Habits both big and small make up much of what we do throughout the day. A habit forms for a variety of reasons, but these are not always conscious choices that are made. Occasionally these habits form as a management strategy for physical or coping mechanisms for psychological factors. For example, individuals who have tennis elbow will often find themselves unconsciously massaging their painful elbow without even thinking about it and the habit helps to decrease pain so they continue to do it. These habits become ingrained in our brain due to a habit forming cycle which consists of three elements; the cue (or trigger), the routine (or behavior), and the reward. Eventually these unconscious habits may be brought to the attention of the individual, but in order to break the habit a conscious effort will need to be taken or something in the habit forming cycle will need to stop. Habits can be both a good and bad thing depending on what purpose it plays and how it affects an individual. That brings us to one of the most common habits: knuckle cracking. It has long been debated on if knuckle cracking is good or bad to do and if this is a habit that needs to be broken. It is not well understood what the reward of knuckle cracking is based on the habit forming cycle, but it may be brought on as a nervous tic, stress release, or simply just because of how it makes someone feel. It is estimated that between 25% and 54% people have a habit of cracking their knuckles, depending on the population studied (deWeber et al., 2011). In order to know what happens when cracking knuckles it is important to first understand the anatomy of the joint being cracked. In order to “crack” a joint, generally this requires an external force causing pressure in a specific direction. Researchers still do not fully understand why some individuals are able to crack specific joints while others cannot, but it is thought that over time with practice our body learns how much and where force should be applied to make it crack. It is also believed that certain individuals are unable to crack a joint if their joint space is too great. Now what actually is a joint? A joint is where two bones articulate or come together to meet. Joints are complex structures which contain connective tissues such as ligaments, tendons, synovial fluid, and cartilage, all of which allow the articulating bones to move in a specific way. There are three types of joints throughout our body which are responsible for protection and motion. Fibrous joints Suture – cranium Gomphosis – between a tooth and the jaw Syndesmosis – between the radius and ulna that allows for pronation and supination. Cartilaginous joints Primary (long bone where bony epiphysis and body joined by and epiphyseal plate) Secondary (symphysis) as in vertebrae between discs Synovial joints Pivot-neck, radius Ball and socket-hip, shoulder Plane/gliding-wrists, ankles, acromioclavicular joint Hinge-elbow, knee Saddle-thumb Condyloid-knuckle Research surrounding what actually causes the sound and happens with knuckle cracking has been challenging to determine thus far. A 2015 study discovered that tribonucleation “two closely opposed surfaces are separated by a thin film of viscous liquid” is responsible for creating the cavitation or surfacing of bubbles within the joint (Kawchuk et al). In a 2018 study, researchers were able to replicate the cause of the popping that cracking knuckles is responsible for using a mathematical model based off of the 2015 theory (Chandran Suja & Barakat). These researchers found that following the joint being manipulated the pressure between the joint decreases therefore causing gasses in the synovial fluid to form bubbles. These bubbles will quickly and partially collapse, which is the cause of the loud sound that is heard. When looking at knuckle cracking, research demonstrates little to no clear benefits but also little to no long-term consequences with knuckle cracking. There are relatively few studies looking at the effects. One 1990 study of 300 individuals found that while there was no increased prevalence of arthritis individuals who crack their knuckles, individuals who crack their knuckles are more likely to have a decreased grip strength and increased hand swelling when compared to those who do not crack their knuckles. (However, it is important to note that habitual knuckle cracking was also associated with manual labor, smoking, and drinking alcohol, which may confound grip strength and hand swelling.) Another, more recent study from 2017 researchers determined that MH cartilage was thicker in the knuckle cracking group compared to the non-knuckle cracking group, but there were no changes in grip strength. In a separate 2017 study, researchers found no significant changes following knuckle cracking vs before in swelling or grip strength, but did report a slight increase in range of motion just after cracking the metacarpophalangeal joint. Ultimately, the evidence is mixed and inconclusive on the benefits or consequences of habitual knuckle cracking. If someone is already a habitual knuckle cracker, then there is no need to put significant effort towards consciously try to change the habit. In fact, if this is a nervous tic or helps relieve stress, then knuckle cracking may be psychologically beneficial to that particular individual. On the other hand, if someone is currently not cracking their knuckles, there are no clear benefits to it either, and therefore no particular reason to start. When looking at knuckle cracking, research demonstrates little to no clear benefits but also little to no long-term consequences with knuckle cracking. There are relatively few studies looking at the effects. One 1990 study of 300 individuals found that while there was no increased prevalence of arthritis individuals who crack their knuckles, individuals who crack their knuckles are more likely to have a decreased grip strength and increased hand swelling when compared to those who do not crack their knuckles. (However, it is important to note that habitual knuckle cracking was also associated with manual labor, smoking, and drinking alcohol, which may confound grip strength and hand swelling.) Another, more recent study from 2017 researchers determined that MH cartilage was thicker in the knuckle cracking group compared to the non-knuckle cracking group, but there were no changes in grip strength. In a separate 2017 study, researchers found no significant changes following knuckle cracking vs before in swelling or grip strength, but did report a slight increase in range of motion just after cracking the metacarpophalangeal joint. Ultimately, the evidence is mixed and inconclusive on the benefits or consequences of habitual knuckle cracking. If someone is already a habitual knuckle cracker, then there is no need to put significant effort towards consciously try to change the habit. In fact, if this is a nervous tic or helps relieve stress, then knuckle cracking may be psychologically beneficial to that particular individual. On the other hand, if someone is currently not cracking their knuckles, there are no clear benefits to it either, and therefore no particular reason to start. When looking at knuckle cracking, research demonstrates little to no clear benefits but also little to no long-term consequences with knuckle cracking. There are relatively few studies looking at the effects. One 1990 study of 300 individuals found that while there was no increased prevalence of arthritis individuals who crack their knuckles, individuals who crack their knuckles are more likely to have a decreased grip strength and increased hand swelling when compared to those who do not crack their knuckles. (However, it is important to note that habitual knuckle cracking was also associated with manual labor, smoking, and drinking alcohol, which may confound grip strength and hand swelling.) Another, more recent study from 2017 researchers determined that MH cartilage was thicker in the knuckle cracking group compared to the non-knuckle cracking group, but there were no changes in grip strength. In a separate 2017 study, researchers found no significant changes following knuckle cracking vs before in swelling or grip strength, but did report a slight increase in range of motion just after cracking the metacarpophalangeal joint. Ultimately, the evidence is mixed and inconclusive on the benefits or consequences of habitual knuckle cracking. If someone is already a habitual knuckle cracker, then there is no need to put significant effort towards consciously try to change the habit. In fact, if this is a nervous tic or helps relieve stress, then knuckle cracking may be psychologically beneficial to that particular individual. On the other hand, if someone is currently not cracking their knuckles, there are no clear benefits to it either, and therefore no particular reason to start.