The Stabilising Effect of the Anterior Oblique Ligament to Prevent Directional Subluxation at the Trapeziometacarpal Joint of the Thumb: A Biomechanical Cadaveric Study

Background: The trapeziometacarpal joint (TMCJ) is inherently unstable, relying on ligament restraint to preventsubluxation. Subluxation of the thumb in a dorsoradial direction is often observed in clinical practice, either after acuteligament injury or more commonly with osteoarthritis (OA). This subluxation follows loss of function of trapeziometacarpalligaments that stabilise this joint, resisting the deforming force of abductor pollicis longus (APL). The exact ligamentsthat stabilise and prevent the thumb from the pull of APL causing dorsoradial subluxation remain unknown, although theanterior oblique ligament (AOL) has been implicated. The aim of this study was to measure the direction of subluxationresisted by the AOL.Methods: In this study we used cadaveric limbs and custom made biomechanical testing to measure the influence AOLhas in stabilising the thumb against subluxation in three planes: radial, dorsal and dorsoradial. Three fresh frozen handswere dissected to expose the TMCJ, leaving all ligaments, capsule and APL attachment in place. The force requiredto create a displacement of 5mm between the first metacarpal and the trapezium in these three planes was measuredbefore and after AOL division.Results: The average force to displace in the dorsoradial plane prior to division was 6.68N, and a statistically significantreduction to 1.15N (P