Dynamic evaluation and early management of altered motor control around the shoulder complex
Magery & Jones (2003)
The programmes suggested in this paper are yet to be subjected to scientific evaluation and rigour, but are follow the basic principles that have shown effectiveness in other areas of the body.
The shoulder relies on muscle control for its mid-range stability and this paper focuses on the dynamic control of shoulder stabilisers. Rotator cuffs importance in this role, and also serratus anterior’s altered function results in painful shoulders, which portrays its importance in shoulder function.
The neural control of the muscles is responsible for maintaining the humeral head in the glenoid. Disruption to the activation pattern can lead to abnormal translation of the humeral head during active movement.
The balance of muscle activity within force couples is more important then the isolated strength of individual muscles. This balance between force couples is determined by the length of the muscles, associated fascial tissues and the pattern of recruitment. Force couples are controlled by feedback from muscle spindle receptors, responding to perturbations of the joint position.
Key force couple is subscapularis and infraspinatus= they draw the head of the humerus in the glenoid to maintain the point of rotation. Failure of this force couple can result in abnormal translation of the head of the humerus due to an abnormal axis of rotation
In early part of the range of elevation, the upper fibres of serratus anterior and trapz are activated (principle rotators). With increasing range, the upper fibres of both are more active.
One component of the rotator cuff antagonist to a movement is always activated, thus providing stabilisation.
It has been found that pain alters the timing of contraction. Research with unstable shoulders has shown altered activation patterns with failure to activate stabilising muscles until after the onset of movement.
Serratus anterior and lower trapz are susceptible to inhibition in painful shoulders. Serratus anterior especially in the painful shoulders of swimmers and throwers. Studies have highlighted serratus anterior as the primary stabiliser of the scapulothoracic region.
Influences on movement patterns: avoidance of pain, general health and mood, length of tissues, strength and activity of muscle, timing of contracion.
A weak muscle can be compensated for by an altered pattern of activity . torque producing muscles can be activated without the presetting of stabilisers.
2 tests to determine the dynamic control of the head of the huerus
*the dynamic rotary stability test
test ability of the RC to hold the humeral head in place with rotation at different speeds, with different weights and positions to find the point where the GHJ goes from being stable to unstable. Determined by a felt translation of the head, clicking or clunking or compensation of other muscles. Head this test towards the positions of pain weakness apprehension or instability in the aim to find that point of change where the joint has control, then looses control.
*the dynamic relocation test
to test if stabilisation of the GHJ comes before the activation of torque producing muscles. Tests the ability of the transverse force couples to be able to stabilise the head of the humerus in the glenoid against a de-stabilising load. Therapist applies a lateral traction , and the pt has to contract the RC muscles to oppose this force.