This week’s Orthopaedic Crossfire® debate was part of the 32nd Annual Current Concepts in Joint Replacement® (CCJR), Winter meeting, which took place in Orlando this past December. This week’s topic is “Extensive Acetabular Bone Loss: Impaction Grafting, a Preferred Solution.” For the proposition is Alejandro Gonzalez Della Valle, M.D., Hospital for Special Surgery, New York, New York. Opposing is Allan E. Gross, M.D., F.R.C.S.(C), University of Toronto, Toronto, Ontario, Canada. Moderating is Daniel J. Berry, M.D., Mayo Clinic, Rochester, Minnesota.
Dr. Gonzalez Della Valle: There are many options to reconstruct a Paprosky Type 3B acetabular defect. One of them is impaction grafting. My interest in this technique started with one of my mentors who showed me a 12-year follow-up impaction grafting patient. In that example, a large defect in the femur and the stress fracture were completely remodeled and the patient’s bone stock was restored 12 years later.
Tom Slooff is responsible for perfecting impaction grafting in acetabular revisions. The precepts are that segmental and cavitary defects must be supported with a mesh. The contained cavity should be filled with impacted bone chips, and acrylic cement may be used to stabilize the graft and provide rigid socket fixation.
For the contained defect in a patient who has an intact rim, I prefer to use a hemispherical non-cemented socket. However, for the patient with a non-contained defect, it is a greater challenge. The defect has to be closed with the mesh; bone graft applied, and then, yes, a new cemented socket has to be cemented in that bone.
My pre-operative assessment includes ruling out infection and requesting X-rays. In limited cases, depending on the need, I request CT scans or MRIs. The typical X-rays of a non-contained defect demonstrate the teardrop, the original position of the socket and due to aseptic loosening, the loss of the roof, the posterior wall and the lateral coverage of the socket. My surgical technique involves a wide exposure, imagining a socket in an anatomic center of rotation, feeling out the defect and containing the defect with a mesh that can be cut and secured to the periphery, utilizing small fragment AO screws. I use large morsel, fresh frozen chips in the defect and firmly pack it to reconstruct the acetabular bone stock. Then I cement an all poly liner into the reconstructed socket.
This is a versatile technique. For example, consider an 85-year-old lady where the socket is virtually hanging from the medial wall. Six weeks, four months, one year after surgery with a radiographically intact reconstruction, her lateral column was preserved and restored, as well as the bone stock in the posterior column.
In a case with longer follow-up…78 months…there was no sign of deterioration of graft, mesh fixation, or socket fixation into the dead bone.
There are concerns with longer follow-ups. Fixation can deteriorate over time, mostly cement fixation and graft resorption can be a problem in very large defects.
In summary, it’s an underutilized revision technique. It restores bone stock and hip biomechanics like few techniques I know. It’s a low cost technique with acceptable outcomes and one has to be aware of the limitations. Needless to say, if failure occurs, restoration of bone stock may be very useful for future revisions.
Dr. Gross: Firstly I would like to say that this is an excellent surgical technique. In the right hands and for the right indications. What are the right indications?
A ‘perhaps’ situation would be contained defects (Type 1 – Toronto classification) in which the surgeon has to be technically proficient, which I’m sure Alejandro is, and has to be proficient with cement and this specific technique. And you have to have abundant allograft chips of the right particle size.
Now, the options are a jumbo cup or a rigid cage, when you have a particularly massive contained defect. In the case of a massive contained defect, we might even use a cup. In the case of a failed arthroplasty, for example, we have used a large cup but we supplemented it with an augment so the cup size didn’t have to be that large, but it is still equivalent to a jumbo cup. And in those cases we used a lot of morselized bone grafting and we impact it and compact it.
The ‘not so much’ situation is the uncontained defect, that’s a segmental defect of less than 50%, Type 3 by our classification. The options here are a minor column allograft in a very young patient or, of course, augment. One of our cases was a very young patient in his 30s who’d already had a failed total hip, and we elected to use a minor column allograft to bring that cup down to the right level and to restore bone stock, which our data supports.
Now the ‘I don’t think so’ case would be uncontained defects of greater than 50%. These are very difficult defects, Type 4. In a paper from Exeter, where they do a lot of impaction grafting on the femoral and acetabular sides, they made a greater use of implants made of highly porous materials to constrain allograft chips and bulk allografts combined with cages and morselized chips in cases with very large segmental and cavitary defects.
We have just published results of structural allografts protected by a cage and presented at the Annual Meeting of the American Academy of Orthopaedic Surgeons in 2010. We showed that we restored bone stock so that the second revision was much easier. So in the very young patient, this is still a viable option.
