Meniscal remodeling following partial meniscectomy--an experimental study in the dog

Augmentation of rotator cuff repair with gelatin-resorcin-formalin glue: a biomechanical study

INTRODUCTION

Rotator cuff tendons are typically reattached to the proximal humerus using transosseous sutures or suture anchors. Their primary mode of failure is at the tendon-bone interface.

METHODS

We investigated the addition of an adhesive, gelatin-resorcin-formalin (GRF) glue, to a single-row rotator cuff repair (RCR) on ex vivo sheep models. We hypothesised the addition of GRF glue would increase the repair construct strength. The study consisted of three groups of six sheep infraspinatus tendons with an inverted-mattress stitch, tension-band configuration. Group 1 was the control group where no glue was applied. Group 2 involved applying 2 × 2 cm of GRF glue to the infraspinatus footprint and a 2-min curing time. Group 3 allowed for a 15-min cure time.

RESULTS

Failure occurred at the tendon-bone-suture interface in 6/6 of the control group, and 4/6 from groups 2 and 3. Failure occurred via the suture pulling out of the anchor in 2/6 of groups 2 and 3. No significant differences were noted between all three groups in ultimate failure load, repair stiffness or total energy to failure (p > 0.05).

DISCUSSION

The addition of GRF glue to the tendon-bone-suture interface did not enhance RCR strength in an ovine model.

Systematic review of the prevalence, risk factors, diagnosis and management of meniscal injury in dogs: Part 2

OBJECTIVE

To systematically evaluate the evidence reporting the diagnosis and management of meniscal injury in dogs with cranial cruciate ligament failure.

STUDY DESIGN

Systematic literature review.

MATERIALS AND METHODS

Research questions relating to the accuracy of diagnostic techniques for meniscal injury and the effects of meniscal treatment were defined. An electronic database search of PubMed and CAB Abstracts was performed during March 2015. Data were extracted for study participants, design, intervention, outcome measures and results. Studies were evaluated using a validated instrument for assessing methodological quality and assigned a Quality Index score. A level of evidence was then assigned to each study.

RESULTS

Eighty-nine studies were identified. The median Quality Index score was 14 out of a possible 26. Twenty-seven studies were prospective case series, 31 retrospective case series, 16 animal research and 15 cadaveric studies. There were no class I or class II studies, 27 class III and 62 class IV studies.

CONCLUSIONS

Despite a large number of publications the quality of evidence was generally low. No one study or combination of studies provided high quality evidence to support one diagnostic or surgical intervention over another for meniscal injuries in dogs with cranial cruciate ligament failure.

BIORESORBABLE POLYMERIC MENISCAL PROSTHESIS: STUDY IN RABBITS

Objective: To induce growth of a neomeniscus into the pores of a prosthesis in order to protect the knee joint cartilage. Methods: 70 knees of 35 New Zealand rabbits were operated. The rabbits were five to seven months old, weighed 2 to 3.8 kilograms, and 22 were male and 13 were female. Each animal underwent medial meniscectomy in both knees during a single operation. A bioabsorbable polymeric meniscal prosthesis composed of 70% polydioxanone and 30% L-lactic acid polymer was implanted in one side. The animals were sacrificed after different postoperative time intervals. The femoral condyles and neomeniscus were subjected to histological analysis. Histograms were used to measure the degradation and absorption of the prosthesis, the growth of meniscal tissue in the prosthesis and the degree of degradation of the femoral condyle joint cartilage. Results: The data obtained showed that tissue growth histologically resembling a normal meniscus occurred, with gradual absorption of the prosthesis, and the percentages of chondrocytes on the control side and prosthesis side. Conclusion: Tissue growth into the prosthesis pores that histologically resembled the normal rabbit meniscus was observed. The joint cartilage of the femoral condyles on the prosthesis side presented greater numbers of chondrocytes in all its layers.

The collagen meniscus implant

Lesions in the meniscus occur particularly in young, active patients in the nonvascularized area which, consequently have a bad intrinsic healing capacity. This has a large impact on the mobility and function of the knee joint. Lesions, and partial lesions, lead to the progression of osteoarthritis over time in a large proportion of patients. The only clinical treatment for severe cases so far is an allograft donor meniscus, which is used mostly in patients with severe osteoarthritis with a completely destroyed meniscus. However, this technique still has to be considered as experimental and, thus, is not yet used on a routine basis. Various technical solutions have been advocated to repair meniscus lesions. One solution is to perform a partial meniscectomy and insert a collagen meniscus implant (CMI) at the site of the lesion. However, the initial mechanical properties of the collagen scaffold are inferior to the native meniscus. Therefore, it is only possible to perform a CMI implantation if the peripheral rim of the meniscus is still intact. Histology of preclinical and clinical biopsies of the implanted CMI demonstrated a repopulation of the scaffold by fibrous tissue and in time a remodeling of the fibrous tissue into fibrocartilaginous-like tissue. Based on histology, the ingrowth of new tissue into the CMI might occur by a process of synovial overgrowth, but other mechanisms of revitalization are also possible. Although some clinical studies demonstrated improvement in outcome scores, the number of patients was small in all studies and the positive effect on the prevention of progression of osteoarthritis was not compared with control groups.

