Articular cartilage preservation and storage. I. Application of tissue culture techniques to the storage of viable articular cartilage

T2 MR imaging vs. computational modeling of human articular cartilage tissue functionality

The detection of early stages of cartilage degeneration remains diagnostically challenging. One promising non-invasive approach is to functionally assess the tissue response to loading by serial magnetic resonance (MR) imaging in terms of T2 mapping under simultaneous mechanical loading. As yet, however, it is not clear which cartilage component contributes to the tissue functionality as assessed by quantitative T2 mapping. To this end, quantitative T2 maps of histologically intact cartilage samples (n=8) were generated using a clinical 3.0-T MR imaging system. Using displacement-controlled quasi-static indentation loading, serial T2 mapping was performed at three defined strain levels and loading-induced relative changes were determined in distinct regions-of-interest. Samples underwent conventional biomechanical testing (by unconfined compression) as well as histological assessment (by Mankin scoring) for reference purposes. Moreover, an anisotropic hyperelastic constitutive model of cartilage was implemented into a finite element (FE) code for cross-referencing. In efforts to simulate the evolution of compositional and structural intra-tissue changes under quasi-static loading, the indentation-induced changes in quantitative T2 maps were referenced to underlying changes in cartilage composition and structure. These changes were parameterized as cartilage fluid, proteoglycan and collagen content as well as collagen orientation. On a pixel-wise basis, each individual component correlation with T2 relaxation times was determined by Spearman's ρ_s and significant correlations were found between T2 relaxation times and all four tissue parameters for all indentation strain levels. Thus, the biological changes in functional MR Imaging parameters such as T2 can further be characterized to strengthen the scientific basis of functional MRI techniques with regards to their perspective clinical applications.

Importance of Donor Chondrocyte Viability for Osteochondral Allografts

BACKGROUND

Osteochondral allograft (OCA) transplantation provides a biological treatment option for functional restoration of large articular cartilage defects in multiple joints. While successful outcomes after OCA transplantation have been linked to viable donor chondrocytes, the importance of donor cell viability has not been comprehensively validated.

PURPOSE

To use a canine model to determine the importance of donor chondrocyte viability at the time of implantation with respect to functional success of femoral condylar OCAs based on radiographic, gross, cell viability, histologic, biochemical, and biomechanical outcome measures.

STUDY DESIGN

Controlled laboratory study.

METHODS

After approval was obtained from the institutional animal care and use committee, adult female dogs (N = 16) were implanted with 8-mm cylindrical OCAs from male dogs in the lateral and medial femoral condyles of 1 knee. OCAs were preserved for 28 or 60 days after procurement, and chondrocyte viability was quantified before implantation. Two different storage media, temperatures, and time points were used to obtain a spectrum of percentage chondrocyte viability at the time of implantation. A successful outcome was defined as an OCA that was associated with graft integration, maintenance of hyaline cartilage, lack of associated cartilage disorder, and lack of fibrillation, fissuring, or fibrous tissue infiltration of the allograft based on subjective radiographic, gross, and histologic assessments at 6 months after implantation.

RESULTS

Chondrocyte viability ranged from 23% to 99% at the time of implantation. All successful grafts had >70% chondrocyte viability at the time of implantation, and no graft with chondrocyte viability <70% was associated with a successful outcome. Live-dead stained sections and histologic findings with respect to cell morphological features suggested that successful grafts were consistently composed of viable chondrocytes in lacunae, while grafts that were not successful were composed of nonviable chondrocytes with infiltration of fibroblasts from the surrounding recipient tissues. In situ polymerase chain reaction (fluorescence in situ hybridization [FISH]) assays were performed in an attempt to distinguish donor (male) cells from recipient (female) cells. Unfortunately, this technique was exceptionally difficult to perform on intact articular cartilage sections, and consistent, repeatable data could not be obtained from this testing. However, the data did support histologic and live-dead data, which strongly suggested that successful grafts retained viable donor (male) chondrocytes and unsuccessful grafts degraded and were replaced by fibrous tissue populated with recipient (female) fibroblasts.

CONCLUSION

Viable chondrocytes in OCAs at the time of transplantation are primarily responsible for maintenance of donor articular cartilage health in the long term.

CLINICAL RELEVANCE

Optimizing chondrocyte viability in all aspects of OCA transplantation-including procurement, processing, storage, transportation, and surgical implantation-needs to be a primary focus for OCA clinical use.

A novel system improves preservation of osteochondral allografts

BACKGROUND

Osteochondral allografting is an option for successful treatment of large articular cartilage defects. Use of osteochondral allografting is limited by graft availability, often because of loss of chondrocyte viability during storage.

QUESTIONS/PURPOSES

The purpose of this study was to compare osteochondral allografts implanted in canine knees after 28 days or 60 days of storage for (1) initial (1 week) safety and feasibility; (2) integrity and positioning with time (12 weeks and 6 months); and (3) gross, cell viability, histologic, biochemical, and biomechanical characteristics at an endpoint of 6 months.

METHODS

With Institutional Animal Care and Use Committee approval, adult dogs (n=16) were implanted with 8-mm cylindrical osteochondral allografts in the lateral and medial femoral condyles of one knee. Osteochondral allografts preserved for 28 or 60 days using either the current tissue bank standard-of-care (SOC) or a novel system (The Missouri Osteochondral Allograft Preservation System, or MOPS) were used, creating four treatment groups: SOC 28-day, MOPS 28-day, SOC 60-day, and MOPS 60-day. Bacteriologic analysis of tissue culture and media were performed. Dogs were assessed by radiographs and arthroscopy at interim times and by gross, cell viability, histology, biochemistry, and biomechanical testing at the 6-month endpoint.

