A Novel Radiographic Methodology to Measure Knee Adduction Moment Using Routine Biplane Radiographs: Initial Results of 20 Patients.

Abstract

Background: Compromised function is a common reason for patient dissatisfaction after total knee arthroplasty. However, objectively evaluating function often requires costly, time-consuming, and highly specialized data collection and analysis in a dedicated motion analysis laboratory. To overcome this practical barrier, we developed a radiographic-based method to quantify knee joint moments in routine clinical care and to explore the relationship between knee moments in the sagittal plane and the Knee Osteoarthritis Outcomes Score for Joint Replacement (KOOS JR).

Methods: Motion analysis was performed on 20 patients (nine women, aged: 38 to 76 years; body mass index: 22.1 to 31.6) during level ground walking preoperatively and 6 weeks after total knee arthroplasty. At the same time points, patients underwent frontal and lateral biplane radiographs that were synchronized spatially and temporally with ground force measurements during bipedal and single leg stances on the operated leg. The knee adduction moment (KAM), in percent body weight times height (%BW·H), was calculated in the coronal plane as the product of the ground force and the perpendicular distance between the force's line of action and the knee center. The dynamic KAM during walking was compared to the radiographic KAM and related to KOOS JR.

Results: The peak dynamic KAM range was -0.5 to 4.3% BW·H preoperatively and 1 to 4.4% BW·H postoperatively. The static KAM, particularly during single leg stance, was strongly correlated with the peak dynamic KAM; however, the KAM was not correlated with KOOS JR.

Conclusions: The radiographic KAM, particularly during single leg stance, was an excellent surrogate metric for the peak dynamic KAM. The KAM was not correlated with KOOS JR; however, our follow-up was short, and we did not consider additional kinetic metrics, like the knee flexion moment. The proposed methodology allows routine clinical evaluation of knee kinetic markers of functional recovery that can complement patient-reported outcome measures.