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

The menisci and their insertions into bone (entheses) represent a functional unit. Thanks to their firm entheses, the menisci are able to distribute loads and therefore reduce the stresses on the tibia, a function which is regarded essential for cartilage protection and prevention of osteoarthrosis. The tissue of the hypocellular meniscal body consists mainly of water and a dense elaborate type I collagen network with a predominantly circumferential alignment. The content of different collagens, proteoglycans and nonproteoglycan proteins shows significant regional variations probably reflecting functional adaptation. The meniscal horns are attached via meniscal insertional ligaments mainly to tibial bone. At the enthesis, the fibres of the insertional ligaments attach to bone via uncalcified and calcified fibrocartilages. This anatomical configuration of gradual transition from soft to hard tissue, which is identical to other ligament entheses, is certainly essential for normal mechanical function and probably protects this vulnerable transition between 2 biomechanically different tissues from failure. Clinical treatment of meniscal tears needs to be based on these special anatomical and functional characteristics. Partial meniscectomy will preserve some of the load distribution function of the meniscus only when the meniscal body enthesis entity is preserved. Repair of peripheral longitudinal tears will heal and probably preserve the load distribution function of the meniscus, whereas radial tears through the whole meniscal periphery or more central and complex tears may be induced to heal, but probably do not preserve the load distribution function. There is no proof that replacement of the meniscus with an allograft can reestablish some of the important meniscal functions, and thereby prevent or reduce the development of osteoarthrosis which is common after meniscectomy. After implantation, major problems are the remodelling of the graft to inferior structural, biochemical and mechanical properties and its insufficient fixation to bone which fails to duplicate a normal anatomical configuration and therefore a functional meniscal enthesis.     

Tie‐fibre structure and organization in the knee menisci

The collagenous structure of the knee menisci is integral to the mechanical integrity of the tissue and the knee joint. The tie‐fibre structure of the tissue has largely been neglected, despite previous studies demonstrating its correlation with radial stiffness. This study has evaluated the structure of the tie‐fibres of bovine menisci using 2D and 3D microscopy techniques. Standard collagen and proteoglycan (PG) staining and 2D light microscopy techniques were conducted. For the first time, the collagenous structure of the menisci was evaluated using 3D, second harmonic generation (SHG) microscopy. This technique facilitated the imaging of collagen structure in thick sections (50–100 μm). Imaging identified that tie‐fibres of the menisci arborize from the outer margin of the meniscus toward the inner tip. This arborization is associated with the structural arrangement of the circumferential fibres. SHG microscopy has definitively demonstrated the 3D organization of tie‐fibres in both sheets and bundles. The hierarchy of the structure is related to the organization of circumferential fascicles. Large tie‐fibre sheets bifurcate into smaller sheets to surround circumferential fascicles of decreasing size. The tie‐fibres emanate from the lamellar layer that appears to surround the entire meniscus. At the tibial and femoral surfaces these tie‐fibre sheets branch perpendicularly into the meniscal body. The relationship between tie‐fibres and blood vessels in the menisci was also observed in this study. Tie‐fibre sheets surround the blood vessels and an associated PG‐rich region. This subunit of the menisci has not previously been described. The size of tie‐fibre sheets surrounding the vessels appeared to be associated with the size of blood vessel. These structural findings have implications in understanding the mechanics of the menisci. Further, refinement of the complex structure of the tie‐fibres is important in understanding the consequences of injury and disease in the menisci. The framework of meniscus architecture also defines benchmarks for the development of tissue‐engineered replacements in the future.     

