Revision of unicompartmental knee arthroplasty using the in situ referencing technique (Revision des unikompartimentellen Kniegelenkersatzes mit der In-situ-Referenzierungstechnik)

Objective: Revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) with the in situ referencing technique aiming to preserve as much ligament function and epi-metaphyseal bone stock as possible. Indications: Aseptic loosening, progression of osteoarthritis, periprosthetic fracture, periprosthetic infection, arthrofibrosis, polyethylene wear, malalignment, instability, femoro-tibial impingement. Contraindications: Unexplained pain, localized or systemic active infection (anywhere). Surgical technique: Referencing for the tibia and the femur cuts is performed prior to implant removal. The tibial cutting jig and the initial tibial resection level is set in a way that the sawblade just fits under the tibial implant. In case too much bone needs to be removed to achieve flush implant sitting on both the medial and lateral tibia, a step cut needs to be performed to build up the medial defect with an augment. Prior to femoral component removal, rotational alignment is determined and intramedullary referencing for the distal femur osteotomy is performed. Level of constraint and additional tibial stem fixation is chosen according to the amount of bone resected and according to ligament stability. Postoperative management: Sterile dressings and elastic compression bandaging. No limitation of active/passive range of motion. Full weight-bearing or partial weight-bearing for 2 weeks postoperatively in the presence of bone or soft tissue defects. Results: Between 2008 and 2019, 84 patients underwent revision of unicompartmental knee arthroplasty. The mean follow-up was 64 months (range 3–132 months). Implant survival after revision of UKA to TKA was 92% (95% CI = 82–97%) at 5 years of follow-up and 86% (95% CI = 69–93%) at 10 years of follow-up. The mean Oxford knee score was 20.1 (6–39, SD ± 6.5) preoperatively and 30.2 (3–48, SD ± 11.3) postoperatively. The mean visual analogue scale was 6.9 (range 1–10, SD ± 1.8) preoperatively and 3.9 (range 0–9, SD ± 2.6) postoperatively.