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ORIGINAL COMMUNICATION
The Developing Juvenile Ischium:
Macro-Radiographic Insights
STEPHEN J. MACLEAN, SUE M. BLACK, AND CRAIG A CUNNINGHAM*
Centre for Anatomy and Human Identification, College of Arts, Science and Engineering,
University of Dundee, Dundee DD1 5EH
Despite the importance of the human pelvis as a weight-bearing structure,
there is a paucity of literature that discusses the development of the juvenile
innominate from a biomechanical perspective. This study aims to add to the
limited body of literature pertaining to this topic through the qualitative analy-
sis of the gross architecture of the human ischium during the juvenile period.
Macro-radiographs of 55 human ischia ranging from 28 intra-uterine weeks to
14 years of age were examined using intensity-gradient color mapping to high-
light changes in gross structural morphology with increasing age. A clear pat-
tern of maturation was observed in the juvenile ischium with increasing age.
The acetabular component and ramus of the ischium consistently displayed low
bone intensity in the postnatal skeletal material. Conversely the posterior body
of the ischium, and in particular the ischial spine and lesser sciatic notch,
exhibited increasing bone intensity which first arose at 1–2 years of age and
became more expansive in older cohorts. The intensity patterns observed
within the developing juvenile ischium are indicative of the potential factors
influencing the maturation of this skeletal element. While the low intensity ace-
tabular fossa indicates a lack of significant biomechanical interactions, the pos-
terior increase in bone intensity may be related to the load-bearing nature of
the posterior ischium. Clin. Anat. 27:906–914, 2014. VC 2014 Wiley Periodicals, Inc.
Key words: ischium; juvenile; macro-radiography; growth; biomechanics
INTRODUCTION
Over the last two centuries, the internal structure of
human bone has been studied extensively in an effort to
better understand the role of trabecular bone, its impli-
cations for biomechanical competency and the factors
which influence the development of its micro-
architecture (von Meyer, 1867; Wolff, 1870, 1892; Sato
et al., 1986; Tobin, 1955; Huiskes, 2000; Huiskes et al.,
2000; Nuzzo et al., 2003; Agarwal et al., 2004; Macho
et al., 2005; Cunningham and Black, 2010). A substan-
tial number of these investigations have focused on a
relatively limited range of skeletal elements, primarily
the major long bones (von Meyer, 1867; Salle et al.,
2002; Ryan and Krovitz, 2006; Perilli et al., 2008; Gos-
man and Ketcham, 2009; Kraus et al., 2009; Barvencik
et al., 2010; Hammer, 2010; Ryan and Walker, 2010;
Liu et al., 2011; Saparin et al., 2011; Reissis and Abel,
2012). More recently, there has been an expansion into
regions of the skeleton previously neglected in terms of
trabecular bone analysis, including weight-bearing ele-
ments such as the ilium (Sato et al., 1986; Volpato
et al., 2008; Cunningham and Black, 2009a,b, 2010;
Abel and Macho, 2011), vertebral bodies (Nuzzo et al.,
2003; Rapillard et al., 2006), the calcaneus (Maga
et al., 2006; Rupprecht et al., 2006) and the talus (Pal
and Routal, 1998). However, in spite of this expanding
literature base, little is known about the biomechanical
loading and resultant cortical and trabecular bone
dynamics of many skeletal elements, including the pel-
vic girdle (Dalstra et al., 1993).
*Correspondence to: Dr. Craig A Cunningham, Centre for Anatomy
and Human Identification, University of Dundee, Dow Street,
Dundee DD1 5EH. E-mail: c.a.cunningham@dundee.ac.uk
Received 18 February 2014; Accepted 18 February 2014
Published online 17 March 2014 in Wiley Online Library
(wileyonlinelibrary.com). DOI: 10.1002/ca.22391
VVC 2014 Wiley Periodicals, Inc.
