Abdel v. Dennis: The Cup Cage Construct: Preferred Solution for Pelvic Discontinuity

This week’s Orthopaedic Crossfire® debate was part of the 35th Annual Current Concepts in Joint Replacement® (CCJR®), Winter meeting, which took place in Orlando. This week’s topic is “The Cup Cage Construct: Preferred Solution for Pelvic Discontinuity.” For is Matthew P. Abdel, M.D., Mayo Clinic, Rochester, Minnesota. Opposing is Douglas A. Dennis, M.D., Colorado Joint Replacement, Denver, Colorado. Moderating is Paul F. Lachiewicz, M.D., Duke University Medical Center, Durham, North Carolina.

Dr. Abdel: Pelvic discontinuity is where the superior and inferior hemi-pelvises are no longer joined. Contemporary reconstructive options include cup-cage construct, which is my preferred method; distraction method as popularized by Paprosky, et al., which encompasses cup-cage construct; and what likely Dr. Dennis will discuss is a custom triflange (Abdel, et al., JAAOS, 2017; Sculco, et al., JBJS Am, 2017).

So, why do I prefer a cup-cage construct for the treatment of pelvic discontinuity? Three simple reasons.

1. I can place a highly porous cup acetabular component directly against host bone and use highly porous augments to supplement bone loss using superior or medially
2. I can plan supplemental screws anywhere that there’s remaining bone, typically that’s superior and inferior, utilizing the acetabular component as if it’s an internal plate for the discontinuity
3. I can utilize a half- or full-cage as reinforcement for the construct.

What is the technique?

First, identify the discontinuity. Then, remove that fibrous tissue and place bone graft. Thereafter, I utilize acetabular augments. Thereafter we’ll reverse ream some bone graft in there. Place cement on those augments and put a highly porous acetabular component directly up against the patient’s own bleeding bone.

Thereafter place supplemental screws and we can use a half-cage. My preference is to remove the inferior flange of that cage and what that allows us to do is avoid that inferior dissection by the sciatic nerve. Remove one screw that’s going through the dome, through the cage and place that up through, unitizing the construct, and cement the polyethylene liner utilizing that whole construct as a unification for that patient.

So, what’s the data with this technique?

There are now multiple series with mid-term follow-up looking at pelvic discontinuities, treated with a cup cage, some survivorship free of revision, some around 90% for some of our most difficult cases (Koshashvili, et al., JBJS Br, 2009; Rogers, et al., JOA, 2012; Amenabar, et al., CORR, 2016).

What about the half-cage technique that I alluded to? We recently published our series in JBJS Am (2017) looking at this technique. The half-cage technique entails removing the inferior flange of the cage. My preference is to utilize a contralateral sided cage; remove the inferior aspect; avoid the dissection by the sciatic nerve; remove one screw that was going through the acetabular component in the dome and place that through the cage, through the acetabular component and into the host bone. Then cement a polyethylene liner.

We looked at 58 patients, with either a full- or half-cage, mean follow-up at five years. In this series looking at aseptic revisions, only one was revised for aseptic loosening…and that was in the full-cage group; three were revised for instability, as you might anticipate, in a difficult cohort of patients like this.

What about the distraction method that you’ve heard about? This really gains pelvic stability by elastic recoil of the pelvis. The superior and inferior hemi-pelvises are distracted, they hold the acetabular component in place and supplemental screws are placed superiorly and inferiorly. When utilizing this technique, I still utilize a half-cage. It’s important to note that the discontinuity in these cases doesn’t actually heal. It’s just holding it distracted for ingrowth into the bony surfaces.

What about what Dr. Dennis is going to discuss? He’s going to discuss custom triflanges. These are custom-designed titanium acetabular components with 3 flanges—iliac, ischial, pubic. I want to highlight the important and numerous limitations with this particular construct.

• Number 1, it requires a CT scan and 8-12 weeks for fabrication.
• Number 2, you need dedicated preoperative design, which is time consuming.
• Number 3, there is a fabrication cost related to this construct.

