UNASSIGNED: Discoid lateral meniscus (DLM) is the most common congenital abnormality of the meniscus. Tears are common; treatment is frequently not definitive, often requiring reoperation.
UNASSIGNED: To report the clinical manifestations, physical characteristics, operative treatments and findings, complications, and reoperations of DLM in pediatric patients from multiple centers across North America.
UNASSIGNED: Case series; Level of evidence, 4.
UNASSIGNED: Consecutive patients who underwent treatment for symptomatic DLM at 9 institutions between 2000 and 2020 were included. Patient data, presenting symptoms and signs, surgical findings, treatments rendered, and postoperative complications, including reoperation rates, were collected. Means with ranges and counts with proportions are reported for continuous and categorical variables, respectively, and comparisons were made using either the chi-square or Fisher exact test.
UNASSIGNED: In total, 784 patients (867 knees) were included with a mean age at diagnosis of 12 years (range, 1-22 years) and a mean follow-up of 22.6 months (range, 0-154 months). Common preoperative symptoms were locking (33%) and snapping (30%). At surgery, tears in the DLM were present in 647 knees (594 patients [76%]); 95 knees (11%) had multiple tears; and in 140 knees, tears extended into >1 zone. Tears, when present, were more common within the posterior horn (41%) or body (34%) than the anterior horn (25%). Peripheral rim instability was reported in 241 knees (28%). Significantly more knees had instability posteriorly (15%; P = .0004) and anteriorly (9%; P = .0013) than along the body (3%). Tear type was most commonly complex (38%) or horizontal (34%). A total of 358 knees in 333 patients with tears (42% of all patients) underwent repair (55% of knees with tears). A total of 175 complications were reported, occurring in 139 knees in 134 patients (17%); 116 of these knees with complications (83%) had a single complication, while 23 (17%) had >1. Of the 784 patients, 105 (13%) underwent reoperation, undergoing 135 additional procedures related to their DLM. Of those, 60 (44%) were repeat arthroscopy and meniscal trim; 40 (30%), arthroscopy and meniscal repair; and 17 (13%), an articular cartilage procedure.
UNASSIGNED: Locking and snapping were common presenting symptoms. Over three-quarters of patients had meniscal tears, which were most often complex and located posteriorly. Seventeen percent of patients experienced complications, and a sixth of patients with complications had >1. Reoperation was typically for persistent symptoms or meniscal retear.

OBJECTIVE: To evaluate the efficacy of surgical treatment of the discoid lateral meniscus with osteochondritis dissecans (OCD) through clinical and radiological evaluations, focusing on recurrent or postoperative OCD occurrence.
METHODS: This retrospective study included patients with symptomatic discoid lateral meniscus with OCD (pre-OCD group) and without OCD (non-OCD group) who had undergone arthroscopic surgery with >5 years of follow-up. Age, sex, Lysholm score, Tegner activity scale, surgical procedure, and recurrent or postoperative OCD lesions were compared. The association between patient variables and postoperative OCD was determined using multivariate logistic regression analysis.
RESULTS: Of the 95 knees, 15 (15%) were in the pre-OCD group. Healing was observed in 14/15 (93%) knees. Recurrent and postoperative OCDs were reported in 4/15 (28.5%) knees in the pre-OCD and 7/80 (8.8%) knees in the non-OCD groups at a mean of 3.2 ± 1.1 and 3.7 ± 1.2 years, respectively. Pre- and postoperative Tegner activity scale and Lysholm scores were higher in the pre-OCD group but similar to those in the non-OCD group. The incidence of recurrent OCD in the pre-OCD group was significantly higher than that of postoperative OCD in the non-OCD group. Younger patients (odds ratio, 0.49; p = 0.003) had an increased risk of experiencing recurrent or postoperative OCD in multivariate analysis. The optimal cutoff age for distinguishing recurrent or postoperative OCD was 9 years.
CONCLUSIONS: Surgical procedures for OCD lesions in the pre-OCD group were successful. Multivariate analysis identified age as a risk factor for recurrent or postoperative OCD; therefore, conservative treatment is recommended for patients with discoid lateral meniscus before preadolescence to prevent postoperative OCD occurrence.
METHODS: Level III.

