UNASSIGNED: Meniscotibial ligament (MTL) has received attention as a major meniscus stabilizer. An MTL injury results in instability and extrusion of the meniscus. Cases of knee ganglion cyst formation due to an MTL tear and medial meniscus extrusion (ME) are extremely rare.
METHODS: A 42-year-old female Japanese childcare worker presented painful ganglion cysts on the proximal medial side of her left tibia. An MTL tear and medial ME were thought to be involved in the ganglion formation. Joint fluid flowed through the meniscotibial side of the extruded meniscus into the space between the medial collateral ligament and tibia, where the MTL tear acted as a check valve, forming ganglion cysts. Ultrasonography-guided aspiration of the ganglion was attempted, but ganglion cysts recurred within 1 month. We used an open excision for the ganglion cysts, and arthroscopic capsulodesis was performed to repair the MTL and internalize the medial meniscus to block the inflow route from the intra-articular space.
UNASSIGNED: We performed capsulodesis, which repaired the MTL and internalized the medial meniscus to prevent the recurrence of the ganglion cyst. Three months have passed since the surgery, with no recurrence of knee pain or ganglion cysts, indicating good short-term results.
CONCLUSIONS: We encountered a rare case of ganglion cyst formation in the knee joint due to MTL tear and medial ME. Arthroscopic MTL repair and internalization of the meniscus by capsulodesis were effective in treating the ganglion cysts.

OBJECTIVE: To establish a reliable ultrasound (US) method of evaluating dynamic extrusion of lateral meniscus in healthy population, and to investigate the pattern of dynamic meniscus extrusion (ME) in lateral meniscus under loading conditions.
METHODS: The lateral ME was examined via US method in unloaded, double-leg standing, and single-leg standing positions. Two different US measurement methods were compared to the magnetic resonance imaging (MRI) results to determine the optimal measurement methods. The US results obtained by different researchers were tested for interobserver consistency and the results obtained by the same researcher on two separate days were tested for intraobserver consistency. The patterns of dynamic extrusion were compared between medial and lateral sides.
RESULTS: A total of healthy 44 volunteers were included in the study, with 86 knees assessed by US, and 25 knees evaluated by MRI. The US evaluation of dynamic lateral ME demonstrated excellent interobserver and intraobserver reliability. The US measurements using method A were consistent with the MRI results with no significant difference (P = .861, intraclass correlation coefficient [ICC] = 0.868), while method B underestimated the lateral ME compared to MRI (P = .001, ICC = 0.649). Lateral ME decreased slightly from unloaded (1.0 ± 0.8 mm) to single-leg standing position (0.8 ± 0.8 mm), whereas medial ME increased significantly in both double-leg and single-leg standing positions (2.4 ± 0.7 mm, 2.6 ± 0.7 mm).
CONCLUSIONS: A novel US evaluation method of lateral ME was established with reliable and accurate results compared to the MRI. Lateral ME in healthy populations decreased slightly as the loadings increased, which was different from the pattern of dynamic extrusion in medial meniscus.

Meniscus pathologies (damage, extrusion) and synovitis are associated with knee osteoarthritis (KOA); however, whether synovitis mediates the relationship between meniscus pathologies and KOA radiographic progression remains unclear. We conducted an observational study in the Osteoarthritis Initiative (OAI) cohort, with a 48-month follow-up. Meniscus pathology and synovitis were measured by MRI osteoarthritis knee score (MOAKS) at baseline and 24 months, and a comprehensive synovitis score was calculated using effusion and Hoffa synovitis scores. The knee osteoarthritis radiographic progression was considered that Kellgren-Lawrence (KL) grade and joint space narrowing (JSN) grade at 48 months were increased compared to those at baseline. This study included a total of 589 participants, with KL grades mainly being KL1 (26.5%), KL2 (34.1%), and KL3 (30.2%) at baseline, while JSN grades were mostly 0 at baseline. A logistic regression model was used to analyze the relationship between meniscus pathology, synovitis, and KOA progression. Mediation analysis was used to evaluate the mediation effect of synovitis. The average age of the participants was 61 years old, 62% of which were female. The medial meniscus extrusion was longitudinally correlated with the progression of KL (odds ratio [OR]: 2.271, 95% confidence interval [CI]: 1.412-3.694) and medial JSN (OR: 3.211, 95% CI: 2.040-5.054). Additionally, the longitudinal correlation between medial meniscus damage and progression of KOA (OR: 1.853, 95% CI: 1.177-2.941) and medial JSN (OR: 1.655, 95% CI: 1.053-2.602) was significant. Synovitis was found to mediate the relationship between medial meniscus extrusion and KL and medial JSN progression at baseline (β: 0.029, 95% CI: 0.010-0.053; β: 0.022, 95% CI: 0.005-0.046) and beyond 24 months (β: 0.039, 95% CI: 0.016-0.068; β: 0.047, 95% CI: 0.020-0.078). However, we did not find evidence of synovitis mediating the relationship between meniscal damage and KOA progression. Synovitis mediates the relationship between medial meniscus extrusion (rather than meniscus damage) and KOA progression.

