Temporal changes in collagen cross-links in spontaneous articular cartilage repair

Review paper: The importance of consideration of collagen cross-links in computational models of collagen-based tissues

Collagen as the main protein in Extra Cellular Matrix (ECM) is the main load-bearing component of fibrous tissues. Nanostructure and architecture of collagen fibrils play an important role in mechanical behavior of these tissues. Extensive experimental and theoretical studies have so far been performed to capture these properties, but none of the current models realistically represent the complexity of network mechanics because still less is known about the collagen's inner structure and its effect on the mechanical properties of tissues. The goal of this review article is to emphasize the significance of cross-links in computational modeling of different collagen-based tissues, and to reveal the need for continuum models to consider cross-links properties to better reflect the mechanical behavior observed in experiments. In addition, this study outlines the limitations of current investigations and provides potential suggestions for the future work.

High rate of return-to-play following meniscal allograft transplantation

PURPOSE

In recent years, meniscal allograft transplantation (MAT) has been established as an effective option for young patients with symptomatic meniscus insufficiency with goals of functional improvement and joint preservation. Currently, there is little available information on return-to-play among patients in this cohort. The purpose of this study is to systematically review the literature and to evaluate the reported rehabilitation protocols, return-to-play guidelines, and subsequent rates of return-to-play following MAT.

METHODS

MEDLINE, EMBASE and the Cochrane Library were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to find studies on MAT. Studies were included if they reported return-to-play data or rehabilitation protocols. The rate and timing of return-to-play was assessed. The rehabilitation protocols were recorded, including time to start range of motion (ROM), full ROM, partial weight bearing (WB), and full WB.

RESULTS

Overall, 67 studies met the inclusion criteria. Eleven studies, including 624 patients, reported 483 out of 624 patients (77.4%) returning to play, with 326 out of a reported 475 patients (68.6%) returning to the same/higher level, at a mean time to return of 9.0 months. There was significant variability in the reported rehabilitation protocols, but the most commonly reported time to begin ROM exercises was within the first week by 42 out of 60 studies (70.0%) and full ROM at 8 weeks by 18 out of 46 studies (39.1%). Partial weight bearing was most commonly begun in the fourth week by 20 out of 46 studies (43.5%), and for full WB the sixth week by 43 out of 65 studies (66.1%). Time elapsed following surgery was the most commonly reported criteria for return-to-play by 44 out of 48 studies (91.6%), with 6 months being the most common time point utilized by 17 out of 45 studies (37.8%). A small proportion of studies, 16 out of 48 (33.3%), advised against returning to competitive/collision sports altogether following MAT.

CONCLUSIONS

In conclusion, there is a high rate of return-to-play following MAT, with the majority of patients returning to the same level of play. However, there is significant variability in reported rehabilitation protocols, and poor-quality reporting in return-to-play criteria in the literature indicates a need for further study and the development of an evidence-based consensus statement for this patient population. The results from this study can be used to better inform patients on their expected outcomes and provide a more informed consent process.

LEVEL OF EVIDENCE

IV.

High reported rate of return to play following bone marrow stimulation for osteochondral lesions of the talus

PURPOSE

The purpose of this study is to systematically review the literature and to evaluate the reported rehabilitation protocols, return to play guidelines and subsequent rates and timing of return to play following bone marrow stimulation (BMS) for osteochondral lesions of the talus (OLT).

METHODS

MEDLINE, EMBASE and the Cochrane Library were searched according to the PRISMA guidelines in September 2017. The rate and timing of return to play was assessed. The rehabilitation protocols were recorded, including time to start range of motion, partial weight-bearing and complete weight-bearing.

RESULTS

Fifty-seven studies with 3072 ankles were included, with a mean age of 36.9 years (range 23-56.8 years), and a mean follow-up of 46.0 months (range 1.5-141 months). The mean rate of return to play was 86.8% (range 60-100%), and the mean time to return to play was 4.5 months (range 3.5-5.9 months). There was large variability in the reported rehabilitation protocols. Range of motion exercises were most often allowed to begin in the first week (46.2%), and second week postoperatively (23.1%). The most commonly reported time to start partial weight-bearing was the first week (38.8%), and the most frequently reported time of commencing full weight-bearing was 6 weeks (28.8%). Surgeons most often allowed return to play at 4 months (37.5%).

CONCLUSIONS

There is a high rate of return following BMS for OLT with 86.8% and the mean time to return to play was 4.5 months. There is also a significant deficiency in reported rehabilitation protocols, and poor quality reporting in return to play criteria. Early weightbearing and early postoperative range of motion exercises appear to be advantageous in accelerated return to sports.

