Minimally Invasive Options for Traumatic Conditions

Kevin Khalsa

Gloribel Le

Tristan B.Weir

Steven C. Ludwig

Kelley E. Banagan

REBUTTAL ▪ The Case agains MIS Thoracic Fractures Fixation

Kirkham Wood

The estimated incidence of spinal fracture is about 64 in 100,000,¹ with 12,500 resulting in a spinal cord injury.² Thirty-eight percent of patients admitted for their spine fracture have an associated injury.¹ In the poly-traumatized patient, the inciting injury (“first hit”) may make the patient more susceptible to physiologic collapse should they require a procedure with longer operative times or more blood loss.³, ⁴, ⁵, ⁶ Additionally, the muscle dissection inherent in an open procedure may lead to muscle morbidity and scarring, with resultant atrophy, reduced muscle endurance and strength, and hampered postoperative rehabilitation.⁷, ⁸, ⁹, ¹⁰, ¹¹ “Damage control” spinal orthopedic procedures, such as minimally invasive techniques, applied to this patient population can potentially reduce the morbidity of surgery and help avoid the disastrous “second hit.”¹² This chapter discusses the relative indications, posterior-based approaches, and complications associated with minimally invasive spine surgery (MISS) for the treatment of thoracic spine fractures.

The thoracolumbar injury classification and severity (TLICS) score was initially developed to characterize and classify thoracolumbar injuries and to assist the surgeon in deciding for, or against, operative intervention as treatment for the fracture¹³,¹⁴ (Table 21.1). The classification system does not address the surgical approach to be utilized. The authors believe the following fracture patterns may benefit from a minimally invasive surgical approach: (a) compression and/or burst fractures with neurologic deficits treated with posterior MISS decompression and MISS pedicle screw fixation; (b) mechanically unstable injuries with posterior ligamentous complex disruption treated with MISS pedicle screw fixation; (c) neurologically intact compression and/or burst fractures not amenable to treatment via an orthosis secondary to patient-related factors and comorbidities; (d) flexion-distraction or extension-distraction injuries requiring MISS pedicle screw instrumentation.¹⁵

Contraindications for posterior thoracic MISS approaches include inability to tolerate prone positioning, soft-tissue injuries with an extensive zone of injury over the proposed surgical site, and poor radiographic visualization of pedicles secondary to body habitus. However, the most crucial contraindication is surgeon inexperience with minimally invasive techniques. Time is crucial in the poly-traumatized patient, and an inexperienced surgeon attempting MISS without prior training can lead to potentially disastrous complications.¹⁵

MINIMALLY INVASIVE OPTIONS FOR TRAUMATIC CONDITIONS

Anatomy

The surgeon relies on fluoroscopic guidance to perform MISS and thus he or she must be well versed in interpreting spinal anatomy on radiographs. Failure to appreciate anatomic intricacies can lead to a medial pedicle breach into the spinal canal or a lateral breach into the spinal
nerves. Thoracic pedicle breach ranges from 16% to 54% in open procedures,¹⁶,¹⁷ and most commonly occurs in a lateral direction.¹⁸ A key component to interpreting the spinal anatomy and obtaining the correct intraoperative radiographic views is effective communication with the radiology technician. Poor communication can unnecessarily expose the patient, surgeon, and operating room staff to excess radiation. Radiation exposure in MISS has been reported to be 10 to 12 times higher (mrem/minute) than in conventional open procedures.¹⁹

TABLE 21-1 Thoracolumbar Injury Classification and Severity (TLICS) Score.¹⁴

TLICS Scoring for Thoracic and Lumbar Spine Injuries
Scoring Criteria	Points
Morphology
Compression fracture	1
Burst fracture	2
Translational/rotational	3
Distraction	4
Neurologic Involvement
Intact	0
Nerve root	2
Cord, conus medullaris
Incomplete	3
Complete	2
Cauda equina	3
Posterior Ligamentous Complex
Intact	0
Suspected injury/indeterminate	2
Injured	3
Total Score
Nonoperative	0-3
Nonoperative or operative	4
Operative	>4
Add points from each of the three categories to find the total score. A total score of <4 generally indicates nonoperative treatment, >4 indicates operative treatment, and a score of 4 is a gray area where operative and nonoperative treatments may be considered.

Kim and Lenke highlighted the unique characteristics of thoracic pedicle anatomy and described anatomic landmarks to assist pedicle screw placement for open procedures.²⁰ Tactile and morphological landmarks, however, are not available for pedicle screw placement via percutaneous methods. Preoperative planning with axial computed tomography (CT) scans is paramount, and the surgeon should choose screws according to the length and width of each pedicle. This will help to avoid a lateral breach into the spinal nerves, or an anterior vertebral body cortex breach into vascular structures from screws that are too wide or long. Lastly, careful attention to maintaining a medial-to-lateral trajectory of the screw will navigate the anatomic pedicle, reducing the incidence of pedicle breach.²¹

Moving cranial to caudal, there are important differences in pedicle anatomy along the length of the thoracic spine (Fig. 21.1). The pedicle width decreases dramatically from T1 to T4, but increases from T4 to T12. According to cadaveric studies by Lien et al.,²² the average pedicle width is 7.7 mm at T1, 3.6 mm at T4, and 7.4 mm at T12. Overall, the pedicle width ranges from 3.6 mm to 7.7 mm in the thoracic spine. The pedicle height, however, gradually increases from an average of 8 mm at T1 to 15 mm at T12. The surgeon should be proficient at recognizing the transverse and sagittal angles of each pedicle, as this knowledge aids in adjusting the pedicle screw trajectory so as to avoid a breach in any direction. T1 has the largest transverse angle of 28 degrees, which decreases to 8 degrees at T12. In terms of the sagittal angle, the thoracic spine ranges from 10 to 16 degrees from a line drawn parallel on
the superior endplate.²² Thus, an understanding of the pedicle anatomy at various thoracic spine levels is crucial for the proper and safe placement of MISS pedicle screws.

Figure 21.1 Notice the relationship of the pedicle anatomy moving cranial to caudal. Pedicle width decreases from T1 to T4, and increases from T4 to T12. Pedicle height increases from T1 to T12, however.

In addition to the thoracic pedicle characteristics stated above, multiple studies have shown a variable relationship between pedicle width and age, gender, and race. McLain et al.²³ found no relationship between pedicle size and gender or race, but Yu et al.²⁴ found significantly larger pedicle dimensions in males compared to females. These studies also demonstrated that pedicle width increased with age, especially in patients from 50 to 70 years old. The decline in bone density and increased porosity may lead to vertebral deformation that accounts for this widening effect of the pedicle. This finding of pedicle widening should be approached with caution, however, as aging also leads to a decrease in tensile properties of the pedicle and a reduced ability to accept and hold implants.²⁴

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