Extract
It has been four decades since Sir John Charnley
introduced the low-friction arthroplasty. Total hip arthroplasty
has become one of the most commonly performed procedures in the United
States, with the number performed annually estimated to be more
than 200,000. Its clinical efficacy and cost-effectiveness have
both been well documented in the literature.
It has been four decades since Sir John Charnley
introduced the low-friction arthroplasty. Total hip arthroplasty
has become one of the most commonly performed procedures in the United
States, with the number performed annually estimated to be more
than 200,000. Its clinical efficacy and cost-effectiveness have
both been well documented in the literature.
Enormous amounts of data on topics related to total hip arthroplasty
are published and presented each year. In this article, we present
some of the latest information. We reviewed all of the papers published
in major orthopaedic journals as well as abstracts presented at
the fall meeting of the Hip Society in September 2000; at the annual
meeting of the American Association of Hip and Knee Surgeons in
November 2000; at the annual meeting of the American Academy of
Orthopaedic Surgeons in February 2001; and at the spring meeting
of the Hip Society in February 2001. A total of 132 papers were
published and 268 abstracts were presented from April 2000 to May
2001. We have organized the topics into seven general categories:
(1) clinical results of primary total hip arthroplasty, (2) clinical results
of revision total hip arthroplasty, (3) special clinical settings,
(4) wear and biological mechanisms, (5) bearing surfaces, (6) complications,
and (7) practice management and outcome measurement.
Total hip arthroplasty has been offered to younger and more active
patients with increasing frequency over the last decade as the clinical
success of this operation continues to be validated. Some of the most
useful data presented over the last year were related to the durability
of the results of total hip arthroplasty in this challenging patient
population.
Femoral Stem
Fixation without Cement
Cementless fixation of the femoral stem has gone through a period
of evolution over the last two decades. More data are being presented
with regard to their medium and long-term clinical performance and
durability at ten to fifteen years. Surface texture is an integral
factor influencing the success of cementless fixation of the stem.
Two main types of surfaces have been in use over the last two decades: porous
and hydroxyapatite. Evaluation of the clinical efficacy of the many
stem designs over this time-period has been complicated by the variables of
stem geometry (straight, curved, tapered, or modular), the extent
of surface treatment (proximal or extensive), and biomaterials (titanium
alloy or cobalt-chromium alloy). Zenos et al. presented recent data
on the Porous Coated Anatomic stem (Howmedica, East Rutherford,
New Jersey), which was one of the earliest designs that was widely
used clinically in the 1980s. Of 100 total hip prostheses followed
prospectively, sixty-five had remained in situ at fourteen to fifteen
years. Two stems (2%) were revised because of loosening,
and sixteen cups (16%) were revised because of osteolysis
and loosening.
Tapered stem geometry has received increasing attention over
the last ten years. Hozack et al. reported the results at a minimum
of fifteen years after forty-nine total hip arthroplasties with
use of the Tri-Lock design (DePuy, Warsaw, Indiana). The mean age
of the patients was fifty-four years. The mean Harris hip score
was 92 points at the time of final follow-up. One stem (2%)
was revised because of loosening. Radiographs demonstrated osseous
stable fixation in 90% of the hips and fibrous stable fixation
in 8%. There was a high rate of cup revisions (32%),
all of which were due to wear and osteolysis. McLaughlin and Lee1 reported on a consecutive series
of 108 total hip arthroplasties with use of another tapered design (Taperloc;
Biomet, Warsaw, Indiana) in patients less than fifty years old.
The mean age of the patients was thirty-seven years, and the mean
duration of follow-up was 10.2 years. No stem was revised because
of loosening, osteolysis was noted in association with 7%,
and osseointegration was judged to have been achieved in 98%.
Hydroxyapatite coating of the stem was introduced in the hope
of improving the fixation stability and durability. At the 2000
meeting of the Hip Society, D’Antonio presented his results
of 230 total hip arthroplasties after a minimum follow-up of five years
(mean, 7.7 years). The mean age of the patients was fifty-six years.
One stem had been revised because of loosening, and four stems had been
revised for other reasons. No other stem showed radiographic signs
of loosening. The rate of mechanical failure was therefore 0.4%.
Hozack et al. performed a prospective comparative analysis of hydroxyapatite-coated
and porous-coated stems, both of which had a tapered design with
a proximal coating. The study included fifty-two pairs of matched
patients who were followed for a minimum of five years (mean, 9.3
years). No stem was revised because of loosening in either group,
and the clinical outcomes were similar in the two groups.
Thigh pain, especially in association with activity, was a major
clinical limitation early in the evolution of cementless fixation
of the stem. This particular problem has been reported in all series
of total hip arthroplasties with cementless fixation of the stem.
Rodriguez and Ranawat demonstrated a difference in the prevalence
of thigh pain as a function of the roughness of the nonporous (diaphyseal)
portion of the stem. Two cohorts of approximately 100 hips each
were analyzed. One group received a stem with a distal roughness
of Ra-50, and the other group received an identical stem with a
distal roughness of Ra-24. Osseointegration was present at the proximal,
porous portion of all stems. The prevalence of thigh pain was significantly
lower in the group with a rougher distal part of the stem. Similarly,
adverse bone-remodeling demarcation lines were substantially less
frequent in the group with the rougher stem. The rougher distal
surface may have led to increased osseointegration along the entire
length of the stem, perhaps changing the stress-distribution pattern
along the femur. Min et al.2 reported
similar findings with regard to the effect of the surface texture
of the distal portion of the stem. Those authors performed a matched-pair analysis
in which one group of forty-two hips received a stem with a grit-blasted
distal surface and another group of forty-two hips received a stem with
a smooth distal surface. There were significantly fewer distal radiolucencies
around the grit-blasted stems (p < 0.05). There also was
significantly less pain, both overall and in the thigh, in the grit-blasted
group (p < 0.05).
Barrack et al.3 reported on
patients’ perceptions of pain following total hip arthroplasty.
In a study of 320 hips, these investigators used standardized clinical
outcome measurement instruments as well as a visual analog pain
scale. In addition, they administered pain diagrams to the patients
before and after surgery. All stems were judged to be stable according
to radiographic criteria. Thigh pain was recorded in association
with 23% of the hips. The only parameter that was associated
with the thigh pain was the type of stem design and fixation; 42% of
the proximally coated stems, 19% of the fully coated stems,
and 16% of the cemented stems were associated with thigh
pain. The difference between the proximally and fully coated groups
was significant (p < 0.01), but that between the fully
coated and cemented groups was not. Interestingly, nearly one-third
of the patients who had had an uncomplicated primary total hip arthroplasty
still had pain after surgery. Patients with preoperative pain that
was principally in the groin according to the pain diagram had the most
predictable relief of symptoms after total hip arthroplasty. Pain-diagram
analysis may be useful in patient selection and in the preoperative
counseling of patients with regard to their expectations after surgery.
