Meniscal Substitution Research Articles

Addressing meniscal deficiency part 2: An umbrella review of systematic reviews and meta-analyses on meniscal scaffold-based approaches.

Meniscal injuries are common in knee surgery and often require preservation techniques to prevent secondary osteoarthritis. Despite advancements in repair techniques, some patients undergo partial meniscectomy, which can lead to postmeniscectomy syndrome. To address these challenges, meniscal substitution techniques like scaffolds have been developed. However, a comprehensive synthesis of the existing evidence through an umbrella review is lacking. A comprehensive search was conducted in the MEDLINE, Embase and Scopus databases to identify relevant systematic reviews and meta-analyses. Studies were screened based on predefined inclusion and exclusion criteria. The quality of included studies was assessed using the AMSTAR-2 tool. A total of 17 studies met the inclusion criteria and were included in the review. Most studies focused on the use of collagen-based scaffolds, with fewer studies evaluating synthetic scaffolds. The majority of studies (52.9%) were rated as having 'Critically Low' overall confidence, with only one study (5.9%) rated as 'High' confidence and most studies exhibiting methodological limitations, such as small sample sizes and lack of long-term follow-up. Despite these limitations, the majority of studies reported positive short-term outcomes, including pain relief and functional improvement, following scaffold implantation. However, some studies noted a relatively high failure rate. Radiographically, outcomes also varied, with some studies reporting morphological deterioration of the implant seen on MRI, while others noted possible chondroprotective effects. Meniscal scaffold-based approaches show promise in the management of meniscal deficiency; however, the current evidence is limited by methodological shortcomings. One notable gap in the literature is the lack of clear guidelines for patient selection and surgical technique. Future research should focus on conducting well-designed randomized controlled trials with long-term follow-up to further elucidate the benefits and indications of these techniques in clinical practice. Additionally, efforts should be made to develop consensus guidelines to standardize the use of meniscal scaffolds and improve patient outcomes. Despite limited availability, synthesizing the literature on meniscal scaffold-based approaches is crucial for understanding research, guiding clinical decisions and informing future directions. Level IV.

Optimized Allogenic Decellularized Meniscal Scaffold Modified by Collagen Affinity Stromal Cell–Derived Factor SDF1α for Meniscal Regeneration: A 6- and 12-Week Animal Study in a Rabbit Model

Background: Total meniscectomy for treating massive meniscal tears may lead to joint instability, cartilage degeneration, and even progressive osteoarthritis. The meniscal substitution strategies for advancing reconstruction of the meniscus deserve further investigation. Hypothesis: A decellularized meniscal scaffold (DMS) modified with collagen affinity stromal cell–derived factor (C-SDF1α) may facilitate meniscal regeneration and protect cartilage from abrasion. Study Design: Controlled laboratory study. Methods: The authors first modified DMS with C-SDF1α to fabricate a new meniscal graft (DMS-CBD [collagen-binding domain]). Second, they performed in vitro studies to evaluate the release dynamics, biocompatibility, and differentiation inducibility (osteogenic, chondrogenic, and tenogenic differentiation) on human bone marrow mesenchymal stem cells. Using in vivo studies, they subjected rabbits that received medial meniscectomy to a transplantation procedure to implement their meniscal graft. At postoperative weeks 6 and 12, the meniscal regeneration outcomes and chondroprotective efficacy of the new meniscal graft were evaluated by macroscopic observation, histology, micromechanics, and immunohistochemistry tests. Results: In in vitro studies, the optimized DMS-CBD graft showed notable biocompatibility, releasing efficiency, and chondrogenic inducibility. In in vivo studies, the implanted DMS-CBD graft after total meniscectomy promoted the migration of cells and extracellular matrix deposition in transplantation and further facilitated meniscal regeneration and protected articular cartilage from degeneration. Conclusion: The new meniscal graft (DMS-CBD) accelerated extracellular matrix deposition and meniscal regeneration and protected articular cartilage from degeneration. Clinical Relevance: The results demonstrate that the DMS-CBD graft can serve as a potential meniscal substitution after meniscectomy.

