DOI: 10.1148/rg.283075085
RadioGraphics 2008;28:771-786
© RSNA, 2008
Total Hip Arthroplasty in Patients with Bone Deficiency of the Acetabulum1
Robert H. Choplin, MD,
Christopher N. Henley, MD,
Eric M. Edds, MD,
William Capello, MD,
James L. Rankin, RT, and
Kenneth A. Buckwalter, MD
1 From the Departments of Radiology (R.H.C., E.M.E., J.L.R., K.A.B.) and Orthopedic Surgery (C.N.H., W.C.), Indiana University School of Medicine, 550 N University Blvd, Room 0279, Indianapolis, IN 46202-5253. Recipient of a Certificate of Merit award for an education exhibit at the 2005 RSNA Annual Meeting. Received April 30, 2007; revision requested August 22 and received October 29; accepted November 2. All authors have no financial relationships to disclose.
Address correspondence to R.H.C. (e-mail: rchoplin{at}iupui.edu).
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Abstract
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Total hip replacement (THR) requires revision in only a minority of cases (approximately 17% of prosthetic hips fail), but when THR failures occur there may be significant acetabular bone deficiency. There is a variety of surgical hardware and strategies available to address this problem. The causes of primary THR revision include aseptic loosening or particle disease, infection, recurrent dislocation, implant failure, periprosthetic fracture, and leg length discrepancy. Almost all patients who need THR revision undergo a standard radiographic evaluation of the pelvis and hip. In general, CT is an excellent tool for evaluating loosening of the prosthesis caused by either mechanical reasons or infection, and MR imaging is best suited for evaluating the soft tissues surrounding the prosthesis. Nuclear medicine studies are performed when results of CT and MR imaging are inconclusive. When patients are evaluated for revision THR, radiologists must check for acetabular cup loosening, the amount and type of bone stock loss, the amount of component migration, and the presence or absence of liner wear. Before revision hardware is placed, bone stock loss must be repaired, either by using bone grafting or by placing accessory acetabular hardware such as cups, rings, or cages. The long-term success of revision acetabular surgery varies; there is acetabular cup presence at 5 years after surgery in 60%–94% of cases. Complications include postoperative infections, repeat liner wear, bone graft failure, periprosthetic or prosthetic fractures, dislocation, vascular injury, and nerve injury.
© RSNA, 2008
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Introduction
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Total hip replacement (THR) is a common procedure that is performed increasingly often. Approximately 235,000 THR procedures were performed in the United States in 2005 (1). Although most patients have satisfactory long-term stability, approximately 17% of prosthetic hips fail, thus requiring revision (2). This failure is attributed to patients being more active and having hip replacements earlier and more frequently than in the past.
Frequently, when hip prosthesis revision is undertaken, there is significant acetabular bone deficiency present; this clinical setting presents one of the most challenging circumstances in hip surgery. There is a variety of surgical hardware and strategies available to address this problem. To provide a comprehensive understanding of hip prosthesis revision in the setting of acetabular bone deficiency, we review the relevant imaging features, the surgical treatment options, satisfactory postsurgical appearance, and some complications of the various procedures. The contributions of conventional radiography, computed tomography (CT), and magnetic resonance (MR) imaging are also presented.
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Total Hip Replacement: Causes of Revision
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When a primary hip replacement requires revision, the acetabular component alone is involved 40% of the time. Both components (acetabular and femoral stem) require revision in 37% of cases, and the femoral stem alone requires replacement in 22% of cases (3). 
The causes of primary THR revision include aseptic loosening or particle disease (70%–94% of cases); infection (3%–9%); recurrent dislocation (2%–10%); and implant failure, periprosthetic fracture, and leg length discrepancy (1%) (3,4). The pathophysiologic processes that lead to reoperation in total hip replacements have been recently reviewed (5).
Patients who undergo revision arthroplasty most commonly present with pain in the hip, back, or thigh. A large number of etiologies may be present and should be systematically evaluated (6). These causes may be categorized as either intrinsic (those relating to the hip prosthesis itself) or extrinsic (those relating to other bodily systems such as the spine or vascular system). Almost all patients who are reevaluated undergo a standard radiographic examination of the pelvis and hip. The use of subsequent studies such as CT, MR imaging, ultrasonography, and nuclear medicine is dictated by the patient’s exact symptoms and results of the physical examination. Although CT and MR imaging may exhibit artifacts related to the prosthesis, current imaging techniques may minimize these artifacts, and studies that reveal specific diagnostic information are frequently achieved. In general, CT is an excellent tool for evaluating loosening of the prosthesis caused by either mechanical reasons or infection. MR imaging is best suited for evaluating the soft tissues surrounding the prosthesis. In our experience, although nuclear medicine studies are still commonly performed, they are used when results of CT and MR imaging are inconclusive.
