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The Leg & Thigh

For the reconstructive urologist, the lower extremity is a donor site and a neuromodulation target — not a primary organ of interest. Two structures in particular matter enough to warrant a dedicated anatomic reference:

  • The gracilis muscle — the workhorse muscle flap of pelvic reconstruction, used for rectourethral fistula interposition, perineal coverage after Fournier's or APR, urethral neosphincter construction, and long-segment urethroplasty in the radiated pelvis.
  • The posterior tibial nerve at the medial ankle — the peripheral target of percutaneous and implantable tibial-nerve stimulation (PTNS / iTNS), a third-line therapy for overactive bladder.

This article focuses on those two territories — thigh donor anatomy for the gracilis, and medial-ankle neurovascular anatomy for tibial-nerve stimulation — with only as much general leg / thigh anatomy as is needed to place them in context.

See also The Perineum for the gracilis recipient bed; The Vulva for Martius flap alternatives; Multiple Sclerosis and Neurogenic Lower Urinary Tract Dysfunction for the clinical indications of tibial-nerve stimulation.

Thigh — Compartment Overview​

The thigh is organized into three fascial compartments by the femur, intermuscular septa, and the surrounding fascia lata:

CompartmentDominant musclesInnervationReconstructive relevance
AnteriorQuadriceps (rectus femoris + three vasti); sartorius; iliopsoas (at proximal end)Femoral nerve (L2–L4)Rectus-femoris and VRAM / vastus-lateralis flaps; femoral-nerve at risk in deep retroperitoneal / retractor placement
Medial (adductor)Gracilis, adductor longus, adductor brevis, adductor magnus, obturator externus, pectineusObturator nerve (L2–L4) + branch to adductor magnus from sciaticGracilis flap territory; obturator nerve at risk in TOT sling and obturator-LN dissection
Posterior (hamstring)Biceps femoris, semitendinosus, semimembranosusSciatic nerve (L4–S3)Hamstring autografts (orthopedic); sciatic-nerve injury with prone / lithotomy positioning

The adductor hiatus in the distal adductor magnus transmits the femoral artery and vein into the popliteal fossa, where they become the popliteal vessels. Above the hiatus, the femoral vessels course within the adductor (Hunter's) canal between adductor longus/magnus and vastus medialis.

The Gracilis Muscle​

The gracilis is a long, thin, strap-like muscle of the medial thigh that spans from the inferior pubic ramus to the pes anserinus on the medial proximal tibia. It is a weak hip adductor and knee flexor and is functionally redundant with the other adductors — harvesting it as a flap produces no clinically detectable lower-extremity deficit, which is the central reason it is the workhorse muscle flap of pelvic reconstruction.[1][2]

Gross anatomy​

  • Length ~37–41 cm.
  • Width tapers from ~25–27 mm at the origin to ~10–11 mm at the musculotendinous junction.
  • Tendon contributes ~6 cm of the musculotendinous length; inserts as part of the pes anserinus alongside sartorius and semitendinosus.
  • Lies superficial in the medial thigh — immediately beneath skin, subcutaneous fat, and fascia lata — which is why it can be harvested through a simple longitudinal medial-thigh incision with minimal muscle dissection.
  • Borders: adductor longus anteriorly, adductor magnus / sartorius posteriorly.

Vascular supply — a Mathes-Nahai Type II pattern​

The gracilis has one dominant pedicle plus one or more minor pedicles (Mathes-Nahai Type II). This is what gives the flap its large, reliable, rotatable proximal segment with a survivable distal extension:[3][4][5]

PedicleOriginLocationCaliberRole
Dominant (major)Profunda femoris artery (87%) or medial circumflex femoral (13%)Enters deep surface ~10 cm from the pubic tubercle1.6–2.5 mm artery, paired venae comitantesSupports the entire muscle; the pedicle preserved in all gracilis flaps
Proximal (minor)Deep branch of medial circumflex femoral~6 cm from pubic tubercle~0.9 mmSupplies the proximal muscle
Distal (1–4 pedicles)Superficial femoral artery~26 cm from pubic tubercle1.4–2.0 mmSupport the distal third of the muscle

The distal pedicles form an anastomotic chain along the anterior border of the muscle — the basis of the distal-based or free gracilis flap.[3][4]

Venous drainage is via paired venae comitantes that accompany the arteries; discrete zones without extensive intramuscular venous anastomoses, so harvest that respects the dominant pedicle's venous drainage is essential.[4]

Neural supply​

The anterior division of the obturator nerve (L2–L4) enters the muscle with the dominant pedicle and splits into 2–3 longitudinal branches running parallel to the muscle fibers.[5] This consistent neurovascular bundle makes the gracilis suitable for functional (innervated) muscle transfer (e.g., dynamic graciloplasty for fecal or urinary continence, facial reanimation).