What do I do? For a first-time pelvic discontinuity, my preference is a cup-cage construct with a half-cage, as I’ve shown you. If a patient has a failed treatment for discontinuity, that’s where I’ll utilize a distraction method combined with a half-cup-cage.

In summary, pelvic discontinuities are certainly challenging to manage. Best success occurs when treatment combines high rates of cup fixation and simultaneous healing or unitization. Cup-cage constructs are my preferred solution for the vast majority of pelvic discontinuities.

Dr. Dennis: I’m going to give you the other side of the fence. But I think Matt’s outlined it well, when we’re dealing with these bad defect discontinuities, probably the most common two methods are cup-cage, with or without distraction and the custom triflanged acetabular component.

Cup-cage, why not? I give you a number of reasons.

• Number 1, modularity. It’s well documented in the literature that a discontinuity imparts very high stresses on the pelvis. Typically, there are multiple connected parts. Fixation is in part dependent on cement, so there’s certainly an increased risk of mechanical failure and a lot of particulate debris from all the modular parts.
• Number 2, strength of construct. Cages are malleable and are often at increased risk of fracture.
• Number 3, increased difficulty restoring the anatomic hip center. Many of these bad Paprosky 3B and 4 defects are associated with massive bone loss, marked migration. Unless you want to stack 500 augments, it’s very difficult to go ahead and get the true hip center.

Others are errors in cup position. When a lot of the bone is gone, a lot of our anatomic landmarks are gone and we have an increased risk of error in cup position.

If we look at the clinical reports, most are short-term…5 years or less…not all are good. And the results are better with a cup-cage without a discontinuity.

One of the articles out of Matt’s center of 57 cases 34 of which had a discontinuity at 4.6 years, there were 2 cage fractures; early migration in 4 cases; 29% with radiolucent lines. And in all of those problematic cases, they were associated with a discontinuity. So, the results do appear to possibly be worse in the discontinuity group (Sculco, Lewallen, et al., JBJS, 2017).

Don Garbuz reported data at 6 years, and to quote the author, “The failure rate due to loosening (4 cases) in this and other reports does prompt the need for refinement of the technique and technology.” (Konan, Garbuz, et al., Hip Intl, 2017)

Why a custom triflanged acetabular component?

It allows for rigid fixation above (into the ilium) and below (primarily the ischium) a large acetabular defect. The fixation, we have found, has been dramatically enhanced with the use of locking screws, particularly in our pelvic discontinuity cases. And shear is limited. Because no matter how high the defect is, there is always a remaining iliac shelf and you can design the globe portion of the custom triflanged device to sit on that ledge, limiting shear on your construct.

It allows for precise reconstruction of the hip center, through the CT scan and the custom design. You can put the hip center wherever you want. Also, it is less dependent on us finding all our normal bone landmarks so it’s very easy to get your cup in the right orientation.

Also, increased construct strength. There is no metal modularity. I’ve never in 15 years of doing these found an implant fracture. It accepts all available acetabular liners. Also, with the potential to cement in a dual mobility construct.

And from that CT I think that is a positive in these cases because you get a lot more pre-operative information: the magnitude; the geometry of the defect. You know what’s left before you walk into the operating room. Also, it shows the presence and severity of the pelvic discontinuity and can even be predictive of the screw length that you need to put in.

I think, also, you can deal with more extensive defects. If you look in the literature, what do a lot do when a cup-cage fails? Go ahead to a custom triflanged device.

Michael Taunton reported on 57 cases treated with a custom triflanged with an associated pelvic discontinuity. They had one case revised for loosening at 11 years, and 81% of the custom triflanged components were stable and the discontinuity healed (CORR, 2012).

In summary, I think favorable results have been obtained with the custom triflanged acetabular component in the pelvic discontinuity cases. It is a stronger, non-modular construct. That pre-op CT provides me with a lot of valuable information including: both the size and shape of the bone defect; the presence and magnitude of the discontinuity; and the precise restoration of the hip center and cup position. And I get rigid fixation on good remaining host bone.

