Rotator cuff disease or impingement that results from glenohumeral joint instability is generally known as secondary impingement. Differentiating primary shock from secondary shock is crucial in the proper management of the two conditions. When the secondary shock is treated as a primary shock, the underlying deterioration of instability is not resolved. Instability in this case is defined as symptomatic hypermobility of the humeral head that occurs during function. Instability is often contrasted with asymptomatic clinical laxity. The following sections examine the classification of secondary impact, which occurs primarily in the athlete throwing from above, the related clinical signs and symptoms, and therapeutic approaches. Primary tensile overload can be defined as failure of the rotator cuff under tensile loads. These tensile loads are primarily the result of eccentric muscle contractions and are associated with activities such as throwing. In this case, the rotator cuff functions to decelerate the forces of horizontal adduction, internal rotation, anterior translation, and distraction observed during deceleration. During the first phase of weapon launch, it has been shown that the supraspinatus activity observed on electromyography (EMG) is 40% of the maximum manual muscle test (MMT), with a 45% increase in MMT during late arming. The peak of activity of the infraspinatus and teres muscle has

It was found in the last stages of arming and follow-up of the launch. DiGiovine et al found that supraspinatus activity peaked in the first cocking phase at 60% of MMT and decreased to 49% and 51% of MMT during the late cocking and acceleration phases, respectively. The infraspinatus activity peaked at 74% of MMT during late cocking, while the round minor activity was found to be 71% of MMT during late cocking and 84% of MMT during deceleration. Therefore, repeated throws put the rotator cuff at risk of failure. Andrews and Angelo described rotator cuff tears in pitchers located from the posterior supraspinatus to the infraspinatus medium, consistent with the deceleration function of these muscles. The main mechanism of traction overload is repetitive microtrauma during deceleration functions which causes fatigue and failure of the dynamic stabilizers.

Secondary Tensile Overload

Secondary tensile overload, like primary tensile overload, is defined as rotator cuff failure under tensile loads. In this case, excessive rotator cuff loading is caused by underlying instability. The concept of dynamic stability is important to appreciate in these patients. The subscapularis, supraspinatus,

infraspinatus, and teres minor function to compress the humeral head into the glenoid and provide dynamic stability. The rotator cuff muscles therefore must provide eccentric control of the humerus during throwing while steering the humeral head along the glenoid fossa. This double function leads to early fatigue failure, tendinitis, and possible secondary mechanical impingement. Evaluation of the shoulder with secondary tensile overload is similar to that of primary tensile overload, with the addition of underlying instability. Instability can be unidirectional or multidirectional and is evaluated by traditional instability testing. However, the symptoms may be those of pain rather than instability, and careful evaluation is necessary to delineate the underlying abnormality. Impingement signs may be positive if secondary compressive impingement coexists. Arthroscopic findings demonstrate instability and an associated undersurface rotator cuff tear. As with primary tensile overload, the treatment principles

should address the underlying pathologic condition. In this case, the emphasis is on dynamic stabilization. Again, supraspinatus, infraspinatus, and teres minor strengthening are important because of their role in both eccentric deceleration and stabilization. Additionally, the subscapularis muscle should be trained because of its role in opposing superior humeral head translation and in contributing to rotator cuff moment. Failure of conservative treatment may necessitate surgical intervention. Stabilization procedures and de´bridement of a partial rotator cuff tear are the appropriate surgical measures to address the underlying pathologic condition

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