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Anthropological Review • Vol. 85(2), 13–62 (2022)
AnthropologicAl review
Available online at: https://doi.org/10.18778/1898-6773.85.2.02
Sacral Spina Bida Occulta:
AFrequency Analysis of Secular Change
Ella R Kelty1, 2, Maciej Henneberg1, 2, 3
1 Anatomical Sciences Unit of the School of Biomedicine, Adelaide University,
Adelaide, Australia
2 Department of Archaeology, Flinders University, Adelaide, Australia
3 Institute of Evolutionary Medicine, University of Zurich, Zurich, Switzerland
AbstrAct: Substantial relaxation of natural selection beginning around 1900 changed the mutation/selec-
tion balance of modern genetic material, producing an increase in variable anatomical structures. While
multiple structures have been affected, the temporal increase in variations of the sacrum, specically, ‘Sa-
cral Spina Bida Occulta,’ have been reliably demonstrated on alocalised scale. Calculation of largescale
frequency has been hindered by the localised nature of these publications, the morphological variability of
this variation, and potential pathological associations, which have produced divergent classications, and
conicting reported rates of occurrence. Asystematic review of the reported literature was conducted to
provide an objective analysis of Sacral Spina Bida Occulta frequency from 2500 BCE to the present. This
review was designed to compensate for observed inconsistencies in reporting and to ascertain, for the rst
time, the temporal trajectory of this secular trend. Asystematic review of Sacral Spina Bida Occulta lit-
erature was conducted through the strict use of clinical meta-analysis criteria. Publications were retrieved
from four databases: PubMed, Embase, the Adelaide University Library database, and Google Scholar. Data
were separated into three historical groups, (1 = <1900, 2 = 1900 to 1980 and 3 = >1980), and frequency
outcomes compared, to determine temporal rates of occurrence.
Atotal of 39/409 publications were included in the nal analysis, representing data for 16,167 sacra,
spanning aperiod of 4,500 years. Statistically signicant results were obtained, with total open S1 frequen-
cy increasing from 2.34%, (79 to 1900CE), to 4.80%, (1900 to 1980CE) and to 5.43% (>1980CE). These
increases were signicant at p<0.0001, with Chi-squared analysis. Aclear secular increase in the global
frequency of Sacral Spina Bida Occulta has been demonstrated from 1900 to the present. This research
provides anovel and adaptable framework for the future assessment of variation distribution, with impor-
tant implications for the elds of biological anthropology and bioarchaeology.
Key words: Sacral Spina Bida Occulta (SSBO), frequency, classication, natural selection
AbbreviAtions: Sacral Spina Bida Occulta (SSBO), Spina Bida Cystica (SBC), Neural Tube Defect (NTD)
Original article
© by the author, licensee Polish Anthropological Association and University of Lodz, Poland
Original article is an open access article distributed under the terms and conditions of the
Creative Commons Attribution license CC-BY-NC-ND 4.0
(https://creativecommons.org/licenses/by-nc-nd/4.0/)
Received: 25.04.2022; Revised: 04.05.2022; Accepted: 05.05.2022
14 Ella R Kelty, Maciej Henneberg
Introduction
The relaxation of natural selection
can be attributed to the decreased rate
of infant mortality and the increased
rate of adult survivability from 1900
onwards (Ulizzi et al. 1998). These
changes were shaped by improved clin-
ical understanding of disease, the in-
vention of increasingly effective medi-
cation, and an improvement in prenatal
and postnatal medical care (Ruhli and
Henneberg 2013; Solomon et al. 2009).
Consequently, survivorship to the age of
reproduction (15 years) increased from
<50% in 1850 to slightly >90% by 1900
(Greene 2001). Overall, the probability
that an average person born into apop-
ulation will be able to pass their genes
to the next generation rose from 0.30
to 0.95 (Saniotis and Henneberg 2011).
This reduction in the opportunity for
selection, altered the mutation/selection
balance which precipitated phenotypic
variation (Cairnes and Gariepy 1990;
Lee et al. 2011). Such an increase has
been observed in anumber of modern
physiological, immunological, and mor-
phological characteristics, the most
well-known of which is the increase in
lactose intolerance and the congenital
absence of the third molar (Ingram et
al. 2009; Swallow 2003). Occurring over
arelatively short period of evolutionary
history, (120 years), these modern secu-
lar changes have been observed in mul-
tiple correlating anatomical structures.
One such example includes increas-
es observed in the retention of the em-
bryonic variant, the median artery. This
embryonic vessel typically regresses at
8 weeks gestation, but retention of this
artery into adulthood has experienced an
increase of 20%, over aperiod of the last
170 years (Lucas et al. 2020). The atypi-
cal fusion of one or more tarsal bones of
the foot has also been subject to observed
increases after 1900, with an increase
of >12%, evidenced over a period of 50
years (Ruhli et al. 2003). The timing of
these changes in anatomical structures,
coincides with observed increases in sa-
cral variations, most specically the ‘ver-
tebral anomaly’ Sacral Spina Bida Oc-
culta, (SSBO).
Sacral Spina Bida Occulta (SSBO) is
acondition difcult to dene due to the
variability with which it is described in
the literature, and the broad spectrum of
defects this condition can represent (Al-
brecht et al. 2007; Eubanks and Cheru-
vu 2009). SSBO is often considered the
mildest manifestation of Neural Tube
Defect (NTD), specically of the highly
debilitating Spina Bida Cystica (SBC),
which has been identied as the most
common congenital anomaly of the 21st
century (Kallen and Lofkvist 1984; Mor-
rison et al. 1998). Characterised skele-
tally, by the absence or non-fusion of one
or multiple posterior vertebral arches,
SSBO variably includes deformation of
the laminae, neural arch, or pedicles of
vertebrae (Post 1966; Sutow and Pryde
1955). While this anomaly can occur at
any level of the vertebral column, the
malformation of the last lumbar verte-
bra and the rst sacral vertebra is the
most routinely observed, studied, and
reported (Sairyo et al. 2006). Due to the
severity of deformation caused by SSBO,
(which typically presents as the expo-
sure of the sacral canal, or absence of
the dorsal wall), this condition is easily
identiable in dry human sacra, and can
be reliably distinguished from post-dep-
ositional erosion or damage, (Figs 1, 2
and 3). Therefore, observations of this
condition in dry human sacra are reli-
able, and publications which provide
Spina Bifda Occulta 15
frequency data in this context can be as-
sumed to be accurate and objective.
Fig. 1. Dry human sacrum with atypically formed dor-
sal wall – fully fused sacral vertebrae. (Photograph
taken by lead author (Kelty 23/09/2021). Speci-
men B53 from St Marys archaeological collection,
ethically held by The University of Adelaide).
Fig. 2. Dry human sacrum demonstrating ‘Total
SSBO’ or non fusion of arches of all sacral seg-
ments. (Photograph taken by lead author (Kelty
23/09/2021). Specimen B79 from St Marys ar-
chaeological collection, ethically held by The
University of Adelaide).
Fig. 3. Dry human sacrum demonstrating non-fu-
sion of sacral segments, S1 and S4-S5. The
most commonly observed conguration of S1
non-fusion. (Photograph taken by lead author
(Kelty 23/09/2021). Specimen B61 from St
Marys archaeological collection, ethically held
by the University of Adelaide).