LEVEL OF EVIDENCE

Level IV.

Nutrient supply and nucleus pulposus cell function: effects of the transport properties of the cartilage endplate and potential implications for intradiscal biologic therapy

OBJECTIVE

Intradiscal biologic therapy is a promising strategy for managing intervertebral disc degeneration. However, these therapies require a rich nutrient supply, which may be limited by the transport properties of the cartilage endplate (CEP). This study investigated how fluctuations in CEP transport properties impact nutrient diffusion and disc cell survival and function.

DESIGN

Human CEP tissues harvested from six fresh cadaveric lumbar spines (38-66 years old) were placed at the open sides of diffusion chambers. Bovine nucleus pulposus (NP) cells cultured inside the chambers were nourished exclusively by nutrients diffusing through the CEP tissues. After 72 h in culture, depth-dependent NP cell viability and gene expression were measured, and related to CEP transport properties and biochemical composition determined using fluorescence recovery after photobleaching and Fourier transform infrared (FTIR) spectroscopy.

RESULTS

Solute diffusivity varied nearly 4-fold amongst the CEPs studied, and chambers with the least permeable CEPs appeared to have lower aggrecan, collagen-2, and matrix metalloproteinase-2 gene expression, as well as a significantly shorter viable distance from the CEP/nutrient interface. Increasing chamber cell density shortened the viable distance; however, this effect was lost for low-diffusivity CEPs, which suggests that these CEPs may not provide enough nutrient diffusion to satisfy cell demands. Solute diffusivity in the CEP was associated with biochemical composition: low-diffusivity CEPs had greater amounts of collagen and aggrecan, more mineral, and lower cross-link maturity.

CONCLUSIONS

CEP transport properties dramatically affect NP cell survival/function. Degeneration-related CEP matrix changes could hinder the success of biologic therapies that require increased nutrient supply.

Mesenchymal Stem/Progenitor Cells Derived from Articular Cartilage, Synovial Membrane and Synovial Fluid for Cartilage Regeneration: Current Status and Future Perspectives

Large articular cartilage defects remain an immense challenge in the field of regenerative medicine because of their poor intrinsic repair capacity. Currently, the available medical interventions can relieve clinical symptoms to some extent, but fail to repair the cartilaginous injuries with authentic hyaline cartilage. There has been a surge of interest in developing cell-based therapies, focused particularly on the use of mesenchymal stem/progenitor cells with or without scaffolds. Mesenchymal stem/progenitor cells are promising graft cells for tissue regeneration, but the most suitable source of cells for cartilage repair remains controversial. The tissue origin of mesenchymal stem/progenitor cells notably influences the biological properties and therapeutic potential. It is well known that mesenchymal stem/progenitor cells derived from synovial joint tissues exhibit superior chondrogenic ability compared with those derived from non-joint tissues; thus, these cell populations are considered ideal sources for cartilage regeneration. In addition to the progress in research and promising preclinical results, many important research questions must be answered before widespread success in cartilage regeneration is achieved. This review outlines the biology of stem/progenitor cells derived from the articular cartilage, the synovial membrane, and the synovial fluid, including their tissue distribution, function and biological characteristics. Furthermore, preclinical and clinical trials focusing on their applications for cartilage regeneration are summarized, and future research perspectives are discussed.

Hyaluronan thiomer gel/matrix mediated healing of articular cartilage defects in New Zealand White rabbits-a pilot study

Background

Articular cartilage defects are limited to their regenerative potential in human adults. Our current study evaluates tissue regeneration in a surgically induced empty defect site with hyaluronan thiomer as a provisional scaffold in a gel/matrix combination without cells on rabbit models to restore tissue formation.

Methods

An osteochondral defect of 4 mm in diameter and 5 mm in depth was induced by mechanical drilling in the femoral center of the trochlea in 18 New Zealand White rabbits. Previously evaluated from an in vitro study hyaluronan thiomer matrix, and a hyaluronan thiomer gel was used to treat the defect. As a control, the defect was left untreated. During the whole study, rabbits were clinically examined and after 4 (n = 3) or 12 (n = 3) weeks, the rabbits were sacrificed. Joints were evaluated macroscopically (Brittberg score) and by histology (O’Driscoll score). Synovial cells from the synovial fluid smear were histopathologically evaluated.

Results

The healing of the defects varied intra-group wise at the first observation period. After 12 weeks the results concerning the cartilage repair score were inhomogeneous within each group, while the macroscopic analysis was more homogenous. In the synovial fluid smear, the mean score of infiltrated synovial and non-synovial cells was slightly increased after 4 weeks and slightly decreased after 12 weeks in both the treatment groups in comparison to the untreated control.

