Material properties of fresh cold-stored allografts for osteochondral defects at 1 year

Fresh Osteochondral Allograft for Large Talar Osteochondral Lesions

Osteochondral lesions of the talus are being recognized as an increasingly common injury. Large osteochondral lesions have significant biomechanical consequences and often require resurfacing with both boney and cartilaginous graft. The current treatment options include osteochondral autograft transfer, mosaicplasty, autologous chondrocyte implantation, or osteochondral allograft transplantation. Allograft procedures have the advantage of no donor site morbidity and ability to match the defect line to line. Careful transportation, storage, and handling of the allograft are critical to success. The failure of nonoperative management, failure of arthroscopic treatment, or large defects are an indication for resurfacing.

Characterizing Osteochondral Allograft Biomechanics for Optimizing Transplant Success: A Systematic Review

Osteochondral allograft (OCA) transplantation has been largely successful in treating symptomatic articular cartilage lesions; however, treatment failures persist. While OCA biomechanics have been consistently cited as mechanisms of treatment failure, the relationships among mechanical and biological variables that contribute to success after OCA transplantation have yet to be fully characterized. The purpose of this systematic review was to synthesize the clinically relevant peer-reviewed evidence targeting the biomechanics of OCAs and the impact on graft integration and functional survival toward developing and implementing strategies for improving patient outcomes. The Cochrane Central Register of Controlled Trials, the Cochrane Database of Systematic Reviews, MEDLINE, PubMed, Cumulative Index to Nursing and Allied Health (CINAHL), Google Scholar, and EMBASE were searched to identify articles for systematic review. This review of relevant peer-reviewed literature provided evidence that the biomechanics related to OCA transplantation in the knee have direct and indirect effects on functional graft survival and patient outcomes. The evidence suggests that biomechanical variables can be optimized further to enhance benefits and mitigate detrimental effects. Each of these modifiable variables should be considered regarding indications, patient selection criteria, graft preservation methodology, graft preparation, transplantation, fixation techniques, and prescribed postoperative restriction and rehabilitation protocols. Criteria, methods, techniques, and protocols should target OCA quality (chondrocyte viability, extracellular matrix integrity, material properties), favorable patient and joint characteristics, rigid fixation with protected loading, and innovative ways to foster rapid and complete OCA cartilage and bone integration to optimize outcomes for OCA transplant patients.

Fresh Osteochondral and Chondral Allograft Preservation and Storage Media: A Systematic Review of the Literature

BACKGROUND

Storage procedures and parameters have a significant influence on the health of fresh osteochondral allograft (OCA) cartilage. To date, there is a lack of agreement on the optimal storage conditions for OCAs.

PURPOSE

To systematically review the literature on (1) experimental designs and reporting of key variables of ex vivo (laboratory) studies, (2) the effects of various storage solutions and conditions on cartilage health ex vivo, and (3) in vivo animal studies and human clinical studies evaluating the effect of fresh OCA storage on osteochondral repair and outcomes.

STUDY DESIGN

Systematic review; Level of evidence, 5.

METHODS

A systematic review was performed using the PubMed, Embase, and Cochrane databases. The inclusion criteria were laboratory studies (ex vivo) reporting cartilage health outcomes after prolonged storage (>3 days) of fresh osteochondral or chondral tissue explants and animal studies (in vivo) reporting outcomes of fresh OCA. The inclusion criteria for clinical studies were studies (>5 patients) that analyzed the relationship of storage time or chondrocyte viability at time of implantation to patient outcomes. Frozen, cryopreserved, decellularized, synthetic, or tissue-engineered grafts were excluded.

RESULTS

A total of 55 peer-reviewed articles met the inclusion criteria. Ex vivo studies reported a spectrum of tissue sources and storage solutions and conditions, although the majority of studies lacked complete reporting of key variables, including storage solution formula and environmental conditions. The effect of various conditions (eg, temperature) and storage solutions on cartilage health were inconsistent. Although 60% of animal models suggest that storage time may influence outcomes and 80% indicate inferior outcomes with frozen OCA as compared with fresh OCA, 75% of clinical studies report no correlation between storage time and outcomes.

CONCLUSION

Given the variability in experimental designs and lack of reporting across studies, it is still not possible to determine optimal storage conditions, although animal studies suggest that storage time and chondrocyte viability influence osteochondral repair outcomes. A list of recommendations was developed to encourage reporting of key variables, such as media formulation, environmental factors, and methodologies used. High-quality clinical data are needed to investigate the effects of storage and graft health on outcomes.

