Plantar Fascia Grooves in Foot Orthoses

December 2002

It is widely acknowledged that the foot should be a supportive structure to resist the forces that are applied to it during the propulsive or push of phase of gait. To do this the arch of the foot should be become elevated and the foot becomes more supinated. There are a number of ways in which the foot can do this, but the most efficient and widely recognized is the windlass mechanism, first described by Hicks (1954):

The windlass mechanism comes about as the plantar aponeurosis or plantar fascia, which primarily attaches to the heel (calcaneus) and the base of the proximal phalanx of all the toes, with the base of the first toe (hallux) being the strongest. When the hallux is dorsiflexed at the first metatarsophalangeal joint, it acts as a lever that winds the plantar fascia around the ‘drum’ of the first metatarsal head (the “windlass effect”). This has the effect of shortening the distance between the hallux and the heel (it raises the arch).

During walking, this windlass effect only starts when the heel comes off the ground (the hallux essentially dorsiflexes, by remaining flat on the ground as the foot moves). This has the effect of making the foot a rigid and stable structure when the propulsive forces from above are applied. As the medial (inside) part of the windlass mechanism (the part attached to the hallux) is more powerful the medial side of the arch raises higher, which has the effect of supinating the foot and externally rotating the leg. As this occurs when the opposite leg is in the swing phase and the pelvis is rotating forward on this swing limb, there is an external rotation force in the leg that is still on the ground. This coincides with the foot supinating from the windlass effect.

As a result of this windlass effect more attention has been given to this mechanism (Aqunio & Payne, 1999) as it is important to more foot function. The clinical significance of the mechanism was first recognized by Dannenberg (1993) who described the clinical entity of functional hallux limitus. In this condition, there is a full range of motion at the first metatarsophalangeal joint during non-weightbearing, but for some reason during weightbearing, the joint does not want to dorsiflex, so the windlass mechanism cannot get established. The result of the windlass not getting established is that the mid foot collapses during propulsion and coordination between the pelvic and limb rotating externally during the opposite leg swing is not in coordination with the foot that should be supinating.

There compensation can result in a number of problems that are commonly seen in the foot. As well as functional hallux limitus, a number of other things can interfere with the establishment of the windlass mechanism, such as foot orthoses that are too high in the anterior part of the arch (these inhibit the first metatarsal from plantarflexing, and this the first metatarsophalangeal joint from dorsiflexing). Roukis et al (1996) show that the first metatarsal must be able to plantarflex so that the first metatarsophalangeal joint can dorsiflex. Hillstrom et al (2002 ), have shown that the foot pronates more when the anterior part of the arch is too high on a foot support. The lack of the windlass working can cause the foot to pronate (flatten) excessively, but the pronated foot (form other causes) is not related to whether the windlass mechanism works or not (Aqunio & Payne, 2001).

Our recent work, as yet unpublished, as identified several characteristics of the windlass mechanism that have implications for foot function. The range of motion at the first metatarsophalangeal joint appears to vary from 4 to 22 degrees between individuals before the windlass starts working. The consequences of a larger range of motion before the windlass starts working is that the heel will already be off the ground and the midfoot is prone to collapse during walking as the windlass has not initiated. This is illustrated in the following two pictures. The picture on the left is a foot in which the windlass has started immediately on heel lift (and the arch rises) and the picture on the right is when there is a greater range of motion before the windlass initiates and the midfoot collapse:

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