Flexor Digitorum Longus Transfer for Tibialis Posterior Dysfunction
Foot & AnkleAdvancedCore Procedure
Flexor Digitorum Longus Transfer for Tibialis Posterior Dysfunction
Operative technique for flexor digitorum longus (FDL) tendon transfer for flexible stage II adult-acquired flatfoot from posterior tibial tendon dysfunction - medial approach, FDL harvest, diseased PTT debridement, navicular fixation, and the mandatory combined medial displacement calcaneal osteotomy
High-yield overview
Joint-sparing reconstruction for flexible stage II adult-acquired flatfoot | advanced
Surgical Imaging
The flexor digitorum longus tendon along the medial foot — transferred to the navicular to reconstruct a dysfunctional posterior tibial tendon, usually with a medialising calcaneal osteotomy.Credit: AI-generated medical illustration · OrthoVellum
Critical Dangers, Contraindications and Exam Traps
FDL Transfer Alone Fails
The trap: Believing the tendon transfer can hold the arch by itself. A transferred FDL cannot withstand the powerful valgus moment of the gastroc-soleus acting lateral to the axis.
The fix: In stage II disease ALWAYS combine the FDL transfer with a medial displacement calcaneal osteotomy, and add a lateral column lengthening when forefoot abduction is marked. The bony procedure unloads and protects the reconstruction.
Operating on a Rigid (Stage III) Foot
The trap: Offering an FDL transfer to a patient with a fixed hindfoot valgus and subtalar arthritis. The transfer cannot correct a deformity that does not passively reduce.
The fix: Confirm flexibility preoperatively AND under anaesthesia. A rigid stage III foot requires realignment arthrodesis; stage IV (ankle valgus) requires an extended fusion. Stage I is treated non-operatively.
Under-correction and Recurrence
The mechanism: The commonest reason for failure. Causes include inadequate medial displacement, failure to address forefoot abduction, an under-tensioned transfer, or non-compliance with the non-weight-bearing period.
The prevention: Aim for about 1 cm of medial displacement, restore talonavicular coverage, tension the FDL with the foot in maximal inversion, and protect the construct with strict non-weight-bearing for six weeks.
Transfer Over-tensioning
The problem: Tensioning the FDL too aggressively or over-displacing the calcaneus drives the hindfoot into varus, limits ankle dorsiflexion, and causes lateral (subfibular) impingement.
The prevention: The foot should sit in slight inversion at rest after fixation, not forced varus. Balance the correction - tension the transfer in inversion and equinus but reposition to neutral to confirm the correction is balanced before closure.
Medial and Nerve Injury
The structures at risk: The tibial nerve and its medial calcaneal and medial plantar branches lie in the tarsal tunnel immediately posterior to the tendon sheath; dissection over the navicular can irritate the medial plantar nerve. The posterior tibial artery sits between FDL and FHL.
The prevention: Stay within the PTT sheath, identify the FDL before dividing it, and make the navicular tunnel from plantar-medial to dorsolateral under direct vision to avoid the neurovascular bundle.
Confusion with Tibialis Posterior Transfer for Foot Drop
The distinction: These are DIFFERENT operations. In FDL transfer for PTTD the DISEASED PTT is excised and a DIFFERENT tendon (the FDL) is rerouted to the NAVICULAR to restore inversion. In tibialis posterior transfer for foot drop the HEALTHY posterior tibial tendon is the donor, rerouted ANTERIORLY through the interosseous membrane to the DORSUM of the foot to restore dorsiflexion.
The rule: PTTD flatfoot needs a medial transfer to oppose valgus; paralytic foot drop needs an anterior transfer to replace dorsiflexion. Different tendon, different direction, different pathology.
