capsule and is thought to be prophylactic because it prevents re- petitive stress to the capsule and ligaments. Research suggests that retroversion occurs mostly between the ages of 12 and 16, when the growth plates are open.5 ThE ThROWER’S PARADOX The subtle nuance of the shoulder in the overhead athlete is what has been termed the “thrower’s paradox.”4 This states that the shoulder should be lax enough to allow for gains in external rotation (cocking), but should be stable enough to prevent symptomatic subluxation or dislocation. In my experience, all throwers, regardless of age, exhibit some degree of shoulder laxity. This is logical considering the excessive range of motion necessary and has been described as “acquired throw- ers laxity.” Unfortunately, current research has not been able to delin- eate what a normal range of laxity may be, and thus a wide spectrum of measurement exists. With respect to injury, there is evidence to show that acquired hyper-laxity, which corresponds to a gradual stretching of the anterior capsuloligamentous structures, can lead to shoulder pa- thology.6 During the cocking position of maximal external rotation, there is obligate posterior translation of the humeral head that concur- rently tightens the anterior structures. With overuse, the anterior cap- sule stretches allowing the humerus to subsequently translate forward causing the humeral head to contact the upper aspect of the glenoid, producing posterior (internal) impingement of the rotator cuff.6 ADAPTIVE RESPONSES Recently, the concept of Posterior Shoulder Tightness (PST) has been introduced as an adaptive response of repetitive throwing. This con- sists of both shortening and the development of fibrotic scar formation of the posterior capsule, as well as the posterior rotator cuff. This oc- curs during the follow-through phase as the rapidly accelerating arm is decelerated by the posterior rotator cuff muscles. Mechanically, this leads to arthrokinematic changes of the shoulder, notably a posterior and superior shift of the humeral head as the tight posterior structures act as a lever.7 body adduction. Research has demonstrated that the acceptable level of IR deficit as a result of PST is 20 degrees.8 shoulder structures can become pathological. This leads to abnormal stresses in both the static and dynamic restraints and has been hypoth- esized to be a major cause of injuries to the labrum. There is much debate as to which of the reported adaptations of the overhead shoulder is the main cause of the ER gain and the IR loss and thus, the cause of pitching injury. The literature documents, with cer- tainty, that bony adaptations do occur. From my clinical perspective in working with these athletes, neither acquired laxity or posterior shoul- der tightness exists in isolation nor can be labelled as the sole culprit of shoulder injury in pitchers. Due to the repetitive and intense nature of the activity, both occur, to some extent, and must be addressed accord- ingly, in any therapeutic program to prevent the “shoulder at risk”.7 All pitchers whom I work with have regular shoulder “performance” goals that have to be met for continued participation. This includes maintaining appropriate ranges of motion, appropriate muscle firing patterns and neuromuscular efficiency of the scapular muscles, rotator cuff and the prime movers, and maintaining appropriate muscle flex- ibility. This is accomplished by in-office “performance” treatments as well as a home stretching protocol and strengthening program. • To read the article with references, please go to our website, www.canadianchiropractor.ca. 16 • CANAdiAN ChirOPrACTOr | JUNE 2009 www.canadianchiropractor.ca This results in a gain in ER with a loss of IR and cross At or above this level, the
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