From June 1982 to December 1991, fifty-five cementless primary
total hip arthroplasties were performed in forty-five consecutive
patients with osteonecrosis of the femoral head. During the study
period, this was the only treatment used for advanced (Ficat and
Arlet stage-III or IV) osteonecrosis at our institution. In all
patients, the diagnosis of osteonecrosis was confirmed by pathological
examination of the resected femoral head. The osteonecrosis was
steroid-related in twenty-one patients (47 percent), idiopathic
in nine (20 percent), posttraumatic in seven (16 percent), and alcohol-induced
in four (9 percent). There were single cases of sickle-cell anemia, Legg-Calvç¬erthes
disease, slipped capital femoral epiphysis, and epiphyseal dysplasia.
The average age of the patients at the time of the primary arthroplasty
was thirty-one years (range, twenty-one to forty years). The series
was composed of thirty men and fifteen women with an average weight
of seventy-seven kilograms (range, forty-six to 100 kilograms).
A posterolateral approach was used in all patients.
All of the femoral components were of a straight, cast cobalt-chromium
stem design with a microporous ingrowth surface of sintered beads.
The components that were used reflected the evolution of the femoral
component design, from the original monoblock stem with a thirty-two-millimeter head
to the modular Prodigy design with a twenty-eight-millimeter head.
Fifty-three (96 percent) of the components were Anatomic Medullary
Locking stems (AML; DePuy, Warsaw, Indiana), and two (4 percent)
were Prodigy stems (DePuy). Of the AML stems, twenty-seven were
monoblock and twenty-six were modular; twenty-seven were coated
on one-third of their surface, twenty-four were coated on five-eighths
of their surface, and two were extensively coated. The two Prodigy components
were extensively coated. The diameter of the femoral head was thirty-two
millimeters in forty-five hips (82 percent) and twenty-eight millimeters
in ten hips (18 percent). The femoral diaphysis was reamed to obtain
greater than five centimeters of cortical contact, with the femoral component
being the same diameter or one-half millimeter larger than the final
reamer.
The patients were treated with several different designs of acetabular
components, including the Lunceford (nonmodular) cup (DePuy) in
eighteen hips, the Arthropor cup (Johnson and Johnson, Stamford,
Connecticut) in fifteen, the Triloc cup (DePuy) in six, the Engh
Revision cup (DePuy) in four, the JMP Oblong cup (Johnson and Johnson) in
four, the Harris-Galante cup (Zimmer, Warsaw, Indiana) in three,
the Gemini cup (DePuy) in two, and the Duraloc-100 (DePuy), the
Duraloc-1200 (DePuy), and the PSL (Osteonics, Allendale, New Jersey)
cup in one each. All were variations of a porous-coated metal shell
with an ultra-high molecular weight polyethylene liner. Again, reflecting
component evolution, the cups inserted before 1984 were nonmodular
and those inserted subsequently were modular. All of the acetabular
components were inserted in a press-fit manner and were one millimeter
larger in diameter than the final reamer.
Patient information was prospectively obtained with the annual
use of questionnaires evaluating the severity and location of pain,
walking ability, overall function, work status, and satisfaction. Standardized
radiographs and physical examination data were obtained prospectively
at annual clinic visits and were entered into a database. Analysis
was performed with use of the SPSS statistical package (SPSS, Chicago,
Illinois). Continuous variables were tested for significance with the
Student t test.
Radiographic evaluation included an assessment of the fixation
of the femoral and acetabular components, femoral stress-shielding,
polyethylene wear, osteolysis, and heterotopic ossification. Femoral
components were classified as bone-ingrown, fibrous stable, or unstable,
according to previously published criteria6,9.
Acetabular components were considered loose if there was a change
in alignment of greater than 4 degrees, two or more millimeters
of change in the position, a circumferential or progressive radiolucent
line, or shedding of beads from the surface. We evaluated stress-shielding
by comparing six-week postoperative and subsequent follow-up radiographs.
Stress-shielding was classified according to the criteria of Engh
et al.7,8, and progression of
stress-shielding was determined by a comparison of annual radiographs. Polyethylene
wear was calculated two-dimensionally, according to the method developed by
Charnley and Cupic3. Heterotopic
ossification was classified according to the system of Brooker et
al.2.
