Expandable cages address an obvious challenge in minimally invasive spine surgery: How do surgeons place a device capable of restoring disc height through an increasingly small surgical corridor?
But Lali Sekhon, MD, PhD, a spine neurosurgeon at Reno (Nev.) Orthopedic Center, thinks spine may now be confronting a harder question.
What happens after the cage expands? That question became harder for Dr. Sekhon to ignore after his research found a striking difference in collapse rates between two expandable cages used in minimally invasive lumbar fusion.
“They’re not all the same,” Dr. Sekhon told Becker’s.
His takeaway is not that surgeons should abandon expandable cages or that one locking mechanism has been proved superior. It is that surgeons should pay close attention to how the devices they choose are performing in their own patients.
The findings also raise a larger question for spine: Has adoption of expandable cages moved faster than the evidence showing which designs provide durable advantages?
When an expandable cage doesn’t stay expanded
Expandable cages offer an intuitive advantage in minimally invasive fusion. A surgeon can insert a relatively small device through a narrow corridor and expand it inside the disc space, with the goal of restoring disc height and spinal alignment while limiting surgical exposure.
“When we finish the surgery and look at the X-ray and say, ‘This looks really good,’ you want it to stay that way,” Dr. Sekhon said.
In Dr. Sekhon’s study, that did not always happen.
The retrospective, nonrandomized analysis included 168 consecutive patients undergoing minimally invasive transforaminal lumbar interbody fusion. Of those, 112 patients received 144 Medtronic Catalyft PL cages and 56 received 80 X-PAC cages from Expanding Innovations.
Secondary cage collapse occurred in 20.5% of patients in the Catalyft PL group, compared with 1.8% in the X-PAC group. At the cage level, collapse occurred in 16.7% of Catalyft PL implants and 1.2% of X-PAC implants.
The patient groups were treated sequentially, and the cages differed in geometry. The study therefore demonstrates an association rather than proving that a particular implant or design feature caused the difference.
Still, the magnitude caught Dr. Sekhon’s attention. He had already seen another research group report a collapse rate of about 20% with the Catalyft PL cage. Finding a similar rate in his own series made the issue worth investigating further, he said.
“Twenty percent for any medical device is too high,” Dr. Sekhon said.
The locking mechanism question
One difference between the cages particularly interests Dr. Sekhon: how they maintain their expanded height.
He described the Catalyft PL as using a screw-based mechanism to expand the implant. The X-PAC uses a different mechanism that he likens to opening an ironing board, with a ratcheting design intended to hold the device in position.
In his series, 24 of 144 Catalyft PL cages experienced secondary collapse, compared with one of 80 X-PAC cages.
Dr. Sekhon said the procedures were performed by the same surgeon using the same general technique, bone graft and fixation approach, making the cage a key difference between the cohorts.
He suspects the expansion mechanism could help explain the disparity. But he is careful not to extend that hypothesis beyond what the study can demonstrate.
“The answer is I don’t know,” he said when asked which design features surgeons should prioritize.
The study does not establish that screw-based expandable cages as a category are more likely to collapse. Dr. Sekhon’s recommendation is more targeted: Surgeons using them should scrutinize their own results.
“Be very careful picking which locking mechanism you use,” he said. “They’re not all the same.”
He likens it to a car jack that fails to hold its position.
“Can you imagine if one in five times you do that, the car fell down?” he said.
For an implant left inside a patient, Dr. Sekhon believes durability should be fundamental.
“In the short term, the device should stay the way it was when the patient left the operating room,” he said.
Has adoption moved ahead of the evidence?
The findings also sharpen a larger question around expandable cages.
Expandable implants can be easier to place through the small surgical corridors used in minimally invasive surgery because they enter the disc space in a smaller configuration before expanding.
They also come at a premium. Dr. Sekhon estimated expandable cages can cost several times as much as static cages. That makes the evidence supporting their advantages particularly important.
“Do we have data that suggest expandable cages are better than static cages? No, we don’t at the moment,” he said.
Dr. Sekhon said studies have yet to clearly demonstrate that the early advantages of expandable cages over static cages persist over time. Subsidence, when an implant sinks into the adjacent bone, can diminish some of the correction initially achieved.
That does not mean expandable cages are not better, he stressed. It means the evidence has not yet established their superiority.
“This may be a case of the technology being ahead of the results,” he said. “We just don’t know.”
The distinction matters because making an implant easier for a surgeon to insert does not necessarily mean it will produce a better long-term result for the patient.
“The evidence at the moment doesn’t show that expandable cages are superior,” Dr. Sekhon said. “That doesn’t mean they’re not. It just means we haven’t been able to show it.”
When does a device problem become unacceptable?
The findings come after a 2025 FDA Class II recall involving Medtronic’s Catalyft PL and PL40 expandable interbody systems over the potential for cage height loss or collapse. The action resulted in updates to the devices’ instructions for use and surgical technique guide.
Dr. Sekhon said he assisted Medtronic with some of the instructions related to the device. But the findings leave him with a question that extends beyond a single implant: At what point should evidence of a device problem prompt stronger action?
He does not claim to know where that threshold should be.
“At what point is a device no longer in the patient’s best interest and should be recalled or taken off the market?” he said. “I think everyone would have a different answer.”
His own assessment of the collapse rate is less ambiguous. “I personally think 20% is too high,” he said.
Dr. Sekhon emphasized that his purpose in publishing the findings was to make surgeons aware of what his group observed so they could examine their own results and make their own decisions about device selection.
“My goal was to put the problem out there so people know,” he said.
What the next cage has to prove
Dr. Sekhon also has a perspective from the development side. He disclosed during the interview that he is involved in the development of nonexpandable cages.
He does not see the answer as abandoning innovation. Instead, he believes interbody devices still have room to improve across several dimensions, including material properties, stiffness, ease of insertion and the amount of tissue disruption required to place them.
For expandable cages, however, he sees one immediate requirement.
“The mechanism that opens these devices up has to be bulletproof,” he said. “It has to be rock solid. We have to be able to completely trust it.”
That may be the larger lesson from the study.
Minimally invasive spine surgery has created demand for implants capable of doing more through smaller corridors. Expandable cages are one answer to that challenge.
But their value ultimately depends on more than what they allow a surgeon to accomplish before the patient leaves the operating room. The correction has to last.
“We’re not where we need to be yet,” Dr. Sekhon said.
For the next generation of expandable cages, the challenge may not simply be designing an implant that can expand.
It is designing one surgeons can trust to stay that way.
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