Letter to the editor: Does the length of the intermediate pedicle screw influence outcome in unstable thoracolumbar burst fractures? A prospective randomized study

To the Editor,

We read with great interest the prospective randomized study by Arumugam et al. [1] evaluating the effect of intermediate pedicle screw (IPS) length on radiological and functional outcomes in unstable thoracolumbar burst fractures treated with short-segment posterior fixation. The authors should be congratulated for addressing a technically relevant and clinically important question using a randomized design.

The study demonstrates that longer intermediate screws resulted in significantly greater immediate postoperative regional kyphosis angle correction, while no significant differences were observed between long and short IPS groups at final follow-up [1]. We believe that these findings highlight an important conceptual distinction that may help refine interpretation of the results.

In their discussion, the authors appropriately cite prior work indicating that the pedicle contributes the majority of construct stiffness and pullout strength, and they reference studies suggesting that deeper advancement of similarly sized screws into the vertebral body does not necessarily increase pullout strength [1]. Based on this, the authors emphasize that the stability of short-segment fixation with an intermediate screw depends primarily on the three-point fixation and push-point effect, rather than screw length alone.

However, an important mechanistic consideration is that the hypothesized advantage of a longer IPS is not limited to pullout strength. Rather, longer screws are often presumed to influence construct-level biomechanics, including load transfer, stress distribution, and bending behavior under flexion and axial loading. High-quality biomechanical and finite element studies have shown that insertion depth can alter stress distribution and stiffness characteristics of pedicle screw constructs, even when differences in pure pullout strength are minimal [2,3]. In thoracolumbar fracture models, these effects appear to be context-dependent and are influenced by fracture configuration and loading conditions [4].

Crucially, for such construct-level effects to translate into sustained clinical benefit, the fixation must actively engage anterior column load sharing, a principle central to the load-sharing classification described by McCormack et al. [5]. In the present study, the operative protocol explicitly avoided aggressive reduction maneuvers such as rod over-contouring, compression, or distraction [1]. Consequently, the anterior column was not intentionally recruited, and no parameters reflecting load sharing or anterior column contribution were evaluated.

Within this framework, the absence of long-term differences between long and short IPS groups should not be interpreted as evidence that IPS length lacks biomechanical relevance. Instead, the findings may indicate that when anterior column load sharing is neither actively optimized nor assessed, variations in IPS length alone are insufficient to influence long-term radiological or functional outcomes. This interpretation also provides a plausible explanation for the observed pattern in this trial—namely, improved immediate correction with longer screws, followed by convergence of outcomes over time.

We suggest that future investigations assessing IPS characteristics may benefit from pairing screw-length comparisons with reduction strategies designed to engage the anterior column and from incorporating surrogate measures of load sharing or construct biomechanics. Such an approach may better clarify whether IPS length has clinically meaningful effects when its proposed biomechanical mechanism is actively utilized.