Deformation at all levels of the sa-
crum can occur with varying degrees
of regularity, dependent on the sacral
segment involved. The most common
observation of non-fusion occurs at seg-
ments S4-S5, which can reach upwards
of 90% of individuals with European
ancestry (Fidas et al. 1987). Thus, this
deformation pattern is clinically recog-
nised as a natural morphological vari-
ation, termed the sacral hiatus (Abera
et al. 2021; Henneberg and Henneberg
1999). Deformations of segments S2 and
S3 have lower frequencies, (1% to 10%),
but to date are also considered natural
variations, due to their sometimes inclu-
sion into the hiatus (Simriti et al. 2017).
This inclusion of S2-S5 in the natural
variation of the sacrum suggests that
16 Ella R Kelty, Maciej Henneberg
these specic patterns of deformation
have no pathological associations and are
therefore of no clinical importance (Ku-
mar and Tubbs 2011).
Non-fusion of the rst sacral segment
usually has alower frequency, similar to
that of S2 and S3, but is unreliably re-
ported, with estimations ranging from
8% (Piontek 1971) to 23% (Sairyo et al.
2006). Unlike the segments S2-S5, S1
has clear pathological associations hav-
ing been reliably correlated with enure-
sis, posterior disk herniation, and lower
back pain (Eubanks and Cheruvu 2009;
Sutow and Pryde 1955). Non-fusion of
sacral segments inclusive of S1 can be
considered morphologically and clinical-
ly important, irrespective of non-fusion
or fusion of other segments. It is for this
reason that Sacral Spina Bida Occulta
can be specically dened as non-fu-
sion inclusive of the rst sacral segment
(Henneberg and Henneberg 1999; Lee et
al. 2011; Solomon et al. 2009).
The Pelvis (Os Coxae) is the most var-
iable aspect of the human skeleton due
to its high levels of sexual dimorphism,
with the sacrum being considered the
most variable aspect within that struc-
ture (Steyn and Iscan 2008). Variations
to the structure of the sacral canal can
also inuence variation in the resulting
morphology of the surrounding Os Cox-
ae (Kurki 2013). The degree to which
these variations can inuence pregnan-
cy, birth, overall health, and forensic sex
identication, has resulted in a relative
wealth of clinical, anthropological, and
archaeological assessments of this var-
iation over the last century (Henneberg
and Henneberg 1999). The identication
and classication of Sacral Spina Bida
Occulta was rst described in the an-
thropological literature by Willis (1923).
Willis popularised the characterisation
of this condition as a ‘vertebral anoma-
ly’ of no clinical signicance, recording
only a 1.2% frequency in 748 historical
subjects (Willis 1923). Anthropological
interest in SSBO was shaped by this de-
nition but was characterised by inconsist-
ency in reported frequencies. Ferembach
(1963) famously reported a76% frequen-
cy in asample from 12,500BCE, but this
was hard to substantiate, due to the small
sample size and the 8% to 23% occur-
rence which typied the literature of this
period. Inconsistencies in reported SSBO
frequencies were further exasperated by
the clinical recognition of this condition,
which aligned with investigations of neu-
ral tube defects in 1980 and introduced
anew generation of conicting classica-
tions and frequency calculation methods
(Molloy et al. 2017; Scatliff et al. 2013).
Investigations into the temporal in-
crease of SSBO frequency in the modern
era, and its correlation to the relaxation
of natural selection around 1900, have
ultimately been impeded by the number
of academic debates, controversies and
disagreements which characterise this
research area (Shore 1930; Zemirline
et al. 2013). A long-standing consensus
within the medical community that ana-
tomically modern humans are no longer
evolving under the operation of natural
selection, has prevented largescale re-
search into these changing anatomical
structures and their potential impact on
the health of future populations (Kumar
and Singh 2003; Rühli and Henneberg
2013). While small scale and localised
studies have been conducted which re-
liably support this correlation between
various changing modern anatomical
structures and the relaxation of natural
selection in the industrialised world from
1900 onwards, (Lucas et al. 2020; Rühli
et al. 2003) large-scale assessments and
Spina Bifda Occulta 17
widespread acceptance of this phenome-
non have yet to be established.
This observed lack of academic con-
sensus has prevented reliable calculation
of SSBO frequency over time, which is
additionally impeded by the small num-
ber of publications which contain reli-
able data for this condition (Zemirline
et al. 2013). These inherent limitations
have been addressed by modern SSBO re-
search, which provides more reliable as-
sessments of frequency than historically
observed (Kumar and Singh 2003). Inter-
estingly, an 11% frequency of this con-
dition was observed in Pompeii (79CE,
Henneberg and Henneberg 1999), being
about one half of modern European as-
sessments of about 20% (Saluja 1988).
This led Henneberg and Henneberg
(1999) to suggest that asecular and mi-
croevolutionary trend could be observed
in SSBO frequency. This increase was
further substantiated by Solomon et al.
(2009) and Lee et al. (2011), who demon-
strated an increase in the frequency of
SSBO at S1 in Australian and European
birth cohorts, from 1940s to 1980s. This
is interesting, as these localised studies
demonstrate an increase that not only
correlates with the observed relaxation of
natural selection around 1900, but that
also coincides with relative increases in
similar anatomical variations during the
same period. It is therefore hypothesised
that the generation of a large-scale, ge-
ographical, and temporal assessment of
SSBO frequency will produce evidence
of aclear secular trend in the increase of
this condition from 1900 onwards.
Materials and Methods
A literature review was performed to
collect all available publications pertain-
ing to SSBO frequency as previously de-
ned. This review generated a total of
409 foundational or peer-reviewed pub-
lications. Predetermined exclusion crite-
ria were used to determine the relevance
of each publication and assess the qual-
ity of their reported segmentation data
(Fig. 4). In total 39 of 409 (<10%) pub-
lications were included in the frequency
analysis, producing atotal sample size
of 16,167 sacra, which spanned 25 in-
ternational regions (Fig. 5) and aperiod
of 4,500 years. Male and female sample
sizes were also recorded where reported,
with a total male sample size of 3,992
and female sample size of 3,818, with
8,357 (51.69% of 16,167) having unde-
signated sex.
In order to reliably evaluate the true
frequency of SSBO it was necessary to
design a method that could enable the
review of all available and relevant liter-
ature, while overcoming observed incon-
sistencies in classication and frequency
calculation. It was also imperative to
demonstrate that modern human skel-
etal anatomy is subject to evolutionary
change, and that increases in SSBO fre-
quency directly correlate with the re-
cent relaxation of selection shift. The
literature was collected, assessed, and
analysed according to strict clinical me-
ta-analysis guidelines to ensure that data
were reviewed systematically (Balduz-
zi et al. 2019; Page et al. 2021). As this
research does not contain clinical trials
or patients, some meta-analysis criteria
could not be applied, and the decision
was made to conduct aquantitative liter-
ature review/frequency analysis instead.
To guarantee cohesion, validity and ac-
curacy within the research design, all
analyses were conducted according to the
requirements of a meta-analysis where
possible (Higgins et al. 2003; Page and
Moher 2017).
18 Ella R Kelty, Maciej Henneberg
Fig. 4. PRISMA Flow chart of literature analysis method, with added inclusion/exclusion criteria.
Fig. 5. World map showing distribution of included SSBO data for the literature analysis. Country of origin
and number of publications per country included.
