Discoid Meniscus Associated with Agenesis of the Anterior Cruciate Ligament in an 8-Year-Old Child

Orthopaedics & Traumatology: Surgery & Research (2011) 97, 874—876

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CASE REPORT Discoid meniscus associated with agenesis of the anterior cruciate ligament in an 8-year-old child

M. Rayar, J. Bouillis, B. Fraisse, S. Marleix, M. Chapuis, P. Violas ∗

Department of Pediatric Surgery, South Hospital, boulevard de Bulgarie, 35200 Rennes, France

Accepted: 11 April 2011

KEYWORDS Summary Among the congenital anomalies involving the lateral compartment of the knee, Agenesis of the the combination of both a discoid meniscus and agenesis of the anterior cruciate ligament anterior cruciate (ACL) is extremely rare and probably underestimated due to the presence of a meniscofemoral ligament; ligament often mistaken for an intact ACL. The therapeutic management of such abnormalities Discoid meniscus; is not univocal and highly depends on their clinical impact. We report on the observations of Meniscal cyst an 8-year-old boy presenting with a cystic formation on a lateral discoid meniscus associated with agenesis of the ACL and the presence of an anterior lateral meniscofemoral ligament. © 2011 Elsevier Masson SAS. All rights reserved.

Introduction for an intact ACL on radiographic images. Agenesis of the ACL may be associated with other pathological ﬁndings such Discoid meniscus is the most common congenital anomaly as hypoplasia of the femoral condyle, shallow intercondylar of the meniscus in children. It typically affects the lateral notch or agenesis of the tibial spines [4,5]. Conversely, this meniscus (0,4 to 17%) [1] and less commonly involves the condition is more rarely combined with a discoid meniscus medial meniscus (0.06 to 0.03%) [1,2]. It is found bilaterally [4—7]. in about 20% of the cases [1]. The clinical impact of discoid The authors report the case of an 8-year-old child who meniscus is variable and this condition may remain uniden- presented with a symptomatic meniscal cyst formation com- tiﬁed since some anatomic variants are asymptomatic. The bined with a discoid meniscus. Arthroscopic examination combination of a discoid meniscus and meniscal cyst is found revealed agenesis of the ACL with a meniscofemoral liga- in about 8% of the cases [3]. Agenesis of the anterior cruciate ment mimicking the course of an intact ACL. ligament (ACL) is an extremely rare clinical entity (0.0017 out of 1000 births) [4], which may be underestimated since it may not have any clinical impact or due to the presence of Observation an anterior lateral meniscofemoral ligament often mistaken An 8-year-old boy presented with a 2-year history of swelling in the lateral compartment of his knee. This initially asymptomatic mass had recently increased in size and was ∗ Corresponding author. Tel.: +0299284321. associated with pain during sporting activities. On exami- E-mail address: [email protected] (P. Violas). nation, a tumefaction facing the lateral tibiofemoral joint

the various classifications that have been proposed, the Watanabe classification is the most commonly used [10].It is based on arthroscopic findings and describes three sub- types of lateral discoid menisci: Type I and II are used to describe complete and incomplete discoid menisci depending on the degree of tibial plateau coverage and feature normal peripheral attachments. The Wrisberg-type (type III) discoid meniscus is defined by the absence of the posterior attachment to the tibia thus responsible for hyper-mobility. Monllau et al. [11] have extended this classification by adding a fourth sub-type of discoid meniscus having a ‘‘ring shape’’. However, this classification does not take into account the absence of attachments except for the posterior one. In a series of Klingele et al. [12], peripheral instability was found in 28% of the cases of which 47% of anterior instability versus 39% of posterior instability and 11% of medial instability. These findings were confirmed by Good et al. [13] who even reported higher rates thus suggesting the use of a new classification system based on the complete or incomplete pattern of the meniscus and the presence or not of instability [13]. Surgical treatment should be considered in case of clinical impact and, as suggested Figure 1 Frontal MRI T2 weighted image of the left knee. by Gicquel et al. [14], will consist in restoring the physi- Meniscal cyst in lateral discoid meniscus. ological shape of the meniscus by resection of the injured areas. Meniscal resection should be systematically carried line was identified. It was painless on palpation with neither out using the most sparing technique in order to prevent restriction in the range of motion nor knee instability. arthritic events in the long term. In children as well as in Standard X-rays did not reveal any pathology. MRI exami- adults, this surgical management should be arthroscopically nation demonstrated a meniscal cyst involving the lateral performed since unstable menisci require suture fixation of meniscus, which was thickened thus suggesting a discoid soft tissues for proper stabilization. meniscus (Fig. 1). There was no evidence of anomaly Agenesis of the ACL may be identified through the regarding both cruciate ligaments as well as the con- appearance of knee instability symptoms or may remain tralateral knee. The patient was arthroscopically examined. asymptomatic. It may be associated or not with a poste- Arthroscopy confirmed the presence of a meniscal cyst rior cruciate ligament (PCL) abnormality, thus defining the located on a complete discoid meniscus with intact peri- basis of the Manner classification [4]. An isolated ACL lesion pheral attachments thus corresponding to a type 1 discoid (hypoplasia or aplasia) corresponds to type I, LCA impair- meniscus according to the Watanabe classification [8,9]. ment associated with PCL hypoplasia corresponds to type II A partial resection was performed preserving most of the whereas aplasia of both the ACL and PCL ligaments corre- meniscus lateral wall and was associated with cyst removal. sponds to type III. Arthroscopic examination also revealed ACL agenesis and a The incidence of ACL agenesis is probably underesti- thin fibrous band stretched between the anterior horn of the mated due to its frequent asymptomatic occurrence and lateral meniscus and the postero-lateral region of the inter- the possible presence of a meniscofemoral ligament. The condylar notch. The PCL as well as the medial compartment meniscofemoral ligament is a fibrous anatomical structure of the knee were intact. A type I ACL agenesis according stretched between the anterior horn of the meniscus and to the Manner classification [4] with an anterior menis- the posterolateral aspect of the intercondylar notch, as cofemoral ligament was diagnosed. In the absence of any described by Silva and Sampaio [7]. clinical impact, no additional treatment was initiated. Ana- The combination of a discoid meniscus and ACL agene- lysis of MR images allowed to identify the meniscofemoral sis has rarely been described in the literature. Noble [6] ligament with its anterior insertion on the anterior horn of was the first in 1975 to report the association of both these the meniscus thus mimicking the course of an ACL (Fig. 2). anomalies during the autopsy of an 85-year-old man who had MRI findings of the contralateral knee were normal. After died of bronchopneumopathy and presented a ring-shaped a 4-year follow-up period, the patient does not report any discoid meniscus associated with ACL agenesis. This patient functional limitations and demonstrates a satisfactory knee had an asymptomatic knee before he died. Manner et al. [4] stability. in 2006, report in their series three cases of discoid meniscus (one lateral, one medial and one bilateral) associated in all cases with a type III ACL agenesis. Finally, Silva and Sampaio Discussion [7] have described the combination of a ring-shaped discoid meniscus and ACL agenesis as well as a meniscofemoral The discoid meniscus was first described by Young in 1889 ligament identified in a 13-year-old girl. [10]. It may appear asymptomatic but the occurrence of In our observation, the patient had a type I discoid menis- a meniscal tear is usually associated with symptoms such cus according to the Watanabe classification associated with as pain, snapping knee or limited knee extension. Among a meniscal cyst and a type I ACL agenesis according to the 876 M. Rayar et al.