Clinical Anatomy 27:906–914 (2014)
The pelvic girdle represents a key junctional com-
plex for the transfer of weight from the head, trunk
and upper extremities to the lower limb (Cunningham
and Black, 2009a; Tardieu et al., 2013), therefore it
should be an important focus for biomechanical and
osteological research. However, the extant literature
which describes pelvic bone structure is primarily
restricted to phylogenetic studies concentrating on the
differences between Homo sapiens and other primate
species (Macchiarelli et al., 1999; Martin�on-Torres,
2003; Volpato et al., 2008), with emphasis typically
placed on iliac shape and structure. These studies
focus almost exclusively on the trabecular patterns of
the adult ilium and typically neglect to consider juve-
nile bone development. Some papers have however
examined the evolutionary importance of variations in
parameters such as the ratio between ischial and iliac
length (Williams and Orban, 2007) and also the evolu-
tion of the morphology of the ischial spine (Abitbol,
1988). As the internal structure of an element is
inherently linked to its mechanical environment
(Huiskes et al., 2000), a detailed understanding of the
developing architecture may provide insight into the
driving processes behind each stage of skeletal
maturation.
The structure of the adult human innominate has
been described as a ‘sandwich construction’ consisting
of a core of relatively isotropic trabecular bone con-
tained between two thin cortical shells (Dalstra et al.,
1993). Discussions of discrete trabecular bundles
within the ischium specifically document a single tra-
jectory: the sacro-ischial trabecular bundle (Aiello and
Dean, 1990). This bundle is described as passing
between the auricular surface of the ilium and the
ischial tuberosity, with the proposed function of trans-
mitting upper body weight through the pelvic complex
when in a seated position (Scheuer and Black, 2000).
This bundle was also described as inter-connecting
with the trabeculae of the acetabular margin, perhaps
to assist in the distribution of forces associated with
the acetabulum during bipedal locomotion (Kapandji,
2011). In a finite element (FE) analysis of the adult
innominate, patterns of stress distribution were pro-
posed, with consideration given to the load transferred
to the femoral head at the acetabulum in conjunction
with the action of 21 muscles that insert on the pelvis
(Dalstra and Huiskes, 1995). It was concluded that
both the cortical bone in the superior portion of the
body of the ischium and the acetabular component
experienced high levels of stress during different
phases of the walking cycle, while limited forces were
experienced by the trabecular element of the bone.
However, it has been noted subsequently that there
were discrepancies in the authors’ consideration of the
trabecular bone (Cunningham and Black, 2009a) and
therefore caution should be used when interpreting
the trabecular models produced.
Beyond this FE analysis, few studies have docu-
mented the biomechanical environment of the
ischium, nor described the factors that may influence
the development of this element.
However, an understanding of the specific soft-
tissue interactions and potential biomechanical influ-
ences acting on the bone at each stage of develop-
ment can be used to inform initial hypotheses
regarding the drivers of skeletal growth, based on an
appreciation of gross structural changes through
development.
This study forms the first stage of an on-going
investigation that will examine the developing struc-
ture of the juvenile human ischium, with particular
reference to the changing biomechanical environment
of the pelvis during growth and development. This
preliminary study documents qualitatively the gross
patterns in bone development within the ischium dur-
ing the juvenile period to provide insights into poten-
tial driving factors behind the maturation of the
ischium, and also to highlight regions of importance
for future quantitative analysis.
MATERIALS AND METHODS
Fifty-five ischia were available to study from the
Scheuer Collection of juvenile skeletal remains held
within the Centre for Anatomy and Human Identifica-
tion, University of Dundee). This unique collectionis
an active osteological repository for juvenile human
skeletal remains and comprises over 120 subadult
individuals from a variety of archaeological, anatomi-
cal and forensic sources. The specimens included
within this study ranged from 28 intra-uterine (i.u.)
weeks to 14 years of age and each specimen was
assigned to one of seven age groups based on the
estimated age held on record for the collection (Table
1). Only those individuals who did not exhibit evi-
dence of ilio-ischial fusion were selected included for
analysis.
Radiography
Each specimen was subjected to macro-
radiography using a Multix Tube and Table (Siemens).
