VARIATION IN THE CLOSURE OF THE SACRAL CANAL
IN THE SKELETAL SAMPLE FROM POMPEII, ITALY, 79 AD
RENATA J HENNEBERG and MACIEJ HENNEBERG
Department of Anatomical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
Closure of the sacral spinal canal is one of the most variable aspects of human
anatomy. Frequencies of the fusion of posterior arches of various sacral segments differ
widely between populations from various geographical regions and time periods. Some authors
report 50% of S 1 posterior arches to be unfused, while others give figures below 2%. It is also
debatable whether various degrees of non-closure of posterior sacral arches are pathological
or just a normal variation. Lack of uniformity in the methods used by various authors and
terminological debates (eg, correct use of spina bifida occulta) complicate the issue even
We have examined 124 adult sacra (70 males and 54 females) from individuals who
died in Pompeii during the 79 AD eruption of Vesuvius. There were four sacra (3%) with a
completely open spinal canal. A completely fused canal (S1 to S5 inclusive) was found in
11% of sacra. The most common condition (47%) was when only the posterior arch of S5
was open. The combination of open S5 and S4 was present in another 35%. Opening of the
sacral canal reaching from S5 to S3 was present in 4% of individuals. Among all sacra, 8%
had unfused posterior arches of S I irrespective of the degree of the spinal canal closure at
other levels. No regular significant sexual dimorphism was noted.
The sample of sacra from Pompeii seems to fall within the ranges reported for
other populations, even with the uncertainties regarding differences in the methods used by
various authors. Due to its frequent occurrence in various populations, incomplete closure of
the sacral canal can hardly be considered to be a true, disabling pathological condition.
Key words: sacrum, spina bifιda occulta, anatomical variation
Anatomical variations of the vertebral posterior arches and posterior segments of the
sacrum were studied previously in archaeological human skeletal series (Stewart, 1932;
Ferembach, 1963; Post, 1966; Bennett, 1972; Suzuki, 1978; Bradtmiller, 1984; Webb, 1995).
A commonly observed condition was the lack of fusion of the posterior arches of the lower
lumbar vertebrae and of the posterior arches of the sacrum. This condition was referred to as
spina bifida occulta.
In the sacrum various researchers used the term spina bifιda occulta to describe different
degrees of open and closed posterior arches. Some authors used spina bifida occulta
exclusively to describe the completely open dorsal part of the sacral spinal canal (Webb.
1995); others used this term when the sacral spinal canal was open from S3 upwards
(Bradtmiller, 1984). Some researchers classified spina bifida occuιlta into two types, complete
and incomplete spina bifιda occulta. without defining which posterior arches were open in the
incomplete type (Suzuki, 1978; Macchiarelli, 1989). Some authors used the term 'neural tube
178 Renata Henneberg and Maciej Henneberg
closure failure' indiscriminately to describe all variants (regardless of the defects or the normal
variation), including a complete opening of the sacrum and a single posterior arch opening at
S5 (Devor and Cordell, 1981).
Despite many published reports on spina bifida occulta, from both historical and modern
skeletal collections, it is difficult to compare frequencies of spina bifιda occulta across
populations and through time. The concern about the lack of a clear definition of spina bifιda
occulta in the sacrum for use in comparative skeletal studies has also been expressed by
previous researchers (Ferembach, 1963; Ortner and Putschar, 1985; Webb, 1995). Most of
the morphological studies of spina bifιda occulta in skeletal series and in various populations
were conducted from the early part of this century up until the 1970s.
Post (1966), in his attempt to classify the vertebral variations of the spine, did not
specify at which level the opening of the sacral canal is still considered normal; instead he
described variations at a level of each sacral vertebra. In the majority of recent studies, the
term spina bifιda occulta in the sacrum was used to denote a failure to close the arches of the
first and sometimes also the second sacral segment, or a complete failure to close the entire
sacral spinal canal (Boone et al, 1985; Fidas et al, 1987; Saluja, 1988; Avrahami et al, 1994;
Webb, 1995). The non-closure of the last three sacral segments (3rd, 4th and 5th) was
considered a normal variation (Romanes, 1981).
