Aims. To evaluate inducing osteoarthritis (OA) by surgical destabilization of the medial meniscus (DMM) in mice with and without a stereomicroscope. Methods. Based on sample size calculation, 70 male C57BL/6 mice were randomly assigned to three surgery groups: DMM aided by a stereomicroscope; DMM by naked eye; or sham surgery. The group information was blinded to researchers. Mice underwent static weightbearing, von Frey test, and gait analysis at two-week intervals from eight to 16 weeks after surgery. Histological grade of OA was determined with the Osteoarthritis Research Society International (OARSI) scoring system. Results. Surgical DMM with or without stereomicroscope led to decrease in the mean of weightbearing percentages (-20.64% vs -21.44%, p = 0.792) and paw withdrawal response thresholds (-21.35% vs -24.65%, p = 0.327) of the hind limbs. However, the coefficient of variation (CV) of weight-bearing percentages and paw withdrawal response thresholds in naked-eye group were significantly greater than that in the microscope group (19.82% vs 6.94%, p < 0.001; 21.85% vs 9.86%, p < 0.001). The gait analysis showed a similar pattern. Cartilage degeneration was observed in both DMM-surgery groups, evidenced by increased OARSI scores (summed score: 11.23 vs 11.43, p = 0.842), but the microscope group showed less variation in OARSI score than the naked-eye group (CV: 21.03% vs 32.44%; p = 0.032). Conclusion. Although surgical DMM aided by stereomicroscope is technically difficult, it produces a relatively more homogeneous OA model in terms of the discrete degree of pain behaviours and histopathological grading when compared with surgical DMM without stereomicroscope. Cite this article: Bone Joint Res 2022;11(8):518–527

We present the first reported case of symptomatic medial dislocation of the medial meniscus in a patient who had no previous history of trauma and who had an otherwise normal knee. The treatment of instability of the medial meniscus is controversial and studies have indicated that certain individuals without a firm meniscal bony insertion may be predisposed to meniscal dislocation. In our patient, the meniscal instability interfered with daily activities. Operative stabilisation by reconstruction of the meniscotibial ligaments cured the symptoms

Background. Meniscus repair can restore the function of torn meniscus in anterior cruciate ligament (ACL)-reconstructed knees. However, few reports investigate the relationship between concurrent meniscus repair with ACL reconstruction and postoperative meniscal position. This study aimed to evaluate the size of the medial meniscus in patients who underwent ACL reconstruction and concomitant all-inside medial meniscus repair. Methods. This study received the approval of our Institutional Review Board. Twenty patients underwent ACL reconstruction and concurrent medial meniscus repair of a peripheral longitudinal tear using the FasT-Fix meniscal repair device. Medial tibial plateau length (MTPL) and width (MTPW) were determined by radiographic images. We evaluated the Lysholm score, anteroposterior instability (difference in KT-2000 arthrometer measurement), meniscal healing, and magnetic resonance imaging (MRI)-based medial meniscal length (MML) and width (MMW). The healing status of repaired medial meniscus was assessed by 2nd-look arthroscopy. Results. ACL reconstruction improved the Lysholm score and anteroposterior instability. All the patients showed complete healing of the repaired meniscus in 2nd-look arthroscopic evaluation. Significant increase of MML and MML percentage (100 × MML/MTPL) was observed after concurrent all-inside medial meniscus repair with ACL reconstruction. However, MMW and MMW percentage (100 × MMW/MTPW) were not affected. Conclusions. Concurrent all-inside medial meniscus repair with ACL reconstruction had satisfactory clinical results. Anteroposterior length of the medial meniscus increased after surgery. Our results suggest that medial meniscus repair associated with ACL reconstruction may affect the biomechanical function of the medial meniscus. Level of Evidence. Case-control study, Level IV. Disclosure. The authors have no conflicts of interest

