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C H A P T E R 7 e Psychology of the Aging Spine, Treatment Options, and Ayurveda as a Novel Approach
35
3. Prasara or preclinical Stage 3 in which the abnormal doshas are dislodged
from their normal resting sites and begin spreading abnormally throughout the body;
4. Stana-Samshraya or clinical Stage 4 in which the abnormal doshas local-
ize in an already defective tissue or organ; an aura of symptoms now
becomes perceptible;
5. Vyakti or clinical Stage 5 during which the consolidated disease mani-
fests in clear-cut signs and symptoms, and
6. Bheda or clinical Stage 6 in which the consolidated disease differentiates
in specific ways along the lines of one’s dosha quotient (prakruti) coupled
with pathological tissue involvement. At this stage, complications arise.
Diagnostic methods in Ayurveda are essentially clinical. Diagnostic eval-
uation of the patient follows a tenfold process originally outlined by Charaka. Some of its features include assessing prakruti, vikruti with its pain and
signs and symptoms of illness, tissue quality by inspection of morphology
and functional status, body proportions, mental and emotional characteristics, digestive strength, energy level and stamina, and age-related abilities
and limitations. An additional eightfold examination formulated in the
1500s also includes Ayurvedic pulse diagnosis.
Ayurveda has developed systems of nutrition as dietetics and specific
food intake (ahara) over the course of thousands of years. It is a unique
system incorporating the aforementioned theoretical elements and matching their analyses to recommendations for food options. An individual’s
prakruti and vikruti in the context of prevailing seasonal influences are
taken into account. Foods function to maintain and enhance health, and, at
specific times, act therapeutically. Ayurvedic therapy aims at balancing the
doshas and restoring their optimal proportions for each dosha’s single and
coordinated efficiency. When doshas are properly aligned, Agni’s operation
optimizes and reinforces dosha stabilization.
Lifestyle and behavioral practices (vihara) are crucial features of Ayurve-
da’s pursuit of wellness. Based on constitutional predispositions, strengths,
weaknesses, and current needs at a specific age and in a specific season,
recommendations for daily hygiene, exercise, development of mental faculties (for example, study, yoga postures, breath expansions/pranayama, and
meditation), and suitable recreational activities are suggested. Guidelines for
highly ethical standards (sadvritta) closely related to classical Western values
and behaviors considered righteous and reasonable are included. Without
requiring the ritualized constraints of a religion, Ayurveda incorporates the
Hindu and Buddhist doctrine of karma, which ethically denotes accountability and taking personal responsibility for thoughts and actions. A proactive life by choice and adherence to medical guidelines includes a specific diet
to maintain constitutional balance, appropriate responsiveness to the effects
of time (for example, chronological age, diurnal variations, and seasons),
and a suitable lifestyle. Besides the absence of disease and disability, wellness promotes functional integrity, strength, endurance, flexibility, and balance. Changes promoting wellness also presume newly-gained insights into
motivations, attitudes, emotional dispositions, and behaviors. Moreover, a
realization of belonging to the shared community of the one human family
and the ultimate unity of all nature counters unrealistic feelings of isolation
or narcissistically-based specialness.
Dravyaguna Shastra is Ayurveda’s age-old science of medicine, a herbo-
mineral pharmacopoeia. Herbal supplementation (aushadha) is used both
prophylactically and as active treatment for disorders. About 700 herbs are
recognized and used, although there are thousands more being employed in
less standardized ways.
Modern research in the therapeutic effectiveness of Ayurvedic herbs has
laid particular emphasis on the role of phytochemicals and natural antioxidants contained in these traditional herbal and spice substances. Phytochemicals are nonessential nutrients. The function of these micronutrients
is protection against tissue damage and for disease prevention. Some of the
proposed mechanisms for these effects include antioxidant activity, antiinflammatory action, glutathione synthesis, effects on biotransformation
enzymes involved in carcinogen metabolism, induction of cell cycle arrest
and apoptosis, and inhibition of tumor invasion and angiogenesis.
Specific fractions of edible substances contain phytochemicals. These are
flavonoids, isoflavones, allyl sulfides, catechins, anthocyanins, polyphenols,
carotenoids, terpenes, and plant sterols. All phytonutrients are of plant
origin – fruits, vegetables, herbs, and spices. They target unstable free
radicals, known as reactive oxygen species (atoms, ions, or molecules with
one or more unpaired electrons that bind to and destroy cellular components) both in general and specific ways to scavenge them and prevent
pathogenic membrane disruption. This beneficial action is accomplished
by neutralizing damaging ions and thereby reducing the oxidative stress
that impairs endothelial cell integrity throughout the entire circulatory
system. For example, phytonutrients make low density lipoproteins (LDL
cholesterol) less likely to be oxidized by free radicals, become trapped in
the intravascular lumen, attract calcium, and form plaques that narrow
arterial patency and encourage blood clot formation. Additionally, antioxidant activity reduces excessive crosslinking of collagen molecules, thus
strengthening connective tissue throughout the body and benefiting bone,
ligaments, and joints. Another important mechanism of herbal treatments
is the role of nitric oxide production by the endothelium to enhance vasodilation and arterial perfusion.