UNASSIGNED: This study aimed to reach a consensus for ideal surgical treatment of discoid lateral meniscus (DLM) and to evaluate its long term surgical and radiological outcome.
UNASSIGNED: All authors independently searched for peer reviewed publications with keywords like discoid lateral meniscus, tibial menisci abnormalities, tibial menisci surgery and clinical outcome and their representative Medical Subjects Headings (MeSH) in databases of PubMed, EBSCO, Cochrane Central Register of Controlled Trials, from inception to December 2022. Original articles in English language on discoid lateral meniscus reporting clinical, surgical, or radiological outcomes with five or more years of follow-up were included in this systematic review. Study details and outcome data were analysed according to the age, follow-up period, kind of surgery, DLM type, and alignment.
UNASSIGNED: Our search strategy yielded 654 articles in PubMed, 222 articles in EBSCO and 5 articles in CENTRAL i.e. a total of 881 articles. After detailed assessment and screening, 12 articles were included in the final analysis, which included 444 DLM cases. The mean patient age at surgery ranged from 9.9 to 35.9 years, and the mean follow-up period ranged from 5.2 to 16 years. Partial meniscectomy and meniscoplasty are the recommended treatment because of the concerns of degenerative arthritis development after the total and subtotal meniscectomies. Two studies have documented better results with meniscal allograft transplantation.
UNASSIGNED: Satisfactory clinico-radiological outcome can be obtained after surgical treatment of discoid lateral meniscus with meniscus reshaping and repair of peripheral unstable part. Meniscal allograft transplantation (MAT) is gaining popularity in patients with total meniscectomy with satisfactory long term functional outcome.

OBJECTIVE: The objective of this study was to develop a machine learning model that would predict lateral compartment osteoarthritis (OA) in the discoid lateral meniscus (DLM), from which to then identify factors contributing to lateral compartment OA, with a key focus on the patient\'s age.
METHODS: Data were collected from 611 patients with symptomatic DLM diagnosed using magnetic resonance imaging between April 2003 and May 2022. Twenty features, including demographic, clinical and radiological data and six algorithms were used to develop the predictive machine learning models. Shapley additive explanation (SHAP) analysis was performed on the best model, in addition to subgroup analyses according to age.
RESULTS: Extreme gradient boosting classifier was identified as the best prediction model, with an area under the receiver operating characteristic curve (AUROC) of 0.968, the highest among all the models, regardless of age (AUROC of 0.977 in young age and AUROC of 0.937 in old age). In the SHAP analysis, the most predictive feature was age, followed by the presence of medial compartment OA. In the subgroup analysis, the most predictive feature was age in young age, whereas the most predictive feature was the presence of medial compartment OA in old age.
CONCLUSIONS: The machine learning model developed in this study showed a high predictive performance with regard to predicting lateral compartment OA of the DLM. Age was identified as the most important factor, followed by medial compartment OA. In subgroup analysis, medial compartmental OA was found to be the most important factor in the older age group, whereas age remained the most important factor in the younger age group. These findings provide insights that may prove useful for the establishment of strategies for the treatment of patients with symptomatic DLM.
METHODS: Level III.