Summary. Our statistical shape analysis showed that size is the primary geometrical variation factor in the medial meniscus. Shape variations are primarily focused in the posterior horn, suggesting that these variations could influence cartilage contact pressures. Introduction. Variations in meniscal geometry are known to influence stresses and strains inside the meniscus and the articulating cartilage surfaces. This geometry-dependent functioning emphasizes that understanding the natural variation in meniscus geometry is essential for a correct selection of allograft menisci and even more crucial for the definition of different sizes for synthetic meniscal implants. Moreover, the design of such implants requires a description of 3D meniscus geometry. Therefore, the aim of this study was to quantify 3D meniscus geometry and to determine whether variation in medial meniscus geometry is size or shape driven. Patients & Methods. Sagittal knee MR images (n=35; 15 males, 20 females, aged 33±12) were acquired at 3 Tesla using a 3D SPACE sequence with isotropic resolution of 0.5×0.5×0.5mm. 3D models were generated by manual segmentation of the medial menisci from the MR scans. The surface of a reference meniscus was then described by 250 landmarks. Using an affine iterative closest point transformation, these landmarks were registered onto the full set of 3D models. Based on the set of corresponding landmarks, a point distribution model was created using the Shapeworks software (NITRC, University of Utah), an open source algorithm for constructing correspondence-based statistical models of sets of similar shapes. Several modules from Shapeworks and the Arthron software (UCD, Dublin) were used to perform principal component analysis (PCA) upon the set of landmarks. The results of the PCA enabled quantification and visualisation of the primary modes of variation in meniscal geometry. Results. The majority (77%) of variation in medial meniscus geometry was found to be due to sizing (principal component (PC) 1). Including the shape-related PC's 2 to 4, increased the cumulative percentage of represented geometry variation to over 90%. The independent shape variations described by PCs 2–4 all display larger variations in geometry of the posterior meniscal horn than the anterior section. Discussion. From this study, we can conclude that geometry variation of the medial meniscus is mainly determined by differences in size. However, since the posterior aspect of the medial meniscus experiences higher loads during daily activities than the anterior part, the shape variations described by PCs 2–4 may have a significant influence on cartilage contact pressures. Therefore, PCA alone does not provide sufficient information to define the number of implant sizes to cover a majority of the population. Analysis of the sensitivity of cartilage contact pressures to the shape variations identified in this analysis could provide the additional information needed

Introduction. Post-meniscectomy syndrome is broadly characterised by intractable pain following the partial or total removal of a meniscus. There is a large treatment gap between the first knee pain after meniscectomy and the eligibility for a TKA. Hence, there is a strong unmet need for a solution that will relieve this post-meniscectomy pain. Goal of this first-in-man study was to evaluate the safety and performance of an anatomically shaped artificial medial meniscus prosthesis and the accompanying surgical technique. Methods. A first-in-man, prospective, multi-centre, single arm clinical investigation was intended to be performed on 18 post-medial meniscectomy syndrome patients with limited underlying cartilage damage (Kellgren Lawrence scale 0–3) in the medial compartment and having a normal lateral compartment. Eventually 5 patients received a polycarbonate urethane mediale meniscus prosthesis (Trammpolin® medial meniscus prosthesis; ATRO Medical B.V., the Netherlands) which was clicked onto two titanium screws fixated at the native horn attachments on the tibia. PROMs were collected at baseline and at 6 weeks, 3, 6, 12 and 24 months following the intervention including X-rays at 6, 12 and 24 Months. MRI scans were repeated after 12 and 24 months. Results. The surgical technique to select the appropriately sized implant and correct positioning of the fixation screws and meniscus prosthesis onto the tibia was demonstrated feasible and reproducible. The surgeries showed that in particular the positioning of the posterior screw is crucial for correct positioning of the prosthesis. Inclusion stopped after 5 patients, who reached the 6 months evaluation. The PROMs did not improve in the first 6 months after surgery. All patients reported knee joint stiffness and slight effusion in their knee at 6 months follow-up. In case of symptomatic patients an evaluation of the device position and integrity was performed by MRI. In three patients the implants were removed because of implant failure and in one patient the implant was removed because of persistent pain and extension deficit. At present one patient has the implant still in situ. The explantations of the implants demonstrated no articular cartilage damage and the fixation screws were securely anchored. Discussion. This is the first clinical study with an artificial meniscus-like prosthesis. Except one, all implants were removed due to implant breakage or discomfort of the patient. Analysis of the torn implants showed fatigue failure resulting from the lack of loadsharing between implant and cartilage: the implant was too stiff and carried all the load in the medial compartment of the knee. Furthermore, the fixation with screws seemed too rigid which restricted the motion of the posterior horn. Based on previous in vitro and animal experiments, we expected more creep of the material and more motion on the screw fixation. Conclusion. This first-in-man clinical study demonstrates that the investigated device design is not safe and did not perform as expected. Therefore, modification of the meniscus prosthesis design and fixation technique is required to allow for more motion of the meniscus prosthesis during knee joint movement

