The Deltoid Muscle: Structure and Function

Dr. Ellison Melrose // #ClinicalTuesday // www.ptonice.com

In today's episode of the PT on ICE Daily Show, Dry Needling faculty member Ellison Melrose discusses the form & function of the deltoid muscle, as well as clinical applications for dry needling to the deltoid for different patient populations.

Take a listen to the podcast episode or check out the full show notes on our blog at www.ptonice.com/blog

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EPISODE TRANSCRIPTION

INTRODUCTION Hey everybody, Alan here, Chief Operating Officer at ICE. Thanks for listening to the PT on ICE Daily Show. Before we jump into today's episode, let's give a big shout out to our show sponsor, Jane. in online clinic management software and EMR. The Jane team understands that getting started with new software can be overwhelming, but they want you to know that you're not alone. To ensure the onboarding process goes smoothly, Jane offers free data imports, personalized calls to set up your account, and unlimited phone, email, and chat support. With a transparent monthly subscription, you'll never be locked into a contract with Jane. If you're interested in learning more about Jane or you want to book a personalized demo, head on over to Jane.app slash switch. And if you do decide to make the switch, don't forget to use our code IcePT1MO at sign up to receive a one month free grace period on your new Jane account.

ELLISON MELROSE Good morning, PT on Ice daily show. We are live on YouTube and on Instagram. My name is Dr. Ellison Melrose. I am lead faculty with the dry needling division of Ice. I'm super excited to be here for deltoid week. So I kind of compare this to like the sharp week from childhood, right? So this is the most exciting week of the year for us. Um, we are here to talk all things about the deltoids. So we came off of yesterday. Jess, um, started talking to us about the importance of deltoid strength during motherhood and how we can maybe implement some deltoid strengthening in some um, early postpartum period, right? Using more of like a hypertrophy style training versus, you know, diving right into things like CrossFit right away. So that was really awesome. Um, I'm here to tell you guys today about the form function and some clinical applications of deltoid strength. So let's dive right in. Um, if you have been to an upper quarter course with either myself or Paul, we spend a few minutes just on the deltoid side, just talking about how cool the deltoid is. THE DELTOID: FORM So let's start with form, right? So if we look at the deltoid, there is no other muscle in our body that is shaped like the deltoid. Some may compare it to the glute, the glute max of the lower quarter width, you know, how it kind of spans that, that joint and has multiple origins to the single point insertion, um, similar to the glute max. But if you actually look at the deltoid, the origin is almost a full circle, right? So it's about 300 degrees of, um, contact with our, lateral third of the spine of the scapula, the lateral border of the acromion, and the lateral third of the clavicle. So it's about 300 degrees to a single point insertion at the deltoid tubercle. Right? That's like really, really cool. There's no other muscle in our body that does this. This allows us to move in multiple planes of motion. And we'll talk about the function in a little bit more depth later. But just by looking at it. There's nothing else like that we have in our body. Next, we have its innervation, which is also fairly unique, right? So the axillary nerve, its number one job, let's see, its number one job is to provide a motor response to the deltoids. I'm having a little bit of issues on Instagram, We'll come back, we'll just keep it going here on YouTube. So, its main motor branch is to the deltoid. It does innervate teres minor, but I would argue that's probably the smallest muscle we have in our shoulder girdle. And likely the most important part of the axillary nerve is its motor contribution to the deltoid. So if we did not have an axillary nerve, what would that look like in the shoulder girdle, right? That would look like a significant sulcus. So we would not be able to use any of the other muscles in the shoulder girdle without the axillary nerve. Next, we have different regions of the deltoid. So we have the deltoid can be separated into three primary regions, right? We have anterior deltoid, we have middle deltoid, we have posterior deltoid. Well, in 2010, what they found, there was a study that looked at those compartments and what they found was there's actually a further fascially subdivided region in both the anterior and the posterior delt. So each of the anterior deltoid and the posterior delt, each of those have three separate fascially subdivided regions. Really cool. What they also, another study looked at was the EMG activation throughout the deltoid. And what they found was there's at least six differentiations with EMG activities. So we have those fascially subdivided regions can be turned on and turned off, maybe independent of each other, which allows us to maybe think about the function of the deltoid a little bit differently. Right? So our form, we have a very unique origin and insertion. We have a very unique innervation with only a single nerve. And that's main job of that nerve is to innervate the deltoid. Our brain perceives that muscle as really