Biological enhancement of the bonding between bone and prostheses
has been investigated. Lind et al.4,
in an animal model, reported the effects of osteogenic protein-1
in a collagen carrier on the mechanical fixation of titanium implants
inserted into bone with a 3-mm gap that would preclude osseous ongrowth.
The amount of ongrowth increased to 21.3% in the group
that received osteogenic protein-1, and it increased to 16.5% in
the group that had application of the collagen carrier alone. A hydroxyapatite
coating had a positive impact on ongrowth; the amount of ongrowth
was 14.8% in the group treated with the prosthesis alone,
37.2% in the group treated with the collagen carrier, and 40.7% in
the group treated with osteogenic protein-1. Such biological adjuncts
to improve fixation stability can be particularly useful when bone
quality is poor.
Fixation with Cement
With regard to cement fixation on the femoral side, two major
topics of interest have been long-term durability, particularly
with improved cementing techniques, and early failure of cemented
stems with a roughened surface.
Sochart and Porter reported the results at a mean of twenty years
after 280 Charnley total hip arthroplasties done with first-generation
cementing techniques in patients less than forty years old. The rates
of survival of the stems were 82% and 81% at twenty
and thirty years. However, the rates for the cups were 71% and
52%, respectively. Patients with osteoarthritis and greater
polyethylene wear were at the highest risk for failure. The clinical
results remained satisfactory in the majority of patients. These
data should serve as one of the standards for evaluating the clinical
efficacy and durability of other systems with or without cement
fixation.
Smith et al.5 reported their
experience with forty-seven total hip prostheses inserted with use
of second-generation cementing techniques in forty patients who
were fifty years of age or less. The rate of survival without loosening
at eighteen years was 95% for the stems and only 63% for
the cups. The cement grades influenced both loosening and femoral osteolysis,
with higher rates of both in hips with a poorer grade. Sanchez-Sotelo
et al. reported the long-term results of a stem with a matte finish inserted
with second-generation cementing techniques. At fifteen years, the
rate of revision-free survival of the stem was 92%. The
principal predictor of failure was age; the survival rate was 72% in patients
less than fifty years of age compared with 95% in patients
older than fifty years.
Sylvain et al.6 reported early
failure with use of stems that were grit-blasted, proximally matte-finished,
and precoated with methacrylate. All stems were inserted with use
of third-generation cementing techniques. The mean duration of follow-up
was only three years. Mechanical failure of the stem occurred in 12% of
hips. There was no association between the cement grade and failure.
Disparate data were reported by Cannestra et al.7,
who followed 102 hips after hybrid total hip arthroplasty with a
precoated stem that had a surface texture of Ra-60. This stem had
a different design from the one used by Sylvain et al. and offered
greater femoral offset. The rate of revision-free survival was 97% at
seven years. The cement grade was associated with failure, with
all of the implants that failed having a grade of C2.
At the annual meeting of the American Academy of Orthopaedic
Surgeons in 2001, two separate groups of investigators reported
their long-term results of total hip arthroplasty done with hybrid
fixation and a similar femoral stem design with a roughened (Ra-60
to Ra-80), precoated finish. In a study of 150 total hip arthroplasties
performed with second-generation cementing techniques, Berger et
al. reported a rate of survival without mechanical failure of 96% at
fifteen years. Lachiewicz et al. reported that, at a mean of nine
years after seventy-four total hip arthroplasties, no stem had been revised
because of loosening or was judged to be loose according to radiographic
criteria. The cement-mantle grade was not associated with failure.
It has been thought that cracks within the cement mantle coupled
with debonding, particularly between the prosthesis and the cement,
are the principal initiating mechanisms leading to failure of stem
fixation. Duffy et al., in a laboratory study, analyzed the micromotion
of smooth (Ra-2) and roughened (Ra-95) stems within the cement mantle when
they were loaded in a previously validated simulated stair-climbing
mode. Third-generation cementing techniques had been used. There
was micromotion of all stems after only one million cycles. There
was no difference between the two types of stems at six million
cycles, with each having a mean motion of >450 mm. Cracks
within the cement developed in all specimens after three million
cycles. However, no debonding was observed in any specimen. An important
finding was that macrotexturing in the proximal portion of the stem actually
resulted in a reduction of the strength of the bone-cement interface
and in hollow voids in the stem-cement interface that could lead
to crack initiation and propagation.
Acetabular Cup
Fixation without Cement
The clinical success of porous-coated hemispherical cups inserted
with or without screws has been widely documented in the literature.
More data became available over the last year, particularly with
regard to medium to early-long-term performance of these cups. Dunkley
et al.8 reported the results of
the use of cementless cups in patients less than fifty years of
age. The Harris Galante-I design (Zimmer, Warsaw, Indiana) was inserted
with supplemental screws. The mean duration of follow-up was seven
years. No cup was revised because of loosening. Six cups required exchange
of the liner because of wear; however, no measurement data on polyethylene
wear were presented. Radiolucency was observed in at least one zone
adjacent to 29% of the cups, and 5.5% of the cups
had radiolucencies in all three acetabular zones. No cup migrated.
One of the major limitations of this study was that 40% of
the patients were in the Charnley class-C functional category and were
thus presumed to have relatively lower activity demands. Crowther
and Lachiewicz evaluated seventy-one hips that had received the
same type of cup. All patients were less than fifty years old. At
a mean of eleven years, there was an 18% rate of radiolucencies
in one acetabular zone and an 11% rate in two zones. No
cup had radiolucencies in all three zones. No cup migrated or was
revised because of loosening. The liner was exchanged in two hips.
The rate of revision-free survival of the cups was 98% at
ten years. The linear wear rate of the polyethylene was 0.15 mm/yr.
An important finding was that greater polyethylene wear was correlated
with a younger patient age and a higher Harris hip score, underscoring
the dilemma of a higher rate of wear complications in patients who
have the best functional outcome.
Urban et al. performed a histological analysis of twenty-six
porous-coated cups that were retrieved post mortem. The mean duration
of in situ usage was sixty-nine months. The mean extent of bone ingrowth
was 35%. These authors concluded that (1) backsided polyethylene
wear increased with a longer duration in situ, (2) the extent and
penetration of the granuloma correlated with a longer duration in
situ, and (3) granuloma infiltration occurred principally in the
passage along the superior rim of the cup and along screw-holes.