Lastly, Ayurveda’s preeminent radical detoxification program – Pancha-
karma – is a five-step process that occurs over a period of several weeks and
which must be closely supervised by a qualified practitioner. A few typicallyused substances and modified treatment protocols will be discussed later in
a consideration of orthopedic problems.
AYURVEDIC PERSPECTIVES ON AGING
Normative fluctuations of doshas and specific dosha dominance are metrics used to denote epochs in the lifecycle. Older age becomes progressively
noticeable in the later 50s and increasingly thereafter. This correlates with
a predominance of Vata dosha. All of Vata’s key qualities begin to affect the
entire person: dryness, coldness, stiffness, rigidity, hardness, roughness, constriction/spasm versus looseness/hypermobility cycles, reduced tissue mass,
and increased frailty. The body’s harmonious symmetry and its proportions
diminish. For example, intervertebral disks tend to become dehydrated and
exert pressure on adjacent nerve roots. Stature and posture change. The
aberrant flow of Vata in vitiated tissues and channels of circulation signals
pain. This influences an individual’s Biopsychospiritual makeup, and a general trend toward ungroundedness (unsteady gait, loss of confidence, and
anxiety) becomes apparent. Cognition, although wiser from years of adaptive experience, may lack the swiftness, alacrity, and recall once present.
The appearance of aging is observed in face, body posture, and attitude.
Older persons may look tired, downtrodden, burdened, dry, even sullen and
angry. Much of this results from pain and the increasing constraints on previously enjoyed levels of functioning.
It is fair to add that an individual’s past history of learning, achievements,
and successes on material, emotional, and spiritual levels also has etched
multiple contours of self-confidence and pragmatic memory. These inner
resources along with social ties counter isolation and loneliness. They add to
the satisfaction a favorable quality of life has engendered as aging proceeds.
AYURVEDIC PERSPECTIVES ON MANAGING THE AGING PROCESS WITH RESPECT TO BONE
A comprehensive discussion of optimal age-management strategies and
therapies unique to Ayurveda is beyond the scope of this chapter. Ayurvedic
interventions always involve a multitiered approach that aims to modulate
the deterioration associated with aging by enhancing the competence of
repair mechanisms. A strong emphasis on Vata modulation and normal-
ization through diet, seasonal, and lifestyle recommendations is the basis
of all treatments. Included are specific prescriptions for physical exercise
(vyayama), oil massage, gentle yoga stretches for musculoskeletal flexibility,
and herbal adjuncts. The entire field of Rasayanas or rejuvenation medicine affords an untapped treasure trove awaiting examination by Western
research. Because Ayurveda is profoundly holistic, all the aforementioned
are components of an intense, one-to-one therapeutic relationship with a
practitioner who acts as physician, coach, and, at times, psychotherapist.
In this way, anxiety, fear, and depression, at times the deepest unconscious
sources of pain and suffering, are addressed and managed.
Bone (asthi) is considered one of the seven major tissues composing the
material substance of the physical body (sharira). Bone, its membranous
coverings (purishadhara kala), articular joints (sandhi), cartilage (tarunashti),
and channels of circulation (asthivaha srotas) are major components of the
36
P A R T I Introduction to the Aging Spine
skeletal system. It is primarily derived from three of the Five Great Gross
Elements or principles of organization of matter: Earth and Water (Kapha
dimension) and Air (Vata dimension). The Sanskrit term asthi means to
stand and endure. A major function of bone is support (dharana); bone also
acts to protect vital organs and contributes to the shape and form of the
body. Vagbhata (c. AD 700) asserts that bone tissue nourishes nerve and
marrow tissue (majja dhatu) in critical ways. In terms of doshas, the sub-
stance of bone is essentially of Kapha origin. Two subspecies of Kapha are
dominant: Avalambaka Kapha, centered in the thorax and vertebral column,
and Shleshaka Kapha, situated in joint fluids and apposing structures such
as disks and articular surfaces.
Bone, moreover, is one of the body’s largest containers of Vata dosha,
particularly Vyana Vata (pulsatile, rhythmic expansion and contraction) and
Apana Vata (downward, eliminative action). Periosteal coverings are considered the membranes (purishadhara kala) containing and contributing to the
nourishment of bone.
The principal repository of Vata in the entire body resides in the large
intestine or colon. The colon’s own membranes share a functional tie and
the same name with all osseous membranes. This important correlation
links the health and pathology of the colon with the health and pathology
of the skeletal system. Its implications for treatment are profound. Western
science regards the colon as having several important functions including
resorption of water, electrolytes, and minerals back into the body, further
digestion of various kinds of sugars and fiber, production of vitamins, especially vitamin K (needed for blood clotting and bone nutrition), and storage
of indigestible foodstuff as stool for eventual elimination. Ayurvedic theory
asserts that Prana Vata carries Prana, the primary life force. The Indian
concept of Prana is equivalent to the Chinese concept of Qi/Chi. Prana
Vata and minerals in foods and herbs rich in Prana are absorbed through
the purishadhara kala membrane of the colon to directly supply bone tissue
all over the body. In addition, Ayurveda regards the marrow internal to bone
to be closely associated with nervous system functioning. This connection
underscores the experience of pain associated with dysfunctions of bone
and bone marrow.
