Randomised controlled-trials, cohort studies, case–control studies and case series including greater than five patients.

Human studies only.

If multiple articles had overlapping cohorts (determined by institution and year), only the most recent publication was included.

Reports published in English language.

Individual case reports and case series with fewer than five patients included.

Articles describing technical aspects of surgical technique or those that purely reported on perioperative or short term outcomes.

Animal studies.

Publications that described surgical techniques that differ significantly from current techniques were excluded; in practice, this removed all publication prior to 1989.