Acute SA of a native joint is one of the most critical orthopedic urgencies. It can affect all synovial joints, although data shows that about 50% of cases involve the knee, and
S. aureus is the most common pathogens. The physiopathology of joint damage is multimodal, both infection itself and joint inflammatory response representing the key elements of it. Particular attention must be paid to all procedures that require access to the articular chamber, mainly if performed outside a sterile setting since a communication is created between the synovial cavity and the external environment. Among these procedures, viscosupplementation and corticosteroids injections are a common practice in the conservative management of symptomatic osteoarthritis. However, intra-articular injections, as well as all diagnostic and therapeutic practices that involve piercing the skin, can bring microorganisms from the skin into the joint, contaminating it and eventually leading to a SA. SA of a native joint represents the most dangerous complication of intra-articular injection, despite a reported low incidence rate (as “higher” as less than 1/1,000) [
5]. SA can cause enormous joint damage, which can lead to irreversible alterations of the joint structures with consequent disability, even leading to the patient’s death by sepsis. Early identification and appropriate treatment – consisting of combined surgical debridement and systemic antibiotic therapy – are of paramount importance. [
1,
2,
5]. Nevertheless, to date, there is no clear consensus on the optimal therapeutic approach, and several surgical options had been successfully applied [
1,
2]. A timely and accurate synovial debridement aiming to remove as much infected material as possible is key to success, and it can be performed with both arthrotomic or arthroscopic techniques. [
1,
2,
3,
15]. Recent studies have shown similar effectiveness of open surgery and arthroscopically procedure in eradicating an infection of a native knee, even though arthroscopic treatment was associated with lower complication rate and better functional recovery [
1,
2,
3,
15]. To obtain the most accurate debridement possible, a coloring method was employed to showcase the infected tissues. Methylene-blue has demonstrated ability to stain bacterial biofilm and nonviable host tissues, and it has been used as an effective debridement guide in the intra-operative setting [
24,
25].
The concept of topical antibiotic therapy appeared before the 1970s when molecules of different antibiotic concentrations were locally administered “naked”. This concept was taken up and developed with the studies of Buchholz and Engelbretch [
26] on the use of antibiotic-loaded polymethylmethacrylate (PMMA) in the treatment of periprosthetic joint infections (PJIs), and then further evolved with calcium-based carriers, hydroxyapatite, or bioactive glass [
27,
28]. The local use of calcium sulfate spheres loaded with antibiotics has been widely studied for the prevention and treatment of multiple infectious conditions, including osteomyelitis and PJIs, but also for soft tissue diseases or preventive purposes in risky situations [
29,
30,
31]. However, the indications for its use have expanded to include also post-operative infections following closed and open fractures, spontaneous bone infections and native joint infections [
21]. The choice of calcium sulfate carrier, in our practice, is dictated by therapeutic needs and its versatile characteristics. These include a known elution profile, its reabsorbability but after an adequate residence time, ability to fill the dead space, and the possibility of being used in beads of different dimensions or as bullets or as a paste [
28]. The device’s manageability has proved a winning feature, allowing its intra-articular administration via arthroscopic means. Although antifungal-impregnated PMMA beads have been described as a viable therapy for fungal septic arthritis of a native joint [
34], to date and to our knowledge, the present is the first case of arthroscopically allocated antibiotic carriers and the first case of reabsorbable antibiotic carrier used in a SA of a native joint reported in Literature. Unlike previous-generation substances, calcium-based carriers can be added to various molecules, even in combination; they guarantee higher concentrations of local antibiotics, avoiding drops in concentrations below the therapeutic threshold for the entire period of their stay. With a 100% release of antibiotic and without exposing the organism to systemic administration, calcium sulfate carriers significantly reduce the risks associated with classic antibiotic therapy, such as hepato- or nephro-toxicity, metabolic de-activation from the hepatic passage before it is delivered where it is needed, and reduced concentration on site, providing a safer alternative [
28,
29,
32]. A further reason for choosing these substances in cases of SA is the ability to actively act against biofilm, a structure which, in its mature phase, thanks to a multi-layered structure, presents an antibiotic resistance 10,000 times higher than the free-floating planktonic microorganisms. Calcium-based carriers allow adequate minimum inhibitory concentration and minimum biofilm eradication concentration values to be achieved and maintained for several weeks [
27,
28,
33]. An important aspect to consider is the risk of “third body wear”. This phenomenon has been widely studied in the literature, especially about total joint arthroplasty. Compared to other substances, such as PMMA, for which microscopic analyses have highlighted a statistically significant relationship with the appearance of signs of wear on the contact surfaces, the use of calcium sulfate-based carriers does not appear to be subject to this phenomenon [
35,
36,
37], with respect to a metallic surface. Therefore, the use of reabsorbable calcium sulfate beads in a prosthetic joint seems to be safe with respect to subsequent wear. On the other hand, sensible doubts are present with respect to cartilage damage in a native joint. Anyway, when calcium sulfate beads are inserted into a joint, they occupy the free space they found (in a knee: the intercondylar notch, the patellar pouch) and therefore the risk of scratching the cartilage is reduced. Also, the beads are reabsorbable and in contact with body fluid they may soften and molder if pressed. Moreover, cartilage damage due to persistent infection can balance the risk of iatrogenic damage due to third body wear of the beads. The literature available regarding the use of antibiotic carriers in cases of periprosthetic infection is much more extensive, both in cases of debridement and implant retention and debridement antibiotic pearls and retention of the implant, as well as in one-stage or two-stage revisions. Certainly, the criteria for choosing the most suitable carrier are different, having to evaluate mechanical resistance, formation of microfractures in the material, articulation and mobility, as well. Of particular importance in this case are the formation of bacterial biofilm on the prosthetic components and third-body wear. However, their use remains debated, as can be seen from studies [
38].
In the present case report, in our opinion, the best available techniques were exploited. First, the most extensive debridement was obtained with the help of methylene blue guide. Secondly, the arthroscopic technique was employed to reduce complication rate and improve functional results. Lastly, a higher and long-lasting local antibiotic concentration was achieved with the use of reabsorbable antibiotic carrier.
Limitations are present in the present paper. This is a case report, and generalizations are obviously not possible. Also, plain radiographs were the only imaging performed at follow up but patient was feeling well and she refused to take a control MRI. On the other hand, the present case is, to our best knowledge, the first report about the use of reabsorbable antibiotic carrier in a native joint, and the first report about the arthroscopic placement of such a device.