Transcript Comparative and Functional Anatomy of the Mammalian Lumbar

Comparative and Functional
Anatomy of the Mammalian
Lumbar Spine
Boszcyk, Bronk M., Alexandra A. Boszczyk and
Reinhard Putz. 2001. Comparative and Functional
Anatomy of the Mammalian Lumbar Spine. The
Anatomical Record Part A 264 (2): 157-168.
Mammals Studied:
•Acinonyx jubatus (Cheetah)
•Equus Przewalski
(Przewalski’s Horse)
•Lama vicugna (Vicugna)
•Capra ibex ibex
(Alpine Ibex)
•Tursiops truncatus (Bottlenose
Dolphin)
•Phoca vitulina (Harbour seal)
•Macropus giganteus
(Kangaroo)
•Pongo pygmaeus (Orangutan)
•Pan troglodytes (Chimpanzee)
•Homo sapiens (Human)
Spine:
• Essential organ of both weight bearing
and locomotion. It must maintain
maximal stability while still maintaining
crucial mobility as well as maintaining
the integrity of neural structures.
• Composed of the Cervical, Thoracic,
Lumbar, Sacrum and Coccyx sections
of Vertebrae
Cat Spine
Human Spine
Lumbar Vertebrae and Sacrum:
Objective of the Study:
• To establish a detailed correlation between
the varied morphological features of a diverse
collection of mammalian lumbar vertebrae
and the differing compositions of spinal
loading patterns in locomotion.
• To determine if human low back problems are
because of the imperfect morphological
adaptation of the spine itself or lifestyle and
environmental causes.
Materials:
• Only clearly taxonomised, undamaged
adult mammalian spines without
extensive degenerative changes from a
zoological collection and human spines
from an anatomical collection were
selected.
• All specimens were dried and free of
soft tissue, except for occasionally
preserved spinal ligaments and
intervertebral discs.
• Lumbar vertebrae and the first sacral
vertebra of each species were studied.
Methods:
• The ten mammalian species were chosen
based on their varying types of
locomotion.
• Mathematical averages were determined
for 14 measurements taken on lumbar
vertebrae of the ten species studied.
• For most species four suitable lumbar
spines were studied, however, in certain
rarer species, only a smaller number
could be obtained as was seen in Table 1.
14 Measurements taken:
Results:
• The Vertebral Body Dimensions
• The terrestrial species all display a
progressive sagittal narrowing of the
vertebral bodies towards the sacrum.
• The marine mammals only display a
slight decrease in sagittal diameter.
• The posterior height of the vertebral
bodies lies constantly between 2 and 3
cm for humans and primates but is
generally between 3 and 5 cm for the
rest of the species.
Results:
• Superior Endplate Surface Area
• Largest superior endplate surface area:
human fifth lumbar vertebra at 13 cm2
Results:
• Superior Endplate Angle
• Consistently parallel endplates are
found only in the dolphin.
• A slight anterior wedge shape of the
vertebral bodies was found in all other
species, except the human fifth lumbar.
Results:
• Articular Process Prominance
• The orangutan, chimpanzee, and
kangaroo possess more prominent
superior then inferior articular processes
whereas for the rest of the species the
opposite is true.
Results:
• Transverse Distance Between the
Inferior Articular Processes
• An increase towards the sacrum is
found in the seal, Przewalski’s Horse,
cheetah, ibex, kangaroo and humans.
• Humans possess the largest value at
the fifth lumbar vertebra with 5.1 cm.
Results:
• Pedicle Length
• The pedicles tend to decrease in length
towards the sacrum in all species,
except the kangaroo.
• The kangaroo shows an increase in
pedicle length of the sacrum compared
to the LL vertebra.
Results:
• Zygapophyseal Joint Profile
Results:
• Joint Surface Area
• Humans possess the largest joint
surface area at the lumbosacral junction
with over 2 cm2.
• Przewalski’s Horse has the largest joint
surface area overall.
Discussion:
• The presented study is currently the
most comprehensive regarding the wide
selection of ten mammalian species and
the extent of the morphological criteria
compared in the more than 200 lumbar
vertebrae.
• The mammals were chosen based upon
selecting a collective with highly
divergent strain patterns of the lumbar
spine in locomotion.
Discussion:
• Although the study was quite intensive,
certain limitations applied:
– Relatively low numbers of individuals were
examined from each of the species.
