Adult acquired flatfoot deformity (AAFD) is a complex pathology defined by the collapse of the medial longitudinal arch of the foot with continued progressive deformity of the foot and ankle 5. It combines multiple static and dynamic deformities, with flattening of the medial arch, eversion of calcaneus, and abduction of forefoot relative to the hindfoot 9. In long-standing cases, the ankle may be involved as well13.
Specific injuries that can lead to pes planus include fractures of the navicular, first metatarsal, or calcaneal bones, and/or trauma to the Lisfranc joint, plantar fascia, and deltoid/spring ligament. Dysfunction of the posterior tibial tendon(PTT) leads to pes planus of various degrees. In severe cases, rupture of PTT occurs commonly at the region of hypovascularity 1.0-1.5 cm distal to the medial malleolus. Diabetics with Charcot neuroarthropathy from sensory neuropathy commonly have collapsed arches with rocker bottom deformity in severe cases 3. Individuals with congenital pes planus may have tarsal coalition, an abnormal connection between tarsal bones due to incomplete differentiation of bones. These patients develop medial foot pain during late childhood or early adolescence as they increase their physical and sporting activities3,6.
Epidemiology and Risk factors for Prevention
Adult acquired flatfoot is a debilitating condition that affects up to 5 million people within the US 4. It is most common in females over the age of 40, peaking at 55 years of age, with comorbidities including diabetes and obesity1,3.
Risk factors of acquired flat foot 1:
- History of trauma
- Degeneration of bones and joints
- Seronegative inflammatory disorders
- Increased age
- Corticosteroid use
Any injury to the structures mentioned above maintaining the arch may lead to pes planus.
Patho-anatomy and Physiology:
One transverse and two longitudinal arches are formed by the aligned wedge-shaped tarsal and metatarsal bones, and their corresponding ligaments. In addition to these static structures, musculo-tendinous structures (tibialis posterior, peroneal, and tibialis anterior tendons) dynamically stabilize the arch. The design of the arches can be understood by picturing the foot as a twisted osteoligamentous plate. The anterior edge of the plate (formed by the metatarsal heads) is horizontal and in full contact with the ground and the posterior edge of the plate (the posterior calcaneus) is vertical. The resulting twist forms one transverse and two longitudinal arches (Figure 1). The medial longitudinal arch (between the calcaneous and first metatarsal) is higher and more flexible compared to the lateral longitudinal arch (between the calcaneous and lateral metatarsal). The actual mechanism of twisting and untwisting is accomplished through motion at the talocalcaneonavicular, transverse tarsal, and tarsometatarsal joints that link the bones of the plantar arches2.
PTT inserts to 9 bones including navicular tuberosity, 3 cuneiforms, 2nd – 4th metatarsal heads, and sustantaculum tali of calcaneous 2,9. The PTT adducts and supinates the forefoot secondarily inverting the subtalar joint. When the hindfoot is everted the transverse tarsal joint (talonavicular, calcaneocuboid) is unlocked which allows the foot to remain supple. When the hindfoot is inverted, the transverse tarsal joint locks and the foot becomes rigid.
Figure 1: Twisted osteoligamentous plate of the foot, resulting in longitudinal and transverse arches
Immediately after heel strike, the subtalar joint is inverted and the foot is supple 13. The plate will untwist, flattening the arches slightly. As the foot unloads weight, the resilient arches return to their original shape 2. The subtalar joint becomes progressively inverted which is initiated by the PTT adducting the transverse tarsal joint. The divergence at the transverse tarsal joint (calcaneocuboidal and talonavicular joints) allows the subtalar complex to become rigid. This enables the gastrocnemius-soleus complex to provide a plantar flexion force against a rigid lever to allow forward progression during the push-off phase of the gait cycle. Therefore, the PTT is critical in inverting the hindfoot and locking the transverse tarsal joint for normal gait and ambulation 13. The PTT also works eccentrically throughout the loading response until midstance where the foot is pronated providing controlled lengthening contraction.