Specimens were placed with the internal (pelvic) sur-
face towards the radiographic plate and the external
(acetabular) surface towards the x-ray source. The
exposure factors applied were 47 kV, 2 mA, Fine
Focus, with an Agfa film screen combination. A focus
film distance of 140 cm and an object film distance of
30 cm were used. Macro-radiography is used to mag-
nify a radiographic image relative to the size of the
object: this is achieved by increasing the object film
TABLE 1. Age Groups, Specimen Numbers, and
Element Distribution in This Study
Age Individuals
Left
ischia
Right
ischia
Total
elements
(n)
28 intra-uterine
weeks
1 1 1 2
Neonatal 3 3 3 6
426 months 3 3 3 6
1–2 years 3 2 3 5
3–5 years 6 6 5 11
6–9 years 6 6 5 11
10–14 years 10 7 7 14
Total 32 28 27 55
The Developing Juvenile Ischium 907
distance relative to a fixed focal film distance (David-
son and Bowman, 2002). Macro-radiography was
established as a useful technique in the gross analysis
of patterns in trabecular architecture when applied to
the developing ilium (Cunningham and Black, 2009a).
Color-Mapping and Gradient Analysis
To create color gradient maps of the macro-
radiographs, each radiograph was converted into a
digital image using a flatbed scanner with a superiorly
mounted radiographic light. The scan resolution was
set to 4,800 dpi to maximize data capture during the
digitization process. Each radiograph was scanned as
a gray-scale image comprising a standard 256 levels
of gray, saved as a .JPEG file without compression.
The digital radiographs were opened in Photoshop
CS5 (Adobe Systems Inc.), which was used to color the
radiographs based on the levels of gray present using
the gradient map tool (Fig. 1). To achieve this, the 256
levels of gray were divided into four discreet groups,
each of which was assigned a single contrasting color.
As the original radiographs were not captured digitally,
slight variations in pixel intensities were present in the
final JPEG images. This required that each specimen be
mapped individually based on the specific grey levels
present by assigning a base-line color to the intensity
associated with the background of the radiograph. The
remaining three colors were assigned an equal propor-
tion of the remaining grey levels (e.g., where the base-
line color was set at 16%, the remaining gray levels
would be distributed evenly between the three remain-
ing colors at intervals of 21%).
Several of the younger specimens (including speci-
mens from the fetal, perinatal, 0–6 months, and 1–2
years groups) displayed a narrower range of intensity
levels due to the small size of the elements. Smaller,
proportional, changes in intensity were visualized in
these specimens using “sensitive” gradient maps. To
create these sensitive gradient maps a maximum
intensity threshold was set at �85% opacity, in addi-
tion to the lower background level threshold estab-
lished previously. The intermediary grey levels were
then distributed evenly between the remaining colors
as before. This narrower threshold window did not
negatively impact the analyses as the gross patterns
evaluated are based on relative differences in local
pixel intensity, not absolute variations.
The gradient mapping process divided the ischium
into a color map comprised of four colors representing
different relative grayscale intensities in the image
from yellow, which represents the background level of
exposure, through violet and orange to blue, which
represents the most radiopaque regions i.e., the
whiter regions in the original radiographs (Table 2).
RESULTS
A progressive pattern of gradient map coloration
was observed between each of the age groups (Fig. 2).
The features highlighted on the specimens presented
Fig. 1. Macro-radiograph [a] and gradient map [b] of the ischium (3–5 years).
Four distinct grades of density are identified within the ischium, represented by the
four colors (yellow, violet, orange, and blue). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
TABLE 2. Density Gradient Levels and Their Corre-
sponding Colors and Opacity Ranges
Relative density
level Colour
Approximate
opacity (%)
Very Low Yellow 0–30
Low Violet 31–50
Medium Orange 51–70
High Blue 71–100
908 Maclean et al.
http://wileyonlinelibrary.com
Fig. 2. Gradient maps of specimens from each age group analyzed. (a) 28 intra-
uterine weeks; (b) neonatal; (c) 4–6 months; (d) 1–2 years; (e) 3–5 years; (f) 6–9
years; (g) 10–14 years. Areas of interest referred to in the text are identified by num-
ber (1–7). Images are not shown to scale. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
The Developing Juvenile Ischium 909
http://wileyonlinelibrary.com
in Figure 2 are representative of all specimens within
their respective groups.
28 Intra-Uterine Weeks (n52)
The majority of the fetal ischium was represented by
a relatively uniform medium intensity of bone as illus-
trated by a preponderance of orange coloration (Fig.
2a). An area of higher intensity was noted passing
antero-inferiorly across the body of the ischium
(between the dashed lines in Fig. 2a) that corresponds
to a small raised crest visible on the external surface of
the bone. Regions of lower intensity were noted in the
acetabular fossa (Label 1 in Fig. 2a), the anterior body
of the ischium (2) and around the perimeter of the bone.
