Horn Of Meniscus Research Articles

Changes of the Posterior Meniscal Horn Height During Loading: An In Vivo Magnetic Resonance Imaging Study

This in vivo magnetic resonance imaging study evaluated the deformation of the meniscal posterior horn during loading. Images of the medial and lateral meniscus were obtained in 20 normal knees in 0 degrees and 30 degrees of flexion, and the height of the posterior horn of both menisci was measured. Mean height of the posterior horn of the medial meniscus under no load and load equal to 50% and 100% body weight was 6.8, 6.3, and 6 mm, respectively (P<.05). Mean height of the posterior horn of the lateral meniscus under no load and load equal to 50% and 100% body weight was 7.6, 7.2, and 6.9 mm, respectively (P<.05). Knee position (0 degree versus 30 degrees of flexion) at a constant load resulted in no significant change in height. These results show height of the posterior horn of the medial and lateral meniscus decrease with increasing loading and angle of knee flexion.

The Reproducibility of Radiographic Measurement of Lateral Meniscus Horn Position

The objective of our investigation was to evaluate whether it is possible to locate and reproduce the tibial insertion areas of the anterior and posterior horns of the lateral meniscus on preoperative radiographs. In 20 tibia heads, we prepared anterior and posterior horn insertions and marked their circumference with radiopaque steel balls of 1.6 mm in diameter. Standardized anteroposterior and lateral radiographs were made. On these radiographs, different landmarks were defined, their distances measured (tibial width and depth, distance from lateral tibia border to meniscus insertion midpoint, distance from anterior tibia border to meniscus insertion midpoint, distance from anterior and lateral tibia border to lateral intercondylar spine), and ratios determined. The anterior horn midpoint is located at 45.1% +/- 1.3% of tibial width and 41.9% +/- 3.2% of tibial depth, and the posterior horn midpoint is located at 49.8% +/- 1.9% of tibial width and 72.1% +/- 2.3% of tibial depth. The statistical analysis of these measures showed a precise and constant positioning of the lateral meniscus insertions on the tibia plateau. We also found constant topographic relations to the lateral intercondylar spine. Anterior and posterior lateral meniscus horn insertions can be determined on radiographs with a high precision and reproducibility. We have developed a technique for precise radiographic tibial horn determination in lateral meniscus transplantation.

Meniscal Allograft Transplantation

Meniscal transplantation has become an accepted treatment option for selected symptomatic patients who have undergone a complete or near-complete meniscectomy. Basic and preliminary clinical studies suggest a meniscal allograft may replicate (though not completely) the shock-absorbing function of the normal meniscus to alleviate pain and provide measurable improvement in knee function. However, there is limited information on which to base crucial clinical decisions in treating the meniscectomized patient. I systematically explored available literature to address four general questions: Who is the ideal patient for a meniscal transplantation? What is the ideal method of graft sizing, preservation, and implantation? What is the accepted means of postoperative rehabilitation and timing of a return to athletic activities? And finally, what is the overall success rate of this procedure? This review of existing clinical trials revealed several crucial treatment principles for surgeons performing this procedure: (1) achieving or reestablishing normal knee alignment and stability; (2) implanting a size-matched, non-irradiated graft with secure fixation of the meniscal horns; and (3) ensuring patients return only to light sports activities to maximize the chances for graft survival. By following these principles, symptomatic improvement can be achieved in the majority of patients.

Failure properties and strain distribution analysis of meniscal attachments

The menisci are frequently injured due to both degeneration and traumatic tearing. 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. Therefore, the objectives of the current study were to (1) determine the failure properties of the meniscal horn attachments, and (2) determine the strain distribution over their surfaces. Eight bovine knee joints were used to study the mechanical response of the meniscal attachments. Three meniscal attachments from one knee of each animal were tested in uniaxial tension at 2%/s to determine the load deformation response. During the tests, the samples were marked and local strain distributions were determined with a video extensometer. The linear modulus of the medial anterior attachment (154±134 MPa) was significantly less than both the medial posterior (248±179 MPa, p=0.0111) and the lateral anterior attachment (281±214 MPa, p=0.0007). Likewise, the ultimate strain for the medial anterior attachments (13.5±8.8%) was significantly less than the medial posterior (23±13%, p<0.0001) and the lateral anterior attachment (20.3±11.1%, p=0.0033). There were no significant differences in the structural properties or ultimate stress between the meniscal attachments ( p>0.05). No significant differences in ultimate strain or moduli across the surface of the attachments were noted. Based on the data obtained, a meniscal replacement would need different moduli for each of the different attachments. However, the attachments appear to be homogeneous.

