Bias in clinical trials: The importance of suture technique

Objective: To study the effect on suture technique of introducing a new sut ure material. Design: Prospective clinical study. Setting: County hospital, Sweden. Subjects: 224 patients included during the first 10 months of a clinical st udy that had been designed to compare two suture materials. Interventions: Wounds were sutured by a continuous technique. The suture le ngth : wound length ratio was recorded together with details of patients an d operations. Main outcome measures: The incidence of incisional hernia after 12 months. Results:. The mean suture length : wound length ratio was 3.6 (95% confiden ce interval (CI) 3.4 to 3.9) in wounds closed with the introduced new mater ial and 3.2 (2.9 to 3.4) with the familiar material (p < 0.01). With the ne w material a higher proportion of wounds were sutured at a ratio of 4 or mo re. Incisional hernias developed in 6% (3 of 50) of wounds sutured with a s uture length : wound length ratio of 4 or more and in 22% (26 of 119) if it was less (p = 0.01). The rate of incisional hernia was lower in wounds sut ured with the new suture material. Conclusion: During the first 10 months of a clinical trial the introduction of a new suture material caused a potential systematic error. The suture t echnique was more meticulous with the new material and this may have affect ed the rate of incisional hernia. The suture technique should therefore be monitored in such studies in the future.