Discoid medial meniscus

A discoid medial meniscus is an extremely rare anomaly. We present 4 cases of symptomatic discoid medial meniscus. Furthermore, magnetic resonance imaging (MRI) of the unaffected knee was obtained in 3 cases, and 1 patient had bilateral discoid medial menisci as well as a unilateral discoid lateral meniscus proven by MRI. Another patient had bilateral discoid medial menisci. In one of the other 2 cases, an MRI of the unaffected knee was not obtained. However, in the involved knees of both cases, medial and lateral menisci were discoid. The incidence of bilateral discoid medial menisci is unknown. In the past, the diagnosis of a discoid meniscus was made with an arthrogram or at arthrotomy. Therefore, whether some of the unilateral cases reported in the literature might have been bilateral is unknown. The reported prevalence of bilateral discoid medial menisci will probably increase, because when a discoid medial meniscus is encountered currently, an MRI is used to find knee disorders, including in the contralateral knee. Axial multiplanar gradient-recalled-echo imaging could provide images of the discoid meniscus, depicted in its entirety in one section. This would make the recognition of a discoid meniscus simple.     

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.     

Anomalies of the discoid medial meniscus

Anomalies associated with a discoid medial meniscus have been described. However, the clinical relevance of these anomalies has not been previously reported. Therefore, we report the clinical relevance of some of these anomalies based on our experience with a 21-year-old soldier with a 3-month history of medial right knee pain. Magnetic resonance imaging (MRI) revealed bilateral discoid medial menisci, cupping of the medial tibial plateau, and an abnormal anteroinferior transposition of the anterior horn of the meniscus. Partial meniscectomy was performed in the usual manner and the meniscus reshaped, including its anteromedial corner.     

Bilateral discoid lateral menisci and unilateral discoid medial menisci

Discoid lateral meniscus is a well-studied and documented entity of the knee whereas discoid medial meniscus is an extremely rare pathology. There are no more than 25 cases of medial discoid menisci reported in the literature. Some articles report bilateral lateral menisci as well as bilateral medial menisci, but there are no publications about medial and lateral discoid menisci in the same knee with lateral discoid meniscus in the contralateral side. This is a report of a case of bilateral discoid lateral menisci and unilateral discoid medial meniscus. Both arthroscopy and magnetic resonance imaging views are presented.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 7 (September), 2001: pp 772–775     

Discoid lateral meniscus in children: limited knee extension and meniscal instability in the posterior segment

BACKGROUND: Limited knee extension is a well-known sign in children with discoid meniscus, but its causative mechanism is controversial. The purpose of this study was to characterize discoid meniscus with this clinical manifestation with a focus on instability of the posterior segment and its morphologic features. METHODS: The authors retrospectively reviewed magnetic resonance imaging and intraoperative arthroscopic videos of 34 knees in 32 consecutive patients (age range, 4.5-15.0 years) who underwent arthroscopic treatment for symptomatic discoid lateral meniscus. Knees were classified into 2 groups, depending on the presence (n = 19) or absence (n = 15) of an extension block, which was defined as a limitation of knee extension by 10 degrees or more under general anesthesia. Meniscal instability in the posterior segment was determined based on arthroscopic findings, and its correlation with knee extension block was analyzed. Using magnetic resonance imaging, the thicknesses of anterior and posterior segments were measured to assess significance of the thickness differences by a presence of knee extension block and by the posterior segment instability. RESULTS: There were 13 knees with a stable posterior segment and 21 knees with an unstable posterior segment. Meniscal instability in the posterior segment was observed in the knees with a surface tear (n = 12), in a hypermobile posterior rim despite the absence of a surface tear (n = 5), and in knees with a freely movable posterior rim without posterior tibial attachment (n = 4). Knee extension block occurred exclusively in complete type menisci and was significantly correlated with meniscal instability in the posterior segment. Magnetic resonance imaging observations suggested that morphologic features characteristic of thick anterior and thin posterior segments were significantly associated with meniscal instability in the posterior segment. Clinically, knee extension block disappeared in all cases within 4 months of arthroscopic treatment. CONCLUSIONS: A redundant anterior segment associated with meniscal instability in the posterior segment is likely to cause limited knee extension in children with discoid lateral meniscus. This correlation mandates that discoid menisci be thoroughly evaluated during arthroscopic treatment to identify any instability that might require stabilization.     

