Radial Width of the Lateral Meniscus at the Popliteal Hiatus: Relevance to Saucerization of Discoid Lateral Menisci

Background: A discoid lateral meniscus (DLM) is a congenital anomaly of the knee in which the lateral meniscus has an “O” shape and contains irregular, abnormal collagenous tissue. A DLM can cause mechanical symptoms and pain. Treatment of a symptomatic DLM is arthroscopic saucerization to reshape the meniscus to a more normal contour. Enough tissue must be removed to eliminate mechanical symptoms but not too much to create instability. The residual width of the meniscus is crucial at the popliteus hiatus because here the peripheral rim is unattached at the capsule. Reports in the literature recommend a residual width of 6 to 8 mm. Purpose/Hypothesis: The purpose of this research was to determine the width of the lateral meniscus at the popliteal hiatus in normal specimens. Our null hypothesis was that a residual width of 6 to 8 mm will be sufficient to approximate normal anatomy. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We made direct measurements of the radial width of the lateral meniscus from the outer rim at the popliteal hiatus to the inner edge in 19 specimens (age, 2-120 months.) We measured one 4-year-old specimen with a bilateral complete DLM. We also measured 39 digital images of specimens (age, 1-132 months) using ImageJ. Finally, we made direct arthroscopic measurements of 8 skeletally mature specimens. Results: The average width of specimens <3 years old was 5.5 mm. The average width of the 10-year-old specimens was 12 mm. The average width of the skeletally mature specimens was 16 mm. A 4-year-old DLM specimen measured 19 mm. Conclusion: We rejected our null hypothesis. Direct measurements suggest that a residual width of 6 to 8 mm is insufficient for children ≥8 years old. A width of at least a full centimeter approximates the normal for 8-year-olds and at least 15 mm for adolescents.

A Useful MRI Classification for Symptomatic Discoid Lateral Meniscus

Purpose The purpose of this study is to classify the discoid lateral meniscus (DLM) according to the signal and shape in magnetic resonance imaging (MRI), and to provide information not only in diagnosis but also in treatment. Materials and Methods We reviewed 162 cases who diagnosed with DLM by MRI and underwent arthroscopic procedures from April 2010 to March 2018. Three observers reviewed MRI findings of all cases and predicted arthroscopic tear using three MRI criteria (criterion 1,2 and 3). Among three criteria, the criterion that most accurately predicts arthroscopic tear was selected. Using this criterion, the cases of predicted tear were named group 1. In addition, group 1 was divided into three subgroups (group 1a, 1b and 1c) by deformation or displacement on MRI and arthroscopic type of tear and procedures were analyzed according to these subgroups. Results The intra-meniscal signal change itself (criterion 3) on MRI showed the highest agreement with the arthroscopic tear. No meniscal deformation and displacement on MRI (group 1a) showed no specific type of tear and more cases of meniscal saucerization. The meniscal deformation on MRI (group 1b) showed more simple horizontal tears and more cases of meniscal saucerization. The meniscal displacement on MRI (group 1c) showed more peripheral tears and more cases of meniscal repair and subtotal meniscectomy. Comparing arthroscopic type of tear and type of arthroscopic procedure between three subgroups, there were significant differences in three groups (P < .05). Conclusions Intra-meniscal signal change itself on MRI is the most accurate finding to predict arthroscopic tear in symptomatic DLM. In addition, subgroup analysis by deformation or displacement on MRI is helpful to predict the type of arthroscopic tear and procedures.

Morphological Changes in the Residual Meniscus After Reshaping Surgery for a Discoid Lateral Meniscus

