Commentary on “Adjacent segment degeneration after superior facet joint violation of the lumbar spine”

McNamee et al. [1] present a retrospective cohort study examining the relationship between superior facet joint violation (FJV) and adjacent segment degeneration (ASD) following lumbar pedicle screw fixation. The authors aimed to determine whether FJV, graded using a three-tier CT-based classification system, is independently associated with radiographic degeneration or reoperation at the cranial adjacent segment.

This is a timely and clinically relevant investigation. ASD occurs in up to 4% of patients annually following lumbar fusion [2] and remains the most common long-term complication of instrumented fusion, yet its pathogenesis is incompletely understood. FJV has been proposed as a potentially modifiable contributor to ASD and is frequently cited as a rationale for adopting navigated and robotic-assisted screw placement [3,4]. However, prior studies have been limited by heterogeneous grading systems, inadequate control of confounders, and selection bias related to the inclusion of patients undergoing postoperative CT for clinical indications [1]. The present study seeks to address several of these limitations.

Patients undergoing lumbar pedicle screw fixation between January 2010 and January 2025 at a tertiary referral center were included if postoperative CT imaging encompassed both the instrumented construct and the cranial adjacent level. Exclusion criteria included malignant or infectious pathology and inadequate imaging. FJV was graded as follows: grade 0 (no violation), grade 1 (breach of the lateral cortex of the superior facet without entering the joint space), and grade 2 (screw traversal involving both articular surfaces). Importantly, the cohort included patients who underwent incidental cross-sectional imaging for non-spine indications, in addition to those with dedicated postoperative spinal imaging, thereby reducing selection bias. Radiographic endpoints included disc height loss, progression of spondylolisthesis, coronal deformity, central stenosis, and a composite degeneration measure; reoperation was also assessed. Inverse probability of treatment weighting (IPTW) was used to balance covariates, and weighted Cox proportional hazards models with robust variance estimation were applied for time-to-event analyses.

Of 1,000 lumbar fusions performed during the study period, only 71 patients met inclusion criteria with evaluable postoperative CT imaging. FJV was identified in 35 patients (49.3%), including 21 (29.6%) with grade 1 and 14 (19.7%) with grade 2 violations. Median event-free follow-up was 3.9 years (IQR 2.17–7.61), with a maximum of 15.2 years. After IPTW adjustment, FJV was not significantly associated with disc height loss (HR 1.21, 95% CI 0.54–2.72), spondylolisthesis progression (HR 0.59, 95% CI 0.13–2.65), coronal deformity (HR 2.18, 95% CI 0.48–10.01), central stenosis (HR 1.35, 95% CI 0.21–8.61), composite degeneration (HR 1.76, 95% CI 0.87–3.56), or reoperation (HR 0.44, 95% CI 0.12–1.62). While coronal deformity and composite degeneration were significant in unadjusted analyses, these associations did not persist following IPTW, suggesting that prior unweighted studies may have been confounded. An exploratory observation raised the possibility that grade 1 violations may contribute to axial instability, whereas grade 2 violations—by engaging both articular surfaces—may confer relative construct stability; however, neither finding reached statistical significance.

This study represents an additional contribution to a literature that has historically been limited by inadequate control of confounding and selection bias. The use of IPTW, robust survival analysis, extended follow-up, and inclusion of incidental imaging are notable strengths that distinguish this work from prior observational studies, yet the small "n" out of the total population is certainly a concern. However, attenuation of previously observed associations after weighting is particularly informative and may help explain inconsistencies in the existing literature.

Several limitations warrant consideration. The modest effective sample size following weighting (45.6 patients) limits statistical power and increases the risk of type II error, as reflected by the wide confidence intervals across multiple endpoints. Residual confounding from unmeasured variables, including body mass index, smoking status, and bone quality, remains possible. Additionally, the reliance on CT for assessing central stenosis may underestimate soft tissue contributions. The absence of patient-reported outcome measures further limits interpretation, particularly given prior work suggesting worse clinical outcomes in patients with FJV [5].

The findings are provocative in that they challenge the prevailing assumption that superior FJV is a key driver of ASD and reoperation following lumbar fusion. If FJV does not meaningfully accelerate adjacent segment degeneration, the justification for adopting costly navigational or robotic technologies primarily to mitigate FJV warrants careful reconsideration [3,4]. While this does not diminish the extreme importance of accurate screw placement, it suggests that FJV prevention alone may not be sufficient to support widespread navigation technology adoption for example.

Future studies should aim to validate the potential grade-specific biomechanical effects observed here using cadaveric or in vivo models, evaluate the impact of FJV on screw fixation strength and fusion outcomes, and incorporate patient-reported measures to better define the clinical significance of FJV across its severity spectrum.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.