Bone mineral density at femoral neck reflect weight bearing condition in patients with knee osteoarthritis

Abstract

Purpose: Weight bearing asymmetry during standing is seen in patients with knee osteoarthritis (OA). It is clinically essential to indicate the loading condition of both limbs to avoid mechanical overload and to improve treatment strategy of bilateral knee OA. However, motion analysis system, which is expensive and not always available in all hospitals, is required to evaluate the loading condition. It was hypothesized that loading condition should reflect the bone mineral density at femoral neck in patients with knee OA. The aim of the present study was to evaluate weight bearing distribution in those patients and to clarify the relationship between gait parameters and bone mineral density. Methods: A total of 36 knees in eighteen patients (mean age = 73.7 ± 6.3 yrs, mean body mass index = 26.7 ± 3.8 kg/m2) were enrolled in the current study. All the subjects had medial compartmental knee osteoarthritis bilaterally. None of the subjects had any history of major injuries to the trunk, and hip osteoarthritis. An informed consent form approved by Institutional Review Board of our university was obtained in each subject. The subjects performed relaxed standing, placing each foot on each force plate, and thereafter, level walking. First, ground reaction force was calculated on bilateral knees during standing. The knees in each patient were divided into Higher and Lower force side for the definition of dominant side limb. Second, gait parameters in each subject were compared between both sides. Gait parameters were calculated by average of three gait cycle. Gait analysis system consisted of 8 cameras (120 frames/s; Pro-reflex, Qualisys, Sweden), two force plates (frequency 600 Hz; AM6110, Bertec, Columbus, OH, USA), and 46 retro-reflective markers (14 mm in diameter) (Figure 1). The force plate collected ground reaction force (GRF) data at 600 Hz and were synchronized to the camera sampling rate (120 Hz). The motion of markers was recorded by Qualisys Track Manager Software (version 2.7). To calculate knee kinematics and kinetics, Visual 3D (C-motion Company) was utilized. To analyze the factors that affect the weight bearing distribution in both limbs, knee data were compared between knees. Knee data included radiographic OA grade, femorotibial angle (FTA) and bone mineral density (g/cm2) at the bilateral femoral neck (PRODIGY Fuga, GE Healthcare). Since side-to-side differences of weight distribution in standing would lead to the gait asymmetry as previously described in the literature, following parameters were also evaluated; knee flexion angles (degrees) in standing and at heel strike during gait, peak values of net knee adduction and extension moment (Nm/kg), peak values of GRF(N/kg), maximum axial loading rate (N/kg per second), GRF impulse (N/kg*Second), and the time from initial contact in first peak GRF (Second). As a statistical analysis, in terms of detailed knee data and gait parameters, two-tailed paired t-test was conducted to determine the differences between Higher and Lower force sides in each patient. P-values of <0.05 were considered as significant. Results: Detailed data were shown in Table 1 and 2. Weight bearing asymmetry was seen in all the subjects between right and left knee. Knees on Higher force side were significantly more extended than on Lower force side during relaxed standing, while the other parameters were not significantly different. As to the clinical data, Higher force side had greater bone mineral density, compared to Lower force side. Conclusions: From the present study, Higher force side had greater bone mineral density, compared to Lower force side. It is necessary for the orthopedic surgeons to examine the side-to-side differences of bone mineral density to evaluate the loading condition in patients with knee OA.Table 1Kinematic data in standing and walking (mean ± SD)Higher sideLower sideP valueaKnee flexion angle in standing (Deg.)4.7 ± 6.98.5 ± 6.6P = 0.012*Knee flexion angle at Heel strike (Deg.)5.5 ± 6.16.7 ± 5.1P = 0.27Peak knee flexion moment in walking (Nm/kg)0.31 ± 0.240.33 ± 0.21P = 0.65Peak knee adduction moment in walking (Nm/kg)0.67 ± 0.190.70 ± 0.19P = 0.38Peak Ground reaction force(N/kg)1.03 ± 0.061.03 ± 0.04P = 0.66Maximum axial loading rate (N/kg per second)25.5 ± 7.525.8 ± 10.1P = 0.82Ground reaction force impulse (N/kg*Second)0.64 ± 0.110.62 ± 0.10P = 0.15Time from initial contact in first peak GRF (Second)(0.23 ± 0.08)0.25 ± 0.09P = 0.15a Values obtained using Paired t-test. *:p < 0.05. Open table in a new tab Table 2Clinical data (mean ± SD)Higher sideLower sideP valueaKellgren–Lawrence grade(grade3/grade4)8/106/12Femorotibial angle (Deg.)184.1 ± 4.2185.9 ± 4.5P = 0.12Bone mineral density (g/cm2)0.84 ± 0.140.81 ± 0.14P = 0.04*a Values obtained using Paired t-test. *:p<0.05. Open table in a new tab a Values obtained using Paired t-test. *:p < 0.05. a Values obtained using Paired t-test. *:p<0.05.