Meniscectomy

To review the meniscus from a historical perspective especially on surgical management and general guidelines for arthroscopic meniscectomy procedures for various types of meniscal tears. We searched MEDLINE and PubMed for the years of 1980-2010 using the terms meniscus, meniscal repair, menisectomy, and arthroscopy. Orthopedic surgeons frequently encounter patients with pain or functional impairment of the knee joint and repair or resection of the injured meniscus is one of the most common orthopedic operative procedures. The object of meniscal surgery is to reduce pain, restore functional meniscus and prevent the development of degenerative osteoarthritis in the involved knee. Historically, total meniscectomy was a common procedure performed for meniscus tear symptoms. However, it has been reported that total meniscectomy has deleterious effects on the knee. In the past, the menisci were thought as a functionless remnant tissue. Currently, it is known that the meniscus is an important structure for knee joint function. Menisci provide several vital functions including mechanical support, localized pressure distribution, and lubrication to the knee joint. It is widely accepted that the function of the meniscus can be preserved through minimal excision. An arthroscopic partial meniscectomy preserving more of the meniscus is preferred over total meniscectomy. In recent decades, this shift toward arthroscopic partial meniscectomy has led to the development of new surgical techniques.

Evaluation of in vitro growth factor treatments on fibrochondrogenesis by synovial membrane cells from osteoarthritic and nonosteoarthritic joints of dogs

OBJECTIVE

To determine the in vitro effects of selected growth factors on fibrochondrogenesis by synovial membrane cells from nonosteoarthritic (normal) and osteoarthritic joints of dogs.

ANIMALS

5 dogs with secondary osteoarthritis of shoulder or stifle joints and 6 dogs with normal joints.

PROCEDURES

Synovial membrane cells were harvested from normal and osteoarthritic joints and cultured in monolayer with or without (control) basic fibroblast growth factor, transforming growth factor-β1, and insulin-like growth factor-1. In the cultured cells, fibrochondrogenesis was measured by use of a real-time reverse transcriptase PCR assay to determine relative expressions of collagen I, collagen II, and aggrecan genes and of 3 genes involved in embryonic chondrogenesis: Sry-type homeobox protein-9 (SOX-9), frizzled-motif associated with bone development (Frzb), and regulator of G-protein signaling-10 (RGS-10). Tissue collagen content was measured via a hydroxyproline assay, and sulfated glycosaminoglycan content was measured via a 1,9-dimethylmethylene blue assay. Cellularity was determined via a double-stranded DNA assay. Immunohistochemical analysis for collagens I and II was also performed.

RESULTS

In vitro collagen synthesis was enhanced by growth factor stimulation. Although osteoarthritic-joint synoviocytes could undergo a fibrocartilage-like phenotypic shift, their production of collagenous extracellular matrix was less than that of normal-joint synoviocytes. Gene expressions of SOX-9 and RGS-10 were highest in the osteoarthritic-joint cells; Frzb expression was highest in growth factor treated cells.

CONCLUSIONS AND CLINICAL RELEVANCE

Autogenous synovium may be a viable cell source for meniscal tissue engineering. Gene expressions of SOX-9 and RGS-10 may be potential future targets for in vitro enhancement of chondrogenesis.

An in vitro model to assess mechanisms and efficacy of a cellular conduit for treatment of avascular meniscal injuries

Tears in the avascular portion of the knee meniscus are commonplace and are frequently incapable of healing spontaneously. Delivery of synovial cells from the meniscal periphery to avascular injuries can result in an effective healing response but is difficult to accomplish surgically. This report describes the development of a novel in vitro model comprised of three-dimensionally cultured cells in agarose used to assess the proof of concept that a cellular conduit device could be used to facilitate the delivery of synovial fibroblasts from a cell source to a remote acellular recipient site. The results indicate that synovial fibroblasts are capable of migrating through a cellular conduit more optimally than a created trephined channel over a clinically relevant distance in response to a chemotactic gradient. This model proved to be a reliable way to assess fibroblast-like synoviocyte migration in a clinically relevant fashion for application to avascular meniscal tear healing methodologies, and provided mechanistic information regarding the successful in vivo testing of this specific biomedical device.

