Superior-capsular elongation and its significance in atraumatic posteroinferior multidirectional shoulder instability in magnetic resonance arthrography.
BACKGROUND
Redundancy of the capsule has been considered to be the main pathologic condition responsible for atraumatic posteroinferior multidirectional shoulder instability; however, there is a paucity of measurements providing quantitative diagnosis.


OBJECTIVE
To determine the significance of superior-capsular elongation and its relevance to atraumatic posteroinferior multidirectional shoulder instability at magnetic resonance (MR) arthrography.


METHODS
MR arthrography was performed in 21 patients with atraumatic posteroinferior multidirectional shoulder instability and 21 patients without shoulder instability. One observer made the measurements in duplicate and was blinded to the two groups. The superior-capsular measurements (linear distance and cross-sectional area) under the supraspinatus tendon, and the rotator interval were determined on MR arthrography and evaluated for each of the two groups.


RESULTS
For the superior-capsular measurements, the linear distance under the supraspinatus tendon was significantly longer in patients with atraumatic posteroinferior multidirectional shoulder instability than in control subjects (P<0.001). The cross-sectional area under the supraspinatus tendon, and the rotator interval were significantly increased in patients with atraumatic posteroinferior multidirectional shoulder instability compared to control subjects (P<0.001 and P=0.01, respectively). Linear distance greater than 1.6 mm under the supraspinatus tendon had a specificity of 95% and a sensitivity of 90% for diagnosing atraumatic posteroinferior multidirectional shoulder instability. Cross-sectional area under the supraspinatus tendon greater than 0.3 cm(2), or an area under the rotator interval greater than 1.4 cm(2) had a specificity of more than 80% and a sensitivity of 90%.


CONCLUSIONS
The superior-capsular elongation as well as its diagnostic criteria of measurements by MR arthrography revealed in the present study could serve as references for diagnosing atraumatic posteroinferior shoulder instability and offer insight into the spectrum of imaging findings corresponding to the pathologies encountered at clinical presentation.
Department of Radiology, Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan, R.O.C.
Yi-Chih
YC
Hsu
Ru-Yu
RY
Pan
Yen-Yu I
YY
Shih
Meei-Shyuan
MS
Lee
Guo-Shu
GS
Huang
D000328:Adult; D001175:Arthrography / Q000379:methods*; D003287:Contrast Media; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D017746:Joint Capsule / Q000293:injuries / Q000473:pathology*; D007593:Joint Instability / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000473:pathology*; D055815:Young Adult
D003287:Contrast Media; D019786:Gadolinium DTPA