As clinicians, we’ve all heard of “regional interdependence” (Sueki et al., 2013), and understand the importance of viewing the body as a global structure. The joint-by-joint approach that was preached by Janda also gave body workers a general guideline with regards to how to approach restoring, maintaining, and optimizing human function and performance. It seems natural and a matter of fact that areas like the thoracic spine requires more mobility in order to optimize function and mitigate injury as per joint-by-joint theory guidelines. Don’t get me wrong, it’s what I followed and still follow till this day, but how much do we know about thoracic mobility and its importance in relation to other parts of the body such as cervical, lumbar spine and the shoulder complex?
After doing a little digging I’ve realized that the thoracic spine may be the least researched region out of all spinal groups. In terms of my personal take on why it may be the least researched out of all spinal groups is because of its complexity when compared to the cervical and lumbar spine. Its intricate connections to the ribs, the scapulothoracic joint, indirect attachment to the sternum, and being "sandwiched" between the lumbar and cervical spine would lead me to assume that it will be difficult to design high quality in-vivo or in-vitro studies. As Borkowski (2016) stated in a cadaveric systematic review “majority of the studies in the literature did not include the intact rib cage in their models”, led me further wonder if the complexity of the thoracic spine confound a lot of study designs. Another reason that led me to believe it may be the least researched area is due to the fact that clinically diagnosed degenerative changes (Teraguchi et al., 2014) seem to focus on the cervical and lumbar regions, and hence more research may be focused on the lumbar and the cervical spine.
Overall, from all the literatures I have read (which is not much..), it seems like the general consensus is that the thoracic spine gains the least attention, a lot of contradictory in-vitro/cadaveric data (let alone in-vivo data - pure assumption), a lot of different measurement methods, and just overall few previous studies to work with (Borkowski et al., 2016; Heneghan et al., 2018; Teraguchi et al., 2014; Wilke et al., 2017), and hence may be the least researched out of all spinal groups. For that reason, I believe it is the least looked at region during clinical practice as well. Due to its complexity, I will only be discussing one of the planes of the thoracic spine - transverse plane.
Spinal rotation is an important component in many functional and sport activities, and a majority of the axial rotation (up to 80%) movement is attributed to the thoracic spine (Bucke et al., 2017). It is well established that the shoulder complex is linked to thoracic mobility specifically in the sagittal plane (Edmondston et al., 2012), so the interdependency between the two structures makes it crucial to maintain or improve thoracic spine mobility in order for athletes or the general population to maintain functional activities. That being said, more studies need to reveal the relationship between the shoulder complex and the thoracic spine in the transverse plane. Along with majority of axial rotation coming from the thoracic spine, it also contributes to an “estimated 55% of the total force and kinetic energy generated during a throw” (Heneghan et al., 2020), and a lack of mobility in the transverse plane in this region of the spine increases injury risk in the elbow and shoulder by three folds (Aragon et al., 2012) in sports that focus on throwing or overhead movements.
When examining the architecture of the thoracic spine, the intervertebral joints, costovertebral joints, costotransverse joints, sternocostal joints, and all the other structures that relates to the ribs all require movement in order to maintain integrity of the joints. This permits proper movement of the thoracic cage, and hence, allows for efficient expansion of the thoracic cage and respiration. This has huge implications not only for proper exchange of air, but allows for proper diaphragmatic breathing, which indirectly facilitates vagus nerve activity, prefrontal cortex activity, autonomic nervous system homeostasis, and mental well being (Gerritsen & Band, 2018).
So what are some ways that we can assess for thoracic rotation?
Standing rotational strategy, incorporates multiple segments of the body in order to achieve the desired rotational movement. When performing a multi-segmental rotation, the feet, ankles, knees, hips, pelvis, scapula, and spine will all provide contributions to the movement. A right multi-segmental rotation will create movements in specific joints shown below:
Notice that I've included the scapula as a joint that contributes to the rotational movement of the thoracic spine, however, studies have shown absolutely no relationship between glenohumeral joint movements with thoracic spine rotation (Webb, 2017), and given the inter-relatedness of the shoulder complex (glenohumeral joint, scapulothoracic joint, acromioclavicular joint, and sternoclavicular joint), it can be hypothesized that the scapulothoracic joint has minimal influence on thoracic rotation, though more studies need to shed light on this relationship. My personal speculation is that it contributes to an overall increase in multisegmental rotation instead of thoracic rotation specifically. It is also possible for an individual to utilize scapular protraction and retraction as a way to increase the perceived rotational range (for example: right scapular retraction plus left scapular protraction can be perceived as right thoracic rotation), and hence, multisegmental rotation range. As the musculoskeletal system is regionally dependent on each other (Sueki, 2013), a rotational movement that incorporates all the joints allows for larger range of motion compared to a strategy where one or few joints along the kinetic link is taken out of the picture or fixed such as a seated rotation, which we will discuss next.