Ayurveda’s three foundational texts, Charaka Samhita, Sushruta Sam-
hita, and Asthanga Sangraha of Vagbhata describe pain syndromes related
to bone. In addition, a later work, Madhava Nidana (c. AD 650–950)
introduced the conceptualization of amavata. This toxic Vata condition has
much in common with rheumatoid arthritis, and is marked by inflammation
and edema.
The etiological field that sets the stage for the development of bone
pathology and pain has general and specific triggers. Included are dietary
practices that lead to impaired Agni and weakened digestive processes (for
example, cold foods, and heavy foods, such as meat and cheeses, in excess),
and Vata aggravating diets (for example, cold, dry foods, lack of sufficient
oil in diet, excess of raw vegetables, use of traditionally incompatible food
combinations: milk and fish, milk and fruit, milk and meat, milk and foods
having sour tastes). Such disease-provoking dietary practices engender the
metabolic toxin called Ama, which not only obstructs the proper flow of
the doshas but also the distribution and assimilation of nutrients. Ama correlates with excess free radical production and inflammation, especially at
the endothelial cell level.
Vata-aggravating lifestyle (for example, excess travel and physical activity, and excessive preoccupation with electronic media), microbial causes
(krimi), trauma, genetic predisposition (sahaja hetu), and older age add to
Vata vitiation and progression of disease. Improper breathing may limit
the body’s adequate intake and absorption not only of oxygen but also of
Prana in the lungs and the colon, both subsequently affecting bone. Proper
oxygenation is a typical benefit of Ayurvedically-prescribed deep breathing
practices. This contributes to natural infection control. Although Vata is
the principal dosha associated with bone pathology, Pitta may also become
involved and manifest as inflammation; when Kapha becomes involved,
edema, osteophytes, and tumors emerge.
The specific form taken by bone pathology is the result of genetic, constitutional, and lifestyle factors, as well as acquired pathology. After careful
assessment of the aforementioned factors and delineation of the course of
pathogenesis, a specific treatment plan is constructed. To give a general idea
of treatment guidelines, the following protocol is outlined. It may not be
universally applicable since each patient and each disease process presents
with unique features. Specific decompensations dictate the specifics of an
individualized treatment regimen. Lower back pain with radiation to the leg
(gridhrasi), for example, is well known in Ayurveda and its treatment follows protocols established thousands of years ago. A qualified practitioner,
not self-help guidebooks, is needed to formulate diagnosis and treatment
recommendations. Treatments may take place in a clinic and through outpatient recommendations for dietary protocols, herbo-mineral prescriptions,
and other adjunctive techniques.
Ayurvedic treatments typically begin with procedures that target Ama
detoxification and optimize the digestive process. In the context of a Vata-
pacifying diet, various detoxifying herbs are used. These may include
triphala (Emblica officinalis, Terminalia chebula, and Terminalia belerica),
turmeric (Curcuma longa), guduchi (Tinea cordifolia),
9
castor oil (Ricinus
communis), and ginger (Zingiber officinale). Substances that reduce inflammation include Boswellia (Boswellia serrata) and guggul (Commiphora
mukul). In osteoarthritis (Sandhigatavata) where degeneration is prominent, ashwaganda (Withania somnifera) and other highly tonic/nutritive herbs are given after a period of stabilization to promote healing and
rebuild tissue. Turmeric (haridra in Sanskrit; jiang huang in Chinese)
is used in Ayurveda and Chinese medicine to stimulate blood flow and
reduce inflammation. Single herbs and compounds with several herbs are
typically given.
Ayurvedic physicians recommend ghee, very modest amounts of highlyclarified butter, to facilitate the assimilation and efficacy of herbs. Ghee
or butter oil is regarded as a medicine, not similar to ordinary butter with
its possible deleterious effects on lipid profiles and cardiovascular system.
Ghee has specific therapeutically targeted effects and is an adjuvant and
potentiator of other medicinal substances. Ghee contains up to 27% monounsaturated and about 66% short-chain fatty acids along with about 3 %
conjugated linoleic acid (CLA). This composition is a beneficial profile.
Taken in moderation, ghee demonstrates antioxidant, antimicrobial, anticarcinogenic, and lipid nondysregulation properties.
10
Ghee contains a fatsoluble fraction of vitamin K, K-2, or meanquinone-7 or menaquinone-7
(MK-7). K-2 produces gamma-carboxylated osteocalcin and facilitates the
incorporation of calcium into bone matrix. InJapan, MK-7 is highly concentrated in a soybean food, “natto,” fermented by Bacillus subtilis. People
8
with osteoporosis and those who might benefit from natto’s significant
blood-thinning properties eat this food.
Ayurvedic treatment includes dietary recommendations that follow
classically-established Vata-pacifying guidelines. These consist of regu-
lar, moderately-sized meals; food choices that include warm, moist foods
emphasizing sweet, salty, and sour tastes in moderation; sweet fruits; most
cooked vegetables excluding mushrooms and excess legumes (beans, peas,
and lentils); rice; all nuts and seeds; dairy products in moderation; and
mild spices such as cinnamon (Cinnamomum zeylanicum), basil (Ocinum
spp.), cardamom (Eletarria cardamomum) and fennel (Foeniculum vulgare).
