Hi all, my apologies if this has been discussed previously;
I work in a clinical motion capture lab and we analyze gait and more recently, sports motions. We always (when appropriateness criteria are met) use a posthoc knee-axis correction (KAC) algorithm to 'correct' the thigh coordinate system, with the optimization goal of minimizing cross-talk between the sagittal and coronal planes (adapted from Baker et al. 1999).
Our thinking was that if we are doing KAC for gait because manual identification of "the correct knee axis" is difficult (in quotes because the knee axis is not static, so any chosen static knee axis is not 'correct', but simply a result of our selected optimization), the same issue may result for sports motions. However, we also though that if we are seeing a different range of motion (RoM) in sports motions (up to 90deg), whereas in gait we are seeing less (60deg), should we also be performing the KAC on an activity representative of the effective RoM for sports motions?
To test what effect this would have, we collected deep squat trials from participants, and ran our KAC on both their gait, and their deep squat, and they are indeed different.
Rather than reasoning the difference, I'd like to explore why/if a KAC should be based on different data (gait vs squat), and if an estimated singular knee axis should always be determined based on the activity being investigated - i.e. large knee RoM activity, use a large RoM for KAC
And should it matter much of the joint is loaded during the trials on which a KAC is performed? Does the knee axis also change in loaded vs unloaded conditions?
I know some labs use the Knee Alignment Device (KAD), and I wonder if there is an analagous situation for that method - is it crucial to identify the KAD attachment points based on the full knee RoM that is expected in the recorded activity?
A 6DOF knee joint might make this a moot concern, but we've unfortunately not been able to implement a marker model for a 6DOF knee that doesn't introduce evident non-physiologic translation between the proximal and distal segments..
Lastly - please feel free to comment just to say that you have a knee axis identification method that you never question! It doesn't seem like there is consensus on this in the field, but please tell me if I'm wrong.
Thanks all!
Tim
I work in a clinical motion capture lab and we analyze gait and more recently, sports motions. We always (when appropriateness criteria are met) use a posthoc knee-axis correction (KAC) algorithm to 'correct' the thigh coordinate system, with the optimization goal of minimizing cross-talk between the sagittal and coronal planes (adapted from Baker et al. 1999).
Our thinking was that if we are doing KAC for gait because manual identification of "the correct knee axis" is difficult (in quotes because the knee axis is not static, so any chosen static knee axis is not 'correct', but simply a result of our selected optimization), the same issue may result for sports motions. However, we also though that if we are seeing a different range of motion (RoM) in sports motions (up to 90deg), whereas in gait we are seeing less (60deg), should we also be performing the KAC on an activity representative of the effective RoM for sports motions?
To test what effect this would have, we collected deep squat trials from participants, and ran our KAC on both their gait, and their deep squat, and they are indeed different.
Rather than reasoning the difference, I'd like to explore why/if a KAC should be based on different data (gait vs squat), and if an estimated singular knee axis should always be determined based on the activity being investigated - i.e. large knee RoM activity, use a large RoM for KAC
And should it matter much of the joint is loaded during the trials on which a KAC is performed? Does the knee axis also change in loaded vs unloaded conditions?
I know some labs use the Knee Alignment Device (KAD), and I wonder if there is an analagous situation for that method - is it crucial to identify the KAD attachment points based on the full knee RoM that is expected in the recorded activity?
A 6DOF knee joint might make this a moot concern, but we've unfortunately not been able to implement a marker model for a 6DOF knee that doesn't introduce evident non-physiologic translation between the proximal and distal segments..
Lastly - please feel free to comment just to say that you have a knee axis identification method that you never question! It doesn't seem like there is consensus on this in the field, but please tell me if I'm wrong.
Thanks all!
Tim