Biologic Resurfacing of the Glenoid Using a Meniscal Allograft

Biologic resurfacing of the glenoid is a treatment alternative for young patients who develop rapid and aggressive destruction of glenoid. In 2001, a technique was developed to allow secure fixation of a meniscal allograft to the glenoid in combination with hemi-arthroplasty replacement of the humeral head. The authors have modified this technique by addressing posterior wear factors, as well as circumferential covering of the glenoid perimeter. The meniscal horns are sutured together to fashion the allograft in an ovoid shape. The meniscus closely matches the circumference of the glenoid and therefore 180 degrees coverage of the glenoid rim is achieved. In addition, the wedge shape of the meniscus may enhance comfort and stability.

Complications in medial meniscus suture: a cadaveric study

The aim of this study was to examine the possibility of complications in medial meniscus repair using an inside-out suturing device. Anatomical cadaveric study. Six fresh frozen cadaveric lower limbs were used. The posterior horn of the medial meniscus was sutured using three vertical stitches. An anatomical dissection was subsequently performed to check for any possible effects upon the structures of the medial aspect of the knee. In addition, an incision was made in a safety zone in order to ascertain whether it was possible to carry out the suture without affecting the aforementioned structures. No vascular or nervous structures were pierced by the needle. On knotting, it was found that a number of different structures had become trapped: the sartorial tendon was affected in each of the specimens used. In four cases, the saphenous vein was trapped by some of the knots. The saphenous nerve was trapped in four instances. Once this had been established, a small accessory incision was made to provide access to a safety zone, where suture can be performed without affecting any neurovascular or tendinous structures. Inside-out suture of the posterior meniscal horn carries a high incidence of entrapment of the neurovascular structures of the medial aspect of the knee. The sartorial tendon is constantly affected. Such complications can easily be avoided by entering the safety zone via a small auxiliary incision. This study provides evidence that complications affecting the peripheral structures of the medial aspect of the knee may arise during inside-out suture of the posterior horn of the medial meniscus and proposes a simple method of averting them.

Human Meniscus Allografts’ in Vivo Size and Motion Characteristics

Background Although many reports have described clinical outcome of meniscus transplants, their size and motion patterns are not well understood. This study assessed postoperative in vivo size and motion patterns of meniscus transplants under full weightbearing conditions. Hypothesis The human meniscus transplant has size and motion characteristics similar to the native menisci. Study Design Case series; Level of evidence, 4. Methods Eight meniscus transplants in 7 knees were studied 15 to 34 months postoperatively. The knees were scanned in an open magnetic resonance imaging 0.5-T superconducting magnet while standing. Single slice sagittal and coronal images were obtained at 0 °, 30 °, 60 °, and 90 ° of flexion in the operative and contralateral knees. Results The mean height and width of the anterior and posterior horns of the transplants were similar to those of native menisci. The millimeters of coronal displacement of motion of the midbody were also similar between the transplants and the native menisci. The anterior horn of the native medial menisci moved a mean of 5 mm more (total anterior to posterior translation, P<. 05) than did the transplants. The posterior horn of the native medial menisci, and both horns of the native lateral menisci, also tended to move more than the corresponding horns of the transplanted menisci, although this result could not be confirmed statistically, given the number of menisci studied. Conclusion Meniscus transplants had similar size and midbody motion characteristics as the native menisci. The horns of the meniscus transplants tended to show decreased motion compared with the native menisci. The operative techniques and subsequent healing of the graft bone and peripheral attachments provided a stable meniscus construct.

Sensitivities of Medial Meniscal Motion and Deformation to Material Properties of Articular Cartilage, Meniscus and Meniscal Attachments Using Design of Experiments Methods

