Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 12 potx

Corpectomy fusion technique. Spinal instability
after corpectomy or after vertebrectomy in the
lumbar spine often requires complex reconstruc-
tive procedures. The type and degree of instrumen-
tation depend strongly on the number of involved
levels and the retained functioning stabilizing
structures. Generally, after corpectomy anterior
support is mandatory and long-term stability can-
not be achieved with rod/pedicle screw instrumen-
tation alone. Furthermore, the combination with an
anterior tension band device still exhibits a certain
instability in extension and rotation. Therefore, from
the biomechanical perspective, substantial anterior
instability requires “front and back” instrumenta-
tion. In the cervical spine, however, single-level cage
stabilization is sufficiently supported by an anterior
tension band device. Multiple-level cervical corpec-
tomies are particularly unstable and anterior plating
may be insufficient; consequently additional pedi-
cle/lateral mass screw devices must be considered.
Anterior tension band technique. Anterior rods/
plates act as tension bands in extension and func-
tion as buttress plates in flexion. For the cervical
spine, the latest generation of “semi-constrained/
dynamic” plates allow locked angle-stable mono-
cortical screw fixation while axial compression of
the graft is permitted. This offers increased stability
combined with a minimized risk of stress-shielding.
In the lumbar spine, anterior rod/double-rod
instrumentation increases anterior stability after
cage or graft implantation especially in extension.

In flexion and lateral bending they are still inferior
to pedicle screw devices.
Biomechanics of the “adjacent segment”. Unphysi-
ologically long and stiff spinal segments increase
motion and intradiscal pressure in the adjacent
segments. However, it is still unclear if adjacent seg-
ment degeneration after spinal fusion is resulting
from the changed biomechanics or exhibits simply
the progression of the natural history.
Disc arthroplasty. Disc arthroplasty offers several
advantages such as preservation of segmental
motion, potential absence of adjacent segment
degeneration and no need for harvesting autolo-
gous bone graft. Current prostheses differ in bear-
ing materials (metal or polyethylene) and kinemat-
ics principles. Constrained prostheses have a fixed
center of rotation whereas unconstrained devices
allow translational movement and thus respect the
physiological helical axis of motion. Kinematics
studies have shown that both types successfully re-
establish almost the physiological range of motion.
Only a few data exist so far on the long-term radio-
logical and clinical outcome.
Posterior dynamic stabilization technique. Improv-
ing primary or iatrogenic spinal instability while
“unloading/protecting” certain spine elements
without performing a spinal fusion are the objec-
tives of posterior dynamic implants. All systems
successfully reduce segmental motion. However,
rotation is poorly controlled while the posterior

devices are particularly stiff in flexion. As it is
unknown how much stability is needed in which
particular entity of spine pathology combined with
the partially undefined clinical indications, an
assessment of this technique is currently impossi-
ble. Finally, only long-term prospective clinical trials
will give the necessary evidence for the efficacy of
this particular treatment method.
Key Articles
Cripton PA, Jain GM, Wittenberg RH, Nol te LP (2000) Load-sharing characteristics of
stabilized lumbar spine segments. Spine 25:170 – 179
Biomechanical cadaver study using pressure sensors, strain gauges and an optoelectronic
tracking system. Load-sharing between an internal fixator and anatomical structures was
assessed in asequential injury scenario. Applied loads were mostly supported by equal and
opposite forces between disc and fixator. Based on the results, the paper highlights the fact
that an anterior column insufficiency may lead to fixator overloads and implant failure.
Laxer E (1994) A further development in spinal instrumentation. Technical Commission
for Spinal Surgery of the ASIF. Eur Spine J 3:347 – 352
Introduction of the Universal Spine System with a single set of implants and instruments
for various spinal disorders and surgical approaches.
Spinal Instrumentation Chapter 3 85
Magerl FP (1984) Stabilization of the lower thoracic and lumbar spine with external
skeletal fixation. Clin Orthop Relat Res 125–141
Classic article introducing the concept of a new angle-stable transpedicular fixation
device which formed the basis for the development of second generation internal spinal
fixation devices.
Panjabi MM (1988) Biomechanical evaluation of spinal fixation devices: I. A conceptual
framework. Spine 13:1129 – 1134
Panjabi M, Abumi K, Duranceau J, Crisco J (1988) Biomechanical evaluation of spinal
fixation devices: II. Stability provided by eight internal fixation devices. Spine