Regional multilineage differentiation potential of meniscal fibrochondrocytes: implications for meniscus repair

The knee menisci are wedge-shaped semilunar fibrocartilaginous structures that reside between the femur and tibia and function to transmit and distribute load. These structures have characteristics of both fibrous and cartilaginous tissues. The cartilage-like inner region and the fibrous vascularized outer region each has a distinct extracellular matrix, and resident meniscal fibrochondrocytes (MFCs) with distinct morphologies dependent on their location. Damage to the meniscus is common, and disruption of tissue structure and function result in erosion of the underlying articular cartilage. It has been observed that damage in the vascular periphery undergoes spontaneous repair, whereas damage of the inner region does not heal. While vascularity of the peripheral region plays a role in healing, recent findings have also suggested that local cellular composition influences local healing capacity. This study examined the variation in multipotential characteristics of cell populations isolated from different regions of the bovine meniscus. MFCs were isolated from the outer (vascular), inner (avascular), and horn (mixed) regions and induced toward chondrogenic, adipogenic, and osteogenic lineages. The results of this study suggest that MFCs from all regions of the meniscus possess a multilineage differentiation capability, particularly toward chondrogenesis and adipogenesis. MFCs from the outer region were most plastic, differentiating along all three mesenchymal lineages. These findings may underlie the experimental observation of improved integration of meniscus grafts from the outer zone and may have implications for developing strategies of cell-based meniscus repair.

Effects of dynamic compressive load on collagen-based scaffolds seeded with fibroblast-like synoviocytes

Synoviocytes have been speculated to play potential reparative and remodeling roles in vascular meniscal injuries. In addition, synoviocytes may mediate the transformation of intraarticularly placed collagen-based scaffolds into fibrocartilage through exposure to dynamic compressive loads. The objectives of this study were to assess the feasibility of using fibroblast-like synoviocytes (FLS) to engineer meniscal-like fibrocartilage and to better understand the mechanosensitivity of FLS by seeding them onto collagen scaffolds exposed to dynamic compressive loads. Canine FLS were seeded onto disks of four commercially available collagen-based scaffolds (Restore, Permacol, Cuff Patch, and Graff Jacket) and subjected either to one of two levels of intermittent dynamic compressive load or no load. The disks were harvested at 1 and 2 weeks and assessed for cell viability, retention, and infiltration, as well as extracellular matrix production. In general, loading regimens decreased cellularity, and nonloaded Restore grafts retained the most cells across time intervals. Spatial distribution of FLS was optimized in Restore grafts and was overall better in non-crosslinked collagen scaffolds (Restore and Graft Jacket) than cross-linked matrices. Collagen production was noted in association with penetrating FLS clusters in the Restore scaffolds only. The applied biomechanical stimulus did not appear to induce fibrochondrogenesis in any treatment group. These data suggest that Restore scaffolds may foster greater cell retention and infiltration when compared to other commercially available, collagen-based biomatrices.

Meniscal Repair With Fibrocartilage Engineering

Injuries to the knee meniscus, particularly those in the avascular region, pose a complex problem and a possible solution is tissue engineering of a replacement tissue. Tissue engineering of the meniscus involves scaffold selection, addition of cells, and stimulation of the construct to synthesize, maintain, or enhance matrix production. An acellular collagen implant is currently in clinical trials and there are promising results with other scaffolds, composed of both polymeric and natural materials. The addition of cells to these constructs may promote good matrix production in vitro, but has been studied in a limited manner in animal studies. Cell sources ranging from fibroblasts to stem cells could be used to overcome challenges in cell procurement, expansion, and synthetic capacity currently encountered in studies with fibrochondrocytes. Manipulation of construct culture with exogenous growth factors and mechanical stimulation will also likely play a role in these strategies.

Histological and biochemical changes of experimental meniscus tear in the dog knee

BACKGROUND

When degeneration is noted in the meniscus, sutures should not be applied even for a tear of the vascularized region of the meniscus because the meniscus may rerupture after suturing. In this study, the degeneration process of bucket-handle tear of the meniscus was investigated using histological and biochemical markers.

METHODS

A bucket-handle tear in the intercondylar notch was prepared in the dog knee. Eight animals each were killed at 2, 4, 12, 24, and 48 weeks; and changes in the articular cartilage were observed. The cell count and morphology in the meniscus were investigated by hematoxylin and eosin staining, and glycosaminoglycans in the matrix were investigated by toluidine blue staining. Glycosaminoglycans were also measured by high-performance liquid chromatography.

RESULTS

Erosion was noted in the weight-bearing region of the articular cartilage after 12 weeks. The cell count in the meniscus was markedly decreased at 48 weeks. Regarding cell morphology, fibrochondrocytes remained in the meniscus until 12 weeks. The cell morphology varied at 24 weeks, but the number of cells was maintained. Cell proliferation, mainly fibroblasts, was noted from 2 weeks and 4 weeks after surgery in the periphery and body of the meniscus, respectively. Fibrochondrocyte-like cells proliferated from 12 weeks in the meniscal body, and metachromasia was detected by toluidine blue staining, indicating meniscal repair. A marked decrease in glycosaminoglycans was noted at 48 weeks, which was consistent with the decrease in the cell count in the meniscus.

