Arthroscopic shoulder decompression surgery is a very common operation. It is often used for patients whose pain is thought to be caused by excessive compression of the rotator cuff and its bursa between the acromion and the humeral head. It is believed that by shaving the bony arch of the acromion and removing the coracoacromial ligament it will reduce compressive forces on the rotator cuff and help it recover and function better.
However, the effectiveness of this surgery first proposed by Neer decades ago has been challenged for many years, by many people, and recently some research has challenged it further. This paper here discusses how removing the coracoacromial ligament and shaving the acromial arch means the rotator cuff has to actually work HARDER not less! This is completely the opposite and contradictory to how this surgery is often explained to patients, and it also explains why many patients don’t do well after this surgery.
In this paper, the authors explain how the acromion and the coracoacromial ligament are normal physical barriers to superior humeral head translation. Contrary to common belief and teaching the cuff and the bursa contact the acromion all the time in all of us whenever we lift our arms up and down (ref, ref), and hence why I hate the term ‘impingement’ as it is meaningless.
Anyway, the authors of this paper continue to explain that by removing this barrier the humeral head it is now free to translate superiorly, forcing the rotator cuff to compensate and work up to 25-30% harder to prevent the humeral head escaping through the gap created by the decompression surgery. Or it doesn’t and the humeral head does actually escape superiorly.
Diagram of how the acromial arch & coracoacromial ligament act as a barrier to the humeral head.
There are some limitations with this study, mainly that it is a cadaveric study so we can not extrapolate these findings onto living patients. But it does make us think and ask some awkward questions.
For example, if we have a painful shoulder that already has a weakened and struggling rotator cuff due to tendinopathy, or a structural defect such as a tear, and we then remove the superior structures of the acromion and its ligament, we could be making matters worse by further overloading the rotator cuff. It may be that the acromion and the coracoacromial ligament are actually helping not hindering matters in many patients with subacromial shoulder pain.
The belief that these sub acromial issues such as rotator cuff tendinopathy, tears and bursitis are caused by excessive compression forces from the acromion pushing down is becoming challenged more and more, and for many years. For example, if the acromion is to blame then why do the majority of the rotator cuff issues seen tend to occur on the opposite humeral head side (ref, ref, ref). And why would an acromion that has been the same shape since skeletal maturity and that doesn’t change shape due to external factors suddenly start causing problems all of a sudden (ref).
The big question is does the acromion push down or the humeral head push up, or is it the tendon and bursal ‘swelling’ in-between? As I said at the start arthroscopic shoulder decompression surgery is a very common procedure, in fact, it is the fastest growing operative procedure in the UK, and has increased nearly 750% in the last decade (ref). However, the common belief of how this helps some is looking more and more doubtful and other less invasive, less costly, and less risky methods such as exercise can be just as effective (ref, ref, ref).
However, as much as I have questions about it, shoulder decompression surgery does appear to work for many patients, I see it every day. The question is how and why? I think we will gain more insights into the effects of this surgery once the first randomised placebo control trial of it is released soon (ref), and I for one am waiting with baited breath…
As always thanks for reading