Spinal Fusion: Role of Perioperative Radiography

Key topics covered include:

The use of imaging techniques before and after surgery.
A checklist-based approach to evaluating radiographs.
The interpretation of cortical lines, vertebral body height, disk spaces, facet joints, and spinal alignment.
The nomenclature and types of surgical hardware used in spinal fusion.
Identification and management of early and late postoperative complications through imaging.
The presentation underscores the critical role radiography plays in ensuring successful outcomes in spinal fusion procedures, offering insights into best practices for healthcare professionals involved in the care of these patients.

1. Spinal Fusion: Role of Perioperative Radiography Dr. Muhammad Rafay Resident Diagnostic Radiology Aga Khan University Hospital

2. Disclosure No financial interest or conflict of interest with the presented material in this presentation.

3. Learning Objectives Discuss the preoperative and postoperative roles of imaging in patients who have undergone cervical spinal fusion, with an emphasis on radiography. Describe the indications, techniques, and nomenclature for different types of cervical spine fusions. Apply a checklist approach to reviewing radiographs, emphasizing expected findings based on when they were obtained (preoperative, early postoperative, and late postoperative).

4. Preoperative Role of Imaging Preoperative Checklist Cortical Lines Vertebral Bodies Disk Spaces and Facet Joints Alignment Postoperative Role of Imaging Postoperative Checklist Early Complications (<3 months) Late Complications (>3 months) Operative Nomenclature Bone Graft Interbody Cages Cages with Integrated Fixation Plates Screws, Tulips, and Rods Disk Arthroplasty Table of Contents

5. Preoperative Checklist Checklist Potential Findings Assess the cortical lines. Disruption of a cortical line can be seen with an underlying fracture, infection, or neoplasm. Assess vertebral body height. Loss of vertebral body height (>20%) indicates a fracture. If possible, acute fractures should be differentiated from more chronic fractures. Assess disk spaces and facet joints. Endplate osteophytes, loss of disk space, and facet joint narrowing can be used to grade the degree of degenerative changes. Infection should be considered in cases of disk space loss and endplate erosions. Assess alignment . Disruption of the spinal lines may indicate acute fracture or subluxation in the proper clinical setting. Degenerative spondylolisthesis may be present in the cervical, thoracic, and lumbar spine. Changes in alignment with functional radiography can be used to assess instability. Exclude other causes of pain. Tumor, infection, or pneumothorax may be present in the upper chest. Degenerative changes in the hips, sacroiliac joints, and pubic symphysis should be noted. Calcifications representing nephrolithiasis in the abdomen or pelvis may be a source of pain depending on their location.

6. Cortical Lines: Osseous Anatomy on the Lateral View Cervical spine: vertebral body , pedicle , lateral mass/facet , lamina , and spinous process .

7. Cortical Lines: Osseous Anatomy on the Anteroposterior (AP) View Cervical Spine: vertebral body , uncinate process , and spinous process . The uncinate process extends from the superolateral margins of the C3-C7 bodies. The uncinate processes articulate with the adjacent superior vertebral body to form the uncovertebral joint .

8. Vertebral Bodies: Height Loss To exclude a fracture, the endplates should be flat and parallel (white lines). The vertebral body heights should be consistent throughout the spine. Loss of height that exceeds 20% in the anterior , middle , or posterior dimension of the vertebral body indicates a compression fracture. 1 Biconcave Crush Wedge Acute Acute Chronic Determining the age of a vertebral body compression fracture can be challenging and often requires advanced imaging. A sharp, buckle of the anterior cortex and compressive medullary sclerosis are acute findings on radiographs. Chronic fractures have a smooth, remodeled contour.

9. Disk Spaces and Facet Joints: Degenerative Changes The disk spaces (ovals) should be uniform throughout the spine. The facet joints are formed by the superior and inferior articular processes. Mild Moderate Severe In the absence of infection, loss of disk space (ovals) typically implies degenerative disk disease, which may be mild, moderate, or severe. Sclerosis (bold lines) along the facets indicates degenerative change. Degenerative disk disease and facet hypertrophy frequently coexist.

10. If there is loss of disk space height or facet joint narrowing, a segmentation anomaly should be considered. The vertebral bodies and/or posterior elements can be involved to varying extents. Disk Spaces and Facet Joints: Segmentation Anomalies

11. Alignment: Normal Lines on the AP View Cervical Spine: lateral margin of vertebral bodies , lateral margin of articular pillars , and interspinous distance (dots) . The articular pillars are the columns formed by the superior and inferior articular processes. Spinous processes should align ( dashed line ) to exclude a rotational injury or deformity.

