Has anyone undergone a hemiarthroplasty?

Yes: Many patients have shoulder hemiarthroplasty surgery, where the ball of the shoulder is replaced, and socket (glenoid) is left alone. Hemiarthroplasty of the hip is performed for hip fractures, and sometimes, a partial knee replacement aka a unicondylar knee arthroplasty is called a knee hemiarthroplasty. These procedures are generally successful at alleviating pain. See your orthopedist for specifics.