To determine, in a preliminary cross sectional study of patients with anterior cruciate ligament (ACL) ruptured knees, which of the radiographic features-subchondral cortical plate thickness, trabecular sclerosis, and osteophytosis-appears before or in association with changes in joint space width (JSW) as a surrogate for articular cartilage thickness in patients with ruptured knees.
19 patients (14 men), mean (95% CI) age 28.7 (23.6 to 33.8) years, had ACL rupture in one knee only, confirmed by arthroscopy. Anterior draw, Lachman's test, and pivot shift tests were performed and x5 posteroanterior macroradiographs of both knees in a standing semiflexed view were taken at a mean (95% CI) time from injury of 34. 3 (26.9 to 41.7) months. In each radiograph, computerised methods were used to measure minimum JSW and fractal signature analysis (FSA) to quantify the vertical and horizontal trabecular organisation, osteophyte area, and the subchondral cortical plate thickness, in the medial and lateral tibial compartments of all knees.
Physical examination confirmed the presence of joint laxity in the injured knees. No statistical difference in either medial or lateral JSW and subchondral cortical plate thickness was detected between ACL ruptured and uninjured knees. FSA showed a significant decrease in fractal dimension for the horizontal trabeculae (size 0.42 mm) in the medial compartment of the ACL ruptured knees compared with the uninjured knees (p<0.01, multivariate analysis of variance). There was an inverse correlation (R -0.74) between the time since knee injury and the difference in FSA values for ACL ruptured and uninjured knees in medial compartment horizontal trabeculae (size 0.4 mm). No significant changes were detected in the lateral compartment. Osteophytes were detected in the medial compartment of nine ACL injured knees.
Compared with the uninjured knee, ACL rupture leads to thickening of subchondral horizontal trabeculae (decreased FSA) in the medial tibial compartment of all knees, reaching significance at about four years after injury. Osteophytes were present in the same compartment in 9/19 knees. No changes in JSW and subchondral cortical plate thickness were detected. Whether the bony changes detected in these ACL ruptured knees presage those of early osteoarthritis requires further study.