Neonatal (n56)
The neonatal cohort demonstrated a similar pattern
to the 28 i.u. weeks group, with an expanded region
of lower intensity present anterosuperiorly defining
the region of the acetabular fossa (Label 1 in Fig. 2b).
A lower intensity region was also identified posterior
to the immature acetabular margin (3) in the approxi-
mate location of the dominant nutrient foramen. The
anterior body of the ischium in this group exhibited a
more uniform, higher intensity than in the 28 i.u.
weeks cohort but the periphery of the bone retained a
lower intensity violet coloration.
4–6 Months (n56)
Several observations from this age group were con-
sistent with the younger groups: lower intensity
regions were evident both anterosuperiorly in the
region of the acetabular fossa (1) and inferior to the
acetabular margin (3) (Fig. 2c). A lower intensity
region was also observed in the anterior body of the
ischium (2) distinct from the orange mid-level inten-
sity of the posterior body (separated by the dashed
line). The developing ramus was also represented by
a region of lower intensity bone (4). It was also noted
that in two specimens in this group, Regions 1, 3, and
4 are of such low relative intensity that they approxi-
mate the background intensity level, with yellow areas
visible which were not apparent in either of the
younger age cohorts.
1–2 Years (n55)
The specimens within this age cohort exhibited sev-
eral features consistent with previous age groups (Fig.
2d). Very low intensity regions were evident in the ace-
tabular fossa (1), anterior body of the ischium (2), and
ramus (4), each with a preponderance of yellow indicat-
ing an intensity level very close to background density
levels. The difference in relative intensity between the
anterior and posterior regions of the body of the ischium
was readily apparent in this group (separated by the
dashed line). The most significant observation in this
group was the developmentof a higher intensity region
on the posterior border of the ischium (5), in the region
of the lesser sciatic notch. A region of lower intensity
bone was also identified along the postero-inferior bor-
der of the ischium in the region of the metaphyseal sur-
face of the future ischial tuberosity (6).
3–5 Years (n511)
Several observed regions in the 3–5 years group
were consistent with the patterns described in younger
age cohorts (Fig. 2e). The acetabular fossa (1) was
defined by a region of low intensity, while the ramus (4)
was represented by a region of low intensity proximally
which transitioned to a lower intensity at its extremity.
The anterior–posterior disparity (separated by the
dashed line) was also present in this group, although it
was noted that while the anterior body of the ischium
maintained a relatively low intensity (2) it did not
exhibit intensity levels approximating the background
level as previously observed. The higher intensity
region in the posterior border of the ischial body around
the lesser sciatic notch (5) was also present in this
group, and was more extensive than observed in the 1–
2 years cohort.
6–9 Years (n511)
This age cohort contained many of the features iden-
tified in previous age groups, including lower intensity
regions in the acetabular fossa (1) and the ramus (4).
The higher intensity region observed in the posterior
body of the ischium was also present in the age group
(5), surrounded by an area of medium intensity
(orange) (Fig. 2f). The differentiation between the lower
intensity anterior body (2) and higher intensity posterior
body of the ischium was also well defined in this age
group (separated by dashed line).
10–14 Years (n514)
The 10–14 years age group exhibited several inten-
sity patterns that were consistent with observations of
the younger age groups, including the very low intensity
regions associated with the acetabular fossa (1) and the
ramus (4) (Fig. 2g). In four specimens, the ramus of the
ischium had fused to the pubic bone; however, there
were no obvious differences evident in the intensity of
the ischiopubic rami of the fused and unfused speci-
mens. The intensity gradient between the anterior and
posterior body of the ischiumwas also identifiable in this
age cohort (separated by the dashed line), with a lower
intensity area evident in the anterior body of the ischium
(2). However, the distinction between these two regions
was less pronounced than previously observed. A more
expansive higher intensity region around the lesser sci-
atic notch was observed in this cohort (5). Seven out of
ten specimens also exhibited variable regions of mid to
high density bone curving posteriorly in the approxi-
mate location of the anterior extremity of the develop-
ing acetabularmargin (7).
