Is it crazy to think about using the differential of distance covered in a lateral bound between the right and left leg to help identify knee valgus, and then use improvements made in subsequent tests to identify improvements in knee tracking and function?
There is a connection between external rotators and healthy knee function, so is this worth adding to my testing regiment?
It is not crazy at all, but it probably isn’t the most efficient approach. If a max effort going each way is asymmetrical, that is a reasonable screen to key you into looking further. The Hop and Stop which is an anterior leap has been shown in the literature to be a valid screening tool for injury. I have never held affinity to the Hop and Stop as a screen, but rather a Return-To-Play indicator.
I like your idea as an indicator, but if that is the focus of the corrective approach, the fix may be a long time in the making. Not only do you have mobility and stability that can be at fault, you are adding an eccentric control component into the screen. I think looking at a lower level movement like Single-Leg Stance or Hurdle Step in terms of a correction approach is a quicker route to culling out the lateral bounding issues as a fundamental issue (mobility or stability) vs. a performance issue (power development and/or eccentric control).
Yes, the connection to ER and knee function is widely evidence-based. My version of the Janda Hip Abduction test is what I use in this regard to implicate basic Hip ABDuction performance vs. rotary stability vs. both.
I coach the setup to be pure/strict sideline. The neck is propped to be centrated and long. The down shoulder can be underneath in a reflexive turning position or in ABD as part of the neck prop.
I will control the torso via the femur as I pull it into extension. I am feeling for stiffness. If the hip can’t extend, there’s no way the person can perform what I am looking for. I will also control the hip into ext/ADD and straight ABD to feel stiffness as well.
Then I centrate the hip in line in the frontal plane. Mild ER is allowed.
I will tell the person I am going to let go on the count of 3. I am expecting a static hold as perfect. Again mild ER is acceptable as that is the neutral centrated position of the hip.
The hip can’t fall, can’t excessively rotate, can’t flex. The torso can’t roll. The top arm, which is on the torso, hand over greater trochanter can’t reach to hold the table.
I will give 2 trys to authenticate the response.
If the leg falls, rolls into flexion/ER, or the trunk falls out (often folks will almost fall right off the table), the breakout is then to hold onto the table as hard as they want with the top arm. If the leg is not in position or at least significantly better, we are looking more at a motor control deficit in rotary stability than a frontal plane hip weakness.
The traditional Hip ABD MMT follows the unsupported position if they can hold it. Then and only then can you grade out hip strength.
Then in the supported position, if the hip grades poorly, you know you have both, a rotary stability issue and a hip weakness.
And the valgus RNT attacks them both in the right movement pattern.
Bottom line is that when you see a little girl go into horrendous valgus collapse, the implication right off the bat can not be weak hips as Chris Powers might suggest. The assumption is the interplay between the hips, pelvis, and lumbar spine, and then the breakout to find where the weak link lies.
And without a doubt, extending to the foot, t-spine, and opposite shoulder can continue to muddy the picture. This test just focuses on the illusion of hip weakness in the presence of a weak core.
I would expect this test to correlate to valgus collapse in the step, lunge, or squat. Correct the movement, reconfirm the test, retest the movement.