The Addition of Platelet-Rich Plasma to Scaffolds Used for Cartilage Repair: A Review of Human and Animal Studies

Infiltration therapy in the context of cartilage surgery

Guideline-based surgical cartilage therapy for focal cartilage damage offers highly effective possibilities to sustainably reduce patients' complaints and to prevent or at least delay the development of early osteoarthritis. In the knee joint, it has the potential to reduce almost a quarter of the arthroses requiring joint replacement caused by cartilage damage. Biologically effective injection therapies could further improve these results. Based on the currently available literature and preclinical studies, intra- and postoperative injectables may have a positive effect of platelet-rich plasma/fibrin (PRP/PRF) and hyaluronic acid (HA) on cartilage regeneration and, in the case of HA injections, also on the clinical outcome can be assumed. The role of a combination therapy with use of intra-articular corticosteroids is lacking in the absence of adequate study data and cannot be defined yet. With regard to adipose tissue-based cell therapy, the current scientific data do not yet justify any recommendation for its use. Further studies also regarding application intervals, timing and differences in different joints are required.

Cellular therapy and tissue engineering for cartilage repair

Articular cartilage (AC) has limited capacity for repair. The first attempt to repair cartilage using tissue engineering was reported in 1977. Since then, cell-based interventions have entered clinical practice in orthopaedics, and several tissue engineering approaches to repair cartilage are in the translational pipeline towards clinical application. Classically, these involve a scaffold, substrate or matrix to provide structure, and cells such as chondrocytes or mesenchymal stromal cells to generate the tissue. We discuss the advantages and drawbacks of the use of various cell types, natural and synthetic scaffolds, multiphasic or gradient-based scaffolds, and self-organizing or self-assembling scaffold-free systems, for the engineering of cartilage constructs. Several challenges persist including achieving zonal tissue organization and integration with the surrounding tissue upon implantation. Approaches to improve cartilage thickness, organization and mechanical properties include mechanical stimulation, culture under hypoxic conditions, and stimulation with growth factors or other macromolecules. In addition, advanced technologies such as bioreactors, biosensors and 3D bioprinting are actively being explored. Understanding the underlying mechanisms of action of cell therapy and tissue engineering approaches will help improve and refine therapy development. Finally, we discuss recent studies of the intrinsic cellular and molecular mechanisms of cartilage repair that have identified novel signals and targets and are inspiring the development of molecular therapies to enhance the recruitment and cartilage reparative activity of joint-resident stem and progenitor cells. A one-fits-all solution is unrealistic, and identifying patients who will respond to a specific targeted treatment will be critical.

Washed Equine Platelet Extract as an Anti-Inflammatory Biologic Pharmaceutical

Mammalian platelets participate in the immediate tissue injury response by initiating coagulation and further promoting tissue injury mitigation and repair. The latter properties are deployed following platelet release of presynthetized morphogens, cytokines, and growth and chemotactic factors, which launch a tissue regenerative, angiogenic, and anti-inflammatory program. Several blood-derived biologic products, like platelet-rich plasma (PRP) and platelet lysate (PL), are currently on the market to allow proper healing and tissue regeneration. However, not all growth factors are released from the platelets and the final products contain plasma proteins such as albumin, fibrinogen, complement, and immunoglobulins, increasing the risks of serum sickness or allergic reaction. To address this problem, we developed a new platelet extract where equine blood platelets are concentrated, washed, and thereafter lysed by detergent Triton X-114. Distinct from PRP, this extract is devoid of albumin, fibrinogen, and immunoglobulins and is 266-fold enriched in platelet-derived growth factor content relative to PRP. Washed equine platelet extract (WEPLEX) is amenable to lyophilization without loss of biological activity. In vitro, WEPLEX significantly inhibits human and equine T cell proliferative response to phytohemagglutinin and also polarizes murine CD45⁺/CD11b⁺ peritoneal macrophages to an IL-10⁺ M2-like phenotype. In vivo, WEPLEX substantially improves clinical outcome of murine experimental dextran sulfate sodium colitis. We propose that equine-sourced, zoonosis-free WEPLEX may serve as an anti-inflammatory biological therapy across mammalian species.

