Saturday, September 17, 2011

A guide to anatomical terms of location and movement for the runner

Introduction

Don't you hate it when you can't find your "distal process on the medial tibial surface"? Or when your doctor tells you that a problem with your posterior tibial tendon is causing excessive foot inversion and possibly decreased knee flexion? Do you ever find you can't tell the difference between the anterior inferior iliac spine and the posterior superior iliac spine? Or just find yourself stumped when your coach tells you you're dorsiflexing your ankle too much? Well have no fear.  Today we're going to decode the mysterious language of anatomical terms of location.  It's a set of vocabulary that describes the orientation and movement of different parts of the human body.  You might wonder, "Why don't we just use 'front,' 'back,' 'inside,' 'outside,' 'up,' 'down,' etc.?" I used to wonder that too.  But I quickly found out that these everyday terms of location are too ambiguous and vague for precise medical use.  For example, do shin splints hurt on the "front" of the shin, or on the "inside"? Is the kneecap in "front" of the femur, fibula and tibia, or on "top" of them? Does turning your foot "in" involve rotating the whole foot or just rolling the ankle? Anatomical terms of location dispel these ambiguities.  Doctors, trainers, and others need to be able to clearly communicate exactly what area of the body they are talking about.

While doctors, trainers, and physical therapists are already well-versed in translating from "normal" speak to medical terms, it is also in your interest to learn them as well.  If your physical therapist mentions that you have some tightness in the medial head of your gastrocnemius, it'd do you well to know what he's talking about.  Additionally, when doing your own research on injuries, rehab, training drills, or biomechanics, you won't make it very far without a good understanding of these anatomical terms of location. Even in this blog, I try to do my best to translate medical mumbo-jumbo whenever possible, but often it's unavoidable.

So, without further introduction, we'll cover most of the terms that a runner will need to know.  I've omitted pretty much all terms having to do with the upper body, as they are mostly irrelevant to the runner, and as such, even I haven't bothered to learn them yet.  The upper spine, shoulders, and hands in particular can move in very complicated ways, making describing their anatomy a difficult feat.  If you've learned anatomical terms of location for other animals, do your best to forget them! For some strange reason, the terms used for a human do not mean the same thing for a fish, for example.  A shark has a "dorsal fin," but on a human, we'd probably call a similar structure in the same location a "posterior fin"!

Terms of location

Anatomical terms of location are relative to the center of the body.  It's best we introduce the planes of the body now, as most the other terms are relative to the centerlines of each of these three planes.  As illustrated in the picture to the left, the body can be bisected by three different planes (in the xy, yz, and xz directions).  The sagittal plane divides the left and right halves of the body.  The frontal or coronal plane divides the front and the back of the body.  The intersection of the sagittal and frontal planes creates the centerline of the body—it runs from the top of the head through the bottom of the pelvis and between the legs.  Finally, the transverse plane divides the upper and lower halves of the body.

Because the body is almost exactly symmetrical in the sagittal plane, the centerline of the body is used as a reference when describing the location and orientation of various parts of the body.  When learning these terms, it makes sense work from the center of the body out.



Medial and lateral

Image from myfit.ca
Medial always refers to locations that are closer to the centerline of the body.  In contrast, lateral refers to locations away from the centerline of the body.  The gastronemius, or calf muscle, for example, is made up of two large "heads."  One is close to the midline of the body, and one is farther from it.  The "inside" head is the medial head; the outside head is the lateral head.  Likewise, "shin splints," a common injury that involves pain on the surface of the shin bone (tibia) is referred to as medial tibial stress syndrome because the pain is on the inside (closer to centerline) portion of the tibia.  Likewise, the lateral aspect of the foot means the outside of the foot, since that's the part further away from the centerline.

Anterior and posterior

Image from disabled-world.com
The frontal plane divides the body into anterior (front) and posterior (back) portions.  An easy way to keep these straight is to remember that good posture involves keeping your back straight—hence, posterior for back. Note that, since these terms are relative, you can use anterior and posterior to compare locations that are still on the same "side" of the frontal plane.  So the main part of a vertebrae is anterior to its spinous process (the bony point that juts out from your back) even though the entire vertebrae is on the posterior aspect of the body, and is posterior to, for example, the rectus abdominus muscle.  Keeping these straight is important, as there are many analogous tendons, ligaments, and muscles on the front and back of the body.  So, for example the anterior tibialis has a different function than the posterior tibialis muscle.  They reside on opposite sides of the tibia bone.
Image from eorthopod.com
Now, can you combine what you've learned about the posterior/anterior and medial/lateral to correctly identify the four ligaments of the knee? Mouse over the image to reveal the answers.



