Clinicoradiological Comparison of Sagittal versus Parasagittal placement of cage in patient undergoing Open or Endoscopic Transforaminal lumbar interbody fusion (TLIF) surgery: A Randomized control trial

Transforaminal Lumbar Interbody Fusion (TLIF) is indicated in a variety of spinal conditions such as disc herniation, degenerative disc disease, and spondylolisthesis which leads to facetal instability. TLIF creates a solid bone between neighboring vertebra and eliminates abnormal movement between them hence it is widely used for stabilization, fusion and treatment of degenerative lumbar disease following failed conservative treatment. While cages are commonly used for intervertebral fusion in TLIF providing mechanical support for the anterior column. These cages aid in the restoration of lumbar lordosis by maintaining the height of the intervertebral space and enhancing sagittal alignment. This results in the restoration of disc height and indirect decompression of the neuroforamen. Good clinical results and fusion rates were documented in earlier research after TLIF using cages. However, there may be some adverse consequences if a single cage is implanted on one side. In summary of the paper published by Quigley et al in 2008 on a synthetic spine model, under axial loading circumstances, Leopard carbon-fiber interbody cages positioned laterally exhibit more strain upon posterior instrumentation and a quicker load to failure than cages more centrally located.1 Cage position and cage subsidence were found to be associated by Abbushi et al., who compartmentalized vertebrae into postero-lateral, medio-lateral, antero-lateral, postero-medial, medio- medial, or antero-medial for placement of cages.2 The medio-medial cage position showed the highest cage migration, followed by the postero-lateral and postero-medial cage position. There was roughly 5 percentage of cage subsidence of >3mm which was observed to be higher in medial than lateral position of cage. The main reason for the same is end plate erosion while preparing the disc and weaker cancellous bone in the central part of the vertebrae. According to anatomical research, the vertebral endplate thickens and becomes denser as it moves towards the periphery. An endplate’s postero-lateral portion is its strongest section, while its centre is its weakest, according to biomechanical and anatomical data. Studies using cadavers provided proof of this theory. Labrom et al. demonstrated that greater construct stiffness was achieved by two smaller titanium mesh cages positioned postero-laterally in a cadaver spine as opposed to centrally located interbody cages.3 This goes in contrast with Comer et al who concluded in a cadaveric model constructs with lateral cage placement showed comparable stiffness to centrally positioned ones in flexion, extension, lateral bending, and torsion, but having much less stiffness under compression. It follows that the coronal location of the cage is thought to have less of an effect on Posterior cage migration.4 However there has been no published data of a prospective study which compare clinico-radiological outcome of sagittal and parasagittal placement of cage with Bilateral posterior instrumentation. With the advent of UBE(Unilateral Biportal endoscopic spine surgeries) which further necessitates to further study the fusion rates and biomechanical difference among the two groups. UBE with its advantage of placement of cage under vision allow us less play and limits the surgeon in sagittal placement of the cage. The study aims to conclude the differences between the cage position and possible complications which could occur through a RCT