In podiatry, dysfunctional flat feet (collapsed medial longitudinal arch) and cavus feet (high, rigid medial longitudinal arch) are often treated as different problems with different causes. In practice, however, both usually end up with the same solution: orthotic insoles.
Evidence for the long-term benefit of these insoles is still lacking. In fact, both patterns often share the same underlying mechanisms: an impaired, “shoe-shaped” forefoot structure, forefoot rotation relative to the rearfoot (MacConaill, 1945), and the resulting instability.
High, rigid arch – “compensated”
shoe-shaped foot
Malaligned toes in the shoe-shaped forefoot create an unstable base. During the stance phase of gait, this instability must be compensated for by muscular effort. If the muscles are strong enough to bear loads of 125–250% of body weight (walking/running), hip external rotation and rearfoot supination relative to the forefoot produce a high, rigid arch and a restricted ankle range of motion (Manoli & Graham, 2018).
The lack of flexibility in the foot and ankle reduces shock absorption; stress fractures and lateral ankle sprains occur more frequently (Williams, McClay & Hamill, 2001). With increasing age and/or body weight, muscle strength declines — making compensation for forefoot instability progressively less effective.
Low, collapsed arch – “decompensated”
shoe-shaped foot
Here too, malaligned toes in the shoe-shaped forefoot create an unstable base. If muscle strength is insufficient to handle loads of 125–250% of body weight, the rearfoot and the entire lower kinetic chain collapse medially.
The repetitive loading pattern and medial collapse progressively damage the foot’s soft tissues — resulting in a dysfunctional low/collapsed arch and knee complaints (Williams, McClay & Hamill, 2001).
Key takeaway
The architecture of the longitudinal arch is determined by rotation from rearfoot to forefoot (MacConaill, 1945; Sarrafian, 1987) — and this depends on how effectively the musculature can counter forefoot instability. Instability caused by a compromised, shoe-shaped forefoot structure is therefore the root cause of both rigid, high arches and low, collapsed arches.
The solution starts at the base: restore functional foot structure.
Therapy — simple and everyday
- Wear foot-shaped (functional) shoes that allow the toes to splay and give the forefoot room.
- Load your feet regularly with your body weight so gravity can stimulate and stabilize the functional form.
References
- MacConaill, MA. The postural mechanism of the human foot. Proceedings of the Royal Irish Academy, Section B: Biological, geological and chemical science. 1945; 50: 265-278.
- Manoli, A und Graham, B. Clinical and new aspects of the subtle cavus foot: a review of an additional twelve year experience. Fuss and Sprunggelenk. 2018; 16: 3-29.
- Sarrafian, SK. Functional characteristics of the foot and plantar aponeurosis under tibiotalar loading. Foot and Ankle. 1987; 8(1), 4-18. Williams, DS, McClay, IS, Hamill, J. Arch structure and injury patterns in runners. Clinical Biomechanics. 2001; 16: 314-347.