June 30, 2015 – From a very philosophical standpoint hip arthroplasty is very unfair towards women!!!
Most men will have a socket size of 52 or over and therefore a 36 mms head can be used in all types of hip replacements. The 36 mms head is technically a “large head” and is a good option having serious resistance against dislocation. In addition men in general or not as lax / flexible as women and the risk of dislocation is significantly smaller. However the typical acetabular size in most women is 46 to 50. The small acetabular size in most women will dictate having a ridiculously small 28 mms or smaller head making it prone for dislocation. Added to this is the flexibility / laxity in women which would accentuate the problems imposing lot of restrictions in active
The decision by smith and nephew to withdraw 46 and below BHR head size will impact women all over the world and more so in countries like the U.S and Canada where good alternative options for high performance are not readily available.
In general it is universally accepted that smaller sizes of resurfacing are extremely sensitive to even very mild component malpositioning and therefore risky . The cut off value is deemed to be 46mms head which will have a 52 socket couple. This is the reason for smith and nephew to withdraw the small sizes. Most women will be condemned to a 28 mms or smaller head size in a traditional THR which would be crippling to an active patient. When I see a 28 or smaller head sized THR patient in my clinic ( done elsewhere) I cannot help but feel sorry for them.
I have no doubt in my mind that the best implant for female patients with small bone size is the deltamotion which has incremental head size like the BHR (ie,proportional to the native head size) and thus allows the same functional level postop as the BHR. This begs the question as to why this delta on delta bearing should not be used as a hip resurfacing and thereby avoiding the stem. Alternatives to metal on metal bearing in resurfacing is not new. Ceramic on ceramic seems to be a logical choice and there are design teams around the world that are trying to develop the same. Now that we have the deltamotion socket with an excellent track record , it would be very easy to develop a ceramic femoral resurfacing component. The other option is ceramic / metal on highly cross linked poly resurfacing. Both these type of resurfacings have been developed many years ago.
However there is one technical issue in my opinion that will be impossible to surmount in a non-metal on metal resurfacing even in the long term.
This is the size differential between the femoral and acetabular component. The size differential in the BHR and all metal on metal resurfacings is 6 mms. This is the thickness of the normal cartilage that the resurfacing replaces. This is ideal. E.g. 46 BHR head will have a 52 mms BHR cup etc.
Any other bearing material in a resurfacing will increase this differential ( usually 10 mms) . This is unacceptable. The only way of installing this would be to remove more bone from the acetabulum which would be a disaster in young patients . The other option of removing more bone from the femoral head would decrease offset causing impingement and a compromised result.
It is easy to install these alternative bearing resurfacings in patients but has some serious pitfalls. This would cause more bone loss from a revision standpoint than a THR. If any resurfacing component removes more bone from the socket than a THR , it defeats the whole purpose of bone conservative surgery . Thus the only way of fixing a delta on delta or any alternate bearing would be on a stem. There is no doubt that a hip resurfacing conserves bone on the femoral side which would make revision easy if required. Combining the deltamotion with a bone conservative stem like the Corail would also make revision easy if required. Thus I am very happy to offer this option for very young patients.
The Stryker MDM dual mobility is another option which will address one issue i.e. dislocation . However as there is poly in the dual mobility it may not be appropriate for younger and very active patients due to wear issues. I have
some info on the deltamotion & Stryker MDM dual mobility hip in my new website on complex hip reconstruction3
I allow running and all unrestricted activities with the deltamotion but not with the stryker dual mobility . I use the stryker dual mobility only in older patients ( instead of standard THR) where return to activity is not critical but resistance to dislocation is the only issue. The gender of the patient has nothing to do with survival rates of MoM hip resurfacing and I would always be very happy to do a BHR for a female patient if the size is available.
I hope the above info is useful.
With warm personal regards
Dr. Vijay C. Bose M.S(orth); FRCS(orth) MCh (orth)
Joint Director & Consultant Orthopaedic surgeon
Asian Joint Reconstruction Institute
SIMS – SRM Institutes for Medical Science
No 1, Jawaharlal Nehru Road (100 ft road.) Vadapalani
Chennai 600 026
Ph: secretary +91 99400 73000