Nanoindentation of the insertional zones of human meniscal attachments into underlying bone

The fibrocartilagenous knee menisci are situated between the femoral condyles and tibia plateau and are primarily anchored to the tibia by means of four attachments at the anterior and posterior horns. Strong fixation of meniscal attachments to the tibial plateau provide resistance to extruding forces of the meniscal body, allowing the menisci to assist in load transmission from the femur to the tibia. Clinically, tears and ruptures of the meniscal attachments and insertion to bone are rare. While it has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau, little is known about the material properties of meniscal attachments and the transition in material properties from the meniscus to subchondral bone. The objective of this study was to use nanoindentation to investigate the transition from meniscal attachment into underlying subchondral bone through uncalcified and calcified fibrocartilage. Nanoindentation tests were performed on both the anterior and posterior meniscal insertions to measure the instantaneous elastic modulus and elastic modulus at infinite time. The elastic moduli were found to increase in a bi-linear fashion from the external ligamentous attachment to the subchondral bone. The elastic moduli for the anterior attachments were consistently larger than those for the matching posterior attachments at similar indentation locations. These results show that there is a gradient of stiffness from the superficial zones of the insertion close to the ligamentous attachment into the deeper zones of the bone. This information will be useful in the continued development of successful meniscal replacements and understanding of fixation of the replacements to the tibial plateau.     

膝关节半月板根部MRI影像解剖

目的 总结半月板根部的MRI解剖特点,确定半月板主体部分与根部的分界。方法 收集2012年10月—2014年2月保定市第一中心医院骨科24例经关节镜证实正常半月板根部的膝关节MRI资料和1例男性成人患者因下肢动脉硬化而截肢的新鲜膝关节标本,对半月板根部的MRI解剖行前瞻性研究,总结半月板根部MRI的形态、走行及附着点的位置,分析信号特点,并测量根部的长度、宽度、高度以及各根部走行角度。另在新鲜膝关节标本上确定半月板主体部分与根部的分界并用铜丝标示之,对标本行MRI扫描。结果 24例患者膝关节MRI显示:内侧半月板后根部呈梳状斜向下走行,信号较半月板主体部分稍高,附着于髁间后区;外侧半月板后根部较内侧半月板后根部明显长,走行于髁间隆起,附着于内侧髁间隆起的外侧面,信号与半月板主体部分类似;内侧半月板前根部较细,附着于髁间前区最前缘,为低或较低信号;外侧半月板前根部呈梳状稍向下向后走行,信号稍高,附着于髁间前区并稍向外下方倾斜的骨表面。各根部测量数据显示:横断面外侧半月板后根部最长,为(15.74±2.03)mm;冠状面内侧半月板后根部最短,为(7.88±1.57)mm;外侧半月板后根部走行与标准冠状面扫描线的夹角角度最大,为34.00°±9.24°。1例新鲜标本MR扫描图片清晰,半月板主体部分与根部分界标记显示清晰。结论 内外侧半月板前后根部各有其特点,MRI能够清晰显示半月板根部的形态、走行、信号特点及附着点位置。     

Collagen morphology in human meniscal attachments: A SEM study

Qualitative analysis of meniscal attachments from five human knees was completed using scanning electron microscopy (SEM). In addition, quantitative analysis to determine the collagen crimping angle and length in each attachment was done. Morphological differences were revealed between the distinct zones of the attachments from the meniscus transition to the bony insertion. Collagen fibers near to the meniscus appeared inhomogeneous in a radial cross-section view. The sheath surrounding the fibers seemed loose compared with the membrane wrapping around the fibers in the menisci. The midsubstance of human meniscal attachments was composed of collagen fibers running parallel to the longitudinal axis, with a few fibers running obliquely, and others transversely. The bony insertion showed that the crimping pattern vanishes as the collagen fibers approach the fibrocartilagenous enthesis. There were no differences between attachments for crimping angle or length. Collagen crimping angles for all attachments were similar with values of approximately 22°. Crimp length values tended to be smaller for the medial attachments (MA: 4.76 ± 1.95 μm; MP: 3.72 ± 2.31 μm) and higher for the lateral (LA: 6.49 ± 2.34 μm, LP: 6.91 ± 2.29 μm). SEM was demonstrated to be an effective method for revealing the morphology of fibrous connective tissue. The data of collagen fiber length and angle found in this study will allow for better development of microstructural models of meniscal attachments. This study will help to better understand the relation between the morphology and the architecture of collagen and the mechanical behavior of meniscal attachments.     

