Nicolae V. Bolog

MR imaging of the posterolateral corner of the knee

The posterolateral corner (PLC) is a complex functional unit, consisting of several structures, which is responsible for posterolateral stabilization. The PLC is not consistently defined in the literature. However, most descriptions include the popliteal tendon (PT), the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the posterolateral capsule, which is reinforced by the arcuate ligament (AL) and the fabellofibular ligament (FFL). Knowledge of PLC anatomy, including its variations, and understanding of the biomechanics is important for correct diagnosis of PLC injuries. An overlooked PLC injury can result in chronic instability, chronic pain, and, eventually, in secondary osteoarthritis. Damage to the PLC also has an adverse effect on the outcome of cruciate ligament repair. Isolated lesions of the PLC are rare. PLC lesions are typically associated with injuries of the cruciate ligaments, the menisci, bone and soft tissue. In the acute phase, clinical findings can be difficult to interpret due to pain and swelling. Magnetic resonance (MR) imaging potentially demonstrates the entire spectrum of PLC injuries and associated lesions of the knee, including those that may be overlooked during clinical examination or arthroscopy.

Muscles and Tendons

The muscles groups around the knee have an antigravity role and offer knee stabilization during standing position and stability in a variety of different positions. They can be classified based on their anatomic location as well as on their function. The muscles of the thigh and lower leg are comprised of compartments defined as distinct anatomical spaces bordered by fascia or bone. The knowledge of the anatomical bounders of the compartments is important especially in describing the extension of the soft tissue tumors (e.g., extra- or intracompartmental). The anterior compartment of the thigh is represented by the quadriceps muscle, the sartorius, and the tensor fascia latae. The posterior compartment includes the hamstring muscles (the semitendinosus, the semimembranosus, and the biceps femoris). The medial compartment contains the gracilis and the adductor muscles. The gastrocnemius muscles are included together with the soleus muscle in the superficial posterior compartment of the lower leg.

Articular Cartilage and Subchondral Bone

The knee articular cartilage is a hyaline cartilage composed of water (65–80 %), collagen (10–20 %, with type II collagen representing 90–95 % of the network), proteoglycans (10–20 %), and chondrocytes (1–5 %) [1]. Morphologically there are four cartilage zones with different composition, structure, and function. The superficial zone is the thinnest zone of the cartilage (10–20 % from the cartilage thickness) and is covered by synovial fluid. It is mainly composed of collagen fibers oriented parallel to the articular surface and provides shear strength. The transitional zone is the thickest zone (40–60 % from the cartilage thickness) and contains randomly oriented fibers, and its role is to distribute stress uniformly [2]. The deep or the radial zone (30 % of the cartilage thickness) contains the largest diameter of collagen fiber. The fibers are oriented perpendicularly to the articular surface, and its role is to anchor the cartilage to the subchondral bone [2]. The calcified cartilage zone (5 % of the cartilage thickness), the deepest zone of the cartilage, is a mineralized thin area and represents a shock absorber along the subchondral bone [1].

Getting Started with Magnetic Resonance Neurography

Abstract This article provides a review of magnetic resonance neurography (MRN) and how to get started. It explains step by step how to establish MRN at an institution: how to set up MRN protocols, how to train technicians, what a report needs to contain, and how relevant findings should be communicated to the referring physician. Advanced imaging techniques such as diffusion tensor imaging are only briefly discussed at the end of the article because most of those techniques are difficult for beginners and are still not considered standard in the clinical routine.

Modic Type 1 Changes: Detection Performance of Fat-Suppressed Fluid-Sensitive MRI Sequences

