Adult acquired flatfoot

Last evidence check April 2010

The arch of the human foot is an important adaptation to our way of walking. Its part-dome transmits forces to and from the ground through relatively limited areas under the calcaneal tuberosity and the metatarsal heads, into the proximal skeleton. The work of Stainsby and Briggs is beginning to unravel the subtle control systems that keep these parts of the foot applied to the ground in many positions of the foot.

The arch provides shock absorption in the early stance phase of gait, and a stiff lever for propulsion forward by the triceps surae in the late stance.

Unlike many arches which are made stable by a locked capstone, the arch of the foot is capped by part of a universal joint, the talonavicular joint, which with the subtalar joint translates between leg and foot rotations. As it does so, it introduces distortions into the arch. Thus the arch of the foot is not entirely stable, but rather flexible with restraints to limit distortion.

Arch stability

The main stabilisers of the arch are:

In every gait cycle, these stabilisers are called into action.

At first contact, the arch is raised by tibialis anterior, which dorsiflexes the ankle in swing phase to prevent tripping. This pull also supinates the subtalar joint and adducts the midfoot, drawing the arch into its most stable configuration.

As heel contact is established, the tibia internally rotates, the subtalar joint pronates and the talar head descends and deviates medially. The navicular and the rest of the midfoot abduct, evert and slightly dorsiflex, as do the metatarsals to a slightly lesser extent.

All of these changes have the effect of moving the apex of the arch downwards and medially. Normally, the restraints control talar movement and arch descent.

By midstance the tibia is externally rotating, the subtalar joint is beginning to supinate and the talus rises up the calcaneum and rotates externally. The arch becomes stiffer, to act as a propulsive lever in late stance.

If the restraints are not competent, internal rotation and descent of the talus, with balancing forefoot abduction, may continue beyond its normal phase of the gait cycle. The “temporary flatfoot” of early stance becomes permanent. Initially the foot is late in supinating. Later it may be flattened throughout the stance phase. Propulsion becomes less efficient.

Incompetence of the restraints may be produced by:

It is the latter syndrome which is described as adult acquired flatfoot. Since Kettlecamp and Alexander’s paper in 1969, the tibialis posterior abnormalities were emphasised and the syndrome often referred to as “tibialis posterior insufficiency”. More recent work has recognised the abnormalities in other structures. X carried out MRI of adult acquired flatfeet and found that abnormalities of the spring ligament were almost as common as those of tibialis posterior tendon, with the superficial deltoid and ITCL not far behind.

It should be noticed that other structural abnormalities of the arch may cause a lowered arch, sometimes with a normal profile in the coronal plane, sometimes with medial deviation and lowering of the talar head and/or midfoot abduction: