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Pes Planus
Introduction
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] The arch of the foot is a tough, elastic connection of ligaments, tendons, and fascia between the forefoot and the hindfoot. The talocalcaneal interosseous ligament, tibionavicular portion of the deltoid ligament, spring ligament, and medial talocalcaneal ligament assist in stabilizing the arch of the foot. [2] The arch serves as an adaptive and flexible base for the entire body.[3] It functions to dissipate the forces of weight-bearing and acts to store mechanical energy within the stretched elastic ligaments during the gait cycle. [4] Dysfunction of the arch complex, specifically relating to flexible flat foot, can frequently be asymptomatic but can alter the biomechanics of the lower limbs and lumbar spine, causing an increased risk of pain and injury.[5]
Etiology
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Etiology
Pes planus can either be congenital or acquired.
Congenital
Pes planus is fairly common in infants.[6] Infants and young children are prone to absent arches secondary to ligamentous laxity and lack of neuromuscular control.[7] Infants have a fat pad under the medial longitudinal arch, which serves to protect the arch during early childhood.[8] Most children develop normal arches by age 5 or 6. Most cases of pes planus in children are flexible. Flexible pes planus describes a normal arch without bearing weight, which disappears with weight-bearing.[1] There is a small percentage of children who fail to develop a normal arch by adulthood. Obesity in children is significantly correlated with the tendency of the longitudinal arch to collapse in early childhood.[9]
Acquired
The function of the posterior tibial tendon is to support the arch as well as inversion and plantarflexion of the foot. Acquired pes planus is most commonly occurs secondary to posterior tibial tendon dysfunction.[10] Posterior tibial tendon dysfunction is most common in females over the age of 40 with comorbidities, including diabetes and obesity.[11] It can also occur in adults with congenital pes planus, especially those who participate in repetitive high-impact sports such as basketball, running, or soccer.[12]
Patients with trauma to the midfoot or hindfoot resulting in navicular, first metatarsal, calcaneal, or Lis-Franc ligament complex demonstrate an increased risk of developing pes planus.[13][14] It occurs more commonly in the malunion of those fractures. Other causes include injuries to soft tissues such as plantar fascia or spring ligament.[15][16] Patients with sensory neuropathy may experience Charcot arthropathy, leading to midfoot collapse over time.[17]
Patients with congenital ligamentous laxity secondary to Down syndrome, Marfan, or Ehlers Danos can present with pes planus.[18][19][20] Ligamentous laxity secondary to pregnancy may also cause pes planus but typically corrects itself post-partum.[21]
Patients with arthropathies are at higher risk for acquired pes planus. These can be either degenerative or inflammatory. Patients with rheumatoid arthritis or seronegative arthropathies should be considered at higher risk for developing pes planus, especially if poorly controlled.[22]
Rigid pes planus is rare. It usually develops during childhood but can occur at any point in life. It develops from the tarsal coalition, accessory navicular bone, congenital vertical talus, or other forms of congenital hindfoot pathology.[23]
Epidemiology
About 20% to 37% of the population is estimated to have some degree of pes planus.[24][25][26] A majority of these cases are flexible pes planus. A 2003 study by Dunn et al. found that the prevalence among non-Hispanic whites was 17% and greater among African Americans at a rate of 34%.[27] There is a 1:1 ratio of men to women. [5] It is typically more common in children, but most children develop a normal arch by age 10. There is a strong genetic component of pes planus, and it typically runs in families.[28] The radiographic or clinical presence of pes planus may be an incidental finding in patients and requires clinical correlation.
Pathophysiology
The medial longitudinal arch is made up of the calcaneus, navicular, talus, first three cuneiforms, and first, second, and third metatarsals.[29] It is supported by the soft tissues of the spring ligament (plantar calcanea navicular ligament), deltoid ligament, posterior tibial tendon, plantar aponeurosis, and flexor hallucis longus and brevis muscles. Dysfunction of any portion of the medial longitudinal arch may result in acquired pes planus. The main factors that contribute to an acquired flat foot deformity are excessive tension in the triceps surae, obesity, posterior tibial tendon dysfunction, or ligamentous laxity in the spring ligament, plantar fascia, or other supporting plantar ligaments.[30] It may also result from a tight Achilles tendon or calf muscle.[31]
Rigid pes planus is rare. It usually develops during childhood but can occur at any point in life. It develops from the tarsal coalition, accessory navicular bone, congenital vertical talus, or other forms of congenital hindfoot pathology.
History and Physical
History
Evaluation should be based on the presentation during the clinic visit. Pes planus is very common in young children and asymptomatic. In rare instances, flat feet can become painful or rigid, which may be a sign of underlying foot pathology, such as tarsal coalition. Thorough developmental history, medical history, past surgical history, family history of pes planus, and activity level (sports participation or avoidance) should be documented.[32]
In adults, pes planus may be an incidental finding. In symptomatic patients, there may be complaints of midfoot, heel, lower leg, knee, hip, and or back pain. Patients with more advanced changes may complain of an altered gait pattern. Patients who typically overpronate will be at high risk for ankle sprains from chronic “rolling of the ankle.” The patient should be asked about the onset of deformity, timing of symptoms, severity of past and current symptoms, history of trauma, family history, surgical history, and past medical history (including hypertension, diabetes, rheumatoid arthritis, sensory neuropathies, seronegative spondyloarthropathies, and obesity).
Physical Exam
The physical exam should consist mainly of inspection, palpation, ROM, muscle strength testing, and gait assessment. A comparison should be made to the unaffected foot.
