Pes Planus

Synonyms: Pes planovalgus, adult acquired flat foot deformity, progressive flat foot deformity, posterior tibial tendon dysfunction (PTTD), flat foot, splay foot, fallen arches (loss of medial longitudinal arch of foot).

This is a disruption in the structure and/or function of the medial longitudinal arch of the foot occurring in adults that previously had normal shape and function. It must be distinguished from constitutional flat foot which is a common congenital nonpathologic foot morphology occurring in children.¹
The aetiology and pathophysiology of the condition is poorly understood. It is thought that there is a failure of the static and active supporting mechanisms of the medial longitudinal arch. Consensus among orthopaedic surgeons supports the concept that the dynamic supporting structures of the arch particularly the posterior tibial tendon - PTT - fail initially and this then leads to disruption of the static restraints. Lateral displacement of the foot under the weightbearing line of the tibia is the end result and this leads to subluxation of the talonavicular and talocalcaneal joints - a process known as lateral peritalar subluxation.² Gross changes caused by failure or contracture of the PTT are inversion of the midfoot and drooping of the medial longitudinal arch due to unopposed tension from the peroneus brevis and peroneus longus tendons moving the hindfoot away from the midline.
The PTT may also be damaged by specific pathologies that can cause the condition such as:

• Fractures and trauma (e.g. transection of the tendon)
• Dislocation of the mid-foot bones
• Neuropathy leading to painless disorganisation of the bones (e.g. Charcot joint in diabetic neuropathy)
• Arthritis affecting the relevant foot joints (e.g. in rheumatoid arthritis)

The exact prevalence is very hard to estimate and seems to be variable depending on the particular population in question and its age. It is thought that PTTD is a common clinical entity but that it does not always cause a clinical problem, may be associated with other conditions making diagnosis difficult, and is frequently not diagnosed.² A prospective epidemiological survey in Hong Kong of foot disease in patients of Chinese ethnicity found that it was the least common condition affecting the feet.³

Risk factors²

• Commoner in middle-aged, overweight women
• Diabetes mellitus
• Corticosteroid therapy
• Previous mid-foot trauma or surgery (including overuse injuries due to sporting activities)
• Hypertension has been found to be an associated condition in several studies but this may be due to the at-risk population, rather than a causally-linked aetiology.
• One series of 67 patients with PTT rupture found that up to 60% of patients had at least one of the above conditions

Symptoms

• Aching feet when standing, along the foot's medial border and medial aspect of the ankle
• Swelling of the midfoot on standing
• Visible deformity of the foot on standing with the medial border of the foot being tipped towards the floor
• Limping with diminution of 'push-off' strength of the foot
• Patient notes that they walk on the inside of their foot and quickly wear out or squash the medial aspect of the soles of their shoes
• Advanced cases may note pain in the lateral ankle due to increased pressure between the calcaneus and fibula

Signs

• Look at the patient's shoes for evidence of excessive wear/squashing of midsole along the medial border of the heel and midfoot
• Look at the patient standing to compare the position of the symptomatic and asymptomatic foot
• Assess arch height of symptomatic compared to asymptomatic foot
• The arch will be lowered and the forefoot abducted
• Look at the foot from behind to seek evidence of forefoot abduction and valgus deformity of the heel
• Assess how many toes can be seen lateral to the heel when looking from behind. Up to 2 toes is normal. If the forefoot is abducted then 3 or more toes may be seen (the 'too-many-toes' test)
• Ask the patient to stand on tiptoes on the affected foot alone (holding on to something solid for support) as you watch from behind. Normally the heel will invert as gastrocnemius and soleus contract and the PTT does so with them. In pes planus and PTT dysfunction the heel does not invert and may cause pain, difficulty in completing the task, or a complete inability to perform a single heel-raise.
• Swelling and fluid in the tendon sheath along the course of the PTT may be noted when examining the foot with the patient seated and foot above the floor (sit them on an examination couch). Test PTT strength by holding the foot in plantar flexion and eversion and ask the patient to invert the foot. Weakness or inability to complete the manoeuvre may be found in PTT dysfunction. Experienced examiners should palpate the PTT to assess its continuity during this manoeuvre.
• Test mobility in the peritalar joints by asking the patient to invert and evert the foot