Now the ‘no way’ cases. In these cases where there is bone loss in association with pelvic discontinuity, we would use a cup cage reconstruction. In the cup cages, we now have 75 of these, including 3 tumor cases; we have lost 4 to follow-up. The average follow-up is just over 6 years and our Kaplan-Meier survivorship is good.
However, with all acetabular reconstructive techniques, it has been shown that the outcome of impaction grafting is less successful in the larger defects.
Now in closing, I think there’s a definite indication for impaction grafting, but this is not a technique that you should be doing once in a while. You have to know the technique and you have to know its indications.
Moderator Berry: You both made some nice points in your discussions. Alejandro, let me ask you first. You obviously know how to do the technique and do it well. With the plethora of other techniques that have become available, highly porous metals, augments, and so forth, which some might argue would be technically simpler, what’s your logic for continuing to use impaction grafting?
Dr. Gonzalez Della Valle: First I have to say that I totally agree with Allan. This corresponds to a small proportion of all my acetabular revisions. The biggest concern that I have and the reason why I continue using this technique is that for some reason, I’m always thinking what’s next. What’s coming next? I have the impression that if these large revisions fail I may have no bone left. And on the other hand, if impaction grafting fails, I’m very comfortable saying that I would see bone graft.
Moderator Berry: Yes, it does look like we get some restoration, at least on the medial side, even if the cup eventually migrates. Allan what about that logic? This is a way of restoring some bone and even if it eventually fails, perhaps the bone would be better than if you got a bunch of metal or maybe an old structural graft in there. Is that logic sound or not really sound?
Dr. Gross: There is a paper that I actually had a slide of that I didn’t show—biopsies of impaction grafting show restoration of bone stock. I’m a big proponent of bone grafting. There’s no question that bone grafting, with all its problems, still leads to easier revision. You just hope that it’s not an early revision and it’s a late revision. I’m sure it does restore bone stock.
Moderator Berry: On the femur, for sure, we can see very clear radiographic evidence of that. It’s harder to see on the acetabulum maybe. Alejandro, you showed some really nice technical jobs of having done the procedure. I have to admit when these patients get referred to me having had it, most of the time the cup’s loose. And it’s migrated within the first few years and that’s why somebody sent me the patient. I get the sense that this is very, very technique dependent methodology. Which is to say you’ve got to do a good job when you’re restoring the rim with the mesh that you showed. And you’ve got to really pack the graft in tightly. If you don’t get it packed in tightly, then the cup just starts moving around eventually. Are those things that I just said true, and if they are true, do you want to give us a few technical tips on how to do it?
Dr. Gonzalez Della Valle: In my view, first, I don’t think this is extremely hard to fix and to trim the mesh. I think that the key to the success of the operation is to have a very wide exposure. I think identifying the rim of the defect absolutely to perfection. Then the trimming of the mesh is relatively simple. Then I use small fragment AO screws placed 1.5cm apart, so a lot of screws, some of them very short, some of them long, and I’m always worried about nearby vascular structures that I can injure by placing so many screws.
Moderator Berry: What about packing that graft in there? How do you get it packed in there densely enough?
Dr. Gonzalez Della Valle: I think the key is the size of the graft. You have to be relatively large morsels.
Moderator Berry: Allan, you know the data on impacted allograft, particularly on the medial side of the acetabulum, is that it does heal. We see lots and lots of examples of that. So even if you’re not going to do a formal impaction grafting with a cemented cup, you must use it when you use large jumbo cups, even with augment cases. So tell us when you’re doing those cases, how do you make the impaction grafting, if you will, when combined with these other techniques that are maybe used more commonly in the audience, effective in a way of restoring bone stock even in those cases?
Dr. Gross: We always do grafting of some sort. It’s often a mixture or auto and allograft because you’ve usually reamed out an acetabulum or you’ve done some reaming. We go for the large particle size with the bank bone and we use what we call these big ball pushers. So if we’re doing a medial defect, we don’t necessary reverse ream because if you’re going to be putting in a hyper porous cup, you want that hyper porous cup to be against bleeding host bone. That’s very important. So you try not to let the dead bone get into that interface where you have bleeding host bone. But where you don’t have it, that’s where we put the bone graft and we really impact it with these big ball pushers and we do it so that when we’re finished impacting it really does look like impaction grafting. And then, of course, we’re using a hyper porous cup.
Moderator Berry: Well, gentlemen, thank you both very much for an excellent discussion and thanks for sharing some tough cases with us.
Please visit www.CCJR.com to register for the 2016 CCJR Winter Meeting, – December 14 – 17 in Orlando.
