Why Don't Most Runners Get Knee Osteoarthritis? A Case for Per-Unit-Distance Loads
ABSTRACT Peak knee joint contact forces ("loads") in running are much higher than they are in walking, where the peak load has been associated with the initiation and progression of knee osteoarthritis. However, runners do not have an especially high risk of osteoarthritis compared to non-runners. This paradox suggests that running somehow blunts the effect of very high peak joint contact forces, perhaps to provide a load per unit distance traveled (PUD) that is relatively low.
To compare peak and PUD knee joint loads between human walking and running.
Fourteen healthy adults walked and ran at self-selected speeds. Ground reaction force and motion capture data were measured and combined with inverse dynamics and musculoskeletal modeling to estimate the peak knee joint loads, PUD knee joint loads, and the impulse of the knee joint contact force for each gait with a matched-pair (within-subject) design.
The peak load was three times higher in running (8.02 vs. 2.72 bodyweights, p < 0.001) but the PUD load did not differ between running and walking (0.80 vs. 0.75 bodyweights·m, p = 0.098). The impulse of the joint contact force was greater for running than for walking (1.30 vs. 1.04 bodyweights·s, p < 0.001). The peak load increased with increasing running speed, while the PUD load decreased with increasing speed.
Compared to walking, the relatively short duration of ground contact and relatively long length of strides in running seem to blunt the effect of high peak joint loads, such that the PUD loads are no higher than in walking. Waveform features other than or in addition to the peak value should be considered when studying joint loading and injuries.
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ABSTRACT: Osteoarthritis (OA) is a musculoskeletal disorder primarily affecting the older population and resulting in chronic pain and disability. Biomechanical variables, associated with OA severity such as external knee adduction moment (KAM) and joint malalignment, may affect the disease process by altering the bone-on-bone forces during gait. To investigate the association between biomechanical variables and KAM in knee OA. A systematic search for published studies' titles and abstracts was performed on Ovid Medline, Cumulative index to Nursing and Allied Health, PREMEDLINE, EBM reviews and SPORTDiscus. Fourteen studies met the inclusion criteria and were considered for the review. The magnitude and time course of KAM during gait appeared to be consistent across laboratories and computational methods. Only two of the included studies that compared patients with OA to a control group reported a higher peak KAM for the OA group. Knee adduction moment increased with OA severity and was directly proportional to varus malalignment. Classifying the patients on the basis of disease severity decreased the group variability, permitting the differences to be more detectable. Biomechanical variables such as varus malalignment are associated with KAM and therefore may affect the disease process. These variables should be taken into considerations when developing therapeutic interventions for individuals suffering from knee OA.The Knee 04/2009; 16(5):303-9. DOI:10.1016/j.knee.2008.12.007 · 1.70 Impact Factor
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ABSTRACT: Large knee adduction moments during gait have been implicated as a mechanical factor related to the progression and severity of tibiofemoral osteoarthritis and it has been proposed that these moments increase the load on the medial compartment of the knee joint. However, this mechanism cannot be validated without taking into account the internal forces and moments generated by the muscles and ligaments, which cannot be easily measured. Previous musculoskeletal models suggest that the medial compartment of the tibiofemoral joint bears the majority of the tibiofemoral load, with the lateral compartment unloaded at times during stance. Yet these models did not utilise explicitly measured muscle activation patterns and measurements from an instrumented prosthesis which do not portray lateral compartment unloading. This paper utilised an EMG-driven model to estimate muscle forces and knee joint contact forces during healthy gait. Results indicate that while the medial compartment does bear the majority of the load during stance, muscles provide sufficient stability to counter the tendency of the external adduction moment to unload the lateral compartment. This stability was predominantly provided by the quadriceps, hamstrings, and gastrocnemii muscles, although the contribution from the tensor fascia latae was also significant. Lateral compartment unloading was not predicted by the EMG-driven model, suggesting that muscle activity patterns provide useful input to estimate muscle and joint contact forces.Journal of Biomechanics 08/2009; 42(14):2294-300. DOI:10.1016/j.jbiomech.2009.06.019 · 2.50 Impact Factor
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ABSTRACT: The external knee adduction moment (KAM) is a useful proxy for medial knee loading. Though many studies examining the KAM report the peak value, recent studies have evaluated other measures from this waveform, including the stance impulse. It is important to understand the impact of varying gait speed on discrete values of the KAM waveform when evaluating differences between samples. The purpose of this study was to compare measures of the KAM waveform, including peak and impulse, during level walking at different speeds. Thirty-two healthy participants (mean age=32+/-8 years, 18 women) were recruited. The KAM peak and impulse were calculated over three ambulation speeds: self-selected, slow (15% slower than self-selected) and fast (15% faster than self-selected). To identify differences between these conditions, a one-way repeated measures analysis of variance was utilized. The peak KAM was greater in the fast compared to the slow condition (p<0.05). The KAM impulse was greater in the slow compared to both self-selected and fast conditions (p<0.05). The KAM impulse appeared more sensitive to changes in gait speed because the impulse reflects the duration of loading. These findings highlight that slowed gait speed increased loading exposure on the medial knee tissues, though the maximum magnitude of the exposure was reduced. This trade-off between the increase in duration and decrease in amplitude at slower gait speeds should be examined, particularly where loading exposure may lead to pathology, such as knee osteoarthritis.Gait & posture 11/2009; 30(4):543-6. DOI:10.1016/j.gaitpost.2009.08.236 · 2.30 Impact Factor