Short Term Clinical Outcome of a Porous Tantalum Implant for
the Treatment of Advanced Osteonecrosis of the Femoral Head
Chantal Séguin, John S Theodoropoulos, Edward J Harvey *
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Abstract: Purpose of the
study: Osteonecrosis of the hip mostly affects young
individuals and often progresses to a debilitating disease.
Several treatment modalities exist, but none are completely
satisfactory. This study evaluates the clinical outcome of
patients treated with core decompression and insertion of a
porous tantalum implant in the femoral head. This procedure
is similar to commonly performed procedures, but has the
additional advantages of providing structural support to the
necrotic femoral head while having no donor-site morbidity.
Methods: We evaluated 15 patients with 18 osteonecrotic hips
with Steinberg stage III (3 hips) and IV (15 hips) disease.
The mean age of the patients was 42 years-old (eldest 66),
and the mean time for follow-up was 23 months. The outcome
measure was hip function, evaluated with the Harris hip
score, and the end point was total hip arthroplasty, or
referral for this procedure. Results: The success rate at
twelve months postoperatively was 77.8%, and the overall
success rate was 44.5%. Failures occurred at a mean time of
11.7 months, and one complication, a periprosthetic
fracture, occurred 4 months postoperatively. On average,
patients who did well improved their Harris hip scores by
21.7 points, and patients who eventually required
arthroplasty decreased their scores by 14 points. Conlusions:
Core decompression with porous tantalum implants showed
encouraging success rates and early clinical results in
patients with advanced stage osteonecrosis, but further
larger scale studies are required to identify the population
best suited for this procedure. Keywords: osteonecrosis,
femoral head, tantalum, core decompression.
Osteonecrosis of the hip, previously named avascular
necrosis, is a naturally progressive disease typically
affecting young individuals (the mean age approximately 35
years old) (1). It occurs when blood supply to the femoral
head is disrupted, resulting in infarction and avascular
necrosis of bone. Several etiologies have been identified,
such as trauma (femoral neck fracture or posterior hip
dislocation), blood disorders (e.g. sickle cell anemia), and
radiation therapy (2, 3, 4). Other important risk factors
identified are the use of alcohol, use of corticosteroids
(e.g. in patients with systemic lupus erythematosus, or
status-post renal transplant) and cigarette smoking, as well
as pregnancy (5, 6). Having HIV has also been associated
with an increased incidence of osteonecrosis of the femoral
head, but it is unclear whether this is related to the virus
or to the antiviral therapy (7). Much is still to be learned
about the etiologies and the pathophysiology of this disease.
When left untreated, 80% of clinically diagnosed cases of
femoral head osteonecrosis will progress, most often
incapacitating the patient due to pain and decrease in hip
mobility (8). The natural history of this condition is that
it is usually initially confined to the superior
weight-bearing portion of the femoral head, but progresses,
rendering the area susceptible to collapse, and leading to
subchondral fractures. Eventually, degenerative changes of
the hip joint ensue (9). In the United States, the estimated
incidence of this condition is 10,000-30,000 per year, and
5-12% of all total hip arthroplasties are performed to treat
patients with osteonecrotic hips. This latter treatment
modality was proven to be highly successful (3). However, it
is not appealing to the young and active patient population
often affected by osteonecrosis of the hip, as they will
most likely outlive their prosthesis and require revision.
Non-operative treatment modalities also exist. They are
divided into external biophysical modalities (extracorporeal
shock-wave therapy, hyperbaric oxygen, or pulsed
electromagnetic field) and pharmacological therapies (lipid-lowering
agents, anticoagulants, or bisphosphonates). Mont MA et al.
did a complete review of the English literature from 1960 to
1993 and found 21 studies where clinical outcomes of
osteonecrotic hips treated non-operatively (excluding
electrical stimulation) were evaluated (3). Together, these
studies yielded an overall clinical success rate 22.7%.
