Search Results

You are looking at 1 - 10 of 11 items for

  • Author or Editor: Ronald A. Lehman x
Clear All Modify Search
Restricted access

James D. Lin, Chao Wei, Jamal N. Shillingford, Eduardo C. Beauchamp, Lee A. Tan, Yongjung J. Kim, Ronald A. Lehman Jr. and Lawrence G. Lenke

OBJECTIVE

To demonstrate that a more ventral starting point for thoracic pedicle screw insertion, produced by aggressively removing the dorsal transverse process bone down to the superior articular facet (SAF), results in a larger margin for error and more medial screw angulation compared to the traditional dorsal starting point (DSP). The margin for error will be quantified by the maximal insertional arc (MIA).

METHODS

The study population included 10 consecutive operative patients with adult idiopathic scoliosis who underwent primary surgery. All measurements were performed using 3D visualization software by an attending spine surgeon. The screw starting points were 2 mm lateral to the midline of the SAF in the mediolateral direction and in the center of the pedicle in the cephalocaudal direction. The DSP was on the dorsal cortex. The ventral starting point (VSP) was at the depth of the SAF. Measurements included distance to the pedicle isthmus, MIA, and screw trajectories.

RESULTS

Ten patients and 110 vertebral levels (T1–11) were measured. The patients’ average age was 41.4 years (range 18–64 years). The pedicle isthmus was largest at T1 (4.04 ± 1.09 mm), and smallest at T5 (1.05 ± 0.93 mm). The distance to the pedicle isthmus was 7.47 mm for the VSP and 11.92 mm for the DSP (p < 0.001). The MIA was 15.3° for the VSP and 10.1° for the DSP (p < 0.001). Screw angulation was 21.7° for the VSP and 16.8° for the DSP (p < 0.001).

CONCLUSIONS

A more ventral starting point for thoracic pedicle screws results in increased MIA and more medial screw angulation. The increased MIA represents an increased tolerance for error that should improve the safety of pedicle screw placement. More medial screw angulation allows improved triangulation of pedicle screws.

Full access

Melvin D. Helgeson, Ronald A. Lehman Jr., Anton E. Dmitriev, Daniel G. Kang, Rick C. Sasso, Chadi Tannoury and K. Daniel Riew

Object

Intraoperative imaging often does not provide adequate visualization to ensure safe placement of screws. Therefore, the authors investigated the accuracy of a freehand technique for placement of pars, pedicle, and intralaminar screws in C-2.

Methods

Sixteen cadaveric specimens were instrumented freehand by 2 experienced cervical spine surgeons with either a pars or pedicle screw, and bilateral intralaminar screws. The technique was based on anatomical starting points and published screw trajectories. A pedicle finder was used to establish the trajectory, followed by tapping, palpation, and screw placement. After placement of all screws (16 pars screws, 16 pedicle screws, and 32 intralaminar screws), the C-2 segments were disarticulated, radiographed in anteroposterior, lateral, and axial planes, and meticulously inspected by another spine surgeon to determine the nature and presence of any defects.

Results

A total of 64 screws were evaluated in this study. Pars screws exhibited 2 critical defects (1 in the foramen transversarium and 1 in the C2–3 facet) and an insignificant dorsal cortex breech, for an overall accuracy rate of 81.3%. Pedicle screws demonstrated only 1 insignificant violation (inferior facet/medial cortex intrusion of 1 mm) with an accuracy rate of 93.8%, and intralaminar screws demonstrated 3 insignificant violations (2 in the ventral canal, 1 in the caudad lamina breech) for an accuracy rate of 90.6%. Pars screws had significantly more critical violations than intralaminar screws (p = 0.041).

Conclusions

Instrumentation of the C-2 vertebrae using the freehand technique for insertion of pedicle and intralaminar screws showed a high success rate with no critical violations. Pars screw insertion was not as reliable, with 2 critical violations from a total of 16 placements. The freehand technique appears to be a safe and reliable method for insertion of C-2 pedicle and intralaminar screws.

Restricted access

James D. Lin, Lee A. Tan, Chao Wei, Jamal N. Shillingford, Joseph L. Laratta, Joseph M. Lombardi, Yongjung J. Kim, Ronald A. Lehman Jr. and Lawrence G. Lenke

OBJECTIVE

The S2-alar-iliac (S2AI) screw is an increasingly popular method for spinopelvic fixation. The technique of freehand S2AI screw placement has been recently described. The purpose of this study was to demonstrate, through a CT imaging study of patients with spinal deformity, that screw trajectories based on the posterior superior iliac spine (PSIS) and sacral laminar slope result in reliable freehand S2AI trajectories that traverse safely above the sciatic notch.

