Original article: A morphometric of the Pedicles of dry human typical lumbar vertebrae Dhaval K. Patil 1 *, Pritha S. Bhuiyan 2 1Resident, Department of Anatomy, Seth G S Medical College, Parel, Mumbai-400012, Maharashtra, India 2Professor and HOD, Department of Anatomy, Seth G S Medical College, Parel, Mumbai-400012, Maharashtra, India Corresponding author: Dr Dhaval K. Patil Date of submission: 21 May 2014; Date of Publication: 29 June 2014 ABSTRACT: Introduction: Pedicle screws are used with an increasing frequency for fixation in spinal fractures and degenerative spinal disorders. Hence the need for adequate anatomical knowledge of vertebral pedicles is imperative. The aimed at measuring the various dimensions of pedicles in typical lumbar vertebrae. Material and methods: Two hundred dry human typical lumbar vertebrae of undetermined gender and age were selected for the. The various parameters of pedicles were measured. Results: The mean pedicle width at the midpoint of the pedicle on the left side was 8.57 ± 1.69 mm and on the right side was 8.41 ± 1.62mm. The mean pedicle height at the midpoint of the pedicle on the left side was of 13.9 ± 1.39 mm and on the right side was 13.96 ± 1.34 mm. The mean transverse pedicle angle on the left side was 11.67 ± 4.09 degrees and on the right side was 11.79 ± 4.03 degrees. The mean sagittal pedicle angle on the left side was 4.67 ± 2.04 degrees and on the right side was 4.78 ± 2.06 degrees. The mean chord length on the left side was 44.65 ± 3.54 mm and on the right was 44.78 ± 3.55 mm. Conclusion: Thus, a comprehensive data set has been presented which will help in development of pedicle instruments for Indian population. Keywords: Typical lumbar vertebra, pedicle, chord length. INTRODUCTION: Spinal instability caused by fracture, deformity or degenerative disease is corrected by spinal fixation. Transpedicular screw fixation of spine has developed as a very successful method of spinal fixation. It is increasingly used worldwide. These screws enable various devices (plates, rods or wires) to be applied to the spine for the purpose of immobilization or fixation. Pedicular fixation is more stable and versatile because it provides threedimensional fixation. Also, it has been proved that the pedicle is the strongest part of the vertebra even in osteoporotic bone 1. Detailed knowledge of pedicle morphometry is critical for proper placement of the transpedicular screw and to avoid inadvertent penetration of the pedicular wall. The aimed at measuring the various dimensions of pedicles in typical lumbar vertebrae. Our aim was to the morphometry of typical lumbar vertebrae with respect to their pedicle. Our objectives were to measure the right and left pedicle width at the midpoint of the pedicle, to measure the right and left pedicle height at the midpoint of the pedicle, to measure the right and left transverse pedicle angle which is the angle made by the pedicle axis with the sagittal plane, to measure the right and left sagittal pedicle angle which is the angle made by the pedicle axis with 428
the transverse plane and to measure the right and 4. Sagittal pedicle angle- It is the angle left chord length (screw path length) which is the between a line passing through the pedicle distance from the most posterior aspect of the axis and superior vertebral body border in junction of the superior facet and the transverse the sagittal plane. process to the anterior cortex of the vertebral body 5. Chord length (Screw path length) - It is along the pedicle axis. the distance from the most posterior aspect METHODOLOGY: of the junction of the superior facet and The was conducted on dry human typical the transverse process to the anterior lumbar