One third of patients have articular cartilage thickness greater than three millimeters measured from femoral resections in kinematically aligned total knee arthroplasty.

Abstract

Kinematic alignment (KA) total knee arthroplasty (TKA) seeks to restore native limb and knee alignments regardless of the degree of preoperative deformity and/or flexion contracture. Hence, the thickness of each femoral resection should match the femoral component after adjusting for cartilage wear and sawblade kerf. Previously, the thickness of worn articular cartilage has been set at 2 mm. If the proportion of patients with thickness ≥3 mm is relatively large however, then adjusting resection thickness to reflect cartilage thickness is a refinement of interest. The objectives were to determine the proportion of patients undergoing KA TKA with cartilage thickness ≥3 mm in each resection. Using calibrated photographs, articular cartilage thickness was measured on 456 unworn resections (i.e. distal medial and lateral, posterior medial and lateral) from 201 patients undergoing KA TKA. The proportion of patients with cartilage thickness ≥3 mm was determined for each resection. The proportions of patients with cartilage thickness ≥3 mm were 29% and 34% for the distal medial and lateral resections, respectively, and 36% and 23% for the posterior medial and lateral resections, respectively. The relatively large proportion of patients with cartilage thickness ≥3 mm motivates taking next steps to assess the clinical practicality of adjusting resection thickness to reflect cartilage thickness. One next step is to determine how accurately cartilage thicknesses of worn distal and posterior surfaces can be predicted by measuring thickness of the contralateral unworn distal surface.