Science Buddies: "Ask an Expert"

Hi,

I have a few questions. I am a bit confused about the project "Deep Knee Bends: Measuring Knee Stres with a Mechanical Model". The objective of the project is to calculate the amount of strain put on the patellar tendon when the knee joint is bent at different angles. However, in the description the guitar string is described as the quadricep tendon. Why is this? Further, while doing my research I found that in order to find the spring constant, I have to calibrate the spring. Do I use the slope of my results from the spring calibration to find the spring constant? Finally, if we are measuring the amount of strain put on the patellar tendon (guitar string), then why are we using the spring to figure out how much force is being applied?

Any information would be helpful. Thank you!

I agree that the terminology in this idea is rather confusing.

It looks to me like the quadricep tendon is the part that's attached to the muscle, and it continues over the patella to become the patella ligament. (you can google for the difference between tendons and ligaments) So it doesn't really matter which one you measure the tension on, because they are basically the same.

Regarding the spring constant, yes the slope from your calibration is the spring constant. You're using it because the string pulls out on the spring when the joint is bent. The stress on the string is the same as the stress on the spring (which is logical, because otherwise the spring would compress or expand).

Hi Ray,

Thank you for clearing things up! However, I was wondering if I still refer to the patella tendon as the patella tendon or as the quadricep tendon.

Once again, thank you!

Experts for anatomy questions are over in the life science forum. Here is one http://www.arthroscopy.com/patendrep.htm semi translucent drawing showing the quadricep tendon fiber bundle with some ligament attachment to the patella bone, additional fibers crossing over the patella bone and becoming ligament attachments to the tibia. All wrapped up in this are other ligament fibers that attach the tibia to the patella. The mechanical model is an over simplification of this intricate over/under lapping bundle of ligament/tendon fibers. If you really want to refine your word choice, post your question in the life science forum with a reference back to this question.

All I can say for certain is that "quadricep tendon" is clearly the end of this interwoven libament/tendon bundle that attaches to the quadricep muscle bundle. I'm guessing that "patella tendon" would be those parts of the ligament/tendon bundle that go over the patella bone and attach to the tibia and "patella ligament" would be those portions of this bundle that attach the patella bone to the tibia; however, there has to be yet another name involved to distinguish the ligament that attaches the patella to the quadricep. I suspect only pathologists and orthopedic surgeons care about the subtle distinctions in wording so they can be precise in discribing things to others who care about that level of distinction.

In this experiment we're supposed to measure the relative stress on the patellar ligament, but the guitar string represents the quadriceps tendon. Another response said that it's basically the same thing, but it still doesn't make sense because they are connected to different bones besides the patella. If I'm supposed to find the relative stress in the patella ligament, then why does the string represent the quadriceps tendon? Thanks in advance!

By the way I need a response as soon as possible because i need the research area of the science notebook done by Monday.

Hello?

Sorry for the slowness of this response. It's a bit outside of normal science fair season...

Anyway, the comment that they were "the same" was referring to the tension, not the identity of the tendons and ligaments in question.

Since the system is "in equilibrium", and force can freely transfer from one side to the other, the tensions on the 2 sides are the same, so it doesn't matter which one you measure.