Growth Factor Delivery to a Cartilage-Cartilage Interface Using Platelet-Rich Concentrates on a Hyaluronic Acid Scaffold

PURPOSE

To determine whether (1) human leukocyte-platelet-rich plasma (L-PRP) or (2) leukocyte-platelet-rich fibrin (L-PRF) delivered on a hyaluronic acid (HA) scaffold at a bovine chondral defect, a simulated cartilage tear interface, in vitro would improve tissue formation based on biomechanical, histologic, and biochemical measures.

METHODS

L-PRF and L-PRP were prepared from 3 healthy volunteer donors and delivered in conjunction with HA scaffolds to defects created in full-thickness bovine cartilage plugs harvested from bovine femoral condyle and trochlea. Specimens were cultured in vitro for up to 42 days. Treatment groups included an HA scaffold alone and scaffolds containing L-PRF or L-PRP. Cartilage repair was assessed using biomechanical testing, histology, DNA quantification, and measurement of sulfated glycosaminoglycan and collagen content at 28 and 42 days.

RESULTS

L-PRF elicited the greatest degree of defect filling and improvement in other histologic measures. L-PRF-treated specimens also had the greatest cellularity when compared with L-PRP and control at day 28 (560.4 μg vs 191.4 μg vs 124.2 μg, P = .15); at day 48, there remained a difference, although not significant, between L-PRF versus L-PRP (761.1 μg vs 589.3 μg, P = .219) . L-PRF had greater collagen deposition when compared with L-PRP at day 42 (40.1 μg vs 16.3 μg, P < .0001). L-PRF had significantly greater maximum interfacial strength compared with the control at day 42 (10.92 N vs 0.66 N, P = .015) but had no significant difference compared with L-PRP (10.92 N vs 6.58 N, P = .536). L-PRP facilitated a greater amount of sulfated glycosaminoglycan production at day 42 when compared with L-PRF (15.9 μg vs 4.3 μg, P = .009).

CONCLUSIONS

Delivery of leukocyte-rich platelet concentrates in conjunction with a HA scaffold may allow for improvements in cartilage healing through different pathways. L-PRF was not superior to L-PRP in its biomechanical strength, suggesting that both treatments may be effective in improving biomechanical strength of healing cartilage through different pathways.

CLINICAL RELEVANCE

The delivery of platelet-rich concentrates in conjunction HA scaffolds may augment healing cartilaginous injuries.

The effect of perioperative platelet-rich plasma injections on postoperative failure rates following rotator cuff repair: a systematic review with meta-analysis

BACKGROUND

Platelet-rich plasma (PRP) has gained significant interest in recent years to potentially add biological augmentation of healing to surgical repairs of soft-tissue injuries. We sought to determine whether perioperative PRP injection influences the risk of failure following rotator cuff repair.

METHODS

A systematic search was performed in the Embase and PubMed databases and identified 16 randomized controlled trials or prospective cohort studies (1045 participants) reporting rates of failure, defined as a subsequent tear on postoperative imaging, after rotator cuff repair with or without perioperative PRP administration. A random-effects meta-analysis of the included studies was performed to determine the pooled effect of PRP administration on the postoperative failure risk.

RESULTS

Among the 16 studies investigating rotator cuff repairs, PRP augmentation resulted in a 25% reduction in the risk of repair failure, with low heterogeneity among the included studies. A significant protective effect was seen for studies of only small to medium tears (7 studies) (P = .007) and studies including large or massive tears (9 studies) (P < .001).

CONCLUSIONS

Intraoperative PRP reduces the failure risk following rotator cuff repair and has a consistent effect regardless of tear size. However, because of the variability in PRP preparations, a specific recommendation cannot be made.