The histological structure of dog knee menisci with comments on its possible significance

Knee-joint menisci are poorly understood terminologically, structurally and functionally in spite of their almost universal occurrence in mammals and their considerable clinical significance in man. A study was therefore undertaken of dog knee menisci utilizing several histological techniques. Terminologically, it is proposed that the part of the meniscus extending between the anterior and posterior horns and exclusive of them be called the meniscal “body.” Structurally, the horns and body differ in a number of ways. The horns are oval in cross section, the body triangular. Hyalinized areas are much more frequent in the body than in the horns. The collagen of the horns is organized into discrete bundles that are separated from one another by loose connective tissue septa, while that of the body is arranged in a “herringbone” pattern; no septa are present in the body. Finally, the meniscal horns are richly supplied with blood vessels and nerves (including large myelinated fibers which apparently terminate in the horns) while the body is almost completely devoid of blood vessels and nerves. Functionally, it is hypothesized that knee-joint menisci may serve important sensory functions.     

Regeneration of whole meniscus using meniscal cells and polymer scaffolds in a rabbit total meniscectomy model

The current treatments of meniscal lesion in knee joint are not perfect to prevent adverse effects of meniscus injury. Tissue engineering of meniscus using meniscal cells and polymer scaffolds could be an alternative option to treat meniscus injury. This study reports on the regeneration of whole medial meniscus in a rabbit total meniscectomy model using the tissue engineering technique. Biodegradable scaffolds in a meniscal shape were fabricated from polyglycolic acid (PGA) fiber meshes that were mechanically reinforced by bonding PGA fibers at cross points with 75:25 poly(lactic-co-glycolic acid). The compressive modulus of the bonded PGA scaffold was 28-fold higher than that of nonbonded scaffold. Allogeneic meniscal cells were isolated from rabbit meniscus biopsy and cultured in vitro. The expanded meniscal cells were seeded onto the polymer scaffolds, cultured in vitro for 1 week, and transplanted to rabbit knee joints from which medial menisci were removed. Ten or 36 weeks after transplantation, the implants formed neomenisci with the original scaffold shape maintained approximately. Hematoxylin and eosin staining of the sections of the neomenisci at 6 and 10 weeks revealed the regeneration of fibrocartilage. Safranin-O staining showed that abundant proteoglycan was present in the neomenisci at 10 weeks. Masson's trichrome staining indicated the presence of collagen. Immunohistochemical analysis showed that the presence of type I and II collagen in neomenisci at 10 weeks was similar to that of normal meniscal tissue. Biochemical and biomechanical analyses of the tissue-engineered menisci at 36 weeks were performed to determine the quality of the tissue-engineered menisci. Tissue-engineered meniscus showed differences in collagen content and aggregate modulus in comparison with native meniscus. This study demonstrates, for the first time, the feasibility of regenerating whole meniscal cartilage in a rabbit total meniscectomy model using the tissue engineering method.     

Regeneration of whole meniscus using meniscal cells and polymer scaffolds in a rabbit total meniscectomy model

