Abstract
Dear editor,
We read with great interest the study by Scheer et al., 1 which investigated the association between preoperative cervical range of motion (ROM) and proximal junctional kyphosis/failure (PJK/PJF) risk. The study provided valuable insights into preoperative ROM as a predictor of postoperative complications and underscored its potential role in risk assessment. Building upon this work, several constructive points for further consideration are offered from statistical, longitudinal, and mechanistic perspectives.
First, regarding statistical methodology, multivariable logistic regression was employed by the authors to reveal the association between preoperative cervical ROM and postoperative PJK/PJF, thereby providing a quantitative basis for clinical risk identification. In future studies, confounding control could be further optimized by introducing methods such as propensity score matching to balance intergroup differences related to osteoporosis, smoking history, and other variables. Additionally, stratified analyses based on key variables such as age, sex, and grade of cervical degeneration could be performed to evaluate the predictive performance of ROM across different subgroups. Furthermore, internal validation of key thresholds (eg, flexion of 22.8° and total ROM of 48.2°) using bootstrap resampling or cross-validation would help to enhance the robustness and generalizability of the findings. These statistical extensions would allow for a more rigorous confirmation of the independent association between ROM and PJK/PJF.
Second, regarding longitudinal and dynamic indicators, the current study relied solely on preoperative, single-time-point ROM measurements. Although this approach demonstrated good predictive capability, it did not reveal the impact of dynamic changes in ROM on postoperative outcomes. Future investigations could incorporate serial postoperative ROM data and employ mixed-effects models or time-series analyses to systematically evaluate the temporal relationship between ROM recovery trajectories and the evolution of the proximal junctional angle, instrumentation failure, and functional outcomes. Such longitudinal analyses would not only help identify early warning signs prior to the development of PJK/PJF but also provide a scientific basis for establishing quantifiable and actionable rehabilitation goals, thereby facilitating a transition from “static prediction” to “dynamic monitoring and intervention.”
Finally, regarding mechanistic exploration and clinical physiological significance, reduced ROM may reflect multiple pathological changes, including cervical degeneration, joint stiffness, paraspinal muscle fatty infiltration, and ligamentous dysfunction. In future studies, preoperative MRI could be incorporated to assess indicators such as disc degeneration, facet joint osteoarthritis, ligamentum flavum hypertrophy, and muscle quality, thereby clarifying the structural basis of reduced ROM. Additionally, finite element biomechanical modeling could be employed to simulate stress distribution under different ROM conditions and test the hypothesis that “low ROM leads to stress concentration at the cervicothoracic junction,” thus elucidating the mechanical mechanisms by which reduced ROM promotes PJK/PJF. Such mechanistic insights would help elevate ROM from a statistical risk factor to an interventional target with clear pathophysiological significance, thereby providing a solid scientific foundation for individualized preoperative surgical strategies and postoperative rehabilitation interventions.
In summary, it was found by Scheer et al. that reduced cervical ROM is linked to PJK/PJF risk. Future serial ROM measurements, mechanistic studies, and confounder adjustments would clarify causality and guide prevention strategies.
