscapularis muscle which has the highest activity of 115% MCIV, not only helps in internal roation but also fixes the humeral head in the glenoid, a delayed movement of the scapula can increase the impingement and other injuries, whereas anterior shoulder instability can lead to superior labral pathology wich is called SLAP lesion(Escamilla and Andrews,2009,p575).
The arm deceleration phase is the final stage of baseball pitching where it begins at ball release and ends in maximum shoulder internal rotation, the rotator cuff muscles are in great stress in this phase where they contract eccentrically to decelerate shoulder adduction and internal rotation and also they prevent shoulder anterior subluxation, during deceleration phase pathologies of the labral and biceps are noted with rotator cuff tears and capsule and tendons injuries (Escamilla and Andrews,2009,p576).
Over head serves and hits during tennis are frequent cause to shoulder injuries(Houglum,2010,p591).The kinetic forces and the mechanical changes during baseball pitching phases are proportionally similar to that of tennis serve(figure4) which is divided to four phases which are windup, cocking, acceleration and deceleration(Escamilla and Andrews,2009,p583 ; Hoeven and Kibler,2006,p435).
Figure 4-Different phases of tennis serve(Hoeven and Kibler,2006,p436).
The shoulder is in abduction, extension and lateral rotation during the windup phase where the muscular activity are in low levels thus rarely injuries are seen during this phase(Houglum,2010,p592).During the cocking phase the infraspiantus externally rotates the shoulder to its maximum of 1700, an approximate of 80% of body weight pressure is the amount of distraction force during cocking phase which is the similar to the baseballs cocking phase(Escamilla and Andrews,2009,p583). The serratus anterior stabilizes the scapula on the thoracic wall and rotates it in respect to the glenouhumeral joint(Houglum,2010,p592).Acceleration is the fastest movement during tennis serve, where an peak shoulder internal rotation of 2500 degrees per second is noted to accelerate the arm forward, pectoralis major, latisimus dorsi and subscapularis contracts to internally rotate the shoulder, the infraspinatus contracts to position the scapula relatively to the shoulder(Escamilla and Andrews,2009,p583-584).Deceleration is the last phase, which starts from ball impact till the end of motion of the arm, as similar to pitching the rapid alteration between acceleration and deceleration is the key of injuries at the athletes().A tremendous activity of rotator cuff muscles is present to resist shoulder distraction(Escamilla and Andrews,2009,p584).
Shoulder pain is the most common pain in swimming athletes, most swimming strokes have two phases, the pull through and recovery phase(Bak,2010,p386 ; Houglum,2010,p593-594).According to Borsa,Launder and Sauers(2008), an average swimming athlete who trains 10 to 12 months in a year does an average of nonstop 16000 overhead shoulder resolutions per day, this is the key factor overuse swimming injuries(p21).The pull through is very similar to do acceleration phase in baseball where just prior to entry to water the shoulder is 90 degrees abducted and externally rotated the upper trapezius and rhomboids work on upwardly rotating the scapula and retracting it, and prior to leaving the water which is the most accelerated movement in swimming the shoulder is adducted and neutrally rotated the pectoralis major and latisimus dorsi provide the accelerating force whereas the deltoids pull the arm upwardly and the seratus anterior and teres minor stabilize the glenoid in the humerus(Houglum,2010,p594).The recovery phase starts when the arm leaves the water and ends when it entering, this phase is similar to cocking phase of baseball, both subscapularis and serratus anterior are highly active during this phase(Houglum,2010,p594-595).Tissues under risk during swimming stroke were highlighted by Bak in table 2.
Table 2-Tissues under risk during swimming(Bak,2010,p388).
Common Injuries of Overhead Athletes
Repetitive micro inujruies during overhead sports can lead to tendonitis, secondary muscle weakness, mechanical imbalance, and secondary shoulder instability(Stracciolini,2007,p47).According to Bonza et al.(2009), “Common shoulder injury diagnoses included sprains/strains (39.6%), dislocations/separations (23.7%), contusions(11.5%), and fractures(6.6%)”(p76). Most of overhead shoulder injuries take place secondary to micro trauma of the stabilizing structures of the glenohumeral joint (Braun,Kokmeyer and Millett,2009,p966).According to Seroyer et al.(20090, tabled(table3) the common shoulder injuries for the examiner and therapist to have a clear understanding of the shoulder pain and for avoiding misdiagnosis(p109).
Table 3-Differential diagnosis of pain in the throwing shoulder(Seroyer et al.,2009,p109).
Rotator cuff injuries
Excessive traumatic and repetitive overloading of the rotator cuff muscles are the major cause of rotator cuff injuries including tendinitis and tearing,that if not treated will lead to other overuse injuries(Braun,Kokmeyer and Millett,2009,p972).Athletes having this kind of injury will complain of shoulder pain that increases during overhead activity mostly trough deceleration phases(Seroyer et al.,2009,p110-111).According to Seitz et al.(2011), the rotator cuff injuries are induced both from intrinsic and extrinsic factors(table 3).
Table 3- Rotator cuff pathological mechanisms(Seitz et al.,2011.p3).
Internal impingement is classified to cause pain in the posterior part of the shoulder, it’s an overuse injury that takes place during maximum abduction and external rotation and extension of the shoulder, when repetitively a portion of the rotator cuff tendons in companion with the posterior superior labrum are pinched between greater tuberosity of the humerus and posterosuperior part of the glenoid, this takes place during cocking phase in throwing(Anderson and Alford,2010,p1139 ; Chrsitoforetti and Carroll,2005,p249 ; Braun,Kokmeyer and Millett,2009,p973). External impingement causes pain to the front part of the shoulder, since the supraspinatus tendon is pinched between corachoacromial arch and humeral head, the main reason is upper distraction of the humeral head in result of weakening of the rotator cuff muscles or osseous changes of the arch can also increase this impingement(Braun,Kokmeyer and Millett,2009,p972 ; Anderson and Alford,2010,p1139).
Glenohumeral internal rotation deficit
Distraction forces during overhead shoulder activities can lead to contracture of the posteroinferior capsule that will lead to decrease in internal rotation and posterosuperior distraction of the humeral head(Seroyer et al.,2009,p111).As a result to GIRD the posterosuperior labrum is injured and rotator cuff tears are induced(Braun,Kokmeyer and Millett,2009,p973).
Superior labrum anterior to posterior tears(SLAP) are common in overhead athletes(Dutcheshen et al.,2007,p96). SLAP is a lesion of the superior labrum and the biceps anchor at the glenoid insertion, and is divided into 4 types, type I shows superior labral strain without any detachment, type II shows detachment of labrum from the supraglenoid area, type III showed a bucket handle tear of a meniscoid-type superior labrum without biceps tendon involvement, finally type IV showed superior labrum detachment extended to the biceps tendon (Anderson and Alford,2010,p1141-1142 ; Wilk et al.,2009,p44).
Thoracic outlet syndrome
Thoracic outlet syndrome is the most common vascular and neurologic injury in overhead athletes, where the brachial plexus,axillary or subclavian vessels get compressed under the coracoid process and pectoralis tendon during excessive shoulder abduction(Seroyer et al.,2009,p114).
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