Dislocating anterior horn of the medial meniscus

Dislocating anterior horn of the medial meniscus was found in 15 knees of 13 patients during arthroscopic examinations done between 1992 and 1995. All of them were available for follow-up evaluation (4 by telephone). There were 11 men and 2 women (average age, 28 years; range, 17 to 49 years). Nine knees had a history of trauma. Only 1 knee had had trauma in two bilateral cases. Duration of symptoms was an average of 3.3 years (range, 3 months to 10 years). The knees were stable clinically. Arthroscopy revealed associated lesions in 13 knees; hypertrophic medial plicae, meniscal, chondral and anterior cruciate ligament (ACL) lesions predominated. Three knees had unusually hypertrophic ligamentum mucosum. Eleven of 13 knees had more than one associated lesions. Only 2 knees (2 patients) had isolated dislocating anterior horn of the medial meniscus. Only the associated lesions were treated (except for ACL lesions) and dislocating anterior horns of the medial menisci were left alone. Follow-up averaged 21 months (7 to 40 months). At follow-up, 11 knees were graded as excellent, 3 as good, and 1 as fair according to the Lysholm scale. Eight knees had minor symptoms and 6 were asymptomatic; no improvement was noted in 1 knee. Overall, 12 patients (14 knees) were satisfied with their treatment. Dislocating anterior horn of the medial meniscus is a normal anatomic variant with little or no clinical significance. When seen during arthroscopy, a significant lesion should be looked for. It is an incidental finding and should be left alone.Arthroscopy 1998 Apr;14(3):246-9     

Management of discoid lateral meniscus tears: Observations in 34 knees

Purpose: The goal of this study was to evaluate arthroscopic partial resection of discoid lateral meniscus tears with an emphasis on radiographic evidence of degenerative changes after this procedure. Type of Study: Retrospective clinical study. Methods: Of 41 patients with an arthroscopic diagnosis of discoid meniscus over an 8-year period, 34 symptomatic lateral discoid meniscus tears in 33 patients were analyzed at an average follow-up of 5.6 years. The average age at operation was 19.8 years and most patients had vague and intermittent symptoms that caused delay in clinical diagnosis. Results: Eight patients were lost to follow-up and were excluded from the study. Magnetic resonance imaging, performed in 12 cases, and arthroscopy in all of these patients provided the precise diagnosis. All of the knees with symptomatic torn discoid menisci underwent arthroscopic partial meniscectomy. Only 1 Watanabe Wrisberg ligament type of discoid meniscus with posterior instability was totally meniscected. Based on Ikeuchi's grading, 39% of the knees had an excellent result, 46% had a good result, and 15% had a fair result; none of the results was poor. Conclusions: At an average 5-year follow-up, partial meniscectomy in patients with a Watanabe complete or incomplete discoid meniscus showed 85% good or excellent clinical results. However, a significant percentage of patients show femoral condyle flattening on radiography.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 4 (April), 2003: pp 346–352     

Arthroscopic treatment of the discoid lateral meniscus: results of long-term follow-up

Twenty-two patients (25 knees) were evaluated at an average follow-up of 54 months for clinical results of arthroscopic treatment of the discoid lateral meniscus syndrome. Discoid lateral menisci were classified arthroscopically as incomplete (92%) or complete (8%); no Wrisberg-type lesions were noted. Three patients (14%) had bilateral lesions. Symptomatic torn discoid menisci (20 knees) and torn discoid menisci with other significant symptomatic lesions (3 knees) underwent arthroscopic partial lateral meniscectomy utilizing the saucerization technique. Asymptomatic intact discoid menisci (2 knees) were left unresected. Using the knee scale of Ikeuchi, 55% of the symptomatic torn lesions were rated as excellent or good, 30% were rated as fair, and 15% were rated as poor at follow-up. Two of the 3 asymptomatic torn lesions were rated as excellent or good, as were both of the intact discoid lesions. Factors associated with an unsatisfactory rating at follow-up included preexistent degenerative changes, age, and sex. Duration of symptoms, type of discoid tear, and length of follow-up were not necessarily related to outcome results. Seven knees (28%) required arthroscopic reevaluation at a postoperative average of 23 months, documenting apparent physiologic function of the saucerized rim in 4 patients and failure of saucerization in 3 patients (12%). Overall, 14 of the 22 patients in this study (64%) resumed a normal activity level postoperatively, including 61% of those with symptomatic torn discoid lateral menisci.     

