Pes planus

What is pes planus?

Pes planus (commonly referred to as 'flat feet') is a relatively common foot deformity and is defined by the loss of the medial longitudinal arch of the foot where it contacts or nearly contacts the ground.¹ It can be flexible or rigid and it results in relative flattening of the plantar surface.

Pes planus may be congenital or acquired. Pes planus is often asymptomatic but may alter the biomechanics of the lower extremities and lumbar spine, increasing the risk of pain and injury to all joints in the legs.¹

Pes planus refers specifically to loss of the arch in the bony structure of the foot. People with hypertrophied plantar foot muscles (eg, lifelong barefoot walkers) might appear to have flat feet but if their bony arches are normal then they do not have pes planus.

The arches of the foot

The arches add elasticity and flexibility to the foot by allowing the midfoot to spread and close. They help the foot to absorb shock and produce strength to push off and to adjust to balance and walk. They also help distribute weight evenly around the foot.

Biomechanical analysis suggests that there are advantages and disadvantages to both high-arched and low-arched feet: the strain on the plantar fascia and metatarsals is greater in the high-arched foot, whereas strain on the calcaneus, navicular and cuboid are greater in the low-arched foot. A happy medium is perhaps ideal.²

Epidemiology¹

20-37% of adults are thought to have pes planus, many of whom are flexible and have no resulting difficulties.

The incidence is reported to be higher in men, young children aged 3-5 years, teenagers, people with obesity, and people of Asian or Black ethnicity.

There is a strong genetic predisposition.

Types of pes planus

• Flexible or fixed.

• Developmental, congenital, or acquired.

Effects of pes planus on foot dynamics¹

The medial longitudinal arch is made up of the calcaneus, navicular, talus, first 3 cuneiforms, and the first, second, and third metatarsals. The arch is supported by the plantar calcaneonavicular ligament, deltoid ligament, posterior tibial tendon, plantar aponeurosis, and the flexor hallucis longus and brevis muscles. Dysfunction of any portion of the medial longitudinal arch may result in acquired pes planus.

Aetiology of pes planus³

Pes planus in children¹

Infants are born with flat feet and arches do not develop until around the age of 7-10 years. The majority of these are flexible pes planus.

A proportion of children do not develop arches by adulthood.

Pes planus is significantly more common in children who are overweight or have obesity.⁴⁵

• Abnormal development of the foot, producing pes planus, may be due to:

  • Neurological problems - eg, cerebral palsy, polio.

  • Bony abnormalities - eg, tarsal coalition (fusion of tarsal bones), accessory navicular bone (a small bone which sits in the posterior tibial tendon, weakening support to the arch).

  • Ligamentous laxity - eg, Ehlers-Danlos syndrome, Marfan's syndrome, Down's syndrome

  • A small proportion of flexible pes planus does not correct with growth (physiological pes planus). These can become rigid if the pes planus leads to bony changes.

Physiological pes planus in adults

Around 20% of adults have pes planus, most of whom lack physiological arch development, probably due to ligamentous laxity. The majority have a flexible foot and no symptoms. However, if there is also heel cord contracture, there may be symptoms (see 'Contributing factors', below).³

Acquired pes planus in adults⁶

This may be due to reduced arch strength, increased load, or a combination of the two. The commonest cause of acquired pes planus is posterior tibial tendon dysfunction. Historically this has been thought to be most common in women over the age of 55 with comorbidities, including diabetes mellitus and obesity. However, more recent epidemiologic data suggests a broader distribution, corresponding with rates of obesity.¹

Injuries to the foot, sensory neuropathy, arthropathies, and arthritis all increase the risk of developing pes planus in adulthood. Ligamentous laxity in pregnancy also often causes pes planus but this normally resolves post-partum.¹

Examination¹

• Observe the pes planus:

  • With the patient standing, look at the feet from above and behind and all sides, note when non-weight-bearing, when weight-bearing and when walking. Loss of the arch is visible in pes planus, with the medial side of the foot close to the ground. Look at the feet from behind - with pes planus the heel moves outwards (valgus) and the toes may also be pointed outwards.

• Assessment of the foot:

  • Establish whether the foot is flexible:

    • Ask the patient to stand on tiptoe. With flexible pes planus, this will reveal the arch, and the heel will move inwards (varus position).

    • Evaluate ankle dorsiflexion and plantarflexion and rearfoot, midfoot, and forefoot ranges of motion.

    • Assess the Achilles tendon - less than 10° of dorsiflexion suggests Achilles tendon contracture.

    • Look at the shoes: flexible flat feet may cause rapid and uneven shoe wear.

• Look for signs of tibialis posterior dysfunction:⁷

  • Ask the patient to do 10 unsupported heel raises (stand on one foot on tiptoe, unsupported). Patients with tibialis posterior dysfunction will be unable to do this.

  • Further assessment of tibialis posterior dysfunction is detailed in the reference below.⁷

• Assess related problems, if relevant - eg, neuropathy or arthritis.

• Observe gait.

Investigations³⁸

X-rays, MRI imaging, and nerve conduction studies may all play a role but there is no role for imaging in general practice.

