Adult-acquired flatfoot deformities pose clinical challenges from assessment to the treatment course. Reviewing the pertinent literature and sharing their experience, the authors propose a conservative clinical pathway for this common condition.
Adult-acquired flatfoot deformity (AAFD) is a common and often debilitating chronic foot and ankle condition. The deformity is characterized by flattening of the medial longitudinal arch and dysfunction of the posterior tibial tendon.1 Chronic partial rupture of the posterior tibial tendon was first described by Key in 1953.2 Subsequent descriptions of the pathology noted an association between posterior tibial tendon dysfunction (PTTD) and flatfoot deformity.3 Although a variety of surgical treatment options are available for adult flatfoot, conservative treatments can be effective in managing the deformity.
Evaluation of an adult flatfoot requires obtaining a pertinent patient history including onset of the deformity, timing and severity of the symptoms. A family history of flatfoot deformity is also relevant. Occupation, activity level, footwear, history of trauma and previous treatment are other possible contributory factors. Completing a review of systems can provide further meaningful information. Myerson notes that a flatfoot deformity can be categorized as either an acquired deformity or a residual deformity from developmental etiologies including abnormal joint development, tarsal coalition, a congenital vertical talus, accessory navicular and ligamentous laxity with Marfan or Ehlers-Danlos syndromes.4
Understanding Overuse Injury With The Tissue Stress Model
Understanding the tissue stress model provides the foundation for developing a thorough examination and management strategy for treating individuals with flatfoot deformity. One can gain insight into the tissue stress model by considering the load-deformation curve.5 As one applies a load to a tendon, an amount of deformation is subsequently introduced. Two regions exist within the curve: an elastic region and a plastic region. There is microfailure zone between the two regions. The elastic region represents the normal “give and take” of soft tissues, which prevents excessive joint movement as the foot is loaded and unloaded. As the individual maintains tissue stress within the elastic region, tissue irritation and inflammation will most likely be maintained at tolerable levels. If, however, the patient’s magnitude of load applied to the tissues increases, tissue could be deformed beyond the microfailure zone and into the plastic region, resulting in an overuse injury. It is important to recognize that individuals will have unique levels of tolerance for the amount of tissue stress they are able to withstand during walking and other activities of daily living.
Regardless of etiology, one principle for management of a flatfoot deformity includes removing any deforming force of the leg onto the foot. Doing so allows the foot to accept the external support it requires to function. A tightness of the triceps surae complex and/or isolated gastrocnemius tightness have a profound effect on the longitudinal medial arch.
After performing a three-dimensional evaluation of the first ray in cadaver models with variable tension on the Achilles tendon, Johnson and Christensen found the influence of the peroneus longus on the medial column diminishes with increasing Achilles load.6 Equinus on an intact longitudinal arch seems to affect the distal components of the medial column, primarily in the frontal plane. Furthermore, the authors Johnson and Christensen state that with increased pull on the Achilles, a measurable arch flattening effect occurs with plantarflexion of the talus and navicular, and dorsiflexion of the first metatarsal and cuneiform.
Keys To Assessing Adult-Acquired Flatfoot Deformity
As part of a thorough physical examination, musculoskeletal examination should account for any gross deformities, symptomatic sites or malalignments. The non-weightbearing biomechanical exam should include the Silfverskiöld test for equinus, subtalar joint range of motion, forefoot to rearfoot alignment, first ray hypermobility and first metatarsophalangeal joint range of motion. When testing for equinus, one must ensure the foot is in a supinated posture to result in a more rigid locking of the forefoot.7,8 Isolated manual posterior tibial muscle testing provides insight into the strength of the tendon. An integral aspect of the physical exam is evaluating the feet, ankles and legs while the patient is standing. Understanding the components of the knee and leg can help determine the compensatory aspects of the pes planus foot type. The hallmark findings of a pes planus foot type are collapse of the longitudinal medial arch, a prominent talar head medially and abduction of the forefoot on the rearfoot.9
A double heel rise test in conjunction with a single leg heel rise test can help clinicians evaluate the posterior tibialis tendon function and deformity reducibility. Dysfunction of the posterior tibialis tendon will be apparent if there is incomplete inversion of the hindfoot during this maneuver and an inability to perform a single leg heel rise. A gait examination can identify if any gait disturbances exist, such as apropulsive gait, early heel rise or an abductory twist. Weightbearing X-ray films of the foot and ankle can also assist in determining the extent of the deformity. Furthermore, obtaining hindfoot views, such as calcaneal axial, allow the clinician to assess the severity of any hindfoot malalignment. Advanced imaging studies are warranted if the information from these studies will affect the management of the deformity.
Staging Flatfoot Deformity: What You Should Know
Formulating a proper treatment course must begin with evaluating and categorizing the deformity. Traditionally, there are four stages for adult-acquired flatfoot deformity with Johnson and Strom describing stages I-III and Myerson adding modifications with a fourth stage.3,4 The staging system is based on the clinical presentation and the severity of the deformity as the disease progresses.