Anomalous insertion of the medial menisci

Many types of meniscal anomalies have been reported. The authors encountered two cases of anomalous insertion of the anterior horn of the medial menisci to the lateral femoral condyle, which ran up along the course of the anterior cruciate ligament (ACL), but was independent of the ACL. These anomalies were noted during arthroscopic examination and surgery of the ipsilateral knee for a torn discoid meniscus and a patellar fracture. A 34-year-old woman had a horizontal tear of the lateral discoid meniscus. We performed arthroscopic partial meniscectomy of the inner torn portion of the lateral discoid meniscus and contoured it to resemble a normal meniscus. An anomalous insertion of the medial meniscus was found on examination of the joint during surgery. A 32-year-old man had a patellar fracture and we performed reduction under arthroscopy and internal fixation with cannulated screws. The same anomalous insertion of the medial meniscus was also found on examination of the joint during surgery. We report the cases with a review of the literature.Arthroscopy 1998 Jul-Aug;14(5):505-7     

Bilateral complete discoid medial meniscus: a case report

Discoid medial meniscus is very rare, and bilateral discoid medial meniscus is extremely rare. We report a case of bilateral discoid medial meniscus. The patient had symptoms in the right knee but was asymptomatic in the left knee. We performed magnetic resonance imaging for both knees. The patient was treated by saucerization and by all inside repair of the anterior horn tear in the right knee. We performed second-look arthroscopy after 18 months.     

Congenital discoid lateral meniscus in children. A follow-up study and evolution of management

Fifty-two children with 62 discoid lateral menisci were reviewed at an average follow-up of 5.5 years. Their average age at operation was 10.5 years and the mean delay in diagnosis was 24 months. Most of the children had vague and intermittent symptoms and the classical clunk was demonstrable in only 39% of the knees. An associated osteochondritis dissecans of the lateral femoral condyle was seen in seven knees. Forty-eight knees with symptomatic torn discoid menisci underwent open total lateral meniscectomy, six had arthroscopic partial meniscectomy and eight knees with intact discoid menisci, were left alone. Based on Ikeuchi's grading (Ikeuchi 1982), 37% of the knees had an excellent result, 47% had a good result and 16% had a fair result: none was poor. Arthroscopic partial meniscectomy is recommended only when the posterior attachment of the discoid meniscus is stable. A total meniscectomy is indicated for the Wrisberg-ligament type of discoid meniscus with posterior instability.     

Bilateral complete discoid medial menisci combined with anomalous insertion and cyst formation

A female student had a complete discoid medial meniscus of right knee combined with a meniscal cyst and anomalous insertion to the anterior cruciate ligament. This was confirmed by magnetic resonance imaging (MRI) and the arthroscopic procedure. Also shown by the MRI, the left knee had the discoid medial meniscus, but it was asymptomatic.     

