Abstract
Background:
Transpedicular fixation depends on accuracy of the entry points, angle of insertion and pedicular isthmus width for adequate screw insertion. Preoperative measurements of pedicle dimensions reduce the chances of failure during insertion. These pedicle dimensions (transverse diameter, longitudinal diameter, and maximum length of purchase [MLP]) vary with sex and race. Such data, from a large-scale study, are not available for our population.
Objective:
The study aims to evaluate the dimensions of pedicle that are relevant for pedicle screw fixation in Southeast Nigerian population.
Materials and Methods:
A prospective multi-slice CT based clinical anatomy study done at Memfys Hospital for Neurosurgery, Enugu. This study is on the lumbar pedicle dimensions that are related to transpedicular fixation (transverse and longitudinal diameters of the pedicle, MLP, pedicle transverse and longitudinal angles of inclination). Sample size (273) was calculated with the confidence interval formula based on the number of patients that present for images. Consent and ethical approval were obtained.
Results:
The mean values are as follow: LD1 8.22 mm, LD2 7.73 mm, LD3 7.40 mm, LD4 7.16 mm, LD5 6.87 mm TD1 5.05 mm, TD2 5.31 mm, TD3 6.72 mm, TD4 8.27 mm, TD5 11.31 mm, MLP1 46.60 mm, MLP2 47.97 mm, MLP3 47.14 mm, MLP4 45.54 mm, MLP5 43.47 mm TA1 17.8°, TA2 19.34°, TA3 20.80°, TA4 22.00°, TA5 25.70° LA1 19.42°, LA2 18.61°, LA3 18.00°, LA4 17.09°, LA5 16.40°. Unlike transverse diameter, transverse angle, longitudinal dimension, longitudinal angle (LA), MLP there was significant correlation between age and mean LA. The mean values also correlated significantly with the gender.
Conclusion:
The mean values varied with the different vertebral levels and was good correlations between some of the parameters with age and gender.
Keywords: CT-scan, dimensions, fixation, lumbar, Nigeria, pedicle, South-Eastern, transpedicular
Introduction
Background
Instrumented spinal fusion, which was first described in 1911, has an edge over non-instrumented spinal fusion because of reduction and higher fusion rate.[1,2,3] Of the different stabilization techniques described, transpedicular method of stabilization is seen as the gold standard of spinal internal fixation.[4] It is safe and offers construct rigidity which is believed to allow stability that is, necessary for spinal arthrodesis and can also be used to correct deformities.[5] These advantages account for the popularity of the method and its increasing use for different lumbar spine diseases especially in patients with obvious risk of pseudoarthrodesis.
Significance of the problem/brief literature review
Transpedicular fixation, as popularized by Boucher depends on the detailed knowledge of the morphometry of the pedicle to prevent mismatch of pedicle and screw since pedicle dimensions vary with level of spine.[6] Generally, the lumbar pedicle is large and strong. According to Zindrick et al[7] the success of transpedicular fixation depends on the ability of the screw to obtain and maintain purchase of bone within body of vertebra. This in turn, is dependent on appropriate size screw for a particular pedicle size and presence or absence of osteoporosis. Entry points, angle of insertion and pedicular isthmus width are important parameters necessary for adequate placement of pedicle screw.[7] This makes it imperative that preoperative determination of the dimensions of the pedicle be done to reduce the chances of failure during insertion. These pedicle dimensions (transverse diameter, longitudinal diameter, and maximum length of purchase (MLP) [Figures 1 and 2] vary with sex and race.[1,8] Such data, from a large-scale study, are not available for our population.[9] Besides, craniocaudal and mediolateral angulations, which are very important in pedicle screw insertion, were not included in the previous local study available.[9]
Figure 1.
Axial views of the lumbar vertebrae showing parameters to be measured: transverse diameter (red arrow), transverse angle (green arc), MLP (red line) (Nkwerem, SPU. “CT image and lumbar vertebra bone” 2016 JPEG file).
Figure 2.
Sagittal view of the lumbar vertebra showing parameters to be measured: longitudinal dimension (red arrow), longitudinal angle (red arc) (Nkwerem, SPU. “CT image and lumbar vertebra bone” 2016 JPEG file).
Aims and objectives
It is hoped that this study and similar studies will address this problem and the problem of targeted screw size manufacture for the Nigerian market.
