Gillies had originally considered specialising in public health but chose instead a career in the developing surgical speciality of orthopaedics. He trained under
Sir Robert Jones, one of the leaders in this new speciality. Initially he worked under Jones as assistant orthopaedic surgeon at the Shropshire Orthopaedic Hospital,
Oswestry, and at the
Royal Southern Hospital, Liverpool. In 1927 he gained further surgical experience at the
Mayo Clinic in Rochester, Minnesota with
William Mayo and the following year was appointed orthopaedic surgeon at the Lockwood Clinic in Toronto. When he returned to New Zealand in 1929, he was appointed orthopaedic surgeon at
Wellington Hospital. He was an enthusiastic supporter of the founding of the
Royal Australasian College of Surgeons in 1927 and became a fellow of the College in 1932. Gillies returned to Liverpool in 1936 to take the degree of
Master of Surgery in orthopaedics (MCh Orth) from the
University of Liverpool. He returned again to the UK in 1940, acting as resident commissioner for the
British Red Cross Society and the
Order of St John of Jerusalem. He became patron of the New Zealand Physical Education Society, which became Physical Education New Zealand (PENZ). In 1953, he was awarded the
Queen Elizabeth II Coronation Medal. Gillies was appointed a
Knight Bachelor, for services to orthopaedic surgery, in the
1959 Queen's Birthday Honours. His name is commemorated in the Sir Alexander Gillies Gold medal which is awarded for distinguished and outstanding service to PENZ. == Family ==