The adductor-compartment anatomy near the gracilis pedicle — adductor longus anteriorly, adductor brevis deep — is what the extended pedicle dissection technique exploits to gain length.[11][12]

Internal architecture​

Contemporary microanatomic studies describe 4–7 longitudinal muscular compartments within the gracilis, each served by a branch of the obturator nerve and dominant arterial pedicle.[4] This compartmentalization is the theoretical basis for segmental / split-gracilis transfers in facial reanimation and specialized functional reconstructions, though for GU applications the muscle is typically harvested as a single unit.

Gracilis Flap — Techniques and Applications​

Harvest technique (overview)​

  • Positioning: supine, with the thigh abducted and externally rotated (frog-leg), knee flexed; often dorsal lithotomy combined with the recipient operation.
  • Incision: longitudinal medial-thigh skin incision along a line from the pubic tubercle to the medial tibial condyle; center the incision over the expected muscle (about 1 fingerbreadth posterior to the palpable adductor longus tendon).
  • Identification: open fascia lata → identify gracilis between adductor longus (anterior) and sartorius / adductor magnus (posterior) → confirm distal tendon at the pes anserinus.
  • Pedicle exposure: trace the dominant pedicle on the deep surface ~10 cm from the pubic tubercle, where it emerges between adductor longus and adductor brevis.
  • Distal release: divide the distal tendon at the pes anserinus; mobilize the muscle proximally toward its origin.
  • Tunnel: create a subcutaneous tunnel from the thigh wound to the perineum, passing the muscle on its pedicle.
  • Inset: position the muscle in the recipient bed (interposition, wrap, or coverage) and secure.

Extended pedicle dissection​

For reconstructions that demand greater pedicle length or arc of rotation — posterior perineum, deep pelvis, rectourethral fistula after prior reconstructive failure — the extended dissection carries the pedicle proximally beyond the adductor longus, divides adductor-longus perforators, and passes the gracilis under the adductor longus to access the profunda femoris directly.[11][12] This adds up to ~54 mm of pedicle length and permits reach into deeper pelvic and superior perineal defects.

Reconstructive applications in GU​

IndicationRole of the gracilisReported outcomes
Rectourethral fistula (post-prostatectomy, post-radiation, post-cryo / HIFU)Interposition flap between urethral repair and rectal repair; brings non-irradiated vascularized tissue into the defect~91% success reported in series of pelvic-fracture urethral defects with rectourethral fistula[8]
Rectovaginal fistula (obstetric, IBD-related, post-radiation)Interposition between rectal and vaginal repairs; alternative to Martius when a bulkier flap is neededHigh success in the non-irradiated setting; more variable in the radiated / Crohn's setting
Perineal wound coverage after APR, pelvic exenteration, radical vulvectomy, Fournier's debridementFills dead space, brings vascularized tissue to irradiated or infected bedsWidely used; the reconstructive standard alongside VRAM for large defects
Non-healing perineal / urogenital fistulae after radiationIntroduces non-irradiated tissue into the repairSelected indications; often the last available tissue option[10]
Long-segment urethroplasty with buccal-mucosa graft in high-risk / irradiated / reoperative fieldsCoverage flap over a buccal-graft urethroplasty to provide a vascularized bed~77% success for mean 7.6 cm strictures; avoids diversion in most cases[9]
Urethral neosphincter (graciloplasty) for post-prostatectomy incontinenceMuscle wrapped around the bulbar urethra as an autologous compressive sphincter; dynamic (stimulated) or static configurationsImproves Valsalva leak-point pressure from ~26 → ~83 cmH₂O; ~75% success for mild-to-moderate incontinence in selected series[6][7]
Neovaginal construction / gender-affirming surgeryOccasional role in secondary / salvage vaginoplastyRarely first-line; intestinal and skin-based techniques preferred

Why the gracilis is preferred for pelvic reconstruction​

  • Long, thin, rotatable — reaches from the medial thigh into the deep pelvis with minimal tension.
  • Reliable dominant pedicle with minor distal pedicles as a safety margin.
  • Functionally redundant — harvest is essentially free of donor-site morbidity.
  • Consistent neurovascular anatomy — predictable dissection, short learning curve.
  • Non-irradiated donor tissue — essential for repair in the post-radiation pelvis.
  • Modest donor-site scar in a concealable medial-thigh position.