Osteolytic lesions were documented and classified on the basis
of both their size and their location, according to previously published
criteria19. Geographic loss of
either cortical or trabecular bone was considered evidence of osteolysis,
and lesions greater than 1.5 square centimeters were considered
large and of potential clinical importance. Femoral osteolytic lesions
were classified according to the zones described by Gruen et al.13, and acetabular lesions were classified
according to the location in the ischium, pubis, or ilium.
Five patients (five hips) died and one patient (two hips) was
lost before the time of the minimum five-year follow-up; this left
thirty-nine patients (forty-eight hips) as the subjects of this
review. All thirty-nine patients (forty-eight hips) were evaluated
both clinically and radiographically from five to thirteen years
(average, ten years and three months) after the primary arthroplasty.
Patients Who Died Less Than Five Years Postoperatively
None of the five patients (11 percent) who died had required
revision of the implant. Two died because of complications related
to acquired immunodeficiency syndrome; two, because of cancer; and
one, because of an unknown cause.
Patient Who Was Lost to Follow-up
Less Than Five Years Postoperatively
One patient (2 percent), a thirty-five-year-old man with a bilateral
arthroplasty, was lost to follow-up one year after the left hip
arthroplasty and six months after the right. At the time of the
early follow-up, he walked without a limp, was pain-free, and had
returned to work as a laborer. Radiographs of the left side revealed
a bone-ingrown femoral stem and a stable acetabular cup. Because
of the inadequate follow-up period, radiographs of the right side
were not analyzed.
Patients Who Were Followed for a Minimum of Five
Years
Reoperations
Of the forty-eight hips (thirty-nine patients), ten hips (ten
patients) required a reoperation during the study interval; thus,
the reoperation rate was high (21 percent). With the small numbers
available, the age and weight of these patients did not differ significantly
from those of the group as a whole (p > 0.05). Complications related
to polyethylene wear accounted for six revisions; recurrent dislocation,
for three revisions; and deep infection, for one resection arthroplasty.
All of the femoral components in the nine aseptic hips were stable
clinically and bone-ingrown radiographically; thus, they were not
revised.
The six reoperations in the six hips (13 percent) with excessive
polyethylene wear and osteolysis were performed at an average of
104 months after the index arthroplasty. Four of the six hips required
revision of the entire acetabular component, and three of these
components were bone-ingrown. Two of the four revisions were in
hips with a nonmodular acetabular component and marked polyethylene
wear. Both had a monoblock femoral component with a thirty-two-millimeter head
and an acetabular shell that would not accommodate a polyethylene
liner of adequate thickness, so a larger hemispherical component
was used for the revision. One patient required revision because of
a fracture of the polyethylene liner in an ACS (Acetabular Cup System)
cup (DePuy, Warsaw, Indiana), a known complication of that design1. The fourth complete acetabular revision
was performed because of osteolysis that had resulted in the only
case of symptomatic cup loosening at the bone-implant interface
(Fig. 1-A, Fig. 1-B, Fig. 1-C, and Fig. 1-D).
Two patients were treated with exchange of the polyethylene liner.
Both patients had a stable acetabular shell that was large enough
to accommodate a liner with a thickness of six millimeters or more.
The patients were asymptomatic; their serial radiographs revealed
progressive periprosthetic osteolysis, which had not affected component
stability. We performed curettage of the osteolytic lesions followed
by application of freeze-dried, particulate, allogenic bone graft.
Five of the six patients had early follow-up (less than twelve
months) after the acetabular revision. At that time, all patients
were satisfied with the result and were employed full-time. Radiographically,
all components were stable.
Three hips (6 percent) in three patients were revised because
of recurrent dislocation. At the time of the revision, all had stable
acetabular and femoral components. Two were treated with exchange of
the acetabular liner and the femoral head, and the third had a complete
acetabular revision. One of these patients subsequently had recurrent
dislocations but continued to work as an occupational therapist
and declined further intervention.
A deep infection with Staphylococcus aureus developed
in one hip (2 percent), in a thirty-four-year-old man, twenty-six
months after the index arthroplasty. This patient was treated with
a two-stage cementless revision, but the infection recurred, requiring
resection arthroplasty and a second course of intravenous antibiotic
therapy.
Clinical Results in Patients Who Did Not Have
a Reoperation
These twenty-nine patients (thirty-eight hips) completed a questionnaire
at least five years postoperatively. The average duration of follow-up was
113 months (range, sixty-one to 160 months).