Cells, soluble factors and matrix harmonically play the concert of allograft integration

Implantation of allograft tissues has massively grown over the last years, especially in the fields related to sports medicine. Beside the fact that often no autograft option exists, autograft related disadvantages as donor-site morbidity and prolonged operative time are drastically reduced with allograft tissues. Despite the well documented clinical success for bone allograft procedures, advances in tissue engineering raised the interest in meniscus, osteochondral and ligament/tendon allografts. Notably, their overall success rates are constantly higher than 80%, making them a valuable treatment option in orthopaedics, especially in knee surgery. Complications reported for allografting procedures are a small risk of disease transmission, immunologic rejection, and decreased biologic incorporation together with nonunion at the graft-host juncture and, rarely, massive allograft resorption. Although allografting is a successful procedure, improved techniques and biological knowledge to limit these pitfalls and maximize graft incorporation are needed. A basic understanding of the biologic processes that affect the donor-host interactions and eventual incorporation and remodelling of various allograft tissues is a fundamental prerequisite for their successful clinical use. Further, the importance of the interaction of immunologic factors with the biologic processes involved in allograft incorporation has yet to be fully dissected. Finally, new tissue engineering techniques and use of adjunctive growth factors, cell based and focused gene therapies may improve the quality and uniformity of clinical outcomes. The aim of this review is to shed light on the biology of meniscus, osteochondral and ligament/tendon allograft incorporation and how collection and storage techniques may affect graft stability and embodiment.Level of evidence V.

Bone Marrow Aspirate Concentrate Does Not Improve Osseous Integration of Osteochondral Allografts for the Treatment of Chondral Defects in the Knee at 6 and 12 Months: A Comparative Magnetic Resonance Imaging Analysis

BACKGROUND

Poor osseous integration after fresh osteochondral allograft transplantation (OCA) may be associated with graft subsidence and subchondral bone collapse after implantation. The augmentation of OCA with bone marrow aspirate concentrate (BMAC) has been hypothesized to improve osseous incorporation of the implanted allograft.

PURPOSE

To evaluate the effect of autogenous BMAC treatment on osseous integration at the graft-host bony interface after OCA.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A retrospective review of patients treated with OCA+BMAC or OCA alone for full-thickness chondral defects of the distal femur from March 2015 to December 2016 was conducted. Seventeen knees treated with OCA+BMAC and 16 knees treated with OCA alone underwent magnetic resonance imaging (MRI) in the early postoperative phase (mean, 6 months). Eighteen knees treated with OCA+BMAC and 16 knees treated with OCA alone underwent MRI in the late postoperative phase (mean, 12 months). Bone, cartilage, and ancillary features on MRI were graded using the Osteochondral Allograft MRI Scoring System (OCAMRISS) by a musculoskeletal radiologist blinded to the patient's history and treatment.

RESULTS

There were no significant differences in the demographics or lesion characteristics between treatment groups in either postoperative phase. In the early postoperative phase, the mean OCAMRISS bone score was 3.0 ± 0.7 and 3.3 ± 0.7 for the OCA+BMAC group and OCA alone group, respectively ( P = .76); 71% (OCA+BMAC) and 81% (OCA alone) of MRI scans demonstrated discernible clefts at the graft-host junction ( P = .69), and 41% (OCA+BMAC) and 25% (OCA alone) of MRI scans demonstrated cystic changes at the graft and graft-host junction ( P = .46). In the late postoperative phase, the mean OCAMRISS bone score was 2.7 ± 0.8 and 2.9 ± 0.8 for the OCA+BMAC group and OCA alone group, respectively ( P = .97); 44% (OCA+BMAC) and 63% (OCA alone) of MRI scans demonstrated discernible clefts at the graft-host junction ( P = .33), and 50% (OCA+BMAC) and 31% (OCA alone) of MRI scans demonstrated the presence of cystic changes at the graft and graft-host junction ( P = .32). The mean OCAMRISS cartilage, ancillary, and total scores were not significantly different between groups in either postoperative phase.

CONCLUSION

OCA augmented with BMAC was not associated with improved osseous integration; decreased cystic changes; or other bone, cartilage, and ancillary feature changes compared with OCA alone.

Large Osteochondral Allografts of the Knee: Surgical Technique and Indications

Large osteochondral allograft (OCA) transplant has become a valid alternative to restore articular surface in challenging articular lesions in young and active patients, either in primary or in revision procedures. Several studies support the effectiveness and safety of OCA, but costs and graft availability limit their use. The indications are the treatment of symptomatic full-thickness cartilage lesions greater than 3 cm ² , deep lesions with subchondral damage, or revision procedures when a previous treatment has failed. The goal of the transplant is to restore the articular surface with a biological implant, allow return to daily/sports activities, relieve symptoms, and delay knee arthroplasty. Grafts can be fresh, fresh-frozen, or cryopreserved; these different storage procedures significantly affect cell viability, immunogenicity, and duration of the storage. Dowel and shell technique are the two most commonly used procedures for OCA transplantation. While most cartilage lesions can be treated with the dowel technique, large and/or geometrically irregular lesions should be treated with the shell technique. OCA transplantation for the knee has demonstrated reliable mid- to long-term results in terms of graft survival and patient satisfaction. Best results are reported: in unipolar lesions, in patients younger than 30 years, in traumatic lesions and when the treatment is performed within 12 months from the onset of symptoms.

