The Influence of Percentile Weight Bearing on Foot Radiographs

Category: Midfoot/Forefoot Introduction/Purpose: Clinical decisions are often made based on the measurements of foot radiographs. Orthopaedic patients who have had lower extremity trauma or surgery are often given different weight bearing conditions including non-weight bearing, touch-down weight bearing, partial weight bearing (of various percent of body weight), and weight bearing as tolerated. However, it is largely unknown how these various weight bearing conditions alter specific parameters of foot radiographs. As such, the purpose of this study was to determine whether percent weight bearing influences radiographic measurements of the foot on anteroposterior (AP) and lateral radiographs? Methods: A total of 20 healthy subjects had AP and lateral radiographs of the foot under five weight bearing conditions (non-weight bearing, 10% body weight, 25% body weight, 50% body weight, and 100% body weight). Measurements were then made of hallux valgus angle (HVA), 1-2 intermetatarsal angle (IMA), talonavicular coverage angle (TNCA), talo-calcaneal angle (TCA), forefoot width, LisFranc distance, cuboid height to ground (CHG), and talo-1st metatarsal angle (TMA) of each weight bearing condition. Statistical differences of each measurement for each weight bearing condition were then determined. Measurements were made by a radiologist and orthopaedic surgeon and inter-observer reliability determined for each measurement. For each radiographic measurement, a single factor ANOVA determined whether measurements were different between non-weight bearing, touchdown weight bearing, 25% weight bearing, 50% weight bearing, and 100% weight bearing. When a significant difference was detected, a post-hoc Tukey’s determined which categories of weight bearing were different. Results: The inter-observer reliability determined by the intraclass correlation coefficient was excellent to good in all measurements except for the TCA which was fair. For measurements made on the AP radiographs of the foot, the measurements that changed with percent weight bearing were the TNCA (p = 0.0009) and TCA (p = 0.0446) (Table 1). Weight bearing did not change the HVA (p = 0.2564, IMA (p = 0.1698), forefoot width (p = 0.2431), or LisFranc distance (p = 0.9854). For measurements made on the lateral radiographs of the foot, the measurement that changed with percent weight bearing was the CHG (p = 0.006). Weight bearing did not change the TMA (p = 0.9889). Conclusion: This study demonstrates a flattening of the medial arch with increasing percent body weight applied to a foot. This results in an increase in the TNCA as well as a decrease in the CHG. In addition, increasing percent body weight to the foot increases the hindfoot alignment. However, percent body weight does not alter measurements of the forefoot. Percentage body weight increase may not influence clinical preoperative/non-operative treatment as much as we expect; however, our findings do show that certain parameters increase with increasing weight bearing