Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Radiographic evaluation of severe acetabular bone loss +/– chronic pelvic discontinuity
Background
Pelvic discontinuity is a complex reconstructive challenge characterized by a dissociation of the superior and inferior hemipelvis secondary to fracture or substantial bone loss in the setting of total hip arthroplasty. Potential massive bone loss and motion through the fracture site have led to poor results following revision surgery. , The ability to describe the location and the amount of bone loss is important when considering reconstructing acetabular defects. For this reason, bone loss is commonly classified by the American Academy of Orthopedic Surgeons (AAOS) or by Paprosky classification systems. Pelvic discontinuity is classified as AAOS type IV, and can be associated with Paprosky types IIC, IIIA and IIIB defects. ,
Early identification of pelvic discontinuity is critical for surgical planning. Several studies have identified a high incidence of failure with primary reconstructive techniques in this patient population. , Therefore, most surgeons advocate more advanced techniques for reconstruction when pelvic discontinuity is present. The literature surrounding pelvic discontinuity primarily focuses on outcomes following various surgical reconstructive options. There are very few studies that focus primarily on radiographic identification. Commonly, the diagnosis of pelvic discontinuity can be made based on a standard radiographic assessment. , In some instances, oblique views may be useful in identifying more subtle pelvic discontinuity. Advanced imaging with the use of computed tomography (CT) has demonstrated mixed results in identifying pelvic discontinuity but can be beneficial for further delineation of bone loss, surgical planning, and designing custom implants. , , The following chapter will discuss the radiographic evaluation of patients with a suspected chronic pelvic discontinuity.
Radiographic classification of acetabular bone loss (please see Chapter 2 for further detail)
Acetabular bone loss is predominantly classified based on one of the two following classification systems: the AAOS Classification System and Paprosky classification. , Both radiographic classification systems are based on an assessment of bone loss identified on an anteroposterior (AP) pelvis radiograph. Like the AAOS classification, the Paprosky classification localizes the position of acetabular bone loss. In addition, the Paprosky classification also describes the location of the cup and the support that the anterosuperior and posteroinferior columns will provide during the reconstruction. Therefore, some surgeons advocate this system as a better method for describing acetabular bone loss because it better guides reconstructive options. ,
Pelvic discontinuity is a unique type of bone loss characterized by dissociation of the superior and inferior hemipelvis. The AAOS classification for pelvic discontinuity is type IV and is subclassified: type IVa (with a cavitary or mild segmental bone loss), type IVb (with a large segmental or combined defect), or type IVc (in a previously irradiated pelvis). , The Paprosky classification does not have a distinct category for pelvic discontinuity. , Therefore, a thorough evaluation of preoperative radiographs is necessary to identify pelvic discontinuity as it often requires a substantial shift in the reconstructive strategy employed.
Anteroposterior radiographs
An AP pelvis radiograph is obtained by aiming the image toward the middle of the line connecting the upper symphysis pubis and anterior-superior iliac spine. The image should include the entire pelvis and demonstrate symmetric obturator rings and iliac wings, and the coccyx should be centered over the pubic symphysis. Several radiographic features are specific to pelvic discontinuity and can be identified on an AP pelvis radiograph. These radiographic findings have been noted in numerous studies and include some combination of the following: 1. a visible fracture line through the ilioischial line, 2. medial migration of the inferior hemipelvis, and 3. obturator ring asymmetry ( Fig. 3.1 ). , , In a retrospective study of 133 patients revised for pelvic discontinuity, the AP view identified medial migration of the inferior hemipelvis in 126 patients (95%), the fracture line was visible in 116 patents (87%), and obturator ring asymmetry was present in 114 patients (86%). It was noted that only 70% of patients presented with all three radiographic features concomitantly. Due to the necessity for advanced reconstructive techniques required for pelvic discontinuity, additional radiographic images may be necessary.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here