SCAPULAR VS GLENOHUMERAL DYSFUNCTION: WHICH IS THE CHICKEN AND WHICH IS THE EGG?
Rotator Cuff Related Shoulder Pain (RCRSP) is an umbrella term for a wide variety of previously described shoulder pathologies such as subacromial impingement, rotator cuff tendinopathy, posterior impingement, biceps tendinopathy and bursal pathology. A common presentation is pain and/or weakness in the region of the shoulder, usually the mid-deltoid region, with the worst movement being shoulder abduction and external rotation. That these vague terminologies are now favoured is because tissues such as the tendon, bursa, muscle and ligament are so interwoven, that isolating a pathology to a certain structure is unrealistic (Salamh & Lewis, 2020). It goes to show that we more we know, the less we know.
When we are presented with a patient with RCRPS how do we decide where to start? When is scapular dysfunction causative & when is it compensatory in shoulder pain? Is scapular dyskinesis diagnostic of different shoulder pathologies? Is there any benefit to a scapular focused treatment approach for shoulder pain? How important is optimal arthrokinematics at the glenohumeral joint?
The principle scapular dysfunctions (dyskinesis) implicated in RCRPS, during shoulder elevation, are a reduction in upward rotation &/or posterior tilt and an increase in scapular elevation and internal rotation. These dysfunctions can occur differently with different shoulder pathologies (Castelein et al, 2017).
It seems that an unstable shoulder will present with a different type of scapular dyskinesis than a stiff shoulder, or a rotator cuff tendinopathy. These dyskinesis’s change the arthrokinematics of the glenoid and thus humero-glenoid articulation during shoulder movement, particularly during overhead activities.
As therapists, we are often told by a referring surgeon to correct scapular ‘winging’. But if we follow our clinical reasoning principles, you will often find that this is not the source of the patient’s problem. If you stick down the path of correcting the patient’s scapular position, how frequently are you disappointed by the results?
This is supported in the literature by multiple meta-analysis studies, that not only is the quality of research poor (low statistical power, low sample numbers, methodological weaknesses etc), but there is currently no evidence to support a scapular focused rehabilitation approach in patients with RCRSP (Ratcliffe et al, 2014; Bury et al, 2016; Reijneveld et al, 2017).
Glenohumeral joint positional dysfunction can mainly present as anterior and/or superior translation of the humeral head. This loss of centring of the humerus in the glenoid and reduction of the subacromial space, especially with shoulder overhead activities, as well as during shoulder abduction and external rotation, is also implicated in RCRPS. Causes of this loss of acromio-humeral space are many. Restriction of the posterior structures (posterior capsule, infraspinatus and supraspinatus) limit posterior translation during elevation and force the humeral head either antero-superiorly during shoulder forward elevation, or postero-superiorly, during abduction and external rotation, such as in the cocking position before accelerating into the throw (Kibler et al, 2013). Posterior structure restriction causes a loss of glenohumeral medial rotation (GIRD). Restriction of clavicular backward rotation, due to changes at the AC or SC joint (Ludewig & Reynolds, 2009), overactive medial rotators such as pectoralis major or latissimus dorsi & swelling of the biceps tendon are just 3 examples of causes of a loss of glenohumeral external rotation range of motion (ROM).
Clinically, I became aware of the importance of optimal arthrokinematics of both internal & external rotation ROM at the glenohumeral joint, so that the Total Arc of Motion (TAM) should be assessed and compared to the unaffected side instead just assessing for GIRD.
A loss of Total Arc of Motion (TAMD) compared to the unaffected side (clinically, I use 10-15% loss in a non-professional thrower) is important as these loss of ranges will force a compensatory ‘give’ at the scapula.
For example, in the cocking position (or any abduction and external rotation movement of the shoulder), a restriction of glenohumeral external rotation ROM, will force a compensatory give of scapula adduction and downward rotation. Yes, this scapula dyskinesis reduces the size of the subacromial space and yes, it is this repetitive loading of the nociceptive structures that can cause pain and weakness, but the scapula is not the source of the problem. The source is the loss of shoulder external rotation ROM.
Clearly, a scapula focused rehabilitation approach will be unsuccessful until optimal glenohumeral external rotation ROM is restored. Until then, only scapular stabilisation exercises that do not demand glenohumeral rotation will be appropriate. As you ponder on this, you’ll realise that all overhead shoulder activities demand internal and external rotation at the glenohumeral joint. For this reason, early rehab, until the TAM is restored should be in GH neutral or below 90° of shoulder elevation.
Lastly, almost all current research on GIRD, TAM & TAMD has been conducted on throwing athletes (Manske et al, 2013; Kibler et al, 2013). But clinically we see this loss of total arc of motion in almost all patients presenting to our clinics with RCRSP. Be cognitive of this, assess for a TAMD and use your clinical reasoning skills to develop a patient centred approach that addresses the source of the presenting patients problem and not just dive into scapular rehabilitation, which is most often a compensatory strategy.