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mm steps and evaluated in comparison with the postoperative
radiographs to see whether they had become smaller spontaneously
or had been obliterated.
RESULTS
Two patients of the overall group (376 hips) were reoperated:
one because of an early infection and one because of cup
breakage. No polyethylene liner was exchanged because of
wear or inestability. The radiographic analysis showed tilting
into the valgus-position in 2 patients, into the varus-position
in 1. These 3 cup shells were radiographically loose at the
follow-up. The surrounding bone stock showed progressive
osseointegration in 134 implants, in 91 cups the bone reaction
was indifferent, 2 cups showed integration and some atrophy,
1 cup stable fibrous ingrowth. In 1 case a severe osteolysis
was found. In this case after the end of the study an exchange
of the PE-liner as well as of the ball head was done. The
cup was stable and left in place. The Kaplan-Meier survival
rate with revision for any reason was 99.3% (95%, CI: 96.9%
– 99.8%) after 10 years. The survival rate with revision for
any reason and radiologic loosening was 98.6% (95%, CI:
96.0% - 99.5%) at 10 years. Triangular cranial gaps were
present postoperatively in 50 hips (21.5%). The gaps tended
to spontaneously fill by newly formed bone. Thirty-six of
these gaps (72%) were completely obliterated at the 10-year
followup. Gaps between the metal shell and the acetabular
floor were present in 47 hips (20.3%) postoperatively. In
thirty-seven of these hips (78.7%), the gaps measured 0 to
2 mm. Nine patients had gaps of as much as 4 mm and one
of as much as 6 mm. These gaps also tended to be spontaneously
obliterated. The two valgus migrations were
associated with newly formed gaps in Position 2.
CONCLUSION
Implant survivorship was comparable to the best published
10-year survival rates with the Harris-Galante and other
types of hemispheric cups, however with an encouragingly
low rate of complications related to the PE liner observed in
our series.. The exclusive use of this implant in all indications
for primary hip replacement demonstrated that the results
of the Bicon Cup will be beneficial in almost all cases including
difficult hips.In the next decade it needs to be determined
whether the fixation method of the metal cup shell in the
pelvis and the stability of the PE-liner in the metal-PE-interface
of the study device will lead to lower occurrence of osteolysis
and an improved longevity.
CEMENTLESS CUP: LESSONS FROM
RETRIEVAL STUDIES
Jorge O. Galante, Robert Urban
Rush Arthritis & Orthopaedic Institute
St. Luke’s Medical Center,
Illinois (USA)
Histopathological findings were reviewed on retrieved autopsy
specimens for the purpose of identifying the causes of long
term failure.
The study group consisted of twenty four primary porouscoated
Ti acetabular cups (HG1 or HG II) retrieved at autopsy
5 to 21 years after implantation.
All specimens exhibited bone ingrowth with more bone present
at the components rim and in the vicinity of screws. The
extent was 35% (7 to 70%).
Particles within granulomas were present within holes and
in the rim in all components.
Expansion of granulomas through the screw holes into the
periprosthetic bone was obvious in the longer term specimens.
Granuloma penetration was deeper along screw tracts extending
often through the whole length of the screw. Screw
holes with or without screws were the main pathway for extension
of granulomas into the retroacetabular bone.
Pelvic granulomas increased from a few millimeters at 5 to10
years to ballooning massive lesions at longer follow up, most
often not visualized on plain radiographs. In all of the long
term cases there was invasion of the interface and of the
porous coating itself.
The mean volumetric wear rate was 47 mm3/yr. Damage to
the back side of the liner was moderate.
The mechanism responsible for long term failure is related
to wear and granuloma formation.
These phenomena can lead to massive pelvic osteolysis and
or eventual loosening by invasion of the porous coating by
granuloma as the actual causes of failure.