CONCLUSIONS

Early application of sutures is desirable for bucket-handle tear of the meniscus because lesions appear in the cartilage within 12 weeks, but suturing may be performed until 24 weeks because of the absence of obvious meniscal degeneration. However, disorder of the meniscus progresses after 48 weeks and may affect the outcome of the meniscal suture.

The effects of cyclic mechanical strain and tumor necrosis factor alpha on the response of cells of the meniscus

OBJECTIVES

Cells of the knee meniscus respond to changes in their biochemical and biomechanical environments with alterations in the biosynthesis of matrix constituents and inflammatory mediators. Tumor necrosis factor alpha (TNF-alpha) is a pro-inflammatory cytokine that is involved in the pathogenesis of both osteoarthritis and rheumatoid arthritis, but its influence on meniscal physiology or mechanobiology is not fully understood. The objectives of this study were to examine the hypothesis that cyclic mechanical strain of meniscal cells modulates the biosynthesis of matrix macromolecules and pro-inflammatory mediators, and to determine if this response is altered by TNF-alpha.

METHODS

Cells were isolated from the inner two-thirds of porcine medial menisci and subjected to biaxial tensile strain of 5-15% at a frequency of 0.5Hz. The synthesis of proteoglycan, protein, nitric oxide (NO), and prostaglandin E(2) were determined.

RESULTS

Cyclic tensile strain increased the production of nitric oxide through the upregulation of nitric oxide synthase 2 (NOS2) and also increased synthesis rates of prostaglandin E(2), proteoglycan, and total protein in a manner that depended on strain magnitude. TNF-alpha increased the production of NO and total protein, but inhibited proteoglycan synthesis rates. TNF-alpha prevented the mechanical stimulation of proteoglycan synthesis, and this effect was not dependent on NOS2.

CONCLUSIONS

These findings indicate that pro-inflammatory cytokines can modulate the responses of meniscal cells to mechanical signals, suggesting that both biomechanical and inflammatory factors could contribute to the progression of joint disease as a consequence of altered loading of the meniscus.

Prospective evaluation of 1485 meniscal tear patterns in patients with stable knees

BACKGROUND

Despite emphasis on classifying meniscal tears based on healing potential of the tear, research has concentrated on unstable knees, and few reports have provided information regarding associated clinical variables in stable knees.

PURPOSE

To report on a large series of meniscal tears in stable knees that have been carefully mapped by tear shape and tear zones to allow comparison with meniscal tears in unstable knees.

STUDY DESIGN

Prospective case series, reviewed retrospectively.

METHODS

A total of 1485 meniscal tears in stable knees were evaluated. Preoperatively, each patient underwent a standardized assessment. Each tear was carefully mapped at arthroscopy. Statistical analysis was performed to determine factors that may be associated with peripheral meniscal tears.

RESULTS

The distribution and shape of tears varied significantly within the radial and circumferential zones in this stable knee population. Five prospective variables were associated with peripheral tears: gender, presence of an effusion, positive McMurray test, varus alignment, or a loss of extension more than 5 degrees.

CONCLUSIONS

Patient demographic information and physical examination can be useful in identifying patients who may have a peripheral meniscus tear.

Regulation of matrix turnover in meniscal explants: role of mechanical stress, interleukin-1, and nitric oxide

The meniscus is an intra-articular fibrocartilaginous structure that serves essential biomechanical roles in the knee. With injury or arthritis, the meniscus may be exposed to significant changes in its biochemical and biomechanical environments that likely contribute to the progression of joint disease. The goal of this study was to examine the influence of mechanical stress on matrix turnover in the meniscus in the presence of interleukin-1 (IL-1) and to determine the role of nitric oxide (NO) in these processes. Explants of porcine menisci were subjected to dynamic compressive stresses at 0.1 MPa for 24 h at 0.5 Hz with 1 ng/ml IL-1, and the synthesis of total protein, proteoglycan, and NO was measured. The effects of a nitric oxide synthase 2 (NOS2) inhibitor were determined. Dynamic compression significantly increased protein and proteoglycan synthesis by 68 and 58%, respectively, compared with uncompressed explants. This stimulatory effect of mechanical stress was prevented by the presence of IL-1 but was restored by specifically inhibiting NOS2. Release of proteoglycans into the medium was increased by IL-1 or mechanical compression and further enhanced by IL-1 and compression together. Stimulation of proteoglycan release in response to compression was dependent on NOS2 regardless of the presence of IL-1. These finding suggest that IL-1 may modulate the effects of mechanical stress on extracellular matrix turnover through a pathway that is dependent on NO.