These dietary guidelines are not mere culinary suggestions. They come
from Ayurveda’s detailed and exacting analysis of the complex actions and
therapeutic properties of food, herbal, and spice substances. Calcium-rich
foods, a normal part of the Ayurvedic diet, include chickpeas, okra, almonds,
sesame seeds, and milk drinks. Traditional cooking techniques for grains
and legumes include presoaking and adequate cooking time to reduce excess
phytic acid (inositol hexakisphosphate, IP6) that tends to chelate calcium
and inactivate niacin. Although not a standard food in traditional Ayurveda,
American practitioners recommend many marine macroalgae or seaweeds
as dietary additions. For example, wakame (Undaria pinnatifida) frequently
used in Japan (ito-wakame), China (qundaicai), and Korea (miyeok) as food
and medicine contains about 980 to 1,300 mg assimilable calcium per 100
grams. Besides calcium, sea vegetables contain generous amounts of potassium, sodium, and magnesium; hence, judicious use of high-quality, guaranteed pure seaweed may be beneficial in patients whose sodium intake is
not restricted.
In addition to diet and herbs, oils specially prepared for therapeutic massage (abhyanga) coupled with topical moist heat fomentation (swedhana) are
a regular part of treatment protocols. Such intermittent mild temperature
elevations aid in infection control. Commonly used therapeutic massage
oils include sesame, castor, and a special compound called Mahanarayan.
Efficacy lies in the mobilization of contracted tissues, alleviating pain, and
reducing swelling and induration. Oil massage is a highly regarded treatment
C H A P T E R 7 e Psychology of the Aging Spine, Treatment Options, and Ayurveda as a Novel Approach
37
intervention, and one that patients perceive as helpful and valuable. InIndia,
specially prepared herbalized oil enemas (basti) are also a regular part of
specialized anti-Vata treatments.
CONCLUSION
The psychology of aging is an important consideration in understanding the
needs of the rapidly emerging generation of older citizens in society. Physical
illnesses, particularly orthopedic problems, cause distortions in body image,
and diminish self-esteem. Limitations in functioning and pain force patients
to become less productive personally, socially, and occupationally. Recent
scientific advances in Western medicine provide many rational choices for
remediation and repair. Eastern medical traditions, such as Ayurveda with
its favorable record of accomplishment, have emerged as complementary
adjuncts. Although currently unexplored by modern scientific methods,
they offer relief and restoration of functioning. For these reasons, the complete physician, not to mention his or her patients, can benefit from a familiarity with newly emerging medical systems and their applications. Agreater
yield of sustained positive outcomes resulting in mental and physical wellness may be attainable.
References
1. F.J. Ninivaggi, Malingering, in: B.J. Sadock, V.A. Sadock (Eds.), Kaplan & Sadock’s comprehensive textbook of psychiatry, ed 9, Lippincott Williams and Wilkins, Baltimore, 2010.
2. J.J. Clayton, Nutraceuticals in the management of osteoarthritis, Orthopedics 30 (8) (2007)
624–629.
3. D. Khanna, G. Sethi, K.S. Ahn, M.K. Pandey, A.B. Kunnumakkara, B. Sung, A. Aggarwal,
B.B. Aggarawal, Natural products as a gold mine for arthritis treatment, Curr Opin Pharmacol 7 (3) (2007) 344–351.
4. F.J. Ninivaggi, Ayurveda: a comprehensive guide to traditional Indian medicine for the west,
Praeger, Westport, Conn, 2008.
5. A.C. Kaviratna, Charaka Samhita, 4 vols, Girish Chandra Chakravarti Deva Press, Calcutta,
1902–1925.
6. J. Trikamji, N. R am, Sushruta Samhita of Sushruta, Chaukhambha Orientalia, Varanasi,
India, 1980.
7. K.R.S. Murthy, translator:Ashtanga Samgraha of Vagbhata, Chaukhambha Orientalia,
Varanasi, India, 2005.
8. K.R.S. Murthy, translator: Madhava Nidanam, Chaukhamba Orientalia, Varanasi, India,
1987.
9. T.S. Panchabhai, U.P. Kulkarmi, N.N. Rege, Validation of therapeutic claims of Tinospora
cordifolia: a review, Phytother Res 22 (4) (2008) 425–441.
10. H. Sharma, Butter oil (ghee) – myths and facts, Ind J Clin Pract 1 (2) (1990) 31–32.
Biomechanics of the Senescent Spine
Boyle C. Cheng
8
k e y p o i n t s
Not all patients diagnosed with osteoporosis by current bone mineral density
levels will experience vertebral fracture, nor will patients above the osteopenic
level necessarily be free of fracture.
e use of bone mineral density as an indicator for outcome success related
to instrumented procedures is inconsistent, particularly in predicting complex
failure loads.
Additional parameters, including Modic changes, are important in the
identification of additional vertebral fracture risk factors for patients.
INTRODUCTION
The microstructural effects of aging on the spine may have dramatic consequences on both the individual vertebrae and the vertebra as a constituent
within an osteoligamentous structure, that is, a functional spinal unit (FSU).
Additionally, the cervical, thoracic, and lumbar regions of the spinal column
may be adversely affected by the deleterious effects of senescence. The consequences may cover a spectrum of physical quality-of-life factors ranging from
the relatively benign to those that dramatically alter the health of a patient.
When clinicians are faced with deteriorating conditions severe enough to
warrant surgical intervention, additional considerations must be made for
the properties of senescent spines. Therefore, the biomechanical capabilities
of the spine should be examined with careful consideration for age along with
this caveat: biomechanical changes do not necessarily become symptomatic.