Advances in the Mechanisms Affecting Meniscal Avascular Zone Repair and Therapies.

Injuries to menisci are the most common disease among knee joint-related morbidities and cover a widespread population ranging from children and the general population to the old and athletes. Repair of the injuries in the meniscal avascular zone remains a significant challenge due to the limited intrinsic healing capacity compared to the peripheral vascularized zone. The current surgical strategies for avascular zone injuries remain insufficient to prevent the development of cartilage degeneration and the ultimate emergence of osteoarthritis (OA). Due to the drawbacks of current surgical methods, the research interest has been transferred toward facilitating meniscal avascular zone repair, where it is expected to maintain meniscal tissue integrity, prevent secondary cartilage degeneration and improve knee joint function, which is consistent with the current prevailing management idea to maintain the integrity of meniscal tissue whenever possible. Biological augmentations have emerged as an alternative to current surgical methods for meniscal avascular zone repair. However, understanding the specific biological mechanisms that affect meniscal avascular zone repair is critical for the development of novel and comprehensive biological augmentations. For this reason, this review firstly summarized the current surgical techniques, including meniscectomies and meniscal substitution. We then discuss the state-of-the-art biological mechanisms, including vascularization, inflammation, extracellular matrix degradation and cellular component that were associated with meniscal avascular zone healing and the advances in therapeutic strategies. Finally, perspectives for the future biological augmentations for meniscal avascular zone injuries will be given.

Labral reconstruction with polyurethane implant.

Surgical treatment of labral injuries has shifted from debridement to preservation over the past decades. Primary repair and secondary augmentation or reconstruction techniques are aimed at restoring the labral seal and preserving or improving contact mechanics. Currently, the standard of care for non-repairable tears favours the use of auto- or allografts. As an alternative, we present our initial experience using a synthetic, off-the-shelf polyurethane scaffold for augmentation and reconstruction of segmental labral tissue loss or irreparable labral damage. Three patients aged 37–44 (two male, one female) with femoroacetabular impingement without associated dysplasia (Wiberg > 25°) or osteoarthritis (Tönnis <2) were included in this series. Labral reconstruction (one case) and augmentation (two cases) were performed using a synthetic polyurethane scaffold developed for meniscal substitution (Actifit®, Orteq Ltd, London, UK) and adapted to the hip. Clinical results were analysed with patient-reported outcomes (PROMs) using non-arthritic hip score (NAHS) and daily live activities hip outcome score (DLA HOS) and magnetic resonance images (MRI) at 2- and 4-year follow-up. Clinically improvement was seen in all PROMs at 4 years. The NAHS scores improved from 57.7 to 82.3 (50.9% improvement) and HOS from 59 to 79.3 (35.3% improvement). Last follow-up MRIs confirmed the presence of the scaffold; however, the scaffold signal was still hyperintense compared to native labrum. There was no shrinkage in any scaffold and no progression to hip osteoarthritis seen. Reconstruction or augmentation of segmental labral defects with a polyurethane scaffold may be an effective procedure. At 4 years after implantation, our small cases series resulted in improved hip joint function, reduced pain and scaffold preservation on follow-up imaging.

Ongoing MRI remodeling 3–7 years after collagen meniscus implantation in stable knees

