Ski Bum said:
that is the essence of biomechanics...each view point will give you another window to look through when evaluating a patient. as you are probably aware of, BM has lots of gray area...not so black and white like other classes you may have taken. you must understand this when applying your knowledge when evaluating your patient and keep an open mind because there is endless variability in regards to functions of the lower extremity...which you will appreciate as you get more experience in the clinic.
Ski Bum,
You seem to have great insight to biomechanics and clinic. How long have you been using the rules of biomechanics in a clinical environment?
I was wondering if you could help me with a concept.
We know that the STJA acts like a "screw with a cone". The axis deviates as motion occurs during stance. What is the range of deviation? What is considered to be abnormal? What ligaments would be affected most severely? Would an excessive supinatory motion during terminal stance cause accelerated external rotation of the hip?
As we know, the tibia has a faster angular rotation than the femur. If there is excessive supination of the STJA during the final stages of stance and directly before it should have began pronation motion to neutral position at toe off, would this excessive supinatin cause the neutral position of the hip joint to be affected, which could lead to hip problems. Would we see more knee flexion? If so, would the additional knee flexion and transverse rotation of the knee joint? If there isn't an additional knee flexion that would counter the extra supination, would the pelvis have more transverse plane rotation to counter the impulse change, or would the pelvis have more lateral rotation? Probably a momentary contribution of both factors. If this is the case, the L5S1 segment would be affected over the long run.
From your clinical experience, what is the best way to treat such a case?
Also, I hate vague test questions that could go either way.
Example: During the end of swing phase and when the foot makes contact with the ground....
What Newton's law of motion describes this interaction?
Then the professor gives all laws as choices.
Let's see.... There is a decrease in velocity and a discontinous change in velocity implies a change in acceleration. There is an continous impulse change in momentum since velocity is changing, and there is a reaction force to the force from the body.
Hmmmm....Can go either way. You can also look at it from the point of view of conservation of energy: As the "body falls" the kinetic energy is increasing and the potential energy is decreasing. Since mass is conserved in classical physics and is appropriate for these dimensions, then the velocity must be changing for KE to be increasing. When the foot makes contact, there is an impulse change in velocity of the extremity and the horizontal force is acting on a "particle" on the plantar surface of the heel. Since mass is constant, this force must have an affect of the acceleration of the lower extremity.
Yet for the GRF action, there is a reaction.... What about the change in momentum. The heel basically stops (not completely) and there is a impluse force between the calcaneous and talus mostly (little transfer of energy to the calcaneocuboid ligaments), and the momentum from the falling leg is conserved by the rotation of the talus, rotation of the calcaneus, and rotation of the tibia, femur, etc... not to mention the "linear" compression of the bones, miniscus, ligaments etc. This compression causes a change in direction of these structures which is a change in velocity and momentum. All lead to conservation of momentum. The real key is conservation of energy though because it is the only way one can truly explain what is happening in a theoretical sence. After all, that change in velocity of the "particle" in the ligament or meniscus is partially a change from mechanical energy to work and heat energy (Internal energy of the elastic component of the meniscus and ligaments). Probably a little enthaply involved also because there is a little "flow" work associated with the viscoelastic materia and enthalpy is internal energy with "flow work" (usually associated with open systems; may also be associated with bonding forces). Not to mention the energy absorbed by the synovial cavity.
Anyhow, back to studying. I just thought some of the questions were very subjective.
Different experiences leads one to see something differently. Different minds think differently. If a question is created and then you take the class average response to decide the "best answer", is this really the best answer?
It is true that N minds are better than ni minds (where N=Summation of ni), but not in every situation. As an example: I went to the planatarium in chicago and participated in the "space ship navigation" where each seat had up, down, left, and right controls. I think there were 100+ seats and each seat was occupied by a person who made a decision on which "control direction" to push based of their perception of the space crafts potential place in space. A computer then averages all inputs and makes a final decision based on the greatest number. Initially, we were in open space and I noticed that it was quite rare that the ship went in a direction that I chose (probably based on random probablility more than anything since each person theoretically had "independent choices"). When we entered the canyon, we were now influenced by what we saw on the screen (we could only go slightly left/right/down and almost always up) so the "experiment was biased" On each try, we crashed very quickly. (kind of like star wars and flying through canyons).Did perception play a crucial role? The people on the far right may have percieved that we were to close to the left wall and over compensated. People on the left may have thought we were to close to the right wall and over compensated. People in the middle may have compensated more appropriately but saw the distant "curves" differently and attempted to anticipate a slight directional change which could have caused over compensation. In addition, were the seats appropriately balanced?
I could create a question and ask: The space ship was going in a straight line, changed direction and crashed..... What caused this?
Pushing of buttons
Peoples perception
Distribution of people in the seating
Back to studying
