Current concepts of articular cartilage restoration techniques in the knee

Continuous Low-Intensity Ultrasound Improves Cartilage Repair in Rabbit Model of Subchondral Injury

Subchondral drilling (SD), a bone marrow stimulation technique, is used to repair cartilage lesions that lack regenerative potential. Cartilage repair outcomes upon SD are typically fibrocartilaginous in nature with inferior functionality. The lack of cues to foster the chondrogenic differentiation of egressed mesenchymal stromal cells upon SD can be attributed for the poor outcomes. Continuous low-intensity ultrasound (cLIUS) at 3.8 MHz is proposed as a treatment modality for improving cartilage repair outcomes upon marrow stimulation. Bilateral defects were created by SD on the femoral medial condyle of female New Zealand white rabbits (n = 12), and the left joint received cLIUS treatment (3.8 MHz, 3.5 Vpp, 8 min/application/day) and the contralateral right joint served as the control. On day 7 postsurgery, synovial fluid was aspirated, and the cytokine levels were assessed by Quantibody™ assay. Rabbits were euthanized at 8 weeks and outcomes were assessed macroscopically and histologically. Defect areas in the right joints exhibited boundaries, incomplete fill, irregular cartilage surfaces, loss of glycosaminoglycan (GAG), and absence of chondrocytes. In contrast, the repaired defect area in the joints that received cLIUS showed complete fill, positive staining for GAG with rounded chondrocyte morphology, COL2A1 staining, and columnar organization. Synovial fluid collected from cLIUS-treated left knee joints had lower levels of IL1, TNFα, and IFNγ when compared to untreated right knee joints, alluding to the potential of cLIUS to mitigate early inflammation. Further at 8 weeks, left knee joints (n = 12) consistently scored higher on the O'Driscoll scale, with a higher percent hyaline cartilage score. No adverse impact on bone or change in the joint space was noted. Upon a single exposure of cLIUS to TNFα-treated cells, nuclear localization of pNFκB and SOX9 was visualized by double immunofluorescence and the expression of markers associated with the NFκB pathway was assayed by quantitative real-time polymerase chain reaction. cLIUS extends its chondroprotective effects by titrating pNFκB levels, preventing its nuclear translocation, while maintaining the expression of SOX9, the collagen II transcription factor. Our combined results demonstrate that healing of chondral defects treated with marrow stimulation by SD can be accelerated by employing cLIUS regimen that possesses chondroinductive and chondroprotective properties. Impact statement Repair of cartilage represents an unsolved biomedical burden. In vitro, continuous low-intensity ultrasound (cLIUS) has been demonstrated to possess chondroinductive and chondroprotective potential. To our best knowledge, the use of cLIUS to improve cartilage repair outcomes upon marrow stimulation, in vivo, has not been reported and our work reported here fills that gap. Our results demonstrated enhanced cartilage repair outcomes under cLIUS (3.8 MHz) in a rabbit model of subchondral injury by subchondral drilling. Enhanced repair stemmed from mesenchymal stem cell differentiation in vivo and the subsequent synthesis of articular cartilage-specific matrix.

Development of a patient specific cartilage graft using magnetic resonance imaging and 3D printing

OBJECTIVES

The goal of this project was to develop and validate a patient-specific, anatomically correct graft for cartilage restoration using magnetic resonance imaging (MRI) data and 3-dimensional (3D) printing technology. The specific aim was to test the accuracy of a novel method for 3D printing and implanting individualized, anatomically shaped bio-scaffolds to treat cartilage defects in a human cadaveric model. We hypothesized that an individualized, anatomic 3D-printed scaffold designed from MRI data would provide a more optimal fill for a large cartilage defect compared to a generic flat scaffold.

METHODS

Four focal cartilage defects (FCDs) were created in paired human cadaver knees, age <40 years, in the weight-bearing surfaces of the medial femoral condyle (MFC), lateral femoral condyle (LFC), patella, and trochlea of each knee. MRIs were obtained, anatomic grafts were designed and 3D printed for the left knee as an experimental group, and generic flat grafts for the right knee as a control group. Grafts were implanted into corresponding defects and fixed using tissue adhesive. Repeat post-implant MRIs were obtained. Graft step-off was measured as the distance in mm between the surface of the graft and the native cartilage surface in a direction perpendicular to the subchondral bone. Graft contour was measured as the gap between the undersurface of the graft and the subchondral bone in a direction perpendicular to the joint surface.

RESULTS

Graft step-off was statistically significantly better for the anatomic grafts compared to the generic grafts in the MFC (0.0 ​± ​0.2 ​mm vs. 0.7 ​± ​0.5 ​mm, p ​< ​0.001), LFC (0.1 ​± ​0.3 ​mm vs. 1.0 ​± ​0.2 ​mm, p ​< ​0.001), patella (-0.2 ​± ​0.3 ​mm vs. -1.2 ​± ​0.4 ​mm, p ​< ​0.001), and trochlea (-0.4 ​± ​0.3 vs. 0.4 ​± ​0.7, p ​= ​0.003). Graft contour was statistically significantly better for the anatomic grafts in the LFC (0.0 ​± ​0.0 ​mm vs. 0.2 ​± ​0.4 ​mm, p ​= ​0.022) and trochlea (0.0 ​± ​0.0 ​mm vs. 1.4 ​± ​0.7 ​mm, p ​< ​0.001). The anatomic grafts had an observed maximum step-off of -0.9 ​mm and a maximum contour mismatch of 0.8 ​mm.

CONCLUSION

This study validates a process designed to fabricate anatomically accurate cartilage grafts using MRI and 3D printing technology. Anatomic grafts demonstrated superior fit compared to generic flat grafts.

LEVEL OF EVIDENCE

Level IV.

The development of a nucleus pulposus-derived cartilage analog scaffold for chondral repair and regeneration

Focal chondral defects (FCDs) significantly impede quality of life for patients and impose severe economic costs on society. One of the most promising treatment options-autologous matrix-induced chondrogenesis (AMIC)-could benefit from a scaffold that contains both of the primary cartilage matrix components-sulfated glycosaminoglycans (sGAGs) and collagen type II. Here, 17 different protocols were evaluated to determine the most optimum strategy for decellularizing (decelling) the bovine nucleus pulposus (bNP) to yield a natural biomaterial with a cartilaginous constituency. The resulting scaffold was then characterized with respect to its biochemistry, biomechanics and cytocompatibility. Results indicated that the optimal decell protocol involved pre-crosslinking the tissue prior to undergoing decell with trypsin and Triton X-100. The residual DNA content of the scaffold was found to be 32.64 ± 9.26 ng/mg dry wt. of tissue with sGAG and hydroxyproline (HYP) contents of 72.53 ± 16.43. and 78.38 ± 8.46 μg/mg dry wt. respectively. The dynamic viscoelastic properties were found to be preserved (complex modulus: 17.92-16.62 kPa across a range of frequencies) while the equilibrium properties were found to have significantly decreased (aggregate modulus: 11.51 ± 9.19 kPa) compared to the non-decelled fresh bNP tissue. Furthermore, the construct was also found to be cytocompatible with bone marrow stem cells (BMSCs). While it was not permissive of cellular infiltration, the BMSCs were still found to have lined the laser drilled channels in the scaffold. Taken together, the biomaterial developed herein could be a valuable addition to the AMIC family of scaffolds or serve as an off-the-shelf standalone option for cartilage repair.

Age influences the efficacy of osteochondral autograft transfer: Promising results for patients under 40

BACKGROUND

Previous research using osteochondral autograft transfer (OAT) has shown poorer outcomes with increasing patient age. The aim of this article is to evaluate a cohort of patients that received an OAT and to correlate their clinical results with their age at procedure.

METHODS

Patients that underwent an OAT to treat an osteochondral (OC) lesion with a minimum 24-month follow-up were included. Patients were categorized into two groups based on their age at procedure (<40 years and ≥40 years). Postoperatively, each patient completed the Knee injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC), and Lysholm scales.