The current treatments of meniscal lesion in knee joint are not perfect to prevent adverse effects of meniscus injury. Tissue engineering of meniscus using meniscal cells and polymer scaffolds could be an alternative option to treat meniscus injury. This study reports on the regeneration of whole medial meniscus in a rabbit total meniscectomy model using the tissue engineering technique. Biodegradable scaffolds in a meniscal shape were fabricated from polyglycolic acid (PGA) fiber meshes that were mechanically reinforced by bonding PGA fibers at cross points with 75:25 poly(lactic-co-glycolic acid). The compressive modulus of the bonded PGA scaffold was 28-fold higher than that of nonbonded scaffold. Allogeneic meniscal cells were isolated from rabbit meniscus biopsy and cultured in vitro. The expanded meniscal cells were seeded onto the polymer scaffolds, cultured in vitro for 1 week, and transplanted to rabbit knee joints from which medial menisci were removed. Ten or 36 weeks after transplantation, the implants formed neomenisci with the original scaffold shape maintained approximately. Hematoxylin and eosin staining of the sections of the neomenisci at 6 and 10 weeks revealed the regeneration of fibrocartilage. Safranin-O staining showed that abundant proteoglycan was present in the neomenisci at 10 weeks. Masson's trichrome staining indicated the presence of collagen. Immunohistochemical analysis showed that the presence of type I and II collagen in neomenisci at 10 weeks was similar to that of normal meniscal tissue. Biochemical and biomechanical analyses of the tissue-engineered menisci at 36 weeks were performed to determine the quality of the tissue-engineered menisci. Tissue-engineered meniscus showed differences in collagen content and aggregate modulus in comparison with native meniscus. This study demonstrates, for the first time, the feasibility of regenerating whole meniscal cartilage in a rabbit total meniscectomy model using the tissue engineering method.     

Regional and Zonal Histo‐Morphological Characteristics of the Lapine Menisci

The menisci have crucial weight‐bearing roles in the knee. Regional variations in structure and cellularity of the meniscus have only been minimally investigated. Therefore, the goal of this study was to illustrate the regional cell density, tissue area, and structure of healthy lapine menisci. Skeletally mature Flemish Giant rabbits were used for this study. Upon sacrifice, menisci were removed, fixed in formalin, and cryosectioned. Histological analysis was performed for the detection of sulfated glycosaminoglycans (GAG), collagen Types I and II, cellular density, and tissue area. ANOVA and paired t tests were used for testing of statistical significance. Glycosaminoglycan coverage of the medial meniscus significantly varied between regions, with the anterior region demonstrating significantly more GAG coverage than the posterior region. Inter‐ and intra‐meniscal comparisons revealed variations between zones, with trends that outer zones of the medial menisci had less GAG coverage. Collagen Types I and II had marked characteristics and varying degrees of coverage across regions. Tissue area varied between regions for both medial and lateral menisci. Cellular density was dependent on region in the lateral meniscus. This is the first study to illustrate regional and zonal variation in glycosaminoglycan coverage, size, and cellular density for healthy lapine meniscal tissue. This data provides baseline information for future investigations in meniscal injury models in rabbits. Anat Rec, 2010. © 2010 Wiley‐Liss, Inc.     

The meniscal insertion of the knee anterolateral ligament

Purpose

The aim of this study is to characterize in detail the meniscal insertion of the anterolateral ligament (ALL) of the knee, establishing parameters regarding the circumference of the lateral meniscus and the popliteal muscle tendon (PMT) groove in addition to its histological analysis.

Methods

A total of 33 knees of cadavers were dissected. The ALL and the lateral meniscus were removed en bloc. After removal of the anatomical specimen, the meniscus circumference, the ALL insertion points on the external surface of the lateral meniscus, and the PMT groove were measured. Eight menisci were subjected to histological analysis.

Results

The ALL was found in all dissections performed. The ALL insertion occurred macroscopically in the transition between the anterior horn and the lateral meniscus body, specifically beginning at 36.0 % and ending at 41.9 % of the meniscal circumference, occupying a mean area of 5.6 mm. The distance between the end of the ALL meniscal insertion and the beginning of the PMT groove averaged 12.9 mm. In the histological evaluation, in longitudinal sections, we observed dense collagen fibers of the ligament inserting on the external surface of the meniscus. It is possible to observe a spreading of collagen fibers at the moment of meniscal insertion.

Conclusions

The ALL meniscal insertion was found in all dissected specimens, beginning with approximately 36 % of the meniscal outer diameter, 12.9 mm anterior to the beginning of the PMT groove. The histological analysis confirmed the presence of true ligamentous tissue in the dissected specimens.

