J. Anal. (1995) 186, pp. 321-328, with I figure
`
`Printed in Great Britain
`
`321
`
`Age-related variations in the horizontal and vertical diameters
`of the pedicles of the lumbar spine
`
`H. S. AMONOO-KUOFI
`
`Department of Anatomy, King Saud University, Riyadh, Saudi Arabia
`
`(Accepted 28 September 1994)
`
`ABSTRACT
`The horizontal and vertical diameters of the pedicles of the lumbar vertebrae were measured from plain
`anteroposterior radiographs of the lumbar spines of male and female subjects aged from 10 to 65 y. The
`results showed that there were significant differences between the pedicle diameters of males and females.
`Horizontal diameters ranged from 7.4 to 13.6 mm in females and from 7.5 to 14.2 mm in males. Female
`vertical diameters ranged from 14.2 to 18.2 mm whilst male vertical diameters ranged from 14.8 to 20.7 mm.
`Generally, there was a cephalocaudal increase of diameters in both sexes. Significant age-related variations
`of pedicle diameters were noted at all segmental levels. Within the adolescent group (10-19.9 y), the
`diameters of the 10-14.9 y group and 15-19.9 y group differed significantly (P < 0.001). When the pedicle
`diameters of the individual age groups were compared, the pedicles of the 10-19.9, 20-29.9, 30-34.9,
`40-49.9, and 50 + y groups were found to be significantly different from each other. The evidence suggests
`that pedicle diameters undergo continuous change throughout the age range studied. The changes are
`characterised by increase of diameters in some age groups and decrease in others, but there was an overall
`increase of both vertical and horizontal diameters as the age groups were followed from the youngest to the
`oldest. The pattern of variation with age differed for horizontal and vertical diameters. After the 5th decade,
`female horizontal and vertical diameters showed a tendency to increase while male diameters decreased.
`
`Key words: Lumbar spine; vertebral neural arch pedicles; age changes.
`
`INTRODUCTION
`The last two decades have seen an increasing use of
`transpedicular screw instrumentation techniques as a
`means of spinal fixation (Stefee et al. 1986; Lorenz et
`al. 1993). Zindrick (1991) described the screw fixation
`procedure as the method of choice for stabilisation of
`the lumbosacral spine. Many types of pedicle screw
`systems have been developed. Basically, they all entail
`the insertion of screws through the pedicle (from the
`posterior aspect) into the vertebral body. The screws
`enable various devices (plates, rods or. wires) to be
`applied to the spine for the purpose of immobilisation
`or fixation. The success of the technique depends
`upon the ability of the screw to obtain and maintain
`purchase within the vertebral body (Zindrick et al.
`1986). This is determined, among other factors, by the
`accuracy of choice of screw, size of the pedicle and the
`
`quality of the bone of the pedicle. Loosening of the
`screw, and penetration or fracture of the cortical bone
`shell of the pedicle are common causes of device
`failure that may be associated with serious complica-
`tions. Penetration of the cortex or fracture of the
`pedicle may result from the use of relatively oversized
`screws. Some of the complications that have been
`reported include dural tears, leakage of cerebrospinal
`fluid and injuries to the nerve roots with neurological
`deficits (Krag et al. 1985; Zindrick et al. 1986; Esses
`& Sachs, 1992; Weinstein et al. 1992). Most surgeons
`prefer to use as large a screw as possible for any
`al. (1986)
`given pedicle because, as Zindrick et
`observed, larger-diameter screws were stronger and
`gave better results. The choice of screw for the
`procedure is, nevertheless, determined by the mini-
`mum (horizontal) diameter of the pedicle (Krag et al.
`1986; Zindrick et al. 1987; Weinstein et al. 1992).
`
`Correspondence to Dr H. S. Amonoo-Kuofi, Department of Anatomy (28), College of Medicine, King Saud University, P.O. Box 2925,
`Riyadh 11461, Saudi Arabia.
`
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`322
`
`H. S. Amonoo-Kuofi
`
`Morphometric data on the diameters of the pedicles
`are therefore useful in preoperative planning and in
`the designing of pedicle screws. Norms of the vertical
`and horizontal diameters of thoracic and lumbar
`pedicles have been published (Saillant, 1976; Krag et
`al. 1986; Roy-Camille et al. 1986; Zindrick et al. 1986,
`1987; Berry et al. 1987; Scoles et al. 1988; Weinstein
`et al. 1992). The reports were based on studies of
`samples of adult material ranging in age from 20 to
`80 y. There appears to be no information on the
`pedicle diameters of younger subjects although, as
`Bauer & Errico (1991) pointed out, a greater pro-
`portion of the patients needing lumbar spinal fixation
`belong to the younger segment of the population.
`Reporting on a follow-up of 19 postoperative cases,
`McLain et al. (1993) cautioned that there was 'an
`alarming rate of early failure of screw fixation' in
`cases of thoracolumbar fracture managed by pedicle
`screw instrumentation. The duration of follow-up of
`the patients ranged from 5 to 28 months. Possible
`weaknesses in the screws and techniques of application
`were suggested as probable causes of device failure. It
`is noteworthy, however, that 16 of the 19 patients
`surveyed (84 %) were younger than 35 y old. Seven
`out of the 16 were aged 20 y or younger. This age
`group is normally characterised by a high velocity of
`growth-the growth spurt that is experienced at
`adolescence. Would the diameters of the pedicles of
`these growing individuals remain unchanged? This
`information would be especially useful in the follow-
`up of growing pedicles that have indwelling screws.
`With the exception of the report of Scoles et al.
`(1988), most published norms of pedicle diameters
`appear to have been based on measurements of mixed
`populations of male and female subjects. The samples
`studied by Berry et al. (1987) and Scoles et al. (1988)
`were apparently obtained from the same source
`(Scoles et al. 1988). Berry et al. (1987) examined 30
`specimens ranging in age from 50 to 80 y. They did
`not separate male and female specimens. The sample
`studied by Scoles et al. (1988) consisted of 25 male and
`25 female spines ranging in age from 20 to 40 y. Scoles
`(1988) not only reported smaller pedicle
`al.
`et
`diameters than Berry et al. (1987), but they also noted
`that there were slight differences between male and
`female pedicle diameters. The questions that arise are:
`(1) Are there significant differences between the
`diameters of the pedicles of young and old indivi-
`duals? (2) Are there significant differences between the
`pedicle diameters of males and females of identical
`ages?
`The present study was undertaken in an attempt to
`find answers to these questions.
`
`MATERIALS AND METHODS
`
`Many techniques, including osteometry (Berry et al.
`1987; Scoles et al. 1988), measurements from plain
`radiographs (Baddely, 1976; Zindrick et al. 1987) and
`computerised tomograms (Krag et al. 1986; Zindrick
`et al. 1987; Weinstein et al. 1992) have been used to
`study vertebral pedicles. Outlines of the pedicles are
`well demarcated on plain anteroposterior radiographs
`and accurate measurements may be made directly
`from the films (Baddely, 1976; Zindrick et al. 1986).
`Comparative studies reported by Zindrick et al. (1986,
`1987), Weinstein et al. (1992), Errico & Palmer (1993)
`established that measurements obtained directly from
`plain films correlated well with values measured from
`computerised tomograms and from anatomical speci-
`mens.
`Plain anteroposterior radiographs of the lumbar
`spines of 540 subjects (270 males, 270 females) with
`ages ranging from 10 to 65 y, were studied. Radio-
`graphs were selected from the records of patients who
`had attended the Accident and Emergency unit of the
`King Khalid University Hospital with suspected
`recent accidental injury to the spine and in whom no
`bony injury could be found. No subjects were
`routinely exposed to x-rays. A standardised technique
`was used in taking all the radiographs. The same
`radiographic equipment was used in all cases. Patients
`were x-rayed in the recumbent position. The x-ray
`beam was centred on the 3rd lumbar vertebra and
`directed at 900 to the film. An anode-film distance of
`100 cm was maintained. The magnification resulting
`from the use of this technique was negligible. All films
`were screened for readability and certified to be free
`from spinal pathology by a diagnostic radiologist.
`
`Selection of subjects
`
`Care was taken to exclude individuals with a history
`of back pain over the past 12 month period or patients
`receiving treatment for back pain. Other exclusion
`criteria that were used to select radiographs were: (1)
`history of surgery for disorders related to the vertebral
`column; (2) history of growth disorders; (3) history of
`systemic bone disease or chronic renal disease; (4)
`history of malabsorption; (5) evidence of scoliosis,
`kyphosis or other spinal pathology.
`Male and female subjects were grouped separately
`into 5 age groups. Each age group spanned 10 y.
`Subjects aged 50 y and over were grouped together as
`50 + y. The age and sex distribution of the sample are
`shown in Table 1.
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`Diameters of the lumbar pedicles
`
`323
`
`Table 1. Distribution of sample according to age groups and
`sex
`
`Age group (y)
`
`Females (n)
`
`Males (n)
`
`10-19.9
`20-29.9
`30-39.9
`40-49.9
`50 +
`
`60
`60
`60
`60
`30
`
`60
`60
`60
`60
`30
`
`Fig. Anteroposterior radiograph of the lumbar spine illustrating the
`landmarks used for measuring the diameters of the pedicle. v,
`vertical diameter; h, horizontal diameter.
`
`Measurements
`
`Pedicle diameters were measured in 2 mutually
`perpendicular planes, v and h (see Fig.). On the plain
`radiograph, the outline of the pedicle is somewhat
`oval. The vertical diameter (v) was taken as the
`maximum dimension of the pedicle in the sagittal
`plane. At the lower lumbar levels, the plane of the
`vertical diameter was oblique, with the upper end
`nearer the midline than the lower. The horizontal
`diameter, h, was the maximum diameter in a plane at
`right angles to the vertical diameter. Pencil marks
`were first placed on the limits of the pedicle. Distances
`were then measured by means of a digitising tablet
`connected to a microcomputer. All measurements
`were made by the author. Each radiograph was
`measured twice,
`at separate sittings, the second
`measurement serving as a check on the first. Right and
`
`left pedicles were measured at each level. No differ-
`ences were noted between the diameters of corre-
`sponding right and left pedicles. The marks were
`completely erased from the films between measure-
`ments to avoid bias during the second reading.
`Differences between initial and repeat readings ranged
`from 0 to 0.1 1 mm with a median of 0.04 mm.
`
`Statistical analyses
`
`The mean (horizontal and vertical) diameters, stan-
`dard errors of the means (S.E.M.) and standard
`deviations (S.D.) of the diameters of the pedicles of all
`the lumbar vertebrae (LI to L5) were calculated
`(separately for males and females) using the StatPac
`Gold statistical analysis package. Differences between
`the mean diameters of the pedicles of males and
`females belonging to the various age groups were
`tested by means of a 2-way analysis of variance (2
`factor factorial ANOVA) in a completely randomised
`design, with vertebral level as a covariate. Multiple 2-
`tailed t tests were used in combination with ANOVA
`test the differences between individual mean
`to
`diameters. 95 % confidence limits of the mean diam-
`eters [mean + 1.96(s.E.M.)] were calculated for all age
`groups at all levels.
`
`RESULTS
`
`General observations
`The mean horizontal and vertical diameters of the
`pedicles of the 1st-5th lumbar (L1-L5) vertebrae of
`males and females are tabulated in Tables 2-6. The
`tables also show the 95 % confidence limits of the
`pedicle diameters calculated for the various age groups
`at all 5 lumbar levels and the results of the t tests of the
`differences between male and female mean diameters.
`There were significant differences (P < 0.00 1) between
`the mean diameters of the pedicles of males and
`females at all lumbar levels in most age groups (Tables
`2-6). As a rule, in the 10-19.9 y age group, the mean
`diameters of female pedicles were greater than the
`mean diameters of male pedicles. A reversal was noted
`from age group 20-29.9 y upwards, with male dia-
`meters exceeding those of females. Differences be-
`tween the pedicle diameters of males and females in
`the 6th decade were mostly not statistically significant.
`At all 5 lumbar levels, differences were noted between
`the mean diameters of the pedicles of the various age
`groups. Differences between contiguous age groups
`were small in some cases. However, ANOVA showed
`that at each of the 5 lumbar levels, the variations of
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`324
`
`H. S. Amonoo-Kuofi
`
`Table 2. Diameters of the pedicles of LI vertebra offemales and males
`
`Age group
`(y)
`
`10-19.9
`
`20-29.9
`
`30-38.9
`
`40-49.9
`
`50+
`
`Diameter
`
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`
`Females
`
`Mean
`diam.
`(mm)
`
`9.8
`15.5
`7.4
`15.1
`8.3
`16.2
`8.7
`16.3
`8.5
`17.2
`
`S.E.M.
`
`0.3
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`
`95%
`confidence
`limits (mm)
`
`9.3-10.3
`15.1-15.9
`7.1-7.7
`14.6-15.5
`8.0-8.7
`15.8-16.6
`8.4-8.9
`15.9-16.7
`8.2-8.8
`16.8-17.6
`
`*P, difference between mean diameters of females and males; ns, not significant.
`
`Table 3. Diameters of the pedicles of L2 vertebra offemales and males
`
`Age group
`(y)
`
`10-19.9
`
`20-29.9
`
`30-39.9
`
`40-49.9
`
`50+
`
`Diameter
`
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`
`Females
`
`Mean
`diam.
`(mm)
`
`10.5
`14.6
`8.1
`15.3
`8.6
`15.7
`9.0
`15.3
`9.1
`16.8
`
`S.E.M.
`
`0.3
`0.3
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.3
`0.2
`
`95%
`confidence
`limits (mm)
`
`10.0-11.1
`14.1-15.1
`7.8-8.4
`14.9-15.7
`8.3-8.8
`15.3-16.1
`8.7-9.4
`15.0-15.7
`8.5-9.7
`16.5-17.1
`
`*P, difference between mean diameters of females and males; ns, not significant.
`
`Table 4. Diameters of the pedicles of L3 vertebra offemales and males
`
`Age group
`(y)
`
`10-19.9
`
`20-29.9
`
`30-39.9
`
`40-49.9
`
`50+
`
`Diameter
`
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`
`Females
`
`Mean
`diam.
`(mm)
`
`11.9
`15.1
`9.0
`15.9
`10.5
`16.3
`10.5
`15.9
`11.3
`17.1
`
`S.E.M.
`
`0.3
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.2
`0.3
`0.2
`
`95%
`confidence
`limits (mm)
`
`11.3-12.4
`14.6-15.5
`8.6-9.4
`15.5-16.2
`10.1-10.9
`15.9-16.6
`10.1-10.8
`15.5-16.2
`10.7-12.0
`16.7-17.5
`
`*P, difference between mean diameters of females and males; ns, not significant.
`
`Males
`
`Mean
`diam.
`(mm)
`
`7.5
`15.4
`9.3
`18.2
`9.6
`17.2
`10.3
`19.4
`9.5
`17.6
`
`Males
`
`Mean
`diam.
`(mm)
`
`8.3
`14.9
`9.9
`17.8
`10.3
`17.5
`10.7
`18.9
`9.9
`17.6
`
`Males
`
`Mean
`diam.
`(mm)
`
`9.7
`14.8
`11.6
`17.7
`11.8
`17.0
`12.1
`19.3
`12.1
`16.8
`
`95%
`confidence
`limits (mm)
`
`7.1-7.9
`14.8-16.0
`9.0-9.6
`17.9-18.4
`9.1-9.9
`16.9-17.5
`9.9-10.6
`18.9-19.9
`9.0-10.0
`17.1-18.0
`
`95%
`confidence
`limits (mm)
`
`7.8-8.7
`14.2-15.6
`9.4-10.4
`17.9-18.1
`9.8-10.7
`17.1-17.8
`10.3-11.2
`18.4-19.4
`9.2-10.6
`17.3-17.5
`
`95%
`confidence
`limits (mm)
`
`9.3-10.2
`14.1-15.4
`11.2-12.0
`17.5-17.9
`11.3-12.4
`16.8-17.2
`11.6-12.6
`18.7-19.9
`11.4-12.8
`16.3-17.3
`
`P*
`
`< 0.001
`ns
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`ns
`
`P*
`
`< 0.001
`ns
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`<0.001
`ns
`ns
`
`P*
`
`< 0.001
`ns
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`< 0.001
`ns
`ns
`
`S.E.M.
`
`0.2
`0.3
`0.2
`0.1
`0.2
`0.2
`0.3
`0.3
`0.2
`0.2
`
`S.E.M.
`
`0.2
`0.3
`0.2
`0.1
`0.3
`0.2
`0.2
`0.3
`0.4
`0.2
`
`S.E.M.
`
`0.2
`0.3
`0.2
`0.1
`0.3
`0.1
`0.3
`0.3
`0.3
`0.2
`
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`

`Diameters of the lumbar pedicles
`
`Table 5. Diameters of the pedicles of L4 vertebra offemales and males
`
`Age group
`(y)
`
`10-19.9
`
`20-29.9
`
`30-39.9
`
`40-49.9
`
`50+
`
`Diameter
`
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`
`Females
`
`Mean
`diam.
`(mm)
`
`11.7
`15.2
`11.4
`16.3
`11.8
`17.3
`11.1
`16.1
`11.9
`17.6
`
`S.E.M.
`
`0.3
`0.2
`0.2
`0.1
`0.1
`0.1
`0.2
`0.1
`0.2
`0.2
`
`95%
`confidence
`limits (mm)
`
`11.1-12.3
`14.8-15.7
`10.9-11.8
`16.1-16.5
`11.5-12.1
`17.0-17.5
`10.6-11.5
`15.9-16.3
`11.5-12.3
`17.3-17.9
`
`*P, difference between mean diameters of females and males; ns, not significant.
`
`Table 6. Diameters of the pedicles of L5 vertebra offemales and males
`
`Age group
`(y)
`
`10-19.9
`
`20-29.9
`
`30-39.9
`
`40-49.9
`
`50+
`
`Diameter
`
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`Horizontal
`Vertical
`
`Females
`
`Mean
`diam.
`(mm)
`
`12.0
`17.3
`11.9
`17.6
`12.4
`18.2
`12.5
`17.5
`13.6
`17.8
`
`S.E.M.
`
`0.3
`0.2
`0.2
`0.2
`0.1
`0.2
`0.2
`0.1
`0.2
`0.2
`
`95%
`confidence
`limits (mm)
`
`11.4-12.6
`16.8-17.8
`11.5-12.2
`17.3-18.0
`12.1-12.7
`17.9-18.5
`12.0-12.9
`17.2-17.7
`13.2-14.0
`17.3-18.3
`
`Males
`
`Mean
`diam.
`(mm)
`
`11.0
`15.5
`12.7
`18.7
`12.8
`17.7
`13.0
`19.9
`13.3
`18.1
`
`Males
`
`Mean
`diam.
`(mm)
`
`11.5
`16.7
`13.6
`19.3
`13.7
`18.8
`14.2
`20.7
`13.3
`18.6
`
`*P, difference between mean diameters of females and males; ns, not significant.
`
`325
`
`P*
`
`< 0.10
`ns
`< 0.001
`< 0.001
`< 0.001
`< 0.05
`< 0.001
`< 0.001
`< 0.001
`< 0.05
`
`P*
`
`ns
`ns
`< 0.001
`< 0.001
`< 0.001
`< 0.02
`< 0.001
`< 0.001
`ns
`< 0.02
`
`95%
`confidence
`limits (mm)
`
`10.4-11.6
`14.2-16.3
`12.2-13.1
`18.5-19.0
`12.3-13.3
`17.4-18.0
`12.7-13.4
`19.4-20.5
`12.9-13.7
`17.8-18.5
`
`95%
`confidence
`limits (mm)
`
`10.9-12.0
`15.9-17.4
`13.3-14.0
`19.0-19.6
`13.2-14.2
`18.4-19.2
`18.8-14.6
`20.0-21.4
`12.8-13.8
`18.1-19.1
`
`S.E.M.
`
`0.3
`0.4
`0.2
`0.1
`0.2
`0.2
`0.2
`0.3
`0.2
`0.2
`
`S.E.M.
`
`0.3
`0.4
`0.2
`0.1
`0.2
`0.2
`0.3
`0.4
`0.2
`0.3
`
`the mean (horizontal and vertical) diameters from age
`group 10-19.9 y to age group 50+ y were highly
`significant in both females and males. The 10-19.9 y
`age group includes the period of the adolescent
`growth spurt during which there is accelerated growth
`activity resulting in marked bodily changes. The
`timing of the onset and the peak of the increased
`growth velocity differ in males and females. Multiple
`2-tailed t tests, done separately for the male and
`female populations, showed that, in general, the
`differences between the mean pedicle diameters of age
`groups 10-14.9 and 15-19.9 y were highly significant
`(P < 0.001). The diameters of the 15-19.9 y age group
`were greater than the diameters of the 10-14.9 y age
`group and the diameters of females belonging to the
`20-29.9 y age group. Furthermore, the mean dia-
`meters of individuals in early life (namely 10-19.9 y)
`differed significantly from the diameters of subjects in
`
`middle life
`Differences
`(30-39.9 and 44-49.9 y).
`between the mean pedicle diameters of individuals in
`the 5th and 6th decades were also found to be
`significant. The details of the variations of the mean
`diameters from the youngest age group to the oldest
`were different for horizontal and vertical diameters.
`These differences are described separately below.
`
`Intersegmental differences
`Horizontal diameters. There was a cephalocaudal
`gradient of increase (from LI to L5) of the horizontal
`diameters of male and female pedicles in all age
`groups except males of the 5th decade. In the latter
`population the mean horizontal diameters of the L3
`pedicles were somewhat greater than the diameters of
`the corresponding L4 pedicles, although the dif-
`ferences were not statistically significant. The smallest
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`326
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`H. S. Amonoo-Kuofi
`
`horizontal diameter of the female pedicles was 7.4 mm
`at LI in the 20-29.0 y age group (Table 2). The
`maximum horizontal diameter was 13.6 mm at L5 in
`the 50 + y age group (Table 6). In males, the minimum
`horizontal diameter was 7.5 mm at LI in the 10-19.9 y
`age group (Table 2), while the maximum horizontal
`diameter was 14.2 mm at L5 in the 40-49.9 y age
`group (Table 6).
`Vertical diameters. In females, there was a cephalo-
`caudal increase of the vertical diameters from L2
`through to L5 in all age groups except the 20-29.9 y
`age group. The mean vertical diameter of the LI
`pedicle was greater than the mean vertical diameter of
`the L2 pedicle, in 4 of the 5 age groups (namely,
`30-39.9; 40-49.9 and 50+ y).
`In the
`10-19.9;
`20-29.9 y age group the mean horizontal diameter of
`the LI pedicle was similar to the diameter of the L2
`pedicle (Tables 2, 3). The differences were statistically
`significant (P < 0.001).
`In males, the lower lumbar pedicles (L4 and L5)
`had greater vertical diameters as expected. The
`diameter of the L5 pedicle exceeded the diameter of
`the L4 pedicle in all age groups (Tables 5, 6). The
`mean vertical diameter of the pedicle of the 3rd
`lumbar vertebra was the smallest among the 5 lumbar
`segments in all age groups except the 3rd and 5th
`decades, while the LI pedicle had a greater mean
`vertical diameter than the L2 pedicle (P < 0.01) in the
`10-19.9, 20-29.9 and the 40-49.9 y age groups. In the
`remaining 2 age groups (30-39.9 and 50+ y), the
`vertical diameter of the pedicle of LI exceeded that of
`L3 only.
`The mean vertical diameters of the lumbar pedicles
`of females ranged from 14.2 mm at L2 level in the
`10-19.9 y age group (Table 3) to 18.2 mm at L5 level
`in the 30-39.9 y age group (Table 6). The cor-
`responding minimum and maximum diameters for
`males were 14.8 mm at L3 in the 10-19.9 y group
`(Table 4) and 20.7 mm at L5 in the 40-49.9 y group
`(Table 6), respectively.
`
`Age-related differences
`There were differences, between the age groups, in the
`horizontal and vertical diameters of the pedicles at all
`the 5 lumbar levels. The pattern of variations differed
`in males and females.
