Condylar-Stabilized Designs in Total Knee Arthroplasty: A Classification System and Review of Outcomes.

Background: Increased use of condylar-stabilized (CS) bearings in primary total knee arthroplasty can be attributed to bony preservation with the option for posterior cruciate ligament resection without compromising kinematics. There are a variety of CS designs, but no system of nomenclature, making comparisons challenging. A comprehensive classification system of differing CS designs based on articular surface and femoral component geometries and kinematic principles is proposed. We reviewed the literature for functional outcomes and survivorship associated with each CS design.

Methods: Using a combination of literature reviews, web searches, surgeon input, and manufacturer correspondence, 31 CS designs from 21 manufacturers were identified. The designs were subsequently categorized into distinct groups based on geometry including the location of polyethylene buildup, conformity compared to their cruciate-retaining counterparts, and the radius of the femoral component. A scoping review was conducted evaluating patient-reported outcome measures, ranges of motion, and survivorships associated with each category. After exclusion, we reviewed 91 studies in the PubMed, Ovid MEDLINE, Embase, Cochrane, Web of Science, and Scopus databases.

Results: We established five distinct categories: (1) anterior-stabilized; (2) ultracongruent; (3) medial-stabilized; (4) medial-pivot; and (5) lateral-stabilized. There were 12 anterior-stabilized design studies, 15 ultracongruent, two medial-stabilized, 55 medial-pivot, and three describing lateral-stabilized designs. All designs demonstrated significant improvements in patient-reported outcome measures and ranges of motion postoperatively, with survivorship of at least 90% and follow-up ranging from 2 to 18 years in some designs CONCLUSIONS: The classification developed allows for appropriate grouping and comparison of distinct CS implants. As presented in this review, there are favorable short-term functional outcomes across all CS subcategories. Although the data associated with these designs appear promising, it remains limited. Further research comparing different designs to understand how differing geometries impact kinematic function and clinical outcomes will inform implant selection and future design.