Platelet-rich plasma combined with injectable hyaluronic acid hydrogel for porcine cartilage regeneration: a 6-month follow-up

Based on our previous study, the utilization of an ultraviolet light photo-cross-linkable hyaluronic acid (HA) hydrogel integrated with a small molecule kartogenin-encapsulated nanoparticles obtained good reconstruction of osteochondral defects in a rabbit model, indicating the superiority of injectable hydrogel-based scaffolds in cartilage tissue engineering. Platelet-rich plasma (PRP), rich in various growth factors, proteins and cytokines, is considered to facilitate cartilage healing by stimulating cell proliferation and inducing chondrogenesis in cartilage defect site. The aim of this study was to test the therapeutic feasibility of autologous PRP combined with injectable HA hydrogel on cartilage repair. The focal cartilage defects with different critical sizes in the medial femoral condyle of a porcine model were used. At 6 months, the minipigs were sacrificed for assessment of macroscopic appearance, magnetic resonance imaging, micro-computed tomography, histology staining and biomechanics. The HA hydrogel combined with PRP-treated group showed more hyaline-like cartilage exhibited by macroscopic appearance and histological staining in terms of extracellular matrix and type II collagen without formation of hypertrophic cartilage, indicating its capacity to improve cartilage healing in the minipig model evaluated at 6 months, with full-thickness cartilage defect of 8.5 mm diameter and osteochondral defect of 6.5 mm diameter, 5 mm depth exhibiting apparent regeneration.

Bioactive factors for cartilage repair and regeneration: Improving delivery, retention, and activity

Articular cartilage is a remarkable tissue whose sophisticated composition and architecture allow it to withstand complex stresses within the joint. Once injured, cartilage lacks the capacity to self-repair, and injuries often progress to joint wide osteoarthritis (OA) resulting in debilitating pain and loss of mobility. Current palliative and surgical management provides short-term symptom relief, but almost always progresses to further deterioration in the long term. A number of bioactive factors, including drugs, corticosteroids, and growth factors, have been utilized in the clinic, in clinical trials, or in emerging research studies to alleviate the inflamed joint environment or to promote new cartilage tissue formation. However, these therapies remain limited in their duration and effectiveness. For this reason, current efforts are focused on improving the localization, retention, and activity of these bioactive factors. The purpose of this review is to highlight recent advances in drug delivery for the treatment of damaged or degenerated cartilage. First, we summarize material and modification techniques to improve the delivery of these factors to damaged tissue and enhance their retention and action within the joint environment. Second, we discuss recent studies using novel methods to promote new cartilage formation via biofactor delivery, that have potential for improving future long-term clinical outcomes. Lastly, we review the emerging field of orthobiologics, using delivered and endogenous cells as drug-delivering "factories" to preserve and restore joint health. Enhancing drug delivery systems can improve both restorative and regenerative treatments for damaged cartilage. STATEMENT OF SIGNIFICANCE: Articular cartilage is a remarkable and sophisticated tissue that tolerates complex stresses within the joint. When injured, cartilage cannot self-repair, and these injuries often progress to joint-wide osteoarthritis, causing patients debilitating pain and loss of mobility. Current palliative and surgical treatments only provide short-term symptomatic relief and are limited with regards to efficiency and efficacy. Bioactive factors, such as drugs and growth factors, can improve outcomes to either stabilize the degenerated environment or regenerate replacement tissue. This review highlights recent advances and novel techniques to enhance the delivery, localization, retention, and activity of these factors, providing an overview of the cartilage drug delivery field that can guide future research in restorative and regenerative treatments for damaged cartilage.