`Horizontal diameters. In females, the horizontal
`diameter was greater in the 10-19.9 y age group than
`in the 20-29.9 y group at all segmental levels. The
`smallest horizontal diameters were noted in the
`20-24.9 y group. At the upper 3 lumbar levels
`maximum horizontal diameters in females were seen
`
`in the 10-19.9 y group. Variations in the horizontal
`diameters at the 4th and 5th lumbar levels with age
`were more subtle, suggesting that at these levels adult
`dimensions were probably attained very early, poss-
`ibly by late adolescence. From the 20-29.9 y age
`group upwards, horizontal diameters of the pedicle
`showed moderate but steady increases at all lumbar
`levels, until the 6th decade. Differences between the
`mean horizontal diameters of the 10-19.9 y group and
`highly
`significant
`the
`20-29.9 y
`group
`were
`(P < 0.001) at LI, L2 and L3 levels and marginal at
`L4 and L5 levels. The horizontal diameters of the
`pedicles of the 10-19.9 y group differed significantly
`(P < 0.001) from the diameters of all the other age
`groups at the various segmental levels. The t tests also
`showed that, at the upper 3 lumbar levels, the
`horizontal diameters of the pedicles of the 30-39.9 y
`group were significantly different (P < 0.001) from the
`diameters of the 10-19.9, 20-29.9 and 50+ y age
`groups.
`In males, the mean horizontal diameters increased
`steadily from age group 10-19.9 y until age group
`40-49.9 y at all lumbar levels except the 4th. A
`detailed study of the adolescent group showed that
`differences between the diameters of the 10-14.9 y
`group and 15-19.9 y group were highly significant
`(P < 0.001). The diameters in these age groups
`(especially the 15-19.9 y group) reflected the effect of
`the adolescent growth spurt. The results of t tests
`showed that the mean horizontal diameters of the
`10-14.9 and 15-19.9 y groups differed significantly
`(P < 0.001) from the diameters of all the other age
`groups. The mean horizontal diameters attained in the
`40-49.9 y group were higher than the mean diameters
`of all the other age groups at all levels. Variations of
`the pedicle diameters at the 4th lumbar level did not
`appear to follow a clearly defined pattern. A decline of
`horizontal diameters was noted in the 50 + y age
`group at all levels. The decline was highly significant
`at the upper 2 and the 5th lumbar levels (P < 0.001).
`The mean diameters of the 50 + y age group were,
`significantly greater (P < 0.01) than
`nevertheless,
`those of the 10-19.9 y group. It is noteworthy that,
`unlike the females of the same age, the 50 + y male
`subjects had smaller pedicle diameters than the
`40-49.9 y group, especially at the upper 2 and the 5th
`lumbar levels. In both males and females,
`the
`differences between the horizontal diameters of the
`40-49.9 and 50 + y groups were highly significant
`(P < 0.001).
`Vertical diameters. In females,
`the differences
`between the mean vertical diameters of the pedicles of
`the 10-19.9 y group and the other age groups were
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`Diameters of the lumbar pedicles
`
`327
`
`highly significant at all lumbar levels. Vertical dia-
`meters showed a decrease from age group 30-39.9 y
`to age group 40-49.9 y except at the 1st lumbar level.
`From age group 40-49.9 y to age group 50 + y,
`significant increases (P < 0.001) in vertical diameters
`were noted.
`In males, there was a marked increase of the vertical
`diameter from age group 10-19.9 y to age group
`20-29.9 y (P < 0.0001) at all 5 lumbar levels. A
`decline of diameters was then observed from age
`until
`30-39.9 y
`20-29.9 y
`group
`age
`group
`(P < 0.00 1). At each lumbar level, differences between
`the vertical diameters of the pedicles of the 30-39.9 y
`group on one hand and the vertical diameters of the
`other age groups (i.e. 10-19.9, 20-29.9 and 40-49.9 y)
`were very significant (P < 0.001). With the exception
`of the 1st lumbar level, the vertical diameters of male
`pedicles increased sharply from age group 30-39.9 y
`to age group 40-49.9 y (P < 0.00 1). This was followed
`by an equally marked decline of diameters in the
`50+ y group. The mean vertical diameter of the
`pedicle of the 40-49.9 y group was markedly greater
`(P < 0.001) than the mean vertical diameters of the
`pedicles of all other age groups.
`
`DISCUSSION
`
`The horizontal diameters of the pedicles of the adult
`subjects in the present sample correlate well with
`figures published by Krag et al. (1986) and Zindrick et
`al. (1987). With respect to sexual dimorphism in the
`diameters of the pedicles, the findings of the present
`study extend the report of Scoles et al. (1988) by
`showing that there are significant differences between
`the diameters of the pedicles of males and females.
