Comparison of hip and knee muscle moments in subjects with and without knee pain

Abstract

Elderly subjects with and without knee pain walked at a comfortable pace during gait analysis. Comparison of peak hip and knee internal extensor generalized muscle moments (GMMs) during loading response was made between groups. Walking velocity, peak hip internal extensor GMM, and knee range of motion (ROM) were significantly less for the group with knee pain than for the group without pain. Peak hip internal extensor GMM was strongly correlated with velocity, but peak knee internal extensor GMM was not. Knee ROM limitations may account for the increased peak knee internal extensor GMM in the knee pain group.

Introduction

Osteoarthritis (OA) is a condition that involves the destruction of articular cartilage, especially in weight-bearing joints (e.g. knee). It is the most common type of arthritis in elderly and it interferes with independent functioning [1]. It is estimated that 80% of the population over the age of 55 have radiographic changes consistent with knee OA [2]. Messier et al. [3] found that people with knee OA exhibit gait deficits such as decreased walking velocity, stride length, cadence, knee range of motion (ROM), and angular velocity, and initial maximal vertical forces relative to age-, mass-, and gender-matched control subjects.

These gait changes are suggestive of pain relieving alterations to reduce loading of painful joints. Reducing the loading of painful joints, however, may necessitate increased use of other joints to compensate for limitations imposed by pain. Messier [4] suggested that subjects with knee OA often accomplish the walking task through the use of a hip compensatory mechanism. His group found that while knee angular velocity decreased, hip angular velocity increased [3]. Similar compensations using internal generalized muscle moments (GMMs) data have been documented in subjects with knee OA during the sit-to-stand movement in which hip extensor GMM were increased during phases of substantial reductions in knee extensor GMM [5].

While no work directly compared sagittal plane internal GMMs in subjects with knee OA and age-matched controls, Fisher et al. [6] reported that subjects with knee OA predominately lacked knee internal extensor GMM during early stance (loading response), indicating a ‘quadriceps avoidance’ pattern due to weak quadriceps. Quadriceps weakness has been well documented in subjects with OA [3], [7] and is considered to contribute to both symptoms and structural deterioration [8]. Messier [4] suggested that the ‘quadriceps avoidance’ pattern was used by subjects with knee OA who had limited knee flexion throughout the stance phase; thereby avoiding any knee flexion that would require eccentric control via the quadriceps muscles. This eccentric contraction of the quadriceps muscles requires more control and also tends to increase the compressive forces on the knee joint [9]. The lack of knee internal extensor GMM, however, creates an unstable knee if external varus moments are not correspondingly decreased [10]. In order to stabilize the varusly deformed knee, knee flexors may be utilized [10] which may necessitate increased use of hip internal extensor GMM to maintain upright stance during the loading response, similar to the increase in hip internal extensor GMM during phases of substantial reduction in knee extensor GMM observed in the sit-to-stand movement [5]. Fisher et al. [6], however, did not present hip internal extensor GMM patterns during this phase of gait. Radin et al. [9] suggested that while tending to unload painful joints, there is the risk of simultaneously loading other joints abnormally. Kinematic [3] and kinetic [6] data from the literature suggest that the hip may be compensating for the painful and weakened knee, which is commonly observed in subjects with OA, but no data have been reported to confirm this hypothesis. During the loading response phase of gait, the knee joint moves into flexion requiring an increase in the extensor GMM in order to control the joint and prevent it from collapsing into further flexion. Additionally, a hip internal extensor GMM is present at initial contact to maintain the trunk in an upright position, countering momentum from the swing phase. The hip internal extensor GMM increases to peak during the loading response phase to cause hip extension which occurs during the first half of stance. Altered angular velocity patterns at the knee and hip are suggestive of compensatory mechanisms for pain relief, but kinematics alone do not provide evidence for altered motor control patterns, which are provided by the GMM data. An expected increase in internal GMM at the hip is presumed to be a compensatory mechanism to keep the trunk in an upright position and, thus maximizing stability of the lower limb while minimizing knee pain by compensating for reduced internal GMMs [4]. Consequently, the purpose of this study was to compare peak hip and knee internal extensor GMM during loading response between subjects with and without knee pain.