Background Fifth metatarsal stress fracture (Jones fracture) is one of the issues of sports-related injuries.

Objective Exploration of unknown risk factor for developing Jones fractures.

Design Case control study.

Setting Retrospective cohort study in male Japanese professional football (soccer) players.

Patients (or Participants) Case control study conducted between with (n=20) and without (n=40) the history of Jones fractures.

Interventions (or Assessment of Risk Factors) Reviewed the medical check data regarding the joint and muscle tightness at the time they joined the team, and compared them between two groups.

Main Outcome Measurements Risk factors to develop developing Jones fracture.

Results The mean age sustaining Jones fracture was 20.5 years old (95% CI, 19.1–21.8, range 17–28). The fracture occurred in their non-dominant (standing) legs in 60% (12/20) of players. Among the physical examination data, Hip internal rotation (HIR) was significantly restricted in players with history of Jones fracture (25.9 degrees on average) compared with those without Jones fractures (40.4 degrees, p<0.0001). Logistic regression demonstrated that the wider range of HIR was associated with a statistically significantly decreased odds of Jones fracture (OR=0.83, 95% CI=0.75–0.91), while other physical examination data were not significant. A post-estimation analyses demonstrated that a 10-degree reduction in HIR of the right hip significantly increased the odds of Jones fracture in ipsilateral or contralateral foot (OR=3.11, 95% CI=1.35–7.16, and OR=2.24, 95% CI=1.22–4.12, respectively). Similarly, a reduction in HIR of the left hip significantly increased the odds of Jones fracture in ipsilateral or contralateral foot (OR=2.77, 95% CI=1.08–7.08, and OR=4.88, 95% CI=1.56–15.28, respectively).

Conclusions Restriction of HIR was significantly associated with increased risk of Jones fracture in professional football players in Japan.