ACR MLG SUDDEN STOP DURING PWR BACK CAUSES PAX TO COMPLAIN OF NECK INJURY.

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CAPT INITIATED PWR BACK AT AUSTIN GATE. ACFT WAS IN A HOLE (RUT IN RAMP); AS PWR WAS APPLIED; ACFT DID NOT MOVE; AS MORE PWR WAS APPLIED ACFT SUDDENLY MOVED FORWARD RAPIDLY TOWARD TERMINAL. THE CAPT STARTED TO APPLY BRAKES; BUT I WAS ON THE BRAKES TOO; AS I COULD NOT TELL IF THE CAPT HAD RECOGNIZED THE PROBLEM. WITH BOTH OF US ON THE BRAKES; THE ACFT STOPPED VERY RAPIDLY. REVERSE THRUST WAS THEN APPLIED AND REMAINDER OF PWR BACK WAS NORMAL. WE WERE INFORMED BY FLT ATTENDANTS THAT A PAX; WHO HAD RECENT NECK PROBLEMS; WAS COMPLAINING OF NECK PAINS. HE IS NOT ATTEMPTING TO HAVE MY AIRLINE PAY FOR MEDICAL TREATMENT AND MAY SUE. HE WAS THE ONLY COMPLAINT FROM ANY PAX. I HAVE NEVER TOUCHED THE BRAKES DURING A PWR BACK; AS THEY 'BELONG' TO THE CAPT. BUT I HAD A SPLIT SECOND TO EVALUATE THE PROBLEM AND DETERMINE IF THE CAPT HAD TAKEN THE CORRECT ACTION. I FELT I NEEDED TO APPLY THE BRAKES TO STOP THE ACFT. IT IS A DECISION I STAND BY AND WOULD DO AGAIN. THIS PROBLEM WAS CAUSED BY AN UNEVEN RAMP SURFACE. I FEEL I AM A VICTIM OF POOR ARPT UPKEEP; AND LIMITED RAMP MANEUVER AREA. MANY ARPT RAMP AREAS ARE UNEVEN AND POORLY MAINTAINED BECAUSE THEY ARE 'JUST RAMPS' AND NOT RWYS.