The OC tissue has the articular cartilage layer as the foremost region of the joint, a highly flexible and supportive tissue. The unique features of cartilage tissue limit its self-renewal capabilities due to lack of vascularization and innervation [41]. Remodeling is rarely seen in cartilage due to low cell number and low metabolic activity of chondrocytes especially mature cells which produce little ECM [42, 43]. The cartilage is present in three different types in the body: hyaline cartilage, fibrocartilage, and elastic cartilage, the predominant one being hyaline cartilage which is also called articular cartilage. It is mostly composed of water, collagen, proteoglycans (PGs), proteins, and chondrocytes. Cartilaginous tissue fulfills a supportive role mainly due to its capacity to withstand high compressive loads. This behavior is intrinsically related to the ECM composition. The glycosaminoglycans (GAGs) attached to the PGs give a strongly negative charge to the ECM. In this way, osmotically active cations are attracted, leading to the entrance of water into the ECM. The intricate ECM network in articular cartilage is structured by the presence of collagen type II intertwining chondroitin, keratin sulfate (GAGs), and aggrecan (PG). The collagen type II fibrils improve the structure and the elastic strength of the cartilage. It is also believed that the existence of collagen type X is responsible for the process of mineralization happening at the interface between cartilage and bone. The overall cartilaginous tissue is formed by the same components. However, its assembly and concentrations vary in different cartilage zones. There are four different zones: superficial, middle, deep (or calcified), and subchondral bone. The presence of this calcified zone between is responsible for connecting the innermost cartilage layer and subchondral bone layer [44].

The OC tissue presents an inner region named the subchondral bone. This is the zone underlying the calcified cartilage zone and is composed of the lamella and the trabeculae [45]. The lamella can also be called the subchondral bone plate, and it is the marked zone that separates the two regions (cartilage and subchondral bone). There is a solid mass of bone underneath, defined as trabeculae. This zone is highly vascularized, and the nutrients exchanged here are utilized by both articular cartilage and subchondral bone. Apart from serving as an anchorage site to collagen fibrils, the other important roles of subchondral bone are absorption and support joint shape [46].

Damage to the articular cartilage and subsequent progression of OC defects (including OCD) and progressive OA are pathological conditions resulting in the loss of joint function. The ECM suffers a destabilization of supramolecular structures affecting collagen expression and molecular secretion [47].

Football is the most popular sport in the world either at amateur or professional level [48]. It is estimated that, worldwide, around 200 million individuals are active football players. But it is associated with a high risk of injury presenting 13–35 injuries per 1000 h of competition on the field [49]. Unfortunately, there is a lack of detailed information about football-related injury as to risk prevention, mechanisms, severity of injuries, and the resulting time lost to play while players recover [50, 51]. In addition, no consensus exists about study design, data collection, and pathological definitions in the epidemiological studies of football injuries to date [51]. For these reasons, epidemiological research should be carried out to devise preventive measures [52].

Over the last 20 years, a new era of medicine has been receiving a lot of attention among clinicians. Orthobiologics is an emergent field in medicine, which has a specific emphasis on tissue’s healing. As previously mentioned, orthobiologics uses autologous therapies to modulate cell signaling allowing the acceleration of healing process. Sports medicine had helped to bring orthobiologics into the current medical practice. It can be attempted as cellular therapies; however, there was a paradigm shift in treatment design where no longer this treatments concern the temporary management of the pathology. Orthobiologics is somewhere in between conservative and surgical methods, and so far it has faced three evolutions over the years. Viscosupplementation, which concerns hyaluronic acid injections, was the first generation. The treatment was first applied in 1997 to relieve patients from the pain symptoms of OA. The outcome was satisfactory, and, unlike oral drug administration (NSAID), viscosupplementation was able to diminish patient’s pain.

The first usage of PRP in sport medics reports to 2006. Some year after viscosupplementation usage, PRP appear as a second generation in orthobiologics. Ferrari et al. [53] was the first to use PRP in an open heart surgery. Unlike viscosupplementation, PRP is an autologous therapy and is performed to stimulate a supraphysiologic response in the body. PRP function as an enriched cocktail of bioactive proteins. The third generation in orthobiologics reports the use of mesenchymal stem cells, either from different sources such as embryonic, bone marrow, adipose, etc. Bone marrow-derived concentrate (BMDC) is often used in clinics, and it is a mixture of mesenchymal stem cell, hematopoietic cells, platelet, and cytokine involved in the regenerative potential of healing [54].