Femoral Revision
Fixation without Cement
The frequency of revision total hip arthroplasty has continued
to increase. The clinical results are inferior to those of primary
surgery, and the rate of complications is greater. Engh et al. reported
the results of twenty-six femoral revisions in which an extensively
coated stem was inserted. At a mean of 13.3 years, the stem had
loosened in 15% of hips. The rate of revision-free survival
was 89% at ten years. An important finding was that a satisfactory clinical
outcome was maintained in 86% of the surviving hips. The
efficacy of an extensively coated long-stem design was also reported
by Paprosky et al., in a series of 192 femoral revisions done with use
of an extended trochanteric osteotomy (mean length, 14 cm). At a
mean of four years, two stems had required revision because of mechanical
failure and nonunion of the osteotomy had occurred in 1.2% of
the hips. The clinical results were satisfactory in the majority
of the patients.
In the most extreme situations, a segmental allograft may be
required for reconstruction. Blackley et al.9 reported
their experience with sixty-three such complex reconstructions.
The mean length of the allograft segment was 15 cm. In general,
the stem was fixed to the allograft segment with cement and was
inserted into the distal host bone without cement. There was a high
rate of reoperation; five stems were revised because of sepsis;
three, because of loosening; three, because of failure at the allograft-host
bone junction; and two, because of recurrent dislocation. Overall,
the rate of success (an improved Harris hip score and a stable implant) was
78% at ten years. These data can be a good reference when
assessing the clinical efficacy and durability of alternative techniques
of femoral reconstruction.
Fixation with Cement
The frequency of femoral revision with cement fixation has decreased
over the last decade. Eisler et al.10 reported
the results of seventy-eight revisions performed with a Charnley
stem and third-generation cementing techniques. One stem was revised because
of loosening, and two were revised because of sepsis. Two additional
stems were scheduled for revision because of loosening. Radiographs
demonstrated definite loosening of 33% of the stems. The overall
rate of mechanical failure was therefore 38%. A poor cement
grade was the most significant predictor of loosening (adjusted
odds ratio = 1.8 [95% confidence interval = 1.1
to 3.0]). Hultmark et al.11 evaluated
the results of 109 stem revisions that were performed with use of
second or third-generation cementing techniques. A long stem was
used in 81% of the hips. The rate of survival without mechanical
failure was 85% at ten years. These authors concluded that
survival was superior in the hips with a long stem, that a younger
patient age and more severe bone-stock deficiency were risks for
rerevision, and that radiolucencies in distal-medial zones (zones
4 and 6) were associated with a higher risk of failure. Schmale
et al.12 reported the clinical
results of fifty-seven revisions in which a precoated stem was inserted
with third-generation cementing techniques as well as those of thirty
revisions in which a proximally coated stem was fixed without cement.
The fixation failed in 23% of the hips that had fixation
with cement and in 7% of those that had fixation without
cement. Radiographic failure was apparent in 29% of the hips
that had fixation with cement and in 10% of those that
had fixation without cement. These data reaffirm the overall poor
results associated with cement fixation in femoral revision. Disappointingly,
these results remained suboptimal even with improved cementing techniques.
Bone-Grafting for the Treatment of Osteolysis
Osteolysis has become one of the major complications following
total hip arthroplasty. Surgeons often have to address these lesions
around a stable femoral stem. Benson et al.13 recently
reported the results of curettage and bone-grafting with use of
particulate allograft in seventeen hips. The cups either were revised
or underwent exchange of the liner, and no stem required revision.
At a mean of three years, the osteolytic lesions had regressed in
fifteen of the seventeen hips. This appears to be a viable method
for preventing further osseous erosion while restoring bone stock
for future reconstructions.
Acetabular Revision
Fixation without Cement
Acetabular revision with use of a cementless hemispherical cup
can offer predictable clinical success, especially if there is sufficient
support from the osseous columns of the acetabulum. Dearborn and Harris14 reported the results of sixty-one
such revisions in fifty-four patients with hip dysplasia. All cups
had supplemental screw fixation, and bone-grafting was done in all
but three hips. Pain relief was achieved in 96% of the
hips. Two cups migrated, and three had radiolucencies in all three
zones without migration. Clinical efficacy and durability were both excellent
in this series.
Use of a Reconstruction Ring
The technical challenges of acetabular reconstruction in hips
with severe bone deficiency are formidable. Hemispherical or even
custom-designed cups are not effective, especially when there is
a lack of posterior column support or when there is pelvic discontinuity.
Pelvic reconstruction rings are used to achieve the fundamental
requirements: adequate bone coverage of the cup; restoration of
bone stock of the pelvis; equalization of limb lengths; and stable,
durable cup fixation.
Saleh et al.15 reported on
the use of massive structural allograft and a pelvic reconstructive
ring in twenty hips in which host-bone support of the cup was <50%. Three
cups required revision, but incorporation of the allograft was evident
in all other hips. Functionally, 77% of the patients were
satisfied as assessed with the Short-Form 36 (SF-36) and the Western Ontario
and McMaster Universities Osteoarthritis Index (WOMAC). Longjohn
et al. reported the results of sixty-four revisions done with use
of a reconstruction ring. The rate of survival without mechanical
failure was only 64% at 6.7 years. The authors concluded
that bulk allograft (not cement or particulate graft) was necessary
if there was a segmental defect of >60% in the
superior weight-bearing dome of the acetabulum. There is also a
high rate of dislocation after these complex reconstructions. Lombardi
et al. described a technique to specifically address this complication.
A pelvic reinforcement ring was used in twelve revisions, and a
porous-coated metallic cup was cemented into the ring. The cup was
then coupled to a constrained polyethylene liner to address instability. There
were no dislocations or loose implants at the time of short-term
follow-up.
Congenital Dysplasia
Callaghan and Johnston, at the 2001 meeting of the American Academy
of Orthopaedic Surgeons, reported the results sixteen to twenty-two
years after seventy-one total hip arthroplasties performed with
cement. All patients had Crowe type-II, III, or IV dysplasia. Aseptic
loosening occurred in 11% of the hips: 8% had
loosening of the cup, and only 3% had loosening of the
stem. These results are similar to those in the extensive experience
of the senior author (Johnston), who had performed nearly 5000 total
hip arthroplasties, in patients with other causes of hip disease.
Osteonecrosis
Hartley et al.16 reported the
long-term results (mean duration of follow-up, 9.8 years) of forty-eight
total hip arthroplasties without cement in young adults who had osteonecrosis.
An extensively coated stem was inserted in all hips. No stem was
revised because of loosening. There were ten revisions (21%):
six because of polyethylene wear, three because of recurrent dislocation,
and one because of sepsis. Of the surviving stems, 97% were
judged to be osseous stable. In terms of the functional outcome,
93% of the patients had no limitations, 86% had
no pain, 79% were able to walk unlimited distances, and 79% were
employed full-time. This study demonstrated the efficacy of cementless
fixation, and the limitations caused by complications related to
the prosthetic bearing surface in this young, high-demand population.
