Defining a safe working zone for lateral lumbar interbody fusion: a radiographic, cross-sectional study
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ORIGINAL ARTICLE
Defining a safe working zone for lateral lumbar interbody fusion: a radiographic, cross‑sectional study Bhavuk Garg1 · Nishank Mehta1 · Vivek Vijayakumar1 · Anupam Gupta1 Received: 7 July 2020 / Revised: 2 September 2020 / Accepted: 30 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose To present a radiographic analysis of the anatomy of the lumbar plexus and retroperitoneal blood vessels with respect to psoas morphology and safe working zones (SWZ) for LLIF. Methods A retrospective radiographic analysis of 158 MRI scans was performed. Selected morphometric measurements were performed at L1–L2, L2–L3, L3–L4 and L4–L5 levels: disc anteroposterior distance, psoas anteroposterior distance, lumbar plexus–anterior disc distance, lumbar plexus–anterior psoas distance, vena cava–anterior disc distance and calculation of SWZ in psoas on both left and right sides. The morphometric measurements were analysed for differences with sex and the level. Results All the morphometric parameters differed significantly at all levels between males and females. The SWZ was significantly wider on the left side compared to the right—at L2–L3, L3–L4 and L4–L5 levels in females and at L3–L4 and L4–L5 levels in males. The SWZ at L4–L5 was narrowest on both left and right sides–and significantly reduced compared to other levels. 6.9% patients had a SWZ > 20 mm on the left side, and 44.9% patients had SWZ 10°), (5) patients who had undergone a prior abdominal/retroperitoneal/spinal surgery and (6) patients with lumbosacral transitional vertebra (LSTV). Relevant clinical details of the recruited patients were recorded. The presence of LSTV was ruled out by studying the AP and lateral radiographs and referring to the radiologists’ report of the MRI where the vertebrae were counted by numbering them from C2 onwards. All MRI scans were studied by 2 independent observers (both orthopaedic surgeons). While all the sequences were studied, the measurements were made on the T2-weighted axial section—in which the psoas margins and the lumbar plexus were best visualized. Prior to studying the MRI scans of the study population, a series of reading sessions were conducted over a period of 1 week in the presence of a musculoskeletal radiologist to ensure that there was clarity and consensus regarding the technique of performing measurements in the MRI images. A series of linear measurements were made on the axial MRI images. These included: the AP disc space diameter (APD), the AP psoas diameter (APP), the lumbar plexus–anterior disc distance (LP–D), the lumbar plexus–anterior psoas distance (LP–PM), the vena cava–anterior disc distance (VC–D) and the safe working zone (SWZ). The SWZ was defined to be the anteroposterior extent of psoas which was anterior to the lumbar plexus, but posterior to the anterior disc margin and/or the retroperitoneal blood vessels. Since accurate wire placement is the primary step for creating a safe passage through the psoas muscle, we also calculated a ‘safe wir
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