Background: Arthroscopic reshaping surgery is the first treatment option for a symptomatic discoid lateral meniscus (DLM) to preserve the peripheral rim. However, the degree of postoperative morphological change in the residual meniscus is unclear. Purpose/Hypothesis: The purpose of this study was to measure the meniscus after reshaping surgery for a DLM, to verify when the morphological change occurred, and to examine the related risk factors. The hypothesis was that the residual meniscal width would decrease throughout the postoperative course. Study Design: Case-control study; Level of evidence, 3. Methods: We retrospectively reviewed the medical records of patients who underwent reshaping surgery for a symptomatic DLM and had undergone follow-up for ≥2 years. Magnetic resonance imaging (MRI) was routinely performed preoperatively and at 3, 6, 12, and 24 months postoperatively, and the width, height, and extrusion of the residual meniscus were measured. According to the width of the midbody on final MRI scans, we compared the preoperative and postoperative data for the preserved group (≥5 mm) and decreased group (<5 mm). The associated risk factors for a decreased meniscal width (<5 mm) of the midbody were analyzed on final MRI scans. Results: We included 61 knees of 54 patients in this study. The mean age at the time of surgery was 11.7 years. The intraobserver and interobserver reliabilities of the midbody width were 0.937 and 0.921, respectively. The width of the anterior horn, midbody, and posterior horn decreased significantly from 3 to 24 months after surgery (from 9.1 to 8.6 mm [ P < .001], from 7.5 to 6.1 mm [ P < .001], and from 9.5 to 8.9 mm [ P = .001], respectively). Meniscal extrusion of the midbody did not change significantly (from 1.2 to 1.5 mm; P = .062). Overall, 46 knees (n = 20/32 in the preserved group and n = 26/29 in the decreased group) had longitudinal tears that required meniscal repair. Clinical outcomes did not differ significantly between the 2 groups. Multivariate logistic analysis showed that intrameniscal degeneration (odds ratio, 4.36; P = .023) significantly increased the risk of a decreased meniscal width. Conclusion: The width of the anterior horn, midbody, and posterior horn decreased significantly from 3 to 24 months after surgery. In particular, the average decrease rate of the midbody was 19%. No clinical difference was seen in patients with a decreased width and height or with peripheral extrusion. Increased intrameniscal signals on preoperative MRI scans were associated with an increased risk of a decreased meniscal width. Surgeons should consider this result to determine the amount of resection.

Effect of discoid lateral meniscus on tibiofemoral joint cartilage damage in middle-aged patients

Purpose: To investigate the effect of discoid lateral meniscus (DLM) on cartilage damage of the medial and lateral compartments of the knee in middle-aged patients.Methods: We analyzed data from 44 patients (54 knees) with symptomatic discoid lateral meniscus (DLM group) and 30 patients (30 knees) with a non-discoid lateral meniscus tear (control group). All patients were over 40 years old. We compared the tibiofemoral angle (TFA) and cartilage injury rate between the two groups. We further classified DLM group patients based on dysmorphic features of the menisci (DLM type), presence/absence of meniscal tear, and symptom durations, then analyzed whether these parameters could affect the number of cartilage injuries in the knee medial and lateral compartments.Results: DLM group showed higher TFA values (2.18°±2.86°) than control group (0.84°±1.35°, P=0.002), and a higher occurrence of medial compartment cartilage damage (P=0.003). Within the DLM group, patients with cartilage damage showed higher BMI than those without cartilage damage (P=0.009 for medial compartment and P=0.001 for lateral, respectively). We found that having symptoms for more than 6 months was associated with cartilage damage in the lateral compartment (P=0.021), but not the medial compartment (P=0.858). Neither presence/absence of a meniscal tear, nor DLM type affected cartilage injury rate in either the medial or lateral compartment (P>0.05).Conclusion: Varus inclination caused by DLM could lead to cartilage injury in the medial compartment in middle-aged patients, but may not reduce the occurrence of chondral damage in the lateral compartment. Rather, lateral compartment chondral damage in patients with DLM was mainly related to symptom duration.

Histological Study of Discoid Lateral Meniscus in Children and Adolescents: Morphogenetic Considerations

Background Discoid lateral meniscus is the most frequent variant of the meniscus. Few studies have focused on the histology of discoid menisci. The aim of the present study was to report the histological findings of discoid lateral meniscus in children and adolescents, after arthroscopic partial resection, to give a possible explanation of its developmental etiology. Methods Five patients aged 9, 10, 13, 15, and 17 years were operated on for a 1-piece excision of a discoid lateral meniscus, and the specimens were histologically examined. Results The extracellular matrix showed a different distribution and characteristics depending on the different side of the meniscus. Irregularly oriented collagen fibers in discoid lateral meniscus were found. Cells of different shapes were observed depending on the surficial or deep location in the tissue. There were no blood vessels in the inner part of discoid lateral meniscus. Conclusion The findings of the current study seem to confirm that discoid lateral meniscus arises from variant morphogenesis. Furthermore, the altered distribution and shape of the cells and disorganization of collagen fibers (irrespectively of the age of the patients) may predispose discoid lateral meniscus to degeneration, damage, and tear in young patients also. Level of Evidence Level of evidence 4 (case series).