OBJECTIVE: The demographic and radiological risk factors of subchondral insufficiency fractures of the knee (SIFK) continue to be a subject of debate. The purpose of this study was to associate patient-specific factors with SIFK in a large cohort of patients.
METHODS: Inclusion criteria consisted of patients with SIFK as verified on magnetic resonance imaging (MRI). All radiographs and MRIs were reviewed to assess characteristics such as meniscus tear presence and type, subchondral oedema presence and location, location of SIFK, mechanical limb alignment, osteoarthritis as assessed by Kellgren-Lawrence grade and ligamentous injury. A total of 253 patients (253 knees) were included, with 171 being female. The average body mass index (BMI) was 32.1 ± 7.0 kg/m2.
RESULTS: SIFK was more common in patients with medial meniscus tears (77.1%, 195/253) rather than tears of the lateral meniscus (14.6%, 37/253) (p < 0.001). Medial meniscus root and radial tears of the posterior horn were present in 71.1% (180/253) of patients. Ninety-one percent (164/180) of medial meniscus posterior root and radial tears had an extrusion ≥3.0 mm. Eighty-one percent (119/147) of patients with SIFK on the medial femoral condyle and 86.8% (105/121) of patients with SIFK on the medial tibial plateau had a medial meniscus tear. Varus knees had a significantly increased rate of SIFK on the medial femoral condyle in comparison to valgus knees (p = 0.016).
CONCLUSIONS: In this large cohort of patients with SIFK, there was a high association with medial meniscus root and radial tears of the posterior horn, meniscus extrusion ≥3.0 mm as well as higher age, female gender and higher BMI. Additionally, there was a particularly strong association of medial compartment SIFK with medial meniscus tears. As SIFK is frequently undiagnosed, identifying patient-specific demographic and radiological risk factors will help achieve a prompt diagnosis.
METHODS: Level IV.

OBJECTIVE: With an aging population, extending healthy life expectancy is a global challenge. Maintaining healthy knee joint function is one of the essential factors to preserve the ability to walk and extend healthy life expectancy. Meniscus centralization was introduced in 2012 as a procedure for meniscus extrusion, one of the causes of knee osteoarthritis (OA). Initially, it was performed only for lateral meniscus (LM) extrusion, and favorable 2-year results were reported in 2016. Gradually, basic studies supporting the effectiveness of meniscus centralization have been reported, and it has also been performed for medial meniscus (MM) extrusion, with some positive results reported. Although the surgical procedures vary among the institutions, the basic concept is to reattach the loosened meniscotibial ligament to the edge of the tibial plateau to re-tension it. This review will discuss the history of development and the current status of meniscus centralization.
RESULTS: Current research shows that meniscus centralization is not performed in isolation but is often used as an augmentation along with the conventional repair of meniscus injuries, particularly posterior root tears. Biomechanical studies demonstrated that MM centralization with a posteromedial anchor can better restore meniscus function.
CONCLUSIONS: Despite its relatively short publication history of just over ten years, meniscus centralization has shown potential as a treatment to curb the progression of knee OA and extend a healthy life. While more evidence is needed, this conclusion underscores the promising role for meniscus centralization, making it a topic of significant interest for knee surgeons and researchers.

