A fully loaded semi-truck can weigh up to 80,000 pounds — roughly 20 times the weight of an average passenger car. That weight difference matters enormously in a collision, because the force transferred to the smaller vehicle’s occupants is a function of both mass and speed. Even at highway speeds that a car-to-car collision might survive without catastrophic injury, the sheer mass of a commercial truck can drive the passenger vehicle’s frame far beyond its designed crumple tolerance, transmitting extreme force directly into the spine.

The mechanism of injury depends heavily on where and how the impact occurs. A rear or frontal collision can cause violent flexion-extension of the spine — the same whiplash-type motion seen in smaller collisions, but at a force multiplier that can fracture vertebrae or cause direct spinal cord compression. A side impact or underride collision, where a passenger vehicle strikes or is struck beneath the truck’s trailer, often causes severe compression or shearing injury to the cervical spine, which is why underride crashes are disproportionately associated with quadriplegia — paralysis affecting all four limbs, resulting from damage high in the neck. Lower-force or lower-impact-point collisions are more likely to result in paraplegia, affecting the legs and lower body while preserving arm and hand function, depending on where along the spine the force is absorbed. In either case, the completeness of the injury — whether some function is preserved or totally lost — often correlates with how much force reached the spinal cord and for how long, which is part of why trucking accident injuries tend toward the more severe end of the SCI spectrum compared to average passenger vehicle collisions.

Because the severity and permanence of these injuries is so closely tied to crash forces unique to commercial vehicles, cases involving trucking accidents often require expert accident reconstruction to establish exactly how the injury occurred — testimony that can be critical both to proving liability and to accurately valuing the lifetime cost of the resulting paralysis.