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Articulated Knee Model and Tendon Hammer

Public summary: 

Come and see the complexity behind how your knee works!

A spare plastic skeleton leg, now with added ligaments.
Useful information
Kit List: 

Plastic skeleton leg with rubber ligaments, tendon hammer

Packing Away: 

Lives in Boris' coffin

Frequency of use: 

Articulated Knee Model

-See the Skeletons explanation for things to discuss about bones - e.g. why they are needed (support, movement, protection).

Ideas for What to Do:
-As always, first get the kids to tell you what it's a model of (the leg) and work out what the joints are etc.
-Talk about bones and skeletons (see above).
-Perhaps start with looking at the ankle (or even another spare bit of skeleton) and ask the kids what's different about this model compared to their real leg (there are lots of bits missing - you are not held together with screws!)
-Ask them if they know what holds the bones together in the body (ligaments - could compare these to tendons holding muscle and bone together if they've had a look at the giant hand model). Ask them if they have heard about ligaments before (they may have heard of injuries to cruciate ligaments etc, common injury to occur to footballers)
-The model shows the patellar ligament, anterior and posterior cruciates and medial and lateral collateral ligaments. It also has the quadriceps tendon, which is not attached at the proximal end because it's a tendon not a ligament and attaches to the quadriceps muscle. You could perhaps flex the knee and get the kid to 'be' the quadriceps, pulling on the tendon to straighten the leg. You could talk about the location of the patella (kneecap) and how it is a vital component in how the knee works mechanically.
-Cruciate ligaments - could talk about how 'cruciate' means 'crossed', let them look at how the ligaments cross within the joint. They may well have heard of these being injured in skiing or something. My first year anatomy notes tell me the following: Anterior cruciate - limits anterior draw of tibia on femur, tight in extension, tested by pulling the tibia forwards. You could perhaps show how, if it was ruptured, the tibia would move excessively far forwards. Posterior cruciate - limits anterior slide of femur on tibia, tested by pushing tibia backwards, used on hills and stairs (so if you've ruptured it, you cannot walk down stairs as the femur will slide too far forwards on the tibia).
-You could also talk about what else is missing from the model - evidently there are lots more tendons and muscle attachments, and also the medial and lateral menisci helping to shape the articulating surfaces (again they may have heard of these in the context of sporting injuries).

Tendon Hammer

-try to demonstrate some common reflexes

- what is a reflex? (see below)
-why do we have reflexes (here you could talk about reflexes in general i.e. blinking) - reflexes are there to protect us
-Why would we want to test reflex action? By testing reflexes, doctors can find out if there is nerve damage etc.

It is often difficult to show the reflexes on the kid. A good idea is to try it out on yourself first. If all else fails, you could try to demonstrate some other reflexes; i.e. demonstrate blinking; demonstrate the pupil reflex (get one kid to close their eyes for a bit and then open them; does the pupil size change?) - you can have one kid doing it whilst the others watch and then swap, so everyone gets to see them


- Getting the reflexes to work can often be tricky. Try to find them on yourself/one of the other demonstrators first. (Hitting a bit harder often also helps.)
- If in doubt, ask a committee medic to show you how to elicit different reflexes.

These are some of the reflexes you could try:

- Do they know where any of the reflexes are?
- Get them to relax and try to elicit the reflexes:

A Arm:
1. Biceps: put your thumb on distal bicep tendon and tap that.
2. Supinator: Put your finger their forearm (distal radius over the supinator muscle) and tap it.
3. Triceps: bend their arm and tap distal tricep tendon.
4. finger: Lay their fingers over your index finger and tap your index finger.

B Leg:
1. Knee: get them to cross their legs and tap the patella tendon.
2. Ankle: Sit them on high ledge (if you have one), dorsiflex the foot and tap the achilles tendon.
3. Babinski's: if they've got shoes that are easy to take off, run your finger up the lateral side of their sole.

Most of these won't work in kids, because they don't relax. You could try reinforcement.
i. Upper limbs: get them to grit their teeth.
ii. Lower limbs: Get them to clasp their fingers together and pull.
iii. NOTE: reinforcement only works for a very short period of time so you must do it at the same time as you bang the reflex.
d. If you can't get a reflex there's no point bashing away at the same limb, because your chance of getting decreases each time -; try the other limb.


a. Start with nerves: wires that carry messages from body to brain (SENSORY) and brain to body (MOTOR). If the kids are small, you can say it's a bit like a telephone line - messages travel from one phone to another.

b. There are some things we need to do so quickly that we haven't got time to send messages to and from our brain.
- Can they think of any?
- Use the example of blinking when something goes near eye.
- We also have reflexes in our arms. What do we need those for?
- Ask them if they've ever touched anything that's very hot.
- We also need reflexes in our legs, why?
- Ever stepped on something sharp.
- So we have reflexes to protect us
- Balance?
- Posture - what keeps us upright? Lots of muscles! If we sway forwards some of our muscles pull us back without us having to think about it
- (Also note in both cases the reflexes stop the tendons being stretched too far)


This usually works better if the kids are a bit older:

- why does a doctor want to test your reflexes
-get them to think about nerve damage and how you could assess that
-usually asking is a good idea (i.e. can someone feel something, see if they can move their arm etc.)
-however, what do you do if someone can't talk and doesn't move (i.e. in an accident when someone is unconscious)
-can then test if reflexes still work (i.e. doctors have pocket lamps; they can test the pupil reflex in an unconscious patient)

Risk Assessment
Date risk assesment last checked: 
Sun, 26/01/2020
Risk assesment checked by: 
Date risk assesment double checked: 
Mon, 27/01/2020
Risk assesment double-checked by: 
Beatrix Huissoon
Risk Assessment: 

Leg from full-size plastic skeleton, with added rubber ligaments in the knee joint, tendon hammer

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Protruding parts Poking injury from protruding parts. 3 2 6 Make sure children do not go too near protruding parts; use tape to cover up the more dangerous parts of the skeleton.
Call first aider in case of injury.
1 2 2
Joints Finger trap between bones (e.g. joints). 3 2 6 Make sure children do not put fingers between bones, and ensure that leg is in a stable position when they do touch it.
Call a first aider in the event of injury.
2 2 4
Leg Leg is surprisingly heavy and could cause injury. 2 2 4 Do not leave the leg where it may fall on someone.
Call a first aider in the event of an injury.
1 2 2
Tendon hammer One end of the hammer tapers to a point - risk of getting into eyes. 3 3 9 Do not let children use tendon hammer without supervision, don't let them get boisterous and over-excited with the tendon hammer. Call first aider in event of injury. 2 3 6
Improper hammer use Risk of bruising if used with excessive force. 2 2 4 Use medics who have been taught how to use the hammer, or someone who has been shown by a committee medic how to use the hammer. Do not use tendon hammer with excessive force.
Call first aider in event of injury.
1 2 2