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Acetabular Defect Classification
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There are two major classifications of bone stock loss associated with a previously placed acetabular cup. The American Academy of Orthopedic Surgeons (AAOS) (7) developed its acetabular defect classification system to improve uniformity in how acetabular revisions are reported (Table 1; Figs 1, 2). Although the appropriate classification category may be suggested by findings seen at radiography or advanced imaging, the final determination of the defect type is made at surgery. The Paprosky acetabular defect classification system (4) was subsequently proposed and includes assessments made both by using radiologic findings and at surgery. In addition, this classification system includes treatment recommendations (Table 2; Figs 1, 2).
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Figure 1. Right anterior oblique views of a three-dimensional volume-rendered innominate bone illustrate both the AAOS and the Paprosky acetabular defect classification systems. The blue-shaded areas represent the affected region of bone. Although the two classification systems do not exactly overlap, they are similar enough that the images reflect the indicated categories for each classification. In general, the higher the classification category is, the more extensive the involvement of the acetabulum and surrounding bone. A = AAOS cavitary, Paprosky type 1 or type 2A; B = AAOS segmental, Paprosky type 2B; C = AAOS combined deficiency, Paprosky type 3A; D = AAOS combined deficiency, Paprosky type 3B.
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Figure 2. AAOS acetabular pelvic discontinuity and Paprosky type 3A and 3B are seen in an innominate bone from an anteroposterior view (A), right anterior oblique view (B) , and lateral view (C).
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Imaging the THR
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Primary THR: Normal Radiographic Appearance
When there is no cement mantle, there should be a minimal or no area of lucency at the bone-prosthesis interface (8). The center of the prosthetic head should be at the same level as the center of the femoral head on the contralateral side. The acetabular prosthesis should be tilted so that there is 30°–50° abduction on the anteroposterior view. The abduction angle is the angle between a line drawn between the ischial tuberosity tips and another line between the most superior and inferior acetabular cup rims (Fig 3a). The Kohler line is a line drawn from the most upper-lateral margin of the iliopectineal line straight downward through the medial margin of the inferior ischium (Fig 3b). There should be minimal or no encroachment on this line by the prosthesis. The acetabular cup should align with the bony acetabulum on a Lauenstein lateral view (Fig 3c) or there should be approximately 5°–25° anteversion on a surgical lateral view. Any screws that have been placed should be unbroken and should have no significant zones of lucency surrounding them. Acetabular cement may be present, since it is used at the orthopedic surgeon’s discretion; cement has been used less often over the past decade, as bone ingrowth cups have been developed and become more common. When present, the cement should be continuous around the cup and contiguous with the metal. There should be no or only a thin (< 1.5-mm) zone of lucency around the cement mantle.
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Figure 3a. Normal radiographic appearances of primary THR in a 57-year-old woman with osteoarthritis. After surgery, the center of hip rotation should be the same as on the contralateral side, there should be minimal or no periprosthetic lucency, the abduction angle (ABC in a) should be 30°–50°, and the screws should be intact. There should be minimal or no encroachment on the Kohler line (K-K in b). The acetabular cup should align with the bony acetabulum on a Lauenstein lateral view (c). Note that the prosthetic rim is parallel to the line drawn from the superolateral acetabular rim (white arrowhead in c) to the posteroinferior acetabular rim (black arrowhead in c). The prosthetic rim may also show 5°–25° anteversion on a surgical lateral view.
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Figure 3b. Normal radiographic appearances of primary THR in a 57-year-old woman with osteoarthritis. After surgery, the center of hip rotation should be the same as on the contralateral side, there should be minimal or no periprosthetic lucency, the abduction angle (ABC in a) should be 30°–50°, and the screws should be intact. There should be minimal or no encroachment on the Kohler line (K-K in b). The acetabular cup should align with the bony acetabulum on a Lauenstein lateral view (c). Note that the prosthetic rim is parallel to the line drawn from the superolateral acetabular rim (white arrowhead in c) to the posteroinferior acetabular rim (black arrowhead in c). The prosthetic rim may also show 5°–25° anteversion on a surgical lateral view.