Setting/type of study
This is a prospective multi-slice CT based clinical anatomy study carried out in Memfys Hospital for Neurosurgery, Enugu.
Materials and Methods
This was a multi-slice CT based clinical anatomy study conducted at Memfys Hospital for Neurosurgery, Enugu. The multi-slice CT (64 slice) has high resolution (isotropic resolution) hence can give submillimeter measurements for reformatted thin slice views (sagittal and coronal), which are comparable to the original axial images because magnification is minimal.[10] It is a prospective study of the lumbar pedicle dimensions that are related to transpedicular fixation. This data was collected between January 2017 and November 2017. This is designed to measure for each of the lumbar vertebrae, the transverse and longitudinal diameters of the pedicle, MLP, pedicle transverse and longitudinal angles of inclination. The mean of each of these parameters was calculated for the population. This was done on consenting adult South-Eastern Nigerians (Igbo Nationality) aged between 20 and 70 years who presented for lumbosacral or abdominopelvic CT scan. The participants, however, should not have antecedent history of back trauma, musculoskeletal malformation, and radiological evidence of fracture or vertebral bone tumors.
Sample size was based on the number of patients that present for lumbosacral and abdominopelvic CT scan, using confidence interval formula, the estimated sample size was 287.
n = sample size= 287.
Ơ = estimated Standard deviation of a pilot study [1.73].
Zα/2 = Standard score based on probability of type 1 error (Zα = 1.96 with α = 0.05).
Zβ = Standard score based on power of the test (Zβ = 0.8416 with β = 0.20).
d = error of precision (d = 0.405).
They were recruited after a structured interview to rule out exclusion criteria while written consent was taken. All the patients underwent lumbosacral CT using the 64-slice scanner with standard protocol (3 mm slice thickness). All measurements were in millimeters, the plane and point of reference is as described by Marchesi et al.,[11] and as depicted in Figures 1 and 2. Data analyses were done using descriptive and inferential statistics. Ethical clearance was obtained.
Results
The study subjects consisted of 287 consecutively selected consenting males and females between the age group 20 and 70 years. The sex distribution showed that 147 males and 140 females were recruited [Figure 3].
Figure 3.
Showing age vs. sex
The age distribution showed that 50 subjects were between the age of 21 and 30 years, 51 participants were between 31 and 40 years, 57 subjects were between age 41 and 50 years, 69 people were between 51 and 60 years, while 61 subjects were between 61 and 70 years.
The transverse diameter (TD) in the study population was lower than what was observed in Egyptians, Indians, and Pakistanis [Figure 4].
Figure 4.
Variation in transverse diameter among different races
Discussion
This study found a craniocaudal increase in the transverse pedicular diameter, similar to what was observed among Pakistanis, Mexicans, Egyptians, and Americans.[1,8,12,13] Badmus et al.[9] also observed similar trend in Lagos. However among the Israelis, Wolf et al.[14] found out that L2 and L3 had the smallest TD while the extremes (L1 and L5) had the largest TD. The current study shows that thicker pedicles are seen at the lower part of the lumbar spine [Table 1]. The implication is that larger pedicle screws are needed in the lower part for a rigid and stable construct.
Table 1.
Shows the mean value of transverse diameter, transverse angle, for the different levels
| Variables | Number | Mean | Standard deviation |
|---|---|---|---|
| TD1 | 287 | 5.05 mm | 1.51 |
| TD2 | 287 | 5.31 mm | 1.64 |
| TD3 | 287 | 6.72 mm | 3.50 |
| TD4 | 287 | 8.27 mm | 1.94 |
| TD5 | 287 | 11.31 mm | 2.47 |
| TA1 | 287 | 17.80° | 4.45 |
| TA2 | 287 | 19.34° | 3.89 |
| TA3 | 287 | 20.80° | 4.25 |
| TA4 | 287 | 22.00° | 4.90 |
| TA5 | 287 | 25.70° | 5.00 |
In the above table; transverse diameter and transverse angle means increase craniocaudally
There was a craniocaudal decrease in the lumbar pedicle longitudinal diameter. Urratia et al.[12] using fluoroscopy also showed a similar pattern among the Mexicans. Among Americans, craniocaudal decrease of the longitudinal diameter was also observed.[15] Badmus et al.[9] found out that L2 has the smallest lumbar longitudinal diameter Southwest Nigeria. The L1 to L3 lumbar longitudinal diameter are larger than the corresponding transverse diameter, while the reverse was seen in L4 and L5 [Table 2]. The implication is that both the longitudinal and transverse diameters should ideally be considered while determining pedicle screw size. This is not in agreement with findings by Zindrick et al.[15] who noted that longitudinal diameters were generally larger than transverse diameter in the Americans.
