Regeneration of ring-shaped lateral meniscus after partial resection of discoid meniscus with anterior cruciate ligament reconstruction

INTRODUCTIONThe ring-shaped lateral meniscus is very rare. Although it is essentially known as a congenital anomaly, a central tear in an incomplete discoid meniscus or an old bucket-handle tear in a meniscus may be easily mistaken for a ring-shaped meniscus. We experienced a ring-shaped lateral meniscus that regenerated after partial resection of a discoid meniscus together with anterior cruciate ligament (ACL) reconstruction.PRESENTATION OF CASEA 37-year-old female patient still experienced unrelenting knee pain 6 months after ACL reconstruction and partial meniscectomy of a discoid lateral meniscus. A repeat arthroscopy was performed. The lateral tibial plateau was covered in the form of a ring by meniscus-like tissue. The meniscus-like tissue appeared to have regenerated inward toward the center from the stump after the partial meniscectomy and was connected from the anterior to posterior horn, forming an interhorn bridge. Partial meniscectomy was repeated. Histologically, the regenerated tissue was not meniscal, but comprised mature fibrocartilage; macroscopically; however, it was very similar to meniscal tissue. Two years after the initial operation, the patient had no complaints and experienced full return of function.DISCUSSIONThe reason for such regeneration is unknown, but may have been attributed to the specific intra-articular environment that developed after the ACL reconstruction.CONCLUSIONThis is the first report of regenerative development of a ring-shaped lateral meniscus. When a ring-shaped lateral meniscus is diagnosed, we must accurately determine whether it is a true congenital anomaly in consideration of the present case.     

膝关节半月板撕裂的磁共振表现

目的进一步认识膝关节半月板撕裂的磁共振成像(MRI)表现。方法回顾分析50例膝关节半月板撕裂的MRI资料,所有病例均经关节镜手术证实。采用永磁型MRI机,场强0.2T。结果50例半月板撕裂中,按照部位分类,半月板撕裂位于内侧半月板前角2例,内侧后角37例,外侧半月板前角5例,外侧后角3例,同时累及半月板前角、体部和后角者内侧2例,外侧1例。按照半月板撕裂的形式分为:水平撕裂8例;垂直撕裂4例;斜形撕裂26例;纵形撕裂3例;放射状撕裂4例;桶柄状撕裂2例;复杂撕裂3例。结论MRI能够清楚显示膝关节半月板撕裂的部位和形式,为临床治疗提供可靠的依据,是目前诊断半月板撕裂的最好的影像学检查方法。     

膝关节内外侧半月板后根部撕裂的MRI诊断价值

目的:探讨MRI对膝关节内外侧半月板后根部撕裂的诊断价值。方法:回顾性分析2012年1月至2016年1月,关节镜下证实为半月板后根部撕裂的患者43例。其中男25例,女18例;年龄27~69(42.5±8.3)岁;右侧27例,左侧16例。由2名医师采用双盲法独立回顾性分析经关节镜证实的43例半月板后根部撕裂患者的MRI表现,计算MRI对半月板后根部撕裂的诊断敏感性、特异性和准确性,并计算膝关节韧带损伤及半月板脱位等伴随情况。结果:143例中,关节镜手术证实43例半月板后根部撕裂,包括内侧撕裂24例,外侧撕裂19例。医师A诊断内侧半月板后根部撕裂的敏感性、特异性、准确性分别为91.67%、86.6%、83.9%,伴内侧半月板突出19例,伴前交叉韧带撕裂2例;外侧半月板后跟部撕裂的敏感性、特异性、准确性分别为73.7%、79.9%、79%,伴外侧半月板突出4例,伴前交叉韧带撕裂16例。医师B诊断内侧半月板后根部撕裂的敏感性、特异性、准确性分别为87.5%、87.4%、87.4%,伴内侧半月板突出19例,伴前交叉韧带撕裂2例;外侧半月板后跟部撕裂的敏感性、特异性、准确性分别为78.9%、82.3%、82.5%,伴外侧半月板突出4例,伴前交叉韧带撕裂16例。2名医师采用MRI诊断内、外侧半月板后根部撕裂的一致性均好,Kappa值分别为0.81和0.67。结论 :膝关节MRI诊断内外侧半月板后跟部撕裂及其伴随征象具有较大价值,为临床医生术前诊断提供依据,值得临床推广应用。     