RESULTS

With the numbers available, there was no difference in infection frequency during storage (5% for SOC and 3% for MOPS; p=0.5). No infected graft was implanted and no infections occurred in vivo. MOPS grafts had greater chondrocyte viability at Day 60 (90% versus 53%; p=0.002). For 60-day storage, MOPS grafts were as good as or better than SOC grafts with respect to all outcome measures assessed 6 months after implantation.

CONCLUSIONS

Donor chondrocyte viability is important for osteochondral allograft success. MOPS allows preservation of chondrocyte viability for up to 60 days at sufficient levels to result in successful outcomes in a canine model of large femoral condylar articular defects.

CLINICAL RELEVANCE

These findings provide a promising development in osteochondral allograft technology that can benefit the quantity of grafts available for use and the quality of grafts being implanted.

Effects of Refrigeration and Freezing on the Electromechanical and Biomechanical Properties of Articular Cartilage

In vitro electromechanical and biomechanical testing of articular cartilage provide critical information about the structure and function of this tissue. Difficulties obtaining fresh tissue and lengthy experimental testing procedures often necessitate a storage protocol, which may adversely affect the functional properties of cartilage. The effects of storage at either 4°C for periods of 6 days and 12 days, or during a single freeze-thaw cycle at −20°C were examined in young bovine cartilage. Non-destructive electromechanical measurements and unconfined compression testing on 3 mm diameter disks were used to assess cartilage properties, including the streaming potential integral (SPI), fibril modulus (Ef), matrix modulus (Em), and permeability (k). Cartilage disks were also examined histologically. Compared with controls, significant decreases in SPI (to 32.3±5.5% of control values, p<0.001), Ef (to 3.1±41.3% of control values, p=0.046), Em (to 6.4±8.5% of control values, p<0.0001), and an increase in k (to 2676.7±2562.0% of control values, p=0.004) were observed at day 12 of refrigeration at 4°C, but no significant changes were detected at day 6. A trend toward detecting a decrease in SPI (to 94.2±6.2% of control values, p=0.083) was identified following a single freeze-thaw cycle, but no detectable changes were observed for any biomechanical parameters. All numbers are mean±95% confidence interval. These results indicate that fresh cartilage can be stored in a humid chamber at 4°C for a maximum of 6 days with no detrimental effects to cartilage electromechanical and biomechanical properties, while one freeze-thaw cycle produces minimal deterioration of biomechanical and electromechanical properties. A comparison to literature suggested that particular attention should be paid to the manner in which specimens are thawed after freezing, specifically by minimizing thawing time at higher temperatures.

Effects of dexamethasone on the functional properties of cartilage explants during long-term culture

BACKGROUND

Intact articular cartilage tissue is used clinically in the form of osteochondral allografts and experimentally as explants in modeling the physiologic behavior of chondrocytes in their native extracellular matrix. Long-term maintenance of allograft tissue is challenging.

HYPOTHESIS

By carefully modulating the preservation environment, it may be possible to preserve osteochondral allograft tissue over the long term while maintaining its original mechanical and biochemical properties.

STUDY DESIGN

Controlled laboratory study.

METHODS

In this study, juvenile bovine, mature bovine, and canine cartilage explants were cultured in chemically defined media with or without supplementation of dexamethasone for up to 4 weeks.

RESULTS

The mechanical properties and biochemical content of juvenile bovine explants cultured in the presence of dexamethasone were significantly enhanced after 2 weeks in culture and remained stable with sustained cell viability thereafter. In contrast, the mechanical properties and biochemical content of juvenile bovine explants cultured in the absence of the dexamethasone significantly decreased after 2 weeks of culture. The mechanical and biochemical content of mature bovine and canine explants were not significantly affected by the presence of dexamethasone and maintained initial (day 0) mechanical and biochemical properties throughout the entire culture period with or without supplementation of dexamethasone.

CONCLUSION

These results suggest that juvenile and mature cartilage explants respond differently to dexamethasone. The functional properties of juvenile cartilage explants can be maintained in vitro through the addition of dexamethasone to culture media. Functional properties of mature cartilage can be preserved for at least 4 weeks in culture regardless of the presence of dexamethasone.

CLINICAL RELEVANCE

Biochemical and biomechanical properties of osteochondral allograft tissue may be enhanced by the addition of dexamethasone to culture media. These findings may translate to longer shelf life of preserved osteochondral allograft transplantation tissue and increased clinical availability of grafts.

Chondrocyte viability is higher after prolonged storage at 37 degrees C than at 4 degrees C for osteochondral grafts

BACKGROUND

Osteochondral allografts are currently stored at 4 degrees C for 2 to 6 weeks before implantation. At 4 degrees C, chondrocyte viability, especially in the superficial zone, deteriorates starting at 2 weeks. Alternative storage conditions could maintain chondrocyte viability beyond 2 weeks, and thereby facilitate increased graft availability and enhanced graft quality.

PURPOSE

The objective of the study was to determine the effects of prolonged 37 degrees C storage compared with traditional 4 degrees C storage on chondrocyte viability and cartilage matrix content.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral samples from humeral heads of adult goats were analyzed (i) fresh, or after storage in medium for (ii) 14 days at 4 degrees C including 10% fetal bovine serum, (iii) 28 days at 4 degrees C including 10% fetal bovine serum, (iv) 28 days at 37 degrees C without fetal bovine serum, (v) 28 days at 37 degrees C including 2% fetal bovine serum, or (vi) 28 days at 37 degrees C including 10% fetal bovine serum. Portions of samples were analyzed by microscopy after LIVE/DEAD staining to determine chondrocyte viability and density, both en face (to visualize the articular surface) and vertically (overall and in superficial, middle, and deep zones). The remaining cartilage was analyzed for sulfated glycosaminoglycan and collagen.