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Figure 3c. Normal radiographic appearances of primary THR in a 57-year-old woman with osteoarthritis. After surgery, the center of hip rotation should be the same as on the contralateral side, there should be minimal or no periprosthetic lucency, the abduction angle (ABC in a) should be 30°–50°, and the screws should be intact. There should be minimal or no encroachment on the Kohler line (K-K in b). The acetabular cup should align with the bony acetabulum on a Lauenstein lateral view (c). Note that the prosthetic rim is parallel to the line drawn from the superolateral acetabular rim (white arrowhead in c) to the posteroinferior acetabular rim (black arrowhead in c). The prosthetic rim may also show 5°–25° anteversion on a surgical lateral view.
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Preoperative Assessment of Revision THR
Standard Radiography.—
When patients undergo imaging before revision THR, radiologists must check for acetabular cup loosening, the amount and type of bone stock loss, the amount of component migration (medial, lateral, or superior), and the presence or absence of liner wear (Fig 4). Acetabular cup loosening is usually present if there is a periprosthetic radiolucent zone that is 2 mm or wider (especially if progressive widening is noted at serial examinations), a change in the abduction angle of 10° or more on comparison radiographs, or movement of the acetabular component of 6 mm or more (corrected for magnification) (9,10). Small metallic beads (bead shedding) may be identified adjacent to the joint; this finding indicates breakage from the surface of an ingrowth prosthesis. Bone stock loss is identified as regions of periprosthetic lucency and should be assessed with consideration paid to the classifications previously described. Protrusio acetabuli is present if the Kohler line is breached; if the line is only minimally breached, the finding is less important. Liner wear is identified by eccentric location of the prosthetic femoral head within the acetabular cup.
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Figure 4. Revision THR (bone stock loss) in a 44-year-old woman with rheumatoid arthritis and left hip pain who underwent left hip replacements at ages 32 and 35 years and right hip replacements at ages 17, 23, and 40 years. Radiograph shows lucent areas adjacent to the acetabulum (arrowheads), findings that represent cavitary bone stock loss in the supraacetabular ilium, acetabular cavity, superior pubic ramus, and inferior ischium. In addition, there is eccentric location of the prosthetic femoral head in the acetabular component (curved arrow), and the superior pubic ramus is fractured (straight arrow).
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Computed Tomography.—
Radiography is limited in identifying regions of periacetabular osteolysis (11–13). CT has been used to preoperatively evaluate patients who are being considered for revision THR because it has greater sensitivity in the detection of bone stock loss than radiography does. CT has demonstrated bone stock loss in 52% of patients who have had prothestic hips in place for 3.2–13.4 years, whereas bone stock loss was visible on radiographs in only 32% of cases (14,15).
State-of-the-art examinations require the use of multidetector CT. We perform our examinations using 350–450 mAs if one hip replacement is being assessed and 450–600 mAs if there are two. We also use 140 kVp, pitch of less than 0.3, and a medium filter; we reconstruct the images at 1.0-mm section width with 0.5-mm reconstruction increment. We scan from the iliac crest to the tips of the femoral stems and include any area containing cement. In addition to the axial plane, images are reconstructed in the coronal and sagittal planes. When interpreting the examination results, we evaluate for cavitary defects at the acetabular roof and the anterior, medial, and posterior walls; segmental defects at the acetabular rim; lysis of the medial wall or posterior ischial wall; liner wear with resultant eccentric location of the femoral head in the acetabular cup; and percentage of host bone in contact with the acetabular cup (Fig 5). The percentage of host bone in contact with the acetabular cup is estimated by "eyeballing" to the nearest 10%–15%. The regions of bone stock loss are frequently associated with pathways of communication through the acetabular cup at screw hole sites or around the rim of the acetabular cup (16). Some cysts may be present from preexisting degenerative joint disease. These cysts are generally smaller and located at the acetabular roof in contradistinction to the cavities of bone stock loss, which are usually located away from the acetabular roof and are larger.
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Figure 5a. Preoperative CT assessment of the same patient as in Figure 4. Coronal (a) and sagittal (b) multiplanar reformatted CT images show cavitary defects in the acetabulum. Large defects in the anterior wall, roof, and posterior wall (arrowheads); liner wear (eccentric location of the femoral head in the acetabular cup); lysis of the medial wall (arrow in a); and an intact posterior ischial wall (ie, there is no discontinuity) are seen. The estimated percentage of host bone in contact with the cup is 20%. There was also a segmental defect at the anterior wall.
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Figure 5b. Preoperative CT assessment of the same patient as in Figure 4. Coronal (a) and sagittal (b) multiplanar reformatted CT images show cavitary defects in the acetabulum. Large defects in the anterior wall, roof, and posterior wall (arrowheads); liner wear (eccentric location of the femoral head in the acetabular cup); lysis of the medial wall (arrow in a); and an intact posterior ischial wall (ie, there is no discontinuity) are seen. The estimated percentage of host bone in contact with the cup is 20%. There was also a segmental defect at the anterior wall.
