Summary
Spontanous rupture at the distal part of the gastrocnemius tendon (GT) is the second
most common non-traumatic tendon injury in dogs, whereas the other strands of the
common calcaneal tendon do not seem to have a predisposition to rupture. In order
to discover why we investigated the common calcaneal tendons of 63 dogs microscopically
and biomechanically. Both the gastrocnemius and superficial digital flexor tendon
(SFT) had multiple low vascularized fibrocartilaginous areas within their distal course
as opposed to regular parallel fibered areas in the proximal tendon areas. Biomechanical
testing revealed that the distal sections in both tendons show a 50% and 70% lower
tensile strength (Fmax/kg BW) than the proximal sections (p<0.01), respectively. On the contrary, tensile
load (Fmax/mm2) only differed minimally between proximal and distal sections in both tendons (8%
and 9%, respectively), whereas the tensile load of the distal gastrocnemius tendon
is 35% lower than of the distal superficial flexor tendon (p<0.01). To the authors'
knowledge, this is the first study to experimentally show that there are different
biomechanical properties within the same tendon. The maximum load to failure is lower
in the GT compared to the SFT within the same dog which explains its higher incidence
of rupture in the field. The avascular fibrocartilaginous structure in the distal
gastrocnemius tendon seems to play a further role in the pathogenesis of spontaneous
rupture.
Keywords
Tendon - biomechanics - fibrocartilage - rupture - dog