Predictive factors for radiographic outcomes and cage subsidence after oblique lateral interbody fusion

Abstract

Degenerative disc disease is often associated with low back pain, a common musculoskeletal condition affecting the quality of life of a large population. Lumbar interbody fusion (LIF) is an established surgical procedure to treat various spinal pathologies including degenerative disc disease, spinal deformities, spondylolisthesis, recurrent disc herniation, pseudarthrosis and trauma. In recent years, favorable clinical results of oblique lateral interbody fusion (OLIF) have been reported. However, complications of OLIF including cage subsidence may lead to compromised clinical results, including loss of disc height restoration, altered spinal alignment, recurrent pain, and vertebral body fracture. Identifying predictive factors for cage subsidence in preoperative clinical parameters will allow surgeons to better plan their surgeries. As a bone quality assessment, Hounsfield units (HU) of the endplate is measured from routine computed tomography (CT) scans that are readily available as a part of the preoperative assessments. Despite an increasing body of evidence about the potential risk factors for cage subsidence, the role of Hounsfield Units (HUs) at the endplate remained unclear. Our study showed that low HU value at the ipsilateral epiphyseal ring was an independent risk factor for intraoperative endplate violation with a cut-off value of 326.21 HUs (sensitivity 79.0%, specificity 77.3%). Low HU values at the central endplate had a significant correlation with delayed cage subsidence in stand-alone cases with a cut-off value of 296.42 HUs (sensitivity 76.9%, specificity 76.6%). One of the main surgical goals of indirect decompression is to expand the dural sac cross-sectional area (CSA) of the surgical level by increasing disc height, stretching ligaments, and unbuckling the ligamentum flavum. However, it is not yet clear which risk factors are associated with poor dural sac SCA expansion (CSA expansion<0) after indirect decompression surgery through OLIF. Our study showed that after adjusting for sex, age and body mass index (BMI), smaller disc height restoration and larger intraoperative cage settling were risk factors for poor dural sac CSA expansion. These studies helped identify predictive factors for the radiological outcomes and complications after OLIF surgery, which will help surgeons select appropriate patients and optimize implant-related factors for indirect decompression.