Orthopaedic traumatology is one of the largest subspecialties! Long after there is a biologic solution to knee arthrosis, people will still be getting in crashes and otherwise sustaining trauma. You can check out the OTA website for more information. Trauma is great! I wonder what your experience in orthopaedics has been to date, because for many people operative fracture care is a big part of their practice even if not subspecialty trained, and fracture care is central to orthopaedic education.
So yes, you can specialize in orthopaedic trauma. If you aim to be in academics you can do fracture care exclusively, and a lot of level 1 trauma centers (where the most broken people end up) are affiliated with an academic institution. If that isn't for you, there are still tons of hospitals and hospital systems big enough that they high trauma specialists. If you are fixing the fractures, it frees up other subspecialists to keep their elective practices busy. In smaller communities, trauma folks often still do some general orthopaedics, but that doesn't necessarily mean joint replacements.
Not many orthopaedists in any subspecialty operate 5 days a week! Trauma clinic is pretty straight forward and you can see a lot of people in a day. At some trauma centers a surgeon would only have 1 day of clinic a week, and operate the rest. Trauma care can be structured a lot of different ways, so you should talk to people in the orthopaedics department at your medical school about it more. The model I saw most was 1 day clinic, 1 day guaranteed OR time, likely one day on call a week with a dedicated OR room that day, and between the other two days you'd probably operate one day and have research one day. Trauma folks work weekends more than most of orthopaedics, too, so sometime they don't work one day during the week. Another system I know of (with three trauma people) is doing one week of call, followed by one week to 'clean up' from non-urgent trauma the week before, and then one week of research. But there are all sorts of models. Some people in trauma like to develop a clinical specialty is something that isn't strictly hot trauma, like nonunions or some sort of reconstructive work, so that they eventually can take less call and still be busy.
Hope this helps!