The menisci of the knee joint. Anatomical and functional characteristics, and a rationale for clinical treatment

Comparison of the structural features between chicken quadratomandibular joint and rat temporomandibular joint with reference to ligament and articular meniscus/disc

OBJECTIVES

The new jaw joint of mammals evolved between the squamosal and the dentary. We investigated the structural features of the chicken quadratomandibular joint (QMJ) (primary jaw joint) and the rat temporomandibular joint (TMJ) (new jaw joint) to determine whether these structures reflect their putative movements from macroscopic and histological perspectives.

METHODS

Chicken QMJ and rat TMJ were dissected, and their joint apparatuses, including ligaments and meniscus/disc, were analyzed macroscopically. Microscopic analysis, incorporating immunohistochemistry and in situ hybridization, was conducted to investigate protein localization and gene expression within the extracellular matrix of cartilage and bone.

RESULTS

The chicken QMJ contained the jugomandibular ligament, running laterally and posteriorly to the QMJ, tightly bound to the articular meniscus. These features suggest a role in supporting and controlling quadrate bone movements. The rat TMJ lacked a lateral ligament, and the mandibular head had an elongated oval shape along the anterior-posterior axis. This morphology indicates that lateral mandibular movements are rare, with jaw motion predominantly occurring in the anterior-posterior direction. The chicken QMJ meniscus contained distinct cartilaginous tissues, whereas the rat TMJ articular disc acquired cartilaginous characteristics after occlusion was established (5 weeks postnatally), suggesting that the meniscus/disc properties are closely associated with mastication.

CONCLUSIONS

The structural features of chicken and rat jaw joints, including their joint apparatuses, appropriately reflect their respective functions, such as movement dynamics and resistance to mastication pressure.

McMurray's test is influenced by perimeniscal synovitis in degenerative meniscus tears

BACKGROUND

McMurray's test is a useful physical examination in determining meniscus tears, yet its sensitivity is only 38-62%. Furthermore, the relationship between degenerative meniscus tears (DMT) and mechanical symptoms during McMurray's test is not well defined. Perimeniscal synovitis occurs in osteoarthritic (OA) knees, inducing localized symptoms such as posterior knee pain in medial meniscus posterior horn DMTs. This study aimed to determine the relationship between McMurray's test with medial meniscus DMT and perimeniscal synovitis in patients with knee OA.

METHODS

We retrospectively analyzed 60 patients who underwent medial unicompartmental knee arthroplasty (UKA) with positive (n = 20) and negative (n = 40) preoperative McMurray's tests. Preoperative magnetic resonance imaging (MRI), intraoperative gross morphology, and histological analysis of meniscus and synovium were evaluated to determine meniscal tears and perimeniscal synovitis. Univariate and multivariate regression analyses were done to determine the effects of meniscus tears and synovitis on McMurray's test results.

RESULTS

Gross morphology of the medial meniscus (MM) showed 14 out of 20 torn menisci in the McMurray's (+) group compared with 22 out of 40 in the (-) group, with no difference in meniscus tear severity among groups. The (+) group showed higher values of synovial thickness (p < 0.001) and area (p < 0.001) compared with the (-) group on magnetic resonance imaging (MRI). Histological analysis showed higher synovitis (p < 0.001) scores and expression of inflammatory markers [interleukin (IL)-1β (p < 0.001), IL-6 (p = 0.007), nerve growth factor (NGF) (p = 0.003), inducible nitric oxide synthase (iNOS) (p < 0.001)] in the perimeniscal synovium of (+) group compared with the (-) group. Multivariable logistic analysis revealed that larger synovial area [odds ratio (OR) = 1.106, p = 0.008] and a higher histologic synovitis score (OR = 2.595, p = 0.011) were independently significant predictive factors for a positive McMurray's test.

CONCLUSIONS

McMurray's test may be influenced by perimeniscal synovitis in DMT patients. The clinical implications of our results may influence not only the interpretation of McMurray's test but also the target tissue in treating mechanical symptoms related to meniscus tears.

LEVEL OF EVIDENCE

Level II.

Differences in the Association Between Medial Meniscus Tears and Focal Cartilage Lesions According to Tear Configuration

Background

There are no statistical analyses on the association between the configuration of medial meniscus tears and the location of focal cartilage lesions.

Purpose

To investigate the association between the configuration of medial meniscus tears and focal cartilage lesions and analyze whether the location of medial meniscus tears corresponds with that of focal cartilage lesions.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

The authors retrospectively evaluated the medical records of 317 patients with isolated medial meniscus tear who underwent arthroscopic surgery from January 2016 to December 2020. The configuration of the medial meniscus tear was determined based on the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) classification. Patients with flap, radial, and longitudinal tears were included in the vertical tear group. For subgroup analysis, vertical tears were divided into medial meniscus posterior root tears and remaining tears. The location of the medial meniscus tear was categorized as anterior, middle, or posterior according to the ISAKOS classification. The cartilage of the medial femoral condyle (MFC) and that of the medial tibial condyle (MTC) were divided into 6 and 4 zones, respectively, and the location of cartilage lesions on the MFC and MTC was evaluated by preoperative magnetic resonance imaging.

Results

There was a higher incidence of focal cartilage lesions with vertical versus horizontal medial meniscus tears (P < .001). For middle and posterior vertical tears with focal cartilage lesions, there was a significant concordance in location between the tear and the lesion (P < .001). In a subgroup analysis of medial meniscus posterior root tears, there was significantly more discordance in location between the tear and the lesion with medial meniscus posterior root tears (23/26 tears; 88.5%) compared with the remaining vertical tears (60/177 tears; 33.9%) (P < .001); instead, the focal cartilage lesions were mainly distributed in the lateral anterior and central portions of both the MFC and MTC.

Conclusion

Vertical tears of the medial meniscus were significantly associated with the presence of focal cartilage lesions, whereas horizontal tears were not. Additionally, middle and posterior vertical tears with focal cartilage lesions showed significant concordance in location between the tear and the lesion.

Relationship Between the Sagittal and Coronary Alignment of the Tibiofemoral Joint and the Medial Meniscus Extrusion in Knee Osteoarthritis

Background/Objectives: This study aims to clarify the reproducibility, validity, and accuracy of tibial external-rotation alignment evaluation using ultrasound imaging and to investigate the relationship between medial meniscus extrusion (MME) and tibiofemoral alignment in both the sagittal and coronal planes in knee osteoarthritis (OA). Methods: Study 1 included 10 healthy participants. The tibial external-rotation angle was calculated using MRI. In the ultrasound imaging evaluation, the differences in the distance from the most posterior points of the tibial and femoral condyles to the skin were calculated as the medial and lateral condyle gaps, respectively. The mediolateral (ML) gap was calculated by subtracting the lateral condyle gap from the medial condyle gap. Study 2 included 63 patients with unilateral OA and 16 healthy controls. MME was compared according to the severity of OA, the degree of tibial rotation, and the presence or absence of a tibial posterior shift. Results: Ultrasound imaging examinations showed high intra- and inter-rater reliabilities (0.786-0.979). The ML gap significantly affected the tibial external-rotation angle, determined using MRI. The ML gap of ultrasound imaging was significantly correlated with the ML gap of MRI. MME was significantly higher in the Early OA group than in the Control group. There was no significant difference in MME based on the tibial rotation degree. The group with a tibial posterior shift exhibited significantly more MME than that without a posterior shift. Conclusions: Ultrasound imaging is useful for evaluating knee alignment. MME was found to be associated with the tibial posterior shift.

Injectable decellularized Wharton's jelly hydrogel containing CD56+ umbilical cord mesenchymal stem cell-derived exosomes for meniscus tear healing and cartilage protection

Traditional meniscectomy or suture for meniscal tear usually leads to failed self-healing, cartilage degeneration and worse osteoarthritis. The strategies that facilitate the healing process of torn meniscus and safeguard knee cartilage against degeneration will be promising for clinical therapy. The CD56+ umbilical cord mesenchymal stem cells (UCSCs) (CD56+UCSCs) were sorted from Wharton's jelly using flow cytometer. Then, the modified decellularized Wharton's Jelly hydrogel (DWJH) was combined with isolated CD56+Exos from CD56+UCSCs to fabricate DWJH/CD56+Exos. The in vitro studies were performed to characterize the DWJ (decellularized Wharton's Jelly). The injectability and rheological properties were assessed by shear rate and frequency sweep analysis. The biocompatibility and chondrogenic differentiation inducibility of DWJH/CD56+Exos were performed on human bone marrow mesenchymal stem cells (hBMSCs) and RAW 264.7 cells. The release dynamics was evaluated in vitro and in vivo experiments. As for the in vivo experiments, the operated rats that subjected to a 2 mm full-thickness longitudinal tear in right medial anterior meniscus were injected a single dose of DWJH/CD56+Exos. At 4 and 8 weeks postoperatively, torn meniscus healing and articular cartilage degeneration were evaluated by hematoxylin and eosin (H&E), safranin O/fast green (SO&FG), and Sirius red staining. In in vitro experiments, the injectable DWJH/CD56+Exos demonstrated excellent biocompatibility, exosome releasing efficiency, injectable property and chondrogenic inducibility. The results of in vivo experiments revealed that DWJH/CD56+Exos degraded over time, promoted meniscal chondrogenesis, organized meniscal extracellular matrix remodeling, safeguard articular cartilage and inhibited secondary cartilage degeneration, which accelerated further facilitated torn meniscus healing. The novel injectable DWJH/CD56+Exos promoted meniscal tear healing by promoting meniscal chondrogenesis, safeguarding articular cartilage, and inhibiting secondary cartilage degeneration.