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When lysis of the posterior ischial wall is present, we pay particular attention to the possibility of pelvic discontinuity (Fig 6).
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Figure 6a. Preoperative CT assessment of a 61-year-old man with right hip pain and a history of femoral head fracture at age 18 years and primary THR at age 45 years. Coronal (a) and sagittal (b) multiplanar reformatted CT images show posterior cavitary bone stock loss (* in b) with pelvic discontinuity (transverse fracture through the posterior ischium) (arrowhead).
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Figure 6b. Preoperative CT assessment of a 61-year-old man with right hip pain and a history of femoral head fracture at age 18 years and primary THR at age 45 years. Coronal (a) and sagittal (b) multiplanar reformatted CT images show posterior cavitary bone stock loss (* in b) with pelvic discontinuity (transverse fracture through the posterior ischium) (arrowhead).
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MR Imaging.—
MR imaging has been used to evaluate the postoperative prosthetic hip; the imaging parameters must be altered from those used in routine examinations to compensate for the prosthetic metal (17,18). MR parameters used to minimize metallic artifacts include avoiding gradient-echo sequences, using fast spin-echo sequences rather than spin-echo sequences, increasing the acquisition matrix, and increasing the bandwidth per pixel. MR imaging can help to identify regions of osteolysis and heterotopic bone formation, and it may assist in evaluating pelvic neurovascular structures.
Parameters that we use for MR imaging are as follows: field strength, 1.5 T; turbo spin-echo; repetition time, 2540 msec; echo time, 40 msec; frequency, 384; phase, 288; echo train length, 19; bandwidth, 765 Hz per pixel; and frequency orientation, superior to inferior for coronal and sagittal, and anteroposterior for axial (Fig 7).
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Figure 7a. Preoperative MR imaging assessment of an 88-year-old woman who underwent THR 20 years before and now has left hip pain and limited range of motion. Radiograph (a) and coronal (b, c) MR images show heterotopic bone anterosuperior to the acetabulum (arrow). Note the excellent depiction of the medial wall of the acetabulum (arrow in c) despite the proximity of metal.
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Figure 7b. Preoperative MR imaging assessment of an 88-year-old woman who underwent THR 20 years before and now has left hip pain and limited range of motion. Radiograph (a) and coronal (b, c) MR images show heterotopic bone anterosuperior to the acetabulum (arrow). Note the excellent depiction of the medial wall of the acetabulum (arrow in c) despite the proximity of metal.
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Figure 7c. Preoperative MR imaging assessment of an 88-year-old woman who underwent THR 20 years before and now has left hip pain and limited range of motion. Radiograph (a) and coronal (b, c) MR images show heterotopic bone anterosuperior to the acetabulum (arrow). Note the excellent depiction of the medial wall of the acetabulum (arrow in c) despite the proximity of metal.
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Treatment Goals and Options
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The two major goals of revision acetabular surgery are relief of pain and restoration of function (19). The two most important principles of revision surgery are (a) restoration of bone stock and (b) restoration of the hip center of rotation (19,20).
Initially, the degree and type of bone stock loss must be assessed and repaired. This may be accomplished by using bone grafting to repair the defect or by placing accessory acetabular hardware. The success of bone grafting depends on a mechanically stable environment and avoidance of graft overload. If the hip center of rotation is not restored, it may result in altered hip mechanics. This alteration, in turn, may result in a limp, increased risk of dislocation, and increased stress on the acetabular component with possible premature loosening. In general, bone graft with relatively standard metallic prostheses is used for minimal defects, and bulk bone graft with specially designed metallic prosthetic parts is used for large defects.
The long-term success of revision acetabular surgery varies; there is acetabular cup presence at 5 years after surgery in 60%–94% of cases (21–26). Complications include postoperative infections; repeat liner wear, which requires re-revision; bone graft failure; periprosthetic or prosthetic fractures; dislocation; vascular injury; and nerve injury.
Multiple treatment options are available. Because of the extensive array of hardware available to orthopedic surgeons, we are unable to illustrate each component. We have chosen instead to illustrate the different categories of hardware to provide radiologists with the knowledge to understand the reasons that a surgical procedure might be performed on a particular patient. The orthopedic hardware illustrated here reflects the choices of our local surgeons and is not a specific endorsement of the products; there are many manufacturers that make similar or identical products. The principles of surgery and choice of hardware, however, are generally applicable to a wide audience. Because of the complexity of the surgery, there are no surgical series that make direct comparisons of the surgical approaches and hardware options. Each patient’s treatment is individualized based on his or her underlying disease process, previous surgical history, the degree of bone stock loss, and the surgeon’s training and experience.