BACKGROUND: The posterior cruciate ligament (PCL) attachment may be damaged in cruciate-retaining total knee arthroplasty (CR-TKA) using the complete resection for tibial preparation, and resection amount varies greatly among individuals. Discoid lateral meniscus (DLM) is one of the most common anatomic knee variants. This study aimed to evaluate the difference in PCL attachment sacrifice in CR-TKA between patients with and without DLM.
METHODS: Fifty-one knees in the study group (DLM group) were matched 1:1 to 51 control knees (non-DLM group) by age, sex, and maximum width of the tibial plateau. The percentage of the sacrificed PCL attachment and the morphological parameters of the tibial plateau were evaluated using magnetic resonance imaging (MRI) in a blind manner.
RESULTS: With a tibial cut simulated at a 0°, 3°, and 7° osteotomy slope, the mean PCL attachment resection percentages in the non-DLM group were 40.5%, 53.6%, and 72.6%, respectively. The corresponding resection percentages in the DLM group were 61.0% (P < 0.001), 73.3% (P < 0.001), and 85.7% (P < 0.001), respectively. The percentage of the minimum meniscus width to the maximum tibia width showed a weak positive correlation with the percentage of PCL attachment sacrifice.
CONCLUSIONS: A significantly greater portion of PCL attachment was sacrificed in DLM patients undergoing CR-TKA using the complete proximal tibia resection. Attention should be paid to PCL attachment resection during CR-TKA in patients with DLM, and alternative techniques or prosthesis types should be considered.

UNASSIGNED: To discuss the application of anterior region suture of the popliteal hiatus (PH) under arthroscopy in the treatment of discoid lateral meniscus (DLM) injury with instability in the popliteal tendon region.
UNASSIGNED: The clinical data of 53 patients (56 knees) with DLM injury who met the selection criteria between March 2014 and November 2022 were retrospectively analyzed. There were 15 males and 38 females, aged 8-55 years with an average age of 36.5 years. Fourteen cases had a history of trauma, while the remaining 39 cases had no clear history of trauma. The disease duration ranged from 1 day to 6 years, with an average duration of 15.6 months. According to the Watanabe classification, there were 40 knees of complete type and 16 knees of incomplete type. The preoperative International Knee Documentation Committee (IKDC) knee joint score was 51.2±8.3, the Lysholm score was 59.6±11.2, and the visual analogue scale (VAS) score was 4.7±1.3. After the arthroscopic meniscal plasty, the instability of the popliteal tendon region meniscus was checked by probing traction. Subsequently, the Out-inside technique or a combination of Out-inside and All-inside techniques was used to suture the anterior region of the PH. The stability of the meniscus after suturing was assessed, and if necessary, further suturing using the All-inside technique at the posterior region of the PH, the posterior horn of the meniscus, and using the Out-inside technique at the anterior horn of the meniscus was performed. Postoperative complications were recorded. The effectiveness was evaluated using pre- and post-operative IKDC scores, Lysholm scores, and VAS scores.
UNASSIGNED: After operation, knee joint pain, crepitus, and locking disappeared, with McMurray and grinding tests turning negative. All patients were followed up 12-93 months with an average of 57.5 months. There was no complication such as common peroneal nerve injury, deep vein thrombosis of the lower limbs, joint infection, or joint stiffness. At last follow-up, the IKDC knee joint score was 76.7±5.5, the Lysholm score was 94.0±4.1, and the VAS score was 1.1±0.8. The differences compared with preoperative scores were significant ( t=-22.090, P<0.001; t=-23.704, P<0.001; t=19.767, P<0.001).
UNASSIGNED: Suturing of the anterior region of the PH is crucial in the treatment of DLM injury with instability in the popliteal tendon region.
UNASSIGNED: 探讨关节镜下腘肌腱裂孔（popliteal hiatus，PH）前区缝合在外侧盘状半月板（discoid lateral meniscus，DLM）损伤并腘肌腱区不稳治疗中的应用。.
UNASSIGNED: 回顾分析2014年3月—2022年11月收治且符合选择标准的53例（56膝）DLM损伤患者临床资料。男15例，女38例；年龄8～55岁，平均36.5岁。14例有外伤史，余39例无明确外伤史。病程1 d～6年，平均15.6个月。根据Watanabe分型：完全型40膝，不完全型16膝。术前国际膝关节文献委员会（IKDC）膝关节评分为（51.2±8.3）分，Lysholm评分为（59.6±11.2）分，疼痛视觉模拟评分（VAS）为（4.7±1.3）分。行关节镜下半月板成形术后，用探钩牵拉检查腘肌腱区半月板均存在不稳，进而采用Out-inside技术或Out-inside技术联合All-inside技术缝合PH前区，检查缝合后半月板稳定性，必要时再采用All-inside技术缝合PH后区、半月板后角和Out-inside技术缝合半月板前角。记录并发症发生情况；采用手术前后IKDC评分、Lysholm评分和VAS评分评价疗效。.
UNASSIGNED: 术后膝关节疼痛、关节弹响及交锁症状消失，McMurray试验及研磨试验转为阴性。53例患者均获随访，随访时间12～93个月，平均57.5个月。无腓总神经损伤、下肢深静脉血栓形成、关节感染和关节僵硬等并发症发生。末次随访时IKDC膝关节评分为（76.7±5.5）分，Lysholm评分为（94.0±4.1）分，VAS评分为（1.1±0.8）分，与术前比较差异均有统计学意义（ t=−22.090， P<0.001； t=−23.704， P<0.001； t=19.767， P<0.001）。.
UNASSIGNED: PH前区缝合是DLM损伤并腘肌腱区不稳治疗的关键。.

