Elsevier

Clinical Biomechanics

Volume 14, Issue 5, June 1999, Pages 297-308
Clinical Biomechanics

New Concepts
A dynamical systems approach to lower extremity running injuries

https://doi.org/10.1016/S0268-0033(98)90092-4Get rights and content

Abstract

In this paper, we are presenting an alternative approach to the investigation of lower extremity coupling referred to as a dynamical systems approach. In this approach, we calculate the phase angle of each segment and joint angle. Pairing the key segment/joint motions, we use phase angles to determine the continuous relative phase and the variability of the continuous relative phase. Data from two studies illustrate the efficacy of the dynamical systems approach. Individuals who were asymptomatic, even though they may have anatomical aberrant structural problems (i.e. high Q-angle vs low Q-angle) showed no differences in the pattern of the continuous relative phase or in the variability of the continuous phase. However, differences in the variability of the continuous relative phase were apparent in comparing individuals who were symptomatic with patellofemoral pain with non-injured individuals. Patellofemoral pain individuals showed less variability in the continuous relative phase of the lower extremity couplings than did the healthy subjects. We hypothesize that the lower variability of the couplings in the symptomatic individuals indicates repeatable joint actions within a very narrow range.

Relevance

We claim that the traditional view of the variability of disordered movement is not tenable and suggest that there is a functional role for variability in lower extremity segment coupling during locomotion. While the methods described in this paper cannot determine a cause of the injury, they may be useful in the detection and treatment of running injuries.

Introduction

Clinical studies [1], [2] reported that the most prevalent site of running injury was the knee. In these studies, knee injuries accounted for over 25% of all running injuries. The etiology for knee injuries in running has not been reported but excessive rearfoot pronation is quite often associated with knee injuries [3]. However, the coupling of excessive rearfoot motion and knee mechanics remains unknown. In fact, there is no clear clinical definition of excessive rearfoot pronation. A mechanism for knee injuries has been alluded to in the biomechanics literature but, to date, there has been little evidence linking the mechanics of the lower extremity to knee injuries.

Bates et al. [3] suggested that injury to the knee may be the result of a disruption of the timing of the normal events in closed chain pronation. The mechanism that was suggested related to the timing of the subtalar and knee joint actions. In the normal situation, they suggested that the maxima of rearfoot eversion, internal tibial rotation and knee flexion should all occur at the same instant in time. It was suggested, therefore, that if the subtalar joint continued to pronate while the knee began to extend, or if the subtalar joint began to re-supinate while the knee continued to flex, timing discrepancies between the joint actions would occur. It would appear, therefore, that the tibia would undergo antagonistic counter rotations at the proximal and distal ends. This would lead to excessive stress at the knee joint and, over many running cycles, may lead to knee injury.

The majority of studies in the biomechanics literature that investigated lower extremity actions have reported on the kinematics of individual lower extremity joints rather than addressing the interaction between the joints [3], [4]. Far fewer studies, however, have investigated the coupling of the subtalar joint and the knee joint during running. Those studies that have investigated lower extremity joint coupling did so by investigating the relative timing of the joint actions [5], [6], [7], [8] or by reporting the calcaneal eversion/tibial internal rotation ratio [9], [10].

Bates et al. [5], [6] reported no significant difference between the time of peak knee flexion and peak calcaneal eversion in runners with normal mechanics and those who over-pronated. However, the mean rearfoot angle for the group that over-pronated was 11°, a value well within the 8–15° range considered to be normal [11].

The subtalar joint is thought to act as a mitre joint with the axis of the joint inclined in the sagittal plane to approximately 45° [12]. In theory, therefore, equal amounts of calcaneal eversion should result in equal amounts of internal tibial rotation during pronation. This would result in a ratio of 1.0 between the excursions of calcaneal eversion and internal tibial rotation [10]. An increase or decrease in the subtalar joint axis, respectively, would decrease or increase this ratio. Nigg et al. [9] investigated the relationship between arch structure and the calcaneal eversion/internal tibial rotation ratio. They reported that calcaneal eversion was no different in the high and low arched groups but internal tibial rotation was less in the low arched group thus the low arched group had greater ratios.

McClay and Manal [10] used the same calcaneal eversion/internal tibial rotation ratio to investigate lower extremity coupling parameters in runners with normal rearfoot mechanics and in runners with excessive pronation. They reported no statistically significant differences between the groups in the timing between the maximum angles of the knee and the rearfoot. While not statistically significant, the values, however, were more closely timed in the normal group. The calcaneal eversion/internal tibial rotation ratio was significantly less in the excessive pronation group due to the greater internal tibial rotation. Most importantly, linear regression analyses revealed significant relationships among calcaneal eversion, internal tibial rotation and internal knee rotation.

It is clear that the actions of the lower extremity are coupled and it is most likely that perturbations to the system can result in injury, particularly to the knee. It is our thesis that the coupling relationships have not been clarified using traditional spatial constructs. A different approach to spatial angles and timing relationships is one that involves dynamical systems. This approach is not new and has been used before in biomechanical studies [13], [14] but it has not been previously used to investigate orthopaedic injuries to runners. In this paper we will demonstrate the use of a dynamical systems approach to investigate the coupling relationships in the lower extremity.

Section snippets

The dynamical systems approach

In a biomechanical system, the high number of available degrees of freedom is reduced through the formation of coordinative structures. Coordinative structures can be defined as muscle synergies, often spanning several joints, that are functionally linked to satisfy the task demands [15]. Coordinative structures enable the organism to achieve (a) the same goal by using different degrees of freedom (e.g. muscles, joints) and (b) use the same degrees of freedom to reach different movement goals.

Subjects

Representative data from individual subjects in two different studies will be presented in this paper. In each case, subjects were required to complete a Physical Activity Questionnaire to verify their health status and to give their consent by signing an informed-consent form. Both procedures were in accordance with University policy. In the first study, subjects with Q-angles greater than 15° and those with Q-angles less than 15° were compared. Individuals with Q-angles greater than 15° have

Results and discussion

The purpose of this paper was to demonstrate the use of a dynamical systems approach to investigate the coupling relationships in the lower extremity. Particularly, we wish to show that the variability of the CRP is an effective means of discriminating between symptomatic and asymptomatic individuals. To begin this discussion, however, we will describe the coupling patterns of individuals who have no lower extremity injury and a Q-angle less than 15°. Figure 2 illustrates the CRP for the

Conclusions

There are important inferences that can be drawn from the CRP standard deviation profiles. The CRP and the variability of the CRP do not appear to define the differences in anatomical structure between the Q-angle groups during running. For example, whether the individual has a Q-angle greater than or less than 15° does not appear to be contained in these data. It is our position that differences in the CRP or the variability of the CRP indicated that no pathology was present. Functionally, the

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