Surgical approach options
The choice of surgical approach depends on the specific clinical task, the patient's anatomical features, and the planned scope of intervention, such as in the correction of scoliotic deformities.
- Anterior approach. A classic example of use is anterior lumbar interbody fusion (ALIF).
- Posterior approach. The most common option. Used to perform canal decompression, foraminotomy, and discectomy. Interspinous spacers and fixation elements (pedicle, transfacet, or translaminar screws) are inserted through this approach. It is also required for posterior (PLIF) and transforaminal (TLIF) lumbar interbody fusion.
- Combined approach (360° fusion). Includes a combination of anterior fusion and robust posterior stabilization.
Imaging evaluation of the postoperative spine
A complex of imaging examinations is used to monitor the condition of structures and hardware (hardware).
1. Radiography A basic, fast, and inexpensive method. Performed in anteroposterior and lateral projections. The main advantage is the ability to acquire images in a vertical position, i.e., under physiological load. The method is excellent for detecting breakage, loosening, or migration of elements. To screen for instability or pseudoarthrosis within the bone block (fusion) zone, radiographs are supplemented with functional tests (flexion and extension).
2. Computed tomography (CT) Ideal for precise spatial evaluation of screw position, spinal axis, and bone healing quality. Titanium alloys are preferable to steel alloys because they produce fewer beam hardening artifacts (beam hardening artefacts). How to reduce artifacts on CT: use helical scanning with a low pitch (pitch), thin slices, high tube voltage, and narrow collimation. Important: for reconstruction, it is better to use a standard or smoothing kernel (kernel), as a bone kernel will only increase noise. Averaged intensity projection (AIP) is useful.
3. Magnetic resonance imaging (MRI) The gold standard for examining soft tissues, nerves, and searching for non-iron-related complications. Important to keep in mind: the presence of spinal implants is not a contraindication to MRI. How to reduce artifacts on MRI: use low-field scanners, small voxel size, short echo time (TE), and high receiver bandwidth (high receiver bandwidth). It is recommended to replace gradient-echo (gradient-echo) with fast spin-echo (fast spin-echo) and use anteroposterior phase encoding. T1-weighted images (WI) are better suited for assessing bone resection than T2-WI.
Complications: approaches and hardware
Surgical intervention carries risks of iatrogenic injuries. With an anterior cervical approach, recurrent laryngeal nerve palsy is possible due to retraction or accidental transection. A rare but catastrophic outcome is vertebral artery injury. The most formidable complication is spinal cord injury, which most often occurs not from direct impact, but as a result of intraoperative hypotension or incorrect patient positioning.
Excessive screw length or aberrant trajectory can damage visceral structures: esophagus, trachea, aorta, pleura, thoracic duct, or bowel.
Special attention is paid to pedicle screws. The rate of their misplacement reaches 40%, although clinically significant nerve compression (radiculopathy) occurs in only 7% of cases. An ideal screw should pass strictly within the pedicle (pedicle), be surrounded by cortical bone on all sides, and its tip should reach the anterior cortical margin of the vertebral body without breaching it. Penetration of the screw into the spinal canal or neural foramen (neural foramen) threatens injury to the cauda equina (cauda equina) or nerve roots. CT is the best method to evaluate their position.
Early Postoperative Complications
Typical early complications include infections, cerebrospinal fluid leakage (cerebrospinal fluid leak), and hemorrhage.
Postoperative hematomas occur in less than 1% of patients, but require special attention:
- In the neck: an enlarging hematoma can compress the airways. This is an urgent situation where diagnostic imaging is not needed — the diagnosis is made clinically, and emergency surgical revision is indicated.
- Epidural hematomas: small asymptomatic blood collections occur almost universally upon opening the spinal canal. Symptomatic hematomas requiring evacuation are rare (up to 4.5% in the thoracic spine). When spinal cord compression is suspected, MRI is the method of choice. On T1-WI in the acute phase, the hematoma appears as an iso- or hypointense mass lesion.
Briefly: answers to topical questions
What are the imaging features of epidural hematomas in the acute phase?
In the acute phase, imaging of epidural hematomas is performed using MRI and CT, revealing specific signal and density changes.
- Magnetic resonance imaging is the method of choice for assessing neural structure compression. An epidural mass lesion is visualized, showing an iso- or hypointense signal on T1-WI.
- Computed tomography reveals a convex (biconvex or lens-shaped), well-demarcated area of hyperdense signal.
An arterial hematoma is limited by the dura mater (dura mater) and does not cross cranial sutures. An acute venous hematoma may cross the tentorium cerebelli (tentorium cerebelli) and cranial sutures.
Which anatomical structures can be injured during an aberrant screw trajectory?
Neural and paraspinal visceral structures can be injured in the event of an aberrant screw trajectory or excessive screw length.
- Neural structures — spinal cord, cauda equina (cauda equina), and spinal nerve roots (when screws penetrate the spinal canal or neural foramen — neural foramen).
- Neck and chest organs — trachea, esophagus, lungs, pleura, heart, and thoracic duct.
- Blood vessels — aorta and other major vessels.
- Abdominal and retroperitoneal organs — peritoneum, bowel, and ureter.
Class and exam questions
Is it safe to perform an MRI in a patient with inserted pedicle screws?
Yes, the presence of spinal implants is not a contraindication to MRI. To minimize metal artifacts, the radiologist uses specialized scanning protocols, such as fast spin-echo.
What is the purpose of flexion and extension radiographs?
Functional tests help assess mobility within the fusion zone. They are necessary to identify latent hardware instability or signs of pseudoarthrosis.
Which method most accurately shows whether a screw is correctly placed in the vertebra?
Computed tomography (CT) is considered the best method. It allows a detailed examination of bone structures to ensure that the screw does not extend beyond the cortical layer of the pedicle.
What else to study on this topic
- Technical CT parameter settings for metal artifact suppression (pitch, kernel)
- Optimization of MRI protocols in the presence of steel and titanium implants
- Differential diagnosis of recurrent disc herniation and postoperative edema on MRI
- Visualization of visceral injuries in aberrant trajectories of spinal screws
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