Figure 2 Sagittal MRI T2 weighted images. White arrow: menisco-femoral ligament. Black arrow: meniscal cyst in discoid meniscus.

Manner classification and reported the presence of a menis- [3] Anderson JJ, Connor GF,Helms CA. New observations on meniscofemoral ligament. The discoid meniscus and ACL agenesis cal cysts. Skeletal Radiol 2010;39:1187—91. were both asymptomatic. The meniscal cyst was the only [4] Manner HM, Radler C, Ganger R, Grill F. Dysplasia of the cru- indication for surgical treatment. ciate ligaments: radiographic assessment and classification. J Bone Joint Surg Am 2006;88:130—7. [5] Thomas NP, Jackson AM, Aichroth PM. Congenital absence Conclusion of the anterior cruciate ligament. A common compo- nent of knee dysplasia. J Bone Joint Surg Br 1985;67: Our observation reveals the presence of congenital intra- 572—5. articular knee anomalies in an asymptomatic child with no [6] Noble J. Congenital absence of the anterior cruciate liga- evidence of antero-posterior instability. The combination of ment associated with a ring meniscus. J Bone Joint Surg Am 1975;57:1165—6. a type I ACL agenesis according to Manner (with a menis- [7] Silva A, Sampaio R. Anterior lateral meniscofemoral ligament cofemoral ligament) and a type I discoid meniscus according with congenital absence of the ACL. Knee Surg Sports Traumatol to Watanabe (with meniscal cyst) is thus reported for the Arthrosc 2011;19:192—5. first time in the literature. Care should be taken by the [8] Watanabe M, Takeda S, Ikeuchi H. Atlas of arthroscopy. Tokyo: physician to perform a thorough analysis of the MR images Igaku-Shoin; 1978. p. 88. necessary when assessing a congenital abnormality of the [9] Neuschwander DC, Drez Jr D, Finney TP. Lateral meniscal vari- meniscus and to keep in mind this possible association. ant with absence of the posterior coronary ligament. J Bone Once the diagnosis has been made, management by liga- Joint Surg Am 1992;74:1186—90. ment reconstruction should be discussed depending on the [10] Young RB. The external semilunar cartilage as a complete disc. symptomatology. In: Cleland J, Macke JY, Young RB, editors. Memoirs and mem- oranda in anatomy. London: Williams and Norgate; 1889. p. 179. Disclosure of interest [11] Monllau JC, León A, Cugat R, Ballester J. Ring-shaped lateral meniscus. Arthroscopy 1998;14:502—4. The authors declare that they have no conflicts of interest [12] Klingele KE, Kocher MS, Hresko MT, Gerbino P, Micheli LJ. Dis- concerning this article. coid lateral meniscus: prevalence of peripheral rim instability. J Pediatr Orthop 2004;24:79—82. [13] Good CR, Green DW, Griffith MH, Valen AW, Widmann RF,Rodeo References SA. Arthroscopic treatment of asymptomatic discoid meniscus in children: classification, technique, and results. Arthroscopy [1] Yaniv M, Blumberg N. The discoid meniscus. J Child Orthop 2007;23:157—63. 2007;1:89—96. [14] Gicquel P, Sorriaux G, Clavert M, Bonnomet F. Rev Chir Orthop [2] Greis PE, Bardana DD, Holmstrom MC, Burks RT, Meniscal Reparatrice Appar Mot 2005;91:457—64. injury: I. Basic science and evaluation. J Am Acad Orthop Surg 2002;10:168—76.