MRA vs. Arthroscopy
MR Arthrography and arthroscopy for shoulder instability.
Review of the literature
D Stone and L Funk, 2005
Multiple different structural lesions have been associated with glenohumeral instability, ranging from the Bankart lesion to rotator cuff damage. The current gold standard diagnostic investigation for such lesions is arthroscopy; however this is an invasive procedure. MR Arthrography (MRA) is routinely used as a diagnostic investigation for instability, but is it as sensitive and specific as arthroscopy for the various lesions associated with shoulder instability?
In this review we investigate the literature with regard to diagnostic arthroscopy and MRA in shoulder instability, discussing the pros and cons of each.
Arthroscopy is the only investigation that allows the orthopaedic surgeon direct visualisation of the shoulder joint. It is considered by many as the best technique for diagnosing shoulder disorders and subsequently creating a treatment plan . It allows the surgeon to identify all the structures of the glenohumeral joint such as the labrum, glenohumeral ligaments, humeral head, joint capsule and undersurface of the rotator cuff,. With its 20-power magnification it permits detection of pathological features that may not be seen with the naked eye.
A good example is SLAP lesions. Arthroscopy allows determination of the grade of the lesion, its stability and whether or not the labrum can be displaced to the glenohumeral joint,. Arthroscopy is said to be the best means by which SLAP lesion may be diagnosed.
Despite being the current favoured investigation for the unstable shoulder, arthroscopy does have its disadvantages. The flaccidity of the capsule can be difficult to determine due to the process of the arthroscopic examination itself altering the laxity of the joint. The procedure is invasive and thus carries small risks of complications such as infection, damage to adjacent structures (e.g. musculocutaneous nerve or articular cartilage) and fluid extravasation. In addition complications may also arise from the anaesthetic.
Magnetic Resonance Arthrography
Magnetic resonance imaging (MRI) provides an effective investigation for assessing the shoulder joint, with excellent resolution, soft tissue contrast and the ability to take images in multiple planes . However magnetic resonance arthrography (MRA) goes a stage further. By utilising the benefits of both distention of the joint (significantly improving the ability to scrutinize the ligaments) and contrast enhancement (increasing the capacity to observe intraarticular anatomy and pathology)  MRA provides superior diagnostic imaging, and is the radiographic tool of choice for diagnosing glenohumeral instability .
Preoperatively, MRA can be beneficial to clarify the intraarticular damage present. MRA is known to better depict intraarticular anatomy than MRI . Normal variants can make the differentiation from pathological lesions by MRA difficult.[16, 21] and interpretation does require an experienced clinician. MRA aids the identification and differentiation of intraarticular pathologies such as the ALPSA lesion from a Bankart lesion, which would necessitate a different approach to the surgical repair .
MRA also has its uses for the observation of extra-articular anatomy , which an arthroscope cannot do. MRA has been shown to be very accurate in its detection of rotator cuff pathology. One study found that when compared to arthroscopic examination, MRA was 100% sensitive for the detection of rotator cuff pathology . This was supported by a further two pieces of research which both stated that for identifying rotator cuff partial undersurface tears, MRA was the most sensitive and specific investigation [14, 20].
It is recognized that MRA is an invaluable tool, but is it as good as an arthroscopy? In order to use MRA instead of arthroscopy, we must be confident that it is an effective tool for identifying all the relevant lesions within the shoulder joint that relate to instability. The ability of MRA to identify rotator cuff pathology has already been discussed above. MRA has been shown to be equally sensitive in identifying bony pathology such as Hill Sach’s lesions (this is a valuable finding as plain films often miss small Hill Sachs lesions) and also has 100% specificity with a 95% sensitivity for recognizing Bankart lesions .
For labral abnormalities, MRA had sensitivities and specificities of 91% and 93% respectively in one study , and 92% for both sensitivity and specificity in another , a detection rate of 96% in a third . This accuracy diminishes when the identification of posterior labral tears were examined , with only 50% of tears being identified . MRA also appears to perform well in the recognition of SLAP lesions with a sensitivity, specificity and accuracy of 89%, 91% and 90% respectively . The incidence of such lesions have seemed to increase with the use of MRA . MRA is often not able to grade of the SLAP lesion. Conflicting research exists with two studies claiming that MRA is an accurate tool for assessing SLAP tears [10, 15], one of which supporting their opinion with a 76% success rate in grading the lesion . However, in direct contrast is another piece of research that claims MRA grading of SLAP tears is inaccurate . Having reviewed the available literature, there appears to be no apparent consensus of opinion, so there is clearly the requirement for further research in this area.
MRA appears to be less effective than arthroscopy with regard to capsular laxity, glenohumeral ligaments and identification of loose bodies. Despite one study reporting a sensitivity of 90% for the identification of lax capsules by arthrography , the majority of opinion is that magnetic resonance arthrography is inadequate in the identification of laxity, even on retrospective analysis [13, 14]. Due to the small study size of the former report, and the bulk of opinion supporting the latter, the current opinion is that there is not enough evidence to support the ability of MRA to adequately evaluate capsuloligamentous laxity. MRA is also less effective at detecting glenohumeral ligament pathology, particularly when referring to the middle glenohumeral ligament, where in one report, 29% of tears were false-positive and 20% were false-negative findings compared to arthroscopic findings . Interestingly, another study found that if inferior labral-ligamentous complex damage was detected on MRA, shoulder instability could be predicted with a sensitivity of 76% and specificity of 98% . Finally, one study noted that MRA had missed loose bodies in three separate patients that were found on arthroscopy .
MRA has a distinct role in certain cases, such as patients who are likely to have non-surgical treatment, and provides information on areas not seen at arthroscopy, like the internal structure of the rotator cuff. Conservative rehabilitation such as physiotherapy is highly effective in many individuals . Such people who do not require surgical repair benefit from not having to undergo the risks of general anesthesia and the recovery from an arthroscopy.
Therefore both MRA and arthroscopy have complimentary roles in the diagnosis of shoulder pathology. The skill is knowing which investigations to use and when.
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