Ebook Handbook of neurological sports medicine: Part 2
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Ebook Handbook of neurological sports medicine: Part 2
11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2associated with a concussive event. As discussed previously, grading scales have been largely replaced by the recognition and characterization of concussion symptomsand their duration for determination of severity. Additionally, appropriate management centers on a symptom-free waiting period of phys Ebook Handbook of neurological sports medicine: Part 2ical and cognitive rest to allow the athlete to, usually, subsequently return to play. However, emerging research now suggests that head impacts may cEbook Handbook of neurological sports medicine: Part 2
ommonly occur during contact or collision sports in which symptoms may not develop and there are no outward or visible signs of neurological dysfuncti11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2ce cannot be overstated. The concept of minimal or "subconcusslve" Injuries thus requires examination and consideration regarding the role they may play In accruing sufficient anatomical or physiological damage or both. Emerging evidence is drawn Irom laboratory data in animal models of mild traumat Ebook Handbook of neurological sports medicine: Part 2ic brain injury, biophysics data, advanced neuroimaging studies, and forensic analyses of brains of former athletes who did not have a diagnosis of coEbook Handbook of neurological sports medicine: Part 2
ncussion during their playing career. Thus,subconcussion is a previously underrecognized phenomenon that needs to be further explored and also contemp11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2s are potentially expressed later in life.1’1A WORKING DEFINITIONSubconcussion is a cranial impact that does not result in known or diagnosed concussion on clinical grounds. It may also occur with rapid acceleration-deceleration to the body or torso, particularly when the brain is free to move withi Ebook Handbook of neurological sports medicine: Part 2n the cranium, creating a "slosh" phenomenon. Subconcussion has its greatest effect through repetitive occurrences whereby cumulative exposure becomesEbook Handbook of neurological sports medicine: Part 2
deleterious. It should be stressed that not all head impacts should be considered potentially harmful. The athlete's risk of experiencing longstandin11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2e, type and magnitude of exposure, recovery periods, differential rates of recovery, genotype, and individual vulnerability. The role of protective equipment and variability in equipment also are factors that may come into play, but their contribution Is unknown.209210 • • • Handbook of Neurological Ebook Handbook of neurological sports medicine: Part 2 Sports MedicineLABORATORY EVIDENCE OF SUBCONCUSSIVE EFFECTSAs discussed earlier in the book, traumatic brain injury (TBI) is traditionally thought ofEbook Handbook of neurological sports medicine: Part 2
as involving both primary and secondary injury phases. |,â| In addition to primary and secondary injury, a tertiary phase of TBI may now be thought o11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2ntegrity.'4-26-’*• 521 u- 6d| This phase ofTB1 potentially could become chronic and also compounded if the individual is subjected to repetitive minor head impacts.Little attention was paid to repetitive mild head injury before the year 2000. with only a few repetitive injury studies having been pub Ebook Handbook of neurological sports medicine: Part 2lished.127 -4’-641 Since that time there has been an increased interest in laboratory’ research focused on repetitive mild TBL''-7-"- ”• ”-2'-2*-MostEbook Handbook of neurological sports medicine: Part 2
of these studies were performed in rodents; a few were performed in pig models of TB1. In one study, DeFord and colleagues showed that as compared to 11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2this was despite no overt cell death in the cortex or hippocampus or blood-brain barrier compromise.Researchers have demonstrated that repetitive mild TBI (mTBI) causes changes in cortical and hippocampal cytoskeletal proteins and increases the brain's vulnerability to subsequent head injury compare Ebook Handbook of neurological sports medicine: Part 2d to single TBI.127-”1 Some studies have reported evidence of central nervous system injury despite no overt behavioral deficits, consistent with subcEbook Handbook of neurological sports medicine: Part 2