RESULTS

The 37 degrees C storage maintained high chondrocyte viability compared with 4 degrees C storage. Viability of samples after 28 days at 37 degrees C was approximately 80% at the cartilage surface en face, approximately 65% in the superficial zone, and approximately 70% in the middle zone, which was much higher than approximately 45%, approximately 20%, and approximately 35%, respectively, in 4 degrees C samples after 28 days, and slightly decreased from approximately 100%, approximately 85%, and approximately 95%, respectively, in fresh controls. Cartilage thickness, glycosaminoglycan content, and collagen content were maintained for 37 degrees C and 4 degrees C samples compared with fresh controls.

CONCLUSION

The 37 degrees C storage of osteochondral grafts supports long-term chondrocyte viability, especially at the vulnerable surface and superficial zone of cartilage.

CLINICAL RELEVANCE

Storage of allografts at a physiologic temperature of 37 degrees C may prolong storage duration, improve graft availability, and improve treatment outcomes.

Storage conditions do not have detrimental effect on allograft collagen or scaffold performance

Musculoskeletal allografts are a valuable alternative to autograft tissue in orthopaedic surgeries. However, the effects of the allografts' storage history on the collagen and subsequent allograft scaffold properties are unknown. In this study, we hypothesized that freezing and refrigeration of allografts for 1 week would alter the biologic performance and mechanical properties of the allograft collagen. Allograft collagen was characterized by SDS-PAGE migration pattern, amino acid profile and measured denaturation. Scaffolds made from allograft collagen were evaluated for fibroblast proliferation, platelet activation and scaffold retraction. Collagen gelation kinetics (elastic and inelastic moduli and the viscous-elastic transition point) were also evaluated. Fibroblast proliferation, platelet activation and scaffold retraction results showed only minor, though statistically significant, differences between the storage groups. In addition, there were no significant differences in rheological properties or collagen biochemistry. In conclusion, this study suggests that freezing or refrigeration for 1 week does not appear to have any detrimental effect on the mechanical properties and biologic performance of the collagen within allografts.

Mechanical and biochemical characterization of cartilage explants in serum-free culture

Allografts of articular cartilage are both used clinically for tissue-transplantation procedures and experimentally as model systems to study the physiological behavior of chondrocytes in their native extracellular matrix. Long-term maintenance of allograft tissue is challenging. Chemical mediators in poorly defined culture media can stimulate cells to quickly degrade their surrounding extracellular matrix. This is particularly true of juvenile cartilage which is generally more responsive to chemical stimuli than mature tissue. By carefully modulating the culture media, however, it may be possible to preserve allograft tissue over the long-term while maintaining its original mechanical and biochemical properties. In this study juvenile bovine cartilage explants (both chondral and osteochondral) were cultured in both chemically defined medium and serum-supplemented medium for up to 6 weeks. The mechanical properties and biochemical content of explants cultured in chemically defined medium were enhanced after 2 weeks in culture and thereafter remained stable with no loss of cell viability. In contrast, the mechanical properties of explants in serum-supplemented medium were degraded by ( approximately 70%) along with a concurrent loss of biochemical content (30-40% GAG). These results suggest that long-term maintenance of allografts can be extended significantly by the use of a chemically defined medium.

Determination of Viability of Human Cartilage Allografts by a Rapid and Quantitative Method Not Requiring Cartilage Digestion

Fresh osteochondral allograft transplantation is increasingly used for the treatment of cartilage pathologies of the knee. It is believed that transplantation success depends on the presence of viable chondrocytes in the graft, but methods to evaluate graft viability require the isolation of chondrocytes by enzymatic digestion of the cartilage and/or the use of radioactive precursors. We have adapted the well-known cell viability assay based on the reduction of tetrazolium derivatives to evaluate cartilage viability. We took advantage from the histological properties of cartilage tissue and the fact that some tetrazolium derivatives (e.g., WST-1, XTT) give soluble reduction products that can permeate the hyaline cartilage matrix. We have validated this assay in human cartilage explants from arthrotomy interventions and deceased donors, measuring the reduced product in the explant supernatant. Using this method we have compared the performance of several culture media in cartilage viability. From those tested, DMEM supplemented with fetal bovine serum results in higher viability of the cartilage and the explants remain viable at least 15 days in culture at 37°C. Cartilage cells continued expressing chondrocyte-specific genes, suggesting the maintenance of chondrogenic phenotype. The described method offers a quantitative and convenient method to measure the viability of human cartilage grafts.

Cryopreservation of articular cartilage. Part 1: Conventional cryopreservation methods

There is increasing interest in the possibility of treating diseased or damaged areas of synovial joint surfaces by grafts of healthy allogeneic cartilage. Such grafts could be obtained from cadaver tissue donors or in the future they might be manufactured by 'tissue engineering' methods. Cartilage is an avascular tissue and hence is immunologically privileged but to take advantage of this is the graft must contain living cells. Preservation methods that achieve this are required to build up operational stocks of grafts, to provide a buffer between procurement and use, and to enable living grafts of a practical size to be provided at the right time for patient and surgeon. Review of the literature shows that it has been relatively straightforward to cryopreserve living isolated chondrocytes, but at the present time there is no satisfactory method to preserve cartilage between the time of procurement or manufacture and surgical use. In this paper, we review the relevant literature and we confirm that isolated ovine chondrocytes in suspension can be effectively cryopreserved by standard methods yet the survival of chondrocytes in situ in cartilage tissue is inadequate and extremely variable.

