Arthroscopic Visualization of Abnormal Movement of Discoid Lateral Meniscus With Snapping Phenomenon  Kengo Harato, M.D., Ph.D., Yasuo Niki, M.D., Ph.D., Masaki Nagashima, M.D., Ph.D., Ko Masumoto, M.D., Ph.D., Toshiro Otani, M.D., Ph.D., Yoshiaki Toyama, M.D., Ph.D., Yasunori Suda, M.D., Ph.D.  Arthroscopy Techniques  Volume 4, Issue 3, Pages e235-e238 (June 2015) DOI: 10.1016/j.eats.2015.02.002 Copyright © 2015 Arthroscopy Association of North America Terms and Conditions

Fig 1 (A) Fat-suppressed T2-weighted coronal image of the right knee in a 13-year-old boy. This magnetic resonance image shows a horizontal tear of the discoid lateral meniscus. (B) T1-weighted sagittal image of the right knee of the same boy. This image shows the “no shift” type of discoid lateral meniscus with a horizontal tear. Arthroscopy Techniques 2015 4, e235-e238DOI: (10.1016/j.eats.2015.02.002) Copyright © 2015 Arthroscopy Association of North America Terms and Conditions

Fig 2 Supine positioning of patient, allowing full range of motion with a standard leg holder. Routine arthroscopy is performed by use of the standard anterolateral and anteromedial portals. We can see the discoid lateral meniscus of the right knee in a 13-year-old boy through the anterolateral portal before excision. The snapping phenomenon with discoid lateral meniscus of the right knee is observed in deep flexion before excision with the standard position (not the figure-of-4 position). This image shows that the central portion of the discoid lateral meniscus moves anteriorly with snapping at deep flexion angles (arrowheads). Arthroscopy Techniques 2015 4, e235-e238DOI: (10.1016/j.eats.2015.02.002) Copyright © 2015 Arthroscopy Association of North America Terms and Conditions

Fig 3 The knee position is changed from the standard position to the figure-of-4 position. Anteromedial and anterolateral portals are used for viewing and working, respectively. The central portion is excised using 12-cm scissors for the anterior aspect (white arrows) and an oval punch for the middle and posterior aspects (black arrows) of the discoid lateral meniscus. Debridement of the piecemeal meniscus is performed with a 3.5-mm shaver. Arthroscopy Techniques 2015 4, e235-e238DOI: (10.1016/j.eats.2015.02.002) Copyright © 2015 Arthroscopy Association of North America Terms and Conditions

Fig 4 After partial meniscectomy of the central portion is performed, the movement of discoid lateral meniscus should be confirmed again in the standard position. Contrary to before excision of the central portion, we can see the normal movement of the remaining meniscus as we bend and extend the patient's knee without snapping. This image shows discoid lateral meniscus in a right knee after excision of the central portion. Arthroscopy Techniques 2015 4, e235-e238DOI: (10.1016/j.eats.2015.02.002) Copyright © 2015 Arthroscopy Association of North America Terms and Conditions