The relation between the lumbar vertebrae and the spinal nerves for far lateral lumbar spinal approaches

The projection of the thoracic nerve roots and their connection with intervertebral discs: a cadaver and radiological study

BACKGROUND

The anatomical features of the thoracic nerve roots in connection with intervertebral discs may prevent surgery-related complications and improve patients' neurological functional status during thoracic spine surgery. There is limited literature evidence regarding this concept using cadavers.

PURPOSE

To elucidate the qualitative anatomical features of the thoracic nerve roots in connection with intervertebral discs.

MATERIAL AND METHODS

Fifteen formalin-preserved spine specimens were used in this study. Small pieces of stainless-steel wires were placed along the root sleeves from their points of origin, after exposing the dural sac and bilateral nerve roots. The standard anteroposterior and lateral radiographs were taken after the placement of the wires. Measurements were done on radiographs using the picture archiving communication system.

RESULTS

Take-off angles of the nerve roots at the coronal plane gradually increased from the level of T2 (36.1°±2.72°) to T9 (84.1°±1.84°) and from T9, it decreased to T12 (46.3° ± 2.67°). Similar variation tendency was discovered in take-off angles of the nerve roots at the sagittal plane. No consistent tendency was found both in the distance from the origin of the root sleeve to its superior and inferior vertebral endplate. Distance from the origin of the root sleeve to the posterior midline (DM) exponentially decreased from T1 (8.2 ± 0.87 mm) to T4 (6.0 ± 0.93 mm). It slowly increased from T5 (5.5 ± 0.68 mm) to T12 (10.9 ± 1.79 mm), with T5 having the smallest DM. Distance between the origins of neighboring nerve roots showed an obvious increase from the T1-T2 interval (23.1 ± 2.22 mm) to T7-T8 interval (30.9 ± 2.68 mm). However, it progressively decreased at the T10-T11 interval (26.0 ± 2.40 mm).

CONCLUSION

The dimensions of the thoracic nerve roots vary greatly from T1 to T12 intervertebral discs. Sound knowledge of these anatomical features of the thoracic nerve is mandatory for the thoracic spine surgery, especially in the posterolateral approach and transforaminal endoscopic surgery.

Comprehensive Anatomic and Morphometric Analyses of Triangular Working Zone for Transforaminal Endoscopic Approach in Lumbar Spine: A Fresh Cadaveric Study

OBJECTIVE

The aim of this study is to provide essential information for endoscopic transforaminal approach by performing morphometric analysis of the triangular working zone (TWZ) in fresh cadavers.

METHODS

Fifteen fresh human cadavers (9 women and 6 men) with no history of spinal surgery were used in this study. Anatomic dissection of 150 foraminal levels were performed. Significant surgical landmarks constructing TWZ were measured bilaterally from L1-2 to L5-S1 on 15 fresh cadavers. The relationship between traversing roots and intervertebral discs was defined.

RESULTS

Base, height, and hypotenuse measurements of TWZ were longer as the level lowered. Mean base height and hypotenuse of TWZ were 12.15 mm, 11.29 mm, and 16.69 mm (L1-2); 17.94 mm, 17.18 mm, and 28.03 mm (L5-S1), respectively. TWZ was triangular shaped at the upper lumbar levels (L1-2, L2-3, and L3-4), and trapezoid at the lower lumbar levels (L4-5 and L5-S1). Going down the levels, the exiting root angle was narrower, the mean exiting angle of the L5 root being 28.23°. All L2 and L3 traversing roots and nearly all L4 traversing roots (86.7%) originated from below the disc level. Forty percent of L5 traversing roots originated above the disc level, and 53.3% originated at the disc level. Most S1 traversing roots originated at the proximal margin of the disc level (80%).

CONCLUSIONS

Our study reveals a detailed morphometric analysis of TWZ. Understanding the foraminal anatomy is crucial for safely performing transforaminal endoscopic surgery. The learning curve of transforaminal surgery can be reduced by garnering knowledge of TWZ anatomy.

Evaluation of Dimensions of Kambin's Triangle to Calculate Maximum Permissible Cannula Diameter for Percutaneous Endoscopic Lumbar Discectomy : A 3-Dimensional Magnetic Resonance Imaging Based Study

Objective

To evaluate 3-dimensional magnetic resonance imaging (MRI) of Kambin’s safe zone to calculate maximum cannula diameter permissible for safe percutaneous endoscopic lumbar discectomy.

