Introducing the Paraspinal Muscle Quality (PMQ) Score

STUDY DESIGN: Retrospective cross-sectional study. OBJECTIVE: To analyze the relationship between the novel paraspinal muscle quality (PMQ) score and muscle atrophy parameters, patient demographics, comorbidities, and functional disability. BACKGROUND: Paraspinal muscle atrophy is linked to degenerative spine conditions, chronic back pain, and poor postoperative outcomes. Conventional parameters like fatty infiltration (FI) and functional cross-sectional area (fCSA) fail to account for lean muscle quality. Increased T2 MRI intensity reflects muscle aging and reduced function. The PMQ score, normalizing T2 intensity of lean muscle to cerebrospinal fluid (CSF), is introduced as a novel metric. METHODS: Patients undergoing primary posterior lumbar surgery for degenerative disease (Dec 2014-July 2023) were analyzed. Demographics, comorbidities, and preoperative Oswestry Disability Index (ODI) were collected. FI and fCSA of erector spinae, and multifidus were quantified at the L4 upper endplate on T2-weighted MRIs. The PMQ score was defined as lean muscle-to-CSF intensity ratio. Inter-rater reliability for the PMQ score was assessed (n=46) using intraclass correlation coefficients (ICC). Spearman correlation and proportional odds models adjusted for age, sex, BMI, and FI evaluated associations with the ODI subsection, back pain intensity. RESULTS: Among 463 patients (53.7% female; median age 66 yr; BMI 28.7 kg/m²), PMQ score correlated positively with age, female sex, BMI, ASA score, hypertension, and FI but negatively with vertebral bone mineral density and fCSA. Pain intensity was predicted by the erector spinae (OR: 6.07, 95% CI: 1.16-31.74, P =0.033) and multifidus PMQ scores (OR: 4.88, 95% CI: 1.31-18.20, P =0.019). Inter-rater reliability was high [ICC: 0.867 (95% CI: 0.720-0.932) for erector spinae, 0.874 (95% CI: 0.767-0.931) for multifidus]. CONCLUSION: The PMQ score correlates with patient demographics, comorbidities, muscle atrophy, and back pain. While serving as a muscle aging parameter, it may also enhance clinical assessment by detecting early changes, such as edema and denervation, that are not initially identifiable with FI and fCSA, warranting further study.