Morrey reported his experience with a short-stem design inserted
without cement in 162 total hip arthroplasties. Osteonecrosis was
a common diagnosis in his series. This "conservative" femoral
arthroplasty was shown to be durable after a mean duration of follow-up
of 6.2 years; however, these data were not superior to those reported
for regular stem designs such as those in the series of Hartley
et al.16.
One-Stage Bilateral Total Hip Arthroplasty
Hozack et al. compared the results of one-stage bilateral total
hip arthroplasty with those of unilateral total hip arthroplasty,
specifically with regard to perioperative morbidity. The demographic
data were similar except for a younger mean age in the group with
the bilateral procedure (fifty-four compared with seventy years).
The group with the bilateral procedure required more homologous
blood transfusion and had lower hemoglobin levels at discharge.
There was, however, no difference in the rate of complications,
particularly cardiopulmonary complications, and there was no difference
in the length of hospital stay or the overall hospital charges.
The success was attributed to a program of thorough preoperative
medical evaluation and to the strict criteria used to select patients
for one-stage bilateral total hip arthroplasty.
Total Hip Arthroplasty Following Acetabular
Fracture
Total hip arthroplasty has been used with increasing frequency
as a salvage procedure and on occasion as a primary mode of treatment
of acetabular fractures. Two recent reports focused on the medium-term
clinical outcomes of total hip arthroplasties following previous
acetabular fracture. Tile et al. reported the results of 101 total
hip arthroplasties in which a variety of implant designs had been
used with or without cement fixation. The mean interval between
the initial fracture and the total hip arthroplasty was 8.2 years.
The mean age of the patients was fifty-three years. At a mean of
7.5 years postoperatively, there had been five periprosthetic infections
and twenty-one dislocations. Twenty-one cups and seventeen stems
loosened, resulting in twenty-four revisions. The authors specifically assessed
functional outcome with use of the WOMAC scale and found substantially
poorer scores for pain, motion, overall function, family relationships,
sleep disturbance, and activities of daily living compared with
the scores of patients who had undergone total hip arthroplasty
because of osteoarthritis. Bellabarba et al. reported the results
of thirty acetabular reconstructions in which a hemispherical cup
was inserted without cement in patients with a previous acetabular
fracture. These results were compared with those of patients who had
undergone total hip arthroplasty because of osteoarthritis. Patients
with a previous acetabular fracture had a longer operating time
as well as greater blood loss, transfusion needs, use of bone-grafting,
and use of cup liners with an elevated rim for stability. At a mean
of five years, the clinical outcomes were no different from those
in the patients with osteoarthritis, with 90% satisfied
with the results. Radiographs showed more radiolucencies around
the cups in the patients who had had an acetabular fracture, although
only one cup had migrated. A higher rate of infection was not reported.
Total Hip Arthroplasty in Older Patients
As the elderly population increases in the United States, data
on the clinical efficacy and safety of total hip arthroplasty in
patients in the eighth and ninth decades of life are becoming increasingly important.
Pagnano et al. reported the results of sixty-six total hip arthroplasties
in sixty-five patients who had a mean age of ninety-two years at the
time of the operation. Medical comorbidities were common: 52% had
cardiac disease, 41% had hypertension, and 33% had
anemia. Most of the components were inserted with cement. At a mean of
4.2 years after the operation, there was a substantial improvement
in the Harris hip scores. Two reoperations were necessary, complications occurred
in seven additional patients, and 25% of the patients required
a stay in the intensive-care unit after surgery.
Keisu et al.17 reported the
results of ninety-two total hip replacements with use of cementless
fixation in eighty-six patients with a mean age of eighty-three
years. All patients received a tapered stem with a proximal porous
coating. At the two to eleven-year follow-up evaluation, 65% of
the patients were able to walk freely in the community without limitations
and 20% required a walker. The mean Harris hip score was
82 points. No revisions had been done because of loosening. Medical
complications occurred in 24% of the patients, although
none of these complications affected the outcome of the total hip
arthroplasty. There were no fatal thromboembolic or cardiopulmonary
complications. These data support the clinical efficacy and safety
of total hip arthroplasty in older patients, provided that comprehensive
preoperative and perioperative medical support is given.
Another challenge is revision surgery in elderly patients. Strehle
et al.18 reported the results
of revision total hip arthroplasty in fifty-three consecutive patients
older than eighty years (mean age, eighty-four years). More than
50% had cardiac disease, and three patients died during
the hospitalization. An additional fifteen patients (28%)
died at a mean of twenty-five months after surgery. Nearly 90% of
the patients who died were in ASA (American Society of Anesthesiologists)
class 3. Moreover, more complications occurred in these patients.
However, the functional outcome was excellent; 80% of the patients
were able to return to their prerevision living environment, and
80% were relatively pain-free. These data underscore the
importance of patient selection and the medical management of elderly
patients.
Miller et al. reviewed the mortality rate following 4967 total
hip arthroplasties (4164 primary and 803 revision operations) performed
by one surgeon over a twenty-seven-year period. The ninety-day mortality
rate was 1% for the primary operations and 0.87% for
the revisions. The rate of in-hospital deaths was 0.45%,
with a slightly higher rate following revision than following primary
surgery. The most common cause of death was myocardial infarction,
and the most important risk factor for death was increased age.
These data should provide a benchmark for other studies focused
on death rates following total hip arthroplasty.
The effects of wear debris on macrophage and monocyte cell lines
have been studied extensively. Recent studies have also shown that
osteoblasts are involved in the phagocytosis of wear debris and may
contribute to the development and progression of osteolysis. Using
cell cultures, Vermes et al.19 demonstrated
that metallic particulate debris affected osteoblast function through
two distinct mechanisms: a direct negative effect on cellular function
by the phagocytosis itself, and an effect mediated through cytokines,
which cause a downregulation of procollagen alpha-1 gene expression along
with decreased cell proliferation. Moreover, this study demonstrated
that osteoblasts stimulated by particulate debris produced interleukin-6
and prostaglandin E2, leading to the activation of osteoclast function.
The addition of other exogenous growth factors to the cell cultures
effectively reversed the suppressive effect of titanium particles on
procollagen alpha-1 mRNA. This work points to the possibility of
pharmacological intervention for the treatment and prevention of
osteolysis.
Andersson et al.20 reported
a negative effect on human osteoblast function (a decrease in H3-thymidine
incorporation into deoxyribonucleic acid) when the cells were exposed
to synovial fluid from hips undergoing revision surgery because
of aseptic loosening. To our knowledge, this was one of the first
studies to demonstrate a direct effect upon cellular function by
the synovial fluid around loose total hip prostheses.
