Introduction: Collagen is the primary structural protein of connective tissues. Disrupting the maintenance and turnover of connective tissues can lead to age-related changes and conditions, potentially influencing surgical outcomes negatively. The identification of reliable predictor biomarkers for revision spinal surgery is crucial. However, literature is scarce in exploring the role of imaging parameters. The intersection of skin ultrasound (US) parameters and their connection to connective tissues and advanced glycation end-products (AGEs), formed through the glycation of proteins like collagen contributing to age-related decline in tissue elastic properties, remains an area of ongoing investigation. For that reason, the aim of this study is to investigate the associations between skin US parameters and revision surgery following spine lumbar fusion.
Methods: We reviewed an institutional database of posterior lumbar fusion patients, prospectively collected from 2014 to 2023 with a minimum of 2-years of follow-up. Patients that had previous fusion surgery and revision not due to adjacent segment disease (ASD) or pseudoarthrosis were excluded. Revision after baseline fusion were classified as cases and non-revision after baseline fusion were controls. US measurements were conducted at two standardized locations on the lumbar back, between the spinous process and the posterior superior iliac spine (PSIS) and 1cm cranial to the first location. Skin echogenicity of the average dermal (AD) layer, upper dermal (UD) layer, upper 1/3 of the dermal layer; papillary dermis, lower dermal (LD), lower 1/3 of the dermal layer; reticular layer, and subcutaneous skin layer were measured. Echogenicity was calculated with the embedded echogenicity function of our institution’s imaging platform (PACS). A rectangular block of the papillary, reticular, and the whole dermis as well as the subcutis was outlined and calculated automatically. Mann-Whitney U and T-tests were used for statistical analysis. Statistical significance was set at p<0.05.
Results: A total of 157 patients (51% female, age 62 [54-72] years) were included in the final analysis with a follow-up of 54 [44-84] months after 1.6 ±0.8 level lumbar fusion. 16 patients required revision surgery because of ASD or pseudoarthrosis. The median interval time between initial fusion and revision was 34 months (IQR = 17–51). AD echogenicity showed significantly higher results among revision cases 124.5 (IQR= 115.75,131.63) compared to the control group 114.3 (IQR= 98.83,124.8). Similarly, UD and LD showed significantly higher echogenicity in the revision group 128.5 (IQR=125,131.63) and 125.5 (IQR= 107.91,136.50), respectively, compared to the non-revision group UD 118.5 (IQR= 109.28,127.50), LD 114 (IQR= 94.20,126.75).
Discussion: The findings of this study demonstrate a significant association between higher echogenicity values in different layers of the dermis and the likelihood of requiring revision surgery. The results provide valuable insights into the potential use of skin US parameters, particularly echogenicity, as predictors for revision surgery following lumbar fusion. The significance of these findings may reflect underlying alterations in collagen and AGEs. Further research is warranted to elucidate the underlying mechanisms driving these associations and to explore the clinical implications of utilizing skin US parameters in preoperative assessment and risk stratification for lumbar fusion patients.