Research Review by Dr. Shawn Thistle©

Date:

May 2008

Study Title:

Sensorimotor disturbances in neck disorders affecting postural stability, head and eye movement control

Authors:

Treleaven J

Author Affiliations: Neck Pain and Whiplash Unit, Division of Physiotherapy, University of Queensland, Australia

Publication Information:

Manual Therapy 2008; 13: 2-11.

Summary:

The control of stable, upright posture relies on input from a variety of afferent sources including the vestibular, visual, and proprioceptive systems, all of which converge in the central nervous system. The cervical spine plays a central role in providing proprioceptive information, as evidenced by its abundance of mechanoreceptors and reflex connections to the visual and vestibular systems (outlined below).

Dysfunction in the cervical spine can alter afferent input to these systems, subsequently changing the integration, timing, and tuning of neuromuscular and sensorimotor control. This paper reviewed recommendations for the clinical assessment and treatment of sensorimotor control disturbances with a special focus on the cervical spine. An executive summary follows:

Introduction and Background:

There are 3 main reflexes in the neck that influence head, eye, and postural stability – they should be kept in mind while reading this review:
  1. Cervico-Collic Reflex: activates neck muscles in response to mechanical stretch in order to maintain head position
  2. Cervico-Ocular Reflex: in combination with the vestibulo-ocular reflex (relation between vestibular apparatus and eye positioning via the extraocular muscles), this reflex also affects the extraocular muscles to assist with clear, smooth vision during neck movement
  3. Tonic Neck Reflex: is evident in newborns – when the face is turned to one side, the arm and leg on the side to which the face is turned extend and the arm and leg on the opposite side bend – in adults it is integrated with the vestibulospinal reflex to achieve postural stability
It is well known that there are significantly more muscle spindles located in the suboccipital region of the cervical spine (200/gram of muscle compared to only 16/gram in the lumbricals of the thumb). This indicates that the suboccipital muscles relay a significant amount of information to the central nervous system, reflected also by the fact that there are numerous connections between the cervical receptors and the visual/vestibular system, as well as the sympathetic nervous system.

Studies which artificially disturb these connections anatomically or through vibration have revealed their potential to alter eye and head positioning, as well as postural sway, and velocity and direction of gait and running. Further, similar effects have been noted after induction of neck muscle fatigue.

It is not surprising then, that patients with neck disorders can have altered cervical joint position sense (JPS), postural stability, and oculomotor control. These patients can have either traumatic or insidious symptoms, which may be associated with complaints of dizziness/unsteadiness, headaches, loss of balance, or visual problems. This obviously necessitates a thorough clinical history and examination to rule out other potential causes such as vertebral artery pathology, central nervous system disease, infection, systemic pathology, tumour/malignancy, medication side effects, and so on. Once these have been sufficiently ruled out, examination for cervical spine causes can be undertaken.

The clinician should bear in mind that sensorimotor symptoms can also be influenced by pain levels in general, and psychosocial stressors. Further, although most of the literature to date has examined those with chronic neck pain, there is evidence suggesting that these changes can occur soon after pain onset.

As manual therapists, there are a couple of ways we could potentially intervene to treat sensorimotor disturbances related to cervical spine structures:
  1. Manual Therapies such as manipulation/mobilization, acupuncture; or
  2. Rehabilitation Programs focusing on gaze stability, eye/head coordination, or cervical position sense
All of the above-mentioned interventions have at least some degree of evidence supporting their efficacy for treating these types of problems. Therefore, the best current recommendation for these patients is to combine local cervical spine treatment with individualized programs for sensorimotor control (see below).

Clinical Assessment of Sensorimotor Control in Neck Disorders:

Current evidence suggests that assessment of sensorimotor control include investigation for dizziness, cervical joint position sense (JPS), postural stability, and oculomotor control. Regarding dizziness, patients should be questioned regarding the temporal pattern, sensation, and associated symptoms (including visual disturbance, loss of balance/falls, difficulty with ambulation, etc.).

Cervical Joint Position Sense (JPS)::
  • refers to a patient’s ability to reproduce a specified head/neck position with visual input removed (blindfolded or eyes closed)
  • most accurately measured using a head mounted laser pointer or torch on a lightweight headband – patient seated 90cm from a wall, initial position marked via laser, patient then moves head (rotation, flexion, or extension) and attempts to return to initial position which is also marked, allowing measurement of error (this could also be done without a head-mounted laser, but accuracy would obviously suffer)
  • previous literature indicates that the laser measurement technique can detect a deficit within 3-4 degrees (4-5cm) which can indicate a deficit in JPS
  • clinically, patients may overshoot/undershoot starting position, exhibit jerky motions, or recreate dizziness or other symptoms
Oculomotor Assessment:
  • incorporates gaze stability and smooth pursuit
  • Gaze Stability: tested by having the patient maintain stable gaze as the head moves into flexion, extension, rotation – looking for awkward cervical motion, reproduction of dizziness, nausea, blurred vision, or other symptoms
  • Smooth Pursuit/Eye Follow: patient maintains a stable head position while the eyes track an object – the literature suggests moving the object 20°/second through a 40° visual angle (this can then be repeated with the trunk rotated up to 45°)
  • can be tested with patient seated, or supine if necessary depending on patient presentation
Eye-Head Coordination:
  • the patient moves the eyes and the head in the same direction, or opposite directions, or various combinations
  • examiner should investigate for symptom reproduction, abnormal eye movements etc.
Postural Stability:
Generally, balance can be assessed in tandem, narrow or wide stance, and uni/bilaterally. Unstable surfaces can be added for to increase difficulty. It is reasonable to expect that a person under the age of 60 can maintain stability for 30 seconds in a comfortable and narrow stance. Subjects under age 45 should also be able to complete 30 seconds in tandem and single leg stance tests.

Management of Sensorimotor Control Disturbances in Neck Disorders:

In general, treatment should include local treatment to involved cervical spine structures to decrease pain and improve neuromuscular function, as well as individually prescribed sensorimotor exercises to improve identified deficits. The exercises described below should be performed 2-5 times per day. Patients should expect temporary reproduction of dizziness, however exacerbation of neck pain or headache should not occur.

Cervical JPS can be practiced at home, with or without the aid of a head mounted laser. Patients can practice with eyes open and then closed by lining up their target positions with objects on the wall to check their accuracy upon return.

Occulomotor exercises are based on assessment findings, and can be made more challenging by increasing the speed of the motions, changing the patient’s position, or altering the visual background. Examples include:
  • Eye follow with stationary head: patient follows a target with the eyes with the head stationary – target example could include tossing a tennis ball in the air
  • Gaze stability: can begin with slow passive neck movements while fixing the eyes on a stationary object, progressing to keeping gaze fixed with the eyes closed (checking gaze maintenance when eyes are opened), or restricting peripheral vision
  • Eye/head coordination: these begin with rotating the eyes and head to the same side/direction, and progressed to the head and eyes moving in opposite directions, or eyes first – then head, or active neck motion to follow a slowly moving object with peripheral vision restricted. Patients can also use their own thumb as a moving target while they walk and move their neck at the same time – any appropriate combinations can be used as progressions.
Postural stability and balance can be trained in similar ways as it is assessed, adding unstable surfaces, external perturbations, and so on, as the patient progresses.

Conclusions & Practical Application:

The cervical spine is clearly important in maintaining postural stability. This review has provided the clinician with simple tools that can be used to assess and treat various sensorimotor disturbances that can occur.

The assessment and treatment methods described above are based on existing evidence. It should be noted that more extensive research is required to refine and optimize these strategies.