Investigation of MRI Technology to Evaluate the Presence and Integrity of the Anterior Oblique Ligament of the Thumb
Evan D. Collins, MD

This investigation examines the reliability and reproducibility of MRI technology to evaluate the presence and integrity of the Anterior Oblique Ligament (AOL) of the trapeziometacarpal (TMC) joint of the thumb more clearly identifying area of potential degenerative conditions.

01. Materials and Methods
From the mid-forearm to the fingertips, AP, lateral and oblique X-rays of the trapeziometacarpal joint were taken from six freshly frozen cadavers and independently rated by hand surgeons experienced with the revised Eaton-Littler classification of basilar joint arthritis.

The specimens were scanned in a MRI machine, with a standard wrist coil to enhance detail. An effort was made to reproduce the image of the AOL to include its origin from the articular margins of the volar trapezium, to its insertion on the volar thumb metacarpal.

Since standard wrist imaging protocols are oriented along the longitudinal axis of the forearm and fingers, a unique technique was employed to obtain images of the obliquely oriented thumb and its ligaments.

Following dissection to expose the AOL, a sharp dissection was carried down to the flexor pollicis longus (FPL) tendon, retracting abductor pollicis muscle dorsally and flexor pollicis brevis muscle volarly to visualize the TMC joint.

A standard MRI fiducial was sewn to the proximal and distal extent of the volar side of the AOL, soft tissues were replaced and the skin closed. Specimens were rescanned, to compare pre and post-dissection ligament-labeled specimens.

02. Results
Dissecting and tagging the ligament and repeating MRI confirmed the location of the AOL and validated the imaging technique.

Using the unique imaging protocol, the ligament was successfully identified in all cases. The open dissection and ligament tagging confirmed that what was visualized was indeed the structure of interest.

03. Conclusion
Of all the joint stabilizers, the AOL is most closely correlated with degenerative arthritis - as confirmed through earlier biomechanical cadaver studies, in which the joint loading patterns were most distinctly altered after sectioning the AOL. While numerous studies support the use of MRI to evaluate the small ligaments and joints of the hand, wrist and forearm, this investigation demonstrated that with appropriate protocol, it is also feasible to guide the scanner to catch appropriate images of this essential ligament.

Special Acknowledgements: Randy Lovell, MD - Contributing Author