Pes Planus (Flatfoot) Workup

Updated: Jun 18, 2019
  • Author: Gregory C Berlet, MD, FRCSC, FAOAO; Chief Editor: Vinod K Panchbhavi, MD, FACS  more...
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Workup

Laboratory Studies

Generally, no laboratory studies are warranted for adult-acquired flatfoot deformity (AAFD) unless a systemic metabolic or inflammatory condition is suspected.

A painless, atraumatic flatfoot deformity in an insensate foot is most likely due to neuroarthropathy (Charcot foot). The most common cause of neuroarthropathy in the United States is diabetes. If diabetes mellitus is not already diagnosed, a fasting blood glucose test is indicated.

If the patient has pain in multiple joints, consider a workup for rheumatoid arthritis (RA) or seronegative spondyloarthropathy with rheumatoid factor (RF), erythrocyte sedimentation rate (ESR), and human leukocyte antigen (HLA)-B27.

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Radiography

Plain radiography

As with most foot and ankle deformities, weightbearing radiographs are mandatory in the workup of AAFD. [48]  The authors' protocol includes three weightbearing views for the foot (anteroposterior [AP], oblique, and lateral) and three weightbearing views for the ankle (AP, mortise, and lateral). (See the image below.)

Anteroposterior and lateral radiographs of lower e Anteroposterior and lateral radiographs of lower extremity in patient with pes planus (flatfoot). Images demonstrate stage 4 posterior tibial tendon (PTT) dysfunction with valgus tilt at ankle.

Evaluation of longitudinal arch collapse is largely dependent upon weightbearing lateral radiographs. As a flatfoot (pes planus) deformity develops, the arch sags at the naviculocuneiform or talonavicular joint, causing a decrease in calcaneal pitch, [20] a decreased lateral first talometatarsal angle, [49] and depression of medial cuneiform height [50] (see the image below). The forefoot moves laterally into abduction, causing lateral subluxation of the talonavicular joint and an increase in the talonavicular coverage angle.

Pes planus (flatfoot). Standing lateral radiograph Pes planus (flatfoot). Standing lateral radiograph of foot of patient with posterior tibial tendon (PTT) dysfunction. A = lateral first talometatarsal angle (normal value, 0°). B = calcaneal pitch (normal value, 20-25°). C = Distance from medial cuneiform to floor (normal value varies with foot size). As deformity increases secondary to PTT dysfunction, talus plantarflexes and medial border of foot is lowered. Therefore, lateral first talometatarsal angle decreases, calcaneal pitch decreases, and medial cuneiform is depressed closer to floor.

The axis of the talar–first metatarsal angle on the lateral weightbearing foot radiograph is the most discriminating radiographic parameter in patients with symptomatic flatfoot. [49]  Alternatively, the distance between the medial cuneiform and the floor is a strong reflection of medial arch collapse and flatfoot. [50]

An AP standing foot projection is primarily used for evaluating talar head uncoverage secondary to lateral deviation of the navicular. As peritalar lateral subluxation increases, the talonavicular coverage angle—created by two reference lines through the centers of the talar head and navicular bone, respectively—reveals increased angles (see the image below). Alternatively, using the talonavicular incongruency angle to measure forefoot abduction results in improved interrater reliability. [51]

Pes planus (flatfoot). Standing anteroposterior ra Pes planus (flatfoot). Standing anteroposterior radiograph of patient with posterior tibial tendon dysfunction shows talonavicular coverage angle; navicular axis is formed by perpendicular line connecting medial and lateral aspects of navicular proximal articular surface. Talonavicular coverage angle is formed by talar and navicular axes. As forefoot abduction increases, talonavicular coverage angle increases.

Standing AP radiographs of the ankle are evaluated for evidence of valgus talar tilt with resultant subluxation, arthrosis, or both. The ankle view is particularly important in patients who have fixed hindfoot valgus. Hindfoot alignment can be further evaluated in the axial plane with the so-called Buck view, as described in a 1995 study by Saltzman and el-Khoury. [26]  The lateral tibial-calcaneal angle as measured on a standing lateral ankle x-ray identifies patients with Achilles tendon contractures. [52, 53]

A study by Dyal et al compared weightbearing radiographs of symptomatic feet with posterior tibial tendon (PTT) dysfunction with those of the contralateral asymptomatic feet. [31]  The measurements of the two feet were strongly correlated, leading the authors to suggest that a predisposing constitutional flatfoot may be an etiologic factor in the development of dysfunction. The authors cautioned against using radiographic measurements alone for diagnosis.

