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Study design: A study comparing the vasculature of the normal and regenerated menisci in rabbits' knees. Objectives: To observe the patterns of the new vessel growth in the regenerating meniscus from its developmental stage to its maturity. Summary of background data: There have been no comparative vascular studies in the normal and regenerated menisci in animals in spite of the well-known previous vascular studies in normal and degenerated menisci in human. Methods: At 3, 4, 6, 10 and 16 weeks after unilateral total meniscectomy in both knees of 25 immature rabbits, aged 6–8 weeks, radiopague blue dye was injected through the abdominal aorta of five rabbits for vascular study before sacrifice, and then the five rabbits were sacrificed at each observation time. A modified Spalteholz clearing technique was employed, and the menisci were examined and photographed under dissecting microscope with reflected light and transillumination. Results: New vessel growth was observed in the regenerating menisci at three weeks after meniscectomy. The blood supply was present in the outer 30–50% of the regenerated meniscus at six weeks postmeniscectomy and then it slightly regressed. The regenerated menisci were smaller in size as compared with normal ones. The anterior and posterior horns were more vascular than the rest of the regenerated menisci. Conclusion: The regenerated medial and lateral menisci had almost the same vascular patterns as those seen in the normal menisci.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) (0, 0.1, 1, or 5 μg) was injected into the autogeneous semitendinosus tendon, and the tendon was transplanted to the region of the medial meniscus defect in a rabbit model to repair the defect. Cartilaginous transformation of the tendon by rhBMP-2 was expected under the less-vascularized intra-articular environment. At four and eight weeks after surgery, the left knee joints were harvested, and the morphological changes of the graft were examined by radiological, histological, and immunohistochemical methods. Cartilaginous tissue within the graft was detected by Safranin O staining and immunostaining of Type-II collagen. At four weeks, fibrocartilagenous tissue, together with small ossicles, was consistently noted in tendon autografts that were injected with 1 or 5 μg of rhBMP-2. At eight weeks, the cartilage located at the basal part of the graft adjacent to the joint capsule was partially replaced with ectopic bone in the 1-μg or 5-μg groups. The ossicles might have been formed by vascular invasion into the rhBMP-2-induced cartilage, but the cartilageous structure remained at the peripheral part of the graft and filled the meniscus defect. The experimental results indicate the potential use of rhBMP-2 in regenerating the cartilaginous meniscus if additional methods to suppress vascular invasion into the rhBMP-2–induced cartilage also inhibit ossification.

Purpose: To evaluate the accuracy of single photon emission computed tomography (SPECT) compared with arthroscopy in the diagnosis of acute knee pain due to meniscal tear. Methods: Patients with knee pain that persisted for less than six months with normal plain radiographs that had arthroscopic surgery following SPECT scan were included. The main scintigraphic criterion for diagnosing a tear of the meniscus was tibial plateau activity on the planar image with at least a half crescent of peripheral tibial plateau uptake. The accuracy of SPECT in detecting meniscal tears was calculated according to the arthroscopic findings as the gold standard. Results: There were 68 patients in the study (46 males and 22 females). The mean age was 45.3 (17–72) years and the mean time between SPECT scan and surgery was 3.5 (1–6) months. The overall sensitivity of SPECT was 90%, specificity 70%, NPV 54%, PPV 95% and accuracy 87%. Conclusion: SPECT was found to be an accurate imaging technique in the diagnosis of symptomatic meniscal tears in patients with acute knee pain and unremarkable plain radiographs. Thus, SPECT may be helpful in selecting candidates for arthroscopy.