In clinical publications, spina bifιda occulta is described as a minor abnormality in the
closure of the spinal canal which is covered only by soft tissues without bone being involved.
In its uncomplicated form only one vertebral arch fails to close. Sometimes more than one
vertebral arch is involved and widening of the spinal canal occurs. Further complications then
follow, such as lipoma, dermatological and neurological lesions (Elwood et al, 1992). The
condition occurs most frequently in the lumbosacral region (James and Lassman, 1981). The
defects of the closure of the spinal canal, including spina bifιda occulta, are heritable and most
probably controlled polygenically (Ricardi, 1977; Elwood et al, 1992).
Until recently in medical practice spina bifιda occulta was seen as a common condition
with little clinical significance, in contrast to more severe malformations such as
meningocoele or myelomeningocoele (Lorber and Levick, 1967; Boone et al, 1985; Elwood et
al, 1992). Renewed interest in the studies of the spina bifιda occulta condition in the
lumbosacral region has been observed recently, because the defect was found to be associated
with lower back pain, posterior disc herniation, urodynamic problems and other abnormalities
of the lower urinary tract (Avrahami et al, 1994; Galloway and Tainsh, 1985; Fidas, 1987;
Fidas et al, 1989).
Family studies revealed a high incidence of spina bifιda occulta among parents of
children with other more severe forms of neural tube defects, although the results of such
studies are not always in concordance with each other (Vannier et al, 1981; Carsin et al, 1986;
Saluja, 1988; Elwood et al, 1992). There were also studies reporting increased incidence of
spina bifida occulta in areas with high levels of fluoride in the drinking water (Gupta et al,
Some recent publications suggest a decrease in more serious neural tube defects in some
populations in the last few decades (Owens et al, 1981; Danks and Halliday, 1983; Carstairs
and Cole, 1984; Lorber and Ward, 1985), while other studies report increased frequency of
spina bifida occulta during the same time (Boone et al, 1985; Fidas et al, 1987; Avrahani et al,
1994). Very few researchers have attempted comparisons between contemporary and
historical samples from, presumably, the same population. In the only such study known to
the authors, Saluja (1988) compared the radiographs of a sample of modem people from
London with the 18th-19th century skeletal sample from one of the church crypts in London.
The Sacral Canal Closure in Ancient Pompeii, 79ÁD 179
and did not find any secular trend in the frequency of spina bifida occulta over the two
In view of these new findings, new questions have arisen, as well as the need for more
data to answer them. The need for more data on the frequency of spina bifιda occulta in
present populations, in clinical context, and also in past populations has already been
expressed by some authors (Saluja, 1988; Elwood et al, 1992).
The purpose of the present study was threefold: 1) to present some new data from
antiquity; 2) to argue for a unified system to collect data on the sacral spinal canal variation,
and to define spina bifιda occulta based on both anatomical and clinical findings; and 3) to
contribute to the debate regarding secular trends in spina bifida occulta.
MATERIALS AND METHODS
The skeletal sample from Pompeii examined in this study has certain unique
characteristics. Firstly, the direct cause of death was known for the entire sample: it was a
mass disaster caused by the volcanic eruption of Vesuvius in August 79 AD. This direct cause
of death seems to be unrelated to any specific diseases. Secondly, it is known that drinking
water in ancient Pompeii and in areas surrounding Vesuvius contained high levels of fluoride.
This fact has been confirmed recently by Torino et al (1995) for a sample of teeth from
ancient Herculaneum, which was destroyed by the same volcanic eruption as Pompeii. Torino
and co-workers found very high levels of fluoride in the tooth enamel of individuals from
Herculaneum, about 14 km from Pompeii.
