Bias in clinical trials: the importance of suture technique.

OBJECTIVE: To study the effect on suture technique of introducing a new suture material.

DESIGN: Prospective clinical study.

SETTING: County hospital, Sweden.

SUBJECTS: 224 patients included during the first 10 months of a clinical study that had been designed to compare two suture materials.

INTERVENTIONS: Wounds were sutured by a continuous technique. The suture length: wound length ratio was recorded together with details of patients and operations.

MAIN OUTCOME MEASURES: The incidence of incisional hernia after 12 months.

RESULTS: The mean suture length: wound length ratio was 3.6 (95% confidence interval (CI) 3.4 to 3.9) in wounds closed with the introduced new material and 3.2 (2.9 to 3.4) with the familiar material (p<0.01). With the new material a higher proportion of wounds were sutured at a ratio of 4 or more. Incisional hernias developed in 6% (3 of 50) of wounds sutured with a suture 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 sutured 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 technique was more meticulous with the new material and this may have affected the rate of incisional hernia. The suture technique should therefore be monitored in such studies in the future.