ABSTRACT
BACKGROUND: There are many possible predisposing factors for Achilles tendon disorders suggested in the literature but their pathogenetic relevance is not proven in most cases. The asymmetric mechanical load distribution within the Achilles tendon during locomotion is frequently addressed as a major risk factor for Achilles tendon disorders. The spatial orientation of the subtalar joint axis (STA) may influence the Achilles tendon loading possibly leading to overload injuries. Hypothesis There is a significant difference between the orientation of the STA in subjects with and without Achilles tendon pathologies. MATERIALS AND METHODS: 614 subtalar joint axes determined in 307 long-distance runners with and without Achilles tendon disorders were included. Achilles tendon disorders were defined as any Achilles tendon-related pain during or following running, existing for more than 2 weeks in the past. Motion analysis of the foot was performed using an ultrasonic pulse-echo-based measurement system. The orientation of the STA was expressed by two angles. RESULTS: The mean inclination angle was 42 ± 16° and the mean deviation angle was 11 ± 2 3°. There was a significant difference (p=0.002) between the mean deviation angle measured in subjects with Achilles tendon pathologies (18 ± 23°) and those without (10 ± 23°). CONCLUSIONS: The results demonstrate a wide interindividual variability of the spatial orientation of the STA. In addition, the mean deviation angle in people with Achilles tendon pathologies is significantly more oblique than in people without. This finding indicates that the spatial orientation of the STA is related to the incidence of overuse injuries of the Achilles tendon in the investigated sample.
Subject(s)
Achilles Tendon/pathology , Cumulative Trauma Disorders/pathology , Running/injuries , Subtalar Joint/pathology , Tendinopathy/pathology , Adult , Chronic Disease , Cohort Studies , Cumulative Trauma Disorders/etiology , Cumulative Trauma Disorders/physiopathology , Female , Humans , Male , Middle Aged , Musculoskeletal Pain/etiology , Musculoskeletal Pain/pathology , Musculoskeletal Pain/physiopathology , Range of Motion, Articular/physiology , Tendinopathy/etiology , Tendinopathy/physiopathology , Young AdultABSTRACT
This article describes a new measuring device to investigate balancing strategies of human stance: the totter-slab, i.e., a standing plate suspended with steel cables to hooks on a steel frame. First, we analysed the physical properties of the device by recording free oscillations under different conditions [varying amplitude, mass and centre of mass (COM) height]. This allowed us to determine the eigenfrequency f and the damping coefficient D<1 Ns/m for each trial. The trials showed that the measured damped eigenfrequency of f is approximately 0.63 Hz is barely dependent on the mass loaded. The ratio D/M is approximately 0.015 1/s is a constant almost independent of the different conditions. Furthermore, we determined the stiffnesses of the suspending cables and their suspension points to check for potential energy storage capacity of the totter-slab. We found that the totter-slab is a useful, well-defined, reliable and developable measuring device for different non-rigid-ground stance conditions. In a second part of the investigation, we compared the frequency spectra of six subjects balancing on the totter-slab with their spectra while standing quietly on a force plate fixed to the ground. The totter-slab spectra showed two distinct, dominant peak regions at approximately 0.3 and 1.1 Hz. This finding enforces the double inverted pendulum to be an adequate model particularly for balancing on the totter-slab. Compared with the firm ground condition, these two peak regions were more pronounced when balancing on the totter-slab. However, there is a variety of frequencies in the region 0.2...1.5 Hz specific for an individual subject in both balancing conditions.