– Results were based solely on the bony
structures on the vertebrae.
– The zygapophyseal joints possess truedimensional surfaces and an in depth
analysis is only possible through 3-D
analysis.
Discussion:
• The Vertebral Bodies
• Marine Mammals:
– The dolphin and the seal both display a balance in sagittal
and lateral flexion during propulsion and both possess
round vertebral endplates. The dolphin furthermore,
possesses parallel endplates throughout.
Seal
Dolphin
Discussion:
• The Vertebral Bodies
• Terrestrial Quadrupedal Mammals:
– A slight anterior wedge shape and a decrease in sagittal
diameter towards the sacrum is recognizable in the
quadruped species, in whom the predominant sagittal
flexion is seen in locomotion.
Przewalkski’s Horse
Lama
Cheetah
Ibex
Discussion:
• The Vertebral Bodies
• Terrestrial Bipedal Mammals and Primates
– The vertebral bodies of humans provide a
structural adaptation to a high degree of axial
loading through a remarkably enlarged cranial
endplate surface area.
– A dorsally-tapering wedge shape is found only in
the human LL vertebra which enhances lordosis.
Discussion:
• The Vertebral Bodies
• Terrestrial Bipedal Mammals and Primates
Human
Chimpanzee
Orangutan
Kangaroo
Discussion:
• The Pedicles
• There is a remarkable similarity of lumbar
pedicle length of approximately 1 cm in all
species regardless of varying body size.
• Only Przewalski’s Horse shows a
comparatively larger pedicle size in the
caudal lumbar vertebrae.
Discussion:
• The Articular Processes and Zygapophyseal
Joints
• Marine Mammals
• Both marine mammals are subjected to a lesser degree of
ventral and dorsal shear than the terrestrial species.
• Dolphin: significant torque only during steering with the
pectoral fins in the area of the thoracic spine, with
resistance provided by the medially-angled zygapophyseal
joints and the wide transverse distance between the
inferior articular processes.
• Seal: higher level of torsion in the lumbar spine finds a
match in the essentially sagittal orientation of the
zygapophyseal joints.
Discussion:
• The Articular Processes and Zygapophyseal Joints
• Marine Mammals
Dolphin
Seal
Discussion:
• The Articular Processes and Zygapophyseal
Joint
• Terrestrial Quadrupedal Mammals
• An increase was seen in the distance between the
inferior articular processes towards the sacrum in
these species which is reflective of an increase in
torsion of this region.
• These species experience dorsal as well as ventral
shear within a motion-segment during locomotion
and may possess encompassing zygapophyseal
joints.
Discussion:
• The Articular Processes and Zygapophyseal
Joint
• Terrestrial Bipedal Mammals and Primates
• Humans and primates possess a comparatively
short total axial span of the articular processes.
• Torsion is similar to the other species in that it
creates a similar widening of the transverse
distance between the inferior articular processes.
• Humans reveal the greatest distance at the
lumbosacral junction.
• Primates contain the maximum values in the upper
lumbar region and tapering towards the sacrum.
Discussion:
• The Articular Processes and Zygapophyseal
Joint
• Terrestrial Bipedal Mammals and Primates
Human
Chimpanzee
Orangutan
Kangaroo
Discussion:
• The Articular Processes and Zygapophyseal
Joint
• Terrestrial Bipedal Mammals and Primates cont’d.
• The chimpanzee posses the greatest distance in all
vertebrae except the last lumbar.
• Humans possess the greatest distance in the last
lumbar vertebra.
• Rotation of the lumbar spine is particularly apparent
in the humans.
• The kangaroo lumbar joints limit rotation however
the first tail vertebra reveals pronounced rotation.
Conclusion:
• With respect to the spine, two principles of evolution
appear to compete:
– Increasing structural support
– Maintaining segmental mobility
• All mammals studied suggest an exact
accommodation of the lumbar spine to the specific
biomechanical demands sustained during the
course of evolution.
Conclusion:
• The functional individuality of mammalian species
should be appreciated when considering nonhuman
spines as biomechanical models for humans.
• Humans reveal a highly advanced level of
differentiation in lumbar spinal morphology.
– Based on the differentiation observed, it may be
more reasonable to attribute the high incidence
of low back problems to our evolving modern
lifestyle rather than to imperfect morphological
adaptation.