Donor-site morbidity​

Generally limited. Reported findings:

  • Seroma — the commonest early complication; typically resolves with aspiration / drains.
  • Hematoma along the thigh wound.
  • Transient medial-thigh / knee-medial sensory paresthesia from small skin-nerve branches.
  • Wound infection / dehiscence — low with primary closure and careful hemostasis.
  • Functional deficit — essentially absent in unilateral harvest; bilateral harvest (rarely needed) can produce subtle adductor weakness.

Medial-Ankle Anatomy for Tibial-Nerve Stimulation​

The posterior tibial nerve​

The posterior tibial nerve is a terminal branch of the sciatic nerve (L4–S3) that descends through the posterior compartment of the leg with the posterior tibial artery and vein. At the medial ankle, the nerve passes behind the medial malleolus within the tarsal tunnel (deep to the flexor retinaculum), where it divides into the medial and lateral plantar nerves that supply sensation and motor function to the sole of the foot.

For urologic neuromodulation purposes, the nerve is targeted just cephalad to the medial malleolus, posterior to the posterior border of the tibia — a site sometimes called the "bladder center" because of its clinical effect on lower-urinary-tract function.[13][15]

Regional neurovascular and tendinous anatomy at the target site​

A cadaveric mapping of the standard PTNS needle insertion site (~3 fingerbreadths / ~5 cm cephalad to the medial malleolus, posterior to the tibial border) found the following structures within the 80% prediction interval of needle placement:[14]

StructureDistance from the standard needle insertion site
Tibial nerve0–12.1 mm (the target)
Posterior tibial artery / vein0–9.5 mm
Flexor digitorum longus tendon0–13.9 mm
Flexor hallucis longus tendonVariable, posterior to the nerve
Tibialis posterior tendonAnterior to the needle target
Great saphenous vein~18–21 mm (asymmetric between legs)
Calcaneal (Achilles) tendon~8–13 mm (asymmetric)

Important surgical corollaries:

  • The tibial nerve sits very close to the posterior tibial artery and vein (<10 mm); this is a procedural consideration for implantable devices, though PTNS needle complications are uncommon in practice.
  • The tibial nerve is shallow at this site — typically at 1–2 cm depth in most adults — which is why a fine-gauge (34 G) needle is used.
  • The great saphenous vein is the commonest bleeding source from misplaced PTNS needles; asymmetry between legs (left vs right) justifies individual mapping rather than fixed distances.

Mechanism of action — retrograde neuromodulation​

Tibial-nerve stimulation produces a retrograde action potential volley that ascends the tibial / sciatic nerve into the sacral plexus (S2–S4) — the same segments that supply the bladder, urethra, and pelvic floor.[13][15][16] Proposed mechanisms:

  • Modulation of detrusor overactivity while preserving the reflex micturition pathway.
  • Central effects on the pontine micturition center and periaqueductal grey via afferent input.
  • Peripheral effects on bladder afferent fibers (including capsaicin-sensitive C-fibers).
  • Neurotransmitter-level effects involving opioid and purinergic systems.

Acute PTNS increases the volume at first involuntary detrusor contraction (~163 → ~232 mL) and maximum cystometric capacity (~221 → ~277 mL).[18]

Clinical applications​

Percutaneous tibial-nerve stimulation (PTNS) is a guideline-recommended third-line therapy for overactive bladder (OAB) and urgency urinary incontinence in patients who have failed behavioral and pharmacologic therapy.[15][17]

  • Standard protocol: fine-gauge needle 3 fingerbreadths cephalad to the medial malleolus + surface return electrode on the medial arch; 10 Hz fixed-frequency stimulation, 200 µs pulse width; 30-minute sessions weekly for 12 weeks, then maintenance.
  • Evidence: efficacy comparable to antimuscarinic medications and superior to sham / conservative therapy in randomized trials; evidence quality moderate.[19]

Implantable tibial-nerve stimulation (iTNS) addresses the limitations of percutaneous therapy (weekly office burden, limited insurance coverage, maintenance).[17]

  • Mechanism: the same retrograde tibial-to-sacral neuromodulation.
  • Implantation site: a small incision at the medial ankle; lead placed adjacent to the posterior tibial nerve proximal to the tarsal tunnel.
  • Patient-controlled at-home stimulation — no weekly office visits.
  • Multiple iTNS devices have received FDA marketing authorization and are entering clinical practice.

