In my previous post we looked at trauma as a cause of shoulder instability, what's called Type I unstable shoulders on the Stanmore Classification System which I discussed in my introduction post here. In this piece we will look at the non traumatic structural causes of instability around the shoulder, what's called Type II's.
The first thing to say here is that traumatic Type I shoulder injuries can, and often do, create structural changes that then lead to repeated episodes of non traumatic shoulder instability, these are classed as Type I/II shoulders, but there are also shoulders that have no history of trauma and have congenital structural abnormalities that predispose them to instability, these are classed as true Type II's, these shoulders are the shoulders that can voluntarily dislocate, or sublux doing normal day to day tasks or by doing their party tricks, these shoulders can be pefectly fine for years only to become troublesome and painful later on in life for a number of reasons.
One of these reasons is thought to be repetitive microtrauma to the shoulders active and/or passive structures gradually over time causing increasing tissue damage and so pain. This is also the mechanism thought to occur to normal shoulders with no congenital issues that start to experience non traumatic instability, for example as seen with throwers such as in baseball or javelin where the forceful repetitive cocking action stresses and strains the anterior structures so creating instability over an extended period of time.
So these structural abnormalities can be separated into congenital bony or soft tissue conditions or via repetitive micro-trauma.
Congenital bony issues that can occur can be misshapen Glenoid's or humeral heads, with torsions or retroversions that place the humeral head at a disadvantage in remaining centred on the Glenoid during arm movement.
Congenital soft tissue abnormalities can be, labral deformations, in that its thinner or not as deep as it should be, or the capsule can be classed as capacious in that it has more volume, or the capsular ligaments can be thinner or even absent.
Other conditions also need to be considered as a cause for non traumatic shoulder instability such as hypermobility and other connective tissue disorders
Finally weakening or poor muscle control of the rotator cuff and scapular muscles through either repetitive micro trauma again or other neurological mechanisms need to be considered here, however these issues also come under the last category on the Stanmore Classification of shoulder instability the Type III's or adverse muscle patterning so I will talk more about this in my next post.
Diagnosing a Type II shoulder
This is mainly done within the subjective history, a patient giving a history of regular episodes of frank dislocations or feelings of instability with no history of trauma and the ability to relocate it themselves or with a little help is of course clear signs of an unstable Type II shoulder, but they don't always, in fact rarely, present that clearly.
Type II shoulders can be subtle and sometimes have only small signs of instability such as an occasional click, pop or feeling of looseness, and sometimes they can just report aches and pains in their shoulders after certain activities, so mimicking other shoulder conditions such as rotator cuff tendinopathy's / tears or bursitis, and to confuse matters these pathologies do commonly tend to co exist in unstable shoulders. I have come across too many shoulders that have had recurrent episodes of so called sub acromial pains and have often been labelled by other therapists as 'failed rehab' or even have had surgery such as acromioplasty's or bursectomies that haven't helped due to them having a missed Type II unstable shoulder.
Physical examination of an unstable shoulder
The physical assessment tests are hopefully used to rule out or confirm an unstable shoulder and also possibly give you an indication of the direction that the shoulder is unstable. The commonly used tests are the anterior apprehension and relocation test for anterior instability, the posterior apprehension for posterior instability, the load shift test (sometimes called the anterior posterior draw) for identifying both anterior and posterior instability and the sulcus test for inferior instability.
However these tests should be used with caution, not only can some of them cause dislocation (I have 'popped' a shoulder out doing an anterior apprehension test and I know many other physios and doctors with similar stories) but they also have different levels of sensitivity and specificity.
For example Hegadus found the anterior apprehension test has good sensitivity at 66% and excellent specificity at 95% but when combined with the relocation test the sensitivity of these tests is improved to 81% and it's specificity up to 98% in diagnosis of anterior instability. For the posterior apprehension test the same paper found its has poor sensitivity at 19% but excellent specificity at 99%, however research is limited on this test due to its much lower prevelance rate.
