Flat Feet in Adults: When They Cause Problems and How to Fix Them

Flat feet in children often resolve on their own — the arch develops as the foot matures. But flat feet in adults are a different story. Some adults have always had flat feet and function perfectly well. Others develop progressively collapsing arches that cause pain, fatigue, and a cascade of problems extending from the feet to the knees, hips, and lower back.

The distinction that matters clinically isn't whether your feet are flat — it's whether they're causing problems, and whether the condition is stable or progressive.

Two Types of Adult Flat Feet

Flexible flatfoot is the more common type. The arch appears when the foot is non-weight-bearing (sitting or on tiptoe) but collapses when standing. Many adults with flexible flatfoot are asymptomatic and require no treatment. When symptoms do occur, they typically respond well to orthotics and supportive footwear.

Rigid flatfoot means the arch is absent regardless of position — the foot lacks the mobility to form an arch even when unloaded. This can result from tarsal coalition (bones fused together), advanced arthritis, or severe posterior tibial tendon dysfunction. Rigid flatfoot is more likely to be symptomatic and more complex to treat.

Adult-Acquired Flatfoot: The Progressive Type

The most clinically significant form is adult-acquired flatfoot deformity (AAFD), primarily caused by progressive dysfunction of the posterior tibial tendon. This tendon is the primary dynamic stabilizer of the arch. When it weakens, stretches, or tears, the arch gradually collapses under body weight.

AAFD develops through predictable stages. In Stage I, the tendon is inflamed but structurally intact — patients have pain along the inside of the ankle but the arch shape is maintained. In Stage II, the tendon has elongated and the arch has visibly collapsed — the "too many toes" sign appears when viewed from behind (more toes are visible on the outside of the affected foot). In Stage III, the hindfoot has become rigid and secondary arthritis is developing. In Stage IV, the ankle joint itself has become involved.

Risk factors include age over 40, female sex, obesity, hypertension, diabetes, and steroid use. Prior ankle injuries and inflammatory arthritis also contribute.

When Flat Feet Cause Problems

Symptomatic flat feet can produce arch pain and fatigue (especially after prolonged standing or walking), medial ankle pain from posterior tibial tendon strain, lateral ankle pain from impingement as the heel tilts outward, shin splints from altered tibial mechanics, knee pain from excessive internal rotation, and lower back discomfort from altered pelvic alignment. Many patients are treated for knee, hip, or back problems without anyone evaluating whether collapsed arches are the upstream cause.

Treatment: The Conservative Approach

Custom orthotics are the cornerstone of conservative treatment for symptomatic flat feet. Unlike over-the-counter insoles that provide cushioning, prescription orthotics are fabricated from a mold or 3D scan of your foot and are designed to control abnormal motion, support the arch, and redistribute pressure. For AAFD specifically, orthotics with medial posting and a deep heel cup help control the hindfoot valgus (outward tilt) that drives the deformity.

Supportive footwear with motion control features, firm heel counters, and adequate arch support works in concert with orthotics. Stability running shoes or structured walking shoes are good starting points. Minimalist shoes, flat sandals, and flexible flats generally worsen flat foot symptoms.

Physical therapy targeting posterior tibial tendon strengthening (heel raises, single-leg balance, resistance band exercises) and Achilles tendon stretching can improve function. A tight Achilles tendon is a common contributor to flatfoot progression because it forces the midfoot to compensate during gait.

In acute flares of posterior tibial tendinitis, a period of immobilization in a walking boot allows the tendon to recover before transitioning back to orthotics and supportive shoes.

When Surgery Is Considered

Surgery enters the conversation when conservative measures have been given an adequate trial (typically 3–6 months) and the patient continues to have significant pain or functional limitation, or when the deformity is progressing despite treatment.

Surgical options depend on the stage of deformity and range from tendon repair and transfer (early stages) to osteotomies that realign the heel bone, to joint fusion procedures for advanced rigid deformity with arthritis. The goal is always to restore alignment, relieve pain, and preserve as much function as possible.

Modern surgical techniques, including minimally invasive approaches, have improved recovery times and outcomes. But prevention through early orthotic intervention and tendon strengthening is always preferable to surgical reconstruction.

The Key Takeaway

Not all flat feet need treatment — but flat feet that cause pain, limit activity, or show signs of progression should not be ignored. Early intervention with custom orthotics and appropriate exercises can often prevent the condition from advancing to a point where more aggressive treatment is needed. If your arches have been gradually collapsing, or if you're experiencing pain along the inside of your ankle, an evaluation can determine where you stand — literally — and what can be done about it.