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Hip Joint Center

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  • Hip Joint Center

    Hello everyone,

    I have a question for the gait people out there. Is there a good way
    to locate the center of the hip joint without measuring
    BOTH ASIS points and the spine. Due to camera
    limitations I can only get one ASIS. I have been collecting data on
    normals and patients and am now in the process of predicting ankle,
    knee and hip loads during various tasks. The markers that I have been
    collecting (which are relative to the hip joint) are the knee, greater
    trochanter, a point on the front of the thigh-midway between the knee
    and hip, the ASIS, the PSIS.

    I have looked in the archives and found references to work by Bell et
    al. (J. Biomech 23(6), 1990 and Hum. Mvmt Sci (8), 1989) and Seidel et
    al. (J. Biomech 28(8), 1995). Although these papers are good, they
    all depend on knowing the pelvic width. I have seen reference to work
    by Cappozzo (Hum. Mvmt, Sci 3, 1984) which is based on the assumption
    of the thigh being rigid and rotating about the hip joint. This
    method may prove useful but it's not ideal because we are studying
    walking and stair climbing, and not simply moving the joint through a
    simple arc.

    In trying to calculate the HJC from the data that I have, I have
    formulated a system of equations. However, I have a made a couple of
    assumptions in order to complete them. Thus I appeal to you in the
    community for any input. I will describe the equations.

    1. Since I do know the location of the ASIS on the side that I'm
    interested in... and can measure pelvic width with a tape measure, one
    of the equations is a sphere centered around the ASIS with a radius of
    38*(Pelvic Width). This is based on the Bell paper stating the
    location of the HJC in relation to the ASIS. Using Pythagoras, I came
    up with a radius of .38* Pelvic Width.

    2. The markers placed laterally on the knee and greater trochanter
    define the long axis of the thigh. I have found reference to the
    angle between the long axis and the femoral head to be 115 to 125
    degrees. Incorporating that information, I can say the dot product
    between the shaft and the line joining the greater trochanter to the
    HJC is sin of 120 degrees. There will be some error associated with
    this, which will depend on the length of the femoral neck.

    3. In the third equation, I want to relate the distance from the
    greater trochanter to the HJC, to the distance from the knee to the
    greater trochanter. This is the information that I have been looking
    for, unsuccessfully.

    If this data is available somewhere (femoral neck length as a
    proportion of shaft length), can you please point me in the
    right direction. This nonlinear system of equations can solved
    iteratively for the three dimensional coordinates of the HJC. I would
    appreciate any input into alternative methods, errors that I will
    encounter, or insights into the limitations of what I am attempting.
    Thank you for reading through this post and your thoughts on the
    matter. I will summarise replies and redistribute shortly.