The difference in anatomy of the lumbar anterior longitudinal ligament in young African-Americans and Scandinavians

Screw Malposition: Are There Long-term Repercussions to Malposition of Pedicle Screws?

BACKGROUND/INTRODUCTION

Pedicle screws have long been part of the continued advancements in spine surgery. Despite the many techniques that have been devised for their safe placement, malposition of screws continues to occur. Studies have evaluated the possible safe limits of screw malposition, and have given some insight on anatomic variation in spinal deformity. Review of the literature reveals several cases of deleterious long-term sequelae of malpositioned screws.

DISCUSSION

With the current experience, proposed recommendations are provided to detect and avoid the potential long-term sequelae. Though the literature has helped to define possible concerning screws, there are no good studies predicting long-term risk.

CONCLUSION

Improvements in technology and techniques, advancements in intraoperative confirmation and postoperative surveillance, studies that assist risk stratification, and expert consensus evaluations will help guide surgeons in their decision for addressing misplaced screws.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

Pedicle Screw Safety: How Much Anterior Breach Is Safe?: A Cadaveric and CT-Based Study

MINI: The objective of this study was to determine the safety limits of anterior/anterolateral pedicle screw breaches. Through clinical and cadaveric study, it appears that less than 4 mm of breach has a significantly lower likelihood of impingement on vital structures (P < 0.001).

STUDY DESIGN

Clinical retrospective chart review and basic science study.

OBJECTIVES

To determine the safety limits of an anterior/anterorolateral misplaced pedicle screw on computed tomography (CT) scan in spinal deformity.

SUMMARY OF BACKGROUND DATA

Although the limits of medial breaches (<4 mm) are known, the safe limits for anterior/anterolateral breaches in spine deformity are not yet defined.

METHODS

The present study had two parts. In part I, postoperative CT scans of 165 patients operated on for spine deformity were reviewed for screw misplacement (2800 screws). The amount of anterior/anterolateral breach was measured. Protrusions were also evaluated for proximity to vital structures. All scans were reviewed by musculoskeletal radiologist. In part II, eight cadavers were instrumented with 6 × 30 and 6 × 40 mm bilaterally from T1-S1. Screws were randomly inserted under navigation guidance either "IN" or "OUT-anterior/lateral." CT scan was performed, followed by gross dissection to determine screw position.

RESULTS

Part I: 116(4.2%) screws were misplaced anterior/anterolaterally. Thirty-one (26.7%) were adjacent to vital structures. Fisher exact test showed 4 mm or less breach has significantly lower likelihood of impingement (P < 0.001). Screws adjacent/impinging the aorta protruded an average 5.7 ± 0.6 mm, whereas screws not involving the aorta breached an average 3.9 ± 0.2 mm, (P < 0.001). Part II: 285 screws were inserted. On CT scan, 125 were misplaced anterior/anterolaterally. On gross dissection, 89 were visibly misplaced; 23 were covered entirely by soft tissue but were palpable; and 13 were contained in bone. All 23 screws did not endanger any structures and protruded less than 4 mm on CT scan.

CONCLUSION

Anterior/anterolateral breaches of 4 mm or less on CT poses no significant risk of impingement and therefore can be considered safe.

LEVEL OF EVIDENCE

3.

First sacral nerve and anterior longitudinal ligament anatomy: clinical applications during sacrocolpopexy

BACKGROUND

The recommended location of graft attachment during sacrocolpopexy is at or below the sacral promontory on the anterior surface of the first sacral vertebra. Graft fixation below the sacral promontory may potentially involve the first sacral nerve.

OBJECTIVE

The objectives of this study were to examine the anatomy of the right first sacral nerve relative to the midpoint of the sacral promontory and to evaluate the thickness and ultrastructural composition of the anterior longitudinal ligament at the sacral promontory level.

STUDY DESIGN

Anatomic relationships were examined in 18 female cadavers (8 unembalmed and 10 embalmed). The midpoint of the sacral promontory was used as reference for all measurements. The most medial and superior point on the ventral surface of the first sacral foramen was used as a marker for the closest point at which the first sacral nerve could emerge. Distances from midpoint of sacral promontory and the midsacrum to the most medial and superior point of the first sacral foramen were recorded. The right first sacral nerve was dissected and its relationship to the presacral space was noted. The anterior longitudinal ligament thickness was examined at the sacral promontory level in the midsagittal plane. The ultrastructural composition of the ligament was evaluated using transmission electron microscopy. Height of fifth lumbar to first sacral disc was also recorded. Descriptive statistics were used for data analyses.

