The Influence of Percentage Weight-Bearing on Foot Radiographs.

INTRODUCTION: Clinical decisions are often made on weight-bearing radiographs. However, it is unknown whether various weight-bearing conditions alter specific radiographic measurements. The purpose of this study was to determine whether percentage weight-bearing influences radiographic measurements of the normal foot.

METHODS: A prospective study with 20 healthy individuals had radiographs of the foot under 5 weight-bearing conditions (non-weight-bearing, 10% body weight, 25% body weight, 50% body weight, and 100% body weight). Measurements were made of hallux valgus angle (HVA), 1-2 intermetatarsal angle (IMA), talonavicular coverage angle (TNCA), talocalcaneal angle (TCA), forefoot width, LisFranc distance, cuboid height to ground (CHG), and talo-first metatarsal angle (TMA) of each weight-bearing condition. Statistical differences of each measurement for each weight-bearing condition were determined.

RESULTS: The TNCA and TCA increased significantly, whereas the CHG decreased significantly with increased percentage body weight. There were no differences in HVA, IMA, forefoot width, LisFranc distance, and TMA with increased percentage body weight.

CONCLUSIONS: This study shows an increase in TNCA and TCA, and decrease in CHG, demonstrating a flattening of the medial arch, increasing hindfoot valgus, and midfoot external rotation and abduction with increasing percentage body weight applied to a foot. Percentage weight-bearing does not change radiographs in the foot between 25% and 100% weight-bearing. The clinical relevance of this finding is that graduated postinjury or postoperative weight-bearing regimens may only be relevant if the patient is either less than or greater than 25% of body weight on their extremity.

LEVELS OF EVIDENCE: Case Series, Level IV: Prospective.