The sample in this study consists of 124 adult sacra of 70 males and 54 females. The
sacra were examined macroscopically by both authors. Chi-squared tests were used for
comparisons of the results and their statistical evaluation.
The majority of sacra belonged to the skeletons excavated during the 19th century in
various parts of Pompeii. Some skeletons were lying on the streets, some inside various
buildings. Five sacra belonged to the occupants of the house of C Iulius Polybius, excavated
during the 1970s. The skeletal material excavated in the 19th century was segregated earlier
according to the type of bone; in most cases, at the time of our study, it was difficult to
reassemble individuals. The skeletons from the house of C Iulius Polybius were reassembled
by M Henneberg during a previous study conducted on this sample (Henneberg et al, 1996).
Except for the sacra from the house of C Iulius Polybius, where various methods of
establishing the sex of an individual could be applied, sex was established according to the
morphological sex differences of the sacrum, using methods described by Kimura (1982) and
Krogman and Iscan (1986).
In our investigation, we adopted the recent definition of the term spina bifιda occulta, as
used in clinical studies and practice. Spina bifτda occulta of the sacrum denotes the variation
in the anatomy of the sacrum where at least the posterior arch of the first sacral segment
failed to fuse. The posterior arches of the other sacral segments can be fused or open,
including the variation where the entire dorsal side of the sacral spinal canal is completely
open. This description is dictated by the anatomy of the spinal cord, where its conus in
normal conditions does not descend below the level of L3, and by clinical findings which
suggest that about two-thirds of the complications which impact on an individual's health,
such as laminal defects and spinal cord anomalies, are associated with non-fusion of the
posterior arches at the lumbosacral joint, mostly at the level L3-Sl. Only about 10% of neural
tissue defects are associated with the S2-S5 area of the sacrum (James and Lassman, 1981).
180 Renata Henneberg and
The Sacral Canal Closure in Ancient Pompeii, 79AD 181
In order to unify data collection on skeletal material and for purposes of
comparative studies, we used a simple system of recording variations in the posterior
sacral canal for each of the sacral segments in two categories: open or closed. The term
spina bifida occulta in the sacrum was used only when at least SI was open. Other
variants of spina bifιda occulta in the sacrum occur when the spinal canal in the dorsal
sacral part is open from SI downwards to S5, including the completely open spinal
canal. Anatomical forms of hiatus sacralis, where the dorsal part of the sacral canal
opens from S5 up to S2 while at the same time the fusion of posterior arches at the level
of S1 is evident, are considered normal variations. This system of recording anatomical
sacral variations is simpler than the one of Post (1966) because it does not include
variations where the opening is half way into the sacral vertebrae. We also suggest the
clinical application of the term spina bifida occulta to skeletal findings for reasons
Examples of the spina bifida occulta found in Pompeii and some of the normal
variations are presented in Figure 1.
In total, there was 11% of spina bifida occulta in the sample from Pompeii. Only
3% of the sacra had all arches open completely. An additional 8% of the sacra had open
arches of the first sacral segment while some other arches were closed normally.
The opposite sides of the posterior arch of S5 were not fused in 82% of sacra. The
most common variation (47%) was when only S5 was open and the other posterior
arches were closed. The combination of posterior part of S5 and S4 open followed as
the second most common variation (36%); however, the difference between the
frequency of these two variations is not statistically significant. Only 4% of sacra had
S5, S4 and S3 simultaneously open. A completely closed posterior sacral canal was
found in 11% of sacra (Tables 1 and 2).
There was no statistically significant difference between sexes in most of the
variants, including spina bifιda occulta. The only statistically significant difference
between females and males was found in the
equency of sacra with only S5 open.
Among males 36% had this variant as opposed to
182 Renata Henneberg and Maciej Henneberg
Other variations found in this sample included sacralisation of L5 (19%) and sacralisation
of coccygeal Col (7%). Sacralisation of L5 occurred more often among males (23%) than
females (13%), but the difference was not statistically significant. Sacralisation of the coccyx
also occurred more frequently in male (11%) than in female sacra (2%), but the difference, as
for the sacralisation of L5, was not statistically significant.
