Most often she sharp pain in the neck from whiplash is damage to the cervical facet joints and capsular ligaments. The capsular ligament surrounds and supports the facet joint.
In normal motion, the facet joints glide on top of one another, like two hockey pucks. In rear-end crashes, the neck goes into a reversed "S" shaped curve in less than 1/10 second, and in the mid to lower neck, the upper facet joint slams its posterior corner into the top of the lower joint, damaging the cartilage and sometimes causing an indent fracture in the lower joint. The capsular ligament gets over stretched, tearing it and leaving a painful damaged ligament and instability of the facet joint. This is that sharp, stabbing pain in the neck people often get. Now, depending on the level in the neck of facet damage involved, you can develop referred pain and spasms to certain areas.
This scenario of facet joint injuries occurs in rear-end crashes even with little or no visible damage to either vehicle. Studies by Panjabi, et al, show facet joint injury and capsular ligament damage occurs at 3 g and 6.5 g forces respectively, and in live human crash testing subjects were exposed to 12 g forces with no visible damage to either vehicle. This leads to Mechanical Neck Pain Syndrome, and we here at Alaska Back Care Center provide the best scientific therapy methods for these injuries. That's why we say "Researched Based Diagnosis and Treatment".