Decreased medial compartment loading and increased medial femorotibial articular cartilage thickness 12 months after limb realignment surgery

Abstract

Purpose: High tibial osteotomy (HTO) is a limb realignment surgery for patients with medial compartment knee osteoarthritis (OA) and varus alignment. The surgery is proposed to improve aberrant knee joint loading and thereby alter disease progression. The purposes of the present study were to explore changes after HTO in: [1] MRI-based measures of articular cartilage thickness and [2] 3D gait analysis-based measures of medial-to-lateral knee load distribution (the external knee adduction moment (KAM) and angular impulse (KAAI)). Methods: Patients with clinical and radiographic evidence of medial compartment knee OA were recruited from an orthopaedic clinic specializing in HTO. Participants were included if they had varus malalignment, early to moderate disease severity (defined using Kellgren and Lawrence Grades 1–3) and knee pain localized to the medial compartment. All patients received an HTO plate and screws made of polyetheretherketone (PEEK) that does not create artifact on MRI. MR images were assessed preoperatively, 6 weeks postoperatively to determine any immediate changes due to surgery, then again at 12 months postoperatively to assess the effects of long-term altered loads. Gait analysis was performed preoperatively and 12 months postoperatively. MR images were acquired on a 3T scanner using sagittal double-echo steady state (DESS) imaging. The medial and lateral femorotibial cartilage compartments were segmented manually and the reader was blinded to disease severity (including masking all but the articular surfaces on the MRIs), alignment, and the order of image acquisition (baseline, 6 weeks and 12 months). The sums of the mean thickness in the medial tibia (MT) and central weight-bearing region of the medial femoral condyle (cMF), and the lateral tibia (LT) and central weight-bearing region of the lateral femoral condyle (cLF), were used to calculate the cartilage thickness in the medial (MFTC) and lateral femorotibial compartments (LFTC) respectively. 3D gait analysis was performed and the external knee moment in the frontal plane was calculated using inverse dynamics to represent medial-to-lateral knee load distribution. The mean changes with 95% confidence intervals (95%CI) were calculated for each follow-up time point, minus baseline. The number of individual patients achieving previously suggested smallest detectable changes (SDC) in medial articular cartilage thickness and peak knee adduction moments were also determined. Results: The demographic and clinical characteristics for eight participants are presented in Table 1. Changes in articular cartilage thickness at 6 weeks and 12 months after surgery are shown in Fig. 1. At 12 months, the KAM decreased 1.3%BWxHt (95%CI: −1.8 to −0.7) and had a moderate-to-high correlation (r = −0.64) with the observed increases in articular cartilage thickness. Similar results were found when the KAM was replaced with the KAAI (−0.7%BWxHts; 95%CI: −1.1 to −0.4; r = −0.76). At the 12-month follow-up, 75% of participants (6 of 8) had an increase in medial articular cartilage thickness greater than the smallest detectable change (SDC) threshold in MFTC (111 μm) previously reported for cartilage thickness loss. Similarly, 63% of participants (5 of 8) had a decrease in KAM greater than the previously reported SDC threshold (1%BWxHt). Conclusions: This is the first study to quantify increases in medial femorotibial articular cartilage thickness that are correlated to decreases in medial knee loading after limb realignment surgery.View Large Image Figure ViewerDownload Hi-res image Download (PPT)