Age and anatomical region-related differences in vascularization of the porcine meniscus using microcomputed tomography imaging

Meniscal lesions in vascularized regions are known to regenerate while lack of vascular supply leads to poor healing. Here, we developed and validated a novel methodology for three-dimensional structural analysis of meniscal vascular structures with high-resolution microcomputed tomography (µCT). We collected porcine medial menisci from 10 neonatal (not-developed meniscus, n-) and 10 adults (fully developed meniscus, a-). The menisci were cut into anatomical regions (anterior horn (n-AH and a-AH), central body (n-CB and a-CB), and posterior horn (n-PH and a-PH). Specimens were cut in half, fixed, and one specimen underwent critical point drying and µCT imaging, while other specimen underwent immunohistochemistry and vascularity biomarker CD31 staining for validation of µCT. Parameters describing vascular structures were calculated from µCT. The vascular network in neonatal spread throughout meniscus, while in adult was limited to a few vessels in outer region, mostly on femoral side. n-AH, n-CB, and n-PH had 20, 17, and 11 times greater vascular volume fraction than adult, respectively. Moreover, thickness of blood vessels, in three regions, was six times higher in adults than in neonatal. a-PH appeared to have higher vascular fraction, longer and thicker blood vessels than both a-AH and a-CB. Overall, neonatal regions had a higher number of blood vessels, more branching, and higher tortuosity compared to adult regions. For the first time, critical point drying-based µCT imaging allowed detailed three-dimensional visualization and quantitative analysis of vascularized meniscal structures. We showed more vascularity in neonatal menisci, while adult menisci had fewer and thicker vascularity especially limited to the femoral surface.

Evaluation of Meniscal Load and Load Distribution in the Sound Canine Stifle at Different Angles of Flexion

OBJECTIVES

 The aim of the study was to investigate the contact mechanics and kinematic changes in the stifle in different standing angles.

STUDY DESIGN

 We performed a biomechanical ex vivo study using pairs of canine cadaver hindlimbs. Motion sensors were fixed to the tibia and the femur for kinematic data acquisition. Pressure mapping sensors were placed between the femur and both menisci. Thirty percent bodyweight was applied to the limbs with the stifle in 125, 135, or 145 degrees of extension.

RESULTS

 Stifle flexion angle influences femoromeniscal contact mechanics significantly. The load on both menisci was significantly higher for 125 and 135 degrees in comparison to 145 degrees. Additionally, the center of force was located significantly more caudal when comparing 125 to 145 degrees in the medial meniscus as well as in both menisci combined.

CONCLUSION

 The angle of knee flexion significantly impacts the contact mechanics between the femur and the meniscus. As the knee flexes, the load on both menisci increases.

Biomechanical impact of meniscal ramp lesions on knee joint contact characteristics in ACL deficient knees: a cadaveric analysis

PURPOSE

To evaluate the changes in contact characteristics of the tibiofemoral joint resulting from a meniscal ramp lesion in the medial meniscus.

METHODS

Twelve cadaveric knees (six matched pairs) were subjected to a 600 N axial load using a custom testing jig, which allowed for knee positioning at 0°, 45°, and 90° of flexion without other constraints. The knees were randomly assigned to either a ramp lesion group (n = 6) or a posterior root lesion group (n = 6). Four testing conditions were examined: (1) intact, (2) isolated ramp lesion, (3) isolated posterior root tear of the medial meniscus, and (4) combined ramp lesion and posterior root tear of the medial meniscus. Contact characteristics were evaluated using a flexible pressure sensor, the I-Scan System.

RESULTS

Peak contact pressure in isolated ramp lesions (4.15 ± 0.98 MPa, P = 0.206) showed non-significant increases compared to the intact condition (3.86 ± 1.32 MPa). Peak contact pressure in isolated posterior root tears (4.58 ± 1.70 MPa, P = 0.040) and, combined ramp and posterior root lesions (4.67 ± 1.47 MPa, P = 0.003) were significantly higher than that in the intact condition. The knee flexion position significantly affected the medial tibiofemoral joint's contact area, contact pressure, and peak contact pressure (P < 0.001 for all).

CONCLUSION

Isolated ramp lesions did not significantly impact force transmission, contact area, or contact pressure. In contrast, isolated root lesions and combined ramp and posterior root tears of the medial meniscus significantly intensified the changes in contact characteristics in the medial tibiofemoral joint compared to the intact condition.

LEVEL OF EVIDENCE

Level III.

Injectable ChitHCl-DDA tissue adhesive with high adhesive strength and biocompatibility for torn meniscus repair and regeneration

Suture pull-through is a clinical problem in meniscus repair surgery due to the sharp leading edge of sutures. Several tissue adhesives have been developed as an alternative to traditional suturing; however, there is still no suitable tissue adhesive specific for meniscus repair treatment due to unsatisfactory biosafety, biodegradable, sterilizable, and tissue-bonding characteristics. In this study, we used a tissue adhesive composed of chitosan hydrochloride reacted with oxidative periodate-oxidized dextran (ChitHCl-DDA) combined with a chitosan-based hydrogel and oxidative dextran to attach to the meniscus. We conducted viscoelastic tests, viscosity tests, lap shear stress tests, Fourier transform infrared (FTIR) spectroscopy, swelling ratio tests, and degradation behavior tests to characterize these materials. An MTT assay, alcian blue staining, migration assay, cell behavior observations, and protein expression tests were used to understand cell viability and responses. Moreover, ex vivo and in vivo tests were used to analyze tissue regeneration and biocompatibility of the ChitHCl-DDA tissue adhesive. Our results revealed that the ChitHCl-DDA tissue adhesive provided excellent tissue adhesive strength, cell viability, and cell responses. This tissue adhesive has great potential for torn meniscus tissue repair and regeneration.

Revealing the complexity of meniscus microvasculature through 3D visualization and analysis

Three-dimensional information is essential for a proper understanding of the healing potential of the menisci and their overall role in the knee joint. However, to date, the study of meniscal vascularity has relied primarily on two-dimensional imaging techniques. Here we present a method to elucidate the intricate 3D meniscal vascular network, revealing its spatial arrangement, connectivity and density. A polymerizing contrast agent was injected into the femoral artery of human cadaver legs, and the meniscal microvasculature was examined using micro-computed tomography at different levels of detail and resolution. The 3D vascular network was quantitatively assessed in a zone-base analysis using parameters such as diameter, length, tortuosity, and branching patterns. The results of this study revealed distinct vascular patterns within the meniscus, with the highest vascular volume found in the outer perimeniscal zone. Variations in vascular parameters were found between the different circumferential and radial meniscal zones. Moreover, through state-of-the-art 3D visualization using micro-CT, this study highlighted the importance of spatial resolution in accurately characterizing the vascular network. These findings, both from this study and from future research using this technique, improve our understanding of microvascular distribution, which may lead to improved therapeutic strategies.

[Meniscus update]

Meniscus tears are classified as horizontal, longitudinal, radial, and complex tears. Flap tears are a specific form in which a portion of the meniscus is displaced from a horizontal or longitudinal tear. The question of whether it is possible to preserve the meniscus by meniscus repair is of crucial therapeutic importance. It is therefore important to specify not only the configuration of the tear but also its extent and location as precisely as possible. Cooper's zonal classification should also be used for this purpose. Lesions of the meniscus roots are of high clinical relevance. On the posterior horn of the medial meniscus, root lesions are usually degenerative; on the posterior horn of the lateral meniscus, they are often traumatic. It is important to familiarize oneself with the normal appearance and anatomical location of the meniscal roots. Ramp lesions have received particular attention in recent years, especially in patients with anterior cruciate ligament tears. Therefore, particularly the integrity of the attachment of the posterior horn of the medial meniscus to the tibial plateau must be analyzed. If the meniscotibial ligament tears along its course or at the insertion to the meniscus or if it avulses with a meniscus fragment, this is a ramp lesion.

Current advances in engineering meniscal tissues: insights into 3D printing, injectable hydrogels and physical stimulation based strategies

The knee meniscus is the cushioning fibro-cartilage tissue present in between the femoral condyles and tibial plateau of the knee joint. It is largely avascular in nature and suffers from a wide range of tears and injuries caused by accidents, trauma, active lifestyle of the populace and old age of individuals. Healing of the meniscus is especially difficult due to its avascularity and hence requires invasive arthroscopic approaches such as surgical resection, suturing or implantation. Though various tissue engineering approaches are proposed for the treatment of meniscus tears, three-dimensional (3D) printing/bioprinting, injectable hydrogels and physical stimulation involving modalities are gaining forefront in the past decade. A plethora of new printing approaches such as direct light photopolymerization and volumetric printing, injectable biomaterials loaded with growth factors and physical stimulation such as low-intensity ultrasound approaches are being added to the treatment portfolio along with the contemporary tear mitigation measures. This review discusses on the necessary design considerations, approaches for 3D modeling and design practices for meniscal tear treatments within the scope of tissue engineering and regeneration. Also, the suitable materials, cell sources, growth factors, fixation and lubrication strategies, mechanical stimulation approaches, 3D printing strategies and injectable hydrogels for meniscal tear management have been elaborated. We have also summarized potential technologies and the potential framework that could be the herald of the future of meniscus tissue engineering and repair approaches.