Pulsed electromagnetic field has been proven to result in
clinical improvement and stabilization of osteonecrosis on
radiographs by two studies done in the late 1980s, but this
modality has never gained popularity (10, 11). Also, new
pharmacological measures as well as the use of growth and
differentiation factors have shown potential in preventing
and treating this disease, but clinical research projects
are still awaiting long-term follow-up results to provide
Joint-preserving surgical procedures are presently the most
commonly used approach to treatment of osteonecrotic hips.
They are described as temporizing measures, possibly
preserving these femoral heads. Most have shown superiority
over symptomatic treatment, but none are completely
satisfactory. The two most common procedures are core
decompression and fibular bone-grafting techniques. Core
decompression alone has the disadvantage of lacking
subchondral support, whereas fibular grafting techniques
have increased morbidity associated with graft harvest,
longer operative time and blood loss, as well as
rehabilitative complications (3, 12, 13). The rationale for
fibular bone-grafting is that it allows decompression of the
femoral head as well as the removal of necrotic bone with
its replacement by the graft. This graft plays the important
role of providing structural support and scaffolding,
facilitating repair and remodeling of subchondral bone (14,
Since the main disadvantages of fibular grafting techniques
are related to the bone-graft harvesting, the use of another
material with characteristics similar to bone graft presents
an interesting modality. Porous tantalum is an expanded (foam-like)
metal currently being used in several orthopedic procedures,
namely hip and knee arthroplasty, spine surgery, and as bone
graft substitute. It was found to have an excellent
biocompatibility and to be safe to use in vivo (16). It has
a high volumetric porosity and is corrosion resistant. Its
modular elasticity is similar to that of subchondral bone,
yet its strength, fatigue properties, endurance limits, and
initial stability against bone are all superior to natural
bone grafts (17,18,19). In fact, a recent study done in
animal models showed that it had rapid tissue ingrowth and
fixation strength, which allows faster return to full
weight-bearing compared to procedures using fibular bone
graft (20). Furthermore, another study which mechanically
tested porous tantalum implants in a model mimicking a
necrotic femoral head, demonstrated that tantalum implants
reduced subchondral plate deflection and that its strength
was 9.3 times greater than the maximum force it sustains
when placed in the femoral head (21). Finally, local foreign
body infection is a possible complication of orthopedic
implants, and in this regard, Schildhauer et al. have
studied the adhesion of the two bacteria that are of most
concern: Staphylococcus aureus and Staphyloccocus epidermis
(22). The former was found to adhere significantly less
(p<0.05) to pure tantalum compared to titanium alloy,
polished stainless steel, and tantalum-coated stainless
steel, and the latter bacteria adhered to pure tantalum to
an extend similar to other materials used in orthopedics.
All of these properties make tantalum implants good
substitutes for fibular bone grafts in decompressing
surgeries for osteonecrosis of the hip. Theoretically,
porous tantalum implants have the advantages of fibular
grafts, providing core decompression and structural support,
and, in addition, they represent a minimally invasive
procedure with no donor-site morbidity. They thus have the
theoretical potential of limiting the progression of the
disease, which could delay, and maybe even prevent, the need
for a hip replacement. This clinical study was performed to
verify this theoretical advantage of the tantalum plug
relative to core decompression alone or to fibular
This study evaluates the early clinical outcomes of patients
with advanced osteonecrotic femoral heads (presenting with
subchondral collapse or femoral head flattening) treated
with insertion of porous tantalum implants. We expected that
this procedure would improve patients' clinical symptoms,
most often being pain and limitations in hip function, and,
in turn, delay the need for revision with total hip
arthroplasty, which was the endpoint of our study.
This prospective study was conducted at the Montreal General
Hospital, from April 2002 to February 2004. Experimental
subjects were taken from patients referred to a single
surgeon for treatment of Steinberg Stage III and IV (Table
1) unilateral or bilateral femoral head osteonecrosis. Only
patients with non-traumatic etiologies for the disease were
considered for participation in the study. Exclusion
criteria also included patients who were actively being
treated with corticosteroids, had previous surgery to the
affected hip, or were unwilling to have surgery at time of
clinical presentation. Patients were offered the tantalum
implant procedure when they were unwilling to have treatment
with free vascularized fibular graft or total hip
arthroplasty. 19 patients with 22 osteonecrotic hips treated
with tantalum implants were initially entered in the study
and signed an informed consent form prior to enrollment.