Introduction. The major function of the medial meniscus has been shown to be distribution of the load with reduction of cartilage stresses, while its role in AP stability has been found to be secondary. However several recent studies have shown that cartilage loss in OA occurs in the central region of the tibia while the meniscus is displaced medially. In a lab study (Arno, Hadley 2013) it was confirmed that the AP laxity was greatly reduced with a compressive force across the knee, while the femur shifted posteriorly and the AP laxity was increased after a partial meniscetomy of the posterior horn. It is therefore possible that under load, the compression of the meniscus and the cartilage, 2–3mm in total, allows load transmission on the central tibial plateau, and causes radial expansion and tension of the meniscus providing restraint to femoral displacements. This leads to our hypotheses that the highest loading on the medial meniscus would be at the extremes of motion, rather than in the mid-range, and that the meniscus would provide the majority of the restraint to anterior-posterior femoral displacements throughout flexion when compressive loads were acting. Methods & Materials. MRI scans were taken of ten knee specimens to verify the absence of pathology and produce computer models. The knees were loaded in combinations of compressive and shear loading over a full flexion range. Tekscan sensors were used to measure the pressure distribution across the joint as the knee was flexed continuously. A digital camera was used to track the motion, from which femoral-tibial contacts were determined by computer modelling. Load transmission was determined from the Tekscan for the anterior horn, central body, posterior horn, and the uncovered cartilage in the center of the meniscus. An analysis was carried out (Fig 2) to determine the net anterior or posterior shear force carried by the meniscus. Results. For the three types of loading (Fig 1); compression only, compression and anterior shear, compression and posterior shear; between 40–80% of the total load was transmitted through the meniscus, the overall average being 58%. The remaining 42% was transmitted directly through the uncovered cartilage. The anterior horn was loaded only up to 30 degrees flexion, and played a role in controlling anterior femoral displacement. The central body was loaded 10–20% and would provide some restraint to medial femoral subluxation. Overall the posterior horn carried the highest percentage of the shear load (Figure 3), especially after 30 degrees flexion when a posterior shear force was applied, for which the meniscus was estimated to carry 50% of the shear force. Discussion. The hypotheses were largely supported. There was high anterior horn loading in early flexion, but in the remaining range, the posterior horn was the highest loaded especially under posterior shear. Supporting the posterior shear force under load bearing conditions is evidently an important role of the meniscus. Hence in any attempts at repair or replacement, these dual functions of load-sharing and stability need to be incorporated

Introduction Magnetic resonance imaging (MRI) is important in non-invasive evaluation of osseous and soft-tissue structures in the post-traumatic knee. However, it is sometimes impossible to determine if a focus of high signal intensity in the meniscus is confined to the substance, or extends to involve the joint surface. This is a critical differentiation as the latter represents menisci tears that can be found and treated arthroscopically, whereas the former represents degradation, intra-substance tears or normal variants not amenable to arthroscopic intervention. The aim of this study was to investigate occurrence of altered signal intensity in the posterior horn of the medial meniscus and correlate with arthroscopic findings. Materials and Methods 64 patients with suspected post-traumatic internal derangement of the knee who underwent MRI prior to arthroscopy were evaluated. All patients initially had MR imaging of the symptomatic knee using a standard protocol in a Siemens Symphony 1.5 Tesle Magnetom. MR images were then interpreted and reported by 2 radiologists experienced in MR and skeletal radiology. Meniscal tears were graded according to the system validated by Lotysch. A Grade 3 signal was considered unequivocal evidence of a meniscal tear. Equivocal tears (Grade 2/3 signal) were diagnosed if it was unclear if there was a small portion of normal intact meniscal tissue between a linear high signal in the meniscus and the articular surface abutting the meniscus. Arthroscopy was subsequently performed by senior surgeons aware of the MR findings within 2 weeks of imaging. Patients were re-assessed clinically and evaluated functionally at a mean follow-up time of 5 months. Radiographic, arthroscopic and clinical results were then correlated and evaluated. Results There were 48 males and 16 females in the group, with a mean age of 28.2 years.. Tears of the posterior horn of the medial meniscus were reported on MRI unequivocally (Grade 3 signal) in 18 patients and equivocally (Grade 2/3 signal) in 10 patients. Subsequent arthroscopic correlation revealed 16 tears (89%) in the unequivocal group and only one tear (10%) in the equivocal group. Discusion The finding that only 10% of patients with an equivocal tear in the posterior horn of the medial meniscus on MRI were subsequently found to have a tear on arthroscopy would suggest that early arthroscopic intervention is not warranted in these cases. We suggest that unless symptoms persist over the course of 3 to 6 months, or if a more compelling symptom complex develops, only then should arthroscopic evaluation be considered. Conclusion Equivocal tears on MRI of the posterior horn of the medial meniscus have a low rate of arthroscopically detected tears and a trial of conservative therapy may be prudent in such cases

