Magnetic Resonance Imaging of Cartilage Repair: A Review

Abstract

Articular cartilage lesions are a common pathology of the knee joint, and many patients may benefit from cartilage repair surgeries that offer the chance to avoid the development of osteoarthritis or delay its progression. Cartilage repair surgery, no matter the technique, requires a noninvasive, standardized, and high-quality longitudinal method to assess the structure of the repair tissue. This goal is best fulfilled by magnetic resonance imaging (MRI). The present article provides an overview of the current state of the art of MRI of cartilage repair. In the first 2 sections, preclinical and clinical MRI of cartilage repair tissue are described with a focus on morphological depiction of cartilage and the use of functional (biochemical) MR methodologies for the visualization of the ultrastructure of cartilage repair. In the third section, a short overview is provided on the regulatory issues of the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) regarding MR follow-up studies of patients after cartilage repair surgeries.

Keywords: articular cartilage; cartilage repair; glycosaminoglycans; knee; magnetic resonance imaging.

Figure 1.

Conventional axial proton density fast spin-echo (PD FSE) sequence (TR/TE: 2400/28) with ultra-high resolution (512 × 512; 12 cm; slice thickness: 2 mm) of a 17-year-old male patient 3 months after matrix-associated autologous chondrocyte transplantation (MACT) of the patella. The double-layered scaffold is still visible.

Figure 2.

High-resolution, isotropic, 0.5 × 0.5 × 0.5-mm fat-suppressed 3-D proton density (PD) SPACE sequence (TR/TE: 1500/34) to assess postoperatively the cartilage repair tissue 6 months after microfracture (arrows, sagittal) (a), the position and orientation after anterior cruciate ligament surgery (coronal) (b), and the menisci (axial) (c) in a 30-year-old male patient using multiplanar angulated reconstruction from one isotropic data set.

Figure 3.

Conventional sagittal proton density fast spin-echo (PD FSE) sequence (TR/TE: 2400/28) with ultra-high resolution (512 × 512; 12 cm; slice thickness: 2 mm) of a 28-year-old male patient 24 months after matrix-associated autologous chondrocyte transplantation (MACT) of the medial femoral condyle shows a partial delamination (incomplete integration of the anterior cartilage and bone interface) of the MACT (arrow).

Figure 4.

Conventional axial proton density fast spin-echo (PD FSE) sequence (TR/TE: 2400/28) with ultra-high resolution (512 × 512; 12 cm; slice thickness: 2 mm) of a 36-year-old female patient 12 months after matrix-associated autologous chondrocyte transplantation (MACT) of the medial femoral condyle. Moderate hypertrophy of the repair tissue is seen.

Figure 5.

Dual flip angle excitation pulse 3-D gradient-echo (GRE) sequence (TR/TE: 15/3.94) (320 × 320; 16 cm; slice thickness: 3 mm). A flip angle of both 4.6° and 26.1° was used. The acquisition of 22 slices took 1 minute and 53 seconds. The sequence was performed before and after the intravenous application of ionic Gd-DTPA²⁻. In a 23-year-old male patient 22 months after matrix-associated autologous chondrocyte transplantation (MACT), the repair tissue shows significantly lower T1 values and thus lower glycosaminoglycan (GAG) content compared with normal hyaline cartilage. This is well demonstrated on the postcontrast T1 map but cannot be differentiated on the precontrast T1 map.

Figure 6.

Axial multi-echo (a) spin-echo T2 (TR/TE: 1200/12.9, 25.8, 38.7, 51.6, 65.5, 77.4; flip angle: 180°) sequence and (b) gradient-echo (GRE) T2* (600/5.7, 9.8, 14.0, 18.1, 22.2, 26.4; flip angle: 20°) sequence with identical high in-plane resolution (384 × 384; 16 cm; slice thickness: 3 mm) visualizing a 29-year-old female patient 24 months after matrix-associated autologous chondrocyte transplantation (MACT) (arrows) within the patella.

Figure 7.

Axial 3-D magnetization transfer (MT)–weighted images of a 17-year-old male patient 3 months after matrix-associated autologous chondrocyte transplantation (MACT) of the patella. MT-saturated (a) and MT-free (b) images and the corresponding MT contrast (MTC) map (c). The MTC map shows clearly lower MTC ratio within the repair tissue (arrows).

Figure 8.

Axial diffusion-weighted images of a patient 24 months after matrix-associated autologous chondrocyte transplantation (MACT) (arrows) of the patella using a high-resolution, 3-D, balanced, steady-state gradient-echo pulse sequence (3-D diffusion-weighted reversed Fast Imaging with Steady State Precession [DW-PSIF]) without (a) and with a diffusion gradient of 130 T*ms*m⁻¹ in 3 directions, slice (b), phase (c), read (d), resulting in an apparent diffusion coefficient (ADC) map (e) furthermore based on a T1 map and given T2 values. A clearly higher diffusivity of the repair tissue in contrast to the healthy surrounding cartilage is visible.