Speed-related increases in plantar tissue stress without affected-side laterality in individuals with unilateral shoulder dislocation.

INTRODUCTION

Unilateral shoulder dislocation may be accompanied by altered upper-limb use and trunk-control strategies; however, whether individuals with unilateral shoulder dislocation exhibit affected-side laterality in foot mechanics during walking remains unclear. This study compared the affected-side laterality in plantar external loading and internal foot tissue stresses in individuals with unilateral shoulder dislocation during 5 km/h and 7 km/h treadmill walking conditions, and further examined whether faster walking was associated with changes in this laterality.

METHODS

Twelve participants completed walking trials at two speeds. Peak forces in the rearfoot and forefoot regions were extracted, and the effects of walking speed, affected-side status, and dominant-foot status were analyzed using foot-level linear mixed-effects models. A simplified peak-force-based finite element analysis was used to estimate relative stress responses in key foot soft tissues during loading-response- and push-off-related loading conditions.

RESULTS

The results showed that increased walking speed significantly elevated forefoot peak force (p = 0.005) and was associated with higher stresses in forefoot soft tissues (p = 0.025) and the plantar fascia (p = 0.003). In contrast, both plantar external loads and internal tissue stresses remained highly symmetrical between the ipsilateral and contralateral feet relative to the affected shoulder, and increasing speed did not amplify affected-side laterality.

CONCLUSION

These findings indicate that, within this cohort, faster walking was associated with higher push-off-related plantar tissue stresses, whereas affected-side laterality relative to the dislocated shoulder was not evident. Because no healthy control group or longitudinal pre-injury comparison was included, the results should be interpreted as within-cohort mechanical responses rather than evidence that shoulder dislocation itself increases plantar tissue stress.