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6. Spine MCQs

Practice Set 10 of 379

This practice set contains high-yield board review questions covering key concepts in 6. Spine. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 181

Topic: 6. Spine

A surgeon plans a unilateral MIS TLIF with unilateral percutaneous pedicle screw fixation for a patient with a paracentral disc herniation. Compared to a bilateral pedicle screw construct, the unilateral construct is significantly weaker in resisting which force?

. Axial rotation (torsion)
. Axial compression
. Sagittal flexion
. Sagittal extension
. Lateral bending away from the side of the screws

Correct Answer & Explanation

. Axial rotation (torsion)

Explanation

Biomechanical studies consistently demonstrate that while unilateral pedicle screw fixation provides adequate stability for flexion/extension, it offers significantly less resistance to axial rotation (torsional stability) compared to bilateral constructs.

Question 182

Topic: Thoracolumbar Spine & Deformity

During a minimally invasive TLIF using a tubular retractor system, the initial docking site for the first dilator is typically the:

. Base of the spinous process
. Spinolaminar junction
. Pars interarticularis and facet joint
. Transverse process
. Pedicle base

Correct Answer & Explanation

. Pars interarticularis and facet joint

Explanation

The tubular retractor is typically docked on the pars interarticularis and the ipsilateral facet joint complex. This provides direct access for the facetectomy and subsequent transforaminal approach to the disc space.

Question 183

Topic: 6. Spine

Which of the following approaches utilizes the interval between the multifidus and longissimus muscles?

. Transpsoas lateral approach
. Midline open approach
. Wiltse approach
. Smith-Robinson approach
. Anterior retroperitoneal approach

Correct Answer & Explanation

. Wiltse approach

Explanation

The Wiltse approach is a muscle-splitting paramedian approach utilizing the natural cleavage plane between the multifidus (medially) and longissimus (laterally) muscles. It is widely used in minimally invasive posterior spinal surgeries.

Question 184

Topic: 6. Spine

Which of the following is a recognized absolute contraindication for a transpsoas extreme lateral interbody fusion (XLIF)?

. Previous abdominal surgery
. Grade I degenerative spondylolisthesis
. Pathology at the L5-S1 level
. Body mass index > 35
. Recurrent disc herniation at L4-L5

Correct Answer & Explanation

. Pathology at the L5-S1 level

Explanation

The L5-S1 level is generally a contraindication for the transpsoas lateral approach due to the obstruction by the iliac crest and the anterior position of the lumbar plexus at this level. An anterior (ALIF) or posterior (TLIF/PLIF) approach is preferred for L5-S1.

Question 185

Topic: Thoracolumbar Spine & Deformity

In cortical bone trajectory (CBT) pedicle screws used for minimally invasive fusions, the screw trajectory is typically described as:

. Lateral to medial, cephalad to caudad
. Medial to lateral, caudad to cephalad
. Lateral to medial, parallel to the endplate
. Medial to lateral, cephalad to caudad
. Directly anterior through the pars interarticularis

Correct Answer & Explanation

. Medial to lateral, caudad to cephalad

Explanation

CBT screws are inserted with a medial to lateral and caudad to cephalad trajectory. This maximizes thread purchase in high-density cortical bone, increasing pullout strength, especially in osteoporotic bone.

Question 186

Topic: 6. Spine

A key mechanism by which minimally invasive lateral lumbar interbody fusion (LLIF) achieves indirect decompression of the neural foramina is through:

. Direct resection of the ligamentum flavum
. Restoration of disc height which tensions and unbuckles the ligamentum flavum
. Resection of the superior articular process
. Removal of the posterior longitudinal ligament
. Wide laminectomy performed through the lateral tube

Correct Answer & Explanation

. Restoration of disc height which tensions and unbuckles the ligamentum flavum

Explanation

Indirect decompression in LLIF relies on placing a large interbody graft to restore disc space height. This distracts the neural foramen and tensions the posterior longitudinal ligament and ligamentum flavum, effectively unbuckling them from the spinal canal.

Question 187

Topic: 6. Spine

Review the clinical image.

When performing a percutaneous transforaminal endoscopic discectomy, instruments are passed through Kambin's triangle. Which of the following defines the medial border of Kambin's triangle?

. Exiting nerve root
. Traversing nerve root (or dura)
. Superior endplate of the inferior vertebra
. Inferior articular process
. Pedicle of the superior vertebra

Correct Answer & Explanation

. Traversing nerve root (or dura)

Explanation

Kambin's triangle is a safe working zone for transforaminal endoscopic access. Its hypotenuse is the exiting nerve root, the base is the superior endplate of the inferior vertebral body, and the medial border (or height) is the traversing nerve root/dura.