Effects of Autogenous Bone Marrow Aspirate Concentrate on Radiographic Integration of Femoral Condylar Osteochondral Allografts

BACKGROUND

Transplantation of fresh osteochondral allografts (OCAs) is an attractive treatment option for symptomatic articular cartilage lesions in young, healthy patients. Because the lack of OCA bone integration can be a cause of treatment failure, methods for speeding and enhancing OCA bone integration to mitigate this potential complication are highly desirable.

PURPOSE

To determine if autogenous bone marrow aspirate concentrate (BMC) treatment of large femoral condylar OCAs would be associated with superior radiographic OCA bone integration compared with nontreated allografts during the critical first 6 months after surgery.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A review of patients enrolled in a prospective registry who were treated with transplantation of large OCAs to one or both femoral condyles at our institution from March 12, 2013 to March 14, 2016 was performed. Patients were stratified into 2 groups based on BMC treatment versus no BMC treatment; the treatment was nonrandomized and was rooted in a shift in practice and a continuing effort to optimize OCA transplantation at our institution. Patients were excluded if they did not have orthogonal view radiographs performed at 6 weeks, 3 months, and 6 months postoperatively. Each condyle undergoing OCA transplantation was assessed individually by an independent musculoskeletal radiologist, who was blinded to the treatment group and time point. OCAs were assessed with respect to graft integration (0%-100%; 0 = no integration, 100 = complete integration) and degree of sclerosis (0-3; 0 = normal, 1 = mild sclerosis, 2 = moderate sclerosis, and 3 = severe sclerosis) of the graft at each time point.

RESULTS

This study identified 17 condyles in 15 patients who underwent OCA transplantation without BMC and 29 condyles in 22 patients who underwent OCA transplantation with BMC. The BMC group had significantly ( P = .033) higher graft integration scores at 6 weeks, 3 months, and 6 months after surgery. Graft sclerosis was significantly ( P = .017) less in the BMC group at 6 weeks and 3 months, with no significant difference at 6 months after surgery. When combining the groups to examine the influence of smoking on graft integration, nonsmokers had significantly ( P = .007) higher graft integration scores at 6 months.

CONCLUSION

Large femoral condylar OCAs treated with autogenous BMC before implantation showed superior radiographic integration to bone and less sclerosis during the initial 6-month postoperative period. BMC treatment of OCAs may mitigate the failure of OCA bone healing.

Pulsed lavage cleansing of osteochondral grafts depends on lavage duration, flow intensity, and graft storage condition

Introduction

Osteochondral allograft (OCA) transplantation is generally effective for treating large cartilage lesions. Cleansing OCA subchondral bone to remove donor marrow elements is typically performed with pulsed lavage. However, the effects of clinical and experimental parameters on OCA marrow removal by pulsed lavage are unknown. The aim of the current study was to determine the effects on marrow cleansing in human osteochondral cores (OCs) of (1) lavage duration, (2) lavage flow intensity, and (3) OC sample type and storage condition.

Methods

OCs were harvested from human femoral condyles and prepared to a clinical geometry (cylinder, diameter = 20 mm). The OCs were from discarded remnants of Allograft tissues (OCA) or osteoarthritis patients undergoing Total Knee Replacement (OCT). The experimental groups subjected to standard flow lavage for 45 seconds (430 mL of fluid) and 120 seconds (1,150 mL) were (1) OCT/FROZEN (stored at -80°C), (2) OCT/FRESH (stored at 4°C), and (3) OCA/FRESH. The OCA/FRESH group was subsequently lavaged at high flow for 45 seconds (660 mL) and 120 seconds (1,750 mL). Marrow cleansing was assessed grossly and by micro-computed tomography (μCT).

Results

Gross and μCT images indicated that marrow cleansing progressed from the OC base toward the cartilage. Empty marrow volume fraction (EMa.V/Ma.V) increased between 0, 45, and 120 seconds of standard flow lavage, and varied between groups, being higher after FROZEN storage (86–92% after 45–120 seconds) than FRESH storage of either OCT or OCA samples (36% and 55% after 45 and 120 seconds, respectively). With a subsequent 120 seconds of high flow lavage, EMa.V/Ma.V of OCA/FRESH samples increased from 61% to 78%.

