A mentally incapacitated 77-year-old woman detained at Rikers Island suffered two fractured arms while being thrown to the ground by a guard in a dispute over the disposal of a paper medication cup, a new federal lawsuit charges.

M.J. Norwick, who has been held awaiting trial since 2013 on attempted murder charges stemming from an assault, had just returned from a stay at Elmhurst Hospital for her heart when the incident inside the Rikers infirmary occurred, says the suit, filed on Saturday.

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The lawsuit, citing an internal corrections department investigation, alleges that guard Charlene Rosado shoved the 106-pound inmate to the ground and then claimed in a report that she fell on her own, but a doctor who witnessed it complained.

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The city is under pressure from federal authorities to make reforms at Rikers to reduce violence and brutality. A Rikers guard and a former guard were charged last week in connection with the beating death of an inmate, and another former guard is scheduled to be sentenced this week for denying medical care to an inmate who died.

A spokesman for the city correction department declined to comment on the new lawsuit in federal court in Manhattan.