Chondropathy after meniscal tear or partial meniscectomy in a canine model

A primary goal in considering treatment for meniscal injuries is the preservation of the health of the articular cartilage. However, the chondroprotective effects of various techniques for meniscal injury treatments are unknown. We used a canine model to quantify articular cartilage degeneration in the medial compartment of the canine knee, resulting from a surgically created tear or a partial meniscectomy (PM) of the posterior region of the medial meniscus (each group, n = 10). After sacrifice at 12 weeks, the development of gross chondropathy and the changes in cartilage tensile stiffness were quantified, and correlations between these measurements were examined. Both treatment surgical treatment groups caused significantly greater gross chondropathy as compared to the unoperated contralateral controls. Cartilage tensile stiffness was significantly lower than unoperated controls by nearly 28% in both experimental groups. However, there were no significant differences observed between the gross chondropathy or the cartilage mechanical property changes between the experimental groups. Importantly, the severity of gross chondropathy was found to significantly correlate with the decrement in tensile stiffness properties of the articular cartilage. These findings indicate that significant degeneration of canine articular cartilage develops to a similar degree in the presence of a partially healed meniscus tear or a PM of the knee.

Kinetic study of the replacement of porcine small intestinal submucosa grafts and the regeneration of meniscal-like tissue in large avascular meniscal defects in dogs

Porcine small intestinal submucosa (SIS) was used to replace large, avascular defects in the medial menisci of dogs. Twelve dogs received SIS grafts and 3 dogs were left untreated as controls. Dogs were evaluated at 4, 8, and 12 weeks by means of lameness scoring and ultrasonography. Dogs were sacrificed at 1, 6, or 12 weeks after implantation, and the tissue at the site of meniscal resection was evaluated for gross and histologic appearance, cross-sectional and surface area, and collagen types I and II. The femoral and tibial condyles were assessed for articular cartilage damage. Control dogs were significantly more lame than grafted dogs 8 and 12 weeks after instrumentation. Grafted dogs' replacement tissue appeared meniscal-like when evaluated grossly and ultrasonographically 12 weeks after instrumentation. The amount of replacement tissue was significantly greater in both cross-sectional and surface area for grafted dogs than for controls at all time points. Histologically, the SIS biomaterial could be identified in all grafted dogs at 1 week post-implantation, but in none at 6 weeks post-implantation. Subjectively, grafted dogs' replacement tissue was histologically superior to that of controls with respect to tissue type, organization, and architecture. Collagen types I and II immunoreactivity in grafted menisci were similar to that of normal menisci. Control dogs had significantly more articular cartilage damage than grafted dogs. SIS appears to induce regeneration of meniscal-like tissue in large, avascular meniscal defects in dogs, resulting in superior clinical function and articular cartilage protection compared to ungrafted controls.

Toward tissue engineering of the knee meniscus

This review details current efforts to tissue engineer the knee meniscus successfully. The meniscus is a fibrocartilaginous tissue found within the knee joint that is responsible for shock absorption, load transmission, and stability within the knee joint. If this tissue is damaged, either through tears or degenerative processes, then deterioration of the articular cartilage can occur. Unfortunately, there is a dearth in the amount of work done to tissue engineer the meniscus when compared to other musculoskeletal tissues, such as bone. This review gives a brief overview of meniscal anatomy, biochemical properties, biomechanical properties, and wound repair techniques. The discussion centers primarily on the different components of attempting to tissue engineer the meniscus, such as scaffold materials, growth factors, animal models, and culturing conditions. Our approach for tissue engineering the meniscus is also discussed.

The long-term effects of hyaluronan during development of osteoarthritis following partial meniscectomy in a rabbit model

OBJECTIVE

The long-term effect of hyaluronan (HA) on meniscus remodeling and articular cartilage preservation was assessed during the development of osteoarthritis following partial meniscectomy in a rabbit model.

DESIGN

Approximately 60% of the region of each medial meniscus of 20 rabbit knees was excised bilaterally. The left knee joint was treated with five weekly intraarticular injections of 0.3 ml of HA, beginning 1 week after surgery. The right control knee was injected with PBS on the same schedule. Six months after surgery, animals were killed and the medial menisci and tibial articular cartilage were evaluated morphologically, histologically and biochemically.

RESULTS

Meniscal regeneration was observed as newly synthesized translucent tissue, and image analysis revealed that the amount of this tissue was significantly greater in the HA-treated menisci than in the vehicle-treated menisci. Safranin-O staining and image analysis revealed the increased presence of glycosaminoglycans in the HA-treated menisci relative to vehicle-treated menisci while vascularity and biochemical parameters (hydration, total GAGs and reducible collagen crosslinks) were statistically similar in HA- and vehicle-treated menisci. Gross morphologic grading with India ink revealed a trend for less deterioration of tibial articular cartilage in the HA group (P=0.09) while Mankin's score of the HA-treated tibial articular cartilage was marginally lower than that of the vehicle group (P=0.06). Biochemical assessments showed a trend for higher total GAGs concentration in the HA-treated articular cartilage when compared to the vehicle treatment group (P=0.06).