Bone Graft
When only a small amount of bone is needed, an autograft may be obtained from the patient (19). If larger amounts are required, allograft may be obtained from bone banks, which provide particulate material of varying sizes and bulk graft (Fig 8a). Parts commonly used for bulk graft include the distal femur, the femoral head and neck, or another donor acetabulum (Fig 8b). Graft incorporation of particulate bone is suggested by cross trabeculation at the host-graft interface, bridging new bone, and physiologic remodeling. Major structural grafts can undergo remodeling for years. Graft collapse or resorption, especially in areas of stress transmission, suggests possible failure of the THR.
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Figure 8a. Allograft bone graft materials. (a) Photograph shows cancellous bone chips (4–10 mm) used as a particulate bone graft. (b) Volume-rendered CT scan shows a femoral condyle allograft bone that will be cut into "figure-7" shapes. The graft is then used to repair large regions of bone stock loss. (Fig 8a, courtesy of Biomet, Warsaw, Ind.)
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Figure 8b. Allograft bone graft materials. (a) Photograph shows cancellous bone chips (4–10 mm) used as a particulate bone graft. (b) Volume-rendered CT scan shows a femoral condyle allograft bone that will be cut into "figure-7" shapes. The graft is then used to repair large regions of bone stock loss. (Fig 8a, courtesy of Biomet, Warsaw, Ind.)
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Acetabular Cups
A variety of acetabular cups, rings, and cages are available to repair defects that range from mild to severe. Acetabular cups currently in use are almost always coated with a material to promote bone ingrowth and to improve cup stability. These coating particles markedly increase the surface area of potential bone contact. Two such materials are titanium metal and tantalum metal. Cancellous-Structured Titanium (Zimmer; Warsaw, Ind) is a mix of powdered titanium and titanium metal that has pores and bridges similar to those of bone trabeculae. Trabecular Metal (Zimmer) is an 80% tantalum alloy that also has a microscopic structure similar to that of bone trabeculae (Figs 9, 10).
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Figure 9a. Acetabular cups. (a) Photograph shows two acetabular shells with polyethylene liners and coated with Trabecular Metal. (Courtesy of Zimmer.) (b) Electron microscope view shows Trabecular Metal, which is an 80% tantalum alloy with structural properties similar to those of trabecular bone. The alloy is used as a prosthetic coating.
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Figure 9b. Acetabular cups. (a) Photograph shows two acetabular shells with polyethylene liners and coated with Trabecular Metal. (Courtesy of Zimmer.) (b) Electron microscope view shows Trabecular Metal, which is an 80% tantalum alloy with structural properties similar to those of trabecular bone. The alloy is used as a prosthetic coating.
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Figure 10a. Acetabular revision (standard cup) with a particulate bone graft in a 56-year-old woman with right hip pain who underwent primary THR 20 years before and revision THR 12 years ago. (a) Preoperative radiograph shows that the acetabular cup is malaligned (straight solid white arrow), the screws are fractured (curved arrow), protrusio acetabuli is present (open arrow), the superomedial acetabular wall is destroyed, bead shedding is present (arrowheads), and there is fractured cement (*). The teardrop is a normal finding (black arrow). (b) Radiograph obtained 12 days after surgery shows a 60-mm cup and 80 mL of particulate bone graft material.
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Figure 10b. Acetabular revision (standard cup) with a particulate bone graft in a 56-year-old woman with right hip pain who underwent primary THR 20 years before and revision THR 12 years ago. (a) Preoperative radiograph shows that the acetabular cup is malaligned (straight solid white arrow), the screws are fractured (curved arrow), protrusio acetabuli is present (open arrow), the superomedial acetabular wall is destroyed, bead shedding is present (arrowheads), and there is fractured cement (*). The teardrop is a normal finding (black arrow). (b) Radiograph obtained 12 days after surgery shows a 60-mm cup and 80 mL of particulate bone graft material.
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Acetabular augments are metal accessories that have various shapes and can be placed adjacent to an acetabular cup to repair bone losses (Fig 11). Revision with a new acetabular cup plus bone graft is undertaken for very large bone defects (Fig 12).