Anatomic implications for the implanter:

  • Know the ankle variability — pre-op ultrasound mapping of the nerve and vessels is reasonable.
  • The tibial artery and vein run with the nerve — blunt dissection and careful lead placement are essential.
  • The flexor retinaculum is the superficial landmark; entry proximal to the retinaculum keeps the device out of the mobile tarsal-tunnel compartment.

Relationship to sacral neuromodulation (SNM)​

PTNS / iTNS and SNM share a sacral-S3 target through very different access routes. In practical terms:

  • PTNS / iTNS — peripheral, less invasive, office-based or small-implant; well-suited to OAB / UUI.
  • SNM — lead at the S3 foramen; broader indications (OAB, non-obstructive retention, fecal incontinence, selected pelvic pain) but a more invasive, more expensive system with MRI-compatibility caveats.

See Neurogenic Lower Urinary Tract Dysfunction for when either is considered.

Clinical Correlations for the Reconstructive Urologist​

  • Gracilis is the default muscle flap of the reconstructive pelvis. Master the harvest: medial-thigh incision, identify between adductor longus and sartorius, trace pedicle at ~10 cm from the pubic tubercle, tunnel subcutaneously to the perineum, inset without tension.
  • Extended pedicle dissection buys ~5 cm of reach for deep or superior pelvic defects — essential for rectourethral fistulae in the radiated or reoperative pelvis.
  • Gracilis vs Martius. Martius (labial fat pad) is thinner, has a shorter arc, and is ideal for urethrovaginal fistula, diverticulectomy, and VVF interposition. Gracilis is bulkier, reaches further, and is the choice when tissue volume or reach matters (rectourethral fistula, APR perineum, long-segment urethroplasty coverage). Both are non-irradiated flaps.
  • Gracilis neosphincter (graciloplasty) remains an option for the highly selected patient with post-prostatectomy incontinence not amenable to AUS — not commonly performed, but the reconstructive surgeon should know the concept.
  • PTNS is the right answer for many motivated OAB patients who fail first-line therapy but are not ready for SNM or botulinum — the anatomic access is simple, complication rate is very low, and the trial cost is modest.
  • iTNS is the emerging option that may bring tibial-nerve neuromodulation into a more SNM-like long-term-device paradigm. Anatomic familiarity with the medial-ankle compartment is the implanter's entry requirement.
  • Obturator nerve is the neural axis of the adductor compartment. Know where it runs (in the adductor canal between adductor longus and brevis, giving anterior + posterior divisions) and why it's at risk in TOT sling, obturator-LN dissection, and Cooper's-ligament-level pelvic-fracture operations.

References​

1. Kumar CG, Vadgaonkar R, Prameela MD, et al. "Morphology of Gracilis Muscle and the Topographic Anatomy of Its Neurovascular Pedicles." F1000Research. 2024;13:299. doi:10.12688/f1000research.144786.2

2. Macchi V, Vigato E, Porzionato A, et al. "The Gracilis Muscle and Its Use in Clinical Reconstruction: An Anatomical, Embryological, and Radiological Study." Clin Anat. 2008;21(7):696–704. doi:10.1002/ca.20685

3. Magden O, Tayfur V, Edizer M, Atabey A. "Anatomy of Gracilis Muscle Flap." J Craniofac Surg. 2010;21(6):1948–1950. doi:10.1097/SCS.0b013e3181f4ed81

4. Fattah AY, Ravichandiran K, Zuker RM, Agur AM. "A Three-Dimensional Study of the Musculotendinous and Neurovascular Architecture of the Gracilis Muscle: Application to Functional Muscle Transfer." J Plast Reconstr Aesthet Surg. 2013;66(9):1230–1237. doi:10.1016/j.bjps.2013.05.012

5. Morris SF, Yang D. "Gracilis Muscle: Arterial and Neural Basis for Subdivision." Ann Plast Surg. 1999;42(6):630–633. doi:10.1097/00000637-199906000-00008

