State of the art review Isolated meniscus injuries in skeletally immature J ISAKOS: first published as 10.1136/jisakos-2020-000496 on 21 May 2021. Downloaded from children and adolescents: state of the art Gustavo Vinagre ,1 Flávio Cruz,2 Khalid Alkhelaifi,3 Pieter D’Hooghe 3 1Department of Orthopaedic ABSTRACT and retaining up to 8 mm of peripheral rim, with or Surgery and Traumatology, The prevalence of isolated meniscal injuries in children without meniscal repair.15 Hospital de Verín, Verín, Galicia, Spain and adolescents is low; however, we see an increase This state- of- the- art review aimed to provide an 2Department of Orthopaedic mainly due to intensified sports-related activities at overview of the most important available evidence Surgery, Universidade Federal an early age. A meniscal repair should be attempted on meniscal injuries in children (below the age of do Estado do Rio de Janeiro, Rio whenever possible as children present with increased puberty) and adolescents (the period from puberty de Janeiro, Brazil meniscal healing potential. The diagnosis and 3Department of Orthopaedic to adulthood). Surgery, Aspetar Orthopaedic management of meniscal tears involve both patient and Sports Medicine Hospital, factors and tear characteristics: size, anatomical location Doha, Qatar and associated injuries. Special attention should be given EPIDEMIOLOGY to the feature of discoid menisci and related tears as The true prevalence of isolated meniscal injuries Correspondence to they require a specific management plan. among skeletally immature children and adoles- Dr Pieter D’Hooghe, Department This state-of- the- art review highlights the most recent of Orthopaedic Surgery, Aspetar cents is still unknown. Initially, meniscal injuries in studies on clinical evaluation, surgical techniques, Qatar Orthopaedic and Sports children were thought to be extremely rare, espe- tips and tricks, pitfalls, outcomes, return-to- sports , Medicine Hospital, Doha, Qatar; cially under 10 years of age, unless associated with pieter. dhooghe@ aspetar. com geographical differences and future perspectives related a discoid meniscus.16 Some authors suggest that the to meniscal injuries in children and adolescents. Received 6 July 2020 occurrence of an isolated meniscal injury is greater Revised 28 November 2020 than previously thought, mainly due to increased Accepted 22 December 2020 sports participation at a younger age.12 13 A study on 1082 meniscal injuries in high school athletes INTRODUCTION reported an overall meniscal injury rate of 5.1 per Meniscal injuries are less prevalent in children and 100 000 athletes and a 40.7 per 100 000 incidence adolescents than in adults. However, the increase in boys’ football and 23.2 per 100 000 in girls’ in sports participation by the skeletally immature soccer.17 Stanitski et al18 reported in their study that athlete has furthermore increased the incidence of 70% of the 47 meniscal injuries in adolescents and meniscal injuries in this population. Those involve children involved the medial meniscus. According meniscal tears and symptomatic discoid meniscus. 17 to Mitchell et al’s study of 1082 meniscal injuries http://jisakos.bmj.com/ The meniscus plays a fundamental role in shock in high school athletes, anterior cruciate ligament absorption, load distribution, knee stability, joint (ACL) injury is highly associated with meniscal inju- lubrication and knee congruity. Meniscal deficiency ries in 36.9% of the cases. is known to compromise the future of the knee, leading to premature, progressive osteoarthritis The prevalence of meniscal tears in 124 skele- (OA).1 2 tally immature patients who underwent ACL recon- structions was 69%, with the lateral meniscus being Surgical meniscectomy can lead to the develop- 19 ment of early degenerative changes of the knee, involved in the majority of cases. ligamentous laxity and pain over time, especially However, the prevalence of ACL- associated ramp on October 1, 2021 by guest. Protected copyright. lesions in children and adolescents is similar to that when the procedure is performed at a young age 20 stage.3–5 in adult populations (15%–24%). Numerous studies have stressed the importance Discoid lateral meniscus has a prevalence that of “meniscus retain, repair or replace” through a ranges from 0.4% to 20%, with higher prevalence 9–14 21 22 meniscal scaffold or meniscal allograft transplan- in Asian children. The presence of a medial tation (MAT) to maintain knee joint homeosta- discoid meniscus is very rare: 0.07%–0.3% when sis.6–8Whenever feasible, meniscus retention or compared with 1.2%–5.2% for the lateral discoid 14 23 repair is indicated to avoid the well- known dele- meniscus. Even more rare is to have ipsilateral terious effects of partial, subtotal, or total menis- lateral and medial discoid meniscus (figure 1). The © International Society of cectomy on the knee. Discoid lateral meniscus prevalence of bilateral DLM is unknown due to its 24 Arthroscopy, Knee Surgery and (DLM) is an abnormal