- Discussion:
    - base of thumb metacarpal articulates w/ saddle shaped trapezium;
    - saddle shaped articulation provides inherent stability;
    - radial lateral ligament, which is covered by APL tendon, inserts into the thumb metacarpal;
    - deep anterior oblique ligament (palmar beak ligament);
           - originates on the tuberosity of the trapezium & insertes on ulnar and volar edge of metacarpal base;
           - anterior oblique ligament provides mobility but prevents dislocation;
           - ligament maintains volar stability of saddle joint;
           - anchors volar lip of first metacarpal to trapezium and second metacarpal;
           - maximum tension occurs in this ligament with the metacarpal in flexion, abduction, and supination;
           - traditionally, it is thought that insufficiency of this ligament leads to basal joint arthritis;
           - ligament may help function as a pivot for the first metacarpal during palmar abduction to allow pronation;
    - dorsal radial capsular ligament
           - is covered by EPB & EPL;
           - some consider this ligament to be more important than the volar ligament;
           - sectioning of this ligament produces dorsoradial subluxation of the thumb metacarpal;
    - ulnar ligament;
           - limits range of abduction & extension of thumb;
           - if this ligament is torn unopposed pull of APL & EPL & EPB muscles dislocates metacarpal shaft radially and proximally

Osteoligamentous guidance of the movements of the human thumb.

Ligamentous stability of the base of the thumb.

An anatomic study of the stabilizing ligaments of the trapezium and trapeziometacarpal joint.