The difference in bone mineral density between femur and tibia is related to tibia deformation in endstage knee...

This study investigated bone mineral density (BMD) around the knee joint to clarify the mechanism by which tibia deformation exceeds that of the femur in patients with end-stage knee osteoarthritis (KOA).

We retrospectively analyzed 193 patients who underwent total knee arthroplasty for end-stage KOA with varus alignment. Preoperative T-score of the femur neck and femur total using dual-energy X-ray absorptiometry (DXA) and hounsfield units (HU) of the distal femur and proximal tibia using computed tomography (CT) were measured to asess the BMD. HU was measured by dividing the femur and tibia into medial, lateral, and total parts, respectively. Patients with medial proximal tibial angle (MPTA) ≥ 85° were considered 'group 1', and MPTA < 85° were 'group 2'. The HU between femur and tibia were compared in group 1. T-score, HU, and HU difference between group 1 and group 2 were compared.

The HU of the proximal tibia was lower than that of the distal femur (femur lateral > femur medial > tibia medial > tibia lateral). T-score (femur neck, femur total) and HU (femur lateral, femur total, tibia lateral) were lower in group 2 than in group 1. There was no difference in femur-tibia HU difference between groups.

The medial tibia collapse more than the medial femur in varus endstage KOA was associated with the lower BMD of the proximal tibia than that of the distal femur, and the MPTA collapse was affected by the absolute value of BMD rather than by the femur-tibia BMD difference.