A Closer Look At The Historic Description Of The Windlass Mechanism

Two-thirds of a century ago, in 1954, an orthopedic surgeon from Birmingham, United Kingdom, John H. Hicks, published one of my favorite research articles on foot biomechanics.¹ In his research on the biomechanical function of the plantar fascia, Hicks analyzed the function of the plantar fascia in not only the living foot, but also in the cadaver foot. He observed that an increase in medial longitudinal arch (MLA) height occurred with hallux dorsiflexion in both the living and non-living foot. Likewise, in the non-living foot, this medial longitudinal arch-raising effect from hallux dorsiflexion nearly completely disappeared after surgical transection of the plantar fascia.¹ From these observations, Hicks concluded that the muscles of the foot were not actually responsible for the medial longitudinal arch-raising effect of hallux dorsiflexion, but rather, it was the plantar fascia.¹

In his landmark article, John Hicks described the medial longitudinal arch-raising effect of the plantar fascia as follows:¹

“When the toe was extended, the phalanx, sliding on to the dorsum of the metatarsal head, pulled after it the plantar pad which thereby came to lie anterior to the metatarsal head and this in turn pulled upon the attached process of the plantar aponeurosis. The effect was as though a cable had been wound one-quarter of a turn on to the drum of a windlass, the drum of the windlass being the head of the metatarsal, the handle which does the winding being the proximal phalanx and the cable which is wound on to the drum being the plantar pad and the plantar aponeurosis. The effective length of the cable was shortened by, in the case of the first ray, about one cm. Actually, the aponeurosis did not shift distally because of its attachment to the calcaneum; instead, it was the windlass which shifted, being pulled one cm proximally towards the calcaneum and the arch was thereby made shorter and higher.”¹

What we now know as the “Windlass Effect of Hicks” came from this classic description of hallux dorsiflexion winding the plantar fascia and sesamoid apparatus around the first metatarsal head, mechanically analogous to the handle of a windlass winding a cable around its drum.¹ Hicks also noted that hallux dorsiflexion produced three other biomechanical actions: supination of the subtalar joint; external rotation of the tibia; and the appearance of a “tight band” on the plantar foot in the region of the plantar fascia.¹ In his experiments, he tested the strength of the plantar fascia in cadaver specimens to discover whether the plantar fascia had sufficient strength to actually raise the medial longitudinal arch. As a result, he found the plantar fascia to have a breaking strength between 1.7 and 3.4 times one’s body weight. Also, as noted earlier, he found that cutting of the plantar fascia produced a near complete loss of the medial longitudinal arch-raising effect of hallux dorsiflexion in the cadaver foot.¹

Finally, and not any less important biomechanically, Hicks’ observations included that this “windlass mechanism” worked in reverse, or what is commonly now referred to as the “reverse windlass effect.”¹ He noted that flattening of the longitudinal arch of the foot tended to plantarflex the hallux and lesser digits, so that when ground reaction force acts on the plantar foot, the hallux and lesser digits plantarflex and press more firmly onto the ground. Hicks experimentally verified that the “reverse windlass effect” would disappear with transection of the plantar fascia. From these observations, Hicks found that the “gripping action” of the toes on the ground were not due only to actions of the digital flexors, but significantly also to the plantar fascia being “unwound” on the metatarsal heads when the plantar forefoot bore weight on the ground.¹

Whether he realized it or not, Hicks’ experiments on the plantar fascia provided the scientific literature with one of the first descriptions of how the human foot is designed to conserve energy during locomotor activities. In other words, by providing us with a better understanding of the unique biomechanical function of the plantar fascia, John Hicks’ 1954 research informed us as to how the bipedal human can walk more efficiently due to the the plantar fascia helping to maintain the medial longitudinal arch, raise the medial longitudinal arch and supinate the subtalar joint during propulsion, keeping the digits firmly stabilized against the ground, all “automatically,” and with minimal muscular effort. 

Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif.

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1. Hicks JH. The mechanics of the foot II. The plantar aponeurosis and the arch. J Anat. 1954;88:24-31.