From the Guidelines
Intraoperative assessment of spinal stability after ACDF should include direct visualization, fluoroscopic imaging, provocative testing, and neuromonitoring to determine the need for a 360 fusion. When considering a 360 fusion, it is essential to evaluate spinal stability using multiple complementary techniques. Direct visualization and palpation of the fusion site allow surgeons to manually test for motion between vertebral segments using specialized instruments. Fluoroscopic imaging provides real-time visualization of alignment and hardware placement, while provocative testing involves applying controlled stress to the operated segments to detect any abnormal movement. Neuromonitoring through somatosensory and motor evoked potentials helps assess spinal cord function during these maneuvers. Intraoperative CT scanning, as discussed in the study by 1, offers detailed three-dimensional assessment of the fusion construct and can aid in detecting adjacent segment degeneration. The study highlights the importance of CT scanning in assessing spinal fusion, with multidetector CT scanning being the most sensitive and specific modality for this purpose. Some key points to consider when assessing spinal stability include:
- Bone quality and the number of levels fused, as these factors can impact the stability of the fusion construct
- Patient comorbidities, such as osteoporosis or prior spinal surgery, which can affect bone healing and stability
- The presence of preoperative instability, which may require additional stabilization measures
- The potential risks and benefits of proceeding with a 360 fusion, including the increased surgical morbidity and recovery time associated with posterior instrumentation. These assessment techniques are crucial because unrecognized instability can lead to hardware failure, pseudarthrosis, and poor clinical outcomes, while unnecessary posterior instrumentation increases surgical morbidity and recovery time.
From the Research
Intraoperative Measures to Assess Spinal Stability after ACDF
When considering a 360 fusion after Anterior Cervical Discectomy and Fusion (ACDF), several intraoperative measures can be taken to assess spinal stability. These measures are crucial for determining the need for additional stabilization procedures.
- Multi-channel Motor Evoked Potential (MEP) Monitoring: This technique, as discussed in 2, can be beneficial for detecting segmental injury as well as long tract injury during single- and multi-level ACDF surgery. MEP monitoring has shown higher sensitivity and specificity compared to somatosensory evoked potentials (SSEPs) in detecting potential neurological compromise.
- Intraoperative Radiographic Examinations: Radiographic examinations, including X-rays and computerized tomography (CT) scans, can be used to assess the fusion status and spinal stability. However, as noted in 3, CT scans may overestimate the fusion rate, especially in the early stages of ACDF healing. Therefore, dynamic X-rays, which can show motion between the fused segments, are also valuable.
- Clinical Evaluation: The patient's clinical presentation, including symptoms of instability such as progressive back pain, neurological deficits, or evidence of segmental instability on physical examination, can guide the decision for additional stabilization.
Considerations for 360 Fusion
The decision to proceed with a 360 fusion after ACDF depends on various factors, including the presence of segmental instability, the extent of degenerative changes, and the patient's overall clinical condition. Studies such as 4 highlight the importance of assessing adjacent segment disease and considering the potential for increased mechanical stress at the motion segments adjacent to the fusion.
- Adjacent Segment Disease: The development of adjacent segment disease (ASD) is a significant concern after spinal fusion procedures. ASD can lead to segmental instability, requiring additional surgical intervention. As discussed in 4, a thorough examination of levels adjacent to the planned spinal fusion is crucial to prevent termination of the fusion at a potentially painful segment.
- Surgical Techniques: Different surgical techniques, such as ACDF and anterior cervical corpectomy with fusion (ACCF), have varying effects on spinal stability and fusion rates. For example, 5 compares the clinical effects of ACDF and ACCF in treating two-segment cervical spondylotic myelopathy, highlighting the importance of choosing the appropriate surgical technique based on the patient's specific condition.
Additional Factors Influencing Spinal Stability
Other factors can influence spinal stability after ACDF, including the use of local retropharyngeal steroids. As noted in 6, the use of retropharyngeal steroids to mitigate postoperative dysphagia is associated with a decreased rate of radiographic fusion in ACDF surgery. This highlights the need for careful consideration of all factors that could impact spinal stability and fusion success.