`Additionally,
`evidence obtained from the study
`suggests that there are significant age-related differ-
`ences in the diameters of the lumbar pedicles. The
`pedicles do not show a simple linear increase in
`diameters from the younger age groups to the older
`ones. Age-related changes could result in an increase
`of diameters in some age groups or a decrease at other
`ages. This trend appears to be in agreement with the
`pattern of age-related changes reported for other
`parts of the vertebrae. Studies reported by Allbrook
`(1956, vertebral bodies), Ericksen (1976, 1978a, b,
`vertebral bodies), Preteux et al. (1985, vertebral
`cancellous bone), Oda et al. (1988, intervertebral
`discs), Amonoo-Kuofi (1991, intervertebral discs)
`clarified the fact that structural changes in the various
`components of the vertebral column during ageing are
`characterised by alternating phases of increase and
`decrease in the respective dimensions. Within the
`
`vertebral body, ageing was associated with remodel-
`ling, thickening and a 6-fold increase in the number of
`the weight-bearing trabeculae (Preteux et al. 1985). In
`the intervertebral discs, histological evidence showed
`that there were cycles of regeneration and remodelling,
`presumably in response to prevailing mechanical
`demands on the vertebral column (Oda et al. 1988).
`Clearly, weight-bearing and mechanical factors ap-
`pear to play important roles in morphological and
`functional adaptation of the vertebral column to the
`changing demands associated with growth. Corrob-
`orative evidence brought by Porter et al. (1989)
`established that in individuals aged 18 y and over,
`increasing levels of physical activity were associated
`with increasing strength of the vertebral column. The
`posterior elements of the vertebral bodies, in par-
`ticular, have a marked ability to undergo regrowth
`and remodelling (Krenz & Troup, 1973; Fidler, 1988;
`Postacchini & Cinotti, 1992). It would seem, therefore,
`that if the pedicles were subjected to changing
`mechanical stresses, they would probably show ap-
`propriate variations in strength (or diameters). Studies
`reported by Pal & Routal (1987) suggested that, in the
`lumbar region, the pedicles play an important part in
`the transfer of weight from the neural arch to the
`anterior part of the vertebral column. The variations
`in the diameters of the pedicles associated with the
`different age groups could therefore be attributed to
`this weight-bearing function. Judging from its larger
`dimension and its wider variations with age, it seems
`reasonable to suggest that the vertical diameter
`probably contributes more to weight-bearing func-
`tions than the horizontal diameter.
`The larger vertical diameter of the pedicle of the 1st
`lumbar vertebra (in both males and females) as
`compared with the vertical diameters of the 2nd and
`3rd lumbar pedicles could also be explained by the
`weight-bearing function. The 1st lumbar pedicle is
`located at the thoracolumbar transitional junction. A
`report by Davis (1955) demonstrated that thisjunction
`was the site of a complex zygapophyseal joint (the
`thoracolumbar mortice joint) which was adapted to
`withstand marked compressive forces transmitted
`from the relatively immobile thoracic segment to the
`highly mobile lumbar segment of the vertebral
`column. He showed that the vertebrae and pedicles at
`this junction were reinforced to withstand the forces
`that had to be transmitted across this junction.
`It was intriguing that, for any given vertebral level,
`the vertical and horizontal diameters did not show
`identical patterns of variation from one age group to
`another. Owing to the lack of corroborative morpho-
`metric information on the growth of the pedicles, it is
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`H. S. Amonoo-Kuofi
`
`difficult to determine the extent to which these
`differences in the variation of the diameters reflected
`normal growth pattern. The present sample was a
`cross-sectional one, and therefore the possibility that
`observed morphometric variations could be due, in
`part, to a secular trend in changing body size could
`not be excluded. Nevertheless, the fact that variations
`of vertical and horizontal diameters of any given
`vertebra were neither synchronous nor in the same
`direction suggests that, perhaps, the observed changes
`did not result from adverse environmental or nu-
`tritional factors.
`
`ACKNOWLEDGEMENTS
`
`The author gratefully acknowledges the help of Dr P.
`J. Patel, Consultant Radiologist at the King Khalid
`University Hospital, with screening and selection of
`the radiographs, and Mr Amir S. Marzouk for
`statistical analyses.
`
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