DISCUSSION
The radiographic representations of the specimens
in this study demonstrate a largely progressive
910 Maclean et al.
pattern of intensity distribution and development with
increasing maturity. The ischium transitioned from a
near-uniform, undifferentiated distribution of bone in
the fetal period to adopt a more regionalized pattern
with defined variations in intensity in the early adoles-
cent period. A recognizable mature morphology began
to manifest in the 1–2 year age group and was clearly
established by the age of 3–5 years.
It is important to consider the limitations of any
imaging modality when interpreting results, particu-
larly with regards to radiographic imaging technolo-
gies. The most significant limitation of plane plate
radiography is the superimposition of structures on a
single plane, which is a result of the compression of a
three dimensional structure into a two dimensional
image (Hsieh, 2003). As a consequence of this com-
pression, variations in the three-dimensional structure
along the z-axis (in the plane of the radiographic
beam) will affect beam attenuation and create varia-
tions in the pixel intensities of the radiograph. To mini-
mize the confuscating effect of superimposition, each
gradient map was considered in conjunction with the
specimen from which the radiograph was obtained.
This made it possible to identify variations in intensity
that could not be attributed solely to the development
of gross external structures. It must also be noted
that radiography does not allow a distinction of tra-
becular and cortical bone tissues; rather it creates an
image which is a composition of both types of bone
tissue. All variations in intensity therefore represent
“combined bone intensity” and highlight relative dif-
ferences in structure within an element and not abso-
lute differences between specimens.
Because of the limited number of specimens avail-
able, the youngest group in this study consisted of a
single individual of 28 i.u. weeks, including both the
left and right ischium. The small group size, combined
with the small size of these specimens and the rela-
tively low density of bone formed, precludes definitive
assessment of the prenatal structure of the ischium.
Rather, this group was included to provide an indica-
tion of the potential structure of the ischium at this
age; however, the results should be treated with cau-
tion. Similarities were observed between these speci-
mens and the more mature, postnatal skeletal
material, for example the lower intensity region in the
acetabular fossa. However, these variations in radiolu-
cency may also be attributed to gross variations in
external morphology. For example, the fetal acetabu-
lar fossa was represented by a lower, flattened region
on the anterosuperior surface while the noted region
of increased intensity corresponds to a small raised
crest passing antero-inferiorly across the body of the
ischium.
This relatively nondescript radiographic appearance
of the fetal ischium contrasts with observations of the
fetal ilium, which displays a precocious and progres-
sive pattern of development from the early fetal
period (Cunningham and Black, 2009a). Rudimentary
buttressing was identifiable in anterior and posterior
trajectories consistent with the mature adult iliac
structure in specimens as young as 23–30 intra-
uterine weeks. In adult specimens, these trajectories
are purported to be responsible for the transfer of
weight between the auricular surface of the ilium and
the femoral head at the acetabulum (Aiello and Dean,
1990; Scheuer and Black, 2000; Kapandji, 2011), and
also to assist in the distribution of associated tensile
forces (Macchiarelli et al., 1999). The discovery of cor-
responding, although immature, trajectories in the
fetal ilium raised questions as to the cause of such
precocious development, as the pelvis is not a weight-
bearing structure prior to birth (Walker, 1991) and tra-
ditional models postulate that bone structure is pri-
marily dictated by mechanical stimuli (Wolf, 1892;
Huiskes, 2000). It was proposed that the early estab-
lishment of supportive trajectories may also be influ-
enced by genetic and non-load-bearing mechanical
interactions (Cunningham and Black, 2009a,b),
although subsequent publications also stressed the
importance of vascular invasion as a factor which may
direct trabecular growth in the ilium (Cunningham and
Black, 2010). The absence of such precocious devel-
opment in the fetal ischium included in this study may
be indicative of a different set of osteogenic instiga-
tors for the ischium, although it is not possible to sug-
gest alternative influences from the study of a single
individual.
