Cervical Movement Control Before and After Anterior Cervical Discectomy and Fusion

Early Changes in Dynamic Cervical Movement Control Following Anterior Cervical Discectomy and Fusion: A Prospective Controlled Longitudinal Study

Degenerative cervical disc disease can cause neck pain, nerve symptoms, dizziness, and problems with balance and head movement control. The neck contains many sensory receptors that provide information about head position and movement to the brain. When cervical discs degenerate or compress nearby structures, this sensory communication may be disrupted. As a result, patients may experience reduced accuracy and coordination of head movements.

Anterior cervical discectomy and fusion (ACDF) is a standard surgical procedure used to relieve nerve or spinal cord compression caused by cervical disc disease. The procedure is effective in reducing pain and neurological symptoms. However, it is not well understood whether ACDF also improves the way the neck and nervous system work together to control head movement.

The purpose of this study is to evaluate early changes in cervical movement control after ACDF. Patients scheduled for ACDF will be assessed before surgery and again one week after surgery. A group of healthy participants without neck pain will be assessed at the same time interval for comparison.

Cervical movement control will be measured using a computer-based head-tracking task. During this task, participants follow a moving target on a screen using controlled head movements. The system records measures of tracking accuracy and timing.

The primary research question is whether ACDF results in measurable short-term improvements in objective cervical movement control compared with healthy individuals over the same time period.

It is hypothesized that patients undergoing ACDF will demonstrate improvement in specific movement-control measures after surgery. However, broader patterns of movement-control impairment may not fully normalize in the early postoperative period.

The results of this study may improve understanding of how cervical spine surgery affects sensorimotor function and may help inform postoperative rehabilitation strategies.

Detailed Description Degenerative cervical disc disease is commonly associated with neck pain and neurological symptoms. In addition to these clinical manifestations, increasing evidence indicates that cervical spine pathology may impair cervical sensorimotor control. The cervical spine contains a high density of muscle spindles and joint mechanoreceptors that provide afferent information about head position and movement. This sensory input is integrated with visual and vestibular systems to regulate head-neck coordination and postural stability. Structural degeneration or neural compression may disrupt afferent signaling and alter this integration, potentially contributing to impaired movement accuracy, dizziness, or imbalance.

Anterior cervical discectomy and fusion (ACDF) is a standard surgical procedure used to relieve nerve root or spinal cord compression caused by cervical disc herniation when conservative treatment fails. While ACDF has demonstrated effectiveness in reducing pain and neurological deficits, its effects on objective cervical movement-control measures remain insufficiently characterized.

The RECAL-ACDF study is a prospective controlled longitudinal investigation designed to evaluate early changes in dynamic cervical movement control following ACDF. The study compares patients undergoing ACDF with time-matched healthy control participants assessed over the same time interval.

Study Design

Participants in the surgical group will be assessed at two time points:

• Preoperative baseline (within one week prior to surgery)
• One week postoperatively Healthy control participants will be assessed at two time points separated by a comparable interval.

The study uses a parallel-group, non-randomized design. The primary purpose is mechanistic evaluation of sensorimotor function.

Assessment of Cervical Movement Control Cervical movement control will be assessed using a validated dynamic head-tracking task (Butterfly test) implemented through the NeckSmart system (NeckCare™, Reykjavik, Iceland). The system uses a head-mounted inertial measurement unit (IMU) to record head movements while participants track an unpredictably moving visual target displayed on a computer screen.

The task includes three predefined difficulty levels (easy, medium, difficult), characterized by increasing target velocity and trajectory complexity. For each difficulty level, three trials will be performed.

The following outcome measures will be derived:

• Time-on-target (percentage of total trial time within the target zone)
• Undershoot (percentage of total trial time behind the target)
• Overshoot (percentage of total trial time in front of the target)
• Amplitude accuracy (mean spatial deviation between target and head-controlled cursor, expressed in millimeters)

Mean values across repetitions will be used for statistical analyses.

Primary Objective To determine whether ACDF results in short-term improvements in dynamic cervical movement control compared with healthy controls over the same time period.

The primary outcome measure is the change in time-on-target at medium difficulty (ToT_m) from baseline to one week postoperatively.

Secondary Objectives

• To evaluate changes in additional movement-control parameters across difficulty levels.
• To assess change in amplitude accuracy at difficult level (AA_d).
• To determine whether surgery is associated with redistribution across predefined multidimensional movement-control impairment clusters (four ordinal severity levels).
• To explore whether parameter-level improvements correspond to broader changes in impairment phenotype.

Cluster allocation (severity levels 1-4) will be determined using a previously established multidimensional classification framework based on standardized movement-control parameters.

Hypothesis It is hypothesized that patients undergoing ACDF will demonstrate measurable improvement in selected dynamic movement-control parameters one week after surgery. However, categorical redistribution across multidimensional impairment clusters may not occur in the early postoperative period.

This study conceptualizes postoperative recovery as an early sensorimotor recalibration process rather than immediate normalization of movement-control phenotype.

Statistical Approach The primary analysis will compare change scores (postoperative minus preoperative values) between the surgical and control groups. Appropriate parametric or nonparametric statistical tests will be applied depending on data distribution. Multiple comparisons will be controlled using the Holm-Bonferroni procedure.

Cluster allocation (ordinal severity levels 1-4) will be analyzed using proportional odds regression models with subject-level clustering to account for repeated measurements.

Clinical Relevance This study aims to clarify whether structural decompression of the cervical spine is associated with early recalibration of cervical sensorimotor control. Improved understanding of postoperative sensorimotor changes may inform development of targeted rehabilitation strategies following ACDF.

Inclusion Criteria

Surgical group:

• Age 18 to 65 years
• Clinical diagnosis of cervical disc pathology at one segment level (e.g., cervical disc herniation or degenerative disc disease)
• Scheduled to undergo anterior cervical discectomy and fusion (ACDF) as part of standard clinical care
• Ability to understand study procedures and provide written informed consent

Non-Surgical neck pain group:

• Age 18 to 65 years
• Clinical diagnosis of neck pain associated with cervical disc pathology
• Not undergoing surgical treatment during the study period
• Ability to understand study procedures and provide written informed consent

Exclusion Criteria:

• Prior cervical spine surgery
• Diagnosed neurological disorders unrelated to cervical disc pathology (e.g., multiple sclerosis, Parkinson's disease, stroke)
• Known vestibular disorders affecting balance
• Severe uncorrected visual impairment
• Acute musculoskeletal injury of the neck or upper limb unrelated to the primary cervical condition
• Inability to perform the head-tracking task
• Cognitive impairment preventing informed consent