Two surgical strategies are possible in total knee arthroplasty (TKA): a measured resection technique, in which bone landmarks are used to guide resections equal to the distal and posterior thickness of the femoral component, or a gap-balancing approach, in which equal collateral ligament tension in flexion and extension is sought before and as a guide to final bone cuts. In this study performed with computer assisted system, we compared the 2 different methods in 126 patients followed prospectively in order to analyze the effect of both the techniques on joint-line (JL) maintenance, axial limb restoration and components position. The gap technique showed a statistical increase in the post-operative value when compared with the measured resection technique, (P = 0.008). When comparing the two groups regarding to the pre-operative deformity, we have found a statistical difference (P = 0.001) in case of moderate pre-operative deformity (less than 10 degrees), and the measured resection technique showed a slight superiority in preserving a joint line more faithful to the pre-operative. We found an ideal alignment for the mechanical axis (180 degrees ± 3 degrees) (95% of cases). In six cases (5%), the mean post-operative value exceeded (varus or valgus) the ideal value by more than 3 degrees. In the frontal plane, a good alignment was observed for both femoral and tibial components without a significant difference between the two techniques. In the sagittal plane was found more alignment variability due to the different implants used and their ideal starting slope, from 7 degrees to 3 degrees. Finally, the surgeon can use the approach with which he has more confidence; however, as the measured resection technique causes less reduction in the post-operative joint-line position, in case of shortening of patellar tendon or patella infera, this technique is preferable.

Purpose The use of traditional cutting guides during knee arthroplasty in some cases could be extremely difficult, if not impossible, because of angular deformities, IM sclerosis, long-stemmed hip implants, or hardware within the femoral canal that cannot be removed. In these difficult cases navigation-assisted knee arthroplasty should be considered as an effective and appealing option. Methods We present 14 cases in which ideal mechanical and prosthetic alignment was achieved with different image-free, computer-assisted navigation systems, because of an extra-articular deformity (group A, nine patients) or because of a retained implant or hardware (group B, five patients).Results After a mean follow-up of 28 months (range 12-53 months), the average knee score increased overall from a mean of 33 points (range 12-63) to 78 points (range 63-90). The average functional score improved from a mean of 32 points (range 10-65) to 72 points (range 40-90). The postoperative mechanical axis ranged between 3°of varus and 3°of valgus. There was an implant revision in one patient who had a traumatic rupture of medial collateral ligament, which occurred 27 months after the index procedure.Conclusions Based on our results we think that the navigationassisted technique provides an alternative approach to the traditional instrumentation for treating these difficult patients in an effective and less invasive manner.

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Navigation has been developed to help surgeons install implants more accurately and reproducibly; at the same time, this tool is able to record quantitative information such as joint range of motion, laxity and kinematics intra-operatively. As for standard surgery, two strategies are possible to achieve either femoral component rotation or overall prosthetic alignment: a measured gap resection approach, in which bone landmarks are used to guide resections equal to the distal and posterior thickness of the femoral component, or a gap-balancing technique, in which equal collateral ligament tension in flexion and extension is tried to find before as a guide to final bone cuts. The purpose of this paper is to compare the two different methods in a 67 patients group submitted to the same procedure using mobile-bearing (MB) prosthesis in order to analyse the effect of both techniques on joint line maintenance, axial limb restoration and components position. The gap group (GG) consists of 31 patients in whom the arthroplasty was performed using a navigated gap-balancing technique. The measured group (MG) consists of 36 patients in whom a computer-assisted measured resection technique was used. The results of imaging and the number of outliers were not statistically different (P = 0.56) for the mechanical axis and prosthetic positioning between the two groups. The gap technique showed a statistically significant alteration of the post-operative value when compared with the measured resection technique, (P = 0.036). The mean elevation of the joint line was 4.09 mm for the GG and 3.50 mm in the MG.