Keys To The Biomechanical Evaluation Of The Symptomatic Adult-Acquired Flatfoot
While the patient is still standing, assess the “flexible versus rigid” deformity to differentiate Stage II from Stage III flatfoot. The practitioner will attempt to move the patient’s foot into a rectus position at the hindfoot by manually inverting the heel or asking the patient to externally rotate the lower leg to supinate the hindfoot. If the hindfoot moves into a more vertical position from resting stance, the deformity is “reducible” and would still be “flexible” rather than rigid. However, the accurate evaluation of this test is quite subjective and evidence of flexibility versus rigidity can be difficult to determine, particularly with obese patients. One must correlate this evaluation with the off-weightbearing exam as well to stage the deformity.
The Hubscher maneuver, also known as the “Jack test,” can determine function of the windlass mechanism, which will be severely compromised by ligament disruption in the adult-acquired flatfoot.1 The examiner passively dorsiflexes the hallux and looks for movement transfer of supination of the hindfoot as well as external rotation of the tibia. In comparison to Stage I flatfoot, a Stage II deformity will lack tension in the plantar aponeurosis and connecting ligaments of the first ray, and no movement transfer will occur.
One should perform a modified Romberg test for balance with the patient in an upright standing position. It is often a revealing experience for both the clinician and the patient to learn how balance is severely compromised with the symptomatic foot. One must address this issue when prescribing a functional rehabilitation program for the patient with symptomatic adult-acquired flatfoot.
Pertinent Pearls On Conducting The Off-Weightbearing Exam
The off-weightbearing or open kinetic chain exam can reveal additional critical features of the patient’s own deformity to further aid in the staging and treatment recommendations. In addition to the general aspects of a biomechanical exam, I recommend the following additional tests.
Manual muscle testing for strength of the tibialis posterior. With the patient in a supine position, press your thumb against the plantar-medial aspect of the first metatarsophalangeal joint and move the foot into a plantarflexed and everted position at the ankle and subtalar joint. Ask patients to push their foot against your thumb. This will activate inversion of the foot using the tibialis posterior muscle. Assess the “push” or resistance produced by the patient’s symptomatic and asymptomatic foot. With this test, it is easy to detect a single grade of strength loss, which occurs with attenuation and eventual rupture of the posterior tibial tendon. Magnetic resonance imaging is rarely needed to document rupture because this test is very reliable when one combines it with other clinical findings.22