Biomechanics 3 Midterm Flashcards
(24 cards)
- What is the difference between stress and load?
Load - amount of force on an object
Stress - load divided by the cross sectional area
- What is the difference between deformation and strain?
Deformation – change in length in response to a load
Strain - change in length divided by the original length
- What are the 5 categories of injury mechanisms outlined in the notes?
High load (single traumatic event). Repetitive loads (end range). Sustained loads (end range) e.g., postural syndromes Sudden unguarded movement. Normal activity coupled with a failure of segmental coordination (especially in an unstable joint)
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- The ACL is stretched but is able to return to its original length. This is due to what?
The elastic property of the collagen.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
Will the cruciate return to its original length immediately? If not, what would we call this temporary deformation?
It may immediately return to its original length but more likely will undergo a temporary lengthening – deformation – and we would call this the “set”.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- It will temporarily lose some of its ability to absorb another blow. What property of viscolelastic tissue is this called?
It will lose energy and stiffness. We call this hysteresis.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- Where on the stress strain curve would you think there will be microscopic tearing and perhaps symptoms. (Think percentage.)
For ligaments this can happen at as little as 4% ultimate strain.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- What is the difference between load and stress?
Load - amount of force on an object – shear, tensile and compressive
Stress – amount of force on an object over a cross sectional area – shear, tensile and compressive
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- What is the difference between deformation and strain?
Deformation – change in length in response to a load
Strain – change in length divided by the original length - % and radians for shear
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- Stress/strain curve- at what point do you think the cruciate would not return to its original length?
When it enters the plastic range.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- Stress/strain curve- at what point do you think that the whole cruciate would fail? What would you call this?
On your graph region 5. We call this ultimate strain and material failure.
Case 1. Your patient’s tibia is hit from behind creating a sudden load on the anterior cruciate ligament.
- Is the cruciate ligament more ductile or more brittle?
Since its ultimate strain (US) is 6-8%, it would be more ductile. Remember, <5% (US) is considered more brittle.
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- What is likely wrong with this patient (what lesion or diagnosis do you suspect)?
Possibly a compression fracture in their spine.
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- Where is the most likely location of this lesion?
T/L junction (T10-L2)
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- What sort of force did her spine sustain?
Sudden compressive load
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- The vertebra was hit by a force generated by well over 200 pounds distributed over the small surface of the T12 end plate. A word to describe this phenomenon would be… elastic deformation, plastic deformation, load, stress, strain, or creep?
This one is a little tricky. Remember that it mentions a surface area in the description. So instead of saying load, the answer would be Stress.
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- In biomechanical terms, did she sustain a strain?
If there is indeed a change in length (height) from the original then yes.
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
- You measure a ½ inch loss of height of the T12 vertebrae. This loss most correctly would be termed… elastic deformation, plastic deformation, load, stress, strain, or creep?
Since we are given a specific measurement and not a % change, the answer would be plastic deformation
While snowmobiling, your patient drove over a mogul, her and her vehicle became momentarily airborne and landed hard. The patient complains of a sudden onset of low back pain. Answer the following questions.
Is this injury likely to be stable or unstable?
Stable but painful.
Your patient broke his forearm playing rugby. With his armed pinned between two players, a third player fell on the middle of his forearm.
- What sort of force did this patient’s forearm sustain?
3 point bending
Your patient broke his forearm playing rugby. With his armed pinned between two players, a third player fell on the middle of his forearm.
- What side of the arm is the fracture most likely located
At the site where the 3rd player fell on his arm. The fracture would be on the side of the bone were the tensile load was. Think of the boot top hitting the tibia. The fracture would be on the posterior side – tensile side.
Your patient broke his forearm playing rugby. With his armed pinned between two players, a third player fell on the middle of his forearm.
- Is this fracture likely to be stable or unstable?
Probably unstable if it went through the bone – remember the forearm x-ray in lecture.
Your patient twisted his leg, fracturing his tibia.
Twisting is a combination of what types of loads/forces?
A combination of shear, tensile and compressive loads.
Your patient twisted his leg, fracturing his tibia.
2 Draw the expected fracture pattern, and referring to the loads/forces involved explain why he has this pattern.
Bone will fracture first along the shear stress lines and then along the tensile stress lines.