Within the group of sacralised L5 there were further variations observed. Asymmetrical
fusion of L5 to the sacrum was found in two cases (1 female and 1 male). Sacralisation of this
female L5 occurred only on the right side while the left side was free. In the male case, L5
was fused with the sacrum on the left side but not on the right side. In another male sacrum,
massae laterales were fused with L5 bilaterally, but disk space remained. One male sacrum
exhibited sacralised Col-Co3. The same male also had L5 completely sacralised and only S5
open. In one male with spina bifida occulta where SI arch was open, L5 was completely
sacralised and also open (spina bífιda occulta at L5-S1). In one female compression of S3 was
observed. Some of the sacra showed arthritic changes, but osteophytes were found only in
one female case with only S5 open.
Only the most frequent and very rare variations have been described above. Frequencies
of major variations in the posterior sacral canal closure and frequencies of some more
common anomalies are shown in Table 1.
The frequency of spina bifιda occulta in Pompeii falls in the middle of results reported
from other archaeological samples (Table 3). It is lower than the frequencies for ancient
Egyptians and the Anglo-Saxons from the 10th century AD, but higher than those found
among the ancient Peruvians and Aleuts. Our results are similar to those obtained for the
Romano-British and Anglo-Saxons of the 6th-7th century AD. Results for Pompeii are
The Sacral Canal Closure in Ancient Pompeii, 79AD 183
intermediate to those reported for most of the modern populations where similar criteria were
applied to assess the frequency of this anomaly (Table 3).
The frequency of what is considered the normal variants of the non-closure of the posterior
sacral arches in adults from Pompeii was also similar to frequencies reported in the literature.
Sacra with only the fifth arch open and the rest closed were the most common variant, closely
followed by sacra with the fifth and the fourth arches open. In most reports, for various
populations, about one-tenth of the sacra studied had all five arches completely closed (Tables 1
Our results do not suggest any specific or strong factors influencing the frequency of spina
bifida occulta among ancient Pompeian. Post in 1966 compared results of studies on various
populations and concluded that the so-called 'civilised' populations have higher frequencies of
spina bifida occulta than the so-called 'non-civilised' ones. He described 'civilised' populations
as those with a longer recorded history, such as ancient Egyptians. He suggested that
technological advancement resulted in the relaxation of natural selection and hence increased the
amounts of variation. His suggestions of secular trend and its causes. however, are very general
and are still under investigation.
The decrease of more serious neural tube defects (anencephaly and spina bifida cystica)
has been attributed to preventive measures, such as periconceptional vitamin supplementation
(Smithells et a1, 1981), screening programs, and termination of pregnancies with neural tube
defects. At the same time, in the same populations, the increase of minor defects such as spina
bifida occulta among younger adults in comparison with older people is suggested to be an effect
of ageing, where degenerative processes can lead to new bone formation (Boone et al, 1985).
Fluctuations in the prevalence of spina bifida occulta has been found in Jamaica, where
routine pelvic radiographs were examined and analysed in four age groups. The steady
184 Renata Henneberg and Maciej Henneberg
increase in spina bifida occulta was observed between people over 35 years old and those of 24-
34 years and 15-24 years old (both sexes). The oldest group of males (55-64 years) had a higher
prevalence of spina bίfida occulta than people of the two other older age groups. This deviation
from the trend was interpreted as some unspecified environmental factors influencing that
particular male age group (Lawrence, 1977).
