Finite Element Analysis Comparing the Biomechanical Parameters in Multilevel Posterior Cervical Instrumentation Model Involving Lateral Mass Screw versus Transpedicular Screw Fixation at the C7 Vertebra.

STUDY DESIGN: Basic research. PURPOSE: This finite element (FE) analysis (FEA) aimed to compare the biomechanical parameters in multilevel posterior cervical fixation with the C7 vertebra instrumented by two techniques: lateral mass screw (LMS) vs. transpedicular screw (TPS). OVERVIEW OF LITERATURE: Very few studies have compared the biomechanics of different multilevel posterior cervical fixation constructs. METHODS: Four FE models of multilevel posterior cervical fixation were created and tested by FEA in various permutations and combinations. Generic differences in fixation were determined, and the following parameters were assessed: (1) maximum moment at failure, (2) maximum angulation at failure, (3) maximum stress at failure, (4) point of failure, (5) intervertebral disc stress, and (6) influence of adding a C2 pars screw to the multilevel construct. RESULTS: The maximum moment at failure was higher in the LMS fixation group than in the TPS group. The maximum angulation in flexion allowed by LMS was higher than that by TPS. The maximum strain at failure was higher in the LMS group than in the TPS group. The maximum stress endured before failure was higher in the TPS group than in the LMS group. Intervertebral stress levels at C6-C7 and C7-T1 intervertebral discs were higher in the LMS group than in the TPS group. For both models where C2 fixation was performed, lower von Mises stress was recorded at the C2-C3 intervertebral disc level. CONCLUSIONS: Ending a multilevel posterior cervical fixation construct with TPS fixation rather than LMS fixation at the C7 vertebra provides a stiff and more constrained construct system, with higher stress endurance to compressive force. The constraint and durability of the construct can be further enhanced by adding a C2 pars screw in the fixation system.

A 2-Year Outcomes and Complications of Various Techniques of Lumbar Discectomy: A Multicentric Prospective Study.

STUDY DESIGN: Prospective Study. OBJECTIVES: There are numerous techniques for performing lumbar discectomy, each with its own rationale and stated benefits. The authors set out to evaluate and compare the perioperative variables, results, and complications of each treatment in a group of patients provided by ten hospitals and operated on by experienced surgeons. METHODS: This prospective study comprised of 591 patients operated between February-2017 to February-2019. The procedures included open discectomy, microdiscectomy, tubular microdiscectomy, interlaminar endoscopic lumbar discectomy, transforaminal endoscopic lumbar discectomy and Destandau techniques with a follow-up of minimum 2 years. VAS (Visual Analogue Score) for back and leg pain, ODI (Oswestry Disability Index), duration of surgery, hospital stay, length of scar, operative blood loss and peri-operative complications were recorded in each group. RESULTS: Post-operatively, there was a significant improvement in the VAS score for back pain as well as leg pain, and ODI scores spanning all groups, with no significant distinction amongst them. When compared to open procedures (open discectomy and microdiscectomy), minimally invasive surgeries (tubular discectomy, interlaminar endoscopic lumbar discectomy, transforaminal endoscopic lumbar discectomy, and Destandau techniques) reported shorter operative time, duration of hospital stays, better cosmesis, and lower blood loss. Overall, the complication rate was reported to be 8.62%. Complication rates differed slightly across approaches. CONCLUSION: Minimally invasive surgeries have citable advantages over open approaches in terms of perioperative variables. However, all approaches are successful and provide comparable pain relief with similar functional outcomes at long term follow up.

"Insert flipping technique:" An effective way of restoring segmental lordosis and disc height with tall bullet cages.

Study Design: The study design was a retrospective study. Objective: The objectives of the present study are dual; to describe a simple and effective way of restoring intervertebral disc (IVD) height by the "Insert Flip Technique" of cage insertion and to demonstrate effective restoration of IVD height and segmental lordosis (SL) and their influence on the functional outcome postoperatively. Methods: IVD height and SL were recorded pre- and postoperatively. Each motion segment was instrumented with pedicle screws to allow segmental stabilization. Patients were called for follow-up at 6 weeks, 3 months, and 1 year postoperatively and were assessed clinically for back pain and leg pain (VAS and Oswestry Disability Index scores recorded).The bullet cages are designed such that they are lordotic in the superior-inferior plane and neutral in the mediolateral plane. Usually, the cage is inserted with superior and inferior surfaces of the cage impacting against superior and inferior end plates of the adjacent vertebral body. However, with the proposed technique, the cages were inserted such that the narrower mediolateral surfaces of the cage engaged with superior and inferior vertebral end plates. The cage was then flipped within the disc space such that the superior-inferior surfaces of the bullet cage impacted against the superior and inferior end plates of the vertebral body to create desired lordosis. Results: There was a significant improvement seen in the postoperative Cobb's angle and disc height after placement of a tall bullet cage compared to the preoperative Cobb's angle and disc height. Conclusion: This modification of technique helped in gaining lordosis with taller bullet cages in minimally invasive surgery transforaminal lumbar interbody fusion with no/minimal complication and also reduced the need for bone resection during insertion of the cage.