Music review: Rihanna's X-rated Millennium Stadium show fails to hit the thigh notes Massive stadium shows by massive stadium-filling pop stars tend to come with a concept. When fans are paying upwards of £60 a ticket, it pays to put in some effort and go all out on spectacle. Beyoncé, Lady Gaga and Madonna festoon their shows with fireworks, crazy hydraulics, "meaningful" am-dram narratives and a vast supporting cast of choirs, dancers and circus performers. Rihanna, who has had more No 1 singles than Beyoncé and Gaga combined, does none of this. Rihanna's concept is her vagina. Given that the mega-selling Barbadian pop star spends a large proportion of her leisure time tweeting close-ups of her arse cheeks to her 30 million followers, perhaps we shouldn't be surprised that her crotch gets top billing here. She strokes it, she thrusts it, she jiggles it, she spanks it and then she strokes it some more. The Diamonds tour is essentially one long celebration of Rihanna's lady-parts. Rumour has it that, at the end of this tour, her vagina will launch a solo career. It would be churlish at this stage not to wish it well. And the music? Seven albums in seven years has ensured that a Rihanna set isn't short of hits, even if some of them are lost in the sticky sludge of trashy Euro-techno/R&B fusion. Her set is divided into five acts, broken up with costume changes and apparently reflecting the various facets of her career (who knew?). It opens in muted fashion with the singer kneeling in a black cape, studded thigh-high boots and hotpants in front of a female statue on a video screen while singing "Mother Mary." It's a rare moment of calm in the relentless and ultimately wearying bump "n" grind- fest to come, which reaches its apogee in "Rude Boy" ("Come here rude boy, is you big enough?") and "Jump" ("Ride it my pony/My saddle is waitin"). Throughout all this Rihanna's face remains impassive and inscrutable. There are moments, however, when she lets the sex-bomb mask slip. For the stomping, Nineties-style raveathon "We Found Love" she emerges in a sequin-encrusted, dollar bill-smothered puffa jacket and matching trainers that EastEnders" Bianca Jackson would deem too tacky, punching the air and bouncing into the crowd to commune with fans. It's here that the show finally comes alive. Rihanna breaks into a smile and her nether regions take a well-earned break. Touring to 16th July