A Captain stopped abruptly because of LGA ground traffic and as a result a Flight Attendant's back hit a cabin door injuring him so that he was removed for medical care at the next stop.

Narrative

As we were about to turn left from Lima to Bravo the First Officer informed me there was an aircraft coming at us already on Bravo. I quickly applied brakes to hold short of Bravo as the other aircraft came into view. We heard noise in the galley that sounded like the closet door coming open. Ground then thanked us for stopping and giving way to the MD80 which was taxiing in front of us. We were then told to taxi Bravo Golf hold short Runway 22. We continued the taxi and departure as normal. After climbing through 10;000 FT and giving 2 chimes the Flight Attendant called and informed the First Officer he had been slammed into the cockpit door and he hurt his back. The First Officer relayed this to me and I called the Flight Attendant back on my own to get a further assessment of the situation. He told me what happened and I asked if we needed to return to LGA and he said no and that he'd see how he feels when we get to our destination. Upon landing the Flight Attendant informed us that the pain had just gradually gotten worse during flight and that he was no longer able to continue. After the passengers deplaned he called his Supervisor and I called the Dispatch Supervisor to advise of the situation. We had the gate agent radio for paramedics to come to the aircraft so that the Flight Attendant could be taken to the hospital to make sure no serious injuries had occurred. The station upon arrival was unable to provide anyone to accompany the Flight Attendant to the hospital and I was told to ferry the airplane back to LGA where we would pick up a new Flight Attendant and finish the trip. This really bothered me that no one was sent to the hospital with the Flight Attendant and I did not wish to have him left alone without any knowledge of the extent of his injuries. This weighed heavily on my mind during the remaining legs and very easily could have caused a distraction which would have caused more incidents further down line.