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Subtrigonal Inlay and Related BMG Approaches for Posterior Urethral Stenosis

The subtrigonal inlay is a buccal mucosal graft (BMG) technique for posterior urethral reconstruction that encompasses several related approaches — the robotic-assisted laparoscopic (RAL) subtrigonal inlay described by Avallone/Flynn/Nikolavsky, the open perineal dorsal onlay (Shahrour/Elmansy), the endoscopic urethroplasty with BMG (Ungerer/Warner), and the single-port robotic BMG urethroplasty (Liu/Zhao). All share the common principle of augmenting the stenotic segment with buccal mucosa rather than excising and re-anastomosing, thereby preserving the external sphincter mechanism and minimizing de novo incontinence.

Conceptual Rationale: Inlay/Onlay Rather Than Excision​

Traditional reconstruction for recalcitrant BNC/VUAS involves excision of the fibrotic segment and re-anastomosis (as in robotic Y-V plasty or excision with primary anastomosis). While effective for patency, excisional techniques carry a significant risk of de novo stress urinary incontinence — up to 83% for VUAS — because they disrupt the external sphincter mechanism and surrounding neurovascular structures.[1] The non-transecting BMG approach avoids circumferential urethral mobilization and transection, instead opening the stricture longitudinally and laying a graft into the defect to widen the lumen. This preserves the sphincter complex and periurethral blood supply.[2][3]

1. Robotic-Assisted Laparoscopic Subtrigonal Inlay (Avallone/Flynn/Nikolavsky)​

This is the index technique specifically termed "subtrigonal inlay," described in 2019 as a case report.[4]

Technique​

  • Approach: Robotic-assisted laparoscopic, transvesical — the robot accesses the bladder neck from above, through the bladder.
  • Cystotomy and exposure: An anterior cystotomy is performed robotically, providing direct visualization of the bladder neck and the stenotic segment from the intravesical side.
  • Incision of the contracture: The fibrotic bladder neck is incised, opening the stenotic segment.
  • Graft harvest: A large BMG is harvested (5 × 5 × 4 cm in the index case).
  • Subtrigonal inlay: The BMG is inlaid into the opened bladder neck from the subtrigonal aspect — positioned beneath the trigone and sutured in place to augment the lumen. The graft sits on the posterior/subtrigonal surface, supported by the underlying tissue bed.
  • Closure: The cystotomy is closed robotically.
  • Catheter management: Urethral catheter for 2 weeks, suprapubic catheter for 4 weeks.

Outcomes (n=1)[4]​

  • No intraoperative complications.
  • Qmax improved from 2 → 27 mL/s.
  • PVR improved from 200 → 3 mL.
  • VCUG at 4 weeks: no obstruction or extravasation.
  • No recurrence at last follow-up.
  • Discharged POD 2.

Key distinction. The "subtrigonal" designation refers to the graft placement position — beneath the trigone, on the posterior bladder neck. This is distinct from dorsal onlay (which approaches from the perineum and places the graft dorsally against the pubic symphysis) and from ventral inlay (which places the graft on the ventral urethral surface).

2. Open Perineal Dorsal Onlay BMG Urethroplasty​

The most extensively studied BMG technique for posterior urethral stenosis, with three major multi-institutional series. See also the dedicated dorsal onlay BMG page.

Technique (Shahrour/Elmansy)[5]​

  • Perineal incision with dissection of the bulbar urethra.
  • Dorsal dissection carried underneath the pubic bone.
  • Urethra opened dorsally to the bladder neck.
  • BMG sutured to the bladder neck at 11, 12, and 1 o'clock positions.
  • Interrupted dorsal quilting through the periosteum of the pubic bone (provides the graft bed).
  • Continuous suture of graft to urethra with 4-0 Vicryl.
  • Catheter removed at 3 weeks.

