01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Ask whether the arch was always low or has changed in adulthood. Progressive disease usually begins with medial ankle pain and fatigue, then visible flattening, shoe asymmetry and eventually lateral impingement. Establish speed of change, trauma, inflammatory arthritis, diabetes, neuropathy, ulcer history, obesity, smoking and vascular symptoms. Ask about walking distance, uneven ground, stairs, heel rise and brace tolerance. Sudden heat and swelling in an insensate foot is a different emergency from gradual painful collapse.
Examine from behind and in front while standing. Count visible lateral toes, observe the medial arch, hindfoot valgus, forefoot abduction and ankle tilt. Perform bilateral and single-leg heel rise: a functioning posterior tibial complex should elevate the heel and invert the hindfoot. Palpate the tendon behind the medial malleolus, spring-ligament and sinus tarsi. Assess whether hindfoot, forefoot supination and ankle equinus correct manually. Document calf tightness, joint motion, skin, callus, sensation and pulses.
Weight-bearing AP and lateral foot, hindfoot alignment and standing ankle radiographs define talar uncoverage, arch collapse, calcaneal valgus, midfoot arthritis and ankle tilt. Ultrasound evaluates tendon continuity dynamically. MRI maps tendon, spring ligament, marrow and joint disease when reconstruction depends on soft tissue. Weight-bearing CT shows three-dimensional impingement and joint degeneration under physiological load. Imaging is adjunctive; a hot neuropathic foot remains offloaded even when initial radiographs are normal.
Flexible early disease is managed by unloading failing medial structures while restoring capacity. A supportive lace-up shoe and medial arch-controlling orthosis may suffice; greater deformity can require a University of California Biomechanics Laboratory-type device or articulated ankle-foot orthosis. A short period in a boot can settle an acute painful tendon flare, followed by transition to support. Check that devices do not create pressure at the talar head, malleoli or toes.
Rehabilitation addresses calf flexibility, posterior tibial inversion and heel-rise strength, intrinsic foot control, hip and balance. Begin within a range that does not collapse the arch painfully, then progress bilateral to unilateral heel rise and longer walking. Weight reduction may reduce load when desired and feasible, but care must not be withheld. Topical or short oral analgesia can enable exercise. Injection around a diseased posterior tibial tendon is avoided routinely because tendon weakening can accelerate failure.
Progression despite orthotic and exercise care deserves early foot-and-ankle referral while the foot remains flexible. Joint-preserving reconstruction may combine flexor digitorum longus transfer with medialising calcaneal osteotomy, spring-ligament treatment, lateral-column lengthening or medial-column correction according to components. A tendon transfer alone cannot correct established bony malalignment. Procedures require prolonged protected weight-bearing and rehabilitation and carry wound, nerve, non-union and over- or under-correction risks.
Rigid subtalar or midfoot deformity with arthritis usually requires selected double or triple fusion rather than flexible reconstruction. Late ankle valgus may need deltoid, osteotomy, fusion or replacement strategies. The goal is a plantigrade, braceable, pain-controlled foot, not a cosmetically high arch. Smoking, diabetes, neuropathy, obesity, vascular disease and bone health alter risk and must be optimised without leaving a progressive deformity unreviewed.
Active Charcot neuroarthropathy must remain prominent in diabetes and neuropathy. Compare foot temperature, inspect for ulcer and assess infection, but do not use absence of fever or pain as reassurance. Make the patient non-weight-bearing, immobilise safely and refer within one working day, or immediately for sepsis, gangrene, deep infection or critical ischaemia. Pregnancy changes imaging and analgesia discussion; anticoagulation requires coordinated procedural planning.
Key points
- Adult acquired flatfoot is now described as progressive collapsing foot deformity because tendon, spring ligament, hindfoot, forefoot and sometimes ankle fail together.
- Key findings are medial ankle pain, hindfoot valgus, forefoot abduction and too-many-toes appearance, with weak or painful single-leg heel rise and failure of the heel to invert.