The purpose of the present study was to evaluate the clinical and radiological 3-7years outcomes of patients who underwent collagen meniscus implantation in stable or stabilized knees. It was the hypothesis that using the collagen meniscus (CMI) good clinical 3-7years outcomes with low pain levels are achieved. Thirty-nine patients (male:female = 30:9, mean age 34 ± 10years) underwent arthroscopic CMI after subtotal medial (n = 32) or lateral meniscectomy (n = 7). A 7-mm CMI was performed due to prophylactic (n = 25) or therapeutic indication (n = 14). IKDC score, Tegner score preinjury, preoperatively and at follow-up, Lysholm score and visual analogue scale for pain and satisfaction (follow-up rate 90%) were assessed. MRI scans were analyzed according to the Genovese criteria (n = 19). Implant failure was defined as infection or mechanical failure of the device. The minimum follow-up time was 36months (range 36-84months). The mean VAS satisfaction preoperatively and at follow-up was 4.0 ± 0 and 1.6 ± 1.0. The mean VAS pain was 4.3 ± 3.2 preoperatively and at last follow-up 2.1 ± 1.7. The median Tegner score preinjury was 7 (range 3-10), it decreased preoperatively to median 3.5 (range 1-8) and nearly reached the preinjury level at last follow-up 6 (range 3-10). The mean Lysholm score before surgery was 66 ± 20 and 91 ± 8 at last follow-up. Seven patients (38.9%) had a normal total IKDC score (A), 10 patients were nearly normal (B) and 1 patient slightly abnormal (C). In MRI the CMI was entirely resorbed in 4 patients (21%) and partially resorbed in 15 (79%). In 4 patients (21%) the CMI was isointense, in 14 (74%) slightly hyperintense and in 1 (5%) highly hyperintense. Ten patients (53%) showed marked signs of bone marrow edema. In 13 patients (68%) an extrusion of the meniscus > 3mm at last follow-up was found. Meniscal substitution with the CMI showed good to excellent clinical 3-7 results. The CMI shows an ongoing remodelling with decreased signal intensity and decreased size. However, as meniscus extrusion remained at the same level and bone marrow edema decreased from 1year to longer term follow-up, it appears that the remodeling comes to an end at about 5years after CMI. IV.

First Clinical Application of Polyurethane Meniscal Scaffolds with Mesenchymal Stem Cells and Assessment of Cartilage Quality with T2 Mapping at 12 Months.

Complex meniscal lesions often require meniscectomy with favorable results in the short term but a high risk of early osteoarthritis subsequently. Partial meniscectomy treated with meniscal substitutes may delay articular cartilage degeneration. To evaluate the status of articular cartilage by T2 mapping after meniscal substitution with polyurethane scaffolds enriched with mesenchymal stem cells (MSC) and comparison with acellular scaffolds at 12 months. Seventeen patients (18-50 years) with past meniscectomies were enrolled in 2 groups: (1) acellular polyurethane scaffold (APS) or (2) polyurethane scaffold enriched with MSC (MPS). Patients in the MPS group received filgrastim to stimulate MSC production, and CD90+ cells were obtained and cultured in the polyurethane scaffold. The scaffolds were implanted arthroscopically into partial meniscus defects. Concomitant injuries (articular cartilage lesions or cartilage lesions) were treated during the same procedure. Changes in the quality of articular cartilage were evaluated with T2 mapping in femur and tibia at 12 months. In tibial T2 mapping, values for the MPS group increased slightly at 9 months but returned to initial values at 12 months (P > 0.05). In the APS group, a clear decrease from 3 months to 12 months was observed (P > 0.05). This difference tended to be significantly lower in the APS group compared with the MPS group at the final time point (P = 0.18). In the femur, a slight increase in the MPS group (47.8 ± 3.4) compared with the APS group (45.3 ± 4.9) was observed (P > 0.05). Meniscal substitution with polyurethane scaffold maintains normal T2 mapping values in adjacent cartilage at 12 months. The addition of MSC did not show any advantage in the protection of articular cartilage over acellular scaffolds (P > 0.05).

3D-Printed Poly(ε-caprolactone) Scaffold Augmented With Mesenchymal Stem Cells for Total Meniscal Substitution: A 12- and 24-Week Animal Study in a Rabbit Model