13:1135 – 1140
Abumi K, Panjabi MM, Duranceau J (1989) Biomechanical evaluation of spinal fixation
devices. Part III. Stability provided by six spinal fixation devices and interbody bone
graft. Spine 14:1249 – 1255
These three publications are milestone papers as they introduced the basic concepts for
testing and evaluation of spinal implants. Guidelines for three categorical biomechanical
tests are stated: assessment of strength, fatigue and stability.
TsantrizosA,AndreouA,AebiM,SteffenT(2000) Biomechanical stability of five stand-
alone anterior lumbar interbody fusion constructs. Eur Spine J 9:14 – 22
The authors compared five different stand-alone cages with respect to stabilizing proper-
ties (kinematics) and pull-out strength using human specimens. The results demon-
strated a general stabilizing effect of all implants but load/displacement curves also sug-
gested micro-instability. Influencing factors of the cage design concerning dimensions,
height and wedge angle were pointed out.
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90 Section Basic Science
4
Age-Related Changes of the Spine
Atul Sukthankar, Andreas G. Nerlich, Günther Paesold
Core Messages
✔
The spinal column degenerates far earlier than
other musculoskeletal tissues
✔
Age-related changes of the spine are not syn-
onymous with painful alterations
✔
Time course and probability of early disc
degeneration are largely determined by
genetic disposition
✔
Theintervertebraldiscisthelargestavascular
structure of the human body resulting in large
diffusion distances to allow for disc nutrition
✔
Compromised disc nutrition is a key factor for

disc degeneration
✔
Changes in the matrix components of the inter-
vertebral disc, especially the proteoglycans,
determine age-related changes of the disc
✔
Orientation and misalignment of the facet
joints correlate with development of early
osteoarthritis of the joint
✔
Changes in bone architecture of the vertebral
bodies and formation of osteophytes alter
mechanical properties of the spinal column
✔
Changes in matrix molecules and fiber orienta-
tion in ligaments alter behavior of the liga-
ments
✔
Age-related changes of the three joint complex
lead to disc herniation, osseous and ligamen-
tous stenosis
Epidemiology
Musculoskeletal impair-
ments are a predominant
health problem in the aging
population
Musculoskeletal impairments are prevalent and symptomatic health problems in
individuals of middle and old age. Naturally, aging of an individual is accompa-
nied by decreasing strength, pain and restricted movement. As a consequence,
increasing age is concomitant with limited abilities for work and leisure activi-

ties. Regular physical activities are important to maintain optimal mobility and
general health. Age-related changes in the musculoskeletal system occur due to
alteration in a multitude of tissues, such as bone and soft tissue including mus-
cles, articular cartilage, intervertebral discs, tendons, ligaments and joint cap-
sules [40]. In addition, a decrease in musculoskeletal function increases proba-
bility and severity of soft tissue and skeletal damage due to trauma and also
enhances the likelihood of complications during surgery.
The number of people over
65 years will double within
25 years
Considering estimations that predict a doubling of the number of people over
65 years of age during the next 25 years, patients suffering from musculoskeletal
impairments will increase significantly [79]. In the USA, musculoskeletal and
associated conditions in the elderly caused direct costs of US $51 billion in 1992
[158]. These facts impressively underline the impact on healthcare systems that
age-related alterations of the musculoskeletal system will have in the future.
Basic Science Section 91
ab
Case Introduction
This spinal specimen shows the extreme course of the result of aging on the lumbar spine. A sagittal section through the
lumbar spine (L3–S1) of an 8-year-old individual (
a) demonstrates that the nucleus pulposus can be clearly distinguished
from the anulus fibrosus. The cartilage endplates are composed of a thick layer of hyaline cartilage. The disc height is
somewhat less than the vertebral body height. The vertebral bodies demonstrate rounded edges. On the contrary, the
parasagittal section (
b) of a 77-year-old individual demonstrates that the disc space has completely collapsed. Anterior
or posterior displacement of the vertebral bodies is visible at all levels. The cartilaginous endplates are partially resorbed
and exhibit severe sclerotic alterations. The vertebral bodies exhibit severe bridging osteophyte formation. Despite
these dramatic changes there is no close link between these alterations and pain.
General Age-Related Changes

