Gap balancing versus measured resection technique using a mobile-bearing prosthesis in computer-assisted surgery

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.