Shrinking follow-up duration in pilonidal sinus surgery, 1970–2020: a patient-weighted longitudinal analysis of 2,285 studies

Reliable estimation of recurrence after pilonidal sinus surgery requires sufficient follow-up (FUP). Despite evidence suggesting ≥ 5 years is necessary, contemporary reports appear to adopt progressively shorter surveillance windows. We assembled a structured database of 2,285 pilonidal surgery series (1850–present) and extracted publication mid-decade, FUP since surgery, and cohort size (n). For 1970–2020, we calculated decade-wise patient-weighted mean FUP. Secular change was estimated using weighted least squares (WLS; weights = n), with unweighted sensitivity analyses. Associations between decade and FUP were assessed via weighted Pearson correlation with Kish effective sample size. We summarized proportions meeting ≥ 2, ≥5, ≥ 10 years and patient shares by FUP bands. Median FUP was 1.67 years; mean 2.50 years. Only 14.2% of studies reported ≥ 5 years and 2.9% ≥10 years. Patient-weighted mean FUP peaked in the 1980s at 6.69 years, declining to 5.26 (1990s), 4.26 (2000s), 3.14 (2010s), and 2.55 years (2020s). Relative to the 1970s (3.78 years), the 2020s were − 1.23 years (− 32.5%), and − 4.14 years (− 61.9%) below the 1980s. The WLS slope was − 0.0766 years·year⁻¹ (95% CI − 0.0856 to − 0.0675; p = 4.57 × 10⁻⁵⁸); unweighted slope − 0.0407 (95% CI − 0.0479 to − 0.0334; p = 1.47 × 10⁻²⁷). Weighted correlation: Rw = − 0.342 (Kish n ≈ 216; p = 2.5 × 10⁻⁷). In the 2020s, patients were distributed as 55.3% <2 years, 26.6% 2–<5, 15.8% 5–<10, 2.3% ≥10. Follow-up windows have contracted substantially, risking under-ascertainment of late recurrences. A minimum of ≥ 5-year FUP with staged reporting at 5 and 10 years and registry-based surveillance is recommended. The absence of a pilonidal core outcome set (COS) in guidelines impedes consistent, long-horizon reporting; COS development and guideline adoption should be prioritized.