Snapping knee caused by a popliteomeniscal fascicle tear of the lateral meniscus in a professional Taekwondo athlete

A 19-year-old male professional Taekwondo athlete presented with a 2-year history of pain-free snapping of his right knee. He reported that his right knee joint gave way during games and training and that he could induce pain-free snapping between the proximal-to-fibular head and the lateral knee joint line. None of these physical findings suggested a meniscal pathology or ligamentous instability. Routine radiographs were normal. Magnetic resonance imaging of his right knee joint showed that the shape of the lateral meniscus was normal, and no lateral meniscus tears existed. On arthroscopic examination, popliteal hiatus view showed a posterosuperior popliteomeniscal fascicle tear between the posterior horn of the lateral meniscus and the posterior joint capsule just posteromedial to the popliteus tendon. With medial traction by probing, this popliteomeniscal tear made visible the significant subluxation of the posterior horn of the lateral meniscus to the center or anterior half of the tibial plateau. Based on the diagnosis of a posterosuperior popliteomeniscal tear of the right knee, Fast-Fix (Smith & Nephew, Andover, Massachusetts) was used for the direct repair of the peripheral portion of the lateral meniscus and joint capsule, targeting the popliteomeniscal junction. At 24 months postoperatively, the patient was performing athletic exercises relevant to his profession and was taking part in Taekwondo games, with no pain or recurrence of snapping. To the authors' knowledge, this is the first report of snapping of the lateral aspect of the knee due to a popliteomeniscal fascicle tear.     

Knee locking and pain mimicking lateral meniscal tear due to unusual location of localized pigmented villonodular synovitis: a diagnostic surprise

Pigmented villonodular synovitis (PVNS) is one of the rare conditions, which typically involves the knee joint. There are two main types of PVNS-localized and diffuse, with localized type relatively rare when compared to diffuse PVNS. This case report describes a 30-year-old man presenting with a short history of swelling, posterolateral joint line pain and intra-articular mechanical locking of the left knee. There was localized tenderness, and McMurray’s test was positive. Arthroscopy revealed a firm pedicular localized pigmented villonodular synovitis originating from the beneath of the body and posterior horn of the lateral meniscus. The lesion was excised arthroscopically. This allowed a return to normal daily activities. Localized pigmented villonodular synovitis (LPVNS) arising from posterolateral aspect of knee mimicking lateral meniscal tear has not been reported in the literature. Though rare, LPVNS should be kept as differential diagnosis of meniscal tear. LPVNS can be managed effectively with arthroscopy.     

Magnetic resonance imaging of the knee in children and adolescents. Its role in clinical decision-making