Four patients were removed from the study as they were
unavailable for follow-up at one year or later. One patient
sustained trauma, more precisely a fall from her own height,
resulting in a periprosthetic fracture one month
postoperatively. This patient was not included in data
analysis, but was rather included in the results as a
complication. Thus, functional outcomes of 14 patients with
17 osteonecrotic hips were used for analysis. The average
age of the patients was 42 years old (range 19 to 66). Table
2 outlines details on patient demographics.
All patients underwent the same operative procedure through
a minimally invasive lateral approach (2-3 cm skin
incision). First, a core decompression technique was done
under c-arm fluoroscopy imaging. It consisted of inserting a
guide pin from the lateral femoral cortex into the femoral
head and using a core reamer over this guide pin to create a
10-mm diameter bone channel. A porous tantalum plug (Zimmer
Trabecular Metal Technology, Trabecular Metal Osteonecrosis
Intervention Implant System, Warsaw, Indiana; see Figure 1),
was then inserted in this bony channel. This implant is
fully made of pure porous tantalum, with an interconnected
porosity of 75-80%. It has a cylindrical shape of 10 mm in
diameter, and comes in lengths of 70 to 130 mm, available in
5 mm increments. The implant is threaded on a 25 mm length
at one end, where the diameter is 14 mm, and a hemispherical
tip at the other, for support of the subchondral plate (see
Figure 2). Bilateral procedures were performed in the same
operative period, whether they were both tantalum implants
or one tantalum implant and one free vascularized fibular
graft, except for one patient who had a tantalum implant
inserted in each hip at 3-month interval. Postoperative care
consisted of prophylactic intravenous antibiotic (Cefazolin
1-2 g IV q8h twice) and anticoagulation therapy (Low
Molecular Weight Heparin 5000 IU SC qd until weight bearing).
Patients were instructed to be non-weight-bearing for 3
weeks, to partial weight-bear for the next 3 weeks, and to
weight bear as tolerated thereafter.
The primary outcome of this study was functional improvement,
which was assessed with the Harris hip score. This
15-question scoring tool for rating hip function was
formulated and published in 1969 by WH Harris, for
evaluation of traumatic arthritis of the hip, and is now the
scoring tool the most commonly used worldwide for assessment
of hip function in general (23). It consists of a point
scale of a maximum of 100 points subdivided into 4 subscales:
pain (44 points), function (47 points), range of motion (5
points), absence of deformity (4 points). A total Harris hip
score below 70 points is considered a poor result, 70 to 80
fair, 80 to 90 good, and 90 to 100 excellent (24). Söderman
and Malchau performed a validity and reliability test for
the Harris hip score (24). They found that test and retest
reliability between two examinations by physicians had
correlation coefficients of 0.94, and concluded that this
scoring system had high content and construct validity. This
score was obtained for each subject at their pre- and post-operative
visits. Because functional improvement after orthopedic
surgeries usually improve mostly throughout the first year
following the procedure and plateaus thereafter, post-operative
scores obtained at 12 months or later were used as data
points for analysis. When more than one follow-up with
Harris hip score recording had been done at one year post-operatively
or later, the best score was taken, which was always the
latest one. Paired T-tests were used to compare
pre-operative and post-operative Harris hip scores among all
patients, as well as within subgroups of patients who
eventually failed and those who did not. Failure, defined as
being referred for or undergoing a total hip arthroplasty
was the end point of this study. Survival rate was
calculated with the Kaplan-Meier Method and refers to
patients' hips which did not progress to the point of
requiring further surgical treatment. These analyses were
performed with SSPS Manager (version 11.5; SSPS Inc,
Chicago, Illinois). Significance was set at p<0.05.
Outcome at 12 months or more
Paired t-test analysis was done to compare pre-operative to
post-operative Harris hip scores of patients' hips that had
not failed at 12 months post-operatively (Refer to Table 3).
