gms | German Medical Science

Objectives: dGEMRIC (delayed gadolinium enhanced MRI of cartilage) and T2 mapping are non-invasive MRI techniques increasingly used to judge cartilage quality, especially in the setting of prearthritic conditions, such as femoroacetabular impingement (FAI). These techniques estimate distinct biochemical substrates of hyaline cartilage. In a clinical setting, the correlation between these novel MRI techniques and the histologic gold standard is very difficult. These limitations can be bypassed by using an ovine FAI model. Hence, we asked (1) whether dGEMRIC and T2 indices correlate with histological cartilage degeneration in a previously validated, experimental ovine FAI model and (2) whether there is a correlation between dGEMRIC and T2 imaging.

Methods: This experimental controlled prospective study on 5 sheep (10 hips) was conducted after IRB approval. The sheep underwent surgical induction of FAI by unilateral varus intertrochanteric osteotomy, which rotates the naturally aspherical ovine femoral head into the acetabulum, inducing typical focal chondrolabral damage as seen in patients with FAI. Correction of the deformity was performed after 70 days (FAI group). No surgery was performed in the 5 contralateral hips (Control group). Sheep were sacrificed after a further 140 days. One hour before sacrifice, sheep received i.v. gadolinium-DTPA and roamed free. Hips were dissected to fit into the coil. dGEMRIC and T2 maps were obtained at a 3 T unit (Philips Ingenia) using inversion recovery techniques. Histologic samples were stained with toluidine blue, and cartilage degeneration was graded with the Mankin score. Linear regression analysis was performed (p< 0.05).

1.

dGEMRIC and T2 times were measured with the help of radial images at the 12 acetabular and femoral clock-face positions and correlated to the Mankin scores.

2.

dGEMRIC indices and T2 values were correlated with each other.

Results and Conclusion:

1.

Overall and regional (up to R= -0.56; p = 0.046) inverse correlation was found between acetabular and femoral dGEMRIC indices and the Mankin score. No overall correlation was found between acetabular and femoral T2 indices and the Mankin score.

2.

No significant overall correlation (p>0.05) between dGEMRIC indices and T2 values could be found.

These promising results support the continuing use of dGEMRIC for monitoring cartilage degeneration in FAI, both in a clinical and experimental setting, in order to improve our understanding of osteoarthritis of the hip. The absent correlation between T2 imaging and dGEMRIC indicates complementary effects in cartilage and requires further investigation.