BACKGROUND: The purpose of this study was to investigate the influence of different residual meniscus volume on the biomechanics of tibiofemoral joint after discoid lateral meniscus (DLM) surgery by finite element analysis.
METHODS: A knee joint model was established based on CT and MRI imaging data. The DLM model was divided into five regions according to conventional meniscectomy, with volumes of 15%, 15%, 15%, 15%, 15%, and 40% for each region. Additionally, the DLM model was divided into anterior and posterior parts to obtain ten regions. The DLM was resected according to the design scheme, and together with the intact discoid meniscus, a total of 15 models were obtained. Finite element analysis was conducted to assess shear and pressure trends on the knee joint.
RESULTS: The study observed significant changes in peak shear stress and compressive stress in the lateral meniscus and lateral femur cartilage. As the meniscus volume decreased, there was an increase in these stresses. Specifically, when the meniscus volume reduced to 40%, there was a sharp increase in shear stress (302%) and compressive stress (152%) on the meniscus, as well as shear stress (195%) and compressive stress (157%) on the lateral femur cartilage. Furthermore, the model grouping results showed that preserving a higher frontal volume in the meniscus model provided better biomechanical advantages.
CONCLUSIONS: The use of finite element analysis has demonstrated that preserving more than 55% of the meniscus volume is necessary to prevent a significant increase in joint stress, which can potentially lead to joint degeneration. Additionally, it is crucial to preserve the front volume of the DLM in order to achieve improved knee biomechanical outcomes.

OBJECTIVE: This study evaluated the differences in meniscal sizes and occupancy between symptomatic and asymptomatic patients diagnosed with discoid lateral meniscus (DLM) using magnetic resonance imaging (MRI) to understand how these variations relate to the presence of symptoms and the patients\' age.
METHODS: A retrospective review of 98 patients with DLM was conducted, excluding those with meniscal displacement. Both the width and extrusion of DLM and the percentage of the meniscus to the tibia were measured using mid-coronal and mid-sagittal MRI and compared between symptomatic and asymptomatic DLM groups. The relationships among each parameter, meniscal size, and patient age were evaluated. Symptomatic cases were divided into those with and without horizontal tears on MRI to compare the differences in meniscal morphology.
RESULTS: A total of 92 knees from 74 patients were included. Sixty-one knees required surgical intervention for symptomatic DLM, while 31 were asymptomatic and included the contralateral side of symptomatic knees. The symptomatic group exhibited larger morphological variations than the asymptomatic group. Moreover, the sagittal meniscal ratio reduced with age in the asymptomatic group (r = - 0.54, p = 0.002) but remained constant in the symptomatic group. The symptomatic cases with horizontal tears demonstrated larger meniscal dimensions and smaller posterior capsule distances than those without tears.
CONCLUSIONS: Symptomatic patients with DLM had larger knee morphological changes than asymptomatic ones. Age affected the meniscal occupancy in the sagittal plane only in asymptomatic patients.
METHODS: III.