Does subchondral bone affect the fate of osteochondral allografts during storage?

BACKGROUND

Osteochondral allografts currently are hypothermically stored for a minimum of 14 days to a maximum of 28 days before surgical implantation, making storage conditions increasingly important. Previous studies have suggested that graft deterioration during storage may result from degradative factors and residual marrow elements in the subchondral bone.

HYPOTHESIS

Allografts stored with large bone-to-cartilage ratios will be compromised after prolonged storage compared with grafts with minimal bone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral plugs were harvested from 16 fresh human femoral condyles and randomly assigned to 1 of 3 groups based on bone-to-cartilage ratios: 1:1, 5:1, or 10:1. These ratios were considered on the basis that the 1:1 ratio is the minimum bone necessary to press-fit an allograft and 10:1 is the present ratio used by tissue banks for allograft storage. After 14 and 28 days of storage at 4 degrees C, the specimens were assessed for viability and viable cell density using confocal microscopy, proteoglycan synthesis by (35)SO4 incorporation, and glycosaminoglycan content.

RESULTS

All grafts underwent a significant decline in viable cell density, proteoglycan synthesis, and chondrocyte viability (particularly in the superficial region) after 14 days of storage, but no differences were observed between the 1:1, 5:1, or 10:1 ratio groups at either day 14 or day 28. In addition, no significant difference was noted in the glycosaminoglycan content in any of the groups.

CONCLUSION

Osteochondral allografts stored with a 10:1 bone-to-cartilage ratio, similar to tissue-banking ratios, performed no worse than allografts stored with minimal bone, suggesting that the bone-to-cartilage ratio plays little to no role in the degradation of allografts during prolonged storage.

CLINICAL RELEVANCE

As the practice of osteochondral allograft resurfacing becomes more commonplace, it is important that surgeons understand the factors that affect graft quality.

Prolonged-fresh preservation of intact whole canine femoral condyles for the potential use as osteochondral allografts

Defects in articular cartilage are often repaired with fresh osteochondral grafts. While fresh allografts provide viable chondrocytes, logistic limitations require surgical implantation within seven days of graft harvest. Here, we provide information on cold preservation of whole intact osteochondral materials that retains cartilage cell viability and function, and histologic and biochemical integrity for 28 days. Canine femoral condyles were obtained and stored at 4 degrees C for 14, 21 or 28 days. At the end of the storage period, cartilage was assessed for cell viability, 35S uptake, proteoglycan content and histologic parameters. The most noticeable histologic change was reduced Safranin-O near the cartilage surface with 14 days of cold preservation, but had recovered with 21 and 28 days. Cartilage thicknesses did not vary significantly. Cell viability was >95% at 14 days, 75-98% at 21 days and reduced to 65-90% at 28 days. Cell function measures showed that the level of 35SO4 incorporation was suppressed in samples stored at 4 degrees C. However, no significant differences were seen among groups at 14, 21 or 28 days of cold preservation. This data has implications for tissue banking protocols for osteochondral allograft material obtained for transplantation suggesting that cold preserved allograft material be implanted within 28 days.

Mini-pig fresh osteochondral allografts deteriorate after 1 week of cold storage

As a well-defined animal transplantation model, the mini-pig potentially is well-suited for large animal studies of fresh osteochondral allograft transplantation. This study was done to determine the histologic characteristics and function of proteoglycan synthesis of mini-pig articular cartilage after refrigeration in basal media for as much as 6 weeks. Osteochondral sections of 10 mini-pig knees were refrigerated in various media at 4 degrees C for 1 to 42 days after slaughter. Four hundred twenty samples were evaluated by 35S uptake and 260 samples by histologic evaluations. Proteoglycan synthesis declined by 7 days to 21% of the level measured on Day 1 and was undetectable at 42 days. Histologic evaluation revealed progressive degeneration. Mankin scores rose from 3.69 +/- 0.27 on Day 1 to 6.40 +/- 0.18 on Day 7, and logarithmically increased to 10.83 +/- 0.07 on Day 42. These results indicate that the metabolic characteristics of porcine articular cartilage were not retained after refrigeration in basal media for 7 days. Optimum cold storage of porcine osteochondral allografts for cartilage transplantation research may be less than 7 days. Because osteochondral grafts for clinical use currently are stored for greater than 7 days, similar studies of the viability of human articular cartilage are needed.

Storing live embryonic and adult human cartilage grafts for transplantation using a joint simulating device

OBJECTIVES

Cartilage transplantation as a means to replace damaged articular surfaces is of interest. A major obstacle is the long-term preservation of cartilage grafts. The commonly used technique of freezing the grafts inevitably leads to cellular death. The current study compares the technique to an innovative approach using a pulsed-pressure perfusion system termed a joint simulating device (JSD), intended to simulate intra-articular mechanical forces.

METHODS

Human articular cartilage explants were harvested from both embryonic epiphyseal tissue and femoral heads of elderly women (over 70 years of age) undergoing a partial joint replacement (hemi-arthroplasty) and were divided in two groups: half of the samples were incubated in the JSD while the remaining half were grown in static culture within tissue culture plates. After 10 days all samples were evaluated for: (a) cell vitality as assessed by image analysis and XTT assay; (b) biosynthetic activity as expressed by radioactive sulfate incorporation into glycosaminoglycans (GAG's); and (c) proteoglycan content as assessed by alcian blue staining intensity.

