The total population of Japan is predicted to decrease by 2050, and a substantial increase is expected in the population of age 85 years and above [1]. With the rapid increase in the elderly population, the number of patients with locomotive syndrome has increased in Japan [23]. Locomotive syndrome increases the societal burdens with respect to mortality, quality of life, and economic costs. Cervical cord compression was present in 5% to 7% of asymptomatic subjects and was associated with physical performances in elderly people. It is suggested that locomotive syndrome involves the early stages of cervical spondylotic myelopathy (CSM). Especially in the elderly people, the gait impairment can be due to CSM which could aggravate the symptoms of cervical cord injury from a relatively minor trauma, such as a fall from a height, or even progress to severe quadriparesis. However, to the best of our knowledge, there are no objective criteria for the evaluation of gait analysis. The number of studies for gait analysis in CSM patients is small, and the indications for the surgery of CSM without severe paralysis still remain controversial [456789]. Quantitative gait analysis and the decision for decompressive surgery in the patients with CSM are important, in order to prevent severe paraplegia resulting from a fall. The objective of our study is to compare the gait patterns in patients with CSM, which is evaluated by the Nurick grades, and to determine the threshold values of gait parameters predicting the occurrence of a fall by using a gait recorder.

The participants had a clinical diagnosis of CSM confirmed by magnetic resonance imaging findings. CSM was defined as a constellation of symptoms and signs supported by appropriate radiological findings, including symptoms (numb clumsy hands, impairment of gait, bilateral arm paresthesia) and signs (corticospinal distribution motor deficits, atrophy of hand intrinsic muscles, hyperflexia, positive Hoffman sign, upgoing plantar responses, lower limb spasticity, broad-based unstable gait). One hundred thirty-two subjects (normal, 34; CSM, 98) underwent gait analysis by using a sheet-type gait analysis system. All subjects provided written informed consent after receiving explanation of the experimental protocol, and this study was approved by the Institutional Review Board of our institution. The patient characteristics are summarized in Table 1. Patients with the following conditions were excluded from this study: hip, knee, and ankle joint disease; other spinal disease; and scoliosis of more than 10°. Participants with clear clinical and radiological evidence of CSM were included in this study.

The walking test was performed by using a 2.4 m long thin-type sensor sheet (Sheet Type Gait Analyzer Walk Way MW-1000, Anima, Tokyo, Japan).

The patients were examined 3 times, and the average of those results were taken. Measurements of gait cycle parameters included the step angle, step length, step width, and gait velocity. Outward rotation of the feet was measured as a positive angle (Fig. 1). The gait cycle consists of a swing phase and a stance phase. Generally, the stance phase and swing phase account for 60% and 40%, respectively (Fig. 2) [10]. The clinical gait disturbance in patients with CSM was evaluated according to the Nurick grade (Table 2) [11].

A medical statistical consultant performed the statistical analyses using the JMP software package, ver. 8.0 (SAS Institute Inc., Cary, NC, USA). The Tukey-Kramer HSD test was used to analyze the differences in the gait parameters among Nurick grades. The correlations among the variables of gait parameters were examined using the Spearman's rank correlation coefficient. The gait parameters and risk factors in the patients with Nurick grade 4 were evaluated by logistic regression analysis. A p-value of less than 0.05 was considered to indicate a statistically significant difference.

Gait analysis without any subjective gait disturbance in patents with CSM.

In order to assess the subclinical findings, we compared Nurick grade 0 and 1. Although clinical symptoms were lacking, grade 1 had significant abnormalities in the parameters of velocity, step length, and step angle (p<0.05) (Fig. 3). The gait velocity and step length decreased as symptoms progressed. In contrast, step angle and step width increased (Fig. 3).

The Japanese Orthopedic Association (JOA) has proposed the term "locomotive syndrome". This syndrome is caused by weakening of the musculoskeletal organs such as bones, joints, and muscles [23]. It is suggested that locomotive syndrome involves the early stages of CSM. Culhane et al. [12] demonstrated that the falls are a major source of morbidity and mortality in the elderly population. Falls occurring in the patients with CSM are particularly likely to result in a permanent, severe quadriparesis. It was reported that the injury in CSM, associated with ossification of the posterior longitudinal ligament, is a poor prognostic factor; and in 15/156 patients (9.6%), CSM became worse by even a minor external injury [13].

Gait analysis was an objective tool for evaluating the gait stability, even when the CSM patients had no subjective gait disturbance. The compensation mechanism for unstable gait in the patients with CSM was the reduction of velocity and prolongation of the stance phase by a greater step angle and smaller step length. When the stance phase in the gait cycle increases to above 70% of the total cycle period, the CSM patients may have an increased fall risk.