Environmental influences are implicated in the decrease of neural tube defects (NTDs)
because the decrease in NTDs is greater in areas where their prevalence was high (Seller, 1987). In
some countries, like the Republic of Ireland, the rapid decrease in neural tube defects occurred
despite a lack of screening programs and no pregnancy termination. It is also argued that overall
better living conditions, better diet and vitamin supplementation in some countries showing
decreased frequencies of neural tube defects are not sufficient environmental factors to explain the
trend and its velocity (Seller, 1987). This dramatic decline in NTDs was also observed in
circumstances where the presence of long term, massive unemployment and a deteriorating social
climate would not suggest improved living conditions, for example in Sheffield (Lorber and Ward,
1985) and Paisley (Shepherd, 1983).
In Sheffield, a drop in NTDs occurred at the same time an increase in other congenital
defects was reported (Lorber and Ward, 1985). On the other hand, an increase in neural tube
defects was found in Jamaica after hurricane Gilbert in 1988, and 'post disaster nutritional scarcity'
was suggested as a factor influencing the trend (Duff et al, 1991).
Interesting changes in the prevalence of NTDs were observed in Hungary, where initially a
decrease was observed, then stabilisation of the trend occurred, followed by a slight increase in
neural tube defects (Czeizel, 1983). In South America, Castilla and Orioli (1985) observed no
changes in the prevalence of neural tube defects over a 12 year period. According to these authors
if a real decrease occurred in the prevalence of NTDs, it was counter-balanced by better recording
systems in hospitals. Most South American countries belong to the group of countries with a low
incidence of neural tube defects.
From the results presented above it is not clear what causes the decline of more serious
neural tube malformations and the increase of minor defects such as spina bifida occulta.
Specific factors, like vitamin supplementation, are the more likely causes of frequency changes, in
contrast to more general factors like improving living conditions or even better quality medical
services. Experimental studies on mice showed that vitamin B6 and vitamin B 12 significantly
reduced valproic acid induced teratogenesis, including a significant 80% reduction in spina bifida
occulta (Elmazar et al, 1992). The higher incidence of neural tube defects, including spina bifida
occulta, and their increase over time in areas with a high fluoride content in drinking water or in
areas with agricultural poisoning (artificial substances) supports the hypothesis of specific
environmental factors influencing changes in the prevalence of NTDs (White et al, 1988; Gupta,
Our results from ancient Pompeii do not suggest that the increased fluoride content in
drinking water in the city triggered the higher frequency of spina bifτda occulta among its
inhabitants. The frequency of this abnormality in Pompeii was similar to, or lower than,-many of the
results from other skeletal series (Tables 3 and 5). It has to be pointed out, however, that in most
skeletal studies factors which could have an influence on the frequency of spina bifida occulta
are unknown. The high frequency of this anomaly found in some archaeological samples is most
commonly interpreted as an indicator of inbreeding and genetic isolation (Ferembach, 1963;
Bennett, 1972; Macchiarelli, 1989).
Studies of consanguinity and the frequency of neural tube defects in living populations
where marriages between relatives are common practice indicate a higher frequency of such
defects compared to populations where marriages between relatives are rare (Kulkarni et al,
The Sacral Canal Closure in Ancient Pompeii, 79AD 185
1989). If consanguinity is low in the population its general effect on the frequency of
neural tube defects will probably be small (Elwood et al, 1992:683-686). There is no
reason to expect high levels of inbreeding in a trading city like Pompeii, and
accordingly, our results from Pompeii do not show any striking difference from past
populations where inbreeding has not been suspected (Table 5).
The most recent findings on living people point towards a rapid secular increase in
spina bifida occulta among Europeans and Israelis during the 20th century. In contrast to
the last few decades of the 20th century, no secular trend in the frequency of spina bifida
occulta has been found between 18th-19th century and modem populations from London
Lack of sufficient data on the modem population of Pompeii restricts us to
comparisons between the results from ancient Pompeii and other modern Italian or
European populations. There are, however, very few published data available to us for
Italian populations which can be used for comparison. Agostini et a1 (1991) published
data for a control group of 264 Italians in which the frequency of spina bifida occulta was
around 25%, in contrast to a group of patients with testicular cancer where the frequency
of this anomaly was 45%. The results for the control group are more than twice that for
the sample from Pompeii (11% including completely open sacral canal) suggesting the
presence of a secular trend among Italians. Unfortunately the control group in Agostiní's
et al (1991) research were patients with radiographs taken mainly for back pain, and in
view of the association of spina bifida occulta with lower back pain (Avrahami, 1994),
this group cannot be used by us as an unbiased representation of the Italian population.
