Adult-acquired flat foot — Rapid

Synopsis

Recognise progressive collapsing foot deformity from posterior tibial tendon and ligament failure, separate flexible from rigid disease and neuropathic collapse, assess skin and circulation, and deliver orthotic, rehabilitation and reconstructive care before fixed disability develops.

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.

Key red flags

A unilateral hot red swollen foot with neuropathy requires immediate offloading and active Charcot assessment rather than continued walking for presumed tendon pain.

Ulceration, drainage, spreading erythema, fever or deep tenderness requires urgent diabetic-foot and surgical infection pathways.

Rest pain, coolness, tissue loss, absent pulses or delayed refill requires vascular assessment before bracing or reconstruction.

Sudden painful collapse after trauma, inability to bear weight or focal bone tenderness requires fracture and ligament imaging.

Rapid rigid deformity, night pain or destructive change without neuropathy requires inflammatory, infectious or tumour investigation.

Investigation priorities

First-line standing flexibility and heel-rise examinationFirst stepFirst line

Confirm progressive deformity, posterior tibial dysfunction and whether hindfoot and forefoot remain correctable.

First-line weight-bearing foot and ankle radiographsFirst line

Quantify arch collapse, talar uncoverage, hindfoot alignment, arthritis and ankle tilt under load.

Management branches

First-lineStage flexibility and tissue safety

A new or progressive adult flatfoot is present without immediate sepsis or ischaemic threat.

Examine standing alignment, single heel rise, manual flexibility, calf tightness, joints, skin, sensation and pulses.
Obtain weight-bearing foot, hindfoot and ankle radiographs when symptoms or progression justify structural assessment.
Separate lifelong painless flexible flatfoot from acquired progression and screen diabetes, neuropathy, inflammatory and vascular disease.
Immediately leave this pathway and offload if unilateral heat and swelling raises active Charcot concern.

Key medicines

Topical diclofenac gelApply 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 appropriateWhen 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.

Open full textbook →Answer 2 questions