BACKGROUND: Recent studies have questioned the utility of magnetic resonance imaging in the diagnosis of pediatric knee disorders because of the morphologic changes during growth and the low accuracy of the formal interpretation of the magnetic resonance imaging scan by a radiologist. The purpose of this study was twofold: (1) to report the accuracy of formal interpretations of magnetic resonance imaging scans of the knee in children and adolescent patients by a radiologist, and (2) to determine the benefit, if any, of a personal review of the magnetic resonance imaging scan of the knee by the orthopaedic surgeon, as a routine part of the diagnostic evaluation. METHODS: A three-year prospective study of all patients who underwent knee arthroscopy performed by a single surgeon, at two children's hospitals, was completed. The analysis focused on the six most common diagnoses: anterior cruciate ligament tear, lateral meniscal tear, medial meniscal tear, osteochondritis dissecans, discoid lateral meniscus, and osteochondral fracture. The preoperative diagnosis of the surgeon was determined by integrating the history and the findings on the clinical examination, plain radiographs, and magnetic resonance imaging scans (including the radiologist's interpretation). RESULTS: Ninety-six patients with ninety-six abnormal knees were included. The mean age was 14.6 years at the time of surgery. Relative to operative findings, kappa values for the formal interpretations of the magnetic resonance imaging scans by a radiologist were 0.78 for an anterior cruciate ligament tear, 0.76 for a medial meniscal tear, 0.71 for a lateral meniscal tear, 0.70 for osteochondritis dissecans, 0.46 for discoid lateral meniscus, and 0.65 for osteochondral fracture. Relative to operative findings, kappa values for the preoperative diagnoses by the surgeon were 1.00 for an anterior cruciate ligament tear, 0.90 for a medial meniscal tear, 0.92 for a lateral meniscal tear, 0.93 for osteochondritis dissecans, 1.00 for discoid lateral meniscus, and 0.90 for osteochondral fracture. The preoperative diagnosis by the surgeon was better (p < 0.05) than the formal interpretation of the magnetic resonance imaging scans by the radiologist with respect to an anterior cruciate ligament tear, lateral meniscal tear, osteochondritis dissecans, and discoid lateral meniscus. CONCLUSIONS: Integration of patient information with an orthopaedic surgeon's review of the magnetic resonance imaging scan of the knee in children and adolescent patients improves the identification of pathological disorders in four of the six categories evaluated. This study questions the necessity for and appropriateness of a routine interpretation of a magnetic resonance imaging scan of the knee in children and adolescents by a radiologist.     

Displacement of the Posterior Horn of the Lateral Meniscus into Posterolateral Compartment: An Unusual Injury Pattern

We report a case of acute ACL injury with an unusual lateral meniscal tear pattern. The entire posterior horn of the lateral meniscus was avulsed from its attachments while remaining in continuity with the body of the meniscus. It was displaced posteriorly and laterally to the popliteus tendon so that it was not immediately visible at the time of arthroscopy. This type of displacement of the posterior horn of the lateral meniscus is difficult to identify at arthroscopy and has not previously been described in the literature to our knowledge. We recommend to surgeons who encounter an absent posterior horn of the lateral meniscus to consider this injury pattern.     

Extension block secondary to partial anterior cruciate ligament tear on the femoral attachment of the posterolateral bundle

Purpose: The purpose of this investigation was to prove that a partial tear of the anterior cruciate ligament (ACL) at the femoral attachment of the posterolateral bundle can result in mechanical knee locking and trigger the injury mechanism of an isolated ACL injury. Type of Study: Case series. Methods: From February 1993 through June 1999, 19 cases of knee locking with observation of a torn ACL, confirmed under arthroscopy, were investigated. Patients’ ages ranged from 22 to 54 years. The causes of injury were sporting activities in 14 patients (8 skiing, 4 soccer, and 2 badminton); slipping and falling in 2 cases; a pedestrian car accident in 2 cases; and an unknown low-velocity injury in 1 case. Results: On physical examination, each patient indicated that the chief complaint was knee pain; all had a locked knee at 5° to 20° of full extension and 4 cases showed a locked knee at full flexion. Of the 19 cases, Lachman testing was positive in 3. With respect to intra-articular injuries, 3 patients had a tear in the medial meniscus and 1 had a tear in the lateral meniscus. The average time span between arthroscopy examinations was 3 months with a range of 1 to 10 months. Arthroscopic diagnosis and treatment were performed and meniscal tear was ruled out as the cause of locking in all patients. Conclusions: The mechanisms of injury for isolated ACL were knee hyperextension and internal rotation of lower extremity brought on especially by a low-velocity injury. The partial ACL tears were found on the femoral attachment site of the posterolateral bundle. The torn segment of the ACL was interposed between the lateral femoral condyle and the lateral tibial condyle and acted as a mechanical obstruction, giving rise to the locking symptom. In all 19 cases, the torn portion of the ACL was excised under arthroscopy and the locked knees were treated properly.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 3 (March), 2002: pp 227–231     