It should be remembered that information on the involvement of soft tissues is
missing from any archaeological skeletal material. Some less severe forms of neural tube
defects in the sacral region may manifest themselves in soft tissues as well as, to a lesser
degree, in bony defects, thus giving incomplete information. On the other hand, the
failure to close the posterior arches of sacral vertebrae is not necessarily associated with
any developmental defects of soft tissues or with causing further health problems
(Elwood et a1, 1992). To answer these more detailed questions regarding the proportion of
various degrees of soft tissue involvement and its relation to neural tube defects, studies
of cadaver collections and living people are needed to supplement the skeletal
The skeletal sample from Pompeii, theoretically, should reflect the demographic
structure of the living population at the time of the volcanic eruption, when people died
indiscriminately in a few days time, generally from suffocation (Henneberg et al, 1996;
186 Renata Henneberg and Maciej Henneberg
Henneberg and Henneberg, n.d.). It is then possible to compare the results from Pompeii with other
living populations, but with caution. In each of their studies Fidas et al (1987) for Edinburgh and
Glasgow, Boone et al (1985) for England, and Avrahami et al (1994) for Israel reported frequencies of
spina bifida occulta among adults at a frequency of at least twice as high as the frequency found in
Pompeii (Table 6). The same authors observed a rapid secular trend in the frequency of spina bifida
occulta within each of the studied populations in the last few decades of the present century. They
found a statistically significant increase of this anomaly among younger adults compared with older
age groups. Compared with these modern populations, the results for Pompeii are lower with regards to
the results for the older groups of 30-70+ years and statistically significantly lower than for the
youngest adult groups (Table 6). The average age of adults who died in Pompeii is lower than the
modern populations (Henneberg and Henneberg, n.d.) and is obviously lower than the 30-70+ years
group. The difference between the results for Pompeii and the modern samples could be even greater if
the possibility of progressive closure of the sacral canal with age and ageing is considered (Boone et
al, 1985; Fidas et al, 1987).
Saluja (1988), in his investigations of the 18th-19th century London skeletal sample from the
crypt of St Bride's Church and the present day sample from London, did not find any secular trend in
the frequency of spina bifida occulta. His results should also be treated with caution, because
archaeological samples from burial places used for many decades or centuries, such as a church
crypt, may not have the same demographic qualities as a cross-section of the living population or a
population from a mass disaster such as Pompeii.
In order to confirm or deny the presence of a secular trend in Italy, or in Pompeii in particular,
ideally, the results for a random sample of adult Pompeians would be needed. although they are
difficult to obtain at the moment. It is known from previous research on neural tube defects,
including spina bifida occulta, that frequencies of such defects differ geographically (Sarin et al,
1981; Castilla and Orioli, 1985; Seller, 1987; Kulkarni et al, 1989; Elwood et al, 1992), thus the
direct comparisons of frequencies between even closely related populations (geographically and
historically) will not be possible.
The Sacral Canal Closure in Ancient Pompeii, 79AD 187
From the existing data, however, it may be suggested that at least in Western Europe there is
a positive secular trend in the frequency of spina bifida occulta, observed especially in the last
century. The subject of secular trends requires further studies on a broader range of populations,
historical as well as living, and if possible on larger and well dated archaeological skeletal samples.
The authors are most grateful to Professor PG Guzzo, the Superintendent of Pompeii, and Dr
Annamaria Ciarallo, the scientific programme co-ordinator for Pompeii, for their permission to study the
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