- Determine flexibility: a deformity that corrects with heel rise or manual positioning can use joint-preserving options, whereas fixed subtalar or midfoot disease often requires fusion-based planning.
- First-line structural investigation is weight-bearing AP and lateral foot plus hindfoot alignment and ankle radiographs; non-weight-bearing images underestimate collapse.
- Ultrasound or MRI answers a posterior tibial tendon and spring-ligament question, while weight-bearing CT maps complex three-dimensional or arthritic deformity for surgery.
- First-line flexible-disease management is supportive footwear, an arch-controlling orthosis or ankle-foot brace, temporary boot for a painful flare and progressive calf, posterior tibial and whole-limb rehabilitation.
- Refer early when deformity progresses, heel rise fails or orthotic care does not preserve function; flexible reconstruction may combine tendon transfer, calcaneal osteotomy, lateral-column or first-ray correction.
- A hot swollen neuropathic foot is not routine posterior tibial tendinopathy: make it non-weight-bearing immediately and obtain urgent multidisciplinary Charcot and infection assessment.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Posterior tibial tendon failure
Degenerative elongation or tearing reduces dynamic inversion and arch support, especially in middle age with obesity, hypertension, diabetes or inflammatory disease.
Spring-ligament failure
Attenuation of the calcaneonavicular spring complex permits the talar head to sag medially and plantarward, worsening forefoot abduction and arch collapse.
Pre-existing foot morphology
Flexible flatfoot, accessory navicular, calf tightness and first-ray or hindfoot alignment can increase load on medial supporting structures.
Inflammatory or traumatic disease
Rheumatoid tenosynovitis, ankle injury and less common acute tendon rupture can initiate or accelerate adult progressive deformity.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Medial dynamic support loss
Posterior tibial dysfunction weakens hindfoot inversion and forefoot stabilisation during stance, making single-leg heel rise difficult or impossible.
- 2Hindfoot valgus
The calcaneus drifts outward beneath the talus, flattening the arch and increasing lateral subfibular impingement as disease advances.
- 3Forefoot abduction
The navicular and forefoot move laterally around an uncovered talar head, creating the too-many-toes sign when viewed from behind.
- 4Fixed joint degeneration
Initially flexible ligament and tendon failure becomes rigid as subtalar and midfoot joints contract and develop arthritis, narrowing reconstruction choices.
- 5Ankle-valgus progression
Late deltoid-ligament failure permits talar tilt within the ankle mortise, producing ankle-level pain and a more complex deformity.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
More lateral toes are visible from behind because the forefoot abducts around the talar head, not because the toes themselves are abnormal.
Pain, inability to rise or failure of the calcaneus to invert indicates posterior tibial complex dysfunction and helps stage functional severity.
Hindfoot valgus and forefoot position correct with manual testing or heel rise, preserving joint-sparing reconstruction options.
Fixed subtalar or midfoot deformity, crepitus and arthritic pain indicates contracture and joint degeneration that often requires fusion-based planning.
Pain beneath the fibula or in the sinus tarsi can dominate late disease when valgus produces lateral bony contact.
Marked unilateral warmth, oedema and erythema in an insensate foot requires immediate offloading despite little pain or normal early radiographs.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
First-line standing flexibility and heel-rise examinationFirst stepFirst line - Why
- Confirm progressive deformity, posterior tibial dysfunction and whether hindfoot and forefoot remain correctable.
- Interpretation and limitations
- Failed inversion on heel rise supports medial-support failure; rigidity narrows joint-preserving options.
- 02
First-line weight-bearing foot and ankle radiographsFirst line - Why
- Quantify arch collapse, talar uncoverage, hindfoot alignment, arthritis and ankle tilt under load.
- Interpretation and limitations
- Standing images are essential because unloaded films can hide deformity; normal early films do not exclude active Charcot.
- 03
Posterior tibial tendon ultrasound - Why
- Assess tenosynovitis, degeneration, tear and dynamic function when tendon anatomy changes treatment.