Analysis of the neonatal and postnatal development
of the ischium revealed progressive patterns of den-
sity in several key regions arising after birth. In both
the neonatal and 4–6 months age groups, a small
elliptical region was identified inferior to the acetabu-
lar rim that was characterized by a lower bone density
relative to the surrounding bone. It is proposed that
this lower region of density is related to vascular
spaces present within the ischium, supported by the
presence of a nutrient foramen located in theexternal
cortical shell in this region. It has been reported that
the acetabular branch of the inferior gluteal artery
provides the arterial supply to the ischium (Beck
et al., 2003) and the proliferation of blood vessels has
been shown to emanate from this approximate region
in the neonatal ischium (Crock, 1996). Angiogenesis
has previously been demonstrated to be of great
importance in bone formation (Brandi and Collin-
Osdoby, 2006) and has been suggested to be highly
influential in the development of the internal architec-
ture of the neonatal ilium (Cunningham and Black,
2010). It is acknowledged that arterial invasion of a
cartilaginous template will create vascularized spaces
within the internal architecture (Eriksen et al., 2007),
which may in turn manifest as an apparent decrease
in trabecular bone volume present in this location.
Throughout the developmental period investigated
in this study, the acetabular fossa was consistently
revealed to be amongst the least dense regions of the
ischium. While this may be partially attributed to the
relatively shallow cross-sectional depth at this point, it
may also be evidence of the absence of any significant
biomechanical forces acting across this region. The
acetabular fossa forms the nonarticular floor of the
acetabulum and is therefore unlikely to be involved
directly in the transfer of mechanical loading (Daniel
et al., 2005): this transfer is instead described as
occurring across the lunate surface, which constitutes
the articular surface of the acetabulum (Scheuer and
Black, 2000). Several authors have indicated that the
The Developing Juvenile Ischium 911
principal contact between the lunate surface and fem-
oral head when bearing weight occurs in the superior
dome of the lunate surface (Greenwald and Haynes,
1972; Ipavec et al., 1999; Daniel et al., 2005; Chuck-
paiwong et al., 2009), which is located in the iliac con-
tribution to the acetabulum. The forces experienced
by the remaining lunate surface are less intense and
vary with types and phases of movement (Ipavec
et al., 1999); for example, load-bearing contact within
the ischial region of the acetabulum is intermittent
during walking (Greenwald and Haynes, 1972). This
diminished level of force in the ischial component of
the acetabulum may explain the discrepancy between
the relatively low volume of bone present in this
region compared with the densities observed in the
ilium (Cunningham and Black, 2009a), and subse-
quent quantitative data supporting increased trabecu-
lar bone reinforcement of the acetabular roof
(Cunningham and Black, 2009b).
Throughout postnatal development the posterior
body of the ischium maintained a higher intensity
than the anterior body, bridging the region between
the acetabulum and the metaphyseal surface of the
ischial tuberosity. From 1 to 2 years of age, an ellipti-
cal, very high intensity region developed adjacent to
the developing lesser sciatic notch. This very high
intensity region extends with increasing age to bridge
the posterior border of the ischium between the ischial
tuberosity’s metaphyseal surface and the inferior
aspect of the ischial spine.
Several potential causative factors can be suggested
for these increases in intensity. The region of very high
intensity originally forms in the lesser sciatic notch,
which contributes to the bony margins of the lesser sci-
atic foramen in life. Several structures pass through this
foramen, most importantly the internal pudendal artery
and the pudendal nerve (Standring, 2008). Evidence
from the literature suggests that both vascular (Lauren-
son, 1964; Brandi and Collin-Osdoby, 2006; Eriksen
et al., 2007; Cunningham and Black, 2010) and neuro-
logical tissues (Laurenson, 1964; Garc�ıa-Castellano
et al., 2000; Jones et al., 2004; Wang et al., 2006) have
an influence on skeletal growth and metabolic regula-
tion, although the precise mechanisms by which this
influence is exerted are currently unknown (Garc�ıa-Cas-
tellano et al., 2000). Therefore, it is possible that this ini-
tial increase in intensity is a result of a neurovascular-
induced increase in bone deposition in the region of the
lesser sciatic notch.
As neurovascular structures in the pelvis are estab-
lished in the embryonic period (Laurenson, 1964; Sche-
uer and Black, 2000; Sadler, 2010) it would be expected
that any increases in density caused by the presence of
these structures would also be evident in the younger
groups. The significance of the age at which the region
of increased intensity arises must also be considered.