This study investigated the role of the material properties assumed for articular cartilage, meniscus and meniscal attachments on the fit of a finite element model (FEM) to experimental data for meniscal motion and deformation due to an anterior tibial loading of 45 N in the anterior cruciate ligament-deficient knee. Taguchi style L18 orthogonal arrays were used to identify the most significant factors for further examination. A central composite design was then employed to develop a mathematical model for predicting the fit of the FEM to the experimental data as a function of the material properties and to identify the material property selections that optimize the fit. The cartilage was modeled as isotropic elastic material, the meniscus was modeled as transversely isotropic elastic material, and meniscal horn and the peripheral attachments were modeled as noncompressive and nonlinear in tension spring elements. The ability of the FEM to reproduce the experimentally measured meniscal motion and deformation was most strongly dependent on the initial strain of the meniscal horn attachments (epsilon(1H)), the linear modulus of the meniscal peripheral attachments (E(P)) and the ratio of meniscal moduli in the circumferential and transverse directions (E(theta)E(R)). Our study also successfully identified values for these critical material properties (epsilon(1H) = -5%, E(P) = 5.6 MPa, E(theta)E(R) = 20) to minimize the error in the FEM analysis of experimental results. This study illustrates the most important material properties for future experimental studies, and suggests that modeling work of meniscus, while retaining transverse isotropy, should also focus on the potential influence of nonlinear properties and inhomogeneity.

Time dependent properties of bovine meniscal attachments: Stress relaxation and creep

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 [Chen, M.I., Branch, T.P., et al., 1996. Is it important to secure the horns during lateral meniscal transplantation? A cadaveric study. Arthroscopy 12(2), 174–181; Alhalki, M.M., et al., 1999. How three methods for fixing a medial meniscal autograft affect tibial contact mechanics. American Journal of Sports Medicine 27(3), 320–328; Haut Donahue, T.L., et al., 2003. How the stiffness of meniscal attachments and meniscal material properties affect tibio-femoral contact pressure computed using a validated finite element model of the human knee joint. Journal of Biomechanics 36(1), 19–34]. The complex loading environment in the knee lends itself to different loading environments for each meniscal attachment. We hypothesize that the creep and stress relaxation characteristics of the horn attachments will be different for the anterior versus posterior, and medial versus lateral attachments. To test this hypothesis, the stress relaxation and creep characteristics of the meniscal horn attachments were determined. The stress relaxation properties of load/stress at the end of the test, and the load/stress relaxation rate demonstrated no significant statistical differences between the attachments. Unlike the stress relaxation properties, the creep properties demonstrated some significant differences amongst the attachments. The normalized displacement at the end of the test, normalized creep rate and strain creep rate for the lateral anterior attachment were significantly different than those of the medial posterior attachment ( p < 0.0 5 ). The two anterior attachments had significantly different strains at the end of the test, as well as significantly different creep strain rates ( p < 0.0 5 ). The two attachments of the medial meniscus revealed no significant differences between any of the creep properties measured ( p > 0.0 5 ). The time dependent properties obtained in this experiment provide insight into the behavior of meniscal horn attachments under various loading situations. The results indicate that a suitable meniscal replacement may require different properties for the lateral and medial horns.

Evaluation of the Neurosensory Function of the Medial Meniscus in Humans

Menisci are known to have receptors mainly concentrated at the anterior and posterior horns. Although they are purported to send afferent impulses to the central nervous system, this function has not been thoroughly evaluated. The purpose of the study was to investigate whether stimulation of the menisci initiates a cortical response. The reaction of the end organ to the reflex arc is also evaluated. Prospective case series. Fourteen patients with normal medial menisci were included in the study. Different parts of the knee joint (the posterior horn and the body of the medial meniscus, the medial femoral condyle, the capsule, and the joint space) were electrically stimulated by a probe during arthroscopy. The cortical response was monitored with somatosensory-evoked potentials (SEPs). The compound muscle action potentials (CMAPs) of the semimembranosus, quadriceps, and biceps femoris muscles were also monitored with electroneuromyography (ENMG). Among the stimulated parts, only the posterior horn of the meniscus produced cortical responses. No response was obtained with stimulation of the medial femoral condyle, the body of the medial meniscus, the capsule, or the joint space. Stimulation of the posterior horn of the medial meniscus produced a measurable amount of CMAP latency for the semimembranosus muscle, but not for the quadriceps and biceps femoris muscles. Stimulation of the posterior horn of the medial meniscus produces reproducible cortical SEPs and results in ENMG-verified response of the semimembranosus muscle where no response of the semimembranosus muscle is detected with stimulation of the other parts of the knee. The knowledge that only the horns of the medial meniscus have mechanoreceptors in the medial compartment of the knee helps to understand patients' signs and symptoms in medial compartment disease.

Allograft interference screw fixation in meniscus transplantation

Allograft meniscus transplantation is indicated to restore proper knee biomechanics and prevent subsequent articular degeneration in patients with a meniscus-deficient knee. A variety of techniques for fixation of meniscal transplants exist, with some techniques using soft-tissue fixation of the meniscal horns and others using bony fixation. The authors present a technique of meniscus transplantation using a tibial slot with allograft interference screw fixation. We have had excellent early results with this technique and believe that a cortical allograft interference screw reliably maintains the anatomic position of the meniscal attachments that are critical to the biomechanics and functional outcome of meniscus transplantation.

