21. Association between paraspinal muscle quality and surgery for adjacent segment disease

Abstract

BACKGROUND CONTEXT

Adjacent segment disease (ASD) is one of the most common complications after spinal fusion, occurring a rate of approximately 2% a year. Increased loading and mobility at the adjacent segments are theorized mechanisms of ASD. The paraspinal muscles act as dynamic stabilizers of the lumbar spine and recently the suboptimal quality of the musculature such as increased fat infiltration has been implicated as a potential risk factor for ASD and need for subsequent surgery.

PURPOSE

To examine the association between paraspinal muscle degeneration and risk of ASD.

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

Patients undergoing lumbar spinal fusion procedures at a single institution.

OUTCOME MEASURES

Paraspinal muscle fat percentage and circumferential surface area (CSA)

METHODS

We conducted a retrospective comparison of adult spinal fusion patients at our institution from 2009-2022. Comparison cohorts were those with ASD and non-ASD patients age, gender, and BMI matched to the ASD cohort. Inclusion criteria were presurgical MRI that included full paraspinal musculature visualization and a minimum one-year follow-up. We measured paraspinal fat percentage and CSA at L3 and at the proximal end of their future construct. We also measured the CSA of the psoas at L3 and at the proximal end of their future construct. Paraspinal fat percentage and muscle surface area were measured using ImageJ (National Institutes of Health, Bethesda, Maryland, USA). Fat percentage was measured by finding the average of the lowest pixel intensity values of the visceral fat ventral and dorsal to the paraspinal musculature. This value was used as the threshold to differentiate fat from other soft tissues in the paraspinal musculature. We used the paired student T-test to evaluate for statistically significant differences with p-value ≤ 0.05.

RESULTS

A total of 110 patients were reviewed, 55 with adjacent segment failure (experimental cohort) and 55 patients in the control group. There were 30 males and 25 females in each cohort. Average age in the experimental cohort was 61.7 vs 61.8 in the control group. Average BMI was 29.5 in the experimental group vs 29.8 in the control group. Overall, patients who underwent surgery for adjacent segment disease had 32% higher paraspinal fat percentage at L3 (13.7 ± 7.5% vs 10.4 ± 5.8%, p = 0.02). Similarly, patients with adjacent segment failure had 28% higher paraspinal fat percentage at the top end of their construct (15.8 ± 8.9% vs 12.3 ± 6.8%, p = 0.05). While there were no significant differences in psoas CSA at L3, patients without adjacent segment failure had larger psoas CSA at the proximal end of the fusion construct (1168.2 ± 512.1 mm² vs 983.6 ± 418.6 mm², p = 0.03).

CONCLUSIONS

Our study found that patients who undergo surgery for adjacent segment disease have significantly greater fat content in their paraspinal musculature at L3 and at the proximal end of their fusion construct. This is potentially a modifiable risk factor that can be optimized preoperatively to help reduce the risk of requiring a subsequent operation.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.