Parameniscal cyst formation in the knee is associated with meniscal tear size: An MRI study Chia-Chun Wu a , Yi-Chih Hsu b , Ying-Chun Chiu c , Yue-Cune Chang d , Chian-Her Lee e , Hsain-Chung Shen a , Guo-Shu Huang b, ⁎ a Department of Orthopaedic Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan b Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan c Department of Radiology, Zuoying Armed Forces General Hospital, Kaoshiung, Taiwan d Department of Mathematics, Tamkang University, Taipei, Taiwan e Department of Orthopedics, School of Medicine, College of Medicine, Taipei Medical University, Taipei Medical University Hospital, Taipei, Taiwan abstract article info Article history: Received 16 October 2012 Received in revised form 6 March 2013 Accepted 8 March 2013 Keywords: Knee joint Meniscal tear Parameniscal cyst Magnetic resonance imaging Background: The relationship between meniscal tears and parameniscal cyst formation is contentious. We in- vestigated whether the development of a parameniscal cyst is related to the size of the meniscal tear by using magnetic resonance imaging (MRI). Methods: OnthebasisofaretrospectivereviewofanMRIdatabase,weidentified parameniscal cysts in 34 patients with adjacent meniscal tears extending to the meniscocapsular junction. The size of the meniscal tear was mea- sured by dividing the length of the tear along two axes: circumferential and radial. We compared parameters, suchasthesizeofthemeniscaltear,thelocationofthetear,thepatternofeachtear,andanyassociatedligamentous injury and intra-articular lesion, between the 34 patients and the 30 control patients who only had meniscal tears with torn components extending to the meniscocapsular junction. Results: Compared with the controls, patients with parameniscal cysts had significantly larger meniscal tears along the circumferential axis (P b 0.001). A critical size of the meniscal tear along the circumferential axis of 12 mm was associated with the formation of a parameniscal cyst. Conclusions: A larger meniscal tear extending into the meniscocapsular junction is more likely to be associated with the occurrence of a parameniscal cyst. The critical size of the meniscal tear, 12 mm along the circumfer- ential axis as identified using MRI, is a discrimination value for parameniscal cyst formation. Level of Evidence: Level III © 2013 Elsevier B.V. All rights reserved. 1. Introduction Parameniscal cysts are commonly identified by magnetic resonance imaging (MRI) of the knee [1]. However, the relationship between the meniscal tear and the parameniscal cyst formation is still contentious [2,3]. Several etiological theories have been presented for the develop- ment of parameniscal cysts. The most common theory is that a combi- nation of trauma and degenerative changes to the meniscus may lead to the development of a horizontal cleavage tear. The motion of the knee is then thought to drive synovial fluid into the tear, which extends to the meniscocapsular junction [2–6]. A parameniscal cyst of the knee is likely to be a complication of a meniscal tear that extends to the site of capsular attachment [5]. Surgeons have become more aware of the association between these cysts and meniscal tears, and their surgical approach must address both the meniscal tear and the excision or decompression of the cyst to avoid its recurrence [7–11]. One large prospective cohort study demonstrated that meniscal damage was not directly linked to the development of knee symptoms in middle-aged patients [12]. In addition, some surgeons choose conservative management, instead of partial menisectomy, for meniscal tears during anterior cruciate ligament reconstruction [13–16]. Under these circumstances, even if the meniscal tear is asymptomatic, the assessment of the likelihood of cyst formation has an important im- pact on treatment for patients with meniscal tears that extend to the meniscocapsular junction. Several studies have investigated the incidence of parameniscal cysts, including medial and lateral cysts, and have compared the sites of parameniscal cysts with the locations and frequencies of meniscal tears [1–4,17–20]. However, the relationship between parameniscal cyst formation and the characteristics of the meniscal tear, such as tear size and pattern, remain poorly defined. In our clinical practice, we have observed that the formation of parameniscal cysts is more fre- quently associated with larger meniscal tears than with smaller ones. Therefore, in this cross-sectional MRI-based study, we tested the hy- pothesis that parameniscal cyst formation is associated with the size The Knee 20 (2013) 556–561 ⁎ Corresponding author at: Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, 325, Section 2, Cheng-Kung Rd., Neihu, Taipei 114, Taiwan. Tel.: +886 2 87927244; fax: +886 2 87927245. E-mail address: gsh5@seed.net.tw (G.-S. Huang). 0968-0160/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.knee.2013.03.008 Contents lists available at ScienceDirect The Knee