Isometric muscle fatigue of the paravertebral and upper extremity muscles after whiplash injury

BACKGROUND: Whiplash-associated disorders (WAD) result from injury of neck structures that most often occur during traffic accidents as a result of rapid acceleration-deceleration. The dominant symptoms manifest in the musculoskeletal system and include increased fatigue. Because of the frequency of whiplash injuries, a simple, cheap and useful diagnostic tool is needed to differentiate whiplash injury from healthy patients or those faking symptoms. OBJECTIVES: To determine muscle fatigue in patients with whiplash injury in six body positions. DESIGN: Analytical cross-sectional study. SETTING: Emergency center, university hospital. PATIENTS AND METHODS: We studied patients with whiplash injury from vehicular traffic accidents who presented to the emergency center within 6 hours of sustaining the injury. We determined whiplash injury grade according to the Quebec Task Force (QTF) classification and measured isometric muscle endurance in six different body positions. Control subjects for each patient were matched by age, gender and anthropomorphic characteristics. Cut-off values were determined to distinguish patients with whiplash injury from controls and for determination of injury grade. MAIN OUTCOME MEASURE(S): QTF grade, time to muscle fatigue in seconds. RESULTS: From September 2013 to September 2016, we enrolled 75 patients with whiplash injury and 75 matching control subjects. In all six positions, the patients with whiplash injury felt muscle fatigue faster than equivalent controls (P<.05) and the time to onset of muscle fatigue decreased with increasing injury grades in all six positions. Assignment to the patient or control group and to injury grade could be predicted with more than 90% accuracy on the basis of time to muscle fatigue. The most efficient position was the highest injury grade, by which 99.9% of the patients were accurately categorized. Isometric muscle endurance correlated with whiplash injury grade in all six positions (P<.01). CONCLUSION: Under clinical conditions, muscle endurance and the appearance of isometric muscle fatigue during testing can be a useful indicator of whiplash injury and grade. LIMITATIONS: The size of the sample was small. An objective parameter such as electromyography is needed to confirm isometric muscle fatigue.