Currently, most of the orthobiologics studies carried out present considerable outcome heterogeneity, mostly being nonrandomized and non-well classified. So, there is still the need to pursue research in a more controlled manner to achieve orthobiologics strategies that are more feasible.

HA injection at the site of lesion appears as a conservative method to treat OC lesions [55]. HA is a high molecular weight and anionic biopolysaccharide [56], discovered in 1934, by Karl Meyer and his assistant John Palmerin [55]. The first medical HA application in humans was in the vitreous substitution/replacement procedure during bovine eye surgery, in the late 1950s [55]. Viscosupplementation (VS) came into clinical use in Japan and Italy in 1987 and in Canada in 1992, but in Europe and the USA, it was adopted in the second half of the 1990s. VS is the intra-articular administration of a high viscoelastic fluid into the synovial joint to reproduce and repair the rheological proprieties of the synovial fluid. VS can enhance the vital joint lubrication and shock absorption ability, essential functions for mobility improvements and pain relief. All products available on the market for VS are based on HA, a high molecular weight (105–107 Da) and unbranched glycosaminoglycan that can be found in the extracellular matrix of human tissue. While HA is used clinically, its functions are not fully known [57]. Chondroprotective effects of HA, observed in vivo, might explain the beneficial long-term effects on articular cartilage. HA also reduces pain-associated nerve impulses and sensitivity. HA is a free, non-sulfated, and negatively charged glycosaminoglycan (GAG) capable of interacting with receptors and ECM proteins [58]. HA can be derived from different sources such as rooster combs, bacterial production, and either animal or human sources [59]. Its properties (e.g., rheological properties) depend on its source. Nevertheless, HA presents high viscosity, is a water-soluble polymer, and has specific enzymatic degradation. Low and high molecular weight are the two forms of HA, differing in chain length (≤2 × 10⁶ Da and 2 × 10⁶–≥4 × 10⁶ Da, respectively). Structural and biological functions of HA are mainly chain size-related to its chains as suggested by Stern et al. [60, 61]. The interactions between tissues and HA occur through hyaladherins. Essential functions such as cell communication, motility, and morphogenesis occur due to interactions between hyaladherins and tissue receptor. These interactions occur through specific receptors, mainly CD44 and RHAMM, at the cell surface. The high molecular weight hyaluronic acid (HMWHA) molecule plays a structural role because it is able to bind 10–10,000 times its weight in water [60, 62, 63]. Thus, being osmotically active in a completely hydrated state, it is able to fill the space and act as a shock absorber as well as a lubricant. From a biological point of view, the HMW chains are anti-angiogenic and anti-inflammatory and possess immunosuppressive capacities [64, 65]. Many studies have reported a decrease in the inflammatory response and apoptosis through the downregulation of a number of factors responsible for ECM. These results suggest that HMWHA impairs the phenomena of phagocytosis, macrophage activation, and inflammatory cytokines production. However, HMWHA chains can break down into low molecular weight chains (LMWHA), which are found to have a pro-inflammatory effect. These fragments have been shown to secrete inflammatory cytokines and stimulate angiogenesis and tissue remodeling after activation of endogenous signaling pathways. They can promote the activation and maturation of dendritic cells and the release of pro-inflammatory cytokines [61, 65, 66]. Molecular changes in the ECM of damaged joints alter the composition and structure of natural HA. Along with molecule secretion and tissue remodeling, the development of pathologies also occurs [60].

HA injection, also known as viscosupplementation, appears to be a conservative method to improve the biomechanical function of the joint mainly due to HA physicochemical characteristics (i.e., hydrogel state) [67, 68]. HA is a gel-like constituent injected in the joint intra-articular cavity guided by ultrasound or X-ray fluoroscopy. It is thought that HA acts as a lubricant providing a cushion effect at the joint. However, the biological mechanism behind this role in cartilage repair remains poorly understood in medical community [69].

Positive effects of HA intra-articular injections are mainly reported in the management of osteoarthritis [70, 71]. Viscosupplementation is usually performed after surgical intervention to treat osteochondral lesions (knee and ankle) [72]. The Food and Drug Administration (FDA) regulates the use of HA for intra-articular injection. Sodium hyaluronate, hylan G-F 20, and HMWHA have received approval for clinical injections, although the biological mechanism of HA is not fully explained. Thus, some studies strongly recommend the use of HMWHA to treat OC defects. However, a strong heterogeneity in studies is found in clinics [73]. Nonetheless, some “off-label” (not FDA approved) HA has been used in clinical practice mainly for hip and knee OA treatments. Table 57.1 summarizes the relevant reports that make use of HA for treating OC defects. The short duration of action, due to the rapid breakdown and reabsorption of HA, is a limitation in the intra-articular injections. HA has a half-life of 17 h after intra-articular injection. Systemic HA injection at end of surgery cannot be recommended, being poorly assessed and showing benefit that are short lived accordingly to the few published studies. It has already been mentioned in clinical trials that a combination of treatments is shown to be more effective than HA alone. Additionally, there is the need to develop sustained-release approaches.

