Cervical Muscle Dysfunction after Whiplash

One of the most frustrating aspects about whiplash is the lack of objective signs that the patient has been injured after a collision. Patients will often report muscle pain and tenderness, and this tension can be palpated by the clinician, but there has been no objective way to measure this muscle dysfunction.

A new study from The Netherlands may change this situation. The authors of this study examined the differences between whiplash patients and healthy controls by means of surface EMG (sEMG). The authors begin with the premise that muscle tenderness is an important clinical sign that can provide important clues as to treatment and recovery:

"It is assumed that the palpable musculoskeletal signs are a reflection of a disturbance in the function of the muscle. However, there is no consensus about how pain, tenderness, and muscle consistency relate to muscle dysfunction, but the onset of pain obviously initiates neuromuscular (and behavioral) responses. Particularly in the acute pain situation, this response is considered an adaptive reaction to prevent or reduce further pain or injury. Persistence of muscle dysfunction in chronic pain patients, beyond the healing phase of such tissue injury, however, may contribute to chronicity of the pain. This unfavorable role of prolonged muscle dysfunction is underlined by some ergonomic studies that show that sustained muscle activity during stereotyped work is a risk factor in the development of work-related myalgia."

The authors' goal was to see if sEMG could be used to detect the presence of abnormal muscle activity in whiplash patients. The study included 18 patients with Grade II whiplash-associated disorder (WAD) for at least six months: "WAD Grade II is characterized by symptoms of neck pain and neck stiffness or tenderness. Signs at physical examination are limited to palpatory abnormalities of musculoskeletal structures, including decreased range of motion and point tenderness." The study also included 19 healthy control subjects without neck pain.

All of the test subjects were then tested with sEMG with the following tests:

Static Postures:
1. Sitting in a comfortable chair with the head supported,
2. Sitting on a stool, and
3. Standing.
Unilateral dynamic activity
1. The test participants were instructed to "continuously move the dominant arm/hand between three targets by putting marks with a pencil in circles with a diameter of 70 mm. During this task the nondominant arm rested on the table without moving. The pace of 88 marks/min was kept constant�for around 2 � minutes."
Static Posture
1. A second standing phase was recorded after the dynamic test.

"The results of this study show that there are two particular conditions in which patients with WAD-II exhibit higher EMG activity of the upper trapezius muscles than the healthy control subjects. First, during the performance of the unilateral dynamic task, the patients with WAD-II showed a substantially higher coactivation level of the upper trapezius muscles of the resting arm as compared with the healthy subjects. Second, even larger differences between the two groups appeared after having finished the dynamic task. Patients with WAD-II were not able to relax the upper trapezius muscles to baseline levels. Both findings indicate that patients with WAD-II exhibit unnecessary muscle activation, particularly in situations in which there is no biomechanical demand for it."

In summary, whiplash patients demonstrate a dysfunction in the cervical musculature that may be responsible for chronic pain. Furthermore, the pattern of this dysfunction may be a useful diagnostic tool that would allow clinicians to document objective signs of injury in whiplash patients.

Nederhand MJ, Uzerman MJ, Hermens HJ, et al. Cervical muscle dysfunction in the chronic whiplash associated disorder grade II (WAD-II). Spine 2000;25(15):1938-1943.

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