Twenty-three patients (79 percent) could walk an unlimited distance,
three (10 percent) could walk three to six blocks, and three (10
percent) could walk two to three blocks. Twenty-four patients (83 percent)
had no limp, and five (17 percent) had an occasional limp. Two patients
(7 percent) occasionally used walking aids. Twenty-seven patients (93
percent) had few or no functional limitations. Twenty-eight (97
percent) reported improved functional ability. All were satisfied
with the result of the operation.
Twenty-five patients (86 percent) with thirty-four hips reported
either no pain in the thigh or only intermittent mild pain that
did not limit activity. Four patients (14 percent) with four hips
reported activity-limiting thigh pain; three of them were able to
walk an unlimited distance, and the fourth could walk more than
three blocks. These four patients did not use walking aids. They
reported increased functional ability and satisfaction. None attributed
missed work to thigh pain. It is noteworthy that each of these patients
had a stem with coating around its proximal third only.
Six (21 percent) of the twenty-nine patients reported activity-limiting
pain elsewhere in the hip region - that is, in the groin, buttocks,
or side. Four of these six patients also had associated thigh pain and
were described above. The fifth patient was the only patient who
did not have an overall decrease in pain or an overall improvement
in function postoperatively. Despite this, he reported that he was
able to walk an unlimited distance and was satisfied with the result
of the surgery. The sixth patient had severe pain in the region
of the greater trochanter at the time of the latest follow-up. However,
before his involvement in a motor-vehicle accident, he had reported
no hip pain, could walk an unlimited distance, and had been satisfied
with the result.
Ten patients (34 percent) had not changed employment, nine patients
(31 percent) had changed to a more strenuous occupation, and four
patients (14 percent) had changed to less strenuous work. Two patients
(7 percent) were retired, and one patient (3 percent) was disabled.
The three remaining patients provided no employment data.
Radiographic Results in Patients Who Did Not Have
a Reoperation
Radiographic results were available for the twenty-nine patients
(thirty-eight hips) at an average of 9.4 years (range, five to fourteen
years) after the operation. Although ten (26 percent) of the thirty-eight
femoral stems were undersized (not canal-filling), thirty-seven
(97 percent) of the components were bone-ingrown radiographically
and had had no deterioration of stability over time. One stem, which
was coated on its proximal third only and was undersized, had a
fibrous-stable interface.
Thirty-one hips (82 percent) had mild stress-shielding, and seven
hips (18 percent) had no stress-shielding. No femora exhibited proximal moderate-to-severe
resorptive changes. After the second postoperative year, we did
not detect progression of stress-shielding.
All thirty-eight acetabular components were bone-ingrown at the
most recent follow-up evaluation. Polyethylene wear was less than
one millimeter in fifteen hips (39 percent), one to two millimeters
in ten hips (26 percent), and greater than two millimeters in thirteen
hips (34 percent).
All unrevised hips with an osteolytic lesion had greater than
one millimeter of polyethylene wear. Six (16 percent) of the thirty-eight
hips had an osteolytic lesion in the periacetabular region, and eight
(21 percent) had an osteolytic lesion in the femur. The lesions
had not affected component stability at the time of follow-up. Two
of the six periacetabular lesions were large (greater than 1.5 square
centimeters). Seven of the eight femoral lesions were small and
not rapidly progressive. Six of these small lesions were located
in zone I or VII of Gruen et al.13,
and the other was in zone III. The single large lesion was located
in zone I.
The results of total hip arthroplasty in younger patients with
osteonecrosis have been disappointing. Clinical results in patients
with osteonecrosis have been inferior to those in patients with
other diagnoses12,14,16-18. Further
complicating the problem, younger patients place higher demands
on the replacement, and, regardless of the primary diagnosis, have higher
failure rates5.
Garino and Steinberg12 reported
shorter-term results of total hip arthroplasty for the treatment
of osteonecrosis in 123 hips in eighty-five patients (average age,
forty-five years); the duration of follow-up was two to ten years
(average, 4.6 years). All femoral components were cemented with
second-generation or later techniques. Seventy-one acetabular components
were cemented, and the rest were press-fit and porous-coated. Thirty-six
patients who were followed for greater than five years (average,
6.6 years) had a combined clinical and radiographic failure rate
of 17 percent. Despite shorter follow-up and an older average patient
age (forty-five years compared with thirty-one years in our study),
the primary mode of failure in that series was aseptic loosening,
in sharp contrast to the present series.