Protective Effects of Extracorporeal Shockwave Therapy on the Degenerated Meniscus in a Rat Model

BACKGROUND

Loss of meniscal function in association with degenerative changes affects the development and progression of knee osteoarthritis, for which there is currently no effective treatment. Extracorporeal shockwave therapy (ESWT) is an established treatment for musculoskeletal disorders. However, the therapeutic effect of ESWT on meniscal degeneration remains unclear.

PURPOSE

To evaluate the therapeutic effect of ESWT on the degenerated meniscus in an anterior cruciate ligament transection (ACLT) model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve-week-old male Wistar rats were randomly assigned to 3 groups (normal, ESWT-, and ESWT+). Unilateral ACLT of the right knee was performed in the latter 2 groups. At 4 weeks after ACLT, the ESWT+ group received 800 shockwave impulses at an energy flux density of 0.22 mJ/mm2 in a single session. Histological changes were examined in the posterior portion of the medial meniscus after ESWT (n = 15 per group). Real-time polymerase chain reaction (PCR) was performed after ESWT (n = 5 per group) to analyze the expression of connective tissue growth factor/CCN family member 2 (CTGF/CCN2), sex determining region Y-box 9, vascular endothelial growth factor α, aggrecan, collagen type 1 alpha 2, and collagen type 2 alpha 1 (Col2α1). Immunohistochemistry was used to analyze the expression of CTGF/CCN2 and Ki-67 (n = 5 per group) after ESWT.

RESULTS

The meniscal histopathological score at 4 weeks after ACLT was significantly higher than that in the normal group, and the score in the ESWT+ group was significantly lower than that in the ESWT- group at 4 and 12 weeks after ESWT. Real-time PCR revealed that the mRNA expression of CTGF/CCN2 and Col2α1 decreased 4 weeks after ACLT. In the ESWT+ group, real-time PCR revealed that the mRNA expression of CTGF/CCN2 increased 24 hours after ESWT, and the expression of Col2α1 increased 4 weeks after ESWT (all significant data were P < .05). The ratio of CTGF/CCN2-positive cells and Ki67-positive cells was significantly higher in the ESWT+ group after ESWT.

CONCLUSION

The present study revealed that ESWT might suppress ACLT-induced meniscal degeneration by stimulating cartilage repair factors and inducing collagen type 2.

CLINICAL RELEVANCE

ESWT can be an effective treatment to protect the degenerated meniscus in a rat model of ACLT.

Allografts for partial meniscus repair: an in vitro and ex vivo meniscus culture study

The purpose of this study was to evaluate the treatment potential of a human-derived demineralized scaffold, Spongioflex® (SPX), in partial meniscal lesions by employing in vitro models. In the first step, the differentiation potential of human meniscal cells (MCs) was investigated. In the next step, the ability of SPX to accommodate and support the adherence and/or growth of MCs while maintaining their fibroblastic/chondrocytic properties was studied. Control scaffolds, including bovine collagen meniscus implant (CMI) and human meniscus allograft (M-Allo), were used for comparison purposes. In addition, the migration tendency of MCs from fresh donor meniscal tissue into SPX was investigated in an ex vivo model. The results showed that MCs cultured in osteogenic medium did not differentiate into osteogenic cells or form significant calcium phosphate deposits, although AP activity was relatively increased in these cells. Culturing cells on the scaffolds revealed increased viability on SPX compared to the other scaffold materials. Collagen I synthesis, assessed by ELISA, was similar in cells cultured in 2D and on SPX. MCs on micro-porous SPX (weight >0.5 g/cm3) exhibited increased osteogenic differentiation indicated by upregulated expression of ALP and RUNX2, while also showing upregulated expression of the chondrogen-specific SOX9 and ACAN genes. Ingrowth of cells on SPX was observed after 28 days of cultivation. Overall, the results suggest that SPX could be a promising biocompatible scaffold for meniscal regeneration.

Could a three-dimensional contralateral meniscus segmentation for allograft or scaffold sizing be possible? A prospective study

PURPOSE

Meniscal allografts and biodegradable meniscal implants are attractive surgical options for painful subtotal or total meniscectomies. In order to get the best results, these should be as similar as possible to the original meniscus in terms of shape, structure, and volume. Three-dimensional meniscus sizing could be an approach to improve the accuracy of meniscus matching. Therefore, the aims of this study were to perform a comparative morphological and volumetric analysis of the healthy meniscus based on manual tri-planar segmentation and to demonstrate that the menisci from the contralateral knee could be used as a reference in the sizing of a meniscal graft or a scaffold.

METHODS

Three-dimensional meniscal models were created based on 120 MRIs in 60 healthy subjects (bilateral knees). The differences between the pairs of menisci concerning the widths, thicknesses, lateromedial distances, anteroposterior distances, angles of coverage, and meniscal volumes were evaluated. T-Student tests were used to compare the quantitative numerical variables of the different groups. Pearson's linear regression was used to determine if correlations existed between demographic variables (age, gender, height, weight) and anatomical parameters. Statistical significance was set at p < 0.05.

RESULTS

Comparing the 120 pairs of menisci of each subject, there was no statistically significant difference for all parameters studied for both the medial and lateral meniscus. When the measurements were stratified by gender, statistically significant differences were observed for all parameters except meniscal coverage angles. We observed that anteroposterior and lateromedial distances were positively correlated with height and body mass index both at the level of the medial meniscus (r = 0.68; r = 0.66; r = 0.65; and r = 0.63) and lateral (r = 0.68; r = 0.69; r = 0.61; and r = 0.60).

CONCLUSION

Our study demonstrated that the intra-individual 3D shapes of the left and right menisci are very similar. Therefore, the contralateral side could be used as a template for the 3D sizing of meniscal allografts or meniscal implants.

Comparison of medial tibiofemoral joint mechanics between all-suture anchors and transtibial pullout technique for posterior medial meniscal root tears

BACKGROUND

The posterior medial meniscal root tear (PMMRT) seriously impacts the tibiofemoral joint biomechanics. Two available techniques for PMMRT repair include the transtibial pullout (TPO) repair and all-suture anchor (ASA) repair techniques. These techniques have not been compared biomechanically.

METHODS

A total of 20 fresh porcine cadaveric knee specimens were used. All 20 knees were randomly and evenly distributed into four groups (five specimens per group): (1) intact posterior meniscal root, (2) PMMRT, (3) TPO repair technique for PMMRT, and (4) ASA repair technique for PMMRT. The tibiofemoral contact mechanics were investigated using a pressure sensor. All knee specimens were tested by being loaded with 600 N axial compressive force at three different flexion angles (0°, 45°, and 90°). The contact surface area, contact pressure, peak pressure, and time-zero displacement were recorded.

RESULTS

The PMMRT caused a significant decrease in contact surface area, an increase in contact pressure, and peak pressure from the reference values observed in the intact meniscus group (P = 0.05, 0.016, and 0.008, respectively). After fixation, no significant difference was observed between the ASA and intact group. Meanwhile, significant differences were found between the TPO and intact group in terms of contact surface area, contact pressure, and peak pressure. In the comparison between the two techniques, the ASA group demonstrated higher contact surface area than the TPO group at the average knee flexion angle (p = 0.05).

CONCLUSION

For most testing conditions, the ASA technique demonstrated superior biomechanical property in terms of contact surface area compared with the TPO technique under compressive loading conditions. The ASA technique could also restore the tibiofemoral contact mechanics to be comparable with those of the native intact knee. Meanwhile, a significant difference in tibiofemoral mechanics, compared with the intact knee, could be observed in the TPO technique.

Anterolateral Radial Meniscus Tear Repair using Traction Suture and Super-Hashtag Technique

Radial meniscus tears occur commonly as traumatic tears in younger patients, as well as in association with concomitant degenerative changes. Traditional management of these tears has centered around partial meniscectomy; however, there has been a more recent trend toward preserving the meniscus and attempting repair. Because of the gapping and displacement that frequently occurs with these tears, repair is often challenging and is done under high amounts of tension. The following article describes a technique using a traction suture to aid in maintaining reduction throughout repair. This is followed by the use of a combination of techniques to form a "super-hashtag" configuration of both vertical and horizontal mattress sutures, leading to a secure repair under little tension.