The aim of this work was to develop a novel, accessible and low-cost method, which is sufficient to measure changes in meniscal position in a whole-knee joint model performing dynamic motion in a knee simulator. An optical tracking method using motion markers, MATLAB (MATLAB, The MathWorks Inc.) and a miniature camera system (Raspberry Pi, UK) was developed. Method feasibility was assessed on porcine whole joint knee samples (n = 4) dissected and cemented to be used in the simulator (1). Markers were placed on three regions (medial, posterior, anterior) of the medial meniscus with corresponding reference markers on the tibial plateau, so the relative meniscal position could be calculated. The Leeds high kinematics gait profile scaled to the parameters of a pig (1, 2) was driven in displacement control at 0.5 Hz. Videos were recorded at cycle-3 and cycle-50. Conditions tested were the capsule retained (intact), capsule removed and a medial posterior root tear. Mean relative displacement values were taken at time-points relating to the peaks of the axial force and flexion-extension gait inputs, as well as the range between the maximum and minimum values. A one-way ANOVA followed by Tukey post hoc analysis were used to assess differences (p = 0.05). The method was able to measure relative meniscal displacement for all three meniscal regions. The medial region showed the greatest difference between the conditions. A significant increase (p < 0.05) for the root tear condition was found at 0.28s and 0.90s (axial load peaks) during cycle-3. Mean relative displacement for the root tear condition decreased by 0.29 mm between cycle-3 and cycle-50 at the 0.28s time-point. No statistically significant differences were found when ranges were compared at cycle-3 and cycle-50. The method was sensitive to measure a substantial difference in medial-lateral relative displacement between an intact and a torn state. Meniscus extrusion was detected for the root tear condition throughout test duration. Further work will progress onto human specimens and apply an intervention condition

Altered mechanical loading is a widely suggested, but poorly understood potential cause of cartilage degeneration in osteoarthritis. In rodents, osteoarthritis is induced following destabilization of the medial meniscus (DMM). This study estimates knee kinematics and contact forces in rats with DMM to gain better insight into the specific mechanisms underlying disease development in this widely-used model. Unilateral knee surgery was performed in adult male Sprague-Dawley rats (n=5 with DMM, n=5 with sham surgery). Radio-opaque beads were implanted on their femur and tibia. 8 weeks following knee surgery, rat gait was recorded using the 3D²YMOX setup (Sanctorum et al. 2019, simultaneous acquisition of biplanar XRay videos and ground reaction forces). 10 trials (1 per rat) were calibrated and processed in XMALab (Knörlein et al. 2016). Hindlimb bony landmarks were labeled on the XRay videos using transfer learning (Deeplabcut, Mathis et al. 2019; Laurence-Chasen et al. 2020). A generic OpenSim musculoskeletal model of the rat hindlimb (Johnson et al. 2008) was adapted to include a 3-degree-of-freedom knee. Inverse kinematics, inverse dynamics, static optimization of muscle forces, and joint reaction analysis were performed. In rats with DMM, knee adduction was lower compared to sham surgery. Ground reaction forces were less variable with DMM, resulting in less variability in joint external moments. The mediolateral ground reaction force was lower, resulting in lower hip adduction moment, thus less force was produced by the rectus femoris. Rats with DMM tended to break rather than propel, resulting in lower hip flexion moment, thus less force was produced by the semimembranosus. These results are consistent with lower knee contact forces in the anteroposterior and axial directions. These preliminary data indicate no overloading of the knee joint in rats with DMM, compared with sham surgery. We are currently expanding our workflow to finite element analysis, to examine mechanical cues in the cartilage of these rats (Fig1G)

