BONE CUT OPTIMISATION TO IMPROVE TOTAL KNEE ARTHROPLASTY FLEXION

Abstract

Purpose of the study: The aim of this study was to investigate the influence of bone cuts on the degree of postoperative flexion for total knee arthroplassty in patients with a potential for good postoperative recovery of flexion.

Material and methods: Adobe Photoshop and Imagika were used to process lateral radiographs of a normal knee and simulate implantation of total knee prostheses using phantom images of femoral components of decreasing size as well as variations in the tibial slope (HLS system, Tornier). The femoral and tibial images were moved until the maximal flexion angle or impingement between the posterior tibial border and the femoral cortical occurred. The same types of implantations were simulated with real implants on cadaveric bones using the Ci navigation system (Depuy) to check the position of the bone pieces and the bone cuts. The different implantations simulated involved four femoral pieces of decreasing size with a constant tibial slope. Then the same femoral implant was used varying the tibial slope by 5° increments from -5° to +10°. Rollback during flexion could be regulated by the software by controlling the position of contact of the condyle son the corresponding tibial plateau.

Results: With the two methods, reducing the posterior condylar rim 3 mm decreased the flexion angle by 10°, modifying the tibial slope 5° induced a 5° variation in the flexion angle at impingement. A 10mm posterior rollback improved the flexion angle 10° and inversely. Cumulatively, these modifications can lead to a loss of 30° flexion.

Discussion: When regulating the space in flexion, it is sometime necessary to modify the tibial slope or the posterior condylar rim by increasing the posterior condylar cut. Depending on the prosthetic kinetics, this may modify the flexion angle intraoperatively, especially if these changes are combined, decrease in the tibial slope often being associated with an increase in the posterior condylar cut.

Conclusion: The technique used for the bone cuts for a total knee arthroplasty can potentially have a significant effect on the maximal angle of maximum flexion achieved by the patient.