The Relationship Between Paraspinal Muscle Atrophy and Degenerative Lumbar Spondylolisthesis at the L4/5 Level

Background/Context Degenerative lumbar spondylolisthesis (DLS) is a prevalent spinal condition that can result in significant disability. DLS is thought to result from a combination of disc and facet joint degeneration, as well as various biological, biomechanical, and behavioral factors. One hypothesis is the progressive degeneration of segmental stabilizers, notably the paraspinal muscles, contributes to a vicious cycle of increasing slippage. Purpose To examine the correlation between paraspinal muscle status on MRI and severity of slippage in patients with symptomatic DLS. Study Design/ setting Retrospective cross-sectional study at an academic tertiary care center. Patient Sample Patients who underwent surgery for DLS at the L4/5 level between 2014-2016 were included. Those with multilevel DLS or insufficient imaging were excluded. Outcome Measures The percentage of relative slippage (RS) at the L4/5 level evaluated on standing lateral radiographs. Muscle morphology measurements including functional cross-sectional area (fCSA), body height normalized functional cross-sectional area (HI) of Psoas, erector spinae (ES) and multifidus muscle (MF) and fatty infiltration (FI) of ES and MF were measured on axial MR. Disc degeneration and facet joint arthritis were classified according to Pfirrmann and Weishaupt, respectively. Methods Descriptive and comparative statistics, univariable and multivariable linear regression models were utilized to examine the associations between RS and muscle parameters, adjusting for confounders sex, age, BMI, segmental degeneration, and back pain severity and symptom duration. Results The study analyzed 138 out of 183 patients screened for eligibility. The median age of all patients was 69.5 years (IQR 62 to 73), average BMI was 29.1 (SD ± 5.1) and average preoperative ODI was 46.4 (SD ± 16.3). Patients with Meyerding-Grade 2 (M2, N=25) exhibited higher Pfirrmann scores, lower MFfCSA and MFHI, and lower BMI, but significantly more fatty infiltration in the MF and ES muscles compared to those with Meyerding Grade 1 (M1). Univariable linear regression showed that each cm2 decrease in MFfCSA was associated with a 0.9%-point increase in RS (95%CI -1.4 to - 0.4, p<0.001), and each cm2/m2 decrease in MFHI was associated with an increase in slippage by 2.2%-points (95%CI -3.7 to -0.7, p=0.004). Each 1%-point rise in ESFI and MFFI corresponded to 0.17%- (95%CI 0.05 - 0.3, p=0.01) and 0.20%-point (95%CI 0.1 – 0.3 p<0.001) increases in relative slippage, respectively. Notably, after adjusting for confounders, each cm2 increase in PsoasfCSA and cm2/m2 in PsoasHI was associated with an increase in relative slippage by 0.3% (95%CI 0.1 - 0.6, p = 0.004) and 1.1%-points (95%CI 0.4 -1.7, p= 0.001). While MFfCSA tended to be negatively associated with slippage, this did not reach statistical significance (p = 0.105). However, each 1%-point increase in MFFI and ESFI corresponded to increases of 0.15% points (95%CI 0.05 – 0.24, p= 0.002) and 0.14% points (95%CI 0.01 - 0.27, p= 0.03) in relative slippage, respectively. Conclusion This study found a significant association between paraspinal muscle status and severity of slippage in DLS. Whereas, higher degeneration of the ES and MF correlate with a higher degree of slippage, the opposite was found for the psoas. These findings suggest that progressive muscular imbalance between posterior and anterior paraspinal muscles could contribute to the progression of slippage in DLS.