RESULTS

A 10-fold increase in sulfate incorporation in samples held in the JSD compared to the static culture group was observed in embryonic cartilage. In adult cartilage culture in the JSD elevated sulfate incorporation by threefold as compared to static culture. Central necrosis was observed in specimens grown in the static culture plates, while it did not occur in the samples held in the JSD. Cell vitality as assessed by XTT assay was significantly better in the JSD group as compared to static culture. The difference was more pronounced in the embryonic specimens as compared to adult cartilage. The specimens cultured within the JSD retained proteoglycans significantly better than those cultured in static culture.

CONCLUSIONS

Maintenance of cartilage specimens in a JSD was highly effective in keeping the vitality of cartilage explants in vitro over a 10-day period. A possible future application may be a long-term preservation of chondral grafts, without freezing. Avoidance of freezing of cartilage grafts, might prevent the cartilage degeneration often observed in frozen osteochondral grafts.

Differential effects of serum, insulin-like growth factor-I, and fibroblast growth factor-2 on the maintenance of cartilage physical properties during long-term culture

The effects of fetal bovine serum, insulin-like growth factor-I, and fibroblast growth factor-2 on the regulation of the functional physical properties of adult bovine cartilage explants during an incubation period of 18-20 days was determined, and the relationship between the measured functional properties of the cartilage and the tissue composition was assessed. Cartilage disks were tested in the uniaxial radially confined configuration by the application of low amplitude oscillatory displacement and measurement of the resultant load and streaming potential. For the control cartilage terminated just after explant, the modulus was 0.39 +/- 0.28 MPa, the open circuit hydraulic permeability was 2.0 +/- 1.0 x 10(-15) m2/(Pa.sec), and the electrokinetic (streaming potential) coefficient was -2.3 +/- 0.6 mV/MPa. Incubation of cartilage in medium supplemented with serum or insulin-like growth factor-I resulted in maintenance of the modulus and electrokinetic coefficient, whereas incubation in basal medium or medium supplemented with fibroblast growth factor-2 led to a marked decrease from control values in the modulus and the amplitude of the electrokinetic coefficient. All of the culture conditions examined resulted in an increase in permeability that was not statistically significant. The variation in the electromechanical properties of all the cartilage samples tested was related to the density of tissue proteoglycan and collagen (hydroxyproline). The modulus was correlated with both the density of tissue proteoglycan (+0.014 MPa/[mg/ml]) and the density of tissue hydroxyproline (+0.008 MPa/[mg/ml]). The electrokinetic coefficient was also correlated with the density of proteoglycan (-0.080 [mV/MPa]/[mg/ml]) and the density of hydroxyproline (+0.064 [mV/MPa]/[mg/ml]). These data indicate that the regulation of chondrocyte matrix metabolism by growth factors can significantly affect the physical properties and function of cartilage.

Mechanical responses of the rabbit patello-femoral joint to blunt impact

Various studies suggest impact trauma may initially soften cartilage, damage subchondral bone, or a combination thereof. The initial damages are commonly thought due to excessive contact pressure generated on cartilage and the underlying bone. The objective of this research was to develop a small animal model for studying post-traumatic OA and to correlate contact pressure with tissue damage. Blunt insult was graded by dropping a rigid mass onto the hyperflexed hind limb of rabbits. Contact pressure in the patello-femoral joint was measured with pressure sensitive film. One, 3, 6, and 14 days later the animals were euthanized. Damage to cartilage and the underlying bone was assessed visually and in microscopic sections. Indentation experiments were performed on the patellar cartilage with a rigid, flat probe. Contact pressures were nonuniform over the articular surfaces and a high frequency of surface fissures were generated on the lateral facet in severe insults. The appearance of surface fissures correlated better with the magnitude of contact pressure gradients in the damage zone than the magnitude of contact pressures on the facet, per se. Blunt trauma causing surface fissures resulted in a measurable degree of softening in the patellar cartilage, especially close to the defects. Surgical intervention of the joint to insert pressure sensitive film, however, also resulted in significant softening of the cartilage.

Effect of tissue culture storage on the in vivo survival of canine osteochondral allografts

In vitro studies in our laboratory have shown that the biomechanical and biochemical characteristics of osteochondral grafts can be preserved for as long as 28 days under tissue culture conditions. This study represents an attempt to extend these results to an in vivo model. In adult mongrel dogs, either an autograft, a fresh allograft, or a stored allograft was placed in a standardized defect on the weight-bearing surface of the medial femoral condyle. The stored grafts were kept at 4 degrees C in tissue culture medium for 14 days prior to implantation. The animals were killed at 12 weeks. Cartilage from the contralateral knee served as a control. The modulus and permeability of the cartilage were assessed with confined compression creep tests. The collagen and glycosaminoglycan contents were measured, and the cartilage was analyzed histologically with hematoxylin and eosin and safranin O stains. Grossly, the cartilage appeared viable at harvest. The histologic results were similar in the treatment groups, with the same spectrum of mild degenerative changes being noted in each group. The glycosaminoglycan content was significantly less in the autograft group than in its control group and than in the fresh allograft group. The glycosaminoglycan content did not differ significantly between fresh and stored allografts. The collagen content, modulus, and permeability did not differ either between experimental and control groups or between graft types. Our results support the conclusion that osteochondral allografts can be stored for as many as 14 days without significantly affecting the results of the procedure.