CONCLUSION

The present study has demonstrated that following partial meniscectomy, treatment with hyaluronan can enhance meniscal regeneration and may inhibit articular cartilage degeneration as long as six months post surgery.

Meniscal injury and repair: clinical status

Repair or resection of meniscal injuries is one of the most common operative procedures in orthopedics today. A variety of techniques for reconstruction have been attempted and experts are still unsure which treatment of meniscal lesions is best. This article reviews different techniques of meniscal repair and some novel approaches that may be used for treatment of meniscal lesions in the coming years.

Current and future directions for meniscus repair and replacement

Torn meniscal cartilages and the consequences of missing meniscus tissue represent the major indications for operative arthroscopy of the knee. After recognizing the importance of the meniscus, clinicians made the shift away from complete meniscectomy to partial meniscectomy aided by the development of arthroscopic instrumentation. Despite extensive basic science data showing the importance of a complete meniscus for normal force transference, meniscus repair occurs in less than 10% of all meniscal tears found at arthroscopy. This paper will discuss the reasons for the common clinical approach and compare that approach with an aggressive approach of salvaging and replacing meniscus tissue, and will offer speculations about future directions for meniscus repair, reconstruction, and replacement.

Technical pitfalls of meniscal surgery

Meniscal surgery is one of the most common orthopedic procedures performed today. Orthopedic surgeons must be familiar with the indications for meniscal excision versus repair and comfortable with the diverse instrumentation used for both techniques. Numerous pitfalls exist in diagnosis, indication, and technical aspects of surgery but can be minimized or avoided by careful preoperative planning and attention to detail during the surgical procedure.

Function of the normal meniscus and consequences of meniscal resection

The principal functions of the meniscus are load transmission and shock absorption, based on the meniscal collagen architecture, the biochemical fluid composition, and the proteoglucan-collagen meshwork. The mobile menisci transmit 50-90% of load over the knee joint, depending on knee flexion angle, femoral translation and rotation. The meniscus contributes to knee joint proprioception and probably also to joint stability. Late consequences of total and partial meniscectomy are radiographic osteoarthritis, with a varying percentage of these patients having symptoms. Malalignment, concomitant articular cartilage lesions, and ligament instability are absolute risk factors, while age, lateral compartment, and continued sport activity are relative risk factors. Acute reinsertion of meniscal tears in the red-red or red-white zones can be performed successfully by arthroscopic technique. Also in chronic tears stable healing can be expected in most cases, if the scar tissue is resected.

Acute and long-term response of the meniscus to partial meniscectomy using the holmium: YAG laser

The purpose of this study was to evaluate the histological effects of holmium:YAG laser partial meniscectomy in an in vivo rabbit model and compare it with scalpel partial meniscectomy at selected time intervals. Twenty-four adult male New Zealand rabbits underwent bilateral partial medial meniscectomies through the avascular zone. In the right knee, partial medial meniscectomy was performed using a standard surgical blade; in the left knee, an anatomically similar partial medial meniscectomy was performed using a Ho:YAG laser (Coherent, Santa Clara, CA). All animals were randomized and three animals were killed at postoperative days I and 3, and postoperative weeks 1, 2, 3, 4, 6, and 10. Samples of all medial and lateral menisci, with attached synovium and vascular rim, from both knees were harvested and submitted for histological and/or ultrastructural examination. The results indicate that (1) at all time periods, laser cut menisci had more cell loss and matrix degradation; (2) synovial necrosis was more common in laser-treated knees; (3) the Ho:YAG laser creates three zones of damage in the meniscal fibrocartilage: a zone of fibrin and debris at the incision site, a zone of necrosis characterized by degeneration of the collagen and loss of viable cells, and a zone of thermal change characterized by collagen degeneration. The zone of thermal change, with its histological injury was thought at the time of surgery to be the viable border. The zone of thermal change may act as a barrier to delay healing, and the scalpel produced a consistently straighter cut.

Evaluation of fibrocartilage regeneration and bone response at full-thickness cartilage defects in articulation with pyrolytic carbon or cobalt-chromium alloy hemiarthroplasties

Hemiarthroplasty is one method used to treat osteoarthritic joints. Often, however, an adverse response of the articular cartilage to the metal implants occurs. The purpose of this study was to evaluate and compare the response of a surgically created defect to pyrolytic carbon and cobalt-based alloy hemiarthroplasties. The cartilage on the lateral side of the tibial plateau of a canine knee joint was abraded to create a full-thickness defect. Two small holes were drilled into the exposed subchondral bone. Next, either a carbon or metal implant was placed in the lateral femoral condyle. The implantation period was 1 year. Histologic examination of the tibial defects revealed a smooth bony surface for both implant groups. In addition, there was no evidence of a residual adverse inflammatory response nor of a significant increase in subchondral bone formation for either group. Surface cracks resulting from the presence of the implant were seen in 14% of the carbon implant specimens and in 100% of the metal implants. Fibrocartilage regeneration was seen in 86% of the carbon implants and in 25% of the metal implants. Thus the carbon appears to be better tolerated mechanically compared to wrought cobalt-chromium alloy. Pyrolytic carbon shows promise for use in hemiarthroplasty.