Spina Bifda Occulta 19
Literature Review Method
Publications for the literature review
were collected through the use of Em-
base, PubMed, Google Scholar, and the
University of Adelaide’s library database.
Embase and PubMed were used primari-
ly for the collection of clinical literature
relating to SSBO and did not include an-
thropological and archaeological data for
this condition, particularly not from the
early 20th century. Google Scholar was
used as a means to nd those publica-
tions not available in the medical liter-
ature databases, and the University of
Adelaide Library was used to gain access
to those publications found in Google
Scholar that were restricted by paywalls.
The Adelaide University Library data-
base was the most practical resource to
use for supplementary access to these
publications, as both authors are mem-
bers of The School of Biomedicine at this
University.
Databases were searched for keywords;
Sacral Spina Bida Occulta, Spina Bi-
da Occulta, Neural Tube Defect, Spina
Bida and Occult Spinal Dysraphism.
Keywords were supplemented by corre-
sponding searches for, incidence, preva-
lence, frequency, and rates. Results from
each database underwent two rounds of
screening, the initial publication screen-
ing, (12/2/2021 – 03/05/2021) and the
internal validity screening, (13/09/2021
– 2/10/2021), which included different
criteria. The initial publication screening
was conducted through aprocess of exam-
ining the abstract, results and conclusions
of each publication, and including/exclud-
ing each publication based on aset of pre-
determined exclusion criteria (Fig.4) (Bal-
duzzi et al. 2019). Publications that were
included through the initial publication
screening were then analysed a second
time with more stringent predetermined
exclusion criteria, which focussed on the
assessment of the internal validity of each
study (Page et al. 2021).
Different retrieval strategies were used
dependent on the database. PubMed and
Embase are clinical databases that were
used to source potential clinical data on
the frequency of SSBO.Due to the vol-
ume of publications generated from such
expansive databases, as a result of the
search strategies outlined (Table 1), only
the top 100 search results were included
for screening. The University of Adelaide
library and Google scholar databases
were used primarily to retrieve anthro-
pological and archaeological data on the
frequency of this condition. Due to the
nature of these databases, specic search
strategies were not used, however, each
afore mentioned key word was searched,
and any relevant publications were re-
trieved. This was further complemented
by the use of these databases to retrieve
publications cited in already analysed
works and to expand upon the key words
to include, sacral hiatus, paleoepidemiol-
ogy, sacral anomaly, sacral deformity and
osteoarchaeology.
It should be noted that due to the na-
ture of SSBO and its presence in histor-
ical and archaeological populations, this
review of the literature is amalgamating
already published data on the frequency of
this condition in dry human sacra, from
cadaver studies and through anonymised
radiographic data. Therefore, this review is
bio-anthropological and does not include
patients, clinical trials, medical equip-
ment, additional reviewers, ethics approv-
al or funding grants. All publications were
reviewed by the lead author manually, no
automation process or equipment was
used, and no additional reviewers or ex-
ternal parties were involved.
20 Ella R Kelty, Maciej Henneberg
Table 1. Search strategies for publication retrieval from each database
Database Keywords Search String* Retrieved/
Generated*
PubMed Sacral Spina Bida Occulta, Spina Bi-
da Occulta, Neural Tube Defect, Spina
Bida and Occult Spinal Dysraphism.
+
Incidence, Prevalence, Frequency, and
Rates
(Sacral Spina Bida Occulta)
OR (Spina Bida Occulta)
OR (Neural Tube Defects)
OR (Spina Bida) OR (Oc-
cult Spinal Dysraphism)
AND (Incidence) OR (Rates)
OR (Frequency) OR (Preva-
lence)
100/
306,548
Embase Sacral Spina Bida Occulta, Spina Bi-
da Occulta, Neural Tube Defect, Spina
Bida and Occult Spinal Dysraphism.
+
Incidence, Prevalence, Frequency, and
Rates
Exp spinal dysraphism / or
exp neural tube defects / or
exp open spinal dysraphism
/ and exp incidence / or exp
frequency / or exp preva-
lence /
100/
1,214,399
The University
of Adelaide
Sacral Spina Bida Occulta, Spina Bi-
da Occulta, Neural Tube Defect, Spina
Bida and Occult Spinal Dysraphism.
+
Incidence, Prevalence, Frequency, and
Rates
+
Sacral Hiatus, Paleoepidemiology, Sa-
cral Anomaly, Sacral Deformity and
Osteoarchaeology
N/A 141
Google Scholar Sacral Spina Bida Occulta, Spina Bi-
da Occulta, Neural Tube Defect, Spina
Bida and Occult Spinal Dysraphism.
+
Incidence, Prevalence, Frequency, and
Rates
+
Sacral Hiatus, Paleoepidemiology, Sa-
cral Anomaly, Sacral Deformity and
Osteoarchaeology
N/A 68
*Search string and number of publications generated are not applicable to the University of Adelaide
Library and Google scholar databases.
Initial publication screening
parameters
Once all 409 publications had been re-
trieved, they underwent the initial
screening process and were included/ex-
cluded based on stringent predetermined
criteria, (Fig. 4). As the primary objective
of this literature analysis was to obtain
frequency data for SSBO, publications
that did not include frequency data for
this condition, data for SSBO specical-
ly, or those that did not include random
samples, were excluded. Case studies
which discussed only single examples
and therefore had no frequency data were
excluded. Surgical texts were also exclud-
ed on the basis that they related to the
diagnosis, management, treatment, and
Spina Bifda Occulta 21
surgical outcomes of spinal dysraphism.
As such the frequency of occurrence was
not reported, as all individuals observed
had already been diagnosed with this
condition. A singular list of abstracts
for a conference on the neurosurgical
management of spinal dysraphism was
also excluded due to lack of detailed fre-
quency data. Publications detailing nov-
el radiographic methods for the identi-
cation of SSBO were also excluded, as
prevalence data were not reported. One
publication pertained solely to ethics,
one was in reference to widescale arsenic
poisoning, and anumber were related to
non-human clinical trials which were of
no relevance to this research.
‘General SSBO’ included publications
that were designed as informative docu-
ments on the identication, diagnosis,
and treatment of SSBO from a clini-
cal perspective. These publications did
not include frequency data, and more
than half were in reference to SBC not
SSBO. This misidentication of SSBO
as the neural tube defect SBC, was also
an exclusion criterion. A number of
publications retrieved from Embase,
and PubMed also included publications
on pathologies completely unrelated to
SSBO. Issues in identifying SSBO data
specically, were further complicated by
the number of associated pathologies re-
searched clinically. Publications relating
to these pathologies, were also assessed,
and included only if the frequency data
were wholly separated from those of the
associated pathology, and if adequate and
appropriate control groups were used
(Page and Moher 2017; Page et al. 2021).
Adisproportionate number of the re-
trieved publications were related to Spi-
na Bida Cystica (SBC) and Neural Tube
Defects, and included no reference to, or
data for SSBO.This was the consequence
of an early proposal to compare frequen-
cy data for these two conditions to as-
certain the importance of their relative
patterns of occurrence. As this research
progressed, it was determined that SBC
frequency was already reliably established
in the literature, and therefore these stud-
ies were not included in the nal analysis
(Fig. 4). Trusted data for SBC, however,
were obtained from national and global
birth registers, derived from these exclud-
ed publications, to compare the relative
prevalence of this condition with that
of SSBO for the same period (Atta et al.
