Mr Bollen was a founder member of the British Orthopaedic Sports & Trauma Association and subsequently was its academic secretary and president.  He has been chairman of the Yorkshire branch of the British Association of Sports and Exercise Medicine and currently is an examiner for the Faculty of Sports & Exercise Medicine (UK).

Mr Bollen specialises in soft tissue injuries of the knee and ankle and, in particular, ligament reconstruction surgery.
Patients are referred from around the country for complex ligament problems.

Mr Bollen is a national and international speaker on knee and ankle injuries and reconstruction. He has published widely in peer reviewed journals on these subjects.

Mr Bollen has treated professional sportsmen/women since 1992 and currently treats players from all levels of the football league and rugby league.

Mr Bollen’s NHS practice is based at the Bradford Royal Infirmary, Bradford Teaching Hospitals Trust. He has been Clinical Director of this busy Orthopaedic Department for the last ten years. His NHS practice is similar to his private practice in that he sees large numbers of patients, performing ligament reconstructions and knee and ankle arthroscopies.

Mr Bollen’s private practice is based at The Yorkshire Clinic in Bingley, West Yorkshire.