Table 2.
Shows the mean value of longitudinal dimension, longitudinal angle, and MLP for the different levels
| Variables | Number | Mean | Standard deviation |
|---|---|---|---|
| LDI | 287 | 8.22 mm | 1.23 |
| LD2 | 287 | 7.73 mm | 1.16 |
| LD3 | 287 | 7.40 mm | 1.02 |
| LD4 | 287 | 7.16 mm | 1.15 |
| LD5 | 287 | 6.87 mm | 1.18 |
| LA1 | 287 | 19.42° | 2.61 |
| LA2 | 287 | 18.61° | 2.58 |
| LA3 | 287 | 18.00° | 2.83 |
| LA4 | 287 | 17.09° | 3.77 |
| LA5 | 287 | 16.40° | 3.27 |
| MLP1 | 287 | 46.60 mm | 4.00 |
| MLP2 | 287 | 47.97 mm | 3.54 |
| MLP3 | 287 | 47.14 mm | 4.30 |
| MLP4 | 287 | 45.54 mm | 3.66 |
| MLP5 | 287 | 43.47 mm | 4.28 |
In the above table; longitudinal dimension, longitudinal angle, and most of MLP values show craniocaudal decrease in mean
The transverse angle was noted to increase from L1 vertebra level to L5 vertebra [Table 1]. Similar trend was seen in other studies.[13,16] The average rate of increase per level is approximately 2°. However, highest increase per level was seen between L4 and L5. The implication is that the angle of placement of pedicle screw increases from L1 to L5, with even larger angle of placement is necessary at L5 level in order to successfully cannulate the pedicle. This is important for surgeons who place pedicle screw under direct vision either because of lack of availability of fluoroscopy or because of preference. The longitudinal angle decreases from L1 to L5. This is in consonance with earlier work done by Zindrick et al.[15]
The maximum MLP was seen at L2. There was craniocaudal decrease from L3 to L5. The same pattern was noted in the Egyptian and Indian population.[13,16] The closeness of great vessels to the anterior part of the vertebral body makes this measurement very important. It is believed that there is less chance of inadvertent anterior cortex penetration when pedicle is inserted along the pedicle axis as against when it is inserted parallel to the midline axis.15 This is why pedicle axis insertion was chosen in this study. The MLP is very important in choosing an implant but should ideally be checked with fluoroscopic control during screw insertion.
The mean LD, TD, and MLP of the lumbar pedicle are higher in males compared to female. The relationship was significant in LD for first, second, and fifth vertebrae. The relationship was also significant for TD and MLP for all the vertebrae levels [Table 3]. This means that pedicles in males are bigger and longer. The relatively bigger statue seen in male may explain this finding.[15] In the Indian and Chinese populations, the mean MLP was higher in male when compared with female.[17,18] This is in consonance with the current study. The clinical relevance of this finding is that longer screws may be necessary to achieve good constructs in males compared to females of South-Eastern Nigeria. The TA and LA are known to be larger in female than in male.[1] The trend was also noted in this study. The relationship was however not significant, for most levels, in the current study [Table 4]. In the Chinese and Indian populations, transverse angle in male population was higher in the third and fifth lumbar vertebrae when compared to female population.[17,18] The reason for this is unclear but may not be unrelated to the genetic and environmental factors among races. Significant negative correlation was seen only between age and mean LA. This means that the angles reduce with increasing age. There was significant correlation in the TD1, LD1, and LA1. This may be explained by fact that it is a transition zone. The movement of first lumbar vertebrae against the relatively immobile thoracic vertebrae may predispose the first lumbar vertebra to wear and tear changes and attendant remodeling which could affect the lumbar dimensions. The other mean pedicle measurements mostly show insignificant correlation with age [Table 5]. Generally, after adolescence, most patients have attained adult size for most skeletal tissues. The subsequent changes seen are as a result of osteoporosis, wear and tear, and subsequent remodeling.[19] Yu et al.[20] found these changes in dimension insignificant in most cases.
