Surgical technique and preliminary results of a moulded, mobile spacer for the treatment of periprosthetic joint infection of the knee.

OBJECTIVE: Mobile knee spacers can be utilized in the first stage of a two-stage exchange in periprosthetic joint infection or septic arthritis of the knee to prevent soft tissue contraction, enable local antibiotic elution, and improve patient mobility. Commercially made moulds enable the surgeon to prepare a reproducible spacer design and match the preparation of the arthroplasty, which will be carried out in a second step. INDICATIONS: Periprosthetic joint infection of the knee and severe cases of septic arthritis of the knee with advanced destruction/infiltration of the cartilage. CONTRAINDICATIONS: Antibiotic resistance of the microbiological pathogen to available antibiotic agents, incompliant patient, large osseous defect preventing proper fixation, known allergy to polymethylmethacrylate (PMMA) or antibiotic, severe soft tissue damage with high ligament instability, especially deterioration of extensor mechanism and insufficient patella/quadricep tendon. SURGICAL TECHNIQUE: After thorough debridement and removal of all foreign material, cutting blocks are used to shape femur and tibia to the implant design required. Using a silicone mould, PMMA with suitable antibiotics is moulded into the shape of the future implant. After polymerization, the implants are fixed onto the bone with additional PMMA without pressurize for the sake of easy removal. POSTOPERATIVE MANAGEMENT: Partial weight bearing with no restriction of flexion/extension while spacer is in place; second stage reimplantation as soon as infection is controlled. RESULTS: In all, 22 cases were treated, mostly with a PMMA spacer containing gentamicin and vancomycin. Pathogens were detected in 13 of 22 cases (59%). We observed two complications (9%). Twenty of 22 patients (86%) were reimplanted with a new arthroplasty; 16 of the 20 patients remained revision-free and infection-free at the last follow-up (average time to follow-up 13 months, range 1-46 months). Average range of motion in flexion and extension at follow-up was 98°.