AJR 2003; 180:1701-1706
© American Roentgen Ray Society
Radiography of the PROSTALAC (Prosthesis with Antibiotic-Loaded Acrylic Cement) Orthopedic Implant
R. Gee1,
P. L. Munk1,
C. Keogh1,
S. Nicolaou1,
B. Masri2,
L. O. Marchinkow1,
J. Ellis1 and
L. P. Chan1
1 Department of Radiology, Vancouver General Hospital and University of British
Columbia, 899 W. 12th Ave., Vancouver, B. C. V5Z 1M9, Canada.
2 Department of Orthopedic Surgery, Vancouver General Hospital and University of
British Columbia, Vancouver, B. C. V5Z 1M9, Canada.
Received September 20, 2002;
accepted after revision November 15, 2002.
Address correspondence to P. L. Munk.
Introduction
Within the United States alone, at least 250,000 joint replacements are
performed annually [1], with
infection rates estimated at 1–2% for primary joint replacements and
3–4% for revision surgery
[2]. Revision of an infected
arthroplasty has had variable success, with severe cases treated with joint
fusion (arthrodesis) or amputation. Revision of septic arthroplasty is a
costly procedure estimated at twice the cost of revising a nonseptic joint
replacement and four times that of implanting a primary arthroplasty
[1]. The PROSTALAC (prosthesis
with antibiotic-loaded acrylic cement) implant was designed to treat infected
hip and knee arthroplasties (components made by DePuy, Warsaw, IN). PROSTALAC
provides a cost-effective treatment that reduces patient morbidity and the
complexity of surgery. This article provides the rationale for the use of the
PROSTALAC implant and shows the radiographic appearance and complications of
this device.
Treatment of Infected Arthroplasties
Patients present with a variety of clinical findings, ranging from
progressive joint pain and swelling, fever, purulent discharge, and exposure
of the arthroplasty through a wound (Fig.
1). Once the diagnosis has been established, treatment usually
requires removal of the infected components and antibiotic therapy for several
weeks to months. Revision of the components can be performed as a single-or
double-stage procedure (Fig.
2). In the single-stage procedure, the infected components are
removed, the surgical field is débrided, and new arthroplasty
components are placed. IV and long-term oral antibiotics are used to eradicate
infection.
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Fig. 1. —55-year-old man with infected left hip arthroplasty.
Photograph shows left hip positioned for débridement and removal of
infected components. Infection has caused local tissue necrosis and ulceration
with exposure of femoral head prosthesis (arrow).
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Fig. 2. —Flow chart shows management of infected knee arthroplasty:
infected arthroplasty (a) revised arthroplasty (b), infected revised
arthroplasty (c), arthrodesis (d), amputation (e), PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) arthroplasty (f), and excised infected
arthroplasty without temporary arthroplasty (g). Arthroplasties in
double-stage arm may rarely ultimately require either arthrodesis or
amputation if revised arthroplasty also becomes infected. Similar flow chart
would apply to management of infected joint arthroplasties at other sites.
Management will vary in different institutions depending on experience and
preference.
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Overall results of single-stage procedures are generally poor
[2], with an infection rate of
up to 30% [3]. Infection is
presumably due to incomplete sterilization of the operative bed. For this
reason, single-stage revision is no longer favored in North America, and the
double-stage procedure has become the more common approach. Two surgical
procedures are performed, with an intervening period of antibiotic therapy.
The first stage entails removal of the arthroplasty components and
débridement of the involved tissue. After 6–12 weeks of IV and
oral antibiotic therapy [2],
infection is eradicated from the bone and soft tissues. During this time, the
limb is held with either external fixation or traction. This method severely
limits mobility, which may lead to muscle atrophy or stiffness of other
joints. Debris fills the potential space left by the removed components, and
soft-tissue contractures commonly occur (80–100%)
[4]. The second stage involves
placement of the final arthroplasty components. Placement can be difficult
because debris and contractures that develop distort normal anatomy, and limb
length discrepancies can occur.