RESULTS

51 patients were included (35<40 years, 16≥40 years). Mean follow-up was 4.2 years (2-7). For patients<40 years, IKDC averaged 80.8 (SD 15.9) versus 71.2 (SD 19.4) in ≥40 years (p=0.03). For patients <40 years, Lysholm averaged 85.9 (SD 10.8) versus 77.0 (SD 21.6) in ≥40 years (p=0.02). For patients<40 years, KOOS averaged 78.3 (SD 11.8) versus 68.9 (SD 18.5) in ≥40 years (p=0.01). There was a 100% sensibility in identifying all the patients with a poor IKDC and Lysholm from 34 years old (AUC 0.76 and 0.8).

CONCLUSIONS

OAT has better outcomes in patients younger than 40 years compared to patients older than 40 years. Based on the prognostic capacity of age, the ideal candidate for an OAT is a patient younger than 34 years old.

In vitro and in vivo efficacy of naturally derived scaffolds for cartilage repair and regeneration

Intrinsically present bioactive cues allow naturally derived materials to mimic important characteristics of cartilage while also facilitating cellular recruitment, infiltration, and differentiation. Such traits are often what tissue engineers desire when they fabricate scaffolds, and yet, literature from the past decade is replete with examples of how most natural constructs with native biomolecules have only offered sub-optimal results in the treatment of cartilage defects. This paper provides an in-depth investigation of the performance of such scaffolds through a review of a collection of natural materials that have been used so far in repairing/regenerating articular cartilage. Although in vivo and clinical studies are the best indicators of scaffold efficacy, it was, however, observed that a large number of natural constructs had very promising scaffold characteristics to begin with, and would often show good in vitro/in vivo results. Finally, an examination of the biochemistry and biomechanics of repair tissues in studies that reported positive outcomes showed that these attributes often approached target cartilage values. The paper concludes with an outline of current trends as well as future directions for the field. STATEMENT OF SIGNIFICANCE: This review offers an exclusive focus on natural scaffold materials for cartilage repair and regeneration and provides a quantitative and qualitative analysis of their performance under a variety of in vitro and in vivo conditions. Readers can learn about environments where natural scaffolds have had the most success and tailor strategies to optimize their own work. Furthermore, given how the glycosaminoglycan (GAG) to hydroxyproline (HYP) ratio and moduli are fundamental attributes of hyaline cartilage, this paper adds to the body of knowledge by exploring how these characteristics reflect in preclinical outcomes. Such perspectives can greatly aid researchers better utilize natural materials for Cartilage Tissue Engineering (CTE).

Bipolar Lesions of the Knee Are Associated With Inferior Clinical Outcome Following Articular Cartilage Regeneration. A Propensity Score-Matched Analysis Including 238 Patients of the German Cartilage Registry (KnorpelRegister DGOU)

PURPOSE

To determine whether bipolar lesions (BL) are associated with inferior clinical outcome following articular cartilage regeneration (CR) compared to unipolar lesions (UL).

METHODS

A registry-based study, including patients undergoing isolated CR for focal knee cartilage lesions was performed. Lesions were considered UL or BL depending on the opposing cartilage. Propensity score matching was applied to eliminate potential confounders. Two groups comprising 119 patients with similar baseline characteristics were matched. The Knee Injury and Osteoarthritis Outcome Score (KOOS) at baseline, 6, 12, 24, and 36 months following CR served as primary outcome measure. KOOS improvement, reaching the minimal clinically important difference (MCID), KOOS subcomponents, and failure rates were calculated.

RESULTS

Autologous chondrocyte implantation (ACI) was the most frequently performed procedure in both groups with 63.0% (BL) and 46.6% (UL). There was a significant difference regarding KOOS at 24 months between UL (76.39 ± 14.96) and BL (69.83 ± 18.83; P = .028), which did not exceed the threshold of MCID. No significant difference was detected at any other follow-up. KOOS improvement from baseline was lower in the BL group at all follow-ups and peaked at 36 months in both groups (UL [26.00 ± 16.12] vs. BL [16.63 ± 17.29]; P = .024). The failure rate in the BL group was higher at 8.2% (9/110) compared to the UL group at 3.9% (4/98) (P = .256).

CONCLUSIONS

BL were associated with worse clinical outcome 2 years following CR compared to UL. However, both groups showed an ongoing clinical improvement up to 3 years postoperatively and a low failure rate. While inferior clinical improvement and a lower clinical response rate may be expected in BL patients, the observed differences do not justify excluding these patients from CR.

LEVEL OF EVIDENCE

Level III, retrospective comparative prognostic trial.

Small-Molecule Loaded Biomimetic Biphasic Scaffold for Osteochondral Regeneration: An In Vitro and In Vivo Study

Osteoarthritis is a prevalent musculoskeletal disorder in the elderly, which leads to high rates of morbidity. Mesenchymal stem cells (MSCs) are a promising approach to promote tissue regeneration in the absence of effective long-term treatments. Small molecules are relatively inexpensive and can selectively alter stem cell behavior during their differentiation, making them an attractive option for clinical applications. In this study, we developed an extracellular matrix (ECM)-based biphasic scaffold (BPS) loaded with two small-molecule drugs, kartogenin (KGN) and metformin (MET). This cell-free biomimetic biphasic scaffold consists of a bone (gelatin/hydroxyapatite scaffold embedded with metformin [GHSM]) and cartilage (nano-gelatin fiber embedded with kartogenin [NGFK]) layer designed to stimulate osteochondral regeneration. Extracellular matrix (ECM)-based biomimetic scaffolds can promote native cell recruitment, infiltration, and differentiation even in the absence of additional growth factors. The biphasic scaffold (BPS) showed excellent biocompatibility in vitro, with mesenchymal stem cells (MSCs) adhering, proliferating, and differentiated on the biomimetic biphasic scaffolds (GHSM and NGFK layers). The biphasic scaffolds upregulated both osteogenic and chondrogenic gene expression, sulfated glycosaminoglycan (sGAG), osteo- and chondrogenic biomarker, and relative mRNA gene expression. In an in vivo rat model, histo-morphological staining showed effective regeneration of osteochondral defects. This novel BPS has the potential to enhance both subchondral bone repair and cartilage regeneration, demonstrating excellent effects on cell homing and the recruitment of endogenous stem cells.

Suppressing Chondrocyte Hypertrophy to Build Better Cartilage

Current clinical strategies for restoring cartilage defects do not adequately consider taking the necessary steps to prevent the formation of hypertrophic tissue at injury sites. Chondrocyte hypertrophy inevitably causes both macroscopic and microscopic level changes in cartilage, resulting in adverse long-term outcomes following attempted restoration. Repairing/restoring articular cartilage while minimizing the risk of hypertrophic neo tissue formation represents an unmet clinical challenge. Previous investigations have extensively identified and characterized the biological mechanisms that regulate cartilage hypertrophy with preclinical studies now beginning to leverage this knowledge to help build better cartilage. In this comprehensive article, we will provide a summary of these biological mechanisms and systematically review the most cutting-edge strategies for circumventing this pathological hallmark of osteoarthritis.

Evaluation of ghrelin as a distinguishing marker for human articular cartilage-derived chondrocytes and chondroprogenitors

Purpose of the study

Cell-based therapeutics for articular cartilage repair primarily employed bone marrow-derived mesenchymal stem cells and chondrocytes. Research to overcome their limitation of formation of a functionally poor fibro-hyaline type of repair tissue led to the discovery of chondroprogenitors (CPCs), cartilage resident stem cells. These cells isolated by adhesion assay using fibronectin (FAA-CPs) and migration of progenitors from explants (MCPs) display higher chondrogenic and lower terminal differentiation potential. During in-vitro culture, chondrocytes tend to de-differentiate and acquire characteristics similar to stem cells, thus making it challenging to distinguish them from other cell groups. Ghrelin, a cytoplasmic growth hormone secretagogue, has been proposed to play a vital role in chondrogenesis, with reports of its higher expression in chondrocytes than BM-MSCs. The aim of this study was to compare the mRNA expression of Ghrelin between BM-MSCs, chondrocytes, FAA-CPs and MCP and the possibility of it serving as a distinguishing marker.

Methods

The four populations isolated from three human osteoarthritic knee joints were characterised by CD marker expression for positive (CD 90, CD73 and CD105) and negative (HLA-DR, CD34 and CD45) MSC markers and trilineage differentiation (adipogenic, osteogenic and chondrogenic) and subjected to qRT-PCR to assess Ghrelin's gene expression.

