One-Year Outcomes of Total Meniscus Reconstruction Using a Novel Fiber-Reinforced Scaffold in an Ovine Model.

BACKGROUND: Meniscus injuries and resulting meniscectomies lead to joint deterioration, causing pain, discomfort, and instability. Tissue-engineered devices to replace the meniscus have not shown consistent success with regard to function, mechanical integrity, or protection of cartilage. PURPOSE: To evaluate a novel resorbable polymer fiber-reinforced meniscus reconstruction scaffold in an ovine model for 52 weeks and assess its integrity, tensile and compressive mechanics, cell phenotypes, matrix organization and content, and protection of the articular cartilage surfaces. STUDY DESIGN: Controlled laboratory study. METHODS: Eight skeletally mature ewes were implanted with the fiber-reinforced scaffold after total meniscectomy, and 2 additional animals had untreated total meniscectomies. Animals were sacrificed at 52 weeks, and the explants and articular surfaces were analyzed macroscopically. Explants were characterized by ultimate tensile testing, confined compression creep testing, and biochemical, histological, and immunohistochemical analyses. Cartilage damage was characterized using the Mankin score on histologic slides from both the femur and tibia. RESULTS: One sheep was removed from the study because of a torn extensor tendon; the remaining 7 explants remained fully intact and incorporated into the bone tunnels. All explants exhibited functional tensile loads, tensile stiffnesses, and compressive moduli. Fibrocartilagenous repair with both types 1 and 2 collagen were observed, with areas of matrix organization and biochemical content similar to native tissue. Narrowing in the body region was observed in 5 of 7 explants. Mankin scores showed less cartilage damage in the explant group (femoral condyle: 3.43 ± 0.79, tibial plateau: 3.50 ± 1.63) than in the meniscectomy group (femoral condyle: 8.50 ± 3.54, tibial plateau: 6.75 ± 2.47) and were comparable with Mankin scores at the previously reported 16- and 32-week time points. CONCLUSION: A resorbable fiber-reinforced meniscus scaffold supports formation of functional neomeniscus tissue, with the potential to prevent joint degeneration that typically occurs after total meniscectomy. Further studies with improvements to the initial mechanics of the scaffold and testing for longer time periods are warranted. CLINICAL RELEVANCE: Meniscectomy is an extremely common orthopaedic procedure, and few options currently exist for the treatment of significant loss of meniscus tissue. Successful development of a tissue-engineered meniscus scaffold could substantially reduce the incidence of postmeniscectomy joint degeneration and the subsequent procedures used for its treatment.

Negative Outcomes of Poly(l-Lactic Acid) Fiber-Reinforced Scaffolds in an Ovine Total Meniscus Replacement Model.

Our objective was to test the efficacy of collagen-hyaluronan scaffolds reinforced with poly(l-lactic acid) (PLLA) fibers in an ovine total meniscus replacement model. Scaffolds were implanted into 9 sheep (n = 1 at 8 weeks, n = 2 at 16 weeks, n = 3 at both 24, 32 weeks) following total medial meniscectomy. From 16 weeks on, explants were characterized by confined compression creep, histological, and biochemical analyses. Articular surfaces were observed macroscopically and damage was ranked histologically using the Mankin score. At sacrifice, three of the nine PLLA scaffolds had completely ruptured, and the intact scaffolds experienced progressive shape changes and severe narrowing in the body region at 16, 24, and 32 weeks. Aggregate compressive modulus and permeability did not improve with time. Histological and biochemical analyses showed significantly less extracellular matrix and less matrix organization compared to native tissue. Osteophytes, bone erosion, and cartilage damage were observed, increasing with time postimplantation. A buildup of lactic acid and/or the rapid loss of scaffold mechanical integrity due to PLLA degradation are probable causes for the joint abnormalities observed in this study. These results are in sharp contrast to those of our previous successful total meniscus replacement studies using polyarylate [p(DTD DD)] fiber-reinforced scaffolds. This suggests that PLLA fiber as produced in this study cannot be used as reinforcement for a meniscus replacement scaffold.