The load shift test is a commonly used and taught clinical test for identifying either or both anterior or posterior instability, however, I find this test a challenge and clinically it doesn't give me any good or reliable information, this is due not only to the difficult nature of the test and the ambiguous measures ie grade 1, 2 or 3, but also due to the automatic reaction of patients to 'guard' and 'splint' when this test is performed making it virtually impossible to do truly passively. This is confirmed by McFarland's paper in which he finds that only when the load shift test produces full subluxation of the humeral head over the Glenoid rim classed as a Grade 3, and, reproduces apprehension or pain does it then only have moderate sensitivity of 53% and good specificity of 85%, and there are not many patients with painful unstable shoulders that will let you happily fully sublux them, so in my opinion this test is best left for the surgeons to use once the patient is under anaesthetic, just like the pivot shift test for the ACL.
Next is the sulcus sign, again as with the load shift test, this test is commonly used and taught to identify inferior or even multidirectional instability, but despite is widespread use there is NO evidence or any published literature on its sensitivity or specificity, in fact McFarland in his paper again discusses that there has only been one paper looking at this test and they conclude that it leads to large false +ve's and substantial over diagnosis if used, which I totally agree with, I have seen many people with +ve sulcus tests with no issues of instability, so again like the load shift test I rarely use it clinically.
On a side note I found this little interesting paper here looking at a test to differentiate between a structural and adverse muscle patterning causing posterior shoulder instability by using a hand squeeze test. It's obviously only a pilot study but the results look interesting, however due to the rarity of these types of shoulders getting the numbers needed to see if it's a reliable test will take a while, if at all!
Other ways to help diagnose a Type II shoulder is of course with imaging such as CT, MRI or MRA, and examinations under anaesthetic EUA, and as a last resort, arthroscopes can used can be used to rule in or out structural abnormalities causing instability.
Management of a Type II unstable shoulder
This should nearly always be conservative to start with and surgery only considered once an extensive rehab programme has been attempted for a period of 6 months or more. If no improvements have been seen or the situation is worsening for the patient then surgical methods can be attempted to restore stability to the shoulder such as with capsular shrinkage or shifts, or even bony block procedures like the Laterjet.
The goals for conservative rehab will obviously be dependant on the shoulder presented in front of you ie the direction, the severity and the frequency of instability, but in a nutshell the goal should be to work on increasing the neuromusclar proprioceptive ability of the shoulder, of which there are many ways, methods and theories on how this is best achieved.
For the sake of brevity I will keep it simple in saying there is no one way that has been found to be any better than another in rehab for these types of unstable shoulders. As always there is no 'one size fits all' approach and I'm afraid no simple answers, but that doesn't mean it has to be complicated to treat a non traumatic unstable shoulder. For a simple straight forward overview of managing non traumatic unstable shoulders this is a nice paper by the Stanmore team here.
A conservative rehab program should of course include strengthening of the rotator cuff and shoulder muscles as well as incorporating the entire kinetic chain, this paper here looks at some commonly used exercises in rehabbing unstable shoulders.
However, strengthening alone will not get you very far with these types of shoulders, there also needs to be a big focus on proprioceptive training, this is best done in my opinion via closed chain exercises such as in four or three point kneeling, or with hand against the wall, gym ball or any other gadget or gizmo you want to use, but perhaps not like the picture below… people do some of the strangest exercises….!!!
I also like to train the shoulder, later on in the rehab process, for quicker speed and transitions between concentric and eccentric actions in an effort to improve the speed of the dynamic activation of the shoulder stabilisers such as with perturbations. Finally there must also be a role for the psychological aspect of an unstable shoulder, training the peripheral and central neurological mechanisms as best as we can, this involves placing the shoulder in positions and actions that feel 'uncomfortable' from a point of instability for our patients shoulder stability and repeating the movements in a slow, controlled and conscious manner progressing them into faster, quicker and sub conscious actions as tolerated.
So in summary, a Type II non traumatic unstable shoulder can be congenital or acquired via micro trauma, some are easy to spot, others a challenge, they often have co-current shoulder pathology such as rotator cuff tendinopathy or bursitis challenging diagnosis, and some tests we use to diagnose them are questionable. With rehab you and the patient need patience and tolerance as results can be slow to appear and getting the balance of strengthening, neurological and psychological training right is difficult.
As always thanks for reading