The Stiffness of Human Apophyseal Articular Cartilage as an Indicator of Joint Loading

The stiffness and thickness distribution of healthy lumbar apophyseal cartilage was measured in 25 lumbar motion segments (L1–4). The cartilage indentation and needling techniques of Swann and Seedhom (37) were suitably altered to cope with the low modulus and small size of the joint surfaces. A load of 3.12 ± 0.19 N (mean ± s.d.) was applied to the cartilage through a hemispherical indenter of 4.756 mm diameter. The stiffness was calculated using the displacement and instantaneous load 150 ms and 2 s after the indenter first contacted the surface, and using the equations of both Waters (46) and Hayes et al. (47). The mean stiffness of apophyseal joint cartilage was 2.8 M Pa ± 4 per cent (mean ± 95 per cent confidence limit), and thickness 1.02 mm ± 3 per cent. Peripheral apophyseal joint cartilage was softer than central cartilage. The stiffnesses of the centres of the superior and inferior joint surfaces were 3.01 MPa ± 12 per cent and 3.55 MPa ± 11 per cent. Inferior surfaces had a mean thickness of 0.93 mm ± 5 per cent and stiffness of 2.88 MPa ± 7 per cent. Superior surfaces had a mean thickness of 1.10 mm ± 4 per cent and stiffness of 2.74 MPa ± 5 per cent. It was found that the stiffness of cartilage calculated according to the formula of Hayes et al. (47), based on a constitutive analysis of a thin isotropic elastic layer, was directly proportional to both the stiffness calculated using the semi-empirical formula of Waters (46), derived to describe indentation of thin rubber sheets, and the nominal compressive creep modulus calculated by dividing the mean contact stress by the strain at the deepest point of indentation. The creep modulus calculated 2 s after contact was directly proportional to the creep modulus calculated 150 ms after indenter contact, implying that deformation behaviour was uniform between these points despite variation of cartilage stiffness.

Metabolic activity of bovine articular cartilage during refrigerated storage

The ability of the chondrocytes in intact bovine articular cartilage (AC) to synthesize glycosaminoglycans (GAG) during short-term refrigerated storage was examined. Closed and exposed bovine carpometacarpal joints were stored in a refrigerator for 4 hours, 1 day, 3 days, 5 days, or 7 days after the death of the animal. Full-thickness 6 mm diameter cartilage disks were obtained from each joint, incubated in Na2(35)SO4, digested and assayed for GAG production. Similarly incubated cartilage samples were processed for autoradiography as a qualitative determination of 35S uptake by chondrocytes. All refrigerated samples of AC showed signs of some cellular metabolic activity. Only at 7 days did chondrocytes demonstrate a significant decline in activity. For all five storage periods, AC from joints exposed to nutrient media synthesized more GAG than cartilage from matched closed joints. These results suggest that some chondrocytes in AC destined for osteoarticular allografting retain the ability to synthesize GAG for as long as 5 days of refrigerated storage and that this synthesis is stimulated by storage of the joint surfaces in a sterile nutrient solution. While the implications of the chondrocytes' survival and metabolism for osteochondral allograft transplantation are unknown, these data indicate that intact bovine AC retains some metabolic activity for several days under the conditions described and would carry on this activity if transplanted within that period of time.

Cell survival after transplantation of fresh meniscal allografts. DNA probe analysis in a goat model

Fibrochondrocytes synthesize and maintain the extracellular matrix responsible for the distinctive material and structural properties of a normal meniscus. Viable meniscal cells are believed to be necessary for the long-term maintenance of these properties in meniscal allografts. The purpose of this study was to determine if the donor cells (fibrochondrocytes) survive after a fresh meniscal allograft transplantation. A DNA probe technique was used to clearly distinguish the DNA patterns in donor cells from the host cells in the Spanish goat. No remaining donor DNA could be demonstrated at 4 weeks in transplanted meniscal tissue; it was all of host origin. The host DNA content at 4 weeks approached or exceeded the amount present in the contralateral control meniscus.

CLINICAL SIGNIFICANCE

The results of this study demonstrate that viable cells in medial meniscal allografts transplanted from one animal to another do not survive. Host cells rapidly repopulate the transplanted meniscus. There is no evidence these new cells will maintain on a long-term basis the extracellular matrix of the meniscus. The evidence in this paper, that the fibrochondrocytes do not survive transplantation, suggests further justification is necessary for using grafts with living cells. Allografts with living cells have an increased expense, more complicated surgical logistics, and have a higher potential risk of disease transmission.

Meniscal transplantation using fresh and cryopreserved allografts. An experimental study in goats

A comparative study of three subgroups of meniscal transplants was undertaken in the goat model: Group 1 (autograft) involved removal and immediate reimplantation of the meniscus; Group 2, fresh meniscal allografts; and Group 3, cryopreserved (30 days) meniscal allografts. Six months after surgery, tissues were evaluated for gross degenerative changes, proteoglycan concentration (as assessed by uronic acid), water content, vascularity, histology, and cell viability. The contralateral knee served as control for all comparisons. There was no statistical difference in the amount of arthritis present and all transplants demonstrated an essentially normal peripheral vascularity compared to controls. Sections revealed reduced numbers of cells in the central portions of the transplanted menisci and these viable cells demonstrated different behavior in multiplication in tissue culture compared to contralateral controls. Grossly and microscopically, the implanted menisci differed little from the controls. The measurement of proteoglycan concentration and water content of the transplanted meniscal cartilage suggest alterations that may affect the long-term mechanical properties. The autograft specimens showed the water content was very slightly increased (3% to 6%), while the proteoglycan concentration was increased (42% in terms of uronic acid). In contrast, the water content of the fresh allograft group and the cryopreserved group was increased 12% to 24%. Proteoglycan concentration in these groups was decreased up to 56% in portions of some menisci compared to controls. Fresh and cryopreserved meniscal allografts showed peripheral healing, revascularization, cellularity, and incorporation, and grossly appeared good at 6 months in the goat model. The biochemical changes in the extracellular matrix at 6 months raises questions on the long-term function of these transplanted menisci.