There were 14 such hips in 12 patients. 2 patients with
unilateral treatment were removed for analysis of hip
function improvement since no pre-operative scores had been
obtained. Of the 12 hips of 10 patients remaining, 8 hips
(75%) in 7 patients improved their Harris hip scores, the
mean improvement was of a magnitude of only 3.8 points.
Standard deviations for the mean postoperative score and
score improvement were very large, which reflects the
discrepancy in individual postoperative values. When looking
closely at these, it is noticed that they were very low in
patients whose hips eventually failed, whereas they were
greatly increased in patients whose tantalum implants
succeeded, preventing the need for joint replacement surgery
before the end of the study. Mean Harris hip score
improvement was thus calculated separately for failed and
non-failed tantalum implant procedures: a 21.7-point
increase was obtained for patients who did well, compared
with a mean decrease of 14.0 points for patients whose
implants failed. This excludes three patients in whom three
hips failed prior to the 12-month mark, and whose
pre-operative Harris hip scores were particularly low (average
The average time of final follow-up and recording of the 14
Harris hip scores used for analysis was 23.2 months (range
12 to 48). This excludes three patients, one of which had
bilateral involvement, in whom one operated hip failed prior
to the 12-month mark, more precisely at 7, 8 and 10 months
post-tantalum insertion, as well as one patient who
sustained mild trauma to her single operated hip (fall from
own height) resulting in a periprosthetic fracture (see
Figure 3). This represents a failure rate of 22.2% at one
year postoperatively. 6 additional hips in 4 patients,
including all 3 patients with bilateral implant intervention
including one whose contralateral hip had failed earlier,
had undergone total hip arthroplasty before the final time
of follow-up. Therefore, 10 out of 18 (55.6%) tantalum
implant procedures failed within the study period. The mean
time for failure, excluding the patient with a
periprosthetic hip fracture, was 11.7 months (SD=3.7, range
7 to 20 months), and the mean age at surgery of the patients
who failed was 50.1 years old (SD=12.1, range 29 to 66),
compared to a mean age of 36.8 years old (SD=12.2, range 19
to 55) for the patients whose tantalum implant did not fail.
Refer to Figure 4 for the Kaplan-Meier survivorship curve.
Osteonecrosis of the femoral head is a debilitating disease
that requires treatment. Since the late 1960s, several
studies have evaluated effectiveness of potential techniques
to treat this condition, such as core decompression,
vascularized and nonvascularized fibular bone grafts, and
angular or rotational osteotomies. Mont et al. performed a
meta-analysis to look at the these studies, which were
almost all performed on precollapse (Steinberg Stage I or II)
osteonecrotic femoral heads and thus their results cannot be
compared to ours (3). Furthermore, the conclusion of the
meta-analysis was that early diagnosis and intervention
prior to collapse of the femoral head, thus in earlier
stages than in our patient population, is key to a
successful outcome of joint-preserving procedures. However,
3 of the studies they looked at evaluated Steinberg Stage IV
osteonecrotic hips treated with vascularized fibular bone
grafts; they showed clinical success rates of 52, 48 and 71%
at mean follow-up times of 12 months or more (25, 26, 27).
Mont et al. concluded in their meta-analysis that for
femoral heads that have already collapsed, such as in our
patients' hips, the results of joint-preserving procedures
are less satisfactory than the results of total hip
In the present study, the success rate, defined as not
requiring further hip treatment after core decompression
tantalum implant insertion, was 77.8% at twelve months
postoperatively. The overall success rate at final time of
follow-up (mean of 23.2 months) was 44.5%. Failures (10 hips,
55.6%) occurred at a mean time of 11.7 months. One
complication occurred: a periprosthetic fracture at four
months postoperatively. This patient was included in the
failure rate, as further surgical hip treatment was done,
but was not included in the mean failure time, as this
failure was due primarily to trauma, and thus does not
reflect the time of failure of the tantalum implant per say.
Patients who did not require further treatment within the
follow-up time improved their Harris hip scores by 21.7
points, and patients who eventually underwent arthroplastic
treatment decreased their score by 14 points, on average.