vertebrae. The vertebrae were obtained cortex of the vertebral body along the from the bone collection of the department of pedicle axis. Anatomy of a tertiary care hospital. Of the total collection of lumbar vertebrae in the department, 200 undamaged typical lumbar vertebrae were selected for the. The vertebrae were of undetermined gender and age. Each vertebra was assigned a serial number. Anatomical measurements were taken on these specimens using a vernier caliper (0-150mm with a precision of 0.02 mm). The vertebrae were photographed with a digital camera and the angular measurements were recorded using MB ruler software. MB ( Markus-Bader ) ruler is a software which is free to use for non-commercial purposes. 2 (Fig. 1-2) The following parameters were recorded in a proforma: 1. Pedicle width at the midpoint of the pedicle- It is the distance between medial and lateral surfaces of pedicle at its midpoint, measured at right angles to the long axis of the pedicle. 2. Pedicle height at the midpoint of the OBSERVATIONS AND RESULTS: pedicle- It is the vertical distance between 1. The pedicle width at the midpoint of the superior and inferior border of pedicle at pedicle on the left side ranged from 4.32 - its midpoint. 13.44 mm with a mean of 8.57 ± 1.69 mm and 3. Transverse pedicle angle- It is the angle on the right side ranged from 5.02-13.02 mm between a line passing through the pedicle with a mean of 8.41 ± 1.62 mm. axis and a line parallel to the vertebral 2. The pedicle height at the midpoint of the midline in the transverse plane. pedicle on the left side ranged from 10.22-17.54 mm with a mean of 13.9 ± 1.39 mm and 429
on the right side ranged from 10.42-17.42 mm with a mean of 13.96 ± 1.34 mm. 3. The transverse pedicle angle on the left side ranged from 4.02-23.69 degrees with a mean of 11.67 ± 4.09 degrees and on the right side ranged from 4.44-23.42 degrees with a mean of 11.79 ± 4.03 degrees. 4. The sagittal pedicle angle on the left side ranged from 1.4-9.31 degrees with a mean of 4.67 ± 2.04 degrees and on the right side ranged from 1.39-9.88 degrees with a mean of 4.78 ± 2.06 degrees. 5. The chord length on the left side ranged from 36.32-53.22 mm with a mean of 44.65 ± 3.54 mm and on the right side ranged from 36.46-53.48 mm with a mean of 44.78 ± 3.55 mm. DISCUSSION: Several quantitative anatomical studies have been carried out for lumbar vertebrae in different countries. Many authors have studied the pedicles of vertebrae using different methods such as computed tomography (CT) scans, Magnetic Resonance Imaging (MRI) scans, plain radiographs, direct specimen measurements and quantitative 3-dimensional anatomic techniques. The following tables present the comparison of means of the various parameters obtained from previous studies with that of the present. 1. PEDICLE WIDTH AT THE MIDPOINT OF THE PEDICLE The range of the pedicle width for typical lumbar vertebrae has been mentioned by Zindrick MR et al 3 as 4-17 mm, Ebraheim et al 4 as 5-17 mm and Aruna N et al 11 as 4.5-20 mm as compared to 4.32-13.44 mm in the present. TABLE 1: Comparison of mean pedicle width at the midpoint of the pedicle in typical lumbar vertebrae with other studies (in mm) Zindrick MR et al 3 1987 USA CT scans, 10.2 radiographs Ebraheim et al 4 1996 USA Dry bones 9.52 Alon Wolf et al 5 2001 Israel CT scans 8.4 Mitra SR et al 1 2002 India Cadaveric 8.72 Singel TC et al 6 2004 India Dry bones 10.28 Tan et al 7 2004 Singapore Dry bones Left: 7.18 Right: 6.98 Shiu-Bii Lien et al 8 2007 Taiwan Dry bones, cadaveric Left: 8.68 Right: 8.68 Urrutia VE et al 9 2009 Mexico CT scans 9.11 Acharya S et al 10 2010 India CT scans 8.73 Aruna N et al 11 2011 India Dry bones 9.15 Present India Dry bones Left: 8.57 Right: 8.41 430
