Abstract
After having completed more than 150 primary knee arthroplasties with a new navigation system both analyzing the position of the implants as well as the soft tissue balancing in each range of motion, we performed the first revision surgeries in February 2001 using this device. At present we have revised 15 arthroplasties with the support of navigation. The reasons for revision were early loosening in 11 cases and instability in 4 cases. Intra-operatively, we were able to analyze the malpositioning of the implants and the disturbed soft tissue balance.
In most cases (n = 12), a femoral internal malposition was found. There was, therefore, extreme polyethylene wear on the medial plateau of the tibia and instability of the soft tissues on the lateral side. We were also able to find an incorrect joint-line and a malrotation of the tibial component. In all these cases specific intra-operative kinematics showed us the primary reason for early loosening. The navigation system screen provides not only information about the incorrect angle of the implant position but also indirectly via the kinematics, information about the relationship of the malpositionings between the implants. In many cases (n = 10) there were combined errors in positioning of the implants.
The first 15 cases show that malpositioning of knee implants can be analyzed with the new generation of navigation systems. These devices help the surgeon, in the operation room, to make his decision how to proceed.
The malpositioned implants showed extreme polyethylene wear demonstrating that the positioning of the implants does influence the outcome very much.
A useful navigation system in revision surgery is the one which is not related to a specific design of an implant but is usable in all cases so that every implant can be measured.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