Mnemonic
S.T.A.G.E.SSTAGES - Johnson-Strom Classification of Posterior Tibial Tendon Dysfunction
Mnemonic
T.E.N.S.I.O.NTENSION - Pitfalls in FDL Transfer for PTTD
The Disease: Posterior Tibial Tendon Dysfunction
The posterior tibial tendon (PTT) is the primary dynamic supporter of the medial longitudinal arch and the prime inverter of the subtalar joint in stance. It arises from the posterior tibia, interosseous membrane and fibula, passes behind the medial malleolus, and inserts principally on the navicular tuberosity with an extensive plantar expansion to the cuneiforms, cuboid and bases of the lesser metatarsals.
Degenerative attrition of the PTT - driven by chronic overload, a hypovascular watershed zone behind the malleolus, age, female sex, obesity, hypertension and diabetes - produces elongation and then rupture. Once the tendon fails, the uncoupled gastroc-soleus, now pulling lateral to the hindfoot axis, drives the calcaneus into valgus; the talonavicular joint uncovers medially (forefoot abduction); the medial arch collapses; and the spring ligament and then the deltoid ligament may fail in sequence. The end state is a rigid, arthritic valgus flatfoot, and ultimately ankle involvement.
Johnson-Strom Classification (with the Myerson Stage IV addition)
The classification that governs operative decision-making. Stage II is the stage for joint-sparing reconstruction.
Johnson-Strom (with Myerson) Classification of PTTD
Indications for FDL Transfer
The operation is built around three requirements:
A flexible (stage II) deformity - the hindfoot passively corrects to neutral. This is the non-negotiable prerequisite.
Failure of an adequate non-operative programme of at least three to six months (orthotic support, activity and weight modification, physiotherapy, with a walking boot for an acute flare of tenosynovitis).
A correctible, symptomatic flatfoot in a patient fit and willing to undergo reconstruction and a structured rehabilitation programme.
The FDL transfer is always the SOFT-TISSUE component of a combined reconstruction. It is paired with a medial displacement calcaneal osteotomy in essentially every case, with additional procedures selected by the specific deformity.
Contraindications
Absolute
A rigid (stage III) deformity - the transfer cannot correct a fixed hindfoot; realignment arthrodesis is required.
Stage IV disease with ankle valgus and deltoid insufficiency - needs an extended fusion.
Active infection around the surgical field.
Relative
Established subtalar or talonavicular arthritis even if the deformity is "flexible" - prefer realignment and fusion.
Morbid obesity, poorly controlled diabetes or active smoking - markedly elevated failure and wound-complication rates; optimise before reconstruction.
A neuropathic or neuromuscular flatfoot in which the FDL itself may be weak or the protective sensation is absent.
Advanced age and low functional demand, where a moulded orthotic or an ankle-foot orthosis may serve the patient better than reconstruction.
Why FDL Transfer Alone Fails - the Central Principle
Biomechanical and clinical evidence converge on one point: a transferred FDL cannot hold a corrected arch against the powerful, lateralised valgus moment of the gastroc-soleus complex. Two bony manoeuvres unload and protect the transfer:
Medial displacement calcaneal osteotomy (Koutsogiannis) translates the calcaneal tuberosity, and with it the Achilles insertion, medially. This recentres the calcaneus under the tibia, corrects the valgus, and reduces the deforming lever arm so that the transferred FDL is not asked to do too much.
Lateral column lengthening (Evans) restores the forefoot's coverage of the head of the talus, corrects abduction, and re-establishes the arch height.
The FDL transfer then provides DYNAMIC medial support and restores active inversion during gait - it augments the bony correction, it does not substitute for it. When the bony correction is omitted or inadequate, the transferred tendon stretches out and the deformity recurs.
Non-operative Treatment - the Prerequisite
Non-operative management is first-line for stage I and is trialled for early stage II before reconstruction is offered:
Orthoses: a medial arch support with a medial heel wedge or post; a University of California Biomechanics Laboratory orthotic for moderate deformity; an articulated or solid ankle-foot orthosis for severe or more rigid deformity.
Activity and weight modification, weight loss where appropriate, and a physiotherapy programme of eccentric strengthening and arch-strengthening exercises.