Methods

Fifty 3D MRIs of 19 males and 31 females (mean, 47 years) were analysed. Oblique, axial and sagittal views were used for image analysis. Three authors calculated the inscribed circle (cannula diameter) individually, within the neural (original) and bony Kambin’s triangle in oblique views, disc heights on sagittal views and root to facet distances at upper and lower end plate levels on axial views and their averages were taken.

Results

The mean root to facet distances at upper end plate level measured on axial sections increased from 3.42±3.01 mm at L12 level to 4.57±2.49 mm at L5S1 level. The mean root to facet distances at lower end plate level measured on axial sections also increased from 6.07±1.13 mm at L12 level to 12.9±2.83 mm at L5S1 level. Mean maximum cannula diameter permissible through the neural Kambin’s triangle increased from 5.67±1.38 mm at L12 level to 9.7±3.82 mm at L5S1 level. The mean maximum cannula diameter permissible through the bony Kambin’s triangle also increased from 4.03±1.08 mm at L12 level to 6.11±1 mm at L5S1 level. Only 2% of the 427 bony Kambin’s triangles could accommodate a cannula diameter of 8mm. The base of the bony Kambin’s triangle taken in oblique view (3D MRI) was significantly higher than the root to facet distance at lower end plate level taken in axial view.

Conclusion

The largest mean diameter of endoscopic cannula passable through “bony” Kambin’s triangle was distinctively smaller than the largest mean diameter of endoscopic cannula passable through “neural” Kambin’s triangle at all levels. Although proximity of exiting root to the facet joint is always taken into consideration before PELD procedure, our 3D MRI based anatomical study is the first to provide actual maximum cannula dimensions permissible in this region.

Usefulness of Oblique Lumbar Magnetic Resonance Imaging for Nerve Root Anomalies and Extraforaminal Entrapment Lesions

Study Design

A retrospective review of prospectively evaluated magnetic resonance (MR) images.

Purpose

Routine lumbar axial and sagittal MR images may not clearly demonstrate nerve root anomalies and entrapments in the extraforaminal region. Thus, lumbar extraforaminal lesions or nerve root anomalies may be underdiagnosed because of unfamiliar radiological anatomy. We aimed to investigate the clinical efficacy of our oblique magnetic resonance imaging (MRI) technique for diagnosing nerve root anomalies and entrapment lesions.

Overview of Literature

Evaluation of clinical usefulness of oblique lumbar MRI for nerve root anomalies and extraforaminal entrapment lesions.

Methods

In total, 162 patients (60 males and 102 females; mean age, 59.8±17.8 years) with suspected nerve root anomalies and entrapments in routine axial and sagittal MR images underwent unilateral or bilateral oblique lumbar T2-weighted MRI. The axial angle of the oblique image was parallel to the foramen. The oblique MRI findings of the symptomatic side were compared with those of the asymptomatic side in cases with unilateral pathologic lesions. Interobserver agreement was analyzed using kappa statistics.

Results

The following abnormal findings were obtained: nerve root entrapment due to foraminal stenosis in 82 cases; extraforaminal disk herniation in 29; conjoined nerve root in six; and foraminal bony cyst in one. Forty-three of the 46 patients experienced unilateral lateralizing symptoms, unilateral nerve root entrapment due to foraminal stenosis, herniated disk, and extraforaminal bony cyst compared with the asymptomatic contralateral side (p <0.05).

Conclusions

Our results suggest that oblique lumbar MRI is a simple and valuable modality for diagnosing anomalous lumbar nerve root lesions and entrapment.

Morphological anatomy of thoracolumbar nerve roots and dorsal root ganglia

The aim of this study is to ascertain the anatomic parameters of the spinal roots and dorsal root ganglia and to demonstrate their clinical significance. Samples from 24 adult autopsy subjects were obtained from roots and dorsal root ganglia at levels L1 through L5. The anatomic parameters of epidural nerve roots: the distance between the epidural nerve roots and the proximal edge of the dorsal root ganglia and the average diameter of the nerve root gradually, increased from L1 to L5. The midline nerve root angle gradually decreased from L1 to L5. The anatomic parameters of subarachnoid nerve roots: the length of subarachnoid nerve roots and both the ventral and dorsal roots' diameter, increased from L1 to L5. The number of ventral and dorsal rootlets per nerve root ranged from one to three. The anatomic parameters of dorsal root ganglia: the length and width of the thoracic and lumbar dorsal root ganglia, gradually increased from L1 to L5. The locations of the dorsal root ganglia were recorded as the intraspinal, intraforaminal and extraforaminal using some bony landmarks. Most dorsal root ganglia located intraforaminally, and the extraforaminal type is more common in the L5 root than other thoracic and lumbar roots, regardless of age. This knowledge is a must not only to avoid complications but also for the success, safety and effectiveness of microsurgical operations.

