AJPM Sept 2001 pages

This study compared neutral position weightbearing casts of the foot using the Foot Alignment System (FAS) to traditional non-weightbearing casts. Using inexperienced undergraduate podiatry students, the FAS was shown to have good repeatability and low variability. The arch profile of the FAS and nonweightbearing casts were different, but when a forefoot alignment curve was used with the FAS, the arch profiles were similar. The FAS system has a number of theoretical advantages over other weightbearing methods of modelling the foot compared to the traditional nonweightbearing casting. INTRODUCTION Foot orthoses are widely used to treat a range of lower limb pathologies. Outcome studies have shown that foot orthoses are successful in treating a large number of pathologies, but the mechanisms by which they achieve these outcomes is unclear. 1,2 Foot orthoses are usually made from negative casts of the foot taken in a non-weightbearing position. There is no evidence as to whether the use of weightbearing or nonweightbearing casts are the most suitable for the manufacture of foot orthoses or related to patient outcomes. The assumed advantage of weightbearing casts are the ease of putting the foot in its defined subtalar joint neutral position, the midtarsal joint in its assumed maximally pronated position and the osseous segments in what is assumed to be their better functional alignment. The main disadvantage of a weightbearing cast is that this is the ‘compensated’ position of the foot, however the rearfoot can still be placed in its defined subtalar joint neutral position. The advantage of a weightbearing cast is that this is assumed to be more representative of the position that the clinician wants the foot to function in if it is placed in it’s defined subtalar joint neutral position. In a weightbearing position, expansion of the soft tissues around the heel are assumed to allow for a better fit of the final orthoses (this is accounted for by additional plaster modifications around the heel of the positive mould made from a non-weightbearing cast). The assumed major disadvantage of weightbearing casts is the difficulty in placing the forefoot in its assumed maximally pronated position and keeping the first ray in its assumed correct alignment. A weightbearing position tends to dorsiflex the first ray and invert the forefoot about the rearfoot. This is assumed to be a functionally poor position for the foot, as the orthoses made of this cast would tend to prevent first ray plantarflexion. The prevention of first ray plantarflexion would inhibit first metatarsophalangeal dorsiflexion and establishment of the windlass mechanism. There have been reported differences in the forefoot to rearfoot relationship of plaster casts of the foot taken in weightbearing and non-weightbearing positions, with only the above theoretical constructs being used to suggest which is the more appropriate alignment. Correspondence: Craig Payne, Department of Podiatry School of Human Biosciences, La Trobe University Vic 3086 Australia Phone (+61) (3) 9479 5820 Fax (+61) (3) 9479 5784 Email c.payne@latrobe.edu. au Australasian Journal of Podiatric Medicine 2001; Vol 35, No.3 : 65-71 AJPM Original