This month’s blog post comes from Shoulder Community of Practice member, Clare Gilsenan. Clare is a Clinical Specialist Musculoskeletal Physiotherapist, working at Beaumont Hospital in Dublin, and specialises in the management of complex shoulder conditions, and in this post shares her expertise in managing atraumatic shoulder instability.
The overall incidence of shoulder dislocations in the general population is between 8 and 25 per 100,000 person years (Nordqvist & Petersson, 1995; Zacchilli & Owens, 2010), with one-quarter of all dislocations occurring in people aged 20-29 years. However I feel the prevalence of shoulder instability is under-reported in the literature, as many reports do not include subluxation events or insidious instability. There are many presentations of shoulder instability in young patients and in order to find the best ways to manage shoulder instability the condition must be clearly defined and classified.
Matsen’s traditional classification system, using the pseudonyms TUBS and AMBRIL, differentiates between structural damage following a traumatic event and a-traumatic instability which results from unbalanced muscle recruitment around a lax shoulder joint. Matsen’s system fails to accommodate an increasingly acknowledged group of young patients with instability as a result of muscle patterning. Muscle patterning refers to a dominance of torque producing muscles, commonly latissimus dorsi and pectoralis major, resulting in a destabilizing shear force across the shoulder joint. This abnormal muscle sequencing is a neurological system disturbance and can present without any structural disturbance. While challenging to treat, physiotherapy is the only management option for this patient population. The concept of instability being caused by a combination of structural and neurological system disturbances has led to the Stanmore Shoulder group developing the ‘Stanmore Triangle’ as a tool for classifying shoulder instability.
- Polar I represents patients with traumatic unidirectional instability
- Polar II represents patients with a-traumatic instability, resulting from unbalanced muscle recruitment of the local stabilizing muscles of the shoulder on a background of a lax capsule.
- Polar III represents neurological dysfunction or ‘muscle patterning’ instability which results from inappropriate activation of torque-producing muscles, commonly Latissimus Dorsi and Pectoralis Major. This results in uncontrolled translation and subluxation of the humeral head.
This classification has the capacity to accommodate the complexity of shoulder instability in young patients and recognizes that the mechanism of instability can change with time. For a review of the Stanmore triangle, along with an excellent guide to the management of shoulder instability have a look at this BJSM paper by Jaggi & Lambert (2010)
Management of shoulder instability
Shoulder instability presentation and management is not black or white but the Stanmore triangle guides us through the grey and ultimately offers clear recommendations regarding management of this complex condition. Surgery has a major role in young patients presenting with a primary traumatic shoulder dislocation with clear structural pathology. Surgery, however, is contraindicated in a pure polar III group where there is no structural pathology. Muscle patterning has been reported as a cause of failure after stabilization surgery (McAuliffe TB et al, 1988) hence the successful management of this type of shoulder instability is dependent on the physiotherapist or doctor identifying the patterning problem.
Assessment of muscle patterning
Polar III patients are typically young, hypermobile adolescents. They may recall a minor innocuous event or have a history of being able to voluntarily sublux their shoulder on demand, only to find that this pattern of movement has now become centrally established and involuntary. Not all patients will present with pain, but many have significant disability with recurrent subluxation of the glenohumeral joint with every day, overhead activity. The objective examination, including assessment of kinetic chain, will confirm the presence of muscle patterning and guide successful rehabilitation of the instability.
These patients typically adopt a passive, sway back posture with a tendency to weigh bear on the unaffected side. Observe the dominance of the torque-producing muscles during active shoulder elevation. A dominance of latissimus dorsi will result in ipsilateral side-flexion in the early to mid-ranges of shoulder elevation. A patient with pectoralis major dominance will elevate their shoulder in internal rotation, with unbalanced anterior tilt and downward rotation of the scapula. I cradle the axilla with my hand during active elevation to confirm the dominant torque producing force; an inferior force with latissimus and an anterior, internal rotation shear with dominance of pectoralis major.