Bone resorption by osteoclasts can be a result of an imbalance
in the regulation of cellular activities, differentiation, proliferation,
or survival. Bi et al.21 showed
a thirtyfold increase in differentiation of cultured osteoclasts
that were exposed to titanium particles. Particle phagocytosis did
not affect cellular survival. The increased cellular differentiation resulted
in measurably increased bone resorption. Neale et al.22 demonstrated that phagocytosis of
metallic particles resulted in a time and dose-dependent reduction
of the osteoclast population and in bone resorption. The effects
were more pronounced with cobalt-chromium and stainless-steel particles
than with titanium particles.
A variety of agents such as alendronate, Lipitor (atorvastatin
calcium), and bafilomycin-A have been studied in search of a pharmacological
treatment for osteolysis. The exact mechanism through which these
agents may have an inhibitory effect upon osteoclasts remains to
be fully defined. Harris et al. reported on a novel inhibitor of
osteoclast activity in vitro, a vascular endothelial growth-factor-neutralizing
antibody (VEGF-NA). With use of an established mouse calvarial bone-resorption model,
a macrophage cell line was activated with exposure to titanium particles.
Bone resorption, concentrations of various bioactive cytokines,
and gene expression of endothelial growth factor were quantitated.
Production of cytokines was substantially greater when the cells
were activated by the particles. Dose-dependent inhibition of bone resorption
was the most intense (97%) with use of VEGF-NA. These data
suggest that inhibition of angiogenesis may be an important way
to develop pharmacological suppression of osteolysis.
Alternative bearing surfaces in total hip arthroplasty have been
an area of intense investigation over the last five years. Bearing
surfaces include hard-on-soft (metal-on-polyethylene and ceramic-on-polyethylene)
and hard-on-hard (ceramic-on-ceramic and metal-on-metal) combinations. Improvements
in the manufacturing, machining, sterilization, and storage of these
materials have made these options increasingly attractive. However,
controversies remain as to which combination is the most effective
clinically.
Polyethylene
Metal-on-polyethylene is the most widely used bearing-surface
combination. Improvement of the wear characteristics of polyethylene
has been a major focus of research and development. Emphasis has
principally been on controlling the amount of free radicals. The
vast majority of polyethylene implants inserted in total hip arthroplasties
over the last three decades were sterilized with gamma radiation
in air. Gamma irradiation produces free radicals, which, when combined
with air, lead to oxidative changes in the polyethylene, resulting
in inferior wear characteristics. At the same time, gamma irradiation
produces cross-linking of the polyethylene, resulting in improved
wear characteristics. Moreover, long durations of shelf storage
of the implant can result in more oxidative changes in the polyethylene
when oxygen diffuses into the implant and reacts with residual free
radicals in the material.
Recently, several polyethylene products have been introduced
to increase cross-linking and to reduce oxidative degradation. These
products differ with regard to the amount of radiation, the type
of radiation (gamma or electron-beam), and whether the polyethylene
is remelted prior to machining to eliminate residual free radicals.
Some concerns have been raised with regard to alterations of the biomechanical
properties of polyethylene with higher doses of radiation and with
remelting. These changes can potentially result in inferior in vivo durability.
McKellop et al.23 demonstrated,
with simulator testing, that the packaging and sterilizing of polyethylene
in a low-oxygen atmosphere leads to increased cross-linking, decreased
oxidation, and improved wear characteristics. However, artificial
aging with heating of the various polyethylene specimens resulted
in inferior wear of the irradiated polyethylene regardless of whether
it was done in air or in an inert environment. McKellop et al. cautioned
that the advantages of radiation-induced cross-linking could be
negated in the long term by in vivo oxidation of residual free radicals.
Muratoglu et al.24 reported
on the in vitro performance of one of the cross-linked polyethylenes.
They demonstrated that the melt-annealing process effectively eliminated detectable
residual radicals. While this polyethylene product showed no detectable
volumetric wear over twenty million cycles in the hip simulator, there
was a reduction in the yield strength, ultimate tensile strength,
elongation, and crystallinity as compared with conventional polyethylene.
However, these values fell within the limits set by the United States
Food and Drug Administration. While these results are exciting,
long-term in vivo studies are still necessary to determine whether
the improved material properties of polyethylene that result from
cross-linking will endure.
At the 2000 meeting of the American Association of Hip and Knee
Surgeons, there was major controversy and extensive discussion following
the presentation of the results of in vitro testing of cross-linked
polyethylene. When the four most commonly used commercial cross-linked
polyethylene products were tested, all four were found to be superior
to the control polyethylene. However, more controversy was generated
by the data on the effects of artificial aging. The wear rate of
one particular product was substantially greater following aging
in air at 80°C for three weeks. In fact, this product performed
worse than the control. Moreover, among all of the samples tested,
this cross-linked product showed the most prominent and extensive
deleterious oxidative changes. The results of this study serve to
further emphasize the wide range of differences among commercially
available products. Testing methodologies need to be standardized
since these products are all made differently and thus will respond
to testing conditions differently. Differences in vitro do not necessarily reflect
differences in vivo, underscoring the need for long-term clinical
follow-up data to support more conclusively the use of these products.
Martell et al. reported improved clinical wear performance of
cross-linked polyethylene after a minimum two-year follow-up in
a well-designed prospective, randomized trial. The mean linear and volumetric
wear rates of the conventional cups were 0.21 mm/yr and
94 mm3/yr, respectively.
These values were significantly lower (p < 0.05) for the
cross-linked cups (0.14 mm/yr and 54 mm3/yr,
respectively). These authors also measured the wear rates in vitro.
The ratio of volumetric wear observed in vivo (cross-linked/control = 0.57) closely
matched the ratio observed with use of the wear simulator (cross-linked/control = 0.56).
These findings further support the use of laboratory testing to
validate the prediction of wear after in situ usage of a total hip
prosthesis.
Cross-linking is not the only methodology available for decreasing
polyethylene wear. Ritter et al. reported their experience with
polyethylene articulations made by compression molding. In compression
molding, a component is manufactured directly from polyethylene
resin by applying heat and pressure with use of a mold that matches
the geometry of the component. The number of free radicals and oxidative
degradation of the polyethylene are expected to be low with this
process. In a series of 378 total hip arthroplasties that were followed
for nearly twenty years, these authors reported a 0.5% rate
of pelvic osteolysis and a 3.2% rate of femoral osteolysis.
The linear polyethylene wear rate was 0.05 mm/yr. Ritter
et al. concluded that compression molding is an effective alternative to
cross-linking.