RESULTS

Median age of specimens was 78 years and median body mass index was 20.1 kg/m². Median vertical distance from midpoint of sacral promontory to the level of the most medial and superior point of the first sacral foramen was 26 (range 22-37) mm. Median horizontal distance from the midsacrum to the first sacral foramen was 19 (range 13-23) mm. In all specimens, the first sacral nerve was located just behind the layer of parietal fascia covering the piriformis muscle, and thus, outside the presacral space. Median anterior longitudinal ligament thickness at the sacral promontory level was 1.9 (range 1.2-2.5) mm. Median fifth lumbar to first sacral disc height was 16 (8.3-17) mm.

CONCLUSION

Awareness of the first sacral nerve position, approximately 2.5 cm below the midpoint of the sacral promontory and 2 cm to the right of midline, should help anticipate and avoid somatic nerve injury during sacrocolpopexy. Knowledge of the approximate 2-mm thickness of the anterior longitudinal ligament should help reduce risk of discitis and osteomyelitis, especially when graft is affixed above the level of the sacral promontory.

Investigation of Sacral Needle Depth in Minimally Invasive Sacrocolpopexy

PURPOSE

The aims of the study were to optimize surgical safety and to minimize vertebral disc puncture during sacral needle placement at the time of minimally invasive sacrocolpopexy. Cadaveric studies report that the anterior longitudinal ligament (ALL), which covers the vertebral disc and vertebrae, has a reported thickness of only 1.4 to 2.3 mm at L5-S1. Intervertebral disc puncture can accelerate disc degeneration, disc herniation, and loss of disc height, a risk that may be avoidable.

MATERIALS AND METHODS

After institutional review board approval, research consent was obtained from women undergoing primary laparoscopic sacrocolpopexy. Intraoperatively, sacral sutures were placed in the ALL with a 1.5 cm diameter CV-2 needle using Gore-Tex suture. Depth measurements were collected using a laparoscopic ultrasound transducer positioned on the sacral promontory (SP) between the 2 ends of the needle visible through the ALL. Two still-frame US images of the single needle were taken using the BK Medical software. Needle depth was calculated by measuring the distance from the top of the ALL to the needle.

RESULTS

Two satisfactory intraoperative images were obtained for all 9 participants. The mean needle depth at the SP was 3.96 mm. The interpatient needle depth varied from 2.07 to 9.04 mm.

CONCLUSIONS

In most participants (78%), the sacral needle depth exceeded 2.3 mm, suggesting that there may be risk to sacral suture placement without depth guidance at the promontory. During minimally invasive sacrocolpopexy, the depth of the ALL and the placement of the needle at the SP may result in inadvertent disc penetration. Surgeons should be conscious of the minimal depth of the ALL and consider placing the suture below the promontory to avoid the disc.

Diffuse idiopathic skeletal hyperostosis association with thoracic spine kyphosis: a cross-sectional study for the Health Aging and Body Composition Study

STUDY DESIGN

A descriptive study of the association between diffuse idiopathic skeletal hyperostosis (DISH) and kyphosis.

OBJECTIVE

To investigate the association of DISH with Cobb angle of kyphosis in a large cohort of older subjects from the Health Aging and Body Composition Study.

SUMMARY OF BACKGROUND DATA

DISH and thoracic kyphosis are well-defined radiographical findings in spines of older individuals. Characteristics of DISH (ossifications between vertebral segments) reflect changes of spine anatomy and physiology that may be associated with Cobb angle of kyphosis.

METHODS

Using data from 1172 subjects aged 70 to 79 years, we measured DISH and Cobb angle of kyphosis from computed tomographic lateral scout scans. Characteristics of participants with and without DISH were assessed using the χ² and t tests. Association between DISH and Cobb angle was analyzed using linear regression. Cobb angle and DISH relationship was assessed at different spine levels (thoracic and lumbar).