The integrity of the talonavicular joint is maintained by the calcaneonavicular ligament (spring ligament) and portions of the superficial deltoid ligament 13. The PTT protects these structures and also plays an essential role in the elastic support of the joint complex 9. The PTT dysfunction results in attenuation of these important ligaments and also leads to diminished hindfoot inversion and the peroneus brevis acting unopposed with a dynamic abduction-eversion force.
The common point in all deformities causing adult flat foot is failure of foot-locking during gait 9. Individuals with pes planus tend to have, or eventually develop, shortening of the gastrocnemius muscle and Achilles tendon due to a pronated calcaneus relative to the tibia. This relative equinus state – which is a lack of having full passive ankle dorsiflexion – drives the subtalar and midtarsal joint into further pronation. Restoring ankle dorsiflexion or accommodating it is a key part of managing symptomatic pes planus.
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time):
Posterior Tibial Tendon Insufficiency Related Pes Planus
- Stage I: It presents with medial ankle pain due to tenosynovitis and/or tendinosis in the PTT. Patients may present without arch collapse or foot deformity 1. In Stage II patients manifest with a more significant deformity 14.
- Stage IIa: It is a mild to moderate flexible deformity with minimal abduction through the talonavicular joint as evidenced by less than 30 % talonavicular uncoverage on a standing AP radiograph of the foot. The interosseous ligament is usually insufficient.
- Stage IIb: It presents with a severe flexible deformity: greater forefoot abduction through more than 30 % talonavicular uncoverage. Patients with lateral impingement at the subtalar joint should be considered stage IIb. The patient is unable to perform a single heel rise1,13.
- Stage III: It clinically presents with a rigid deformity in the hindfoot and forefoot which is not passively correctable beyond the neutral position. The rigidity arises at the triple joint complex (talonavicular, subtalar, and calcaneocuboid joints) leading to fixed hindfoot valgus and abduction through the midfoot.
- Stage IV: It is a hindfoot valgus deformity which results from the lateral tilt of the talus as a consequence of deltoid ligament failure. Stage IVa is characterized by hindfoot valgus with flexible ankle valgus without significant ankle arthritis. Stage IVb refers to hindfoot valgus and rigid or flexible ankle valgus with significant arthritis 1.
Table 1. Myerson Modification of Johnson and Strom Classification of Adult-Acquired Flatfoot Deformity
|I||Mild medial pain and swelling with no deformity, can perform heel-rise test but demonstrates weakness on repetition, tenosynovitis on pathology with normal tendon length|
|II||Moderate pain with or without lateral pain, flexible deformity, unable to perform heel-rise test, elongated tendon with longitudinal tears|
|II a||< 30% talar head uncoverage|
|II b||> 30% talar head uncoverage|
|III||Severe pain, fixed deformity, unable to perform heel-rise test, visible tears on pathology|
|IV||Lateral talar tilt|
|IV a||Flexible ankle valgus without severe arthritis|
|IV b||Fixed ankle valgus with or without arthritis|
Specific secondary or associated conditions and complications:
- Midfoot arthritis (strain of medial midfoot, compression of lateral midfoot)
- Sprain of spring/deltoid ligaments
- 1st MTPJ Valgus deformity (bunion)
- Medial ankle pain
- Sinus tarsi pain
- Shortening of gastrocnemius
- Knee valgus deformity
- Tibial/femoral internal rotation
2. ESSENTIALS OF ASSESSMENT
Clinical assessment is important to determine the severity of the deformity and its reducibility9. Majority of patients with PTT dysfunction describe a gradual onset of unilateral medial ankle and foot pain and deformity without clear history of trauma 9. Upon palpation, tenderness is along the PTT between medial malleolus and navicular bone 13. Pain on the plantar and deep region may suggest spring ligament lesion 10. In the late stage, patients can have pain in the lateral aspect of the hindfoot (including below the tip of fibula) due to bone impingement within the sinus tarsi or the calcaneofibular region, or calcaneocuboid impingement in severe forefoot abduction6,9.
