AJR 2003; 180:115-120
© American Roentgen Ray Society
Imaging of the Painful Hip Arthroplasty
Ciaran F. Keogh1,
Peter L. Munk,
Richard Gee,
Lai Peng Chan and
Laurel O. Marchinkow
1 All authors: Department of Radiology, Vancouver Hospital and Health Sciences
Center, University of British Columbia, 910 W. 10th Ave., Vancouver, B. C.,
V5Z 4E3, Canada.
Received March 5, 2002;
accepted after revision June 5, 2002.
Address correspondence to P. L. Munk.
Introduction
Hip arthroplasties are commonly performed throughout the world, with over
125,000 procedures undertaken in North America annually
[1]. Despite advances in
surgical technique and prosthetic design, a small but significant minority of
patients (1-5%) develops complications, many of which require revision.
Recognizing and diagnosing these complications are often challenging because
the presentation and findings are often nonspecific and frequently subtle.
Radiography remains the cornerstone of evaluation and is complemented by
arthrography, radionuclide scanning, sonography, CT, and MR imaging.
Our aims were to illustrate the complications of hip arthroplasty, with the
emphasis on radiographic findings, and to examine specific instances when
other techniques can be used.
Loosening
Mechanical loosening remains the most common indication for revision.
Patients are usually symptomatic, although asymptomatic radiographic changes
may be seen. A lucent zone greater than 2 mm in diameter around the prosthesis
is a common radiographic manifestation of loosening
(Fig. 1). Depending on the type
of arthroplasty, this zone can involve the interface between the prosthesis
and bone, cement and bone, or cement and prosthesis
[2]. Even a thin radiolucent
zone (< 2 mm) is considered potentially unstable or loose and requires
close clinical and radiologic follow-up
[1]. However, caution must be
exercised in diagnosing a loose prosthesis on the basis of this sign in
isolation if serial radiographs are not available. Radiolucent cement will
give a similar appearance but is not frequently encountered. In addition,
revision arthroplasties may have a wider radiolucent zone than primary
procedures. In the absence of symptoms, clinically significant loosening is
unlikely regardless of the degree of radiographic radiolucency. Other signs of
loosening include fracture of the cement and the development of bony sclerosis
adjacent to the distal tip of the prosthesis (pedestal formation)
[1]. Evidence of prosthesis
movement is a strong indicator of loosening, particularly component rotation
or increasing varus orientation
[3]. Progressive shedding of
beads in noncemented arthroplasties indicates loosening
(Fig. 2). In general,
comparison with previous radiographs is the most helpful method of detecting
loosening.
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Fig. 1. —63-year-old woman with persistent left-hip pain 3 years after
undergoing uncemented total arthroplasty. Radiograph shows subtle zone of
radiolucent bone around medial aspect of femoral component (arrows).
Radiolucent zone greater than 2 mm should raise possibility of loosening. Note
adjacent sclerotic line, which is frequently seen and serves to emphasize
periprosthetic radiolucency.
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Fig. 2. —71-year-old woman with pain 3 years after undergoing hip
replacement. Radiograph shows multiple small metallic densities projected over
joint (arrows). These are beads shed from uncemented acetabular
component. Beads were not present on initial radiograph after surgery (not
shown), suggesting that loosening had occurred. Comparison with previous
imaging is vital in such cases because beads may enter hip joint during
surgery, simulating loosening on later radiographs.
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Arthrography may be performed for evaluation of loosening and in
conjunction with aspiration and synovial biopsy to assess infection. The
presence of contrast agent in an interface below the intertrochanteric line
(Fig.
3A,3B)
has been shown to be both specific and sensitive for detection of loosening of
the femoral component. Arthrographic assessment of acetabular loosening is
less sensitive and lacks specificity
[3]. Debris and inflammatory
cells often fill the space between bone and prosthesis, preventing the passage
of contrast material, which significantly limits the value of the
technique.
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Fig. 3A. —Marked loosening in 74-year-old man with pain and disability
7 years after total hip replacement. Radiograph shows wide zone of
radiolucency (arrows) lateral to femoral component. Note increased
varus deformity of stem.
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Fig. 3B. —Marked loosening in 74-year-old man with pain and disability
7 years after total hip replacement. Arthrogram shows free flow of contrast
agent into radiolucent area between prosthesis and bone laterally (short
arrow). This finding confirms loosening. Note irregularly lobulated
collection of iodinated contrast agent at inferomedial aspect of femoral
component, consistent with small pseudobursa (long arrow).
