Cartilage defect repair by osteochondral allografts : role of tissue surfaces and interfaces

Articular cartilage exhibits limited intrinsic healing, and when defects are left untreated, they can increase in size and cartilage degeneration may progress to end-stage joint failure. Osteochondral allografting has been widely used in the clinic to treat large or multiple focal defects, or as a salvage procedure to avoid total joint replacement, and aims to restore mature, hyaline cartilage in a biologically, structurally, and functionally appropriate manner. Repair outcomes may be influenced by the presence of viable chondrocytes within graft cartilage and the integration of the graft bone to surrounding host tissue. Thus, the overall motivation of this dissertation work was to develop an integrative and multi-scale approach to cartilage defect repair analysis by osteochondral allografts in order to expand the current understanding of in vivo cartilage and bone remodeling. A novel approach for analyzing in vivo cartilage defect repair by osteochondral allografts was developed using interdisciplinary and multi-scale analysis methods in the goat model. Maintenance of cartilage load-bearing function in allografts in vivo was associated with zonal maintenance of cartilage cellularity and matrix content. Reduced cellularity at the articular surface, resulting from 4°C storage, was associated with variable long-term outcomes, while allograft failure was accompanied with cartilage softening, loss of cells/matrix, and/or graft subsidence. Production of the lubricant, proteoglycan-4 (PRG4), from allografts was a useful marker of biological performance. 37°C storage supports long-term chondrocyte viability, especially at the vulnerable articular surface. Bone structure in allografts was altered in vivo compared to non-operated bone, with allografts displaying bone cysts, and bone surface channels with or without roughening at the bone-cartilage interface. This work has further elucidated the interrelationship between biological and structural aspects of cartilage and bone remodeling in vivo after osteochondral allografting. Such analysis has established the inferiority of 4°C stored allografts versus fresh allografts, identified potential biomarkers of allograft performance and alternative storage protocols, and provided insight into the pathogenesis of subchondral bone cysts during cartilage defect repair. Analyzing cartilage and bone biology, structure, and function in an integrative manner identified properties of the osteochondral tissue that are critical to repair efficacy and potential mechanisms of graft success/failur

Cartilage defect repair by osteochondral allografts : role of tissue surfaces and interfaces

Articular cartilage exhibits limited intrinsic healing, and when defects are left untreated, they can increase in size and cartilage degeneration may progress to end-stage joint failure. Osteochondral allografting has been widely used in the clinic to treat large or multiple focal defects, or as a salvage procedure to avoid total joint replacement, and aims to restore mature, hyaline cartilage in a biologically, structurally, and functionally appropriate manner. Repair outcomes may be influenced by the presence of viable chondrocytes within graft cartilage and the integration of the graft bone to surrounding host tissue. Thus, the overall motivation of this dissertation work was to develop an integrative and multi-scale approach to cartilage defect repair analysis by osteochondral allografts in order to expand the current understanding of in vivo cartilage and bone remodeling. A novel approach for analyzing in vivo cartilage defect repair by osteochondral allografts was developed using interdisciplinary and multi-scale analysis methods in the goat model. Maintenance of cartilage load-bearing function in allografts in vivo was associated with zonal maintenance of cartilage cellularity and matrix content. Reduced cellularity at the articular surface, resulting from 4°C storage, was associated with variable long-term outcomes, while allograft failure was accompanied with cartilage softening, loss of cells/matrix, and/or graft subsidence. Production of the lubricant, proteoglycan-4 (PRG4), from allografts was a useful marker of biological performance. 37°C storage supports long-term chondrocyte viability, especially at the vulnerable articular surface. Bone structure in allografts was altered in vivo compared to non-operated bone, with allografts displaying bone cysts, and bone surface channels with or without roughening at the bone-cartilage interface. This work has further elucidated the interrelationship between biological and structural aspects of cartilage and bone remodeling in vivo after osteochondral allografting. Such analysis has established the inferiority of 4°C stored allografts versus fresh allografts, identified potential biomarkers of allograft performance and alternative storage protocols, and provided insight into the pathogenesis of subchondral bone cysts during cartilage defect repair. Analyzing cartilage and bone biology, structure, and function in an integrative manner identified properties of the osteochondral tissue that are critical to repair efficacy and potential mechanisms of graft success/failur