It's not always easy to remember these right away, but at least now you understand why each ligament has its own respective name.

Distal and proximal

Distal and proximal relate locations relative to the center of the body.  Something distal (think "distant") to another object is further away from the body's center.  So the tibia is distal to the femur.  Proximal simply means closer (think "proximity").  So, let's suppose we read an article that talks about the "proximal tibiofibular joint."  The tibia and fibula, the two long bones that make up the lower leg, touch (and presumably form a joint) at two points: near the ankle and near the knee. So our article must be talking about one of these two points.  The joint near the ankle is further from the center of the body than the joint near the knee, so that one must be the distal tibiofibular joint.  So the joint of concern is the one at the knee.  Decoding medical mumbo-jumbo isn't so hard now, is it?

Superior and inferior

Locations towards the top of the body (the head) are superior to a reference location below it.  Likewise, a location is inferior to another if it is closer to the feet than the other.  As an example, the femur is superior to the tibia.  Usually, though, superior/inferior are used to differentiate between two similar structures.  It's a fairly rare pairing, and is mostly used for the various surfaces and bumps of the pelvis, which has a very complex shape.  The picture below illustrates the use of superior/inferior to differentiate between different structures.
Image adapted from home.comcast.net/~wnor/
Greater and lesser

The above picture also illustrates the usage of greater and lesser as terms to differentiate between two similar structures or locations.  They aren't anatomic terms of location per se.  They are used only when there are two similar structures, one larger or more prominent than the other. It's only rarely encountered in lower-body anatomy.  One example is in the trochanters of the femur.  As the femur rises towards the hip joint, there are two large bony protrusions.  One, the greater trochanter, makes up the outermost part of the femur.  You can feel it jutting out on the outer surface of your upper thigh.  The other protrusion, the lesser trochanter, faces inward.  The two were obviously labeled according to their size, though there is no standardization of this.  One could easily picture doctors in the early days of anatomy deciding to name these the "lateral" and"medial" trochanters, but this was not the case.  So if you hear about a "lesser such-and-such," realize that there is invariably a "greater such-and-such," probably in close proximity to its partner. 

Dorsal and plantar

These terms are used exclusively for the feet.  The dorsal surface of the foot is the top, and the plantar surface is the bottom.  That's all there is to these! They'll come up again when we talk about anatomical terms of movement.

Terms of movement

 Now that we have locations more or less figured out, we can talk about how the body can orient and move itself in three dimensions.  The lower body is magnificently complex, and the joints can combine to move the limbs of the body in many different ways.  "In," "out," "up," and "down," just aren't sufficient to accurately describe how the legs and body can move and rotate in space.
Prone and supine

Prone and supine actually refer to position instead of movement, but they are still important to know regardless.  Simply put, a prone position is lying on your stomach, and supine is lying on your back.  Remember that Pushups are done in a Prone position and Situps are done in a Supine position.

Flexion and extension

These terms describe how a muscle is moving a joint.  In the runner, they apply principally to the spine, hips, knees, and toes.  A joint is essentially a pivoting connection between two bones.  You can describe the position of the joint and its motion by measuring the angle between the two bones, across the joint.  So movement of the knee can be described by the changing angle between the femur and the tibia/fibula (shin).  Flexion is a motion that involves decreasing the angle a joint forms: bringing your heel towards your butt is knee flexion.  Likewise, bringing your knee towards your chest is hip flexion.  Colloquially, flexion is roughly the same thing as "bending," although not always: a "back bend" is actually a form of extension, not flexion.  As you might guess, extension is simply the opposite: it occurs when the joint angle increases.  So, straightening your knee or pushing backwards from your hips are forms of extension.  A clever reader might realize that "increasing the angle between the bones" is not a reliable definition for extension: using the tendons on the top of your foot to pull your toes away from the ground, for example, is an extension, and arching the back is too, but both of these motions technically involve bending a formerly-straight joint.  There are also problems as to what side of the body the "angle" is measured from.  In these cases, memorization is your best bet. 