Three-Years Outcome of Microdiscectomy via Paramedian Approach for Lumbar Foraminal or Extraforaminal Disc Herniations in Elderly Patients over 65 Years Old

OBJECTIVE

Lumbar foraminal or extraforaminal disc herniations (FEFDH) have unusual clinical features and higher incidence in elderly patients compared to usual intraspinal canal disc herniations. We evaluated the efficacy of microdiscectomy via paramedian approach for lumbar FEFDH in elderly patients over the age of 65.

METHODS

Retrospective study was performed in 68 patients over the age of 65 (23 male and 45 female patients; 71.46±3.87 years) who underwent microdiscectomy via paramedian approach for unilateral lumbar FEFDH causing sciatica. The radiological factors including degree of slippage, presence of instability, disc height, and degree of disc degeneration; pain and functional status by the means of visual analogue scale score, Oswestry Disability Index score, and Macnab classification were analyzed preoperatively and during the postoperative follow-up period of 3 years to evaluate the efficacy of the surgical treatment.

RESULTS

Pain and functional status improved according to short- and long-term follow-up evaluations after surgery. Radiological changes following surgery, which can be understood as structural deteriorations and deformations, did not represent patient condition. Nine patients underwent additional surgery due to sustained or recurring leg pain of aggravation of back pain, and fusion surgery was required for 3 patients. Degree of preoperative slippage was the only statistically significant factor related to additional surgery (p<0.05).

CONCLUSION

Microdiscectomy via paramedian approach for FEFDH may be a good surgical alternative in elderly patients. Radiological changes after surgery did not show a concordance with patients' actual functional status. The excessive preoperative slippage tended to lead to unfavorable result after surgery and was associated with additional surgery.

The projection of nerve roots on the posterior aspect of spine from T11 to L5: a cadaver and radiological study

STUDY DESIGN

A cadaver and radiological study.

OBJECTIVE

To investigate the projection of nerve roots on the posterior aspect of the spine from T11 to L5.

SUMMARY OF BACKGROUND DATA

Understanding the projection of nerve roots on the posterior lamina will help to determine the decompressing areas of lamina and avoiding unnecessary bony resection. It can prevent segmental instability and postoperative scar formation. No studies regarding this subject are available.

METHODS

Fifteen formalin-preserved spine specimens were used for this study. After exposing the dural sac and bilateral nerve roots, small pieces of stainless steel wires were placed along the root sleeves from their points of origin, and then standard anteroposterior and lateral radiographs were taken. Parameters were measured directly on radiographs using the picture archiving communication system. Measurements included: (1) take-off angles of the nerve roots at the coronal (CA) and sagittal planes (SA); (2) distance from the origin of the root sleeve to the posterior midline (DM); (3) distance from the origin of the root sleeve to the superior (DS) and inferior margin (DI) of its corresponding lamina; and (4) distance between the origins of neighboring nerve roots (DR).

RESULTS

The CA statistically decreased from T11 (52.4° ± 3.13°) to L5 (25.8° ± 3.10°). An opposite variation tendency was observed in SA. The DS increased from 1.8 ± 0.32 mm for T11 to 5.84 ± 1.05 mm for L5. No consistent change was found at DI. The DR was largest at the L1-L2 interval (33.9 ± 1.40 mm) and it decreased progressively to L4-L5 (25.5 ± 2.40 mm). DM statistically increased from T11 (8.9 ± 1.51 mm) to L1 (10.9 ± 1.11 mm) and then progressively decreased until it reached a minimum at L5 (8.1 ± 0.83 mm).

CONCLUSION

The precise projection of nerve roots to the posterior aspect of spine and intraspinal take-off angles at the sagittal plane have been presented. Surgical interventions of the lumbar disc and nerve root may benefit from this quantitative anatomical study.