Adult-acquired flatfoot (progressive collapsing foot deformity)

What is adult-acquired flatfoot?

The arch of the foot is held up by bones, ligaments and tendons working together. The posterior tibial tendon runs behind the inner ankle bone and along the arch, and it is one of the main supports of the arch.^[6] When that tendon is inflamed, stretched or torn — or when the ligaments supporting the arch weaken — the arch can slowly flatten, the heel can drift outward, and the front of the foot can turn out.

The condition has been called adult-acquired flatfoot deformity (AAFD) and posterior tibial tendon dysfunction (PTTD), and the names have sometimes been used interchangeably. A consensus of foot and ankle specialists proposed the term progressive collapsing foot deformity, because the deformity involves more than one joint and is not always due to the tendon alone.^[1]

Swipe sideways to see the whole drawing.

Who gets it?

PCFD is more common in women and in people over 40. Obesity, diabetes and high blood pressure add to the risk. Other contributors include midfoot arthritis, injury, repetitive overuse, and inherited foot shape.^[2] It is usually progressive, which means it tends to worsen if it is not treated.^[6]

Symptoms

• pain and swelling along the inside of the ankle and arch
• an arch that looks lower than it used to, or a foot that seems to point outward
• fatigue or weakness in the foot with walking, and difficulty with impact exercise
• in later stages, pain on the outer side of the ankle as the heel shifts outward^[2]

How it’s evaluated

The examination looks at how the arch and heel line up when you stand, and how they change when you rise onto your toes. We check how strong and painful the posterior tibial tendon is, whether the deformity can be corrected by hand (flexible) or is stiff (rigid), and whether the ankle and midfoot are involved. Weight-bearing X-rays show the bone alignment under your body weight. CT can show bone in three dimensions and MRI can show tendon and ligament damage when more detail is needed.^[2,7]

Historically the condition was described in four stages, from tendon inflammation without deformity (stage I), to a flexible flatfoot (stage II), a rigid flatfoot (stage III) and involvement of the ankle joint (stage IV). Newer classification systems describe the deformity in more detail.^[5,1]

Non-surgical care

Non-surgical treatment should always be tried first, and in the earlier stages it often controls symptoms.^[5] Prompt, well-organized treatment is important because early diagnosis is one of the most important factors in the outcome.^[3]

• Support: a brace or custom orthotic to hold the arch, and sometimes a short period in a walking boot to calm severe inflammation.^[2,6]
• Rest, ice and anti-inflammatory medicine when the tendon is painful.^[2]
• Physical therapy: strengthening and calf stretching.^[2]

In one structured program for stage I and II disease, patients used an orthosis and did high-repetition exercises; after a median of ten therapy visits over about four months, 39 of 47 patients (83%) had a successful result, and five (11%) went on to surgery.^[4] The study did not have a comparison group, so it can’t show how much of the improvement came from the program. Evidence for orthoses in adult flatfoot is limited: a systematic review found few high-quality studies.^[8]

When surgery is considered

Surgery is considered if pain does not improve after several months of appropriate treatment, or if the deformity is progressing.^[2,3] The goals are to relieve pain, restore alignment and keep as much natural motion in the foot as possible.^[3]

The operation depends on the stage and on the joints involved:

• Flexible deformity: a combination of soft-tissue procedures — such as repairing or replacing the failing tendon with a tendon transfer, lengthening a tight calf muscle (see gastrocnemius recession), or repairing ligaments — with a bone-realigning procedure such as a heel-bone (calcaneal) osteotomy.^[5,2]
• Rigid deformity: fusion of the painful, stiff joints in the hindfoot, often a triple arthrodesis.^[5]
• Ankle involvement: procedures such as ankle fusion or ankle replacement, sometimes with reconstruction of the deltoid ligament.^[5,2]

The evidence on which procedure is best is limited, and surgical techniques continue to be studied.^[5] For one commonly used combination in stage II, a tendon transfer with a heel-bone osteotomy, a study of 31 patients followed for an average of 15 years found significant improvement in scores, with 27 (87%) pain-free and functioning well.^[9] Complications can include incomplete pain relief, failure of a fusion to heal, and infection, with higher risk in people who smoke or have diabetes.^[2] See flatfoot reconstruction for what the operations involve.

Recovery

After surgery, healing is measured in months. A period of protected weight-bearing in a cast or boot is usual, and it typically takes six months or more before healing is complete.^[2] See recovery after foot and ankle surgery.

When to seek care

Consider an evaluation if the inside of your ankle or arch has been painful or swollen for more than a few weeks, if your arch seems to be flattening, or if your heel is tilting outward. Earlier evaluation gives more treatment options.