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Figure 11a. Acetabular revision (standard cup) with an augment in a 53-year-old woman with osteoarthritis who underwent THR 1 year before. (a) Preoperative radiograph shows that the acetabular cup is malaligned and the cup position is high and lateral (arrowheads). Note the position of the inferior acetabular rim (arrow). (b) Radiograph obtained 3 days after surgery shows a 58-mm Trabecular Metal acetabular cup placed in the normal position of the acetabulum. A 58 x 10-mm augment was placed superolaterally (arrow) to fill the space occupied by the displaced first cup.
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Figure 11b. Acetabular revision (standard cup) with an augment in a 53-year-old woman with osteoarthritis who underwent THR 1 year before. (a) Preoperative radiograph shows that the acetabular cup is malaligned and the cup position is high and lateral (arrowheads). Note the position of the inferior acetabular rim (arrow). (b) Radiograph obtained 3 days after surgery shows a 58-mm Trabecular Metal acetabular cup placed in the normal position of the acetabulum. A 58 x 10-mm augment was placed superolaterally (arrow) to fill the space occupied by the displaced first cup.
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Figure 12a. Acetabular revision (jumbo cup) with a bulk bone allograft in a 64-year-old man who underwent THR 15 years before and had a recent onset of left hip pain. (a) Preoperative radiograph shows that the acetabular cup is malaligned and is displaced high and laterally (white arrowheads). There is major bone stock loss with an absent inferior acetabular rim, teardrop, and absence of a posterior acetabular wall (cf Fig 3 and Fig 11a). The acetabular screws are fractured (black arrowhead). (b) Radiograph obtained 147 days after surgery shows a 66-mm Trabecular Metal acetabular cup placed in the normal location of the acetabulum and a distal femur bulk allograft that fills the space formerly occupied by the acetabular cup (arrows).
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Figure 12b. Acetabular revision (jumbo cup) with a bulk bone allograft in a 64-year-old man who underwent THR 15 years before and had a recent onset of left hip pain. (a) Preoperative radiograph shows that the acetabular cup is malaligned and is displaced high and laterally (white arrowheads). There is major bone stock loss with an absent inferior acetabular rim, teardrop, and absence of a posterior acetabular wall (cf Fig 3 and Fig 11a). The acetabular screws are fractured (black arrowhead). (b) Radiograph obtained 147 days after surgery shows a 66-mm Trabecular Metal acetabular cup placed in the normal location of the acetabulum and a distal femur bulk allograft that fills the space formerly occupied by the acetabular cup (arrows).
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Success rates for acetabular revision increase when the new acetabular prosthetic part contacts at least 50% of the host bone (25). Depending on the amount of bone loss, acetabular revision may be accomplished with a standard-sized cup, a standard cup with an augment, or a jumbo cup. A cup is considered to be jumbo when it exceeds 62 mm for women or 66 mm for men, or it is at least 10 mm larger than the contralateral normal side. Orthopedic hardware manufacturers designate size by the diameter of the cup at its rim.
Acetabular Roof Reinforcement Rings
Acetabular roof reinforcement rings are used when a regular-sized or jumbo acetabular cup will not adequately span the bone defect (Fig 13) (27,28). Initially, reinforcement rings were simple shields made in a saddle shape. Subsequent rings have been constructed with flanges that may be attached to the ilium or ischium. The reinforcement rings are used with cement, and a liner is inserted to receive the prosthetic femoral head (Fig 14). Bone graft may or may not be used as part of the revision process.
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Figure 13a. Noncustom rings for acetabular roof reinforcement. (a) Photograph shows a Müller ring, a device used to reinforce the acetabular roof and medial wall. (b) Photograph shows a Ganz-modified Müller ring, which provides a more substantial cup plus a hook for the obturator foramen. (Courtesy of Zimmer.)
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Figure 13b. Noncustom rings for acetabular roof reinforcement. (a) Photograph shows a Müller ring, a device used to reinforce the acetabular roof and medial wall. (b) Photograph shows a Ganz-modified Müller ring, which provides a more substantial cup plus a hook for the obturator foramen. (Courtesy of Zimmer.)
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Figure 14a. Acetabular revision with roof reinforcement and particulate bone graft in the same patient as in Figure 7. (a) Preoperative radiograph shows that the acetabular cup is malaligned, is displaced superiorly (arrowheads), and has liner wear (note eccentric location of the femoral head in the cup). (b) Radiograph obtained 363 days after surgery shows a Ganz roof reinforcement ring with a new radiolucent liner that was cemented in position (its orientation is identified by a marker ring [arrow]). The particulate bone graft used in the revision has a nearly solid appearance, indicating healing and incorporation of the graft.