Background: Total meniscectomy leads to knee osteoarthritis in the long term. The poly(ε-caprolactone) (PCL) scaffold is a promising material for meniscal tissue regeneration, but cell-free scaffolds result in relatively poor tissue regeneration and lead to joint degeneration. Hypothesis: A novel, 3-dimensional (3D)–printed PCL scaffold augmented with mesenchymal stem cells (MSCs) would offer benefits in meniscal regeneration and cartilage protection. Study Design: Controlled laboratory study. Methods: PCL meniscal scaffolds were 3D printed and seeded with bone marrow–derived MSCs. Seventy-two New Zealand White rabbits were included and were divided into 4 groups: cell-seeded scaffold, cell-free scaffold, sham operation, and total meniscectomy alone. The regeneration of the implanted tissue and the degeneration of articular cartilage were assessed by gross and microscopic (histological and scanning electron microscope) analysis at 12 and 24 weeks postoperatively. The mechanical properties of implants were also evaluated (tensile and compressive testing). Results: Compared with the cell-free group, the cell-seeded scaffold showed notably better gross appearance, with a shiny white color and a smooth surface. Fibrochondrocytes with extracellular collagen type I, II, and III and proteoglycans were found in both seeded and cell-free scaffold implants at 12 and 24 weeks, while the results were significantly better for the cell-seeded group at week 24. Furthermore, the cell-seeded group presented notably lower cartilage degeneration in both femur and tibia compared with the cell-free or meniscectomy group. Both the tensile and compressive properties of the implants in the cell-seeded group were significantly increased compared with those of the cell-free group. Conclusion: Seeding MSCs in the PCL scaffold increased its fibrocartilaginous tissue regeneration and mechanical strength, providing a functional replacement to protect articular cartilage from damage after total meniscectomy. Clinical Relevance: The study suggests the potential of the novel 3D PCL scaffold augmented with MSCs as an alternative meniscal substitution, although this approach requires further improvement before being used in clinical practice.

Partial meniscus substitution with a polyurethane scaffold does not improve outcome after an open-wedge high tibial osteotomy.

The aim of the study was to determine whether medial meniscal substitution with a polyurethane scaffold (Actifit(®)) improves the outcome of medial meniscal-deficient varus knees undergoing open-wedge high tibial osteotomy. Sixty patients with symptomatic varus knees those who underwent open-wedge high tibial osteotomies were prospectively studied. In 30 patients, the medial meniscus was left with a defect larger than 25 mm (Group M). An Actifit(®) device was implanted (Group A) in the remaining 30 patients. Patients were functionally evaluated with WOMET, IKDC and VAS. Patient satisfaction was graded from 0 (not satisfied) to 4 (very satisfied). Both groups were comparable preoperatively. They had similar follow-up periods (31.2 months; range 24-47.5; n.s.). WOMET improved a mean of 53.4 ± 8.4 and 42.4 ± 17.2 points in Groups M and A, respectively (p = 0.002). IKDC improved a mean of 56.7 ± 12 and 50.3 ± 15.6 points in Groups M and A, respectively (n.s.). VAS dropped 5.9 ± 2.1 and 4.7 ± 2.8 points in Groups M and A, respectively (p = 0.006). Patient satisfaction averaged 3.3 ± 0.8 and 3.3 ± 1 in Groups M and A, respectively (n.s.). Patients with symptomatic varus knees were treated with open-wedge high tibial osteotomies, and a meniscectomy was improved more at short-term follow-up in most of the evaluated functional scores than those patients with concomitant implantation of a medial Actifit(®) implant. However, there was no difference in terms of patient satisfaction with the procedure. Based on the short-term functional results of this study, no data were provided to support medial meniscal substitution with a polyurethane scaffold when an open-wedge high tibial osteotomy is being performed. Prospective comparative study, Level II.

Unicompartmental osteoarthritis: an integrated biomechanical and biological approach as alternative to metal resurfacing