congenital morphological asymptomatic nature. The longitudinal type of Orthopaedic Sports Medicine anomaly of the knee characterised by a wide and tears accounts for 50%–90% of meniscal injuries in 2021. Re- use permitted under the young, while bucket-handle meniscal tears repre- CC BY-NC . No commercial re- thick meniscus that typically covers a larger area of use. Published by BMJ. the tibial plateau, and is easily prone to damage as a sent approximately 14% of all meniscal tears, mostly result.9–14 A symptomatic DLM is usually linked to affecting the medial meniscus.24–27 According to To cite: Vinagre G, a meniscal tear or an unstable discoid meniscus, and Shieh et al,26 a retrospective study of 293 children Cruz F, Alkhelaifi K, et al. J ISAKOS Epub ahead of can be treated with partial meniscectomy, ‘normal and adolescents with meniscal tears who under- print: [please include Day reshaping’ of the discoid meniscus with menisco- went arthroscopic surgery showed that patients with Month Year]. doi:10.1136/ plasty/saucerisation, removing the central part of discoid tears had a lower mean age (12.7) than those jisakos-2020-000496 the meniscus to restore its standard crescent shape with non- discoid tears (15.7). Vinagre G, et al. J ISAKOS 2021;0:1–8. doi:10.1136/jisakos-2020-000496. Copyright © 2021 ISAKOS 1 State of the art review J ISAKOS: first published as 10.1136/jisakos-2020-000496 on 21 May 2021. Downloaded from Figure 3 Watanabe classification of discoid lateral meniscus: (A) type I: block- shaped stable, complete meniscus; (B) type II: block- shaped stable, partial meniscus; (C) type III: unstable meniscus, with stability arising only from the ligament of Wrisberg. Figure 1 Right knee MRI—a rare case of an adult patient with an instead of a normal ‘semilunar’ shape and covers more tibial ipsilateral lateral and medial discoid meniscus. (A) Coronal view and (B) plateau. The histology and ultrastructure of the discoid meniscus sagittal view: medial discoid meniscus horizontal tear. are different from those of a normal meniscus. In the discoid meniscus, there are decreased collagen fibres and the presence of irregularly oriented collagen fibres. Intrameniscal mucoid degen- EMBRYOLOGY AND ANATOMY 31 32 The menisci arise from mesenchymal tissue within the limb eration is common, and mucoid material has been found. bud and are formed in the knee joint between the 8th and 10th The precise aetiology of a discoid meniscus is unknown, week of embryonic life, being evident by week 8 and having a although some authors suggested that it is congenital, with a normal appearance by week 14 of embryological development.28 genetic or familiar predisposition for the development of discoid menisci.14 33 34 Blood supply arises from the periphery through the perimeniscal 35 capillary plexus, being fully vascularised at birth, two- thirds According to Aydın Kabakçı et al on human fetal cadavers, peripheral by 9 months and then gradually decreases.21Adult a fetal lateral meniscus classification was described, leading to a morphology is reached by the age of 10 years. Commonly, the better understanding of the morphological development of fetal peripheral rim is known as the ‘red–red’ (R- R) zone and the meniscal development. The Watanabe classification describes three types of DLM inner one- third as the ‘white–white’ zone (figure 2). By adult- 36 37 hood, only the peripheral 10%–30% will receive blood supply. based on their shape and tibial attachments (figure 3). The inner two- thirds of the mature menisci receive nutrition by diffusion from the synovial fluid. Medial meniscus has a C- shape MECHANISM OF INJURY and covers approximately 50% of the medial tibial plateau while Traumatic meniscus tears in children and adolescents have a clin- the lateral meniscus is more circular and covers approximately ical presentation similar to those in adults but are highly associ- 70% of the lateral tibial plateau. The inner structure of the ated with ACL injuries. meniscus consists of mostly type I collagen fibres arranged in a Most of non- discoid meniscal injuries (80%–90%) occur http://jisakos.bmj.com/ circumferential pattern parallel to its long axis. Radial, oblique during sports events. The mechanism of injury is a sudden twist and vertically oriented fibres help the circumferential fibres to of flexed knee with the foot planted during cutting and pivoting reduce the (hoop) stresses.29 30 sports activities such as soccer, American football, basket- 18 29 30 38–40 A discoid meniscus is an abnormal congenital morpholog- ball, skiing or wrestling. We did not find any report ical anomaly: it is thicker, has less vascularity, has a ‘disc’ shape describing a specific mechanism of injury for discoid meniscal tears, as the true natural history of discoid menisci is still thought to be unknown.41 on October 1, 2021 by guest. Protected copyright. RISK FACTORS AND ASSOCIATED CONDITIONS Box 1 presents known risk factors and associated conditions related to meniscal injuries in children and adolescents.