Impact of Axial Component Alignment in Total Knee Arthroplasty on Lower Limb Rotational Alignment: An In Vitro Study.

Correct rotational implant alignment is associated with increased postoperative function and implant survival in total knee arthroplasty (TKA). Due to conformity between tibial and femoral implants, particularly in full extension, we assumed a mutual interference of femoral and tibial component rotations. We, therefore, hypothesized that different rotational alignments of the tibial or femoral components change the rotational postures between the tibia and femur after TKA. In 10 healthy knees of whole body cadavers, TKA was performed. Both femoral and tibial components were implanted in different internal (6 degrees) and external (3 and 6 degrees) rotational alignments. Consequential osseous rotational changes between the tibia and the femur were measured in full extension using a commercial computer navigation device. External rotation of the femoral component resulted in significant external rotation of the tibia, while external rotation of the tibial component caused a significant internal rotation of the tibia. The opposite applied to femoral and tibial component internal rotations. Therefore, largest changes of the osseous tibiofemoral rotational postures were found by the combination of 6 degrees femoral component internal and 6 degrees tibial component external rotations (mean 11.2 degrees, standard deviation 5.0, p < 0.001), as both cause tibial internal rotation. In conclusion, the present results suggest that axial component alignment significantly affects lower limb rotational alignment. However, its clinical impact on forefoot progression, Q-angle, the patella, collateral, and cruciate ligaments, and surrounding soft tissues has to be clarified in further clinical and biomechanical studies.

Appropriate sagittal femoral component alignment cannot be ensured by intramedullary alignment rods.

PURPOSE: The intraoperative sagittal cutting block alignment when intramedullary alignment rods are used was investigated. Its absolute orthogonal orientation in relation to the mechanical femoral axis should be analysed. It was hypothesized that (1) alignment rods do not ensure a desired deviation within a range between 0° and 3° flexion as it has been shown to be favourable for clinical and functional outcome. Further, the degree of flexion cannot be (2) foreseen by the surgeon or (3) estimated by clinical or radiological parameters. METHODS: Forty knees allocated to total knee arthroplasty were included. The distal femoral cutting block was aligned using an intramedullary rod. By means of a navigation device, the sagittal alignment of the cutting block in degrees of flexion was measured. RESULTS: The mean measured flexion of the cutting block was 4.4° (3.6 SD). Twenty-five per cent (10/40) of the values were within a corridor between 0° and 3° of flexion. The mean difference between expected and measured flexion was -1.5° (-7.6 to 4.7 95 % limits of agreement). The dorsoventral diameter of the distal femur showed a significant influence on measured flexion (R (2) = 0.112, p = 0.035). CONCLUSION: Intramedullary alignment rods used in the present study do not ensure a distal cutting block alignment between 0° and 3° of flexion in relation to the femoral mechanical axis. The extent of flexion could not be foreseen either by the surgeon. The dorsoventral diameter of the distal femur correlated with measured flexion. However, only limited data is available on influence of femoral component flexion on implant failure or clinical and functional outcome. LEVEL OF EVIDENCE: Diagnostic study, Level II.