Routine radiographic series has long been the standard evaluation for detecting radiolucent lines and subsequent glenoid loosening. However, the accuracy of radiographs for measurement of radiolucent lines has been debated because differences in patient positioning and individual variations in glenoid version can produce incomparable serial radiographs, making assessment of the bone-cement interface difficult (19,37,38). Although fluoroscopy and computerized tomography (CT) both may improve the accuracy of evaluating the bone-implant interface (40,41), the senior author feels that anteroposterior (AP) and axillary views can be considered as accurate when the outline of the glenoid component can be seen in profile with sharp edges on both views. With increasing glenoid rotation, the accuracy of determining the size and presence of lucent lines is decreased. Some authors suggest that all radiographs be made within 10 degrees of neutral to allow accurate assessment of radiolucent lines about the glenoid (38).

Radiolucent lines found at the bone-cement interface of the glenoid component have been a common finding. Reported rates range from 12% to 94% (4,6,16, 17, 18, 19, 20, 21, 22, 23). The significance, the location, and the size of radiolucent lines have long been a controversial topic (10,19,24). Although longer term follow-up has correlated an increased incidence of radiolucent lines with component loosening and symptoms (4,18,20,23,25, 26, 27), others found no relation between the incidence of radiolucent lines to symptomatic clinical loosening (4,6,19,28, 29, 30). More recent studies have found an increased incidence of radiolucencies with keel versus pegged components (36). Although the mere presence of a radiolucent line does not itself signal component loosening, the progressive widening of radiolucent lines on serial radiographs likely does (4,20,26,28,31,32). Radiographic loosening has in the past been defined as a line that is greater than 2 mm wide at the bone-cement interface, or overall progressive radiolucency (Fig. 4-1) (4,6,24,33,34). Collectively, most studies do agree that operative technique, glenoid preparation, and cementing protocol are all important surgical factors in avoidance of radiolucent lines. However, no definitive protocol has been delineated. Early techniques for placing glenoid components generally have used manual cement pressurization, with no specifically designed instruments, and resulted in a high incidence of radiolucent lines. Modern techniques for
pressurizing the cement have been developed using specifically designed instruments, which can decrease the incidence of immediate radiolucent lines (35). However, a study in 2002 still described a 94% incidence of radiolucent lines (36). The senior author has helped to develop a specific protocol for glenoid resurfacing using modern instrumented cement pressurization. This technique, which will be described in detail, when compared to the previous manual packing technique, has been found to reduce the overall incidence of radiolucent lines for both keeled and pegged components. Furthermore, when comparing components that were implanted with the new cementing technique, pegged components appeared to have fewer radiolucent lines than keel components. This finding has also been confirmed in a previous study (36), yet it is uncertain why this may be. This may be related to the geometry of the peg component, which may allow for a more precise fit, or the rounded design of pegs, which may make it difficult to visualize a clear border; possibly it could signify better pressurization of the cement in a smaller space. Still, both keeled and pegged components placed with instrumented pressurization techniques resulted in a low incidence of radiolucent lines; thus the senior author feels that either component still can be used based on preference. Although long-term follow-up is not yet available, the hope is that the reduction of radiolucent lines will also decrease glenoid loosening and improve overall component survival (Fig. 4-2).

A major technical factor limiting the use of glenoid components has been glenoid bone stock deficiency. Initial assessment of bone deficiency can be made on routine radiographs of the glenohumeral joint. A true AP of the glenohumeral joint, an axillary, and a scapular lateral are the standard radiographs obtained in preparation for a shoulder arthroplasty. The axillary can best evaluate posterior glenoid wear; however, true asymmetry at times is difficult to ascertain. Thus, if there is significant asymmetry or the bony wear pattern is unclear, a CT scan can be obtained.