Inspection: The examiner should evaluate the patient with and without weight-bearing. The flat foot should be apparent on inspection. The flexible flat foot will have an arch without weight-bearing, which will disappear with weight-bearing. The patient will be noted to overpronate. Looking at the patient from the back will show the “too many toes” sign. [33] Both feet should be compared for asymmetry.
Palpation: The examiner should palpate the posterior tibial tendon, lateral rearfoot, and plantar fascia.
ROM: This will differentiate flexible versus rigid pes planus. Flexibility can also be assessed using the Hubscher maneuver (Jack test) to determine if the deformity is reducible.
Muscle strength testing: The examiner can evaluate muscle strength by having the patient perform a single toe raise. Posterior tibial tendon muscle strength can be evaluated by having the patient invert the foot against resistance. [34]
Gait assessment: The patient may have an antalgic gait. Examiners may notice overpronation with ambulation.
Evaluation
Plain Radiographs
Weight-bearing lateral radiographs of the feet are often sufficient for diagnosis. Simulated weight-bearing radiographs should be obtained if a patient can not bear weight. Additional radiographic views to assess for coalition can also be obtained as indicated.
On lateral weight-bearing radiographs, the following findings are often noted:
- A Meary's angle greater than 4 degrees convex downward suggests pes planus. This angle is also called the talus-first metatarsal angle and constitutes the angle obtained from lines drawn from the center longitudinal axes of the talus and metatarsal.
- A calcaneal inclination angle less than 18 degrees is indicative of pes planes. This angle is obtained from the calcaneal inclination axis and the horizontal surface on which the foot is placed.
MRI
MRI can be performed if posterior tibial tendon dysfunction or injury to the spring ligament or other supporting soft tissue structures is suspected.
EMG/NCS
EMG and nerve conduction studies can be performed to evaluate for sensory neuropathy.
Treatment / Management
Children
Children rarely require treatment for pes planus. Foot orthotics are indicated for foot pain secondary to pes planus alone or in combination with leg, knee, and back pain.[6] Surgery is only indicated for rigid pes planus.[35]
Adults
In adults, treatment is based on etiology. Foot orthotics and NSAIDS are sufficient for pain. The patient should be counseled on proper footwear. Patients with pes planus could benefit from motion control shoes. Patients with obesity should be counseled to lose weight through diet and exercise. For posterior tibial dysfunction, treatment initially consists of rest, NSAIDs, and orthotics. Physical therapy can be done to minimize pain, increase foot flexibility, strengthen weak muscles, and train proprioception. Surgery is reserved for cases resistant to therapy.[1][36]
Differential Diagnosis
The various causes of pes planus have been described above and have primary and secondary causes. A few presentations can mimic pes planes. Differential diagnosis is often limited to the following and can be excluded based on clinical evaluation and imaging:
- Prominent fat pad (pediatric patients)
- Edema mimicking flat foot (most commonly secondary to venous stasis or congestive heart failure)
- Benign and malignant neoplasms effacing the plantar arch, such as plantar fibroma/fibromatosis, giant cell tumors of the tendon sheath, lipoma, osseous lesions, and rarely melanoma
Prognosis
Flat food constitutes a multifactorial entity. Prognosis varies depending on etiology, length of time a patient has symptoms, and treatment course. Degenerative and inflammatory arthritis, as well as Charcot arthropathy as the cause of flat foot, is often difficult to treat, and the symptoms worsen over time. Surgery for pathologies such as posterior tibial tendon tear, a tight gastrocnemius muscle, or Achilles tendon has a favorable prognosis.[36] Activity modification in patients performing high impact activities can also help guide conservative treatment.
Complications
Postoperative complications depend on the particular surgery involved and include:[36]
- Surgical site infection
- Malunion/non-union
- Persistent pain
- Implant dislocation/fracture
- Various other hardware complications
Advanced deformities have higher failure rates during recovery post-surgery.[37]
Deterrence and Patient Education
Patient education should focus on risk factors for pes planus that can be potentially mitigated. These include:[38]
- Obesity with an emphasis on weight loss
- Diabetes with a goal of preventing sensory loss and eventual Charcot arthropathy
- Limitations on activities for those engaging in high impact repetitive trauma
Patients should also be counseled on adhering to the prescribed orthotic device.[38]
Pearls and Other Issues
- Pes planus is a common finding on clinical exams and may be an incidental finding in patients. It can be acquired or congenital.
- Treatment is typically non-surgical and requires modification of footwear and orthotics.
Enhancing Healthcare Team Outcomes
Pes planus is best managed by an interprofessional team that also includes orthopedic nurses and therapists. Clinicians should be fully aware that Children rarely require treatment for pes planus. Foot orthotics are indicated for foot pain secondary to pes planus alone or in combination with leg, knee, and back pain. Surgery is only indicated for rigid pes planus. Unnecessary surgery in children can lead to more harm than good. Surgery may be an option for pes planus in adults, but overall, the results are not satisfactory. Most patients have acceptable outcomes with the use of orthotics.
Media
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pes planus or flat feet Image courtesy S Bhimji MD
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Pes Planus Note the lack of the longitudinal arch, increased talar declination, and decreased calcaneal pitch. Contributed by Mark A. Dreyer, DPM, FACFAS
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Single lateral radiograph demonstrating pes planus. No other abnormalities are visualized. Contributed by Dr.Dawood Tafti, MD.
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Single lateral radiograph demonstrates moderate to severe pes planus. Contributed by Dr.Dawood Tafti, MD.
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Single lateral radiograph of the left foot demonstrates pes planus as evidenced by a decreased calcaneal inclination angle. Contributed by Dr.Dawood Tafti, MD.
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