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A Simple Predictor of the Efficacy of Hip Arthroscopy
17 July 2017 (online)
With the recent advancements in hip arthroscopy, the indications for it have expanded and an increasing number of arthroscopic procedures are being performed for various conditions. Success rates of hip arthroscopy show considerable variation, which is largely dependent on appropriate patient selection. A major reason for failed hip arthroscopy is the presence of concomitant osteoarthritis (OA). Studies have reported that patients with OA who undergo hip arthroscopy are at a higher risk of conversion to total hip arthroplasty (THA) and have poor functional outcomes.  In a systematic review of 15 studies involving more than 2,000 patients, it was shown that approximately 80% of the patients who underwent a conversion to THA had signs of OA. Therefore, it is important to assess the presence of OA to identify the patients who will benefit the most from arthroscopy. Choosing the right patient for arthroscopy is harder than it sounds. Most surgeons use plain radiographic images as the screening tool to assess OA. Although several radiographic findings have been shown to correlate with OA, joint space narrowing is the most commonly used feature to diagnose OA. Some studies have reported that patients with joint space width (JSW) less than 2 mm are at an increased risk of failure of arthroscopy, suggesting that this might be a reliable measure to screen patients with OA.   But, can we use this as a cutoff to rule out OA? The answer is probably “no” based on the findings of “Joint Space Width and Osteoarthritis in Patients Undergoing Hip Arthroscopy” by Pidgeon et al published in the current issue of Journal of Hip Surgery.
In the study by Pidgeon et al, the authors retrospectively evaluated patients with a grade 3 or grade 4 OA based on the Outerbridge classification, who underwent a hip arthroscopy at their institution. The authors reviewed the standing radiographs and measured the JSW. Out of the 48 patients with a grade 3 or 4 arthroscopic osteoarthritic change in their study, only 4 patients had a JSW < 2 mm, indicating it to be a less sensitive marker for predicting intraoperative OA. However, the study did find that there was a negative correlation between JSW and arthroscopic osteoarthritic findings.
Although the findings of the study suggested that JSW < 2 mm may not be a sensitive marker for OA, it is not clear if a higher JSW cutoff is necessary to rule out OA. As the this study only included the patients with a severe OA, the specificity of JSW could not be calculated. It is very well possible that the proportion of patients with a JSW < 2 mm will be much lower in those with grade 1 or grade 2 osteoarthritic changes, in which case, this measure may be useful to rule in OA. Also, the JSW measurements in this study were made by a single observer. Even though this will reduce the variation within the study cohort, these measurements may have been different if performed by a different observer. The JSW cutoff of <2 mm is based on a few studies with some of them performed by the same group of authors.    While minor changes in the cutoffs are possible depending on the observer, it is important to note that the findings of this study and other studies have consistently shown that decreased joint space correlates with an increased likelihood of OA. However, an ideal JSW cutoff to reliably diagnose OA is still lacking and diagnosis of OA might be challenging, especially when patients have a JSW close to 2 mm. It is important to recognize that severe osteoarthritic changes might be encountered even in patients with JSW > 2 mm.
The study by Pidgeon et al contributes to our understanding of the correlation between radiographic and arthroscopic findings of patients with OA. Although newer techniques such as gadolinium-enhanced magnetic resonance imaging (MRI) are available to detect the cartilage thickness, these measures are expensive; therefore, plain radiographs will probably continue to serve as the initial screening method for OA. Therefore, it is important to accurately identify patients with OA using plain radiographs. As JSW alone might not be a reliable marker for OA, other radiographic features may need to be combined. Future studies like this one will hopefully help us in identifying a reliable measure to assess OA in patients undergoing hip arthroscopy.
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