Short-leg cast or walking boot for an acute, painful exacerbation of tenosynovitis.
Reconstruction is offered when a compliant, well-fitted programme of at least three to six months has failed in a flexible stage II foot. Comorbidity and patient goals weigh heavily, as reconstruction is a major procedure with a long recovery.
The Posterior Tibial Tendon
The PTT is the dynamic mainstay of the medial arch. It originates from the posterior tibia, interosseous membrane and fibula, descends in the deep posterior compartment, turns in the retromalleolar groove behind the medial malleolus, and passes through the flexor retinaculum in its own fibro-osseous tunnel. It then crosses anterior to the flexor digitorum longus to reach its broad insertion on the navicular tuberosity, with plantar expansions to the cuneiforms, cuboid and the bases of the second to fourth metatarsals.
The PTT is roughly twice the cross-sectional area of the FDL and is the anteriormost structure in the retromalleolar groove. It functions as the prime inverter of the subtalar joint in stance, locks the midfoot into a rigid lever for push-off, and supports the medial longitudinal arch.
A hypovascular watershed zone lies just posterior to the medial malleolus - the region where degenerative change and rupture most often occur.
The Flexor Digitorum Longus
The FDL originates from the posterior tibia below the soleal line and runs in the deep posterior compartment immediately posterior (and slightly lateral) to the PTT. In the retromalleolar groove the order from anterior to posterior is tibialis posterior, flexor digitorum longus, the posterior tibial artery and vein, the tibial nerve, and flexor hallucis longus - remembered as Tom, Dick, and a very nervous Harry.
Distally the FDL crosses the FHL at the knot of Henry on the medial midfoot before dividing into four slips that pass to the lesser toes.
Why the FDL Is the Ideal Substitute
Position: it lies immediately adjacent to the PTT, so it can be harvested and rerouted through a short medial transfer.
In phase: it fires through midstance and push-off, much like the PTT, so its timing suits arch support and inversion.
Repurposable function: it is already a weak inverter and plantarflexor, which is precisely the function to be restored.
Expendable: its loss is well compensated by flexor hallucis longus and quadratus plantae, so most patients have no clinically important clawing of the lesser toes after harvest.
The Medial Approach
A curvilinear or longitudinal medial incision is made from just distal to the tip of the medial malleolus, following the course of the PTT, to and slightly beyond the navicular tuberosity. It can be extended proximally to expose more of the PTT and distally to expose the navicular.
The saphenous vein and nerve cross the field superficially over the malleolus and are protected.
The PTT sheath is opened longitudinally and the tendon inspected. The diseased segment - usually an attenuated, frayed or frankly ruptured portion at the retromalleolar watershed zone - is identified.
The FDL is found immediately deep and posterior to the PTT, traced distally to the knot of Henry, and divided with maximum length preserved. The proximal stump is then mobilised and delivered into the wound adjacent to the PTT course.
Positioning
Supine with the ipsilateral hip supported and the leg externally rotated so that the medial border of the foot faces the surgeon.
A thigh tourniquet for a bloodless field.
Image intensifier (fluoroscopy) is used throughout to confirm the calcaneal osteotomy cut, the medial displacement, and the screw and tunnel positions.
Anatomy - Danger Structures
Tibial nerve and branches (medial calcaneal, medial and lateral plantar) - lie in the tarsal tunnel posterior to the tendons; dissection over the navicular can irritate the medial plantar nerve and is a source of postoperative medial nerve irritation.
Posterior tibial artery - between FDL and FHL in the tarsal tunnel; protected by staying anterior within the sheath.
Saphenous vein and nerve - subcutaneous over the medial malleolus; identified and protected.
Sural nerve - on the lateral side, at risk during the lateral exposure for the calcaneal osteotomy.
Spring (plantar calcaneonavicular) ligament and deltoid - their integrity is assessed intraoperatively, as spring-ligament failure contributes to the deformity and may need plication or reconstruction.
