Abstract and Introduction
Study Design: Systematic review.
Objective: The aim of this study was to review the current spine surgery literature to establish a definition for adequate spine decompression using intraoperative ultrasound (IOUS) imaging.
Summary of Background Data: IOUS remains one of the few imaging modalities that allows spine surgeons to continuously monitor the spinal cord in real-time, while also allowing visualization of surrounding soft tissue anatomy during an operation. Although this has valuable applications for decompression surgery in spinal canal stenosis, it remains unclear how to best characterize adequacy of spinal decompression using IOUS.
Methods: We conducted a systematic search of multiple databases including: Medline, Embase, and Cochrane Central Register of Controlled Trials Strategy. Our search terms were spine, spinal cord diseases, decompression surgery, ultrasonogra-phy, and intraoperative period. We were interested in studies that used intraoperative use of ultrasound imaging in spinal decompression surgery for the cervical, thoracic, and lumbar spine. Study quality was evaluated using the Methodological Index for Non-Randomized Studies (MINORS).
Results: Our search strategy yielded 985 of potentially relevant publications, 776 underwent title and abstract screening, and 31 full-text articles were reviewed. We found IOUS to be useful in spine surgery for decompression of degenerative cases in all regions of the spine. The thoracic spine was unique for IOUS-guided decompression of fractures, and the lumbar spine for decompressing nerve roots. Although we did not identify a universal definition for adequate decompression, there was common description of decompression that qualitatively described the ventral aspect of the spinal cord being "free floating" within the cerebrospinal fluid. Other measurable definitions, such as spinal cord diameter or spinal cord pulsatility, were not good definitions given there was insufficient evidence and/or poor reliability.
Conclusion: The systematic review examines the current literature on IOUS and spinal decompression surgery. We identified a common qualitative definition for adequate decompression involving a "free floating" spinal cord within the cerebrospinal fluid which indicates that the spinal cord is free from contact of the anterior elements.
Level of Evidence: 1
Intraoperative ultrasound (IOUS) has been used by spine surgeons since the early 1980s.[1–3] It offers many advantages in providing real-time, dynamic assessments of the spinal cord that can help guide surgical decision-making. Traditionally, its use has been limited to localizing intradural lesions including resection of intramedullary and extramedullary tumors, and drainage of spinal cysts and syringomyelia. Although technological advances have allowed other spinal technologies such as stereotactic neuronavigation systems to become more precise in their anatomic localization, the increased resolution now available to IOUS has similarly expanded its indications. Furthermore, IOUS remains one of the few imaging modalities that allows surgeons to continuously monitor the spinal cord in realtime while also allowing the visualization of surrounding soft tissue and bony anatomy during an operation. This has valuable applications for spinal decompressive surgery.
Compression of the spinal cord due to trauma, degeneration, infection or tumor can lead to progressive neurological symptoms including pain, paresthesia, weakness, and loss of bowel and bladder function and paralysis. Surgery is the mainstay for most types of spinal compression and involves decompressing structures around the spinal cord; such as bony fragments associated with fractures, disc herniation, or metastatic epidural cord compression. During these surgeries, a laminectomy is frequently performed for improved exposure of the operative field, and for decom-pression. This creates an "interlaminar window" that is convenient for placement of an ultrasound (US) probe in the operative field. One of the challenges encountered in this technique can be creating a sufficient interlaminar window due to bone hypertrophy secondary to degenerative diseases. IOUS can then be used to determine if there is adequate decompression has been performed around the dural sac or spinal cord.[4,5]
Historically, numerous definitions of what constitutes an adequate decompression of the spinal cord can be found. The most common definition is obtained by be qualitatively using IOUS to look for the presence or absence of spinal cord floating relative to the anterior elements of the spinal canal.[8–10] Alternatively, spinal cord morphology can also be quantified by measuring spinal cord diameter and cross-sectional area. Operational definitions, such as compression ratio (sagittal diameter/transverse diameter spinal cord), have been derived to objectively compare the cord diameter before and after decompression. Despite having numerous definitions, to date, it remains unclear how to best characterize adequacy of spinal decompression using IOUS. Moreover, we still do not fully understand the clinical relevance of these different definitions and how they may predict clinical outcomes.
The purpose of our study was to perform a comprehensive systematic review of the current literature on IOUS and spinal decompression surgery for the cervical, thoracic, and lumbar spine. Our primary goal is to establish a robust operational definition of what is considered adequate decompression of the spine via IOUS for surgeons to help guide surgical decision-making during operations. Secondarily, we were also interested in understanding if adequate decompression as measured by IOUS correlates with clinical outcomes.
Spine. 2022;47(2):E73-E85. © 2022 Lippincott Williams & Wilkins