Magnetic resonance imaging has emerged as an important modality in the non-invasive evaluation of osseous and soft-tissue structures in the post-traumatic knee. However, it is sometimes radiologically impossible to determine with confidence if a focus of high signal intensity in the meniscus is confined to the substance of the meniscus or if it extends to involve the joint surface. This is a critical differentiation because the latter represents menisci tears that can be found and treated arthroscopically, whereas the former represents degradation, intrasubstance tears or perhaps normal variants that are not amenable to arthroscopic intervention. The aim of this study was to investigate the occurrence of altered signal intensity in the posterior horn of the medial meniscus in correlation with arthroscopic findings. Sixty-four patients with suspected post-traumatic internal derangement of the knee who underwent magnetic resonance imaging prior to arthroscopy were evaluated retrospectively. There were 48 males and 16 females. Mean age was 28.2 years. Tears of the posterior horn of the medial meniscus were diagnosed unequivocally (Grade 3 signal) in 18 patients and equivocally (Grade 2/3 signal) in 10 patients. Arthroscopic correlation revealed 16 tears (89%) in the unequivocal group and only one tear (10%) in the equivocal group). A meniscal tear is unlikely when magnetic resonance imaging shows a focus of high signal intensity in the posterior horn of the medial meniscus that does not unequivocally extend to involve the inferior or superior joint surface. An appropriate trial of non-operative treatment is recommended in such questionable cases. Magnetic resonance imaging is a useful diagnostic tool, however, it should be used selectively, and in conjunction with history and clinical examination in evaluating internal derangement of the knee

The meniscus is a fibrocartilaginous tissue that plays an important role in controlling the complex biomechanics of the knee. Many histological and mechanical studies about meniscal attachment have been carried out, and medial meniscus (MM) root repair is recommended to prevent subsequent cartilage degeneration following MM posterior root tear. However, there are only few studies about the differences between meniscus root and horn cells. The goal of this study was to clarify the differences between these two cells. Tissue samples were obtained from the medial knee compartments of 10 patients with osteoarthritis who underwent total knee arthroplasty. Morphology, distribution, and proliferation of MM root and horn cells, as well as gene and protein expression levels of Sry-type HMG box (SOX) 9 and type II collagen (COL2A1) were determined after cyclic tensile strain (CTS) treatment. Horn cells had a triangular morphology, whereas root cells were fibroblast-like. The number of horn cells positive for SOX9 and COL2A1 was considerably higher than that of root cells. Although root and horn cells showed similar levels of proliferation after 48, 72, or 96 h of culture, more horn cells than root cells were lost following 2-h CTS (5% and 10% strain). SOX9 and COL2A1 mRNA expression levels were significantly enhanced in horn cells compared with those in root cells after 2- and 4-h CTS (5%) treatment. This study demonstrates that MM root and horn cells have distinct characteristics and show different cellular phenotypes. Our results suggest that physiological tensile strain is important for activating extracellular matrix production in horn cells. Restoring physiological mechanical stress may be useful for promoting healing of the MM posterior horn

In 20 skeletally mature female merino sheep, divided into four groups, we performed total medial meniscectomy, removal of the middle third of the patellar tendon, and tenotomy of the calcaneal tendon of the right hind leg. Group I (control) had no additional procedures. In the other three groups the medial meniscus was replaced by the middle third of the patellar tendon from the ipsilateral knee. The animals were killed at three (group II), six (group III), or 12 months (group IV) and the tendon-meniscus examined macroscopically, by light and scanning electron microscopy, and biomechanically. Remodelling of the tissue had taken place by 12 months but the failure stress and tensile modulus for the tendon-meniscus were lower than for the normal meniscus. Our evidence suggests that, in sheep, replacement of a meniscus by a tendon autograft may decrease the severity of the degenerative changes that occur after meniscectomy