Controversy remains regarding the clinical correlation between
hip-simulator testing and the in situ use of total hip prostheses.
Schmalzried et al. monitored thirty-one patients with a Step Activity
Monitor (SAM) to measure their walking activity in real time. They
found that (1) male subjects walked at higher speed, and spent more
time doing so, than did female subjects; (2) male subjects had a
greater rate of polyethylene wear; (3) a slower walking speed was
associated with less wear; and (4) two million cycles of simulator
testing may correspond to one year of in situ usage. Thus, laboratory
testing of newer polyethylene for more than ten million cycles,
rather than for the more traditional six million cycles, may be
indicated. Moreover, a simple and relatively inexpensive device
such as the Step Activity Monitor may be of value in identifying patients
who may be at greatest risk for accelerated wear following total
hip arthroplasty. Schmalzried et al.25,
in another study, reported a correlation between polyethylene wear
and activity level. Their series comprised thirty-seven patients
with a mean bone-mass index of 27.5. Liners made of conventional polyethylene
or of Hylamer (DePuy-DuPont Orthopaedics, Wilmington, Delaware)
were sterilized with gamma radiation in air. These authors found, in
vivo, a linear wear rate of 0.14 mm/yr and a volumetric
wear rate of 73 mm3/yr. Regression analysis demonstrated
the strongest correlation between male gender and increased wear.
Other factors that significantly influenced wear included the patient’s height
(p = 0.007) and weight (p = 0.04) (correlated with
male gender), the liner thickness (p = 0.03), and the hip-rotation
center (p = 0.015). Pedometric data showed that the patients
walked an average of 1.9 million cycles/yr. Combining the
wear and pedometric data, Schmalzried et al. concluded that the
mean volumetric wear of conventional polyethylene sterilized with
gamma irradiation in an oxygen-rich environment is 30 mm3/million cycles for a 70-kg
patient. This value can serve as a target wear rate for hip-simulator
studies when newer polyethylene materials are tested.
A critical question in clinical practice concerns the correlation
between wear-rate measurements and the prediction of bearing-surface
failure after total hip arthroplasty. Dowd et al.26 analyzed
the wear and clinical performance of forty-eight total hip prostheses
with a single cup design and a 32-mm femoral head over a ten-year period.
These patients were at risk for wear because the mean polyethylene
thickness was only 4.9 mm and the mean age was fifty-six years.
All cups were sterilized in ethylene oxide. The mean linear wear rate
as measured on radiographs was 0.18 mm/yr. The slope of
the wear rates at different time-intervals was relatively linear.
Osteolysis was strongly correlated with wear (p < 0.001).
No osteolysis was observed in hips with wear of <0.1 mm/yr.
The most important conclusion was that future wear rates can be
predicted accurately on the basis of wear rates in the early postoperative
period.
Joint kinematics can influence function and durability after
any reconstructive arthroplasty. Recently, Dennis et al. used established
and validated fluoroscopic imaging techniques to evaluate joint
kinematics in seven patients who were awaiting a revision total
hip arthroplasty. They found that hip separation was greater in
the patients who had a failed prosthesis (mean, nearly 10 mm) than
in those who had a well-functioning one and were asymptomatic (mean,
3.6 mm). The principal locus of the separation was in the superior
and lateral directions, which corresponded to the areas of maximal
polyethylene wear on retrieval. Hip separation is theorized to contribute
to cup failure by several mechanisms: (1) eccentric loading resulting
in polyethylene wear, (2) impulse loading resulting in loss of fixation,
(3) pumping of wear debris leading to migration of the particles
and subsequent osteolysis, and (4) instability.
Ceramic
Clarke and Gustafson27 reported
that the wear rate of ceramic-on-polyethylene bearings was 50% of
that of metal-on-polyethylene bearings in hip-simulator testing.
In contrast, Oonishi et al.28 reported
that the mean linear wear rate was 0.05 mm/yr both for
a gamma-irradiated polyethylene cup articulating against a ceramic
femoral head and for the same polyethylene cup articulating against
a metallic head. Thus, cross-linked polyethylene may negate the
potential benefits of ceramic-on-polyethylene.
Two separate clinical studies on ceramic-on-polyethylene articulation
were reported at the 2000 Hip Society meeting. Wroblewski et al.
reported a linear wear rate of 0.03 mm/yr in a small series
of cemented total hip arthroplasties with an articulation of ceramic
and cross-linked polyethylene. The wear rate was fivefold less than
that seen with traditional metal-on-polyethylene articulations.
Ranawat et al. reported wear-rate measurements at a mean of 5.5
years in fifty-two pairs of patients; the only difference between
the two groups was that one had a ceramic-on-polyethylene articulation whereas
the other had a metal-on-polyethylene articulation. The linear wear
rate in the ceramic-on-polyethylene group was 0.13 mm/yr
compared with 0.17 mm/yr in the metal-on-polyethylene group
(p < 0.05). It remains to be determined if the wear-rate differential
will remain constant or become even greater with longer-term follow-up.
Most of the available data on the clinical efficacy of ceramic-on-ceramic
articulation have been reported by European investigators. Improved
cup fixation has been reported with use of porous-coated acetabular
shells29. Additional improvements
in the locking mechanism of the ceramic liner have decreased the
frequency of chipping during impaction30.
D’Antonio and Capello reported their experience in a multicenter
investigational study in which 504 total hip arthroplasties performed
over a two-year interval were randomized to either a ceramic-on-ceramic
or a metal-on-polyethylene articulation. A major difference between
the two groups was that 90% of the ceramic femoral heads
were 32 mm in diameter while 83% of the metallic heads
were 28 mm. Otherwise, the prosthetic design was identical in the
two groups. At the time of a two to four-year follow-up, there was
no difference in the clinical performance of the two types of articulation.
Small osteolytic lesions were observed in the proximal femoral zones
in the polyethylene group, whereas none were noted in the ceramic
group. No ceramic fractures or failures of the locking mechanism
were reported. Additional clinical trials of ceramic-on-ceramic
articulations are ongoing in the United States. The short-term results
have shown no apparent mechanical failures of the biomaterial, as
previously reported.
Metal-on-Metal
Metal-on-metal articulations provide another hard-on-hard combination
with a low rate of reported volumetric wear. Dorr et al.31 found no osteolysis after fifty-six
total hip arthroplasties that were followed for a mean of 5.2 years. Wagner
and Wagner32 also reported no
osteolysis after seventy-five total hip arthroplasties that were
followed for a mean of five years. However, one cup was revised
because of loosening. In a separate study, Dorr reported his experience
with a modular cup with use of metal-on-metal coupling. The particular
cup design offered a modular polyethylene locking mechanism with
a 3-mm-thick metal articulation surface machined into the polyethylene.