A Study on the Morphometry of a Medial Meniscus in the Knee Joint of Human Cadavers in the South Indian Population

Introduction The knee joint is a complex system containing various hard and soft tissue components necessary for functioning in a coordinated manner. The menisci help to deepen the tibial plateau. Knowledge of the dimension of menisci in the knee joint is of paramount importance in arthroscopic surgery and the management of injuries due to sports or degeneration. The present study aims to describe the morphometric data of the medial meniscus and document the morphometric variation in the medial menisci. Methodology This study was conducted in the department of anatomy in two medical colleges under MGR University by measuring the dimensions of 100 medial menisci taken from 50 formalin-fixed embalmed cadavers. The width and thickness of the medial menisci were measured using digital vernier calipers. The outer and inner circumferences were measured using a measuring tape, non-elastic threads, and metallic pins. The area of the medial meniscus and the tibial plateau was measured by counting the small squares present in the circumference of the menisci drawn over the graph paper. The weight of the medial menisci was measured using the electronic weigh scale. Results The widest part of the medial meniscus was the posterior one-third, and the narrowest part was the anterior one-third. The thickest part was the middle one-third, followed by the anterior one-third. The average inner and outer circumferences of the menisci were 6.25 cm and 10.05 cm, respectively. The medial meniscus covers more than half of the area of the tibial plateau. Conclusion The present study provides a good understanding of the morphometric features of the medial menisci and will be of great help for managing knee joint pathologies and designing prostheses.

An Update on Clinical Utility of Musculoskeletal Ultrasonography in Knee Osteoarthritis

In knee osteoarthritis (KOA), timely and accurate assessment of the severity is essential to help orthopedic surgeons determine the most appropriate therapeutic strategies and evaluate disease outcomes and responses for corresponding treatments. In KOA, musculoskeletal ultrasonography (MSUS) could effectively help detect various abnormalities, including synovitis, osteophytes, and cartilage damage. Further, MSUS could be used to monitor the response to different therapies in KOA, to guide local diagnostic and therapeutic procedures. In the future, applications based on continuously evolving US tools could enhance the clinical utility of MSUS in KOA.

A Cadaveric Study to Define Morphology and Morphometry of Human Knee Menisci in the Region of Central India

Introduction The medial and lateral menisci of the knee joint are the functional unit that helps to increase the depth of articular surfaces on the head of a tibia for the reception of femoral condyles. Menisci are important for the distribution of load and thus help to reduce stress on the knee joint. The anatomical knowledge of morphology and morphometry of menisci is vital while performing surgeries in cases of meniscal injury. The study aimed to define the variational anatomy of the menisci of the knee joint. Material and Methods Ninety-six cadaveric knees of 48 cadavers were included in the study. Different shapes of both; lateral and medial menisci were recorded. The peripheral lengths and inner lengths of the menisci were measured with the nonelastic cotton thread. Menisci were divided into three parts; anterior, middle, and posterior. The maximum width and thickness of each part of the menisci were measured and documented. Distance between the medial and lateral meniscus in each knee was measured at the anterior and posterior ends. The most anterior and the most posterior part of each meniscus was determined and the distance between these parts of each meniscus was measured and recorded as the distance between two horns. Results Four morphological types of menisci were found; in medial menisci, the most common was crescent‑shaped (53%), and in lateral menisci, the most common shape was c‑shape (62.5%). The average peripheral length of the medial menisci was 92.0 mm and the lateral menisci was 96.08 mm while the average inner length of the medial and lateral meniscus was 56.19 mm and 58.92 mm respectively. The anterior third of the medial as well as lateral meniscus was thinnest while the posterior third was thickest. The width of the medial menisci was less at the anterior end and was more at the posterior ends while the width of the lateral meniscus was almost the same at the anterior, middle, and posterior ends. Conclusion The findings of the present study will be helpful for surgeons while planning and performing surgical procedures and for anatomists during routine teaching.

Low reoperation rate following lateral meniscus root repair: clinical outcomes at 2 years follow-up

PURPOSE

The aim of this study was to review the outcomes of lateral meniscus posterior root tears repair at the time of ACL reconstruction at a minimum 2-year follow-up.

METHODS

Between March 2015 and August 2018, 2017 patients underwent primary ACL reconstruction and were considered for study eligibility. Lateral meniscus posterior root tears were identified arthroscopically, and repair was performed with a transtibial pull-out suture technique or a side-to-side suture technique. Clinical outcomes were recorded at the time of physical examination. At the end of the study period, patients were contacted to determine whether they had required reoperation.

RESULTS

Lateral meniscus posterior root tears were identified in 153 out of the 2,017 primary ACL reconstructions (7.6%). Ninety-nine patients were included for analysis: 23 transtibial pull-out sutures and 76 side-to-side repairs. At a mean follow-up of 42 ± 10 months, one patient (1%) had undergone reoperation for failure of the side-to-side repair. There were 11 reoperations in 10 patients (10.1%), including 6 cyclops syndrome, 1 graft rupture, 1 tibial bone cyst, 1 medial and 1 lateral meniscus repair failure, and 1 arthrolysis. Postoperatively, ninety (90.9%) patients were graded A for the IKDC objective score and 9 (9.1%) patients were graded B, with an IKDC subjective score of 86.9 ± 7.6, a Lysholm score of 90.7 ± 6.7 and a median Tegner Activity Scale of 6 (3-9). All of their objective and subjective evaluations improved after surgery (p < 0.001) except for the Tegner Activity Scale. Ten patients underwent second look arthroscopy (10.1%), lateral meniscus healing was observed in 9 out of 10 patients (90%).

CONCLUSION

This study demonstrated that lateral meniscus posterior root tear repair is a safe procedure with a very low reoperation rate at a minimum follow-up of 2 years.

LEVEL OF EVIDENCE

IV.

Ontogeny of the meniscus in the anuran Xenopus laevis

The anuran knee joint is subjected to the jump, one of the tetrapods' most demanding mechanical stresses. Consistent with this continuous effort, the knee of the anurans has a complex structure comparable to that of an amniote. Here, we describe the ontogeny of the Xenopus knee tissues and study the morphogenesis of the knee joint shape by performing a geometric morphometric analysis of specially selected anatomical structures: the menisci and the long bone epiphyses. A meniscus is a crescent-shaped fibrocartilaginous structure, with a triangular cross-section inserted between joints surfaces. A meniscus transmits load across the tibiofemoral joint by increasing congruity of the long bone epiphysis and decreasing the resulting stress exerted on the articular cartilage. We ask two questions: (1) what is the tissue composition along the ontogeny of the menisci of a swimming frog? (2) How do the menisci acquire the shape that will allow their adjustment? We studied the structures and tissue ontogeny of the knee of several specimens of Xenopus laevis and evaluated the congruity of the knee structures across the species ontogeny. Histological sections showed that the cavitation process responsible for separating the menisci and the epiphyses seems to be pivotal in shaping the conformity of these structures and the long bone epiphyses of the hindlimbs. The geometric morphometric analysis allowed us to interpret three phases of differentiation associated with limb functionality. The characteristic shape of the meniscus appears early in the ontogeny of the knee, simultaneously with the epiphysis contours.

The Evaluation of Meniscus Regenerative Effects of LIPUS-Induced CCN Proteins: Induction by LIPUS of CCN2 and Meniscus-Related Genes in Cultured Meniscus Cells and Meniscus Tissues

Menisci are a pair of crescent-shaped fibrocartilages and composed primarily of type I collagen. Inner region of the meniscus has similar characteristics to articular cartilage. Low-intensity pulsed ultrasound (LIPUS) has been reported to have chondroprotective effects on chondrocytes by inducing the expression of chondrocyte differentiation markers and CCN2/CTGF production. Here, we describe an experimental approach that investigates the distinct cellular behavior of human inner and outer meniscus cells in response to LIPUS stimulation. Our experimental model can analyze the relationships between LIPUS-induced CCN2 and its repairing role in the meniscus.

Comparative Morphological and Morphometric Study between Medial and Lateral Menisci in Aged Male and Female Human Cadavers

Background

The meniscal cartilages are fibrous discs that are important for knee structures and have the ability to bear weight and stabilize joints. However, morphological and standard data for the meniscus are limited. Therefore, this work will compare anatomical and histological parameters of meniscal cartilages. The results will be important for the different measurements that are necessary for knee joint surgery.

Materials and Methods

A total of 24 aged cadavers (12 males and 12 females) were included. Knee joints were dissected and the menisci were excised and labeled as medial or lateral, right or left, male or female. Then, the menisci were kept in 10% formalin solution. Morphological variations of the meniscal shapes were macroscopically categorized. Different measurements, including the distance between anterior and posterior horns, outer and inner circumferences, width (breadth), and thickness, were done using a digital Vernier caliper and recorded manually.

Results

48 medial menisci (MMi) cartilages were studied, they were 54.6% crescent-shaped, 34.6% V-shaped, and 10.8% U-shaped. 48 lateral menisci (LMi) cartilages were studied, 41.6% were crescent-shaped, 56.4% were C-shaped, and 2% were disc-shaped articular cartilage. Findings included differences in their lengths and thickness.

Conclusion

The findings of this study were significant in providing new information on various morphological and morphometric parameters of the MMi and LMi in aged males and females, which are necessary to require more precise and comprehensive fundamental data that will be helpful for many specialists for better diagnostic and therapeutic approaches; aiming to restore normal joint conditions in senile people complaining of different meniscal pathologies.

