Osteoarthritis (OA) is the most common form of arthropathy, with a prevalence of approximately 10% in the population aged over 60 years, representing one of the major causes of pain, disability, and health economic costs worldwide [1]. OA can be initiated by different mechanisms and conditions but, independently form its aetiology, ultimately results in a common end point. If not properly treated, it can evolve towards symptomatic and advanced stages which may require sacrificing procedures. Unfortunately, current conservative treatments for OA are not very effective, explaining the increasing demand for prosthetic replacement. Indeed, nonsurgical treatments such as physiotherapy, anti-inflammatory, and anti-pain medications all have modest and short-lasting efficacy. In particular, early OA onset poses special therapeutic challenges for active patients; thus, the reward for any prevention strategy or delay of the disease is very relevant. In this context, biological injective approaches (such as PRP, BMC, SVF) have recently gained increasing attention due to their anti-inflammatory and immunomodulatory properties, tolerability, and regenerative potential [2].
Intraarticular injections of these biological products for the treatment of early OA can offer great advantages by allowing bioactive molecules and/or cells within the joint space to target the injured tissues through the interaction with recipient cells, possibly leading to better outcomes without significant risks due to the minimally invasive nature of the injective approach.
Growth factors (GFs) play a significant role in musculoskeletal tissues homeostasis and repair, and GFs showed the ability to stimulate cartilage matrix synthesis and pro-anabolic responses in chondrocytes. The limited success of pre-clinical and clinical trials with various GFs, and the recent developments in blood derivatives led to a potential paradigm shift in GF therapy for OA treatment. In fact, it might be more reasonable to consider a cocktail of GFs rather than a single GF treatment, and blood derivatives have been proposed as safe, easy, cost-effective, and minimally invasive strategy to influence the joint environment favouring the restoration of a homeostatic balance and possibly the regeneration of degenerating tissues. In particular, among blood-derived products PRP is gaining more and more attention due to the GFs and anti-inflammatory molecules stored in platelet α-granules. Beside an extensive preclinical literature supporting PRP, only a few high-level studies have been currently published. Nonetheless, existing RCTs provide the evidence of superiority in comparison to placebo, and overall they show the benefit of PRP injections for knee OA treatment with superior effects to what reported for viscosupplementation [3]. Importantly, outcomes depend on age and the level of cartilage degeneration with better results in younger patients with early OA, although the duration of the beneficial effect, roughly 6–12 months, does not support a regenerative effect on articular cartilage, but rather suggests only a temporary homeostatic improvement of the joint environment, especially in less advanced cases [3]. Lately, the potential of PRP and the superiority with respect to HA injections have been questioned by a double-blind RCT on a large cohort of patients, which documented a similar response to treatments at 12 months and only a slight and questionable superiority of PRP up to 5 years [4].
Mesenchymal stem cells (MSCs) are considered another promising option for OA treatment. MSCs are multipotent progenitor cells with capability of self-renewal, high plasticity, immunosuppressive and anti-inflammatory action, and the possibility to differentiate into selected lineages. Moreover, these cells, derived from perivascular cells called "pericytes", play a key role in the response to tissue injury not only by differentiating themselves but also by inducing repair/regeneration processes at the site of damage through the secretion of several bioactive molecules [5]. Despite extensive preclinical research and promising findings reported in the clinical practice [6], both their potential and limitations for the use in patients remain controversial [2]. The use of many cells through expansion has been questioned by studies showing similar or even better results through the use of concentrates which may offer a lower number of cells but on the other hand the benefit of administering MSCs in their niche and therefore allowing them to act in more favourable conditions [7]. Mesenchymal and haematopoietic stem cells form a unique bone marrow niche and their co-presence could lead to the best results [8]. Similarly, the progenitor cell-rich product obtained intraoperatively from adipose tissue, named SVF, contains preadipocytes, vascular endothelial cells, and pericytes (ASCs). Also in this case, the maintenance of the stromal cell niche architecture could provide an advantage [7]. Based on these observations, MSC-rich concentrates from bone marrow and adipose tissues have been applied, suggesting promising clinical results in the treatment of OA.
However, despite the promising findings in both in vitro and pre-clinical biological studies, there is still a lack of clear clinical evidence to support the clinical efficacy of PRP, BMC, and SFV in OA. In fact, this research area is still in its infancy, and more robust studies are needed to confirm and optimize their efficacy by identifying the most suitable preparation procedure, the best application modality, and the most responsive patients and disease phases.
1. Glyn-Jones S, Palmer AJ, Agricola R, Price AJ, Vincent TL, Weinans H, Carr AJ. Osteoarthritis. Lancet. 2015 Jul 25;386(9991):376-87.
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3. Filardo G, Kon E, Roffi A, Di Matteo B, Merli ML, Marcacci M. Platelet-rich plasma: why intra-articular? A systematic review of preclinical studies and clinical evidence on PRP for joint degeneration. Knee Surg Sports Traumatol Arthrosc. 2015 Sep;23(9):2459-74.
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A. Boffa, C. Cavallo, G. Merli