Shoulder: labrum and bicipital tendon.

Shoulder instability can be due to a single, acute traumatic event, generalized joint laxity, or repeated episodes of microtrauma. The later occurs in the throwing athlete. The most common lesion involving the labrum is the anterior inferior labral tear, associated with capsuloperiosteal stripping (classic Bankart lesion). A number of variants of the Bankart lesion have been described recently and include the ALPSA lesion, SLAP lesion, and HAGHL lesion, among others. Lesions of the long head of the biceps tendon can be seen in isolation (tears, tendinosis, dislocation) or in association with rotator cuff and labral lesions. Conventional MR and MR arthrography have been extensively used for the preoperative diagnosis of these lesions, with reportedly good accuracy. An understanding of the normal anatomy and biomechanics of the shoulder joint is essential for proper interpretation of the MRI manifestations of these conditions.

Continuous depinning transition with an unusual hysteresis effect.

We identify a strange hysteresis which occurs in models of the depinning transition with both elastic and transient overshoot stresses. This hysteresis occurs generically despite the fact that the phase transition is still second order. We calculate the size of the hysteresis gap exactly in a large class of models. Because it is caused by irrelevant perturbations, the hysteresis does not show up in the field theory of the continuum limit. But since it is a real phenomenon it may be a cause for the hysteresis observed in natural depinning. We therefore discuss its experimental and numerical signatures which include microscopic nucleation.

The distal semimembranosus complex: normal MR anatomy, variants, biomechanics and pathology.

OBJECTIVE: To describe the normal MR anatomy and variations of the distal semimembranosus tendinous arms and the posterior oblique ligament as seen in the three orthogonal planes, to review the biomechanics of this complex and to illustrate pathologic examples. RESULTS AND CONCLUSION: The distal semimembranosus tendon divides into five tendinous arms named the anterior, direct, capsular, inferior and the oblique popliteal ligament. These arms intertwine with the branches of the posterior oblique ligament in the posterior medial aspect of the knee, providing stability. This tendon-ligamentous complex also acts synergistically with the popliteus muscle and actively pulls the posterior horn of the medial meniscus during knee flexion. Pathologic conditions involving this complex include complete and partial tears, insertional tendinosis, avulsion fractures and bursitis.