Time to learn about motion and the lower extremity!

General kinesiology and anatomy of the lower extremity:

Alright, so I figured I needed a basic lesson on terms I'm going to be using consistently in this blog. The material may seem kind of dry, but it's important to know if you ever want to describe specific movement. This is important because the more specific you are when describing something to a healthcare professional, the more information they can work with. I figured I'd start with the base of our bodies – the lower extremities. The lower extremity consists of the foot, ankle, leg, knee, thigh, and hip. At each joint there are specific movements that occur. Very quickly though, let's define the anatomical planes.

I'm sure most of you have taken Algebra 2 or Trigonometry (or whatever) at some point and learned about three dimensional graphs with x, y, and z axes. If you look straight down one axis, you get a plane that only includes two of the measurements. Essentially, those who deal with the human body have arbitrarily named them relative to the position of the person. These planes are the frontal, sagittal, and coronal planes. You are looking at the frontal plane when you look straight on at an individual. For the sagittal plane, you would be looking at the side of an individual. And lastly, with the coronal plane, you would be looking down on them from above (or up from below). Please refer to the image on the right. These are extremely important to know because certain motions occur in certain planes. For example, flexion of the hip and knee occur in the sagittal plane. I just wanted to present these to you because I'll refer to them later.

The ankle itself has multiple joints – the main/obvious ones being the talocrural joint and the subtalar joint. These are fairly self explanatory if you know the names of the bones. The talocrural joint is between the talus and the crus. The talus is the bone on the bottom of the ankle and the “crus” (crural) is Latin for leg. This is the joint between the talus and the leg. Refer to the image on the right. It is responsible primarily for the motions of dorsiflexion and plantarflexion (image below). Dorsiflexion occurs as your foot comes up toward your shin. This is a sagittal plane motion.

Plantarflexion occurs as your foot points away from your shin. The next joint, called the subtalar joint, is just as it sounds. If you look at the first picture, it's the joint directly below the talus. This is responsible primarily for inversion and eversion. Inversion occurs when you move your foot inward and you can see more of the inside of your foot. Eversion occurs when you move your foot outward. Refer to the image below. This is a frontal plane motion.

The ankle is relatively complex due to the involvement of the foot, which has dozens of joints that can modify the way the ankle performs. For example, in running, a common problem is excessive eversion (or over-pronation). This can be caused by a foot deformity OR (more commonly) it can be caused by a lack of dorsiflexion range of motion. Why would this occur? Well, due to the orientation of the talocrural and subtalar joints, motion doesn't strictly occur in the sagittal and frontal planes respectively. This is where you may have heard the terms pronation and supination. These terms are dirty, highly general descriptions of the motions that are coupled together in normal ankles.

It's a “dirty” description because it doesn't say anything about proportion of movement (for example ratio of dorsiflexion to eversion). Pronation can occur at both the talocrural and subtalar joints and involves dorsiflexion, eversion, and abduction (a hyper specific term not necessary for general discussion). Well, reduced dorsiflexion range at the talocrural joint can result in compensation at the subtalar joint. The subtalar joint undergoes pronation because there is a slight dorsiflexion component to it. The bad part is that there's also massive eversion motion that occurs to get that dorsiflexion. It's that eversion that flattens the foot arch and causes a lot of problems with running mechanics, shock absorption, and overuse (like posterior tibialis tendonitis, plantar fasciitis, etc). This is something I'm sure we'll get into at another date when I'm answering questions. Now let's move onto the knee.

The knee is one of the simplest joints to describe with regards to motion. It simple undergoes two movements: flexion and extension. Extension occurs as you straighten your leg out while flexion occurs when you bend your knee toward your butt. It's that simple, but if you have problems here's a picture . This is almost purely a sagittal plane motion. The knee can experience side-to-side, frontal plane motion, which is abnormal. These are induced by varus (pushing the knee outward) and valgus (pushing the knee inward) forces. Refer to the image below. Your knee ideally is not supposed to move very much in the frontal plane so resisting those forces with hip musculature activation is key.

Well that was quick and easy, right? The hip isn't as friendly, but it's pretty straight forward. Because the hip is a ball-and-socket joint, it can move in all three planes (frontal, sagittal, and coronal). The sagittal plane motions, like the knee, are flexion and extension. Flexion occurs when you bring your thigh toward your chest while extension occurs when you bring your thigh back (image right) . In the frontal plane, abduction and adduction occur. Abduction occurs when you bring the thigh away from the midline of your body, while adduction occurs when you bring it toward your midline. Refer to the above image for that as well. Lastly, the hip is able to rotate in the coronal (also known as the transverse) plane. These motions are coined internal and external rotation. Since we haven't reviewed much anatomy and don't have anatomical landmarks to describe this motion, I'll just describe it in reference to the foot. If you rotate your hip and your toes point outward, that is external rotation. If you rotate and your toes point inward, that's internal rotation. Refer to the image on the right.

When you think about motion at each individual joint, use the landmarks directly around it (for the knee, think what's happening between the relationship of the thigh and the leg). People get easily confused sometimes when they see the motion occur with complex movements. For example, with the squat, you must undergo movement at each joint. Think about it – what movement occurs at the hip? The knee? The ankle? I'll post the answers at the end of this so you can practice.

Overall, knowing these provides a foundation for everything else I'm going to talk about – muscle actions, lengthening musculature (stretching), limitations in ROM, compensations, everything. I know it's not the most stimulating info, but it is info you should know if you're active. To be honest, I think there is some basic information everybody should know about their own bodies. General joint motions are one of them. They provide a tool for precise communication and allow for you to describe human movement. If you'd like, give me some feedback on the article or questions you may have. Also, let me know if you'd prefer for me to go more in depth on lower extremity stuff (anatomy, muscle, kinesiology, sport specific stuff) or if you'd like me to move onto the trunk and upper extremities. I don't know how large the response to this stuff will be, but I may or may not be able to get to all of your questions. Thanks for reading.

+Brent

Answer for squat: hip flexion, knee flexion, ankle dorsiflexion (mostly at talocrural joint).