12. Alignment: anterior spinal line , posterior spinal line , spinolaminar line , interspinous distance (dots), retrotracheal line , and retropharyngeal line . All the spinal lines should be smooth. Disruption of these lines could indicate fracture or instability (traumatic or degenerative). Splaying suggests ligamentous injury in trauma. C7 T1 The lateral view is the most important for alignment, and the level of C7-T1 should always be visualized. C6 C5 C4 C3 C2 C1 Alignment: Normal Lines on the Lateral View

13. C3-7: Lines Five lines to evaluate: Prevertebral soft tissues: May become thickened with trauma, infection, or mass lesion Retropharyngeal: Normal at C3 < 4 mm, > 7 mm abnormal or > 1/3 vertebral width When > 7 mm, prediction of upper cervical spine injury sensitivity = 45%, specificity = 83% 1 When >1/3 vertebral width, prediction sensitivity = ~50%, specificity = ~80% 1 Retrotracheal: Abnormal > 18 mm at C7 (> 14 mm in kids) or > 90% of vertebral width When > 18mm, prediction of lower spine injury sensitivity = 35%, specificity=88% 1 When > 90% vertebral width, prediction sensitivity = 22%, specificity = ~88% 1 Anterior vertebral line (ALL) Posterior vertebral (George’s) line (PLL) Spinolaminar line (ligamentum flavum) Tips of Spinous Processes All lines should be smooth Disruption indicates fracture, dislocation, or subluxation

14. Spondylolisthesis can be degenerative or traumatic. The shape and position of the facets should be assessed. With trauma, there is an acute change in position of the facets. Their shape, however, may remain normal. Traumatic anterolisthesis with bilateral jumped facets. The inferior articular facets move anterior to the superior articular facets , which can occur unilaterally or bilaterally. CT image in the same patient. The facets are often widened, and/or fractured (arrow) with traumatic spondylolisthesis. The shape of the facets remains normal, which is not the case with degenerative slippage. Alignment: Traumatic Spondylolisthesis

15. In almost all cases, anterior or posterior slippage occurs at a level with facet disease. The facet joints narrow, leading to bone-on-bone contact. The facet surfaces will change shape to a more ribbonlike configuration, 2 and there will be more laxity at that level. A common pattern of adjacent level spondylolisthesis occurs in the cervical spine. Degenerative disk disease occurs at a level that forms a fixed segment of the spine. There can be anterior slippage at the adjacent level, despite less disk disease at that level. 3 Degenerative anterolisthesis of C3 on C4 and C4 on C5. The degenerative disk disease is mild at these levels compared to that at C5-6. There is facet disease at C3-4, C4-5, and C5-6. Disk space loss leads to osteophyte formation (arrow), which helps to “fix” the spine at this level. C5 C4 C3 C6 Alignment: Degenerative Spondylolisthesis

16. Alignment: Spondylolisthesis Anterolisthesis and retrolisthesis can be measured in millimeters on lateral radiographs based on the superior vertebral body with respect to the inferior vertebral body. Both anterolisthesis and retrolisthesis are typically measured in the cervical spine. Retrolisthesis is measured in the lumbar spine.

17. Alignment: Instability Sagittal translation can be measured as previously described. Sagittal rotation can be measured by the angle between the inferior endplate of the cranial vertebral body compared to the superior endplate of the more caudal vertebral body. If the apex points posteriorly, the angle is positive.

18. Preoperative Role of Imaging Preoperative Checklist Cortical Lines Vertebral Bodies Disk Spaces and Facet Joints Alignment Postoperative Role of Imaging Postoperative Checklist Early Complications (<3 months) Late Complications (>3 months) Operative Nomenclature Bone Graft Interbody Cages Cages with Integrated Fixation Plates Screws, Tulips, and Rods Disk Arthroplasty Table of Contents

19. Nomenclature Term Bone graft Interbody cages Cages with integrated fixation Plates Screws, tulips, and rods Intervertebral disk replacements

20. Bone Graft To promote osseous fusion, bone graft can be placed within cages or within facets (arrows). The bone graft may be autograft from the same patient or allograft from a cadaver. Osteoinductive materials, including demineralized bone matrices or bone morphogenic proteins, can also be used. 5 Bone Graft

21. Bone Graft (Continued) Lateral radiograph shows bone graft placed around the facets and posterior fixation hardware. CT image from the same patient (3 months after the procedure) shows the bone graft more clearly. Again, the graft has the same attenuation as that of adjacent bone. Lateral radiograph shows mature osseous fusion at the levels of C5-6 and C6-7 at 12 months after surgery. CT image from the same patient shows osseous bridging at the levels of C5-6 and C6-7. The graft should have the same attenuation as bone on radiographs and CT images.

