Correlation of static knee angle in kinematic and radiographic in medial knee osteoarthritis

The hip-knee-ankle (HKA) angle measured on a full-length weight bearing X-ray made in standing position is considered the gold standard to measure the knee static alignment. However, this method requires special equipment, involves significant radiation exposure and generates extra costs. The 3D motion capture can assess knee angles in a reliable and accurate way. Objectives This study aimed to analyse the correlation between the HKA angle achieved in full-length X-ray and the in static knee kinematic analysis in patients with medial knee osteoarthritis (OA). Methodology A descriptive study was design. Anterior-posterior full-limb radiographs were obtained using standard procedures in the same hospital. The HKA angle was measure by an experimental orthopaedic doctor. The kinematics were obtained using Visual3D software after 3D motion capture in two static positions: static comfortable position (Static-1) and a static standard position (Static-2). Kinematic data were filtered (6 Hz) and expressed in degrees (°). The knee joint was created by the distance between the distal end of the thigh and the proximal end of the shank. The angles lower than 180° were considered as varus alignment and those higher than 180° valgus alignment. Results This study includes 36 patients (22 females; mean age 61,6 ± 8,4; weight 75,8 ± 12,7 kg, and height 161 ± 9,2 cm) with diagnosed medial knee OA Kellgren/Lawrence grade 2 (16 patients) or 3. The patients presented a mean of HKA of 176,2° ± 3,2 in X-ray; 182,1° ± 6,0 in Static-1 and 180,0° ± 5,6 in Static-2. A significant correlation was found between HKA angle and Static-1 (r = 0,525; p = 0,001) and between HKA angle and Static-2 (r = 0,556; p = 0,000). Conclusion A moderate but significant correlation was found between X-ray and two measure of 3D motion capture in frontal knee angle. Clinically, 3D analysis may help health care professionals in a more practical way to identify the joint angles.