Results

This study showed that all groups exhibited similar expression of CD markers and multilineage potential. Though chondrocytes showed greater expression of Ghrelin, it was not statistically significant to classify it as a distinguishing marker between these cell populations.

Conclusion

Ghrelin does not serve to differentiate the subpopulations in terms of their mRNA expression. Further evaluation using their associated enzymes and receptors could provide valuable information to uncover their potential as unequivocal biomarkers.

Design and Fabrication of Micro Saw Enabling Root-Side Cutting of Bone

A novel micro saw was fabricated using a combination of photolithography and electroplating techniques, resembling a miniature timing belt with sideways blades. The rotation or oscillation direction of the micro saw is designed to be perpendicular to the cutting direction so that transverse cutting of the bone is attainable to extract a preoperatively planned bone-cartilage donor for osteochondral auto-graft transplantation. The mechanical property of the fabricated micro saw obtained using the nanoindentation test shows that the mechanical properties of the micro saw are almost an order of magnitude higher than bone, which indicates its potential bone-cutting application. To demonstrate the cutting capability of the fabricated micro saw, an in vitro animal bone cutting was performed using a custom test rig consisting of a microcontroller, 3D printer, and other readily available parts.

Adhesive Hydrogel Building Blocks to Reconstruct Complex Cartilage Tissues

Cartilage has an intrinsically low healing capacity, thereby requiring surgical intervention. However, limitations of biological grafting and existing synthetic replacements have prompted the need to produce cartilage-mimetic substitutes. Cartilage tissues perform critical functions that include load bearing and weight distribution, as well as articulation. These are characterized by a range of high moduli (≥1 MPa) as well as high hydration (60-80%). Additionally, cartilage tissues display spatial heterogeneity, resulting in regional differences in stiffness that are paramount to biomechanical performance. Thus, cartilage substitutes would ideally recapitulate both local and regional properties. Toward this goal, triple network (TN) hydrogels were prepared with cartilage-like hydration and moduli as well as adhesivity to one another. TNs were formed with either an anionic or cationic 3rd network, resulting in adhesion upon contact due to electrostatic attractive forces. With the increased concentration of the 3rd network, robust adhesivity was achieved as characterized by shear strengths of ∼80 kPa. The utility of TN hydrogels to form cartilage-like constructs was exemplified in the case of an intervertebral disc (IVD) having two discrete but connected zones. Overall, these adhesive TN hydrogels represent a potential strategy to prepare cartilage substitutes with native-like regional properties.

Cartilage Repair of the Tibiofemoral Joint With Versus Without Concomitant Osteotomy: A Systematic Review of Clinical Outcomes

Background

The extent to which concomitant osteotomy provides an improvement in clinical outcomes after cartilage repair procedures is unclear.

Purpose

To review the existing literature to compare clinical outcomes of patients undergoing cartilage repair of the tibiofemoral joint with versus without concomitant osteotomy.

Study Design

Systematic review; Level of evidence, 4.

Methods

A systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines by searching PubMed, the Cochrane Library, and Embase to identify studies that directly compared outcomes between cartilage repair of the tibiofemoral joint alone (group A) versus cartilage repair with concomitant osteotomy (high tibial osteotomy [HTO] or distal femoral osteotomy [DFO]) (group B). Studies on cartilage repair of the patellofemoral joint were excluded. The search terms used were as follows: osteotomy AND knee AND ("autologous chondrocyte" OR "osteochondral autograft" OR "osteochondral allograft" OR microfracture). Outcomes in groups A and B were compared based on reoperation rate, complication rate, procedure payments, and patient-reported outcomes (Knee injury and Osteoarthritis Outcome Score [KOOS], visual analog scale [VAS] for pain, satisfaction, and WOMAC).

Results

Included in the review were 5 studies (1 level 2 study, 2 level 3 studies, 2 level 4 studies) with 1747 patients in group A and 520 patients in group B. The mean patient ages were 34.7 and 37.5 years in groups A and B, respectively, and the mean lesion sizes were 4.0 and 4.5 cm², respectively. The mean follow-up time was 44.6 months. The most common lesion location was the medial femoral condyle (n = 999). Preoperative alignment averaged 1.8° and 5.5° of varus in groups A and B, respectively. One study found significant differences between groups in KOOS, VAS, and satisfaction, favoring group B. The reoperation rates were 47.4% and 17.3% in groups A and B, respectively (P < .0001).

Conclusion

Patients undergoing cartilage repair of the tibiofemoral joint with concomitant osteotomy might be expected to experience greater improvement in clinical outcomes with a lower reoperation rate compared with those undergoing cartilage repair alone. Surgeons preparing for cartilage procedures of the knee joint should pay particular attention to preoperative malalignment of the lower extremity to optimize outcomes.

Emerging polymeric material strategies for cartilage repair

Cartilage is found throughout the body, serving an array of essential functions. Owing to the limited healing capacity of cartilage, damage or degeneration is often permanent and so requires clinical intervention. Established surgical techniques generally rely on biological grafting. However, recent advances in polymeric materials provide an encouraging alternative to overcome limits of auto- and allografts. For regenerative engineering of cartilage, a polymeric scaffold ideally supports and instructs tissue regeneration while also providing mechanical integrity. Scaffolds direct regeneration via chemical and mechanical cues, as well as delivery and support of exogenous cells and bioactive factors. Advanced polymeric scaffolds aim to direct regeneration locally, replicating the heterogeneities of native tissues. Alternatively, new cartilage-mimetic hydrogels have potential to serve as synthetic cartilage replacements. Prepared as multi-network or composite hydrogels, the most promising candidates have simultaneously realized the hydration, mechanical, and tribological properties of native cartilage. Collectively, the recent rise in polymers for cartilage regeneration and replacement proposes a changing paradigm, with a new generation of materials paving the way for improved clinical outcomes.

Ultra-High Modulus Hydrogels Mimicking Cartilage of the Human Body

The human body is comprised of numerous types of cartilage with a range of high moduli, despite their high hydration. Owing to the limitations of cartilage tissue healing and biological grafting procedures, synthetic replacements have emerged but are limited by poorly matched moduli. While conventional hydrogels can achieve similar hydration to cartilage tissues, their moduli are substantially inferior. Herein, triple network (TN) hydrogels are prepared to synergistically leverage intra-network electrostatic repulsive and hydrophobic interactions, as well as inter-network electrostatic attractive interactions. They are comprised of an anionic 1^st network, a neutral 2^nd network (capable of hydrophobic associations), and a cationic 3^rd network. Collectively, these interactions act synergistically as effective, yet dynamic crosslinks. By tuning the concentration of the cationic 3^rd network, these TN hydrogels achieve high moduli of ≈1.5 to ≈3.5 MPa without diminishing cartilage-like water contents (≈80%), strengths, or toughness values. This unprecedented combination of properties poises these TN hydrogels as cartilage substitutes in applications spanning articulating joints, intervertebral discs (IVDs), trachea, and temporomandibular joint disc (TMJ).

Small Chondral Defects Affect Tibiofemoral Contact Area and Stress: Should a Lower Threshold Be Used for Intervention?

BACKGROUND

Chondral defects in the knee have biomechanical differences because of defect size and location. Prior literature only compares the maximum stress experienced with large defects.

HYPOTHESIS

It was hypothesized that pressure surrounding the chondral defect would increase with size and vary in location, such that a size cutoff exists that suggests surgical intervention.

STUDY DESIGN

Controlled laboratory study.

METHODS

Isolated chondral defects from 0.09 to 1.0 cm2 were created on the medial and lateral femoral condyles of 6 human cadaveric knees. The knees were fixed to a uniaxial load frame and loaded from 0 to 600 N at full extension. Another defect was created at the point of tibiofemoral contact at 30° of flexion. Tibiofemoral contact pressures were measured. Peak contact pressure was the highest value in the area delimited within a 3-mm rim around the defect. The location of the peak contact pressure was determined.

RESULTS

At full extension, the mean maximum pressures on the medial femoral condyle ranged from 4.30 to 6.91 MPa at 0.09 and 1.0 cm2, respectively (P < .01). The location of the peak pressure was found posteromedial in defects between 0.09 and 0.25 cm2, shifting anterolaterally at sizes 0.49 and 1.0 cm2 (P < .01). The maximum pressures on the lateral femoral condyle ranged from 3.63 to 5.81 MPa at 0.09 and 1.0 cm2, respectively (P = .02). The location of the peak contact pressure point was anterolateral in defects between 0.09 and 0.25 cm2, shifting posterolaterally at 0.49 and 1.0 cm2 (P < .01). No differences in contact pressure between full extension and 30° of flexion were found for either the lateral or medial condyles.

