One doesn’t wish to make assumptions, but if you hire a pair of identical twin sisters to write and direct a horror movie, you probably aren’t going to take delivery of a standard-issue, Odeon-ready slasher flick. So it is with Canada’s Jen and Sylvia Soska, who’ve followed up their direct-to-DVD debut Dead Hooker in a Trunk by doing something a little more leftfield with sharp blades.

American Mary comes on from the outset like a latter-day Horatio Alger story, told through filed teeth, with a forked tongue. Heroine Mary Mason (Katherine Isabelle) is a financially struggling surgical student who learns there are big bucks to be made upon straying into the world of body modification: the kind of non-essential, elective cosmetic surgery that has turned men into tigers and given Channel Five’s primetime schedule a whole new freakshow strand.

An opening shot of a scalpel slicing through turkey flesh serves as an early warning for the squeamish, yet for the longest time, the real horror here comes away from Mary’s makeshift operating tables, located instead in the cold, dead eyes of her (almost exclusively male) surgical colleagues, presented – with a certain sophomoric bluntness – as date-raping hacks who like to exercise a warped power over the prostrate human form.

Beyond them, however, the Soskas embrace the body-mod community enthusiastically, welcoming on women who’ve attempted to turn themselves into real-life Barbie dolls or Betty Boops, and men who’ve had painfully elaborate things done to their genitalia. They give themselves a funny walk-on role, sporting thick Slavic accents and elaborate, stitched-in human corsetry, immediately going further than Hitchcock ever did in his directorial cameos.

Theirs is a radical sensibility, using genre horror as a framework to argue in favour of surgical modification as a way of regaining control over the body: no judgement is permitted of Mary’s patients, and titillation is kept to a minimum. Yet for all American Mary’s better instincts and ideas, it proves fatally messy in its construction, the envelope-pushing coming at the expense of any clear sense of narrative progression: scenes and subplots have the feel of having been sewn together entirely arbitrarily.

The Soskas have an asset in the still underemployed Isabelle – the feisty heroine of the Ginger Snaps franchise – whose smarts and timing carry the film through some of its rougher stretches, yet the second half’s freefloating physical and psychological tortures come to seem as wearying as anything in Les Mis.

Its unusual shape may be deliberate, how American Mary seeks to marry content with form: like its characters, it doesn’t easily fit in. More than the bloodletting, though, it may also be the one element that turns off those who most need to see it.

American Mary opens in selected cinemas from Friday, ahead of its DVD release on January 21.

American Mary UK Trailer