Merck Manual

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Professional Version

Fragmentation of the Patella in Horses


Jane C. Boswell

, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS

Reviewed/Revised Sep 2015 | Modified Oct 2022

Fragmentation of the apex of the patella usually occurs secondary to medial patellar desmotomy for management of upward fixation of the patella. Lesions are believed to develop due to patellar instability as a result of the surgery. The severity of lameness varies from mild stiffness to moderate lameness. A proximal limb flexion test usually exacerbates lameness, and femoropatellar joint effusion is usually present. Lameness is localized by diagnostic anesthesia of the femoropatellar joint, and diagnosis is confirmed by radiography. Arthroscopic debridement of the apex of the patella with removal of the osteochondral fragments is the treatment of choice. Prognosis is reasonable but depends on the severity of the condition.

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