- Interpretation and limitations
- Structural abnormality must align with weakness and deformity; ultrasound does not stage every ligament or arthritic component.
- 04
MRI foot and ankle - Why
- Map posterior tibial tendon, spring ligament, deltoid, marrow and joint pathology for complex differential or reconstruction.
- Interpretation and limitations
- MRI is useful for soft tissue but not required before first-line orthotic care in an otherwise typical flexible presentation.
- 05
Weight-bearing CT - Why
- Define three-dimensional peritalar subluxation, lateral impingement and joint arthritis for selected surgical planning.
- Interpretation and limitations
- Use when load-dependent bone relationships alter osteotomy or fusion strategy, not as routine screening.
- 06
Diabetic-foot and vascular testing - Why
- Assess temperature, ulcer, protective sensation, pulses, Doppler waveforms and toe pressure when neuropathy or perfusion risk exists.
- Interpretation and limitations
- Calcified arteries can make ankle pressure falsely reassuring; tissue threat and Charcot suspicion require specialist pathways.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Constitutional flexible flatfoot
A lifelong bilateral painless low arch that reforms on tiptoe and has normal strength differs from new unilateral progressive collapse.
Charcot neuroarthropathy
Neuropathy, major warmth and swelling, modest pain and fragmentation or subluxation require immediate offloading rather than routine tendon rehabilitation.
Tarsal coalition
Rigid painful flatfoot beginning earlier in life, restricted subtalar movement and recurrent sprains suggests congenital bony or fibrous bridging.
Inflammatory arthritis
Several swollen joints, prolonged morning stiffness and systemic features indicate synovitis and ligament failure from inflammatory disease.
Isolated ankle or midfoot arthritis
Joint-line tenderness, stiffness and radiographic degeneration may flatten the foot secondarily without primary posterior tibial tendon disease.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01First-lineStage flexibility and tissue safetyFirst stepFirst lineA new or progressive adult flatfoot is present without immediate sepsis or ischaemic threat.+
- 1Examine standing alignment, single heel rise, manual flexibility, calf tightness, joints, skin, sensation and pulses.
- 2Obtain weight-bearing foot, hindfoot and ankle radiographs when symptoms or progression justify structural assessment.
- 3Separate lifelong painless flexible flatfoot from acquired progression and screen diabetes, neuropathy, inflammatory and vascular disease.
- 4Immediately leave this pathway and offload if unilateral heat and swelling raises active Charcot concern.
02Flexible diseaseSupport the arch and restore muscleThe deformity remains correctable and posterior tibial pain or weakness limits walking.+
- 1Fit supportive footwear and an arch-controlling orthosis or ankle-foot brace matched to deformity and skin tolerance.
- 2Use a short boot period only for a painful flare, then transition into support rather than prolonged deconditioning.
- 3Progress calf flexibility, inversion, heel-rise, intrinsic foot, hip and balance exercises with walking goals.
- 4Review skin pressure, brace adherence, heel-rise function and deformity progression over six to twelve weeks.
03ReconstructionRefer before flexibility is lostFlexible deformity progresses or remains substantially disabling despite credible brace and rehabilitation treatment.+
- 1Refer with weight-bearing images and document which hindfoot, forefoot, medial-column and ankle components remain flexible.
- 2Use ultrasound, MRI or weight-bearing CT only for the soft-tissue and bony questions that determine reconstruction.
- 3Discuss combined tendon, ligament and osteotomy procedures rather than expecting one tendon transfer to correct every component.
- 4Optimise smoking, diabetes, skin, perfusion, bone and home support for prolonged protected weight-bearing.
04Rigid or CharcotUse the correct limb-preservation routeThe deformity is rigid and arthritic, or the foot is acutely hot, swollen and neuropathic.+
- 1For rigid painful deformity, discuss braceability and fusion-based reconstruction to create a plantigrade foot.
- 2For suspected active Charcot, make the patient non-weight-bearing, immobilise and obtain multidisciplinary foot assessment within one working day.