Penetration of the polyethylene liner was initially 0.03 mm/yr
from creep and settling, and subsequently it was 0.003 mm/yr.
No osteolysis was observed. The reported complications of metal-on-metal
articulations have been rare. Dorr et al.31 reported
disassociation of a modular liner and one case of metallosis due
to impingement and recurrent dislocation.
Potential systemic effects of disseminated metallic wear debris
are of concern; however, the clinical relevance remains undefined.
Urban et al.33 reported dissemination
of wear debris to the paraaortic lymph nodes in 68% of
twenty-eight patients. Moreover, they reported a 38% rate
of metallic debris and a 14% rate of polyethylene debris
in the liver and spleen. Lymphatic transport was the major mechanism
of dissemination. The clinical effects of debris dissemination were
essentially undetectable. In one patient, however, high concentrations
of titanium particles in the liver and spleen resulted in a granuloma
that required treatment. While there are case reports of malignant tumors
arising in proximity to joint-replacement prostheses34, a recent review of the available
epidemiologic studies showed no causal link between total hip or knee
arthroplasty and the development of cancer35.
Metal hypersensitivity has also been a subject of debate. Hallab
et al.36 provided a comprehensive
review of this subject. The prevalence of metal hypersensitivity
is higher in patients with a prosthetic joint replacement than it
is in the general population. Careful long-term follow-up is necessary
to further establish the clinical impact of wear debris upon the
immune and distant organ systems.
Infection
Infection remains the most feared complication following any
prosthetic arthroplasty. Some interesting data were made available
last year with regard to this particular complication in patients
with the human immunodeficiency (HIV) virus. Lehman et al.37 reported on a series of twenty-nine
patients who were either HIV-positive or intravenous drug users at
the time of a total hip or knee replacement. These patients had
a total of forty-one joint arthroplasties. The overall rate of deep
infection was 18% for HIV-positive patients; the rate was
much higher (40%) in patients who both were HIV-positive
and used intravenous drugs. The highest rate (66%) was seen
in patients who were active intravenous drug users. Sullivan et
al. reported the outcomes of twenty joint arthroplasties (in eleven
knees and nine hips) in fifteen patients with HIV infection who
were treated at a large tertiary-care center. In only one patient
was the HIV infection due to intravenous drug use; most of the infections
were in patients with hemophilia. Forty percent of the patients
had died during the follow-up period; half had died within the first
two years. The reoperation rate was alarmingly high (65%),
with 70% of the reoperations done because of infection.
Thromboembolism
Thromboembolic disease remains the most frequent complication
following total hip arthroplasty. At present, there is little controversy
with regard to the need for routine prophylaxis. However, there
is substantial disagreement with regard to which method is superior.
Freedman et al.38 presented data
from a meta-analysis of fifty-two studies comprising nearly 11,000
total hip arthroplasties performed over a thirty-three-year period. All
selected studies were prospective and randomized, and all utilized
venography to document deep-vein thrombosis. All methods of prophylaxis
were found to be superior to the use of a placebo. Overall, warfarin
and low-molecular-weight heparin were more effective than the other
agents (aspirin, a compression device, and fixed-dose heparin).
Low-molecular-weight heparin and fixed-dose heparin were associated
with a higher rate of bleeding complications. Freedman et al. concluded
that the most effective, least risky prophylactic agent was warfarin
while the least effective, most risky agent was fixed-dose heparin.
The efficacy of warfarin has been well established; however,
its use is labor-intensive and can result in bleeding complications.
Farber et al. studied the efficacy of in-hospital warfarin prophylaxis.
Their protocol included administration of adjusted-dose warfarin
until contrast venography was performed. Prophylaxis was discontinued
if there was no deep-vein thrombosis, it was continued for six to
twelve weeks if there was distal deep-vein thrombosis, and intravenous
heparin therapy was initiated if there was proximal deep-vein thrombosis.
Thromboembolism occurred in fourteen (0.73%) of 1920 patients
following hospital discharge. Six patients (0.31%) had
nonfatal pulmonary emboli, and eight (0.42%) had deep-vein
thromboses. This protocol appeared to be effective while minimizing
the risk of complications associated with continued warfarin prophylaxis
following hospital discharge. Cost was also reduced. Bern et al.
reported the results of a prophylactic protocol with use of low-fixed-dose
warfarin. This was a novel protocol in that the patients received
a 1-mg dose of warfarin starting seven days prior to surgery. This
dose was continued after surgery, until discharge. These patients
were compared with a group of patients who received adjusted-dose
warfarin. Ultrasound did not reveal deep-vein thrombosis in either
group. There was no difference in the estimated blood loss during
surgery or in the transfusion requirements between the two groups.
Elevation of prothrombin time was not observed in the low-dose group.
This protocol appears to be effective and also would minimize the
potential for complications and the need for monitoring after hospital
discharge.
In contrast, Comp et al.39 documented
the need for prolonged prophylaxis after hospital discharge when
enoxaparin was used. Nearly 1000 patients were enrolled in this
multicenter, prospective, randomized study. All patients received
injections of 30 mg of enoxaparin twice daily during hospitalization.
Then the patients were randomized into a double-blind protocol,
receiving either one 40-mg injection of enoxaparin or a placebo
injection daily for three weeks. There was a significant difference
(p < 0.001) in the overall rates of deep-vein thrombosis
(8% in the enoxaparin group compared with 23% in
the placebo group). There was also a significant difference (p < 0.001)
in the rates of proximal deep-vein thrombosis (2.7% and
13%, respectively). A nonfatal pulmonary embolus developed
in only one patient.
The most commonly used methods for the detection of deep-vein
thrombosis are contrast venography and duplex ultrasound. Both methods
have limitations. Colwell et al. reported the results of a new radioisotope
test (AcuTect) that specifically identifies acute thrombi by detecting
activated platelets. In their series of 100 patients, who also underwent ultrasound,
sensitivity and specificity of the AcuTect scans were both 88% and
accuracy was 79%. These results are preliminary and remain
to be validated by other centers. However, this test may serve as
an alternative method of detection, particularly of acute thrombi
in patients with a history of deep-vein thrombosis.
Dislocation
A distinct subgroup of patients who have a dislocation for the
first time many years after a successful total hip arthroplasty
has been identified. Berry et al., in a review of the results of
25,465 primary total hip arthroplasties performed over a twenty-six-year period
at the Mayo Clinic, found the overall dislocation rate to be 2.4%,
with 0.6% of the dislocations occurring for the first time
more than five years following the arthroplasty. The most common direction
of dislocation was posterior (62%), and the median time
to the first dislocation was 11.3 years. Women were more likely
to have this complication. Other risk factors included episodes
of subluxation, trauma, and the onset of cognitive or motor neurological
impairment. There was also a correlation with polyethylene wear
of >2 mm and with cup loosening and migration. An interesting finding
was that 18% of the cups were initially placed beyond the
recommended limits of cup position. In this study, 55% of
the dislocations became recurrent and 30% of the recurrent
dislocations required revision surgery.