The immunology of bone and cartilage transplantation

Bone tissue was one of the earliest human transplanted tissues, yet little is known about its transplant biology. For many years, bone and cartilage tissues were though to be immunoprivileged tissues because of the absence of acute rejection phenomenon. Advances in the understanding of transplant immunology of vascularized tissue grafts (kidney, heart, liver, etc) have led to a renewed interest in the immunobiology of bone and cartilage allograft transplantation. Since prosthetic materials used in orthopedic reconstructive surgery have a limited lifespan, there is great interest in the transplantation of bone and cartilage tissue. The first half of the article discusses transplant terminology, basic principles of immunology, and experimental studies on the immunogenicity of bone and cartilage tissue. The second half of the article discusses how allotransplanted bone and cartilage behaves in human transplants, storage and preservation techniques, and future directions in bone and cartilage transplantation.

Long-term storage effects on canine osteochondral allografts

We have studied long-term (to 60 days) effects of 4 degrees C storage in culture media on the histologic, mechanical, and chemical properties of the cartilage from osteochondral shell allografts from the dog. The structural integrity of the cartilage matrix was intact up to 60 days of storage, for the mechanical properties represented by the aggregate modulus and apparent permeability remained normal. These data are supported by normal safranin-O staining as well as normal glycosaminoglycan content and total collagen concentration. However, chondrocyte viability, as assessed by 35SO4 uptake and hematoxylin and eosin preparations, decreased dramatically with time. We believe that the longer storage to 60 days is not indicated, unless conditions can be modified to maintain cell viability.

Cryopreservation of cartilage

We have investigated the viability and function of cells in cartilage slices after various methods of preservation, and have examined the viability of cells by measuring the incorporation of Na2(35)SO4 at different concentrations, temperatures and times of exposure to cryopreservatives. We have assessed the viability of cells when exposed to pre-freezing temperatures, and after preservation at -80 degrees C. The best survival rate was found to be with a concentration of cryopreservatives of approximately 10%, with pre-freeze exposure for four hours at 4 degrees C. In the stage cooling technique, the best initial cooling was at -30 degrees C for 30 minutes, followed by rapid cooling of the cartilage to -80 degrees C. The best survival rate for cryopreserved cartilage in 10% DMSO was, on average, 19% in intact slices and 34% when holes had been made in the slices. Proteoglycan synthesis after thawing appeared normal, and proteoglycan labelled after 48 hours in culture also showed a normal pattern.

Histological and biomechanical assessment of articular cartilage from stored osteochondral shell allografts

Normal and stored articular cartilage from the medial tibial plateaus of mature canine knee joints were evaluated histologically and biomechanically. The medial plateaus from the right knee (control) were assessed fresh, while the left (stored) were preserved in culture media at 4 degrees C for 3, 7, 14, or 28 days and then evaluated. Biomechanically, confined compression tests were performed on all specimens to determine the aggregate modulus and apparent permeability of the articular cartilage. Histologically, Safranin O- and hematoxylin and eosin (H&E)-stained sections were evaluated. All stored cartilage specimens had an aggregate modulus on average lower than normal, but the differences were not significant (p greater than 0.10). The apparent permeability was on average higher than but also not significantly different from normal (p greater than 0.10). Time in storage (up to 28 days) did not have a significant effect on the biomechanical properties of stored cartilage normalized by control values (p greater than 0.50). Safranin O and H&E histological evaluation also showed no overall changes in cell appearance or staining of the stored cartilage when compared with control for the time periods studied.

A histological and biochemical assessment of the cartilage matrix obtained from in vitro storage of osteochondral allografts

Fresh osteochondral allografts were stored at 4 degrees C in tissue culture media at variable time periods (3, 7, 14 and 28 days). Sterilely dissected tibial plateaus with a standardized 1/2 cm subchondral bone "shell" were obtained from canines 1-3 hrs post mortem. X-rays were taken to determine maturity of the animals. Only mature animals (closed epiphyses) were considered for the study. Histologically, safranin 0 (metachromatic stain for glycosaminoglycans) was observed in all experimental specimens. H&E stained sections showed at all time periods of 3, 7, 14 and 28 days that the cell morphology and arrangements were similar in the superficial and deep areas of the cartilage obtained from the stored osteochondral allograft when compared to the control articular cartilage. The cells were in lacunae and arranged in clusters. Biochemically, glycosaminoglycans and collagen content showed no difference at the 95% level of confidence during the duration of the study (28 days) when compared to the 0 day control cartilage. Collagen typing, based on the assessment by HPLC of the CNBr peptides showed the major presence of type II collagen (no evidence of dedifferentiation was observed). No type I was found to be present. Some apparent variations in the proportions of minor collagen components were noted--e.g. at 14 days the cartilage appeared to contain increased amounts of type XI but little or no type IX collagen (HMW, LMW) when compared to the day 0 control. At 28 days a shift to a larger amount of type IX collagen occurs, especially in the LMW component, with a small amount of type XI collagen when compared to normal day 0 articular cartilage. Cell viability, i.e., the ability of the allograft tissue to incorporate 35SO4 in the synthesis of glycosaminoglycans, was intact up to 28 days of storage.

