Abstract
To the Editor:
We read with great interest the recent article by Issani et al. examining the long-term association between total hip arthroplasty (THA) and subsequent lumbar spine surgery in patients with concomitant hip osteoarthritis (HOA) and lumbar degenerative disease (LDD). 1 We commend the authors for utilizing large national databases to investigate this important and clinically relevant issue, providing valuable data suggesting that total hip arthroplasty (THA) may be associated with a reduced incidence of subsequent lumbar decompression fusion in patients with concurrent hip osteoarthritis and lumbar degenerative disease.
Simultaneously, we identify a methodological issue that may require further clarification: potential time-to-event bias. In the current study design, only patients diagnosed with lumbar disc degeneration (LDD) and hip osteoarthritis (HOA) who underwent THA were included, while those who had previously undergone lumbar decompression or fusion prior to THA were excluded. Consequently, the interval between initial LDD diagnosis and THA surgery may represent a zero-event period in the THA group. This design may have confounded the THA group and partially explains the observed significant reduction in subsequent lumbar decompression fusion incidence and the significantly prolonged reporting time from LDD diagnosis to subsequent spinal surgery. Therefore, the study findings should be interpreted with caution as signals of significant association. Supplementary analyses using time-varying exposure frameworks may better reflect the true therapeutic benefits of the observed protective effects.
Another point worthy of discussion is whether the primary adjustment analysis remains susceptible to substantial residual confounding factors. We commend the authors’ efforts in multivariable adjustment and risk factor characterization analysis in the THA cohort; however, in the primary comparison between THA and non-THA patients, despite significant baseline characteristics differences between the 2 groups, adjusted variables appeared limited to age, sex, ECI, and scoliosis. Notably, subsequent subgroup analyses by the authors revealed that multiple spine-specific diagnoses were the strongest predictors of subsequent lumbar spine interventions: in the fusion model, multivariable odds ratios for nerve root lesions, spinal stenosis, spinal cord lesions, and spondylolisthesis approached or exceeded 2.0, with scoliosis odds ratios reaching as high as 4.5. These results indicate that the likelihood of subsequent lumbar spine interventions largely depends on the severity and clinical presentation of spinal pathology itself. If such critical clinical factors were not fully incorporated into the primary comparison model, the protective association of THA might have been partially overestimated.
Meanwhile, 2 methodological aspects warrant further clarification. First, although the authors reported a reduced incidence of THA and subsequent lumbar decompression fusion surgery, and noted a significantly prolonged mean interval from LDD diagnosis to subsequent spinal surgery in the THA group, the primary analytical framework primarily relied on logistic regression models. While suitable for event probability modeling, these models demonstrated limited efficacy in evaluating temporal differences in event occurrence among patients with varying follow-up durations. The adoption of time-event analysis methods could enhance the explanatory power of THA delaying lumbar surgery. Second, given that claims-based research heavily depends on precise coding definitions, we emphasize the importance of clarifying terminology: the abstract and methods section mentioned isthmic spondylolysis, whereas the results table and corresponding text reported lumbar spondyloarthropathy. Although this may represent a reporting consistency issue rather than a substantive analytical limitation, more uniform definition standards would improve the interpretability and reproducibility of study findings.
Overall, we believe this study makes a meaningful contribution to the literature on hip-spine syndrome. Our comments are offered in the spirit of constructive scientific discussion and add to the ongoing discussion regarding surgical sequencing in hip-spine syndrome.
