An enthesis was previously viewed as a focal attachment point to the bone. Consequently enthesitis related pathology was viewed as focal in nature. However, the pain related to diseases of the enthesis may be diffuse.
The purpose of this page is to highlight the complexity of insertions and how many are closely interlinked. This is of broad relevance for understanding the difficulty in localising entheseal related pain. It is key to appreciate that insertions may not be focal in nature.
Large insertions such as the Achilles enthesis are directly attached to the plantar fascia of the foot. This is because the outermost superficial fibres of the Achilles may run over the bone and directly fuse with the fibres from the outer aspect of plantar fascia. This direct attachment may contribute to movement of the underlying bone in the maturing skeleton.
The quadriceps tendon insertion in the knee sends fibres that merge directly into the patellar tendon below the knee cap. The role that this structure plays in joint pains is not well understood (See reference)
Many tendons have multiple slips or tributaries attached to different sites of the bone. A good example of this is the tibialis posterior tendon where distinct attachments occur to different bones on the sole of the foot.
Some enthesis split over the joint and form two completely distinct attachments from the same tendon. For example, this arrangement occurs in the tibialis anterior tendon attachment site in the foot.
The common extensor tendon origin at the elbow fuses with the collateral ligament of the radius. As a result apparent tennis elbow pain may be diffuse.
The enthesis in the hands and toes that are derived from the extensor tendon and from the collateral ligaments actually splits at the bone attachment and also anchors the enthesis directly to the nail.
Many enthesis fibres attach along the periostium or bone surface and not focally.
Entheses may fuse with the adjacent supporting tissues called fascia and behave like a body glove.
This anatomical configuration of entheses has implications for understanding why pain may not be focal. Such examples include tennis elbow where pain is sometimes quite diffuse.
It also explains some diseases for example Severs disease in children where the Achilles and plantar fascia interconnection may contribute to movement in the growth plate in the heel bone thus leading to pain.