Published outcomes​

StudyNPopulationPatencyDe Novo SUIFollow-Up
Angulo 2021 (multi-institutional)[3]107Post-TURP / endoscopic BPH90.7%0.9% (1/107)59.3 mo (mean)
Sterling 2024 (multi-institutional)[2]45Post-prostatectomy + radiation84.4%0%21 mo (median)
Policastro 2021 (multi-institutional)[12]79Post-radiation (all modalities)82.3%8.1% (3/37 continent pts)21 mo (median)
Shahrour 2019[5]4Post-RP (75% radiated)100%N/A (all preop incontinent)3 mo
Doležel 2024 (perineal + endourethroplasty)[11]38PUS/VUAS (mixed)65% 3-yr SRFS (81% with auxiliary DVIU)11% (2/18 continent pts)Long-term

The Angulo et al. series is the largest and longest-follow-up study of dorsal onlay BMG for posterior urethral stenosis, with 107 patients at a mean follow-up of nearly 5 years. The 0.9% de novo SUI rate is the most compelling argument for this non-transecting approach.[3]

Independent predictors of recurrence (Angulo et al.)[3]​

  • Postoperative complications (OR 12.5, p = 0.009)
  • History of radiation (OR 8.3, p = 0.016)
  • ≥2 prior dilations before urethroplasty (OR 8.3, p = 0.032)

3. Endoscopic Urethroplasty with BMG (Ungerer/Warner)​

A fully endoscopic approach to BMG placement, described in 2023.[13]

Technique​

  • Stricture is dilated cystoscopically.
  • A 1 cm wide strip of superficial mucosa is resected from the bladder neck past the stricture, creating a raw bed for graft take.
  • BMG harvested in standard fashion.
  • Using the RD180 endoscopic suturing device, a suture is placed through the proximal graft end, then through the bladder neck, and back through the graft.
  • A "pulley phenomenon" advances the graft into position on the bladder neck as the suture is pulled.
  • The graft is anchored to the posterior urethra with secure straps; sutures secured with the Ti-Knot fastener.
  • Catheter placed to hold graft flat during healing; removed at 4 weeks.

Outcomes (n=1)[13]​

  • Operative time: 2.5 hours; EBL: 50 cc.
  • Same-day discharge.
  • Cystoscopy at 10 weeks: good graft viability.
  • Qmax improved from 4 → 20 mL/s.
  • No recurrence at 6 months.

This technique is conceptually related to TUITMR (Abramowitz) — both use endoscopic suturing devices transurethrally to bring tissue across the stenotic defect. However, the Warner technique uses a free buccal graft rather than advancing native bladder mucosa.[13]

4. Single-Port Robotic BMG Urethroplasty (Liu/Zhao)​

A robotic approach using BMG with ancillary tissue transfer for complex cases.[14]

Technique​

  • Single-port robotic access via supraumbilical incision.
  • Intraabdominal or extraperitoneal transvesical approach.
  • Cystoscopy identifies extent of stenosis.
  • Anastomosis completed with BMG.
  • Ancillary flap harvest as needed: rectus abdominis, omental, or gracilis flaps for tissue interposition (particularly in radiated fields).

Outcomes (n=9)[14]​

  • Mean defect length: 3.9 cm (longer than typical Y-V plasty candidates).
  • 5/9 required ancillary flap procedures.
  • Median operative time: 377 minutes (reflecting complexity).
  • No intraoperative complications.
  • Median LOS: 2 days; EBL: 200 mL.
  • 30-day complications: UTI, epididymitis, anemia, recurrent stricture, SBO requiring surgery (each n=1).
  • Median follow-up: 11.7 months.

5. Endourethroplasty (Doležel)​

A distinct endourological approach with the longest follow-up data for BMG in posterior stenosis.[11]

Technique​

  • BMG transferred as onlay or tubular grafts into dilated/incised strictures through an endourological approach.
  • If recurrence occurs with short stenosis within 12 months, treated with cold-knife DVIU ("auxiliary DVIU").