Regeneration of meniscal cartilage with use of a collagen scaffold. Analysis of preliminary data

A collagen scaffold was designed for use as a template for the regeneration of meniscal cartilage and was tested in ten patients in an initial, Food and Drug Administration-approved, clinical feasibility trial. The goal of the study was to evaluate the implantability and safety of the scaffold as well as its ability to support tissue ingrowth. The study was based on the findings of in vitro and in vivo investigations in dogs that had demonstrated cellular ingrowth and tissue regeneration through the scaffold. Nine patients remained in the study for at least thirty-six months, and one patient voluntarily withdrew after three months for personal reasons. The collagen scaffold was found to be implantable and to be safe over the three-year period. Histologically, it supported regeneration of tissue in meniscal defects of various sizes. No adverse immunological reactions were noted on sequential serological testing. On second-look arthroscopy, performed either three or six months after implantation, gross and histological evaluation revealed newly formed tissue replacing the implant as it was resorbed. At thirty-six months, the nine patients reported a decrease in the symptoms. According to a scale that assigned 1 point for strenuous activity and 5 points for an inability to perform sports activity, the average score was 1.5 points before the injury, 3.0 points after the injury and before the operation, and 2.4 points at six months postoperatively, 2.2 points at twelve months, 2.0 points at twenty-four months, and 1.9 points at thirty-six months. According to a scale that assigned 0 points for no pain and 3 points for severe pain, the average pain score was 2.2 points preoperatively and 0.6 point thirty-six months postoperatively. One patient, who had had a repair of a bucket-handle tear of the medial meniscus and augmentation with the collagen scaffold, had retearing of the cartilage nineteen months after implantation. Another patient had debridement because of an irregular area of regeneration at the scaffold-meniscus interface twenty-one months after implantation. Magnetic resonance imaging scans demonstrated progressive maturation of the signal within the regenerated meniscus at three, six, twelve, and thirty-six months. These findings suggest that regeneration of meniscal cartilage through a collagen scaffold is possible. Additional studies are needed to determine long-term efficacy.

The effects of hyaluronan on the meniscus and on the articular cartilage after partial meniscectomy

The effect of hyaluronan (molecular weight = 8 x 10(5)) on the meniscus and on the articular cartilage was assessed after partial meniscectomy in a rabbit model. On gross examination, remodeled meniscus appeared as newly synthesized translucent tissue, and was seen in both vehicle- and hyaluronan-treated menisci. Histologically, safranin O staining revealed the strong presence of glycosaminoglycans in the newly remodeled tissue, and polarized light demonstrated the absence of mature collagen architecture. Hydration of the hyaluronan-treated menisci was significantly less than that of the vehicle-treated menisci, and the reducible collagen cross-link dihydroxylysinonorleucine was significantly increased in the hyaluronan-treated menisci compared with the vehicle-treated menisci, indicative of a greater degree of collagen remodeling. In situ hybridization of vehicle- and hyaluronan-treated menisci revealed a high level of type I procollagen mRNA expression and minor expressions of types II and III mRNA. Expression of the type I collagen gene appeared to be more pronounced in the hyaluronan-treated menisci than in the vehicle-treated menisci. The tibial plateaus revealed mild cartilage fibrillation after partial meniscectomy. A statistically significant difference between vehicle- and hyaluronan-treated cartilage was not demonstrated in the present study because of the slow development (i.e., 12 weeks) of osteoarthritis after partial meniscectomy in the rabbit model. These results suggest that in the rabbit model, hyaluronan enhances collagen remodeling and inhibits meniscal swelling after partial meniscectomy in the avascular region.

Meniscal repair by fibrocartilage? An experimental study in the dog

Longitudinal lesions in the avascular part of the dog's meniscus were repaired by implantation of a porous polyurethane. Ingrowing repair tissue was characterized by biochemical and immunological analysis. Histologically, repair tissue initially was composed of fibrous tissue containing type I collagen. After 3 months, fibrocartilaginous tissue developed inside the implants, whereas control defects only showed fibrous repair tissue. Both type I and II collagen, the major collagen types of normal meniscal fibrocartilage, could be detected in this newly formed fibrocartilage. It is concluded that fibrocartilage resembling normal meniscal tissue is formed and that longitudinal lesions can be healed after meniscal repair by implantation of a porous polymer.