Pes planus treatment and management^{8 9}

Treatment in children

The treatment of paediatric flexible pes planus is controversial; there is clear consensus that the condition is normal in young children, reduces with age, and that most children are asymptomatic. Treating paediatric flat feet is almost always unnecessary.

Where foot orthoses are indicated, generic appliances are usually sufficient. Customised orthoses should be reserved for:

• Children with foot pain and arthritis.

• Unusual morphology.

• Unresponsive cases.

Surgery is rarely indicated for children unless the pes planus is rigid or if it is symptomatic and progressive.

Treatment in adults¹

In many cases, pes planus does not require treatment. Most flexible flat feet are asymptomatic.

Symptomatic and inflexible pes planus may require treatment. Initial options include activity modification, footwear and orthoses, exercises, ice, and medication (non-steroidal anti-inflammatory drugs (NSAIDs). Comorbidities should be identified and managed. Weight loss should be advised in obesity. When treatment is required and non-surgical treatment options have failed then surgery is considered. Consider referral or treatment if:

• Pes planus is fixed, new, asymmetrical or progressing.

• There is foot pain.

• If the patient has another disease which may be contributing (eg, neuropathy, inflammatory arthritis).

• There is tibialis posterior dysfunction. This should be treated in its own right: treatment may involve rest, NSAIDs, orthotics or surgery.⁷

Non-surgical treatment

• Physiotherapy to strengthen weak muscles, increase foot flexibility and improve proprioception helps.

• Heel cord stretching helps to stretch and lengthen the Achilles tendon and posterior calf muscles, as a tight Achilles tendon tends to pronate the foot. The patient should be instructed as follows:

  • Stand facing a wall with hands on the wall at about eye level. Put the leg you want to stretch about a step behind your other leg.

  • Keeping the back heel on the floor, bend the front knee until you feel a stretch in the back leg.

  • Hold the stretch for 15-30 seconds. Repeat 2-4 times. Do this exercise 3-4 times a day.

• Orthotics (inserts or insoles):¹⁰

  • These usually contain a heel wedge to correct calcaneovalgus deformity, and an arch support. In patients with fixed pes planus or arthropathy, customised insoles may help relieve symptoms.

  • No high-level evidence supports the use of foot orthoses for flexible pes planus in adults, although low-level evidence suggests that foot orthoses improve pain and reduce rearfoot eversion, and there is slightly better evidence that they improve foot biomechanics when walking. Further research is needed.¹¹

  • Arch supports used without correcting heel cord contracture can make symptoms worse.

• Reduce contributing factors:

  • Wear shoes with low heels and wide toes.

  • Lose weight if appropriate.

  • Do exercises to strengthen foot muscles - walking barefoot (if appropriate), toe curls (flexing toes) and heel raises (standing on tiptoe).

Surgery^{3 8}

The goals of surgery are pain reduction/resolution and realignment of the foot.

Common indications for surgery are:

• Cerebral palsy with an equinovalgus foot, to prevent progression and breakdown of the midfoot. Subtalar fusion is effective in ambulatory patients, although there is a high recurrence rate.¹²

• Rigid and painful pes planus.

• To prevent progression - eg, with a Charcot joint.

• Tibialis posterior dysfunction, where non-surgical treatment has been unsuccessful.

Complications and prognosis

Physiological pes planus

It is generally accepted that physiological pes planus is unlikely to cause significant foot problems.³

However, some authors suggest that excessive foot pronation may contribute to the development of foot pain and foot problems such as:

• Tibialis posterior dysfunction (because hyperpronation stretches this tendon).

• Hallux valgus (because more weight is borne by the medial metatarsals when the foot hyperpronates).

• Metatarsalgia (for the same reason).

• Plantar fasciitis.

• Knee pain: one study found that off-the-shelf foot orthoses were beneficial for patello-femoral pain.¹³ Another study suggested that foot deformity may be linked to greater disability from knee osteoarthritis.¹⁴

• Pes planus may reduce the shock-absorbing features of the foot, potentially contributing to low back pain, although it may be protective against metatarsal stress fracture.³

The role of pes planus in these problems has not been proved.

Symptomatic or rigid pes planus¹⁵

Depending on the cause, pes planus can deteriorate, with loss of the longitudinal arch, leading to collapse of the midfoot. With deterioration, a flexible foot can become rigid and/or painful. This can cause significant difficulties with walking and may require surgery.

Situations where deterioration is likely without treatment include:

• Neuropathy - eg, with a Charcot joint there may be rapid and progressive loss of the arch.

• Tibialis posterior dysfunction.

• Cerebral palsy.³

Famous athletes with pes planus

The following athletes are all reported to have flat feet. It may be helpful to inform parents or patients about this to reduce their anxieties about activity or prognosis.

• Usain Bolt.

• Cristiano Ronaldo.

• Michael Jordan.

• Kobe Bryant.

• Lionel Messi.

• Michael Phelps.

• LeBron James.

• Pele.

Dr Mary Lowth is an author or the original author of this leaflet.