The intrinsic physiological tissue remodeling and homeostasis is strongly influenced by GFs. GFs contribute to many processes such as chemotaxis, differentiation, proliferation, and cellular responses in OC tissues (cartilage and bone tissue). Therefore, the use of autologous and recombinant GFs is emerging in orthopedics. The main objective is to manipulate GFs and secretory proteins aiming at both cartilage and bone repair.

Bone-derived growth factors (BMPs), mainly used for bone regeneration and autologous blood-derived growth factors (used for cartilage and soft tissue regeneration), are the most widely used GFs in clinics. The GFs can mostly be obtained from patient’s own blood (autologous), and they become available after the platelet-activation procedure and are thus called PRP. The extensive clinical use of PRP (Table 57.2) for addressing OC lesions relies on its easy application and low cost [81]. PRP is part of the patient’s blood plasma, composed of platelet concentrations above baseline. Normal platelet count ranges between 150,000 and 350,000 platelets/μL of human blood [82]. Clinical studies have shown efficacy of PRP using concentrated platelets (4–5 times higher than normal blood). Thus, definition of PRP concerns a concentration of 10⁶ platelets/μL. To our knowledge, there are no studies showing improvements when platelet concentrations are higher than 10⁶. However, biological activity of various PRP preparations may vary in efficacy. In the existing literature, the use of different terminologies for PRP is often seen as plasma rich in platelets or plasma very rich in platelets, and it also can appear as preparation rich in growth factors or platelet lysates.

The natural healing process in any tissue encompasses three major phases: (1) acute inflammatory phase (platelet clot formation is seen, degranulation of growth factors occurs, coagulation cascade is activated, and migration of granulocytes and macrophages occurs), (2) mesenchymal cell proliferation and differentiation phase, and (3) tissue regeneration by specific cells. All the three phases of the inflammatory response are regulated mainly by the platelets [89]. The most important role is at the proliferation and differentiation phase. Platelets are derived from megakaryocytes which are small blood cells with a size between 1 and 3 μm. The presence of alpha-granules in megakaryocytes produces the GFs. More than 30 bioactive proteins are found in megakaryocytes and play an important role in tissue homeostasis and healing processes. PRP, in different platelet-activation methods, are able to differentially produce growth factors [90].

Bioactive GF promotes a wide range of physiological processes such as cell proliferation, differentiation, and chemotaxis. In this way, it is understood that administration of PRP may improve healing through the action of growth factors and cytokines secreted from alpha-granules present in platelets. Tissue damage triggers a cascade of molecules to promote self-repair. Platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), transforming growth factor-β (TFG-β), fibroblast growth factor (FGF), and, more recently, connective tissue growth factor (CTGF) are all growth factors enriching the PRP environment to foster the regeneration of OC tissues, cartilage, and bone [91].

PRP has been employed in a wide range of clinical applications such as orthopedics including sports medicine. Many clinical questions still remain concerning the use of orthobiologics, HA, stem cells, and PRP/GF particularly regarding the therapy timing (when to start therapy and for how long), cell numbers, volume or dose, and frequency of treatment about which consensus in clinical practices has still not been reached.

Large OC lesions (greater than 1 cm) cannot be addressed simply by means of using biomaterials. Stem cell-based therapies potentially allow treating these defects. Particular interest has arisen about MSCs due to their differentiation capacity toward mesodermal lineages [92]. The modulation of adult MSC pathways can lead to chondro-, osteo- and adipogenesis (chondrocytes, osteoblasts, and adipocytes, respectively) [93, 94]. MSCs are found in many different tissues in the body including the bone marrow, skin, adipose and synovial tissue, and muscles. MSCs (Fig. 57.3) are easy to prepare from aspirates such as bone marrow, adipose, or synovial tissue and are readily available from the surgery room [92, 95].

