Objective: To investigate the effect of the in situ screw implantation region and angle on the stability of lateral lumbar interbody fusion (LLIF) from a biomechanical perspective.Methods: A validated L2-4 finite element (FE) model was modified for simulation. The L3-4 fused segment undergoing LLIF surgery was modeled. The area between the superior and inferior edges and the anterior and posterior edges of the vertebral body (VB) is divided into four zones by three parallel lines in coronal and horizontal planes. In situ screw implantation methods with different angles based on the three parallel lines in coronal plane were applied in Models A, B, and C (A: parallel to inferior line; B: from inferior line to midline; C: from inferior line to superior line). In addition, four implantation methods with different regions based on the three parallel lines in horizontal plane were simulated as types 1-2, 1-3, 2-2, and 2-3 (1-2: from anterior line to midline; 1-3: from anterior line to posterior line; 2-2: parallel to midline; 2-3: from midline to posterior line). L3-4 ROM, interbody cage stress, screw-bone interface stress, and L4 superior endplate stress were tracked and calculated for comparisons among these models. Results:The L3-4 ROM of Models A, B, and C decreased with the extent ranging from 47.9% (flexion-extension) to 62.4% (lateral bending) with no significant differences under any loading condition. Types 2-2 and 2-3 had 45% restriction, while types 1-2 and 1-3 had 51% restriction in ROM under flexion-extension conditions. Under lateral bending, types 2-2 and 2-3 had 70.6% restriction, while types 1-2 and 1-3 had 61.2% restriction in ROM. Under axial rotation, types 2-2 and 2-3 had 65.2% restriction, while types 1-2 and 1-3 had 59.3% restriction in ROM. The stress of the cage in types 2-2 and 2-3 was approximately 20% lower than that in types 1-2 and 1-3 under all loading conditions in all models. The peak stresses at the screw-bone interface in types 2-2 and 2-3 were much lower (approximately 35%) than those in types 1-2 and 1-3 under lateral bending, while no significant differences were observed under flexion-extension and axial rotation. The peak stress on the L4 superior endplate was approximately 30 MPa and was not significantly different in all models under any loading condition.

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Objective Full endoscopic lumbar interbody fusion (ELIF) is a representative recent emerging minimally invasive operation, and its effectiveness has been continuously proved. This study aimed to evaluate the hidden blood loss in ELIF procedure and its possible risk factors. Methods The blood loss was calculated by Gross formula. Sex, age, BMI, hypertension, diabetes, ASA classification, fusion levels, surgical approach type(the count of trans-Kambin approach and interlaminar approach), surgery time, preoperative RBC, HGB, Hct, PT, INR, APTT, Fg, postoperative mean arterial pressure, postoperative heart rate, Intraoperative blood loss (IBL), patient blood volume were included to investigate the possible risk factors by correlation analysis and multiple linear regression between variables and hidden blood loss. Results 96 patients (23 males, 73 females) who underwent ELIF were retrospective analyzed in this study. The total blood loss was 303.56 (120.49, 518.43) ml(median [interquartile range]), of which the hidden blood loss was 240.11 (65.51, 460.31) ml, accounting for 79.10% of the total blood loss. Multiple linear regression analysis indicated that fusion levels(P = 0.002), age(P = 0.003), hypertension(P = 0.000), IBL(P = 0.012), PT(P = 0.016), preoperative HBG(P = 0.037) were the possible risk factor for HBL. Conclusion The fusion levels, younger age, hypertension, PT, preoperative HBG are possible independent risk factor of HBL during ELIF procedure. In clinic, we should pay attention to the possibility of large perioperative blood loss even in minimally invasive surgery.

In this paper, we consider covering graphs obtained by lifting trees as voltage graphs over cyclic groups. We generalize a tool of Hell, Nishiyama, and Stacho [6], known as the billiard strategy, for constructing Hamiltonian cycles in the covering graphs of paths. We show that our extended tool can be used to provide new sufficient conditions for the Hamiltonicity of covering graphs of trees that are similar to those of Batagelj and Posanski [3] and of Hell, Nishiyama, and Stacho [6]. Next, we focus specifically on covering graphs obtained from trees lifted as voltage graphs over cyclic groups Z p of large prime order p. We prove that for a given reflexive tree T with random nonzero voltage labels from Z p on its edges, the corresponding lift is almost surely Hamiltonian for a large enough prime-orderd cyclic group Z p . Finally, we show that if a reflexive tree T is lifted over a group Z p of a large prime order, then for any assignment of nonzero elements of Z p to the edges of T , the corresponding cover of T has a large circumference.