The ages of 1–2 years follows the initial development of
unassisted upright standing and walking between 9 and
18 months (WHOMGRSG, 2006). Therefore it is impor-
tant to consider the alteration in load transfer and those
muscles and ligaments which are involved in a bipedal
gait as potential mechanisms driving an increase in
bone intensity in this region. The forces passing through
the pelvis during walking were not only described as
passing through the ilium to the superior acetabulum
(Dalstra and Huiskes, 1995), but it was also observed
that the ischium transmitted a degree of force through
the body and acetabular rim during several of the gait
phases. While Dalstra and Huiskes (1995) proposed
that this force is primarily transmitted through the corti-
cal shell, with only a limited trabecular involvement,
specific ischial acetabular trabeculae have been
described as radiating posteriorly from the acetabulum
to assist in the dispersal of forces (Kapandji, 2011). An
additional trabecular trajectory, the sacro-ischial tra-
becular bundle, has also been described in the ischium
as arising between the auricular surface of the ilium and
the ischial tuberosity, to transmit the load of the upper
body while in a seated position (Aiello and Dean, 1990;
Scheuer and Black, 2000; Kapandji, 2011). The devel-
opment of unassisted sitting precedes walking, arising
between 4 and 9 months (WHOMGRSG, 2006), which
may also be a factor in the observed increase in bone
intensity in the posterior border of the ischium from 1 to
2 years of age.
The posterior body of the ischium has also been
described as an important location for muscular and lig-
amentous attachment to support both the upright orien-
tation of the pelvis (Scheuer and Black, 2000) and the
pelvic viscera (Abitbol, 1988). Insertions on the poste-
rior aspect of the ischium include the sacrospinous and
sacrotuberous ligaments, the hamstring muscle group
and numerous small pelvic muscles (Standring, 2008).
The actions of these structures generate varying forces
within the posterior ischium; for example the hamstring
group have been described as creating a relatively high
level of force during the walking cycle (Crowninshield
and Brand, 1981). The sacrospinous and sacrotuberous
ligaments are described as being important inmaintain-
ing the upright position of the pelvis while bearing
weight and resisting anterior rotation at the sacro-iliac
joint (Scheuer and Black, 2000). It has subsequently
been suggested that the sacrotuberous ligament does
not have a significant load-bearing role (Woodley and
Kennedy, 2005) while the sacro-spinous ligament, in
association with the iliococcygeal muscles, have been
described as generating high tensile stresses between
the sacrum and ischium (Tardieu et al., 2013). However,
no data has been published describing the specific
forces acting through either of these ligaments, there-
fore this postulationmust be consideredwith caution.
There is a well-established relationship which dic-
tates that mechanical strains trigger the remodelling
and optimization of both cortical and trabecular bone
structure (Wolff, 1892; Huiskes, 2000; Huiskes et al.,
2000; Ruff et al., 2006). Therefore, it is reasonable to
expect that the high number of muscular interactions,
ligamentous constraints and force transmissions
should result in a reinforcement of the skeletal archi-
tecture in the region. That the high-density region
arises after the attainmentof bipedal locomotion lends
further support to this hypothesis.
CONCLUSIONS
Macro-radiographic analysis of the ischium has
revealed several distinctive patterns of bone intensity
912 Maclean et al.
arising during the development of this skeletal ele-
ment. Evidence of vascular invasion during infancy
may be identifiable inferior to the ischial acetabular
margin. From the age of 1–2 years, areas of increased
intensity develop in the posterior region of the body of
the ischium, which are consistent with the reinforce-
ment of the skeletal architecture in this location. This
may be a response to the biomechanical forces attrib-
uted to the development of adult posture and gait in
addition to the forces imparted through soft tissue
interactions in this region, although potential neuro-
genic influences in the lesser sciatic notch should not
be discounted. Evidence also indicates that the ischial
contribution to the acetabulum may not have a signifi-
cant role in the transfer of force to the femoral head,
due to the absence of reinforcement to the bone in
this region.
However, it must be reiterated that this investiga-
tion forms only the preliminary stage of a larger inves-
tigation to quantify changes to the structure of the
developing ischium.
ACKNOWLEDGMENTS
The authors thank Margaret Low for assistance with
radiographic procedures and for sharing her expertise
and insight. The authors would also like to thank Her
Majesty’s Inspector of Anatomy for Scotland for grant-
ing permission to utilise the Scheuer Collection for the
purposes of this research.
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