This is relatively rare injury so not much research exists whether patients with this injury need surgery. Hope this helps surgeons or doctors make decisions about treatment.
My first injury was when I was in university during lacrosse game. A guy in the national team made a shoot and hit my thumb. I felt unusual amount of pain so took a glove off, saw my thumb was hyperextended and something comes out of my palm side of the IP joint.
It was an open dislocation where the dislocation occurs with some soft tissues coming out of the skin. The first one did not require the open reduction (surgery) as the closed reduction was successful. Although, it took 4-6weeks to get a full ROM.
The second one happened last month and again, a lacrosse ball hit my thumb. It was not a crazy fast shoot, but my thumb got dislocated with a tiny open scar. I went straight to the emergency service to get my joint back in. Three doctors tried but all attempts failed, leading me to go back to the hospital next day. Next day, doctors tried but failed again, resulting in open reduction (surgery). As a case report says , soft tissues such as the volar plate and flexor pollicis longus tendon can impede closed reduction. Doctor reckoned that some soft tissues are in the joint, requiring open reduction. I underwent surgery on the same day. I was listening to doctor’s conversation during surgery, it did not seem there is anything in the joint that impeding the closed reduction. They assumed that the osteophyte on the palmer side of the distal thumb IP may be the reason why closed reduction failed. They put K-wire in to make sure dislocation did not happen post-surgery as volar plate and collateral ligament were torn and removed it 3 weeks after surgery.
I was using a splint while I had a K-wire. I could not move IP joint but my MCP joint was stiff too though not sure why. I tried to use MCP joint as much as I could.
In order to improve ROM, active, passive, resisted movement and massage the scar tissue are the options. OT gave me active and passive exercises, yet I find resisted exercise and massage the scar more effective to improve ROM than others. It is better to do all though.
 Shah, S. R., Bindra, R., & Griffin, J. W. (2010). Irreducible Dislocation of the Thumb Interphalangeal Joint With Digital Nerve Interposition: Case Report. The Journal of Hand Surgery, 35(3), 422–424. https://doi.org/10.1016/j.jhsa.2009.11.017