Although knee osteoarthritis (OA) is diagnosed by radiographic evidence of degenerative changes, it is difficult for a single definition to encompass all instances of OA [1]. Problematically, radiographic diagnosis of knee OA provides a weak association with symptoms and function [2]. A survey study found that 1,004 (14.6%) of 6,880 subjects experienced knee pain [3]. Of these patients with knee pain, 59% were diagnosed with knee OA by a physician, but only about 15% had radiographic stage (2–4) changes of knee OA. Therefore, a clinician diagnoses knee OA on the basis of clinical and/or radiological features [4] including the diagnostic criteria of pain, stiffness, age, bony tenderness, crepitus, and bony enlargement [5].
Structural changes in knee OA are thought to be caused by multiple pathways involving various risk factors [1]. The continuous formation and decomposition of the cartilaginous matrix are disrupted by these harmful influences, resulting in a reduction of total cartilage at the knee joint [6]. Direct measurement of articular cartilage has several potential advantages over indirect measurement via radiographs [7]. Several previous studies have used magnetic resonance imaging to investigate the relation between cartilage volume and knee OA [7–9]. A linear reduction in cartilage volume was associated with a narrowing of the joint space [7]. Articular cartilage loss (but not radiographic score) was a risk factor for undergoing a knee replacement, an intervention at end-stage knee OA [9]. However, cartilage volume is limited in detecting early knee OA due to swelling at the early stages of injury [10]. Causes of degenerative changes in articular cartilage are affected by the interrelation of mechanical, structural, and biological pathways [11].
The progression of knee OA has been associated with biomechanical disruption, which shifts the normal bearing region of the knee joint [12]. Thus, degenerative changes in cartilage can be affected by kinematic changes [11]. Several previous studies have attempted to predict or identify knee OA through an investigation of biomechanical changes [13–18]. Most biomechanical studies investigate the gait of patients with knee OA because gait is the most functional and common use of the lower extremities [14–18]. The main consequences for gait analysis, however, were increased knee adduction moment and internally rotated tibia [14, 16, 17, 19].
Tibial rotation accompanying sagittal movement contains the phenomenon of screw-home movement (SHM) of the knee, which plays an important role in knee stability during extension [20–22]. However, SHM is affected by weight-bearing or loaded conditions [23]. For example, external rotation occurred during the loading response phase, which was a reversal of the SHM [24]. To the best of our knowledge, only one previous study has evaluated the tibial rotation for the non-weighted bearing state in patients with knee OA [13]. However, their study reported tibial rotation only during the five-degree flexion position in a non-weight-bearing state, which was insufficient to demonstrate the dynamic state of SHM. It is difficult to determine how biomechanical changes are involved in soft tissue degenerative changes or compensation mechanisms [14].
To understand the mechanical factors of knee stability in patients with knee OA, herein we investigate the SHM changes in a group of these patients during dynamic movement.