Arthroscopic one-piece reshaping for symptomatic discoid medial meniscus with anomalous amalgamating into anterior cruciate ligament.

Discoid shapes of lateral menisci are relatively common finding, whereas discoid medial menisci are less common. Discoid medial meniscus with associated anomalous variants has been reported. However, symptomatic complex tear of complete type discoid medial meniscus with anomalous blending with anterior cruciate ligament is an extremely rare pathology. A 35-year-old male was admitted to our hospital with left knee pain and loss of terminal extension for 2 years. On physical examination, the patient presented with clicking and restriction during the extension motion of the knee joint. Magnetic resonance imaging and arthroscopy indicated complex tear of complete discoid medial meniscus in association with anomalous connection between entire apical portion of discoid medial meniscus and tibial insertion portion of the anterior cruciate ligament. We obtained a successful outcome with arthroscopic resection and shaping in one-piece method using no. 11 scalpel blade.

INTRODUCTION

The discoid shape is an atavistic meniscal derangement which is significantly less common in the medial meniscus compared with the lateral meniscus.1 Several variants of the discoid meniscus have been documented and with variation from semilunar configuration, which extends across the unilateral or medial joint space.2 The first symptomatic discoid medial meniscus was represented as a complete disc by Jones3 in 1930 and subsequently by Cave and Staples4 in 1941. The reported prevalence of discoid medial meniscus may vary between 0.06% and 1.5% without sex predominance.56 However, a high rate of asymptomatic nature would affect the exact prevalence estimate. Magnetic resonance imaging (MRI) is a valuable tool for prediction of meniscal morphology and accompanying degeneration or tear configuration of the meniscus compared to radiologic findings such as squaring of the medial femoral condyle or cupping of the medial hemiplateau and widening of the joint space may reveal. Discoid lateral meniscus presents with classic snapping of knee, unlike discoid medial meniscus.6 Although, morphological abnormal variation of complete discoid medial meniscus has only rarely been reported,7 anomalous insertion of the anterior horn of the medial meniscus may occur around the anterior cruciate ligament.68 In this report, the author describes a patient with complex tear of complete type discoid medial meniscus with anomalous amalgamation between entire apical margin of discoid medial meniscus and anterior cruciate ligament including MRI and arthroscopy findings. The patient was treated successfully by arthroscopic resection and shaping in one-piece method using no. 11 scalpel blade.

CASE REPORT

A 35 year old male presented to our outpatient clinic with complaints of intermittent vague pain with clicking on his left knee joint for 2 years. On physical examination, there was elastic resistance and clicking during the terminal extension. There was no evidence of any ligamentous instability or malalignment. Simple radiography was not remarkable. Coronal and Sagittal MRI of left knee revealed complex tear with intrameniscal degeneration with diagnosis of incomplete discoid medial meniscus [Figure 1]. The patient underwent arthroscopy of his left knee under general anesthesia. Arthroscopy revealed medial hemiplateau to be completely covered by complete type of discoid medial meniscus and apical margin of the discoid medial meniscus was amalgamating into the anterior cruciate ligament [Figure 2a].

Figure 1

Magnetic resonance images of the left knee demonstrating complete discoid meniscus with tear and wide intrasubstance degeneration

Figure 2

(a) Arthroscopic view of the left knee showing complete type discoid meniscus and apical portion of the meniscus was complete amalgamating into the anterior cruciate ligament. (b) A complex tear in the posterior horn was observed in arthroscopic examination, which is continuous to apical portion of the discoid medial meniscus and fiber of the anterior cruciate ligament

Probing of the meniscal surface revealed central softening with dimpling, which suggested intrameniscal degeneration. In addition, there was complex tear from the mid to posterior horn which extended to the anterior cruciate ligament [Figure 2b]. Using no. 11 scalpel blade and basket forceps, we performed an arthroscopic one piece resection and shaping. The initial resection was started from the tear edge of the posterior horn including the amalgamating portion to anterior horn close and without injuries to anterior cruciate ligament fiber and the articular cartilage [Figure 3a]. Next, the anterior portion was resected using no. 11 scalpel blade in a similar manner. Finally, the remaining medial portion was completely transected by straight and angled basket forceps up to the tear edge with smooth inclination and balancing [Figure 3b]. Resected meniscal fragment was extracted with arthroscopic grasper. We checked the residual rim stability and width with a probe, which was approximately 6 mm, and inspected for intraarticular residual debris or meniscal fragment. After surgery, the patient used disposable knee supporter for 3 days and was encouraged to perform ranges of motion and quadriceps exercise. Full range of motion was achieved within a week after index arthroscopic surgery. At 30-month followup, there was no pain or mechanical symptoms including elastic resistance to the terminal extension or clicking during motion. In addition, patient taking part in many sports activities, such as football, basketball, jogging. Finally, the clinical results were excellent on subjective and objective evaluation according to the Ikeuchi grading system.

