“Anatomy is to physiology as geography is to history; it describes the theatre of events.”
The anatomy is quite similar in the musculoskeletal apparatus. Just think at the correlations between shoulder and hip antomy; the gluteus medius and gluteus minimus externally rotate the thigh and a bursa separates the tendons from the surface of the trochanter over which they glide (that anatomy ring a bell with you?). Performing an ultrasound study at the trochanter site, you can find lots of similarities with the shoulder anatomy.
Sagittal ultrasound scans of shoulder extra-rotator cuff (left) and gluetus medius-minumus tendons (right).
Don’t forget these similarities, regarding both to anatomy and function, because it will be helpful for your clinical and ultrasound evaluation.
Dynamic hip ultrasound exam; painful trochanteric bursitis in a professional football player.
Correlation between ultrasound and MRI images (coronal T2w Spair – 1.5T) in the same patient.
Measuring rotator cuff thickness is not easy; using the ultrasound probe (linear) on a circular surface (humeral head), may create lots of artifacts. What in Mri is called “magic angle”, with ultrasound imaging is the “anisotropy” and can be a source of interpretation error for inexperienced practitioners. Normal thickness of a rotator cuff goes from 2.5-3 mm to 6.5-7 mm, depending on anthropometric characteristics of each subject. Before every examination try to think at these important variabilities: how old is the patient? Male or female? Any kind of professional or sport activity? Recent trauma? Hyperactivity and no-activity make damages both. I always remind you to perform a comparative evaluation with the contralateral shoulder. A common mistake is to start the measurement directly from the cortical bone. Pay attention… before the tendon attachment you’ll find two important layers: cartilage and joint capsule. Take always in mind and count every time all the layers. Starting from the bone we have:
1 – cortical surface –
2 – cartilage
3 – joint capsule
4 – rotator cuff
5 – bursa (a hyperechoic line if synovial fluid is absent)
6 – deltoid muscle deep aponeurosis
7 – deltoid muscle
8 – deltoid muscle superficial aponeurosis
9 – subcutaneous tissue
10 – cutis
Incorrect scan (left) – Correct scan (right)
To find the right postion, take the acromion as a landmark and put the probe just below as seen in the video at the bottom of the page.