Keys To The Biomechanical Evaluation Of The Symptomatic Adult-Acquired Flatfoot

Douglas Richie, DPM, FACFAS, FAAPSM

   It is helpful to assess true first ray instability versus forefoot inversion by holding the foot in the classic neutral suspension cast position with the forefoot loaded and pronated at the midtarsal joint. The examiner then presses the first metatarsal downward in a plantarflexed direction. One can measure the relative flexibility or reducibility of the supinatus and make a visual assessment comparing first ray motion versus eversion of the entire forefoot. Using this assessment as well as weightbearing radiographs, one can make critical decisions regarding arthrodesis versus soft tissue corrective procedures on the medial column for stage II flatfoot.

   Evaluation of the triceps and heel cord. Consider the powerful influence of the triceps in both the pathomechanics and the treatment of adult-acquired flatfoot. It is well recognized that the triceps through the tendo-Achilles is a significant deforming force in the progression of the adult-acquired flatfoot. When the tibialis posterior tendon fails to stabilize the hindfoot and midfoot, the triceps provides a plantarflexion force across the midfoot, which eventually leads to subluxation.

   The valgus alignment of the hindfoot changes the direction and moment arm of the tendo-Achilles in the adult-acquired flatfoot. The rationale for the medializing calcaneal osteotomy is to realign the direction of force of the Achilles to provide an inversion moment on the rearfoot.25

   One can evaluate the deforming influence of the tendo-Achilles in the patient with any stage of flatfoot by performing a simple clinical test with the patient in a supine position. Starting with the hindfoot in neutral position, passively dorsiflex the entire foot with equal pressure against the plantar aspect of both the first and fifth metatarsal heads. With a valgus deforming tendo-Achilles, the hindfoot will noticeably move into a valgus position as the tendo-Achilles bears tension with passive ankle joint dorsiflexion. This rotation of the hindfoot into valgus with tensioning of the Achilles does not occur in healthy feet.

   With the patient in a supine position, perform the Silfverskiold test to detect a contracture of the gastrocnemius versus a global contracture of the triceps or heel cord. Measure passive range of dorsiflexion of the ankle with the knee extended and then with the knee flexed. Significant reduction of dorsiflexion with the knee extended may be an indication for gastrocnemius recession.26

In Summary

The adult-acquired flatfoot is a potentially disabling condition that results in significant biomechanical dysfunction of the human foot. One can evaluate and stage the progression of the disorder with numerous clinical tests. After assessing the stage or severity of the condition, the physician can select the appropriate conservative and surgical intervention.
Multiple studies have reported the success of non-surgical interventions, particularly for Stage II deformity, and one should consider conservative solutions before contemplating more disabling surgical procedures.

   Dr. Richie is an Adjunct Associate Professor in the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University. He is a Past President of the American Academy of Podiatric Sports Medicine.

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