Although traditionally not indicated for the treatment of osteoarthritis (OA), regenerative procedures are becoming a focus of increased interest due to their potential to provide pain relief and alter the progression of degenerative diseases. The purpose of this study was to assess whether a combined biomechanical and biological approach could offer good results in unicompartmental OA, thus delaying the need for unicompartmental arthroplasty in patients too young or refusing metal resurfacing. Forty-three patients (mean age = 40.1 ± 11 years, 33 men and 10 women, mean BMI = 25 ± 3) affected by unicompartmental OA (Kellegren-Lawrence score = 3) in stable joints were enrolled and treated consecutively. Fifteen patients were treated with osteotomy and osteochondral biomimetic scaffold implant (3 of them also with meniscal substitution), 11 with osteotomy and meniscal scaffold implant, 9 with osteotomy and meniscal allograft implant, and 8 with both cartilage and meniscal reconstruction, depending on the specific joint compartment main requirements. Clinical evaluation was performed at 3-year (2-4) median follow-up using the following scoring systems: IKDC subjective and objective, VAS for pain, and Tegner scores. Failures, adverse events, and complications were also reported. The IKDC subjective score improved from 47.3 to 79.6 at the final evaluation (p < 0.0005), VAS improved from 6.1 to 2.3 (p < 0.0005), and also sport activity level evaluated with the Tegner score showed a significant improvement, from 2 (1-5) to 4 (3-10; p < 0.0005), even if without achieving the pre-injury level (6, p = 0.001). A further subanalysis confirmed the positive outcome obtained in all the treatment subgroups and showed a higher clinical improvement in patients under the age of 40 years (IKDC subjective 84.4 ± 13.2 vs 76.5 ± 17.3; p = 0.03). This integrated biological and biomechanical approach produced a marked improvement at short-medium follow-up in patients affected by unicompartmental OA. Even though a good outcome was achieved at all ages, patients under the age of 40 years presented a greater clinical and subjective improvement. Longer follow-up studies are needed to show results over time and confirm this approach as an effective alternative to unicompartmental implants.

Tissue Engineering for Total Meniscal Substitution: Animal Study in Sheep Model—Results at 12 Months

The aim of the study was to investigate the use of a hyaluronic acid/polycaprolactone material for meniscal tissue engineering and to evaluate the tissue regeneration after the augmentation of the implant with expanded autologous chondrocytes. Eighteen skeletally mature sheep were treated. The animals were divided into three groups: cell-free scaffold, scaffold seeded with autologous chondrocytes, and meniscectomy alone. The implant was sutured to the capsule and to the meniscal ligament. At a 12-month gross assessment, histology and histomorphometry were used to assess the meniscus implant, knee joint, and osteoarthritis development. All implants showed excellent capsular ingrowth at the periphery. The implant gross assessment showed significant differences between cell-seeded and cell-free groups (p=0.011). The histological analysis indicated a cellular colonization throughout the implanted constructs. Avascular cartilaginous tissue formation was significantly more frequent in the cell-seeded constructs. Joint gross assessment showed that sheep treated with scaffold implantation achieved a significant higher score than those underwent meniscectomy (p<0.0005), and the Osteoarthritis Research Society International score showed that osteoarthritic changes were significantly less in the cell-seeded group than in the meniscectomy group (p=0.047), even though results were not significantly superior to those of the cell-free scaffold. Seeding of the scaffold with autologous chondrocytes increases its tissue regeneration capacity, providing a better fibrocartilaginous tissue formation. The study suggests the potential of the novel hyaluronic acid/polycaprolactone scaffold for total meniscal substitution, although this approach has to be further improved before being applied into clinical practice.

Outcome After Partial Medial Meniscus Substitution With the Collagen Meniscal Implant at a Minimum of 10 Years' Follow-up

The aim of the study was to evaluate the clinical outcome of a collagen meniscus graft implanted in an injured medial meniscus after a minimum of 10 years' follow-up. Twenty-five patients underwent arthroscopic implantation of the collagen meniscus device. They had either persistent compartmental joint line pain due to a previous medial meniscus resection (5 cases) or a large irreparable meniscus tear at arthroscopy (20 cases). Implant failure was defined as infection due to the implant or mechanical failure of the device. Twenty-two patients returned for clinical, functional, and radiographic evaluation. Magnetic resonance imaging was also performed and was analyzed with the criteria of Genovese et al. (where type 3 indicates normal and type 1 indicates completely abnormal). All the aforementioned evaluations were carried out at a minimum of 10 years (range, 10.1 to 12.5 years) after the procedure. The mean Lysholm score improved from 59.9 preoperatively to 89.6 at 1 year (P < .001), and it was 87.5 at final follow-up (P < .001). The results were good or excellent in 83% of the population. No differences were observed when we compared the Lysholm score at 1 year of follow-up with the score at final follow-up (P > .05). The mean pain score on a visual analog scale improved by 3.5 points at final follow-up. Patient satisfaction with the procedure was 3.4 of 4 points. Radiographic evaluation showed either minimal or no narrowing of the joint line. Magnetic resonance imaging showed type 2 in 64% of cases and type 3 in 21%. All cases showed less volume than expected (size type 2 in 89%). The failure rate in the patient population was 8% (2 of 25). There were no complications related to the device. Although there were several different types of patients and acute and chronic tears were treated in a limited number of patients, meniscal substitution with the collagen meniscal implant provides significant pain relief and functional improvement after a minimum of 10 years' follow-up. The implant generally diminished in size, but the procedure proved to be safe and had a low rate of implant failure on a long-term basis. No development or progression of degenerative knee joint disease was observed in most cases. Level IV, therapeutic case series.