Positioning and Preparation
The patient is positioned supine with the ipsilateral hip bumped and the leg externally rotated so the medial foot faces the surgeon. A thigh tourniquet is used and image intensification is available throughout. Anaesthesia is general or regional, and the patient is usually admitted overnight given the magnitude of the reconstruction and the strict postoperative non-weight-bearing requirement.
Clinical Pearl
Technical Tip: 'Before I drape, I re-examine the foot under anaesthesia to confirm the deformity is passively correctible - this is my final check that a joint-sparing transfer is appropriate. I also re-check the Silfverskiold test for an equinus contracture and the anteroposterior talonavicular coverage for abduction, because these decide whether I add a gastrocnemius recession and a lateral column lengthening to the calcaneal osteotomy.'
Step 1 - Expose and Assess the PTT
The medial incision is made along the PTT course and the sheath is opened longitudinally. The tendon is inspected and the degenerate or ruptured segment is identified, typically at the retromalleolar watershed zone. Any healthy distal stump is preserved for later tenodesis. The spring ligament is examined and plicated or reconstructed if it is grossly incompetent, as uncorrected spring-ligament failure undermines the arch support.
Step 2 - Harvest the FDL
The FDL is identified immediately deep and posterior to the PTT. It is traced distally to the knot of Henry, traction is applied to confirm that it flexes the lesser toes, and it is then divided with maximum length preserved. The proximal stump is mobilised proximally so that it lies freely adjacent to the PTT course, ready for transfer.
This is the bony component that unloads the reconstruction and is performed in virtually every stage II case.
A separate lateral oblique incision is made over the calcaneal tuberosity, posterior to the peroneal tendons and the sural nerve, which are protected.
The osteotomy is cut obliquely, from posterosuperior to anteroinferior, across the tuberosity just posterior to the peroneal tubercle and parallel to the posterior facet, taking care not to enter the subtalar joint or breach the medial cortex onto the neurovascular bundle.
The tuberosity fragment is translated medially by approximately one centimetre, which recentres the calcaneus and medialises the Achilles insertion.
Clinical Pearl
Technical Tip: 'I make the calcaneal osteotomy cut parallel to the posterior facet and check it with the image intensifier in both planes before I displace the fragment. I translate the tuberosity about one centimetre medially and hold the reduction with one or two guide wires before I fix it. I aim for the foot to rest in two to five degrees of valgus - corrected, but not driven into varus.'
When forefoot abduction is marked (stage IIb) and the talonavicular joint is not adequately covered after the calcaneal osteotomy, an opening-wedge lateral column lengthening is added through the anterior calcaneus at the calcaneocuboid joint. A tricortical iliac crest autograft or allograft wedge is inserted to restore the arch and the talonavicular coverage. This procedure also tensions the lateral soft tissues and indirectly supports the transfer.
Step 5 - (Optional) Gastrocnemius Recession
If the Silfverskiold test demonstrates a gastrocnemius equinus, a Strayer or Baumann recession is performed. Releasing a tight gastrocnemius reduces the deforming force on the reconstruction and protects the corrected alignment.
Step 6 - Prepare the Navicular and Route the FDL
The navicular tuberosity - the principal insertion of the PTT - is exposed. A tunnel is drilled through the navicular from plantar-medial to dorsolateral and dilated to the size of the FDL. The harvested FDL is then passed from plantar to dorsal through the tunnel using a tendon passer or a whip-suture technique.
Dangers at this step
Injuring the medial plantar nerve branches or the posterior tibial artery while drilling the navicular tunnel - keep the starting point plantar-medial on the tuberosity and direct the drill dorsolateral, away from the tarsal tunnel.
Making the tunnel too large, which weakens the navicular, or too small, which strips the tendon - dilate incrementally.
Losing FDL length during harvest, leaving insufficient tendon to reach and cross the navicular - divide the FDL as far distally as the knot of Henry allows.