     

The radioscapholunate ligament: A gross and histologic description

The anatomic relationships of the carpal radioscapholunate ligament to its contiguous structures were analyzed by studying (1) 12 grossly dissected fresh adult wrists, and (2) multiple histologic sections from six adult wrists. Observations indicate that the radioscapholunate ligament originates from the prominence between the scaphoid and lunate articular facets on the distal articular surface of the radius, and from the palmar margin of the distal radius, deep and medial to the origin of the radiotriquetral and radiocapitate ligaments. The primary insertion of the radioscapholunate ligament is the medial margin of the proximal pole of the scaphoid. The ligament secondarily inserts into the lateral margin of the lunate and significantly contributes to the proximal portion of the scapholunate interosseous ligament. The radioscapholunate ligament is distinguished morphologically from the other palmar radiocarpal ligaments by its loosely organized collagen fibers and relatively high degree of vascularity. The radiotriquetral and radiocapitate ligaments are composed of densely fasciculated collagen fibers surrounded by perpendicularly oriented perifascicular and epiligamentous fibers. A fibrous capsular layer covers the most superficial aspect of each carpal ligament. On the deep surfaces of these ligaments, a condensation of epiligamentous fibers forms a synovial capsular layer. The palmar radiocarpal ligaments are truly intracapsular structures, as they are interposed between the fibrous and synovial capsular layers. No histologic evidence of elastin is present within the substance of these ligaments.     

Regional and fiber orientation dependent shear properties and anisotropy of bovine meniscus

Imaging of meniscal tissue reveals an extracellular matrix comprised of collagen fibrils arranged in circumferential bundles and radially aligned tie fibers, implicating structural material anisotropy. Biochemical analyses demonstrate regional disparities of proteoglycan content throughout the meniscal body, a constituent known to affect the shearing response of fibrocartilagenous tissue. Despite this phenomenological evidence and previous mechanical testing implicating otherwise, the meniscus if often modeled as a homogeneous, transversely isotropic material with little regard for regional specificity and material properties. The aim of this investigation was to determine if shear stress response homogeneity and directionality exists in and between bovine menisci with respect to anatomical location (medial and lateral), region (anterior, central, and posterior) and fiber orientation (parallel and perpendicular). Meniscus explants were subjected to lap shear strain at 0.002?s(-1) with the circumferential collagen fibers oriented parallel or perpendicular to the loading axis. Comparisons were made using a piecewise linear elastic analysis. The toe region shear modulus was calculated from the first observed linear region, between 3% and 13% strain and the extended shear modulus was established after 80% of the maximum shear strain. The posterior region was significantly different than the central for the extended shear modulus, correlating with known proteoglycan distribution. Observed shearing anisotropy led to the use of an anisotropic hyperelastic model based on a two-fiber family composite, previously used for arterial walls. The chosen model provided an excellent fit to the sample population for each region. These data can be utilized in the advancement of finite element modeling as well as biomimetic tissue engineered constructs.     

Indentation properties and glycosaminoglycan content of human menisci in the deep zone

Menisci are two crescent shaped fibrocartilaginous structures that provide fundamental load distribution and support within the knee joint. Their unique shape transmits axial stresses (i.e. “body force”) into hoop or radial stresses. The menisci are primarily an inhomogeneous aggregate of glycosaminoglycans (GAGs) supporting bulk compression and type I collagen fibrils sustaining tension. It has been shown that the superficial meniscal layers are functionally homogeneous throughout the three distinct regions (anterior, central and posterior) using a 300 μm diameter spherical indenter tip, but the deep zone of the meniscus has yet to be mechanically characterized at this scale. Furthermore, the distribution and content of GAG throughout the human meniscal cross-section have not been examined. This study investigated the mechanical properties, via indentation, of the human deep zone meniscus among three regions of the lateral and medial menisci. The distribution of GAGs through the cross-section was also documented. Results for the deep zone of the meniscus showed the medial posterior region to have a significantly greater instantaneous elastic modulus than the central region. No significant differences in the equilibrium modulus were seen when comparing regions or the hemijoint. Histological results revealed that GAGs are not present until at least ～600 μm from the meniscal surface. Understanding the role and distribution of GAG within the human meniscus in conjunction with the material properties of the meniscus will aid in the design of tissue engineered meniscal replacements.     