The ankle: dorsiflexion and plantarflexion

Image from legacy.owensboro.kctcs.edu/GCaplan/anat/Study Guide
The ankle is a very complex joint and can move in all three planes at once.  These motions are broken down by the plane in which they occur, even though the various motions can happen simultaneously, and many muscles cause multiple motions (ex. the peroneus longus, which everts and. For some odd reason, the ankle is exempt from the usual flexion/extension terminology.  Instead, the ankle's movement in the sagittal plane (you do remember which one that is, right?) is described using dorsiflexion and plantarflexion.  Because you know that "dorsal" refers to the "top" of the foot, you can probably infer that dorsiflexion involves pulling the top of the foot towards the shinbone, as you would if you were to walk only on your heels.  Likewise, plantar refers to the bottom of the foot, and plantarflexion is pointing your foot "down," as you would if you were to walk only on your toes.

The ankle: inversion and eversion

 First, inversion and eversion are rotations in the frontal plane.  When you "roll" your ankle, that is either an inversion or eversion.  Eversion involves rotating your foot "outward," in that the sole of your foot points away from the centerline of the body.  Inversion is the opposite motion: pointing the sole of your foot towards the centerline of the body—or "inwards."   
Image from legacy.owensboro.kctcs.edu/GCaplan/anat/Study Guide

The hips: adduction and abduction

Image from gla.ac.uk/ibls/US/fab
The hips are even more complex than the ankles.  We've already covered hip flexion and extension above, which are movements in the sagittal plane.  But the hips can also move in the frontal plane.  Adduction is when the muscles on the medial side of your hip pull your leg inward towards your body's centerline.  Squeezing a soccer ball between your legs involves adducting both hips at once.  Abduction is the opposite: using the lateral hip muscles to pull your leg outward, away from your body's centerline.  Like inversion and eversion, the terms themselves are very similar, and it takes many people a while to remember which is which.  They also sound very similar when spoken, so it pays to emphasize the first syllable: abduction vs. addduction. 

The hips: internal and external rotation

Finally, the hips can rotate the femur in the transverse plane.  In a standing position when the knee is straight (extended), this has the effect of pointing the foot inwards or outwards.  These two, at least, are easy to remember: internal rotation occurs when the knee and foot are pointed inward, towards the centerline of the body, and external rotation occurs when the knee and foot are pointed outward, away from the centerline of the body.  If the knee is bent, however, or if the hips are flexed, hip rotation can result in all sorts of foot and knee positions.  Remember that internal and external rotations are motions of the femur relative to the pelvis.  Figure out how the femur moves in internal and external rotation with the hips and knee extended, and it's easy to figure out what's happening when the hip or knee is flexed.  It's important to note that internal and exeternal rotation are tied very closely to adduction and abduction.  Indeed, many of the same muscles control both motions.  In the image above, illustrating adduction and abduction, the man in the photo has slightly externally rotated his right leg, as well as abducting it. However, you can easily prove to yourself that it is possible to do contrasting motions: external rotation with adduction, for example.

Conclusion

Few people will have all this memorized, but hopefully this post can serve as a reference or a refresher if you need to know the difference between, say, eversion and inversion.  While this probably isn't the most enjoyable post you've read on my blog (it certainly wasn't the most enjoyable to write!), it's something I needed to put out so I won't feel guilty diving in-depth into topics where these sorts of terms come up without explaining the terminology being used.  These terms are fairly easy to understand on their own, but the biomechanical magic of the body is that they do not operate independent of each other.  The hips, for example, can be flexed, abducted, and externally rotated, all at the same time.  And the various joints can contort the body into an amazing array of shapes, enabling this sort of display:

Now, can you discern what lower-body motions are happening in this photo? Good luck!

7 comments:

  1. Wow! Thanks so much for taking the time to explain all that! Stumbled across your site while researching leg anatomy to try to figure out a pain that is nagging me and preventing me from fully pursuing marathons (and eventually ultras).

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  2. Clear description, good post. Had to point out however that the description of inversion and eversion of the ankle is opposite to what's shown in the picture.

    Jay

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  3. Whoops! Thanks for pointing that out Jay. Should be fixed now. The image was correct.

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  4. Really useful for AP&P studies, thankyou

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  5. Very informative and well written. Thanks for posting!

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  6. Thanks for a great gathering job.

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