CONCLUSION

Full-thickness chondral defects bilaterally had a significant increase in contact pressure between defect sizes of 0.49 and 1.0 cm2. The location of the maximum contact pressures surrounding the lesion also varied with larger defects. Contact area redistribution and cartilage stress change may affect adjacent cartilage integrity.

CLINICAL RELEVANCE

Size cutoffs may exist earlier in the natural history of chondral defects than previously realized, suggesting a lower threshold for intervention.

Advances in Biomaterial-Mediated Gene Therapy for Articular Cartilage Repair

Articular cartilage defects caused by various reasons are relatively common in clinical practice, but the lack of efficient therapeutic methods remains a substantial challenge due to limitations in the chondrocytes’ repair abilities. In the search for scientific cartilage repair methods, gene therapy appears to be more effective and promising, especially with acellular biomaterial-assisted procedures. Biomaterial-mediated gene therapy has mainly been divided into non-viral vector and viral vector strategies, where the controlled delivery of gene vectors is contained using biocompatible materials. This review will introduce the common clinical methods of cartilage repair used, the strategies of gene therapy for cartilage injuries, and the latest progress.

Articular cartilage delamination at eight years following cellular-based repair procedures: a case reports

This report describes two cases of late cartilage delamination in two young adults after two different autologous cell-based techniques for cartilage restoration: 1. Matrix-assisted autologous chondrocyte implantation (MACI) and 2. Hyaluronic acid-bone marrow aspirate concentrate (HA-BMAC). Both cases demonstrate that even in patients who do not present with any ongoing symptoms after primary surgery, a cellular-based graft's subsequent delamination can occur later. It is possible that regardless of the technique used or the time passed since the surgery, a graft failure may occur at some level, causing delamination of a previously asymptomatic cartilage restoration graft and a traumatic event with long-term follow-up. Surgeons must be alert to this injury and describe histologic findings to determine where failure occurs.

Osteochondral Allografts in Knee Surgery: Narrative Review of Evidence to Date

Knee articular cartilage defects can result in significant pain and loss of function in active patients. Osteochondral allograft (OCA) transplantation offers a single-stage solution to address large chondral and osteochondral defects by resurfacing focal cartilage defects with mature hyaline cartilage. To date, OCA transplantation of the knee has demonstrated excellent clinical outcomes and long-term survivorship. However, significant variability still exists among clinicians with regard to parameters for graft acceptance, surgical technique, and rehabilitation. Technologies to optimize graft viability during storage, improve osseous integration of the allograft, and shorten recovery timelines after surgery continue to evolve. The purpose of this review is to examine the latest evidence on treatment indications, graft storage and surgical technique, patient outcomes and survivorship, and rehabilitation after surgery.

In vitro and in vivo investigation of a zonal microstructured scaffold for osteochondral defect repair

Articular cartilage is comprised of zones that vary in architecture, extracellular matrix composition, and mechanical properties. Here, we designed and engineered a porous zonal microstructured scaffold from a single biocompatible polymer (poly [ϵ-caprolactone]) using multiple fabrication strategies: electrospinning, spherical porogen leaching, directional freezing, and melt electrowriting. With this approach we mimicked the zonal structure of articular cartilage and produced a stiffness gradient through the scaffold which aligns with the mechanics of the native tissue. Chondrocyte-seeded scaffolds accumulated extracellular matrix including glycosaminoglycans and collagen II over four weeks in vitro. This prompted us to further study the repair efficacy in a skeletally mature porcine model. Two osteochondral lesions were produced in the trochlear groove of 12 animals and repaired using four treatment conditions: (1) microstructured scaffold, (2) chondrocyte seeded microstructured scaffold, (3) MaioRegen™, and (4) empty defect. After 6 months the defect sites were harvested and analyzed using histology, micro computed tomography, and Raman microspectroscopy mapping. Overall, the scaffolds were retained in the defect space, repair quality was repeatable, and there was clear evidence of osteointegration. The repair quality of the microstructured scaffolds was not superior to the control based on histological scoring; however, the lower score was biased by the lack of histological staining due to the limited degradation of the implant at 6 months. Longer follow up studies (e.g., 1 yr) will be required to fully evaluate the efficacy of the microstructured scaffold. In conclusion, we found consistent scaffold retention, osteointegration, and prolonged degradation of the microstructured scaffold, which we propose may have beneficial effects for the long-term repair of osteochondral defects.

Rehabilitation Variability Following Osteochondral Autograft and Allograft Transplantation of the Knee

OBJECTIVE

The aim of this study is to assess the variability of postoperative rehabilitation protocols used by orthopedic surgery residency programs for osteochondral autograft transplantation (OAT) and osteochondral allograft transplantation (OCA) of the knee.

DESIGN

Online postoperative OAT and OCA rehabilitation protocols from US orthopedic programs and the scientific literature were reviewed. A custom scoring rubric was developed to analyze each protocol for the presence of discrete rehabilitation modalities and the timing of each intervention.

RESULTS

A total of 16 programs (10.3%) from 155 US academic orthopedic programs published online protocols and a total of 35 protocols were analyzed. Twenty-one protocols (88%) recommended immediate postoperative bracing following OAT and 17 protocols (100%) recommended immediate postoperative bracing following OCA. The average time protocols permitted weight-bearing as tolerated (WBAT) was 5.2 weeks (range = 0-8 weeks) following OAT and 6.2 weeks (range = 0-8 weeks) following OCA. There was considerable variation in the inclusion and timing of strength, proprioception, agility, and pivoting exercises. Following OAT, 2 protocols (8%) recommended functional testing as criteria for return to sport at an average time of 12.0 weeks (range = 12-24 weeks). Following OCA, 1 protocol (6%) recommended functional testing as criteria for return to sport at an average time of 12.0 weeks (range = 12-24 weeks).

CONCLUSION

A minority of US academic orthopedic programs publish OAT and OCA rehabilitation protocols online. Among the protocols currently available, there is significant variability in the inclusion of specific rehabilitation components and timing of many modalities. Evidence-based standardization of elements of postoperative rehabilitation may help improve patient care and subsequent outcomes.

Update: Posttreatment Imaging of the Knee after Cartilage Repair

Focal cartilage lesions are common pathologies at the knee joint that are considered important risk factors for the premature development of osteoarthritis. A wide range of surgical options, including but not limited to marrow stimulation, osteochondral auto- and allografting, and autologous chondrocyte implantation, allows for targeted treatment of focal cartilage defects. Arthroscopy is the standard of reference for the assessment of cartilage integrity and quality before and after repair. However, deep cartilage layers, intrachondral composition, and the subchondral bone are only partially or not at all visualized with arthroscopy. In contrast, magnetic resonance imaging offers noninvasive evaluation of the cartilage repair site, the subchondral bone, and the soft tissues of the joint pre- and postsurgery. Radiologists need to be familiar with the different surgical procedures available and their characteristic postsurgical imaging appearances to assess treatment success and possible complications adequately. We provide an overview of the most commonly performed surgical procedures for cartilage repair at the knee and typical postsurgical imaging characteristics.

Expedited gene delivery for osteochondral defect repair in a rabbit knee model: A one-year investigation

Objective:

To evaluate a single-step, gene-based procedure for repairing osteochondral lesions.

Design:

Osteochondral lesions were created in the patellar groove of skeletally mature rabbits. Autologous bone marrow aspirates were mixed with adenovirus vectors carrying cDNA encoding green fluorescent protein (Ad.GFP) or transforming growth factor-β₁ (Ad.TGF-β₁) and allowed to clot. The clotted marrow was press-fit into the defects. Animals receiving Ad.GFP were euthanized at 2 weeks and intra-articular expression of GFP examined by fluorescence microscopy. Animals receiving Ad.TGF-β₁ were euthanized at 3 months and 12 months; repair was compared to empty defects using histology and immunohistochemistry. Complementary in vitro experiments assessed transgene expression and chondrogenesis in marrow clots and fibrin gels. In a subsequent pilot study, repair at 3 months using a fibrin gel to encapsulate Ad.TGF-β₁ was evaluated.