Conclusions

Taken together with results from the in vivo study indicated that implantation of hyaluronan thiomer as a combination of gel and matrix might enhance articular cartilage regeneration in an empty defect. Despite their benefits, the intrinsic healing capacity of New Zealand rabbits is a limitation for comparative test subject in pre-clinical models of cartilage defects.

Immediate Unrestricted Postoperative Weightbearing and Mobilization after Bone Marrow Stimulation of Large Osteochondral Lesions of the Talus

OBJECTIVE

There remains no consensus on a postoperative protocol following arthroscopic treatment of osteochondral lesions of the talus (OLTs) and most studies report a period of immobilization and nonweightbearing. Outcomes are believed to decrease with larger size. The purpose of our study was to evaluate patients who underwent arthroscopic treatment of large (≥150 mm²) OLTs with immediate unrestricted weightbearing and mobilization postoperatively.

DESIGN

Patients who underwent arthroscopic bone marrow stimulation for osteochondral defects were identified. Exclusion criteria included lesions less than 150 mm², additional procedures other than ligament reconstruction, incongruent ankle joint, arthritis, and tibial plafond lesions. Postoperatively, all patients were placed into a soft dressing and were allowed immediate weightbearing as tolerated. Patients were considered failures if their AOFAS (American Orthopaedic Foot and Ankle Society) score was less than 80 or if they underwent osteochondral transplant.

RESULTS

Thirteen patients were available for follow-up. Two patients underwent osteochondral transplant and were considered failures. Of the remaining 11, the average follow-up time after surgery was 33 months (range, 7-59 months). Average age was 37 years (range, 15-56 years), and lesion size averaged 239 mm² (range, 150-400 mm²). Average postoperative scores included foot function index 50 (range, 23-136), visual analog scale 3 (range, 0-8), and AOFAS hindfoot 82 (range, 40-100). The group's overall success rate was 54% (7/13).

CONCLUSION

The results of our study are higher than those previously published studies on large lesions with a more restricted postoperative rehabilitation, suggesting that unrestricted weightbearing and range of motion does not diminish patient outcomes.

LEVEL OF EVIDENCE

IV, Case series.

A multi-scale elasto-plastic model of articular cartilage

Collagen damage is one of the earliest signs of cartilage degeneration and the onset of osteoarthritis (OA), but the connection between the microscale damage and macroscale tissue function is unclear. We argue that a multiscale model can help elucidate the biochemical and mechanical underpinnings of OA by connecting the microscale defects in collagen fibrils to the macroscopic cartilage mechanics. We investigated this connection using a multiscale fibril reinforced hyperelastoplastic (MFRHEP) model that accounts for the structural architecture of the soft tissue, starting from tropocollagen molecules that form fibrils, and moving to the complete soft tissue. This model was driven by reported experimental data from unconfined compression testing of cartilage. The model successfully described the observed transient response of the articular cartilage in unconfined and indentation tests with low and high loading rates. We used this model to understand damage initiation and propagation as a function of the cross-link density between tropocollagen molecules. This approach appeared to provide a realistic simulation of damage when compared with certain published studies. The current construct presents the first attempt to express the aggregate cartilage damage in terms of the cross-link density at the microfibril level.

Monitoring the Progression of Spontaneous Articular Cartilage Healing with Infrared Spectroscopy

OBJECTIVE

Evaluation of early compositional changes in healing articular cartilage is critical for understanding tissue repair and for therapeutic decision-making. Fourier transform infrared imaging spectroscopy (FT-IRIS) can be used to assess the molecular composition of harvested repair tissue. Furthermore, use of an infrared fiber-optic probe (IFOP) has the potential for translation to a clinical setting to provide molecular information in situ. In the current study, we determined the feasibility of IFOP assessment of cartilage repair tissue in a rabbit model, and assessed correlations with gold-standard histology.

DESIGN

Bilateral osteochondral defects were generated in mature white New Zealand rabbits, and IFOP data obtained from defect and adjacent regions at 2, 4, 6, 8, 12, and 16 weeks postsurgery. Tissues were assessed histologically using the modified O'Driscoll score, by FT-IRIS, and by partial least squares (PLS) modeling of IFOP spectra.

RESULTS

The FT-IRIS parameters of collagen content, proteoglycan content, and collagen index correlated significantly with modified O'Driscoll score (P = 0.05, 0.002, and 0.02, respectively), indicative of their sensitivity to tissue healing. Repair tissue IFOP spectra were distinguished from normal tissue IFOP spectra in all samples by PLS analysis. However, the PLS model for prediction of histological score had a high prediction error, which was attributed to the spectral information being acquired from the tissue surface only.

