Effects of ACL interference screws on articular cartilage volume and thickness measurements with 1.5 T and 3 T MRI.

ABSTRACT

OBJECTIVE: To assess the effects of interference screws, which are commonly used to surgically fix an anterior cruciate ligament (ACL) graft in the ACL-deficient knee, and magnetic field strength on cartilage volume and thickness measurements with quantitative magnetic resonance imaging (qMRI). METHODS: Five cadaver knees were imaged using a cartilage-sensitive sequence (T1-weighted water-excitation, three-dimensional (3D) fast low-angle shot) on 1.5T and 3T scanners with and without interference screws implanted. The tibiofemoral articular cartilage was segmented and reconstructed from the magnetic resonance images, and volume and thickness measurements were made on the resulting 3D models. RESULTS: Although several load-bearing regions showed significant differences in volume and thickness between magnet strengths, most showed no significant difference between screw conditions. The medial tibial cartilage showed a mean decrease in volume of 5.9% and 8.0% in the presence of interference screws at 3T and 1.5T, respectively. At 3T and 1.5T, the medial tibial cartilage showed a mean decrease in thickness of 7.0% and 12.0%, respectively, in the presence of interference screws. CONCLUSIONS: Caution should be used when interpreting thickness and volume of cartilage at 3T in the presence of interference screws, particularly in the medial tibial compartment. Additionally, 3T and 1.5T qMRI should not be used interchangeably to assess structural changes in tibiofemoral articular cartilage during longitudinal studies.