Figure 3

(a) The initial resection was started from tear edge of posterior horn including the amalgamating portion to anterior horn using no. 11 scalpel blade closely to anterior cruciate ligament fiber. (b) Arthroscopic view after arthroscopic one piece resection and shaping with the stable peripheral rim

DISCUSSION

The reported prevalence of discoid meniscus was higher among races Asian (17%) compared to Caucasian (5%). In contrast to the lateral meniscus, the highest reported prevalence of a discoid medial meniscus is 1.5%.69 Discoid lateral meniscus is symptomatic in children and adolescents,710 while discoid medial meniscus seems to be symptomatic in adulthood.11 Atay et al.12 in their study have reported that decreased amount of collagen fibers with heterogenous configuration under the electron microscopic findings may be the causative factor of vulnerability of the discoid meniscus. Others may include relatively weak attachments to the joint capsule of the posterior horn, insufficient vascular supply and thickness of discoid shape.13 Associated anomalous findings with discoid medial meniscus have been reported, including an anomalous insertion of the anterior horn of the medial meniscus into anterior cruciate ligament, cyst, pathologic medial plica, discoid lateral meniscus in the same knee.14 This report describes anomalous morphological condition of discoid medial meniscus in which apical portion of complete type discoid medial meniscus was fully amalgamated into anterior cruciate ligament and describes arthroscopic one piece resection and shaping using a scalpel in conventional arthroscopic portal. Arthroscopy ensured identification and determination of the actual type of discoid meniscus, direct inspection and evaluation of associated anomalous variants, and permitted reshaping procedure as one stage. Currently, there is a partial etiologic explanation and pathogenesis of discoid meniscus.

Smillie5 implicated the congenital developmental arrest leading to resorption processing failure of the central meniscus. In contrast to Smillie's assumption, Kaplan15 implicated the biomechanical assumption that discoid shape result from hypermobility on the unstable meniscal attachment of the posterior horn though it did not clearly explain the cases of discoid medial meniscus. Middleton16 described hereditary effect as a contributor to transmission of discoid lateral meniscus. Microscopic tissue examinations through human embryos knee joint revealed the meniscus and cruciate ligament develops directly from an intermediate mesodermal blastoma, which has the shape of a thick plate in the early embryonic period.121516 According to this present case, medial meniscus and anterior cruciate ligament may be differentiated from same embryonic tissue and it may provide evidence of congenital developmental assumption of discoid meniscus. Our patient had a history of pain with extension block in accordance with standard surgical treatment indicated in symptomatic patients with persistent pain or recurrent locking or catching like mechanical block. Many authors have reported that the principles in surgically managing a discoid medial meniscus should be similar for discoid lateral meniscus including limited resection so as to maximally lessen the probability of early degenerative arthritis, which may result from removal of excessive meniscal cartilage.710 Several arthroscopic meniscal resection methods have been reported.17 Although one-piece resection method may be technically demanding procedure, it may have some advantages such as less injury to the normal articular cartilage, least remaining residual meniscal fragment within the joint cavity, and relatively easy checkup of tear configuration. In addition, regarding arthroscopic resection method, there are no reports on arthroscopic one piece resection with shaping using a scalpel through conventional arthroscopic anteromedial and anterolateral portal for complete type discoid medial meniscus, which was amalgamated into anterior cruciate ligament. Currently, the optimal extent of remaining peripheral rim is not clearly established and can be dictated by the type of the meniscus and extent of tear pattern.12 In this case, we obtained the 6 mm remaining peripheral rim.

In conclusion, the author reports the case of symptomatic complex tear of complete discoid medial meniscus amalgamated into the anterior cruciate ligament. We achieved an excellent result after arthroscopic one piece resection and shaping using no. 11 scalpel blade on the latest followup.