Rearfoot biomechanics in Achilles tendon function

Pain and disorders of the human Achilles tendon can impact on the quality of life of those involved in leisure activities as well as professional sports, and also activities of daily living. Clinically, Achilles problems are challenging as no ‘golden standard’ exists for assessment of risk factors nor management. There is therefore a need to seek evidence for the risk factors associated with Achilles injury and evidence related to treatments.&#13;\n&#13;\n The focus of the first part of this thesis is to outline the current state of scientific research on the Achilles tendon covering anatomical, tissue mechanics and biomechanical (kinematics and kinetics) factors. This is followed by a discussion of the theoretical background associated with causative factors and treatment options, with a specific focus on rearfoot function and foot orthoses. From this review research questions are defined and experimental studies proposed. &#13;\n&#13;\n Based on the outcomes of the review, the overall aim of this thesis was to identify how (1) rearfoot movement and (2) foot orthoses, might affect Achilles tendon function. In the first experimental study changes in 3D kinematics due to foot orthosis were evaluated during walking and running. The objective was to gain a better understanding of how rearfoot angular position and movement change due to an orthosis since orthoses have been proposed as an effective treatment strategy. This involved thirty three symptom free subjects. The mean reduction in rearfoot eversion due to the foot orthosis was 3.91° for walking and 2.29° for running.&#13;\n&#13;\n In the second experimental study changes in tension on the medial and lateral sides of the Achilles tendon where studied during inversion/eversion movement of the rearfoot. The aim was to gain a better understanding of how tissue displacement in the medial and lateral parts of the tendon relate to changes in the frontal plane position of the rearfoot (such as changes that occur due to foot orthoses). This was conducted using ultrasound to measure tendon displacement in seventeen healthy subjects during passive pronation and supination of the foot. The study found that increasing rearfoot eversion increased displacement (stretch) on the medial side of the tendon, and reduced displacement on the lateral side. This was reversed for rearfoot inversion. The relationship between rearfoot position/motion and lengthening and shortening in the medial and lateral parts of the Achilles tendon was strong based on the mean data for the sample. The data allows the change in rearfoot position due to foot orthoses (study 1) to be put into a tendon displacement context. &#13;\n&#13;\n This thesis is the first to report that different displacements occur in the medial and lateral parts of the Achilles tendon relative to frontal rearfoot position and movement in vivo. The results might have important clinical relevance for understanding how rearfoot movement could pose a risk to increases in medial Achilles strain and thereafter tissue damage. This thesis also indicates how the use of foot orthoses may affect strain in the medial and lateral parts of the Achilles tendon, and thus proves some insight into the biomechanical basis for orthotic use in cases of Achilles injury.

Topic: Tendon Structure and Treatment
Subfield: Orthopedics and Sports Medicine
Field: Medicine
Domain: Health Sciences