The relationship of cervical joint position error to balance and eye movement disturbances in persistent whiplash

Abstract

Cervical joint position error (JPE) has been used as a measure of cervical afferent input to detect disturbances in sensori-motor control as a possible contributor to a neck pain syndrome. This study aimed to investigate the relationship between cervical JPE, balance and eye movement control. It was of particular interest whether assessment of cervical JPE alone was sufficient to signal the presence of disturbances in the two other tests. One hundred subjects with persistent whiplash-associated disorders (WADs) and 40 healthy controls subjects were assessed on measures of cervical JPE, standing balance and the smooth pursuit neck torsion test (SPNT). The results indicated that over all subjects, significant but weak-to-moderate correlations existed between all comfortable stance balance tests and both the SPNT and rotation cervical JPE tests. A weak correlation was found between the SPNT and right rotation cervical JPE. An abnormal rotation cervical JPE score had a high positive prediction value (88%) but low sensitivity (60%) and specificity (54%) to determine abnormality in balance and or SPNT test. The results suggest that in patients with persistent WAD, it is not sufficient to measure JPE alone. All three measures are required to identify disturbances in the postural control system.

Introduction

Evidence is emerging to suggest that patients with persistent whiplash-associated disorders (WADs) have impairments in the postural control system. These include altered kinaesthetic sense with increased cervical joint position error (JPE) (Heikkila and Astrom, 1996; Treleaven et al., 2003), altered eye movement control, detected in the smooth pursuit neck torsion test (SPNT) (Tjell and Rosenhall, 1998; Tjell et al., 2003; Treleaven et al., 2004a) and altered standing balance (Kogler et al., 2000; Michaelson et al., 2003; Sjostrom et al., 2003; Treleaven et al., 2004b, Treleaven et al., 2003). These impairments are more pronounced when the whiplash patient reports dizziness and or unsteadiness in association with their neck pain (Tjell and Rosenhall, 1998; Treleaven et al., 2004a, Treleaven et al., 2004b, Treleaven et al., 2003). The impairments have also been shown to be independent of the patient's anxiety level, medication use and compensation status suggesting that the symptom of dizziness is related to disturbances in the postural control system (Treleaven et al., 2004a, Treleaven et al., 2004b, Treleaven et al., 2003). It is probable that these impairments reflect abnormal cervical afferent input to the postural control system especially in cases where there is no evidence of a concurrent head injury or primary injury to the vestibular apparatus associated with the whiplash injury (Hildingsson et al., 1993; Rubin et al., 1995; Gimse et al., 1997; Tjell and Rosenhall, 1998; Wenngren et al., 2002).

The measure of cervical JPE is considered to primarily reflect afferent input from the neck joint and muscle receptors (Taylor and McCloskey, 1991; Mergner et al., 1998). It is used regularly as an objective measure of cervical afferent input in both cross-sectional and intervention studies (Revel et al., 1991; Heikkila and Astrom, 1996; Heikkila and Wenngren, 1998; Treleaven et al., 2003). In appraising the intervention studies, there seems to be a presumption that JPE is the pivotal test for cervical afferent disturbance and abnormalities in JPE reflect other impairments such as disturbances to eye movement control and even balance. For example, JPE has been the representative quantitative outcome measure for programmes which have addressed either eye/head co-ordination, gaze stability as well as cervical joint repositioning practice (Revel et al., 1994), exercises for eye, head and arm co-ordination (Humphreys and Irgens, 2002), body awareness retraining (Heikkila and Astrom, 1996) or neck manipulation and acupuncture (Heikkila et al., 2000). In defense of the use of JPE as the representative measure, Heikkila and Wenngren (1998) did find that whiplash subjects with oculomotor disturbances were less accurate in head repositioning than subjects with normal oculomotor tests, suggesting a possible relationship between these measures. Such a suggestion may oversimplify the complex reflex and central interactions between the cervical afferents and other areas important for postural control, particularly the vestibular and visual systems (Chan et al., 1987; Dutia, 1991; Fischer et al., 1995; Bolton, 1998).

There was a need to further investigate whether there were any relationships between the suite of measures (i.e. measures of cervical (JPE), balance and SPNT), contributing to disturbance of postural control in patients following a whiplash injury.

Thus, the aim of this study was to determine whether any relationships existed between cervical JPE, SPNT and balance, and in particular, whether the tests were highly correlated which would support the notion that assessment of cervical JPE alone is sufficient to detect postural control disturbances following a whiplash injury. A secondary aim was to determine the incidence of postural control abnormalities (based on normative data) in both subjects with whiplash complaining and not complaining of these symptoms as well as the usefulness of an abnormal score in cervical (JPE) in indicating abnormalities in the other tests. Knowledge of such relationships is important for future direction in assessment and management of postural control disturbances in whiplash patients.