Outcomes (n=11 endourethroplasty, within 38-patient cohort)[11]​

  • 3-year SRFS: 73% (endourethroplasty) vs 63% (perineal approach).
  • With auxiliary DVIU: 3-year SRFS improved to 81% overall.
  • De novo incontinence: 2/18 preoperatively continent patients (11%).

Comparison of BMG Approaches​

TechniqueApproachBest ForPatencyDe Novo SUIOR TimeKey Advantage
RAL subtrigonal inlay[4]Robotic transvesicalRefractory BNC100% (n=1)0%Not reportedDirect intravesical visualization
Open perineal dorsal onlay[2][3][5]PerinealBNC post-TURP, VUAS ± radiation82–91%0–8.1%177 minLargest evidence base; lowest SUI
Endoscopic BMG[13]TransurethralShort membranous strictures100% (n=1)0%150 minFully endoscopic; same-day discharge
Single-port robotic BMG[14]Robotic ± perinealComplex/long defects (>3 cm)Comparable to openVariable377 minHandles long defects with flap interposition
Endourethroplasty[11]EndourologicalPUS/VUAS73% (3-yr)11%VariableMinimally invasive alternative to perineal

Subtrigonal Inlay vs. Robotic Y-V Plasty​

FeatureSubtrigonal / BMG InlayRobotic Y-V Plasty
PrincipleAugmentation (non-transecting)Flap advancement (may involve excision)
Tissue sourceFree buccal mucosal graftNative bladder wall flap
Graft bedPeriosteum / subtrigonal tissueN/A (vascularized flap)
De novo SUI (BNC)0–0.9%0%
De novo SUI (VUAS)0–8.1%83.3%
Stricture lengthCan handle longer defects (>2 cm)Best for ≤2 cm
Radiation toleranceGood (82–84% patency in radiated pts)Poor (60–80% re-intervention in radiated pts)
Graft take requirementYes (needs vascularized bed)No (vascularized flap)

The most critical distinction is in VUAS management: dorsal onlay BMG achieves 0% de novo SUI in the largest multi-institutional series (Sterling et al., n=45), compared to 83.3% de novo SUI with robotic Y-V plasty for VUAS (Viegas et al.).[1][2] This makes the non-transecting BMG approach particularly attractive for VUAS, especially in patients with preoperative continence.

Impact of Radiation on BMG Outcomes​

Radiation remains the most important adverse prognostic factor, but BMG approaches appear to tolerate radiation better than excisional techniques:

  • Post-radiation D-BMGU (Policastro, 10 institutions, n=79): 82.3% patency at 21 months, 8.1% de novo SUI. Radiation modality did not significantly affect recurrence rates (EBRT 45.6%, brachytherapy 16.5%, combination 12.7%, EBRT + RP 25.3%).[12]
  • Post-prostatectomy + radiation D-BMGU (Sterling, 8 institutions, n=45): 84.4% patency at 21 months, 0% de novo SUI. Significant improvements in PVR, uroflow, IPSS, and QoL. Overall satisfaction ≥+2 GRA in 86.6%.[2]
  • Radiation is an independent predictor of recurrence (OR 8.3, p = 0.016) in the Angulo series, but the absolute recurrence rate remains acceptable.[3]

Graft Biology: Why Buccal Mucosa Works​

The AUA recommends oral mucosa as the first choice for graft material in urethroplasty (Expert Opinion), with buccal and lingual grafts considered equivalent alternatives (Strong Recommendation; Grade A).[6] Buccal mucosa is preferred because of:[19]

  • Thick, non-keratinized epithelium resistant to infection.
  • Rich submucosal vascular plexus facilitating graft take (imbibition → inosculation → neovascularization).
  • Thin lamina propria allowing rapid revascularization.
  • Ease of harvest with low donor site morbidity.
  • Large graft area available from inner cheeks (up to 5 × 5 cm).

