[Magnetic resonance of the elbow: technique optimization and definitions of normal anatomical features and their variations].

INTRODUCTION

MRI is a very accurate technique to study the elbow joint, tendon, ligament and chondral structures. In the last years elbow disorders were described by several MR investigators, while we studied MR capabilities in depicting normal elbow anatomy. This investigation might permit the correct differentiation of normal from abnormal MR patterns.

MATERIAL AND METHODS

Eleven healthy volunteers (6 men and 5 women, mean age: 27.5 years) were examined. All studies were performed on a 1.5 T imager (Magnetom SP 4000) with two types of receiver: the knee coil was used in 7 volunteers examined in the prone position, with the arm above their head, the elbow extended and the forearm supine and the shoulder coil was used in 4 volunteers examined in the prone position, with the arm above their head, the elbow flexed and the forearm prone. We acquired T1-weighted SE sequences (TR/TE = 690/15 ms, FA 90 degrees, MA 256 x 512, NEX 2,20 3-mm sections with .3-mm interslice gap, FOV 20-22 cm) on the axial, coronal and sagittal planes and T2-weighted GE sequences (TR/TE = 450/10 ms, MA 256 x 256, 3 NEX, 18 4-mm sections with .4-mm interslice gap, FOV 13-18 cm) on the coronal plane. Two MR-expert radiologists studied the images and identified the main anatomical structures of the elbow and 12 smaller reference elements (2 anatomical variants, 4 ligaments, 3 nerves and 3 arteries) describing their MR appearance and pointing out the most effective planes for their representation. Finally, the image quality of the knee coil was compared with that of the shoulder coil.

RESULTS

All bones were clearly depicted on the coronal and axial planes, while the semilunar groove and its anatomical variants were best seen on the sagittal plane. The joint cartilage was best depicted on the coronal plane with T2-weighted GE sequences. Collateral ligaments were best seen with the elbow extended and the forearm supine (knee coil), on coronal T1-weighted SE images, where the radial and ulnar collateral ligaments were visible in 71.4% and 85.7% of the subjects, respectively. Annular ligaments, muscles and tendons were best demonstrated on the axial plane with the elbow extended and the forearm supine (knee coil), while the triceps tendon was best recognized on the sagittal plane with the elbow flexed and the forearm prone (shoulder coil). Vessels and nerves were also best seen on the axial plane with the elbow extended and the forearm supine; in particular, the median nerve was visible in 71.4% of the subjects.

DISCUSSION AND CONCLUSION

MRI is very effective in representing elbow anatomical structures. Its accuracy depends on elbow (flexed or extended) and forearm (prone or supine) position. The coronal images with the elbow extended and the forearm supine (knee coil) are the most effective to show the ligaments and the joint surfaces between the radial head and the coronoid process of ulna with the capitellum and trochlea of distal humerus, while the axial images best depicted the muscles, vessels and nerves. The coronal and axial planes, with the elbow flexed and the forearm prone (shoulder coil) are poorly effective for anatomical detailing, even though this position is more comfortable for the patient, while the sagittal plane is best suited to depict the triceps tendon. This position may be used when the elbow cannot be fully extended or when the triceps tendon is studied.