Characteristics of the immediate postarthroscopic blood clot formation in the knee joint

The immediate postoperative bleeding and blood clot formation was observed in 26 human knee joints following a variety of arthroscopic surgical procedures. Observations were made following lavage with lactated Ringer's and normal saline solutions. Bleeding occurred from all incised vascular tissue. Blood clot accumulated after each solution within 5 min following tourniquet release and decompression of the joint. Most of the blood clot remained unattached within the joint cavity. Blood clot did attach to all surgically incised or excised surfaces. The clinical relevance of these observations is related to the potential role of the blood clot in intraarticular tissue repair following arthroscopic surgery.

Effects of irrigation fluid on human menisci: an experimental comparison of water, normal saline, and glycine

A technique has been developed to demonstrate the macroscopic morphology of collagen fiber arrangement in human menisci. It was observed that 0.9% normal saline solution removed the ground substance of the meniscus, leaving intact collagen bundles. This suggests that meniscal damage may occur as a direct result of using normal saline for irrigation during knee arthroscopy. Experiments were conducted using demineralized water and 1.5% glycine for comparison. The disruption of collagen fiber binding in the meniscus by normal saline is time and temperature dependent. Glycine solution causes fibroblast lysis and a lesser degree of collagen alteration. Demineralized water can cause edema in the fibroblast but no notable change in collagen fibers. None of the irrigation solutions tested has proved to be completely safe. Demineralized water is not the ideal solution but is preferable to normal saline or glycine solution, especially when it can be used in conjunction with electrosurgery.

Meniscal repair following meniscectomy: mechanism and protective effect. Experimental study in the dog

Meniscal repair was studied to evaluate the mechanism and its potential protective effects on the articular cartilage in an experimental model consisting of 68 knees of adult dogs on which five different types of medial meniscectomy were performed. The results were assessed by macroscopic, microangiographic, and histological methods, after a sequential follow-up period of 10-450 days. Two different mechanisms of meniscal repair were observed, depending on whether meniscal section had been performed in vascular (total meniscectomy) or avascular (subtotal or partial meniscectomy) zones. It was also observed that the repaired meniscal tissue does not prevent articular cartilage degeneration. This is more closely related to the size of the meniscal fragment preserved at meniscectomy. Due to the biomechanical importance of the meniscus and the lack of functional relevance of the repaired meniscal tissue, the most conservative approach possible to meniscectomy is recommended.

The use of the contact Nd:YAG laser in arthroscopic surgery: effects on articular cartilage and meniscal tissue

The contact Nd:YAG laser's small size, tip variety, fiberoptic application, and suitability for use in a saline medium make it a particularly appealing tool for use in arthroscopic procedures. This study was performed to investigate the laser's effects on articular cartilage and meniscal tissue with respect to depth of damage (canine cadaver model) and healing response (rabbit model). Depth of damage in the canine cadaver model was greater in meniscal tissue than in articular cartilage at each wattage level. In the presence of a saline bath, depth damage in both tissues was diminished. Scalpel articular cartilage lesions showed no response over time. Electrocautery lesions uniformly showed significant wide margins of hyaline cartilage necrosis which increased over time. Laser articular cartilage lesions showed vigorous healing responses characterized by fibrocartilage healing by 6 weeks. Scalpel meniscectomies showed characteristic fibrocartilagenous remodeling by 6 weeks, while electrocautery meniscectomies showed wide margins of necrosis with no specimen showing remodeling capability. Laser meniscectomies showed an intermediate response with a small number of menisci remodeling in a normal fashion. This article represents the first comprehensive look at the effects of the Nd:YAG laser on articular cartilage and meniscal tissue in terms of depth of damage and healing response over time, and indicates this laser's biological advantage over scalpel and electrocautery in arthroscopic procedures.

Treatment of longitudinal injuries in avascular area of meniscus in dogs by trephination

A study promoting the healing of longitudinal injuries in an avascular area of the meniscus in 21 male dogs is reported. One horizontal hole from the peripheral vasculature to one of the artificial longitudinal injuries to both medial menisci of the knee in each dog was made with a needlelike trephine. The knee joints were not immobilized and the samples were taken 2, 4, 8, 12, and 24 weeks, respectively, after the operation. [3H]Thymidine was injected into the joint cavity 72 h before the sample was taken. Healed lengths were measured, and pathologic examinations and autoradiography were performed. The results showed that all of the injuries treated with trephination were partly or totally healed whereas those in controls were not healed at all, suggesting that trephination may be the procedure of choice for clinic orthopedists dealing with such injuries. By the 8th week, the healed length stopped increasing, the scar tissue began to mature, and the DNA synthesis of the fibroblasts in the granulation tissue and the fibrochondrocytes in the trephined meniscus reduced. It is thought that the fibrochondrocyte of the meniscus and the fibroblast in the granulation might be capable of obtaining the thymidine directly from the synovia of knee joint for their DNA metabolism. Multiplication of the fibrochondrocyte in the injured meniscus was also found.