[Effect of distraction by various forces on the elbow joint in rabbits]

The elbow joints of 115 adult live rabbits have been subjected to experimental distraction by various forces and for different intervals. The forces applied were one tenth and one half, respectively, of the mean body weights; thus, a calculated reduction of one eleventh and five elevenths, respectively, of the force transmitted through the articulating joint surfaces was achieved. The distraction was performed for periods of 1, 2, 4 and 8 weeks. The forces were administered by means of an extraarticular device which allowed motion of the joints. Controls had been provided for to prove the noneffectiveness of the distraction device per se to the joint structures under study. Both upper limbs--one side always served as control--were subjected to radiological, histological/histochemical, angiographic and cytological examination; cartilage in addition was treated by vital staining or, alternatively, by producing splitting lines. The results were as follows: (1) Extensive local and more generalized hyperemia involving the whole limb in question was produced regardless of strength and duration of distraction. (2) Under all experimental conditions subsynovial hemorrhage and hemarthrosis developed. (3) Subsynovial hemorrhage caused the development of granulomatous and, subsequently, fibrous synovitis with simultaneously demonstrable hemosiderin depots. (4) Hemarthrosis was persistent during the entire period of observation. (5) Articular cartilage revealed moderate signs of degeneration and also irregularities of the usual pattern of splitting lines after continuous distraction for 8 weeks. At the same time, subchondral bone atrophy appeared. Vital staining revealed increased cartilage staining under mild distraction; moderate and marked distraction caused definitively less staining. Subsynovial hemorrhage and hemarthrosis are explained as partial vacuum effects. Concerning the moderate cartilage changes, a multifactorial genesis is presumed; the possible role of chemical, nutritional and mechanical factors is discussed. The widespread hyperemia most likely is caused by mechanical stimulation going along with joint distraction; capsular hyperemia might be a phenomenon immediately related to synovitis. Finally, the experimental results are discussed relative to observations made during clinical traction therapy.