Head and neck position sense in whiplash patients and healthy individuals and the effect of the "chin tuck" action
Whiplash injury is a common problem in the modern world. Whiplash injury may damage many passive and active structures within the neck including the deep neck flexor (DNF) muscles and the mechanoreceptors they host. Anatomical studies and clinical observation indicate that the DNF muscles play an integral role in maintaining head and neck stability. The DNF and the dorsal muscles of the neck contain complex arrangements of high densities of muscle spindles, mechanoreceptors that play a primary role in position sense. Efficient head and neck position sense mechanisms are essential for postural control and head and neck stability. Loss of strength and endurance has been observed in both the superficial and DNF muscles following whiplash. A few studies have also shown head and neck position sense to be impaired following whiplash injury. Study findings are supportive of the notion that head and neck position sense may be rehabilitated in the short term. It is unclear whether active muscle contraction, or internal bracing, during position matching enhances impaired position sense. It has been suggested that DNF retraining may reduce impairments of head and neck position sense. The “chin tuck” action is thought to activate the DNF muscles. To date, no research has investigated the effect of the “chin tuck” action on head and neck position sense. This study further investigated whether impairment of head and neck position sense existed in individuals experiencing chronic Whiplash-Associated Disorders (WAD) following whiplash injury. The effect of the “chin tuck” action on head and neck position sense was also examined. A randomised two group (control and whiplash) repeated measures factorial design was used for the comparison of dependent measures related to head and neck position sense. Twenty-three subjects who met specific inclusion/exclusion criteria were selected for each group and were anthropometrically, gender and age-matched. Those in the whiplash group had sustained the whiplash injury at least three months previously but not longer than five years ago, and experienced continued Grade II or Grade III signs and symptoms according to the Whiplash Associated Disorders (WAD) Classification System described by the Quebec Task Force (Spitzer et al, 1995). Whiplash subjects were assessed and detailed profiles documented as recommended by the Quebec Task Force (Spitzer et al, 1995). Parameters of pain were assessed using Quebec Task Force Minimum Data Forms and the 101-point Numerical Rating Scale (NRS-101) and a Pain Scale questionnaire. Active range of motion (AROM) of the cervical spine was measured. The Neck Disability Index (NDI) and Patient Specific Functional Scale (PSFS) were used to measure functional impairment and disability. Subjects were randomly assigned to either the control or intervention group. Subjects were required to perform head and neck position matching tasks whilst blindfolded with or without the intervention, the performance of the “chin tuck” action. The 3- Space FASTRAK electromagnetic tracking system was utilised to measure the position and orientation of the head and neck in space during each position-matching task. The dependent variables were the absolute, constant and variable error scores for each head and neck position matching task when performed with or without the “chin tuck” action. Two types of position matching tasks performed in the “neutral position” and the “mid range” were compared. Correlations between pain intensity and duration, range of motion, PSFS and NDI functional outcome scores, and head and neck position sense scores, were also explored. Results showed that there were no significant differences between whiplash and healthy groups in position matching accuracy. NDI and PSFS outcome measurement scores indicated the whiplash group to be mildly disabled. Overall significant differences (p < 0.05) in active range of motion measurements were observed between the two groups. No effect on error scores was observed when position matching tasks were performed with and without the “chin tuck” action. A trend of greater absolute error but smaller variable error scores was observed for “neutral” compared to “mid-range” position matching tasks. A significant moderate correlation (r = 0.45, p < 0.05) existed between the NDI and PSFS outcome measurement questionnaire scores was seen. No other correlations were observed between NDI, pain intensity or duration, and position sense scores. One moderate correlation (r = -0.38, p < 0.05) was observed between range of motion in extension and position sense scores measured in the same direction of motion. In conclusion, no evidence of head and neck position sense impairment was observed in this mildly disabled group of Grade II and III whiplash patients. Differences in head and neck position sense may exist in sub-groups of the neck pain population with varying degrees of disability. The performance of the “chin tuck” action during position matching had no effect on head and neck position sense in either the whiplash or healthy group, in this study. Future research investigating head and neck position sense within the chronic neck pain population should investigate position sense accuracy within subgroups of the chronic neck pain population. Additionally, the role of the DNF muscles in head and neck position sense could be further investigated by assessing the effects of retraining the deep neck flexor muscles over a period of time.