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How to restore sovereignty of the hip to prevent dislocation - Dr. David Kirwan on BoneChat #66

9 Mar 2025 · 2 min

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In this segment of the BoneChat #66 podcast, Dr. David Kirwan argues that detailed spinal‑pelvic analysis is unnecessary for preventing hip dislocation if the prosthetic components are correctly sized and positioned. He contends that the commonly cited normal range of hip version (‑19° to +33°) is misleading, because much of the apparent variation actually stems from the obliquity of the knee joint line and the spiral deformity of the femoral shaft, not the hip itself. Kirwan explains that altering femoral shaft length or rotating the femur has negligible effect on hip stability, emphasizing that restoring the "sovereignty" of the hip—i.e., ensuring the prosthesis aligns with true hip anatomy—should be the primary focus for dislocation prevention.

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So the spinal pelvic analysis isn't necessary if you get the prosthesis right. So if 40:20 is correct, maybe it's 40:15, then the stems will match it in any hip, in any patient, in any position, position of the femur, in any position of the spine. If you think about it, if you lengthen the femoral shaft or you shorten the femoral shaft, say by 150mm, 6 inches, what difference does that make to the Hip? None. Okay, so if you then do that osteotomy where you're either lengthening or shortening the femur, instead just rotate it. Rotate it 90 degrees if you like, so the foot's pointing sideways, inwards or outwards, I don't mind. What difference does that make to the hip? None. So we have all this rubbish about— and by the way, normal version is supposed to be -19 to +33 degrees. Rubbish. It's not. You're describing variation of human anatomy with respect to, one, the obliquity of the joint line of the knee, because if the knee joint line is, say, 10 degrees oblique, then the retrocondylar line of the femur is 10 degrees, uh, tilted as well. So if it's varus, then it's going to be internally rotated, etc. So of that so-called normal variation of hip, the version. It's not hip version at all. Um, 10 degrees of it comes from the knee, and that's 10 degrees either way, so let's call that 20 degrees. The other thing, there's this variation in terms of the spine, uh, spiral deformity, the rifling of the femoral shaft. And most of that variation, that -90 to +33 degrees, that 50-degree range of hip version, it's not true. There's a 50-degree range of variation below the lesser trochanter, all outside the hip. And none of that matters to the hip. Restore the sovereignty of the hip.