Symptoms of sensorimotor impairment include dizziness, giddiness, light-headedness, unsteadiness and feeling off-balance. As many as 75% of whiplash injured patients demonstrate these symptoms in some cohorts.
The muscle spindle
There is a high density of muscle spindles in the small intrinsic musculature of the neck, as a result the neck musculature has an important role to play in postural control. A plethora of experimental studies have demonstrated reduced postural control following neck muscle vibration and fatigue, including a classic case of ataxia following injection of local anaesthetic into the cervical tissues (see http://www.ncbi.nlm.nih.gov/pubmed/407834).
Assessing sensorimotor impairment
Assessing sensorimotor impairment of the neck involves the assessment of
- proprioception / joint position error – download here.
- oculomotor control
- postural stability.
Research has demonstrated impaired control of the head and neck, altered eye movements and reduced postural control in both neck pain patients and whiplash injured patients.
The assessment of the smooth pursuit neck torsion test and gaze stability is an important part of evaluating sensorimotor impairment following whiplash injury.
Smooth Pursuit Neck Torsion Test (SPNT)
Smooth pursuit involves the subject keeping their head still and following a slow moving object with just their eyes from about 30° one side of the midline to 30° on the opposite side. The clinician closely observes the subjects eye movements, looking for jerky or fast movements. Reproduction of dizziness or pain, increased effort or difficulty performing the test all suggest sensorimotor impairment.
Here’s a close up of a normal smooth pursuit test:
A progression of the smooth pursuit test is the Smooth Pursuit Neck Torsion test (SPNT). This test involves comparison of smooth pursuit performance in a neutral head position – as seen above – with performance in a neck torsioned position, 45° degrees left and then 45° right. It is termed ‘neck torsion’ because the trunk is rotated on the neck to avoid stimulation of the vestibular system.
Here’s an abnormal SPNT test (note the ‘saccades’):
Gaze stability can be assessed by asking the subject to look at an object roughly arm’s-length from their face and to slowly flex and extend their head and neck or gently rotate their head and neck whilst keeping their eyes still. Reproduction of symptoms or difficulty performing the test suggests sensorimotor impairment.
There are a number of studies that demonstrate reductions in neck pain and disability following just a couple of months of performing sensorimotor control exercises alone.
Tjell, C. and U. Rosenhall (1998). “Smooth pursuit neck torsion test: a specific test for cervical dizziness.” Otology & Neurotology 19(1): 76.
Treleaven, J., G. Jull, et al. (2003). “Dizziness and unsteadiness following whiplash injury: characteristic features and relationship with cervical joint position error.” Journal of Rehabilitation Medicine 35(1): 36-43.
Treleaven, J., G. Jull, et al. (2005). “Smooth pursuit neck torsion test in whiplash-associated disorders: relationship to self-reports of neck pain and disability, dizziness and anxiety.” Journal of Rehabilitation Medicine 37(4): 219-223.
Treleaven, J., G. Jull, et al. (2005). “Standing balance in persistent whiplash: a comparison between subjects with and without dizziness.” Journal of Rehabilitation Medicine 37(4): 224-229.
Jull, G., D. Falla, et al. (2007). “Retraining cervical joint position sense: The effect of two exercise regimes.” Journal of Orthopaedic Research 25(3): 404-412.