important when things, when we have one nerve and its main job is to just provide motor function to that muscle. So it's super important. We also have the form as the we can divide it further from those original three divisions that we kind of think about back in PT school to seven different subdivisions that we may be able to activate, turn on and turn off independent of each other. THE DELTOID: FUNCTION So let's dive into the function, right? There are four main functions of the deltoid. The first is it's a mover, right? And that's what we think about when we think about the deltoid. We think that it moves into flexion, abduction, extension, internal rotation, external rotation, right? It's a mover in our primary planes of motion. It can also fine tune movements, right? So now that we know that like the deltoid has all of those subdivisions and we can maybe recruit those independent of each other, we can fine tune specific movements. It acts as a synergist with other primary movers in different planes. For example, the posterior deltoid is a great synergist with infraspinatus. We're thinking about, you know, end range external rotation or external rotation in that abducted position. The deltoid may be able to help or maintain that movement pattern and act as a synergist with the infraspinatus. Really cool stuff. So it's a mover. It's also a stabilizer. So I mentioned earlier that if we had an axillary nerve lesion, that would look like a detrimental sulcus sign to the glenohumeral joint, right? So the deltoid, when we think back to PT school, we were like, I at least put a lot of emphasis on the bicep tendon, you know, maintaining its humeral head placement, the rotator cuff, fine-tuning those movements so that it stays in that ball, the humeral head stays in the glenoid fossa appropriately. But if you took away the bicep tendon, right? People do that all the time. We have biceps tenodesis. We still have a functioning shoulder, right? If you took away the rotator cuff, we see that a lot. People have full thickness tears of specific rotator cuff muscles, and they still have function of their shoulder. If you took away the deltoid, you would not, right? you would not have the ability to use the rotator cuff, to use the bicep tendon, to do their primary movements. So it is a stabilizer to the glenohumeral joint. It almost provides an accessory like suction to that labrum to help maintain that humerus in the glenoid fossa. It also provides stability to other joints in that area. So if we think about where it crosses, it spans the AC joint. There's only one other muscle in our body that spans the AC joint, and that's the upper trap. So when we think about if we have damage to the AC joint or our passive structures have maybe been or have been impaired, we have an active stabilizer in the deltoid and the upper trap that cross that AC joint. So again, deltoid strength may be able to help maintain that stability in the AC joint when some of those passive structures have been lost. So it's a mover, it's a stabilizer. Next, it's a cushion. So we don't really think about this often when we think about muscles, but muscles cushion the bones, right? So they cushion the bones, they protect some higher, more sensitized structures in the region. And in this region, in the axillary region, we have brachial plexus and all of its branches exiting the axilla. So we have some very important neurovascular structures close by. So what could be very detrimental to those tissues would be a proximal humeral head fracture. So what the deltoid can do is it can cushion or kind of dampen the blow to a blunt trauma to that bone, which may help reduce the impact, and reduce the likelihood of a proximal humeral head fracture. So really cool stuff. So we're thinking maybe patient populations, that would be beneficial for. And we'll talk about that in a second. So it's a mover. It's a stabilizer. It's a cushion. Last but not least, it's a pump. A lot of what we do in physical therapy, we're just pumping fluid. Our goal is to reduce chemical irritation in that tissue. if we have pain, for instance, right? So we need muscles that help facilitate hemodynamics. When we look at the upper quarter, one of the best muscles to do that is the deltoid, not only by its pure mass, but its capillary density. So it has a higher density of capillaries, which helps with it both, you know, the hemodynamics and the perfusion in that area, but also its proximity to the lymphatic axillary watershed. and just the venous structures, right? So if we think about our venous return coming up into the axilla, all of those things are very important. And when we look at research that was surrounding lymphedema and edema reduction in the upper quarter, what they found was that the deltoid plays a key role in edema evacuation from that upper quarter. So function, right? We have, it's a mover. Not only is it a gross mover, but it's a fine tuner. It's a stabilizer. We would have no upper quarter function without the deltoid. It is a cushion. So it can provide some cushioning for any trauma that occurs in that upper quarter, which is going to protect some of those more sensitized structures we have in this area. And it's a pump. We're pumping fluid, right? So it can help with edema reduction, any sort of acute injury in the distal extremity, not only thinking lymphedema, but also thinking like acute injury. Maybe we don't want to target those tissues. Speaking