Reliable casting of pes cavus to minimise errors in custom orthosis fabrication

Many different methods exist for obtaining an impression of the foot prior to the fabrication of custom moulded foot orthoses. The purpose of taking an impression is to accurately replicate the plantar surface of the patient’s foot, ie arch height, forefoot to rearfoot alignment and general foot morphology.While foam box, vacuum casting and laser scanning are occasionally used, neutral plaster casting previously described by Root et al is the most commonly used technique for obtaining a foot impression in Australia and New Zealand. Pes cavus is seen in approximately ten percent of the population, and foot pain in these patients is particularly challenging to treat with orthotic therapy due to the extent of the foot deformity. Therefore, the ability of the clinician to accurately and reliably cast a patient with pes cavus is paramount when that cast is used to manufacture custom foot orthoses. In the absence of reliable casting, a foot orthosis cannot be termed ‘custom’ and could introduce considerable error in fabrication and potential failure in treatment. There have been several studies comparing various impression techniques of the foot, however the reliability of the neutral plaster casting technique has only briefly been investigated in the literature. Chuter et al reported wide variability of frontal plane, forefoot-torearfoot alignment in ten casts taken by an experienced clinician. However, this study was limited in that the casts were taken using a ‘preferred method’ from a single subject only and reliability coefficients were not reported. In a larger study of 15 young asymptomatic participants, Laughton et al reported excellent reliability for forefoot to rearfoot alignment, rearfoot width and forefoot width (ICC2, 1 = 0.83 to 0.92), but only fair reliability for medial arch height (ICC2, 1 = 0.67). However, the generalisability of this study may be limited because only the prone casting technique (direct pressure) was examined: a technique less favoured than casting the patient in a supine position (suspension). In light of these limitations, the aim of our study was to investigate the reliability of the neutral suspension casting technique in people with a painful pes cavus foot deformity.