A seated rotation eliminates rotational involvement of the feet, ankles, knees, hips, and fixes the pelvis on the chair. With the ischeal tuberosity closing the kinetic chain, there is a restriction of movement at the sacroiliac joint and hence, the significant rotational movement will occur from the lumbar spine and up. There are a few things to consider, however. Firstly, having the feet fully planted on the floor helps eliminate movement of the pelvis, not having the feet fully planted allows movement to occur from the pelvis and hence confounds the rotation (by way of anterior movement of the knees during the rotation); secondly, to effectively decrease the involvement of the pelvis, strategies such as blocking the knees or knocking the knees together should be utilized to ensure attempted isolation of spinal range of motion; thirdly, the cervical spine and the shoulder complex needs to be fixed, this takes away confounding factors influencing thoracolumbar rotation. When the above three factors are addressed, the mobility of the thoracolumbar spine rotation can be properly assessed. The total rotational range in the thoracic spine amounts to about 35 degrees (Soames, 2019, p. 472), whereas the total rotational range in the lumbar spine is in the range of 3-18 degrees (Magee, 2014, p. 570). The presence of iliolumbar ligament provides stability in the sacroiliac joint and hence limits the amount of nutation and counter-nutation available (Pool-Goudzwaard, 2003). When in a seated position, the fixed pelvis will largely affect the amount of motion at the L5, leaving four available lumbar vertebrae for available movements, which further decreases the lumbar contribution to rotation. Therefore, it should be noted that due to the lesser range of motion in the transverse plane in the lumbar spine (still however, important), which can be explained by its articulating facets sitting more in a sagittal plane (Soames, 2019, p. 472), seated rotation mainly targets movement in the thoracic spine.
In order to differentiate between lumbar motion and thoracic motion, a popular "lumbar lock" rotation is commonly used in clinic as an assessment tool. I personally prefer the term "heel-sit rotation", the term "lumbar lock" postulates that maximally flexing the lumbar spine by sitting all the way back will “lock” the lumbar spine and hence permit movement only in the thoracic spine. Although more of an issue of semantics, heel-sit may be a better term used to describe this exercise, as the lumbar spine is not “locked” in place, instead, it is less efficient in doing so (Heneghan et al., 2020). That being said, this strategy definitely targets rotational motion in the thoracic spine more than a seated rotation, however, it is important to consider the difference in resistance the rotational muscles need to overcome - heel-sit rotation requires the muscles to fight against gravity and hence warrants more strength to achieve the motion compared to seated rotation.
An interesting side note is that the interdependency between the cervical spine and thoracic spine has been established and study have shown that T1, T6, and T12 generates motion during all cervical spine movements (Bucke et al., 2017). The heel-sit quadruped rotation as shown in the video is demonstrated to be a reliable intervention to assess for thoracic rotation (Bucke et al., 2017) and hence is also a good exercise to facilitate osteo- and arthrokinematics involved with thoracic rotation as well as improving strength of muscles necessary to promote thoracic rotation.
Some caveats to consider when we are assessing for thoracic mobility in the transverse plane:
Rotational movements largely depends on the starting posture of a person. Having a starting position in a relatively flexed or extended position will greatly affect the available rotation in both the thoracic and lumbar spine; with a relatively flexed position increasing available rotation, and a relatively extended position eliminating possible rotation in the thoracolumbar spine (Soames, 2019, p 472-473). Hence, a proper postural analysis should be incorporated before the utilization of standing and seated rotation assessment is done. It is also important for the person to maintain the same lumbar spine position as he/she was in standing when performing the seated rotation.
There is a significant age-related influence on available rotational range in both the thoracic and lumbar spine. Soames (2019) mentions that in the thoracic spine “A 50% reduction in range has been observed between age 30 and 80 (Fitzgerald et al 1983).” (p. 474), where as in the lumbar spine, the opposite finding is observed with no changes in the transverse motion with increasing age (Intolo, 2009).
When tying all these variables together, it becomes particularly interesting and complex when discussing rotational strategies in people. Utilizing standing versus seated rotational versus heel-sit rotation movements can shed light on the mobility of the spine, however, multiple factors need to be addressed in order to properly use it in a systematic manner for reliable analysis of the spinal movement in the transverse plane.
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