Does Knee Osteoarthritis Differentially Modulate Proprioceptive Acuity in the Frontal and Sagittal Planes of the Knee

A number of factors which alter the local biomechanics of the knee may contribute to the observed “wear and tear” of articular degeneration in osteoarthritic (OA) joints (1–3). Evidence suggests that abnormal loading in the frontal plane of the knee, in particular, is associated with the progression of OA. Indeed, modulations in frontal plane joint laxity, alignment, and joint kinematics and kinetics during gait have been demonstrated in knee OA populations (4–8), which may lead to abnormal loading on the articular cartilage. Understanding the underlying physiological factors which could contribute to these alterations in frontal plane joint stability may be useful in developing therapies and interventions designed to slow the progression of knee OA. In a healthy joint, frontal plane knee stability is maintained not only by passive restraints (i.e. ligaments, bone/cartilaginous contact forces), but also through coordinated voluntary and reflexive muscle activation (9–11). The latter, neuromuscular control, is especially dependent on proprioceptive feedback to enable protective muscular stabilization in situations of normal and abnormal loading. Indeed, proprioceptive deficits have been associated with pain and functional limitations in knee OA (3, 12–14). Given the importance of frontal plane joint loading on the pathomechanics of knee OA (1, 15), examination of the proprioceptive characteristics in this plane may elucidate the potential neuromechanical underpinnings of the progression of the disease. Joint proprioception in the sagittal plane of the knee has been extensively studied in both healthy and pathological populations (16–18). On the contrary, little is known about proprioceptive characteristics of the joint in the frontal plane and how it is modulated with OA. While significant, technical difficulties associated with the ability to isolate varus and valgus movements at the knee may have contributed to the lack of data on frontal plane proprioception in the literature. We have recently developed a testing paradigm to characterize knee joint proprioception in the varus/valgus direction in young, healthy participants (19). This methodology can be used to evaluate whether the previously reported sagittal plane proprioceptive deficits in knee OA represent a global decline in sensation at the joint or are direction-specific. Accordingly, the aim of this study was to quantify proprioceptive acuity in both the frontal and sagittal planes in healthy and osteoarthritic knees. We hypothesized that proprioceptive acuity in both planes will be decreased in the knee OA population. However, given the disease-induced changes in frontal plane joint mechanics (7, 20), we propose that proprioceptive differences between healthy and arthritic knees will be greater in the frontal plane as compared to the sagittal plane. As frontal and sagittal plane rotations at the joint primarily target different joint structures, direction-specific variations in proprioception with knee OA may indicate that the disease differentially affects the contribution of specific joint tissues and sensory afferents. We argue that knowledge of proprioceptive acuity in the frontal plane in knee OA may help to elucidate some of the neuromechanical factors that contribute to the progression of the disease.