The third mechanism occurs when the chest is compressed from front to back, causing it to widen from side to side.[14] The lungs adhere to the chest wall because of the negative pressure between them and the pleural membranes lining the inside of the chest cavity; thus when the chest widens, they are pulled apart.[14] This creates tension at the carina; the airway tears if this tensile force exceeds its elasticity.[14] This mechanism may be the cause of injury when the chest is crushed.[15] Most TBI are probably due to a combination of these three mechanisms.[6]