Radial Displacement of Lateral Meniscus After Partial Meniscectomy

Radial displacement or extrusion of the meniscus has been reported as a complication after meniscal transplantation and is sometimes observed in knees with advanced osteoarthritis. In this report, the case of a patient with radial displacement of the lateral meniscus after partial meniscectomy is presented. He had an incomplete discoid lateral meniscus with an anterior horn tear. The inner portion of the lateral meniscus was excised to leave a width of 8 to 10 mm. However, follow-up magnetic resonance imaging showed radial displacement of the mid-body of the lateral meniscus and a compatible finding of chondromalacia of the lateral compartment of the knee.     

Lateral meniscal variant with absence of the posterior coronary ligament.

We reviewed the cases of 3468 patients who had had arthroscopy of the knee between January 1976 and December 1988. Twenty-six patients (0.8 per cent) had a partial or a complete discoid lateral meniscus, and seven (0.2 per cent) had the Wrisberg-variant-type lateral meniscus. Of the seven patients, six had operative stabilization of the meniscus and one had a partial lateral meniscectomy because of an irreparable complex tear. Subjective, objective, and radiographic evaluations were performed on the patients who had had stabilization of the meniscus. According to the scale of Tegner and Lysholm, the result was excellent in four patients, good in one, and fair in one. None of the six patients had a tear of the sutured meniscus after an average follow-up of thirty-two months (range, twenty-four to forty months). Two patients had progressive symptoms attributable to osteoarthrosis, but the changes in the articular cartilage had been present at the time of the index procedure. None of the seven Wrisberg-variant-type menisci demonstrated a true discoid shape of the meniscus. We therefore classified this lesion as a lateral meniscal variant with absence of the posterior coronary ligament.     

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.     

外侧半月板桶柄样撕裂联合缝合技术的应用

 目的 探讨关节镜下自内向外联合全内缝合技术修复外侧半月板桶柄样撕裂的临床效果。方法 2004年11月至2009年11月,应用关节镜下联合缝 合技术修复外侧半月板桶柄样撕裂17例,男10例,女7例;年龄17~42岁,平均27.8岁。使用自内向外缝合技术对外侧半月板腘肌腱前方区域的撕裂进行缝合,使 用全内缝合技术对半月板后角区域的撕裂进行缝合。随访时进行体格检查、MR检查和二次关节镜探查,评估半月板愈合情况。结果 13例患者获得随访,随访时 间1~5年,平均23.7个月。随访期间症状消失者12例（92.3％,12/13）,绞锁复发1例（7.7％,1/13）。MRI证实半月板完全愈合11例（84.6％,11/13）,部分 愈合1例（7.7％,1/13）,不愈合1例（7.7％,1/13）。12例患者行二次关节镜探查,其中完全愈合10例（83.3％,10/12）,部分愈合1例（8.3％,1/12）, 未愈合1例（8.3％,1/12）。结论 应用自内向外联合全内缝合技术修复外侧半月板桶柄样撕裂,经术后MRI和二次关节镜探查证实半月板愈合率超过90%。     

Bilateral PCL hypoplasia resulting in posterior, posterolateral rotatory instability and tears of the lateral meniscus anterior horn