Conclusions

The spatial and temporal pattern of marrow space clearance was consistent with gradual fluid-induced extrusion of marrow components. Pulsed lavage of OCAs with consistent time and flow intensity will help standardize marrow cleansing and may improve clinical outcomes.

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.

Osteochondral allograft

Over the past decade, osteochondral allograft transplantation has soared in popularity. Advances in storage techniques have demonstrated improved chondrocyte viability at longer intervals and allowed for potential of increased graft availability. Recent studies have stratified outcomes according to location and etiology of the chondral or osteochondral defect. Unipolar lesions generally have favorable outcomes with promising 10-year survival rates. Though those undergoing osteochondral allograft transplantation often require reoperation, patient satisfaction remains high.

Long-term storage and preservation of tissue engineered articular cartilage

With limited availability of osteochondral allografts, tissue engineered cartilage grafts may provide an alternative treatment for large cartilage defects. An effective storage protocol will be critical for translating this technology to clinical use. The purpose of this study was to evaluate the efficacy of the Missouri Osteochondral Allograft Preservation System (MOPS) for room temperature storage of mature tissue engineered grafts, focusing on tissue property maintenance during the current allograft storage window (28 days). Additional research compares MOPS to continued culture, investigates temperature influence, and examines longer-term storage. Articular cartilage constructs were cultured to maturity using adult canine chondrocytes, then preserved with MOPS at room temperature, in refrigeration, or kept in culture for an additional 56 days. MOPS storage maintained desired chondrocyte viability for 28 days of room temperature storage, retaining 75% of the maturity point Young's modulus without significant decline in biochemical content. Properties dropped past this time point. Refrigeration maintained properties similar to room temperature at 28 days, but proved better at 56 days. For engineered grafts, MOPS maintained the majority of tissue properties for the 28-day window without clearly extending that period as it had for native grafts. These results are the first evaluating engineered cartilage storage.

Impact of storage conditions on electromechanical, histological and histochemical properties of osteochondral allografts

BACKGROUND

Osteochondral allograft transplantation has a good clinical outcome, however, there is still debate on optimization of allograft storage protocol. Storage temperature and nutrient medium composition are the most critical factors for sustained biological activity of grafts before implantation. In this study, we performed a time-dependent in vitro experiment to investigate the effect of various storage conditions on electromechanical, histological and histochemical properties of articular cartilage.

METHODS

Osteochondral grafts derived from goat femoral condyles were frozen at -70 °C or stored at 4 °C and 37 °C in the medium supplemented with or without insulin-like growth factor-1 (IGF-1). After 14 and 28 days the cartilage samples were quantitatively analysed for electromechanical properties, glycosaminoglycan distribution, histological structure, chondrocyte viability and apoptosis. The results were compared between the experimental groups and correlations among different evaluation methods were determined.

RESULTS

Storage at -70 °C and 37 °C significantly deteriorated cartilage electromechanical, histological and histochemical properties. Storage at 4 °C maintained the electromechanical quantitative parameter (QP) and glycosaminoglycan expression near the normal levels for 14 days. Although hypothermic storage revealed reduced chondrocyte viability and increased apoptosis, these parameters were superior compared with the storage at -70 °C and 37 °C. IGF-1 supplementation improved the electromechanical QP, chondrocyte viability and histological properties at 37 °C, but the effect lasted only 14 days. Electromechanical properties correlated with the histological grading score (r = 0.673, p < 0.001), chondrocyte viability (r = -0.654, p < 0.001) and apoptosis (r = 0.416, p < 0.02). In addition, apoptosis correlated with glycosaminoglycan distribution (r = -0.644, p < 0.001) and the histological grading score (r = 0.493, p = 0.006).

CONCLUSIONS

Our results indicate that quality of allografts is better preserved at currently established 4 °C storage temperature. Storage at -70 °C or at 37 °C is unable to maintain cartilage function and metabolic activity. IGF-1 supplementation at 37 °C can enhance chondrocyte viability and improve electromechanical and histological properties of the cartilage, but the impact persists only 14 days. The correlations between cartilage electromechanical quantitative parameter (QP) and metabolic activity were detected. Our findings indicate that non-destructive assessment of cartilage by Arthro-BST is a simple and reliable method to evaluate allograft quality, and could be routinely used before implantation.

