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Editorial Commentary: The Pediatric Knee: Ultrasound Could Replace Magnetic Resonance Imaging for Evaluating a Discoid Lateral Meniscus

      Abstract

      Magnetic resonance imaging has been referred to as the gold standard diagnostic modality for meniscal pathology in the adult knee. However, there are multiple issues with reliance on magnetic resonance imaging for evaluating the meniscus in children. Diagnostic accuracy for meniscus pathology in children is not as high as with adults. Additionally, young children often cannot tolerate lying still for the study and require sedation, with a small but non-zero risk of anesthetic complication and risk motion artifact even with sedation. Ultrasound can be used to reliably diagnose a discoid lateral meniscus in a testing environment that is well tolerated by young children.
      Magnetic resonance imaging (MRI) is a workhorse diagnostic modality for meniscal pathology in the adult knee. The sensitivity for meniscal tears and meniscal variants in adults is high.
      • Phelan N.
      • Rowland P.
      • Galvin R.
      • O'Byrne J.M.
      A systematic review and meta-analysis of the diagnostic accuracy of MRI for suspected ACL and meniscal tears of the knee.
      ,
      • Chambers S.
      • Jones M.
      • Michla Y.
      • Kader D.
      Sensitivity of magnetic resonance imaging in detecting meniscal pathology.
      However, it is far from an ideal study for the pediatric patient. Diagnostic accuracy of meniscus pathology may not be as high in children as it is in adults.
      • Schub D.L.
      • Altahawi F.
      • Meisel A.F.
      • Winalski C.
      • Parker R.D.
      • Saluan P.M.
      Accuracy of 3-Tesla magnetic resonance imaging for the diagnosis of intra-articular knee injuries in children and teenagers.
      ,
      • McDermott M.J.
      • Bathgate B.
      • Gillingham B.L.
      • Hennrikus W.L.
      Correlation of MRI and arthroscopic diagnosis of knee pathology in children and adolescents.
      The test requires the patient to remain still for several minutes in a loud, confined environment, which can be difficult for some adults and nearly impossible for anxious children. As a result, sedation may be required in children to obtain an MRI study without significant motion artifact, and significant motion artifact has been reported 12% of pediatric MRI or computed tomography studies even with sedation.
      • Malviya S.
      • Voepel-Lewis T.
      • Eldevik O.P.
      • Rockwell D.T.
      • Wong J.H.
      • Tait A.R.
      Sedation and general anaesthesia in children undergoing MRI and CT: Adverse events and outcomes.
      Although safe sedation protocols have been developed,
      • Schulte-Uentrop L.
      • Goepfert M.S.
      Anaesthesia or sedation for MRI in children.
      risks still remain with sedation in the pediatric patient including cardiorespiratory depression, as well as the potential for lasting effects on brain development.
      • Ward C.G.
      • Loepke A.W.
      Anesthetics and sedatives: Toxic or protective for the developing brain?.
      ,
      • Arlachov Y.
      • Ganatra R.H.
      Sedation/anaesthesia in paediatric radiology.
      In our experience, a thorough clinical history and physical examination combined with radiographs can provide a reasonable diagnosis of a discoid meniscus, particularly in unstable variants with lateral joint line mechanical symptoms. Confirmation of a discoid meniscus with advanced imaging is still warranted for surgical decision-making. The irony of this current approach is that we, and many other providers, are relying on MRI, a test that may require sedation in children, to minimize the risk of performing an unnecessary knee arthroscopy requiring anesthesia. What is needed is a noninvasive, noiseless diagnostic imaging modality that is ideal for a child. Here enters the diagnostic ultrasound to confirm a discoid meniscus: an advanced imaging technique that has no radiation, no sedation, real-time imaging, and the parents can be in the room.
      In this elegant study, “A Reliable, Ultrasound-Based Method for the Diagnosis of Discoid Lateral Meniscus” by Yang, Zhang, Li, Xue, and Chen,
      • Yang S.J.Z.M.
      • Li J.
      • Xue Y.
      • Chen G.
      A reliable, ultrasound-based method for the diagnosis of discoid lateral meniscus.
      the authors both develop and validate a simple method of diagnosing discoid lateral meniscus. Of the standardized ultrasound measurements investigated, the meniscus angle measurements were found to have the best diagnostic value. The authors provide clear pictures of how to position the probe, as well as representative ultrasound images. As you can imagine, a partial or complete discoid has a smaller meniscus angle owing to the greater distance between the meniscus periphery and the central edge. The authors investigate and validate specific meniscus angle cutoff values to diagnose complete or partial discoid lateral meniscus: less than 28.45° at the anterior joint line, less than 27.85° at the meniscus body, and less than 29.15° at the posterior joint line.
      • Yang S.J.Z.M.
      • Li J.
      • Xue Y.
      • Chen G.
      A reliable, ultrasound-based method for the diagnosis of discoid lateral meniscus.
      Musculoskeletal ultrasound should be readily available in most centers treating pediatric patients and particularly centers treating infants as it is a commonly used modality for evaluation of infantile hip dysplasia. As with any technician-dependent test, there is undoubtedly a learning curve with ultrasound applied to the knee. Consistent probe placement and measurement of the meniscus will be crucial. If we implement this test in our practice, we will review the measurement protocol with our ultrasonographers and, ideally, have some willing children and parents with clinically obvious discoid menisci initially to complete the ultrasound prior to widespread use as a diagnostic test.
      Finally, we would like to commend the authors on a rigorous study design. It is still uncommon for studies published in the orthopaedic surgery literature to properly develop and validate a diagnostic test. Historically, authors in our field presented a new test that was developed by a single surgeon on a single patient series. The test would have reported a diagnostic accuracy that was optimistically high and frequently failed to be replicated in subsequent studies. Physical examination tests for SLAP lesions in the shoulder are a great example of this, with every confirmatory study reporting worse diagnostic performance compared with the originating study in a review by Jones and Galluch.
      • Jones G.L.
      • Galluch D.B.
      Clinical assessment of superior glenoid labral lesions: A systematic review.
      In the current study, the authors preselected 12 possible measures and identified 3 ideal candidate measures and their proposed cutoff values in a sample of 180 patients.
      • Yang S.J.Z.M.
      • Li J.
      • Xue Y.
      • Chen G.
      A reliable, ultrasound-based method for the diagnosis of discoid lateral meniscus.
      They then validated these candidate measures and their cutoffs in a separate sample of 324 patients. The study was adequately powered (still the exception rather than the rule in orthopaedics) and the authors appropriately separated the exploratory phase of the study from the confirmatory analysis.
      • Tukey J.W.
      We need both exploratory and confirmatory.
      ,
      • Thompson B.
      Exploratory and confirmatory factor analysis: Understanding concepts and applications.
      This was a well thought-out and precisely executed study that provides strong data for use of ultrasound to diagnose discoid lateral meniscus.

      Supplementary Data

      References

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