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center is only recommended when the dysplastic process
has led to remodeling of adequate bone to support the implant
in this position-most commonly Crowe II. Leg length discrepancy
must be kept in mind and appropriate intervention on
the femoral side made as needed. Crowe III or IV defects
are best treated by bringing the socket to its anatomic location.
Several acetabular component designs have incorporated
the use of a hydroxyapatite (HA) coating to improve bony
ingrowth or ongrowth. Hydroxyapatite is an osteoconductive
material that in animal models, has been shown to optimize
bone attachment to fixation surfaces. The most popular initial
designs that incorporated an HA coating were smooth,
hemispherical components that relied on a press-fit for obtaining
initial implant stability without screws for fixation.
Unfortunately, these components have been associated with
poor intermediate term results as with time, the HA resorbed
and without a biological surface available for osseointegration
to occur, aseptic loosening ensued. In one comparative study
of porous coated cups, HA coated smooth press-fit acetabular
components and HA coated threaded screw in cups, the
highest rate of failure (11%) was seen with the HA coated,
smooth press fit cup at a minimum of five years. In response
to the problems of early failure, HA has since been applied
to grit blasted and porous coated implants with acceptable
results at short and intermediate term follow-up. One clinical
trial that compared a titanium fiber metal mesh component
with and without HA coating among 23 pairs of patients. Although
the clinical results were similar, the components with
HA coating were associated with less migration and fewer
radiolucencies when studied with radiostereometry analysis.
No clear clinical benefits were identified. Similar animal
studies have suggested that HA applied to a titanium fiber
mesh coating enhances early bone ingrowth but there may
not be a longer-term benefit in terms of overall implant stability.
A potential concern with the use of HA coatings is that
as the HA delaminates with time, these particles may enter
the joint space causing damage to the bearing surface.
CEMENTED CUPS: RESULTS AND
TECHNIQUE
A. John Timperley
Princess Elisabeth Orthopeadic Hospital,
Exeter (Great Britain)
THREADED CUPS, WHEN?
Karl Zweymüller
Orthopädische Krankenhaus Gersthof
Wien (Austria)
INTRODUCTION
Although very popular in the late seventies and early eighties
of the last century, threaded cups are scarcely used today,
because the outcome achieved with their first generation
was poor. We introduced in 1985 a new generation of threaded
cups. From 1993 a further development was used. The
aim of this study was to analyse the minimum 10 years results
with this cup and to compare the results with those
obtained with hemispheric cups.
MATERIAL AND METHODS
Between January 1993 and June 1994 400 patients (412
hips) were provided with primary implantations in our department.
After excluding other combinations than ceramicpolyethylene
and the previously used Alloclassic system this
left a group of 365 patients (376 hips) provided with the Biconcup
and SL-Plus-stem. No other cementless system was
used and no implants inserted during that period were cemented.One
hundred sixty-one patients (167 hips, or 72%)
had idiopathic osteoarthritis, 37 patients (38 hips, 16.4%)
had developmental dysplasia, 11 patients (11 hips, 4.7%)
had osteonecrosis of the femoral head, 10 patients (10 hips,
4.3%) had post-traumatic arthritis, and six patients (six hips,
2.6%) had other abnormalities. In all cases, we used cementless
threaded cups in combination with straight cementless
stems with a double taper made of hot forged titanium
alloy (Plus Orthopedics AG) and a ceramic ball head (Ceramtec,
Plochingen, Germany) in contact with an ultrahighmolecular-weight
PE liner (Plus Orthopedics AG). The cup
shells were made of commercially pure titanium. The surface
was roughened through grit blasting. The mean surface
roughness was 5 µm; therefore, no coating was applied.225
patients (232 hips) were followed clinically and radiologically.
The age of the patients was 19.8 – 83.3 years at operation,
mean 62.6, the follow-up time was 10.0 – 13.1 years, mean
10.3. We also evaluated gaps on postoperative radiographs.
Two types of gaps were distinguished. The first type involved
incomplete bony coverage of the metal cup shell in Position
1 (ie, between the cranial circumference of the implant and
the iliac bone). Usually triangular, these gaps were called
cranial dead space or triangular cranial gaps. Their appearance
on 10-year followup radiographs was compared with the
postoperative radiographs to see whether they had become
smaller or were obliterated by newly formed bone. The second
type were gaps between the front end of the implant and the
acetabular floor. Because these were measurable on the
monitor-controlled radiographs, they were determined in 2-