Stage I consists of painful tenosynovitis of the posterior tibial tendon without tendon elongation. A patient in this stage is able to perform a single and double limb heel rise. Stage II is characteristic of a flatfoot deformity with pain and dysfunction of the posterior tibial tendon. Patients typically have normal hindfoot motion but are usually unable to perform a single leg heel rise. These patients often display the “too many toes” sign and a pes plano valgus deformity.
Stage III patients have a fixed, irreducible flatfoot deformity and cannot perform a single or double limb heel rise. Further posterior tibial tendon attenuation occurs and lateral symptoms begin to predominate with sinus tarsi pain. Myerson’s proposed stage IV classification is categorized by deltoid insufficiency and valgus ankle instability.4,10
Formulating An Effective Conservative Treatment Plan
The history and physical exam should allow the clinician to formulate an appropriate treatment plan. An understanding of the patient’s goals is critical to outcome success. Initially, one is seeking to relieve pain and discomfort in the inflammatory stage. At the initial appointment, immobilization, oral steroids, ankle bracing, a CAM boot, taping, and RICE (rest, ice, compression, elevation) therapy are treatment options that can address the symptoms. Controlling the initial symptomology allows the clinician to formulate a proper subsequent treatment plan. Immobilization for an additional period of two to four more weeks may be necessary to reduce the painful condition. It is essential to treat the equinus deformity in order to remove any deforming force of the leg onto the foot. The clinician should have the patient institute a stretching protocol to improve range of motion.
A Closer Look At Stage-Based Orthotics and Bracing
Once one has controlled the initial symptoms, the clinician may employ external supportive devices. First-line therapy for stage I treatment includes custom orthoses. Typically, this involves a semi-rigid device with a deep heel cup to have more predictable control of the rearfoot. If the clinician determines that the patient may overpronate over the device, he or she may consider a maximally corrective orthotic.
For patients with stage II adult-acquired flatfoot, one may utilize a Blake inverted device or a Mueller tibialis posterior dysfunction (TPD) device. The Blake orthotic can correct a significant amount of deformity via a high medial flange, a deep heel cup and a wider area at the medial arch.11 The Mueller TPD device has a deep heel cup, high medial and lateral flanges that extend distally to limit the transverse motion, and an accommodation for the navicular. Clinicians can commonly have patients wear these devices within a sneaker or an extra-depth shoe. An additional consideration for treatment of a flexible deformity is the Richie Brace®. The brace provides an orthotic footplate articulated to adjustable lower leg uprights to stabilize deforming forces.
Once a patient’s classification encompasses a stage III or IV flatfoot deformity, clinicians should consider an ankle-foot orthosis or an external ankle brace, such as an Arizona AFO™ (Arizona AFO) or a TayCo™, respectively. The Arizona AFO extends proximally to the midshaft of the tibia and distally to the metatarsal heads. As Augustin and colleagues note, the Arizona AFO functions by decreasing hindfoot valgus alignment, lateral calcaneal displacement and medial ankle collapse.12 The external brace provides benefits including fixed and range of motion capabilities, lightweight design, no limb length imbalance, and the ability for the patient to utilize his or her own footwear.
Formulating a proper non-surgical treatment plan for a patient with adult flatfoot can present challenges. Although surgical treatment of adult-acquired flatfoot deformity can yield excellent results, operative care is not without inherent risks and requires a prolonged period of convalescence.13 Nielsen and colleagues revealed successful treatment for 87.5 percent of patients utilizing non-operative measures.13 Their study showed that BMI was not statistically significant to the outcome of the treatment. Furthermore, the use of any form of bracing was associated with successful non-surgical treatment. Likewise, Alvarez and coworkers reported successful non-operative treatment, including physical therapy and orthotics, of PTTD in 83 percent of patients.14
Many patients can have effective treatment with conservative management protocols as we have described above. The goal of the clinician should be to aggressively alleviate or significantly decrease patient pain and discomfort. The clinician should then institute long-term treatment options to decrease progression of the deformity and limit discomfort.
Dr. DeHeer is the Residency Director of the St. Vincent Hospital Podiatry Program in Indianapolis. He is a Fellow of the American College of Foot and Ankle Surgeons, a Fellow of the American Society of Podiatric Surgeons, a Fellow of the American College of Foot and Ankle Pediatrics, a Fellow of the Royal College of Physicians and Surgeons of Glasgow, and a Diplomate of the American Board of Podiatric Surgery. He is the inventor of The Equinus Brace® and an owner of IQ Medical.
Dr. Wolfe is the Assistant Residency Director of St. Vincent Hospital Podiatry Program in Indianapolis, IN. He is an Associate of the American College of Foot and Ankle Surgeons.
Dr. Camp is a second-year resident with St. Vincent Hospital in Indianapolis, IN.
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