Application of individualized navigation template in the location of femoral and tibial prosthesis in Oxford single condylar replacement

Objective To investigate the accuracy of the positioning of the prosthesis of the femur and tibia by the individual navigation template assisted Oxford unicompartmental arthroplasty and to evaluate of the value of navigation template in unicompartmental arthroplasty. Methods Twenty cadaveric legs were randomly divided into two groups (n=10), group 1 for navigation template and 2 for conventional method. A CT scan was performed preoperatively on the lower limb for navigational group. Geomagic software was used to process the CT data. A navigational template was constructed as the inverse of the distal femur and proximal tibia surface with an osteotomy gap. Two drills were used to define the rotational alignment of the femur in the computer. The navigational templates were produced using a rapid prototyping (RP) technique to assist UKA. The traditional method group was guided by the tibial extramedullary localization and the femoral intramedullary localization for the osteotomy and prosthesis placement. Both groups were performed according to the same standard. The position of the single condyle was evaluated by the anteroposterior X-ray films of the knee joint. The vertical relationship between the osteotomy surface and its mechanical axis was evaluated by CT. The parallel relationship between the central placement of femoral prosthesis and the posterior femoral cortex was also evaluated. Results The navigation template was close to the femoral condyle and tibial plateau without obvious movement. The mean operative duration of the navigation template group were 50.75±2.3 min and the traditional method group were 58.57±1.5 min (P>0.05). The postoperative femoral prosthesis flip angles of the navigation template group and the traditional group were 2.5°±-0.65° and -7.8°±3.26° respectively (P<0.05). The femoral prosthesis flexion angles were -2.9°±4.18° and-6.5°±4.25° (P<0.05), and the tibial prosthesis varus and valgus angles were -1.5°±0.50° and -5.8°±3.15° respectively (P<0.05). The tibial implant posterior inclination angles were 4.50°±1.55°and 3.05°±3.63° respectively (P<0.05). The average angles between navigational group distal femoral osteotomy surface and mechanical shaft were 89.5°±2.3° (range 87.5°-91.8°). The average angle between the proximal tibial resected surface and the mechanical axis was 90.3°±0.5° (range 89.4°-90.7°). There were 17 specimens of central column of femoral prosthesis parallel with the posterior femoral cortex. However, the angle of remaining 3 samples were less than 5°. In the traditional method group, the osteotomy surface and its mechanical axis were all angled. The deviation of distal femur distal surface in 7 specimens from the mechanical axis was larger than 10°, while that in 5 specimens was larger than 5°. Conclusion The navigation template can improve the accuracy of the femoral prosthesis localization, orientation and tibial prosthesis implants in the direction of valgus and valgus. However, there was no significant effect on the tibial prosthesis in the direction of posterior inclination. Key words: Arthroplasty, replacement, knee; Computer-aided design; Imaging, three-dimensional