A Guide To Orthotic Therapy For Adult-Acquired Flatfoot

Author(s): 
Paul R. Scherer, DPM

Given the complex pathology associated with adult-acquired flatfoot, this author reviews the pathomechanics of the condition, discusses keys to appropriate staging and offers recommendations for effective, pathology-specific orthotic therapy.

Adult-acquired flatfoot (AAF) may be the most difficult of all foot pathologies to treat successfully with the possible exception of calcaneal fractures. The complexity surrounding this pathology originates in the continued confusion about etiology, classification, pathomechanics and surgical and non-surgical treatment. The loss of the active and passive pull of the tibialis posterior tendon is strongly associated with the development of adult-acquired flatfoot but no one is quite sure of the exact pathomechanics of this clinical disaster.1

   Hirano and colleagues performed a cadaveric study to determine whether the abnormal flatfooted position of some individuals increases friction on the tibialis posterior in its sheath, leading to an inflammatory condition that deteriorates or attenuates the tendon.2 Using six lower limbs mounted in a foot simulator and applying axial load to the tendon, they monitored the tendon’s gliding resistance. When they added a functional orthosis to the apparatus, it did not affect this resistance but did somewhat restore the normal anatomic position of the foot. The important aspect of this experiment was the confirmation that the abnormal flatfooted position does create resistance on the tibialis posterior tendon and increases the work of friction. This finding may provide some insight into the etiology of this pathology.

   Adding to the lack of understanding of the etiology is the mystery of why this problem seems to have been increasing in prevalence over the last 20 years.2 Is it a result of the increased aging of the susceptible flatfooted population or are we, as clinicians, just starting to recognize the problem more frequently as an entity in itself?

   Although the tibialis posterior muscle plays an important role in the deformity, authors since 1999 have begun to describe this clinical scenario as adult-acquired flatfoot, rather than posterior tibial tendon dysfunction, since the dysfunction or non-function of the tendon alone cannot account for the character and severity of the deformity and foot disability.3

   In 2004, Richie postulated that “significant ligamentous rupture occurs” as the flattening of the longitudinal arch and disarticulation of the rearfoot develop along with the attenuation or complete destruction of the spring ligament, superficial deltoid, plantar fascia and, finally, the long and short plantar ligaments.3 This may truly be the reason that repair or anastomosis of the tibialis posterior tendon alone is rarely effective in restoring the structural integrity of the foot.3 Recognizing that a multilevel and interrelated pathology is occurring is essential for the successful treatment of adult-acquired flatfoot, whether the treatment is surgical or non-surgical.

Emphasizing The Need For Appropriate Staging

The progression from simple weakness of the tibialis posterior through ligamentous disruption and finally rearfoot subluxation creates various stages of pathology that are probably best to approach as individual entities. Treating the more advanced stages with methods used in the initial stages is not effective. As the pathology in adult-acquired flatfoot progresses from moderate to severe, the deformation and dysfunction of the foot pass through several thresholds that conservative and often surgical treatment cannot reverse. It is therefore useful to approach each stage of the deformity as a separate, distinct pathology with the primary objective being to prevent the next more severe stage from occurring.

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