Purpose of the study: One of the most frequent complications of medial meniscal suture is injury to the saphenous nerve or its branches. The purpose of this study was to ascertain the relations of the medial meniscus with the infrapatellar branches of the saphenous nerve. Material and methods: Twenty lower limbs were dissected to study the pathways of the saphenous nerve and its branches in relation to different landmarks of the medial meniscus and palpable bony zones. Sixteen measurements were made on each knee held in extension. Results: The infrapatellar trunk of the saphenous nerve exhibited two terminal branches in all knees dissected. Level of the bifurcation in relation to the joint space varied. Similarly the position of the branches varied greatly in relation to different landmarks. The most frequent configuration was a main trunk situated 8 mm anteriorly to the tubercle of the great adductor and 60 mm from the mid point of the medial border of the patella. The bifurcation into two branches was situated 23 mm above the joint space. The two branches ran obliquely anteriorly and inferiorly forming an angle of 55° on average with a vertical line. The superior branch ran 24 mm behind the anterior meniscal point and 55 mm from the posterior meniscal point; the inferior branch ran 42.6 mm and 38 mm from these two points. Discussion: Injury to the saphenous nerve or its branches is mainly observed for suturing techniques done medially to laterally. Incidence has reached 38% in certain series. This incidence has declined with the increasingly widespread use of arthroscopy, but saphenous injury still occurs for meniscal repairs using a posteromedial approach. The risk is similar for medially to laterally or laterally to medially sutures. Since there is no safety zone, it would be advisable to prefer an «all medially» technique. Conclusion: Measurements made on dissection specimens enabled us to delimit three zones of increasing risk for nerve injury. The zone with the highest risk measures 20 mm wide. Its anterior limit is situated behind the most anterior meniscal point and its posterior limit is situated 28 mm from the posterior meniscal point

Although osteoarthritis (OA) is characterized by articular cartilage damage, synovial inflammation is a prominent feature contributing to disease progression. In addition to synovial tissue resident macrophages, infiltrating macrophages and monocytes, their lineage precursors, may also contribute to pathological processes. In mice, peripheral blood monocytes may be categorized according to pro-inflammatory/classical and patrolling/non-classical subsets. The aim of this study was to identify profiles of peripheral blood monocyte subsets as well as different synovial macrophage phenotypes during disease development. OA was induced in knees of C57BL/6 mice by destabilization of the medial meniscus (DMM). Blood was harvested from the facial vein 7 days prior to and 1, 7, 14, 28, and 56 days post induction of OA. Separate mice were sham-operated as a control. Monocyte subsets and synovial macrophage populations were identified by flow cytometry. Levels of classical monocytes were significantly higher at day 14 (p<0.001) and day 28 (p=0.031) in peripheral blood of DMM-operated mice compared to control. Furthermore, the percentage of non-classical monocytes was significantly lower in DMM-mice at day 14 (p=0.026). At day 56 post OA-induction, an increase in total synovial macrophages (CD11b+F4/80+ cells) was observed between DMM and sham operated knees (p=0.021). The ratio between pro-inflammatory (CD11b+F4/80+CD86+) and tissue repair (CD11b+F4/80+CD206+) synovial macrophage subsets tended to be higher in DMM knees, however this finding was not statistically significant (p>0.05). In light of the present findings, further investigation is required to elucidate the relationship of peripheral blood monocyte subsets to synovial inflammation and features of OA pathogenesis

Introduction: Instability of the anterior horn of the medial meniscus (MM) has been described as dislocating, subluxating or hypermobile, but it is still controversial whether segments of the MM of the knee were surgically treated by arthroscopic stabilization. The average age of the patients was 28.7 (range 12 to 56). There were 9 men and 4 women. All patients complained of medial knee pain and felt tenderness in the medial joint space, most of them on the anterior side. None showed an apparent tear of the meniscus by arthroscopy or on MRI images, but all arthroscopically showed hypermobility (or easy dislocation from the edge of the tibial plateau) of the anterior to middle segment of the MM. No other apparent pathological changes were found. Six knees had marked limitations in the range of knee motion before operation. Arthroscopic stabilization of the hypermobility was performed in order to restrain the movement of the MM by fixing it to the tibial edge, using staples (2 cases), Kirschner wires (2 cases) or suture anchors (9 cases). Using the Japanese Orthopaedic Association meniscus injury score (maximum 100 points), the result was evaluated. The average follow up period was 20.1 months (range 9 to 49 months). Results: The result of arthroscopic fixation was satisfactory (excellent in 8 cases good in 1, fair in 1, and poor in 1). The average meniscus score at follow up was 87.8, while that of before operation was 41.9. It is suggested that instability of the anterior segment of the MM can be effectively treated by arthroscopic fixation of this site. Discussion: Since all of the knees in this study had an isolated lesion of instability in the anterior segment of the MM, the marked improvement in medial knee pain that resulted from fixation of this site does show that this lesion can be symptomatic. After excluding other possible pathological lesions, stabilization of this lesion by arthroscopic fixation is a good choice of treatment