Knee salvage procedures: The indications, techniques and outcomes of large osteochondral allografts

The overall incidence of osteochondral defect in the general population is estimated to be 15 to 30 per 100000 people. These lesions can become symptomatic causing pain, swelling and decreased function of the knee, and may eventually progress to osteoarthritis. In the young and active population, partial or total knee arthroplasty (TKA) is rarely the treatment of choice due to risk of early failure. Osteochondral allograft transplantation has been demonstrated to be a safe and effective treatment of large osteochondral and chondral defects of the knee in appropriately selected patients. The treatment reduces pain, improves function and is a viable limb salvage procedure for patients, especially young and active patients for whom TKA is not recommended. Either large dowels generated with commercially available equipment or free hand shell allografts can be implanted in more posterior lesions. Current recommendations for fresh allografts stored at 4C advise implantation within 21-28 d of procurement for optimum chondrocyte viability, following screening and testing protocols. Higher rates of successful allograft transplantation are observed in younger patients, unipolar lesions, normal or corrected malalignment, and defects that are treated within 12 mo of symptom onset. Patients with bipolar lesions, uncorrectable malalignment, advanced osteoarthritis, and those over 40 tend to have less favourable outcomes.

Effect of Cold Storage and Freezing on the Biomechanical Properties of Swine Growth Plate Explants

Ex vivo biomechanical testing of growth plate samples provides essential information about its structural and physiological characteristics. Experimental limitations include the preservation of the samples since working with fresh tissues involves significant time and transportation costs. Little information is available on the storage of growth plate explants. The aim of this study was to determine storage conditions that could preserve growth plate biomechanical properties. Porcine ulnar growth plate explants (n = 5 per condition) were stored at either 4 °C for periods of 1, 2, 3, and 6 days or frozen at −20 °C with slow or rapid sample thawing. Samples were tested using stress relaxation tests under unconfined compression to assess five biomechanical parameters. The maximum compressive stress (σmax) and the equilibrium stress (σeq) were directly extracted from the experimental curves, while the fibril-network reinforced biphasic model was used to obtain the matrix modulus (Em), the fibril modulus (Ef), and the permeability (k). No significant changes were observed in σeq and Em in any of the tested storage conditions. Significant decreases and increases, respectively, were observed in σmax and k in the growth plate samples refrigerated for more than 48 h and in the frozen samples, when compared with the fresh samples. The fibril modulus Ef of all stored samples was significantly reduced compared to the fresh samples. These results indicate that the storage of growth plates in a humid chamber at 4 °C for a maximum of 48 h is the condition that minimizes the effects on the measured biomechanical parameters, with only Ef significantly reduced. Refrigerating growth plate explants for less than 48 h maintains their maximal stress, equilibrium stress, matrix modulus, and permeability. However, cold storage at 4 °C for more than 48 h and freezing storage at −20 °C significantly alter the biomechanical response of growth plate samples. Appropriate growth plate sample storage will be beneficial to save time and reduce transportation costs to pick up fresh samples.

Osteochondral allograft of the talus

Osteochondral lesions of the talus are being recognized as an increasingly common injury. They are most commonly located postero-medially or antero-laterally, while centrally located lesions are uncommon. Large osteochondral lesions have significant biomechanical consequences and often require resurfacing with osteochondral autograft transfer, mosaicplasty, autologous chondrocyte implantation (or similar methods) or osteochondral allograft transplantation. Allograft procedures have become popular due to inherent advantages over other resurfacing techniques. Cartilage viability is one of the most important factors for successful clinical outcomes after transplantation of osteochondral allografts and is related to storage length and intra-operative factors. While there is abundant literature about osteochondral allograft transplantation in the knee, there are few papers about this procedure in the talus. Failure of non-operative management, initial debridement, curettage or microfractures are an indication for resurfacing. Patients should have a functional ankle motion, closed growth plates, absence of cartilage lesions on the tibial side. This paper reviews the published literature about osteochondral allograft transplantation of the talus focusing on indications, pre-operative planning, surgical approaches, postoperative management, results and complications of this procedure.

Bone cysts after osteochondral allograft repair of cartilage defects in goats suggest abnormal interaction between subchondral bone and overlying synovial joint tissues