Role of Antibiotic-Impregnated Cement
Bone cement (polymethylmethacrylate) is used to affix orthopedic prosthetic
components to bone. Bone cement can be manufactured into various shapes and
deployed as a spacer to occupy the potential joint space left after the
infected arthroplasty has been removed. Placement of a bone spacer prevents
debris from accumulating in the potential joint space and soft-tissue
contractures.
Antibiotics can be combined with ALAC (antibiotic-loaded acrylic
cement), a bone cement that is proven to elute local antibiotics for at least
4 months [5,
6]. Pharmacokinetics studies
estimate that local concentrations are up to 200 times higher than those for
systemic administration. A wide range of antibiotics can be deployed in this
format; the most common are gentamycin, tobramycin, and vancomycin
[7].
The PROSTALAC Implant
The PROSTALAC implant is a temporary articulating joint prosthesis covered
in antibiotic cement. This implant acts as an articulating spacer with a
structure and function similar to the traditional arthroplasty components and
has a proven high rate (90–95%) for eradicating infection in comparison
with rates as low as 70% or less
[6].
The PROSTALAC was first developed by Duncan and Beauchamp
[8] to treat infected hip joint
replacements. The original design was composed of a metal femoral endoskeleton
component covered with ALAC (Figs.
3A,
3B,
4A,
4B,
4C,
5). The cement of the femoral
head articulated with the bone of the acetabular bed, which could
unfortunately lead to bone erosion and discomfort. An acetabular cement
component was therefore introduced, preventing loss of acetabular bed bone,
but the cement-on-cement articulation limited motion and caused discomfort.
The current design consists of an articulating polyethylene acetabular liner
and a metal femoral head prosthesis. The nonarticulating surfaces are coated
or embedded with ALAC.
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Fig. 3A. —Intraoperative preparation of PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) arthroplasty. Photograph shows metal core of
arthroplasty placed within mold and cement poured into it. ALAC
(antibiotic-loaded acrylic cement) surrounds nonarticulating surfaces of
femoral component. Femoral head, neck (solid arrow), and cement
(dotted arrow) project above edge of mold (arrowheads).
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Fig. 3B. —Intraoperative preparation of PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) arthroplasty. Photograph of arthroplasty
shows that half mold has been removed, revealing formed implant. Femoral neck
(solid arrow) and ALAC around femoral stem (dotted arrows)
are exposed. Hip PROSTALAC implant is cementcoated metal component in contrast
to knee PROSTALAC design in which metal and polyethylene cover only
articulating surfaces.
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Fig. 4A. —62-year-old man with septic hip arthroplasty. Frontal
radiograph of left hip obtained before surgery shows minimal evidence of
loosening of femoral component, with slight widening of bone–cement
interface superomedially, but clinical symptoms were strongly suggestive of
infection.
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Fig. 4B. —62-year-old man with septic hip arthroplasty. Radiograph
obtained after débridement of tissues and removal of infected
components shows placement of PROSTALAC (prosthesis with antibiotic-loaded
acrylic cement) implant. Device has ALAC (antibiotic-loaded acrylic cement)
embedded in acetabular cup liner (solid arrows) and ALAC-coated
femoral prosthesis (dotted arrows).
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Fig. 4C. —62-year-old man with septic hip arthroplasty. PROSTALAC
implant has eradicated infection and preformed cavity, allowing easy placement
of final arthroplasty components. Radiolucency between prosthesis and bone
(arrows) is normal, representing cavity left from original prosthetic
implant.
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Fig. 5. —Photograph of knee PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) implant taken in posterior view shows that
metal bridging bar located posteriorly between femoral skids (solid
arrow) and tibial post (dotted arrows) provides stability.
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The radiographic appearance is that of a slim tapered femoral stem and
attached femoral head with a wide zone of surrounding bone cement from the
femoral neck distally that also projects above the margins of the proximal
femoral bone. The acetabular component appears to be almost entirely composed
of cement, except for a thin uniform radiolucent rim of the polyethylene liner
cup that encompasses the femoral head (Fig.
6).
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Fig. 6. —48-year-old woman with infected left knee joint.
Intraoperative photograph shows placement of knee PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) implant after removing infected components
and débridement. Femoral skid (solid black arrow) and tibial
block (dotted arrow) are shown resting on resected proximal tibial
platform (white arrow).