Comparison of incidence of medial meniscal injury in small dogs (≤15 kg) and medium-to-large dogs (>15 kg) with naturally occurring cranial cruciate ligament disease undergoing tibial plateau levelling osteotomy: 580 stifles (2015 to 2019)

OBJECTIVES

To investigate whether a difference exists in incidence of medial meniscal tears between small (≤15 kg) and medium-to-large (>15 kg) dogs with naturally occurring cranial cruciate ligament disease.

MATERIALS AND METHODS

Records were retrospectively reviewed to identify the incidence of medial meniscal tears in dogs undergoing tibial plateau levelling osteotomy. Degree of cruciate insufficiency, method of identification (arthroscopy or arthrotomy), tibial plateau angle, weight and signalment were recorded. A two-proportion z-test with clustering adjustment was used to compare the meniscal tear rate between the two groups. Logistic regression analysis was used to investigate the effects of variables on medial meniscal tears.

RESULTS

Seventy-six stifles in 67 small dogs and 504 stifles in 384 medium-to-large dogs were included. The rate of meniscal injury at index surgery was 38.2% in small dogs and 36.7% in medium-to-large dogs. The subsequent meniscal tear rate was 1.3% in small dogs and 8% in medium-to-large dogs. The difference in meniscal tear rate was not statistically significant at either index surgery or subsequently. Degree of cruciate ligament insufficiency and use of arthroscopy were significantly associated with medial meniscal tears at index surgery. No variables were significantly associated with subsequent medial meniscal tears.

CLINICAL SIGNIFICANCE

No significant difference exists in medial meniscal tear rate between small and medium-to-large dogs either at index surgery or subsequently. The index of suspicion of concurrent medial meniscal tears should be higher in dogs with complete tear of the cranial cruciate ligament but a partial tear does not preclude meniscal pathology.

Biomechanics of the lateral meniscus: evidences from narrative review

Lateral meniscus plays a crucial role in the knee stability and function. Although complex settings are required for lateral meniscus biomechanical assessment, such characteristics have been investigated over time to optimize the daily clinical practice surgical procedure. The aim of the present study was to provide an overview of literature knowledge regarding the biomechanics of lateral meniscus and give further insights about novel experimental analyses. Studies regarding lateral meniscus mobility, effect on knee laxity, and contact mechanics were included in the review. The effect of meniscal lesion, meniscal repair, partial meniscectomy, and meniscus allograft transplantation were retrieved for either in vivo, cadaveric, or in-silico computational settings. Knee laxity was evaluated both in presence of isolated meniscal tears and in anterior cruciate ligament (ACL) deficient knees. Surgical navigation systems and robots were mainly used for the investigations in vivo and in cadaveric studies, while accelerometers emerged as an alternative for ambulatory assessments. Contact mechanics was only assessed in cadaveric and computational studies. Great effort has been put into exploring lateral meniscus biomechanics from multiple perspectives. Strong evidence emerged regarding the importance of lateral meniscus repair: increased knee stability at high degrees of knee flexion and reduction of peak contact pressures on tibial cartilage were the most reported benefits. The meniscus allograft transplantation also emerged as a concrete solution for irreparable tears and further studies are needed to investigate its long-term influence on knee stability.

Anatomy of lateral meniscus

The anatomy of the lateral meniscus underlies the understanding of its unique biomechanics. Moreover, the knowledge of its microscopic structure, its vascularization and its ligament insertions can make us understand the rationale for its surgical treatment. It is well known as the respect of the anatomy leads to better results in reconstructive surgery. Knowing the differences in the shape and in the areas of insertion of the meniscal roots can be useful in case of reinserting a root or when performing a meniscal transplant. Learning about the capsular insertions, the anchoring ligaments and the areas of greatest mobility of the lateral meniscus is useful during meniscal repair and replacement surgery. This information can let us choose the most appropriate technique and the best device to face any kind of meniscal lesion. In this article, we will consider both the micro and the macro meniscal structure in order to be able to give a description as complete as possible of this fundamental structure. We will consider the interrelation of the meniscus with the neighboring anatomical structures with which it contributes to the biomechanical control of the joint. It is important to understand the interrelation with both anterior and posterior cruciate ligament (PCL) given that frequently a combined meniscal and ligamentous reconstruction is necessary.

Osteoarthritic meniscal entheses exhibit altered collagen fiber orientation

PURPOSE/AIM

The knee menisci are vital for maintaining the stability of the joint, allowing for force distribution, and protecting the underlying articular cartilage during loading. Each meniscus is attached to the underlying bone via two ligamentous entheses composed of collagen fibers that are continuous throughout all four zones of the attachment: ligament, uncalcified fibrocartilage, calcified fibrocartilage, and subchondral bone. The collagen fibers of the meniscal entheses are important for proper functionality of the entheses, particularly in preventing meniscal extrusion which is a common hallmark of osteoarthritis. The goal of this work was to assess changes in collagen fiber orientation present in osteoarthritic knee joints.

MATERIALS AND METHODS

Entheses were harvested from patients undergoing total knee arthroplasties and prepared histological sections were stained with picrosirius red to identify collagen fiber angle and fiber deviation.

RESULTS

In the calcified fibrocartilage the collagen fibers of the lateral anterior enthesis inserted at significantly (p < 0.1) shallower angles, and the fiber deviation was significantly (p < 0.1) less compared to the lateral posterior enthesis. These differences in the calcified fibrocartilage may occur as an adaptation to loading regimes of the osteoarthritic joint. When compared to the collagen fiber orientation of healthy entheses, collagen fibers in osteoarthritic tissue inserted at shallower insertion angles and demonstrated higher levels of deviation.

CONCLUSIONS

Changes to meniscal enthesis collagen fiber orientation with end stage osteoarthritis could offer an explanation for the change in functionality of diseased tissue and may contribute to meniscal extrusion and ultimately the degeneration of articular cartilage.

Ultrasound-Guided Perimeniscal Injections: Anatomical Description and Feasibility Study

OBJECTIVES

To anatomically describe the ultrasound (US)-guided perimeniscal injection technique, and evaluate its feasibility in the treatment of meniscal pain.

METHODS

This work was initially undertaken in four cadaveric specimens with US-guided medial and lateral perimeniscal injection of China ink, followed by cadaveric dissection to assess injectate distribution, and potential injury to intra-articular and peri-articular structures. Then, 35 consecutive patients who underwent US-guided perimeniscal corticosteroid injection under local anesthesia for the treatment of symptomatic medial (30/35) or lateral (5/35) degenerative meniscal tear were retrospectively evaluated. Clinical outcome was assessed using a 0-10 numerical verbal rating scale (VRS) to evaluate severity of pain before, during, and after procedure at 6 weeks follow-up.

RESULTS

Seven of eight (87.5%) ex vivo injections were accurate. A single inaccurate medial perimeniscal injection infiltrated the tibial collateral ligament instead of the perimeniscal area. No anatomical specimen exhibited intrameniscal injection or injury to regional structures. All procedures (35/35) performed clinically were technically successful. Median VRS scores were: 7 (range, 3-9) before procedure, 5 (range, 0-10) during procedure, and 1.5 (range, 0-9) after procedure at 6 weeks follow-up (P <.0001). No complication was observed.

CONCLUSIONS

US-guided perimeniscal injections can accurately and safely deliver injectates in the perimeniscal area. In addition, our data suggest that perimeniscal corticosteroid injection provides significant symptom relief at 6 weeks in patients with meniscal pain. Further studies with long-term follow-up will be required to evaluate the role of perimeniscal injections in the nonoperative management of meniscal pathology.

The Perimensical Capsule: Potential Supporting Structure Surrounding Meniscus

This study analyzed the morphological and biomechanical characteristics of perimeniscal capsule in knee joint thus establishing the roles of these tissues. A total of 10 human cadaver knees were used in this study. Medial meniscus and the adjacently surrounding joint capsules were harvested then sectioned both axially and coronally, followed by scanning electron microscopy analysis. The medial meniscus (anterior, middle, posterior) and the adjacent perimeniscal capsules (superior, peripheral) were biomechanically assessed to ascertain the tensile modulus. Among the perimeniscal capsules, the peripherally located capsules were morphologically different from the superiorly located capsules: The peripheral perimeniscal capsule was thicker and showed circumferentially oriented fibers whereas the superior perimeniscal capsule fibers were thinner and arranged in vertical orientation. The peripheral capsule also yielded significantly greater tensile modulus compared with the superior capsule biomechanically. We conclude that depending on its anatomical location, the perimeniscal capsule consists of fibers of varying orientations. This may be important in maintaining the circumferential hoop tension of the meniscus especially in the presence of circumferentially oriented and thick peripheral capsule fibers, which coincidentally have higher tensile modulus.