Question 188

Topic: 6. Spine

The use of continuous free-running electromyography (EMG) is considered standard of care in the transpsoas lateral lumbar approach to avoid injury to which structure?

. Sympathetic trunk
. Cauda equina
. Lumbar plexus
. Superior hypogastric plexus
. Conus medullaris

Correct Answer & Explanation

. Lumbar plexus

Explanation

Directional EMG monitoring is critical during the transpsoas approach to map the lumbar plexus within the psoas muscle. It helps the surgeon identify the safe zone (usually the anterior third of the psoas) to place the retractor.

Question 189

Topic: Thoracolumbar Spine & Deformity

A major disadvantage of the minimally invasive posterior lumbar interbody fusion (MIS PLIF) approach compared to MIS TLIF is:

. Lower fusion rates
. Inability to perform bilateral decompression
. Higher risk of thecal sac and traversing nerve root injury due to greater retraction
. Increased disruption of the lateral pars interarticularis
. Requirement for an anterior abdominal incision

Correct Answer & Explanation

. Higher risk of thecal sac and traversing nerve root injury due to greater retraction

Explanation

MIS PLIF requires bilateral laminotomies and significant medial retraction of the thecal sac and traversing nerve roots to insert the interbody cages. This increases the risk of dural tears and neurologic injury compared to the unilateral transforaminal approach of MIS TLIF.

Question 190

Topic: 6. Spine

Review the radiograph of a MIS stabilization construct.

To ensure proper placement of percutaneous pedicle screws, a true anteroposterior (AP) fluoroscopic image is essential. What confirms a true AP view of a lumbar vertebra?

. The spinous process is centered between the pedicles and the superior/inferior endplates are parallel
. The pedicles are superimposed on the anterior vertebral body line
. The spinous process aligns with the medial border of the pedicle
. The facet joints are clearly visualized without overlap
. The pars interarticularis appears as a Scottie dog neck

Correct Answer & Explanation

. The spinous process is centered between the pedicles and the superior/inferior endplates are parallel

Explanation

A true AP fluoroscopic image is achieved when the spinous process is exactly equidistant from both pedicles and the superior and inferior endplates appear as sharp, single lines (parallel). This ensures accurate medial-lateral trajectory during percutaneous screw placement.

Question 191

Topic: 6. Spine

In a patient undergoing MIS TLIF for a degenerative spondylolisthesis, which of the following is an advantage of placing a banana-shaped interbody cage anteriorly in the disc space?

. Decreased risk of cage subsidence
. Improved restoration of lumbar lordosis
. Facilitation of indirect decompression of the central canal
. Reduced need for pedicle screws
. Prevention of adjacent segment disease

Correct Answer & Explanation

. Improved restoration of lumbar lordosis

Explanation

Placing an interbody cage in the anterior third of the disc space acts as a fulcrum to increase segmental lordosis when posterior compression is applied. This helps restore sagittal balance, which is a key goal in degenerative spine surgery.

Question 192

Topic: 6. Spine

A major established disadvantage of minimally invasive spine surgery (MISS) techniques when compared to traditional open posterior techniques is:

. Increased early postoperative pain scores
. Higher rate of deep surgical site infection
. Increased intraoperative radiation exposure to the surgical team
. Greater intraoperative blood loss
. Increased risk of symptomatic adjacent segment disease

Correct Answer & Explanation

. Increased intraoperative radiation exposure to the surgical team

Explanation

Because MISS relies heavily on fluoroscopy or navigation for localization and instrument placement due to limited direct vision, radiation exposure to the surgeon and OR staff is significantly increased. Postoperative pain, SSI, and blood loss are typically reduced.

Question 193

Topic: 6. Spine

When performing an "over-the-top" bilateral decompression for central canal stenosis through a unilateral minimally invasive tubular approach, which critical stabilizing structure is intentionally preserved?

. Ipsilateral facet joint capsule completely
. Contralateral pars interarticularis
. Midline interspinous and supraspinous ligaments
. Ligamentum flavum
. Ipsilateral lamina

Correct Answer & Explanation

. Midline interspinous and supraspinous ligaments

Explanation

The over-the-top technique allows the surgeon to undercut the spinous process and reach the contralateral recess while completely preserving the midline tension band (interspinous and supraspinous ligaments), maintaining biomechanical stability.

