A striking finding from the reviews of biomedical and other literature was the heterogeneity of definitions and classifications of all clinical aspects related to Whiplash-Associated Disorders (WAD). Accordingly, it became an early priority and a central challenge for the Task Force to propose definitions and classifications that would facilitate the evaluation of original research and would be unambiguous and helpful to the clinician. After extensive discussion of the anatomical, pathological and clinical relationships, and drawing from the best groupings encountered in the literature, 42, 73 certain important terms and definitions were adopted by the Task Force to be put forward to the international scientific and clinical community.

The most important contribution of the Task Force may be the Quebec Classification of Whiplash-Associated Disorders proposed herein. The classification provides categories that are jointly exhaustive and mutually exclusive, clinically meaningful, stand the test of common sense and are "user-friendly" to investigators, clinicians and patients. Future research will decide whether refinement is required to enhance the discriminating properties of the classification and to establish the validity of the categories proposed.

One difficulty in evaluating the whiplash literature is that the term "whiplash" is used to describe a mechanism of injury, the injury itself, the various clinical manifestations consequent to the injury and constellations of signs and symptoms designated as "whiplash syndrome." Typically, authors reporting studies do not specify the time after a collision (or in the evolution of the injury) when certain treatments or diagnostic tests are being evaluated. In other cases it is unclear whether the underlying condition is complicated or uncomplicated (without objective aggravating signs) or whether comorbidity is present. The Task Force adopted the following definition of whiplash.

Whiplash is an acceleration/deceleration mechanism of energy transfer to the neck. It may result from rear-end or side-impact motor-vehicle collisions, but can also occur during diving or other mishaps. The impact may result in bony or soft-tissue injuries (whiplash injury), which in turn may lead to a variety of clinical manifestations (Whiplash-Associated Disorders).

"Whiplash-Associated Disorders" (WAD) is the term adopted by the Task Force to describe the clinical entities associated with the injury. We propose a classification of WAD on two axes:

1) a clinical-anatomic axis and

2) a time axis.

The clinical-anatomic axis has five grades that correspond roughly to severity. Of the five grades, the Task Force did not consider two. Namely, when there are "no complaints about the neck" and "no signs," either immediately or within a short time, no disorder is manifest (Grade 0). We also excluded spinal-cord injury and bony-tissue injury, such as fracture or dislocation (Grade IV). The latter were not within the Mandate of the Task Force. There remain, then, the three grades of WAD associated with soft-tissue injury: I) general, nonspecific complaints or symptoms about the neck without objective signs, II) neck complaints plus signs limited to musculoskeletal structures, and III) neck complaints with neurological signs. (Table 7) The footnotes in Table 7 clarify the classification, to simplify use by clinicians during patient care. Certain symptoms and disorders, such as deafness, dizziness, tinnitus, headache, memory loss, dysphagia and temporomandibular joint disorders, may manifest in any Grade. These associated findings may be highly relevant in the evaluation of individual patients by clinicians designing a treatment plan, planning judicious referrals or contemplating a rehabilitation strategy.

Turning to the time axis, patients are further classified within each grade as those less than four days from the time of the injury, those 4-21 days from the date of injury, those from 22-45 days, those from 46-180 days and finally patients with symptoms or signs for durations more than six months. This time axis guides the clinical management of WAD (See Section 5: Conclusions). By consensus, patients still symptomatic or with residual disability six months or more after the injury are designated as "chronic." We deem the status of chronic or the inception of chronicity as a serious clinical development with public-health implications. We are of the view that it is important to act to prevent chronicity at all stages of WAD.

Continued complaints and residual disability after 45 days are important warnings of chronicity, justifying vigorous clinical intervention and mandatory interdisciplinary clinical consultation. Identifying the subgroup of patients at risk of chronicity within each of the three Grades is crucial to efforts to prevent chronicity.

Clinical colleagues in the Task Force identified common clinical manifestations and commonly used terms that correspond to the grades defined. In Table 8, we present a brief summary of these items to assist clinicians in adapting designations already in use to a new classification intended to be more rational and easier to use.