Results:

At 2 weeks, GFP expression was seen at variable levels within the cartilaginous lesion. At 3 months, there was no statistically significant improvement (p > 0.05) in healing of lesions receiving Ad.TGF-β₁ and variability was high. At 12 months, there were still no significant difference (p > 0.05) between the empty defects and those receiving Ad.TGF-β₁ in the overall, cartilage, and bone scores. Variability was still high. In vitro experiments suggested that variability reflected variable transduction efficiency and chondrogenic activity of the marrow clots; using fibrin gels instead of marrow may address this issue but more research is needed.

Conclusions:

This approach to improving the repair of osteochondral lesions needs further refinement to reduce variability and provide a more robust outcome.

Corncob Cellulose Scaffolds: A New Sustainable Temporary Implant for Cartilage Replacement

Tissue engineering using scaffolds is a promising strategy to repair damaged articular cartilage, whose self-repair is inefficient. Cellulose properties have been recognized for their application in the biomedical field. The aim of this study was to fabricate and characterize novel scaffolds based on poly(ɛ-caprolactone) (PCL) and sustainable cellulose. Thus, the performance of corncob-derived cellulose (CC) in scaffolds as an alternative to wood cellulose (WC) was also investigated to reduce the environmental footprint. Two concentrations of CC in scaffolds were tested, 1% and 2% (w/w), and commercial WC using the same concentrations, as a control. Morphologically, all the developed scaffolds presented pore sizes of ~300 µm, 10 layers, a circular shape and well-dispersed cellulose. Thus, all of these characteristics and properties provide the manufactured scaffolds suitable for use in cartilage-replacement strategies. The use of 2% CC results in higher porosity (54.24%), which promotes cell infiltration/migration and nutrient exchange, and has similar mechanical properties to WC. As for the effects of enzymatic degradation of the scaffolds, no significant changes (p > 0.05) were observed in resistance over time. However, the obtained compressive modulus of the scaffold with 2% CC was similar to that of WC. Overall, our results suggest that the integration of 2% corncob cellulose in PCL scaffolds could be a novel way to replace wood-cellulose-containing scaffolds, highlighting its potential for cartilage-replacement strategies.

Current Reviews in Musculoskeletal Medicine: Current Controversies for Treatment of Meniscus Root Tears

PURPOSE OF REVIEW

The role of the meniscus in preserving the biomechanical function of the knee joint has been clearly defined. The hypothesis that meniscus root integrity is a prerequisite for meniscus function is supported by the development of progressive knee osteoarthritis (OA) following meniscus root tears (MRTs) treated either non-operatively or with meniscectomy. Consequently, there has been a resurgence of interest in the diagnosis and treatment of MRTs. This review examines the contemporary literature surrounding the natural history, clinical presentation, evaluation, preferred surgical repair technique and outcomes.

RECENT FINDINGS

Surgeons must have a high index of suspicion in order to diagnose a MRT because of the nonspecific clinical presentation and difficult visualization on imaging. Compared with medial MRTs that commonly occur in middle age/older patients, lateral meniscus root injuries tend to occur in younger males with lower BMIs, less cartilage degeneration, and with concomitant ligament injury. Subchondral insufficiency fractures of the knee have been found to be associated with both MRTs and following arthroscopic procedures. Meniscus root repair has demonstrated good outcomes, and acute injuries with intact cartilage should be repaired. Cartilage degeneration, BMI, and malalignment are important considerations when choosing surgical candidates. Meniscus centralization has emerged as a viable adjunct strategy aimed at correcting meniscus extrusion. Meniscus root repair results in a decreased rate of OA and arthroplasty and is economically advantageous when compared with nonoperative treatment and partial meniscectomy. The transtibial pull-through technique with the addition of centralization for the medial meniscus is associated with encouraging early results.

Biochemical Aspects of Scaffolds for Cartilage Tissue Engineering; from Basic Science to Regenerative Medicine

Chondral defects are frequent and important causes of pain and disability. Cartilage has limited self-repair and regeneration capacity. The ideal approach for articular cartilage defects is the regeneration of hyaline cartilage with sustainable symptom-free constructs. Tissue engineering provides new strategies for the regeneration of functional cartilage tissue through optimized scaffolds with architectural, mechanical, and biochemical properties similar to the native cartilage tissue. In this review, the basic science of cartilage structure, interactions between proteins, stem cells, as well as biomaterials, scaffold characteristics and fabrication methods, as well as current and potential therapies in regenerative medicine will be discussed mostly from a biochemical point of view. Furthermore, the recent trends in scaffold-based therapies and supplementary factors in cartilage tissue engineering will be considered.

Bipolar Cartilage Lesions of the Knee: A Systematic Review of Techniques, Outcomes, and Complications

OBJECTIVE

The purpose of this systematic review was to determine (1) treatment options for bipolar cartilage lesions of the knee, (2) patient-reported outcomes following various surgical treatments, and (3) complication and failure rates following surgery.

DESIGN

A literature search of PubMed, the Cochrane Library, and CINHAL was performed using PRISMA guidelines. Patients were included if they had bipolar cartilage lesions of the knee treated surgically. Lesion characteristics, surgical technique, patient-reported outcomes, complication rates, failure rates, and survivorship were recorded.

RESULTS

Fourteen studies yielded 301 knees treated surgically. Patient age ranged from 15 to 74 years. Surgical techniques included 138 autologous chondrocyte implantation (ACI), 156 osteochondral allograft transplantation (OCA), and 7 osteochondral autograft transfer system (OATS). Seven studies reported a concomitant procedure rate that ranged from 0% to 88%. Eight studies reported that both reciprocal lesions received surgical treatment, while 6 studies did not specify. Lesion size ranged from 1 to 41 cm². All reported postoperative improvements in patient-reported outcomes, but the measures were very heterogeneous. There were no major complications and the rate of minor complications ranged from 0% to 50%. Survivorship ranged from 40% to 100% for OCA, 76% to 95% for ACI, and 100% for the 1 study evaluating OATS.

CONCLUSIONS

Bipolar cartilage lesions of the knee typically involve a large surface area and are most commonly treated with ACI or OCA, while OATS may be an option for smaller lesions. Improvements in mid-term patient-reported outcomes were reported for all surgical procedures and they can be performed safely with a low rate of major complications.

Tibial Plateau Cartilage Lesions: A Systematic Review of Techniques, Outcomes, and Complications

OBJECTIVE

The purpose of this systematic review is to determine (1) current reported treatment options for isolated tibial plateau (TP) cartilage lesions, (2) patient reported outcomes following various treatments, and (3) complication rate and survivorship following various treatments.

DESIGN

A literature search of PubMed, the Cochrane Library, and CINAHL was conducted adhering to PRISMA guidelines. Patients were included if they had TP cartilage lesions treated with surgery. Lesion characteristics, surgical procedure details, patient reported outcomes, complication, and failure rates were collected.

RESULTS

Thirteen studies yielded 205 knees with TP cartilage lesions treated surgically. Ages ranged from 12 to 77 years. Surgical techniques included 138 treated with osteochondral allograft transplantation (OCA), 37 treated with osteochondral autograft transfer system (OATS), 11 treated with microfracture, 11 treated with an osteochondral scaffold, and 8 treated with autologous chondrocyte implantation (ACI). The patient-reported outcome measures were heterogeneous, but all reported improvements with the notable exception of one study evaluating microfracture. The rate of complications ranged from 0% to 4.6%. Failure rate ranged from 22% to 46% for OCA and 0% to 16% for OATS. No failures were reported for the additional techniques.

CONCLUSIONS

Various surgical techniques have been utilized for the treatment of TP cartilage lesions. Patient-reported outcome measures were heterogeneous, but improvements were reported following all surgical treatments except for microfracture, which resulted in decreased scores at mid-term follow-up. The complication rate was low for all techniques described. However, the failure rate was higher following unicondylar OCA for salvage treatment of posttraumatic deformities.

Osteochondral Autograft Plugs versus Paste Graft: Ex Vivo Morselization Increases Chondral Matrix Production

OBJECTIVE

Patients undergoing articular cartilage paste grafting have been shown in studies to have significant improvement in pain and function in long-term follow-ups. We hypothesized that ex vivo impacting of osteochondral autografts results in higher chondrocyte matrix production versus intact osteochondral autograft plugs.

