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).