Arthroscopic revisions in failed meniscal surgery.

The aim of this study was to classify meniscal tear forms as found in 195 revision arthroscopies. Interval between primary arthroscopy and revision was 7.8+/-5.6 month. All patients were available for control after 1 year. In 174 knees the lesion was located in the medial meniscus and in 21 knees in the lateral meniscus. In the medial meniscus an unstable posterior meniscal horn was seen in 93 knees followed by incomplete horizontal tear and meniscal destruction in 37. Flap tear, circumferential tear, and failed meniscal repair were also seen. In the lateral meniscus destruction of a discoid meniscus, instability near the popliteal hiatus, and various tear forms were seen with nearly equal frequency. Postoperatively Lysholm score increased significantly in both groups. Most meniscal tears, found in revision arthroscopy, are caused by an insufficient primary operation. A diligent analysis of the tear form is absolutely necessary. An adequate radical resection technique to establish a smooth meniscal crest is indispensable.

The shapes of the tibial and femoral articular surfaces in relation to tibiofemoral movement.

We report a study of the shapes of the tibial and femoral articular surfaces in sagittal, frontal and coronal planes which was performed on cadaver knees using two techniques, MRI and computer interpolation of sections of the articular surfaces acquired by a three-dimensional digitiser. The findings using MRI, confirmed in a previous study by dissection, were the same as those using the digitiser. Thus both methods appear to be valid anatomical tools. The tibial and femoral articular surfaces can be divided into anterior segments, contacting from 0 degrees to 20 +/- 10 degrees of flexion, and posterior segments, contacting from 20 +/- 10 degrees to 120 degrees of flexion. The medial and lateral compartments are asymmetrical, particularly anteriorly. Posteromedially, the femur is spherical and is located in a conforming, but partly deficient, tibial socket. Posterolaterally, it is circular only in the sagittal section and the tibia is flat centrally, sloping downwards both anteriorly and posteriorly to receive the meniscal horns. Anteromedially, the femur is convex with a sagittal radius larger than that posteriorly, while the tibia is flat sloping upwards and forwards. Anterolaterally, both the femoral and tibial surfaces are largely deficient. These shapes suggest that medially the femur can rotate on the tibia through three axes intersecting in the middle of the femoral sphere, but that the sphere can only translate anteroposteriorly and even then to a limited extent. Laterally, the femur can freely translate anteroposteriorly, but can only rotate around a transverse axis for that part of the arc, i.e., near extension, during which it comes into contact with the tibia through its flattened distal/medial surface as against its spherical posterior surface.

The shapes of the tibial and femoral articular surfaces in relation to tibiofemoral movement

We report a study of the shapes of the tibial and femoral articular surfaces in sagittal, frontal and coronal planes which was performed on cadaver knees using two techniques, MRI and computer interpolation of sections of the articular surfaces acquired by a three-dimensional digitiser. The findings using MRI, confirmed in a previous study by dissection, were the same as those using the digitiser. Thus both methods appear to be valid anatomical tools. The tibial and femoral articular surfaces can be divided into anterior segments, contacting from 0° to 20 ± 10° of flexion, and posterior segments, contacting from 20 ± 10° to 120° of flexion. The medial and lateral compartments are asymmetrical, particularly anteriorly. Posteromedially, the femur is spherical and is located in a conforming, but partly deficient, tibial socket. Posterolaterally, it is circular only in the sagittal section and the tibia is flat centrally, sloping downwards both anteriorly and posteriorly to receive the meniscal horns. Anteromedially, the femur is convex with a sagittal radius larger than that posteriorly, while the tibia is flat sloping upwards and forwards. Anterolaterally, both the femoral and tibial surfaces are largely deficient. These shapes suggest that medially the femur can rotate on the tibia through three axes intersecting in the middle of the femoral sphere, but that the sphere can only translate anteroposteriorly and even then to a limited extent. Laterally, the femur can freely translate anteroposteriorly, but can only rotate around a transverse axis for that part of the arc, i.e., near extension, during which it comes into contact with the tibia through its flattened distal/medial surface as against its spherical posterior surface.

The reference point to measure the anterior intermeniscal ligament's thickness: an MRI study.

