Paraspinal muscle endurance and morphology (PMEM) score: a new method for prediction of postoperative mechanical complications after lumbar fusion.

BACKGROUND CONTEXT: Although the relationships between paraspinal muscles and lumbar degenerative disorders have been acknowledged, paraspinal muscle evaluation has not been incorporated into clinical therapies. PURPOSE: We aimed to establish a novel paraspinal muscle endurance and morphology (PMEM) score to better predict mechanical complications after lumbar fusion. STUDY DESIGN: Prospective cohort study. PATIENT SAMPLE: A total of 212 patients undergoing posterior lumbar interbody fusion with at least 1 year of follow-up were finally included. OUTCOME MEASURES: Mechanical complications including screw loosening, pseudarthrosis and other complications like cage subsidence, and patient-reported outcomes were evaluated at last follow-up. METHODS: The PMEM score comprised 1 functional muscular parameter (the performance time of the endurance test) and 2 imaging muscular parameters (relative functional cross-sectional area [rFCSA] of paraspinal extensor muscles [PEM] and psoas major [PS] on magnetic resonance imaging). The score was established based on a weighted scoring system created by rounding ß regression coefficients to the nearest integer in univariate logistic regression. The diagnostic performance of the PMEM score was determined by binary logistic regression model and receiver operating characteristic (ROC) curve with the area under the curve (AUC). Additionally, pairwise comparisons of ROC curves were conducted to compare the diagnostic performance of the PMEM score with conventional methods based on a single muscular parameter. Moreover, differences of mechanical complications and patient-reported outcomes among the PMEM categories were analyzed using Chi-square test with Bonferroni correction. RESULTS: The PMEM score, calculated by adding the scores for each parameter, ranges from 0 to 5 points. Patients with higher PMEM scores exhibited higher rates of mechanical complications (p<.001). Binary logistic regression revealed that the PMEM score was an independent factor of mechanical complications (p<.001, OR=2.002). Moreover, the AUC of the PMEM score (AUC=0.756) was significantly greater than those of the conventional methods including the endurance test (AUC=0.691, Z=2.036, p<.05), PEM rFCSA (AUC=.690, Z=2.016, p<.05) and PS rFCSA (AUC=0.640, Z=2.771, p<.01). In terms of the PMEM categories, a score of 0-1 was categorized as low-risk muscular state of mechanical complications; 2-3, as moderate; and 4-5, as high-risk state. Moving from the low-risk state to the high-risk state, there was a progressive increase in the rates of mechanical complications (13.8% vs. 32.1% vs. 72.7%; p<.001), and a decrease in the rates of clinically significant improvement of patient-reported outcomes (all p<.05). CONCLUSIONS: The PMEM score might comprehensively evaluate paraspinal muscle degeneration and exhibit greater ability in predicting mechanical complications than the conventional evaluations after lumbar fusion. Surgeons might develop individualized treatment strategy tailored to different muscle degeneration statuses reflected by the PMEM score for decreasing the risk of mechanical complications.

Role of the Paraspinal Muscles in the Sagittal Imbalance Cascade: The Effects of Their Endurance and of Their Morphology on Sagittal Spinopelvic Alignment.

BACKGROUND: The role of paraspinal muscle degeneration in the cascade of sagittal imbalance is still unclear. This study aimed to compare paraspinal muscle degeneration in the 4 stages of sagittal imbalance: sagittal balance (SB), compensated sagittal balance (CSB), decompensated sagittal imbalance (DSI), and sagittal imbalance with failure of pelvic compensation (SI-FPC). In addition, it aimed to compare the effects paraspinal muscle endurance and morphology on sagittal spinopelvic alignment in patients with lumbar spinal stenosis. METHODS: A cross-sectional study of 219 patients hospitalized with lumbar spinal stenosis was performed. The isometric paraspinal extensor endurance test and evaluation of atrophy and fat infiltration of the paraspinal extensor muscles and psoas major on magnetic resonance imaging were performed at baseline. Spinopelvic parameters including lumbar lordosis, pelvic tilt, sacral slope, pelvic incidence, and the sagittal vertical axis were measured. RESULTS: The patients with lumbar spinal stenosis were divided into 67 with SB, 85 with CSB, 49 with DSI, and 17 with SI-FPC. There were significant differences in paraspinal muscle endurance and morphology among the 4 groups. Furthermore, the SI-FPC group had poorer paraspinal muscle endurance than either the SB or the CSB group. In multiple linear regression analysis, paraspinal muscle endurance and the relative functional cross-sectional area of the paraspinal extensor muscles were the independent predictors of the sagittal vertical axis, and the relative functional cross-sectional area of the psoas major was the independent predictor of relative pelvic version. CONCLUSIONS: This study indicated that paraspinal muscle degeneration is not only an initiating factor in pelvic retroversion but also a risk factor for progression from a compensated to a decompensated stage. Specifically, the impairment of muscle endurance in the CSB stage may be the reason why patients experience failure of pelvic compensation. In addition, paraspinal muscle endurance and muscle morphology (relative functional cross-sectional area of the paraspinal extensor muscles and psoas major) had different clinical consequences. LEVEL OF EVIDENCE: Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.

Biomechanical Analysis of Lumbar Interbody Fusion Cages With Various Elastic Moduli in Osteoporotic and Non-osteoporotic Lumbar Spine: A Finite Element Analysis.

