Mid-term uroflowmetry trajectories after TIP versus Onlay urethroplasty for distal hypospadias

Background and objective: This study aimed to compare the mid-term uroflowmetry trajectories and postoperative urinary patency between tubularized incised plate (TIP) and Onlay urethroplasty for distal hypospadias. Methods: In this retrospective cohort study, 210 boys aged 2–6 years who underwent primary distal hypospadias repair (TIP group, n = 127; Onlay group, n = 83) were included. Uroflowmetry was performed preoperatively and at 3 months, 1 year, and 2 years postoperatively. Parameters including maximum flow rate (Qmax) and flow-curve patterns (classified as abnormal or bell curve) were analyzed. Results: A consistent “V-shaped” uroflowmetry trajectory (early decline at 3 months followed by recovery at 1–2 years) was observed in both groups. Qmax decreased significantly at 3 months postoperatively (both P < 0.001), with a more pronounced reduction in the TIP group (from 9.8 to 4.9 mL/s) than in the Onlay group (from 9.6 to 6.3 mL/s; inter-group P = 0.001). By 1 year, Qmax recovered to near-preoperative levels in both groups (TIP: 8.3 mL/s; Onlay: 8.9 mL/s; P = 0.090) and remained stable at 2 years. The proportion of abnormal flow curves was higher in the TIP group at 3 months (74.8% vs. 51.8%, P < 0.001), but decreased markedly and showed no significant inter-group difference at 1 and 2 years. Overall complication rates were comparable (TIP 9.4% vs. Onlay 10.8%). Conclusion: Both techniques exhibit similar “V-shaped” uroflowmetry recovery. Although TIP presents more pronounced obstructive patterns within the first 3 months, the two techniques achieve comparable mid-term (≥1 year) urinary patency. Consequently, uroflowmetry follow-up should extend for at least 1 year, and early asymptomatic reductions can often be managed conservatively.