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Infection
Radiologic findings in patients with indolent infection may be unremarkable
or may mimic loosening or aggressive granulomatous disease. With more
aggressive organisms, progression can be rapid, with bone destruction and
sinus tract formation (Fig. 4). Radionuclide bone scans may show findings similar to those occurring in
loosening, and correlation with dedicated radionuclide techniques for
infection such as gallium scanning or indium-labeled WBC or immunoglobulin G
can be invaluable. However, findings may be confounded by the presence of
cellulitis or inflammatory arthritis
[1]. Negative findings on a
radiograph and bone scan suggest that no infection exists
[1]. Most researchers advocate
joint aspiration and synovial biopsy (under fluoroscopic or sonographic
guidance) to fully assess infection
[4]. Several samples should be
taken to minimize confusion caused by skin contaminants.
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Fig. 4. —Infected joint in 71-year-old woman. Arthrographic image
shows contrast agent filling ill-defined irregular cavity laterally
(bottom arrow), with subsequent tracking of contrast agent to skin
(top arrow), consistent with fistula formation caused by
infection.
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Histiocytic Response
Originally called cement disease, histiocytic response occurs as a result
of macrophage reaction to any of the components of arthroplasty. These
aggressive granulomatous lesions present as focal radiolucencies around the
prosthesis. The condition tends to occur between 1 and 5 years after surgery
and is associated with smooth endosteal scalloping
[5]. These characteristics help
to distinguish histiocytic response from infection, which often has more
aggressive features, although the distinction is not always possible (Figs.
5A,5B
and
6A,6B,6C).
Inflammatory pseudobursae may be present, but sinus tracks to the skin usually
indicate infection. The increased risk of fracture necessitates close
follow-up to assess the rates of growth and expansion.
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Fig. 5A. —Histiocytic reaction. Radiograph shows histiocytic reaction
in right hip of 47-year-old woman, 3 years after joint replacement. Note
extensive radiolucency (arrows) around femoral component associated
with endosteal scalloping. Multiple radiolucencies caused by histiocytic
reaction are also present in acetabulum.
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Fig. 5B. —Histiocytic reaction. Drawing shows histiocytic reaction. MAC
icon represents macrophages, and arms represent release of destructive
biochemical products in response to presence of wear debris (arrows).
Boxes represent proteolytic enzymes and chemotactic factors, which destroy
bone and attract inflammatory cells.
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Fig. 6A. —Histiocytic reaction simulating aggressive lesion in
54-year-old man. Radiograph of femur shows aggressive expansile lesion
(arrow) adjacent to distal tip of femoral component. Note associated
cortical destruction.
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Fig. 6B. —Histiocytic reaction simulating aggressive lesion in
54-year-old man. Axial CT image obtained through mid femur shows soft-tissue
mass and cortical destruction (arrows). Surrounding muscle appears
normal.
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Fig. 6C. —Histiocytic reaction simulating aggressive lesion in
54-year-old man. Axial MR image of mid femur shows normal hypointense cortical
bone (arrow) and posterior cortical destruction by soft-tissue mass.
Patient subsequently underwent surgery, with pathologic diagnosis of
histiocytic reaction.
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Stress Shielding
The presence of a prosthesis alters stress-loading on the native bone. This
alteration leads to reduced bone mass and osteoporosis in areas of decreased
loading. Bone loss typically occurs in the proximal femoral shaft and is more
severe in uncemented arthroplasties (Fig.
7), leading to increased risk of pathologic fractures
[1].
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Fig. 7. —Stress shielding in 73-year-old man with increasing hip pain.
Radiograph of left hip shows extensive periprosthetic radiolucency extending
along upper third of femur. Transition point to normal-appearing bone
(arrows) emphasizes degree of osteopenia and bone loss. Development
of stress shielding predisposes to fracture and loosening and is more common
in uncemented prostheses.
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Pseudobursae
Pseudobursae are irregular recesses that communicate with the joint and are
detected on arthrography or sonography
[6]
(Fig. 8). Pseudobursae may
track large distances around the hip joint, and although they may be
associated with infection, they can be an incidental finding. Inflammation may
simulate infection or loosening. This is an important diagnosis because
pseudobursitis may be treated conservatively with steroid and anesthetic
injections. The presence of irregular walls, sinus tracks, bone destruction,
or debris in the cavity suggest infection. Aspiration and injection of local
anesthetic can provide symptomatic relief, and if symptoms recur and findings
of culture of aspirated fluid are negative, steroid injection may be of
benefit. Filling of pseudobursae at arthrography reduces joint pressure; this
reduction may prevent contrast material from entering spaces around the
prosthesis and producing a false-negative result for loosening
[3].
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Fig. 8. —80-year-old woman with pain and swelling of hip and suspected
infection. Arthrogram shows extensive irregular collection of contrast agent
along lateral aspect of femur (arrows), consistent with pseudobursae.
Aspirated fluid was negative for infection, and symptoms responded to
conservative therapy, consisting of oral antiinflammatory drugs and local
steroid injection.