Purpose: The collagen meniscus implant (CMI, Sulzer) is a meniscal substitute with a collagen matrix serving as a tutor for autologous regeneration of meniscal tissue. The goal is to prevent mid-term degradation after meniscectomy. The CMI is inserted arthroscopically. The purpose of this multicentric European study was to verify the safety, technical feasibility, and short-term clinical efficacy of the CMI in a population of patients undergoing medial meniscectomy. The long-term results should be obtained within a delay of five years at least. Material and results: The series included patients with medial meniscus lesions alone, with or without lesions of the anterior cruciate ligament (present in 44% of the patients and repaired at the same time). Patient consent was obtained in all cases (in France in accordance with the Huriet law). Patients with lesions of the lateral ligament, associated trade IV cartilage lesions, or lesions of the posterior cruciate ligament were excluded. The study included 98 patients, mean age 33 years. Four patients were excluded from the analysis due to complications. Currently, 66 patients are available for evaluation one year after insertion of the CMI. Subjective outcome, the Lysholm score, and x-ray and MRI findings were recorded. Evaluation up to five years follow-up is scheduled. Results: Complications: There were four early complications: infectious arthritis (n=1), puriform arthritis without germ (n=2), implant rupture (n=1). There were no implant-related postop complications. Clinical results: At one year follow-up, the Lysholm score was 97. Pain was mild (1 on the visual analogue scale) and was only observed in one out of six patients: 87% of the patients had a normal or nearly normal knee. Radiological results: There were no radiological signs of early degeneration. It was difficult to interpret the MRI results which visualised a structure with an intermediary signal in the form of a meniscal triangle. MRI did on show any sign of deleterious effect on the neighbouring cartilage. Discussion: This technique for replacing the meniscus is an alternative to allogenic grafting. These preliminary results must of course be interpreted with caution. They show that arthroscoic implantation of the CMI is feasible but difficult. There was no evidence of an immunological reaction. Complications were related to the operative difficulty. Clinical results were satisfactory at one year, particularly in terms of pain. On the other hand, the biomechanical value of the implant cannot be assessed until longer follow-up data becomes available. Conclusion: In light of the operative difficulty, the long postoperative recovery due to the rehabilitation protocol, the CMI should be used for symptomatic knees after meniscectomy, particularly in case of anterior laxity

Aims. To fully quantify the effect of posterior tibial slope (PTS) angles on joint kinematics and contact mechanics of intact and anterior cruciate ligament-deficient (ACLD) knees during the gait cycle. Methods. In this controlled laboratory study, we developed an original multiscale subject-specific finite element musculoskeletal framework model and integrated it with the tibiofemoral and patellofemoral joints with high-fidelity joint motion representations, to investigate the effects of 2.5° increases in PTS angles on joint dynamics and contact mechanics during the gait cycle. Results. The ACL tensile force in the intact knee was significantly affected with increasing PTS angle. Considerable differences were observed in kinematics and initial posterior femoral translation between the intact and ACLD joints as the PTS angles increased by more than 2.5° (beyond 11.4°). Additionally, a higher contact stress was detected in the peripheral posterior horn areas of the menisci with increasing PTS angle during the gait cycle. The maximum tensile force on the horn of the medial meniscus increased from 73.9 N to 172.4 N in the ACLD joint with increasing PTS angles. Conclusion. Knee joint instability and larger loading on the medial meniscus were found on the ACLD knee even at a 2.5° increase in PTS angle (larger than 11.4°). Our biomechanical findings support recent clinical evidence of a high risk of failure of ACL reconstruction with steeper PTS and the necessity of ACL reconstruction, which would prevent meniscus tear and thus the development or progression of osteoarthritis. Cite this article: Bone Joint Res 2022;11(10):739–750

