Validation of Articular Cartilage Depth in Total Knee Arthroplasty

Background: Understanding cartilage thickness is critical for execution of an unrestricted, calipered kinematic total knee arthroplasty (TKA). Historically, condylar cartilage was assumed to be 2 mm thick. However, thickness may vary based on age, sex, body mass index, anterior cruciate ligament (ACL) status, and alignment. This study aimed to determine in vivo cartilage thickness in patients undergoing TKA and evaluate which factors affect variation. Our hypothesis was in vivo cartilage thickness would be 2 mm on average, but some patients would have greater than 2 mm based on demographic factors. Methods: This multicenter, prospective cross-sectional cohort study evaluated condyle cartilage thickness from resected fragments. Univariate statistics and general linear models were used. Results: Among 806 TKA cases, the mean unworn femoral cartilage thickness was as follows: distal medial 2.0 mm; distal lateral 2.2 mm; posterior medial 2.0 mm; and posterior lateral 2.2 mm. The mean unworn tibia cartilage thickness was as follows: medial spine 2.4 mm; medial center 1.4 mm; lateral spine 2.1 mm; and lateral center 2.5 mm. In patients with unworn femoral cartilage, approximately 18.5% had cartilage greater than 3 mm. In patients with unworn tibial cartilage, approximately 34.7% had cartilage greater than 3 mm. An incompetent ACL was correlated with thinner posteromedial femoral cartilage. Increased thickness was correlated with younger age, men. Conclusions: A subset had unworn cartilage thickness greater than 3.0 mm, supporting our hypothesis. In an ACL deficient knee, the posteromedial cartilage was partially worn and should be considered for MCL isometry. Significant correlations were found based on age, gender, ACL status, alignment, body mass index, and race. Level of Evidence: Level 2, Prospective cohort study.