My New Year's mind is wandering...

 

The term "orthopedic testing" has often been a poor descriptor of the methods used to provoke symptoms. "Provocative testing" should be the standard term, and thankfully, we have been moving in this direction.

 

However, provocative testing is frequently taught with a focus on the specific structure it aims to provoke, such as the O'Brien's Active Compression Test for evaluating the superior labrum to rule out SLAP tears. Concentrating solely on the targeted structure limits the potential information gained from:

1. Developing a keen understanding of the mechanics involved.
2. Building a complete picture of a patients positions and patterns of sensitivity and load tolerance.
3. Understanding the underlying function or dysfunction that may have led to tissue overload.
4. Prioritizing and developing a treatment and rehab plan to calm things down and build shit back up (credit to Gregory Lehman for popularizing that phrase)

Let's use the O'Brien's Active Compression Test to illustrate. If you do a basic search on this test you will find a multitude of articles defining the maneuver and the evidence related to its ability to diagnose SLAP tears. You will find VERY little in terms of describing the biomechanics. In O'Briens original writing and research (1) on the test they do a pretty good job of outlining its mechanisms related to the labrum and ACJ. However, they omit the other relevant anatomy and biomechanics. Jobe performed an anatomy evaluation of the test on cadavers, adding more detail to our understanding of the test. Most articles after this limit their discussion to its intended purpose (for example Physiopedia article or this research article).

 

In the following paragraphs, I will outline each step of the test and describe the potential information we can gather from it. Forgive me for any omitting some references; all the concepts I describe below are supported by research on shoulder anatomy and biomechanics, but I am relying on memory and have included only a few essential references.

 

Step 1 - Raise the arm to 90° shoulder flexion - Information gained

 

- trunk stability (timing, control and coordination) as it stabilizes against the weight of the arm.

- functional joint centration of the scapulothoracic and glenohumeral joints, and intermuscular coordination related to the same.

- basic cuff competency and load tolerance. I would also perform manual muscle testing, including resisted forward flexion, before the Active Compression test as well.

- basic capsulolabral competency; this position exposes a fairly low level strain on these structures but it is nonetheless relevant as the posterior inferior capsulolabral complex lengthens and takes on more strain as the humeral head moves into small amount of posterior inferior glide relative to glenoid (in early to MROM). If there is shortening of the this complex there will be increased scapular up rotation due to poor dissociation of the humerus and scapula, and an increase in the anterior-superior glide of the humeral head.

Note: at mid to late and end range of motion of shoulder flexion the humeral head moves anterior superior as the posterior inferior capsulolabral complex lengthens to the point in which it 'lifts' the humeral head in this direction. 

- Even at 90° of shoulder flexion there is a small amount of subacromial compression, relative to the arm hanging in a dependent position. This is not typically a provocative "impingement" position unless there is a high degree of  dysfunction, or there is swelling/thickening of the structures in this space.

 

Step 2: Add 10-15° of Horizontal Adduction 

 

- anterior slide of acromial articular surface over clavicle and increased compression at the ACJ

- low level compression at the anterior superior labrum and glenoid relative to the undersurface of the anterior supraspinatous and superior subscapularis, as well as the other structures of the rotator interval, which includes the superior glenohumeral and coracohumeral ligament, long head biceps tendon and the biceps reflection pulley. This is entering into an Anterior Superior (internal) Glenoid Impingement (ASGI) (3).

 

The rotator interval - from Habermayer et al, 2004

 

- low level compression of the external surface of the supraspinatous, the sub-acromial, sub-coracoid bursa - in a sub-acromial our 'outlet' impingement mechanism

- low level compression of the subscapularis and subscapular bursa relative to the coracoid, in a sub-coracoid impingement mechanism

- increased length and strain placed on the posterior inferior > posterior capsulolabral complex

- lengthening and eccentric loading of the posterior cuff, which is coordinating with the concentric activity of the anterior cuff (you could throw in other muscles here as well, i.e. posterior vs anterior deltoid, rhomboid/trapezius vs serratus and pectoral muscles

 

Step 3: Fully Internally Rotate the Glenohumeral Joint

 

Internal rotation of the GHJ increases tension of the posterior < posterior capsulolabral complex, causing anterior superior translation of the humeral head relative to the glenoid. There is also increased length and tension placed on the posterior cuff, imposing late range eccentric contraction of these muscles coordinated with short range concentric contraction of the anterior cuff (subscapularis).

 

Good coordinated function of the anterior and posterior cuff should limit any aberrant translation of the humeral head, but, it will nonetheless occur and in doing so will increase subacromial, subcoracoid, and especially Anterior Superior Glenoid Impingement (ASGI) forces on the rotator interval and biceps reflection pulley, which stabilizes the long head of the proximal long head biceps tendon. In this position, these structures are compressed against the anterior superior glenoid and labrum.

 

In the presence of a shortened posterior or posterior inferior capsule, there will be more of the above. The same is true if the posterior cuff cannot eccentrically engage; that is, lengthen and contract at the same time. This is a relatively challenging task when it comes to functional joint centration and motor control, and is often lost in the presence of dysfunction.

 

If there is laxity of the posterior or posterior inferior capsule, there will be LESS anterior superior humeral head translation. If you are focused on subacromial impingement, you might think this is a good thing. It is not. Abnormal posterior inferior translation increases the angulation of the humeral head relative to glenoid and increases ASGI. If there is instability of the posterior/posterior inferior capsule this movement can provoke pain and/or posterior apprehension as the humeral head can sublux or dislocate posterior/posterior inferior.