Tissue Engineering for Total Meniscal Substitution: Animal Study in Sheep Model

The aim of the study was to investigate the use of a novel hyaluronic acid/polycaprolactone material for meniscal tissue engineering and to evaluate the tissue regeneration after the augmentation of the implant with expanded autologous chondrocytes. Two different surgical implantation techniques in a sheep model were evaluated. Twenty-four skeletally mature sheep were treated with total medial meniscus replacements, while two meniscectomies served as empty controls. The animals were divided into two groups: cell-free scaffold and scaffold seeded with autologous chondrocytes. Two different surgical techniques were compared: in 12 animals, the implant was sutured to the capsule and to the meniscal ligament; in the other 12 animals, also a transtibial fixation of the horns was used. The animals were euthanized after 4 months. The specimens were assessed by gross inspection and histology. All implants showed excellent capsular ingrowth at the periphery. Macroscopically, no difference was observed between cell-seeded and cell-free groups. Better implant appearance and integrity was observed in the group without transosseous horns fixation. Using the latter implantation technique, lower joint degeneration was observed in the cell-seeded group with respect to cell-free implants. The histological analysis indicated cellular infiltration and vascularization throughout the implanted constructs. Cartilaginous tissue formation was significantly more frequent in the cell-seeded constructs. The current study supports the potential of a novel HYAFF/polycaprolactone scaffold for total meniscal substitution. Seeding of the scaffolds with autologous chondrocytes provides some benefit in the extent of fibrocartilaginous tissue repair.

Arthroscopic collagen meniscus implant results at 6 to 8 years follow up

Meniscal substitution is a fundamental procedure to prevent osteoarthritis of the knee after massive meniscectomy. Stone, Steadman and Rodkey have developed a bioreadsorbable collagen matrix (CMI) which acts as a scaffold to restore the original medial meniscal. The objective of this study was to prospectively evaluate the results of CMI implantation at a follow up from a minimum of 6 to a maximum of 8 years. Eight patients (mean age 25) were evaluated at a final observation point from 6 to 8 years after CMI implantation. Inclusion criteria were an irreparable meniscal tear or a previous meniscectomy involving the medial meniscus. Follow up evaluation included Cincinnati Knee Rating Scale (CKRS), IKDC, subjective evaluation and X-ray and MRI control. There were no complications related to the device. All patients were able to return to day activities without limitations 3 months after surgery. Both subjective CKRS score and objective IKDC score showed improvement in all cases except one patient with an ACL re-injury. In two cases scores were slightly worse from 2 years after surgery to the final observation point. The other five cases obtained maximum score at final follow-up. In four cases the absence of pain remained until the final observation point, while in four cases a low entity of pain was described at long term follow-up. MRI showed in five cases mixoid degeneration signal, two had normal signal with reduced size, while one patient had no recognizable implant. Six patients had preserved cartilage and articular space, with no changes respect to pre-op control. Arthroscopic second look evaluation has been performed in three cases, revealing in two cases the presence of the implant, although with a reduced size respect to the original one, while in one case the CMI was almost disappeared. Our small series of eight patients prospectively followed from 6 to 8 years of follow-up has shown highly satisfactory results. Although the aspect of the implant was mostly abnormal, the implant may have helped reduce the deterioration of the knee joint at final observation time.

