The relationship between ankle plantar flexor muscle moments and knee compressive forces in subjects with and without pain
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 () and compressive knee joint reaction force at time of peak ankle plantar flexor moment (). Only a moderately negative correlation with gait velocity (), and little to no correlation with age () 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)
Pain assessment in osteoarthritis: experience with the WOMAC osteoarthritis index
Semin Arthritis Rheum
(1989)- et al.
Correlations between education and arthritis in the 1971–1975 NHANES I
Soc Sci Med
(1994) Do occupation-related physical factors contribute to arthritis?
Baillieres Clin Rheumatol
(1994)- et al.
Quantitative effects of physical therapy on muscular and functional performances in subjects with osteoarthritis of the knees
Arch Phys Med Rehabil
(1993) Women, men and osteoarthritis
Arthritis Care Res
(1995)- et al.
Tibiofemoral contact pressures in degenerative joint disease
Clin Orthopa Relat Res
(1998) - et al.
Estimates of prevalence of selected arthritis and musculoskeletal disease in the United States
J Rheumatol
(1998) - et al.
The incidence and natural history of knee osteoarthritis in the elderly
Arthritis Rheum
(1995) Osteoarthritis of the knee and associated factors of age and obesity. Effects on gait
MSSE
(1994)- et al.
Muscle function and gait in patients with knee osteoarthritis before and after muscle rehabilitation
Disabil Rehabil
(1997)
Rehabilitation of the elderly patient with arthritis
Geriatric Rehabil
Quadricips weakness and osteoarthritis of the knee
Ann Internal Med
Knee adduction moment, serum yaluronan level, and disease severity in medial tibiofemoral osteoarthritis
Arthritis Rheum
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