The effect of cryopreservation on canine menisci: a biochemical, morphologic, and biomechanical evaluation

This study evaluated the effect of cryopreservation on the structural organization, biosynthetic activity, and material properties of canine menisci. The menisci were cryopreserved by incubating them in a 4% solution of dimethyl sulfoxide (DMSO) in physiologic media and freezing them to -100 degrees C using a controlled rate freezing system. The menisci were then stored for varying periods of time from zero to 12 weeks in liquid nitrogen (-196 degrees C). Following rapid thawing, changes in the histological appearance and biosynthetic activity of the menisci were evaluated as functions of storage time. In addition, the effects of the cryopreservation process on the tensile strength and modulus of the meniscal tissue were assessed. Although cryopreservation and short-term storage did not appear to affect the morphological appearance or biomechanical character of the menisci, biosynthetic activity, as determined by Na2S35SO4 incorporation, was diminished to less than 50% of normal control values immediately following cryopreservation and thawing. Autoradiographic examination of these tissues revealed that only approximately 10% of the meniscal cells were metabolically active, however, indicating that a marked increase in the metabolic activity of individual cells occurs following the freeze-thaw cycle. Total metabolic activity continued to decline with storage time.

Magnetic resonance imaging of knee hyaline cartilage and intraarticular pathology

Injuries to the hyaline cartilage of the knee joint are difficult to diagnose without invasive techniques. Even though these defects may be the most important prognostic factors in assessing knee joint injury, they are usually not diagnosed until arthrotomy or arthroscopy. Once injuries to hyaline cartilage are found and/or treated, no technique exists to follow these over time. Plain radiographs, arthrograms, and even computed tomography fail to detail most hyaline cartilage defects. We used magnetic resonance imaging (MRI) to evaluate five fresh frozen cadaver limbs and 10 patients whose pathology was known from arthrotomy or arthroscopic examination. Using a 0.35 Tesla superconducting magnet and spin-echo imaging technique with a head coil, we found that intraarticular fluid or air helped to delineate hyaline cartilage pathology. The multiplane capability of MRI proved to be excellent in detailing small (3 mm or more) defects on the femoral condyles and patellar surface. Cruciate ligaments were best visualized on sagittal oblique projections while meniscal pathology was best seen on true sagittal and coronal projections. MRI shows great promise in providing a noninvasive technique of evaluating hyaline cartilage defects, their response to treatment, and detailed anatomical information about cruciate ligaments and menisci.

Sequential changes in the mechanical properties of viable articular cartilage stored in vitro

Viable articular cartilage from the medial femoral condyles of rabbits was stored in vitro in tissue culture medium with various additives and the same site of each specimen was mechanically tested sequentially throughout a 12-day storage period. Indentation testing was performed with instantaneous and sustained loads. Preservation of sustained-load carrying capacity was observed in the condyles stored with additives, indicating maintenance of an intact cartilage matrix. However, initial testing with small sustained loads (preload) showed changes not observed at higher load levels. The changes noted at small sustained initial loads may reflect alterations in cartilage surface structure and may be an early indicator of its mechanical integrity. Chondrocyte viability and proteoglycan content, as measured by 35S incorporation and hexosamine concentration, were unchanged in comparison to fresh articular cartilage.

Fresh and cryopreserved fetal bones replacing massive bone loss in rats

Cartilaginous fetal bones from rat preserved by deep freezing procedures were compared to comparable fresh bones with regard to the following parameters: chemical composition, water and uronic acid contents; cell viability measured by the rate of proteoglycan synthesis; mineralization-ossification status by calcium binding; matrix integrity by the release of uronic acid containing substances; and biological activity as transplants inducing the formation of bone. The transplanted material was chemically analyzed and checked for its rate of proteoglycan synthesis. The quality of the formed bone was similar whether isogeneic or allogeneic, fresh or cryopreserved bone was employed as transplant material. Evidently those various fetal bones may be of clinical value whenever the need for replacement of massive bone loss arises. Although the viability and the cartilaginous nature of the graft are critical, the isogeneity and freshness are of a quantitative advantage only. These biochemical observations were confirmed by roentgenological and histological evaluations of the grafts. An optimal cryopreserving procedure and tests for examining bone candidates for successful grafting are described.

Landmarks in chondrocyte differentiation and maturation as envisaged by changes in the distribution of calcium complexes: an ultrastructural histochemical study

Organ cultures of fetal condylar cartilages have been examined using the K-pyroantimonate-osmium fixation method to follow alterations in cellular calcium distribution in maturing cartilage. Special attention has been given to analyzing the temporal and spatial relationships among intracellular calcium accumulation, cell maturation, and matrix mineralization. The findings of this study suggest that concomitant with the change in cellular metabolism from aerobic respiration to glycolysis there is a distinctive change in the distribution of cellular and matrical calcium complexes. This ultrastructural histochemical method can thus be used to evaluate the maturational state of chondrocytes actively involved in endochondral ossification.

Articular cartilage preservation and storage. II. Mechanical indentation testing of viable, stored articular cartilage

Mature rabbit articular cartilage in the form of distal femoral condyles, composite osteoarticular structures, were incubated in the presence of alpha-tocopherol (200 micrograms/ml) over a period of time. Indentation testing and 35S uptake indicate preservation of sustained load carrying capacity and viability, respectively, in the presence of alpha-tocopherol for up to 30 days in organ culture. Condylar cartilage stored in the absence of alpha-tocopherol as well as frozen cartilage demonstrated progressive inability to resist sustained loading over time. Nonoptimal synthetic function apparently occurred in these latter two groups when compared to alpha-tocopherol stored material.