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Figure 14b. Acetabular revision with roof reinforcement and particulate bone graft in the same patient as in Figure 7. (a) Preoperative radiograph shows that the acetabular cup is malaligned, is displaced superiorly (arrowheads), and has liner wear (note eccentric location of the femoral head in the cup). (b) Radiograph obtained 363 days after surgery shows a Ganz roof reinforcement ring with a new radiolucent liner that was cemented in position (its orientation is identified by a marker ring [arrow]). The particulate bone graft used in the revision has a nearly solid appearance, indicating healing and incorporation of the graft.
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Acetabular Anti-protrusio Bone Cages
Antiprotrusio bone cages, which rest on the acetabular rim, are used when an extensive defect at the acetabular base needs repair (Fig 15). These cages provide a large surface area that helps to convert point loading to surface loading that, in turn, protects any graft from being overloaded and prevents component-allograft motion. There is no bone ingrowth into the cage; the cage is oriented to best cover the defect. A liner that has proper acetabular orientation is cemented into the cage (Fig 16).
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Figure 16a. Acetabular revision with an antiprotrusio cage in a 68-year-old man who underwent THR at age 64 for osteonecrosis and who recently displayed worsening hip pain. (a) Preoperative radiograph shows that a Ganz roof reinforcement ring is malaligned, the acetabular screws are fractured (arrowheads), and protrusio acetabuli and an inferior pubic ramus fracture (arrow) are present. (b) Radiograph obtained 12 days after surgery shows a 60-mm Burch-Schneider–type antiprotrusio cage (white arrows). No bone graft was used, and cement was used to fill the defect. A constrained acetabular insert (black arrow) was placed to prevent dislocation.
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Figure 16b. Acetabular revision with an antiprotrusio cage in a 68-year-old man who underwent THR at age 64 for osteonecrosis and who recently displayed worsening hip pain. (a) Preoperative radiograph shows that a Ganz roof reinforcement ring is malaligned, the acetabular screws are fractured (arrowheads), and protrusio acetabuli and an inferior pubic ramus fracture (arrow) are present. (b) Radiograph obtained 12 days after surgery shows a 60-mm Burch-Schneider–type antiprotrusio cage (white arrows). No bone graft was used, and cement was used to fill the defect. A constrained acetabular insert (black arrow) was placed to prevent dislocation.
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Treatment Complications
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Complications of revision arthroplasty of the hip include nerve or vessel damage, postoperative infections, periprosthetic or prosthetic fractures, prosthesis dislocation (Fig 17), bone graft failure (Fig 18), and dislocation of the prosthetic liner (Fig 19). Prosthesis or liner dislocation occur in 12% of patients. Repair of repeated dislocation may simply require the addition of a constraining ring, or an entirely new prosthesis may be needed. Postoperative infections occur in 1%–14% of patients. The frequency of bone graft resorption is not well documented, but it is low. Sporer et al (10) suggested that categories of bone resorption are none, 0%; mild, less than 25%; moderate, 25%–50%; and severe, more than 50%. Bone resorption is thought to result from micro-motion of the replaced prosthesis.
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Figure 17a. Recurrent prosthetic dislocation in a 64-year-old man who underwent revision THR because of pain and dislocation of the prosthesis placed in the primary THR. (a) Collimated anteroposterior radiograph of the right hip shows placement of a new acetabular cup with particulate bone graft. The abduction angle is 68°. (b) Collimated anteroposterior radiograph obtained 9 days after surgery shows recurrent dislocation of the femoral component (arrowheads). (c) Collimated anteroposterior radiograph obtained after another revision THR shows an antiprotrusio cage (curved arrows) that was placed to achieve stability. Note the constrained acetabular insert identified by the marker ring (straight arrow).
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Figure 17b. Recurrent prosthetic dislocation in a 64-year-old man who underwent revision THR because of pain and dislocation of the prosthesis placed in the primary THR. (a) Collimated anteroposterior radiograph of the right hip shows placement of a new acetabular cup with particulate bone graft. The abduction angle is 68°. (b) Collimated anteroposterior radiograph obtained 9 days after surgery shows recurrent dislocation of the femoral component (arrowheads). (c) Collimated anteroposterior radiograph obtained after another revision THR shows an antiprotrusio cage (curved arrows) that was placed to achieve stability. Note the constrained acetabular insert identified by the marker ring (straight arrow).
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Figure 17c. Recurrent prosthetic dislocation in a 64-year-old man who underwent revision THR because of pain and dislocation of the prosthesis placed in the primary THR. (a) Collimated anteroposterior radiograph of the right hip shows placement of a new acetabular cup with particulate bone graft. The abduction angle is 68°. (b) Collimated anteroposterior radiograph obtained 9 days after surgery shows recurrent dislocation of the femoral component (arrowheads). (c) Collimated anteroposterior radiograph obtained after another revision THR shows an antiprotrusio cage (curved arrows) that was placed to achieve stability. Note the constrained acetabular insert identified by the marker ring (straight arrow).