22. Lateral radiograph shows a carbon fiber interbody cage at C4-5. Because carbon fiber and PEEK cages are radiolucent, osseous integration across the cage is easier to visualize. The three radiopaque beads (two anterior, one posterior) at the edges of the cage can be used to ensure proper positioning. Interbody Cages: Materials Lateral radiograph shows a PEEK interbody cage at C5-6. PEEK cages have an elastic modulus close to bone that helps eliminate stress shielding. This image was obtained 1 month after surgery with no osseous bridging . Posterior radiopaque markers should be at least 2 mm from the posterior margin of the vertebral body. 6 Cages are manufactured from various materials, including carbon fiber polymers, polyetheretherketone (PEEK), and titanium. Currently, the most common cages are PEEK and titanium. With nanotechnology, the surface of titanium cages can be roughened to promote osseous integration. 7 There may be stable osseous integration without complete osseous bridging across the cage . Titanium Cage

23. Plates Following cage placement (arrow), plates can be placed in the cervical, thoracic, or lumbar spine in an anterior, anterolateral, or lateral position. They typically span two or more vertebral bodies. They help maintain the disk space, decrease subsidence, and increase fusion rates. 8 Anteroposterior and lateral radiographs at 2 months after surgery show an ACDF at C5-7 with interbody cages at both levels and an anterior plate that spans C5-7. There is incomplete osseous bridging across the spacers. The plate helps maintain disk height and normal lordotic curvature while osseous fusion is occurring. C6 C5 C7 Sagittal CT image from the same patient obtained 10 years later (for a trauma workup) shows no hardware complications with mature osseous fusion at C5-6 and C6-7 . C6 C5 C7

24. Screws, Tulips, and Rods Screw and plate combinations are typically used with an ACDF. Posteriorly, screws with a tulip at the head can be used to support a rod. An interlocking nut helps hold the rod in place. Radiologists should be familiar with these different components, which can loosen and migrate in the soft tissues. Tulip Rod Interlocking Nut Sagittal CT image shows a corpectomy at C5 with anterior plate and screw fixation at C4 through C6. A second sagittal CT image from the same patient shows posterior rod and screw fixation. The pedicle screws at C7 and T1 are directed inferomedially, and the lateral mass screws at C3 through C6 have a superolateral orientation to avoid the vertebral artery. C5 Volume-rendered CT images from the same patient further illustrate the hardware, including screw orientation. The lateral mass screws are directed in the superolateral direction, and the pedicle screws are directed inferomedially down the pedicle. Lateral View Frontal View Screw and Plate

25. Postoperative Checklist Checklist Potential Findings All Cases Assess the cortical lines. Disruption of a cortical line can be seen with an underlying fracture or infection. Assess vertebral body height. Loss of vertebral body height (>20%) indicates a fracture. If possible, acute fractures should be differentiated from more chronic fractures. Assess alignment. Disruption of the spinal lines may indicate acute fracture or subluxation. <3 Months Assess hardware. Assess for hardware migration and cage subsidence. Confirm that the level of surgery corresponds to level of the pathologic finding on preoperative workup. Assess retrotracheal and retropharyngeal lines. Prevertebral edema of 6 mm or greater at C2 and 22 mm or greater at C6​ are considered abnormal. >3 Months Assess ossification spanning the disk space. Absence of any osseous bridging with a persistent radiolucent gap are concerning for a pseudoarthrosis. Assess motion between the spinous processes. Motion >1 mm suggests a pseudoarthrosis. Assess the adjacent level disk spaces. Adjacent segment degenerative disk disease is common after fusion. Assess hardware. Delayed loose or fractured hardware suggests a pseudoarthrosis.

