To Scan Or Not To Scan? That Is A Question.
Ultrasound or MRI for shoulder injuries?
There is often a debate regarding the efficacy of Ultrasound (USS) versus Magnetic Resonance Imaging (MRI) in the diagnosis of shoulder injuries and pathology.
Both have a beneficial and vital role to play but both also have subtleties that differentiate them from one another.
MRI has a broader use as it is able to penetrate deeper into the joint and demonstrate the anatomical structures deep within the joint and therefore injuries or pathology far beyond the reach of the more superficial penetration of USS.
The sound waves of USS work in a similar way to the sonar of a submarine or air traffic control. The sound waves are reflected from hard materials such as bone. The anatomy of the shoulder blade and upper arm can limit the views obtained by USS providing a narrower field of view- similar to viewing a hallway of a house through the letter box.
The rotator cuff tendons and the biceps tendon of the shoulder are however areas that the two imaging modalities can find common ground.
The rotator cuff is a group of four muscles and tendons that both move the shoulder but also play a crucial role in stabilising the joint.
The subscapularis arises from the deep surface of the scapula against the posterior rib cage. The tendon passes to the front of the shoulder and is an internal rotator of the arm i.e. bring the forearm across the belly.
The infraspinatus arises from the lower superficial surface of the scapula and passes to the posterior aspect of the shoulder and externally rotates the arm away from the body. The smaller teres minor performs a similar role.
The supraspinatus muscle arises from the upper superficial aspect of the scapula. It passes under the acromion or ‘corner of the shoulder’ on to the upper shoulder and acts to lift the arm upwards away from the body.
Wear and tear and age-related changes of these tendons are an unavoidable part of the human aging process. This does not mean however symptoms (pain, weakness or dysfunction) are guaranteed however it is a very common complaint making up to 70% of referrals to an average UK shoulder specialist.
USS and MRI have been thoroughly investigated over the years and compared. It is generally accepted that in the hands of an experienced sonographer that the sensitivity and specificity in detecting full thickness tears of the rotator cuff tendons are comparable.
Ultrasound scans are often quicker to obtain in many departments and are also cheaper to undertake. They are also not precluded in patients with claustrophobia or metallic implants such as pacemakers of certain metallic implants as in the case of MRI. USS is however hugely reliant on the skills and experience of the sonographer. The images produced are dependent on the position and angle of the probe. This commonly means the images are more difficult to interpret unless viewing them ‘live’. Clinicians are therefore often reliant on the typed report of the scan.
MRI images on the other hand are far more transferrable and open to review and general interpretation after the scan is complete. Whilst almost all MRI scans will also be reported, I will always personally review the images and formulate my own opinion of the images and hence diagnosis prior to reading a radiologist’s report.
Shoulder ultrasound course for clinicians and surgeons are growing in popularity around the world with increasing numbers of non-radiology staff undertaking these investigations. From personal experience I can confirm that the basic skills can be developed relatively quickly and after ten or twelve scans the operator can confidently visualise and diagnose full thickness tears of the rotator cuff tendons or the long head of biceps or large calcific deposits.
It does however take significantly more exposure to confidently diagnose partial thickness tear, microcalcification, intrasubstance or delamination tears and tendinopathy.
There is good evidence in the literature to support the use of surgeon lead USS in ‘One Stop Clinics’ to improve the patient experience and also reduce costs of an already over stretched health care system.
Who do I USS and who do I MRI??
If I have a simple question of ‘Does this patient have a full thickness tear of the rotator cuff?’ then an USS is probably my imaging modality of choice.
This will probably be used in the younger patient with a history of injury or sudden onset of symptoms that are suspicious of a full thickness cuff tear. I utilise this rationale as in this cohort of patients if a tear is confirmed I am likely to discuss the pros and cons of surgery regardless of the anatomy of the tear.
In an older patient or one with longer standing symptoms when I am suspecting a more chronic tendon pathology or the so called ‘acute on chronic’ tears the decision to offer surgery may well be less clear cut. In these patients an MRI can furnish me with further information to facilitate the decision-making process giving clues to possible chronicity of the tear such as size and shape of the tendon tear (tears often retract and increase in size over time) and evidence of fatty atrophy of the muscle belly, another sign of longer-term problems. This observation was described by Goutallier, Fuchs and JP Warner.
In these patients this added information is invaluable in making a fully informed and patient centred decision surrounding conservative or surgical intervention. Many patients with chronic or acute on chronic tendon injuries can make an excellent recovery without surgical intervention and focus centred on analgesia initially with specific shoulder physiotherapy including strengthening of residual cuff and deltoid recruitment. Some unfortunately will not make these improvements and may require surgery at a later date.
Sadly, neither an MRI nor an USS will reliably provide this information.