Letter to the Editor

Dear Dr Curran,

We write with regard to the recent publication by Spaulding et al. ¹ to propose an alternative interpretation for why the Blue Rocker Toe-Off Ankle Foot Orthoses (AFO) were unable to restore the normal centre of pressure (CoP) excursion.

We hypothesize that the toe sections of the Blue Rocker Toe-Off AFO were too compliant to normalize CoP excursion or restore the effective foot length.

A previous investigation that compared CoP excursion in two conditions, an insole only and a Blue Rocker Toe-Off AFO with insole, was able to normalize the CoP excursion in a single person with transmetatarsal amputation.^2,3 We hypothesize that the study by Wilson^2,3 differed in that the Blue Rocker Toe-Off AFOs were oversized for the client’s shoe. The most distal portion of the AFO footplate was then ground away to fit into the shoe leaving the thick central core of the AFO footplate extending the full length of the shoe. In this way, the footplate of the Blue Rocker Toe-Off AFO would be much stiffer than would be the case when sized in a conventional way as we expect was the case in the investigation by Spaulding and colleagues. ¹

This interpretation is consistent with previous literature that suggests that the effective foot length can only be restored when the prosthesis/orthosis includes a suitably stiff forefoot that can support body mass, a means to lock or stiffen the ankle against dorsiflexion, and a large anterior leg shell to comfortably distribute to the leg the interface pressures caused by loading the forefoot.^4-6

We hope that this alternative interpretation of the authors’ results helps reconcile differences in the findings of this investigation with previous work on the topic.