26. Early Complications: Hardware Migration (Cervical) Lateral radiograph on the day of surgery shows ACDF at C3 through C6 with anterior plate and screw fixation and corpectomy at C4. C3 C4 C5 C6 Postoperative day 1 shows the hardware better. There is slight anterior migration of the distal half of the plate and screws with respect to the C5-6 interbody graft. Postoperative day 5 shows further anterior migration of the distal half of the plate and screws with respect to the C5-6 interbody graft. There is minimal intraosseous purchase of the C5 and C6 screws. There is also anterior angulation and migration of the C3-5 interbody strut graft.

27. Lateral radiograph of the cervical spine shows advanced multilevel degenerative disk disease and facet hypertrophy. Anterolisthesis is in a stepwise configuration from C3 through T1. Lateral radiograph, immediately after surgery, shows ACDF at C5 through C7 with anterior plate and screw fixation and interbody spacers. The anterolisthesis is improved with 4 mm of persistent anterolisthesis of C4 on C5. Lateral radiograph shows subsidence of the C5-6 cage into the inferior endplate of C5. The superior margin of the anterior plate now abuts the inferior surface of C4. There is subsidence of the C6-7 cage into the superior endplate of C7. The inferior aspect of the plate and the screws at C7 have migrated inferiorly into the inferior half of the vertebral body. Early Complications: Subsidence (Cervical) C3 C4 C5 C6 C7 C2 C4 C5 C6 C7 T1 C4 C5 C6 C7

28. Early Complications: Prevertebral Edema Lateral radiograph obtained 4 days after ACDF at C4 through C6 with plate and screw fixation and cages at C4-5 and C5-6. The patient reported “neck swelling and painful swallowing.” There is 14 mm prevertebral soft-tissue swelling at C2 and 24 mm of prevertebral soft-tissue swelling at C6 (normal values are 6 mm and 22 mm, respectively). The radiologist communicated these findings to the neurosurgeon who reported no clinical signs of infection. The patient was started on steroid dose pack. C4 C5 C6 C2 Lateral radiograph obtained 1 month later shows a decrease in the prevertebral soft-tissue swelling. The patient is also asymptomatic at this time. In the interval, there has been approximately 4 mm of retraction of one of the screws at C6 . Screw loosening and migration in the early postoperative stage can be seen in patients with poor bone quality and/or if there was difficulty placing the hardware at surgery. Inflammation around the screw may have contributed to the prevertebral edema.

29. Late Complications: Pseudoarthrosis (Cervical) Lateral radiograph 2 years after surgery shows late hardware complications, including fractures of the bilateral C7 pedicle screws and loosening of the screws at C3, as evidenced by periscrew lucency (halo). If the spinous processes are absent to assess splaying, late hardware complications will be another sign of a pseudoarthrosis. A CT image was obtained to assess for pseudoarthrosis and characterize the hardware complications. There was complete osseous fusion across the facets at C4-5 and partial osseous fusion at C5-6 . There was no fusion at C3-4 and C6-7 . The screw fracture at C7 is again noted.

30. Sagittal T1-weighted MR image shows low-signal-intensity marrow centered at C5. Edema-like signal confirmed in the marrow with fluid-sensitive sequences (not shown). This combination of findings suggests acute osteomyelitis, given the clinical picture. Sagittal CT image shows osseous erosions and confirms the anterior migration of the hardware away from the vertebral bodies. Lateral radiograph obtained approximately 1 year after ACDF at C4-5 and PCF at C3 through C6. The anterior plate and screws have migrated anteriorly , and the screws no longer have purchase in the vertebral bodies. The C5 vertebral body is sclerotic with loss of height anteriorly, leading to kyphosis and anterolisthesis of C4 on C5. The C6 lateral mass screws are retracted posteriorly . Clinically, there is a concern for infection. C4 C5 C6 Late Complications: Hardware Failure, Infection Sagittal MRI Sagittal CT C5

31. Late Complications: Adjacent Level Disease, Fracture Lateral radiograph obtained many years after an ACDF at C4 through C6 with mature osseous fusion across the cages at C4-5 and C5-6. There is advanced degenerative disease at the adjacent C3-4 and C6-7 levels, including bulky osteophytes with mass effect on the posterior pharynx at the C3-4 level. C4 C5 C6 C3

32. Cervical spinal fusion relies heavily on imaging, particularly radiography, for successful patient outcomes. Radiographs provide a roadmap preoperatively, a baseline postoperatively, and a tool to monitor healing and identify complications throughout the process. Understanding the different types of cervical fusions, their imaging appearances at various stages, and a systematic approach to reviewing radiographs empowers healthcare professionals to optimize patient care Take Home Message.

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