A Quantitative Study of the Microstructure and Biochemistry of the Medial Meniscal Horn Attachments

Little quantitative data is available on the structure of meniscal attachments. Therefore, as an aid to designing meniscal replacements as well as a possible explanation for mechanical behavior, this study was designed to further the knowledge of the microstructure and biochemistry of native meniscal attachments. Bovine medial meniscal attachments (the external ligamentous portion as well as the transition zones at the bony insertion) were removed and prepared for microstructural evaluation. After embedding in paraffin, the samples were sliced on a microtome and stained for quantitative analysis. The anterior and posterior insertion sites are known to contain three zones: subchondral bone, calcified fibrocartilage, and uncalcified fibrocartilage. Additionally, others have shown that the anterior insertion site contains a ligamentous zone. The insertion zones were further divided into proximal, middle, and distal zones. The posterior attachment’s insertion site had a significantly greater thickness of interdigitations, subchondral bone, uncalcified fibrocartilage, and calcified fibrocartilage zone thickness compared to the anterior attachment insertion. The anterior attachment’s insertion had the greatest GAG fraction in each zone when compared to the posterior attachment’s insertion. GAG fraction decreased from the meniscus to the subchondral bone. Both GAG fraction and normalized thickness varied within a given zone, decreasing from the distal to proximal regions in both the anterior and posterior attachments’ insertion zones. Crimp frequency of the collagen fibrils in the external ligamentous portion of the tissue was homogeneous along the length. The findings from this study agree with previously published material property data on the medial meniscal attachments, and could be used in the future to design methods of attachment for tissue engineered replacement menisci.     

The menisco-femoral ligaments

The menisco-femoral ligaments were studied in 60 knees from 30 dissecting room cadavers. The anterior horns of the menisci were attached to the intercondylar area of the femur by discrete antero-medial or antero-lateral menisco-femoral ligaments, separate from the anterior cruciate ligament, in 15% of knees for each meniscus, more frequently than previously appreciated; these anterior horn ligaments may exacerbate a meniscal tear. The posterior horn of the lateral meniscus was connected with the intercondylar area of the femur in 100% of knees. In 93% of knees a ligament ran behind the posterior cruciate ligament while in 33% of knees a ligament ran in front of the posterior eruciate ligament. We propose renaming these the pre-cruciate postero-lateral menisco-femoral ligament and post-cruciate postero-lateral menisco-femoral ligament, respectively, to avoid confusion with the ligaments of the anterior horns. The menisco-femoral ligaments may function in controlling movement of the menisci, especially during rotation of the knee. The posterior horn of the medial meniscus has no direct femoral attachment and this may be a factor in the increased risk of injury to this meniscus. © 1995 WiIey-Liss, Inc.     

Clinical significance of meniscal abnormalities on magnetic resonance imaging in an older population

This study examined the prevalence of degenerative changes of knee menisci in aging and evaluated the diagnostic values of magnetic resonance (MR) imaging for assessing meniscal pathology in an older population. Eighty-five knees of asymptomatic volunteers over the age of 40 were scanned using MR imaging. Meniscal abnormalities were graded from 0 to 3 according to intrameniscal MR signals. The subjects were divided into two groups based on the presence or absence of radiographic osteoarthritis. Group I included 43 knees that had normal radiographs and group II consisted of 42 knees that had radiographic evidence of osteoarthritis. Degenerative changes in the menisci involved primarily the posterior segment of the medial meniscus in both groups. Signal changes in the other segments were of a significantly lesser grade than that in the posterior segment of the medial meniscus. The meniscal grade in each segment was significantly higher in group II than in group I. In group I, only two menisci (4.6% ) showed grade 3 signals, even in the posterior portion of the medial meniscus, compared to 21 (50.0%) in group II. Frequency of asymptomatic grade 3 was relatively low even in older subjects if there was no evidence of radiographic osteoarthritic changes. Abnormal MR signals are more likely to have clinical significance, in patients with radiographic changes on plain X-ray.     

