On August 31, 1997, at 1740 mountain daylight time, a Beech E-90, N16NM, operating as a lifeguard flight from Santa Rosa, New Mexico, to Albuquerque, New Mexico, collapsed the right main landing gear during landing roll at Albuquerque. The airline transport pilot, 2 flight nurses, and the patient were not injured and the aircraft sustained substantial damage. Visual meteorological conditions prevailed and an IFR flight plan was filed for this Title 14 CFR Part 135 medical flight which departed Santa Rosa, New Mexico, at 1634. According to the pilot, when the landing gear was raised after departure, he heard a grinding noise emitting from under the cabin floor and noted that the "gear in transit" light in the landing gear handle remained illuminated. The pilot said he pulled the landing gear motor circuit breaker and the noise stopped. He then attempted to recycle the gear with negative results. When the landing gear was lowered on arrival at Albuquerque, an unsafe right main landing gear indication was present. The pilot secured the right engine, feathered the right propeller, and made a precautionary landing. During landing roll, the right main landing gear collapsed. As a result of the right main landing gear collapse, the right wing sustained buckling damage. Examination of the right main landing gear by a FAA airworthiness inspector provided evidence of a failure of the torque tube assembly (part number 50-810240). No other deficiencies were noted during the examination. The part had a total of 5,616 cycles since factory overhaul and had been in service approximately 3.5 years. The part is required to be overhauled at 7,500 cycles or 5 years whichever occurs first. The affected part was removed and sent to the Board's Materials Laboratory. According to the laboratory analysis, the torque tube failed in fatigue. The origin of the fatigue could not be determined. The aircraft has since been repaired and returned to service with no further difficulties noted.