Does an Anterior-Lipped Tibial Insert Adequately Substitute for a Post-Cam Articulation in Total Knee Arthroplasty.

INTRODUCTION: Newer tibial inserts with enhanced conformity (cruciate stabilizing anterior lip; CS) to obviate the need for a posteriorly stabilized (PS) post-cam articulation in posterior cruciate ligament-deficient knees have been recently introduced in modern total knee arthroplasty (TKA). The purpose of this study was to evaluate whether clinical and functional outcomes differ in TKA cohorts without a posterior cruciate ligament (PCL) utilizing either CS anterior-lipped or PS post-cam articulation. MATERIALS AND METHODS: Prospectively collected outcomes were compared in matched cohorts of modern TKAs implanted with either CS anterior-lipped tibial inserts or PS post-cam articulations. The PCL was resected in all knees. Modern Knee Society Scores (objective, function, and satisfaction scores), walking and stair pain, EuroQol five dimensions (EQ-5D) health-related quality of life, and UCLA activity level were assessed at minimum one-year follow-up. RESULTS: Forty-three anterior-lipped and 39 PS TKAs were matched on sex, age, BMI, and ASA classification at the time of surgery and months of follow-up. CS knees had significantly higher preoperative function scores than PS knees (p = 0.033), but both groups had equivalent function scores at minimum follow-up of one-year (p = 0.687). Eight-one percent of patients in each group reported being satisfied or very satisfied with their TKA (X2 = 0.072, p = 0.964). CONCLUSIONS: This study supports the hypothesis that an anterior-lipped insert is an adequate functional substitute for a post-cam articulation in patients undergoing TKA with PCL excision. These findings suggest that a PS post-cam articulation may not be necessary given the introduction, availability, and clinical performance of anterior-lipped and more conforming tibial bearings. Further study and longer term follow-up is warranted.

Anatomical factors influencing patellar tracking in the unstable patellofemoral joint.

PURPOSE: The current study was performed to relate anatomical parameters to in vivo patellar tracking for pediatric patients with recurrent patellar instability. METHODS: Seven pediatric patients with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo patellofemoral function. Computational models were created from high-resolution MRI scans of the unloaded knee and lower-resolution scans during isometric knee extension at multiple flexion angles. Shape matching techniques were applied to replace the low-resolution models of the loaded knee with the high-resolution models. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the tibial tuberosity-trochlear groove distance, the Insall-Salvati index and the Caton-Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters. RESULTS: The bisect offset index and lateral tilt were significantly correlated with the lateral trochlear inclination (p≤0.002) and TT-TG distance (p<0.05), but not the Insall-Salvati index or the Caton-Deschamps index. For both the bisect offset index and lateral tilt, the standardized beta coefficient, used to identify the best anatomical predictors of tracking, was larger for the lateral trochlear inclination than the TT-TG distance. CONCLUSION: For this population, the strongest predictor of lateral maltracking that could lead to patellar instability was lateral trochlear inclination. LEVEL OF EVIDENCE: Diagnostic study, Level II.