Elsevier

Clinical Biomechanics

Volume 15, Issue 7, August 2000, Pages 522-527
Clinical Biomechanics

The relationship between ankle plantar flexor muscle moments and knee compressive forces in subjects with and without pain

https://doi.org/10.1016/S0268-0033(00)00007-3Get rights and content

Abstract

Objective. The purpose of this study was to compare the compressive knee joint reaction force and ankle plantar flexor muscle moment during the terminal stance phase in symptomatic osteoarthritic and non-symptomatic subjects.

Design. The study design was a comparative investigation of walking patterns.

Background. Patients with knee osteoarthritic symptoms may employ altered gait patterns to reduce the loading of painful joints. Speculation is that decreased ankle plantar flexor moments in the terminal stance phase may be an attempt to minimize compressive knee joint reaction forces.

Methods. Twenty community-dwelling men (52–83 years old), ten with knee osteoarthritis and ten non-symptomatic, were studied while walking across a walkway containing two force plates at a comfortable speed. Retroreflective markers were placed in accordance with the Helen Hayes marker system and recorded with six 120 Hz cameras. Three-dimensional kinematics and kinetics were computed.

Results. Group means for gait velocity, peak ankle plantar flexor moment and compressive knee joint reaction force were significantly less for the osteoarthritic group relative to the non-symptomatic group. When accounting for the decreased velocity in the osteoarthritic group, however, no group differences were observed. There were significant correlations between all three gait parameters (r>0.75), but peak ankle plantar flexor moment was the greatest predictor of compressive knee joint reaction force.

Conclusions. While no group differences were found for compressive knee joint reaction forces when accounting for gait velocity, it appears that subjects with osteoarthritis utilize gait velocity as a mechanism to reduce compressive knee joint reaction forces.
Relevance

An understanding of compressive knee joint reaction forces is important to the understanding of the disabling effects of knee osteoarthritis on physical function and to the understanding of appropriate and safe interventions to improve not only global parameters (e.g., pain, gait velocity), but also to “re-program” the locomotor pattern to develop “normal” muscle moments without increasing compressive knee joint reaction forces to painful levels.

Introduction

Osteoarthritis also referred to as degenerative joint disease, and degenerative arthritis, is the most common chronic disease affecting older persons [1]. Osteoarthritis is a degenerative disease that leads to a progressive loss of articular cartilage, that is accompanied by inadequate repair of articular cartilage, remodeling of subchrondral bone, and in many instances, the formation of osteophytes [2]. As a result, osteoarthritis (OA), especially knee osteoarthritis is a major cause of disability and dysfunction, exerting a devastating effect on the ability to live independently by causing joint pain, muscle weakness, and gait disturbances. Radiographic changes of osteoarthritis increase with age and are observed in 80% of people older than 55 [3]. Symptomatic knee osteoarthritis affects almost 10% of adults over age 65 [4]. People with symptomatic knee osteoarthritis have the clinical symptoms of pain, stiffness, and decrease range of motion causing increased morbidity and a diminished quality of life. Patients with knee osteoarthritic symptoms may employ altered gait patterns in an attempt to reduce the loading of painful joints. For example, it has been shown that subjects with knee osteoarthritis have reduced walking velocity, relative stride length, cadence, knee range of motion, stance phase knee flexion/extension, initial peak vertical forces [5] and knee extensor strength [6], [7], [8]. These gait changes are suggestive of pain relieving alterations, but can not provide data for determining altered motor patterns.

The association between knee osteoarthritis and pain is well established [9], but the natural history of knee osteoarthritis is still poorly understood. Several factors have been associated with morphologic progression of knee osteoarthritis, such as high serum hyaluronan level [10] and abnormal mechanical forces on the joint. These mechanical forces are measured as compressive joint reaction forces (equal and opposite forces acting at the proximal and distal aspects of a joint that tend to push the bones of the joint together) and muscle moments (the net result of muscular, ligamentous, frictional, gravitational, and acceleratory forces acting to alter the angular rotation of a joint). Muscle moments elucidate impaired motor control patterns and can, therefore, help determine the criterion for optimization or compensation in subjects with osteoarthritis.

