This news release describes an unpublished study looking at hip replacement outcomes among patients who underwent a new assessment protocol prior to surgery. Compared with those who did not undergo the protocol, these patients had lower rates of hip dislocation after their surgery, which would presumably reduce the need for revision surgeries to replace a failed implant. How did the protocol help? The release suggests that pre-operative imaging scans helped identify and guide the treatment of patients with spinal problems who needed so-called dual mobility implants. These implants allow a greater range of motion and are credited with decreasing the risk of a hip dislocation.
Here’s what we liked about the release: It features a relatively thorough description of how the study was conducted, quantifies the benefits in absolute terms, and gives good insight on why such a presurgical assessment might be helpful to direct patient care. Our main concern is this: The release suggests that the new protocol deserves all the credit for the better outcomes, when in reality it’s not clear whether other factors played a role. Information about costs and the potential harms of dual mobility implants would also have been helpful for readers.
Update 3/16/18: Due to an editing error, the release was scored 2 stars. We have updated the review to indicate the release scored 3 stars.
Hip dislocation is one of the reasons that hip replacement surgeries can fail, leading to pain, disability, and possibly a costly second surgery. If there were a way to predict which patients were more likely to suffer hip dislocations, and use implants that would reduce the risk, it would represent an advance for patient care and likely reduce the overall costs of treatment.
Total hip replacement surgery is commonly performed in older individuals with pain and impaired function due to hip arthritis. It is also done in younger individuals for a number of reasons including trauma or congenital conditions. Hip dislocation following surgery is an uncommon but scary complication. Though not stated in this release, most dislocations occur soon after the surgery and can be treated non-surgically under anesthesia. Around 30-40% may require repeat surgery. Fortunately, hip dislocation is an uncommon complication occurring in only 1-2% of procedures. Regardless, identifying those at increased risk for dislocation and working to prevent this complication would seem like a good thing.
There are three costs not mentioned in this news release that are critical in evaluating the relevance of this unpublished study.
First, the release could have compared the costs of “dual mobility cup” hip transplants vs. conventional implants. We’re told the former are “more expensive” but it would be helpful to know by how much, since the study suggests dual mobility cup transplants may be indicated in patients at high risk for dislocation.
Second, the study is based on a “novel risk assessment tool” which suggests pre-operative scans in the sitting and standing positions. How much does this cost? It’s not mentioned.
Third, how much money could potentially be saved by reducing the need for “revision surgeries” in patients whose implant becomes dislocated? It is unlikely that this will reduce costs overall given the small number of individuals who may require repeat surgery, even in this high risk group. Thus, the question is whether this is a cost-effective strategy or not.
This study was done in two parts.
Part one: a retrospective review of 1,082 conventional (not dual cup) total hip replacements (THRs), over 2 years, in which the dislocation rate was 1.8% (19 patients). We’re told about a third of the total cohort (320 of the 1,082) had “spinal disease and deformity” on imaging scans. In this group of 320, 10 patients (3.1%) had subsequent dislocations.
Part two: Beginning in 2016 researchers began employing their risk assessment tool — pre-operative sitting/standing scans of the hip, and factoring in other risk factors like previous spinal fusion — and identified 192 of 1,009 patients (19%) as ‘high risk’ for dislocation. About three-fourths of these patients received dual cup transplants with only 1 having a subsequent dislocation (0.5%).
The news release gives us the absolute rate of dislocations in both high-risk groups (3.1% vs. 0.5%), which is vital information to understand the scope of the potential benefit. And on that basis we’ll award a satisfactory grade here. However, we note limitations under the Evidence criterion below that have a bearing on these statistics.
The news release does not mention any risks associated with hip replacement surgery in general, nor does it address potential harms specific to dual mobility cups, which are described in the release as the recommended approach to reduce risk for dislocations. The release notes that dual mobility cups may carry risks “if implanted unnecessarily” but doesn’t describe or quantify those risks. Of note, there is some concern that this type of replacement joint may release higher levels of metal ions than conventional joints when implanted in younger, more active patients.
As presented, the only downside of these newer devices are the increased cost. It would be helpful to know if there are any other risks. Newer devices may have some risk simply due to not having long-term experience with them. Current hip replacement devices have been shown to work for 20+ years. It will take considerable time to know whether the same may hold for these newer devices.
The release provides a relatively thorough description of how the study was conducted, noting that one group of patients was treated before the introduction of a new assessment protocol (in 2014-2015), and that the second group had their treatment guided by the new protocol (introduced in 2016). The fact that the second group had better outcomes (i.e. a lower rate of dislocations following hip replacement) indicates that the protocol must be helpful for identifying high-risk patients and treating them more appropriately, the release suggests.
What’s lacking, though, is any acknowledgment that these two groups of patients might not be directly comparable. For example, did these two groups have the same types of “spinal disease and deformity” — the nature of which might impact the failure rate for their hip replacements? Did they also have the same level of mobility and co-existing illnesses? Did anything else about the treatment provided to patients change in the time between the first group’s treatment and the second group? Were both groups followed for the same length of time post-surgery?
Differences in any of these areas could have biased the results. To conclusively demonstrate the effectiveness of the new protocol, researchers would need to randomly assign patients to receive the new protocol, or not, and document how both groups fared following treatment. A brief note to that effect, or at least a mention of some of the limitations inherent in the current study’s design, would have been helpful.
The report should have mentioned that the comparison was not a direct one. The best way to examine these outcomes would be to compare patients screened to be at high risk and then randomize them to the new device or a standard one. It is possible that the benefit is from knowing that they are at higher risk. For example, physical therapy or other instruction may be given to mitigate the risk, irrespective of the device inserted.
No disease mongering. The release states that dislocations occur in about 1% of patients following hip replacement.
The release doesn’t discuss funding for the study or possible conflicts of interest among the study authors. A quick search of the federal Open Payments database shows that the lead author, Dr. Jonathan Vigdorchik, receives payments from a number of device companies, including those that make dual mobility hip implants.
Since we’re not aware of alternatives to this tool we’ll rate this criteria Not Applicable.
It’s clear that patients who undergo hip replacement at NYU Langone Orthopedic Hospital have access to the risk assessment screening and treatment algorithm prior to surgery. But what about patients who can’t travel to New York? Is anything similar in use at other institutions? The release is silent on this point.
The release clarifies the problem this new assessment tool is trying to solve and why it’s worth reading about:
Some newer hip implants are designed with dual mobility cups that allow for increased range of motion, which helps reduce dislocation risk. However, no guidelines currently exist to aid clinicians in deciding when to use these more flexible implants, which are often more expensive than conventional implants, may not be medically necessary, and may carry added risks if implanted unnecessarily.
No unjustifiable language.