RESULTS

DISH was identified on computed tomographic scout scan in 152 subjects with 101 cases in only the thoracic spine and 51 in both thoracic and lumbar spine segments. The mean Cobb angle of kyphosis in the analytic sample was 31.3° (standard deviation = 11.2). The presence of DISH was associated with a greater Cobb angle of 9.1° and 95% confidence interval (95% CI) (5.6-12.6) among African Americans and a Cobb angle of 2.9° and 95% CI (0.5-5.2) among Caucasians compared with those with no DISH. DISH in the thoracic spine alone was associated with a greater Cobb angle of 10.6° and 95% CI (6.5-14.7) in African Americans and a Cobb angle of 3.8° and 95% CI (1.0-6.5) in Caucasians compared with those with no DISH.

CONCLUSION

DISH is associated with greater Cobb angle of kyphosis, especially when present in the thoracic spine alone. The association of DISH with Cobb angle is stronger within the African American population.

Biomechanical properties of isolated fascicles of the Iliopsoas and Achilles tendons in African American and Caucasian men

OBJECTIVES

To investigate biomechanical properties of the Iliopsoas and Achilles tendons in young African American (AA) and Caucasian (CC) men, and attempt to clarify whether the difference in Achilles tendon ruptures between AA and CC can be explained by differences in material properties.

METHODS

Tissue from 12 young males (AA, n=6; CC, n=6) was obtained from routine forensic autopsies. Iliopsoas and Achilles tendon samples were obtained from cadavers that were age, height and weight matched. Tendon collagen fascicles were tested micromechanically in a Deben mechanical testing rig.

RESULTS

Peak failure stress in Iliopsoas tendon fascicles was considerably higher (p<0.05) in AA (22.4 ± 7.2MPa) than CC (6.8 ± 2.1MPa) whereas peak strain did not differ (AA: 19.7 ± 5.2%, CC: 18.3 ± 3.5%). Likewise, Young's modulus was greater (p<0.05) in AA (165.3 ± 67.3MPa) than CC (63.6 ± 23.6MPa). In contrast, peak failure stress in Achilles tendon fascicles was similar (p>0.1) in AA (21.9 ± 9.9MPa) and CC (28.1 ± 9.8MPa), and peak strain did not differ (p>0.1) between AA (16.3 ± 3.5%) and CC (13.8 ± 4.4%). Young's modulus was slightly greater in CC (316.8 ± 110MPa) than AA (222.8 ± 84.6MPa), yet not significantly (p>0.1).

CONCLUSIONS

These findings indicate that Iliopsoas tendon fascicles are stronger in young AA compared to CC males, which is suggested to reflect differences in muscle mass and force generating capacity. This could not be confirmed in Achilles tendon fascicles.

Optimal location and orientation of suture placement in abdominal sacrocolpopexy

OBJECTIVE

To estimate the strongest location and optimal orientation of suture placement in the anterior longitudinal ligament for abdominal sacrocolpopexy in female cadavers.

METHODS

The anterior longitudinal ligament was exposed below the level of the aortic bifurcation in 23 unembalmed female cadavers. To the right of midline of the vertebral column, sutures were placed in a horizontal orientation into the ligament at the sacral promontory, 1 and 2 cm above (sacral promontory+1 and sacral promontory+2), and 1, 2, and 3 cm below (sacral promontory-1, sacral promontory-2 and sacral promontory-3). At these same locations, but to the left of midline, sutures were placed in a vertical orientation. Pull-out force and ligament thickness at each level of testing were measured. Data were analyzed using Student t test and repeated measures analysis of variance.

RESULTS

Sutures (either horizontally or vertically placed) had greater pull-out strengths at or above, compared with those placed below, the level of the sacral promontory. At sacral promontory and sacral promontory+1, there were no differences in the pull-out strengths of the ligament when sutures were placed in either orientation. However, horizontally placed sutures had significantly greater pull-out strengths than vertically placed sutures at sacral promontory+2, sacral promontory-1 and sacral promontory-2. Ligament thickness decreased from 2 cm above (mean+/-standard error of the mean sacral promontory+2, 1.8+/-0.1 mm) to 3 cm below (sacral promontory-3, 1.3+/-0.1 mm) the sacral promontory.

CONCLUSION

Sutures placed in the anterior longitudinal ligament at or above the sacral promontory are more secure than those placed below. Horizontally oriented sutures should be considered for mesh attachment below the sacral promontory because they are significantly stronger when compared with vertically placed sutures.