Understanding Articular Cartilage Injury and Potential Treatments

The goals of all orthopaedic surgeons treating articular cartilage injuries have been anatomic reduction and stable fixation of the articular cartilage surface with restoration of limb alignment and/or reestablishment of the joint stability, all while minimizing the risk of surgical complications. Recent developments in the study of articular cartilage injury have shown that there is a robust cellular response to joint injury. This response has been shown to involve the synoviocytes, chondrocytes, and osteocytes in and around the injured joint and if these responses are left unchecked, they can lead to the development of posttraumatic osteoarthritis (PTOA). Therefore, to predictably and successfully treat articular cartilage injuries, it is not sufficient to just restore articular congruity, limb alignment, and joint stability, but we must also recognize and attempt to mitigate this associated cellular response. Understanding not only the mechanical aspects of these joint injuries but also the biological aspects is paramount to giving our patients the best opportunity to heal their injuries, recover full function, and avoid the potential devastating development of PTOA. Gone is the simplistic view that if one can achieve articular congruity after intraarticular fracture, as well as joint stability after ligamentous injury, that our patients will do just fine. This review sheds new light on the molecular response to cartilage injury, how residual joint incongruity and instability affect the joint's ability to recover from injury, and how chondrocyte apoptosis in response to injury can influence joint. This article then briefly reviews how cellular and growth factors may be beneficial to the treatment of articular cartilage injury and how ultimately cartilage regeneration may be used in the future to salvage the joints ravaged by PTOA in response to injury.

Effect of Autologous Platelet-Rich Plasma and Gelatin Sponge for Tendon-to-Bone Healing After Rabbit Anterior Cruciate Ligament Reconstruction

PURPOSE

To investigate platelet-rich plasma (PRP) combined with gelatin sponge (GS) to improve tendon-bone interface healing and structure formation.

METHODS

Characterization of the GS scaffold was performed with a scanning electron microscope, and the release curve after loading with PRP was evaluated. A real-time reverse transcription quantitative polymerase chain reaction assay was performed to test the levels of tendon-to-bone healing-related gene expression. Finally, 18 New Zealand white rabbits were randomly divided into 3 groups and underwent semitendinosus autograft anterior cruciate ligament reconstruction: autograft group without PRP, PRP group, and PRP-GS group. All rabbits were killed 8 weeks after the operation. Magnetic resonance imaging scans, biomechanical testing, and histologic evaluation were performed.

RESULTS

An enzyme-linked immunosorbent assay and cell counting kit-8 assay showed that the GS could control the release of PRP and prolong its bioactivity time, as well as promote bone marrow mesenchymal stem cell proliferation. In the PRP-GS group, the levels of related genes were upregulated compared with the PRP group (P < .05). Lower signal in the magnetic resonance images indicated fibrocartilage formation in the 2 groups with PRP. In addition, histologic staining showed that the tendon-bone connection had a greater fibrocartilaginous transition region in the PRP-GS group, and the histologic scores were higher (vs the PRP group, P = .039). The maximum failure load and stiffness were higher in the PRP-GS group than in the other 2 groups.

CONCLUSIONS

GS loading with PRP could prolong the bioactivity time of PRP and promote bone marrow mesenchymal stem cell proliferation and osteogenic gene expression in vitro. It also promoted the early healing process at the tendon-bone junction in a rabbit anterior cruciate ligament reconstruction model.

CLINICAL RELEVANCE

GS is a natural material and offers satisfactory biocompatibility. Using GS as a scaffold to control the release of bioactive factors in bone tunnels may be useful, but additional studies in human subjects will be necessary to evaluate its clinical prospects.

