Kinematic magnetic resonance imaging of the normal shoulder: assessment of the labrum and capsule.

OBJECTIVE

To examine the normal shoulder, specifically the labrum and the capsule, with kinematic magnetic resonance imaging (MRI) in asymptomatic volunteers.

SUBJECTS AND METHODS

Fourteen asymptomatic volunteers 22 to 53 years of age were studied with a 1.5-T Signa Advantage imager (GE Medical Systems, Milwaukee). Successive static gradient-echo images were obtained in the transverse plane at the mid-glenoid level as the shoulder was successively positioned from full internal to full external rotation. These images were correlated with standard transverse T1-weighted spin-echo images and gradient-echo volume images obtained in the neutral position.

RESULTS

The anterior labrum was slightly mobile during rotation in 11 subjects and changed shape from blunted or round to triangular in 8 subjects. A wide variation in morphologic features of the anterior labrum was observed. During rotation, a slight increase in signal intensity was noted in the anterior labrum of five of the subjects. The posterior labrum maintained a relatively stable triangular shape in most cases. Dynamic study allowed assessment of the anterior capsule insertion in all cases. Three subjects had type 1 and 11 had type 2 capsular insertion. No cases of type 3 insertion were identified.

CONCLUSIONS

Variation in the shape and signal intensity of the anterior labrum observed in normal asymptomatic volunteers during transverse kinematic examination of the shoulder should be taken into account during evaluation of shoulder instability, since this variation may be clinically insignificant. Kinematic MRI allows easy evaluation of the anterior capsule.