2016). This was achieved through the
calculation of mean values for reported
births with SBC per 1000, in European
populations. These are not included in
the results but were generated for the pur-
pose of aiding the discussion.
Internal Validity Screening
Parameters
Once these publications had been
screened for the more basic parameters,
(inclusion of SSBO frequency data), the
remaining 178 publications were sub-
jected to an additional, more stringent,
screening process, to access the internal
validity and address the risk of bias in
their results (Higgins et al. 2003). The
quality of included segmentation data was
assessed, and those that did not include
data for deformation of S1 specically,
or which reported duplicate data, were
excluded. Archaeological and anthropo-
logical texts from the early 20th century
which included purely textual anecdotes,
were thoroughly scrutinised to ensure
that sample sizes and case numbers were
accurate and did not contain any missing
or unclear data. Any uncertainty as to the
clarity, totality, or accuracy of the data
22 Ella R Kelty, Maciej Henneberg
from these publications resulted in them
being excluded to ensure the generation
of meaningful and reliable results (Hig-
gins et al. 2003). Publications that in-
cluded duplicate data already screened in
previous publications, or data that could
not be reliably differentiated from other
osteological assessments from similar or
sometimes the same archaeological sites,
were also excluded.
Those publications which assessed
the association between SSBO, and
arange of pathologies were also assessed
to ensure that frequency data for SSBO
were wholly separable from those of the
associated pathology, and that adequate
control groups had been used. Those
which did not provide adequate control
groups, or studies which included only
patients with a pathology, or deformity,
reliably associated with SSBO, (eg: Cu-
taneous stigmata), were excluded on the
basis that they did not represent the true
frequency of this condition. Radiological
assessments of this condition, which fo-
cussed on novel methods for the identi-
cation of SSBO, were also excluded if
they contained zero or duplicate frequen-
cy data for this condition, or if the level of
deformity, (segment), was not reported.
Once completed, this review of the
current literature produced 39/409 pub-
lications for inclusion into the frequency
data analysis. The included publications,
as outlined in detail in the appendix,
ranged in publication date from 1932 to
2019, 30 of these were peer reviewed,
with the remaining nine having been pub-
lished before the introduction of the peer
review system. All included publications
reported SSBO frequency data that were
analysed and deemed reliable, and no
publication was assessed which examined
the frequency of SSBO and did not pro-
duce at least one case of this condition.
Frequency Analysis Methods
A total of 39/409 publications were in-
cluded in the nal frequency analysis hav-
ing conformed to the outlined inclusion
criteria, (Fig. 4). Numbers were allocated
to each publication and citation, location
and dating details were recorded for each.
Reported case numbers of identied SSBO
were divided by reported sample sizes, and
multiplied by 100, to produce percentage
values. This was completed for each possi-
ble combination of reported deformation,
across all sacral segments. This included
deformation of segments inclusive of S1,
(ie: L5-S1, S1andS5), and calculation of
male and female frequencies (Henneberg
and Henneberg 1999; Lee et al. 2011; Sol-
omon et al. 2009).
Recalculations were made where re-
ported prevalence was not clearly present-
ed, with some cases and sample sizes be-
ing combined where necessary, (control/
patient and multiple juvenile samples).
Patient groups that were proven to be ran-
dom (not commonly or primarily associat-
ed with SSBO) were combined with control
group sample sizes, and case numbers, to
determine frequency for the whole group.
Publications that separated subadults
(1–15 years) into smaller sub-divisions of
age, (eg: 1–2 years, 3–4 years etc.) were also
grouped together, and an identical method
was used to determine the relative frequen-
cy (Page et al. 2021). Similar additions were
also made with the male and female fre-
quency calculations. This occurred where
male and female cases were recorded for
both the control and patient groups, which
were then combined to determine the fre-
quency, as per the method outlined above.
Instances where sex was separated into age
categories, of girl/boy, female/male struc-
ture, were also combined to determine the
frequency by sex (Fidas et al. 1987).
Spina Bifda Occulta 23
Once this information had been col-
lected for all 39 publications, the result-
ing data were separated into three distinct
historical groups. This was done to con-
sider the 4,500-year time span, to test the
hypothesised increase of this condition af-
ter 1900 and 1980 and to ensure that each
study would be accurately weighted. This
separation was determined according to
calculated date of birth of each group.
Birth dates were either used as reported
in more modern publications or estimat-
ed by subtracting average life expectancy
gures from burial dates for historical col-
lections (WHO 2012; WHO 2020). His-
torical Group 1 (HG1) included date range
2,500BCE to 1,900CE, the second Histor-
ical Group (HG2) encompassed all mate-
rial dating from 1,900 to 1980CE while
Historical Group 3 (HG3) included the
remaining data for the period 1980CE to
2020CE.Male and female frequency data,
where available, were also separated into
historical groups, although an absence of
reported sex data for HG3 did affect the
results of this group.
Statistical methods
While data for SSBO were recorded for
each sacral segment, only data for defor-
mation inclusive of S1 were included
into the statistical analysis. Total sa-
cra observed, and total number of cas-
es were determined for each historical
group. Contingency tables were gener-
ated in the SSPS.25 software, (Tables2
and 3) and Chi-squared calculation with
Yates’s correction, and corresponding
p-values, were used to assess the di-
rection of effect for these three groups
(Henneberg and Henneberg 1999; Lee
et al. 2011; Solomon et al. 2009). The
available male and female data for all
three historical groups were treated in
the same way.
All statistical calculations were per-
formed using the SSPS.25 software by
the primary author with instruction and
assistance from the secondary author. No
external resources were used to complete
this analysis and no additional reviewers
were integrated into the assessment.
Table 2. Contingency table used to generate Chi-Squared statistic for the total frequency of SSBO
Historical Group 1
<1900
Historical Group 2
1900-1980
Historical Group 3
>1980
Total Sacra Observed 6,901 8,074 1,192
Total SSBO Cases Identied 922 1,503 281
Total frequencies determined for comparison of Historical Groups 1 and 2, 2 and 3 and 1 and 3.
Table 3. Contingency table used to generate Chi-Squared statistic for the male/female frequencies of SSBO
Historical Group 1
<1900
Historical Group 2
1900-1980
Historical Group 3
>1980
Total Male Sacra Observed 790 2,883 319
Total Male Cases of SSBO 98 738 46
Total Female Sacra Observed 720 2,830 268
Total Female Cases of SSBO 69 458 74
Male and Female frequencies determined through comparison of Historical Groups 1 and 2, 2 and 3 and
1 and 3.
24 Ella R Kelty, Maciej Henneberg
Results
Atotal of 39 publications were included
from the 409 retrieved and screened dur-
ing the literature review process (Fig.4).
The results of both screening processes,
with exclusion/inclusion criteria outlined
for each publication, throughout each
process, are presented in the appendix.
Citation details and exact frequency data
collected from each included study are
also included in the appendix.
The frequency analysis results demon-
strated aclear and statistically signicant
increase in the frequency of SSBO after
1900 (Table 4 and Fig. 6). The calcula-
tion of the total frequencies for historical
groups one and two, evidenced a 5.25%
increase in SSBO frequency, (<1900 to
1980), Chi-squared 54.503 (p<0.0001).
