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Radiographic Image Distortion Between the Distal Edge of the First Metatarsal and the Tibial Sesamoid

Establishing a Reliable Radiographic Relationship

Michael Durrant, DPM, MPH ^* and Tucker McElroy, PhD 

^* Private practice, Redlands, CA; Borrego Community Health Foundation, Thermal, CA.
University of California, San Diego, San Diego, CA; United States Census Bureau, Washington, DC.

Corresponding author: Michael Durrant, DPM, MPH, 16 E Fern Ave, Ste B, Redlands, CA 92373. (E-mail: Durrant.michael{at}gmail.com)

Abstract

Background: After failing to statistically confirm a perceived pattern noted on radiographs that the sesamoids were proximally positioned in patients with hallux limitus compared with a control population without evidence of the deformity, the probable causes of this failure were examined. Measurement error was briefly considered but rejected owing to the careful manner in which the measurements were taken. The most plausible explanations were that the observations were incorrect and that the radiographs, which were retrospectively analyzed, were taken in a manner that distorted the spatial relationships between the metatarsal and the tibial sesamoid to a point that the results did not reflect reality.

Methods: This study examines potential difficulties in obtaining consistently reliable radiographic data regarding the spatial relationships of the metatarsal and the tibial sesamoid and establishes guidelines to minimize experimental error. Criteria for measuring metatarsal sesamoidal distances to the radiographic plate are established, along with application of the criteria to a control population. The principle of radiographic image distortion as it relates to these objects is presented, and, based on a predetermined range of radiographic angles, radiographic image distortion is calculated for the metatarsal head and the tibial sesamoid separately.

Results: By using accepted trigonometric principles, a mathematical model is developed that makes it possible to collectively quantify image shift between the two objects.

Conclusions: Criteria are established that, if followed, should minimize image distortion when it is important to measure metatarsal sesamoidal distances. (J Am Podiatr Med Assoc 100(1): 1–9, 2010)