Development of a Pressure-Sensitive Conductive Rubber Sensor for Analyzing Meniscal Injury in Porcine Models

The assessment of the distribution of contact pressure on the meniscus is important in the elucidation of kinematics, etiology of joint diseases, and establishment of treatment methods. Compared with sensors widely used in recent years, pressure-sensitive conductive rubber sensors are easy to mold, flexible, durable, and resistant to shearing forces. This study is aimed at developing a rubber sensor for meniscal research and evaluating the pressure distribution after meniscal injury using porcine models. After confirming the reliability of the rubber sensor, contact pressure was obtained from the rubber sensor using the medial meniscus and femur of the porcine knee. Three test conditions of intact meniscus, radial tear, and meniscectomy were prepared, and a compressive load of 100 N was applied. After confirming the high reliability of the rubber sensor, the intact meniscus had the most uniform pressure distribution map, while the pressure in the meniscectomy model was concentrated in the resection region. The high-pressure region was significantly smaller in the intact group than in the radial tear models after 80 and 100 N (P < 0.05). The rubber sensor captured the pressure concentration specific to each examination group and was useful for evaluating the relationship between the pattern of meniscal injury and changes in the biomechanical condition of the knee.

Anisotropy and inhomogeneity of permeability and fibrous network response in the pars intermedia of the human lateral meniscus

Within the human tibiofemoral joint, meniscus plays a key role due to its peculiar time-dependent mechanical characteristics, inhomogeneous structure and compositional features. To better understand the pathophysiological mechanisms underlying this essential component, it is mandatory to analyze in depth the relationship between its structure and the function it performs in the joint. Accordingly, the aim of this study was to evaluate the behavior of both solid and fluid phases of human meniscus in response to compressive loads, by integrating mechanical assessment and histological analysis. Cubic specimens were harvested from seven knee lateral menisci, specifically from anterior horn, pars intermedia and posterior horn; unconfined compressive tests were then performed according to three main loading directions (i.e., radial, circumferential and vertical). Fibril modulus, matrix modulus and hydraulic permeability of the tissue were thence estimated through a fibril-network-reinforced biphasic model. Tissue porosity and collagen fibers arrangement were assessed through histology for each region and related to the loading directions adopted during mechanical tests. Regional and strain-dependent constitutive parameters were finally proposed for the human lateral meniscus, suggesting an isotropic behavior of both the horns, and a transversely isotropic response of the pars intermedia. Furthermore, the histological findings supported the evidences highlighted by the compressive tests. Indeed, this study provided novel insights concerning the functional behavior of human menisci by integrating mechanical and histological characterizations and thus highlighting the key role of this component in knee contact mechanics and presenting fundamental information that can be used in the development of tissue-engineered substitutes. STATEMENT OF SIGNIFICANCE: This work presents an integration to the approaches currently used to model the mechanical behavior of the meniscal tissue. This study assessed in detail the regional and directional contributions of both the meniscal solid and fluid phases during compressive response, providing also complementary histological evidence. Within this updated perspective, both knee computational modeling and meniscal tissue engineering can be improved to have an effective impact on the clinical practice.

Fibrin Clot Augmented Repair of Longitudinal Tear of Medial Meniscus

Repair of meniscus injuries always posed a significant problem, especially in relatively avascular zones. Several methods to augment the repair were devised, but only a few had convincing results. Fibrin clot augmentation is one of the augmentation procedures that shows good promise in this premise. The major hurdle to it is difficulty in delivering into the meniscus tear under constant irrigation during arthroscopic procedures. This article presents a simple and unique way to prepare and transfer a fibrin clot into a meniscal tear in a step-by-step manner.

Morphological and morphometric features of knee joint in wild boar (Sus scrofa)

In the study, it was aimed to reveal the structure of the knee joint anatomically and morphometrically in the wild pig known as the ancestor of the domestic pig. In the study, the left and right knee joints of mature 10 wild boars were used as material. For this purpose, the materials were fixed with 10% formaldehyde solution. Macroanatomical and morphometrical examinations of bones, menisci and ligaments involved in joint formation were performed after fixation. Trochlea and condyles of femur were examined, and various measurements were made. Trochlear labia were found to be the same size, and the condyles did not show a significant difference in size. The shape of lateral condyle of the tibia was trapezoid, and the shape of medial condyle was triangular. Moreover, the lateral intercondylar tubercule was higher according to the medial one. The presence of a shallow groove on the tibial tuberosity was detected. It was found that the width difference between apex and base was more pronounced on the anterior and lateral surface of the patella. Joint surface of the fibula was found to be flat in all materials. The menisci were 'C' shape, but the medial meniscus is more convex than the lateral one. It was observed that the outer edges were thick, while the inner edges were thin. Ligaments of the knee joint were well developed. When the findings of the study were compared with the literature, domestication seemed to have no significant effect in terms of the morphologic properties of the knee joint of wild boar.

Degenerative Joint Disease After Meniscectomy

The meniscus has an important role in stabilizing the knee joint and protecting the articular cartilage from shear forces. Meniscus tears are common injuries and can disrupt these protective properties, leading to an increased risk of articular cartilage damage and eventual osteoarthritis. Certain tear patterns are often treated with arthroscopic partial meniscectomy, which can effectively relieve symptoms. However, removal of meniscal tissue can also diminish the ability of the meniscus to dissipate hoop stresses, resulting in altered biomechanics of the knee joint including increased contact pressures. This makes meniscal repair an important treatment consideration whenever possible. Understanding the incidence and mechanism of osteoarthritis development after arthroscopic partial meniscectomy as it relates to different tear morphologies and other treatment alternatives (ie, meniscus repair) is important to appropriately treat meniscus tears.

Continuous Meniscal Suture in Radial Meniscal Tear: The Hourglass Technique

The key to preventing early knee osteoarthritis is meniscal preservation. The main functions of the meniscus are impact absorption, mechanical load transmission, lubrication, joint stability, and proprioception. Radial lesions that extend to the joint capsule are called complete radial tears. This type of injury compromises 2 of the main meniscal functions, which are impact absorption and load distribution, which is equivalent, from a biomechanical perspective, to a total meniscectomy. In the recent past, the treatment of choice for this type of injury was partial meniscectomy. However, several studies have observed progressive joint degeneration after this type of treatment. Recently, different types of meniscal sutures involving radial lesions of the meniscus have been developed. It is believed that such repairs may bring a decrease in future osteoarthritis in this patient profile. The purpose of this article is to describe the steps of continuous meniscal suture for the treatment of radial tears of the medial and lateral menisci.

The Functionally Grading Elastic and Viscoelastic Properties of the Body Region of the Knee Meniscus

The knee meniscus is a highly porous structure which exhibits a grading architecture through the depth of the tissue. The superficial layers on both femoral and tibial sides are constituted by a fine mesh of randomly distributed collagen fibers while the internal layer is constituted by a network of collagen channels of a mean size of 22.14 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu $$\end{document}μm aligned at a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$30^{\circ }$$\end{document}30∘ inclination with respect to the vertical. Horizontal dog-bone samples extracted from different depths of the tissue were mechanically tested in uniaxial tension to examine the variation of elastic and viscoelastic properties across the meniscus. The tests show that a random alignment of the collagen fibers in the superficial layers leads to stiffer mechanical responses (E = 105 and 189 MPa) in comparison to the internal regions (E = 34 MPa). All regions exhibit two modes of relaxation at a constant strain (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau _1 = 6.4$$\end{document}τ1=6.4 to 7.7 s, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau _2$$\end{document}τ2 = 49.9 to 59.7 s).

Quantitative three-dimensional collagen orientation analysis of human meniscus posterior horn in health and osteoarthritis using micro-computed tomography

OBJECTIVE

Knee osteoarthritis (OA) is associated with meniscal degeneration that may involve disorganization of the meniscal collagen fiber network. Our aims were to quantitatively analyze the microstructural organization of human meniscus samples in 3D using micro-computed tomography (μCT), and to compare the local microstructural organization between OA and donor samples.

METHOD

We collected posterior horns of both medial and lateral human menisci from 10 end-stage medial compartment knee OA patients undergoing total knee replacement (medial & lateral OA) and 10 deceased donors without knee OA (medial & lateral donor). Posterior horns were dissected and fixed in formalin, dehydrated in ascending ethanol concentrations, treated with hexamethyldisilazane (HMDS), and imaged with μCT. We performed local orientation analysis of collagenous microstructure in 3D by calculating structure tensors from greyscale gradients within selected integration window to determine the polar angle for each voxel.

RESULTS

In donor samples, meniscus bundles were aligned circumferentially around the inner border of meniscus. In medial OA menisci, the organized structure of collagen network was lost, and main orientation was shifted away from the circumferential alignment. Quantitatively, medial OA menisci had the lowest mean orientation angle compared to all groups, -24° (95%CI -31 to -18) vs medial donor and -25° (95%CI -34 to -15) vs lateral OA.

CONCLUSIONS

HMDS-based μCT imaging enabled quantitative analysis of meniscal collagen fiber bundles and their orientations in 3D. In human medial OA menisci, the collagen disorganization was profound with overall lower orientation angles, suggesting collagenous microstructure disorganization as an important part of meniscus degradation.