This article describes a case of bilateral sagged knees presenting as posterior, posterolateral rotatory instability with tears of the anterior horn of the lateral meniscus. Each knee had identical tears of the lateral meniscus anterior horn. A 42-year-old woman reported bilateral anterior knee pain and painful instability during running or jarring exercises. She reported no major trauma to her knees. Arthroscopic findings of her right knee revealed a posterior cruciate ligament that looked hypoplastic but was without acute injury, and the anterior horn of the lateral meniscus showed chronic complex tears with some degeneration. Posterior cruciate ligament reconstruction, posterolateral corner sling, and meniscal repair of the lateral meniscus anterior horn was performed on her right knee. Three months later, a similar operation was performed on her left knee. However, menisectomy was performed because the lateral meniscus anterior horn tear was in the junction of the red-white and white zones. At 18 months postoperatively, the patient reported no symptoms and was satisfied with her results. Physical examination showed no joint line tenderness, and posterior stress radiographs on both knees showed grade I posterior instability. She showed no posterolateral subluxaion by supine dial test, and her prone dial test also improved approximately 15° on both knees. Lysholm score was 74 preoperatively and improved to 92 postoperatively.     

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.     

Discoid meniscus

The discoid meniscus is an uncommon but not remote meniscal anomaly. Watanabe classified discoid menisci into three types: complete, incomplete, and Wrisberg-ligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation.The complete and incomplete types are usually incidental arthroscopic findings unless they present with symptoms of an associated meniscal tear. The Wrisberg variant presents with the snapping knee syndrome, with visible, and often audible dunking with flexion and extension of the knee. The complete and incomplete types should be left alone unless there is an associated meniscal tear, in which case a saucerization procedure should be performed. The Wrisberg variant should have attachment of its hypermobile posterior horn.     

Die arthroskopische Meniskusrefixation mit einem All-inside-Nahtsystem

OBJECTIVE: Application of an arthroscopic suture system to restore the form and function of the meniscus by adaptation of a longitudinal tear close to the base. INDICATIONS: Unstable longitudinal tears near the base of the meniscus, mainly in the posterior horn of the medial or lateral of the meniscus. Dislocated bucket-handle tears of the medial and lateral meniscus close to the base. CONTRAINDICATIONS: Poor tissue quality with fibrillated meniscal tissue. Meniscal tears in the avascular zone (zone I). Insufficient blood supply from the joint capsule and the base of the meniscus. Degenerative meniscal lesions. Anterior or posterior knee joint instability. Allergic reactions to nonresorbable suture material. SURGICAL TECHNIQUE: Standard anterior arthroscopic portals. Arthroscopic assessment of the meniscal tear using the probe. Revitalization of the tear margins and perforation of the meniscal base to induce bleeding. Adaptation of the tear margins and fixation with a suture-anchor system using an ipsilateral standard portal for tears in the posterior horn or by way of a contralateral standard portal for tears in the lateral horn. POSTOPERATIVE MANAGEMENT: Full weight bearing with the knee in extension in a knee immobilizer, relative to the pain threshold in the 1st postoperative week. Range of motion exercises without weight bearing from full extension to 90 degrees knee flexion (0/0/90). If simultaneous reconstruction of the anterior cruciate ligament (ACL) is being performed, rehabilitation protocols follow the principles for ACL reconstruction. RESULTS: Since the year 2000, meniscal tears in more than 300 patients have been repaired with the all-inside suture system. In the context of a multicenter study by ESSKA (European Society for Sports Medicine, Surgery and Arthroscopy) involving 20 patients, the result was evaluated by direct MRI arthrography (gadolinium). The suture bar anchors were generally not detectable, the incision channels produced a hypodense signal in the meniscus tissue. If re-rupture occurred, it was because the meniscus had pulled out of the suture loop. Cartilaginous lesions were not found. There were no complications related to the nonresorbable suture bar anchors.     

The effect of complete radial lateral meniscus posterior root tear on the knee contact mechanics: a finite element analysis

Background

In recent years, with technological advances in arthroscopy and magnetic resonance imaging and improved biomechanical studies of the meniscus, there has been some progress in the diagnosis and treatment of injuries to the roots of the meniscus. However, the biomechanical effect of posterior lateral meniscus root tears on the knee has not yet become clear. The purpose of this study was to determine the effect of a complete radial posterior lateral meniscus root tear on the knee contact mechanics and the function of the posterior meniscofemoral ligament on the knee with tear in the posterior root of lateral meniscus.