CONCLUSION

The strong correlations between FT-IRIS data and histological score support further development of the IFOP technique for clinical applications, although further studies to optimize data collection from the full sample depths are required.

Novel scaffold-based BST-CarGel treatment results in superior cartilage repair compared with microfracture in a randomized controlled trial

BACKGROUND

Microfracture, the standard of care, is recognized to be an incomplete solution for cartilage damage. BST-CarGel, a chitosan-based medical device, is mixed with autologous whole blood and is applied to a microfractured cartilage lesion in which it physically stabilizes the clot and guides and enhances marrow-derived repair. An international, multicenter, randomized controlled trial was conducted to evaluate BST-CarGel treatment compared with microfracture alone in the repair of cartilage lesions in the knee.

METHODS

Eighty patients between the ages of eighteen and fifty-five years with a single, symptomatic focal lesion on the femoral condyles were randomized to BST-CarGel and microfracture treatment (n = 41) or microfracture treatment alone (n = 39). The primary end points of repair tissue quantity and quality at twelve months were assessed by quantitative three-dimensional magnetic resonance imaging measuring the degree of lesion filling and T2 relaxation time with use of standardized one and twelve-month posttreatment scans. The secondary end point at twelve months was clinical benefit determined with the Western Ontario and McMaster Universities Osteoarthritis Index. The tertiary end point was quality of life determined by the Short Form-36. Safety was assessed through the recording of adverse events.

RESULTS

Patient baseline characteristics were similar in the two groups, although baseline lesion areas were slightly larger on quantitative magnetic resonance imaging for the BST-CarGel group compared with the microfracture group. Blinded quantitative magnetic resonance imaging analysis demonstrated that, at twelve months, when compared with microfracture treatment alone, BST-CarGel treatment met both primary end points by achieving statistical superiority for greater lesion filling (p = 0.011) and more hyaline cartilage-like T2 values (p = 0.033). The lesion filling values were 92.8% ± 2.0% for the BST-CarGel treatment group and 85.2% ± 2.1% for the microfracture treatment group, and the mean T2 values were 70.5 ± 4.5 ms for the BST-CarGel treatment group and 85.0 ± 4.9 ms for the microfracture treatment group. Western Ontario and McMaster Universities Osteoarthritis Index subscales for pain, stiffness, and function yielded equivalent improvement for both groups at twelve months, which were significant (p < 0.0001) from baseline. Treatment safety profiles were considered comparable.

CONCLUSIONS

At twelve months, BST-CarGel treatment resulted in greater lesion filling and superior repair tissue quality compared with microfracture treatment alone. Clinical benefit was equivalent between groups at twelve months, and safety was similar.

Clinical outcome of autologous chondrocyte implantation is correlated with infrared spectroscopic imaging-derived parameters

OBJECTIVE

To investigate whether Fourier transform infrared imaging spectroscopy (FT-IRIS), a modality based on molecular vibrations, is a viable alternative to histology and immunohistochemistry (IHC) for assessment of tissue quality and patient clinical outcome.

METHODS

Osteochondral biopsies were obtained from patients (9-65 months post-surgery) who underwent an autologous chondrocyte implantation (ACI) procedure to repair a cartilage defect (N = 14). The repair tissue was evaluated histologically by OsScore grading, for the presence of types I and II collagen by IHC, and for proteoglycan (PG) distribution and collagen quality parameters by FT-IRIS. Patient clinical outcome was assessed by the Lysholm score.

RESULTS

Improvement in Lysholm score occurred in 79% of patients. IHC staining showed the presence of types I and II collagen in all samples, with a greater amount of collagen type II in the deep zone. The amount and location of immunostaining for type II collagen correlated to the FT-IRIS-derived parameters of relative PG content and collagen helical integrity. In addition, the improvement in Lysholm score post-ACI correlated positively with the OsScore, type II collagen (IHC score) and FT-IRIS-determined parameters. Regression models for the relation between improvement in Lysholm score and either OsScore, IHC area score or the FT-IRIS parameters all reached significance (p < 0.01). However, the FT-IRIS model was not significantly improved with inclusion of the OsScore and IHC score parameters.

CONCLUSION

Demonstration of the correlation between FT-IRIS-derived molecular parameters of cartilage repair tissue and patient clinical outcome lays the groundwork for translation of this methodology to the clinical environment to aid in the management of cartilage disorders and their treatment.