Moderator Lachiewicz: This has brought up a lot of issues I’d like to ask each speaker. So first let’s talk about exposure. Matt, with the cup-cage do you have less dissection, less exposure than with the triflanged?

Dr. Abdel: Good question, Paul. I think both Dr. Dennis and I can agree that for both of these cases you need excellent exposure. In my hands utilizing a cup-cage construct, particularly with the half cage, there’s much less exposure inferiorly. I think we can all agree at the ischium and the pubis there’s less exposure with the half cage cup-cage construct and superiorly I can usually elevate the abductors without going far superior, place the cage and then place my iliac screws at an angle.

Moderator Lachiewicz: One follow-up question. Let’s say you’re planning a cup-cage with a well-fixed femoral component and a modular head. Will you have to do an ETO to do this procedure? Or some type of osteotomy?

Dr. Abdel: You will not have to, but if it’s difficult, I would do an ETO to remove that femoral component.

Moderator Lachiewicz: How often would you say someone in the audience would have to do a trochanteric osteotomy to put your cup-cage in?

Dr. Abdel: 5-10% of the time.

Moderator Lachiewicz: Okay, Doug, custom triflanged…you’ve got the model, you’ve got the component…and I want you to do a custom triflanged in a patient with a well-fixed femoral component of whatever kind…you can take the head off. What type of exposure would be typical for you?

Dr. Dennis: I will agree that I do think the exposure for custom triflanged is a bit greater. Obviously, the ischium is one, but with the iliac flange…I’ll tell you…in the old days the first ones I did we had three rows of screws way up the ilium. I’ve had one case where my assistant was retracting the abductor and it went right through the abductor, obviously injuring the superior gluteal nerve. If I have a good trochanter that’s not severely osteolytic, I won’t hesitate to do a standard trochanteric osteotomy. I’ve published on a technique with the cables, how to put that back and that is a good thing with these. If you do that, it provides a lot of advantages. It gives you great exposure, but then you can also advance the greater trochanter.

And if you look at the literature of every one of the techniques utilized to try to solve this problem, they are all associated with high complication rates. Lots of dislocation. So, I like to do a standard trochanteric osteotomy then advance the trochanter and I don’t do that, Paul, if it’s one of those paper-thin trochanters and in a lot of these people the trochanters are already gone. But, that’s one area, Matt, I will give you. I do think the exposure would be greater.

Moderator Lachiewicz: Just give the audience a rough figure. In what percent of custom triflanges that you will do a trochanteric osteotomy.

Dr. Dennis: I would say one-third. But I have a low threshold because I think I know how to put the trochanter back and I get the advantage as far as instability.

Moderator Lachiewicz: Let me go to cost. I believe Tom Fehring did a study that says it’s a wash between the custom triflanged and putting two augments and a cage and a cup and so forth. Matt, what do you think?

Dr. Abdel: Another good question. The Fehring-Taunton paper looked at cost between those two constructs. I think the one thing that we’re missing in the cost here is the CT scan, the time that the patient waits. In a cup-cage construct it depends on how much you do it. If you do a cup-cage with a simple cup, acetabular screws and a half cage, it’s a lot cheaper than if you put in 3-4 additional augments. In these high-level, pelvic discontinuity cases, cost isn’t the issue. It’s giving them one good surgery and taking care of the problem.

Moderator Lachiewicz: Doug, who bears the CT cost—the patient, the company, how does that work?

Dr. Dennis: In the bundled payment model, if there are cost overruns it’s probably the hospital that ends up bearing that cost. The way I look at this is that these are typically multiply operated patients. They’re distraught. They’re very disabled. Cost is not high on my list. Giving them a functional limb that will allow them to walk again is the most important thing in my hands.

Moderator Lachiewicz: Thank you gentlemen. Excellent debate.

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