DESIGN

This institutional review board-approved study characterizes the effects of impacting osteochondral plugs harvested from the intercondylar notch of 16 patients into a paste, leaving one graft intact as a control. Cell viability/proliferation, collagen type I/II, SOX-9, and aggrecan gene expression via qRT-PCR (quantitative reverse transcription-polymerase chain reaction) were analyzed at 24 and 48 hours. Matrix production and cell morphology were evaluated using histology.

RESULTS

Paste samples from patients (mean age 39.7) with moderate (19%) to severe (81%) cartilage lesions displayed 34% and 80% greater cell proliferation compared to plugs at 24 and 48 hours post processing, respectively (P = 0.015 and P = 0.021). qRT-PCR analysis yielded a significant (P = 0.000) increase of aggrecan, SOX-9, collagen type I and II at both 24 and 48 hours. Histological examination displayed cell division throughout paste samples, with accumulation of aggrecan around multiple chondrocyte lacunae.

CONCLUSIONS

Paste graft preparation resulted in increased mobility of chondrocytes by matrix disruption without loss of cell viability. The impaction procedure stimulated chondrocyte proliferation resulting in a cellular response to reestablish native extracellular matrix. Analysis of gene expression supports a regenerative process of cartilage tissue formation and contradicts long-held beliefs that impaction trauma leads to immediate cell death. This mechanism of action translates into clinical benefit for patients with moderate to severe cartilage damage.

Differences in the Demographics and Preferred Management of Knee Cartilage Injuries in Soccer Players Across FIFA Centers of Excellence

OBJECTIVE

We sought to report on the demographics and epidemiology of knee cartilage injuries and preferred management in soccer players, across FIFA Medical Centers of Excellence (FMCE).

DESIGN

A descriptive questionnaire focusing on characteristics of knee cartilage injuries and their management in soccer players during the 10-year period prior to the distribution of the questionnaire was sent to all FMCE around the world in September 2019 via an online platform. Voluntary responses from centers were processed and analyzed. Descriptive characteristics were reported using median and interquartile ranges (IQR) for continuous variables and frequencies and percentages (%) for discrete variables.

RESULTS

A total of 15 centers from 5 continents responded to the questionnaire and reported on a total of 4526 soccer players. Among centers, the median age was 27 years (IQR: 23-38), the median rate of male players was 75% (IQR: 68-90), and the median rate of professional players was 10% (IQR: 5-23). The most common reported etiology for cartilage injury was traumatic (median 40%, IQR: 13-73). The most common nonoperative treatment utilized was physical therapy (median 90%, IQR: 51%-100%) and the most common operative treatment utilized was bone marrow stimulation/micro-fracture (median 40%, IQR: 19-54%). The utilization of other cartilage restoration procedures varied across centers.

CONCLUSIONS

Our findings highlight different tendencies in the management of these injuries across FMCE and emphasize the need for collaborative efforts focusing on establishing consensus guidelines for the optimal management of these challenging injuries in soccer players.

Prospective Outcomes of Cryopreserved Osteochondral Allograft for Patellofemoral Cartilage Defects at Minimum 2-Year Follow-up

OBJECTIVE

To analyze the clinical outcomes, knee function, and activity level of patients after treatment of full-thickness cartilage defects involving the patellofemoral compartment of the knee with cryopreserved osteochondral allograft.

DESIGN

Nineteen patients with cartilage defects involving the patellofemoral compartment were treated. The average age was 31 years (range 15-45 years), including 12 females and 7 males. Patients were prospectively followed using validated clinical outcome measures including Veterans RAND 12-item Health Survey (VR-12), International Knee Documentation Committee (IKDC), Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Tegner activity scale. Graft incorporation was evaluated by magnetic resonance imaging (MRI) or second-look arthroscopy.

RESULTS

The cartilage defects included the patella (n = 16) and the femoral trochlea (n = 3). Mean VR-12 scores increased from 31.6 to 46.3 (P < 0.01), mean IKDC increased from 40.0 to 69.7 (P < 0.01), mean KOOS increased from 53.9 to 80.2 (P < 0.01), and mean Tegner scores increased from 3.0 to 4.9 (P < 0.01), at average follow-up of 41.9 months (range 24-62 months). Of the 3 patients who underwent second-look arthroscopy, all demonstrated a well-incorporated graft. Mean MOCART score for the 6 patients with follow-up MRI was 62.5 (range 25-85). The reoperation rate was 21.1% and 2 patients (12.5%) experienced progressive patellofemoral osteoarthritis requiring conversion to patellofemoral arthroplasty.

CONCLUSION

Patients with unipolar cartilage defects involving the patellofemoral compartment of the knee can have positive outcomes at minimum 2-year follow-up after surgical treatment with a cryopreserved osteochondral allograft when concomitant pathology is also addressed, but the reoperation rate is high and bipolar cartilage lesions may increase the failure rate.

Arthroscopic Osteochondral Autograft Transfer System Procedure of the Lateral Femoral Condyle with Donor-Site Backfill Using Osteochondral Allograft Plug

The osteochondral autograft transfer system (OATS) procedure is at the forefront of cartilage restoration surgeries of the knee, offering superior return to sport rates and long-term functionality. This technique reports an arthroscopic OATS procedure of the lateral femoral condyle with donor-site backfill using an osteochondral allograft plug. Potential complications from unfilled donor site sockets are eliminated through donor site backfill with an allograft plug.

Fabrication and characterization of microstructure-controllable COL-HA-PVA hydrogels for cartilage repair

Polyvinyl alcohol (PVA) hydrogel has gained interest in cartilage repair because of its highly swollen, porosity, and viscoelastic properties. However, PVA has some deficiencies, such as its poor biocompatibility and microstructure. This research aimed to design novel hydroxyapatite (HA)-collagen (COL)-PVA hydrogels. COL was added to improve cell biocompatibility, and the microstructure of the hydrogels was controlled by fused deposition modeling (FDM). The feasibility of the COL-HA-PVA hydrogels in cartilage repair was evaluated by in vitro and in vivo experiments. The scanning electron microscopy results showed that the hybrid hydrogels had interconnected macropore structures that contained a COL reticular scaffold. The diameter of the macropore was 1.08-1.85 mm, which corresponds to the diameter of the denatured PVA column. The chondrocytes were then seeded in hydrogels to assess the cell viability and formation of the cartilage matrix. The in vitro results revealed excellent cellular biocompatibility. Osteochondral defects (8 mm in diameter and 8 mm in depth) were created in the femoral trochlear of goats, and the defects were implanted with cell-seeded hydrogels, cell-free hydrogels, or a blank control. The in vivo results showed that the COL-HA-PVA hydrogels effectively repaired cartilage defects, especially the conditions inoculated with chondrocyte in advance. This research suggests that the COL-HA-PVA hydrogels have promising application in cartilage repair.

Identifying Consensus and Open Questions around Assessing or Predicting the Quality and Success of Cartilage Repair: A Delphi Study

A range of surgical techniques have been developed for the repair or regeneration of lesioned cartilage in the human knee and a corresponding array of scoring systems have been created to assess their outcomes. The published literature displays a wide range of opinions regarding the factors that influence the success of surgical cartilage repair and which parameters are the most useful for measuring the quality of the repair at follow-up. Our objective was to provide some clarity to the field by collating items that were agreed upon by a panel of experts to be important in these areas. A modified, three-round Delphi consensus study was carried out consisting of one idea-generating focus-group and two subsequent, self-completed questionnaire rounds. In each round, items were assessed for their importance and level of consensus against pre-determined threshold levels. In total, 31 items reached consensus, including a hierarchy of tissues in the joint based on their importance in cartilage repair, markers of repair cartilage quality and the implications of environmental and patient-related factors. Items were stratified into those that can be employed for predicting the success of cartilage repair and those that could be used for assessing the structural quality of the resulting repair cartilage. Items that did not reach consensus represent areas where dissent remains and could, therefore, be used to guide future clinical and fundamental scientific research.

Reconstruction of Tibial Plateau Fracture Malunion in the Setting of a Large Cartilage Defect in an Adolescent: A Case Report

CASE

An 18-year-old adolescent boy presented with knee pain and stiffness secondary to tibial plateau valgus malunion and osteochondral defect, 8 months after initial injury/fixation. We opted for a novel technique that reconstructs the convex lateral tibial plateau by using osteotomy and an osteochondral autograft harvested from the lateral aspect of the ipsilateral femoral condyle.

