Agreement in component size between preoperative measurement, navigation and final implant in total knee replacement.

BACKGROUND: One of the possible causes of dissatisfaction reported by many patients after total knee replacement (TKR) is the lack of agreement between component size and bone structure. To avoid this complication and facilitate the procedure, preoperative planning with digitized templates is recommended. Surgical navigation indicates the best position and the most adequate size of arthroplasty and may therefore replace preoperative radiographic measurement. The objective of the study was to check agreement between the sizes of TKR components measured before surgery with digitized templates, the size recommended by the navigation and sizes actually implanted. METHODS: In 103 patients scheduled for TKR, preoperative full-limb radiography was performed to measure the mechanical and anatomical axes of the limb, femur and tibia. The most adequate size of the femoral and tibial components was planned by superimposing digitized templates. The size recommended in navigation and the size of the finally implanted components were also recorded. RESULTS: A high level of agreement was found between the sizes of femoral and tibial components measured by X-rays and in navigation (0.750 and 0.772, respectively) (intraclass correlation and Cronbach's alpha). Agreement between the sizes recommended by X-rays and navigation and those finally implanted was 0.886 for the femur and 0.891 for the tibia. Agreement levels were not different in cases with prior deformities of limb axis. CONCLUSIONS: The high level of agreement found in component sizes between radiographic measurement with digitized templates and navigation suggests that preoperative X-ray measurement is not needed when navigation is used for placement of implants during TKR. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: Computer-assisted surgery may avoid preoperative measurement with templates in TKR.

Total knee replacement modifies the preoperative tibial torsion angle-similar results between computer-assisted and standard technique.

BACKGROUND: Malpositioning of the components in total knee replacement (TKR) can result in failure or deficient outcomes of the surgical procedure. In the tibial segment, the rotational position of the tray should reproduce the mechanical axis without modifying physiological tibial torsion. METHODS: A randomised, prospective study was made of 74 patients subjected TKR involving the standard technique (38 cases) and navigation surgery (36 cases). A computed tomography study of the knee and ankle was made before the operation and after arthroplasty implantation, in order to identify the position of the prosthetic tibial tray in the transverse axis and the tibial torsion angle. RESULTS: The rotation of the tibial tray changed from its preoperative to postoperative range, but no significant differences were found between the navigated and the standard groups. The presence of preoperative deformities in the frontal plane did not modify the changes in the rotation of the tibial component. The mean preoperative tibial torsion angle was 17.76º (SD =10.15) of external rotation, with no significant differences in relation to the previous frontal deformity. After TKR, the tibial torsion angle was 15.36º (SD =7.16) (P=0.021). There were no differences in final tibial torsion between the knees operated upon with the standard instruments and those subjected to computer-assisted surgery (CAS; P=0.157). CONCLUSIONS: TKR surgery modifies preoperative tibial torsion. Neither mechanical instrumentation nor navigation surgery precisely reproduces the rotational axis of the leg.

Computed tomography is not necessary to assess rotation of the femoral component in navigation-assisted total knee replacement.

Objective To demonstrate that postoperative computed tomography (CT) is not needed if navigation is used to determine the rotational position of the femoral component during total knee replacement (TKR). Methods Preoperative CT, navigational, and postoperative CT data of 70 TKR procedures were analysed. The correlation between the rotational angulation of the femur measured by CT and that measured by perioperative navigation was examined. The correlation between the femoral component rotation determined by navigation and that determined by CT was also assessed. Results The mean femoral rotation determined by navigation was 2.64° ± 4.34°, while that shown by CT was 6.43° ± 1.65°. Postoperative rotation of the femoral component shown by CT was 3.09° ± 2.71°, which was closely correlated with the angle obtained through the intraoperative transepicondylar axis by navigation (Pearson's R = 0.930). Conclusions Navigation can be used to collect the preoperative, intraoperative, and postoperative data and final position of the TKR. The rotation of the femoral component can be determined using navigation without the need for CT.

Hinged total knee arthroplasty in the presence of ligamentous deficiency.

BACKGROUND: Rotating-hinge total knee prostheses may be used for the treatment of global instability about the knee. The designs of previous generations were associated with suboptimal outcomes. QUESTIONS/PURPOSES: We evaluated the clinical and radiographic outcomes of salvage knee reconstructions using modern-generation, modular, kinematic rotating-hinge total knee prostheses. METHODS: We retrospectively reviewed 26 rotating-hinge arthroplasty devices to examine whether acceptable results were obtainable using a single arthroplasty design. The average age of the patients was 77 years (SD, 9 years); the minimum followup was 24 months (mean, 46 months; range, 24-107 months). The indication was revision surgery in 21 patients and complex primary surgery in five. Patients were evaluated clinically (Knee Society score) and radiographically (positions of components, signs of loosening, bone loss). RESULTS: Knee Society pain scores improved from 40 preoperatively to 77 postoperatively, and function scores improved from 36 to 51. ROM improved from -15 masculine to -10 masculine. None of the patients' knee pain or function worsened. No loosening of implants was observed. Nonprogressive radiolucent lines were identified around the femoral and tibial components in three knees. Three patients required reoperations: one showed a supracondylar periprosthetic fracture treated by open reduction and internal fixation, whereas the other two had periprosthetic infections. CONCLUSIONS: Reconstruction with rotating-hinge total knee prostheses can provide substantial improvement in function and a reduction in pain in extreme circumstances, such as gross instability. We believe this salvage procedure should be reserved for severe ligamentous deficiencies in elderly and sedentary patients or whenever revision surgery techniques fail. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Computer assistance increases precision of component placement in total knee arthroplasty with articular deformity.

BACKGROUND: The accuracy of computer navigation applied to total knee arthroplasty (TKA) in knees with severe deformity has not been studied. QUESTIONS/PURPOSES: The purpose of this study was to compare the radiographic alignment achieved in total knee replacements performed with and without navigation and to search for differences in the final alignment of two groups of patients (with and without previous joint deformities) using the same system of surgical navigation. METHODS: The first series comprised 40 arthroplasties with minimal preoperative deformity. In 20 of them, surgical navigation was used, whereas the other 20 were performed with conventional jig-based technique. We compared the femoral angle, tibial angle, and femorotibial angle (FTA) by performing a post-TKA CT of the entire limb. In the second series, 40 additional TKAs were studied; in this case, however, they presented preoperative deformities greater than 10 masculine in the frontal plane. RESULTS: The positioning of the femoral and tibial component was more accurate in the group treated with surgical navigation and FTA improvement was statistically significant. When comparing the results of both series, FTA precision was always higher when using computer-assisted surgery. As for optimal FTA, data showed the use of surgical navigation improved the results both in the group with preoperative deformity greater than 10 degrees in the frontal plane and in the group with minimal preoperative knee deformity. CONCLUSIONS: Surgical navigation obtains better radiographic results in the positioning of the femoral and tibial components and in the final axis of the limb in arthroplasties performed on both deformed and more normally aligned knees. LEVEL OF EVIDENCE: Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.