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- PATIENTS AND METHODS
The knee is commonly affected by osteoarthritis (OA), often causing severe disability (1). This progressive degenerative disease is known to affect various changes in articular cartilage, subchondral bone, synovium, and joint capsule, and consequently these structures have been studied widely (2, 3). The effect of OA on muscles, however, has been investigated less frequently, although it is likely muscles also are involved. For example, the quadriceps muscles are weaker in elderly people with OA than in healthy, age-matched controls; the muscles are also incompletely activated (4). It is unclear whether such changes precede or result from the development of OA (2, 5). Because proprioceptive input arises from muscle, joint, and cutaneous afferents, altered input from any of these could impair proprioception (6).
Although proprioception at the OA knee has been studied extensively (4, 7–9), all studies to date have focused on one aspect, position sense. These studies have consistently found an impairment from OA in subjects with unilateral (9, 10) and bilateral (4, 7) knee OA. However, other aspects of proprioception, such as the ability to perceive movement (11), have not been studied. Because it is unknown whether the 2 sensations are affected in the same way, although preliminary work suggests no correlation between the 2 (12), conclusions cannot be drawn about the effect of OA on movement detection. The ability to perceive movement may be closely linked to stability and function (4), and therefore its integrity may be even more important than the ability to perceive a change in position. In the young healthy knee, very small movements (∼1.0° for movements imposed at 0.1°/second) can be detected (13), probably because such proprioceptive information is essential to good stability. It is possible, therefore, that even a small decrease in proprioceptive acuity has an important effect.
Many patients with OA bandage the knee to reduce symptoms of pain and swelling. However, it is also thought that application of bandages improves proprioceptive acuity by increasing cutaneous input (14). The application of a tubular bandage (e.g., Tubigrip) improved position sense in OA knees (15), but this effect has not been consistently found in other conditions (16), or other joints (17). The effect on movement detection of wearing a bandage at the knee has not been evaluated. If bandage application improves proprioception, and thereby potentially improves stability, this would be an easy clinical intervention to apply with patient-relevant benefits. The present study was therefore designed to investigate the effect of knee OA and the effect of wearing a tubular bandage on movement perception.
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- PATIENTS AND METHODS
The present study found that moderate to severe OA impaired subjects' ability to perceive movements imposed at the knee compared with age-matched controls with no clinical evidence of knee OA. We also found that application of a bandage did not alter movement detection. Furthermore, within the restricted range of disease severity and age studied here, neither age nor severity measured by the WOMAC score correlated with ability to perceive knee movement.
Although joint position sense has consistently been shown to be impaired by OA (7, 8, 15), the present study is the first to investigate movement perception. Together, these findings suggest that OA causes a generalized proprioceptive deficit including both sensations, although a relationship between the position and movement sense should not be assumed. It is unclear whether this proprioceptive deficit is caused by destruction of joint structures and the associated receptors, loss of muscle function, or joint instability.
Because muscle function is more amenable to rehabilitation than articular structures, the mechanism by which proprioceptive acuity is altered is particularly relevant. It seems unlikely that loss of articular receptors, per se, is the problem, because acuity improves after joint replacement (15), i.e., after removal of joint receptors. In contrast, a number of findings suggest that OA impairs several aspects of muscle function (4), and an exercise program aimed at improving muscle function and joint stability (12) also improved proprioception. Thus, it seems more likely that either muscle function or joint stability, or both, are the critical factors.
As argued by Hurley et al (4), the explanation may not be simple, but rather may be a combination of factors. For example, destruction of articular structures by OA may produce abnormal afferent discharge (25, 26). Afferent fibers from articular mechanoreceptors also project onto gamma-motoneurones (27), which control muscle spindle sensitivity (28). If the abnormal information from the articular afferents inhibits the gamma-motoneurones, then sensitivity of muscle spindles would decrease, with a consequent reduction in proprioceptive acuity (27, 29). That is, articular damage may impair muscle function and, secondarily, proprioception in patients with OA.
Alternatively, destruction of the joint by OA with subsequent deformity may cause an altered line of action of the muscles that cross the knee, thereby changing the length–tension relationship. This would also alter the muscle spindles' sensitivity to change in muscle length, resulting in decreased proprioceptive acuity.
The lack of effect of bandage application on proprioception was unexpected. Work to date is unclear, with previous studies showing some improvement in position sense with application of a bandage to OA knees (8) and in electromyographic activity in anterior cruciate ligament-deficient knees (15). More recently, however, Birmingham et al (30) found that bandaging the knee of young healthy subjects using a neoprene sleeve had no effect on passive or active position matching, the only difference occurring during 1 active, nonaxial, loaded condition. The lack of improvement in movement detection found in the present study may be because either the appropriate receptors were not stimulated, or the additional information from cutaneous receptors did not provide coherent signals. Instead, the increased input may constitute “noise,” and therefore not be interpreted as movement signals by the central nervous system.
Unlike previous studies on joint position sense (7, 8, 24), we did not find a relationship between movement detection and either severity of OA measured by the WOMAC score or age. This may reflect the lack of variation in our subjects: all subjects had severe OA, whereas other studies included subclinical controls (7); and the age range included subjects within a decade (65–76 years), whereas differences were previously found between decades. If differences do exist within the moderate to severe range of disease severity, or within a decade in an older population, it is likely that the small subject numbers studied precluded significant findings.
In conclusion, subjects with moderate to severe OA of the knee had decreased ability to perceive movement compared with healthy controls matched for age, BMI, and activity levels. Because an impairment in joint position sense has also been found, it appears that patients with knee OA have a generalized proprioceptive deficit. However, application of a bandage did not change the ability to detect movements in the flexion-extension plane in either group.