Biomechanical measurements can be affected by numerous indicators,
and it is important to distinguish which are related to global measures, for
example, body mass index, and which may be relevant specifically to the
local spinal elements, e.g., friability of a vertebral body. Two distinct but
related indicators should be evaluated with spinal pathologies: the advancement of age and degenerative changes resulting in anatomical transmutation
that potentially leads to abnormal loading of the spine. Anatomical changes
may be attributed to the primary degenerative conditions associated with
age. Miller et al reported an approximate 10% occurrence of severely degenerated intervertebral discs in 50-year-old males, with an increase to 60%
in 70-year-olds.1 The degenerative conditions result in several anatomical
changes and, of particular importance to an aging population, is the potential for constriction of the spinal canal diameter. The cause of the constriction may be from a single specific etiology or from a combination of factors,
including spinal canal stenosis, disc herniation, osteophyte growth into the
canal, hypertrophy of the ligamentum flavum, and calcification of the posterior longitudinal ligament and the ligamentum flavum.
A combination of interrelated mechanobiological conditions and associated kinematic response of the spine due to degenerative diseases is also known
to occur with age. Changes in proteoglycan concentration within the intervertebral disc along with matrix disorganization result in a cascade of events over
time that affect the anatomical structures within an FSU. The range of motion
(RoM) and the ability to absorb and transmit load in the spine are biomechanical capabilities that may be compromised by microstructural changes within
the anterior and posterior columns. Under the worst conditions, the degenerative pathology within a FSU results in a significantly different kinematic
response to physiologic motion, and abnormal loading may occur.
AGING AND DEGENERATIVE CHANGES ON THE EFFECTS OF BIOMECHANICAL RANGE OF MOTION
The relationship be tween age, degeneration, and RoM has been studied
both in human cadaveric FSU testing and in clinical studies. The instability
of the lumbar spine was proposed by Kirkaldy-Willis and Farfan to be categorized into three diskrete stages of degenerative change. In order of progression, the clinical assessment of the lumbar spine categorized pathologic
changes as temporary dysfunction, the unstable phase, and finally, stabiliza-
2
tion.
Well-defined, controlled, biomechanical testing and clinical studies
involving well-documented patient profiles have tested various aspects of
this initial hypothesis on spinal instability.
Traditional methods of comparing the effects of age, degeneration, or
subsequent treatments have been subjected to biomechanical characterization through the flexibility test method. The methodology of flexibility
testing has been well described in the literature, originating with Panjabi’s
early description of load input utilizing pure moments.3 Subsequent comparisons, particularly relevant in fixation instrumentation via flexibility testing, have described the performance of these devices relative to the intact
spine. often with high mean age donor specimen. Additionally, comparisons
between fixation treatments, as well as comparison of fixation treatments
from laboratory to laboratory, have been possible. The standardization of
the pure moment test protocol by Goel et al has contributed to the repeatability despite biologic variability inherent in cadaveric testing.
It is important to understand the rationale of the test methodology
when considering clinically relevant biomechanical studies. The basis of
the traditional flexibility test, or pure moment testing, is to apply a uniform
moment across all FSUs in a given specimen. Figure 8-1 is an example of a
mounted lumbar specimen that will be subjected to flexion-extension bending. The ability to extrapolate the biomechanical effects to clinical outcomes
is dependent on study design and successful interpretation of the resulting
data. Clinically relevant biomechanical testing in the appropriate form is an
important parameter for clinicians to consider in the triage of patients with
spinal pathologies.
In a cadaveric human lumbar study by Mimura et al, the authors were
able to demonstrate a statistically significant difference between RoM in lateral bending, but not in flexion-extension bending, for intervertebral discs
with degenerative ratings in whole lumbar specimens under a flexibility pro-
5
tocol.
Biomechanical studies involving age as a variable in the analysis are
often shown to be correlated to RoM. Board et al reported on the results
of a human cadaveric cervical biomechanical study. Their results suggest
that biomechanical flexion-extension in pure moment loading decreases
the RoM as a function of the age of the specimen.6 These findings agreed
with published articles, when extrapolated and compared to equivalent
test parameters. In a similar clinical evaluation on bending in the cervical
spine involving only males, Sforza et al concluded that young adult males
exhibited statistically significant larger flexion-extension RoM compared to
their middle-aged counterparts who participated in the study.7 Similarly, in
a clinical cervical study involving multiple factors including both age and
degeneration, Simpson et al determined age to be the most significant factor
on RoM.
cal treatment may be warranted, but subsequent conditions and outcomes
related to the specific implant or procedure for the elderly patient may not
8
Confounding these results are clinical considerations in which surgi-
4
41
42
F IG UR E 8 -1 Biomechanical test setup subjected to flexibility protocol,
with a lumbar specimen mounted in flexion-extension test.
P A R T I I Basic Science of the Aging Spine
be clear. For example, symptomatic spine pathology resulting in instability
of a FSU and suitable for an instrumented fusion procedure must consider
the interaction of the hardware and the patient’s local host tissue. In addition
to global metrics of bone quality, the local bone purchase dependent upon
the microstructural integrity of bony trabeculation at the index FSU may
have undergone severe anatomical changes. These differences affect the load
response, exacerbate degenerative pathologies, and require additional considerations for the type of instrumentation suitable for the patient preoperatively. Intraoperatively, additional factors may further alter the structural
integrity of the FSU, for example, endplate preparation or pilot hole drilling
combined with tapping.
