Laxity and rupture of the patellar tendon in systemic lupus erythematosus. Association with secondary hyperparathyroidism.

We describe a patient with systemic lupus erythematosus, chronic renal failure and secondary hyperparathyroidism who developed laxity and elongation of the patellar tendon, followed by its rupture one year later. Hydroxyapatite and urate crystals were identified from the chalky material surrounding the patellar tendon observed at surgery. These findings suggest that tendon laxity and elongation could possibly be detected before its rupture and that secondary hyperparathyroidism could be considered as another causative factor of tendon damage in patients with systemic lupus erythematosus.