Reduced physiological extrusion of the medial meniscus in axial load-bearing condition in anterior cruciate ligament deficiency.

PURPOSE: In this study, ultrasonography was used to measure medial meniscus (MM) extrusion under weight-bearing and nonweight-bearing conditions in both anterior cruciate ligament (ACL)-deficient and ACL-intact knee groups. This study aimed to determine the possible differences between these groups with an eventual impact on meniscal tears in ACL-deficient knees. METHODS: A total of 107 patients who underwent ACL reconstructive surgery between June 2022 and April 2023 were enroled. After applying exclusion criteria, 37 patients met the conditions for inclusion in the study and formed the ACL deficiency group (Group D). Of the 141 patients presenting to an outpatient clinic who agreed to have ultrasonography conducted on their nondiscomforting contralateral knee, 37 patients matched for age, sex, hip-knee-ankle angle and body mass index with Group D patients were selected for the ACL intact group (Group I). Ultrasonography was used to measure MM extrusion in weight-bearing and nonweight-bearing conditions for all participants. RESULTS: Seventy-four patients were included in the study (n = 37 per group). The supine position showed an MM extrusion of 1.2 ± 0.7 mm in Group I and 1.2 ± 0.7 mm in Group D (not significant). In the standing position, MM extrusion measured 2.0 ± 0.6 mm in Group I and 1.3 ± 0.8 mm in Group D. The difference in extrusion (Δextrusion) between the two positions was 0.8 ± 0.6 in Group I and 0.1 ± 0.2 in Group D, with statistical significance (p < 0.01). A consistent reduction in MM extrusion during weight-bearing was observed in patients with ACL deficiency, irrespective of the duration of ACL deficiency, age, sex and BMI. CONCLUSION: ACL deficiency did not significantly impact MM extrusion during nonweight-bearing conditions; however, less MM extrusion was observed in response to axial loading conditions. These findings indicate altered MM biomechanics due to increased anterior-posterior meniscal motion and rotational instability after ACL injury. LEVEL OF EVIDENCE: Level III.

Bis[bis(trimethylsilyl)amino]silylene, an unstable divalent silicon compound.

The title compound, [(Me3Si)2N]2Si: (1), was prepared by the reduction of [(Me3Si)2N]2SiBr2 (2) with potassium graphite at -78 degrees C. Unlike the corresponding germanium and tin compounds, 1 is unstable, but it can be studied in solution at low temperatures. The 29Si NMR chemical shift of 1 measured at -20 degrees C was 223.9 ppm, in good agreement with a value obtained from model calculations of 233 ppm. Reaction of solutions of 1 with methanol or phenol gave the trapping products expected for the silylene, [(Me3Si)2N]2Si(H)OR (R = CH3, C6H5).