Table 3.
Shows the relationship between gender and measured values [longitudinal dimension, longitudinal angle, and MLP]
| Variables | Sex | Number | Mean | T | P value |
|---|---|---|---|---|---|
| LD1 | Male | 147 | 8.48 mm | 3.869 | 0.000 |
| Female | 140 | 7.93 mm | |||
| LD2 | Male | 147 | 8.05 mm | 5.098 | 0.000 |
| Female | 140 | 7.38 mm | |||
| LD3 | Male | 147 | 7.51 mm | 1.783 | 0.076 |
| Female | 140 | 7.30 mm | |||
| LD4 | Male | 147 | 7.23 mm | 1.083 | 0.028 |
| Female | 140 | 7.09 mm | |||
| LD5 | Male | 147 | 7.11 mm | 3.656 | 0.000 |
| Female | 140 | 6.61 mm | |||
| LA1 | Male | 147 | 19.31° | -0.833 | 0.406 |
| Female | 140 | 19.56° | |||
| LA2 | Male | 147 | 18.36° | -1.802 | 0.073 |
| Female | 140 | 18.90° | |||
| LA3 | Male | 147 | 17.62° | -2.267 | 0.024 |
| Female | 140 | 18.90° | |||
| LA4 | Male | 147 | 16.72° | -1.744 | 0.082 |
| Female | 140 | 17.50° | |||
| LA5 | Male | 147 | 16.05° | -1.922 | 0.056 |
| Female | 140 | 16.79° | |||
| MLP1 | Male | 147 | 48.04 mm | 6.962 | 0.000 |
| Female | 140 | 45.02 mm | |||
| MLP2 | Male | 147 | 48.03 mm | 8.025 | 0.000 |
| Female | 140 | 46.36 mm | |||
| MLP3 | Male | 147 | 48.91 mm | 8.232 | 0.000 |
| Female | 140 | 45.15 mm | |||
| MLP4 | Male | 147 | 46.88 mm | 7.102 | 0.000 |
| Female | 140 | 44.04 mm | |||
| MLP5 | Male | 147 | 45.04 mm | 7.165 | 0.000 |
| Female | 140 | 41.70 mm |
The relationship was significant for all MLPs
Table 4.
Shows the relationship between gender and measured values [transverse diameter and transverse angle]
| Variables | Sex | Number | Mean | T | P value |
|---|---|---|---|---|---|
| TD1 | Male | 147 | 5.69 mm | 8.426 | 0.000 |
| Female | 140 | 4.34 mm | |||
| TD2 | Male | 147 | 5.95 mm | 7.749 | 0.000 |
| Female | 140 | 4.58 mm | |||
| TD3 | Male | 147 | 7.44 mm | 3.648 | 0.000 |
| Female | 140 | 5.92 mm | |||
| TD4 | Male | 147 | 8.84 mm | 5.527 | 0.000 |
| Female | 140 | 7.64 mm | |||
| TD5 | Male | 147 | 12.05 mm | 5.625 | 0.000 |
| Female | 140 | 10.49 mm | |||
| TA1 | Male | 147 | 17.72° | -0.305 | 0.761 |
| Female | 140 | 17.88° | |||
| TA2 | Male | 147 | 18.74° | -2.827 | 0.005 |
| Female | 140 | 20.03° | |||
| TA3 | Male | 147 | 20.62° | -0.727 | 0.468 |
| Female | 140 | 20.98° | |||
| TA4 | Male | 147 | 21.36° | -2.408 | 0.017 |
| Female | 140 | 22.72° | |||
| TA5 | Male | 147 | 25.22° | -1.805 | 0.072 |
| Female | 140 | 26.30° |
The relationship was significant for all transverse diameters
Table 5.
