Last Saturday I reviewed a terrific performance of George Gershwin's Piano Concerto, played by the RSNO with music director Peter Oundjian conducting and Canadian pianist Jon Kimura Parker as soloist.

There were many strong features to the performance, including a wonderfully loose feel to its structure and attitude, and a full-on, flamboyant approach by Parker in his delivery of the piece. It bristled with life, energy and drive, and the music bounded off the page.

But there was more to it than that. The concerto isn't played that often: the Rhapsody In Blue is a more popular selection, and tends to be first choice among pianists, conductors and orchestras when some Gershwin is required. You can see why: it wears no classical structure as its garb; it's directly out of the jazz tradition. Indeed it was written for a jazz outfit and premiered in 1924 by the Paul Whiteman Jazz Band. The Rhapsody In Blue works extremely well with a symphony orchestra in accompaniment, though there has been much interest in recent decades in getting it back to its original state by using smaller forces and emphasising more the jazz feel of the music.

Maybe the Piano Concerto has never quite achieved the status of the Rhapsody In Blue because of its hybrid nature. It's a concerto, and the word itself has all those classical connotations. It has the traditional classical three-movement structure. Gershwin even headed up the movements with classical Italian tempo markings: Allegro, Adagio and Allegro agitato. Gershwin did pull back a bit from the classical descriptions by saying: "the first movement is in sonata form... but!".

That qualification didn't really help the piece. The Piano Concerto has grown up with its full classical livery and is played less often than it deserves. Possibly the fact that it has to be played by a classical pianist with a spectacular technique has held it back. What has certainly held it back is the fact that so many pianists, conductors and orchestras that do give it an airing play it as an absolutely straight, classical piano concerto.

But it isn't. Within that strict, formal, three-movement structure you can hear the racy, bracing jazz; you can feel and hear the mournful blues with a lovely touch of sleaze as the music gets dirty in the second movement. The problem is that you don't often experience that in "classical" performances. All these elements from jazz, the blues and Tin Pan Alley are there to be found within the belly of the concerto. But they have to be brought out by the musical forces – all of them – who play the piece.

And it is precisely that which made the RSNO, Oundjian and Kimura Parker performance last Saturday so memorable and thrilling. It didn't have the strict feel of the concerto as a format: it actually had the feel of a jam session, tearing itself away from the structural and linguistic boundaries of the concerto form.

What do I mean by that? Kimura Parker's playing, for a start, had a buccaneering quality to it, which gave the structure a thorough shake up. But it went right through the band. In my review I drew attention to the trumpet playing. Last Saturday the RSNO brought in Hedley Benson as guest principal trumpeter, a big player with a big sound, well-known on the circuit. Presumably with the blessing and encouragement of conductor Oundjian, Benson took the brilliant music for the lead trumpet right to the edge, outstandingly in the slow movement where he filled his trumpet with the authentic sound of the blues, just a hair's breadth short of bendy-note improvising, but a light year away from the sound and language of classical trumpeting. That did it and, along with all the other factors, Gershwin's Piano Concerto was liberated, as I have never heard it before.

Gershwin begged Maurice Ravel, who was touring the States, to give him composition lessons. Ravel declined, telling the American that he would only end up writing poor Ravel instead of good Gershwin. Ravel was right.