The term arthrokinetic reflex (arthro meaning “joint” and kinetic meaning “motion”) was coined by University of Pittsburgh researchers to describe how sensory input from joint movement reflexively activates or inhibits muscles.1 In no other place in the body is this concept more applicable than the joints and connective tissues of the shoulder girdle (Image 1). If sensory input from the sternoclavicular (SC), acromioclavicular (AC), and glenohumeral (GH) joints conveys that the shoulder movement is safe, the nervous system will loosen its governor on rotator cuff strength and range of motion.
If the information suggests the movement is dangerous, however, the brain may protectively guard the shoulder via muscle stiffness, pain, weakness, or altered coordination. In these cases, the myoskeletal method aims to first restore shoulder girdle function—by clearing SC, AC, and GH joint fixations—and then assess for possible rotator cuff injury. In this column, we’ll first discuss SC neuromechanics and biomechanics, and then I’ll demonstrate a couple of my favorite techniques to help your clients presenting with rotator cuff impingement syndrome.

Movement Map Issues

Articular mechanoreceptors in shoulder girdle ligaments and joint capsules transmit movement information to the brain at a speed of 300 miles per hour. The brain uses this data to create a movement map, or an idea of the type of movement taking place. Depending on the stimulus or lack thereof, these receptors can inhibit or facilitate surrounding muscle tone. A simple way to think about this is that “jammed joints” typically result in weaker muscles, whereas mobile joints promote stronger muscles. So, when a joint has been strained or locked in an abnormal position, it causes a map clarity issue, resulting in mild muscle strength alterations and loss of functional range. This is a protective mechanism the brain uses when it can no longer predict the movement that’s occurring. In my experience, many rotator cuff injuries involve map problems due to dysfunctional joints.

Testing and Treating Common SC Joint Fixations

Rotator cuff impingement syndrome occurs when the supraspinatus tendon gets squashed between the humerus and the scapula’s acromion process during arm abduction. One of the primary—and frequently missed—causes is insufficient SC joint elevation of the clavicle. The SC joint should always move in an opposing direction to the scapula, but tension, trauma, and suboptimal posture can cause the clavicle to get locked in a superior (or anterior) position on the manubrium, preventing normal downward glide as the arm is raised. In these cases, manual and movement therapy to treat a frayed rotator cuff tendon is pointless until the SC joint fixation is corrected.
To begin, we first must determine whether the client’s medial clavicular heads drop inferiorly as the client elevates (shrugs) his shoulders. In Image 2, I assess for an SC joint elevation restriction by placing my index and middle fingers on the superior border of the client’s medial clavicle and asking them to shoulder-shrug. If one side does not drop down, there is a ligament or articular disc restriction in that SC joint. Try this on yourself by placing your left index finger on top of your right medial clavicle while you shrug the shoulder. Does it drop down?
Image 3 demonstrates a contract-relax technique for correcting a superiorly fixated SC joint. Notice how my fingers gently depress the superior clavicular border as my left hand abducts the client’s arm to barrier. The client gently pushes down against my resistance to a count of five and relaxes, and I slowly increase arm abduction to the new restrictive barrier. Repeat 3–5 times and retest. I’ve found this technique very effective in mobilizing fibrotic soft tissues that restrict shoulder elevation and arm abduction, but not always.
The most common restriction seen at this very mobile SC saddle joint occurs during shoulder girdle protraction. To assess whether the client’s right clavicle is dropping posteriorly, my thumb contacts the anterior clavicular head and the client is asked to reach toward the ceiling (Image 4). Shoulder protraction should cause my thumb to palpate the medial clavicle translating posteriorly. If it does not move back, the restriction may be triggering an arthrokinetic reflex that alters rotator cuff integrity.  
To treat a right anteriorly fixated SC joint, the client grasps my neck and I create a counterforce by gently depressing his medial clavicle while my left hand lifts his scapula (Image 5). To enhance this myoskeletal technique, the client is asked to gently pull down on my neck against resistance to a count of 5 and relax. Again, a counterforce is applied by lifting the client’s shoulder while gently depressing the anteriorly fixated clavicle. Repeat 3–5 times and retest for improved posterior clavicular glide.
Such arthrokinetic reflex techniques are often helpful in relieving protective rotator cuff guarding associated with SC joint fixation. By working with the client’s nervous system to increase tolerance, mobilization with movement also psychologically reinforces to the client that they can move their arm through a normal range of motion.

Note

1. L. Cohen and M. Cohen, “Arthrokinetic Reflex of the Knee,” American Journal of Physiology 184, no. 2 (1956): 433–37.