Inspect for valgus deformity in heel, collapse of the medial longitudinal arch, and forefoot abduction. Clinicians should look for the ‘Too many toes sign’ (more than 1 or 2 toes are visible on lateral border of foot when clinicians view patient from behind) which simply indicates forefoot abduction, not the entire pronation deformity of the foot 10. Clinicians should ensure the patellae face forward to avoid false positive results 10. To evaluate the strength and integrity of the PTT, heel rise tests are performed with the patient standing 2 feet away from the wall with the hands placed against the wall. The patient is then asked to rise up on the balls of the feet with the knees extended. When the heels rise, calcaneal motion is observed. Failure of inversion of the heel suggests PTT dysfunction. A single heel rise test is then performed. Inability to raise the heel and to maintain heel inversion and elevation suggests PTT dysfunction.
2a: Location of maximum tenderness on PTT dysfunction
2b. Everted calcaneus on the left side
2c. Bilateral pes planus with forefoot abduction in a patient with PTT dysfunction
Range of motion:
The mobility of the ankle, subtalar joint, and transverse tarsal joint should be assessed. It is also important to determine whether the flatfoot deformities (tibiotalar and subtalar joints and Chopart and Lisfranc joint-lines) are reducible for orthotic management. With stage III PTT dysfunction, the flat foot deformity can no longer be passively corrected requiring accommodative management10.
Evaluation of ankle flexibility and shortening of the gastrocnemius and Achilles tendons should be done since ankle equinus drives the subtalar and midtarsal joints into pronation. Normally, 20 degrees of dorsiflexion and 50 degrees of plantar flexion occur at the ankle joint. Care should be taken to check the dorsiflexion of ankle with foot in slight inversion if the subtalar joint is supple. This reveals the true motion at the ankle joint.
The motion at the subtalar joint is evaluated by stressing the calcaneus into varus (normal <30 degrees) inversion and valgus (normal <10 degrees) while grasping the calcaneus with one hand and locking the ankle joint with the other. The motion of the transverse tarsal joint should be evaluated next for abduction and adduction. With the heel placed into inversion, there is a moderate degree of rigidity to the transverse tarsal joints. Degenerative process in these joints may restrict the motion13.
Evaluate for tenderness and swelling along course of PTT which is generally seen during stage I PTT dysfunction. Tenderness in sub-fibular region may indicate calcaneofibular impingement. To assess for the integrity of the PTT, ask the patient to invert and plantarflex the foot against resistance while the examiner applies an eversion force10.
The patient’s gait is evaluated while walking down a hallway. Any antalgic gait or limp on the affected limb with external rotation should be noted. The external rotation of the limb decreases the stress on the subtalar-ankle joint complex13
There are no specific laboratory studies indicated for pes planus.
Radiographic evaluation :
Weight-bearing radiographs of the foot and ankle remain the gold standard for the diagnosis of adult-acquired flatfoot deformity. Anteroposterior, lateral and hindfoot views should be obtained.
- Anteroposterior (AP) view: Forefoot abduction and talar head uncoverage may be demonstrated. Different parameters have been described to assess talar head uncoverage, including the anterior talus-first metatarsal angle (normal, 0° to 20°), talonavicular coverage angle (normal<7°), talonavicular uncoverage percent (normal, 10% to 30%), and lateral incongruency angle (normal, 5°26°).
- Lateral radiographs view: Naviculocuneiform and first tarsometatarsal joint collapse should also be investigated . The lateral talar-first metatarsal angle (Meary angle) is evaluated which is the angle between the longitudinal axes of the talus and first metatarsal (normal, 0° 4°). Calcaneal pitch is used to measure the angle between a line drawn along the most inferior part of the calcaneus and the supporting surface or the transverse plane (normal, 10° to 20°).
- Hindfoot alignment view: Hindfoot valgus can be evaluated. The apparent moment arm (described by Saltzman and El-Khoury) can be measured and is defined as distance between the most distal point at the plantar calcaneal contour to tibial shaft axis (normal averages 3.2 mm in varus) 12. Talar tilt secondary to deltoid ligament insufficiency would suggest stage IV.
All radiographs should be carefully examined to identify arthritic changes that could substantially affect treatment choice (i.e., joint fusion vs soft tissue procedures and osteotomies)1.
