Flat feet (pes planus)
A condition in which the arch of the foot is lower than normal, with the sole of the foot flattening towards the ground during weight-bearing. May be flexible (correctable) or rigid, and either painless or associated with significant problems.
📊 Flat feet affect approximately 20-30% of the adult population, although only a minority cause symptoms. Symptomatic adult-acquired flat foot - usually due to posterior tibial tendon dysfunction - affects around 3-10% of adults over 40.
What are flat feet?
The arch of the foot is a complex structure supported by bones, ligaments, and the posterior tibial tendon - the main tendon supporting the medial (inner) arch. In flat feet, the arch collapses during standing or walking, the heel tilts outwards (valgus), and the forefoot tilts upwards and outwards. Flat feet may be present from childhood (flexible flat foot) or develop in adulthood, usually due to weakness or rupture of the posterior tibial tendon.
It is important to distinguish flexible from rigid flat feet. Flexible flat feet have a normal arch when sitting or standing on tiptoes, but lose the arch on weight-bearing - this is common, often painless, and rarely needs treatment. Rigid flat feet have no arch in any position, are often painful, and may be due to underlying conditions such as tarsal coalition (an abnormal bony or fibrous connection between foot bones). Adult-acquired flat foot (AAFD) is a progressive condition in which the arch collapses over time, usually due to posterior tibial tendon dysfunction (PTTD).
Treatment depends on the cause and severity. Many people with flat feet need no treatment. Those with symptoms are typically managed initially with supportive footwear, orthotics, and physiotherapy. Surgery is reserved for those with persistent symptoms despite conservative treatment, or with advanced deformity. The earlier in the disease process treatment is started, the more likely it is to be successful.
Common causes
- Genetic predisposition - flexible flat foot often runs in families
- Posterior tibial tendon dysfunction (PTTD) - the most common cause in adults
- Tarsal coalition - an abnormal connection between bones (causing rigid flat foot)
- Inflammatory arthritis - rheumatoid, psoriatic
- Diabetes and Charcot foot
- Obesity and pregnancy (transient)
- Trauma to the foot or ankle
- Neurological conditions affecting muscle balance
Who is at risk? Risk factors for adult-acquired flat foot include female sex (4 times more common), age over 40, obesity (BMI greater than 30), diabetes, hypertension, steroid use, and previous foot or ankle injury. A family history of flat feet is also relevant. Pregnancy can cause temporary flattening of the arch.
Symptoms
Symptoms vary depending on the severity and duration of the condition. Common symptoms include:
- Pain along the inside of the foot and ankle, around the posterior tibial tendon
- Difficulty walking on tiptoes (single-leg heel raise test is often abnormal)
- Visible collapse of the arch and outward tilt of the heel ("too many toes" sign when viewed from behind)
- Lateral foot pain in advanced cases due to bony impingement
- Fatigue or aching in the feet, especially after prolonged standing
- Calf pain or tightness due to compensatory mechanics
- Difficulty finding comfortable footwear, especially as the deformity progresses
- Symptoms typically worse with activity, better with rest
When to seek help: See a foot specialist if you have ongoing foot or ankle pain, if you notice progressive flattening of the arch, if you cannot easily rise onto your tiptoes, if you have asymmetric flat feet (one foot flatter than the other), or if your child has a rigid or painful flat foot.
How is it diagnosed?
Your foot and ankle specialist will take a detailed history and examine the foot. The following investigations may be arranged to confirm the diagnosis:
- Clinical examination - assessment of arch height standing and sitting, heel alignment, "too many toes" sign, single-leg heel raise test, and posterior tibial tendon palpation
- Weight-bearing X-rays - the standard imaging, measuring arch collapse and assessing for any bony abnormalities
- MRI - assesses posterior tibial tendon damage, hindfoot ligaments, and spring ligament integrity
- CT scan - useful for evaluating bony deformity and ruling out tarsal coalition
- Staging - the Johnson and Strom classification (Stages I-IV) guides treatment
Adult-acquired flat foot is staged from I (tendinitis, no deformity) through IV (rigid deformity with ankle arthritis). Early diagnosis at Stages I-II offers the best chance of joint-preserving treatment. Once the deformity becomes rigid (Stage III) or affects the ankle joint (Stage IV), more extensive surgery is required.
Treatment pathway
Treatment is tailored to the severity of the condition, your age, activity level, and overall health. Most conditions are treated in a stepwise fashion, starting with the least invasive options.
Observation - no treatment needed
Children and adults with flexible, painless flat feet do not require treatment. There is no good evidence that orthotics or special shoes change the natural history of flexible flat feet in asymptomatic individuals.
Supportive footwear and orthotics
For symptomatic flat feet, supportive shoes with medial arch support and a heel cup reduce pain. Custom or off-the-shelf orthotics can offload the posterior tibial tendon and improve foot mechanics. Weight loss provides additional benefit.