Shows the relationship between age and mean transverse diameter, transverse angle, longitudinal dimension, longitudinal angle, and MLP
| Variables | Pearson correlation | P value |
|---|---|---|
| LD1 | 0.177 | 0.003 |
| LD2 | 0.143 | 0.016 |
| LD3 | 0.086 | 0.145 |
| LD4 | 0.095 | 0.109 |
| LD5 | 0.035 | 0.552 |
| TD1 | 0.141 | 0.017 |
| TD2 | 0.097 | 0.101 |
| TD3 | 0.063 | 0.029 |
| TD4 | 0.142 | 0.016 |
| TD5 | 0.038 | 0.526 |
| TA1 | 0.105 | 0.075 |
| TA2 | -0.054 | 0.361 |
| TA3 | -0.145 | 0.014 |
| TA4 | -0.094 | 0.114 |
| TA5 | -0.002 | 0.972 |
| LA1 | -0.187 | 0.001 |
| LA2 | -0.296 | 0.000 |
| LA3 | -0.302 | 0.000 |
| LA4 | -0.260 | 0.000 |
| LA5 | -0.202 | 0.001 |
| MLP1 | 0.059 | 0.321 |
| MLP2 | 0.012 | 0.835 |
| MLP3 | 0.123 | 0.037 |
| MLP4 | 0.088 | 0.137 |
| MLP5 | 0.161 | 0.006 |
There was significant correlation in all the vertebral levels in the mean longitudinal angle. Whereas for mean transverse diameter, transverse angle, longitudinal dimension, and MLP, significant correlation was seen only in some vertebral levels
Most of the mean TD and MLP in the study population are smaller than the mean values seen in the Egyptians, Indians, and Pakistanis. The average transverse angle at each level appears to be higher than what was seen among the Indians, and Pakistanis. This may be explained by the subtle differences in body builds. The implication is that relatively smaller pedicular screws are needed for lumbar transpedicular fixations for the study population when compared to what is needed in Egyptians, Indians, and Pakistanis. This is an important consideration for both the biomedical engineer and the local surgeon for operations on patients from this region.
There are however some limitations in this study. Firstly, a non-probability sampling method was used which may have introduced some level of bias to the study. Secondly, this is a hospital-based study. Ideally, participants who are apparently healthy should have been used in this study. This was mitigated by ensuring that candidates for the study had no complaints referable to the spine. The use of patients presenting for spine imaging was based on the daunting logistics of recruiting from the normal population. Furthermore, the exposure of people to radiation when they do not necessarily need it makes the use of apparently healthy population morally and ethically unwise. Notwithstanding, the use of patients with no clinical and radiological evidence of spine injury, and by extension pedicle fracture, will make this measurement comparable to the normal population. A multicenter study will be necessary in order to obtain measurements that may be a true representation for the entire nation. A measurement of the height and weight of the participants to know the true relationships with the pedicle dimensions may also be enriching.
The data obtained however will serve as a reference for the South East population and possibly entire Nigerian population. Transpedicular screw fixation is widely believed to be superior to other lumbar spine fixations. This method of spinal fixation is now available in many centers in Nigeria.
It is important that biomedical industries are encouraged to produce implants that are targeted to this study population and local industries should also be encouraged to produce implants. These will ensure the availability of implants of desired biomechanics for the study population.
Conclusion
The mean value of pedicle dimensions that are relevant in transpedicular fixation in the South-Eastern Nigeria population are as follows, LD1 8.22 mm, LD2 7.73 mm, LD3 7.40 mm, LD4 7.16 mm, LD5 6.87 mm, TD1 5.05 mm, TD2 5.31 mm, TD3 6.72 mm, TD4 8.27 mm, TD5 11.31 mm, TA1 17.80°, TA2 19.34° TA3 20.80° TA4 22.00° TA5 25.70°. LA1 19.42°, LA2 18.61°, LA3 18.00° LA4 17.09° LA5 16.40°, MLP1 46.60 mm MLP2 47.97 mm MLP3 47.14 mm MLP4 45.54 mm MLP5 43.47 mm. The mean pedicle longitudinal and transverse diameters are higher in males when compared to females of South East Nigerians. However, the pedicles are more widely spaced from the midline in females. There appears not to be any significant relationship between age and pedicle dimensions. The values obtained were different from what had been reported in other races. The data obtained should be used as a reference data for research and clinical use.
Conflict of interest
There are no conflicts of interest.
Data availability
The data used to support the findings of this study are available from the site on request.
Ethical approval and consent to participate
Ethical approval was obtained from Ethics Committee, Memfys Hospital for Neurosurgery, Enugu.
Financial support and sponsorship
This was provided by the management of Memfys Hospital for Neurosurgery, Enugu.
Acknowledgement
The management and staff of Memfys Hospital for Neurosurgery for approving this work and providing the logistics.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data used to support the findings of this study are available from the site on request.