• Midfoot trauma leading to peritalar dislocation/subluxation
• Neuropathic foot with Charcot joints
• Deformity of the lower limb leading to secondary midfoot deformity
• Foot deformity secondary to rheumatoid arthritis or spondyloarthropathy

• Blood tests not usually necessary unless an underlying undiagnosed metabolic abnormality such as diabetes is suspected. Consider urinalysis/capillary glucose assay if the foot is deformed but not painful.
• If rheumatoid arthritis or seronegative spondyloarthropathy may be present consider testing ESR, rheumatoid factor and/or HLA-B27 status
• Most useful test in primary care are standing anteroposterior and lateral radiographs of the foot and ankle
• Specialist radiological/orthopaedic interpretation of the lateral first talometatarsal angle, calcaneal pitch, distance from medial cuneiform base to the floor and talonavicular coverage angle are needed to make the diagnosis⁴
• Orthopaedic clinic investigations may involve tenography and MRI imaging

See risk factors in epidemiology section above.

• Stage 1 - PTT peritendonitis and degeneration with normal tendon length. Clinically presents as pain and swelling along the course of the PTT sheath.
• Stage 2 - PTT lengthening with supple flat foot deformity. Clinically presents as deformed foot when weightbearing but hindfoot and midfoot deformities that can be passively returned to normal.
• Stage 3 - Hindfoot rigidly set in valgus position with rigid passively non-correctable flat foot deformity.
• Stage 4 - Deltoid ligament failure leading to valgus deformity of the talus within the structure of the ankle.

• Conservative therapy:
  • Stage 1 - Rest, NSAIDs, short-leg walking cast or removable walking cast boot for 6-8 weeks to treat tenosynovitis; in long-term use full-length semi-rigid custom-moulded orthosis and physiotherapy to strengthen PTT.
  • Stage 2 - Rest, NSAIDs and moulded rigid orthosis or short articulated ankle orthosis
  • Stages 3 and 4 - Moulded ankle-foot orthosis, double-upright brace or patellar tendon-bearing brace
• Surgical intervention
  • Stage 1 - If conservative treatment fails then release of the tendon sheath, tenosynovectomy, debridement of the tendon with excision of flap tears or repair of longitudinal tears in the tendon may be used.
  • Stage 2 - There is no definite consensus on optimal surgical intervention where conservative therapy is inadequate. Tendon repair or transfer procedures, ligament repair, osteotomies and arthrodeses have all been used successfully, each having their own proponents. Achilles tendon lengthening may be carried out if ankle dorsiflexion is ≤10 degrees. The multitude of surgical procedures used for stage 2 dysfunction demonstrates that there is no clear curative surgical intervention.
  • Stage 3 - Subtalar fusion procedure or triple peritalar joint arthrodesis. Post-operative orthosis or bracing is often needed.
  • Stage 4 - Tibiotalocalcaneal fusion procedure or pantalar fusion with post-operative bracing or orthosis

Untreated advanced cases of pes planus can lead to increasing pain and deformity of the foot, and in the older patient can lead to them 'going off their feet'. Sufferers may have an inability to wear shoes, or pressure ulceration of the skin of the foot.
Complications of the surgical procedures used to treat the problem include:

• Continuing post-operative pain and dysfunction
• Undercorrection or overcorrection of the deformity
• Neurovascular injury
• Inability to tolerate normal footwear
• Loss of walking function of foot due to excessive rigidity

Outcomes in individual patients are highly variable and dependent on age, pre-existing mobility, stage of deformity and the therapy used to treat the problem. Stage 1 and 2 deformity usually respond well to treatment.

• Prevention of diabetic neuropathic foot disease through improved glycaemic control and annual diabetic review clinics
• Avoidance of putting on excessive weight through healthy eating
• Monitoring of foot symptoms and deformity in patients on long-term corticosteroid therapy
• Avoidance of sporting overuse injury through moderation, foot-strengthening exercises, appropriate footwear and insoles/orthoses