Regional variations in the distribution and colocalization of extracellular matrix proteins in the juvenile bovine meniscus

A deeper understanding of the composition and organization of extracellular matrix molecules in native, healthy meniscus tissue is required to fully appreciate the degeneration that occurs in joint disease and the intricate environment in which an engineered meniscal graft would need to function. In this study, regional variations in the tissue-level and pericellular distributions of collagen types I, II and VI and the proteoglycans aggrecan, biglycan and decorin were examined in the juvenile bovine meniscus. The collagen networks were extensively, but not completely, colocalized, with tissue-level organization that varied with radial position across the meniscus. Type VI collagen exhibited close association with large bundles composed of type I and II collagen and, in contrast to type I and II collagen, was further concentrated in the pericellular matrix. Aggrecan was detected throughout the inner region of the meniscus but was restricted to the pericellular matrix and sheaths of collagen bundles in the middle and outer regions. The small proteoglycans biglycan and decorin exhibited regional variations in staining intensity but were consistently localized in the intra- and/or peri-cellular compartments. These results provide insight into the complex hierarchy of extracellular matrix organization in the meniscus and provide a framework for better understanding meniscal degeneration and disease progression and evaluating potential repair and regeneration strategies.     

Design and mechanical evaluation of a novel fiber-reinforced scaffold for meniscus replacement

A fiber-reinforced degradable scaffold for replacement of meniscal tissue was designed, fabricated, and mechanically evaluated. The hypotheses were that (1) the fiber network design would share a portion of compressive loads via the generation of circumferential tensile loads, and (2) the scaffold tensile properties would be similar to those of the meniscus. Two meniscus scaffold designs varying in fiber content (1000 or 500 fibers: MS1000, MS500) underwent cyclic compressive loading up to 100 and 250N, with resultant tensile loads measured at the anterior and posterior anchors. Standard tensile testing was also performed on each device and ovine menisci. Both scaffolds generated tensile loads directly proportional to the applied compressive loads, with MS1000 scaffolds generating approximately twice the tensile loads of MS500 scaffolds. The tensile strength of MS1000 scaffolds was significantly higher than that of the medial and lateral ovine menisci, and approximately twice that of the MS500 scaffolds. The stiffness of MS1000 scaffolds was lower than that of the lateral meniscus, but not statistically different from that of the medial meniscus. These results support our hypotheses that this novel fiber-reinforced scaffold can mimic the tensile and hoop stress behavior of normal meniscal tissue under compressive loading. The circumferential tensile strength and stiffness are appropriate for a meniscus replacement device.     

Failure strengths of suture vs. biodegradable arrow and staple for meniscal repair: an in vitro study

A study was performed to determine the in vitro biomechanical behaviour of two 'all inside' meniscal repair techniques (Meniscal Arrow [Bionx Implants Inc.] and Meniscal Staple [Surgical Dynamics Inc.]) and compare these directly with both a horizontal and vertical suture repair. Using 30 fresh bovine medial menisci, vertical 'bucket handle' tears were created 4 mm from the meniscus periphery. Repairs were subsequently performed, using four techniques, with 15 repairs in each group, a horizontally placed 3-metric Ethibond suture, a vertically placed 3-metric Ethibond suture, a single 13-mm arrow and a single 7-mm staple. A tensile test was performed to determine the force at failure for each technique. The mean force at failure of the horizontal and vertical suture groups was 63.2 and 73.9 N, respectively, 44.3 N for the arrow group and 17.8 N for the staple group. The mean forces at failure were significantly different (P < 0.005). The mean tensile strength of the meniscal staple was significantly lower than that of both suture and arrow groups. The 7-mm staple design may not allow adequate interdigitation between the barbed legs and the semicircular collagen fibres of the meniscus.