Posterior tibial tendon rehabilitation
A structured physiotherapy programme focusing on strengthening the posterior tibial tendon, intrinsic foot muscles, and calf muscles. Combined with orthotics and activity modification, this can be effective in early disease.
Joint-preserving reconstruction
For flexible deformities that fail conservative treatment, surgery typically involves a combination of soft tissue and bony procedures - medial displacement calcaneal osteotomy (realigning the heel), lateral column lengthening, and tendon transfer (usually FDL to posterior tibial tendon). Preserves joint motion and aims for long-lasting correction.
Hindfoot fusion
For rigid deformities, joint fusion (subtalar, double, or triple arthrodesis) provides definitive correction. Motion is permanently lost in the affected joints, but pain is reliably eliminated and the foot is correctly aligned. Recovery takes 3-6 months.
Combined ankle and hindfoot procedures
When the deformity has progressed to affect the ankle joint, more extensive surgery is required - either pantalar fusion or, in selected cases, total ankle replacement combined with hindfoot fusion. These are major operations and patient selection is critical.
Recovery
Recovery depends entirely on the type of treatment. Conservative management with orthotics and physiotherapy can give substantial relief within 3-6 months. Surgical recovery is prolonged - patients are non-weight-bearing for 6 weeks followed by progressive loading in a boot. Most patients are walking comfortably by 3-4 months, but full recovery and final outcome assessment is typically at 12 months.
- Conservative trial: 3-6 months minimum
- Recovery from joint-preserving surgery: 4-6 months
- Recovery from hindfoot fusion: 6-12 months
- Final outcome assessment: 12 months
- Long-term durability of correction: usually maintained at 10+ years
What results can I expect?
Asymptomatic flexible flat feet do not progress and require no treatment. For adult-acquired flat foot, early diagnosis and treatment (Stage I-II) gives the best outcomes, with around 70-80% improving with conservative measures. Joint-preserving surgery for flexible deformities has good outcomes in around 80% of patients. Fusion provides durable, reliable pain relief but at the cost of joint motion.
In numbers
When can I…?
Typical activity timelines for this condition. These are approximate and vary considerably between patients. Always follow the specific guidance given by your surgeon and physiotherapist.
| Activity | Typical timeline | Notes |
|---|---|---|
| Walk normally | Always | Painless flat feet need no treatment and no restriction. Asymptomatic flat feet are a normal variant.[2] |
| Drive | No restriction | Flat feet do not affect fitness to drive. |
| Start an orthotic | When symptomatic | An over-the-counter medial-arch insole or custom orthotic can substantially relieve symptoms in early AAFD.[1] |
| Strengthen the calf and arch | Daily | Heel raises (calf raises), tibialis posterior strengthening, and balance work are all useful.[1] |
| Consider surgery | After 6+ months of non-op | Reconstructive surgery is considered when symptoms persist despite at least 6 months of optimised non-surgical treatment.[1] |
| Return to activity after surgery | 4-6 months | Reconstructive flatfoot surgery has a long recovery; full activity often takes 6-12 months.[1] |
Is this normal?
Common concerns from patients with this condition or recovering from treatment, and whether they are expected or worth mentioning to your team.
Preparing for surgery?
Read our step-by-step guide: what to expect before, during, and after your procedure.
Related conditions
Your questions, answered
Plain-English answers to the things people most often ask, grounded in published guidance. Tap a question to open it.
About thisAre flat feet actually a problem?
For many people flat feet are simply a normal variation, cause no symptoms and need no treatment. Treatment is only for feet that are painful or changing.
Long-standing flat feet that have never hurt rarely need anything done.
About thisWhat is adult-acquired flat foot?
When a previously normal arch starts to flatten in adulthood, it is often due to the tibialis posterior tendon on the inside of the ankle wearing out and failing to support the arch.
This type can be progressive, so it is worth getting assessed if your arch is dropping.
Your choiceWhat helps?
Supportive footwear, arch-support insoles or orthotics, calf stretching, weight management, and sometimes a brace for tendon problems are the mainstays.
These control symptoms and support the foot rather than rebuilding the arch.
Your choiceWhen is surgery considered?
Surgery is reserved for painful, progressive or rigid deformity that is not helped by insoles and bracing. The operation is tailored to your foot and can combine tendon, bone and sometimes fusion procedures.
Recovery is lengthy, so it is a considered step.
Getting backWhat is recovery from reconstruction like?
Expect a cast or boot and a period of limited weight-bearing, followed by months of rehabilitation.
Your team will set out the stages for your specific operation.
UrgentWhat warrants prompt review?
A rapidly collapsing or painful arch, or sudden inability to stand on tiptoe, can mean the supporting tendon has failed and should be assessed promptly.
Early review gives more treatment options.
References & further reading
- 1.British Orthopaedic Foot & Ankle Society: Adult acquired flatfoot patient information
- 2.NHS: Flat feet
References are to UK clinical guidance and patient information from recognised organisations. This page is for general information and does not replace personalised advice from your own clinical team.