Step 7 - Fix the FDL into the Navicular under Tension
With the foot held in maximal inversion and equinus, the FDL is tensioned and secured:
An interference screw (bioabsorbable or metallic, commonly 5.5 to 7.0 millimetres) is seated in the tunnel alongside the tendon to wedge it against the navicular wall, and/or
A suture anchor is placed into the navicular, and/or
The FDL is tenodesed to the residual PTT stump and the spring ligament with a strong non-absorbable braided suture.
The transfer should feel snug and the foot should rest in slight inversion. Over-tensioning - forcing the foot into varus - is avoided.
Clinical Pearl
Technical Tip: 'I tension the FDL with the foot held in maximal inversion and equinus, then I reposition the foot to neutral to check that the correction is balanced - the hindfoot should sit in slight valgus, not varus. If I have over-tensioned, the foot will not come to neutral comfortably and I will see lateral opening, so I back off the tension. I always combine the interference screw with a tenodesis suture to the residual PTT stump for redundancy.'
Step 8 - Closure and Final Checks
The PTT sheath is closed over the transfer where possible. The foot is repositioned to neutral to confirm that the correction holds. Intraoperative fluoroscopy confirms the calcaneal axis, the displacement, and the position of the screws and tunnel. The wounds are closed in layers and a well-padded short-leg posterior splint is applied with the foot held in slight inversion and equinus.
Implants and Fixation
Medial displacement calcaneal osteotomy: one or two partially threaded cannulated cancellous screws (commonly 6.5 to 7.3 millimetres), directed from posteromedial to anterolateral to engage the anterior calcaneus and the sustentaculum; a locking calcaneal plate is added if the fixation is tenuous.
FDL to navicular: a bioabsorbable or metal interference screw (5.5 to 7.0 millimetres) and/or a suture anchor, with a non-absorbable braided suture for tenodesis to the residual PTT stump.
Lateral column lengthening: a tricortical iliac crest autograft or allograft wedge, occasionally supplemented with a small plate across the calcaneocuboid joint.
Complications - Recognition, Prevention and Management
Post-operative Protocol
The rehabilitation protects both the calcaneal osteotomy and the tendon-to-bone healing of the transfer.
Weeks 0 to 2
A well-padded short-leg posterior splint holds the foot in slight inversion and equinus.
Strict non-weight-bearing, with elevation to control swelling.
Wound inspection at the first review.
Weeks 2 to 6
Suture removal and transition into a non-articulated short-leg cast or controlled-ankle-motion boot, continuing non-weight-bearing.
Radiographs to confirm maintenance of the calcaneal displacement and hardware position.
Weeks 6 to 8
Radiographic confirmation of osteotomy healing permits protected weight-bearing in the boot.
Gentle active ankle and subtalar range-of-motion exercises begin; the boot is gradually weaned as comfort and control allow.
Weeks 8 to 12
Full weight-bearing in a supportive shoe with a medial arch orthotic.
Progressive inversion and eversion strengthening, proprioception work, and the start of single-heel-rise training.
Months 3 to 6
Return to most daily activities; physiotherapy continues with functional and sport-specific rehabilitation.
Months 6 to 12
Continued maturation of the reconstruction; full recovery is typically judged at around twelve months, with most patients reaching their functional plateau by six to nine months.
Orthotic and Footwear Management
A medial arch support orthotic is generally used long-term to protect the reconstruction and support the corrected alignment. Supportive, lace-up footwear is recommended, and an ankle-foot orthosis is reserved for the elderly or low-demand patient with residual weakness or imbalance.
Distinction - FDL Transfer for PTTD vs Tibialis Posterior Transfer for Foot Drop
This is a frequent exam point of confusion. The two operations share the words "transfer" and the medial hindfoot, but they are entirely different procedures.
FDL transfer for posterior tibial tendon dysfunction
The pathology is a flexible stage II flatfoot in which the PTT is diseased and has been excised or debrided.