The purpose of this study was to identify a reliable reference point for measuring anterior intermeniscal ligament thickness and to investigate the morphological characteristics of the ligament at its attachment site to anterior horns of both menisci by MRI. MRI was performed in 98 knees of randomly chosen patients. The anterior intermeniscal ligament was detected in 61 knees (62.2%). The average ligament length was 29.8 mm. Men had significantly longer anterior intermeniscal ligament than women patients (32.5 vs. 27.8 mm). The thickness of anterior intermeniscal ligaments at their attachment sites to menisci was usually less than 3 mm; a thickness of 3 mm or more at the attachment site to anterior horns of the meniscus was defined as "cordlike." It is suggested that the "cordlike" pattern is a variation of the anterior intermeniscal ligament's attachment characteristics, and that this might have a significant role in meniscal translations during knee motion, and also that the "cordlike" pattern could be clinically important with respect to its relationship to the anterior horn of medial meniscus. The attachment site of the ligament is a reliable reference point for measuring its thickness.

MR imaging of displaced meniscal tears of the knee. Importance of a "disproportional posterior horn sign".

Meniscal tears associated with displaced fragments are clinically significant. We propose the "disproportional posterior horn sign" as a supportive criterion to identify a posterocentrally displaced meniscal fragment on MR imaging studies. If the meniscal posterior horn in the central portion appears larger than that in the peripheral section, it is considered positive for "disproportional posterior horn sign". MR images obtained in 42 patients with 43 lesions, confirmed to have displaced meniscal tears, were included in this study. The MR images were retrospectively evaluated for the presence of the "disproportional posterior horn sign", as well as the other known signs. The "disproportional posterior horn sign" was seen in 9 (20.9%) of 43 lesions, including 1 lateral discoid meniscal tear, 5 lateral meniscal tears and 3 medial meniscal tears. Five of them also had other signs of a displaced meniscal fragment. However, the remaining 4 cases only exhibited the "disproportional posterior horn sign". For the other MR signs, the "absent bow tie sign" was detected in 40 (93%) of 43 lesions, the "flipped meniscus sign" in 27 (62.8%) of 43 lesions, the "double posterior cruciate ligament sign" in 17 (39.5%) of 43 lesions and the "notch fragment sign" in 22 (51.2%) of 43 lesions. The "disproportional posterior horn sign" is helpful in demonstrating a posterocentrally displaced meniscal fragment, especially when other characteristic signs are unremarkable or absent.

MR IMAGING OF DISPLACED MENISCAL TEARS OF THE KNEE. Importance of a "disproportional posterior horn sign"

Purpose: Meniscal tears associated with displaced fragments are clinically significant. We propose the “disproportional posterior horn sign” as a supportive criterion to identify a posterocentrally displaced meniscal fragment on MR imaging studies. If the meniscal posterior horn in the central portion appears larger than that in the peripheral section, it is considered positive for “disproportional posterior horn sign”. Material and Methods: MR images obtained in 42 patients with 43 lesions, confirmed to have displaced meniscal tears, were included in this study. The MR images were retrospectively evaluated for the presence of the “disproportional posterior horn sign”, as well as the other known signs. Results: The “disproportional posterior horn sign” was seen in 9 (20.9%) of 43 lesions, including 1 lateral discoid meniscal tear, 5 lateral meniscal tears and 3 medial meniscal tears. Five of them also had other signs of a displaced meniscal fragment. However, the remaining 4 cases only exhibited the “disproportional posterior horn sign”. For the other MR signs, the “absent bow tie sign” was detected in 40 (93%) of 43 lesions, the “flipped meniscus sign” in 27 (62.8%) of 43 lesions, the “double posterior cruciate ligament sign” in 17 (39.5%) of 43 lesions and the “notch fragment sign” in 22 (51.2%) of 43 lesions. Conclusion: The “disproportional posterior horn sign” is helpful in demonstrating a posterocentrally displaced meniscal fragment, especially when other characteristic signs are unremarkable or absent.