Among GURS members, 99% prefer buccal mucosa as the primary graft site, and 95% harvest their own grafts. For posterior stenosis specifically, 66% favor dorsal graft placement over ventral. A 2025 meta-analysis of 655 patients found no difference in success rates between dorsal and ventral onlay (RR 1.00, p = 0.97), though ventral onlay was associated with significantly lower transient erectile dysfunction (RR 0.24, p = 0.006).[20][21]

Where Subtrigonal Inlay / BMG Fits in the Treatment Algorithm​

  1. Recalcitrant BNC (post-TURP / BPH surgery) → Open perineal dorsal onlay BMG is the best-studied option with the longest follow-up (91% patency at 5 years, 0.9% de novo SUI); robotic subtrigonal inlay is a promising alternative with limited data.[3][4]
  2. Recalcitrant VUAS (nonradiated) → Dorsal onlay BMG preferred over Y-V plasty due to dramatically lower de novo SUI (0% vs 83%).[1][2]
  3. Recalcitrant VUAS (radiated) → Dorsal onlay BMG is the technique of choice (84% patency, 0% de novo SUI in the Sterling multi-institutional series); excisional techniques have unacceptably high incontinence rates in this population.[2]
  4. Long defects (>3 cm) → Single-port robotic BMG with ancillary flap interposition.[14]
  5. Short membranous strictures → Endoscopic BMG urethroplasty (Warner technique) offers a minimally invasive option with same-day discharge.[13]
  6. Post-BMG SUI → AUS placement is safe and effective; the non-transecting approach preserves the perineal field for future AUS implantation.[2][3]

References​

1. Viegas V, Freton L, Richard C, et al. "Robotic YV Plasty Outcomes for Bladder Neck Contracture vs. Vesico-Urethral Anastomotic Stricture." World Journal of Urology. 2024;42(1):172. doi:10.1007/s00345-024-04814-8

2. Sterling J, Simhan J, Flynn BJ, et al. "Multi-Institutional Outcomes of Dorsal Onlay Buccal Mucosal Graft Urethroplasty in Patients With Postprostatectomy, Postradiation Anastomotic Stenosis." The Journal of Urology. 2024;211(4):596-604. doi:10.1097/JU.0000000000003848

3. Angulo JC, Dorado JF, Policastro CG, et al. "Multi-Institutional Study of Dorsal Onlay Urethroplasty of the Membranous Urethra After Endoscopic Prostate Procedures: Operative Results, Continence, Erectile Function and Patient Reported Outcomes." Journal of Clinical Medicine. 2021;10(17):3969. doi:10.3390/jcm10173969

4. Avallone MA, Quach A, Warncke J, Nikolavsky D, Flynn BJ. "Robotic-Assisted Laparoscopic Subtrigonal Inlay of Buccal Mucosal Graft for Treatment of Refractory Bladder Neck Contracture." Urology. 2019;130:209. doi:10.1016/j.urology.2019.02.048

5. Shahrour W, Hodhod A, Kotb A, Prowse O, Elmansy H. "Dorsal Buccal Mucosal Graft Urethroplasty for Vesico-Urethral Anastomotic Stricture Postradical Prostatectomy." Urology. 2019;130:210. doi:10.1016/j.urology.2019.04.022

6. Wessells H, Morey A, Souter L, Rahimi L, Vanni A. "Urethral Stricture Disease Guideline Amendment (2023)." The Journal of Urology. 2023;210(1):64-71. doi:10.1097/JU.0000000000003482

7. Wu MH, Liu JX, Zhang YF, et al. "Bladder Neck Contracture Following Transurethral Surgery of Prostate: A Retrospective Single-Center Study." World Journal of Urology. 2024;42(1):14. doi:10.1007/s00345-023-04715-2

