Objective: To examine the glycosaminoglycan (GAG) content in cartilage and that in synovial fluid and determine whether they are associated, in patients with an acute anterior cruciate ligament (ACL) injury.
Methods: Twenty-four patients (14 of whom were male) with a mean age of 27 years (range 17-40 years) were assessed with delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage an average of 3 weeks after an ACL rupture and compared with 24 healthy volunteers. Two hours after an intravenous injection of Gd-DTPA(2-) (0.3 mmoles/kg body weight), quantitative measurements of the T1 relaxation time (T1(Gd) [T1 relaxation time in the presence of Gd-DTPA]) were made in lateral and medial femoral weight-bearing cartilage. In the patients, synovial fluid was aspirated immediately before the MRI, and GAG was analyzed using dye precipitation with Alcian blue.
Results: Fifteen of the 24 patients had an isolated bone bruise in the lateral femoral condyle, where the cartilage T1(Gd) was shorter than that in the controls (mean +/- SD 385 +/- 83 msec and 445 +/- 41 msec, respectively; P = 0.004), consistent with decreased GAG content. However, the T1(Gd) was also decreased in the medial femoral cartilage, where bone bruises were rare (376 +/- 76 msec in patients versus 428 +/- 38 msec in controls; P = 0.006). The mean +/- SD synovial fluid GAG concentration in patients was 157 +/- 86 mug/ml and showed a positive correlation with the T1(Gd) (r = 0.49, P = 0.02).
Conclusion: This study indicates that an ACL injury causes posttraumatic edema of the lateral femoral cartilage but initializes a generalized biochemical change within the knee that leads to GAG loss from both lateral and medial femoral cartilage. In cartilage with a high GAG content (long T1(Gd)), more GAG is released into the synovial fluid, suggesting that cartilage quality is a factor to consider when interpreting cartilage biomarkers of metabolism.