Healthy_back (healthy_back) wrote,
Healthy_back
healthy_back

Щелканье суставов

http://www.geo.ru/nauka/tainyi-khrust
Такая обычная вещь — похрустеть пальцами. Одни делают это по привычке, а других этот звук сильно раздражает. Однако ответ на вопрос, почему, если потянуть за палец, раздается хруст, — был предметом полемики среди врачей со второй половины прошлого столетия. Точный физический механизм, как ни странно, до сих пор был плохо изучен. Разобраться в природе хруста пальцев решили канадские ученые под руководством профессора реабилитационной медицины Грегори Ковчука из Университета Альберты в Эдмонтоне (Канада). При помощи МРТ они отследили, что происходит с пальцами. Как и предполагалось, причина характерного звука — пузырьки, которые образуется при оттягивании пальца. Они заполняются газом — и «лопаются», когда суставы возвращаются в нормальное положение.

Для эксперимента канадские ученые соорудили устройство, которое позволяет автоматически тянуть за палец. Кисть руки в этот момент находилась в томографе: аппарат фиксировал процесс со скоростью 3,2 кадра в секунду. При помощи устройства исследователи тянули за каждый палец руки добровольца по очереди. И позже отслеживали полученный результат на видео.

Оказалось, что при оттягивании пальца, контакт между поверхностями костей исчезает. Таким образом давление синовиальной жидкости — эластичной массы, заполняющей полость суставов — падает. А растворенный в ней газ выделяется в пузырьки — они и дают характерный лопающийся звук. Причем для их нового появления необходимо около 20 минут.

В 1947 году похожую гипотезу о причинах хруста пальцев выдвинули врачи из больницы Святого Томаса в Лондоне. Вокруг пальцев добровольцев они обвязывали шнурки — и тянули до тех пор, пока не раздастся характерный «хлопок». Данные испытаний врачи фиксировали при помощи рентгеновского аппарата. Тогда, однако, предположение британских врачей так и не стало общепринятым. И только сейчас их данные вновь были подтверждены канадскими учеными.

Теперь исследователи ищут ответ на вопрос, почему у одних людей получается хрустеть пальцами, а у других — нет, и можно ли по хрусту или его отсутствию судить о состоянии синовиальной жидкости и здоровье суставов.

К слову, привычка хрустеть пальцами на руках, вопреки распространенному мнению, не приводит к артриту. На собственных пальцах это проверил доктор Дональд Унгер из Калифорнии, специалист по внутренним болезням. Каждый день на протяжении 60 лет Унгер хрустел пальцами только левой руки. В 2009 году после ряда медицинских обследований поражений суставов у доктора обнаружено не было. geo_icon

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0119470
Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking.

http://www.sciencealert.com/new-study-confirms-what-really-happens-when-you-crack-your-knuckles
New study confirms what really happens when you crack your knuckles "Like a firework exploding in the joint."

Scientists have used ultrasound machines to figure out exactly what’s going on in our joints when we crack them, putting an end to a decades-old debate about where that distinctive cracking sound comes from.

Back in April, researchers from the University of Alberta published a paper based on MRI imaging of finger joints being cracked saying that the popping sound is caused by the collapse of air bubbles that form in the fluid that surrounds our joints - called synovial fluid. But ultrasound machines can record what’s going on inside our bodies up to 100 times faster than MRIs, so another team of scientists decided to investigate this claim further.

Led by radiologist Robert D. Boutin from the University of California, Davis, the team recruited 40 healthy participants, 30 of whom were regular joint-crackers, and 10 who were not. Of those who were habitual crackers, the older ones admitted to cracking their knuckles up to 20 times a day for the past 40 years.

The participants were asked crack the knuckle at the base of each finger, known as the metacarpophalangeal joint (MPJ), while being observed through an ultrasound machine. They ended up imaging 400 MPJ cracks, and recorded the sounds so they knew which ones came with a 'pop'.

While the researchers expected to see something occur within the joints - Boutin told Rachel Feltman at The Washington Post that ultrasound machines can capture events 10 times smaller than MRIs are capable of - they weren’t prepared for the result to be so… explosive.

"What we saw was a bright flash on ultrasound, like a firework exploding in the joint," Boutin said. "It was quite an unexpected finding."

The flashes in the ultrasound were coupled so consistently with the popping sound that the researchers could predict with 94 percent accuracy which MPJ cracks 'popped' just by looking at the images.

The researchers suspect that the cracking and visual flash in the ultrasound images is related to changes in pressure that occur in the synovial fluid, as Boudin explained to Richard Hartley-Parkinson at the Metro:

"There have been several theories over the years and a fair amount of controversy about what’s happening in the joint when it cracks. We’re confident that the cracking sound and bright flash on ultrasound are related to the dynamic changes in pressure associated with a gas bubble in the joint."

But a big mystery still remains. Back in 1947, a paper was published saying that the popping sound occurred when a bubble first formed in the synovial fluid of the joint. This hypothesis was refuted 30 years later when another group of researchers said it made more sense that the sound came from the bubble bursting.

In April, the University of Alberta team backed up the bubble-collapsing hypothesis with their MRI recordings, but they still hadn’t come up with any conclusive proof. So which is it, does the sound result from a bubble popping in the joint or from a bubble being created in the joint?

"That's a surprisingly tough question to answer," Boudin told Feltman at The Washington Post. "I will tell you that we consistently saw the bright 'flash' in the joint only after we heard the audible crack. Never the other way around. Perhaps that supports the bubble formation theory, not the bubble popping theory."

What the researchers can say is they detected no immediate pain, swelling, or damage being done to the joints as they were cracked, and found no discernible difference between the joints of their habitual knuckle-crackers and those who never did it. This backs up the results of an experiment by a Californian medical doctor who spent 60 years cracking the knuckles on one hand and not the other, only to find no difference between the two.

While Boudin did say more research needs to be done to confirm that no long-term damage is being done, there’s also the possibility that maybe joint-cracking is actually good for us. "After a joint cracks, the range of motion for that joint increases significantly," he told Feltman.
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