The comparison of total frequencies be-
tween historical groups two and three also
provided avery statistically signicant re-
sult, with a4.98% increase, Chi-squared
10.543 (p<and ap-value of <0.0012). To-
tal frequency comparison was also com-
pleted between historical groups one and
three, which demonstrated an increase of
10.23% from the period <1900, to the
present, Chi-squared 57.843 (p<0.0001).
Fig 6. Total SSBO frequency by historical group. Data derived from numerical analysis of
included literature and frequency calculations outlined in Table 4).
Fig. 6. Total SSBO frequency by historical group. Data derived from numerical analysis of
included literature and frequency calculations outlined in Table 4.
Table 4. Total data included in each historical group
Historical Group 1
<1900
Historical Group 2
1900-1980
Historical Group 3
>1980
Total Included Publications 18 17 7
Total Included Studies 28 40 7
Total Sacra Observed 6,901 8,074 1,192
Total SSBO Cases Identied 922 1,503 281
Total Frequency 13.36% 18.61% 23.59%
Total Increase 2.40% 5.25% 4.98%
Chi-Square Value HG1-HG2
54.503
HG2-HG3
10.543
HG1-HG3
57.843
p-Value <0.0001% <0.0012% <0.0001%
Spina Bifda Occulta 25
Detailed representation of the total
data for each historical group includes
signicance calculations and data used
to calculate frequency.
The male and female frequency cal-
culations for the three historical groups
also produced statistically signicant
results for an increase of SSBO after
1900 and 1980. A clear increase was
demonstrated in males (13.19%) and
females (6.60%) for historical groups
one and two, generating Chi-squared
values of 40.618 and 14.737 (for both
p<0.0001). A decrease was observed
in male frequency of -11.17%, (Chi-
squared=12.209, p<0.0005) between
historical groups two and three, but an
increase was demonstrated for females
(Chi-squared = 14.105, p<0.0002). (Ta-
ble 5 and Fig. 7).
Table 5. Male and female data included by historical group
Historical Group 1
<1900
Historical Group 2
1900-1980
Historical Group 3
>1980
Total Included Publications 6 10 4
Total Included Studies 10 23 4
Total Male Sacra Observed 790 2,883 319
Total Males Cases of SSBO Identied 98 738 46
Total Frequency 12.40% 25.59% 14.42%
Total Increase/Decrease N/A +13.19% -11.17%
Chi-Squared Value N/A HG1-HG2
40.618
HG2-HG3
12.209
P-Value N/A <0.0001% <0.0005%
Total Female Sacra Observed 720 2,830 268
Total Female Cases of SSBO Identied 69 458 74
Total Frequency 9.58% 16.18% 27.61%
Total Increase/Decrease N/A 6.60% +11.43%
Chi-Squared Value N/A HG1-HG2
14.737
HG2-HG3
14.105
p-Value N/A <0.0001 <0.0002
Fig 7. Male and female frequency by historical group. Data derived from numerical
analysis of included literature and frequency calculations outlined in Table 8.
Fig 7. Male and female frequency by historical group. Data derived from numerical
analysis of included literature and frequency calculations outlined in Table 8.
Fig. 7. Male and female frequency by historical group. Data derived from numerical analysis of included
literature and frequency calculations outlined in Table 8.
26 Ella R Kelty, Maciej Henneberg
Discussion
Almost all results pertaining to the overall
frequency of SSBO demonstrated asub-
stantial, statistically signicant increase
after 1900. These results provide com-
pelling conrmation for the hypothesised
increase in the frequency of SSBO and its
correlation with the relaxation of natural
selection around 1900. The importance
of these results for the determination of
current evolutionary change can be con-
ceptualised by outlining the frequency for
each historical group. HG1, (2,500BCE
to 1900CE), had a total frequency of
13.36%, compared to HG2, (1900 to
1980) at 18.61%, which demonstrates
a clear increase of 5.25% over a small
80-year period. HG3, (>1980) produced
a frequency of 23.59%, and an increase
of 4.98% from HG2, despite representing
a smaller sample size and shorter peri-
od of history (40 years). When compared
to HG1 (<1900), HG3 demonstrated an
even more signicant result, of a10.23%
increase in the frequency of SSBO be-
tween 1900CE and the present. When
converted to increase per decade, these
gures: 1.31% and 2.49%, demonstrate
an accelerating non-linear increase in the
frequency of SSBO in the modern era (Sa-
niotis and Henneberg 2011).
The calculation of male and female
prevalence for HG1 and HG2 also pro-
duced statistically signicant results
in support of an increase of SSBO after
1900. These results demonstrated high-
er percentages of increase than the total
frequency calculation for these historical
groups. Despite the sample sizes of each
sex (3,992 males and 3,818 females) be-
ing similar, male prevalence was much
higher and demonstrated a6.59% great-
er increase than among females (13.19%
male to 6.60% female) between HG1
and HG2. This could potentially rep-
resent a sex based evolutionary trend
that has yet to be fully investigated, as
male frequency was consistently higher
with the exception of the decrease ob-
served for males in HG3. This 11.17%
decrease observed for males after 1980 is
the only decrease noted across the entire
analysis and is accompanied by a sub-
stantial 11.43% increase for females in
this group. These calculations for >1980
are based on just four publications, with
small numbers of sacra, and thus, may
reect regional differences rather than
temporal trends. It is important to note
that additional data are needed for HG3
to ensure that these relative increases/de-
creases can be substantiated.
While this research does represent
the largest assessment of SSBO in the
literature (16,167 sacra), the scarcity of
relevant literature and the acknowledged
limitations of these studies suggest that
these results represent only afraction of
potentially recoverable data. The increase
in the frequency of SSBO is relatively
modest compared to the median artery,
which shows an increase of 20% over the
same 120-year period, about double that
of the increase in SSBO (Lucas T et al.
2020). Similarly, tarsal coalitions experi-
enced an increase of 12% over a50-year
period, double the reported frequency
demonstrated for SSBO for this period
(Ruhli et al. 2003). These modest in-
creases in frequency recorded for SSBO
may be the product of the lack of data
and academic consensus. It may be pos-
sible that with the inclusion of addition-
al, larger, and targeted datasets, rates of
SSBO frequency may increase again, to
parallel those observed in these other an-
atomical structures.
This research holds important im-
plications for the general application of
Spina Bifda Occulta 27
both biological anthropology and bioar-
chaeology. The recognition of implica-
tions of natural selection on widescale
secular change can improve the accu-
racy of differential diagnosis in skele-
tal remains. Awareness of this increase
in skeletal variation, its frequency, and
patterns of presentation, can improve
future bioarchaeological interpretations
of trauma, pathology, and health status.
The potential for this phenomenon to
produce previously unobserved skeletal
changes must also be recognised and at-
tempts to identify pathological associa-
tions with new forms of variation must
be addressed. By acknowledging that the
human skeleton is changing, collabora-
tion with the medical community and
the use of clinical methodology, can
strengthen the capacity of bioarchaeolo-
gy to provide insight into global future
health outcomes as they relate to secular
changes.