specifically from a needler, maybe we don't want to needle the tissue that's the issue because it's in an acute inflammatory stage. We want to think proximally. What can we do proximally? we can needle and stem the deltoid, which may help with that fluid dynamics. THE DELTOID: CLINICAL APPLICATION Lastly, I want to talk about three different patient populations that may be beneficial to think about improving the robustness of the deltoid. I'd argue that every single patient population could benefit from a more robust deltoid. But when you look at the research, First, let's talk about operations. So shoulder surgeries. When you look at the research, the deltoid, the strength and mass of the deltoid is one of the number one predictors of a positive outcome from both rotator cuff surgery and something like a reverse total shoulder. So no matter what the surgery, what they're finding is that if you have a stronger deltoid going into it, you have better outcomes coming out of it. Right. So say we had a patient who, you know, they've come, they've been seeing us for a few months, conservative methods of rotator cuff for rotator cuff tissue healing. Right. And they're like, you know what? I'm still in pain. I think I'm going to get the surgery. And you're like, great. Let's keep hammering that deltoid. Right. You have six weeks until surgery. Six weeks is a great time for some progressive overload, some hypertrophy and strength building to that deltoid. It's only going to set you up for more success post-op. So I believe Paul will be putting out some research for that or a post about post-operative implications with deltoid strength today. So look for that on Instagram. Next, we have our hypermobile shoulders. So when we think about shoulder instability, may have had some recurrent subluxations or have had trauma to this area where some of those passive structures have been stretched or maybe aren't doing the job that they were meant to do, right? When we think about the detrimental effect of not having a deltoid, not having the ability to maintain that humeral head in the glenoid fossa or at the glenoid fossa, like how detrimental that can be to upper quarter function. We know that strengthening the deltoid, or we should know, we should implicate that the strengthening of the deltoid would significantly improve their tolerance to loading that shoulder girdle, right? So we kind of, you know, you think about, we're always hammering people with rotator cuff exercises. And sometimes I think we forget about the big guy of the deltoid. because we don't necessarily contribute that to maintaining that glenohumeral joint support, right? So we're thinking pre and post-op, we're thinking shoulder instability, and last but not least, we're thinking our older adult population. So this is going to kind of follow into tomorrow, where we'll have the older adult division diving into the importance of deltoid strength in that older adult population. But let's speak a little bit to the research. So as we all age, we know that we have some sarcopenia that typically occurs, right? So we have a little bit of change in our muscle mass. And when we look at independence in the older adult population, one of the things that helps folks maintain their independence is being able to lift things overhead, right? Their overhead capacity. So deltoid not only does that movement, but as we age, what we find is we have a shift in fiber type or maybe mass. And we'll talk about that gender specifically. So males, as they age, they don't necessarily see significant atrophy in the number of fibers or the overall size of the deltoid. But what they do see is they see this shift from type 2 fibers to type 1 fibers. So we have atrophy of type 2 fibers and more preferential activation of type 1 fibers, which is going to limit their power producing ability in the upper quarter. Females, it's a little bit different. We don't see that shift in fiber type, but what we do see is we see general atrophy, right? So we see loss of muscle mass in the deltoid, which is significantly going to impair their independence with that overhead movement. Don't want to steal too much of that for tomorrow, but three main patient populations that may benefit from a more robust deltoid, pre and post-op, hypermobile or instability, and then the older adult population. SUMMARY So today we kind of dove into all things form, function, and clinical application of the deltoid. Hopefully we can get this post up onto Instagram so our folks over on Instagram can also enjoy today's content. So for those that are looking to learn a little bit more about the deltoid, head on over to our Instagram. This whole week we're going to be posting different things of how to load the deltoid. Paul will be posting some different ways of how to needle the deltoid to access both the anterior and the posterior shoulder in different positions. So head on over to Instagram and check out those posts this week. If you're looking to join us on the road, Paul and I will both be Doing a lower quarter course at the end of this year, we have a few upper quarter courses remaining this year, where you can learn how to, you know, needle the upper quarter and particularly the deltoid. So hop on to PT on ice. Yeah, ptonice.com to check out some of those courses coming up this fall, and I hope to see you on the road. Have a great Tuesday.

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