Reweighting of the sensory inputs for postural control in patients with cervical spondylotic myelopathy after surgery

Abstract

Background: Cervical spondylotic myelopathy (CSM) is a degenerative cervical disease in which the spinal cord is compressed. Patients with CSM experience balance disturbance because of impaired proprioception. The weighting of the sensory inputs for postural control in patients with CSM is unclear. Therefore, this study investigated the weighting of sensory systems in patients with CSM.

Method: Twenty-four individuals with CSM (CSM group) and 24 age-matched healthy adults (healthy control group) were analyzed in this observational study. The functional outcomes (modified Japanese Orthopaedic Association Scale [mJOA], Japanese Orthopaedic Association Cervical Myelopathy Questionnaire [JOACMEQ], Nurick scale) and static balance (eyes-open and eyes-closed conditions) were assessed for individuals with CSM before surgery, 3 and 6 months after surgery. Time-domain and time-frequency-domain variables of the center of pressure (COP) were analyzed to examine the weighting of the sensory systems.

Results: In the CSM group, lower extremity function of mJOA and Nurick scale significantly improved 3 and 6 months after surgery. Before surgery, the COP mean velocity and total energy were significantly higher in the CSM group than in the control group for both vision conditions. Compared with the control group, the CSM group exhibited lower energy content in the moderate-frequency band (i.e., proprioception) and higher energy content in the low-frequency band (i.e., cerebellar, vestibular, and visual systems) under the eyes-open condition. The COP mean velocity of the CSM group significantly decreased 3 months after surgery. The energy content in the low-frequency band (i.e., visual and vestibular systems) of the CSM group was closed to that of the control group 6 months after surgery under the eyes-open condition.

Conclusion: Before surgery, the patients with CSM may have had compensatory sensory weighting for postural control, with decreased weighting on proprioception and increased weighting on the other three sensory inputs. After surgery, the postural control of the patients with CSM improved, with decreased compensation for the proprioceptive system from the visual and vestibular inputs. However, the improvement remained insufficient because the patients with CSM still had lower weighting on proprioception than the healthy adults did. Therefore, patients with CSM may require balance training and posture education after surgery.

Trial registration: Trial Registration number: NCT03396055 Name of the registry: ClinicalTrials.gov Date of registration: January 10, 2018 - Retrospectively registered Date of enrolment of the first participant to the trial: October 19, 2015.

Keywords: Center of pressure; Gabor transform; Sensory integration; Time-frequency analysis.

Fig. 1

Integration of the sensorimotor system. The sensorimotor system integrates the afferent, efferent, and central nervous system, and is controlled by two control systems: feedback control and feedforward control. Feedback control involves the sensory processing, in which the cerebellar system regulates the visual, vestibular and somatosensory (i.e., proprioception, pain…etc.) inputs. The sensory feedback is conveyed to the cortex to be processed, and the reactive motor command is descended to the muscle properties. Feedforward control is described as an anticipatory action with a direct descending command without sensory feedback

Fig. 2

Frequency band of the sensory systems

Fig. 3

Flow diagram of this study

Fig. 4

COP mean velocity at 3 time points in the CSM group and the control group. a COP mean velocity under EO condition. b COP mean velocity under EC condition. # Indicated a significant difference between the CSM group and the control group: p < 0.05. * Indicated a significant difference within the CSM group before and after surgery: p < 0.05/3 = 0.016

Fig. 5

Total energy content at 3 time points in the CSM group and the control group. a Total energy content under EO condition. b Total energy content under EC condition. # Indicated a significant difference between the CSM group and the control group: p < 0.05

Fig. 6

Percentage of energy content in each frequency band under the EO condition. a Moderate-frequency band (1.56–6.25 Hz, proprioception and spinal reflexive loop). b Low-frequency band (0.39–1.56 Hz, cerebellar system). c Very-low-frequency band (0.1–0.39 Hz, vestibular system). d Ultralow-frequency band (< 0.1 Hz, visual system). # Indicated a significant difference between the CSM group and the control group: p < 0.05

Fig. 7

Percentage of energy content in each frequency band under the EC condition. a Moderate-frequency band (1.56–6.25 Hz, proprioception and spinal reflexive loop). b Low-frequency band (0.39–1.56 Hz, cerebellar system). c Very-low-frequency band (0.1–0.39 Hz, vestibular system). d Ultralow-frequency band (< 0.1 Hz, visual system)