Abstract
Many recent studies emphasise the importance of surgical technique for achieving long-lasting, pain-free, optimally functioning TKR. However, little information exists in the accuracy with which each step of the TKR procedure is performed using current instrumentation. This study examines the accuracy with which each step of the TKR procedure using current, intramedullary instrumentation.
Twenty primary TKR were performed using a current, intramedullary instrumentation system. The accuracy of each femoral and tibial cut and the accuracy of the final frontal and sagittal limb alignment were measured using an image-free computer assisted navigation system. The system made it possible to measure: 1) frontal femoral implant alignment; 2) sagittal femoral implant alignment; 3) femoral implant rotational alignment; 4) frontal tibial implant alignment; 5) sagittal tibial implant alignment; 6) frontal limb alignment; 7) sagittal limb alignment. Alignment results are expressed in terms of the mechanical axis. Optional results are a frontal and sagittal axis of 90° relative to the mechanical axis. The optimal femoral rotational alignment is 3 degrees externally rotated from the posterior femoral condyles or zero degrees externally rotated from Whitesides line.
The alignment results were: 1) frontal femoral alignment: 89° (range 87 to 92°); 2) sagittal femoral alignment: 89 (range 88 to 193°); 3) femoral rotational alignment: 1° external rotation vs. femoral condyle; 2 degrees internally rotated vs. Whitesides line (range 0.5° to 3.5°); 4) frontal tibial alignment: 88° (87° to 93°); 5) sagittal tibial axis: 87° (range 86° to 91°); 6) frontal limb alignment: 179° (range 177 to 181°); 7) sagittal limb alignment 179° (range 174 to 180°).
Intramedullary instrumentation allows reasonably accurate and reproducible frontal limb alignment. There is a tendency to leave the limb in slight flexion when using intramedullary instruments. There is also a consistent tendency to internally rotate the femur with current anterior –posterior alignment guides and to excessively posteriorly flex the tibial component, although almost all of the 20 TKR’s resulted in final limb alignment within 3 degrees of frontal and sagittal axes. Very few (4) TKR’s were performed in which all of the measured steps were within 3 degrees of the optimal position.
The study emphasises that current intramedullary instrumentation does not result in a high incidence of accuracy when each step of the procedure is measured. Computer assisted techniques permit measurement of the steps of the TKR procedure with a high degree (error < 1°) of accuracy. Longevity, pain-relief and funtion should be related to the total accuracy with which TKR are performed.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
