Oblique lumbar interbody fusion (OLIF) has been driven to the maturity stage in recent years. However, postoperative symptoms such as thigh paresthesia resulting from intraoperative retraction of the psoas major (PM) have sometimes occurred. The aim of this study was to assess the different positions and morphology of PM muscles and their relationship with clinical outcomes after OLIF by introducing the Moro zones. Patients who underwent L4-5 OLIF at our institution between April 2019 and June 2021 were reviewed and all data were recorded. All patients were grouped by Moro zones into a Moro A cohort and a Moro I and II cohort based on the front edges of their left PM muscles. A total of 94 patients were recruited, including 57 in the Moro A group and 37 in the Moro I and II group. Postoperative thigh pain or numbness occurred in 12 (21.1%) and 2 (5.4%) patients in the Moro A group and the Moro I and II group, respectively. There was no difference in the psoas major transverse diameter (PMTD) between groups preoperatively, while longer PMTD was revealed postoperatively in the Moro A group. The operating window (OW) and psoas major sagittal diameter (PMSD) showed significant differences within and between groups. Thirteen patients had teardrop-shaped PM muscles, with 92.3% in the Moro A group showing significantly worse clinical scores at 1-week follow-up. The Moro zones of the PM affected the short-term outcomes after OLIF. Preoperative measurements and analysis of OW, PMSD and PM morphology should be performed as necessary to predict short-term outcomes.

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Background: Adjacent segment disease (ASD) is a well-known complication after interbody fusion. Pedicle screw-rod revision possesses sufficient strength and rigidity. However, is a surgical segment with rigid fixation necessary for ASD reoperation? This study aimed to investigate the biomechanical effect of different instrumentation on lateral lumbar interbody fusion (LLIF) for ASD treatment. Methods: A validated L2~5 finite element (FE) model was modified for simulation. ASD was considered the level cranial to the upper-instrumented segment (L3/4). Bone graft fusion in LLIF with bilateral pedicle screw (BPS) fixation occurred at L4/5. The ASD segment for each group underwent a) LLIF + posterior extension of BPS, b) PLIF + posterior extension of BPS, c) LLIF + lateral screw, and d) stand-alone LLIF. The L3/4 range of motion (ROM), interbody cage stress and strain, screw-bone interface stress, cage-endplate interface stress, and L2/3 nucleus pulposus of intradiscal pressure (NP-IDP) analysis were calculated for comparisons among the four models. Results: All reconstructive models displayed decreased motion at L3/4. Under each loading condition, the difference was not significant between models a and b, which provided the maximum ROM reduction (73.8% to 97.7% and 68.3% to 98.4%, respectively). Model c also provided a significant ROM reduction (64.9% to 77.5%). Model d provided a minimal restriction of the ROM (18.3% to 90.1%), which exceeded that of model a by 13.1 times for flexion-extension, 10.3 times for lateral bending and 4.8 times for rotation. Model b generated greater cage stress than other models, particularly for flexion. The maximum displacement of the cage and the peak stress of the cage-endplate interface were found to be the highest in model d under all loading conditions. For the screw-bone interface, the stress was much greater with lateral instrumentation than with posterior instrumentation. Conclusions: Stand-alone LLIF is likely to have limited stability, particularly for lateral bending and axial rotation. Posterior extension of BPS can provide reliable stability and excellent protective effects on instrumentation and endplates. However, LLIF with the use of an in situ screw may be an alternative for ASD reoperation.

ObjectsOblique lumbar interbody fusion (OLIF) has gained increasing popularity recently. However, complications resulting from intraoperative retraction of psoas major (PM) sometimes occur. The aim of this study is to evaluate the degree of PM swelling by developing a scoring system called the Psoas Major Swelling Grade (PMSG), and to investigate the correlation between the PMSG and clinical outcomes after OLIF.MethodsPatients who underwent L4‐5 OLIF at our hospital from May 2019 to May 2021 were reviewed and all data were recorded. The extent of postoperative PM swelling was determined by calculating the percentage of change in the PM area before and after surgery on MRI and divided into three grades subsequently. Swelling within the range of 0% to 25% was defined as grade I, 25%–50% was grade II, and more than 50% was grade III. All patients were grouped into the new grade system and followed up for at least 1 year, during which the visual analog scale (VAS) and Oswestry disability index (ODI) scores were recorded. Categorical data were analyzed using chi‐square and Fisher's exact tests, while continuous variables were assessed with one‐way ANOVA and paired t‐tests.ResultsEighty‐nine consecutive patients were enrolled in this study, with a mean follow‐up duration of 16.9 months. The proportion of female patients in the PMSG I, II, and III groups was 57.1%, 58.3%, and 84.1%, respectively (p = 0.024).  Furthermore, the total complication rate was 43.2% in the PMSG III group, significantly higher than 9.5% and 20.8% in the PMSG I and II groups (p = 0.012). The incidence of thigh paraesthesia was also considerably higher in the PMSG III group at 34.1% (p = 0.015), compared to 9.5% and 8.3% in the PMSG I and II groups. Among the patients, 12.4% exhibited a teardrop‐shaped PM, with the majority (90.9%) belonging to the PMSG III group (p = 0.012). Additionally, the PMSG III group demonstrated a higher estimated blood loss (p = 0.007) and significantly worse clinical scores at the 1‐week follow‐up assessment (p < 0.001).ConclusionPM swelling adversely affects the OLIF prognosis. Female patients with teardrop‐shaped PM are more likely to develop swelling after OLIF. A higher PMSG is associated with a higher complication rate of thigh pain or numbness and worse short‐term clinical outcomes.

Background: Foraminoplasty is a critical step in percutaneous endoscopic transforaminal discectomy (PETD) for the treatment of lumbar disc herniation (LDH). It is usually performed using trephine under fluoroscopy guidance and is especially suitable for beginners. However, foraminoplasty with trephine may sometimes leave the cut bone in the body and then even cause neural symptoms. We designed a new tool named anchor drill to assist trephine in performing foraminoplasty. The purpose of this study was to evaluate efficacy and safety for combination of trephine with anchor drill in foraminoplasty.Methods: A retrospective review was performed to identify patients with lumbar disc extrusion or sequestration between January 2018 to January 2021 who underwent PETD. Foraminoplasty using trephine alone or trephine combined with anchor drill under fluoroscopy guidance was performed in all surgeries. Duration of foraminoplasty, endoscopic operation time, fluoroscopy time, bone residual incidence after foraminoplasty and perioperative complications were reviewed. Visual analog scale (VAS) and Japanese Orthopedic Association (JOA) scores were assessed before, 1 day, 3 months and 12 months after surgery for all patients.Results: A total of 100 patients were included (55 in combination group, 45 in trephine group). Bone residual incidence after foraminoplasty of combination group was 9.09%, which was significantly lower than that of trephine group with 33.33% (P＜0.05). Mean endoscopic operation time of combination group was significantly shorter than that of trephine group (P＜0.05). Fluoroscopy time and duration of foraminoplasty showed no significant differences between two cohorts. Total perioperative complication incidence was lower in combination group, among which the neural irritation incidence showed significant difference (combination group: 3.64%, trephine group: 17.78%, P＜0.05). No severe vascular and neurological complications occurred in perioperative period. VAS and JOA scores were compared before and after surgery and differences were statistically significant for all patients (P＜0.001). At each follow-up visit, no significant differences were found in VAS and JOA scores between two cohorts. Conclusions: Combination of trephine with anchor drill was demonstrated to be safe and effective in foraminoplasty in PETD, improving success rate of foraminoplasty and reducing neurological complications relative to using trephine alone.