2. PEDICLE HEIGHT AT THE MIDPOINT OF THE PEDICLE Pedicle height also influences pedicle screw selection. However, in all studies, it has been established that the pedicle height is always greater than the pedicle width. The present agrees with this finding. Thus, from a practical point of view, pedicle height carries lesser importance in deciding pedicular screw diameter. TABLE 2: Comparison of mean pedicle height at the midpoint of the pedicle in typical lumbar vertebrae with other studies (in mm) Ebraheim et al 4 1996 USA Dry bones 13.68 Alon Wolf et al 5 2001 Israel CT scans 14.8 Mitra SR et al 1 2002 India Cadaveric 15.21 Singel TC et al 6 2004 India Dry bones 14.65 Tan et al 7 2004 Singapore Dry bones Left: 12.8 Right: 13.03 Shiu-Bii Lien et al 8 2007 Taiwan Dry bones, cadaveric Left: 13.5 Right: 13.68 Aruna N et al 11 2011 India Dry bones 14.3 Present India Dry bones Left: 13.9 Right: 13.96 The range of pedicle height for typical lumbar vertebrae has been mentioned by Ebraheim et al 4 as 10-18 mm and Aruna N et al 11 as 10.5-20 mm as compared to 10.22-17.54 mm in the present. 3. TRANSVERSE PEDICLE ANGLE Knowledge of transverse pedicle angle is important while placing screws because any inadvertent medial perforation due to wrong placement of the pedicle screw can put the spinal cord at risk or cause vascular injury. TABLE 3: Comparison of mean transverse pedicle angle in typical lumbar vertebrae with other studies (In degrees) Ebraheim et al 4 1996 USA Dry bones 28.82 Alon Wolf et al 5 2001 Israel CT scans 12.42 Mitra SR et al 1 2002 India Cadaveric 11.24 Shiu-Bii Lien et al 8 2007 Taiwan Dry bones, cadaveric Left: 13.4 Right: 14.07 Acharya S et al 10 2010 India CT scans 14.2 Present India Dry bones Left: 11.67 Right: 11.79 431 429
Ebraheim et al 4 found that the transverse pedicle angle ranged between 20-40 degrees for typical lumbar vertebrae as compared to 4.02-23.69 degrees in the present. 4. SAGITTAL PEDICLE ANGLE Sagittal pedicle angle is important in accurate screw placement as inferior migration of the screw may result in injury to the nerve root. TABLE 4: Comparison of mean sagittal pedicle angle in typical lumbar vertebrae with other studies (In degrees) Ebraheim et al 4 1996 USA Dry bones 4.65 Mitra SR et al 1 2002 India Cadaveric 9.16 Shiu-Bii Lien et al 8 2007 Taiwan Dry bones, cadaveric Left: 4.65 Right: 5.3 Present India Dry bones Left: 4.67 Right: 4.78 Ebraheim et al 4 found that the sagittal pedicle angle ranged between 2-9 degrees for typical lumbar vertebrae as compared to 1.39-9.88 degrees in the present. 5. CHORD LENGTH (SCREW PATH LENGTH) Chord length determines the safest length of any screw that can be used for pedicular fixation. It is important in preventing anterior cortex perforation and therefore consequent injury to vital organs and major blood vessels which lie anterior to the vertebral body. TABLE 5: Comparison of mean chord length in typical lumbar vertebrae with other studies (in mm) Ebraheim et al 4 1996 USA Dry bones 48.87 Alon Wolf et al 5 2001 Israel CT scans 46.73 Mitra SR et al 1 2002 India Cadaveric 46.55 Tan et al 7 2004 Singapore Dry bones 41.78 Acharya S et al 10 2010 India CT scans 47.68 Present India Dry bones Left: 44.65 Right: 44.78 Ebraheim et al 4 noted that the range of chord length for typical lumbar vertebrae is 38-58 mm as compared to 36.32-53.48 mm in the present. CONCLUSION: Thus, this provides various dimensions of lumbar pedicles. Racial morphometric differences international transpedicular screw systems. The dimensions in this may help in the development of pedicular screws for Indian must be taken into account when using population. 432 430
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