PTTD vs Achilles Tendonitis: How to Tell the Difference

Your foot hurts. You know that much. But figuring out exactly what’s causing the pain isn’t always straightforward. Two conditions that get confused all the time are posterior tibial tendon dysfunction (PTTD) and Achilles tendonitis. They both involve tendon pain in the back of the leg and ankle, but that’s where the similarities end.

Getting the right diagnosis matters because treatment approaches differ. Here’s how to tell them apart.

Quick comparison

The simplest way to understand the difference: PTTD affects the tendon on the inside of your ankle, while Achilles tendonitis affects the tendon at the back of your heel. The location of your pain is usually the first clue.

But let’s dig deeper, because location alone isn’t always clear—tendons can refer pain elsewhere, and you can technically have both conditions at once.

PTTD symptoms

Posterior tibial tendon dysfunction typically causes pain and swelling along the inside of the ankle and midfoot. The tendon runs behind the medial malleolus (that bony bump on the inside of your ankle) and attaches to the arch of your foot.

Common symptoms include:

  • Pain along the inside of the ankle, especially during activity
  • Swelling around the medial malleolus
  • Flattening of the arch over time
  • Weakness when pushing off on your toes
  • Pain that worsens with activity, particularly walking or standing
  • A rolling inward of the ankle (overpronation)

The pain from PTTD often develops gradually. You might notice it more in the morning or after prolonged sitting—when you first start moving, it hurts, then warms up as you get going.

One key feature: PTTD often leads to progressive flatfoot. If your arch is dropping and your ankle rolling inward, that’s a strong indicator.

Achilles tendonitis symptoms

Achilles tendonitis, on the other hand, affects the large tendon that connects your calf muscles to your heel bone. The pain is typically felt at the back of the heel, anywhere from 2-6 centimeters above where the tendon attaches.

Typical symptoms include:

  • Pain in the back of the heel, especially after running or climbing stairs
  • Stiffness and tenderness in the Achilles tendon, particularly in the morning
  • Thickening or nodules in the tendon
  • Pain that worsens with activity and improves with rest
  • Weakness when pushing off on your toes
  • In severe cases, a creaking sensation when moving the ankle

Unlike PTTD, Achilles tendonitis doesn’t typically cause arch collapse. The pain is more localized to the tendon itself, and you won’t see the same progressive flattening of the foot.

How to tell the difference

Here’s a practical breakdown:

Location is the biggest clue. If the pain is on the inside of your ankle, it’s more likely PTTD. If it’s at the back of your heel or calf, think Achilles.

Watch for arch changes. PTTD often causes the arch to progressively flatten. If your foot looks more flat than it used to, that’s a red flag for PTTD.

Consider the activities that aggravate it. PTTD pain often flares with walking and standing. Achilles pain typically flares with running, jumping, or climbing.

Check for swelling location. PTTD swelling tends to be around the medial malleolus. Achilles swelling is along the tendon itself.

Test your single-leg heel rise. Both conditions can make this difficult, but with PTTD you’ll often notice your ankle rolling inward as you try to lift.

Can you have both?

Yes, actually. It’s not uncommon to have posterior tibial tendon dysfunction and Achilles tendonitis at the same time. The biomechanics that contribute to one can stress the other. If you have flat feet (from PTTD), you may be putting extra strain on your Achilles tendon, which can lead to overuse and inflammation.

This is why seeing a specialist is important. An accurate diagnosis ensures you’re treating the right problem—or all the problems, if there are multiple.

Getting a proper diagnosis

If you’re experiencing persistent foot or ankle pain, here’s what to expect from a proper evaluation:

  1. Physical exam. Your doctor will press on specific points to identify exactly where the pain is. They’ll also watch you walk and observe your foot mechanics.

  2. Range of motion tests. Checking how far your ankle can move in different directions helps differentiate between tendon issues.

  3. Imaging. X-rays can show bone alignment and arthritis. An MRI or ultrasound can visualize tendon damage and inflammation in detail.

  4. Gait analysis. Watching you walk provides valuable information about how your foot is functioning.

Don’t try to self-diagnose based on internet articles (yes, even this one). The specifics matter, and what feels like one condition might actually be something else entirely.

The bottom line

PTTD and Achilles tendonitis are different conditions affecting different tendons in different locations. PTTD causes pain on the inside of the ankle with progressive arch flattening. Achilles tendonitis causes pain at the back of the heel with morning stiffness.

Both benefit from early treatment. If you’re experiencing persistent ankle or foot pain, especially if you notice changes in your arch, don’t wait. See a podiatrist or foot specialist who can give you an accurate diagnosis and appropriate treatment plan.

The right diagnosis is the first step toward the right treatment—and getting back to doing what you love without pain.

Sources

  • American College of Foot and Ankle Surgeons: Posterior Tibial Tendon Dysfunction and Achilles Tendonitis
  • American Academy of Orthopaedic Surgeons: Achilles Tendinitis treatment guidelines
  • Journal of Foot and Ankle Surgery: PTTD differential diagnosis studies