The ski bindings which hold your boots on to downhill skis are designed to let them jolt free when you crash.
However, most knee injuries from skiing result from the bindings not releasing and the boots staying locked on to the skis.
This is like encasing your feet in plaster casts, bolting crowbars to their soles, and leaping from a moving vehicle on to snow of varying hardness.
It is how most of the leg bone fractures, ligament ruptures and cartilage tears happen.
Of all the skiing patients I have seen over 25 years as a physiotherapist, not one knew how to test if their own ski bindings were releasing correctly.
Here is what you need to know and how you do it yourself, and why you should.
You can adjust the amount of tension with which the bindings hold your boots on to your skis.
It is called the DIN setting.
If this is set too lightly, the boots can release from the skis under normal skiing conditions.
This generally means a tumble, and usually is not too big a deal.
But if the DIN is set too high, the bindings will not release if you fall, and your boots will stay locked on to your skis.
The bad news is that you cannot rely on the ski shops or gear hire to get this right.
Staff training and expertise vary.
The good ones are very good, and will have ski technician qualifications and expertise.
But any skifield gear fitter can make mistakes working through a crowd of impatient skiers, eager to get out on to the slopes.
As well, the official DIN setting is a combination of the skier's height, weight, ski boot sole length, skiing style and age.
It's a first estimate only, and may not fit you or your children accurately.
You can easily do a practical test before you get into the tow queue.
You need a buddy and two types of screwdriver.
Most DIN adjustment screws are slot type but some are Phillips cross types.
You want large-bladed screwdrivers, as the screws are quite large.
The very short shaft types are easiest to fit into a pocket or pack.
(1) To test the back binding release, have the buddy stand across the backs of your skis, then fall forward on to your hands.
The back bindings should release and the heels of your ski boots snap free.
If they do not, then unscrew the big tension screw a figure or so and retest until they do.
Smaller figures mean less holding tension, for example a "2" will release much more easily than a "5".
(2) To test the front binding release, have the helper just kick the toe of each ski boot sideways.
It should pop out with a moderate kick.
If not, loosen the binding and retest until it does.
If the bindings will release in these practical tests, then they'll almost certainly do the same on the slopes when you need it.
The tests will take a minute or two to perform.
If you think that is inconvenient, try a knee ligament rupture.