Noncontrast Magnetic Resonance Imaging of Superior Labral Lesions
August 1, 1999 4 minutes read
Noncontrast Magnetic Resonance Imaging of Superior Labral Lesions
Abstract & Commentary
Synopsis: The use of high-resolution, noncontrast MRI can accurately diagnose superior labral lesions and aid in surgical management.
Source: Connell DA, et al. Noncontrast magnetic resonance imaging of superior labral lesions. Am J Sports Med 1999; 27:208-213.
Connell and colleagues note that previous studies of noncontrast magnetic resonance imaging (MRI) of the labrum have yielded limited specific results. They have chosen from a large database of more than 2500 patients, and they prospectively were able to identify 104 patients with superior labral lesions who eventually went on to have arthroscopic surgery. The MRI technique was specific in that Connell et al used the phased array surface coil design that increased the signal:noise ratio. The matrix or pixel 512 ´ 256 or 384 pixels yields a smaller pixel size, which translates into superior spatial resolution, thereby enhancing a subtle labral fraying and detachment. The fast spin echo imaging technique decreases imaging time and is invaluable in the postoperative setting because of occasional metallic artifacts.
MRI was used to assess and identify a variety of SLAP lesions, including fraying, flap tears, bucket-handle tears, or displaced flap tears of fibrocartilage. During this assessment they also made an effort to evaluate the biceps tendon. SLAP lesions were categorized according to Snyder’s classification and then correlated with the MRIs. One hundred of the 104 tears suspected on the images were confirmed at the time of surgery. There were four false positives and two false negatives. Using arthroscopic surgery as the standard, MRI had a sensitivity of 98%, a specificity of 89%, and an accuracy of 95% for detection of superior labral lesions. Connell et al’s conclusion was that the use of high-resolution, noncontrast MRI can accurately diagnose superior labral lesions and aid in surgical management.
Comment by James P. Tasto, MD
Snyder’s classification has been used throughout the literature to identify four types of lesions that occur in the superior labrum. This is in the labral tissue that is located from 9 o’clock to 3 o’clock on the face of the glenoid.1 It is important to understand the various types of SLAP lesions that are encountered. Type I merely reflects fraying of the labrum, as one would see in a degenerative meniscal tear. Type II is tearing of the labral tissue and the biceps off the superior glenoid labrum. Type III is a bucket-handle displacement with an intact biceps anchor, again similar to a bucket-handle tear of the meniscus. Type IV is a combination of the Type II avulsion off the glenoid, but also a partial disruption of the biceps tendon. Not all SLAP lesions fit comfortably into this classification, as there are many variations.2
One must remember that there is a significant histological, as well as biomechanical, difference between the inferior labrum and superior labrum.3 The superior labrum is rather loosely attached, much more mobile, and appears as more of a meniscal structure. The inferior labrum is attached much more rigidly and has a much better blood supply than the superior labrum. It has been postulated that this may be one of the reasons that there is a much higher degree of degenerative changes in the superior labrum than in the inferior labrum and that it may detach more easily with activity. There also is a correlation between bicipital labral complex disruptions in the throwing athlete and microinstability. The relationship between these two entities has yet to be determined. In some cases, repair of bicipital labral SLAP II lesions has seemed to alleviate microinstability. Other authors have suggested that repair of the SLAP lesion along with some type of thermal modification of the collagen or plication of the capsular structures is necessary. There are not enough long-term data on this correlation to draw any significant conclusions. One must remember that the incidence of SLAP lesions as reported by Snyder was only 3.9%, and Connell et al have had a rather significant number of SLAP lesions in their series. They did draw upon seven different surgeons to gain significant numbers, and they do have a rather skewed population of young athletes. With this in mind, to make a diagnosis of the SLAP lesion in the general population with shoulder pain, one should keep in mind that this is not a particularly common diagnosis. It is also encouraging to note that if we use high-resolution MRI, the ability to visualize tears is greatly enhanced by this new technology and, therefore, does not require gadolinium-enhanced versions, which not only can distort the intra-articular capsular structures but also are more invasive.
References
1. Snyder SJ, et al. SLAP lesions of the shoulder. Arthroscopy 1990;6:274-279.
2. Maffet MW, et al. Superior labrum-biceps tendon complex lesions of the shoulder. Am J Sports Med 1995; 23:93-98.
3. Cooper DE, et al. Anatomy, histology, and vascularity of the glenoid labrum: An anatomical study. J Bone Joint Surg Am 1992;74:46-52.
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