PURPOSE To assess the performance of fat-suppressed fluid-sensitive MRI sequences compared to T1-weighted (T1w) / T2w sequences for the detection of Modic 1 end-plate changes on lumbar spine MRI. MATERIALS AND METHODS Sagittal T1w, T2w, and fat-suppressed fluid-sensitive MRI images of 100 consecutive patients (consequently 500 vertebral segments; 52 female, mean age 74 ± 7.4 years; 48 male, mean age 71 ± 6.3 years) were retrospectively evaluated. We recorded the presence (yes/no) and extension (i. e., Likert-scale of height, volume, and end-plate extension) of Modic I changes in T1w/T2w sequences and compared the results to fat-suppressed fluid-sensitive sequences (McNemar/Wilcoxon-signed-rank test). RESULTS Fat-suppressed fluid-sensitive sequences revealed significantly more Modic I changes compared to T1w/T2w sequences (156 vs. 93 segments, respectively; p < 0.001). The extension of Modic I changes in fat-suppressed fluid-sensitive sequences was significantly larger compared to T1w/T2w sequences (height: 2.53 ± 0.82 vs. 2.27 ± 0.79, volume: 2.35 ± 0.76 vs. 2.1 ± 0.65, end-plate: 2.46 ± 0.76 vs. 2.19 ± 0.81), (p < 0.05). Modic I changes that were only visible in fat-suppressed fluid-sensitive sequences but not in T1w/T2w sequences were significantly smaller compared to Modic I changes that were also visible in T1w/T2w sequences (p < 0.05). CONCLUSION In conclusion, fat-suppressed fluid-sensitive MRI sequences revealed significantly more Modic I end-plate changes and demonstrated a greater extent compared to standard T1w/T2w imaging. KEY POINTS · When the Modic classification was defined in 1988, T2w sequences were heavily T2-weighted and thus virtually fat-suppressed.. · Nowadays, the bright fat signal in T2w images masks edema-like changes.. · The conventional definition of Modic I changes is not fully applicable anymore.. · Fat-suppressed fluid-sensitive MRI sequences revealed more/greater extent of Modic I changes.. CITATION FORMAT · Finkenstaedt T, Del Grande F, Bolog N et al. Modic Type 1 Changes: Detection Performance of Fat-Suppressed Fluid-Sensitive MRI Sequences. Fortschr Röntgenstr 2018; 190: 152 - 160.

Lateral Collateral Ligament (LCL) and Posterolateral Corner (PLC)

The posterolateral corner (PLC) of the knee is a complex functional unit consisting of several important ligaments and is responsible for posterolateral stabilization of the joint [1]. There is some variability in the definition of the posterolateral corner (PLC) in the literature, but most descriptions include the lateral collateral ligament (LCL), the anterior oblique band (AOB), the popliteal tendon (PT) with the anterolateral ligament (ALL), the popliteomeniscal fascicles, and the popliteofibular ligament (PFL), as well as the posterolateral capsule including the arcuate ligament (AL) and the fabellofibular ligament (FFL) [1]. These structures are reinforced by the biceps femoris tendon and the iliotibial tract.

Posterior Cruciate Ligament (PCL) and Meniscofemoral Ligaments

The posterior cruciate ligament (PCL) is the strongest ligament of the knee. It is intra-articular and extrasynovial. The PCL arises from the anterolateral surface of the medial femoral condyle and reaches the posterior intercondylar area of the tibia. The femoral origin is more anterior than that of anterior cruciate ligament (ACL), and in contrast to the ACL, the PCL is larger at its femoral origin than at its tibial insertion [1]. The tibial attachment is extra-articular, and it is approximately 1 cm distal to the plane of the articular surface [2]. PCL is the primary restraint to posterior tibial translation relative to the femur and becomes more important in preventing distraction of the joint as the knee reaches higher degrees of flexion [3, 4].

Patella, Femoropatellar Joint, and Infrapatellar Fat Pad

The patella is the largest sesamoid bone in the body and is part of the extensor mechanism of the knee together with the quadriceps muscle and tendon, patellar tendon, and patellar retinaculum [1]. The bone has two surfaces, three borders, a base, and an apex. The vastus intermedius and the rectus femoris tendons attach to the base (syn. proximal pole) of the patella and the vastus medialis and vastus lateralis to the medial and, respectively, lateral border. The quadriceps muscle is the active stabilizer of the patella. The apex (syn. distal pole) of the patella is extra-articular and is the site of the attachment of the patellar tendon. The patellar tendon, the major passive stabilizer of the patella, inserts distally to the tibial tuberosity and has a length of approximately 4–6 cm. The thickness of the tendon is 5–6 mm and the width is 3 cm at the patellar insertion and 2.5 cm at the tibial insertion [2]. Normal tendons have uniformly low signal intensity on all MRI sequences and display distinct margins [3]. The quadriceps muscle and tendon, patellar tendon, patella, and patellar retinaculum represent the extensor mechanism of the knee [1].

Medial Collateral Ligament (MCL) and Medial Supporting Structures

The medial supporting structures of the knee can be divided into three layers [1]. Layer 1 consists of the deep crural fascia that is seen on MR images as a thin low-intensity structure on all MR sequences (Fig. 3.1). Anteriorly, the deep crural fascia joins the superficial layer of MCL into the medial patellar retinaculum that appears on MR images as a low-signal-intensity structure that extends from the vastus medialis muscle to the tibia inferiorly (Fig. 3.2) [2]. In some cases, two band-like structures may be seen [2].

Synovium and Capsule

The articular capsule of the knee consists of a thick outer layer, the fibrous capsule, and a thinner inner layer, the synovial membrane or the synovium.