Gross v. Berend: The Cup Cage Construct: Preferred Solution for Pelvic Discontinuity

Consider the case of a patient who had a right total hip replacement. Felt something crack or pop. Felt like her leg seemed shorter. The resulting major problem is a significant pelvic discontinuity with significant bone loss. And in myhands the preferred solution is a custom triflange.

But why is that?  Number 1: I receive the images ahead of time. I know exactly what I’m dealing with. I don’t have to pull the box of toys out to figure out which widget, which Lego—the green, the blue or the red—is going to fit this patient best. In myhands I want to know ahead of time exactly how I’m going to attack this reconstruction. It also helps me with the dissection during the operating room.

Number 2: I receive a model preoperatively that I can play with and plan my attack and a sterile model intraoperatively of both the pelvis and the implant that I can play with in the operating room. Figure out my anatomic and boney landmarks. Figure out the level of dissection I need. And then also, finally, I can take the whole thing and put it together in a web-based conference with the manufacturer and plan out the operation. Plan out the procedure ahead of time. And for me, having that plan; having those instructions, is the preferred solution.

The final thing is the fact that with this design you actually get a cheat sheet. You have your model in the operating room. And then you drill your holes.

You don’t have to worry about deep penetration, injuring neurovascular structures, etc. You know right where the good bone is. In addition, you can use locking screws to enable this thing to become an internal/external fixator between the discontinuity. Just as Dr. Gross mentioned, we’re not trying to get the discontinuity to heal, we’re trying to get a stable construct above and below the discontinuity to span it such that we’ve got stable fixation in 3 planes.

As I mentioned, you get a model preoperatively and intraoperatively, which helps with “Where do I need to remove bone?” “Where do I need the implant to sit?” “Where do I need to do my dissection?” I think, in my hands, this is safer and easier than trying to just play it by ear and wing it out of a box.

We were part of a multicenter cohort study which looked at 95 hips and represented just under 4% of all the hip revisions at these sites. BMI [body mass index] was light. They averaged just under 2 prior surgeries per patient. And they had an average of about 5 years since their last surgery.

In this group of 95 hips, there were 8 discontinuities, but also 29 subsequent femoral revisions were performed as well.

We ended up using an average of 12 screws per implant; 3 of those were locking screws. We’ve had no dislocations. Most common head size was 36mm. We used 14 constrained liners. There’s HA [hydroxyapatite] coating on all of the devices.

Again, one big advantage is that the screw map gives me the ability to put in the so-called “home run” screw up into the ilium. Instead of trying for where the best bone is, I know exactly where it is. The implant itself drives the screw into that home run position. And you can place a 40, 50, 60 or even sometimes a 70mm screw to obtain excellent fixation.

The clinical results…3-5-year follow-up…the Harris hip scores improved modestly as you’d expect in this difficult group of patients (47 pre-op vs. 69 post-op).

But this is not for the faint of heart—22% had at least 1 complication; 6 dislocations; 6 infections; and 2 femoral-related issues. One cup was repositioned at 6 weeks to the same implant and has achieved fixation. One loosened due to metastatic cancer to the pelvis.

Aside from the one loosening for metastatic cancer, there were no other cases of aseptic loosening.

So, the question is…the cup cage…is it preferred? I say it’s okay. And it’s okay if you’re very good. It’s okay if you’re good with Legos.

In my hands it is not the preferred solution. A custom triflange is. I believe that it works. I believe it’s easier. And it may, in fact, be better because of all the tools that come along with it. The web conference call to design helps you. The screw map helps you. A modular poly locking mechanism allows you to use whatever level of constraint or size of ball you feel you need.

We use liberal constraint particularly in the abductor deficient hip. We’re able to use locking screws, which we believe increases the ability to achieve fixation and stable fixation above and below the discontinuity. We’ve had 1 case of aseptic loosening, but it was not in a discontinuity.