Some work has been done to describe the knee adduction moment in relation to abnormal joint loading suggesting excessive contact pressure medially [2], [10], [11]. Limited information regarding muscle moments within all joints during gait is available in the osteoarthritic population, however. Fisher et al. [6] speculated that muscle moments in the sagittal plane may be involved in compensatory mechanisms to reduce pain for subjects with knee osteoarthritis. They observed that subjects with knee osteoarthritis used the hip flexors rather than the ankle plantar flexors to propel the lower limb. Specifically, subjects with knee osteoarthritis demonstrated decreased ankle plantar flexor moments in the terminal stance phase of the gait cycle [6]. During this phase of gait, there is the greatest reliance upon plantar flexors to control the forward propulsive momentum of the leg [12]. The reduction in plantar flexor muscle moments by subjects with knee osteoarthritis may be an attempt to minimize the compressive joint reaction forces at the knee since ankle plantar flexor muscle moments may increase compressive knee joint reaction forces when restraining the forward rotation of the tibia about the ankle, [6] thus reducing the tibial deviation from the vertical. The smaller deviation from the vertical puts a larger component of the joint reaction force in line with the femur, thereby creating a larger compressive force. In normal subjects, compressive knee joint reaction forces are expected to be at their highest level during the terminal stance of the gait cycle, due to the plantar flexor muscle action restraining the tibial deviation. Compressive knee joint reaction forces and data from non-symptomatic subjects, however, were not reported in the Fisher et al. study [6].

While healthy subjects generally use metabolic cost as the criterion for gait optimization, subjects with knee osteoathritis probably are more concerned with minimizing pain and maximizing stability [5]. Consequently, we propose that individuals with knee osteoarthritis unload a painful knee via compensatory mechanisms during walking to reduce compressive knee joint reaction forces. Specifically, we wish to test the hypothesis that plantar flexor muscle moments are reduced in subjects with knee osteoarthritis to reduce compressive knee joint reaction forces. The purpose of this study was to compare the compressive knee joint reaction force at the time of peak ankle plantar flexor muscle moment and peak ankle plantar flexor muscle moment during the terminal stance phase of the gait in ten symptomatic osteoarthritic subjects and ten aged-matched non-symptomatic subjects.

Section snippets

Subjects

Ten community-dwelling men with the diagnosis of knee osteoarthritis and ten “normal”, i.e., non-symptomatic community-dwelling aged-matched men were recruited from the outpatient clinics and staff of the VA Greater LA Healthcare System – West Los Angeles Healthcare Center. All subjects voluntarily agreed to participate and signed informed consent forms approved by the VA Greater LA Healthcare System Institutional Review Board. Inclusion criteria for all subjects included the ability (1) to

Results

Exemplar data of ankle plantar flexor muscle moments and the normal (in line with the femur) component of the knee joint reaction forces throughout the gait cycle are presented in Fig. 1, Fig. 2. Peak ankle plantar flexor muscle moment occurred during the terminal stance phase of the gait cycle (approximately 51% of the gait cycle) (note the arrow on Fig. 1). The knee joint reaction force at the time of peak ankle plantar flexor muscle moment was compressive (positive) and at or close to peak

Group comparisons

Group means for all three gait parameters (i.e., gait velocity, peak ankle plantar flexor moment and compressive knee joint reaction force at time of peak ankle plantar flexor moment) were significantly less for the osteoarthritic group relative to the non-symptomatic group (Table 1). When accounting for the decreased velocity in the osteoarthritic group, however, no group differences were observed.

Relationships between parameters

Age was only fairly correlated with any of the gait parameters and only age versus gait velocity was significantly correlated. There were strong and significant correlations, however, between all three gait parameters (Table 2). When the step-wise regression was used to predict the compressive knee joint reaction force at time of peak ankle plantar flexor moment, peak ankle plantar flexor moment and gait velocity were included in the model (adjusted r2 value =0.770, P<0.0001), but gait velocity

Relationship between pain and gait parameters

Within the subset of subjects with osteoarthritis, strong and significant negative correlations were observed between the WOMAC score and peak ankle plantar flexor moment (r=−0.700,P=0.0217) and compressive knee joint reaction force at time of peak ankle plantar flexor moment (r=−0.809,P=0.0029). Only a moderately negative correlation with gait velocity (r=−0.500,P=0.1463), and little to no correlation with age (r=0.205,P=0.5824) were observed with the WOMAC score.

Discussion

As Fisher et al. [6] speculated, ankle plantar flexor moments were related to compressive knee joint reaction forces. As the ankle plantar flexors restrain forward rotation of the tibia, the component of the knee joint reaction force in line with the femur increases, thereby causing a larger compressive force at the knee. The soleus is responsible for slowing tibial displacement and controlling knee flexion during the terminal stance phase [19], thus pulling the tibia backwards into the femur.

Acknowledgements

The authors would like to thank Mark Bragas and Maria Manzano for their assistance with data collection and analysis. Work supported by the Hartford/Gleitsman Medical Student Geriatric Scholars Program of the American Federation for Aging Research (AFAR).

References (26)

  • B. Daly et al.

    Rehabilitation of the elderly patient with arthritis

    Geriatric Rehabil

    (1993)
  • C. Slemenda et al.

    Quadricips weakness and osteoarthritis of the knee

    Ann Internal Med

    (1997)
  • L. Sharma et al.

    Knee adduction moment, serum yaluronan level, and disease severity in medial tibiofemoral osteoarthritis

    Arthritis Rheum

    (1998)
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