Arthroscopic studies of variants of the anterior horn of the medial meniscus

The objective of this study was to arthroscopically analyse the morphology and dynamics of variants of the anterior horn of the medial meniscus of the knee (VAMM) and to then consider the pathological significance of these variants. VAMM was defined as knees in which the anterior horn of the medial meniscus is not attached to the tibia. Between April 1992 and March 1995, arthroscopy was performed on 953 knees of 903 patients. At the time of this examination, observation and probing were performed to determine the condition of the synovium, the synovial plica, the cartilage in all compartments, the meniscus, the cruciate ligaments, and the popliteal tendon. In particular, detailed examination was made of the anterior horn of the medial meniscus with regard to the point of insertion to the tibia and the degree of movement in knee flexion/ extension. Cases of VAMM diagnosed on the basis of the arthroscopic findings were classified into the following four categories: the ACL (anterior cruciate ligament) type, where the anterior horn of the medial meniscus was attached to the ACL; the transverse ligament type, where the anterior horn of the medial meniscus was attached to the transverse ligament; the coronary ligament type, where the anterior horn of the medial meniscus was attached to the coronary ligament; and the infrapatellar fold type, where the anterior horn of the medial meniscus was attached to the infrapatellar synovial fold. These patients were then analyzed with regard to the arthroscopic findings and the intra-articular lesions other than VAMM. In 98 (10.9%) of the total patients, 103 knees were classified as VAMM. Classification of those 103 knees using the above criteria showed 39 ACL type knees, 51 transverse ligament type knees, 11 coronary ligament type knees, and 2 infrapatellar fold type knees. The arthroscopic findings indicated that the anterior horn of the medial meniscus was not attached directly to the tibia in any of these knees. Probing and flexion/extension of the knee revealed hypermobility at the anterior horn of the medial meniscus. In this study, anterior knee pain syndrome was diagnosed in 12 (11.7%) of the 103 VAMM knees. In addition, there was no clear history of trauma in 20 of 23 knees found to have an isolated medial meniscus tear. In these cases, even detailed arthroscopic observation proved the causes of the symptoms or injury. On the basis of these findings, we surmised that the anterior portion shows hypermobility at the time of flexion/extension of the knee, regardless of the type of VAMM. In this study, we discussed the possibility that the existence of VAMM may become the cause of pain or injury to the meniscus.     

Discoid medial meniscus with a horizontal cleavage tear: a juvenile who suffered for 3 years

It is very rare to see medial discoid meniscus, and there have been only 82 knees in 61 cases reported to date. The investigators found discoid medial meniscus with horizontal cleavage tear in a 13-year-old juvenile who had been injured while playing basketball, and endured for 3 years. Both magnetic resonance images and the arthroscopic findings were presented. Saucerization of the torn discoid medial meniscus was performed successfully, and the clinical outcomes were satisfying according to the follow-up of 14 months.     

Discoid lateral menisci in older patients

Twenty-three knees of 21 patients over 40 years of age with discoid lateral menisci were examined by radiography. The mean age of the patients was 59.7 years (range: 40-78 years). No patient had symptoms before the age of 40 and only 12 knees gave symptoms from the lateral compartment, although tears of a discoid lateral meniscus were diagnosed by arthrography in 21 of the 23 knees. Varus inclination occurred more frequently than valgus inclination. Subchondral bone sclerosis was more common in the medial compartment. However, high incidences of marginal osteophytes in the lateral compartment and morphological anomalies (cupping or flattening) of the lateral tibial plateau were revealed by radiography.     

Radial displacement of the medial meniscus in varus osteoarthritis of the knee

The macroscopic and histologic findings for 31 medial menisci and medial tibial plateaus obtained during total knee arthroplasty were examined to clarify the etiology and progression of varus osteoarthritis. Medial menisci were preserved fairly well in cases of severe osteoarthritis in which the medial joint space had already disappeared. The anterior segment was preserved in 26 (84%) menisci and the posterior segment was preserved in 11 (35%). The medial meniscus may have been preserved because of its radial displacement. Exposure of subchondral bone of the medial tibial plateau occurred in all 31 knees. The exposure of subchondral bone was centered in the anterior, middle, and posterior in nine, 10, and 12 medial tibial plateaus, respectively. There was a mechanical inconsistency between the pattern of preservation of the medial menisci and the location of exposure of subchondral bone on the medial tibial plateaus. The inconsistency reflects that the segment of the medial meniscus on which the excessive load was considered to exist was preserved fairly well. The authors' hypothesis for explaining this inconsistency is that radial displacement of the medial meniscus precedes narrowing of the medial joint space during progression of varus osteoarthritis, so that the displaced meniscus is saved from severe degeneration or attrition.     