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Fractures
Bone fractures occur in patients with osteoporosis, typically adjacent to
the tip of the stem, at the point of maximal difference in shaft strength
(Fig. 9). Ironically,
insufficiency fractures may also occur in these patients because of increased
activity related to their successful hip replacement. A component fracture is
less common and is usually related to severe trauma or metal fatigue (Fig.
10A,10B).
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Fig. 9. —Pathologic fracture in 72-year-old woman after fall.
Radiograph shows periprosthetic radiolucencies associated with endosteal
scalloping (arrows) due to histiocytic reaction or loosening. Stress
shielding and infection also predispose patients to fractures, which typically
occur at prosthetic tip.
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Fig. 10B. —Component fracture. Radiograph of 73-year-old man with acute
pain after trauma, 6 years after hip replacement, shows fracture and
displacement of acetabular component (arrows). Note cranial migration
of femoral head, confirming component dissociation.
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Dislocation and Subluxation
Dislocation or subluxation of the components may occur because of patient
factors including poor muscle tone or trauma or because of surgical factors
such as a posterior (rather than lateral) surgical approach and difficulty in
achieving ideal angulation of the acetabular component (usually the result of
severe degenerative changes or dysplasia)
(Fig. 11). Signs of
subluxation may be subtle. The femoral head should be carefully inspected to
ensure that it articulates appropriately with the acetabulum and that no
malalignment exists. For some types of arthroplasty, an eccentric lie in the
acetabulum is normal. An eccentric lie has an asymmetric acetabular component,
which is thicker laterally, causing the femoral head to lie in a medial
position. An eccentric lateral lie is abnormal, suggesting significant wear or
subluxation. Comparison with previous radiographs is always helpful.
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Fig. 11. —Radiograph shows subtle prosthetic dislocation in 79-year-old
woman. Femoral head is not situated in center of acetabulum and has migrated
superiorly (arrows) through metal acetabular cup. Note high-riding
position of femoral shaft, with shoulder of prosthesis close to
acetabulum.
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Component dissociation, as opposed to frank hip dislocation, most commonly
develops when the plastic liner of the acetabulum slips from its backing.
Arthrography may be useful to outline the ectopic component
[7]
(Fig. 12).
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Fig. 12. —Acetabular component dissociation in 82-year-old man, 9 years
after total hip replacement. No history of trauma was reported. Arthrograpm
shows femoral head in abnormal superolateral position, mimicking subluxation.
Contrast agent (large black arrow) has collected between metal
acetabular component and radiolucent plastic liner (white arrow),
which has slipped inferiorly. Straight superior margin of liner is clearly
delineated by contrast agent (small black arrows). Recognition of
this complication is important in cases of apparent dislocation or subluxation
because acetabular component should be refitted, and femoral component may
require replacement if articular surface has been damaged.
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Component wear manifests as subluxation and loss of joint space and may be
associated with metallosis—a dense joint effusion due to shedding of
microscopic metallic fragments. More common in the knee, the finding is
difficult to detect on radiographs, unless extensive metal deposition occurs
in the synovium. Diagnosis may be made at aspiration when dense black fluid is
obtained (Fig. 13).
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Fig. 13. —Photograph shows black fluid aspirated from hip joint of
71-year-old woman with suspected infection. Dense metal fragment containing
fluid in this patient with worn arthroplasty components and metallosis could
not be detected on radiographs.
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Heterotopic Ossification
Heterotopic new bone formation occurs in 15-50% of patients, but clinically
significant limitation of motion is rare (1-5%)
(Fig. 14). Predisposing
factors include infection, post-traumatic arthritis, ankylosing spondylitis,
and previous hip surgery [8].
In selected patients, indomethacin or low-dose radiotherapy may be used to
prevent heterotopic ossification
[8].
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Fig. 14. —Heterotopic ossification in 69-year-old man with pain and
limited mobility. Radiograph shows extensive ossification extending from
greater trochanter to ilium (arrows). This site is typical for
formation of new bone.
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MR imaging and CT are rarely performed to assess painful hip arthroplasty
because of the associated metallic artifact. MR imaging may be performed to
evaluate the extent of radiolucent cement in the femoral shaft before
revision. In addition, White et al.
[9] suggest that specific MR
imaging sequences that reduce metallic artifact are useful in diagnosing
complications and that the findings may alter treatment in some patients.
Further experience is necessary before the role of MR imaging is fully
defined.
In summary, the painful hip arthroplasty remains a common problem, both for
the clinician and radiologist. Serial radiography is often the most useful
method of addressing this issue. Injection and aspiration of the joint are
important for preoperative diagnosis of infection and may also show loosening
and pseudobursae. Changing surgical practices and increasing patient longevity
have led to complications such as histiocytic granuloma formation, stress
shielding, and product wear becoming more important. MR imaging and other
techniques may have a role in addressing specific questions, although
treatment ultimately depends on the patient's clinical features.
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Introduction
Loosening