Chondrogenic effect of liquid and gelled platelet lysate on canine adipose-derived mesenchymal stromal cells

Osteoarthritis associated with hip dysplasia is one of the most common orthopedic abnormalities in dogs, with an incidence of up to 40% in some breeds. Tissue therapy of cartilage has received great attention, with use of mesenchymal stromal cells and different types of biomaterials. The present study aimed to evaluate the effect of platelet lysate (PL) on the proliferation and differentiation of canine adipose tissue-derived mesenchymal stromal cells (ASCs), in liquid culture or hydrogels. PL was prepared from blood collected from healthy dogs and submitted to freezing-thawing cycles, and hydrogel was formed with canine thrombin. The effect of PL on the proliferation and differentiation of canine ASCs was evaluated in liquid and hydrogel systems, with microscopy, quantification of dsDNA, histology and quantification of glycosaminoglycans. The addition of 5% or 10% PL to the culture medium induced a greater proliferation rate than the presence of 10% fetal bovine serum. The cultivation of ASCs in PL gel, with normal or chondrogenic medium, resulted in maintenance of proliferation level similar to the conventional 2D cultivation, and induction of chondrogenic differentiation, especially in the presence of the chondrogenesis induction medium.

Rationale and pre-clinical evidences for the use of autologous cartilage micrografts in cartilage repair

BACKGROUND

The management of cartilage lesions is an open issue in clinical practice, and regenerative medicine represents a promising approach, including the use of autologous micrografts whose efficacy was already tested in different clinical settings. The aim of this study was to characterize in vitro the effect of autologous cartilage micrografts on chondrocyte viability and differentiation and perform an evaluation of their application in racehorses affected by joint diseases.

MATERIALS AND METHODS

Matched human chondrocytes and micrografts were obtained from articular cartilage using Rigenera® procedure. Chondrocytes were cultured in the presence or absence of micrografts and chondrogenic medium to assess cell viability and cell differentiation. For the pre-clinical evaluation, three racehorses affected by joint diseases were treated with a suspension of autologous micrografts and PRP in arthroscopy interventions. Clinical and radiographic follow-ups were performed up to 4 months after the procedure.

RESULTS

Autologous micrografts support the formation of chondrogenic micromasses thanks to their content of matrix and growth factors, such as transforming growth factor β (TGFβ) and insulin-like growth factor 1 (IGF-1). On the other hand, no significant differences were observed on the gene expression of type II collagen, aggrecan, and SOX9. Preliminary data in the treatment of racehorses are suggestive of a potential in vivo use of micrografts to treat cartilage lesions.

CONCLUSION

The results reported in this study showed the role of articular micrografts in the promoting chondrocyte differentiation suggesting their potential use in the clinical practice to treat articular lesions.

Should orthopedic surgeons consider reducing the negative effects of Outerbridge grade 2 patellofemoral chondral lesion on early postoperative recovery during anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to comparatively evaluate the effectiveness of intra-articular PRP and HA injections applied as the treatment of Outerbridge grade 2 chondral lesions in patellofemoral joint during arthroscopic ACL reconstruction.

METHODS

The clinical and radiographic data of 61 patients between 18 and 45 years of age were evaluated. The patients were separated into three groups. Hyaluronic acid injection was applied in 22 knees (Group 1), PRP injection was applied in 18 knees (Group 2), and 21 knees did not have any specific treatment except ACL reconstruction (Group 3). All patients were followed clinically at least for 12 months. Clinical examination of the operated knee, visual analogue scale (VAS) score, Lysholm knee score, and Tegner activity scale were the outcome measures. Routine X-ray and MRI were also performed for all patients at 12-month postoperative follow-up visit.

RESULTS

Although the mean VAS and Lysholm scores at 3-month follow-up were better in Group 1 and 2 than Group 3, the efficacy of intra-articular PRP on healing process regarding progression of the mean VAS and Lysholm scores through 6- and 12-month follow-ups was significantly better and longer than HA. No statistically significant differences were detected according to Tegner activity scale between the groups at 3 and 6 months; however, Group 2 had better activity level than both Group 1 (p < 0.001) and 3 (p < 0.001) at the end of 12 months after surgery.

CONCLUSION

Intra-articular PRP injection applied as the treatment of concomitant Outerbridge grade 2 chondral lesion in patellofemoral joint during ACL reconstruction revealed better and durable clinical outcomes via decreasing the potentially negative effects of chondral pathology on postoperative healing with respect to HA injection.