Various mechanisms on a cellular and systemic level have been identified to con-
tribute to age-related changes in the musculoskeletal system [45].
At the cellular level:
cellular senescence, leading to a decreasing ability of somatic cells to repli-
cate, repair, and maintain tissue
apoptosis (programmed cell death), leading to decreased cell numbers in
the affected tissue
accumulation of post-translational modifications of matrix proteins, lead-
ing to altered properties of the extracellular matrix
increasing generation of oxidative stress due to generation of reactive oxy-
gen species (ROS), leading to cell damage
genetic predisposition, leading to premature aging or phenotypic changes
in the musculoskeletal system
At the systemic level:
Systemic and cellular factors
contribute to musculo-
skeletal age-related changes
declining levels of trophic hormones, leading to altered tissue environment
and response of tissue to use and injury
general age-related changes,suchasadecreaseinreactiontime,proprio-
ception, vision, hearing, pulmonary and cardiovascular function, leading to
decreased mobility and therefore affecting the musculoskeletal system
socioeconomic and psychosocial factors alsocontribute,mainlybyinflu-
encing the individual variation regarding the age-related impairment of
mobility
The diversity of contributing factors on cellular and systemic levels underlines
the multifactorial nature of age-related changes that will finally lead to alter-
92 Section Basic Science
ations of the local environment within the affected tissue. These local alterations
can then directly affect the function of the respective tissue. Although the result,

i.e. altered tissue function, can be observed and analyzed, the exact relationships
and interactions between cellular and systemic changes are not yet clear.
The spine is most frequently
affected by
age-related alterations
Although any part of the musculoskeletal system can be affected by age-
related alterations, lower extremities and especially the lumbar spine are the
most frequently reported locations of musculoskeletal impairment (
Case Intro-
duction
). Between 70% and 85% of the population in Western industrialized
countries will experience back pain at least once during their lives, underlining
the impact of age-related alterations to the spine [33, 35, 86, 151, 152]. These epi-
sodes of back pain often lead to sickness leave and sometimes to chronic disabili-
ties (approx. 10%) causing an enormous socioeconomic burden on society [80].
In this context, it is important to notice that normal age-related degenerative
changes and pathological degeneration leading to back pain have to be distin-
guished. Several studies have shown that between 7% and 72% of individuals
that exhibit signs of disc degeneration never experienced relevant low back pain
[15, 115, 155].
Among age-related alterations of the spine, the so-called “degenerating spon-
dylosis” or spinal osteoarthritis is the most common and is probably inevitable
Degenerative spondylosis
is inevitable with aging
with increasing age. This alteration is radiologically characterized by osteophy-
tes (bone spurs) arising from the margin of the vertebral body and is usually
accompanied by disc space narrowing. The term “spondylosis” was historically
an effort to distinguish between degenerative changes in the spine and those in
synovial joints (osteoarthritis) such as facet joints [145]. However, it has been
shown that pathological changes in the spine and osteoarthritis of the synovial

joints coexist and in most cases are interrelated [145]. Autopsy studies by
Schmorl and Junghanns [64] reported evidence of spondylosis in 60% of women
and 80% of men by the age of 49 years, and in 95% of both sexes by the age of
70 years.
Functional Spine Unit
The motion segment is the
functional unit of the spine
The spine is a multi-segmented column, which provides stability and mobility to
the body at each segmental level and gives protection to the nerve roots and the
spinal cord. The smallest anatomical unit of the spine which exhibits the basic
functional characteristics of the entire spine is called the “motion segment”or
“functional spine unit”(
Fig. 1). It was first described by Schmorl and Junghanns
[64]. Each motion segment consists of two adjacent vertebrae, separated dorsally
by the zygapophyseal joints or facet joints and anteriorly by the interposed inter-
vertebral disc. The vertebrae are further connected by spinal ligaments, joint
capsules and segmental muscles. The spinal ligament complex consists of the
interspinous, supraspinous intertransverse, yellow, anterior and posterior longi-
tudinal ligaments. In contrast to the extrinsic muscles, the intrinsic muscles span
over two vertebrae and consist of splenius, erector spinae, transversospinal and
segmental muscles. Spine motion, stability and equilibrium are achieved by the
antagonist action of the powerful flexor and extensor muscle groups.
The motion segment
is a three joint complex
The normal spinal function largely depends on the integrity of these compo-
nents and their coordinated interplay. Kirkaldy-Willis [71] introduced the term
“the three joint complex” to highlight the importance of a normal interaction of
the three joints in a segment, i.e. the intervertebral disc and the two facet joints.
Any alterations in one of these components will result in a disturbance of their
interplay with subsequent dysfunction, finally leading to back pain, deformity

and neurological compromise.
Age-Related Changes of the Spine Chapter 4 93
a
b
Figure 1. Functional spinal unit
Schematic representation of a functional spinal unit (motion segment) in a the cervical and b lumbar spine.
94 Section Basic Science