Background The discoid lateral meniscus (DLM) is a unique anatomical variant characterized by a larger, thicker lateral meniscus. For clinical diagnosis of DLM, coronal and sagittal slices in two-dimensional (2D) MRI and arthroscopic imaging are typically employed. However, evaluating the entire shape of the DLM is challenging due to the limited views and details provided by these methods. Three-dimensional (3D) visualization with MRI offers a more comprehensive view of the entire meniscus. The purpose of this study was to demonstrate the entire shape of a DLM using 3D images and unveil its unique characteristics. Methods The study population consisted of 31 knees diagnosed with DLM through arthroscopic examination at our hospital between 2017 and 2021. This group comprised 20 males (65%) and 11 females (35%), with ages ranging from 9 to 49 years (mean age, 24.2 years). Furthermore, a control group of 43 knees without DLM was included for comparative analysis. This control group consisted of 22 males (51%) and 21 females (49%), with ages ranging from 9 to 69 years (mean age, 28.5 years). 3D images of the medial meniscus (MM) and lateral meniscus (LM) were reconstructed from 1.5T-MRI images with semi-automatic segmentation using free software. From the coordinate information, the anterior-to-posterior lengths of the MM and LM were obtained, and the medial-to-lateral anterior-to-posterior length (L/M ratio) ratio was calculated and compared with the value of the non-DLM population. Results Our method allows for the detailed delineation of the DLM\'s unique morphology. The DLM group exhibited a significantly smaller L/M ratio compared to the non-DLM group (DLM: 0.66±0.06, non-DLM: 0.74±0.05, p<0.001). Conclusions Reconstructed 3D images could help to demonstrate the whole morphology of DLM and reveal its unique features, in which DLM shows a significantly smaller L/M ratio as compared to non-DLM.

BACKGROUND: This study aimed to evaluate the meniscal size of asymptomatic discoid lateral meniscus (DLM) and compare it with that of normal lateral meniscus (LM) and to compare changes in meniscal dimensions with age among patients with asymptomatic DLM and those with normal LM using magnetic resonance imaging (MRI).
METHODS: We retrospectively reviewed the medical records, including MRI data, of patients with asymptomatic DLM (DLM group) or normal LM (control group). Width and extrusion of both DLM and normal LM and tibial length were measured and compared using mid-coronal and mid-sagittal MR images. Meniscal size and sagittal and coronal meniscal ratio according to age, as well as differences between DLM and normal menisci, were also evaluated.
RESULTS: Thirty-four knees were included in the DLM group, whereas the control group comprised of 50 patients. The DLM group showed significantly less meniscal extrusion, greater coronal width, posterior capsule distance, sagittal meniscal length, and sagittal meniscal ratio than the control group (DLM: 0.1 ± 0.3 mm, 23.3 ± 2.2 mm, 5.4 ± 2.4 mm, 25.1 ± 2.8 mm, 61 ± 6%, and control: 0.4 ± 0.4 mm, 9.5 ± 2.3 mm, 2.5 ± 1.2 mm, 30.2 ± 2.6 mm, 71 ± 4%, respectively). The coronal meniscal ratio decreased with age in both the control (p = 0.001) and DLM (p = 0.037) groups. The sagittal meniscal ratio (p = 0.001) and minimum height (p = 0.04) decreased and the anterior capsule distance (p = 0.035), posterior capsule distance (p = 0.026), and entire sagittal length (p = 0.005) increased with age in the DLM group, while the distance between the meniscal inner margins (p = 0.019) increased with age in the control group.
CONCLUSIONS: The meniscal ratio in the sagittal plane of the DLM group was significantly lower than that of the control group. The sagittal meniscal ratio of asymptomatic DLM decreased with age, indicating that the size of asymptomatic DLM does not change with age.
METHODS: III: Retrospective comparative study.