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The PROSTALAC implant of the knee developed and tested by Masri et al.
[6] was refined through a
similar progression of design. The implant uses articulating femoral and
tibial components, with the nonarticulating surfaces covered with ALAC (Figs.
7A,
7B,
7C and
8). A femoral cam and tibial
post compensate for loss of ligament stability normally provided by the
posterior cruciate ligament. This loss of stability with the previous design
has eliminated tibiofemoral instability and motion discomfort, which were
reported earlier [6].
Radiographically, there is a conspicuous absence of metal compared with a
conventional knee arthroplasty, with thin femoral skids and a bridging
posterior femoral cam. In contrast to the usual arthroplasty, in which a
radiolucent spacer between the femoral and tibial components is expected, an
ALAC block with a thin polyethylene track articulates with the femoral
runners.
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Fig. 7A. —66-year-old man with bilateral infected knee joint
replacements. Bilateral frontal radiograph shows widening of bone interface
prosthesis (arrows), suggesting loosening. Infection was confirmed by
fluoroscopically guided aspirations.
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Fig. 7B. —66-year-old man with bilateral infected knee joint
replacements. Bilateral radiograph shows placement of PROSTALAC (prosthesis
with antibiotic-loaded acrylic cement) implants. Femoral skids (solid
arrows) with bridging posterior femoral cam and tibial cement post
(dotted arrows) are shown. 66-year-old man with bilateral infected
knee joint replacements.
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Fig. 8. —72-year-old man after first stage of two-stage revision
procedure for infected knee arthroplasty. Detailed lateral radiograph shows
knee PROSTALAC (prosthesis with antibiotic-loaded acrylic cement) implant in
situ.
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The use of smoothly articulating embedded PROSTALAC components permits
sufficient support to allow partial weight bearing and early hospital
discharge. A home-based IV antibiotic treatment program ensures adequate
antibiotic coverage until the second stage of the procedure. At the second
stage, the removed PROSTALAC implant leaves a conveniently preshaped cavity
and forms a well-vascularized bed of tissue
[8], allowing ready acceptance
of the final arthroplasty.
Complications Associated with the PROSTALAC Implant
At a tertiary referral center for complex joint reconstruction, PROSTALAC
is commonly used for septic joint revisions. Our experience is anecdotal, but
the uniform impression from surgeons and radiologists is that PROSTALAC
failure is rare. This failure has taken the form of cement fracture (Figs.
9A,
9B) and migration of
components (Figs. 10 and
11).
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Fig. 9A. —52-year-old woman after first stage of revision procedure. Lateral
(A) and anteroposterior (B) radiographs of knee show that
fracture through cement of femoral component anterior to femoral skids has
allowed fragment to detach and migrate (solid arrows). Intramedullary
stem of tibial component helps reduce cement–bone interface motion
(dotted arrows).
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Fig. 9B. —52-year-old woman after first stage of revision procedure. Lateral
(A) and anteroposterior (B) radiographs of knee show that
fracture through cement of femoral component anterior to femoral skids has
allowed fragment to detach and migrate (solid arrows). Intramedullary
stem of tibial component helps reduce cement–bone interface motion
(dotted arrows).
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Fig. 10. —63-year-old woman after first stage of revision procedure.
Radiograph shows that tibial component of knee PROSTALAC (prosthesis with
antibiotic-loaded acrylic cement) implant has separated and migrated
anteriorly (arrows) from anchoring cement and intramedullary
post.
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Fig. 11. —72-year-old man after first stage of revision procedure.
Lateral radiograph shows migration of femoral component (solid
arrows) without cement fracture. Tibial block is anchored by
intramedullary stem (dotted arrow).
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Summary
The design of the PROSTALAC implant provides an effective means to treat
patients with infected arthroplasties of the hip and knee. The use of this
device significantly reduces hospital admission time, overall rehabilitation,
and operating time. The PROSTALAC provides effective treatment of sepsis,
reducing patient morbidity and rehabilitation from prolonged immobility and
permits a less complicated approach to placement of the final arthroplasty
components.
References
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Introduction
Treatment of Infected...