Bioreabsorbable polymer scaffold as temporary meniscal prosthesis.

Menisci have an important role in load bearing, shock absorption, knee joint stability, and joint lubrication. Meniscal lesions and meniscectomy are followed by osteoarthritis in a high percentage of patients. At present, there is no ideal prosthesis for meniscal substitution. In this work, a bioreabsorbable polymer scaffold made of poly(L-lactic acid) (PLLA) and poly(p-dioxanone) (PPD) blend was developed to be used as a temporary meniscal prosthesis to stimulate the formation of an in situ meniscal replication while the scaffold is reabsorbed by the organism. Total meniscectomy of medial meniscus and arthrotomy was made in both back knees of 34 adult New Zealand white rabbits by medial parapatellar incision. The scaffolds were sutured in one of the knees, and other was used as a control. A meniscal replica was developed, suggesting that this material has great potential to be used as a meniscal prosthesis, especially because the new meniscus promoted a significant protection of cartilage, and cartilage degeneration in the control condyles was observed.

Immunolocalization of types I, II, and X collagen in the tibial insertion sites of the medial meniscus.

The medial meniscus of the rabbit knee joint attaches to the tibial plateau via anterior and posterior insertions. Intact meniscal tibial insertions are essential for meniscal function. In the present study the distributions of types I, II, and X collagen in meniscal tibial insertions were investigated by indirect immunohistochemistry in a rabbit model. Four tissue zones were histologically identified in the anterior insertion site, including the ligamentous zone, uncalcified and calcified fibrocartilaginous zones and bone; the ligamentous zone was not observed in the posterior insertion site. Labeling for type I collagen was found to be strong in the ligament tissue and bone, and weak in the fibrocartilages which were also labeled for type II collagen. Tissues positive for different types of collagen overlapped and formed an irregular interface with various angles and depths, especially at the interface between the calcified fibrocartilage and bone. Positive labeling for type X collagen was identified only in the calcified fibrocartilage zone. The coexistence of types I and II collagen in the meniscal tibial insertions may indicate that this structural unit is subjected to both compressive and tensile loads. Type X collagen may play a role in maintaining the calcifying status of this tissue zone, so that its mechanical stiffness is kept between that of uncalcified fibrocartilage and hard bone. Restoration of the insertional structure including the distinct collagen distribution should be considered for a functional meniscal substitution.

Postoperative follow-up and rehabilitation after meniscus replacement.

Even though basic scientific knowledge about the meniscal loading pattern may advocate restrictive rehabilitation after meniscus repair, experience and one controlled study favour accelerated rehabilitation. The current protocols for rehabilitation after meniscal substitution follow personal experience with parameters such as pain, effusion, locking, and gait pattern used as clinical guidance. Controlled clinical studies on rehabilitation should be encouraged. An example of a rehabilitation protocol is given. As meniscus replacement is a new treatment option, it is essential to document details about the graft, the knee status at operation and the surgical procedure. The goal of a postoperative follow-up is to control quality, to measure patient satisfaction and to show whether meniscus replacement is beneficial in relation to the natural history of meniscectomy cases. There is a need for a standard follow-up evaluation of patients after meniscus replacement, and the development of a meniscus transplantation score including subjective and objective data is suggested.

