Fractures of the elbow can be very challenging to treat. Sometimes there's nothing to do but wait until the bone knits itself together. This is especially true with comminuted fractures such as you described. The bone is broken into many fragments. If they dont'shift out of place, the body will fill in with new bone and heal itself.
There are elbow joint replacements. There are different types depending on the problem. A displaced comminuted fracture is a good candidate for joint replacement when stable internal fixation with plates, wires, and/or screws isn't possible. Elbow joint replacement is strongly considered when the ligaments around the joint have also been torn.
There are two bones in the forearm that form the bottom half of the elbow: the ulna and the radius. Sometimes just the top of the radius bone called the radial head is fractured. There are implants that just replace the radial head.
In some cases, the radial head is just removed altogether. This procedure should not be done if the soft tissues are torn. There are problems with each treatment choice for elbow fractures. Pain, joint instability, elbow stiffness, and decreased strength are possible. Long-term complications can include deformity and arthritis.
It's likely the surgeon has suggested the best course of action given the type of fracture. More information would be needed to understand what is going on and what to expect in the next few weeks.