US police mock dementia sufferer during arrest

US police officers are seen mocking a 73-year-old dementia sufferer as they watch video of her shoulder going "pop" during her forcible arrest, according to footage released by her lawyer.

Karen Garner was detained on 26 June last year after she walked out of a Walmart in the state of Colorado without paying for $13 of items.

Her elbow was fractured and shoulder dislocated, says her attorney.

An investigation has been launched into the Loveland Police Department arrest.

In the footage released on Monday from the booking area of the police station on the day of the arrest, officers are seen fist-bumping one another as they review body camera video of the incident.

Video from inside Ms Garner's nearby holding cell shows the frail-looking grandmother slumped handcuffed to a bench while the officers joke about the incident, says her lawyer.

"Ready for the pop? Hear the pop?" one of the officers says at one point, referring to Ms Garner's shoulder.

As they continue to watch the footage, the same officer says: "I love it."