Methods

A finite element model of the knee was developed to simulate different cases for intact knee, a complete radial posterior lateral meniscus root tear, a complete radial posterior lateral meniscus root tear with posterior meniscofemoral ligament deficiency, and total meniscectomy of the lateral meniscus. A compressive load of 1000 N was applied in all cases to calculate contact areas, contact pressure, and meniscal displacements.

Results

The complete radial posterior lateral meniscus root tear decreased the contact area and increased the contact pressure on the lateral compartment under compressive load. We also found a decreased contact area and increased contact pressure in the medial compartment, but it was not obvious compared to the lateral compartment. The lateral meniscus was radially displaced by compressive load after a complete radial posterior lateral meniscus root tear, and the displacement took place mainly in the body and posterior horn of lateral meniscus. There were further decrease in contact area and increases in contact pressure and raidial displacement of the lateral meniscus in the case of the complete posterior lateral meniscus root tear in combination with posterior meniscofemoral ligament deficiency.

Conclusions

Complete radial posterior lateral meniscus root tear is not functionally equivalent to total meniscectomy. The posterior root torn lateral meniscus continues to provide some load transmission and distribution functions across the joint. The posterior meniscofemoral ligament prevents excessive radial displacement of the posterior root torn lateral meniscus and assists the torn lateral meniscus in transmitting a certain amount of stress in the lateral compartment.     

Osteonecrosis of the knee after arthroscopic surgery for meniscal tears and chondral lesions.

PURPOSE: Avascular necrosis of the knee following arthroscopic surgery has been described. The purpose of this article is to report a large series of patients who developed avascular necrosis after arthroscopy of the knee in an effort to delineate casual factors and results of treatment. TYPE OF STUDY: Case series. METHODS AND MATERIALS: The charts, radiographs, and magnetic resonance imaging (MRI) scans of patients who developed osteonecrosis (ON) of the knee after routine arthroscopic surgery were reviewed. Only those patients with no evidence of ON on preoperative MRI performed 6 weeks or longer after symptom onset and who postoperatively developed ON confirmed by repeat MRI and/or by pathological testing (specimens obtained at subsequent total knee arthroplasty) were included in the study. Seven patients with average age of 60 years (range, 41 to 79 years) met these inclusion criteria. RESULTS: The lesions noted at arthroscopy included 4 medial meniscus tears, 3 lateral meniscal tears, 6 chondromalacia of the medial femoral condyle, 2 chondromalacia of the medial tibial plateau, 1 chondromalacia of the lateral femoral condyle, 1 chondromalacia of the lateral tibial plateau, and 2 chondromalacia of the patella. The location of postarthroscopy ON correlated geographically with pre-existing pathology. All 7 patients had meniscal and/or chondral lesions addressed surgically in the compartment that subsequently developed ON. Six of the 7 patients had an adjacent ipsilateral meniscus tear treated with partial meniscectomy (4 medial, 2 lateral). In addition, of the 4 patients who developed ON of the medial femoral condyle, all had overlying chondromalacia, 3 of whom were treated with arthroscopic chondroplasty. Of the 2 patients with lateral meniscal tears, 1 developed ON of the lateral femoral condyle and the other developed ON of the lateral tibial plateau. Three patients went on to require total knee arthroplasty, and 2 high tibial osteotomy. One patient's ON resolved and another patient was lost to follow-up. CONCLUSION: ON should be considered in patients who have worsening symptoms after arthroscopy of the knee. These findings suggest a possible relationship between arthroscopic treatment of chondral and meniscal lesions and later appearance of ON in some patients. The role of arthroscopy in the development of ON needs to be further studied. Those at risk are elderly patients with chondral and meniscus lesions.     

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.