8. Britton CJ, Sharma V, Fadel AE, et al. "Vesicourethral Anastomotic Stenosis Following Radical Prostatectomy: Risk Factors, Natural History, and Treatment Outcomes." The Journal of Urology. 2023;210(2):312-322. doi:10.1097/JU.0000000000003488

9. Nealon SW, Bhanvadia RR, Badkhshan S, et al. "Transurethral Incisions for Bladder Neck Contracture: Comparable Results Without Intralesional Injections." Journal of Clinical Medicine. 2022;11(15):4355. doi:10.3390/jcm11154355

10. Ramirez D, Zhao LC, Bagrodia A, et al. "Deep Lateral Transurethral Incisions for Recurrent Bladder Neck Contracture: Promising 5-Year Experience Using a Standardized Approach." Urology. 2013;82(6):1430-5. doi:10.1016/j.urology.2013.08.018

11. Doležel J, Hrabec R, Uher M, et al. "Substitution Urethroplasty With Buccal Mucosal Graft in the Management of Stricture of Vesicourethral Anastomosis or Membranous Urethra: Single-Institution Long-Term Experience With Perineal Approach and Endourethroplasty." Urology. 2024;192:126-132. doi:10.1016/j.urology.2024.05.034

12. Policastro CG, Simhan J, Martins FE, et al. "A Multi-Institutional Critical Assessment of Dorsal Onlay Urethroplasty for Post-Radiation Urethral Stenosis." World Journal of Urology. 2021;39(7):2669-2675. doi:10.1007/s00345-020-03446-y

13. Ungerer G, Kemble J, Sischka M, Balzano FL, Warner JN. "Endoscopic Urethroplasty Using Buccal Graft for Male Membranous Urethral Stricture." Urology. 2023;181:e200-e203. doi:10.1016/j.urology.2023.05.059

14. Liu W, Shakir N, Zhao LC. "Single-Port Robotic Posterior Urethroplasty Using Buccal Mucosa Grafts: Technique and Outcomes." Urology. 2022;159:214-221. doi:10.1016/j.urology.2021.07.049

15. Shinchi M, Horiguchi A, Ojima K, et al. "Deep Lateral Transurethral Incision for Vesicourethral Anastomotic Stenosis After Radical Prostatectomy." International Journal of Urology. 2021;28(11):1120-1126. doi:10.1111/iju.14650

16. LaBossiere JR, Cheung D, Rourke K. "Endoscopic Treatment of Vesicourethral Stenosis After Radical Prostatectomy: Outcomes and Predictors of Success." The Journal of Urology. 2016;195(5):1495-1500. doi:10.1016/j.juro.2015.12.073

17. Klein R, Vasan R, Guercio C, Rusilko P. "Minimally Invasive Management of Posterior Urethral Stricture/Stenosis With DVIU and Mitomycin C Injection." Urology. 2024;183:e317-e319. doi:10.1016/j.urology.2023.10.006

18. Lee M, Lesgart M, McPartland C, Lee R, Eun DD. "Robotic Transvesical Bladder Neck Reconstruction: A Novel Approach to Managing Vesicourethral Anastomotic Stenosis." European Urology. 2025. doi:10.1016/j.eururo.2025.04.026

19. Gn M, Sterling J, Sinkin J, Cancian M, Elsamra S. "The Expanding Use of Buccal Mucosal Grafts in Urologic Surgery." Urology. 2021;156:e58-e65. doi:10.1016/j.urology.2021.05.039

20. Hassan AA, Soliman AM, Shouman HA, et al. "Dorsal- Vs Ventral-Onlay Buccal Mucosal Graft Urethroplasty for Urethral Strictures: A Meta-Analysis." BJU International. 2025. doi:10.1111/bju.16811

21. Berg C, Singh A, Hu P, et al. "Current Trends in the Use of Buccal Grafts During Urethroplasty Among Society of Genitourinary Reconstructive Surgeons." Urology. 2024;191:139-143. doi:10.1016/j.urology.2024.06.019