Enthesis

Entheses and Enthesis Organs

Entheses introduction Stress concentration
 The attachment of a tendon, ligament or joint  Entheses attaches tendon (soft) to bone
capsule to bone (hard)
 Smooth and effective transfer of muscle force to  When trying to attach something hard to
bone. something soft, the point in the middle where
 Prone to pathology and a challenge to engineer! these attach is most likely to fail
 Entheses are a common site of ‘Over use  Locomotion, results in the angle between the
Injuries’ (sport- jumpers knee, throwers elbow, tendon or bone which is moving relative to
Achilles, rotator cuff, groin strains) one and another insertional angle change
 Don’t know the underlying cause. (are they  insertional angle change  makes
inflammatory, degenerative, both? We dk), so it attachment site potentially weaker
is any pathological change to an enthesis  Ground reaction forces  Contact with the
Enthesopathy (also known as insertional ground causes movement of the soft tissue,
tendinopathies, enthesitis) these are also focussed at the tissue interface
(at attachment site).
 These give an increased risk for rupture or
Stress dissipation damage of entheses. However, it is
 Strongest structure in the muscle-tendon-bone anatomically adapted (stress dissipation) to
unit, more likely to have a rupture in these prevent the likelihood of injury.
structures rather than entheses.
 ^ due to the macroscopic and microscopic
adaptations
Macroscopic
Microscopic  Tendon flaring- increase surface
 Two histological types of entheses (types of tissue area of the attachment site- decrease
present) stress concentration
o Fibrous  Common attachment sites-
increases surface area (seen at
o Fibrocartilaginous
elbow and foot with achilles and
plantar fascia)
 Fibrous entheses- most commonly present, where  Fibrous connections- to share the
tendon or ligament attaches to the diaphysis (shaft of load, decrease stress concentration
the bone) - e.g. Achilles continues
 Quite broad, span out to increase surface area from calcaneus all the
 Collagen fibres of the tendon insert almost directly way over the back of the
under the underlying bone heel and into the sole of
 Not much is know about the attachment, but most the foot. Fibres of
people think the mechanism of attachment is by the Achilles also insert and
collagen fibres of the tendon inserting directly into the anchor into the calcaneal
bone underlying it, so the fibres penetrate into the fat pad
bone itself for anchorage – Sharpey’s fibres
 Retinacula- ligaments that hold tendons
 Fibrocartilaginous entheses- has a plug of closely to the bone minimises
fibrocartilage between tendon and underlying bone insertional angle change
(intermediate material)
 Usually found on ends of long bones and short bones
of hand and feet
 Not as soft as tendon and not as hard as bone, so Fibrocartilaginous Entheses
provides a gradual transition between the soft and hard 4 zones
tissues, reducing the likelihood of damage or rupture  Dense fibrous connective tissue
at the site  Gradual bending - fibre bending is not  Uncalcified fibrocartilage
focused at the tissue interface= reduced fraying +  Calcified fibrocartilage
dissipates stress away from the tissue interface  Bone
 Fibrocartilaginous entheses are much more prone to
overuse injuries, it is also more widely studied