oncussive injury. One study-used microtubule-associated protein-2 (MAP-2) staining techniques to demonstrate that local and remote injury was signific11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2mental head injury'.1’”Some researchers have demonstrated evidence of deleterious effects following a single subcon-cussive experimental head injury. Some have modified the Marmarou weight drop method concussion model to diminish impact forces toeffect a non-response-altering reaction, thus simulati Ebook Handbook of neurological sports medicine: Part 2ng less than concussive injury.12 *0’421 In these mice, staining for amyloid precursor protein (APP) has shown that these subconcussive impacts reliabEbook Handbook of neurological sports medicine: Part 2
ly produce tearing of axons and the formation of axonal retraction bulbs in the brain stem-level descending motor pathways. These animals exhibited no11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2In another rodent vertical impact mTBl model, Lado and Persinger found that there was minimal change in the animals' behavioral response following injury, yet at sacrifice the animals showed dark, swollen neuronal soma J*”Lifshitz and Lfsembee, in a rodent fluid percussion brain injury model, found Ebook Handbook of neurological sports medicine: Part 2at 28 days that thalamic ventral basal neurons exhibited atrophic changes without neuronal death.1’21 It has been noted that persistence in a chronicEbook Handbook of neurological sports medicine: Part 2
atrophic state after ipsilateral hippocampal injury deprives the deafferented basal cholinergic neurons of trophic support, a finding consistent with 11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2oncusslve brain-injured mice had abnormal spatial acquisition and working memory as measured by Morris water maze over the first 3 days (p< 0.001) but not later than the fourth day postinjury.1121 At I and 3 days postinjury, intra-axonal accumulation of APP in the corpus callosum and cingulum was as Ebook Handbook of neurological sports medicine: Part 2sociated with neuronlament dephosphorylation, abnormal transport of Fluoro-Gold and synaptophysin, and deficits in axonal conductance, which continuedEbook Handbook of neurological sports medicine: Part 2
until 14 days when axonal degeneration was apparent. What this showed was that although there may be recovery from acute cognitive deficits, even sub11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2 fluid percussion injury (0.50-0.99 atmosphere (atm) on rat behavior and neuropathological changes in an attempt to belter understand subconcussive brain injury.In their study, male Long-Evans rats received either a single mild lateral fluid percussion injury or a sham injury, followed by either a s Ebook Handbook of neurological sports medicine: Part 2hort (24 hours) or long (4 weeks) recovery period. NoThe Emerging Role 0Í SuoccMKussion • • • £11significant group differences were found on behavioraEbook Handbook of neurological sports medicine: Part 2
l and axonal injury measures; however, rats given one subconcussive mild fluid percussion injury displayed a significant increase in microglial activa11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2ncussive impact.18'As noted in these studies, such animal models of inTBI have resulted in a significant numlrer of damaged corticospinal tract axons, created permeability in the blood-brain barrier, caused remote eflects away from the cortical impact site, and altered neuronal soma. All of these al Ebook Handbook of neurological sports medicine: Part 2terations can occur in the absence of behavioral changes. Thus, there is laboratory evidence that subconctissive-level impacts can lead to anatomicalEbook Handbook of neurological sports medicine: Part 2
and physiological alterations and that these occur particularly if the blows are repetitive.CLINICAL EVIDENCE OF SUBCONCUSSIONMuch of the current clin11The Emerging Role of SubconcussionClinical care of the athlete with concussion has traditionally centered on the recognition of signs and symptoms a Ebook Handbook of neurological sports medicine: Part 2menon of subconcussion. Here we review these clinical data.Biophysics DataConcussion and subconcussion can occur in any sport; however, American foolhall has a high incidence* of concussion, largely due* to the style of play, the high rale* of impacts, and the expanse ot participation.1251 The manda Ebook Handbook of neurological sports medicine: Part 2tory use of helmets in American football has allowed for the systematic analysis of injury biomechanics and real-t ime* measurements of forc es, velocEbook Handbook of neurological sports medicine: Part 2
it ies, accelerations, and frequencies of head impacts via implanted telemetry devices (figure 11.1). Our understanding of the issue of subconcussionGọi ngay
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