After Tim gets off the steamroller his arm is no longer in a brace.
A hospital can not force a patient to stay. If you want to leave you can check yourself out at anytime. The only except is if you are deemed mentally incapable of making your own decisions.
When Tim is lying on the operating room table just before he undergoes surgery, one can hear the steady beep of a heart rate monitor. However, his chest is exposed and he clearly has no electrodes attached.
On the show they call the roller a "Steamroller." This refers to a roller that is powered by a steam engine. However, steamrollers have not been used in the U.S. since the 1950s, at which time they were replaced with rollers powered by more efficient diesel engines. Despite not being actual steamrollers anymore, they are still commonly referred to as such.
When Tim shows up at the Tool Time site, he has a sling on his arm. However, when Tim is sitting in the steam roller, the sling is gone. Tim then waves his supposedly hurt shoulder around when joking about losing control of the steam roller.