Stulberg et al.18 reported
on a series of fifty-seven patients (eighty-seven hips) in whom
advanced osteonecrosis had been treated with cementless total hip
arthroplasty. Again, the patients were older (average age, forty-one
years) than those in the current series, and the follow-up was shorter
(average, 7.3 years; range, 2.3 to 11.2 years). Four different types
of femoral components were used. Eighteen hips (21 percent) had
a revision, and four (5 percent) had radiographic signs of failure,
for an overall failure rate of 26 percent. As in the present series,
polyethylene wear and osteolysis were problems, resulting in eleven
revisions, but, in contrast to our results, fixation was also a
problem. Ten components (seven femoral and three acetabular) required
revision because of loosening.
The fact that numerous acetabular designs were used in our series
limits the conclusions that can be drawn from our results. However,
since only one acetabular component was revised because of loosening
and there were no cases of impending (radiographic) loosening, we
are encouraged by the ability of cementless hemispheric porous-coated
implants to obtain and maintain at least intermediate-term fixation
in patients with osteonecrosis.
It is clear that concerns about wear, osteolysis, and stability
are common in most series, as they were in ours. However, the main
difference between our series and previous ones is that component
stability was not a major concern, despite our longer follow-up.
In contrast to other authors, we found that fixation of the femoral
component was durable. It appears that the extent of the porous
coating did not influence the ability to obtain a stable implant,
but the numbers are too small for us to make any definitive conclusions
about the optimum design characteristics for femoral components
in these patients.
Despite good functional outcomes (including gainful employment)
and patient satisfaction, it is troubling that activity-limiting
thigh pain was reported by four patients (14 percent). All four
patients had a proximally porous-coated stem, and no patient with
an extensively coated stem reported activity-limiting thigh pain.
In our clinical experience with this implant design, thigh pain
has been more common in association with more proximally coated
stems. Micromotion between the stem and the femoral cortex is known
to be inversely related to the extent of the porous coating and
is believed by some to be related to thigh pain10.
These findings reinforce our preference for extensively coated femoral
components, which we have used exclusively since 1986. However,
the use of extensively coated stems does not eliminate the issue
of thigh pain.
We are concerned about the high revision rate of 21 percent (ten
of forty-eight). Polyethylene wear and osteolysis, which were the
reasons for six of the ten revisions, have limited the success of
this procedure for the treatment of osteonecrosis as they have for
the treatment of other diagnoses. We also recognize that the large
number of socket designs in our series limits our ability to draw
conclusions. The numbers are clearly inadequate to allow comparison
of acetabular designs and their wear characteristics or to allow
comment on the advantages or disadvantages of individual designs.
The two-dimensional estimation used in this study was intended
to provide only a rough indication of true socket wear. Three-dimensional,
computerized wear analysis is currently performed at our institution,
but the requisite cross-table lateral radiographs were not routinely
made during the early period of this study. Considering the small numbers
of cases and the inherent imprecision of two-dimensional measurements,
meaningful analysis of polyethylene wear cannot be performed in this
series of patients. However, it is troubling that, even with use
of this relatively insensitive technique, 34 percent (thirteen)
of the thirty-eight unrevised hips followed for more than five years were
found to have greater than two millimeters of wear of the polyethylene
liner. Since osteolysis is related to the volume of wear particles15 and has the potential to damage
bone stock and affect component stability, we fully expect more
acetabular reoperations with longer follow-up.
Although osteolysis can jeopardize the femoral bone-implant interface,
none of the patients in this series had a distal femoral lesion
and the stability of the femoral components did not deteriorate
over time. We therefore are hopeful that osteolysis will not adversely
affect the stability of the femoral component or increase the prevalence
of femoral revision with time.
Although there was a high frequency of reoperations in this series,
the outcomes of the revisions, albeit after short-term follow-up
(average, 4.4 years), have been encouraging. There have been no
subsequent reoperations in the revised hips. With the exception
of the patient who required resection because of infection, all
patients were satisfied with the result of the revision. Despite
the high revision rate, we are encouraged by the documented functional
capabilities and the durable, stable fixation of the porous-coated
acetabular and femoral components at an average of 9.4 years postoperatively
in these young patients with osteonecrosis. However, as is true
for other diagnoses, the success of the procedure remains limited
by the bearing surface and debris generation.