Annegret Mündermann

Purpose: Symptomatic lumbar spinal stenosis (sLSS) is associated with sagittal imbalance and degeneration of paraspinal muscles. While morphological changes are well documented, the functional relationships between electromyographic paraspinal fatigability, endurance, and global imbalance remain unclear. This study aimed to examine these relationships in preoperative patients with sLSS. Methods: In this cross-sectional study, 109 preoperative patients with sLSS underwent magnetic resonance imaging, EOS radiography, and a modified Biering-Sørensen test with bilateral surface electromyography (EMG) of the longissimus, iliocostalis and multifidus muscles. Paraspinal muscle fatigability was defined by three EMG-based indices: slope of median frequency (MDF) decline (Hz/s), normalized slope (%/s), and absolute MDF decrease (Hz). Endurance was defined as the duration of the modified Biering-Sørensen test. Global spinal imbalance was quantified using the Full Balance Integrated (FBI) score. Associations between fatigability, endurance, and FBI were assessed using Pearson correlation and stepwise multiple regression analyses. Results: Valid EMG data were available for 90 of the 109 patients who performed the modified Biering-Sørensen test. Greater absolute MDF decreases (but not MDF slopes) were significantly associated with lower FBI scores ( r = -0.38, p < 0.001). Longer endurance times correlated with both lower FBI scores ( r = -0.41, p < 0.001) and greater absolute MDF decreases ( r = 0.40, p < 0.001). Regression analysis revealed that absolute MDF decrease (β = -0.3, p = 0.004), endurance time (β = -0.1, p = 0.005), and age (β = 0.31, p < 0.001) independently predicted FBI, explaining 35% of its variance. Mediation analysis confirmed that the association between absolute MDF decrease and FBI was predominantly direct (71%) and only partially mediated through endurance time. Conclusion: In preoperative patients with sLSS, both reduced paraspinal endurance and lower absolute MDF decrease were independently associated with greater global spinal imbalance. The association between absolute MDF decrease and imbalance was only partially mediated through endurance time, indicating that these two measures capture complementary aspects of paraspinal muscle function. Since lower absolute MDF decrease coincided with shorter endurance times, reduced electromyographic fatigability in this population likely reflects diminished physiological reserve rather than enhanced neuromuscular efficiency.

Background: InternalBrace-augmented anterior cruciate ligament repair (ACL-IB) is believed to restore natural knee mechanics. However, there is a dearth of data on in vivo leg biomechanics after ACL-IB and comparability with gold standard surgery. Purposes: To (1) investigate differences in sagittal and frontal landing biomechanics of the legs in patients after ACL-IB (Comparison I) and after anterior cruciate ligament reconstruction (ACLR; Comparison II), compare the involved legs with controls (Comparison III), and (2) identify leg differences that were greater than those typically observed in controls. Study Design: Cross-sectional study, Level of Evidence 3. Methods: A total of 29 patients who had ACL-IB, 27 sex- and age-matched patients who had ACLR, and 29 matched controls were asked to perform single-leg hops (SLH) for maximum forward distance 2 years postoperatively, assessed by marker-based motion analysis. Sagittal (hip, knee, and ankle) and frontal (hip and knee) plane angles and peak moments, joint work contribution, and peak vertical ground-reaction force and loading rates during landing were calculated. Differences between the involved and uninvolved legs in patients (paired t tests) and between the involved legs in patients and the nondominant legs in controls (1-way analysis of variance) were analyzed. To determine whether these differences exceeded the typical variation seen in the control legs, we compared the overlap of the 95% CIs of the differences with the 95% CIs of the within-control differences (the nondominant versus dominant leg). Results: Patients who underwent ACL-IB (ACL-IB group) and ACLR (ACLR group) showed significant differences in their legs’ SLH landing biomechanics. Only leg differences in the ACL-IB group were greater than those in in the control group (no overlap): smaller peak knee flexion angle (leg difference: −8.3° [95% CI, −13 to −3.7]; d = −0.85; P = .001; controls [95% CI, −1.7 to 4.2]) and lower peak knee flexion moment (−0.60 Nm/kg [95% CI, −0.72 to −0.31]; d = −0.72; P < .001; controls [95% CI, −0.06 to 0.35]) in the involved compared with the uninvolved leg; and lower peak knee flexion moment in the involved leg compared with control legs (−0.50 Nm/kg [95% CI, −1 to −0.07]; d = −0.71; P = .020). Conclusion: Persistent differences in SLH landing biomechanics 2 years after ACL surgery suggest that ACL ruptures cause alterations that cannot be restored by augmented repair or reconstruction alone. The greater differences between the legs in the ACL-IB group than those typically seen within controls highlight the need for further research to understand the full potential or limitation of ACL preservation techniques.