LEVEL OF EVIDENCE

III-retrospective comparative study.

Therapeutic Effects of the Addition of Platelet-Rich Plasma to Bioimplants and Early Rehabilitation Exercise on Articular Cartilage Repair

BACKGROUND

Treating articular cartilage lesions is clinically challenging. However, whether the addition of autologous platelet-rich plasma (PRP) to bioimplants along with early rehabilitation exercise provides therapeutic effects and regenerates the osteochondral defect remains uninvestigated.

HYPOTHESIS

The addition of PRP to a polylactic-co-glycolic acid (PLGA) scaffold along with continuous passive motion (CPM) in osteochondral defects may offer beneficial in situ microenvironment changes to facilitate hyaline cartilage and subchondral bone tissue repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

In 26 rabbits, 52 critical osteochondral defects were created in bilateral femoral trochlear grooves. The rabbits were allocated to 1 of the following 3 groups: PRP gel (PG group), PRP + PLGA scaffold (PP group), and PRP + PLGA scaffold + CPM (PPC group). At 4 and 12 weeks after surgery, the specimens were assessed by a macroscopic examination, a histological evaluation with immunohistochemical staining, and micro-computed tomography.

RESULTS

The PPC group exhibited the most favorable therapeutic outcomes in terms of hyaline cartilage regeneration. At week 4, the PPC group exhibited significantly higher levels of glycosaminoglycan (GAG) and collagen (COL) II and modest increases in COL I, matrix metalloproteinase-3 (MMP-3), and inflammatory cells with tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). At week 12, the PPC group had significantly higher tissue repair scores, corresponding to a sound articular cartilage surface and chondrocyte and collagen arrangement. This group demonstrated restored hyaline cartilage and mineralized bone volume per tissue volume, which had an integrating structure in the repair site. However, the PG and PP groups exhibited mainly fibrous tissue and fibrocartilage, corresponding to higher expressions of COL I, TNF-α, IL-6, and MMP-3.

CONCLUSION

PRP with a PLGA graft along with early CPM exercise is promising for the repair of osteochondral defects in rabbit knee joints.

CLINICAL RELEVANCE

This study demonstrates the efficacy of a triad therapy involving the addition of PRP to bioimplants along with early CPM intervention for hyaline cartilage and subchondral regeneration. However, PRP alone (with or without PLGA implants) is limited to osteochondral defect repair without significant regeneration.

Clinical Management in Early OA

Knee osteoarthritis affects an important percentage of the population throughout their life. Several factors seem to be related to the development of knee osteoarthritis including genetic predisposition, gender, age, meniscal deficiency, lower limb malalignments, joint instability, cartilage defects, and increasing sports participation. The latter has contributed to a higher prevalence of early onset of knee osteoarthritis at younger ages with this active population demanding more consistent and durable outcomes. The diagnosis is complex and the common signs and symptoms are often cloaked at these early stages. Classification systems have been developed and are based on the presence of knee pain and radiographic findings coupled with magnetic resonance or arthroscopic evidence of early joint degeneration. Nonsurgical treatment is often the first-line option and is mainly based on daily life adaptations, weight loss, and exercise, with pharmacological agents having only a symptomatic role. Surgical treatment shows positive results in relieving the joint symptomatology, increasing the knee function and delaying the development to further degenerative stages. Biologic therapies are an emerging field showing early promising results; however, further high-level research is required.

