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Abstract
Purpose
To compare the radiologic measurements of the mechanical axis and the implant position of Total Knee Arthroplasty (TKA) using a computer-assisted navigation system with those using conventional TKA in varus deformity.
Materials and Methods
From January 2004 to January 2005, 49 TKAs using a CT-free navigation system (Vector Vision®, BrainLab, Heirnstetten, Germany) (Group I) and 24 TKAs using the conventional technique (Group II) were performed on patients who had a preoperative varus deformity >10°. The patients were also subdivided into two groups, patients with a varus deformity <20° (group A) and patients with varus deformity >20° (group B). The PFC Sigma implants were used in both groups. The mechanical axis and implant position were measured by 2 observers according to the reontgenographic evaluation system of the American Knee Society.
Results
There was no significant difference in α, β, δ angle and mechanical axis between group I and II. There was a significant difference in the γ angle between group I and II (p<0.05). There was a significant difference in the α and β angle and mechanical axis between group IA and IB (p<0.05). There was a significant difference in the α angle and mechanical axis between group IIA and IIB (p<0.05). There was a positive correlation between the measured angle by the respective observers in all groups (p<0.05).
Conclusion
Patients with a preoperative varus deformity >20° tended to have more postoperative varus mechanical alignment than those with a preoperative varus deformity between 10° and 20° after TKA. More careful attention during the registration of the femoral mechanical axis should be paid in patients with a larger varus deformity in TKA using a computer-assisted navigation system. On the other hand, a reasonable mechanical valgus angle should be considered in femoral bone cutting for a varus deformity of the distal femur in conventional TKA. In addition, inadequate positioning of intramedullary rod should be recognized in conventional TKA.
Figures and Tables
Fig. 1
(A) The femoral component angle (A) was measured between a line parallel to the femoral condyle and the mechanical axis of the femur on the anteroposterior view. (B) The tibial mechanical angle (B) was measured between a line parallel to the tibial condyle (a) and a line parallel to the ankle joint (b).
Fig. 2
Post-operative measurement of the femoral and tibial component. α, The inclination angle of the femoral component was formed with the anatomical axis of the femur. β, The inclination angle of the tibial component was formed with the mechanical axis of the tibial. γ, The angle of the femoral component was formed between the anatomical axis of the femur and perpendicular line to the prosthesis. δ, The angle of the tibial component was formed with the mechanical axis of the tibial.
Fig. 4
Comparison of the different distributions of the postoperative mechanical axis between Group IA and IB.
Fig. 5
Comparison of the different distributions of the postoperative mechanical axis between Group IIA and IIB (ed note: I think the highlighted can be deleted).
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