Medial-to-lateral ratio of tibiofemoral subchondral bone area is adapted to alignment and mechanical load

Abstract

Malalignment is known to affect the medial-to-lateral load distribution in the tibiofemoral joint. In this longitudinal study, we test the hypothesis that subchondral bone surface areas functionally adapt to the load distribution in malaligned knees. Alignment (hip-knee-ankle angle) was measured from full limb films in 174 participants with knee osteoarthritis. Coronal magnetic resonance images were acquired at baseline and 26.6 +/- 5.4 months later. The subchondral bone surface area of the weight-bearing tibiofemoral cartilages was segmented, with readers blinded to the order of acquisition. The size of the subchondral bone surface areas was computed after triangulation by proprietary software. The hip-knee-ankle angle showed a significant correlation with the tibial (r (2) = 0.25, P < 0.0001) and femoral (r (2) = 0.07, P < 0.001) ratio of medial-to-lateral subchondral bone surface area. In the tibia, the ratio was significantly different between varus (1.28:1), neutral (1.18:1), and valgus (1.13:1) knees (analysis of variance [ANOVA]; P < 0.00001). Similar observations were made in the weight-bearing femur (0.94:1 in neutral, 0.97.1 in varus, 0.91:1 in valgus knees; ANOVA P = 0.018). The annualized longitudinal increase in subchondral bone surface area was significant (P < 0.05) in the medial tibia (+0.13%), medial femur (+0.26%), and lateral tibia (+0.19%). In the medial femur, the change between baseline and follow-up was significantly different (ANOVA; P = 0.020) between neutral, varus, and valgus knees, with the increase in surface area being significantly greater (P = 0.019) in varus than in neutral knees. Tibiofemoral subchondral bone surface areas are shown to be functionally adapted to the medial-to-lateral load distribution. The longitudinal findings indicate that this adaptational process may continue to take place at advanced age.

FIG 1

Coronal MR image, acquired with an SPGR sequence with water excitation. The image shows the tibiofemoral cartilage plates: MT= medial tibia, LT= lateral tibia, cMF= medial weight-bearing femur; cLT= lateral weight-bearing femur, and the subchondral bone area that was segmented in these areas a) Neutrally aligned knee: MT = medial tibia, cMF = central (weight-bearing) medial femur, LT = lateral tibia, cLF = central (weight-bearing) lateral femur b) Knee with varus malignment: lines and brackets indicate the subchondral bone contour over which the subchondral bone area is measured in the medial femorotibial compartment c) Knee with valgus malignment: lines and brackets indicate the subchondral bone contour over which the subchondral bone area is measured in the lateral femorotibial compartment

FIG 2

3D reconstruction of the knee with subchondral bone areas (tAB) being shown in color a) Graph showing a reconstruction of the tibial, patellar and femoral bones (brown color), a coronal and a (secondary) axial MR slice: medial tibia (MT) = blue; central (weight-bearing) medial femur (cMF) = yellow, lateral tibia (LT) = green, central (weight-bearing) lateral femur (cLF) = red b) Reconstruction of the femoral bone only and of the tAB of the above cartilages c) Reconstruction of the tibial bone only and of the tAB of the above cartilages

FIG 3

Scatter plots showing the correlation between the hip-knee-ankle angle (alignment) and the ratio of the subchondral bone surface area (tAB) between the medial and lateral part of the tibiofemoral joint: A) Tibia B) Femur Negative values for the hip-knee-ankle angle show valgus malalignment, and positive values varus malalignment

FIG 4

Scatter plots showing the correlation between the hip-knee-ankle angle (alignment) and the increase in the subchondral bone surface area (tAB) between baseline and follow up (in cm² normalized to one year): A) Medial tibia (MT) B) Medial weight-bearing femur (cMF) Negative values for the hip-knee-ankle angle show valgus malalignment and positive values varus malalignment