Introduction: Computer assisted-surgery (CAS) brings in a great precision to the alignment of the components and the axis of the extremity in total knee arthroplasty (TKA). On the other hand, even though the MIS technique exerts a lesser aesthetic impact, favours the faster recovery of the patient and preserves the soft parts better, it can also lead to mistakes in the alignment of the implant due to the deficient visualization. Adding CAS to MIS may solve this potential complication.

Objective: To compare the alignment of the components with regard to the mechanical axis in four TKA groups (standard surgery, MIS surgery, standard surgery with CAS, and MIS with CAS).

Materials and Methods: Prospective and randomized study. 100 patients with Alhbäck degree III primary degenerative osteoarthritis of the knee and less than 10° of varus-valgus were included. The patients were randomly distributed in 4 groups of 25 patients each, and the same surgeons performed the surgery. Two CT surviews were performed on every patient, one preoperatively and one during the immediate postoperative period, including hip and ankle, where the femoral, tibial and femoro-tibial axis measurements were carried out.

Results: Mean age was 71.63 years (SD 6.68); 81 % of patients were women. Preoperative mean varus was of 7.57° (SD 1.10). No significant differences were found in the femoro-tibial alignment nor in the components with regard to the mechanical femoral axis between the four groups (Table 1). Nevertheless, significant differences in favour of the MIS-CAS technique group for the alignment of the tibial component with regard to the mechanical tibial axis were found.

Conclusions: The MIS technique allows for a well-aligned TKA implantation. Nevertheless, when CAS is coupled with this technique, the alignment of the tibial component is improved. It is possible for the association of MIS and CAS to become a true advance in TKA implantation.

Aims: To study the utility of a computer assisted orthopaedic surgery (CAOS) wireless system (navigator) in Total Knee Arthroplasty (TKA). Methods: Randomised prospective study. A sample of 40 TKA patients was randomised in two groups: CAOS was used in 20 of them. In the other group standard technique with manual alignment was performed. Femoral angle (formed between the femoral mechanical axis and the femoral component), tibial angle (formed between the tibial mechanical axis and the tibial platform) and femorotibial angle (formed between femoral and tibial mechanical axes) were measured from Computed Tomography Surviews taken in the immediate postoperative period. Results: In the standard group (without navigator) the femoral angle mean was 91.7° (ranged 90 to 94°). Tibial angle mean was 90.2° (87°–95°) and femorotibial angle mean was 175.9° (172°–180°) showing a slight prevalence of varus deviation of the extremity mechanical axis. In the group with navigator the femoral angle mean was 90.2∞ (87–93°), tibial angle mean 89.6°(85°–93°) and femorotibial angle mean 179.2° (177°–182°). There were statistically significant differences between groups for the femoral angle (p=0.001), and the femorotibial angle (p < 0.001). An ideal femorotibial angle (180±3°) was achieved for all the patients of the CAOS group but only 9 patients of the standard technique group reached this objective (p< 0.001). Conclusions: The use of CAOS for TKA favors the implant placement in a position nearer to the ideal mechanical axis.