High Resolution Micro-Computed Tomography Reveals a Network of Collagen Channels in the Body Region of the Knee Meniscus

The meniscus is an integral part of the human knee, preventing joint degradation by distributing load from the femoral condyles to the tibial plateau. Recent qualitative studies suggested that the meniscus is constituted by an intricate net of collagen channels inside which the fluid flows during loading. The aim of this study is to describe in detail the structure in which this fluid flows by quantifying the orientation and morphology of the collagen channels of the meniscal tissue. A 7 mm cylindrical sample, extracted vertically from the central part of a lateral porcine meniscus was freeze-dried and scanned using the highest-to-date resolution Microscopic Computed Tomography. The orientation of the collagen channels, their size and distribution was calculated. Comparisons with confocal multi-photon microscopy imaging performed on portions of fresh tissue have shown that the freeze-dried procedure adopted here ensures that the native architecture of the tissue is maintained. Sections of the probe at different heights were examined to determine differences in composition and structure along the sample from the superficial to the internal layers. Results reveal a different arrangement of the collagen channels in the superficial layers with respect to the internal layers with the internal layers showing a more ordered structure of the channels oriented at 30[Formula: see text] with respect to the vertical, a porosity of 66.28% and the mean size of the channels of 22.14 [Formula: see text].

Lateral meniscus "PASTA injury": Partial-thickness radial tear of the lateral meniscus: A case report

INTRODUCTION

We report a relatively rare case of partial-thickness radial tear in the inferior surface of lateral meniscus, while the superior surface is intact. This situation was similar to PASTA rotator cuff tear. Meanwhile, there is a full-thickness radial tear in the edge.

CASE PRESENTATION

A 17-year-old boy twisted the left knee while playing basketball. Magnetic resonance imaging (MRI) revealed radial tear of the lateral meniscus. During arthroscopy, it was found that there was a full-thickness radial tear of about 2 mm located in the edge. Partial meniscectomy was performed to treat radial meniscal tear located in the white area. After that, we found that the superior surface of the lateral meniscus was intact. However, in the inferior surface of the lateral meniscus, partial-thickness radial tear was found extending to red zone. We used FASTFIX (Smith & Nephew) for all-inside suture. As of three months after this surgery, the patient recovered smoothly.

DISCUSSION

Suspect that the force acts on a special position of meniscus and the thickness of the meniscus is uneven. Thus, it leads to partial-thickness radial tear in the inferior-surface, while the superior surface is intact.

CONCLUSION

Partial-thickness radial tears in the inferior surface of lateral meniscus are relatively rare. This situation was similar to PASTA rotator cuff tear. Because the superior surface of the meniscus is intact, it may results in misdiagnosis. It's easy to ignore the inferior surface injury.

Experimental and Finite Element Investigations on the Biomechanical Effects of Meniscal Tears in the Knee Joint: A Review

The knowledge of the complex biomechanical behaviour of the injured knee joints is of paramount importance in various clinical situations. A review of the biomechanical effects of meniscal tears based on experimental and finite element analysis has not been reported in the literature. The objective of this study is to present a review of experimental and finite element investigations on the consequences of meniscal tears such as longitudinal, radial, horizontal cleavage and root tears in the medial and lateral menisci. It is found that larger longitudinal tear in the medial meniscus has a significant impact on the magnitude of strain in the meniscus associated with a dramatic increase in CP in the tibial cartilage. Also, the untreated fragment of the torn meniscus leads to a significant rise in contact pressure in the cartilage resulting in the progressive degeneration of the cartilage surface. The radial tears in the lateral meniscus of more than 66% width and those in the medial meniscus of more than 75% width result in a substantial increase in the contact pressure in the cartilage compared to that in the intact knee joint. The root tears in the menisci demonstrate a significant influence on the biomechanical response of the knee joint. The results of finite element analysis studies are compared with experimental findings. Finally, some recommendations for future work are proposed to predict the realistic biomechanical response of the knee joints with meniscal tears. The results of this study present a rationale that could help surgeons in making clinical decisions when managing patients with meniscal tears.

Forces at the Anterior Meniscus Attachments Strongly Increase Under Dynamic Knee Joint Loading

BACKGROUND

The anatomic appearance and biomechanical and clinical importance of the anterior meniscus roots are well described. However, little is known about the loads that act on these attachment structures under physiological joint loads and movements.

HYPOTHESES

As compared with uniaxial loading conditions under static knee flexion angles or at very low flexion-extension speeds, more realistic continuous movement simulations in combination with physiological muscle force simulations lead to significantly higher anterior meniscus attachment forces. This increase is even more pronounced in combination with a longitudinal meniscal tear or after total medial meniscectomy.

STUDY DESIGN

Controlled laboratory study.

METHODS

A validated Oxford Rig-like knee simulator was used to perform a slow squat, a fast squat, and jump landing maneuvers on 9 cadaveric human knee joints, with and without muscle force simulation. The strains in the anterior medial and lateral meniscal periphery and the respective attachments were determined in 3 states: intact meniscus, medial longitudinal tear, and total medial meniscectomy. To determine the attachment forces, a subsequent in situ tensile test was performed.

RESULTS

Muscle force simulation resulted in a significant strain increase at the anterior meniscus attachments of up to 308% (P < .038) and the anterior meniscal periphery of up to 276%. This corresponded to significantly increased forces (P < .038) acting in the anteromedial attachment with a maximum force of 140 N, as determined during the jump landing simulation. Meniscus attachment strains and forces were significantly influenced (P = .008) by the longitudinal tear and meniscectomy during the drop jump simulation.

CONCLUSION

Medial and lateral anterior meniscus attachment strains and forces were significantly increased with physiological muscle force simulation, corroborating our hypothesis. Therefore, in vitro tests applying uniaxial loads combined with static knee flexion angles or very low flexion-extension speeds appear to underestimate meniscus attachment forces.

CLINICAL RELEVANCE

The data of the present study might help to optimize the anchoring of meniscal allografts and artificial meniscal substitutes to the tibial plateau. Furthermore, this is the first in vitro study to indicate reasonable minimum stability requirements regarding the reattachment of torn anterior meniscus roots.

Risk Factors for Rapid Chondrolysis After Partial Lateral Meniscectomy: A Scoping Review of the Literature

BACKGROUND

The occurrence of rapid chondrolysis after partial lateral meniscectomy is rare. The pathophysiology, risk factors, and outcomes of treatment have not been established.

PURPOSE

The primary aim of this study was to perform a scoping review of the literature to determine the potential risk factors and pathogenesis of rapid chondrolysis. The secondary objective was to report outcomes of treatment.

STUDY DESIGN

Systematic (scoping) review.

METHODS

A scoping review of the literature was conducted in accordance with the framework of Arksey and O'Malley. A search strategy based on the terms "chondrolysis" AND "knee," "chondrolysis" AND "meniscus," and "chondral damage" AND "lateral meniscus" was applied to the PubMed database on March 31, 2020. All relevant studies were included. Patient demographics and clinical data were extracted from these studies and analyzed in order to investigate the potential risk factors, pathogenesis, and outcomes of treatment for rapid chondrolysis.

RESULTS

Five articles (22 cases) featuring rapid chondrolysis in the lateral compartment after partial lateral meniscectomy were identified and included. The condition occurred most frequently in patients who were young (mean age, 25.6 years), male (20/22 cases; 91%), and participating in high-intensity sports (19/22 cases; 86.4%) within 1 year of the index procedure. Half of the included study population underwent surgery for a radial tear. All professional athletes (13/13) returned to the preinjury level of sport. All authors of included studies suggested that the main causal risk factor was mechanical focal cartilage overload in the lateral compartment of the knee.

CONCLUSION

Rapid chondrolysis after partial lateral meniscectomy is a rare condition that typically occurs within 12 months of the index procedure. Younger age, male sex, high-intensity sports participation, and some meniscal tear patterns (eg, radial tear) are potentially important risk factors. Return-to-sport rates at short-term follow up are high, but no long-term studies were identified. The pathogenesis of rapid chondrolysis seems to relate to mechanical focal cartilage overload.

Different effects of the lateral meniscus complete radial tear on the load distribution and transmission functions depending on the tear site

PURPOSE

To compare the effect of the lateral meniscus (LM) complete radial tear at different tear sites on the load distribution and transmission functions.

METHODS

A compressive load of 300 N was applied to the intact porcine knees (n = 30) at 15°, 30°, 60°, 90°, and 120° of flexion. The LM complete radial tears were created at the middle portion (group M), the posterior portion (group P), or the posterior root (group R) (n = 10, each group), and the same loading procedure was followed. Finally, the recorded three-dimensional paths were reproduced on the LM-removed knees. The peak contact pressure (contact area) in the lateral compartment and the calculated in situ force of the LM under the principle of superposition were compared among the four groups (intact, group M, group P, and group R).

RESULTS

At all the flexion angles, the peak contact pressure (contact area) was significantly higher (lower) after creating the LM complete radial tear as compared to that in the intact state (p < 0.01). At 120° of flexion, group R represented the highest peak contact pressure (lowest contact area), followed by group P and group M (p < 0.05). The results of the in situ force carried by the LM were similar to those of the tibiofemoral contact mechanics.