Supplemental assessment tools
MRI is typically not needed for evaluation of adult acquired flatfoot. However, it may be beneficial for some patients with ligamentous involvement to consider surgical treatment options. This is particularly relevant for patients with medial peritalar instability who have improved functional outcomes with deltoid-spring ligament reconstruction. Several studies indicate that ultrasound may be a useful modality in assessing the PTT when compared to the more time consuming and costly MRI. Results from an ultrasonographic evaluation of the PTT were equivalent to MRI in 87% to 94% of patients4.
Early predictions of outcomes
Reduction of pain and improved gait is the best predictor of outcome.
Johnson and Strom described 4 stages of PTT dysfunction 18. These stages are used to dictate treatment.
- Stage 1: is characterized by peritendinitis and tendon degeneration, but the tendon length remains normal. This stage presents clinically as pain and swelling along the PTT sheath.
- In Stage 2, the PTT elongates, and a supple flat foot deformity develops. Although deformed on weight bearing, the hindfoot and midfoot deformities are passively correctable to neutral position.
- Stage 3: occurs over time as the hindfoot becomes rigid in a valgus position, and the patient develops a rigid flatfoot deformity.
- Stage 4: develops as the deltoid ligament becomes incompetent and the talus tilts into valgus within the ankle mortise.
Running or walking on uneven ground (e.g. slanted pavement) may exacerbatepain and discomfort. Footwear with an antipronation design may help the pain and position of the foot.
Social role and social support system
Vocations requiring long hours of standing and walking may tax the feet. Appropriate footwear with pronation support with orthoses can be beneficial to patients.
Vocations requiring dress shoes may be a problem for these individuals. People with pes planus tend to have wide feet and may need specially lasted footwear.
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
Initial treatment for all stages of PTT dysfunction includes various non-operative treatments including activity modification and nonsteroidal anti-inflammatory drugs (NSAIDs) 10. If patients continue to have pain after non-operative interventions or non-operative therapy for 3 to 4 months, then surgical intervention may be considered. Surgery should address thevcomponents of the deformity and its reducibility at 3 levels: the talonavicular, tibiotarsal, and midfoot joints 9.
At different disease stages
- Stage I: It may be treated with immobilization in a short-leg cast or walking boot for 4 to 6 weeks to allow for healing of the PTT. The patient may participate in physical therapy for eccentric strengthening of the PTT after cast immobilization. Anti-inflammatory medications may assist in reducing inflammation 18. If immobilization and physical therapy are successful, transitioning into custom-molded orthotics or ankle foot orthosis (AFO) is beneficial to maintain relief. Emphasis on medial forefoot posting is critical. University of California Biomechanics Laboratory (UCBL) orthoses are a form of a custom insert with a lace-up component that can help maintain midfoot height 11. Ankle stirrup braces may also be used in stage 1 PTT dysfunction 18.
- Stage IIa: It is treated with orthoses as recommended in stage 1. Stage IIa may involve some deformity or impending deformity, thus necessitating support of the longitudinal arch and heel. An orthotic device with a deep heel cup is usually sufficient.
- Stage IIb: Patients may require a University of California Biomechanics Laboratory (UCBL) device or AFO for reducing forefoot abduction 13,16. Modifications in footwear, such as an extended medial counter or medial heel wedge, may be helpful. In the acutely painful foot, immobilization may be warranted 13.
- Stage III: Patients may require some type of custom AFO or supramalleolar (SMO) brace. The AFO should be articulated to permit ankle joint range of motion. Unfortunately, once the deformity is fixed, the patient may have difficulty tolerating corrective types of AFOs. Partial correction with a heel lift to accommodate the equinus of ankle can be attempted.
- Stage IV: Non-operable stage IV PTT dysfunction is usually treated with footwear with medial posting and a buttress to accommodate the deformity.
- Stage I: If non-operative treatment fails, a tenosynovectomy may be considered. Tenosynovial tissue should be resected and any tears should be debrided and repaired.
- Stage IIa: It occurs as a consequence of the elongation of the PTT. Therefore, a reconstructive surgery is indicated including PTT debridement and medial calcaneal osteotomy. Other procedures should be taken into consideration: flexor digitorum tendon (FDL) transfer, spring ligament reconstruction, or Achilles tendon lengthening 12. For Stage IIb, lateral column lengthening or isolated subtalar joint arthrodesis is usually performed.