 

With combined shoulder flexion, adduction and internal rotation there is anterior superior humeral head translation, an increased anterior superior and medial glide of the acromion relative to the clavicle causing increased compression forces at the ACJ.

 

O'Brien proposed that this position would tension the long head of the biceps and superior labrum, and in the presence of a SLAP tear "the biceps tendon displaces medially and inferiorly, putting tension on the bicipital-labral complex". This tension mechanism has not yet been validated, however, what has been validated is that in the presence of bicipital instability, which may be secondary to a SLAP tear or a type 3-4 biceps reflection pulley lesion, the biceps can sublux medially and increase ASGI. Bicipital instability, whether from a SLAP or biceps reflection pulley lesion, can cause anterior instability due to the fact the long head biceps (in some positions) contributes to anterior GHJ stability. All together, this predisposes proximal long head biceps tendinopathy - inflammatory and degenerative changes - and tear.

 

O'Brien's illustration of a SLAP tear, during the Active Compression Test

 

Anterior Superior Glenoid (Internal) Impingement in a position of 90° shoulder flexion + adduction and internal rotation, in the presence of a type 3 biceps reflection pulley lesion - from Habermayer et al, 2004

 

 

Step 4: Patient holds this position while resisting the practitioners downward directed force

O'Brien et al, Figure 1 (1)

 

This may be obvious, but adding force resisting a downward force increases compression, most significantly to the ASGI mechanism, and the ACJ.

This is also an incredibly challenging position for the cuff to co-contract and stabilize against an external force. Thus it may be painful in this position by virtue of loading the cuff in a disadvantaged position. If there is posterior laxity, loading this position may provoke pain secondary to ASGI, excessive/abnormal load on the posterior cuff, or apprehension/instability.

 

Image taken during arthroscoy of a patient (me, actually) with a Positive O'Brien's test, pre-surgically diagnosed as a probable SLAP tear, surgically diagnosed as as superior glenohumeral ligament (SGHL) tear with associated biceps reflection pulley / bicipital instability, complicated by laxity of the posterior capsule.

 

Lastly, resisted shoulder flexion places tension on the long head biceps tendon and therefore also the superior labrum. This completes the proposed mechanism relative to the superior labrum and SLAP tears. The increased load to the biceps also increases shear at the reflection pulley, which if compromised, may cause pain and/or provoke bicipital instability.

 

Step 5: Fully supinate the hand - external rotation of the GHJ

O'Brien et al, Figure 1 (1)

 

External rotation at the GHJ reduces ASGI and the shear stress placed on the long head biceps tendon at the reflection pulley and labrum. It also reduces tension/load on the posterior capsule and cuff, and significantly limits compression forces at the ACJ.

 

O'brien's test is considered positive only when there is pain provoked with internal rotation that is then relieved while repeating the same maneuver with the shoulder in external rotation - palm up position. If there is pain in both positions, the test is technically NOT positive for a SLAP lesion.

 

It may be clear from the above description that this test is not mechanically specific to the labrum. Yet, it is 100% specific to the position, the anatomy and mechanics subject to the test and the provocation from it. Provocative testing helps define the anatomical structures involved, just not to the degree of tissue specificity we may like. Specificity may take on a particular statistical meaning for diagnostic testing that loses sight that every movement and every test has specific mechanisms full of information we can gain from them. 

 

We can glean a LOT of information from this test, beyond whether or not the ACJ or labrum are the source of a patients pain; and especially when you compare it to other movements, positions, and loads. I don't believe it distinguishes between ASGI, rotator interval pathology and SLAP tears well. When combined with our movement, range of motion, and manual muscle testing it builds our understanding of how the shoulder girdle manages this movement and load across varied postures, patterns and positions. This is essential for defining first and next steps in our rehab plan, i.e. don't start rehabilitating your patients in positions known to provoke their pain, i.e. know what function you will need to fully restore to rehabilitate their shoulder to tolerate this position again. This is not to say we advocate training for O'briens test, but rather that it should be possible to stabilize and load the shoulder in this position without pain. 

 

Zooming out, this illustration applies to every provocative (orthopedic) test. Provocative testing gives us one window into the anatomy, mechanics, and function that relates to varied positions, patterns of movement and load tolerance. Using this information gives insight and helps guide our treatment and rehab plans.

 

 

1. O'Brien SJ, Pagnani MJ, Fealy S, McGlynn SR, Wilson JB. The active compression test: a new and effective test for diagnosing labral tears and acromioclavicular joint abnormality. Am J Sports Med. 1998 Sep-Oct;26(5):610-3. doi: 10.1177/03635465980260050201. PMID: 9784804.

2. Michael A Parentis, Christopher M Jobe, Marilyn M Pink, Frank W Jobe, An anatomic evaluation of the active compression test, Journal of Shoulder and Elbow Surgery, Volume 13, Issue 4, 2004, Pages 410-416, ISSN 1058-2746, https://doi.org/10.1016/j.jse.2004.01.029.

3. Habermeyer P, Magosch P, Pritsch M, Scheibel MT, Lichtenberg S. Anterosuperior impingement of the shoulder as a result of pulley lesions: a prospective arthroscopic study. J Shoulder Elbow Surg. 2004 Jan-Feb;13(1):5-12. doi: 10.1016/j.jse.2003.09.013. PMID: 14735066.