Long Digital Extensor (LDE) Tenosynovitis

The long digital extensor tendon is the main structure used by the horse to extend its posterior extremity.
Like all tendons that run on or under the joints, the LDE tendon is housed within a synovial sheath. The functions of the sheath as a “lubricating cuff” that allows easy movement of the tendon during flexion and extension of the limb. The sheath contains the synovial fluid identical to that found in the joints. The fluid lubricates the tendon as it slides into the sheath.

Occasionally due to hyperextension ( excessive stretching) of the LDE tendon triggers an inflammatory response within the sheath. This, in turn, results in the accumulation of additional synovial fluid (called “effusion”). effusion inside the sheath is the main indicator of tenosynovitis, which denotes the inflammation associated with the tendon and / or its sheath.
Long Digital Extensor (LDE) Tenosynovitis
It should be noted that in most cases there is a strong correlation between horses that have sustained an LDE hyperextension and those with a history of biomechanical interference of the stifle.
Horses with LDE tenosynovitis show characteristic swelling along the dorsal (front) side of the hock. (indicated by arrows in the photograph below)
LDE tendon synovial
Tenosynovitis LDE is uncommon to cause lameness but if these are present they can be painful. The inflammation present within the LDE sheath tends to “persist” once it develops. In rare cases, swelling spontaneously resolves; The inflammation persists until it is treated.
Treatment usually involves fluid drainage through needle aspiration and subsequent injection with a combination of synthetic hyaluronan, atropine and / or corticosteroids.
The rate of recurrence after treatment is approximately 50%.

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