Keys To The Biomechanical Evaluation Of The Symptomatic Adult-Acquired Flatfoot
Look for the timing of heel rise and evidence of inversion of the hindfoot during heel rise, which can indicate function of the posterior tibial tendon. Peak ankle joint dorsiflexion normally occurs at about 75 percent of the stance phase of gait. This is followed by rapid ankle joint plantarflexion, which will lead to visible heel rise. Heel rise will be delayed in Stage II flatfoot because the triceps has reduced leverage to plantarflex the entire foot as one stable unit.4
Houck has shown that plantarflexion of the hindfoot will lower the medial longitudinal arch and dorsiflex the first metatarsal.20 Plantarflexion of the ankle occurs in the absence of heel rise as the rearfoot will plantarflex on the forefoot across an unstable midtarsal joint. The key features of Stage II adult-acquired flatfoot during gait are: increased ankle plantarflexion (without resulting heel rise); increased hindfoot eversion; increased first metatarsal dorsiflexion (lowering of medial longitudinal arch); and increased forefoot abduction.20
After comparing foot alignment and function, evaluate the entire lower extremity as well as the hips, arms and shoulders for other postural alignment abnormalities. A common secondary deformity in Stage II and III adult-acquired flatfoot is the development of valgus alignment of the knee. This can cause symptoms and disability that will be as severe or worse than those in the foot itself.
Essential Insights On The Static And Dynamic Stance Evaluations
After watching the patient walk, ask him or her to stand next to a wall or countertop, and perform the single and double leg heel rise test. This is the single most important clinical exam to determine the stage of deformity in the adult-acquired flatfoot. Ask patients to touch the wall or countertop for balance only without pushing or pulling themselves upward.
The first test is the double leg heel rise test in which the patient does five consecutive heel rise maneuvers raising as high off the floor as possible. It is best to demonstrate these tests yourself to the patient in addition to providing verbal instruction. Look for the height that the patient can elevate the heels and also look for any evidence of inversion of the hindfoot as the heel rises off the ground. Look for asymmetry in both measurements.
Next, ask the patient to perform the single leg heel rise starting with the asymptomatic foot. Ask him or her to do five heel rises per leg and compare for height of heel rise and evidence of hindfoot inversion. Healthy patients should be able to lift their heel as high during single leg heel rise as they can during the double leg heel rise.
Lack of heel rise and inversion of the hindfoot is a reliable indicator of function of the tibialis posterior muscle as well as ligamentous stability of the midfoot. With loss of stability of the midfoot, the contraction of the triceps surae during heel rise will cause a plantarflexion of the rearfoot on the forefoot rather than a plantarflexion of the entire foot, which functions as one rigid lever.21 This loss of stability is a result of more than just an “unlocked” midtarsal joint. With a lack of ligament stabilization provided by the spring ligament and plantar ligaments, the forefoot becomes disconnected from the hindfoot. Inability to perform a single leg heel rise is the hallmark of Stage II adult-acquired flatfoot deformity. Impaired heel rise is present in early Stage II and diminishes to become completely absent in late Stage II.