Background: The trapeziometacarpal joint (TMCJ) is inherently unstable, relying on ligament restraint to prevent
subluxation. Subluxation of the thumb in a dorsoradial direction is often observed in clinical practice, either after acute
ligament injury or more commonly with osteoarthritis (OA). This subluxation follows loss of function of trapeziometacarpal
ligaments that stabilise this joint, resisting the deforming force of abductor pollicis longus (APL). The exact ligaments
that stabilise and prevent the thumb from the pull of APL causing dorsoradial subluxation remain unknown, although the
anterior oblique ligament (AOL) has been implicated. The aim of this study was to measure the direction of subluxation
resisted by the AOL.
Methods: In this study we used cadaveric limbs and custom made biomechanical testing to measure the influence AOL
has in stabilising the thumb against subluxation in three planes: radial, dorsal and dorsoradial. Three fresh frozen hands
were dissected to expose the TMCJ, leaving all ligaments, capsule and APL attachment in place. The force required
to create a displacement of 5mm between the first metacarpal and the trapezium in these three planes was measured
before and after AOL division.
Results: The average force to displace in the dorsoradial plane prior to division was 6.68N, and a statistically significant
reduction to 1.15N (P<0.001) was found after division of the AOL. A statistically significant increase in force (P<0.001)
from 2.89N to 4.04N was seen in the radial plane, while no change was seen dorsally (P=0.98), with average forces of
2.74N and 2.62N found pre and post division.
Conclusion: There is clinical significance in reporting quantifiable data in this field, as subluxation of the thumb is often
seen with OA. The results of our study provide support for surgical reconstruction of the AOL as the primary surgical
stabilizer against dorsoradial subluxation of the thumb.