[Individualized unicondylar knee replacement : Use of patient-specific implants and instruments]

Objective: Unicompartmental knee replacement in patients with osteoarthritis (OA) of the medial compartment. Individualized instruments and implants with a planning protocol for optimal fit. The individualized instruments and implants (ConforMIS Inc.; Burlington, MA, USA) are manufactured based on a computed tomography scan of the affected lower extremity and are provided together with a planning protocol (iView®) of the surgery.

Indications: Unicompartmental OA of the knee (Kellgren & Lawrence stage IV) or Morbus Ahlbäck after unsuccessful conservative or joint preserving surgery.

Contraindications: Bi- or tricompartmental OA, knee ligament instabilities, knee deformities >15° (varus, valgus, extension deficit). Relative contraindication: body mass index >40.

Surgical technique: Limited medial arthrotomy, identification of mechanical contact zone of the femoral condyle (linea terminalis); removal of remaining cartilage and all osteophytes that may interfere with the correct placement of the individually designed instruments. Balancing of knee in extension using patient-specific balancing chips of incremental heights. Resection of tibia with a fitted individualized tibial cutting block; confirmation of axial alignment with an extramedullary alignment tower; balancing flexion gap using spacer blocks in 90° flexion. Final femur preparation with the individual cutting instruments. Final tibial preparation with an individual drill jig for the placement of cavities fitting the cement pegs of the prosthesis. Lavage, cementing of implants in 45° of knee flexion, removal of excess cement, and wound closure.

Postoperative management: Sterile wound dressing, compressive bandage. Unlimited active/passive range of motion. Functional rehabilitation with partial weight bearing first 2 weeks, then transition to full weight bearing. Clinical/radiographic follow-up directly after surgery, at 12 and 52 weeks, then every 1-2 years.

Results: In all, 31 patients with medial OA (27 medial knee osteoarthritis, 4 osteonecrosis) were treated. Mean age 60 years. Minimum follow-up 17 months. One aseptic loosening needed exchange; one acute late-onset infection with consecutive implant removal. No further revisions/reoperations or complications. X-rays showed an ideal fit of the implant with less than 2 mm subsidence or overhang in all cases. Clinically the VAS changed from 6.51 preoperatively to 1.11 postoperatively. The mean KSS (Knee Society Score) improved from 111.23 preoperatively to 180.61 postoperatively; the functional part of KSS improved from mean 60.39 to 94.51.