OBJECTIVE: This study aimed to evaluate the association between the progression of medial joint space (MJS) narrowing, medial meniscus extrusion (MME) and clinical scores and the tibial tunnel position in pullout repairs for medial meniscus posterior root tears (MMPRTs).
METHODS: This retrospective study examined 54 patients. Changes in MJS (ΔMJS), MME (ΔMME) and clinical scores and their relationship with the tibial tunnel position were evaluated using correlation coefficients. The distance from the anatomical to technical attachment position in the tibial tunnel position was measured in the anterior and medial directions, and the direct distance was measured using the Pythagorean theorem.
RESULTS: The mean ΔMJS and ΔMME were 0.6 ± 0.8 and 1.3 ± 1.3 mm, respectively, and the mean anterior, medial and direct distances were 1.4 ± 2.3, 2.2 ± 1.7 and 3.4 ± 1.7 mm, respectively. ΔMJS had a significant positive correlation with the medial (r = 0.580, p < 0.001) and direct (r = 0.559, p < 0.001) distances, while ΔMME had a significant positive correlation with direct distance (r = 0.295, p = 0.030). Several clinical scores were significantly negatively correlated with these distances.
CONCLUSIONS: In transtibial pullout repair for MMPRTs, accurate tibial tunnel position delayed the progression of MJS narrowing and MME, leading to improved clinical outcomes. The progression of MJS narrowing was associated with the mediolateral direction of the tibial tunnel position, while the clinical scores were associated with the anteroposterior direction of the tibial tunnel position. These findings indicate the need to orient the tip of the guide in a more posterolateral direction when creating the tibial tunnel.
METHODS: Level IV.

OBJECTIVE: The second-look arthroscopic score of pullout repair for medial meniscus posterior root tears (MMPRTs) is associated with contemporaneous clinical scores and progression of cartilage damage. However, the relationship among these scores, midterm clinical scores and magnetic resonance imaging (MRI) evaluations is unknown. The relationship between the second-look arthroscopic score at 1 year and the clinical scores or MRI at 3 years was evaluated.
METHODS: Sixty-three patients were included. Medial meniscus extrusion (MME) was evaluated preoperatively and at 3 years postoperatively. Clinical scores were evaluated preoperatively, and 1 and 3 years postoperatively. Meniscal healing status was assessed using the semiquantitative second-look arthroscopic score at 1 year postoperatively. Correlation coefficients between patient characteristics, postoperative clinical scores or second-look arthroscopic score and the change in MME (ΔMME) were evaluated. Multiple regression analysis was performed on the ΔMME to evaluate the effects of patient characteristics and second-look arthroscopic scores.
RESULTS: No significant correlation was observed between patient characteristics and ΔMME. In contrast, a significant correlation was found between the second-look arthroscopic score and ΔMME (p < 0.001) and visual analogue scale pain score (p = 0.016) at 3 years postoperatively. In the subitems of the second-look arthroscopic score, width (p < 0.001) and stability (p = 0.009) scores also showed significant correlations with ΔMME. Multiple regression analysis showed a significant association between the second-look arthroscopic score and ΔMME (p = 0.001).
CONCLUSIONS: The second-look arthroscopic score at 1 year postoperatively correlated with the ΔMME and clinical score at 3 years postoperatively. Second-look arthroscopic scores predict midterm meniscal function after pullout repair of MMPRTs.
METHODS: Level IV.