Aims. The aim of this study was to compare patient-reported outcomes (PROMs) following isolated anterior cruciate ligament reconstruction (ACLR), with those following ACLR and concomitant meniscal resection or repair. Methods. We reviewed prospectively collected data from the UK National Ligament Registry for patients who underwent primary ACLR between January 2013 and December 2022. Patients were categorized into five groups: isolated ACLR, ACLR with medial meniscus (MM) repair, ACLR with MM resection, ACLR with lateral meniscus (LM) repair, and ACLR with LM resection. Linear regression analysis, with isolated ACLR as the reference, was performed after adjusting for confounders. Results. From 14,895 ACLR patients, 4,400 had two- or five-year Knee injury and Osteoarthritis Outcome Scores (KOOS) available. At two years postoperatively, the MM repair group demonstrated inferior scores in KOOS pain (β = −3.63, p < 0.001), symptoms (β = − 4.88, p < 0.001), ADL (β = − 2.43, p = 0.002), sport and recreation (β = − 5.23, p < 0.001), quality of life (QoL) (β = − 5.73, p < 0.001), and International Knee Documentation Committee (β = − 4.1, p < 0.001) compared with the isolated ACLR group. The LM repair group was associated with worse KOOS sports and recreation scores at two years (β = − 4.264, p < 0.001). At five years, PROMs were comparable between the groups. At five years, PROMs were comparable between the groups. Participants undergoing ACLR surgery within 12 weeks from index injury demonstrated superior PROMs at two and five years. Conclusion. Our study showed that MM repair, and to a lesser extent LM repairs in combination with ACLR, were associated with inferior patient-reported outcome measures (PROMs) compared to isolated ACLR at two years postoperatively, while meniscal resection groups exhibited comparable outcomes. However, by five years postoperation, no significant differences in PROMs were evident. Further longer-term, cross-sectional studies are warranted to investigate the outcomes of ACLR and concomitant meniscal surgery

Aims. Osteoarthritis (OA) is a common degenerative disease. PA28γ is a member of the 11S proteasome activator and is involved in the regulation of several important cellular processes, including cell proliferation, apoptosis, and inflammation. This study aimed to explore the role of PA28γ in the occurrence and development of OA and its potential mechanism. Methods. A total of 120 newborn male mice were employed for the isolation and culture of primary chondrocytes. OA-related indicators such as anabolism, catabolism, inflammation, and apoptosis were detected. Effects and related mechanisms of PA28γ in chondrocyte endoplasmic reticulum (ER) stress were studied using western blotting, real-time polymerase chain reaction (PCR), and immunofluorescence. The OA mouse model was established by destabilized medial meniscus (DMM) surgery, and adenovirus was injected into the knee cavity of 15 12-week-old male mice to reduce the expression of PA28γ. The degree of cartilage destruction was evaluated by haematoxylin and eosin (HE) staining, safranin O/fast green staining, toluidine blue staining, and immunohistochemistry. Results. We found that PA28γ knockdown in chondrocytes can effectively improve anabolism and catabolism and inhibit inflammation, apoptosis, and ER stress. Moreover, PA28γ knockdown affected the phosphorylation of IRE1α and the expression of TRAF2, thereby affecting the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signalling pathways, and finally affecting the inflammatory response of chondrocytes. In addition, we found that PA28γ knockdown can promote the phosphorylation of signal transducer and activator of transcription 3 (STAT3), thereby inhibiting ER stress in chondrocytes. The use of Stattic (an inhibitor of STAT3 phosphorylation) enhanced ER stress. In vivo, we found that PA28γ knockdown effectively reduced cartilage destruction in a mouse model of OA induced by the DMM surgery. Conclusion. PA28γ knockdown in chondrocytes can inhibit anabolic and catabolic dysregulation, inflammatory response, and apoptosis in OA. Moreover, PA28γ knockdown in chondrocytes can inhibit ER stress by promoting STAT3 phosphorylation. Cite this article: Bone Joint Res 2024;13(11):659–672

We report the clinical and arthroscopic findings in 20 cases of medial meniscal cyst with a mean follow-up of 20 months. These were studied prospectively from a series of 7435 knee arthroscopies in which there were 1246 stable non-arthritic knees with medial meniscal tears. The diagnosis on referral was incorrect in seven, and incomplete in seven. There was coexistent meniscal injury in 17 (85%), but in the other three no tear was visible at arthroscopy. Ten knees had additional intra-articular abnormalities. Treatment of the cyst was by open resection in 12 and arthroscopic evaluation at meniscectomy in seven. In one case the cyst resolved after arthroscopic partial meniscectomy alone. Meniscal tears were treated by arthroscopic partial medial meniscectomy. Medial meniscal cysts are an important but under-diagnosed cause of knee pain and are frequently related to arthroscopically diagnosable and treatable meniscal pathology. Treatment should be directed towards both the meniscus and the cyst, which may require open surgery.