In the longest study ever preformed on whiplash-injured patients (a study looking at the health status 17 years after injury), 55% of the patients still suffered from pain caused by the original trauma. (Accident Analysis and Prevention, 2002). If so many patients have chronic pain from whiplash, then why are they being diagnosed with sprain/strain injuries, if a sprain/strain diagnosis is not supposed to be chronic? In order to understand this, we need to look at the four phases of whiplash.
Phase 1: The thoracic spine is struck by the seat losing its curve and drives upward, creating some initial flexion of the lower cervical spine.
Phase 2: As the thoracic spine drives upward, it creates axial compression. The 6th cervical vertebra begins to go into hyper-extension. The head, which had remained in its original position due to inertia of the early phase, begins to drive down causing compression and flexion of the upper cervical segments. With the weight of the head combined with the G force, there could be upwards of several hundred pounds of pressure driving downward. According to Yang et al, a compressive force of 40 pounds results in a 73% reduction in ligament stiffness at C5-6. (1) This is the point where a lot of the damage can occur due to the slack in the ligaments, and this "s" shaped curve happens between .53-.75 milliseconds.
Phase 3-4: Extension and shearing forces occur in the cervical spine.
Normally, there is an equal glide of the facets. When the spine is compressed, the mechanics of the facets change drastically. This causes the instantaneous axis of rotation (IAR) to move, which jams the facets, leading to facet joint injury. In a study by Ono et al, a crash simulating a 3.7 mph velocity change, the IAR of C5 is shifted superiorly into the body of C5, resulting in extension bending that compresses the facet joints of C5 and C6, and adversely affecting the disc as well. (2)
A sprain/strain diagnosis might be correct for some patients, but as you can see, there can be damage to other structures such as the discs and facets. Also, if there has been significant damage to the ligaments, then this needs to be documented better than a sprain/strain diagnosis. At The Health Connection, we have a test that can identify the exact level of ligament damage and determine if there is an impairment due to the damaged ligament.
(1) Yang KH, Begman PC, Muser M, Niederer P, Waltz F. On the role of cervical facet joints in rear end impact neck injury mechanisms. SAE SP-1226, Motor Vehicle Safety Desgin Innovations, SAE Paper 970497, 997, p 127-129.
(2) Ono K, Kaneoka K, Wittek A, Kajzer J. Cervical injury mechanism based on the analysis of human cervical certebral motion and head-neck-torso kinematics during low speed rear impacts. 41st Stapp Car Crash Conference Proceedings. SAE 973340, 1997, p.339-356.