Moreover, MSCs are immunoprivileged, which can allow their transplantation without any immune response being elicited. Friedstein et al. [96] conducted the first investigation to characterize multipotent stromal precursor cells which were later on named as MSCs [97]. Depending on the harvesting site, MSCs show a better performance in certain strategies. Bone marrow stem cells are the most extensively studied. Despite the invasiveness for harvesting and isolation after collection, MSCs are ready for usage [98]. Bone marrow aspirates from the iliac crest have been used to treat focal traumatic chondral and OC defects [99–102]. Different approaches can be applied when it comes to application of MSCs. After aspiration, MSCs are capable of undergoing expansion within 2–3 weeks for further application, or the concentrated aspirate can be immediately implanted (BMDC). Usually, the use of natural matrices to embed the MSCs is employed based on platelet-rich fibrin gel [83, 101, 103–105], fibrin glue [100], collagen gel [78, 99, 100, 103, 104] or collagen scaffolds [99, 100, 105, 106], and HA [78, 101, 103, 104]. Natural matrices to embed MSCs create a cell environment that mimics the natural one, which is beneficial from a biological point of view.

In the past years, patients presenting focal chondral and OC lesions that were treated with MSCs have shown definitive clinical improvement. Knee [100, 101, 105–110] and ankle [78, 103, 104] were the two joints extensively investigated following football injuries. So far, there are no studies for periods greater than 24 months concerning treatments of focal chondral defects with the implantation of MSCs. Giannini et al. [78] reported a slight decrease in symptoms at 36 and 48 months compared to 24 months post-implantation. A study by Wakitani et al. [100] reported a long-term evidence (137 months post-surgery) of MSCs implantation taking into account only the safe use of these cells. Different studies, involving arthroscopy and MRI, assessed the efficient production of hyaline cartilage by MSCs implantation, and additionally neo-tissue formation showed good integration within 24 months postimplantation [78, 101, 103, 106, 108, 110]. Subchondral bone tissue remodeling is a longer process when compared to that of cartilage. Giannini et al. [78] have shown that, when 24 months had elapsed following MSC implantation in the talus, unhealthy subchondral tissue was formed. Two comparison studies [104, 107] of MSCs/BMDC implantation to chondrocyte implantation (ACI/MACI) found similar outcomes. However, MSCs showed better function than chondrocytes implantation did. Both strategies were able to produce neo-hyaline cartilage. Pak et al. [111] implanted autologous adipose tissue-derived stem cells in 4 patients, and all patients showed improvement after 12 weeks of treatment. The infrapatellar fat pad tissue, also known as Hoffa’s body, is located under and behind the patella bone within the knee. During an arthroscopy, Hoffa’s body can be removed to allow a better visualization of the knee because it is inflamed or damaged [112]. From this perspective, this tissue can be also considered a promising source of stem cells (ASCs) for use in clinics, as ASCs are already known to possess potential to differentiate into chondrocytes and osteoblasts.

Table 57.3 summarizes the relevant studies involving stem cell implantation for treating OC defects. Despite the current studies, little is known as yet as to the best dosage and cell numbers to be implanted at the defect sites. Standardization cell type and subpopulations, cell number, and culturing conditions should be performed in the clinics, in the near future.

A major goal in orthopedics concerns the repair of OC tissues that avoids successive surgical interventions. Only a few studies have investigated the histological outcomes of one-step procedures in the treatment of articular OC lesions [99, 103, 116, 117]. Of these studies, Giannini et al. [103] combined BMC and PRP gel with HA membrane or collagen powder to treat talar OC lesions. All the patients had shown a functional improvement. Tissue remodeling was clearly observed by histological biopsies, toward hyaline-like cartilage [103]. Siclari et al. [117] harvested 5 biopsies by means of arthroscopy. Macroscopic observation revealed a whiter appearance of the repairs, some hypertrophic tissue, and irregularity at the surface. A good subchondral integration with neo-hyaline cartilage was observed in histological analysis. Enea et al. carried out an investigation that showed tissue formation and repair documented in accordance with ICRS CRA [109], even though some one-step procedures combining scaffolds have shown the presence of osteophytes formation. All the studies above mentioned are denominated in the clinics as one-step procedures. The concept of one-step implies that the patient undergoes surgery only once. In addition, the strategy itself satisfies all the requirements for good regeneration of the affected tissue. Commonly in these strategies, what is envisioned is an approach with more than one orthobiologic components. Others have also been mentioned in Table 57.4. The recent use of multilayered scaffolds composed of collagen type I with hydroxyapatite nanoparticles is also appealing [118]. This one-step procedure has as its final goal the treatment of chondral and osteochondral knee defects at once.