Background No firm consensus has been established regarding the risk factors for stress fracture of the 5th metatarsal because of a lack of large-scale prospective studies.

Objective The purpose of this study was to clarify the risk factors for a stress fracture of the 5th metatarsal.

Design Cohort study.

Setting Prospective study with well-trained varsity players.

Participants One hundred and sixty healthy collegiate male football (soccer) players.

Assessment of Risk Factors The medial lateral arch ratio of the foot, leg-heel alignment with weight-bearing (WLHA), LHA without weight-bearing (NLHA), relative angle of the forefoot to the hindfoot (FA-H), and plantar pressure during the heel raise position were measured. Rearfoot and forefoot alignment were evaluated from images using Image J. The plantar pressure distribution was measured using a plate-type lower limb GP-6000 weighted meter and pressure distribution-measuring MD-1000 device from Anima Co., Ltd.

Main Outcome Measurements The measurements from players who were diagnosed with a stress fracture of the 5th metatarsal were compared with the measurements from non-injured players.

Results Four players were diagnosed with a stress fracture of the 5th metatarsal. The arch ratio, WLHA, and FA-R of the injured players were higher than those of the non-injured players (17.8±0.21 vs. 1.68±0.26, −3.79±2.5° vs. −4.24±2.93°, 4.34±3.62° vs. 3.19±5.18°). The NLHA of the injured players was lower than that of the non-injured players (3.08±2.29° vs. 6.03±4.51°). The plantar pressure of the injured players tended to be located in a more lateral position compared with the non-injured players during heel raise (55.41±1.59% vs. 47.93±4.59%).

Conclusions Stress on the lateral side of the foot during heel raise may cause stress fractures of the 5th metatarsal.