STUDY DESIGN: Finite element analysis (FEA). OBJECTIVE: This study aimed to explore the effects of cage elastic modulus (Cage-E) on the endplate stress in different bone conditions: osteoporosis (OP) and non-osteoporosis (non-OP). We also explored the correlation between endplate thickness and endplate stress. METHOD: The FEA models of L4-L5 with lumbar interbody fusion were designed to access the effects of Cage-E on the endplate stress in different bone conditions. Two groups of the Young's moduli of bony structure were assigned to simulate the conditions of OP and non-OP, and the bony endplates were analyzed in 2 kinds of thicknesses: .5 mm and 1.0 mm, with the insertion of cages with different Young's moduli including .5, 1.5, 3, 5, 10, and 20 GPa. After model validation, an axial compressive load of 400 N and a flexion/extension moment of 7.5Nm was performed on the superior surface of L4 vertebral body in order to analyze the distribution of stress. RESULT: The maximum Von Mises stress in the endplates increased by up to 100% in the OP model compared with non-OP model under the same condition of cage-E and endplate thickness. In both OP and non-OP models, the maximum endplate stress decreased as the cage-E decreased, but the maximum stress in the lumbar posterior fixation increased as the cage-E decreased. Thinner endplate thickness was associated with increased endplate stress. CONCLUSION: The endplate stress is higher in osteoporotic bone than non-osteoporotic bone, which explains part of the mechanism of OP-related cage subsidence. It is reasonable to reduce the endplate stress by reducing the cage-E, but we should balance the risk of fixation failure. Endplate thickness is also important when evaluating the cage subsidence risk.

Does paraspinal muscle morphometry predict functional status and re-operation after lumbar spinal surgery? A systematic review and meta-analysis.

OBJECTIVES: Whether paraspinal muscle degeneration is related to poor clinical outcomes after lumbar surgery is still indistinct, which limits its clinical application. This study aimed to evaluate the predictive value of paraspinal muscle morphology on functional status and re-operation after lumbar spinal surgery. METHODS: A review of the literature was conducted using a total of 6917 articles identified from a search of PubMed, EMBASE, and Web of Science databases through September 2022. A full-text review of 140 studies was conducted based on criteria including an objective assessment of preoperative paraspinal muscle morphology including multifidus (MF), erector spinae (ES), and psoas major (PS) in addition to measuring its relationship to clinical outcomes including Oswestry disability index (ODI), pain and revision surgery. Meta-analysis was performed when required metrics could be calculated in ≥ three studies, otherwise vote counting model was a good alternative to show the effect direction of evidence. The standardized mean difference (SMD) and 95% confidence interval (CI) were calculated. RESULTS: A total of 10 studies were included in this review. Of them, five studies with required metrics were included in the meta-analysis. The meta-analysis suggested that higher preoperative fat infiltration (FI) of MF could predict higher postoperative ODI scores (SMD = 0.33, 95% CI 0.16-0.50, p = 0.0001). For postoperative pain, MF FI could also be an effective predictor for persistent low back pain after surgery (SMD = 0.17, 95% CI 0.02-0.31, p = 0.03). However, in the vote count model, limited evidence was presented for the prognostic effects of ES and PS on postoperative functional status and symptoms. In terms of revision surgery, there was conflicting evidence that FI of MF and ES could predict the incidence of revision surgery in the vote count model. CONCLUSION: The assessment of MF FI could be a viable method to stratify patients with lumbar surgery by the risk of severe functional disability and low back pain. KEY POINTS: • The fat infiltration of multifidus can predict postoperative functional status and low back pain after lumbar spinal surgery. • The preoperative evaluation of paraspinal muscle morphology is conducive for surgeons.

Clinical and Surgical Characteristics of Patients with Atlantoaxial Dislocation in the Setting of Sandwich Fusion: A Case-Control Analysis of Over 500 Patients with Mid-Term to Long-Term Follow-up.

BACKGROUND: Patients with "sandwich" fusion (concomitant C1 occipitalization and C2-C3 nonsegmentation), a subtype of Klippel-Feil syndrome, are at particular risk for developing atlantoaxial dislocation (AAD). However, the clinical and surgical characteristics of AAD in patients with sandwich fusion have not been clearly defined. METHODS: A retrospective case-control study with a large sample size and a minimum 2-year follow-up was performed. From 2000 to 2018, 253 patients with sandwich AAD underwent a surgical procedure; these patients constituted the case group, and a matching number of patients with non-sandwich AAD were randomly selected to form the control group. Clinical data from electronic medical records and various imaging studies were analyzed and compared. The Japanese Orthopaedic Association (JOA) scale was used to evaluate neurological function. RESULTS: Patients with sandwich AAD, compared with patients with non-sandwich AAD, had symptom onset at a younger age (34.8 compared with 42.8 years; p < 0.001) and had a higher likelihood for myelopathy (87.4% compared with 74.7%; p < 0.001). Patients with sandwich AAD had a higher incidence of lower cranial nerve palsy (7.9% compared with 0.0%; p < 0.001), a lower preoperative JOA score (13.4 compared with 14.2; p < 0.001), and higher incidences of accompanying Type-I Chiari malformation (20.9% compared with 1.2%; p < 0.001) and syringomyelia (21.3% compared with 1.6%; p < 0.001). Finally, patients with sandwich AAD had higher likelihoods of undergoing transoral release (28.5% compared with 5.1%; p < 0.001) and use of salvage fixation techniques (34.4% compared with 6.3%; p < 0.001), and had lower postoperative results for the JOA score (14.9 compared with 15.9; p < 0.001) and improvement rate (43.8% compared with 58.2%; p < 0.001). CONCLUSIONS: Patients with sandwich AAD demonstrated distinct clinical manifestations. Versatility involving the use of various internal fixation techniques and transoral release procedures was frequently required in the surgical management of these patients, and meticulous and personalized preoperative planning would be of paramount importance. LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.