The biomechanical changes inherent to aging are complex in nature.
Many steps have been taken toward the understanding the fundamental
process of maintaining a healthy spine, including bone healing, the role of
the intervertebral disc, and the significance of endplate changes. However,
understanding the nature of biomechanical measurement and the clinical
relevance of each metric may help further elucidate the suitability of the
treatment for the senescent patient and, ultimately, improved treatment
options may be developed.
ASSESSING ANATOMICAL CHANGES
Accurate measurements of bone strength are essential to the clinical management of a diseased spine. Both the diagnosis of disease, such as osteoporosis, and also its triage, such as the surgical treatment of an unstable spinal
motion segment with hardware, would benefit from explicit descriptions of
vertebral bone quality. Dual-energy x-ray absorptiometry(DXA)–obtained
measures of bone mineral density are widely regarded across many medical
diskiplines as the gold standard for assessing fracture risk. The guidelines set
by the World Health Organization based on the standard deviation units of
bone mineral density (BMD), referred to as T-scores, have limitations that
are documented in the literature. Also, BMD has not consistently supported
correlations with patient fracture in all risk groups, and additional indicators
to further enhance DXA scores would be particularly beneficial to lowerrisk patients with higher T-scores.
Two primary reasons for the frequency of DXA measurements are the
relatively noninvasive, nondestructive nature of the test and documented
correlations associated with DXA measurements. Imaging modalities that
assist in the classification of degeneration have been useful in FSU pathophysiology and could be useful in understanding the relationships between
aging, degeneration, and biomechanics of the FSU. Therefore, through the
use of known techniques in detecting degeneration of the osteoligamentous
structures, such as magnetic resonance imaging (MRI) and the Modic classification of vertebral endplate change, stronger correlations may be established between age and degeneration. Ideally, earlier fracture diagnostic
capabilities for all risk groups may be added to a clinician’s armamentarium.
OSTEOPOROSIS, AGING, AND BIOMECHANICAL PROPERTIES
The use of clinical guidelines based primarily on BMD results has been
widely accepted. The ability to identify patients with high risk of fracture
via low BMD measurements, defined by T-scores of −2.5 or lower, and to
subsequently provide effective pharmacological treatments, has been proved
through large double-blinded placebo-controlled trials. Several challenges
remain in identifying low-risk population and ultimately a means in cost
effectively managing fracture risk. In an examination of 149,524 postmenopausal women 50 years of age and older with fractures, 82% had T-scores
above the threshold criterion of −2.5.9 Thus, it has been suggested that the
value of BMD would be enhanced with additional risk factors for improved
diagnostic capabilities.
Vertebral fracture is the most common result of osteoporosis in postmenopausal women older than 60 years of age. Surgical management
through vertebral body augmentation involving the injection of polymethylmethacrylate (PMMA) has been diskussed as a method of fracture
treatment in the literature. Understandably, the preferred course should
be prevention, as opposed to surgical intervention. In addition, iatrogenic
effects from vertebral body augmentation, including adjacent level implications, have not been assessed in well-controlled studies.
Analysis of available data regarding fracture in moderate-risk patient
populations shows that the increase in fracture risk with decreasing ageadjusted BMD and other factors, including a prior history of fractures, are
also important considerations. In short, not all patients diagnosed with current threshold values for osteoporosis will go on to fracture. Moreover, not
all patients above the osteopenic level will be free of fracture related to bone
structure and density.
BMD AND IMPLICATIONS ON INSTRUMENTED PROCEDURES
Another use for BMD as measured by DXA is to determine the quality of
bone for screw purchase. BMD has been shown to be correlated to pull-out
strength, and for many fixation devices, screw purchase plays an important
role in providing immediate stability and longer-term fixation. The screwbone interface is integral to many constructs, such as anterior cervical plating
and lumbar pedicle screw fixation, and adequate screw purchase is necessary
for treatment of any spinal pathology depending on such instrumentation
for stabilization and fixation. In patients showing an insufficient BMD, purchase becomes cause for concern. For the osteoporotic spine, the screw-bone
interface may be augmented through various techniques in order to provide additional purchase strength. However, methods such as augmentation
through PMMA should be exercised with caution, as complications may
arise from the use of bone cement.
Biomechanical measures used to test screw-bone i nterfaces have been
evaluated in a number of different ways. Axial pull-out strength has been
frequently reported in the literature, including in human cadaveric spines
that would be considered osteoporotic. Figure 8-2 illustrates a common test
method for determining axial screw-bone interface strength. However, cyclical loading has been suggested to mimic more realistic modes of failure for
implanted constructs. Studies have examined bending failure as an appropriate method of loading.
The limitation of any test protocol is the ability to directly compare
against native human conditions. Several of the published studies have considered various test materials including both cadaveric and synthetic test
specimens. The utility of such tests should still be recognized but it must be
tempered w ith an appropriate understanding of the clinical ramifications.