METHODS

Fifty consecutive patients (age ≥ 18 years) who underwent primary spinal deformity surgery were included in the study. Simulated S2AI screw trajectories were analyzed with 3D visualization software. The cephalocaudal coordinate for the starting point was 15 mm cephalad to the PSIS. The mediolateral coordinate for the starting point was in line with the lateral border of the dorsal foramina. The cephalocaudal screw trajectory was perpendicular to the sacral laminar slope. Screw trajectories, lengths, and distance above the sciatic notch were measured.

RESULTS

The mean sagittal screw angle (cephalocaudal angulation) was 44.0° ± 8.4° and the mean transverse angle (mediolateral angulation) was 37.3° ± 4.3°. The mean starting point was 5.9 ± 5.8 mm distal to the caudal border of the S1 foramen. The mean screw length was 99.9 ± 18.6 mm. Screw trajectories were on average 8.5 ± 4.3 mm above the sciatic notch. A total of 97 of 100 screws were placed above the sciatic notch. In patients with transitional lumbosacral anatomy, the starting point on the lumbarized/sacralized side was 3.4 mm higher than on the contralateral unaffected side.

CONCLUSIONS

The PSIS and sacral laminar slope are two important anatomical landmarks for freehand S2AI screw placement.

Free access

Mohamad Bydon, Vance Fredrickson, Rafael De la Garza-Ramos, Yiping Li, Ronald A. Lehman Jr., Gregory R. Trost and Ziya L. Gokaslan

Sacral fractures are uncommon lesions and most often the result of high-energy trauma. Depending on the fracture location, neurological injury may be present in over 50% of cases. In this article, the authors conducted a comprehensive literature review on the epidemiology of sacral fractures, relevant anatomy of the sacral and pelvic region, common sacral injuries and fractures, classification systems of sacral fractures, and current management strategies. Due to the complex nature of these injuries, surgical management remains a challenge for the attending surgeon. Few large-scale studies have addressed postoperative complications or long-term results, but current evidence suggests that although fusion rates are high, long-term morbidity, such as residual pain and neurological deficits, persists for many patients.

Restricted access

Mario J. Cardoso, Anton E. Dmitriev, Melvin D. Helgeson, Frederick Stephens, Victoria Campbell, Ronald A. Lehman, Patrick Cooper and Michael K. Rosner

Object

Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique.

Methods

Nine fresh-frozen C-7 cadaveric specimens were scanned for bone mineral density using dual energy x-ray absorptiometry. Prior to testing, all specimens were imaged using CT to obtain 1-mm axial sections. Caliper measurements of both pedicle width and laminar thickness were obtained. On the right side, pedicle screws were first inserted and then pulled out. Salvage intralaminar screws were inserted into the left lamina from the right spinous process/lamina junction and then pulled out. All screws were placed by experienced cervical spine surgeons under direct fluoroscopic visualization. Pedicle and lamina screws were 4.35- and 3.5-mm in diameter, respectively. Screws sizes were chosen based on direct and radiographic measurements of the respective anatomical regions. Insertional torque (IT) was measured in pounds per inch. Tensile loading to failure was performed in-line with the screw axis at a rate of 0.25 mm/sec using a MiniBionix II system with data recorded in Newtons.

Results

Using lamina screws as a salvage technique generated mean pullout forces (778.9 ± 161.4 N) similar to that of the index pedicle screws (805.3 ± 261.7 N; p = 0.796). However, mean lamina screw peak IT (5.2 ± 2.0 lbs/in) was significantly lower than mean index pedicle screw peak IT (9.1 ± 3.6 lbs/in; p = 0.012). Bone mineral density was strongly correlated with pedicle screw pullout strength (r = 0.95) but less with lamina screw pullout strength (r = 0.04). The mean lamina width measured using calipers (5.7 ± 1.0 mm) was significantly different from the CTmeasured mean lamina width (5.1 ± 0.8 mm; p = 0.003). Similarly, the mean pedicle width recorded with calipers (6.6 ± 1.1 mm) was significantly different from the CT-measured mean pedicle width (6.2 ± 1.3 mm; p = 0.014). The mean laminar width measured on CT at the thinnest point ranged from 3.8 to 6.8 mm, allowing a 3.5-mm screw to be placed without difficulty.

Conclusions

These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.