- 3Admit immediately for sepsis, deep infection, gangrene, critical ischaemia or rapidly progressive tissue threat.
- 4Do not inject or start routine tendon loading until acute neuropathic fracture and infection have been excluded.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Topical diclofenac gel
Apply 2–4 g of diclofenac 1.16% gel to intact painful medial-foot or ankle skin per dose, no more than three or four times daily for a short trial within the product maximum.Avoid ulcers, pressure injury, infected or insensate uninspected skin and NSAID hypersensitivity, and account for pregnancy and other NSAID exposure.
Oral naproxen with gastroprotection when appropriate
When justified, take oral naproxen 250–500 mg with food twice per day and stop after the shortest useful course; where gastroprotection is needed, prescribe omeprazole 20 mg once daily during exposure.Review renal function, ulcer and bleeding history, cardiovascular disease, hypertension, frailty, anticoagulants and antiplatelets; avoid combined NSAIDs and apply pregnancy restrictions from 20 weeks.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Progressive rigid deformity
A flexible correctable foot can become fixed and arthritic, changing treatment from tendon and osteotomy reconstruction to multi-joint fusion.
Lateral impingement
Severe hindfoot valgus brings calcaneus and lateral talus beneath the fibula, causing painful subfibular contact despite medial disease origin.
Pressure injury
Prominent talar head, midfoot collapse and ill-fitting orthoses create callus and ulcer, especially in diabetes, neuropathy or vascular insufficiency.
Ankle arthritis
Late deltoid failure and talar tilt overload ankle cartilage and may require ankle-level reconstruction or fusion.
Surgical non-union and wound harm
Osteotomy and fusion carry infection, nerve injury, hardware irritation, non-union and adjacent-joint loading, with higher risk from smoking, diabetes and poor perfusion.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Record standing hindfoot position, too-many-toes appearance, single heel-rise height and inversion, walking distance and brace tolerance.
- Inspect medial talar-head, malleolar, plantar and toe skin after every orthosis change, especially with neuropathy.
- Repeat temperature comparison and urgent Charcot screen if swelling, redness or shape changes unexpectedly.
- Follow weight-bearing radiographic progression when deformity or ankle tilt is changing, not merely tendon pain scores.
- After reconstruction or fusion, monitor wound, neurovascular status, alignment and union before advancing weight-bearing.
- Reassess arterial supply when skin fails, rest pain appears or healing is delayed, using vascular expertise beyond ankle pressure alone.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
The tendon is not the whole deformity
Spring ligament, hindfoot, forefoot and ankle progressively participate, so isolated tendon treatment cannot correct established bony collapse.
Heel rise shows dynamic function
A normal heel rise both lifts and inverts the calcaneus; height without inversion still indicates abnormal posterior tibial mechanics.
Flexibility determines reconstruction
Correctable deformity permits osteotomy and soft-tissue balancing, whereas fixed arthritic joints require fusion to regain plantigrade alignment.
Lateral pain can have medial origins
Posterior tibial and spring-ligament failure drives valgus until the lateral hindfoot impinges beneath the fibula.
A brace must be skin safe
The strongest correction is harmful if it creates pressure over a neuropathic talar head, malleolus or toe prominence.
Warmth changes everything
A rapidly hot neuropathic foot enters a non-weight-bearing Charcot pathway even when a chronic flatfoot deformity already exists.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling a lifelong painless flexible flatfoot new posterior tibial tendon failure without a progression history.
- 02
Assessing alignment seated or on non-weight-bearing radiographs and missing load-dependent collapse.
- 03
Recording heel-rise height without observing whether the hindfoot inverts.
- 04
Prescribing an orthosis without checking pressure areas, protective sensation and arterial supply.
- 05
Delaying referral until a correctable deformity becomes rigid and requires multi-joint fusion.
- 06
Treating a hot swollen neuropathic foot as tendinopathy and allowing continued weight-bearing.