Thumb MCP joint lateral stability test

Test Procedure:
- Stabilize the thumb metacarpal with one hand, and with the other hand grasp the thumb proximal phalanx. With the MP joint in 0° extension, gently push the proximal phalanx in an ulnar direction and then a radial direction. Repeat the test with the MP joint in 30° flexion.
Positive results:
+ Passive lateral deviation greater than 35 degrees
+ Passive lateral deviation 15 degrees more than the uninjured side
+ Also, pain with this test and point tenderness at the collateral ligament indicates at least mild sprain
Negative Results:
- No excessive deviation
Implications of positive test result:
- Collateral ligament rupture (partial or complete)

[@Prvs39]

Hello, I am unable to bend both my thumbs at the MP joint. Its by birth and my father and my son has the same problem. Seems like this is a deformity and genetically transmitted. Could you please let me know what is this deformity called. We dont have any pain in any of the thumb.