Siôn is a Professor of Orthopaedic Surgery at the University of Oxford. He is also a Consultant at the Nuffield Orthopaedic Centre. 

Siôn trained in Cambridge, London and Oxford. He specialises in hip arthroscopy (keyhole surgery of the hip) and hip replacement in the more active individual. Siôn leads the Oxford Hip Preservation and Young Adult Hip Units. He leads the hip research at Oxford University, with a team dedicated to the prevention and treatment of hip osteoarthritis. Sion treats elite athletes from many sports, including rowing, soccer, cricket and tennis.  

He is also a former National Lead for the National Institute of Health Research and sits on the several other international panels. He is a member for several international specialist societies and teaches worldwide in the field of hip arthroscopy and hip replacement. 

Sion specialises in keyhole surgery of the hip and less invasive total hip replacement.