No we’re not making this one up – though it’s an injury that can apply to many different sports.
It’s an injury to the ulnar collateral ligament, or UCL, of the thumb at the base. This can happen when you fall onto an outstretched hand and the thumb gets forced away from the index finger.
With any ligament injury, the treatment will depend on the severity. Assuming surgery is not required, the thumb is often splinted like this.
The splint will likely be on for somewhere between 3-6 weeks. Depending on the extent of the injury, treatment will often involve a combination of stretching/range of movement exercises in order to regain full movement in the thumb.
This should be accompanied by strengthening exercises to ensure the ligament is good and strong, as well as returning the muscles and tendons to full strength as the de-conditioning associated with prolonged rest will need to be reversed – this will also help prevent secondary injuries to these tissues.