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Original article
Spatial orientation of the subtalar joint axis is different in subjects with and without Achilles tendon disorders Claudia A Reule,1 Wilfried W Alt,1 Heinz Lohrer,2 Harald Hochwald1 1Institute of Sport and Exercise Science, University of Stuttgart, Stuttgart, Germany 2Institute for Sports Medicine, Frankfurt, Germany
Correspondence to Dr Claudia A Reule, Institute of Sport and Exercise Science, University of Stuttgart, Allmandring 28, 70569 Stuttgart, Germany; claudia.
[email protected] Accepted 5 May 2011 Published Online First 1 July 2011
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±23°. 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.
INTRODUCTION Achilles tendon pathologies are of major importance in sports. Five to eighteen per cent of long-distance runners were affected.1– 3 Foot anatomy,4 poor vascularity, 5 training errors,6 age, bodyweight, 7 or ankle kinematics8 are discussed in the literature as intrinsic risk factors for Achilles tendon pathologies but their pathogenetic relevance is not proven.7 However, the mechanical loading of the Achilles tendon during locomotion is likely a main pathologic agent.6 9 10 The subtalar joint axis (STA) runs from anterodorsomedial to posteroplantarlateral through the foot and is proposed to be a constant anatomical factor primarily resulting from the bony structures constituting the subtalar joint.11 In the Br J Sports Med 2011;45:1029–1034. doi:10.1136/bjsm.2010.080119
literature, there is a great interindividual variability of the STA’s orientation noticed.11–13 This means that in some cases, the STA passes through the Achilles tendon while in other cases it runs outside the Achilles tendon (figure 6 ). In principle, the Achilles tendon antagonises the pronation movement at heel strike and in the initial stance phase. During toe-off, the Achilles tendon is the main plantar flexor and additionally inverts the rear foot.10 It can be assumed that the stress in the Achilles tendon is connected to the orientation of the STA.9 It is conceivable that a specific orientation of the STA causes asymmetrical tensile loads in the Achilles tendon, which can be regarded as a reason for Achilles tendon pathologies.7 14 15 The variation of the distance between specific Achilles tendon fibre insertions and the subtalar axis likely results in different torques acting on these fibres during locomotion. The crucial problem is to locate the STA. In the literature, the STA is discussed to be associated with acute or chronic overuse injuries.16 17 However, because of methodical limitations and the small number of subjects, previous studies do not satisfactorily shed light on the dependence between the STA orientation and overuse injuries. Most methods previously used to analyse the spatial orientation of the STA are restricted to in vitro11 18 or invasive application.19 20 MRI-based methods and techniques in vivo are expensive and time consuming. 20 21 The in vitro measurement technique described by Isman et al11 determines the STA on the basis of the shape of articulating surfaces. Ligaments, tendons and the capsule of the joint are disregarded in this case. A capable method has to be suitable for field application and has to allow inexpensive, in vivo, non-invasive measurements. To meet these recommendations, an ultrasonic pulse-echo–based measurement system was developed to determine the spatial orientation of the STA. Specific software and mathematical methods have been developed for this device. According to existing in vivo procedures for the determination of the ankle axis, this method is based on motion analysis of the subtalar joint. 21–23 The method allows to capture a great number of subjects in vivo, non-invasively, in real time and on the field. The purpose of this study was to assess the spatial orientation of the STA in a large cohort of runners. The relation between chronic Achilles tendon problems and the spatial orientation of the STA was retrospectively analysed. 1029
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Original article Table 1.
Anthropometric data from 307 subjects with average and effect size for the significant data pairs
Sample (N)
Body height (cm)
Body weight (kg)
Age (years)
BMI (kg/m2)
Mileage (km/week)
Total (307) Female (89) Male (218) Achilles tendon disorders (95) Uninjured (212)
174±24 168±7* 176±28* 178±8** 173±22**
68±15 60±6*** 72±17*** 72±10† 68±15†
39±17 38±12 39±19 47±15†† 36±17††
23 21 23 23 23
32.4±25 26.4±20††† 34±28††† 44±25‡ 29±24‡
*p=0.008, d=0.4; **p=0.032, d=0.3; ***p