Question 194

Topic: 6. Spine

Regarding the learning curve for minimally invasive lumbar fusion (MIS TLIF), literature demonstrates that during a surgeon's early experience, there is a statistically higher incidence of which of the following complications?

. Deep wound infections
. Incidental durotomies and cage malposition
. Retroperitoneal bowel injuries
. Major vascular lacerations
. Postoperative cauda equina syndrome

Correct Answer & Explanation

. Incidental durotomies and cage malposition

Explanation

The steep learning curve of MIS TLIF is associated with increased operative times, higher radiation exposure, and an increased incidence of technical complications like incidental durotomies and cage malposition/subsidence.

Question 195

Topic: Thoracolumbar Spine & Deformity

In Cortical Bone Trajectory (CBT) screw fixation, often utilized in minimally invasive lumbar surgeries, the pedicle screw path is fundamentally directed:

. Lateral to medial and cephalad to caudal
. Medial to lateral and caudal to cephalad
. Lateral to medial and caudal to cephalad
. Medial to lateral and cephalad to caudal
. Directly anterior without sagittal angulation

Correct Answer & Explanation

. Medial to lateral and caudal to cephalad

Explanation

CBT screws maximize cortical bone contact by starting medially at the pars interarticularis and directed laterally and cephalad. This trajectory allows for a smaller midline incision and increased pullout strength.

Question 196

Topic: 6. Spine

Which of the following is considered an absolute or strong relative contraindication for a minimally invasive direct lateral transpsoas lumbar interbody fusion (LLIF/XLIF)?

. Grade 1 degenerative spondylolisthesis
. L5-S1 level pathology
. Recurrent disc herniation
. Adjacent segment disease
. Severe disc space collapse

Correct Answer & Explanation

. L5-S1 level pathology

Explanation

The direct lateral transpsoas approach is generally contraindicated at L5-S1 due to obstruction by the iliac crest and the anterior position of the lumbar plexus and major iliac vessels at this level.

Question 197

Topic: 6. Spine

What is the primary indication for the utilization of continuous intraoperative neuromonitoring (EMG) during a minimally invasive direct lateral interbody fusion (XLIF)?

. To detect subclinical cauda equina compression
. To monitor for anterior spinal artery ischemia
. To identify and avoid elements of the lumbar plexus within the psoas muscle
. To map the exiting nerve root in Kambin's triangle
. To monitor sacral nerve root integrity

Correct Answer & Explanation

. To identify and avoid elements of the lumbar plexus within the psoas muscle

Explanation

The transpsoas approach places the lumbar plexus at risk. Directional EMG mapping is mandatory to navigate safely through the psoas major muscle and avoid damaging the plexus nerves.

Question 198

Topic: 6. Spine

A 45-year-old morbidly obese patient requires an L4-L5 fusion for a mobile grade 1 spondylolisthesis. A primary advantage of selecting an MIS tubular approach over a standard open approach in this specific patient population is:

. Easier placement of an anterior lumbar plate
. Complete independence of tubular retractor depth from the patient's subcutaneous fat thickness
. Significantly reduced risk of postoperative deep surgical site infection
. Increased direct visual field allowing faster decompression
. Lower risk of pedicle screw misplacement

Correct Answer & Explanation

. Significantly reduced risk of postoperative deep surgical site infection

Explanation

MIS spine surgery drastically reduces the incidence of deep surgical site infections compared to open surgery. This is particularly beneficial in obese patients, where large open incisions create massive dead space in poorly vascularized adipose tissue.

Question 199

Topic: 6. Spine

When an osteoblastoma occurs in the spine, it can involve all of the following except:

. Facets
. Transverse processes
. Pedicles
. Lamina
. Vertebral body

Correct Answer & Explanation

. Vertebral body

Explanation

When an osteoblastoma occurs in the spine, involvement of the posterior elements of the vertebra is typical and includes: Lamina Pedicles Transverse processes Facets Rib heads adjacent to thoracic vertebrae

Question 200

Topic: 6. Spine

What percentage of osteoblastomas occur in the spine:

. 20% to 30%
. 30% to 40%
. 40% to 50%
. 50% to 60%
. 60% to 70%

Correct Answer & Explanation

. 40% to 50%

Explanation

Osteoblastomas are: Osteoblastic bone-forming lesions measuring more than 2 cm in size characterized by marked growth potential Similar in histology and presentation to osteoid osteoma with the main difference being the size of the tumor Most common in the 2nd and 3rd decades of life Twice as common in men than in women Common in the spine: Spinal osteoblastomas account for 40% to 45% of all osteoblastomas Over half of spinal osteoblastomas occur in the lumbar spine

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