- Stage III: This results from hindfoot valgus deformity with or without arthrodesis. A medial double arthrodesis or triple arthrodesis (subtalar, calcaneocuboid, and talonavicular arthrodesis) is indicated with or without deltoid ligament repair as it involves hindfoot arthritic changes. Additionally, such patients require lengthening of the gastrocnemius muscle group to address the equinus deformity 13,18.
- Stage IV: As ankle joint (tibiotalar) changes are noted, a triple arthrodesis in combination with deltoid ligament repair and a medializing calcaneal osteotomy may be considered in patients with valgus deformity of the ankle without degenerative joint disease. In severe cases, a pantalar fusion (tibiotalar, subtalar, talonavicular, and calcaneocuboid joints) may be necessary 13,18.
Coordination of care
Parallel practice: Patients may be rehabilitating but still working or competing.
Coordinated: Employers, coaches, and family may need to be involved to promote a successful outcome.
Multidisciplinary: Athletic trainers, physical therapists, and orthotists may be involved.
Interdisciplinary: Foot-ankle trained orthopedic surgeons or podiatrists can be consulted in refractory cases.
Patient & family education
Educate on the importance of gastrocnemius stretching, appropriate training volume and intensity, appropriate shoe (and orthotic) wear. Different athletic shoes should be worn every 6 months and can be rotated for longer wear.
Measurement of Treatment Outcomes including those that are impairment-based, activity participation-based and environmentally-based
The Foot Function Index (FFI) is a 0-10 scale of pain and foot function over time in standing, walking, etc. The Foot Health Status Questionnaire (FHSQ) is a 42-item questionnaire assessing quality of foot health. The Foot and Ankle Ability Measure (FAAM) is an activities-of-daily-living scale of foot health.) These measures can be used to assess pain severity and to monitor response to treatment.
Translation into Practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
Assessing the pain at initial presentation and measuring the improvement in pain score with footwear and orthosis will be needed. The minimal clinical meaningful difference for pain scale (0-10) is 2. Orthotic interventions often do not correct deformities.
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Key point in orthoses
UCBL, SMO, and short rear-entry AFO are designed to align the subtalar complex by directly controlling calcaneal eversion and forefoot abduction allowing healing of the PTT. The lateral border of the UCBL or SMO is formed up to the fifth metatarsal shaft for proper control of forefoot abduction. Short rear-entry AFO is also designed to control the internal rotation of tibia associated with subtalar pronation. However, the effectiveness of this AFO for tibial control is questionable. In patients with excessive obesity, fixed deformity of the subtalar joint, or tight heel cords, there are not many options other than an AFO. In controlling pronation of the flatfoot, the goal is dampening rather than completely blocking pronation. Completely blocking pronation may lead to other symptoms such as knee or back pain since pronation allows normal gait. In order to avoid irritation of the plantar fascia, the medial arch of the FO or UCBL should not be too prominent 17.
New treatment techniques include extracorporeal shockwave therapy (ESWT), ultrasound guided corticosteroid injection, percutaneous needle tenotomy, platelet rich plasma (PRP), prolotherapy, and potentially in the future, stem cell therapies to promote healing.
Newer materials for orthotics and knowledge of different shoes for different activities are important. Minimally invasive surgical techniques are emerging.
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
New techniques of pain management include different types of foot orthotics and ankle bracing. The role of PRP, prolotherapy, botulinum toxin, percutaneous needle tenotomy, and stem cells needs to be evaluated. Considerable controversy remains about the appropriate treatment of all stages of PTT dysfunction. Comparison-outcome trials are needed to provide better data to evaluate the treatment options. The current controversy in the reconstruction of these deformities is whether to proceed with osteotomies and tendon transfers or arthrodesis.
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Original Version of the Topic
David Berbrayer, MD. Pes Planus/Cavus. 09/15/2015.
Mooyeon Oh-Park, MD
Nothing to Disclose
Lawrence Chang, DO, MPH
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Yusik Cho, MD
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