The incorporation of clinical param-
eters, statistical calculations, and bias
assessments into this bioarchaeological
assessment of SSBO frequency has pro-
vided a unique opportunity to design
asystematic methodology which can be
applied to a range of skeletal and ana-
tomical variations. This framework has
allowed for the traditionally small scale
and localised anthropological datasets to
be amalgamated into a broad temporal
and geographic ‘map’ of SSBO frequen-
cy, emphasising overarching patterns
not identiable in smaller studies. This
method allows for small datasets to be
incorporated with ahigh degree of accu-
racy and can facilitate acontinuous addi-
tion of new data. Potentially, this could
produce an ever increasing ‘map’ of SSBO
frequency, where the addition of datasets
from arange of researchers would allow
the eventual creation of a truly global
representation of SSBO frequency and
its secular trajectory. This method could
then be expanded to include additional
anatomical variations, from independ-
ent or future researchers, that would also
lead to the creation of global ‘maps’ of di-
verse conditions frequencies.
Future bioarchaeological assess-
ments of skeletal variation should be
reconceptualised, with the tradition-
al focus on individual and localised
assessments of change replaced with
wide reaching systematic evaluations of
broad scale frequency. Clear patterns of
secular change could be reliably assessed
on aglobal scale, and these trends sys-
tematically compared. The potential
for this style of analysis to identify
trends that have explicit implications
for public health and medicine, can be
demonstrated through the comparison
of SSBO and SBC frequency. The 4.98%
increase in SSBO frequency observed
after 1980 demonstrates asustained in-
crease of this condition and conforms
with Solomon et al. (2009) and Lee et
al. (2011) results on the conrmation
of this microevolutionary increase and
secular trend, despite the introduction
of folate supplementation in 1980.
This is in direct opposition to expect-
ed clinical outcomes for SSBO after
folate supplementation introduction,
which has resulted in a sharp decline
of NTD related births worldwide after
1980, (Fig. 8) (Atta et al. 2016). This
would suggest that SSBO potentially
does not follow the same embryonic
and etiological trajectory as SBC and
has a separate cause altogether. While
these results do not conrm or identify
the underlying cause of SSBO, the large
scale and systematic nature of this as-
sessment, provides the foundation to
test such hypotheses further.
28 Ella R Kelty, Maciej Henneberg
Fig 8. Comparison between SBC and SSBO frequency by date. Resulting frequency data
from literature analysis compared with reliably reported SBC prevalence
Fig 8. Comparison between SBC and SSBO frequency by date. Resulting frequency data
from literature analysis compared with reliably reported SBC prevalence
Fig 8. Comparison between SBC and SSBO frequency by date. Resulting frequency data
from literature analysis compared with reliably reported SBC prevalence
Fig. 8. Comparison between SBC and SSBO frequency by date. Resulting frequency data from literature
analysis compared with reliably reported SBC prevalence.
While the results of this literature anal-
ysis were limited by the data available in
the current literature, the primary objective
of this analysis was achieved. The frame-
work that this analysis has provided will
facilitate the inclusion of additional SSBO
data which will expand our understanding
of this little-known condition and provide
auniform structure to ensure the replica-
bility of all future research. In combination
with the establishment of the most reliable
frequency calculation to date, this frame-
work will also enable the investigation of
untested aspects of this condition, such as
underlying etiology and additional patho-
logical associations. Other anatomical
variations, which have yet to be systemati-
cally evaluated, could also be incorporated
into this framework, to establish abroader
understanding of the trajectory and impli-
cations of secular evolutionary change in
modern human populations.
Acknowledgments
We would like to Acknowledge Dr Teghan
Lucas who initiated this project and Dr
Jaliya Kumaratilake and Angela Gurr for
assistance with specimen organisation.
This project would not have been possi-
ble without them.
Due to the nature of this project no
funding was required or requested.
Authors’ contribution
Both authors formulated the hypothesis.
ERK collected data and drafted the text.
MH helped with the analysis and edited
text.
Conict of interests
The Authors have no competing inter-
ests concerning this review.
Registration and Protocol
This review has not been registered as it
is bioarchaeological.
The Protocol used for this review can
be accessed in the appendix.
No amendments have been made due
to registration or protocol.
Data Availability
PRISMA Flow Chart template 2020:
http://www.prisma-statement.org/
Data for each individual study included
in this analysis is available in the appendix.
Spina Bifda Occulta 29
Corresponding author
Ella Kelty, Anatomical Sciences Unit of
the School of Biomedicine, Adelaide Uni-
versity, Adelaide, Australia; ella.kelty@
inders.edu.au
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Spina Bifda Occulta 49
Supplementary Material
Table 6. Results of the initial screening process. Inclusion/exclusion criteria and number of publications
included/excluded by database outlined
Exclusion reason
Number
Excluded:
Embase (n=)
Number
Excluded:
PubMed (n=)
Number
Excluded:
Adelaide
Library (n=)
Number
Excluded:
Google
Scholar (n=)
Total
(n=)
/409
Duplicates 9 2 1 1 13
Case Studies 11 5 1 1 17
Surgical Texts 12 13 2 27
Responses/Abstracts/Reviews 1 1
Radiographical Methods 6 3 2 11
Ethics 1 1
Non-Human Studies 1 3 1 5
General no % data 6 16 1 3 26
SBC not SSBO 10 13 10 5 38
Unrelated Clinical Conditions 26 25 16 2 68
Nonrandomised 11 7 4224
Total Included 08/100 12/100 103/141 53/68 178
Total Excluded 92/100 88/100 38/141 15/68 231
Table 7. Results of the internal validity screening process. Inclusion/exclusion criteria and number of pub-
lications included/excluded by database outlined
Exclusion Criterion Publications Excluded (n=)
Duplicate data 3
Unreliable data 2
Case Studies 5
Surgical Texts 3
SBC not SSBO 55
No segment data 5
No S1 data 6
Nonrandomised 15
Non-Human 2
Radiograph method 7
General no % data 10
Unrelated condition 26
Total Included 39/178
Total Excluded 139/178
50 Ella R Kelty, Maciej Henneberg
Table 8. Included studies with sample size, date of samples as well as characteristics and any necessary
assessments for bias in each publication
(n=) Publication
Sample Size
+
Date
Characteristics Risk of Bias Assessment*
1Zemirline Aet al. Lumbo-sa-
cral malformations and spi-
na bida occulta in medieval
skeletons from Brittany. Eur
J Orthop Surg Traumatol.
2013;23: 149–153.
30
768 CE
Archaeological study
of recovered skeletal
human remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
2Molto JE, et al. The paleoepi-
demiology of sacral spina bi-
da occulta in population sam-
ples from the Dakhleh Oasis,
Egypt. Int J Palaeopathol.
2019;26: 93–103.
116
116 BCE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
3Urrutia J, et al. Spondylolysis
and spina bida occulta in pa-
ediatric patients. Prevalence
study using computed tomog-
raphy as ascreening method.
Eur Spine J. 2016;25: 590–
595.
228
2005 CE
Radiographic study
of live patients with
associated pathology.
CT and well-structured nu-
merical results.
SSBO and Spondylolysis
data separate
Clear, accurate and included
segment data for SSBO, S1
4 Saluja PG.The incidence of
spina bida occulta in a his-
toric and a modern London
population. J Anat. 1988;158:
91–93.
112
1816 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
5Lee YC et al. Conrmation
of microevolutionary increase
of spina bida occulta among
Swiss birth cohorts. Eur Spine
J. 2011;20: 776–780.
384
1965 CE
Radiographic study
of birth cohorts. An-
onymised CT data.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
6Ali S, et al. The prevalence of
spina bida occulta in aPaki-
stani population: a study of
dry human sacra. Anaesth,
Pain Intensive Care. 2014;18:
157–161.
