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Health condition · Clinically reviewed

Adult acquired flat foot, posterior tibial tendon dysfunction — from orthoses to reconstruction.

Progressive collapse of the medial longitudinal arch, most commonly from posterior tibial tendon dysfunction (PTTD). Modern management is stratified by Johnson–Strom stage — orthoses and physiotherapy early, reconstruction (osteotomy + tendon transfer) for fixed deformity, arthrodesis for arthritic hindfoot.

Jump to treatment See red-flag foot signs
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Every claim is checked against BOFAS, NICE or peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects current UK foot and ankle surgery practice on orthoses, tendon transfer and reconstruction.

Key facts

Adult acquired flat foot at a glance.

The essentials, in plain English — what PTTD is, how it is staged, and how the treatment pathway escalates from orthoses to reconstruction.

  • Definition

    Adult acquired flat foot is progressive collapse of the medial longitudinal arch, most commonly caused by posterior tibial tendon dysfunction (PTTD).

  • Johnson–Strom stages

    A four-stage classification (I–IV) guides management, from tendinitis with a normal arch to fixed deformity with hindfoot arthritis.

  • Single-heel-rise test

    Inability to perform a single-leg heel-rise on the affected side is the key clinical sign of posterior tibial tendon insufficiency.

  • Too-many-toes sign

    Viewed from behind, more toes are visible lateral to the heel — a hallmark of hindfoot valgus and forefoot abduction.

  • MRI grades tendon disease

    MRI of the posterior tibial tendon and spring ligament grades tendinosis, partial or complete rupture and coexisting arthritis.

  • Stage-based surgery

    Planning ranges from osteotomy with FDL tendon transfer in flexible deformity to triple arthrodesis for stage IV arthritic hindfoot.

Why this guide matters

Stage the deformity, then plan.

PTTD is one of those conditions where the right operation depends entirely on the stage — orthoses for early disease, reconstruction for flexible deformity, arthrodesis for arthritic hindfoot.

  • Orthoses do a lot of the work

    Custom orthoses and Arizona braces control the hindfoot and offload the PT tendon — first-line care in stages I and II.

  • Reconstruction for flexible deformity

    Medial calcaneal osteotomy plus FDL tendon transfer is the workhorse operation for stage II disease.

  • Arthrodesis for stage IV

    Fixed, arthritic hindfoot needs a triple arthrodesis — a bigger operation with real relief.

How the diagnosis is made

From collapsing arch to a clear plan.

The steps a UK GP and foot and ankle surgeon will normally follow, in order — so you know what to expect and why.

  1. 01

    Recognising

    Symptom and activity history

    Onset of medial arch pain, difficulty walking or fatigue on standing, and any change in shoe wear or gait.

  2. 02

    Recognising

    Standing foot examination

    Inspection from behind for the too-many-toes sign, hindfoot valgus and loss of the medial longitudinal arch.

  3. 03

    Recognising

    Single-heel-rise test

    The key clinical test — inability to lift the heel on the affected leg strongly suggests posterior tibial tendon dysfunction.

  4. 04

    Confirming

    Weight-bearing X-ray

    Standing radiographs quantify arch collapse, talonavicular uncoverage and any established hindfoot arthritis.

  5. 05

    Confirming

    MRI of PT tendon and spring ligament

    MRI grades tendinosis, partial and complete rupture, and assesses the spring ligament complex.

  6. 06

    Confirming

    Assess coexisting arthritis

    Look for subtalar, talonavicular and calcaneocuboid joint arthritis — a decisive factor in surgical planning.

  7. 07

    Managing

    Foot & ankle surgery consultation

    Referral to a specialist foot and ankle surgeon for stage-based reconstructive planning where conservative care fails.

Typical timeline: 4–8 weeks from first appointment to a settled surgical or non-operative plan.

Symptoms

What adult acquired flat foot actually feels like.

Medial midfoot pain, a visibly flattening arch and increasing difficulty on single-leg heel-rise — the classic PTTD pattern.

  • Medial midfoot pain

    Pain and tenderness along the medial midfoot and behind the medial malleolus — the course of the posterior tibial tendon.

  • Loss of medial arch

    A visibly flattened medial longitudinal arch on weight-bearing, often progressing over months to years.

  • Too-many-toes sign

    Viewed from behind, more toes are visible lateral to the heel — a classic sign of hindfoot valgus and forefoot abduction.

  • Hindfoot valgus

    The heel drifts into valgus (outward) alignment as the arch collapses and the deformity progresses.

  • PT tendon tenderness

    Focal tenderness and swelling along the posterior tibial tendon behind and below the medial malleolus.

  • Inability to single heel-rise

    The affected leg cannot lift the heel off the floor — the single most useful clinical sign.

  • Difficulty walking / fatigue

    Foot fatigue on standing or walking, altered gait and reduced tolerance for uneven ground.

  • Red flag

    Acute posterior tibial tendon rupture with sudden loss of the arch — needs urgent foot and ankle surgical review.

Treatment

How adult acquired flat foot is treated in the UK.

A stage-based approach — orthoses and physiotherapy early, medial calcaneal osteotomy with FDL tendon transfer for flexible deformity, and triple arthrodesis for stage IV arthritic hindfoot.

  • Custom orthosis (medial post + arch)

    A custom-moulded orthosis with a medial post and arch support offloads the posterior tibial tendon and is first-line care in early stages.

  • Ankle brace / Arizona AFO

    A rigid Arizona-style ankle-foot orthosis controls hindfoot valgus and midfoot collapse in stage II disease.

