Abstract Update

The following abstract has been replaced:
Musculoskeletal: Knee
008: Does marathon running cause acute lesions of the knee? Evaluation with MR Imaging
Schueller-Weidekamm C, Schueller G, Uffman M, Bader TR; Department of Radiology, Medical University of Vienna, Vienna, Austria.

NEW 008: Characterization of Meniscal Tears and Degree of Meniscal Extrusion in Patients with Spontaneous Osteonecrosis of the Knee
Omar I.M.¹; Zoga A.C.¹. Thomas Jefferson University Hospital, Department of Radiology, Philadelphia, PA.
Objective: We sought to characterize the types of meniscal tears and degree of meniscal extrusion in the entity termed spontaneous osteonecrosis of the knee (SONK) which may help identify populations at risk for its development.
Materials and Methods: The knee MRI database at our institution was searched for reports describing spontaneous osteonecrosis and insufficiency fractures. MR images were retrospectively reviewed by 2 musculoskeletal radiologists. Inclusion criteria for SONK were bone marrow edema out of proportion to osteoarthritis, extending from the subchondral surface toward midline. Patients with SONK were evaluated for age, gender, weight, type and location of meniscal tear, presence of radial tear, extension into the root, and presence of flipped meniscal fragment. Radial tears were classified into less than 50 % total meniscal width (small) or 50 % or more (large) tears. Meniscal extrusion was measured on mid coronal images and classified into less than 4 mm (minor) or 4 mm or greater (major) extrusion.
Results: 104 cases in 102 patients (48 men and 54 women; age range 32-91; mean 59 years) met criteria for SONK. 93 of 104 lesions (89%) involved the medial compartment, and 11 (11%) occurred in the lateral compartment. Of these 104 lesions, 63 (60.5%) were femoral, and 39 (37.5%) were tibial. 73 meniscal tears (70.2%) primarily involved either the body or posterior horn, and 44 (42.3%) involved the posterior root. There were radial tears in 37 of these 44 cases, and exclusively radial root tears in 18 cases (17.3%). There was meniscal extrusion in 77 of 104 lesions (74.0%) which was major in 53 cases (50.1%). Overall mean extrusion was 3.2 mm. However, it was 4.6 mm if there was a radial tear, and 5.0 mm if there was a large radial posterior root tear. When only medial SONK cases were evaluated the mean extrusion was 3.4 mm, but 6.9 mm when there was also a large radial posterior root tear. Four cases of lateral SONK had associated medial meniscal tears and another was associated with medial meniscectomy. Finally, 21 flipped fragments were seen in 20 cases (19.2%).
Conclusions: Most SONK cases involved medial meniscal pathology with a surprising number of radial tears, particularly involving the posterior root. Meniscal tears seen in SONK were often associated with meniscal extrusion, and large radial and root tears were associated with greater extrusion. Based on our results, patients with medial meniscus tears involving the root or allowing extrusion may be susceptible to the development of SONK.