200
1954 CE
Modern anatomical
study of archived dry
human sacra.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
7Shin SH et al. Spina bida
occulta: not to be overlooked
in children with nocturnal
enuresis. Int J Urol. 2013;20:
831–835.
160
1999 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results. SSBO and enuresis
data separated
Clear, accurate and included
segment data for SSBO, S1
Spina Bifda Occulta 51
(n=) Publication
Sample Size
+
Date
Characteristics Risk of Bias Assessment*
8Wu L et al. Variable morphol-
ogy of the sacrum in aChi-
nese population. Clin Anat.
2009;22: 619–626.
203
1961 CE
Modern anatomical
study of archived dry
human sacra.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
9Cakiroglu B et al. The ad-
verse inuence of spina bida
occulta on the medical treat-
ment outcome of primary
monosymptomatic noctur-
nal enuresis. Archive Italian
Urol. 2014;86: 270–273.
233
1999 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
10 Solomon LB et al. Secular
trend in the opening of the
sacral canal: An Australian
study. Spine. 2009;34: 244–
248.
200
1945 CE
Radiographic study
of birth cohorts. An-
onymised CT data.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
11 El-Din A et al. Congenital
anomalies of the vertebral
column: a case study on an-
cient and modern Egypt. Int
J Osteoarchaeol. 2006;16:
200–207.
270
2424 BCE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
12 Maat GJ et al. Analysis of hu-
man skeletons from aHellen-
istic period, buried at aruined
Bronze Age building on Faila-
ka, Kuwait. Maison de l’Ore-
int. 1990;18: 85–102.
12
1770 BCE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
13 Kim DW et al. Morphological
diversities of sacral canal in
children: three-dimensional
computed tomography study.
Korean J Pain. 2014;27: 253–
259.
143
1996 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results. SSBO data and oth-
er anomaly data separated
Clear, accurate and included
segment data for SSBO, S1
14 Wu JW et al. Prevalence of
spina bida occulta and its
relationship with overactive
bladder in middle-aged and
elderly Chinese people. Int
Neurouro J. 2016;20: 151–
158.
1061
1954 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results. SSBO and bladder
dysfunction data separated
Clear, accurate and included
segment data for SSBO, S1
15 Fidas A et al. Prevalence and
patterns of spina bida oc-
culta in 2707 normal adults.
Clin Rad. 1987;38: 537–542.
2707
1911 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
52 Ella R Kelty, Maciej Henneberg
(n=) Publication
Sample Size
+
Date
Characteristics Risk of Bias Assessment*
16 Shore LR. Abnormalities of
the vertebral column in ase-
ries of skeletons of Bantu na-
tives of South Africa. J Anat.
1930;64: 206–238.
155
1945 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
17 Masnicova S et al. Develop-
mental anomalies in skele-
tal remains from the great
Moravia and Middle Ages
cemeteries at Devin, (Slo-
vakia). Intl J Osteoarchaeol.
2003;13: 266–274.
150
1115 BCE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
18 Hussien FH et al. Spinal
pathological ndings in an-
cient Egyptians of the Gre-
co-Roman period living in
Bahriyah Oasis. Int J Osteo-
archaeol. 2009;19: 613–627.
77
289 BCE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
19 Mays S. Spondylolysis,
spondylolisthesis, and lum-
bo-sacral morphology in
a medieval English skeletal
population. Am J Phys An-
thropol. 2006;131: 352–362.
422
1465 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results. SSBO and Spon-
dylolysis data separate
Clear, accurate and included
segment data for SSBO, S1
20 Kim Yet al. Lumbosacral de-
fects in a 16th – 18th century
Joseon Dynasty skeletal series
from Korea. Biomed Res Int.
2018;28: 1–8.
198
1666 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
21 Schweitzer ME et al. Spina bi-
da occulta: incidence in pa-
rents of offspring with spina
bida cystica. Spine. 1992;18:
785–786.
177
1932 CE
Radiographic study
in live patients with
associated pathology.
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
22 McGrath M et al. Anatomical
observations related to radio-
logical ndings in spina bi-
da -occulta of the lumbo-sa-
cral spine. J Osteopath Med.
2004;7: 70–78.
40
1994 CE
Radiographic study
specically designed
for SSBO.
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
23 Papp T et al. Changes of the
lumbar spinal canal proximal
to spina bida occulta. An
archaeologic study of clinical
signicance. Spine. 1994;19:
1508–1511.
104
367 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
Table 8 (cont.)
Spina Bifda Occulta 53
(n=) Publication
Sample Size
+
Date
Characteristics Risk of Bias Assessment*
24 Jankauskas R.Variations and
anomalies of the vertebra col-
umn in Lithuanian palaeoost-
eological samples. Anthropol.
2001;39: 33–38.
633
1467 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
25 Merbs CF. Sagittal clefting of
the body and other vertebral
development errors in Cana-
dian Inuit skeletons. Am J
Phys Anthropol. 2004;123:
236–249.
218
1867 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results. SSBO and other
anomaly data separated
Clear, accurate and included
segment data for SSBO, S1
26 Stewart TD. The vertebral
column of the Eskimo. Am J
of Anthropol. 1932;17: 123–
136.
217
1990 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
27 Eubanks J et al. Prevalence
of sacral spina bida occulta
and its relationship to age,
sex, race, and the sacral table
angle. Spine. 2009;34: 1539–
1543.
2866
1885 CE
Radiographic study
specically designed
for SSBO.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
28 Sutow WW et al. Incidence
of spina bida occulta in re-
lation to age. Am J Dis Child.
1955;90: 211–217.
540
1921 CE
Radiographic study
specically designed
for SSBO.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
29 Albrecht TL et al. Radio-
graphical method to access
the prevalence of sacral spi-
na bida occulta. Clin Anat.
2007;20: 170–174.
53
1937 CE
Radiographic study
specically designed
for SSBO.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
30 Karlin IW.Incidence of spina
bida occulta in children with
and without enuresis. Am J
Dis Child. 1935;3: 374–393.
75
1840 CE
Radiographic study
in live patients with
associated pathology.
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
31 Jozsa L et al. The occurrence
of spina bida occulta in me-
dieval and contemporaneous
Hungarian populations. An-
thropol Hunarica. 1992;22:
51–60.
233
1328 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
+
Radiographic study
specically for SSBO.
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
32 Avrahami Eet al. Spina bida
occulta of S1 is not an inno-
cent nding. Spine. 1994;19:
12–15.
1200
1949 CE
Radiographic study
specically designed
for SSBO.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
54 Ella R Kelty, Maciej Henneberg
(n=) Publication
Sample Size
+
Date
Characteristics Risk of Bias Assessment*
33 Piontek J. Variation in the
level of closure in the sacral
canal of man. Folia Microbiol.
1971;4: 459–464.
316
1911 CE
Modern anatomical
study of archived dry
human sacra.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
34 Kubauat DM et al. Astudy of
non-fusion of laminae of the
rst sacral vertebrae in West-
ern India. Int J Recent Trends
Sci Tech. 2013;6: 122–124.
302
1953 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
35 Groza VM et al. Frequency of
spina bida occulta and oth-
er occult spinal dysraphism’s
in the medieval population
of Isas city: skeleton palaeo-
pathology in the necropolis
discovered in the eastern part
of the Princely Court, 17th
century. Biol Anim. 2012;58:
195–204.