The efficacy of osteochondral allografts (OCAs) may be affected by osseous support of the articular cartilage, and thus affected by bone healing and remodeling in the OCA and surrounding host. Bone cysts, and their communication pathways, may be present in various locations after OCA insertion and reflect distinct pathogenic mechanisms. Previously, we analyzed the effect of OCA storage (FRESH, 4°C/14d, 4°C/28d, FROZEN) on cartilage quality in fifteen adult goats after 12months in vivo. The objectives of this study were to further analyze OCAs and contralateral non-operated (Non-Op) CONTROLS from the medial femoral condyle to (1) determine the effect of OCA storage on local subchondral bone (ScB) and trabecular bone (TB) structure, (2) characterize the location and structure of bone cysts and channels, and (3) assess the relationship between cartilage and bone properties. (1) Overall bone structure after OCAs was altered compared to Non-Op, with OCA samples displaying bone cysts, ScB channels, and ScB roughening. ScB BV/TV in FROZEN OCAs was lower than Non-Op and other OCAs. TB BV/TV in FRESH, 4°C/14d, and 4°C/28d OCAs did not vary compared to Non-Op, but BS/TV was lower. (2) OCAs contained "basal" cysts, localized to deeper regions, some "subchondral" cysts, localized near the bone-cartilage interface, and some ScB channels. TB surrounding basal cysts exhibited higher BV/TV than Non-Op. (3) Basal cysts occurred (a) in isolation, (b) with subchondral cysts and ScB channels, (c) with ScB channels, or (d) with subchondral cysts, ScB channels, and ScB erosion. Deterioration of cartilage gross morphology was strongly associated with abnormal μCT bone structure. Evidence of cartilage-bone communication following OCA repair may favor fluid intrusion as a mechanism for subchondral cyst formation, while bone resorption at the graft-host interface without affecting overall bone and cartilage structure may favor bony contusion mechanism for basal cyst formation. These findings suggest that cysts occurring after OCAs may result from aberrant mechanobiology due to (1) altered compartmentalization that normally separates overlying cartilage and subchondral bone, either from distinct ScB channels or more general ScB plate deterioration, and (2) bone resorption at the basal graft-host interface.

In vivo efficacy of fresh versus frozen osteochondral allografts in the goat at 6 months is associated with PRG4 secretion

The long-term efficacy of osteochondral allografts is due to the presence of viable chondrocytes within graft cartilage. Chondrocytes in osteochondral allografts, especially those at the articular surface that normally produce the lubricant proteoglycan-4 (PRG4), are susceptible to storage-associated death. The hypothesis of this study was that the loss of chondrocytes within osteochondral grafts leads to decreased PRG4 secretion, after graft storage and subsequent implant. The objectives were to determine the effect of osteochondral allograft treatment (FROZEN vs. FRESH) on secretion of functional PRG4 after (i) storage, and (ii) 6 months in vivo in adult goats. FROZEN allograft storage reduced PRG4 secretion from cartilage by ∼85% compared to FRESH allograft storage. After 6 months in vivo, the PRG4-secreting function of osteochondral allografts was diminished with prior FROZEN storage by ∼81% versus FRESH allografts and by ∼84% versus non-operated control cartilage. Concomitantly, cellularity at the articular surface in FROZEN allografts was ∼96% lower than FRESH allografts and non-operated cartilage. Thus, the PRG4-secreting function of allografts appears to be maintained in vivo based on its state after storage. PRG4 secretion may be not only a useful marker of allograft performance, but also a biological process protecting the articular surface of grafts following cartilage repair.

Anatomic variation of depth-dependent mechanical properties in neonatal bovine articular cartilage

Articular cartilage has well known depth-dependent structure and has recently been shown to have similarly non-uniform depth-dependent mechanical properties. Here, we study anatomic variation of the depth-dependent shear modulus and energy dissipation rate in neonatal bovine knees. The regions we specifically focus on are the patellofemoral groove, trochlea, femoral condyle, and tibial plateau. In every sample, we find a highly compliant region within the first 500 µm of tissue measured from the articular surface, where the local shear modulus is reduced by up to two orders of magnitude. Comparing measurements taken from different anatomic sites, we find statistically significant differences localized within the first 50 µm. Histological images reveal these anatomic variations are associated with differences in collagen density and fiber organization.

Treatment of articular cartilage defects in the goat with frozen versus fresh osteochondral allografts: effects on cartilage stiffness, zonal composition, and structure at six months

BACKGROUND

Understanding the effectiveness of frozen as compared with fresh osteochondral allografts at six months after surgery and the resultant consequences of traditional freezing may facilitate in vivo maintenance of cartilage integrity. Our hypothesis was that the state of the allograft at implantation affects its performance after six months in vivo.

METHODS

The effect of frozen as compared with fresh storage on in vivo allograft performance was determined for osteochondral allografts that were transplanted into seven recipient goats and analyzed at six months. Allograft performance was assessed by examining osteochondral structure (cartilage thickness, fill, surface location, surface degeneration, and bone-cartilage interface location), zonal cartilage composition (cellularity, matrix content), and cartilage biomechanical function (stiffness). Relationships between cartilage stiffness or cartilage composition and surface degeneration were assessed with use of linear regression.