Successful Total Meniscus Reconstruction Using a Novel Fiber-Reinforced Scaffold: A 16- and 32-Week Study in an Ovine Model.

BACKGROUND: Meniscus injuries in the United States result in an estimated 850,000 surgical procedures each year. Although meniscectomies are the most commonly performed orthopaedic surgery, little advancement has been made in meniscus replacement and regeneration, and there is currently no total meniscus replacement device approved by the Food and Drug Administration. HYPOTHESIS: A novel fiber-reinforced meniscus scaffold can be used as a functional total meniscus replacement. STUDY DESIGN: Controlled laboratory study. METHODS: A tyrosine-derived, polymer fiber-reinforced collagen sponge meniscus scaffold was evaluated mechanically (tensile and compressive testing) and histologically after 16 and 32 weeks of implantation in an ovine total meniscectomy model (N = 20; 16 implants plus 4 meniscectomies, divided equally over the 2 time periods). The extent of cartilage damage was also measured on tibial plateaus by use of toluidine blue surface staining and on femoral condyles by use of Mankin scores on histological slides. RESULTS: Scaffolds induced formation of neomeniscus tissue that remained intact and functional, with breaking loads approximating 250 N at both 16 and 32 weeks compared with 552 N for native menisci. Tensile stiffness values (99 and 74 N/mm at 16 and 32 weeks, respectively) were also comparable with those of the native meniscus (147 N/mm). The compressive modulus of the neomeniscus tissue (0.33 MPa at both 16 and 32 weeks) was significantly increased compared with unimplanted (time 0) scaffolds (0.15 MPa). There was histological evidence of extensive tissue ingrowth and extracellular matrix deposition, with immunohistochemical evidence of types I and II collagen. Based on significantly decreased surface damage scores as well as Mankin scores, the scaffold implants provided greater protection of articular cartilage compared with the untreated total meniscectomy. CONCLUSION: This novel fiber-reinforced meniscus scaffold can act as a functional meniscus replacement, with mechanical properties similar to those of the native meniscus, while protecting the articular cartilage of the knee from the extensive damage after a total meniscectomy. CLINICAL RELEVANCE: This meniscus replacement scaffold has the potential to improve surgical treatment and provide better long-term outcomes for those suffering from severe meniscus damage.

Macrophage tropism of HIV-1 depends on efficient cellular dNTP utilization by reverse transcriptase.

Retroviruses utilize cellular dNTPs to perform proviral DNA synthesis in infected host cells. Unlike oncoretroviruses, which replicate in dividing cells, lentiviruses, such as human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus, are capable of efficiently replicating in non-dividing cells (terminally differentiated macrophages) as well as dividing cells (i.e. activated CD4+ T cells). In general, non-dividing cells are likely to have low cellular dNTP content compared with dividing cells. Here, by employing a novel assay for cellular dNTP content, we determined the dNTP concentrations in two HIV-1 target cells, macrophages and activated CD4+ T cells. We found that human macrophages contained 130-250-fold lower dNTP concentrations than activated human CD4+ T cells. Biochemical analysis revealed that, unlike oncoretroviral reverse transcriptases (RTs), lentiviral RTs efficiently synthesize DNA even in the presence of the low dNTP concentrations equivalent to those found in macrophages. In keeping with this observation, HIV-1 vectors containing mutant HIV-1 RTs, which kinetically mimic oncoretroviral RTs, failed to transduce human macrophages despite retaining normal infectivity for activated CD4+ T cells and other dividing cells. These results suggest that the ability of HIV-1 to infect macrophages, which is essential to establishing the early pathogenesis of HIV-1 infection, depends, at least in part, on enzymatic adaptation of HIV-1 RT to efficiently catalyze DNA synthesis in limited cellular dNTP substrate environments.