The mean age at tantalum implant insertion in patients who
failed was 50.1 years old, compared to 36.8 in patients who
did well. This 13.4 years of age difference is statistically
significant (p=0.040). The average preoperative Harris hip
score of patients who failed was 44.3, compared with 59.5
for patients who did well. This represents a 15.2-point
difference, which is also statistically significant
(p=0.039). This suggests that age at surgery and
preoperative hip function have prognostic implications for
the porous tantalum implant insertion: the younger, less
symptomatic, and less debilitated patients had the most
favorable outcomes. Our patient population is not large
enough to make an association between outcome and etiology
or uni/bi-lateralism of the disease process. Our statistical
findings are also limited in power because of the small
number of subjects. The follow-ups, and thus postoperative
score recording, were not done at the same time interval
with respect to the surgery, making the results not as
reproducible and precise as they could have been.
Tsao et al performed the only other published study to date
evaluating the clinical outcome of porous tantalum implants
in osteonecrotic human hips (28). They evaluated 113 hips
treated with tantalum implants. Intraoperative
classification yielded 7 and 12 hips of Steinberg Stage III
and IV respectively. The mean Harris hip scores of hips
improved by 26 and 9 points in patients with stage III and
IV osteonecrotic hips respectively. This is comparable to
our 21.7-point average improvement in our patients' hips.
One (14%) stage III and three (25%) stage IV were revised,
which is similar to our failure rate of 22.2% at one year.
Their success rate for all stage II disease, which
represented the bulk of their experimental data, was 85.3%
at twelve months. They concluded that treatment of early
stage osteonecrosis of the femoral head with core
decompression and a porous tantalum implant show encouraging
success rates, especially in association with early stage
Veillette et al. have also recently done a study, with a
publication in press, assessing clinical and radiographic
outcomes of osteonecrotic hips treated with core
decompression and porous tantalum implant (28). They
evaluated 60 hips: 1 Steinberg stage I, 49 stage II, and 8
stage III. They used the same hip function evaluation tool
and end point as we did. Their one-year survival rate was
91.8% at one year. This is higher than ours, but it is
likely due to the fact that most of their hips had stage II
osteonecrosis, compared to a majority of stage IVs in our
study. Overall, 3 of their 8 hips with stage III disease
were converted, representing a success rate of only 62.5%,
which is more similar to our results. They concluded that
treatment of early stage osteonecrosis of the femoral head
with core decompression and a porous tantalum implant show
encouraging success rates, especially in patients with early
In conclusion, core decompression with porous tantalum
implant insertion provides a minimally invasive surgical
treatment option to treat advanced osteonecrotic hips, with
clinical outcomes and success rates comparable to other
commonly used surgical procedures. It has the advantage of
providing structural support without having associated
donor-site morbidity. It seems however that this treatment
modality is more successful in younger patients with more
functional and less symptomatic hips. This is fortunate as
it is for younger patients that the only definitive
treatment so far, total hip replacement, is least appealing,
as they are likely to outlive a hip prosthesis, thus
requiring one or more revisions. In further studies, it
would be useful to perform larger studies, perhaps at a
multicenter level, to clearly elucidate the association
between pre-operative stage and etiology of the disease, as
well as patients' age with success rate. This would enable
us to make clear recommendations for choosing the best
treatment modality for the individual patient.
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is a fourth-year medical student at McGill University, class
of 2007 (M.D.C.M.). She plans to do a Orthopedics Residency
Chantal Séguin, M.D., is an assistant Professor at
McGill University, in the division of Haematology,
practicing at the Montreal General Hospital.
John S Theodoropoulos, M.D., did an orthopedic
residency at McGill and graduated in 2004. He now practices
in the community of Toronto and is the Maple Leaf`s team
doctor, and will soon be staff at Mount Sinai and the
University of Toronto.
Edward J Harvey, M.D.C.M., MS,c FRCSC, is an
associate Professor McGill University and co-Director:
J.T.N. Wong Labs for Bone Engineering. He practices
Orhopedics at the
Montreal General Hospital.