Estimation of Mechanical Properties of the Distal Radius from Bone Mineral Content and Cortical Width

Abstract

The effect of continuous passive motion (CPM) on the clearance of blood from the knee joint and synovium was studied in 16 adolescent New Zealand rabbits (weight, 2.1–2.3 kg). Two milliliters of autologous anticoagulated erythrocytes that had been labelled with indium-111-oxine and reconstituted in normal saline were injected into both knees in seven rabbits. With the left hind limb in a cast, quantitative scanning of each knee was performed on days 0, 1, 2, 3, 4, and 7 using a collimated gamma camera. Throughout the experiment the left knee joint of each rabbit was immobilized, and the right knee joint was moved continuously from 40% to 110% of flexion, except during the scans. After the day 7 scan, the rabbits were killed and all tissues dissected from the knees, leaving the capsules intact. The intact knees were removed from the body and scanned. The joints were incised, irrigated, and rescanned. Sections of synovium were examined histologically. Nine additional rabbits were treated identically with unlabelled blood and killed one to seven days later for gross inspection. After three days there was no blood in the CPM knees, but some of the cast knees still contained blood after seven days. The rate of clearance was more than twice as fast with CPM than with cast immobilization (t% = 2.2 versus t% = 5.5 days; p < 0.001). Significantly less blood remained in the synovium after seven days with CPM than with cast immobilization (7.1% versus 13.2%; p < 0.01). Histologic examination showed less trapping of erythrocytes with CPM. Labelled erythrocytes were demonstrated free in the systemic circulation.