Neuromuscular dynamics refers to the nervous system controlling the function of the musculoskeletal system.  Precision nervous system control is critical for function movement such as walking or lifting an arm above the head.  This nervous system output from the brain and spinal cord is generally modified by sensory input from the periphery.  Minor abnormalities in the sensory or motor control of the nervous system can have enormous impacts in functional movements.

Shoulder:  The shoulder is an excellent of a musculoskeletal complex almost purely under neuromuscular rather than structural control.  Section A of the figure shows the shoulder complex with the muscles removed.  The bones of the shoulder complex include the arm (humerus), shoulder blade (scapula), clavicle, and indirectly the rib cage.  The first three all move together in relationship to the rib cage.  The joints can’t be viewed in isolation. 

Looking at first where the arm connects to scapula (red arrow), it is held in place actively by muscle action as described below.  Many people envision the stability as structural.  This is equivalent to the golf ball (figure B) is held in place by the structure of the tee.  But the shoulder joint is dynamically held in place more similar to an elephant in a ball (C).  The ball stays localized by elephant muscles contracting and relaxing in a precise manner under control of the nervous system.  The shoulder operates in an analogous manner.  If the shoulder muscles are not firing or inhibited to precision, the shoulder will rock in place and lead gradually to joint damage.

Ankle Sprains:  The final example of accounting for neuromuscular control involves ankle sprains.  Of patients who get ankle sprains, approximately 70% will get recurrent sprain.  But the likelihood of sprain is equal in both ankles.  Studies indicate this is because dysfunctional walking patterns have been imprinted on the brain (basal ganglia) which need to be corrected rather than issues directly at the ankle.

How this influences injury restoration and prevention is illustrated in the figure to the left.  In A, we see that the arm is controlled at multiple levels.  One is directly at the arm-scapula interface (glenohumeral joint) where the rotator cuff muscles finely controls the joint (green arrow).  But the shoulder blade forms the foundation of arm movement, maintaining relationship to the central (axial) skeleton.  For example, this muscles control scapular rotation which accounts for 1/3 the motion of the arm overhead.  The blue arrow shows two important muscle attaching the scapula to the axial skeleton and controlling its motion.  These are serratus anterior and the rhomboids. 

So in the patient in B with shoulder pain (red), the primary pathology is not the glenohumeral junction but the muscles controlling scapular motion.  This leads to rotator cuff entrapment (secondary entrapment) and is illustrated in C.  When the arm is lifted over the head, again one third of the rotation is due to the scapula.  When the scapula fails to rotate, a rotator cuff muscle is pinched between the humeral head and scapula.  Therefore, while locally treating the area of pain may give temporary relief, it is not treating the underlying problem.

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