This study in rabbit knees was carried out to clarify the effect of the application of CPM, after meniscectomy, on the regeneration rate of the meniscus and histology of the regenerated menisci. Twenty-seven mature rabbits were used: three rabbits as control (non-CPM) and 24 rabbits as experimental ones. Among them, four rabbits were used as the immediate CPM group and 20 rabbits as the delayed CPM group. In each animal, the medial meniscus was totally excised from the right knee, and the lateral meniscus was totally excised from the left knee. In three control animals, 16 weeks after meniscectomy, there was (hold) Grade II to III meniscal regeneration in two, and small meniscal mold was formed in one. In the immediate CPM group, meniscal regeneration failed and there was would disruption in all four knees. In the delayed CPM group, grades II to III regeneration was observed in 15 of the 20 medial meniscectomized knees, while in the lateral meniscectomized knees, the same size of meniscal regeneration was observed only in 3 of the 20 knees. The regenerated menisci in the delayed CPM group overall looked normal in appearance. Application of the delayed CPM induced the early fibrocartilaginous metaplasia of the regenerated fibrous menisci even at 6 to 12 weeks after meniscectomy.

It is speculated that the application of delayed CPM promotes early focal fibrocartilagenous metaplasia of the fibrous meniscus following meniscectomy.

Injuries to the knee joint are common and often have an adverse impact on a patient's quality of life. It is therefore important to understand the load transfer mechanism of the knee, especially with regard to the loading of the menisci in different positions and under different conditions.

To date, only contact pressure between joint surfaces and menisci, as well as circumferential strain, have been measured by pressure sensors and strain gauges. Therefore, the aim of this study was to investigate the spread of axial load within the menisci and the effect of the knee flexion angle on the axial load within the menisci.

Intrameniscal forces were measured with Fiber Bragg Grating (FBG) sensors and conductive rubber sensors in porcine knee joint specimens. The changes in pressure were measured under different loading conditions. Measurement of the intrameniscal pressure is feasible. Although, there is some existence of variations in readings, some trends can be inferred. From the overall trend, it was observed that higher stress occurs at lateral central and lateral posterior regions. As the occurrences of injuries are mainly at the medial meniscus, this may imply that the level of stress is secondary to the mobility of the meniscus in incidents of injuries. It was found that the posterior meniscofemoral ligament plays a crucial role in the mechanics of the lateral meniscus.

The meniscus is a multifunctional fibrocartilage tissue in the knee joint which stables joint movement, bears load and absorbs impact. Improper collisions will cause damage to meniscus tissue and lose its original functionality. However, it is difficult to fully evaluate the mechanical properties of the meniscus based on static test results alone. In this study, Split Hopkinson Pressure Bar (SHPB) and hydraulic material testing system (MTS) were utilized to examine the quasi-static and dynamic properties of the porcine meniscus along with two different orientations. The results showed that the meniscus is a strain rate sensitive material and its mechanical properties mainly depend on the orientation of collagen fiber bundles in the peripheral direction. The meniscus tissue did not show obvious yield characteristics under quasi-static test conditions. However, the meniscus showed clear yield behavior under dynamic loading. When the strain rate increased, the elastic modulus of the radial meniscus remained around 35 MPa while the elastic modulus of the axial meniscus increased from 30 MPa to 80 MPa. This study demonstrates that the meniscus is sensitive to strain rate at both dynamic and quasi-static conditions, and the meniscus is an anisotropic biological tissue.

In this study, we adopt different material models to study the strength and stiffness of menisci of the knee joint using finite element method. The three-dimensional (3-D) knee joint finite element model is constructed based on the Magnetic Resonance (MR) images of a human knee joint, and the strength of menisci is analyzed under a specific vertical loading case. In this paper we categorize and implement three types of appropriate material properties, namely isotropic linearly elastic, transversely isotropic elastic and isotropic hyperelastic for menisci of the knee joint. Different strain energy models are also studied and compared under hyperelastic category. The comparative study demonstrates that the hyperelastic model with Ogden form is more appropriate in modeling menisci of the knee joint. By referring to the test data of different material properties from earlier studies by various researchers, we hope to provide a comparative study leading to appropriate menisci material models and properties for finite element analyses of knee joint structures.