Cartilage glycosaminoglycan loss in the acute phase after an anterior cruciate ligament injury: Delayed gadolinium‐enhanced magnetic resonance imaging of cartilage and synovial fluid analysis

Abstract

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-DTPA²⁻ (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 μg/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.