Ellis et al concluded that weightbearing multiplanar imaging also provides a reliable means of assessing lateral pain in patients with flexible flatfoot deformity. [54]

Tenography

Tenography has been used to diagnose PTT rupture, with limited success. For this test, 5 mL of radiopaque dye is injected into the sheath between the medial malleolus and navicular tuberosity. In later stages of dysfunction, the tendon and sheath become adherent, and injection of dye becomes impossible. After tendon rupture, the sheath often is not palpable, and injection is very difficult.

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Magnetic Resonance Imaging

Although highly dependent on technique and the experience of the interpreter, magnetic resonance imaging (MRI) can be extremely sensitive and specific in the evaluation of AAFD, providing highly detailed evaluations of both bony and soft-tissue anatomy. (See the image below.) In most instances, however, PTT dysfunction can be adequately diagnosed with a thorough physical and radiographic examination. Because of the expense of MRI, the cost-to-benefit ratio must be considered; most MRI examinations should be reserved for patients who have a confusing clinical picture.

Pes planus (flatfoot). Axial magnetic resonance im Pes planus (flatfoot). Axial magnetic resonance image demonstrating medial calcaneal shift.

Conti et al used MRI to describe three types of PTT degeneration, as follows [55] :

  • Type I - A partially torn tendon with tendon enlargement and vertical splits
  • Type II - A partially torn attenuated tendon
  • Type III - A complete rupture with a tendon gap

Although it is sensitive, MRI can cause overestimation of the degree of tendon degeneration as compared with surgical assessment, with a mere 40% correlation between MRI findings and surgical findings. This MRI classification is useful in predicting the outcome of tendon transfer, with higher grades of tendon degeneration faring worse than mild grades.

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Computed Tomography

Determining the amount of joint degeneration with computed tomography (CT) in patients who have chronic disease may be beneficial; however, this modality does not provide comprehensive information on tendon pathology. In patients with late-stage AAFD and lateral hindfoot pain, CT may show two frequently occurring extra-articular sources of bone impingement (sinus tarsi and calcaneofibular impingement). [56] Weightbearing CT scans allow the surgeon to view multiplanar images in a weightbearing mode with less radiation and shorter image acquisition times. [57]

Several studies have demonstrated that weightbearing CT allows improved prediction of AAFD through analysis of angles presenting hindfoot valgus, along with improved deformity appreciation in those with a definitive diagnosis. [58, 59]

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Staging

The severity of AAFD varies, depending on the degree of pathologic anatomy and the resultant changes in biomechanics. Therefore, staging the spectrum of dysfunction can be extremely helpful in guiding treatment protocols. In their 1989 report, Johnson and Strom described an initial three-stage continuum of PTT dysfunction. [16] In 1997, Myerson added a fourth stage to Johnson and Strom's original description. [17]

Stage 1 dysfunction

Initial stage 1 findings include mild tenderness along the inframalleolar course of the PTT, with minimal (if any) loss in tendon strength as assessed by the single-limb heel-rise test. When the patient bears weight only on the involved extremity, performing the heel-rise test demonstrates not only adequate strength but also initiation of heel inversion, which signals an intact tendon. The foot and ankle typically demonstrate normal alignment without fixed deformity. [7]

Stage 2 dysfunction

The key to diagnosis of stage 2 disease is a dynamic deformity, typically hindfoot valgus with forefoot abduction.

Palpation along the course of the PTT demonstrates pain and possibly hypertrophy or defects. Observing the patient's stance from behind reveals increased visualization of the lateral toes (too-many-toes sign) on the affected extremity secondary to weakness. [15] Single-limb heel rise may not be possible due to weakness, and if performed, corrective heel inversion is generally absent. With the exception of possible gastrocnemius-soleus contracture, hindfoot and midfoot motion testing usually yield normal results.

Stage 2 disease has been further subclassified according to the degree of talonavicular coverage, as originally proposed by Vora. [60] Radiographic measurements quantify talar head uncovering as either mild deformity with less than 30% uncovering (2A) or more severe deformities with greater than 30% uncovering (2B). [4]

Stage 3 dysfunction

As the continuum of disease progresses to stage 3, chronic dysfunction and lengthening of the PTT lead to fixed hindfoot deformity. In order to achieve a plantigrade foot in the setting of a fixed hindfoot valgus, the forefoot typically compensates into a fixed supination position. With stage 3 disease, patients often present with lateral pain secondary to subfibular impingement as the calcaneus subluxes and the flatfoot deformity progresses. [7, 61]

Stage 4 dysfunction

In stage 4, as described by Myerson, long-standing hindfoot valgus places increasing stress on the deltoid complex, with eventual loss of competence. The resultant valgus tilt of the talus leads to eccentric loading of the ankle with subsequent tibiotalar arthrosis. [20, 61]

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