In Vivo Knee Kinematics: How Important Are the Roles of Femoral Geometry and the Cruciate Ligaments?

BACKGROUND: While posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component. METHODS: Tibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant. RESULTS: In early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar. CONCLUSION: Subjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.

Functional advantage of articulating versus static spacers in 2-stage revision for total knee arthroplasty infection.

Infection is an unfortunate complication of total knee arthroplasty. Current literature supports 2-stage reimplantation as the gold standard. Controversy exists whether static or articulating spacers are the best interim treatment method. Seventy-six 2-stage reimplantation procedures met the study inclusion criteria. There were 28 static spacers and 48 articulating spacers. The eradication rate was 94.7% in the articulating group compared with 92.1% in the static group (P = 0.7). There were no significant differences in postoperative Knee Society Scores pain scores. There were 28 (58%) good to excellent function scores in the articulating group and 10 (36%) in the static group (P = .05). Interim use of an articulating spacer maintains excellent infection eradication rates and may improve function over the use of static spacers.