Dr. Kurtz had an article online that had concerns about the head neck rations of hip resurfacing compared to total hip replacement. We wanted to provide potential hip resurfacing patients with opinions of other top resurfacing surgeons to explain their views.
I read over the discussion of the head-neck ratios and impingement that you forwarded which was very thorough. There is no question that the head to neck ratios of a total hip arthroplasty with a small diameter neck are larger than with resurfacing arthroplasty, especially a metal on metal big femoral head construct. This would translate into less impingement and greater stability which increases as the head size increases. If biomechanics were the only factor involved in the choice of a prosthesis then I would opt for the MoM Big Femoral head type every time. However, there are many other factors to consider including the technique used in the procedure.
As you can see from the discussion even small traditional heads with small necks have a better head-neck ratio than resurfacing and yet in clinical practice traditional hips have a dislocation rate in most series of 3-4% in primary replacement which increases up to about 20% in revisions. This compares with a dislocation rate around 0.3-0.4% in resurfacing series. Factors that explain this dichotomy are the more natural soft tissue balance and more accurate leg length and offset that are associated with resurfacing and the decreased “jump distance” of a small head prosthesis when compared to large head prostheses (the actual distance the head has to move before it dislocates is much less for a small head than a large even though the head-neck ratios may be greater in the small head).
In our series and especially in McMinn’s and Treacy’s 10 year series, late neck fracture has not been a clinical problem so if impingement with a resurfacing was such a detriment we would expect to see 1) impingement pain, 2) decreased range of motion, or 3) late neck fracture. This does not appear to be the case if care is taken technically to not notch the superior neck of the femur during the procedure. Of the late neck fractures reported, the biggest factor seems to be avascular necrosis rather than impingement. Obviously, this is very rare also since the 10 year survivorship for osteoarthritis is 99.6%!
In summary, I agree with the statements presented regarding head-neck ratio and feel it particularly supports using a large head vs. a small head traditional prosthesis. However, clinical results and other biomechanical factors would seem minimize its importance as regards to resurfacing arthroplasty as noted above. The other major advantages of resurfacing in a young, active patient population ( bone sparing, high activity friendly, diminished proximal femur osteopenia, and ease of later revision) far outweigh the theortical considerations presented.