28
1660 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
36 Henneberg RJ et al. Varia-
tion in the closure of the
sacral canal in the skeletal
sample from Pompeii, Italy,
79AD. Perspect Hum Bio.
1999;4: 177–188.
124
79 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
37 Singh R. Classication caus-
es and clinical implications
of sacral spina bida occulta
in Indians. Basic Sci Med.
2013;2: 14–20.
140
1953 CE
Archaeological study
of recovered human
remains.
(Dry human sacra)
Anecdotal data
Clear, accurate and included
segment data for SSBO, S1
38 Al-Dahhan MH et al. Evalu-
ation of spina bida occulta
in young patients presented
with lower back pain. Eur
J Mol Clin Med. 2020;10:
4416–4422.
180
2016 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
39 Kumar P et al. Spina bida oc-
culta in functional enuresis.
Indian J Paediatr. 2005;72:
223–225.
48
1997 CE
Radiographic study
in live patients with
associated pathology.
Well-structured numerical
results
Clear, accurate and included
segment data for SSBO, S1
Table 8 (cont.)
Spina Bifda Occulta 55
Table 9. Raw data from frequency analysis
S1-S3
0.76
1.20
Percentage values for each sacral segment recorded. Publications 1–4. SS=Sample Size.
S1-S2
0.86
1.56
0.51
3.36
3.57
3.17
3.84
8.51
1.20
S1
13.79
10.93
17.30
2.59
9.32
8.69
11.11
16.80
19.64
14.28
6.15
6.37
6.02
S1-S5
0.74
0.74
0.74
8.30
5.17
7.80
1.92
3.10
54.54
51.21
60.00
4.2
7.4
1.58
0.76
2.12
Female SS
135
52
35
63
83
Male SS
135
64
23
41
56
47
Total SS
270
12
116
77
193
144
77
119
119
130
130
Date
-2424
-1770
-874
-860
-868
1766
-289
124
124
110
110
Publication
El-Din and El Banna 2006
2. Maat et al. 1990
3. Molto et al. 2019
4. Hussein et al. 2009
56 Ella R Kelty, Maciej Henneberg
S1andS3-S5
0.77
1.61
1.09
1.09
Percentage values for each sacral segment recorded in each publication. Publications 5–13.
S1-S2andS4-S5
0.23
2.00
3.27
1.47
3.94
5.26
3.57
3.47
S1
4.50
82.60
6.66
13.46
13.46
29.62
10.38
12.95
0.42
4.04
7.40
1.47
S1-S5
1.18
3.33
2.21
1.71
1.09
1.51
0.50
1.23
Table 9 (cont.)
Female SS
65
28
62
68
Male SS
61
38
62
66
81
Total SS
422
115
30
124
104
27
77
150
76
633
233
28
129
91
198
Date
1465
1515
768
39
367
617
967
1115
865
1467
1328
1660
1662
1670
1666
Publication
5. Mays 2006
6. Zemirline et al. 2013
7. Henneberg and Henneberg 1999
8. Papp and Porter 1994
9. Masnicova and Benus 2003
10. Jankauskas 2001
11. Jozsa et al. 1992
12. Groza et al. 2012
13. Kim et al. 2018
Spina Bifda Occulta 57
Table 9 (cont.)
S1andS4-S5
8.29
8.41
9.37
S1-S2
1.78
2.85
8.00
13.00
3.00
9.50
15.00
4.00
S1
11.60
10.00
43.11
10.50
17.00
4.00
16.50
23.00
10.00
24.24
28.46
20.58
22.77
27.48
17.96
19.35
25.00
13.33
8.73
8.10
9.32
S1-S5
1.78
2.14
2.76
4.67
1.04
Percentage values for each sacral segment recorded in each publication. Publications 14–18.
Female SS
100
100
96
136
128
120
118
Male SS
100
100
107
137
131
128
111
Total SS
112
140
218
200
200
217
273
259
248
229
Date
1816
1928
1867
1945
1985
1900
1968
1958
1948
1938
Publication
14. Saluja 1988
15. Merbs 2004
16. Solomon et al. 2009
17. Stewart 1932
18. Avrahami et al. 1994
58 Ella R Kelty, Maciej Henneberg
L5-S5
12.00
9.03
10.46
7.24
6.31
9.09
3.92
4.62
10.41
2.19
3.79
0.97
S1-S2
11.13
16.00
S1
6.80
7.52
6.12
2.34
2.57
2.10
62.00
3.84
51.61
46.51
57.97
44.21
47.72
41.17
39.81
52.08
30.00
14.83
54.43
20.38
23.91
16.57
22.18
Percentage values for each sacral segment recorded in each publication. Publications 19–23.
Table 9 (cont.)
S1-S5
1.22
12.00
Female SS
98
190
69
51
60
103
Male SS
93
194
86
44
48
79
Total SS
191
2866
384
75
78
155
95
108
182
46
87
87
Date
1928
1885
1965
1913
1840
1945
1941
1936
1921
1902
1902
1902
Publication
Avrahami et al. 1994 (cont)
19. Eubanks and Cheruvu 2009
20. Lee et al. 2011
21. Karlin 1935
22. Shore et al. 1932
23. Sutow and Pryde 1955
Spina Bifda Occulta 59
L5-S2
15.81
15.62
13.50
16.98
16.07
1.28
4.16
1.26
1.60
0.77
10.41
S1-S2
0.85
0.66
5.55
3.48
4.81
1.55
3.50
4.16
15.40
18.20
0.65
S1
10.92
22.31
3.31
65.27
22.50
22.22
27.77
3.48
2.67
4.65
16.66
11.96
S1-S5
3.57
1.26
1.60
0.77
4.50
2.95
Percentage values for each sacral segment recorded in each publication. Publications 24–34.
Female SS
37
56
72
20
129
Table 9 (cont.)
Male SS
32
53
151
20
187
Total SS
140
302
177
233
40
316
200
48
143
203
1061
Date
1953
1953
1932
1999
1994
1911
1954
1997
1996
1961
1954
Publication
24. Singh 2013
25. Kubauat et al. 2013
26. Schweitzer 1992
27. Cakiroglu et al. 2014
28. Mith and Tayles 2004
29. Piontek 1971
30. 0 et al. 2004
31. Kumar et al. 2005
32. Kim 2014
33. Wu et al. 2009
34. J.W.Wu et al. 2016
60 Ella R Kelty, Maciej Henneberg
L5-S5
4.40
Percentage values for each sacral segment recorded in each publication. Publications 25–39.
S1
28.59
37.20
18.95
20.98
29.68
13.47
20.97
23.72
18.15
20.58
25.00
15.11
16.76
16.25
17.20
19.23
20.83
17.85
16.25
35.08
18.5
1.25
Female SS
269
460
325
172
93
28
Male SS
301
411
333
208
80
24
Table 9 (cont.)
Total SS
570
877
658
380
173
52
160
228
180
53
Date
1941
1931
1921
1911
1901
1891
1999
2005
2016
1937
Publication
35. Fidas et al. 1987
36. Shin et al. 2013
37. Urrutia et al. 2016
38. Al-Dahhan et al. 2020
39. Albrecht et al. 2017
Spina Bifda Occulta 61
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