CONCLUSION

The reported novel reconstruction technique is inexpensive, achievable with routine techniques, and demonstrated a favorable short-term outcome. At 3 years of follow-up, the patient had excellent, asymptomatic, left knee mobility and function with radiographic evidence of mild posttraumatic arthritis despite normal knee alignment.

Osteochondral Tissue Engineering: The Potential of Electrospinning and Additive Manufacturing

The socioeconomic impact of osteochondral (OC) damage has been increasing steadily over time in the global population, and the promise of tissue engineering in generating biomimetic tissues replicating the physiological OC environment and architecture has been falling short of its projected potential. The most recent advances in OC tissue engineering are summarised in this work, with a focus on electrospun and 3D printed biomaterials combined with stem cells and biochemical stimuli, to identify what is causing this pitfall between the bench and the patients' bedside. Even though significant progress has been achieved in electrospinning, 3D-(bio)printing, and induced pluripotent stem cell (iPSC) technologies, it is still challenging to artificially emulate the OC interface and achieve complete regeneration of bone and cartilage tissues. Their intricate architecture and the need for tight spatiotemporal control of cellular and biochemical cues hinder the attainment of long-term functional integration of tissue-engineered constructs. Moreover, this complexity and the high variability in experimental conditions used in different studies undermine the scalability and reproducibility of prospective regenerative medicine solutions. It is clear that further development of standardised, integrative, and economically viable methods regarding scaffold production, cell selection, and additional biochemical and biomechanical stimulation is likely to be the key to accelerate the clinical translation and fill the gap in OC treatment.

Chondral Lesions of the Knee: An Evidence-Based Approach

➤

Management of chondral lesions of the knee is challenging and requires assessment of several factors including the size and location of the lesion, limb alignment and rotation, and the physical and mental health of the individual patient.

➤

There are a multitude of options to address chondral pathologies of the knee that allow individualized treatment for the specific needs and demands of the patient.

➤

Osteochondral autograft transfer remains a durable and predictable graft option in smaller lesions (<2 cm2) in the young and active patient population.

➤

Both mid-term and long-term results for large chondral lesions (≥3 cm2) of the knee have demonstrated favorable results with the use of osteochondral allograft or matrix-associated chondrocyte implantation.

➤

Treatment options for small lesions (<2 cm2) include osteochondral autograft transfer and marrow stimulation and/or microfracture with biologic adjunct, while larger lesions (≥2 cm2) are typically treated with osteochondral allograft transplantation, particulated juvenile articular cartilage, or matrix-associated chondrocyte implantation.

➤

Emerging technologies, such as allograft scaffolds and cryopreserved allograft, are being explored for different graft sources to address complex knee chondral pathology; however, further study is needed.

Optimizing Outcomes in Articulating (Kissing) Patellofemoral Joint Osteochondral Lesions: Case Report and Review of the Literature

A 32-year-old woman with bipolar patellofemoral chondral lesions caused by traumatic patella dislocation underwent autologous chondrocyte implantation with concomitant tibial tubercle osteotomy and MPFL reconstruction. At 1- and 2-year follow-ups, the patient had returned to all previous activities with considerable improvement in all patient-reported outcome scores. This is an encouraging treatment option for a historically difficult therapeutic problem.

A Graded, Porous Composite of Natural Biopolymers and Octacalcium Phosphate Guides Osteochondral Differentiation of Stem Cells

Lesions involving the osteochondral unit are difficult to treat. Biomimetic scaffolds are previously shown as promising alternative. Such devices often lack multiple functional layers that mimic bone, cartilage, and the interface. In this study, multilayered scaffolds are developed based on the use of natural extracellular matrix (ECM)-like biopolymers. Particular attention is paid to obtain a complex matrix that mimics the native osteochondral transition. Porous, sponge-like chitosan-collagen-octacalcium phosphate (OCP) scaffolds are obtained. Collagen content increases while the amount of OCP particles decreases toward the cartilage layer. The scaffolds are bioactive as a mineral layer is deposited containing hydroxyapatite at the bony side. The scaffolds stimulate proliferation of human adipose-derived mesenchymal stem cells, but the degree of proliferation depends on the cell seeding density. The scaffolds give rise to a zone-specific gene expression. RUNX2, COL1A1, BGLAP, and SPP1 are upregulated in the bony layer of the scaffold. SOX9 is upregulated concomitant with COL2A1 expression in the cartilage zone. Mineralization in presence of the cells is prominent in the bone area with Ca and P steadily increasing over time. These results are encouraging for the fabrication of biomimetic scaffolds using ECM-like materials and featuring gradients that mimic native tissues and their interface.

Focal articular surface replacement of knee lesions after failed cartilage repair using focal metallic implants: A series of 132 cases with 4-year follow-up

BACKGROUND

Focal articular lesions of the knee can be treated using several different techniques with generally good results, but failures are difficult to manage. Focal articular surface replacement (FASR) using metal implants could be a promising technique that allows defect geometry matching, congruency restoration and defect propagation prevention.

METHODS

132 patients were included who underwent FASR between January 2009 and December 2013. Three different implants were used: 1. HemiCAP®; 2. UniCAP® and 3. HemiCAP® PF Classic for trochlear lesions. Primary outcome parameter was knee function assessed by Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score with a 4-year follow-up, secondary outcomes included survivorship and complications. Statistical analyses were performed using GraphPad Prism.

RESULTS

For all 132 surgeries combined (102 HemiCAP®, 11 UniCAP® and 19 HemiCAP® PF Classic implants), WOMAC scores significantly improved from 6 weeks onward until the end of the study (p < 0.001 for all time points). 4-year survival rate was 97.7%, and a re-operation rate of 12.1% was found. The HemiCAP® group revealed a slower WOMAC improvement in patients aged ≥40 years, combined with a trend towards lower final WOMAC scores and a higher re-operation rate in patients with a BMI ≥ 25.

CONCLUSIONS

This report shows good to excellent clinical results of FASR as a salvage procedure after failed cartilage repair, with a low re-operation rate and a high survival of 97.7% at 4-year follow-up. Although longer follow-up is required, this could be a valuable treatment option in these challenging cases, without limiting future options for surgical interventions when deemed necessary.

Characterization of Properties, In Vitro and In Vivo Evaluation of Calcium Phosphate/Amino Acid Cements for Treatment of Osteochondral Defects

Novel calcium phosphate cements containing a mixture of four amino acids, glycine, proline, hydroxyproline and either lysine or arginine (CAL, CAK) were characterized and used for treatment of artificial osteochondral defects in knee. It was hypothesized that an enhanced concentration of extracellular collagen amino acids (in complex mixture), in connection with bone cement in defect sites, would support the healing of osteochondral defects with successful formation of hyaline cartilage and subchondral bone. Calcium phosphate cement mixtures were prepared by in situ reaction in a planetary ball mill at aseptic conditions and characterized. It was verified that about 30–60% of amino acids remained adsorbed on hydroxyapatite particles in cements and the addition of amino acids caused around 60% reduction in compressive strength and refinement of hydroxyapatite particles in their microstructure. The significant over-expression of osteogenic genes after the culture of osteoblasts was demonstrated in the cement extracts containing lysine and compared with other cements. The cement pastes were inserted into artificial osteochondral defects in the medial femoral condyle of pigs and, after 3 months post-surgery, tissues were analyzed macroscopically, histologically, immunohistochemically using MRI and X-ray methods. Analysis clearly showed the excellent healing process of artificial osteochondral defects in pigs after treatment with CAL and CAK cements without any inflammation, as well as formation of subchondral bone and hyaline cartilage morphologically and structurally identical to the original tissues. Good integration of the hyaline neocartilage with the surrounding tissue, as well as perfect interconnection between the neocartilage and new subchondral bone tissue, was demonstrated. Tissues were stable after 12 months’ healing.

Wide Variation in Methodology in Level I and II Studies on Cartilage Repair: A Systematic Review of Available Clinical Trials Comparing Patient Demographics, Treatment Means, and Outcomes Reporting

BACKGROUND

The management of complex cartilage pathology in young, otherwise healthy patients can be difficult.