膝盘状软骨的关节镜治疗

目的：探讨关节镜诊断治疗膝关节盘状软骨的作用。材料与方法：1995年9月－1999年12月关节镜治疗外侧盘状软骨38例。部分切除20例,次全切除14例,全切4例。结果：随访6个月－4年3个月,关节功能正常、症状消失30例。偶有疼痛3例,关节弹响1例,肌萎缩无改善2例,膝关节屈伸轻度受限2例。结论：盘状软骨镜下切除术保留软骨的宽度取决于盘状软骨的类型、撕裂范围和位置。保留的软骨应稳定、紧张;保留软骨形成的“半圆箍”应完整;术中活动膝关节无弹跳。     

Arthroscopic meniscectomy for discoid lateral meniscus in children and adolescents: 4.5 year follow-up

We retrospectively reviewed the 4.5 year (range, 21-88 months) follow-up results of arthroscopic partial meniscectomies performed in 11 knees between 1994 and 2000 to treat a symptomatic discoid lateral meniscus. The average age at surgery was 11.5 years (range, 5-17 years). All except one of the discoid menisci were of a complete type, and all except three were torn menisci. At the latest follow-up examination, the result was excellent for nine knees, and good for two; no degenerative changes were evident on the roentgenograms. Arthroscopic partial meniscectomy should be the treatment of choice for the complete type symptomatic lateral discoid meniscus, even if it is intact. Preoperative lack of the knee extension requires a gentle rehabilitation program postoperatively.     

Discoid lateral meniscus: prevalence of peripheral rim instability

The purpose of this study was to determine the prevalence of peripheral rim instability in discoid lateral meniscus. A consecutive series of 112 patients (128 knees) (mean age 10.0 years [range 1 month to 22 years]) who underwent arthroscopic evaluation and treatment of a discoid lateral meniscus between 1993 and 2001 was reviewed. Of those discoid menisci classified intraoperatively (n = 87), 62.1% (n = 54) were complete discoid lateral menisci and 37.9% (n = 33) were incomplete discoid lateral menisci. An associated meniscal tear was present in 69.5% (n = 89) of all knees studied. Overall, 28.1% (n = 36) of discoid lateral menisci had peripheral rim instability: 47.2% (n = 17) were unstable at the anterior-third peripheral attachment, 11.1% (n = 4) at the middle-third peripheral attachment, and 38.9% (n = 14) at the posterior-third peripheral attachment. Thirty-one of the 36 unstable discoid menisci underwent repair of the peripheral meniscal rim attachment. One patient underwent a complete, open meniscectomy. Peripheral rim instability was significantly more common in complete discoid lateral menisci (38.9% vs. 18.2%; P = 0.043) and in younger patients (8.2 vs. 10.7 years; P = 0.002). The frequency of peripheral instability mandates a thorough assessment of meniscal stability at all peripheral attachments during the arthroscopic evaluation and treatment of discoid lateral meniscus, particularly in complete variants and in younger children.     

Radiographic knee dimensions in discoid lateral meniscus: comparison with normal control.

We reviewed the knee radiographs of 68 cases of arthroscopically proven discoid lateral meniscus, including 42 cases of complete type and 26 cases of incomplete type discoid lateral meniscus. Knee radiographs of 70 cases that had no arthroscopic evidence of pathology of the meniscus were used as controls. We excluded patients who had significant trauma history and who were under 16 years of age or over 60 years to avoid measuring radiographs of skeletally immature or degenerative knees. The absolute values and relative normalized values of specific knee dimensions, such as a squared-off appearance of the lateral femoral condyle, widened femorotibial joint space, cupping of the lateral tibial plateau, obliquity of the lateral tibial plateau articular surface, high fibular head, and hypoplasia of the lateral intercondylar spine, were compared between the patients with discoid lateral meniscus and the normal controls. Among those dimensions, high fibular head and widened lateral tibiofemoral joint space showed statistically significant differences between the discoid lateral meniscus group and normal control group. We suggest that these findings would be useful in screening lateral discoid meniscus on plain radiography.