Could a displaced rib cause pleural effusion?

While a severely displaced rib that punctures the lung could theoretically create a pneumothorax (air in the pleural space) or hemothorax (blood in the pleural space), it would typically result in a tension pneumothorax or hemothorax which presents much differently and with more urgency. This would not likely cause a simple fluid buildup known as a pleural effusion unless it's a hemothorax which is blood collecting in the pleural space.