very large bump towards the bottom of my thumb

when i bend my thumb towards the inner part of my hand i feel a lot of tight pain and a bone (or somthing big) stick out near my wrist right in line with my thumb...it is getting worse and i am losing more and more movement with my thumb. does anybody have any ideas?

thanks  

[Michael L Gross, MD]

This is basal joint arthritis of the thumb. The joint affected is the CMC (carpal metacarpal) joint formed by the first metacarpal and the triquetrum.  As CMC arthritis progresses, the joint becomes unstable and subluxes. The diagnosis is made by physical examination and xrays.  MRI is usually not necessary.
Initial treatment is usually oral NSAID's and bracing,  cortisone injections in the joint can also be effective.  In severe cases, surgery is needed and very effective.  
I would recommend evaluation by a hand surgeon.