Originally Posted by 2-turn
I don't know what you're trying to say, but what Starthaus said is that a binding's release setting is not to protect your knee from ligament damage. Release settings are set to release before there is enough torque to break your lower leg.
If your ligament is put in a dangerous position, healthy or not, it will tear way before the binding ever feels enough torque to release.
OK, I'll try to restate more clearly: Starthaus's second point I quoted does not follow from his argument. Why? Well, the first premise we all agree on: bindings are designed to release upon achieving a certain load transmitted through the hard skeleton. The second premise we also agree on: Ligaments have less mechanical strength than bone and therefore if loaded will tear before bone will break.
But Starthaus's conclusion - that bindings will not protect ligaments from injury - does NOT follow from these premises.
Why? First because binding release for a particular F is engineered to be well below the F required to break bone (call this a margin of safety to make the lawyers happy), and this puts releases within ligament strength ranges. Just think about it; if it were not so, we'd be seeing far higher percentages of breakage and corollary ligament damage out of total releases. We do not, and it's not just blind luck of the fall.
Bindings just do not put joint soft tissue in as much danger as Starthaus implies because they are not designed to release close to bone failure. Yes, obviously you can max your DIN and get to that point, which is well past the safety zone for ligaments, but that's not how bindings are designed to be used. (You can also just screw your boots to the skis, which is cheaper than bothering with a binding and saves 7 lbs of weight per ski.)
Second, I suggested his conclusion needs qualification because many skiers have ligaments that are already stretched and less compliant from old injuries. As a result, the ligament is never under full load; that falls on the cartilage, or worse, the bone, directly. So a key piece of one of his premises (ligaments fully loaded) is not met. A lot of us have sloppy knees.
Put another way, stretched ligaments are not actually supporting the knee through part of its range of motion and therefore are not part of the mechanical system transmitting force. As you know, this is why rehab works on building up large muscle groups that can take over some of the load bearing from the ligaments. The ligaments are already out of the loop, biomechanically speaking.
Now about your own argument: First, cannot quite see what you mean by "dangerous position." If you mean, "at risk of immediate tear from the forces already acting on it," then IMO your argument is circular. You're saying that an extended taut ligament ready to tear (in dangerous position) is ready to tear (at release in dangerous position) before the bone breaks. Well, yes, but so what? My point was rather that not all ligaments are taut and extended and ready to tear at release.
Or if "dangerous position" simply means loaded, period, a ligament's risk of being in a "dangerous position" depends on the effective length of that ligament and its relation to other load bearing structures in the knee joint as force is applied. Thus my point about previously injured ligaments. They have longer effective lengths and less elasticity. They will not tear when a shorter, fully extended ligament will.
Or we can look at this empirically: The literature I know doesn't support your assumption ("healthy or not") of no significant difference between responses of healthy vs previously injured ligaments to loading. Nor am I aware of any data that shows that ligaments will inevitably tear before a binding "feels" enough torque to release. Unless you're just restating the earlier premise, that ligaments aren't as strong as bone and will tear before it will break, and sure, you're right.
Finally, why do I bring up braces? Because the literature again shows that previously injured ligaments will not much aid the meniscus cartilage/articular surfaces in dealing with new forces. So the brace appears in most studies to do some of the work. The joint, you might say, is sloppy enough to benefit. As you know, and as I stated, braces are ineffective in preventing injury to healthy knees because of insufficient slop: the difference between the time it takes to tear a fully loaded and extended ligament and the time it takes for the brace to stabilize the leg externally and handle enough force to prevent the tear.