Yes, a subluxation of the finger should be grounds for termination of a typing job, regardless of the duration of the injury, because a person who wants a job should still have to perform the basic functions of the job. If the person cannot type any more for whatever reason, the employer should be able to hire someone who can.
As with any type of condition or injury, subluxation of the finger can be from a variety of causes and the duration of the injury can vary significantly. Whether a person should be terminated from their typing job because of subluxation of the finger should be based upon the person's prognosis and expected healing time, not on the diagnosis itself.
I do not believe that subluxation of the finger should automatically be grounds for termination from a typing job. I think that an individual should get a reasonable period of medical leave. If after the medical leave is over the individual can still not perform well enough to be proficient in the job, then it may unfortunately be grounds for termination.
When one of your hirees goes down with an injury the best thing to do is find a replacement until they get back. It lets them keep their job and at the same time you potentially find someone else to hire and bring into the fold. Termination would be very draconian.
I disagree that subluxation should be cause for termination. I believe that a wound like that is likely to heal over time, and there are ways to type without use of all fingers. Yes, effeciency may be impacted, but it is terribly unfair and immoral to fire someone because they're slightly less effecient than before.