This meta-analysis was the most comprehensively synthesis of evidence for currently available comparison between DF and TVF flap techniques for hypospadias and fistula patients in comparative studies. We included 9 comparative studies, comprising 564 patients performed hypospadias or fistula repair with the use of DF or TVF flaps. Evidence of our findings came from the pooled estimate size for the outcomes, which showed that TVF was better than DF for the repair of hypospadias and fistula in terms of UCF (RR=0.21, 95% CI: 0.09-0.51) and skin necrosis (RR=0.17, 95% CI: 0.03-0.88). No significant difference was found in meatal stenosis/urethral stricture (RR=0.87, 95% CI: 0.28-2.70) and glans dehiscence/wound dehiscence (RR=1.33, 95% CI: 0.41-4.35). No significant statistically difference was found in different surgery type, study design, with or without magnification technique subgroups. In addition, publication bias test verified the robustness of the results in this meta-analysis. Reoperation for failed hypospadias or fistula repair has been considered to be a seriously problem because the dense fibrotic tissue causes difficulties in wound healing and increases the rate of complications . Various surgical methods and modifications have been developed for repairing the hypospadias and fistula while UCF are still one of the most common complications of these techniques . The total UCF rate is 7.71% in our study, consistent with the 7.5% incidence in a systematic review . Patients age, glans size, urethral defect length, urethral operation history, surgical procedure, type of surgical repair, chordee degree, magification technique, caudal anesthesia, preoperative hormonal stimulation and other many factors are may related to the development of UCF and other complications postoperatively [21-25]. Additional soft coverages on the neourethra are also introduced to avoid these complications especially for decreasing the incidence of postoperative UCF. TVF, DF, Buck’s fascia, spongious tissue, external spermatic fascia, adipose tissue of scrotum, adipose tissue of speramtic cord, combination of tissues and paltelet rich plasma are used in different studies [26-32] with various outcomes. Among them, TVF and DF are the most popular flaps in the repair of hypospadias and fistula.
DF is a layer of connective tissue found in the penile dorsal or ventral, foreskin, and scrotum and can be used in hypospadias or fistula repair in different techniques [33, 34]. Excellent vascularity, easy availability and adequate source are advantages of DF, making this flap technique more popular for many pediatric urologists especially for young surgeons. Penile rotation and preputial skin necrosis were common reported relevant complications and could be avoided by careful operation and technical improvement. Snodgrass described additional interposition of vascularized tissues between the tubularized plate and glans closure dissected from dorsal prepucial and shaft skin . Duckett has described that when dartos is separated from skin, it compromises the vascularity of the overlying skin . So the dissection of DF may compromise the vascularity of the preputial skin covering and result in subsequent skin necrosis. This is consistent with the conclusion of our secondary outcomes. TVF can be harvested through penile incision by degloving till the root of penis  or additional scrotal incision which reach and cover the neourethra through a subcutaneous scrotal tunnel  which however may damage to the vas or vessels of the testicular therefore resulting in scrotal abscess or scrotal hematoma. The blood supply of the neourethra tissue may be affected due to the dissection and utilization of DF, which mainly comes from the shortage of dartos or preputial skin necrosis. However, this is rarely affected in TVF technique for its ventral skin covering is rarely compromised. All these can theoretically explain the advantage of TVF over DF. And we performed this meta-analysis to prove the advantages of TVF over DF with the data.
The results of our meta-analysis were partially consistent with the result of a systematic review by Fahmy et al . However, there were several differences among the two studies. The study of Fahmy et al included not only comparative studies but cases series, it weakened the evidence. In addition, literature retrieval process should be as comprehensive as possible while there is only one database (PubMed) in his study. Our included only comparative studies and searched 4 databases (PubMed, EMBASE, the Cochrane Library and Web of Science), a clinical trial register(clinicaltrial.gov) and several international meeting abstract archives. All these enhanced our evidence.
There are several limitations in our meta-analysis. First, although a comprehensive retrieval was performed, only limited studies without any unpublished study was included, which might bias the results. Second, although statistical heterogeneity was not high (CEBM levels of evidence: 1b to 2b), difference in clinical characteristics including study settings, hypospadias and surgery type, patients age, follow-up duration, complications criteria exists. The contribution of these differences to final outcomes was unknown. So we performed subgroup analyses to find potential sources of heterogeneity but no significant results were found due to the limited number of studies.
Although many uncontrollable confounders factors may affect the hypospadias surgery outcomes especially the wide variability for individual surgical experience and complexity for hypospadias cases, more large sample size, well-designed, single-urologist studies need to be conducted for optimal comparison betwween this two flap techniques.