Where Are We Now?
Hip arthroscopy has gone from a niche endeavor to widespread use within the past 20 years . Femoroacetabular impingement, a term not coined until 2003, is the principal indication for hip arthroscopy; however, as more surgeons have started to perform hip arthroscopy, and more patients have become aware of it, the range of conditions being treated has expanded, and the complexity of the reconstructive procedures being attempted has increased .
We have good evidence, including from two well-conducted, large, randomized controlled trials [3, 8], that patients with mechanical symptoms and pain in the hip because of femoroacetabular impingement and with no or minimal evidence of osteoarthritis can have substantial improvements in quality of life in the first year after arthroscopic osteochondroplasty and labral débridement or repair. An increasing number of observational studies are helping us to determine which patients are likely to fare well and which are likely to fare poorly after surgery for femoroacetabular impingement, both in terms of early clinical outcomes and long-term hip survival [1, 5].
The linked study of Yao et al.  is one such study. They reported the outcomes of more than 4700 patients who underwent arthroscopic osteochondroplasty and who were identified using a large healthcare claims database. Overall, 7% of patients undergoing hip arthroscopy had undergone THA by the end of the second postoperative year. Smokers, those with a diagnosis of osteoarthritis or inflammatory arthropathy, and older patients were the most likely to undergo THA; more than 10% of patients between the ages of 40 and 54 years and nearly 20% of those aged above 54 years underwent THA by 2 years after arthroscopy. This is likely to be the tip of the iceberg; for every patient who agrees to undergo arthroplasty so soon after arthroscopic intervention, how many are there for whom arthroscopic surgery has given them no meaningful improvement but who have not yet decided to proceed to THA?
Where Do We Need To Go?
The study of Yao et al.  is part of an increasingly large body of studies guiding us in selecting patients for hip arthroscopy, but we are still a long way from having the kind of granular longitudinal data that we have for other procedures, in particular arthroplasty. While we have a growing understanding of the broad patient and disease factors that affect the potential improvement patients can expect from arthroscopic hip surgery , many of these studies originated from large, single-center series that by definition represent the surgeons who are the most expert, technically and in terms of patient selection, and it is not clear how this translates to the population of hip arthroscopists as a whole . The studies we do have give us important information to help counsel patients as to the risk that they face when agreeing to surgery, both in general and stratified into broad demographic groups [1, 5]. However, they lack the fine patient-level data, particularly in terms of preoperative imaging, that would make them useful when discussing the likely outcome of surgery for a patient encountered in clinic. Even in high-risk patients—for instance, patients with evidence of early osteoarthritis on MRI—we do not know whether there is an identifiable subgroup who might benefit from arthroscopic intervention in spite of the high chance of an unfavorable outcome on the population level. It is not clear in the medium- to long-term how durable the improvement in patient-reported outcomes is after hip arthroscopy, and, in turn, how successful these hip preservation techniques are in actually delaying or avoiding arthroplasties in patients who do not respond to treatment compared with those who do not undergo surgery. It is also not clear how much value is added by providing more-complex reconstructive procedures over and above simple osteochondroplasty and débridement.
The most important question remaining relates to patient selection, particularly in terms of the disease itself. This is perhaps the hardest to answer. While register studies similar to that of Yao et al.  and others [1, 5] can provide some facts—for example, that older patients, smokers, and users of opiates fare worse than those without these factors, and people without the International Classification of Diseases code for inflammation or osteoarthritis fare better than those with this code—these provide only limited guidance to help the patient in the clinic. The clinician and the patient need more personalized guidance; although osteoarthritis and dysplasia are both seen as potential contraindications, many patients presenting to hip preservation surgeons are somewhere on the spectrum of hip dysplasia or osteoarthritis. Where do we draw the line and say that the osteoarthritis is too bad or the hip’s morphology is too abnormal to give the patient a chance of getting better with arthroscopy (when the alternative treatment strategy is doing nothing and putting up with their symptoms?). This question is hard to answer and neither randomized trials nor registries will necessarily help.
How Do We Get There?
The good news is that answering these questions, even with a relatively young technique such as hip arthroscopy, is much easier in 2020 than it was in the early days of hip arthroplasty. For one, more than 500 patients have been enrolled in randomized trials comparing hip arthroscopy with rehabilitation alone [3, 8], with placebo-controlled trials anticipated . If these trials continue into the medium- to long-term while avoiding loss to follow-up (always a danger, but more so in the young, mobile population of patients who undergo hip arthroscopy), within a decade, we should have an answer as to whether these procedures provide lasting symptomatic benefit and even whether they confer any real benefit in terms of joint preservation. Hip arthroscopy registers that are modelled on national joint registries, which have proven informative in arthroplasty [4, 7], are to be encouraged. These should give us an idea on the population level of how surgical factors and patient selection affect outcomes and could give us early warning of the success (or otherwise) of emerging procedures and technologies. However, without a degree of compulsion from regulatory bodies, these registers face an uphill task in achieving universal coverage akin to that achieved by national joint registries; these also have the advantage of being tied to a prosthesis, allowing straightforward checking of how many patients or procedures are not entered.
We need large, longitudinal studies in which preoperative scans and intraoperative findings are examined with reference to the clinical and radiologic outcomes of hip arthroscopy. Again, we have some infrastructure to support such studies, with the emergence of consensus groups to drive international collaboration of high-volume units and surgeons . Perhaps the use of artificial intelligence will allow the development of risk calculators and decision aids for which patient demographics and scans can be used to give the patient a personalized idea of his or her likely functional outcome and long-term survival. The base of high-quality research evidence for hip arthroscopy has grown more rapidly than any other procedure in orthopaedic surgery. However, much still remains to be learned.
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