Posterior Tibial Tendonitis and Adult-Acquired Flatfoot

That nagging ache along the inside of your ankle that you've been chalking up to overuse? If it comes with a slowly flattening arch or a heel that seems to be drifting outward, it may be more than a minor strain. Posterior tibial tendonitis — and the arch collapse it can cause — is one of the most commonly missed progressive conditions I see in the clinic, often because patients wait years before coming in.

The good news: caught early, this condition often responds very well to conservative care. Left untreated, it can progress to a rigid flatfoot that requires significantly more complex treatment. Here's what you need to know.

What is the posterior tibial tendon — and why does it matter?

The posterior tibial tendon runs from a muscle in the back of your lower leg, around the inside of the ankle, and attaches to the bones of the midfoot. Think of it as the main dynamic support cable for your arch. Every time you take a step, this tendon contracts to hold your arch up and control how your foot rolls through the stride.

When the tendon becomes inflamed, degenerates, or tears — a spectrum doctors call posterior tibial tendon dysfunction (PTTD) — that cable can no longer do its job. Over time, without the tendon's support, the ligaments on the inside of the foot stretch out and the arch collapses. This is adult-acquired flatfoot deformity, and PTTD is its most common cause. Research in peer-reviewed journals estimates that the condition affects roughly 3–10% of adults, with rates approaching 10% in women over 40. Learn more on our posterior tibial tendonitis service page.

Who is most at risk?

PTTD can affect almost anyone, but certain factors put you at higher risk:

• Age and sex — the condition disproportionately affects women in their 40s, 50s, and 60s.
• Excess body weight — increased load amplifies every repetitive stress on the tendon.
• Prolonged standing — jobs that keep you on hard surfaces for hours accelerate wear.
• High-impact activity without proper support — running or hiking in worn-out or unsupportive footwear.
• Prior ankle injury — an old sprain can alter how forces travel through the tendon.
• Inflammatory conditions — rheumatoid arthritis and other connective tissue diseases can weaken the tendon sheath.
• Pre-existing flatfoot — a low arch puts the posterior tibial tendon in a chronically stretched position from the start.

Here in the Treasure Valley, we see a lot of PTTD in people who spend their summers hiking the Ridge to Rivers trail network or standing at outdoor events — then come in during fall when the season's accumulated strain finally catches up with them.

Symptoms: what does posterior tibial tendonitis feel like?

The hallmark is pain and swelling along the inner ankle and the inside of the foot, typically just below and behind the bony bump on the inside of the ankle (the medial malleolus). Common signs include:

• Aching or burning on the inside of the ankle that worsens with activity.
• Difficulty or pain with the single-leg heel raise (standing on one foot and rising onto your toes).
• A gradual flattening of the arch that you or your family notice over months.
• The heel drifting outward and the front of the foot splaying to the outside.
• The “too many toes” sign — when viewed from behind, more toes than normal are visible beyond the outer edge of the heel.
• Increasing difficulty with shoes that used to fit comfortably.

Understanding the four stages

Clinicians stage PTTD from I through IV based on the degree of tendon damage and how much the foot structure has changed. Stage matters enormously because it directly determines what treatment options are on the table.

Most patients who come in early are Stage I or II, and that’s exactly where we want to catch this. A flexible arch can be supported and stabilized; a rigid one requires removing or fusing joints that have already developed arthritis. If you’re wondering how PTTD-related flatfoot compares to other causes of fallen arches, our article on flat feet and fallen arches has a broader overview.

Conservative treatment: what works and how long it takes

For Stage I and early Stage II, a structured non-operative program can be highly effective. In one published study, 83% of patients with Stage I or II PTTD achieved successful outcomes after a median of about ten physical therapy visits over four months. The key components are:

• Custom orthotics — a well-fitted, medial-posted orthotic lifts the arch and reduces the load on the tendon with every step. Learn about our approach to custom orthotics.
• Ankle-foot orthosis (AFO) or supportive brace — for more advanced Stage II, an AFO that wraps around the ankle can provide significantly more control than an insole alone.
• Walking boot or cast — short-term immobilization can calm an acutely inflamed tendon and allow it to settle before starting rehab.
• Physical therapy — targeted strengthening of the tibialis posterior and the intrinsic foot muscles, combined with calf stretching and gait training.
• Activity modification — temporarily stepping back from high-impact activities like running or jumping while the tendon heals.
• Supportive footwear — motion-control or stability shoes with a firm midsole; sandals and flat shoes without arch support are the enemy of PTTD recovery.

Expect conservative treatment to take three to four months to show its full effect. Patience matters here — the tendon heals slowly, and rushing back into activity too soon is one of the most common reasons patients plateau.

When is surgery necessary?

Surgery is considered when the arch deformity has become rigid (Stages III–IV), or when a patient with flexible Stage II deformity has not improved sufficiently after a genuine trial of conservative care — typically six months or more. The type of surgery depends on the stage:

• Tendon debridement or repair — for Stage I disease where the tendon is inflamed or partially torn but structure is preserved.
• Calcaneal osteotomy + tendon transfer — the most common procedure for Stage II. The heel bone is cut and shifted to realign the foot, and a neighboring tendon is transferred to replace the failing posterior tibial tendon.
• Subtalar or double arthrodesis — for Stage III with fixed deformity and joint arthritis; one or more hindfoot joints are fused in a corrected position.
• Triple arthrodesis or ankle reconstruction — reserved for Stage IV when the ankle itself is involved.

Surgical recovery typically ranges from two to four months depending on procedure complexity. Research on surgical outcomes shows that the large majority of patients report meaningful pain relief and functional improvement, though results are best when surgery is performed before arthritis has set in. For more on what the surgical process involves, see our page on foot and ankle care.

When to see a doctor — and when it’s urgent

See a podiatrist if:

• You have persistent inner ankle or arch pain lasting more than a few weeks.
• You’ve noticed one arch looking lower or flatter than the other.
• Your foot or heel seems to be rolling inward when you walk.
• You’re finding it difficult to rise onto your toes on one side.
• Over-the-counter insoles and supportive shoes haven’t helped after several weeks.

Seek same-day or urgent care if:

• You have sudden, severe pain on the inner ankle after a twist, fall, or athletic event — this can indicate an acute tendon rupture.
• There is marked swelling, warmth, and redness that develops rapidly, which could indicate infection or a tear.
• You are unable to bear weight at all after an ankle injury.
• You have diabetes or poor circulation, as any foot or ankle injury in these patients needs prompt evaluation to prevent complications.

Medical disclaimer: this article is for educational purposes only and is not a substitute for a professional medical evaluation. Only an in-person examination, imaging, and clinical history can determine the correct diagnosis and appropriate treatment for your individual situation.

Frequently asked questions

The bottom line

Posterior tibial tendonitis is a progressive condition — and that word “progressive” cuts both ways. Left alone, it can march through all four stages and turn a treatable tendon problem into a complex flatfoot reconstruction. Caught early, it can often be stabilized with orthotics and physical therapy, letting you stay active on the Greenbelt, the foothills trails, and everywhere else you love to be.

If you’ve been noticing inner ankle aching, a flattening arch, or difficulty with heel raises, now is the right time to get it looked at — not after another hiking season goes by.

Dr. Clark Johnson is a board-certified foot and ankle surgeon at Treasure Valley Foot & Ankle in Meridian, Idaho. To schedule an evaluation, request an appointment online or call (208) 272-9253.