Intraarticular measurement of forces acting on the canine medial meniscus during motion

SummaryMeniscal injuries are currently under much clinical investigation. With regard to tissue engineering strategies for meniscal repair or replacement, the direct measurement of forces applied on the meniscus, during range of motion, could provide important information. This in vitro study using canine cadaver limbs evaluated the possibility of measuring the tibial reaction force, at the medial meniscal level, with film pressure sensors.The sensors were placed between the medial meniscus and the tibial plateau. With different preloads of the stifle, in proportion to the dog’s total body weight measurements were taken under constant motion with intact and artificially transected cranial cruciate ligament. With an intact cranial cruciate ligament the force peak, under the cranial horn, was found in extension, and under the caudal horn in flexion. Transection of the cranial cruciate ligament led to a rise in mean force under both of the horns. The rise in mean force was higher under the caudal horn compared to the cranial horn. Transection of the cranial cruciate ligament resulted in an altered curve pattern under the caudal medial meniscal horn, which was most apparent with the highest preloads. The sensors were easy to apply, the results substantiated commonly accepted biomechanical predictions and the experimental set-up was found to be a useful tool for the investigation of forces acting on the menisci.A thin film pressure sensor was implanted under the cranial and caudal medial meniscal horn in 18 canine cadaver stifles and the forces recorded during a constant range of motion with intact and artificially transected cranial cruciate ligaments. The results reflected biomechanical predictions, and the experimental set-up was found to be a useful tool in the investigation of forces acting on the menisci.

Contact mechanics of the medial tibial plateau after implantation of a medial meniscal allograft. A human cadaveric study.

The goal of this study was to determine how well a medial meniscal allograft restores the normal contact mechanics of the medial tibial plateau at the time of implantation. We measured maximum pressure, mean pressure, and contact area of the intact human cadaveric knee, the knee after meniscectomy, the knee with the original meniscus removed and reimplanted as an autograft, and the knee with an allograft. Measurements were made using pressure-sensitive film in 10 specimens loaded in compression to 1000 N at 0 degrees, 15 degrees, 30 degrees, and 45 degrees of flexion. The autograft and the allograft were identically implanted by cementing bone plugs attached to the meniscal horns in anatomic transtibial tunnels and suturing the outer edge of the meniscus to the remnant of the original meniscus. A medial meniscal allograft did not consistently restore normal contact mechanics because the process of implantation and the degree of match between the original and allograft meniscus affected the immediate load-bearing performance of the transplant. However, the allograft did significantly reduce the contact pressure compared with the knee after meniscectomy. If the results from this study can be extrapolated to patients, then using an allograft to restore contact mechanics to normal may require improvements in surgical technique and graft selection.

Meniscal substitutes--human experience.

A number of clinical series have described the effect of meniscus allograft replacement in humans. The general indication has been disabling pain following loss of a meniscus in a skeletally mature individual. Overall, healing of the graft to the capsule occurs in up to 80% of all transplants. Revascularization and cell repopulation is found in all grafts but is highly variable. The risk for graft failure seems to be greater with irradiated grafts and in patients with grade III or IV osteoarthritic changes. In most series, patients experienced a decrease in pain and an increase in activity level postoperatively. In many series, concominant surgery (cruciate ligament reconstruction or osteotomy) had been performed. Meniscus replacement with frozen or cryopreserved allografts seems to give the most promising short-term results in patients with post-meniscectomy pain. Controlled, randomized prospective studies are needed to confirm a long-term benefit and better define transplantation indications. Viable meniscus allografts seem to survive transplantation, as donor cells were found in the graft after 2 years. Clinically, pain was reduced and activity increased following transplantation, but after 4 years some of these gains were lost. There was no correlation between postoperative findings on MRI and clinical outcome. Meniscal replacement with a quadriceps tendon autograft in humans resulted in pain reduction, but at second-look arthroscopy, only 2 of 9 tendon autografts looked like a meniscus. Six were in position but still looked like tendons. Total medial meniscus replacement by quadriceps tendon autrograft is still an experimental procedure. There is no proof at present that meniscal substitutes (meniscus allografts or tendon autografts) in humans can protect the hyaline cartilage of the knee from the degeneration, following loss of a meniscus. There is some evidence in animal experiments that under circumstances not yet exactly known, a meniscus substitute can have a protective effect on articular cartilage. Three factors have been identified that prevent proper meniscal function: poor fixation of the meniscal horns, no contact of the graft with the articulating surfaces under load and incorrect positioning of the horns. Meniscal allograft transplantation sensitizes humoral and cell mediated immune systems. Bone plugs attached to meniscal allograft tissue may increase cell surface antigenicity. Deep freezing and especially freeze drying of meniscal tissue decreases host immunogenicity. Cryopreservation maintains the content of donor HLA encoded antigens and is likely more sensitizing to the host. The clinical importance of immune responses to meniscal allografts is not known, but it has not been shown to result in graft failure or rejection. Prospective studies are needed.