This is a post-traumatic problem, and could be a cyst or could be an inflamed and swollen bursa (bursitis) which can on occasion actually become a cyst or cyst-like. It may well respond positively to non-steroidal anti-inflammatories such as Advil or Aleve. If not, you'll need to have it examined by an orthopedist, who may be able to drain it or, if necessary, surgically repair it.
In any case, the main problem with this sort of thing is the discomfort and limited range of motion it can cause. Hopefully it will resolve on its own or with use of NSAIDs. If not, by all means make an appointment with an ortho specialist.
Best of luck to you. Please follow up here as needed.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist