Leonardo B. C. Brasiliense, Ramon Navarro, Paul Brazis and Rabih G. Tawk
Quantitative analysis of misplaced pedicle screws in the thoracic spine: how much pullout strength is lost?
Presented at the 2009 Joint Spine Section Meeting
Leonardo B. C. Brasiliense, Nicholas Theodore, Bruno C. R. Lazaro, Zafar A. Sayed, Fatih Ersay Deniz, Volker K. H. Sonntag and Neil R. Crawford
The object of this study was to investigate the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of thoracic pedicle screws.
Forty human thoracic vertebrae (T6–11) from human cadavers were studied. Before pedicle screws were inserted, the specimens were separated into 4 groups according to the type of screw used: 1) standard pedicle screw (no cortical perforation); 2) screw with medial cortical perforation; 3) screw with lateral cortical perforation; and 4) “airball” screw (a screw that completely missed the vertebral body). Consistency among the groups for bone mineral density, pedicle diameter, and screw insertion depth was evaluated. Finally, each screw was pulled out at a constant displacement rate of 10 mm/minute while ultimate strength was recorded.
Compared with well-placed pedicle screws, medially misplaced screws had 8% greater mean pullout strength (p = 0.482) and laterally misplaced screws had 21% less mean pullout strength (p = 0.059). The difference in mean pullout strength between screws with medial and lateral cortical perforations was significant (p = 0.013). Airball screws had only 66% of the mean pullout strength of well-placed screws (p = 0.009) and had 16% lower mean pullout strength than laterally misplaced screws (p = 0.395).
This in vitro study showed a significant difference in mean pullout strength between medial and lateral misplaced pedicle screws. Moreover, airball screws were associated with a significant loss of pullout strength.
Sam Safavi-Abbasi, Leonardo B. C. Brasiliense, Ryan K. Workman, Melanie C. Talley, Iman Feiz-Erfan, Nicholas Theodore, Robert F. Spetzler and Mark C. Preul
✓In 25 years, the Mongolian army of Genghis Khan conquered more of the known world than the Roman Empire accomplished in 400 years of conquest. The recent revised view is that Genghis Khan and his descendants brought about “pax Mongolica” by securing trade routes across Eurasia. After the initial shock of destruction by an unknown barbaric tribe, almost every country conquered by the Mongols was transformed by a rise in cultural communication, expanded trade, and advances in civilization. Medicine, including techniques related to surgery and neurological surgery, became one of the many areas of life and culture that the Mongolian Empire influenced.
Fatih Ersay Deniz, Leonardo B. C. Brasiliense, Bruno C. R. Lazaro, Phillip M. Reyes, Anna G. U. Sawa, Volker K. H. Sonntag and Neil R. Crawford
The authors investigated the biomechanical properties of transpedicular discectomy in the thoracic spine and compared the effects on spinal stability of a partial and total facetectomy.
Human thoracic specimens were tested while intact, after a transpedicular discectomy with partial facetectomy, and after an additional total facetectomy was incorporated. Nonconstraining pure moments were applied under load control (maximum 7.5 Nm) to induce flexion, extension, lateral bending, and axial rotation while spinal motion was measured at T8–9 optoelectronically. The range of motion (ROM) and lax zone were determined in each specimen and compared among conditions.
Transpedicular discectomy with and without a total facetectomy significantly increased the ROM and lax zone in all directions of loading compared with the intact spine (p < 0.008). The segmental increase in ROM observed with the transpedicular discectomy was 25%. The additional total facetectomy created an insignificant 3% further increase in ROM compared with medial facetectomy (p > 0.2).
Transpedicular discectomy can be performed in the thoracic spine with a modest decrease in stability expected. Because the biomechanical behavior of a total facetectomy is equivalent to that of a medial facetectomy, the additional facet removal may be incorporated without further biomechanical consequences.
Bruno C. R. Lazaro, Fatih Ersay Deniz, Leonardo B. C. Brasiliense, Phillip M. Reyes, Anna G. U. Sawa, Nicholas Theodore, Volker K. H. Sonntag and Neil R. Crawford
Posterior screw-rod fixation for thoracic spine trauma usually involves fusion across long segments. Biomechanical data on screw-based short-segment fixation for thoracic fusion are lacking. The authors compared the effects of spanning short and long segments in the thoracic spine.
Seven human spine segments (5 segments from T-2 to T-8; 2 segments from T-3 to T-9) were prepared. Pure-moment loading of 6 Nm was applied to induce flexion, extension, lateral bending, and axial rotation while 3D motion was measured optoelectronically. Normal specimens were tested, and then a wedge fracture was created on the middle vertebra after cutting the posterior ligaments. Five conditions of instrumentation were tested, as follows: Step A, 4-level fixation plus cross-link; Step B, 2-level fixation; Step C, 2-level fixation plus cross-link; Step D, 2-level fixation plus screws at fracture site (index); and Step E, 2-level fixation plus index screws plus cross-link.
Long-segment fixation restricted 2-level range of motion (ROM) during extension and lateral bending significantly better than the most rigid short-segment construct. Adding index screws in short-segment constructs significantly reduced ROM during flexion, lateral bending, and axial rotation (p < 0.03). A cross-link reduced axial rotation ROM (p = 0.001), not affecting other loading directions (p > 0.4).
Thoracic short-segment fixation provides significantly less stability than long-segment fixation for the injury studied. Adding a cross-link to short fixation improved stability only during axial rotation. Adding a screw at the fracture site improved short-segment stability by an average of 25%.
Benjamin L. Brown, Demetrius Lopes, David A. Miller, Rabih G. Tawk, Leonardo B. C. Brasiliense, Andrew Ringer, Eric Sauvageau, Ciarán J. Powers, Adam Arthur, Daniel Hoit, Kenneth Snyder, Adnan Siddiqui, Elad Levy, L. Nelson Hopkins, Hugo Cuellar, Rafael Rodriguez-Mercado, Erol Veznedaroglu, Mandy Binning, J Mocco, Pedro Aguilar-Salinas, Alan Boulos, Junichi Yamamoto and Ricardo A. Hanel
The authors sought to determine whether flow diversion with the Pipeline Embolization Device (PED) can approximate microsurgical decompression in restoring function after cranial neuropathy following carotid artery aneurysms.
This multiinstitutional retrospective study involved 45 patients treated with PED across the United States. All patients included presented between November 2009 and October 2013 with cranial neuropathy (cranial nerves [CNs] II, III, IV, and VI) due to intracranial aneurysm. Outcome analysis included clinical and procedural variables at the time of treatment as well as at the latest clinical and radiographic follow-up.
Twenty-six aneurysms (57.8%) were located in the cavernous segment, while 6 (13.3%) were in the clinoid segment, and 13 (28.9%) were in the ophthalmic segment of the internal carotid artery. The average aneurysm size was 18.6 mm (range 4–35 mm), and the average number of flow diverters placed per patient was 1.2. Thirty-eight patients had available information regarding duration of cranial neuropathy prior to treatment. Eleven patients (28.9%) were treated within 1 month of symptom onset, while 27 (71.1%) were treated after 1 month of symptoms. The overall rate of cranial neuropathy improvement for all patients was 66.7%. The CN deficits resolved in 19 patients (42.2%), improved in 11 (24.4%), were unchanged in 14 (31.1%), and worsened in 1 (2.2%). Overtime, the rate of cranial neuropathy improvement was 33.3% (15/45), 68.8% (22/32), and 81.0% (17/21) at less than 6, 6, and 12 months, respectively. At last follow-up, 60% of patients in the isolated CN II group had improvement, while in the CN III, IV, or VI group, 85.7% had improved. Moreover, 100% (11/11) of patients experienced improvement if they were treated within 1 month of symptom onset, whereas 44.4% (12/27) experienced improvement if they treated after 1 month of symptom onset; 70.4% (19/27) of those with partial deficits improved compared with 30% (3/10) of those with complete deficits.
Cranial neuropathy caused by cerebral aneurysm responds similarly when the aneurysm is treated with the PED compared with open surgery and coil embolization. Lower morbidity and higher occlusion rates obtained with the PED may suggest it as treatment of choice for some of these lesions. Time to treatment is an important consideration regardless of treatment modality.