Using ultrasound to assess connective tissue quality in spine surgery: cutoffs and predictive value for adjacent...

Collagen integrity is essential for connective tissue maintenance, and its deterioration may contribute to postoperative complications. Dermal ultrasound (US) echogenicity has been associated with collagen quality, with changes in echogenicity reflecting alterations in collagen composition. These changes may indicate increased susceptibility to revision surgery in lumbar fusion patients, particularly due to adjacent segment disease (ASD). However, no study has established a specific cutoff value for skin US echogenicity to predict the need for ASD-related revision surgery. This single-center prospective cohort study aimed to evaluate the association between dermal echogenicity and ASD revision, and to determine echogenicity cutoff values that could help identify patients at higher risk of requiring revision surgery.

Patients undergoing posterior lumbar fusion from 2014 to 2023 were included. US measurements were conducted at two standardized locations on the lumbar back. Echogenicity values for the average dermal (AD), upper dermal (UD), and lower dermal (LD) layers were calculated using our institution's PACS imaging software. Statistical significance set at p < 0.05.

Among 383 patients (51% female, median age 63), those undergoing ASD revision were significantly older (median age 66.8 vs. 62 years, p = 0.012). Higher echogenicity in the LD (OR = 1.03, p = 0.008), UD (OR = 1.03, p = 0.027), and AD (OR = 1.03, p = 0.005) layers was associated with increased ASD risk. The optimal LD echogenicity cutoff was 124.3 (AUC = 0.654, sensitivity = 0.6, specificity = 0.69).

We identify echogenicity cutoff values that correlate with an increased risk of revision surgery for ASD. Higher dermal US echogenicity may reflect alterations in collagen, contributing to poorer tissue quality. These findings support the use of dermal US parameters as a potential biomarker for high-risk lumbar fusion patients.