Aims: (1) Assess the level of available evidence regarding fistula occurrence in cleft lip and palate patients, (2) identify main research areas in the original studies, (3) evaluate the quality of original studies, and (4) summarize the evidence.
Methods: Two independent researchers searched the Cochrane Database of Systematic Reviews, Medline, Web of Knowledge, Web of Science and EMBASE, the Grey literature, and the reference lists of main references. The level of evidence was assessed based on study design and according to the Hierarchy of Evidence. The quality assessment was done using the adapted Consolidated Standards of Reporting Trials and Strengthening the Reporting of Observational Studies in Epidemiology checklists and a validity scoring system. Main findings were summarized, and fistula rates were compared between early and more recent articles, also between high-quality and low-quality studies.
Results: The systematic search and relevance assessment identified a total of 127 sources of evidence. The overall level of evidence was weak because it was dominated by small studies (<30 subjects), retrospective cohort studies, and case series. Main research areas were either: (1) focused on surgeries or (2) focused on risk determinants associated with fistula occurrence. Recent reports were of higher quality than the older ones, but the overall quality in the majority of reports was low. Knowledge synthesis demonstrated a wide range of rates for primary fistula (0-78%). No significant difference was found in the fistula rates of older studies compared with more recent studies or among different quality studies. Multiple risk determinants were studied and age at surgery, surgeon's experience, type and severity of cleft were the most frequently examined risk determinants. However, findings concerning different risk determinants and fistula occurrence were not consistent.
Conclusions: The research mainly focused on surgeries and fistula-related risk determinants. The available evidence was low level and of poor quality. No consistent pattern between fistula occurrence and any of the risk determinants could be detected. Reported fistula rates did not differ significantly when comparing older studies with more recent studies or when high-quality studies were compared with low-quality studies.