Testing on cadaveric animal models is a consideration that should be taken
10
Force
F IG UR E 8- 2 Method of testing the screw-bone interface strength in
axial pull-out.
into account when evaluating screw-bone interface results. Bending modes
of failures are considered more realistic complications, but test protocols are
more difficult to execute. This is often due to the difficulty in defining the
appropriate test methodology.
The bending moment and the associated load levels are one set of test
parameters. A depiction of testing the effects of the screw-bone interface
through bending moments in vertebrae is shown in Figure 8-3. The construct configuration is another study design consideration with implications
for unilateral versus bilateral constructs with and without crosslinks. Fatigue
is also another major factor difficult to mimic in a cadaveric test environment during biomechanical testing. Screw pull-out tests can be performed
along the bone screw axis, but the flexion-extension type of bending should
be executed under a cyclical protocol that eventually fails the screw-bone
interface through off-bone screw axis loading. This results in a markedly different biomechanical response at the FSU and, in turn, may have different
complications, for example, screw loosening. Gau et al reported modes of
radiological failure in a clinical radiographic study that examined implanted
constructs that exhibited “windshield-wipering,” which may be an indication
of bending fatigue at the screw-bone interface, and classified them accord-
11
ingly.
Interestingly, these were not symptomatic complications.
The ability to derive a specific BMD measurement has been published
in a study by Wittenberg et al12 The authors hypothesized an equivalent
mineral density of 90 mg/ml from quantitative computed tomography
(qCT) as a threshold level to expect complications associated with screw
loosening and 120 mg/ml as a threshold for fewer problems. This has not
been validated in a clinical outcomes trial. Often, it is surgeon perception
on the adequacy of bony purchase that governs the decision to instrument
a patient with hardware. Additional data to provide a validated standardized DXA metric with positively correlated clinical outcomes for specific
threshold levels would provide a higher confidence in BMD measurements
as a preoperative indicator for instrumented procedures.
DUAL ENERGY X-RAY ABSORPTIOMETRY AND MECHANICAL STRENGTH
The mechanical properties of both a FSU and its components may be analyzed by a number of different measurements and techniques. For ultimate
strength and stiffness property studies, both localized indentation studies
as well as compressive failure tests of vertebral bodies en bloc and complete
FSUs have been reported in the literature. Due to differences used in the
test protocols to determine strength, the correlation between bone mineral
content (BMC) and BMD as reflected by DXA measurements have varied
with failure loads.
Studies have shown the failure strength of vertebral bodies as measured by indentation testing differs between superior and inferior endplates; and also between locations on the same vertebral body endplate; for
example, posterolateral regions tend to have the highest relative strength.
With exceptions, the authors concluded from their study that a decrease
in BMC correlated to a decrease in strength. In addition, the same research
C H A P T E R 8 Biomechanics of the Senescent Spine
Applied
torque
F IG UR E 8 - 3 Application of cyclical bending moments necessary for
creating “windshield-wiper” failures.
group13 later reported removal of the endplate resulted in a significant
decrease in compressive failure strength. Howe ver, it was not clear if
removal of the endplate affected DXA meas urements.
DXA is a measurement reflective of the underlying bone mineralization.
In order to d etermine the effects of surgical site preparation, for example.,
removal of the cartilaginous endplate for intervertebral spacer implants, the
effects of surgical approaches on the structural integrity should be understood. DXA and vertebral strength have been shown to correlate closely in
the native state. Vertebral body endplates have been shown to affect failure
strength. When overly manipulated, the endplates can potentially result
in the collapse of a vertebral body, but the relationship between iatrogenic
complications due to surgical preparation and implant stiffness coupled
with low BMD patients has not been studied.
The consistency of DXA measurements, particularly as it relates to
strength, is dependent upon a number of factors, including artifacts from
soft tissue. The correlations are especially problematic with higher BMD
content. In a study utilizing DXA and cadaveric spine positioning, Myers
et al suggested clinical studies to confirm supine lateral patient positioning would be more effective in determining BMD measurements.14 The
aging phenomenon that occurs within every human body may potentially
cause global osteoarthritic changes, including BMC and BMD within the
spine, that subsequently affect local DXA measurements. Utilizing animal
models to control the homogeneity of specimens has not resulted in more
significant correlations between BMD and strength. Contrarily, in a study
involving porcine cervical spines,15 the investigators reported no significant
correlation between BMC or BMD with compressive failure strength. Furthermore, large animal models rarely exhibit vertebral body fractures even
with reduced BMD levels, and thus would not be characterized into high
risk for low-trauma fracture categories.
In conclusion, DXA has been a widely used indicator for osteoporotic pa tients and for assessing the risk of fracture. Potentially, it has
validity as a gauge for the screw-bone in terface in axial pull-out, but the
more complex modes of loading often found in bone-anchoring devices
require a better understa nding of the failure modes. In addition, with
the current DXA standard as an indicator of bone strength, the implications of implant failu res and resistance to fracture are not well defined
for T-scores above −2.5. However, other mo dalities exist that may augment the current metrics in quantifying the usefulness of current BMD
measurements.
MODIC CLASSIFICATION OF VERTEBRAL ENDPLATE CHANGE
Degenerative changes of the lumbar spine have been observed with MRI
techniques. Specific signal changes from vertebral body endplates and marrow have been differentiated through imaging techniques that increased tissue contrast. A classification system of MRI scans using two different pulse
sequences was published by Modic et al16 Optimizing T1 and T2 relaxation
times in pulse sequences during MRI studies helped define and characterize the i maged tissues. Three different types of change were recognized
43
44
P A R T I I Basic Science of the Aging Spine
from T1-weighted and T2-weighted MRI scans of the same spine segment.