A different tendon - the FDL - is harvested and rerouted to the navicular, on the medial side of the foot.
The goal is to restore medial arch support and active inversion, opposing the valgus and abduction of the flatfoot.
It is always combined with a bony realignment (calcaneal osteotomy plus lateral column lengthening as indicated).
Tibialis posterior transfer for foot drop
The pathology is a paralytic foot drop, most often from a common peroneal or peroneal nerve palsy, in which the dorsiflexors are weak or absent but the posterior tibial tendon is healthy.
The healthy posterior tibial tendon is detached from its navicular insertion, rerouted anteriorly through the interosseous membrane, and reattached to the dorsum of the foot (for example the lateral cuneiform or the lateral ray), often as part of a Bridle procedure with a split tibialis anterior and the peroneus longus.
The goal is to restore dorsiflexion, replacing the function of the paralysed anterior tibial and peroneal muscles.
In short: PTTD flatfoot needs a medial transfer to oppose valgus (different tendon, to the navicular); paralytic foot drop needs an anterior transfer to replace dorsiflexion (the posterior tibial tendon itself, to the dorsum). Different donor tendon, different direction, and a fundamentally different pathology.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioAdvanced
Clinical prompt
“A 56-year-old woman presents with worsening medial ankle pain and a progressive flattening of her right arch over two years. She has tried a moulded orthotic and physiotherapy for eight months with no lasting benefit. Examination shows a flexible hindfoot valgus, a positive too-many-toes sign, and she cannot perform a single heel rise. How do you manage her?”
Practical approach
This woman has a flexible stage II posterior tibial tendon dysfunction that has failed an adequate non-operative programme of eight months - the standard indication for a joint-sparing reconstruction. I would confirm the stage, counsel her thoroughly, and plan a combined FDL transfer with a calcaneal osteotomy.
**Confirming the stage and the deformity**: I would document that the hindfoot valgus passively corrects to neutral, both in the clinic and again under anaesthesia, because a rigid stage III foot is a contraindication to a transfer and would instead need realignment arthrodesis. I would weight-bear radiographs to assess the anteroposterior talonavicular coverage and the talus-first metatarsal angle, and I would perform a Silfverskiold test to detect an equinus contracture. I would screen her comorbidities - obesity, diabetes, hypertension and smoking - because these markedly affect wound healing and recurrence, and I would optimise them before surgery.
**Counselling**: I would be honest that this is a major reconstruction with a long recovery. I would explain the rationale for combining a tendon transfer with a bony procedure, the expected six weeks of strict non-weight-bearing, and the realistic functional outcome - a corrected, more comfortable foot with improved single-heel-rise strength, though not a normal foot.
**Operative plan**: A medial approach to expose and debride the diseased PTT, harvest the FDL, and transfer it to the navicular under tension in maximal inversion and equinus. This is combined with a medial displacement calcaneal osteotomy, and a lateral column lengthening is added if the talonavicular coverage is not restored. A gastrocnemius recession is added if the Silfverskiold test is positive. The FDL is fixed with an interference screw and a tenodesis suture to the residual PTT stump.
**Post-operative**: Six weeks of strict non-weight-bearing in a splint then a boot, followed by protected weight-bearing, then strengthening and single-heel-rise training, with a medial arch orthotic long-term. I would warn her that full recovery takes up to a year, and that some persistent single-heel-rise weakness is expected because the FDL is weaker than the original PTT.
Viva scenarioAdvanced
Clinical prompt
“Describe the operative technique of a flexor digitorum longus transfer for stage II posterior tibial tendon dysfunction, and explain why the tendon transfer is always combined with a bony procedure.”
Practical approach
I will describe the technique and then the biomechanical rationale for combining it with a calcaneal osteotomy.