CONCLUSION

The detrimental effect of the LM complete radial tear on the load distribution and transmission functions was greatest in the posterior root tear, followed by the posterior portion tear and the middle portion tear in the deep-flexed position. Complete radial tars of the meniscus, especially at the posterior root, should be repaired to restore the biomechanical function.

The Role of Collagen-Based Biomaterials in Chronic Wound Healing and Sports Medicine Applications

Advancements in tissue engineering have taken aim at treating tissue types that have difficulty healing naturally. In order to achieve improved healing conditions, the balance of exogenous matrix, cells, and different factors must be carefully controlled. This review seeks to explore the aspects of tissue engineering in specific tissue types treated in sports medicine and advanced wound management from the perspective of the matrix component. While the predominant material to be discussed is collagen I, it would be remiss not to mention its relation to the other contributing factors to tissue engineered healing. The main categories of materials summarized here are (1) reconstituted collagen scaffolds, (2) decellularized matrix tissue, and (3) non-decellularized tissue. These three groups are ordered by their increase in additional components beyond simply collagen.

Morphological Analysis of Normal Meniscus on Magnetic Resonance Imaging (MRI)-Based Three-Dimensional Reconstruction Models in Healthy Chinese Adults

Background

The purpose of this cross-sectional observational study was to determine the morphological meniscus characteristics in a normal Chinese population and assess possible relationships between demographic data and meniscal morphological parameters.

Material/Methods

We examined 116 menisci (58 lateral and 58 medial) from 29 healthy Chinese volunteers (10 men, 19 women, mean age 26 years [range, 20–33 years]) with MRI and three-dimensional reconstruction using Mimics software. The width, thickness, anteroposterior distance (APD), lateral-medial distance (LMD), and covering angle (CA) were measured on reconstructed models. Univariate analysis was used to evaluate the differences of morphological parameters between the medial and lateral menisci, between sides, and between males and females. Pearson correlation analysis was used to evaluate the correlation between meniscal morphological parameters and body height, weight, and body mass index (BMI).

Results

Univariate analysis demonstrated that the width, thickness, APD, LMD, and CA were significantly different between lateral and medial menisci. The LMD and APD of menisci in men were significantly larger than in women. There was no significant difference in meniscal thickness and CA between males and females. The lateral meniscus dimensions were slightly larger in the right knee. According to Pearson correlation analysis, the APDs of both lateral and medial menisci were strongly correlated with height and weight (lateral: r=0.596, r=0.500; medial: r=0.684, r=0.680).

Conclusions

The morphologies of medial and lateral menisci were different and were not significantly correlation with each other. The meniscal width and diameter were correlated with demographic data, but the thickness and CA did not significantly differ by sex, height, or BMI.

Degeneration Affects Three-Dimensional Strains in Human Menisci: In situ MRI Acquisition Combined With Image Registration

Degenerative changes of menisci contribute to the evolution of osteoarthritis in the knee joint, because they alter the load transmission to the adjacent articular cartilage. Identifying alterations in the strain response of meniscal tissue under compression that are associated with progressive degeneration may uncover links between biomechanical function and meniscal degeneration. Therefore, the goal of this study was to investigate how degeneration effects the three-dimensional (3D; axial, circumferential, radial) strain in different anatomical regions of human menisci (anterior and posterior root attachment; anterior and posterior horn; pars intermedia) under simulated compression. Magnetic resonance imaging (MRI) was performed to acquire image sequences of 12 mild and 12 severe degenerated knee joints under unloaded and loaded [25%, 50% and 100% body weight (BW)] conditions using a customized loading device. Medial and lateral menisci as well as their root attachments were manually segmented. Intensity-based rigid and non-rigid image registration were performed to obtain 3D deformation fields under the respective load levels. Finally, the 3D voxels were transformed into hexahedral finite-element models and direction-dependent local strain distributions were determined. The axial compressive strain in menisci and meniscal root attachments significantly increased on average from 3.1% in mild degenerated joints to 7.3% in severe degenerated knees at 100% BW (p ≤ 0.021). In severe degenerated knee joints, the menisci displayed a mean circumferential strain of 0.45% (mild: 0.35%) and a mean radial strain of 0.41% (mild: 0.37%) at a load level of 100% BW. No significant changes were observed in the circumferential or radial directions between mild and severe degenerated knee joints for all load levels (p > 0.05). In conclusion, high-resolution MRI was successfully combined with image registration to investigate spatial strain distributions of the meniscus and its attachments in response to compression. The results of the current study highlight that the compressive integrity of the meniscus decreases with progressing tissue degeneration, whereas the tensile properties are maintained.

Mineral Distribution Spatially Patterns Bone Marrow Stromal Cell Behavior on Monolithic Bone Scaffolds

Interfaces between soft tissue and bone are characterized by transitional gradients in composition and structure that mediate substantial changes in mechanical properties. For interfacial tissue engineering, scaffolds with mineral gradients have shown promise in controlling osteogenic behavior of seeded bone marrow stromal cells (bMSCs). Previously, we have demonstrated a 'top-down' method for creating monolithic bone-derived scaffolds with patterned mineral distributions similar to native tissue. In the present work, we evaluated the ability of these scaffolds to pattern osteogenic behavior in bMSCs in basic, osteogenic, and chondrogenic biochemical environments. Immunohistochemical (IHC) and histological stains were used to characterize cellular behavior as a function of local mineral content. Alkaline phosphatase, an early marker of osteogenesis, and osteocalcin, a late marker of osteogenesis, were positively correlated with mineral content in basic, osteogenic, and chondrogenic media. The difference in bMSC behavior between the mineralized and demineralized regions was most pronounced in an basic biochemical environment. In the mineralized regions of the scaffold, osteogenic markers were clearly present as early as 4 days in culture. In osteogenic media, osteogenic behavior was observed across the entire scaffold, whereas in chondrogenic media, there was an overall reduction in osteogenic biomarkers. Overall, these results indicate local mineral content of the scaffold plays a key role in spatially patterning bMSC behavior. Our results can be utilized for the development of interfacial tissue engineered scaffolds and understanding the role of local environment in determining bMSC behavior. STATEMENT OF SIGNIFICANCE: Soft tissue-to-bone interfaces, such as tendon-bone, ligament-bone, and cartilage-bone, are ubiquitous in mammalian musculoskeletal systems. These interfacial tissues have distinct, hierarchically-structured gradients of cellular, biochemical, and materials components. Given the complexity of the biological structures, interfacial tissues present unique challenges for tissue engineering. Here, we demonstrate that material-derived cues can spatially pattern osteogenic behavior in bone marrow stromal cells (bMSCs). Specifically, we observed that when the bMSCs are cultured on bone-derived scaffolds with mineral gradients, cells in contact with higher mineral content display osteogenic behavior at earlier times than those on the unmineralized substrate. The ability to pattern the cellular complexity found in native interfaces while maintaining biologically relevant structures is a key step towards creating engineered tissue interfaces.

Radial Meniscal Tears Are Best Repaired by a Modified "Cross" Tie-Grip Suture Based on a Biomechanical Comparison of 4 Repair Techniques in a Porcine Model

Background:

The tie-grip suture can fix radial tears more rigidly than simple conventional sutures. However, one shortcoming is the residual gap at the central margin of the tear. The tie-grip suture was modified to address this issue and named the “cross tie-grip suture.”

Purpose/Hypothesis:

The purpose of this study was to compare the suture stability and strength among 4 suturing techniques: the original tie-grip, cross tie-grip, and 2 conventional sutures (double horizontal and cross). It was hypothesized that the cross tie-grip suture would show the least displacement and resist the greatest maximum load.

Study Design:

Controlled laboratory study.

Methods:

A total of 40 fresh-frozen porcine knees were dissected to acquire 80 menisci; 20 menisci were tested in each suture group. A radial tear was created at the middle third of the meniscal body. Repair was performed with the following: original tie-grip, cross tie-grip, double horizontal, and cross sutures. The mechanical strength of sutured menisci was evaluated using a tensile testing machine. All menisci underwent submaximal loading and load to failure. The gap distance and ultimate failure load were compared using analysis of variance. The failure mode was recorded after load-to-failure testing.

Results:

Displacement after 500 cycles was significantly smaller in the cross tie-grip group (0.4 ± 0.3 mm) compared with the tie-grip (0.9 ± 0.6 mm), double horizontal (1.2 ± 0.7 mm), and cross suture groups (1.4 ± 0.6 mm) (P < .05). The ultimate failure load was significantly greater in the cross tie-grip (154.9 ± 29.0 N) and tie-grip (145.2 ± 39.1 N) groups compared with the double horizontal (81.2 ± 19.9 N) and cross suture groups (87.3 ± 17.7 N) (P < .05). Tissue failure was the most common mode of failure in all groups.

Conclusion:

Upon repair of radial meniscal tears, the cross tie-grip suture showed less displacement compared with that of the tie-grip, double horizontal, and cross sutures and demonstrated equivalent load to failure to that of the tie-grip suture at time zero.

Clinical Relevance:

The cross tie-grip suture provided high resistance to displacement after repair of radial tears and may be advantageous in healing for radial meniscal tears.