MR arthrography, with the injection of intra-articular gadolinium, is used by many institutions to better evaluate the dynamic and static stabilizers of joints, most commonly the shoulder and hip. MR arthrography of the shoulder is frequently advocated to differentiate tendinosis from partial or full-thickness rotator cuff tears (Stetson et al. 2005) as well as labral pathology of the shoulder (Major et al. 2011) and hip (Sutter et al. 2014). It has been our experience that noncontrast MR techniques, with optimized spatial resolution and fluid contrast, can reliably and accurately demonstrate both partial thickness rotator cuff tears and labral tears of the shoulder (Connell et al. 1999; Gusmer et al. 1996) and hip (Mintz et al. 2005). This eliminates the potential, albeit low, risk of an adverse reaction to gadolinium and added cost while maintaining the throughput of each magnet (Hash and Potter 2012).

Perfusion imaging, on the other hand, requires intravenous administration of gadolinium. Dynamic contrast-enhanced MRI techniques can be used to confirm the suspicion of avascular necrosis of the scaphoid in the setting of nonunion (Ng et al. 2013) or of the femoral head following traumatic posterior hip subluxation or dislocation.

Depending on the type of injury in question and body part, specific modifications to routine protocols are made at the radiologist’s discretion. For example, when the clinical question is the presence and/or stability of an osteochondral lesion or chondral shear injury of the talar dome, a straight coronal, cartilage-sensitive sequence is performed in addition to the routine oblique coronal sequence (Fig. 4.2).

When evaluating injuries to the chest and abdominal wall and underlying structures, e.g., the external oblique, pectoralis major, or latissimus dorsi, imaging planes orthogonal to the anatomic structure of clinical concern are obtained (Fig. 4.3). Orthogonal planes are also used when structures are in nonanatomic alignment; e.g., when imaging a patient with fixed flexion following an elbow dislocation, 2 FSE moderate TE axial sequences, 1 perpendicular to the axis of the humerus, and 1 perpendicular to the axis of the ulna are prescribed. In addition, the coronal sequence should be parallel to the axis of the ulna to evaluate the collateral ligaments (Fig. 4.4).

MRI provides the necessary high spatial resolution and soft tissue contrast to evaluate small joints with complex anatomy, such as the wrist. Morphological changes seen on MRI correlating to a patient’s clinical presentation can indicate injuries to the interosseous intercarpal ligaments and triangular fibrocartilage complex.

Another advantage of MRI lies in its ability to provide a large field of view of the area of concern. As such, clinically unsuspected entities based on patient history and physical examination, which are subjective and sometimes nonspecific, can be diagnosed (Fig. 4.5). For example, when imaging the hip, it is important to routinely obtain large field-of-view coronal STIR and axial intermediate-weighted FSE sequences, which afford visualization of the entire osseous pelvis, including the sacrum, as well as intrapelvic structures, such as the ovaries and inguinal region, pathologic conditions of which may refer pain to the hip and/or groin area.

Due to its inherent high soft tissue contrast capabilities, MRI is particularly sensitive for evaluating cartilage injury and wear. For example, MRI can detect surface and basilar delamination in the setting of femoroacetabular impingement, not infrequently diagnosed in the elite athlete with hip and groin pain (Gold et al. 2012). In the setting of an acute injury, it can identify whether a chondral shear has occurred and, if so, the integrity and location of the displaced chondral fragment. MRI aids in preoperative planning for cartilage repair, in which lesion size and 3D joint geometry are important determinants of the type of repair to be performed and of the potential osteochondral donor site, particularly in the case of autologous osteochondral transplantation. MRI also functions as a noninvasive, objective means of long-term monitoring following cartilage repair surgery by assessing percent fill, morphology and signal intensity of the repair tissue, adverse synovial reaction, and the integrity of the underlying subchondral bone (Hayter and Potter 2011). Quantitative MRI techniques, such as T2 mapping to assess collagen orientation (Xia et al. 2001), and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) (Williams et al. 2004) and T1rho (Wheaton et al. 2005), to assess proteoglycan content depletion, provide more objective measurements of repair cartilage ultrastructure and integrity.

In adolescent athletes, a 3D, fat-suppressed T1-weighted gradient recalled echo physeal-sensitive sequence is obtained to evaluate the degree of skeletal maturity. This is particularly helpful in the setting of a complete anterior cruciate ligament (ACL) tear. Orthopedic surgeons will often perform a physeal-sparing ACL reconstruction to prevent growth arrest and use either allograft or the iliotibial band, rather than autologous hamstring or patellar tendon, to restore anterior-posterior stability and rotational control in prepubescent adolescents (Fabricant et al. 2013) (Fig. 4.6).

A physeal-sensitive sequence is also valuable when evaluating little league shoulder, i.e., a chronic type I Salter-Harris fracture of the proximal humeral physis most commonly seen in adolescent baseball throwers (Fig. 4.7). MRI will demonstrate irregularity, sclerosis, and widening of the lateral physeal margin, preferentially affecting the metaphyseal side. Physeal-sensitive MR sequences, which are amenable to semiautomated segmentation and 3D modeling, can also be obtained to accurately quantify the volume of physeal interruption and illustrate its geometry following fracture involving the physis (Lurie et al. 2014) (Fig. 4.8).

While the focus of most sports imaging is on soft tissue structures, peripheral nerves are often involved, particularly with high-velocity injuries. In the setting of a high-velocity mechanism, such as a posterior knee dislocation resulting in a posterolateral corner injury, the common peroneal nerve is frequently affected, with palsy of the nerve seen in 25 % of all dislocation cases in 1 series (Niall Et al. 2005) (Fig. 4.9).