It's also a very tricky scenario when deal with a moderate deficient acetabulum as for choosing the proper bone coverage and abduction of the cup in THA., in case of avoiding bone graf, does anyone have a practical technique and surgic philosophy in this aspect to share with me?
In my opinion there are three options if yo do not want to use a bone graft after the Harris technique: 1. smaller cup and head down to 22 mm; 2. medialization of the head center, that's to say to make a deeper bed for the cup; 3. apply a special cup with enhanced and protruded upper part/arch.
Dr. Tanchev: As for type II ddh, it is possible to achieve a good fuctional result and longevity by altering the cup abduction angle to 60-70degrees to ensure the effective boney coverage of the cup in the case with remarkble upper part deterioration. This might be the furth option add to the techniques you metioned above. But, of course the X-ray is aesthetically not good.
Of course, Dr. Wu, your proposal is also possible. Unfortunately, the x-ray cosmesis is not the only drawback. I have in mind the unhappy situation of repeated dislocations.
I would not propose cup abduction above 45 deg. Cup coverage is usually not an issue in terms of long time stability, it is a question of primary stability. First, put the cup as medially as possible, you can even do a little bit of medial wall fracture (cotyloplasty), then aim the cup abduction angle 40-45 deg. If you are not happy with primary stability then use screws (2-3) to fix the cup and have primary stability. You can leave up to 30% of the superior part of the cup uncovered with no problems with long term stability.
Even better if you use newer cups (trabecular metals).
Take a look here
http://www.ncbi.nlm.nih.gov/pubmed/25232518
http://www.ncbi.nlm.nih.gov/pubmed/25232518
Dear Dr. Tanchev: Indeed, the cup abuction has something to do with postoperative dislocation, but in my mind the main reason of dislocation in this situation is the anteversion of the cup. Whereas, the bigger abduction angle of the cup might be related to strength concentration around the upper quater of it when articulate with head, which latter may theoretically lead to additional upper part wearing in the long run. The reason i raise a question concerning this routine dilemma is that we frequently confronted with cohort of patinets to whom there is restricted bone stock of the deficient acetabulum which can offer little choice for us in terms of preserve the least safe coverage (for example 50-60% covering), and it is even worse, this scenario usually coupled with an under- developed femoral head leaving no resource for bone grafting. When we are in this situation, I think carefully alter the abduction may be a resonable choice.
thank you very much.
Dear Dr. Parsa: I feel happy to see that we had reached a consensus as you underlined that 75% coverage(some considered 60% or even less) was the minimum request aimed to obtain a reliable stability of the cup. The question is that what will you do if you cann't pursue that much of coverage by means of choosing a smaller sized cup or aggressively doing cotyloplasty? Yes, the last resort of us is to use allograft, or special managements for example use TM augments and so on. In fact , the various procedures have various uncertain results. In my point of view, the simple the better when we need to handle this embarrassed situation.
Thank you.
Dear Dr. Bicanic: Its a great pleasure to down load your paper in WJO. I will read it attentively latter on. As it is the midnight in Xi'an China now. Please allow me to talking over the answer you presented here tomorrow. Tomorrow I am scheduled to conduct 2 bilateral TKA and 1 TAA coupled with an ipsilateral TKA. in three patients.
Thank you again
Dear Dr. Wu, In any case I would prefer 100% coverage as compared to 60 % for many reasons which were mentioned above. It is understandable that there are cases in which this could be achieved by a greater cup abduction positioning. It seems to me to choose the less evil.
- As far as the causes for dislocations are concerned the greater anteversion is very bad positioning but not the only one. The same could be said for a greater retroversion after posterior approach. In any case the combination of extreme neck version with a greater cup abduction is the worst situation.
One of the best ways is to use an allograft for reconstruction of the acetabulum roof with screws.
Another method is to us a neck/head- component with a varus-constructed angle, so that lateral dislocation is not so easy.
In several cases of recurrent dislocations I have used a thick resolvable cord with which the femoral neck/head is held medially in the cup. You may have to fix it through either the hip capsule or the lower acetabular rim. The result is, that dislocation cannot occur during the first few weeks during which the scars get mor tight to hold the head into the cup.
For special cases if your cup is jsut a cemented PE-Cup, there also exist cups with a dislocation-protection rim (company W.Link), but here the chance for early cup loosening is higher.
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