The Proteoglycan Metabolism of Articular Cartilage in Joint-Scale Culture

Understanding and controlling chondrocyte and cartilage metabolism in osteochondral tissues may facilitate ex vivo maintenance and application, both for allografts and tissue-engineered grafts. The hypothesis of this study was that maintenance of chondrocyte viability and matrix content and release of sulfated glycosaminoglycan (sGAG) in the articular cartilage of joint-scale osteochondral fragments are temperature and metabolism dependent. The aims were to assess, for adult goat joints, the effects of incubation temperature (37°C vs. 4°C) on cartilage chondrocyte viability and tissue matrix content and mechanical function, and the effects of temperature and cellular biosynthesis on sGAG release. Chondrocyte viability was maintained with 37°C incubation for 28 days, but decreased by ∼30% with 4°C incubation. Concomitantly, with 37°C incubation, cartilage sGAG was depleted by ∼52% with the lost sGAG predominantly unable to aggregate with hyaluronan, whereas collagen content, tissue thickness, and tissue stiffness were maintained. The depletion of sGAG was diminished by slowing metabolism, with 4°C decreasing release by ∼79% compared with 37°C incubation, and cycloheximide inhibition of cell metabolism at 37°C decreasing release by ∼47%. These results indicate that the articular cartilage of joint-scale grafts have enhanced chondrocyte viability with incubation at 37°C, but may need anabolic stimuli or catabolic inhibitors to maintain sGAG content

Development of a Comprehensive Osteochondral Allograft MRI Scoring System (OCAMRISS) With Histopathologic, Micro–Computed Tomography, and Biomechanical Validation

OBJECTIVE: To describe and apply a semiquantitative MRI scoring system for multifeature analysis of cartilage defect repair in the knee by osteochondral allografts and to correlate this scoring system with histopathologic, micro–computed tomography (µCT), and biomechanical reference standards using a goat repair model. DESIGN: Fourteen adult goats had 2 osteochondral allografts implanted into each knee: one in the medial femoral condyle and one in the lateral trochlea. At 12 months, goats were euthanized and MRI was performed. Two blinded radiologists independently rated 9 primary features for each graft, including cartilage signal, fill, edge integration, surface congruity, calcified cartilage integrity, subchondral bone plate congruity, subchondral bone marrow signal, osseous integration, and presence of cystic changes. Four ancillary features of the joint were also evaluated, including opposing cartilage, meniscal tears, synovitis, and fat-pad scarring. Comparison was made with histologic and µCT reference standards as well as biomechanical measures. Interobserver agreement and agreement with reference standards was assessed. Cohen’s κ, Spearman’s correlation, and Kruskal-Wallis tests were used as appropriate. RESULTS: There was substantial agreement (κ > 0.6, P < 0.001) for each MRI feature and with comparison against reference standards, except for cartilage edge integration (κ = 0.6). There was a strong positive correlation between MRI and reference standard scores (ρ = 0.86, P < 0.01). Osteochondral allograft MRI scoring system was sensitive to differences in outcomes between the types of allografts. CONCLUSIONS: We have described a comprehensive MRI scoring system for osteochondral allografts and have validated this scoring system with histopathologic and µCT reference standards as well as biomechanical indentation testing

Development of a Comprehensive Osteochondral Allograft MRI Scoring System (OCAMRISS) with Histopathologic, Micro-Computed Tomography, and Biomechanical Validation.

ObjectiveTo describe and apply a semi-quantitative MRI scoring system for multi-feature analysis of cartilage defect repair in the knee by osteochondral allografts, and to correlate this scoring system with histopathologic, micro-computed tomography (μCT), and biomechanical reference standards using a goat repair model.DesignFourteen adult goats had two osteochondral allografts implanted into each knee: one in the medial femoral condyle (MFC) and one in the lateral trochlea (LT). At 12 months, goats were euthanized and MRI was performed. Two blinded radiologists independently rated nine primary features for each graft, including cartilage signal, fill, edge integration, surface congruity, calcified cartilage integrity, subchondral bone plate congruity, subchondral bone marrow signal, osseous integration, and presence of cystic changes. Four ancillary features of the joint were also evaluated, including opposing cartilage, meniscal tears, synovitis, and fat-pad scarring. Comparison was made with histological and μCT reference standards as well as biomechanical measures. Interobserver agreement and agreement with reference standards was assessed. Cohen's kappa, Spearman's correlation, and Kruskal-Wallis tests were used as appropriate.ResultsThere was substantial agreement (κ&gt;0.6, p&lt;0.001) for each MRI feature and with comparison against reference standards, except for cartilage edge integration (κ=0.6). There was a strong positive correlation between MRI and reference standard scores (ρ=0.86, p&lt;0.01). OCAMRISS was sensitive to differences in outcomes between the types of allografts.ConclusionsWe have described a comprehensive MRI scoring system for osteochondral allografts and have validated this scoring system with histopathologic and μCT reference standards as well as biomechanical indentation testing