RESULTS

Fresh allografts maintained cartilage load-bearing function, while also maintaining zonal organization of cartilage cellularity and matrix content, compared with frozen allografts. Overall, allograft performance was similar between fresh allografts and nonoperative controls. However, cartilage stiffness was approximately 80% lower (95% confidence interval [CI], 73% to 87%) in the frozen allografts than in the nonoperative controls or fresh allografts. Concomitantly, in frozen allografts, matrix content and cellularity were approximately 55% (95% CI, 22% to 92%) and approximately 96% (95% CI, 94% to 99%) lower, respectively, than those in the nonoperative controls and fresh allografts. Cartilage stiffness correlated positively with cartilage cellularity and matrix content, and negatively with surface degeneration.

CONCLUSIONS

Maintenance of cartilage load-bearing function in allografts is associated with zonal maintenance of cartilage cellularity and matrix content. In this animal model, frozen allografts displayed signs of failure at six months, with cartilage softening, loss of cells and matrix, and/or graft subsidence, supporting the importance of maintaining cell viability during allograft storage and suggesting that outcomes at six months may be indicative of long-term (dys)function.

CLINICAL RELEVANCE

Fresh versus frozen allografts represent the "best versus worst" conditions with respect to chondrocyte viability, but "difficult versus simple" with respect to acquisition and distribution. The outcomes described from these two conditions expand the current understanding of in vivo cartilage remodeling and describe structural properties (initial graft subsidence), which may have implications for impending graft failure.

Allogenic serum improves cold preservation of osteochondral allografts

BACKGROUND

Although several types of culture medium have been used for preservation of osteochondral allografts, the viability of chondrocytes decreases with increasing storage duration. We previously showed the University of Wisconsin solution is more suitable for graft preservation than culture medium.

QUESTIONS/PURPOSES

We determined whether the addition of allogenic serum to University of Wisconsin solution increases chondrocyte survival during prolonged storage of osteochondral allografts.

METHODS

Osteochondral tissue samples harvested from the distal femora of rats were preserved in University of Wisconsin solution supplemented with 0%, 1%, 10%, and 50% allogenic serum at 4 °C for 14 days. Cell viability and chondrocyte degenerative changes of the samples then were assessed using a tetrazolium assay and histologic methods. We also evaluated time-dependent changes in cell viability and histologic findings of samples preserved for 7, 14, and 21 days in University of Wisconsin solution supplemented with or without 10% allogenic serum.

RESULTS

After 14 days of preservation, osteochondral tissue samples maintained in University of Wisconsin solution containing 10% or greater allogenic serum exhibited the highest cell viability and lowest degenerative changes in chondrocytes. In the evaluation of time-dependent changes, we found the chondrocyte degenerative changes were greater in cartilage preserved in University of Wisconsin solution alone than in University of Wisconsin solution containing 10% allogenic serum after day 7 or later.

CONCLUSIONS

Our results suggest the addition of 10% allogenic serum to University of Wisconsin solution enhances viability of osteochondral tissue samples.

CLINICAL RELEVANCE

The use of allogenic serum-supplemented University of Wisconsin solution is expected to prolong the duration of osteochondral allograft storage and result in higher-quality grafts.

The use of osteochondral allografts in the management of cartilage defects

Large symptomatic osteochondral defects in a young active population represent a therapeutic challenge for orthopedic surgeons, since standard interventions such as debridement, microfracture and autologous osteochondral transfer are not suitable for the treatment of these larger lesions. Fresh osteochondral allograft transplantation provides a surgical option for these challenging defects, both as a primary procedure and for salvage of prior failed treatment attempts. This article reviews the basic science, indications, technique, and evidence for osteochondral allograft transplantation in the knee.

The in vivo performance of osteochondral allografts in the goat is diminished with extended storage and decreased cartilage cellularity

BACKGROUND

Currently, osteochondral allografts (OCA) are typically used after 4°C storage for prolonged durations (15-43 days), which compromises chondrocyte viability, especially at the articular surface. The long-term in vivo performance of these fresh-stored allografts, in association with variable cellularity, is unknown.

PURPOSE

To determine the effect of 4°C storage duration (14, 28 days) versus the best (fresh) and worst (frozen) conditions of chondrocyte viability on structure, composition, and function of cartilage in the goat and the association of retrieved chondrocyte cellularity with those tissue properties.

STUDY DESIGN

Controlled laboratory study.

METHODS

The effect of allograft storage on in vivo repair outcomes was determined for OCA transplanted into 15 recipient goats and analyzed at 12 months. Repair outcomes were assessed by examining cartilage structure (gross, histopathology), composition (cellularity by depth, matrix fixed charge), and biomechanical function (stiffness). Relationships between cellularity and structural scores, matrix fixed charge, and stiffness were assessed by linear regression.

