Hi Erin,
You raise some great points.
I agree that “bursitis” is over-diagnosed and often used as a reason for symptoms incorrectly.
In answer to your first question about the thickness of a bursa before I get excited about it. I don’t have a number. This may disappoint you, but I am really not a numbers person, even in obstetrics I prefer to take a global perspective rather than fixate on the biometry.
The first thing to understand is that bursitis is not a stand alone entity. It exists in a spectrum of disease. If you watch the MSK principles webinar on the website I do cover some of this in the early part of that presentation.
In the MSK system as we use our bodies we get degenerative changes in the tendons and the enthesis attachments to the skeleton. When we develop degeneration in these areas as a response to overuse it sets up an inflammatory response in what is known as the synovial entheseal complex (SEC). Now this all sounds a bit fancy but it is simple really. All tendons have a SEC and they are comprised of a combination of either (bursas, fat pads, syvovial sheaths or peritenons) . For example the Achilles has a peritenon, subtendinous bursa, subcutaneous bursa and Kagers fat pad. Supraspinatus has the subacromial -subdeltoid bursa. Tibialis posterior has a synovial sheath. Gluteus medius has the trochanteric bursa and the sub-tendinous bursa.
So when a tendon gets degenerative changes in the collagen or at the enthesis this triggers an inflammatory response in the SEC.
So with trochanteric bursitis there is always a degenerative process underway in the tendon (tendinosis) or an enthesopathic process under way and this triggers the trochanteric bursitis.
The point in treating the trochanteric bursa with a steroid injection is NOT to make the patient better. The injection will relieve the pain by temporarily reducing the inflammation in the SEC and while the patient has some relative comfort they must be doing physiotherapy to regenerate the degenerative tendinosis in the gluteal tendons or they will end up right back where they started. We are just part of management package if the patient is being well managed and this is not always the case.
I think the only time you see bursitis in the setting of a perfect tendon is in rheumatoid patients where the synovium in the bursa simply gets cranky as part of the synovium proliferative process.
Propper assessment of any tendon requires assessment of the enthesis, tendon, musculotendinous junction, muscle belly and the associated SEC. The you have done a complete job. This is how I approach all tendons.
As for when I call the diagnosis of bursitis I am not really interested in an absolute measurement. I look at the tendon and enthesis for changes. Palpate with the transducer to see if it tender and ask about the clinical presentation. Bursitis often causes nocturnal pain and sleep disturbances as well as being point tender on palpation. If the patient has these symptoms I will guide an injection even if the bursa looks normal. I know we live in an imaging world, but I think we need to treat the patient and not the imaging, so if the symptoms are typical we should inject as a diagnostic trial even if the scan is fairly normal. Comparison with the other side can be helpful but again I am guided mainly by the clinical presentation.
I hope this helps Erin,
Please continue the conversation with me,
Happy scanning,
Steve.