A 73 year-old right-hand-dominate male who originally underwent a right total shoulder replacement at an outside hospital approximately 18 months prior to presentation with pain and limited function. Physical exam revealed pseuodoparalysis with attempted elevation and anterosuperior escape. Radiographs show superior and anterior subluxation (Fig. 19.6a, b), and MRI showed subscapularis dehiscence with retraction to the coracoid (Fig. 19.7) and fatty infiltration of the muscle belly.

Patient underwent conversion of his total shoulder replacement to a reverse shoulder arthroplasty (Fig. 19.8). Four years later the patient now has 150° of forward flexion, 15° of external rotation, and internal rotation to the back pocket all with minimal pain.

Rotator cuff tears can be assessed radiographically by observing superior migration of the humeral head and measuring a reduction of the acromio-humeral distance. However, this measurement can be imprecise because it varies according to the projection, size, and sex of the patient. Instead, Skirving [30] advocated the importance of the continuity of the scapulohumeral line (analogous to Shenton’s line in the hip) on a true AP of the shoulder taken with the arm in neutral or external rotation. When there is a break in this line, it is a more sensitive indicator of superior migration of the humeral head and, therefore, of rotator cuff tears. Despite these findings, plain radiographs have limited ability to assess the integrity of the cuff, the quality of the muscle, and the degree of retraction of a torn tendon.

Consequently, MRI has been relied upon to provide a more accurate diagnosis in the face of clinical and conventional imaging limitations [63]. MRI, however, presents its own particular set of imaging challenges in shoulder arthroplasty due to the magnetic susceptibility generated by the implant resulting in local field distortions that obscure the regional structures. The intensity of the susceptibility artifact is a function of the relative ferromagnetism of the components, with titanium being less ferromagnetic (and thus causing less artifact) than cobalt-chrome alloy components, as well as the orientation of the components relative to the external magnetic field. Additionally, the eccentric location of the shoulder relative to the isocenter of the imaging bore and the large spherical component increase the susceptibility artifact of shoulder arthroplasty when compared to knee or hip arthroplasty [63, 64].

Modifications in conventional fast spin echo techniques have improved visualization of the soft tissues around implants. In an MRI study of 42 painful shoulder arthroplasties, Sperling et al. [63] suggested that MR imaging is a useful tool to determine the integrity of the rotator cuff; however, they found that the lesser tuberosity and glenoid component were obscured by artifact created by the proximal spherical humeral component. Relatively new commercially available pulse sequences, multiacquisition variable-resonance image combination (MAVRIC) and slice-encoding metal artifact correction (SEMAC), can further reduce susceptibility artifact near implants [65–67]. These new pulse sequences rely on conventional imaging techniques and can be used with standard clinical 1.5-T and 3-T MRI hardware.

Early studies have shown that MAVRIC images can detect pathology not visible with standard metal artifact-reduction FSE sequences. Hayter et al. [65] evaluated the quality of MAVRIC images compared with that of metal artifact-reduction FSE images of 27 patients who underwent shoulder arthroplasty. Their findings included significantly improved visualization of the synovium, periprosthetic bone, glenoid osteolysis, and supraspinatus tendon. Importantly, detection of supraspinatus tears was significantly increased with MAVRIC compared with FSE imaging alone (Fig. 19.9a, b). Although the lesser tuberosity and subscapularis footprint often remain obscured, the muscle tendon junction and its muscle belly are typically visualized and should be carefully evaluated for failure, as this is a common cause of anterior instability. Application of MAVRIC or SEMAC to axial images could potentially better elucidate subscapularis tears at the footprint (Fig. 19.7).

By decreasing image distortion and improving visualization of the bone-prosthesis interface, these new metal reduction techniques (MAVRIC/SEMAC) serve to complement conventional FSE images, which ultimately offer higher spatial resolution than MAVRIC images, thus providing greater detail of the visualized soft tissues [65].

Similar to MRI, ultrasound is able to assess periarticular soft tissues without radiation; however, sonography has the added benefits of eliminating interference from the implant and allowing dynamic examinations. Westhoff et al. [68] performed static and dynamic ultrasound examinations on 22 patients, and results were correlated with clinical outcome. Pathologic changes within the supraspinatus and infraspinatus tendons were found in several shoulders. A halo sign around the biceps tendon was detected in seven shoulders (Fig. 19.10). This low-echogenic halo around the biceps tendon correlated well with fluid in the synovial sheath and indicated effusion within the glenohumeral joint according to a study by Rupp et al. [69] Increased intra-articular volume was detected in five patients, two of whom also had a halo sign around the biceps tendon. Subdeltoid bursitis was found in only one shoulder. Loosening of the glenoid during dynamic examination was detected in one shoulder. Pathological findings also correlated well with poorer outcomes, while lack of findings correlated with better outcomes.

Sofka and Adler [57] performed ultrasound examinations on 11 shoulder arthroplasty patients who had clinical suspicion of rotator cuff tear, pain, and decreased range of motion. Sonographic findings included six supraspinatus tendon tears and three infraspinatus tendon tears. Nine patients had biceps tendinosis. The prosthesis did not hinder examination of the rotator cuff in any patient (Fig. 19.11). The authors concluded that sonography is a rapid and reliable method to use for evaluating the periprosthetic soft tissues, including the rotator cuff, in patients who have undergone shoulder replacement. Disadvantages of ultrasound are that it does not give a global picture of the joint and it provides limited evaluation of component loosening [70].

Despite the relatively common use of MRI and ultrasound for evaluation of most soft tissue shoulder abnormalities, CT arthrography can also provide an accurate assessment of the rotator cuff, the capsular-labral-ligamentous structures, and the articular cartilage of the glenohumeral joint [71, 72]. Multi-detector CT (MDCT) is a development that has provided excellent spatial resolution and multiplanar capability, thus markedly improving the diagnostic power of CT arthrography of the shoulder [73]. Some authors [74, 75] prefer MDCT arthrography for imaging patients with shoulder prostheses because the images have minimal artifacts while allowing sufficient assessment of prosthetic and periprosthetic bony and soft tissue abnormalities. Post-processing of volume-rendered 3D CT can also substantially reduce beam-hardening artifacts and can be used to assess hardware integrity [76]. Additionally, joint fluid can be aspirated during the intra-articular administration of contrast medium and sent for culture and sensitivity testing if clinical suspicion of infection warrants [77]. General indications for MDCT arthrography pertain to the inability to perform MRI or failure of MRI to adequately evaluate the shoulder. For example, indications include the presence of metal hardware close to the joint, the presence of MRI-incompatible implanted medical devices, and a history of claustrophobia. In patients who have undergone shoulder surgery, MDCT arthrography has been found to be more accurate than nonarthrographic MRI [78]. However, to date there has not been a direct comparison of MDCT arthrography and MR arthrography.