PURPOSE

To determine the nature of the design, endpoints chosen, and rate at which the endpoints were met in published studies and ongoing clinical trials that investigate cartilage repair and restoration procedures.

STUDY DESIGN

Systematic review.

METHODS

A systematic review of the publicly available level I/II literature and of the publicly listed clinical trials regarding cartilage repair and restoration procedures for the knee was conducted adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Seventeen published studies and 52 clinical trials were included. Within the 17 published studies, the most common procedure studied was microfracture (MFX) + augmentation (N = 5; 29.4%) and the most common comparison/control group was MFX (N = 10; 58.8%). In total, 13 different cartilage procedure groups were evaluated. For published studies, the most common patient-reported outcome (PRO) measures assessed is the Knee Injury and Osteoarthritis Outcome Score (KOOS) and Visual Analog Scale-Pain (VAS) (N = 10 studies, 58.8% each, respectively). Overall, there are 10 different PROs used among the included studies. Ten studies demonstrate superiority, 5 demonstrate noninferiority, and 2 demonstrate inferiority to the comparison or control groups. For the clinical trials included, the most common procedure studied is MFX + augmentation (N = 16; 30.8%). The most common PRO assessed is KOOS (N = 36 trials; 69.2%), and overall there are 24 different PROs used among the included studies.

CONCLUSIONS

Recently published studies and clinical trials evaluate a variety of cartilage repair and restoration strategies for the knee, most commonly MFX + augmentation, at various time points of outcome evaluation, with KOOS and VAS scores being used most commonly. MFX remains the most common comparison group for these therapeutic investigations. Most studies demonstrate superiority versus comparison or control groups. Understanding the nature of published and ongoing clinical trials will be helpful in the investigation of emerging technologies required to navigate the regulatory process while studying a relatively narrow population of patients.

Gradient scaffold with spatial growth factor profile for osteochondral interface engineering

Osteochondral (OC) matrix design poses a significant engineering challenge due to the complexity involved with bone-cartilage interfaces. To better facilitate the regeneration of OC tissue, we developed and evaluated a biodegradable matrix with uniquely arranged bone and cartilage supporting phases: a poly(lactic-co-glycolic) acid (PLGA) template structure with a porosity gradient along its longitudinal axis uniquely integrated with hyaluronic acid hydrogel. Micro-CT scanning and imaging confirmed the formation of an inverse gradient matrix. Hydroxyapatite was added to the PLGA template which was then plasma-treated to increase hydrophilicity and growth factor affinity. An osteogenic growth factor (bone morphogenetic protein 2; BMP-2) was loaded onto the template scaffold via adsorption, while a chondrogenic growth factor (transforming growth factor beta 1; TGF-β1) was incorporated into the hydrogel phase. Confocal microscopy of the growth factor loaded matrix confirmed the spatial distribution of the two growth factors, with chondrogenic factor confined to the cartilaginous portion and osteogenic factor present throughout the scaffold. We observed spatial differentiation of human mesenchymal stem cells (hMSCs) into cartilage and bone cells in the scaffolds in vitro: cartilaginous regions were marked by increased glycosaminoglycan production, and osteogenesis was seen throughout the graft by alizarin red staining. In a dose-dependent study of BMP-2, hMSC pellet cultures with TGF-β1 and BMP-2 showed synergistic effects on chondrogenesis. These results indicate that development of an inverse gradient matrix can spatially distribute two different growth factors to facilitate chondrogenesis and osteogenesis along different portions of a scaffold, which are key steps needed for formation of an osteochondral interface.

Small Cartilage Defect Management

Cartilage defects in the knee are common resulting in significant pain and morbidity over time. These defects can arise in isolation or concurrently with other associated injuries to the knee. The treatment of small (< 2-3 cm²) cartilage deficiencies has changed as our basic science knowledge of tissue healing has improved. Advancements have led to the development of new and more effective treatment modalities. It is important to address any associated knee injuries and limb malalignment. Surgical options are considered when nonoperative treatment fails. The specific procedure depends on individual patient characteristics, lesion size, and location. Debridement/chondroplasty, microfracture, marrow stimulation plus techniques, fixation of unstable osteochondral fragments, osteochondral autograft transfer, and osteochondral allograft transplantation, all have roles in the treatment of small cartilage defects.

Mechano-activated biomolecule release in regenerating load-bearing tissue microenvironments

Although mechanical loads are integral for musculoskeletal tissue homeostasis, overloading and traumatic events can result in tissue injury. Conventional drug delivery approaches for musculoskeletal tissue repair employ localized drug injections. However, rapid drug clearance and inadequate synchronization of molecule provision with healing progression render these methods ineffective. To overcome this, a programmable mechanoresponsive drug delivery system was developed that utilizes the mechanical environment of the tissue during rehabilitation (for example, during cartilage repair) to trigger biomolecule provision. For this, a suite of mechanically-activated microcapsules (MAMCs) with different rupture profiles was generated in a single fabrication batch via osmotic annealing of double emulsions. MAMC physical dimensions were found to dictate mechano-activation in 2D and 3D environments and their stability in vitro and in vivo, demonstrating the tunability of this system. In models of cartilage regeneration, MAMCs did not interfere with tissue growth and activated depending on the mechanical properties of the regenerating tissue. Finally, biologically active anti-inflammatory agents were encapsulated and released from MAMCs, which counteracted degradative cues and prevented the loss of matrix in living tissue environments. This unique technology has tremendous potential for implementation across a wide array of musculoskeletal conditions for enhanced repair of load-bearing tissues.

Human articular cartilage is orthotropic where microstructure, micromechanics, and chemistry vary with depth and split-line orientation

OBJECTIVE

Quantitative, micrometer length scale assessment of human articular cartilage is essential to enable progress toward new functional tissue engineering approaches, including utilization of emerging 3D bioprinting technologies, and for improved computational modeling of the osteochondral unit. Thus the objective of this study was to characterize the structural organization, material properties, and chemical composition of human skeletally mature articular cartilage with respect to depth and defined morphological features: normal to the articulating surface, parallel to the split-line, and transverse to the split-line.

METHOD

Three samples from the lateral femoral condyles of 4 healthy adult donors (55-61 years old) were evaluated via histology, second harmonic generation, microindentation, and Raman spectroscopy. All metrics were evaluated as a function of depth and direction relative to the split-line.

RESULTS

All donors presented with intact and healthy tissue. Collagen fiber orientation varied significantly between testing directions and with increasing depth from the articular surface. Both compressive and tensile modulus increased significantly with depth and differed across the middle and deep zones and depended on orthogonal direction relative to the split-line. Similarly, matrix components varied with both depth and direction, where chondroitin sulfate steadily increased with depth while collagen prevalence was highest in the surface layer.

CONCLUSIONS

Microscale measurements of human articular cartilage demonstrate that properties are both depth-dependent and orthotropic and depend on the underlying tissue structure and composition. These findings improve upon existing knowledge establishing more accurate measurements, with greater degree of depth and spatial specificity, as inputs for tissue engineering and computational modeling.

Perspectives on Synthetic Materials to Guide Tissue Regeneration for Osteochondral Defect Repair

Regenerative engineering holds the potential to treat clinically pervasive osteochondral defects (OCDs). In a synthetic materials-guided approach, the scaffold's chemical and physical properties alone instruct cellular behavior in order to effect regeneration, referred to herein as "instructive" properties. While this alleviates the costs and off-target risks associated with exogenous growth factors, the scaffold must be potently instructive to achieve tissue growth. Moreover, toward achieving functionality, such a scaffold should also recapitulate the spatial complexity of the osteochondral tissues. Thus, in addition to the regeneration of the articular cartilage and underlying cancellous bone, the complex osteochondral interface, composed of calcified cartilage and subchondral bone, should also be restored. In this Perspective, we highlight recent synthetic-based, instructive osteochondral scaffolds that have leveraged new material chemistries as well as innovative fabrication strategies. In particular, scaffolds with spatially complex chemical and morphological features have been prepared with electrospinning, solvent-casting-particulate-leaching, freeze-drying, and additive manufacturing. While few synthetic scaffolds have advanced to clinical studies to treat OCDs, these recent efforts point to the promising use of the chemical and physical properties of synthetic materials for regeneration of osteochondral tissues.