Evaluation of implant position and knee alignment after patient-specific unicompartmental knee arthroplasty

Implant positioning and knee alignment are two primary goals of successful unicompartmental knee arthroplasty. This prospective study outlines the radiographic results following 32 patient-specific unicompartmental medial resurfacing knee arthroplasties. By means of standardized pre- and postoperative radiographs of the knee in strictly AP and lateral view, AP weight bearing long leg images as well as preoperative CT-based planning drawings an analysis of implant positioning and leg axis correction was performed.The mean preoperative coronal femoro-tibial angle was corrected from 7 degrees to 1 degrees (p<0.001). The preoperative medial proximal tibial angle of 87 degrees was corrected to 89 degrees (p<0.001). The preoperative tibial slope of 5 degrees could be maintained. The extent of the dorsal femoral cut was equivalent to the desired value of 5 mm given by the CT-based planning guide. The mean accuracy of the tibial component fit was 0 mm in antero-posterior and + 1 mm in medio-lateral projection. Patient-specific fixed bearing unicompartmental knee arthroplasty can restore leg axis reliably, obtain a medial proximal tibial angle of 90 degrees, avoid an implant mal-positioning and ensure maximal tibial coverage. (C) 2010 Elsevier B.V. All rights reserved.