6. Chancellor MB, Watanabe T, Rivas DA, et al. "Gracilis Urethral Myoplasty: Preliminary Experience Using an Autologous Urinary Sphincter for Post-Prostatectomy Incontinence." J Urol. 1997;158(4):1372–1375. doi:10.1016/s0022-5347(01)64218-6

7. Guo H, Sa Y, Xu Y, Wang L, Fei X. "Adynamic Graciloplasty With a Pedicled Gracilis Muscle Flap Wrapped Around Bulbar Urethra for Treatment of Male Acquired Urinary Incontinence." Urology. 2016;91:208–214. doi:10.1016/j.urology.2015.12.073

8. Guo H, Sa Y, Fu Q, Jin C, Wang L. "Experience With 32 Pelvic Fracture Urethral Defects Associated With Urethrorectal Fistulas: Transperineal Urethroplasty With Gracilis Muscle Interposition." J Urol. 2017;198(1):141–147. doi:10.1016/j.juro.2017.01.071

9. Rozanski AT, Vanni AJ. "Ventral Buccal Mucosa Graft Urethroplasty With Gracilis Muscle Flap for High Risk, Long Segment Urethral Strictures: A 20-Year Experience." Urology. 2020;140:178–180. doi:10.1016/j.urology.2020.03.008

10. Ryan JA, Gibbons RP, Correa RJ. "Urologic Use of Gracilis Muscle Flap for Nonhealing Perineal Wounds and Fistulas." Urology. 1985;26(5):456–459. doi:10.1016/0090-4295(85)90153-0

11. Hasen KV, Gallegos ML, Dumanian GA. "Extended Approach to the Vascular Pedicle of the Gracilis Muscle Flap: Anatomical and Clinical Study." Plast Reconstr Surg. 2003;111(7):2203–2208. doi:10.1097/01.PRS.0000060114.95065.C5

12. Ducic I, Dayan JH, Attinger CE, Curry P. "Complex Perineal and Groin Wound Reconstruction Using the Extended Dissection Technique of the Gracilis Flap." Plast Reconstr Surg. 2008;122(2):472–478. doi:10.1097/PRS.0b013e31817d607d

13. Stewart F, Gameiro LF, El Dib R, et al. "Electrical Stimulation With Non-Implanted Electrodes for Overactive Bladder in Adults." Cochrane Database Syst Rev. 2016;12:CD010098. doi:10.1002/14651858.CD010098.pub4

14. Warehime JM, Gaskins JT, Gupta AS, et al. "Proximity of Percutaneous Tibial Nerve Stimulation Needle Insertion to Surrounding Anatomic Structures: A Cadaveric Study." Am J Obstet Gynecol. 2023;229(4):430.e1–430.e6. doi:10.1016/j.ajog.2023.06.048

15. Panicker JN, Fowler CJ, Kessler TM. "Lower Urinary Tract Dysfunction in the Neurological Patient: Clinical Assessment and Management." Lancet Neurol. 2015;14(7):720–732. doi:10.1016/S1474-4422(15)00070-8

16. Li X, Li X, Liao L. "Mechanism of Action of Tibial Nerve Stimulation in the Treatment of Lower Urinary Tract Dysfunction." Neuromodulation. 2024;27(2):256–266. doi:10.1016/j.neurom.2023.03.017

17. Lee UJ, MacDiarmid S, Matthews CA, Gillespie E, Peters KM. "Tibial Nerve Stimulation for Urge Urinary Incontinence and Overactive Bladder: Narrative Review of Randomized Controlled Trials and Applicability to Implantable Devices." Adv Ther. 2024;41(7):2635–2654. doi:10.1007/s12325-024-02864-3

18. Amarenco G, Ismael SS, Even-Schneider A, et al. "Urodynamic Effect of Acute Transcutaneous Posterior Tibial Nerve Stimulation in Overactive Bladder." J Urol. 2003;169(6):2210–2215. doi:10.1097/01.ju.0000067446.17576.bd

19. Tahmasbi F, Salehi-Pourmehr H, Naseri A, et al. "Effects of Posterior Tibial Nerve Stimulation (PTNS) on Lower Urinary Tract Dysfunction: An Umbrella Review." Neurourol Urodyn. 2024;43(2):494–515. doi:10.1002/nau.25343