RESULTS

Repair outcomes in 4°C-stored OCA were similar after 14 and 28 days of storage, and both were inferior to fresh OCA and were accompanied by diminished cellularity at the surface, matrix fixed charge, and histopathological structure. Overall, cellularity by depth and matrix fixed charge in cartilage of fresh OCA were similar to nonoperated controls. However, cellularity at the articular surface and matrix fixed charge in 4°C-stored OCA were lower than fresh, by ~55% (95% confidence interval [CI], 32%-76%) and ~20% (CI, 9%-30%), respectively. In frozen OCA, cellularity and matrix fixed charge were lower than 4°C-stored OCA, by ~93% (CI, 88%-99%) and ~22% (CI, 10%-35%), respectively. Cellularity correlated negatively with cartilage health indices, including structural scores, and positively with matrix fixed charge and stiffness.

CONCLUSION

Reduced cellularity at the articular surface, resulting from 4°C storage, was associated with variable long-term outcomes versus consistently good repair by fresh allografts. Cellularity at the articular surface was an important index of biological performance.

CLINICAL RELEVANCE

Normal chondrocyte density in vivo, especially in the superficial region of cartilage, is important for maintaining long-term cartilage function and matrix content. In human cartilage, containing cells at ~3 to 5 times lower density than goat, repair outcomes may be related to absolute minimum number of cells rather than density.

Scanty integration of osteochondral allografts cryopreserved at low temperatures with dimethyl sulfoxide

PURPOSE

To compare the integration of osteochondral allografts cryopreserved at different temperatures and different concentrations of dimethyl sulfoxide in an in vivo sheep animal model.

METHODS

Thirty-six adult sheep were randomly allocated to 6 groups of allograft osteochondral transplantation. Six osteochondral cylinders were stored for 6 weeks at -80°C; 6 at -80°C with 10% dimethyl sulfoxide (DMSO); 6 at -80°C with 10% DMSO for 90 min; 6 at -186°C; 6 at -186°C with 10% DMSO; 6 at -186°C for 90 min. After transplantation, all animals were euthanized at 6 months. Harvested specimens underwent gross morphologic and histologic evaluation.

RESULTS

We found no statistically significant differences when comparing the gross cartilage morphology and histopathologic scores of each group. The Mankin and OARSI scores and the modified Wakitani and OARSI scores showed a good correlation grade. The Mankin and modified Wakitani scores showed a fair correlation grade.

CONCLUSION

The cryopreservation protocols adopted in the present study provided scanty integration in an in vivo sheep model of osteochondral allograft transplantation. Therefore, their use in the clinical practice is discouraged.

Chondrocytes within osteochondral grafts are more resistant than osteoblasts to tissue culture at 37°C

It is proposed that an ideal osteochondral allograft for cartilage repair consists of a devitalized bone but functional cartilage. The different modes of nutrient supply in vivo for bone (vascular support) and cartilage (diffusion) suggest that a modulation of storage conditions could differentially affect the respective cells, resulting in the proposed allograft. For this purpose, osteochondral tissues from porcine humeral heads were either cultured at 37°C for up to 24 hr or stored at 4°C for 24 hr, the temperature at which osteochondral allografts are routinely stored. Functionality of the cells was assessed by in situ hybridization for transcripts encoding collagen types I and II. At 37°C, a time-dependent significant reduction of the bone surface covered with functional cells was observed with only 5% ± 5% coverage left at 24 hr compared with 41% ± 10% at 0 hr. Similarly, cartilage area containing functional cells was significantly reduced from 84% ± 7% at 0 hr to 70% ± 3% after 24 hr. After 24 hr at 4°C, a significantly reduced amount of functional cells covering bone surfaces was observed (27% ± 5%) but not of cells within the cartilage (79% ± 8%). In the applied experimental setup, bone cells were more affected by tissue culture at 37°C than cartilage cells. Even though chondrocytes appear to be more sensitive to 37°C than to 4°C, the substantially reduced amount of functional bone cells at 37°C warrants further investigation of whether a preincubation of osteochondral allografts at 37°C--prior to regular storage at 4°C--might result in an optimized osteochondral allograft with devitalized bone but viable cartilage.

Osteochondral allografts: state of the art

The use of osteochondral allografts to treat focal osteochondral lesions continues to gain popularity, supported by long-term results. Clinicians must be knowledgeable concerning the possible risks of disease transmission, graft rejection, infection, and graft failure to advise the patient and obtain an informed consent. With advancing scientific and clinical research, future operative indications will likely continue to expand. A significant amount of literature regarding storage methods has recently been published; it is hoped that continued research will lead to techniques for prolonged graft storage to prevent availability concerns.