Shoulder impingement – is it what we think it is?

If your shoulder pinches you, you pinch it right back.
If you have shoulder pain, chances are you’ve been told its from impingement. So what is impingement?
Impingement means something is being pinched, and in the shoulder, this refers to the rotator cuff being pinched by the top of the shoulder blade called the acromion. Why would it do this? Normally, the acromion is like a roof to the rotator cuff, but it seems like in some people, it hooks downward instead of being flat, leading to an impingement problem when they reach overhead.
That explanation seems to make sense, especially when you go to an orthopedic surgeon who takes an x-ray and shows you a bone spur in your shoulder. But does it really make sense?
Impingement probably does happen in some people, but its likely nowhere near as common as people are led to believe. Research has shone a light on some of the key findings that the impingement theory is based on.
Rotator cuff tear location
First is the location of most rotator cuff tears. If the rotator cuff is being poked by a spiky bone spur from above, it would stand to reason that the tear is on the top of the rotator cuff, directly beneath the bone spur. However, most tears are actually on the bottom of the rotator cuff and its tendon. They also tend to be posterior and lateral to where the bone spur would touch.
Why is this? Well if we assume that the impingement isn’t causing the damage, then the next thing would be overload. After all, most people with rotator cuff tears have a history of a lot of overhead work, like athletes, electricians, and other people who work with their hands. There are 5 portions of your rotator cuff tendon but we’ll just classify them as the top, middle, and bottom. They are not equally strong. When the shoulder is in the overhead position, the bottom portion is about half as strong as the other two sections. Therefore, it makes a lot of sense that the bottom portion is the most frequently injured, with the cause being overload and lower tissue tolerance, and not impingement.
This also explains why physical therapy helps so frequently. The exercise strengthens the tissues of the shoulder which helps both overload and tissue tolerance. By making the other muscles stronger, it helps shift load away from the weaker portion. By safely exercising the rotator cuff, both the muscle and then tendon gain strength and load tolerance.
Side to side comparison
Many people have shoulder pain on both sides, but its usually worse on one side. However, x-rays of the bone spurs and MRIs of the muscles and tendons show that the sides look the same. This is also the case when people have pain on one side but not the other! How is it possible to have the bone spur, the ‘cause’ of impingement, on both sides, but one side hurts and the other doesn’t? That would both imply that the presence of a bone spur may not guarantee pain. On the other hand, some of the people with impingement-type pain have x-rays and MRIs that show no significant findings.
Medical interventions
A common pain relieving intervention is getting a steroid (cortisone) injection. This is to reduce inflammation in the shoulder. As a temporary measure to hold out before getting surgery, I can understand the rationale. But often its used in hopes that it will make the problem go away. I am all for this, because sometimes the pain does go away. However, if its paired with the impingement explanation due to a bone spur, I question the rationale. By telling someone that their pain is due to a bone spur, then giving them an intervention that doesn’t address that bone spur, it seems like you’re planting a seed that eventually their pain must return and they will have to get surgery.
Most surgeons also inform their patients that cortisone injections can weaken the tendon if given too often (most cap it at 3-4/year). Since a large part of the problem probably is poor tissue tolerance of the rotator cuff, this precaution is very important.
I’m not against cortisone injections as long as they are given with an explanation that more accurately leaves the door open for longer-term pain relief and doesn’t imply that surgery is inevitable. Generally my attitude is, try it and see. If it helps, great! If it doesn’t, let’s move on.
Surgical outcomes
In the study “Bursectomy compared with acromioplasty in the manage- ment of subacromial impingement syndrome: a prospective randomised study” by Henkus et al. they compare removing the bursa (a friction reducing structure in the shoulder that has many nerves and is thus a likely source of pain) vs removing both the bursa and the bone spur. They found that removing the bone spur didn’t improve results over just removing the bursa.
Rotator cuff tears
This article is about impingement but most people will be wondering more about surgery. First, if you’re told your shoulder pain is due to impingement and you have a bone spur and/or rotator cuff tear – don’t panic. This doesn’t necessarily mean you need surgery.
Surgery works better for people younger than 60. Many of the people seeking rotator cuff surgery are over 60, however, as we all know, the older you are, the lower your healing potential. Over the age of 60, research indicates actual healing from the rotator cuff surgery is less likely. It has been said that the reality of rotator cuff surgery for this population may be less about fully repairing the tear, and more about turning a painful, symptomatic tear into an asymptomatic tear. On the other hand, people younger than 60 tend to heal very well which makes surgery a more viable option.
Another component is how did the tear happen? Was it traumatic like from a fall? Or did it just happen gradually over time. For a traumatic tear, surgery is often preferred. If its just due to degeneration over time, then more weight is given to the size of the tear.
If the tear is large (the definition varies here but your surgeon would tell you), then surgery is generally preferred. The exception is for older adults (over 60). Its generally recommended that they try physical therapy first for 3 months and then reassess. For tears that are not large, physical therapy is becoming the standard course of action, with good results reflected in the research.
For adults over 60 who have a large tear, physical therapy has also been demonstrated to be helpful. You will know within 3 months whether or not you may opt for surgery. The research indicates by 3 months you’ll probably have your answer, but in my experience, people will very often notice improvements in the first 2-4 weeks.
Ultimately, the decision for surgery will come from a frank discussion with your surgeon on what they realistically think your outcome will be. The research shows that surgery has good outcomes for shoulder pain and function, especially when paired with physical therapy afterwards.
Read more
Read the 2011 narrative review “Subacromial impingement syndrome: a musculoskeletal condition or a clinical illusion?” by Jeremy S. Lewis for a much more thorough analysis.

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