**Positioning and approach**: The patient is supine with the ipsilateral hip bumped and the leg externally rotated, a thigh tourniquet is applied, and image intensification is used throughout. A curvilinear medial incision runs from just distal to the medial malleolus along the PTT to the navicular tuberosity. The saphenous vein and nerve are protected, the PTT sheath is opened longitudinally, and the diseased segment of tendon is inspected and debrided, preserving any healthy distal stump.
**Harvesting the FDL**: The FDL lies immediately deep and posterior to the PTT. It is traced distally to the knot of Henry, traction confirms it flexes the lesser toes, and it is divided with maximum length preserved. The proximal stump is mobilised into the wound.
**The bony component - why it is mandatory**: A transferred FDL cannot hold a corrected arch against the powerful valgus moment of the gastroc-soleus, which now pulls lateral to the axis. A medial displacement calcaneal osteotomy translates the calcaneal tuberosity and the Achilles insertion medially by about one centimetre, recentring the calcaneus and reducing the deforming lever arm. A lateral column lengthening is added when forefoot abduction is marked, to restore the talonavicular coverage and arch height. Without these, the transferred tendon stretches out and the deformity recurs.
**Preparing and tensioning the transfer**: A tunnel is drilled through the navicular tuberosity from plantar-medial to dorsolateral, and the FDL is passed through it. With the foot held in maximal inversion and equinus, the FDL is tensioned and fixed with an interference screw and a tenodesis suture to the residual PTT stump. The foot should rest in slight inversion at rest - corrected, but not over-tensioned into varus.
**Closure**: The foot is repositioned to neutral to confirm the correction holds, fluoroscopy confirms the calcaneal displacement and hardware, and a padded short-leg splint holds the foot in slight inversion and equinus for six weeks of strict non-weight-bearing.
Viva scenarioAdvanced
Clinical prompt
“A candidate in a viva states that 'a posterior tibial tendon transfer is used to correct a flatfoot.' Clarify the confusion between a flexor digitorum longus transfer for posterior tibial tendon dysfunction and a tibialis posterior transfer for foot drop.”
Practical approach
The candidate has conflated two entirely different operations. They share the words transfer and the medial hindfoot, but the donor tendon, the direction of the transfer, and the underlying pathology are all different.
**Flexor digitorum longus transfer for PTTD**: The pathology is a flexible stage II adult-acquired flatfoot in which the posterior tibial tendon itself is diseased and has been excised or debrided. A DIFFERENT tendon - the flexor digitorum longus - is harvested and rerouted to the navicular on the medial side of the foot. The goal is to restore medial arch support and active inversion, opposing the valgus and abduction of the flatfoot. It is combined with a bony realignment - a medial displacement calcaneal osteotomy, plus a lateral column lengthening if abduction is marked. So here the posterior tibial tendon is the DISEASED structure being replaced, and a different tendon is brought in to do its job on the medial side.
**Tibialis posterior transfer for foot drop**: The pathology is a paralytic foot drop, usually from a common peroneal or peroneal nerve palsy, in which the dorsiflexors are paralysed but the posterior tibial tendon is healthy. The healthy posterior tibial tendon is detached from its navicular insertion, rerouted anteriorly through the interosseous membrane, and reattached to the dorsum of the foot, for example to the lateral cuneiform or lateral ray, often as part of a Bridle procedure with a split tibialis anterior and the peroneus longus. The goal is to restore dorsiflexion, replacing the function of the paralysed muscles. Here the posterior tibial tendon is the healthy DONOR being redirected to a new job on the dorsum.
**The key teaching point**: In PTTD flatfoot we need a medial transfer to oppose valgus, using the FDL because the PTT is dead. In paralytic foot drop we need an anterior transfer to replace dorsiflexion, using the posterior tibial tendon itself because it is healthy and available. The candidate should be corrected: a posterior tibial tendon transfer is for foot drop, not for a flatfoot; a flatfoot with PTTD is managed with an FDL transfer to the navicular plus a calcaneal osteotomy.
Exam day cheat sheet
Flexor Digitorum Longus Transfer for Tibialis Posterior Dysfunction - exam day summary