The Meniscus in the Cruciate-Deficient Knee

Evidence clearly implicates meniscectomy as a primary factor in the premature development of OA of the knee joint. Although data demonstrate the ability of the menisci to transmit load, they do not contribute to the primary stability of the knee. In the absence of the ACL, the menisci have been shown to enhance the knee's stability in the AP, varus-valgus, and internal-external directions in vitro. Clinically, the argument that the menisci are important secondary stabilizers is less clear. The restraining capacity of the menisci to AP translation is much smaller than the forces the knee is subjected to in vivo during activities of daily living. Additionally, these forces can increase as much as threefold during strenuous athletics. It becomes apparent, on review of the literature, that the menisci clearly are not designed to participate as a significant restraining mechanism for the ACL-deficient knee. The incidence of acute meniscal tear is 52% and increases to 83% in the long run. It is important to realize that although the menisci contribute in part to the stability of the ACL-deficient knee, such a role places them at risk for injury. When meniscal lesions are noted in the ACL-deficient knee, it is important to bear in mind the patient's goals, including his or her willingness to have an ACL reconstructive procedure and desire to return to sports. Also, the tear's configuration and location dictate its the ability to heal. One final area of interest relates to the fate of an ACL reconstruction in the meniscus-deficient knee. Although the meniscus is not a participant in primary stability, the subtle alteration in knee joint kinematics may create unfavorable conditions for the ACL graft. It is possible that the menisci may provide some protection to an ACL-reconstructed knee by restoring normal knee joint kinematics. Such a situation may explain why some ACL reconstructions in the meniscectomized knee fail over time. Prosthetic meniscal substitution or allograft meniscal transplantation are techniques on the horizon and may prove useful in the future when the remaining meniscus cannot be repaired.

Cartilage mechanics and morphology, synovitis and proteoglycan fragments in rabbit joint fluid after prosthetic meniscal substitution

The effects of meniscal substitution with a Dacron® or Teflon® prosthesis on rabbit knee-joint cartilage were studied by indentation tests, gross and histological inspection, analysis of proteoglycan fragments in joint fluid and an evaluation of synovial changes. Cartilage mechanics and cartilage morphology were similarly abnormal after meniscectomy and meniscal substitution. The elevated concentrations of proteoglycan fragments in joint fluid and the more severe synovial changes in joints with a meniscal substitute, as compared to meniscectomy, probably resulted from irritation of the artificial implant, but also reflected the remaining effects from the necessary bone drilling. In this short-term experiment, the use of an artificial meniscal substitute could not prevent cartilage degeneration after meniscectomy.

Proteoglycan fragments in rabbit joint fluid correlated to arthrosis stage.

Proteoglycan fragment concentrations in joint fluid of rabbit knees with various degrees of secondary arthrosis after meniscal resection, meniscal substitution, and anterior cruciate ligament transection, were related to the gross appearance of the articular cartilage. Knees with normal cartilage were distinguishable by the concentration of proteoglycan fragments in joint fluid from knees with arthrosis. We found a correlation (r 0.61) between increasing arthrosis and increasing concentrations of proteoglycan fragments.

Treatment of the Anterior Cruciate Ligamentabsent Knee with Associated Meniscal Tears Instrumented Testing and Clinical Evaluation of Two Patient Groups

The UCLA instrumented clinical testing apparatus was used to measure postoperative stiffness and laxity for two groups of patients with documented chronic absence of the anterior cruciate ligament (ACL) and associated meniscal tears. Group 1 consisted of 76 patients (average age, 25 years) who had undergone anterior cruciate substitution using the torn meniscus, and a second group of 34 patients (average age, 31 years) who had partial meniscectomy alone without ACL substitution. Subjective and objective evaluations were significantly higher and symptoms of pain and buckling significantly lower in the substitution group. In addition, 29% of Group 1 and only 7% of Group 2 patients were able to return to their preinjury sports without limitations, while 5% of the former and 12% of the latter could not return to any sport. At 90 degrees of flexion, there were no significant differences in stiffness or laxity between the patient groups. At 20 degrees of flexion and neutral foot rotation, the meniscal substitution group had an average of 1.4 mm less side-to-side laxity difference than the partial meniscectomy patients; 51% of the substituted patients still had an injured knee laxity that was at least 2 mm greater than the uninjured knee, as contrasted to 67% of the partial meniscectomy patients who exceeded this upper limit of the normal range. At 20 degrees, anterior stiffness of the injured knees of the substitution patients was 28% greater than the injured knees of the partial meniscectomy group; 42% of the substituted patients had an injured knee stiffness within the normal range, while only 18% of the partial meniscectomy patients fell within normal limits. There were no statistical correlations of stiffness or laxity values with clinical scores or patient symptomatology in either group.