Advanced Assessment of Muscle Strength

by Stephen Holt, MD, MS

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    00:00 So, we're going to start with the cervical spine and I always start with the #5 because cervical roots 1, 2, 3 and 4 are more involved with muscles around the neck and they're a little bit more tricky to tease apart and more importantly people rarely get radiculopathy involving those nerve roots. So we'll start with C5 and I like to envision that you draw a #5 and then if you actually tilt that #5 90 degrees and have it flat and then put another #5 mirroring that on the other side we actually start to get the shape of a person who is actually flexing their muscles. They're actually showing off their biceps and at the same time they have got their shoulders abducted, which means that they are flexing their deltoid muscles. So, it turns out that that simple mnemonic helps us to remember that the C5 nerve root is innervating your biceps muscles and your deltoid muscles. "So how about just with your right arm, show me your C5s." So, by him doing this position, he is showing me his deltoids and showing me his biceps. This is the C5 nerve root.

    01:10 Next up, we'll do C6 where I want him to extend his wrist, like so. That's C6. And very simply the other way, it's just lifting your wrist up and that's C7. Now you'll know it by the way when I say strength, you really want to make sure you're isolating one joint at a time. A lot of times I see people when they're testing strength they'll do something like this. "Put your hand up like this and now push me away." When he does this, now he's winning because he's stronger than I am." I am testing his deltoid muscle, the stabilizing forces around his scapula, his rhomboids, he is doing his triceps muscle in this case and his wrist extensors all at the same time. That is not an effective way to assess or to locate a specific area of weakness. So instead, "Go like up this again for me. Now I want you to push me away." I'm now testing a single muscle group. Just the muscles that work around to extend his elbow. So it's important to really make sure you're isolating your muscle groups by going basically just hold between 1 joint and the next to make sure that you're not going to get confused. So again, start off with C5. "Go like this for me and I'm just going to push down." That's his C5s. "Up like this." This is also C5s. Now we'll do C6. "Put your wrist out like this, or flip them over like this, excuse me." And wrist extension and I'm just going to pull up, testing wrist extension. That's C6. "Now have your wrist go up, and I'm going to pull down." That's wrist flexion which is C7. C8 and T1 all involve the interosseous muscles and the muscles of the thumb. It's not important to know exactly which one is which. It's just important to know how to test very quickly the musculature of the hand so I simply do this exercise. "Put your fingers out like this. And we do finger cutting where I just want you to basically squeeze my fingers with your fingers. Perfect. Make an okay sign. And don't let me pull through. Great. Haha. Pulled through but that's okay." "I'm ready." "That's okay, you'll do the same thing on both sides." Anytime you're checking strength, you're always want to be comparing 1 side and then the other to make sure you're able to get an accurate control group in a person who has symptomatology. So this is C5, C6, C7, C8, and T1 are going to involve the thumb, the opponens pollicis brevis and the interosseous muscles here in the hand. So guys we're about to move on to assessing strength. It's important for us to use the right terminology to describe how strong somebody is or how weak they are and there's an accepted scale that we use from 0 to 5, 5 being full strength and 0 meaning we don't feel any muscle activity whatsoever. So 5 strength, "Put your arm up for me like this." And he can push me away with ease. He's got full strength in his triceps in this case. 4 out of 5 is actually broken up into 3 parts; 4+, 4, and 4-. 4+ is 75% strength so he's still going to probably win, but I will be able to fight back. 4 is just 50% strength, it's clearly going to be noticeably weaker. And then 4- is only 25% strength. From 4 to 3, means that if he was lifting his biceps he could lift it against gravity so that's at least a 3. But if I pull down on his arm, he's no longer able to compete against me with gravity. So it means you can only lift against gravity if you have 3 out of 5 strength. "So go ahead and show me 3 out of 5." And I'm going to resist them and now he can't fight back. 2 out of 5 strength is where, while he couldn’t lift against gravity, he can still move the arm left and right which is where gravity is not competing with him. "So just move your forearm left and right there." So that's 2 out of 5 strength." And then lastly, 1 out of 5 strength is where I can feel his biceps tensing, I can feel him trying to move but he actually doesn't have enough strength to actually move his forearm in space. So that will be 1 out of 5 strength as opposed to 0 out of 5 strength which is there's just no muscle tone whatsoever.

    About the Lecture

    The lecture Advanced Assessment of Muscle Strength by Stephen Holt, MD, MS is from the course Assessment of the Neuromuscular and Neurological System (Nursing).

    Included Quiz Questions

    1. C5
    2. C6
    3. C7
    4. C2
    1. 3
    2. 2
    3. 1
    4. 4-

    Author of lecture Advanced Assessment of Muscle Strength

     Stephen Holt, MD, MS

    Stephen Holt, MD, MS

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