This study aims to clarify the factors associated with the long-term occurrence of mechanical complications following spinal fixation.
Seventy-seven patients with ASD (mean age: 73.8 years) who underwent spinal fixation from the thoracic vertebrae to the pelvis were evaluated through three-dimensional gait analysis at a comfortable velocity. Fifty gait characteristics were calculated, including kinetic and kinematics on the trunk, hip, knee, and ankle in sagittal and frontal planes. Knee extension strength, radiographic parameters, and the Global Alignment and Proportion (GAP) score were assessed. All measurements were conducted approximately six months after surgery. Mechanical complications comprising rod fracture, proximal junctional kyphosis or failure, and set-screw dislodgement were investigated using standing X-rays. The follow-up days and the duration between the date of gait analysis and the date of the first discovered mechanical complication were recorded.
The time-to-event analysis was performed using a univariable Cox proportional-hazards regression model to predict mechanical complications, and the hazard ratio (HR) was computed. The gait characteristics, including kinetics, kinematics, gait speed, and step length, as well as GAP score, age, and muscle strength, were utilized as parameters. The proportional-hazards assumption was confirmed by the Schoenfeld residuals method before the analysis. Considering death as a competing risk, we censored at a time point beyond the last surviving subjects. All statistical analyses were performed using R software.
Ankle plantarflexion angle at toe-off (HR: 0.95, 95% CI: 0.89–1.00, p = 0.039), knee flexion moment in terminal stance (HR: 0.62, 95% CI: 0.42–0.91, p = 0.014), and minimum hip extension moment (HR: 1.27, 95% CI: 1.02–1.57, p = 0.031) were significantly associated with mechanical complications. In contrast, GAP score (HR: 1.06, 95% CI: 0.95–1.19, p = 0.30), gait speed (HR: 0.99, 95% CI: 0.97–1.00, p = 0.13), age (HR: 1.02, 95% CI: 0.97–1.07, p = 0.50), step length (HR: 0.97, 95% CI: 0.93–1.01, p = 0.093), and knee extension strength (HR: 1.15, 95% CI: 0.46–2.86, p = 0.80) were not significantly associated with mechanical complications.
The lower limb angle and moment during the late stance phase are associated with the occurrence of mechanical complications following spinal fixation, rather than with known risk factors such as the GAP score. Proper control by the lower limbs during gait may contribute to protecting the fixed spine and instrumentation after surgery
This study suggests that gait analysis and exercise therapy focused on optimizing lower limb kinetics and kinematics, particularly in the late stance phase during gait, are vital to reducing mechanical complications following spinal fixation.
adult spinal deformity
mechanical complication