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Figure 18a. Severe bone graft resorption in a 78-year-old woman who underwent revision THR because of hip pain. (a) Radiograph obtained on the day of the revision surgery shows a 62-mm Trabecular Metal cup and 80 mL of bone graft (arrowheads). (b, c) Radiographs obtained 60 days (b) and 16 months (c) after surgery show progressive resorption of the bone graft (arrowheads) and cup malalignment. The cup is also displaced cephalad and has broken screws that are hidden by the cup.
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Figure 18b. Severe bone graft resorption in a 78-year-old woman who underwent revision THR because of hip pain. (a) Radiograph obtained on the day of the revision surgery shows a 62-mm Trabecular Metal cup and 80 mL of bone graft (arrowheads). (b, c) Radiographs obtained 60 days (b) and 16 months (c) after surgery show progressive resorption of the bone graft (arrowheads) and cup malalignment. The cup is also displaced cephalad and has broken screws that are hidden by the cup.
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Figure 18c. Severe bone graft resorption in a 78-year-old woman who underwent revision THR because of hip pain. (a) Radiograph obtained on the day of the revision surgery shows a 62-mm Trabecular Metal cup and 80 mL of bone graft (arrowheads). (b, c) Radiographs obtained 60 days (b) and 16 months (c) after surgery show progressive resorption of the bone graft (arrowheads) and cup malalignment. The cup is also displaced cephalad and has broken screws that are hidden by the cup.
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Figure 19a. Dislocation of the prosthetic liner in a 44-year-old woman (same patient as in Fig 4) who underwent a third THR revision. (a) Radiograph obtained on the day of the surgery shows the space for the acetabular liner (arrowheads). (b) Radiograph obtained 4 months after surgery shows absence of the liner space with abutment of the femoral head against the acetabular cup (arrowheads). The liner is just lateral to the greater trochanter (arrow). (c) Collimated view of the left hip soft tissues shows the liner as a lucent half-circle in the soft tissues (arrowheads).
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Figure 19b. Dislocation of the prosthetic liner in a 44-year-old woman (same patient as in Fig 4) who underwent a third THR revision. (a) Radiograph obtained on the day of the surgery shows the space for the acetabular liner (arrowheads). (b) Radiograph obtained 4 months after surgery shows absence of the liner space with abutment of the femoral head against the acetabular cup (arrowheads). The liner is just lateral to the greater trochanter (arrow). (c) Collimated view of the left hip soft tissues shows the liner as a lucent half-circle in the soft tissues (arrowheads).
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Figure 19c. Dislocation of the prosthetic liner in a 44-year-old woman (same patient as in Fig 4) who underwent a third THR revision. (a) Radiograph obtained on the day of the surgery shows the space for the acetabular liner (arrowheads). (b) Radiograph obtained 4 months after surgery shows absence of the liner space with abutment of the femoral head against the acetabular cup (arrowheads). The liner is just lateral to the greater trochanter (arrow). (c) Collimated view of the left hip soft tissues shows the liner as a lucent half-circle in the soft tissues (arrowheads).
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New Alternatives for Primary
The most obvious technique to manage prosthesis failure is to prevent it from occurring in the first place (29). To that end, newer prostheses and bearing surfaces have been designed and implanted in the last several years. New formulations of ceramic-on-ceramic bearing surfaces, metal-on-metal bearing surfaces, and mixed-material bearing surfaces have been developed. New generations of polyethylene that have much-improved wear characteristics have come to market and promise to have longer life and to reduce the risk of developing particle disease. The efficacy of these new technologies will not be known for several years.
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Conclusions
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Acetabular revision is challenging for the patient, the surgeon, and the radiologist. Because an increasing number of THRs are being performed, evaluations for acetabular revision are now more frequently encountered in the general radiology practice.
Although there is a large number of orthopedic hardware manufacturers and devices on the market, there is a limited number of types of hardware and surgical procedures that must be learned by the radiologist. We have reviewed the general types of acetabular cups and the types of bone grafts that are used by orthopedic surgeons to repair these difficult medical situations.
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Acknowledgments
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The authors thank Sita Hanki for assistance with preparation of the manuscript.
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Footnotes
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Abbreviations: AAOS = American Academy of Orthopedic Surgeons, THR = total hip replacement
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References
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Abstract
Introduction
