Several factors of pathogenesis come into play contributing to IUFP. Most common is
the anatomical design
, (similar to posture in humans) of the horse’s hind leg. Ideally the articular angle of the stifle joint should be about 150 degrees. A leg with decreased angulations formed by the interplay of joints of the pelvis, hip, stifle and hock (excessively straight hind limb) is more prone to stifle problems. This can be due to heredity (genetics)
or breed dominant traits. A horse that has low muscle tone from poor conditioning
with low activity level is prone to IUFP. The timing and strength of the muscle contractions is vital, hence the relative tone or laxity of the muscle controls or doesn’t , patella motion and the medial ligament stays locked around or “hung up” on the medial femoral condyle. An injury
to the stifle,
associated musculature or pelvis, combined with prolonged stall rest, may contribute to muscle atrophy and the
development of IUFP. In very fit horses it has been noted that with one week of stall
confinement, horse’s stifles may begin to lock. Muscle and neurological conditions
such as spasticity, muscle spasm, myopathies, hypertoncity of the quadriceps, along with
poor neuromotor coordination between flexors and extensors may cause IUFP.
Abnormal tension of the patellar ligaments
and abnormal conformation of the
fibrocartitlage of the pateall or proximal medial trhochlear ridge can cause IUFP.
Medial ligament pathology or desmitis
may be the cause or effect of IUFP. Excessive
that places excessive stress on the joint such as in Standardbred racing in one
direction on steeply
banked tracks can cause excessive force on the stifle1. Abnormal
consisting of long toe, low heels, and higher medial wall is also
thought to contribute to IUFP. Other conditions common at the stifle joint such as: osteochondrosis dessicans, bone cyst, patellar fracture, cruciate ligament injury, congenital malformation of the medial condyle and or the patella, ligament sprain, degeneration of articular surfaces, or fracture, can be common found.