Summary

Debridement, Antibiotic Pearls and Retention of the Implant (DAPRI) is a DAIR technique augmented by using methylene blue intra-articularly as biofilm stainer, the argon beam coagulator and a chlorhexidine gluconate brush as a biofilm remover and calcium sulphate antibiotic impregnated beads to prolong and elevate the intra-articular antibiotic concentration in the setting of TKA PJI.

Abstract

We describe a novel surgical technique developed to enhance the classical irrigation and debridement procedure to improve the possibilities of retaining an infected TKA. This technique, Debridement Antibiotic Pearls and Retention of the Implant (DAPRI), aims to remove the intra-articular biofilm allowing a higher and prolonged local antibiotic concentration by using calcium-sulphate beads. The combination of three different surgical techniques (Methylene blue staining, Argon Beam electrical stimulation and Chlorherxidine-Gluconate brushing) might enhance the identification, disruption and finally removal of the bacterial biofilm which is the main responsible of antibiotics and antibodies resistance.
The DAPRI procedure is only applicable in the settings of acute (4-6 weeks from the original surgery) or early hematogenous (within 7 days from clinical onset) periprosthetic joint infections (PJI) with a known micro-organism. DAPRI has a stepwise approach. Following anesthesia and prior to skin incision, 50 cc of diluted 0.1 % methylene blue is instilled in the knee. Methylene blue is a cationic dye that is able to bind, and stain devitalized eukaryotic cells in the bacterial biofilm, guiding the surgeon to adequately removing nonviable infected tissue. After instillation, the knee undergoes several passive ROM cycles to allow for intra-articular dissemination of the staining dye: an arthrocentesis is then performed to aspirate the excessive dye.
Following a standard parapatellar approach and capsulotomy, staining of all intra-articular surfaces can be noted. The knee is then irrigated with pulsatile lavage: an aggressive and radical “tumor-like” synovectomy including the synovial layer on the posterior capsule is performed removing all stained soft tissue. Next, the biofilm on retained surfaces is addressed by mechanical disruption with an argon beam coagulator, as electrical stimulation has been shown to enhance detachment of biofilm from orthopaedic implant surfaces. The argon beam coagulator is set to 120 watts and has a probe that applies the beam in a painting brush-like fashion for all visible surfaces on the femoral and tibial components.
At this point, a 4% chlorhexadine gluconate-added brush is used to scrub all visible components surface (femoral, tibial and patellar): this is performed to mechanically remove biofilm.
Lastly, abundant pulse irrigation with 9 litres of bacitracin added saline is performed.
Calcium sulphate antibiotic-impregnated beads are then prepared on a sterile work station. A 10ml kit of PG-CSH (Stimulan; Biocomposites Ltd., UK) is mixed with 1000 mg of vancomycin hydrochloride powder, 6ml of a 40mg/ml tobramycin solution, and a third antibiotic powder according to the preoperative antibiogram. A smooth paste is formed by mixing all components for 60 seconds and is pressed into 4.8mm diameter hemispherical cavities in a flexible mold. The beads harden and are ready for implantation after resting for at least 30 minutes. Ordinarily, the antibiotic beads are inserted in the suprapatellar pouch and in proximity of the proximal tibia and distal femur in order to allow for a high intraarticular concentration. After placing an hemovac intra-articularly, the capsule is closed with Stratafix size-1 suture, the subcutaneous tissue with 2-0 PDS suture and the skin with staples.