  • Physiotherapy

    Structured tibialis posterior strengthening and calf stretching — a core part of non-operative management.

  • Weight loss + activity modification

    Reducing load through the medial arch — often the highest-value modifiable factor alongside orthoses.

  • Steroid injection AVOIDED

    Cortisone injection into the posterior tibial tendon is avoided because of the real risk of tendon rupture.

  • Medial calcaneal osteotomy + FDL transfer

    The standard reconstruction for flexible stage II disease — realigns the heel and augments the failed PT tendon with FDL.

  • Lateral column lengthening

    Adds correction of forefoot abduction in stage IIB disease, often combined with medial calcaneal osteotomy and FDL transfer.

  • Triple arthrodesis

    Fusion of the subtalar, talonavicular and calcaneocuboid joints — reserved for stage IV disease with a fixed, arthritic hindfoot.

What this guide is based on

The sources behind every claim on this page.

UK national guidance, foot and ankle society standards and the original PTTD classification, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP, podiatrist or foot and ankle team knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • British Orthopaedic Foot and Ankle Society (BOFAS). Patient information and clinical standards.

  • NICE. Musculoskeletal guidance on tendon and foot disorders.

  • American Orthopaedic Foot & Ankle Society (AOFAS). Adult acquired flatfoot deformity resources.

  • Johnson KA, Strom DE. Tibialis posterior tendon dysfunction — the original four-stage classification.

Red flags

When flat foot needs urgent review.

Most PTTD progresses slowly and is managed electively. These are the situations where the picture changes and specialist review is needed sooner.

  • Acute PT tendon rupture

    Sudden loss of the arch with acute medial pain suggests posterior tibial tendon rupture — urgent surgical review.

  • Charcot foot collapse

    Rapid midfoot collapse and warmth in a person with diabetes suggests Charcot neuroarthropathy — an emergency.

  • Post-op non-union

    Persistent pain and swelling months after osteotomy or fusion may reflect non-union — imaging and specialist review.

  • Wound infection

    Increasing pain, redness, discharge or fever after foot surgery — same-day contact with the surgical team.

  • Deep vein thrombosis post-surgery

    Calf swelling, pain and warmth after foot or ankle surgery — needs urgent assessment for DVT.

  • Nerve injury

    New numbness, burning or motor weakness after surgery may reflect nerve injury — report to the surgical team promptly.

  • Failed reconstruction

    Recurrent deformity, ongoing pain and functional decline after reconstruction — needs revision assessment.

  • Recurrent deformity

    Progressive return of hindfoot valgus after surgery suggests loss of correction — imaging and specialist review.

  • Diabetic tendon disease

    Tendinopathy and deformity in a person with diabetes carries higher risk of rupture, ulceration and Charcot change.

Living with it

A progressive condition, but a well-mapped one.

Four things that make the biggest difference day to day — orthoses, tibialis posterior strengthening, load management and staged review.

A quiet reminder

Right treatment, right stage.

PTTD is a staged condition — matching the intervention to the Johnson–Strom stage is what gets the best outcome.

  1. 01 Orthoses

    Wear the orthosis, every day

    Custom orthoses only work when worn — full-time indoor and outdoor use is what supports the tendon and slows progression.

  2. 02 Physio

    Strengthen tibialis posterior

    Daily eccentric strengthening and calf stretching, done for months — the backbone of non-operative care.

  3. 03 Load

    Manage weight and activity

    Reducing load through the medial arch — modest weight loss and lower-impact activity make a real difference.

  4. 04 Reviews

    Reassess by stage, not weeks

    Progression through the Johnson–Strom stages guides when to escalate to bracing, reconstruction or fusion.

Frequently asked

Everything we get asked about adult acquired flat foot.

Quick answers on staging, orthoses, tendon transfer, arthrodesis and when to seek help.

  • What is adult acquired flat foot?

    It is progressive collapse of the medial longitudinal arch of the foot, most commonly caused by failure of the posterior tibial tendon (PTTD). Over time the hindfoot drifts into valgus and the forefoot abducts, producing the classic too-many-toes sign.

  • What is the Johnson–Strom classification?

    A four-stage classification of PTTD. Stage I is tendinitis with a normal arch. Stage II is a flexible flat foot deformity. Stage III is a fixed deformity. Stage IV adds ankle arthritis. It guides whether orthoses, reconstruction or fusion is appropriate.

  • What is the single-heel-rise test?

    You are asked to stand on one leg and lift the heel off the floor. Inability to do so on the affected side is the key clinical sign of posterior tibial tendon dysfunction and often the trigger for MRI and surgical referral.

  • Why are steroid injections avoided?

    Cortisone injected into or near the posterior tibial tendon carries a real risk of tendon rupture, which can precipitate acute arch collapse. Injection is therefore avoided in PTTD in favour of orthoses, physiotherapy and, where needed, surgical reconstruction.

  • What does reconstructive surgery involve?

    For flexible stage II disease, the standard operation is a medial calcaneal osteotomy combined with flexor digitorum longus (FDL) tendon transfer to augment the failed posterior tibial tendon, sometimes with lateral column lengthening for forefoot abduction.

  • When is a triple arthrodesis needed?

    When the deformity is fixed and there is established arthritis in the subtalar, talonavicular or calcaneocuboid joints — typically stage IV disease. Triple arthrodesis fuses those three hindfoot joints to realign the foot and relieve arthritic pain.

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