The Validity of Measurements Made on Standard Foot Orthoroentgenograms

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Abstract
In certain clinical settings, standard x-rays may be misleading since they only provide two-dimensional representations of three-dimensional structures. After metatarsal osteotomy, the actual first metatarsal shortening may appear magnified on standard x-rays. We investigated variations in metatarsal and intermetatarsal angle (IMA) in a cadaver model and variations of first metatarsal length following in vivo Chevron osteotomies. For skeletal models, changing the foot arch from pes planus to pes cavus changed the first metatarsal length by as much as 19%, whereas the measured IMA remained relatively unchanged. Pronation of the first metatarsal was found to alter the IMA (decreased for planus, increased for cavus). In vivo studies revealed a 3.2-fold difference when actual metatarsal length change following chevron osteotomy was correlated to corrected x-ray change in length (9.5% versus 2.9% P ≤ .005). Previous investigators have evaluated hallux valgus deformities with emphasis on metatarsal lengths and IMAs to determine choices of procedure. 3 , 5 , 10 Based on the results of this study, treatment plans and further evaluation for forefoot surgery may be inaccurate if based solely on x-ray measurements.

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