The following is the accepted classification used for Modic changes:
Type 1: hypointense on T1-weighted and hyperintense on
T2-weighted MRI signal
Type 2: hyperintense on T1-weighted and hyperintense on
T2-weighted MRI signal
Type 3: hypointense on T1-weighted and hypointense on
T2-weighted MRI signal
The interobserver and intraobserver error in a clinical study has been
documented and the consistency of this imaging classification system was
confirmed.17 The study involved five independent observers of various clinical spine experience who graded 50 sagittal T1-weighted and T2-weighted
MRI scans. The evaluation of the same scans was repeated by each participant following a 3-week interval with no reference to the first assessment.
The intraobserver agreement, or consistency between the first and second
evaluations by the same observer, was assessed based on Landis and Koch’s
use of the kappa statistic,18 which was equal to 0.71. Additionally, interobserver agreement or consistency among al l the observers was calculated to
be 0.85 for the study. This study demonstrated the intraobserver agreement
was substantial while interobserver agreement was excellent for the Modic
classifications.
Although the original imaging studies were designed to investigate degenerative disc disease, the impact of these changes is not well understood nor
is the clinical implication. One of the early findings of Modic type 1 change
was fissures in the endplates, which were confirmed by histological findings.
The intensity changes from MRI scans have been deduced to reflect osteocartilaginous fracture signs. Disc herniations that include components of the
endplate, namely hyaline cartilage, are then suggestive of avulsion-type disc
herniations. Reportedly, this form of intervertebral disc herniation is predominant in the elderly and may warrant investigations into failure strength.
Magnetic Resonance Imaging and Modic Changes in 40-Year-Old Men and Women
A 5-year prospective study was conducted on a large sample of 40-year-old
men and women drawn from the general population.19 In this study, every
ninth person born in the county of Funen, Denmark between May 27, 1959
and May 26, 1960 was selected by the Central Office of Civil Registration.
Of the 625 selected study subjects, 412 agreed to participate (66%). The
study included 199 males and 213 females.
Of the total number of participants, 92 patients (22%) had Modic
changes. This was considered as a rare event when compared to other
measured factors. For example, irregular nucleus shape was found in 306
patients (74%). Nonetheless, Modic changes were strongly associated with
lower back pain (LBP) occurring within the year prior to the study. Of the
92 patients exhibiting Modic changes, 81 had LBP in this time interval
while the remaining 11 did not.
Significance of the Modic Classification to the
Degenerative Process in the Spine
The changes within the Modic classification are generally accepted to signal
a change within the FSU, which is composed of both vertebral bodies and
the intervertebral disc. The structural components of the FSU i nclude the
superior vertebral body as well as the inferior body. In addition, a normal
intervertebral disc can also be considered structural and is capable of transmitting load from one vertebral body to the other. However, over time, this
capability within a patient’s FSU may become diminished due to ag ing and
its effects.
The complex loading vectors absorbed and transmitted by a FSU will
change as the aging process affects specific components of the FSU. Vertebral bodies are subjected to changes that include fissuring, regenerating
chondrocytes, and granulation tissue. Morever, the hydrostatic condition of
the intervertebral disc may become altered and potentially result in reduction of hydration in the disc. From an imaging standpoint, an MRI study
has shown a T2-weighted image was reduced in intensity when correlated to
a loss of hydration and proteoglycan content. Such changes may eventually
lead to abnormal distribution of load at the endplates and thus potentially
result in morphological change, e.g., amorphous fibrocartilage within the
nucleus, as well as loss in functionality.
Changes to FSUs are sufficiently widespread that they are considered a
part of the normal phenomenon of senescence. From a clinical perspective,
the Modic type 1 changes are considered more acute changes, with fissures
in the vertebral endplates. Type 2 changes are consistent with fatty degeneration of the bone marrow. Type 3 changes are observed in vertebral bodies exhibiting sclerotic changes. Additionally, Modic has shown that type
1 changes may convert to typ e 2 changes within 1 to 3 years. However, it
remains to be proven whether type 2 and type 3 changes must first take on
the characteristics of a ty pe 1 change. Due to these known changes within
the vertebrae, failure strength studies on the vertebral bodies exhibiting
Modic changes would seem logical.
Studies should combine DXA measurement with imaging classifications, i.e., Modic changes of the vertebral body endplates, to enhance
prediction based on relationships with compressive failure strength and subsequent intraoperative and postoperative implications. Current DXA-based
osteoporosis measures are good models for high-risk patients, but all at-risk
patient groups may benefit from more comprehensive indicators. Modic
changes have not been tested for correlations to BMD or compressive vertebral strengths, but have been studied relative to degenerative changes within
the spine. Understanding the relationship between Modic changes and vertebral strength could potentially augment DXA measurements for bone
quality and subsequent risk of fracture with patients outside the current
high-risk category. Finally, the ability to assist in determining appropriate
treatments for low BMD patients at risk of traumatic fracture and predicting the clinical outcome is the end goal of clinically relevant biomechanics
of the senescent spine.
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