Identification of Novel Chondroprotective Mediators in Resolving Inflammatory Exudates

We hypothesized that exudates collected at the beginning of the resolution phase of inflammation might be enriched for tissue protective molecules; thus an integrated cellular and molecular approach was applied to identify novel chondroprotective bioactions. Exudates were collected 6 h (inflammatory) and 24 h (resolving) following carrageenan-induced pleurisy in rats. The resolving exudate was subjected to gel filtration chromatography followed by proteomics, identifying 61 proteins. Fractions were added to C28/I2 chondrocytes, grown in micromasses, ions with or without IL-1β or osteoarthritic synovial fluids for 48 h. Three proteins were selected from the proteomic analysis, α1-antitrypsin (AAT), hemopexin (HX), and gelsolin (GSN), and tested against catabolic stimulation for their effects on glycosaminoglycan deposition as assessed by Alcian blue staining, and gene expression of key anabolic proteins by real-time PCR. In an in vivo model of inflammatory arthritis, cartilage integrity was determined histologically 48 h after intra-articular injection of AAT or GSN. The resolving exudate displayed protective activities on chondrocytes, using multiple readouts: these effects were retained in low m.w. fractions of the exudate (46.7% increase in glycosaminoglycan deposition; ∼20% upregulation of COL2A1 and aggrecan mRNA expression), which reversed the effect of IL-1β. Exogenous administration of HX, GSN, or AAT abrogated the effects of IL-1β and osteoarthritic synovial fluids on anabolic gene expression and increased glycosaminoglycan deposition. Intra-articular injection of AAT or GSN protected cartilage integrity in mice with inflammatory arthritis. In summary, the strategy for identification of novel chondroprotective activities in resolving exudates identified HX, GSN and AAT as potential leads for new drug discovery programs.

Treatment of Articular Cartilage Defects With Microfracture and Autologous Matrix-Induced Chondrogenesis Leads to Extensive Subchondral Bone Cyst Formation in a Sheep Model

BACKGROUND

Microfracture and the autologous matrix-induced chondrogenesis (AMIC) technique are popular for the treatment of articular cartilage defects. However, breaching of the subchondral bone plate could compromise the subchondral bone structure.

HYPOTHESIS

Microfracture and AMIC will cause deleterious effects on the subchondral bone structure.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 36 sheep received an 8-mm-diameter cartilage defect in the left medial femoral condyle. Control animals (n = 12) received no further treatment, and the rest received 5 microfracture holes either with a type I/III collagen scaffold implanted (n = 12; AMIC group) or without the collagen scaffold (n = 12; microfracture group). Macroscopic infill of defects, histology, and histomorphometry of the subchondral bone were performed at 13 and 26 weeks postoperatively, and micro-computed tomography (CT) was also performed at 26 weeks postoperatively.

RESULTS

Microfracture and AMIC resulted in subchondral bone cyst formation in 5 of 12 (42%) and 11 of 12 (92%) specimens at 13 and 26 weeks, respectively. Subchondral bone changes induced by microfracture and AMIC were characterized by an increased percentage of bone volume, increased trabecular thickness, and a decreased trabecular separation, and extended beyond the area below the defect. High numbers of osteoclasts were observed at the cyst periphery, and all cysts communicated with the microfracture holes. Cartilage repair tissue was of poor quality and quantity at both time points and rarely reached the tidemark at 13 weeks.

CONCLUSION

Microfracture technique caused bone cyst formation and induced severe pathology of the subchondral bone in a sheep model.

CLINICAL RELEVANCE

The potential of microfracture technique to induce subchondral bone pathology should be considered.

Editorial Commentary: "All That Glitters Is Not Gold"

For the treatment of osteochondral lesions of the talus, the addition of concentrated bone marrow aspirate to marrow stimulation procedures results in repair tissue that, by magnetic resonance imaging, appears to be similar to native articular cartilage. But, functional outcomes are no different when compared with marrow stimulation alone. Moreover, the true "gold" is that the repair tissue not only has the magnetic resonance imaging appearance of native articular cartilage but also should have the same organizational structure and composition so that it may function like native articular cartilage.

Editorial Commentary: Effects of PRP on Cartilage Repair Using Scaffolds Are Inconclusive

Effects of PRP on cartilage repair using scaffolds are, in the clinical setting, inconclusive. Biologics research is confounded by the variety and heterogeneity of stem cells, scaffolds, PRP preparations, other growth factors, and other biological stimulants.