UNASSIGNED: Excessive mechanical stress accumulates and causes knee injury. Meniscal extrusion is a key factor in detecting the reaction to cumulative mechanical stress. The accumulation of stress strongly depends on environmental conditions such as flat ground or uphill/downhill, and accumulates in knee compartments; only a few studies have reported the effects of different environments on lateral and medial meniscus extrusion. This study aimed to investigate the effects of cumulative uphill/downhill stress on the meniscal extrusion in each compartment.
UNASSIGNED: A total of 30 healthy volunteers with 30 affected knees were involved in this cohort study (mean age, 22.0 ± 1.1 years; men, n = 14). The participants were divided into flat-walking, uphill/downhill-walking, and uphill/downhill-jogging groups and their numbers of steps taken were recorded during the effort. Moreover, medial and lateral meniscal extrusions during walking were evaluated using ultrasound three times, before and after efforts (T1) and (T2), and one day after efforts (T3), respectively.
UNASSIGNED: In the flat-walking group, no significant differences were observed between the follow-up periods. Conversely, in the uphill/downhill-walking and jogging groups, the medial meniscus extrusion at T2 was significantly higher than that at T1. Conversely, the medial meniscus extrusion at T3 was significantly lower than that at T2. By contrast, the lateral meniscus did not show any difference between the follow-up periods in any group.
UNASSIGNED: Temporary extrusion of the meniscus occurred after uphill/downhill tasks in healthy volunteers, and its reaction was observed only in the medial meniscus.

OBJECTIVE: We aimed to evaluate the longitudinal changes in medial meniscus extrusion (MME) and clinical scores at multiple time points up to 3 years after pullout repair for medial meniscus posterior root tears (MMPRTs).
METHODS: This retrospective case series study included 64 patients who underwent pullout repair for MMPRTs and four MRI evaluations (preoperatively and at 3 months, 1 year, and 3 years postoperatively). MME was measured during the same time points. Clinical scores were assessed four times: preoperatively and at 1, 2, and 3 years postoperatively. Additionally, a multivariate analysis was performed on the change in MME (ΔMME) from the preoperative measurement point to 3 years postoperatively.
RESULTS: The ΔMME per month from the preoperative measurement point to 3 months postoperatively, from 3 months to 1 year postoperatively, and from 1 to 3 years postoperatively were 0.30, 0.05, and 0.01 mm/month, respectively. All clinical scores significantly improved 3 years postoperatively (p < 0.001). In a multiple regression analysis for ΔMME from the preoperative measurement point to 3 years postoperatively, sex significantly affected the outcome (p = 0.039).
CONCLUSIONS: Following pullout repair for MMPRTs with well-aligned lower extremities, although MME progression could not be entirely prevented, the rate of progression decreased over time, and clinical scores improved. In particular, MME progressed markedly during the first 3 months postoperatively. Additionally, sex had a significant influence on MME progression, suggesting that males may be able to expand the indications of pullout repair for MMPRTs.

BACKGROUND: Only a few studies have assessed signal intensity after pullout repair for medial meniscus posterior root (MMPR) tears (MMPRTs) based on mid-term magnetic resonance imaging (MRI) evaluations. Therefore, this study aimed to assess the quantitative signal intensity of repaired posterior roots over time, up to 3 years postoperatively, and the related factors.
METHODS: This study included 36 patients who underwent pullout repair for MMPRTs and MRI examinations using the same MRI system. The signal intensity of the repaired posterior roots was quantitatively evaluated using the signal-to-noise quotient (SNQ). Medial meniscus extrusion (MME), the SNQ for MMPR, and clinical scores were assessed over 3 years postoperatively.
RESULTS: MME progressed over time until 3 years postoperatively, and its progression during this period was 1.61 ± 1.44 mm. The SNQ for MMPR decreased over time until 3 years postoperatively, and the change in the SNQ from 3 months to 3 years postoperatively (ΔSNQ) was 2.69 ± 1.69. All clinical scores significantly improved (p < 0.001). ΔSNQ was significantly correlated with body weight (correlation coefficient = -0.424, p = 0.010) and body mass index (correlation coefficient = -0.330, p = 0.050). However, ΔSNQ was not significantly correlated with preoperative or postoperative clinical scores.
CONCLUSIONS: After pullout repair for MMPRTs, MME progressed to 3 years postoperatively. However, the signal intensity of the repaired posterior roots decreased, and clinical scores improved over time until 3 years postoperatively. Patient weight and body mass index were significantly correlated with the reduced signal intensity of the repaired posterior roots, suggesting that weight assessment in patients with MMPRTs is crucial.
METHODS: IV.