Many different treatment options have been proposed for recurrent
dislocation. Shapiro et al. reported on the use of a constrained
liner in eighty-five total hip arthroplasties. The patients had
had an average of four dislocations prior to revision with the constrained
liner. Redislocation occurred in 2.4%. Toomey et al. reported
on the use of liner exchange in fourteen hips with a modular cup;
79% had no more dislocations. Moreover, only one patient
had recurrent instability following the liner exchange. This technique
may be useful in carefully selected patients. Earll et al. reported
the results of twenty-seven bipolar reconstructions for the treatment
of instability and compared them with those of revisions performed
with a liner-exchange technique similar to that reported by Toomey
et al. No dislocation occurred following the bipolar revisions,
whereas 55% of the hips with liner exchange had dislocation
and 31% had recurrent instability. However, the group that
had had bipolar revision had significantly (p = 0.03) lower
Harris hip scores, principally because of persistent pain. Parvizi
and Morrey40 reported the results
in twenty-eight hips that were revised with use of a bipolar prosthesis
because of recurrent instability. This technique was successful in
81% of the hips, with 11% requiring additional surgery.
The Harris hip scores were poor; the mean score was only 55 points
at the time of final follow-up. This technique may be as effective
as other options, but the patient must be made aware of the potential
for a suboptimal functional outcome.
A new alternative to these methods is the use of larger femoral
heads, especially those with the improved wear characteristics of
cross-linked polyethylene. Bartz et al.41 reported
the effects of increasing head size with regard to impingement and
posterior dislocation. They found a significant improvement (p < 0.05)
in flexion prior to impingement and dislocation when the head size
was increased from 22 to 28 mm. The difference in these flexion
values between 28 and 32-mm heads was not significant. The principal source
of impingement of the 22-mm heads was the stem neck on the cup edge,
while that of the 32-mm heads was osseous impingement of the femur
on the pelvis. Bartz et al. presented additional data at the 2001
meeting of the American Academy of Orthopaedic Surgeons. They reported
that the use of 38-mm heads was associated with an increase in the
range of flexion prior to dislocation. However, impingement was
sensitive to the neck taper diameter. There was no advantage in
using a 38-mm head instead of a 28 or 32-mm head when a stem with
a larger neck diameter was used. It is therefore important for the
surgeon to carefully evaluate the efficacy and risks of using larger
heads when addressing recurrent dislocation.
Stress-Shielding
Adverse bone-remodeling as a result of stress-shielding remains
a topic of concern. Engh et al.42 demonstrated
the inadequacies of routine radiographs for analysis of bone-remodeling.
Interobserver agreement regarding the presence of bone loss was
73%. Agreement decreased to 66% when the investigators
quantitated bone loss. Bone loss was not reproducibly recognized
on routine radiographs until 70% loss had occurred as documented
with dual-energy x-ray absorptiometry. Yamaguchi et al.43 used sequential dual-energy x-ray
absorptiometry scans to quantitate bone loss around fully and proximally
coated stems at twenty-four to thirty months following surgery.
With both stem types, the greatest amount of bone loss was observed
in the proximal part of the femur at twelve to eighteen months. Greater
bone loss in the distal zones (zones 3 and 6) was observed in association
with the fully coated stems. There was no difference in the clinical
outcome or the stability of fixation. The long-term clinical sequelae
of stress-shielding remain to be fully established.
The costs of total hip arthroplasty, particularly revision surgery,
have continued to escalate. Two studies specifically evaluating
the costs of revision total hip arthroplasty were presented at the
2001 meeting of the American Academy of Orthopaedic Surgeons. Lavernia
et al. have been analyzing quality of life following total hip arthroplasty
for the last five years. In a study in which they used the Quality of
Well Being Index to analyze the results of fifty-three revisions
at one to three years, they demonstrated that the mean cost per
Quality Well Year was $11,977 at one year and $7955
at three years. These costs indicate that revision total hip arthroplasty
is extremely cost-effective compared with medical interventions
in other disciplines. Crowe et al. specifically analyzed the costs
of fifty-one revision total hip arthroplasties, with stratification
for complexity. The actual costs were then compared with the reimbursement
received by the hospital. The hospital lost an average of $5400
for each revision operation. These authors concluded that the hospital
continued to lose money despite improvements in cost containment
over the last decade, which included the establishment of critical
pathways, shortened length of stay, price control with regard to
implants, and improved surgical techniques.
In the last decade, much discussion has focused on the use of
patient-directed outcome measurement instruments such as the SF-36
and the WOMAC in the evaluation of patients who have had a total
hip arthroplasty. In a study by Soderman and Malchau44, a Harris hip score was assigned
to 350 patients who had had a total hip arthroplasty and already had
been assigned SF-36 and WOMAC scores. All three instruments were
found to be valid, reproducible, and reliable. There was good interobserver reliability
among the investigators who assigned the Harris hip scores. The
correlation was especially good with regard to pain and function.
Soderman and Malchau concluded that the Harris hip scale was as
valid for outcome measurement as the SF-36 and the WOMAC. This finding
is of some importance since many studies have provided only Harris hip
scores as the clinical outcome measure. Valid comparisons of different
series can therefore be made.
The two major organizations with focused interest in total hip
arthroplasty and related disciplines are the Hip Society and the
American Association of Hip and Knee Surgeons. The Hip Society routinely holds
a spring meeting in conjunction with the annual meeting of the American
Academy of Orthopaedic Surgeons. Its members also participate extensively
in American Academy of Orthopaedic Surgeons symposia and Instructional
Course Lectures and in meetings of regional orthopaedic societies.
The American Association of Hip and Knee Surgeons has an annual
meeting in the fall. Its members routinely conduct surveys, particularly with
regard to practice-management issues such as prophylaxis for deep-vein
thrombosis, management of infections, and cost analysis. Extensive
information on scientific, social, and political issues is exchanged
at these meetings. Members of both societies participate widely
with other national and regional instructional meetings throughout
the year. The requirements for and timing of scientific abstract
submission for the American Association of Hip and Knee Surgeons
is generally the same as that for the meeting of the American Academy
of Orthopaedic Surgeons. The upcoming meetings for these organizations
in 2002 will both be held in Dallas.
Note: The authors are grateful to John J. Callaghan, MD, and
Vincent D. Pellegrini Jr., MD, for their time and effort in editing
this manuscript.
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