WHAT’S NEW PolarTypeI Traumatic structural


TABLE 1. POLAR GROUP CHARACTERISTICS I Traumatic structural


Rehabilitation Surgery Significant trauma


Often a Bankart lesion Usually unilateral No abnormal muscle patterning


PolarTypeIII Muscle


patterning Figure 1. The Stanmore Triangle


result of muscle patterning. Muscle pat- terning refers to inappropriate activation, commonly of the torque-producing mus- cles (eg. latissimus dorsi, pectoralis major, anterior/posterior deltoid) of the glenohumeral joint, resulting in uncon- trolled translation and often dislocation or subluxation of the humeral head. Abnormal muscle sequencing disrupts the normal compressive forces governing glenohumeral joint stability thereby resulting in creation of a destabilising shear force across the joint.


The Stanmore group have described the use of the Stanmore triangle (Fig 1.) as a tool for classifying shoulder instability. Bayley advocates using the model of a triangle to highlight the continuum of presentations which can occur between the 3 polar groups: ● Type I (the ‘old’ TUBS) ● Type II (where the old AMBRIL would fit)


● Type III (muscle patterning disorders).


The triangle has the capacity to accommodate the complexity of shoulder instability and recognises that a continu- um may exist between two different aetiologies. It further recognises that pathology may change with time. Patients are placed into one of the three polar groups or along the lines which join them.


This system enables us to successfully identify those patients who are most suit- able for rehabilitation and those for whom surgery is likely to be a positive option. For example a Type I/III patient eg. a first time dislocator who develops symptoms of recurrent instability and demonstrates a muscle patterning component, should have rehabilitation as a first line treat- ment. Surgery is not an option in the presence of a patterning component.


12 Rehabilitation


PolarTypeII Atraumatic structural


No trauma II Atraumatic structural


III Muscle patterning (non-structural) No trauma


Articular surface damage No structural damage Capsular dysfunction No abnormal muscle patterning


Capsular dysfunction Abnormal muscle patterning


Uni/bilateral


Muscle patterning is reported as a cause of failure after stabilisation surgery (2). Inappropriate stabilisation surgery reduces the success of rehabilitation by up to five times (3). Alarmingly it has also been demonstrated that inappropriate stabili- sation surgery is associated with a 57% incidence of degenerative changes within the glenohumeral joint (3). In a situation where inappropriate facilitation of the pectoralis major, latissimus dorsi or other shoulder muscle is not addressed prior to surgical intervention any stabilisation procedure is likely to fail. Hence the road to failure starts at the initial assessment


Abnormal sequence Often bilateral


when the assessor fails to identify the patterning problem.


Unbalanced net force


MUSCLE PATTERNING INSTABILITY – THE EVIDENCE Malone’s (3) landmark paper reported that up to 45% of patients presenting to a tertiary referral unit with shoulder instability exhibited muscle patterning. Sinha (4) reported the role of tonic spasm of pectoralis major in causing and main- taining dislocation of the glenohumeral joint. Paralysis of the muscle with Botulinum toxin resulted in successful relocation of the joint. Matsen described a stability ratio (5) calculated on the basis of shoulder muscle action between displacing and compressive forces. It is easy to see that in the presence of compromised compressive forces (eg. loss of normal force couples of the rotator cuff) then the more superficial muscles will create greater shear (ie. a displacing force across the joint) (Fig.2).


‘Normal’ sequencing


Similarly any component potentially decreasing normal force couple activation at the glenohumeral joint may result in increased shear created by the more superficial muscles eg. scapula instability, poor posture etc. This group of patients have been poorly understood and are commonly poorly managed. More traditional rehabilitation programmes with a strengthening bias often result in exacerbation of symptomology due to rein- forcement of the abnormal sequencing.


Balanced net force


Figure 2: Effects of normal and abnormal sequenc- ing of the shoulder musculature on displacing forces across the glenohumeral joint


David et al (6) demonstrated a pre-setting phase where the rotator cuff is activated immediately prior to onset of movement and theorised that this functioned to enhance joint stiffness and therefore stability. EMG of patients with muscle patterning demonstrates dominance and commonly, initiation of movement with the patterning muscle. Research has demonstrated that the deep stabilisers are inhibited in the presence of pain and


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