An employee was on a row of box culverts clearing some material that was in front of the trench box spreader bars. The employee then crossed over the spreader bars while an excavator was pulling the slack out of the cables attached to each side of the trench box. The cables became taut and pulled the trench box forward, catching the injured employee's left foot between the top of the concrete box and the lower spreader bar. The spreader bar then slid on top of the injured employee's left foot, resulting in a left foot/toe injury that required surgery.