Assess for any change in this force by challenging the kinetic chain. It is my experience that the dominant inferior force of latissimus will be reduced with ipsi-lateral single leg stand that recruits core and proximal hip stability. This stability allows dissociation of the trunk and pelvis. This allows elongation of the ipsi-lateral trunk with guidance from your palpating hand. Kinetic chain rehabilitation is my priority with this type of presentation.
Dominance of pectoralis major can be inhibited with facilitation of the posterior cuff on a background of good posture and core stability. This can be achieved with light resistance bands or by elevating the upper limb with an ER force against a wall. Dynamic scapular and local glenohumeral stability are my priority with this type of presentation. Anju Jaggi and colleagues (2012) examined these muscle patterning issues using fine wire EMG and reported that pectoralis major was found to be more active in 60% of shoulders presenting with anterior instability while lat dorsi was found to be more active in 81% of shoulders with anterior instability and 80% with posterior instability.
Rehabilitation of Muscle patterning instability
The primary aim of this treatment is to facilitate scapular stability and force couple efficiency to restore dynamic stability of the glenohumeral joint throughout range of motion. This involves regaining normal neuromuscular control and sequencing throughout the kinetic chain. Highly cognitive motor control and recruitment are the priority with this patient group; not strength and flexibility.
As with all patients I would spend time explaining the clinical reasoning and treatment plan. I would reassure the patient and parents that it is unlikely any structural damage has been caused to the joint. I would encourage participation in normal activities of daily living, identifying and avoiding provocative postures in the early stages of rehabilitation.
Early feedback of posture and shoulder girdle position is important for these patients to avoid inappropriate muscle patterning. I find postural tape and mirrors invaluable in providing sensory feedback to facilitate correct muscle activation. I use tape that is anchored in the axilla and lifts the glenoid up to draw the scapula into external rotation and upward rotation.
This tape provides a resistance to the downward force of the torque-producing muscles and guides upward rotation, providing feedback to the patient on the ‘neutral’ resting position of the scapula. I find this tape assists in motor control by eliminating symptoms, improve length tension relationships of the rotator cuff and scapulothoracic muscles and facilitates proprioception.
Following good postural alignment and a reasonable scapular base, exercises to retrain dynamic glenohumeral control in the direction of the instability should be encouraged. I usually work into flexion in crook lying with emphasis on good trunk alignment. Posterior cuff recruitment with a yellow theraband can inhibit the dominant pectoral force and provide some feedback to the patient regarding the neutral zone of the GH joint. The strategy here is to control the ‘give’ at the point of instability, usually at mid-range of flexion. The movement should be slow and should only be performed through the range that the dysfunction is controlled actively by the patient.
End-stage rehabilitation focuses on continued strength and endurance, and must be about retraining patterns of movement biased towards functional tasks, facilitating feed forward processing. Jo Gibson’s papers on Shoulder instability from Sport Ex Medicine are an excellent resource for the management of patients presenting with polar III instability. At the end of the rehab programme, I like to have a few exercises that reverse the dominant ‘adduction – internal rotation’ movement patterns that day to day life or sporting activities can encourage. I advise these patients that they are susceptible to this muscle patterning following minor trauma and that, just like brushing their teeth to avoid tooth decay, they should check in with their shoulder once a day to avoid poor postural habits to creep back in.
There remains a dearth of research evidence or clincial trials to support this approach to managing atraumatic shoulder instability, made challenging by the need for an individualised approach to patient management. A recent case series from Blacknall et al 2014 reported the outcome of physiotherapy rehabilitation for patients with atraumatic posterior instability, demonstrating a mean improvement of 37% in WOSI scores, which exceeded the clinically important difference for this measure, but further development of the evidence base is needed to support this approach.
Gibson J, Elphinston J. Shoulder instability part I: Shoulder instability. What’s new? Sportex Medicine 2005; 24:11-14.
Gibson J, Elphinston J. Shoulder instability part II: Assessment of shoulder instability. Sportex Medicine 2005; 24:15-18.
Gibson J, Elphinston J. Shoulder instability part III: Treatment and rehabilitation of shoulder instability. Sportex Medicine 2005; 24:18-22.