Abstract
Background: The Hip Resurfacing System
offers an attractive option for the treatment of coxarthrosis
with gratifying outcome in the young and active patients.
Achieving full seating of the acetabular component in shallow or
anatomically deficient sockets can sometimes be technically
difficult while performing Metal-on-Metal hip resurfacing.
Methods: In shallow or deficient sockets, we described a
simple technique by 1800 rotation of the Cormet 2000
metal-on-metal resurfacing pegged acetabular prosthesis. This
works by utilising ischio-pubic splines for superolateral socket
engagement. Between June 2000 to November 2001, we have used
this technique in four hips (three patients, one bilateral)
performed in a district general hospital of the UK.
Results: The mean age at primary operation was 37.3 years
(range. 34 to 44 years). There were one male and two female
patients. There were 2 right sided and 2 left sided procedures.
Two cases had dysplastic disease of the hip (DDH), while
bilateral case was diagnosed with multiple epiphyseal dysplasia.
The follow up ranged from a minimum of 27 months to a maximum of
48 months with an average follow up of 37.2 months. None of the
patients needed revision of the components, dislocation or deep
infections.
Conclusions: Rotating the acetabular component 1800 in
shallow or deficient sockets works satisfactorily by utilizing
the ischio-pubic splines for superolateral socket engagement and
should be considered as one of the viable option with or without
structural augmentation.
Keywords: Metal-on-Metal hip
resurfacing, Cemented, Uncemented, Acetabular component, Femoral
component.
J.Orthopaedics 2006;3(1)e4
Introduction:
The Hip Resurfacing System offers an
attractive option for the treatment of coxarthritis in the young
and active patients with gratifying outcome.2,3,5,6 Currently
available Metal-on-Metal Resurfacing Hip Systems include Cormet
2000 (Corin Medical), the Birmingham Hip (Midland Medical
Technologies) and Conserve Plus (Wright Cremascoli).7 The Cormet
2000 implant design utilises the hybrid principle with an
uncemented acetabular and a cemented femoral component.
Achieving full seating of the acetabular
component in shallow or anatomically deficient sockets can
sometimes be technically difficult while performing
Metal-on-Metal hip resurfacing. On occasion, structural
tricortical autografts or allografts are required to obtain a
satisfactory positioning of the acetabular component. We
describe a simple technique to aid fixation of the uncemented
acetabular component in patients with shallow or deficient
sockets.
Material and Methods :
The
Cormet 2000 acetabular component is available as pegless and
pegged cup. In both Cormet cups, there are two sets of
anti-rotation splines. These two sets of fins engage the ischium
and pubis snugly. In routine cases, the uncemented cup is firmly
impacted in place using the cup introducer ensuring
anti-rotation splines engaging the ischium and pubis (Figure 1).
In shallow or deficient sockets, we describe
a simple technique by 1800 rotation of the Cormet 2000
metal-on-metal resurfacing pegged acetabular prosthesis. This
works by utilising ischio-pubic splines for superolateral socket
engagement (Figure 2). We have used this technique in four hips
(three patients, one bilateral) in a district general hospital
of
the UK between June 2000 to November 2001. We obtained a
successful outcome in all the patients and managed to avoid the
need of structural allograft/autograft augmentation in three
hips. In one patient, this technique was supplemented with
cadaveric allograft.
Results :
The mean age at primary operation was 37.3
years (range-minimum-34, maximum-44 years). There were two
females and one male. There were 2 right sided and 2 left sided
procedures. Two cases had dysplastic disease of the hip (DDH),
while bilateral case was diagnosed with multiple epiphyseal
dysplasia. Posterior approach was used by single operating
surgeon.
A cementless acetabular component and
cemented femoral component were used using single manufacturer
implants (Cormet 2000). The follow up ranged from a minimum of
27 months to a maximum of 48 months with an average follow up of
37.2 months. None of the patients needed revision of the
components, experienced dislocation or had deep infections.
Discussion :
The Hip Resurfacing System offers a rapidly
growing option for the treatment of coxarthritis in the young
and active patients.2,3,5,6 Out of currently available
Metal-on-Metal Resurfacing Hip Systems (Cormet 2000, Birmingham
Hip and Conserve Plus, the Cormet 2000 implant design utilises
the hybrid principle with an uncemented acetabular and a
cemented femoral component.
Corin Medical started using an uncemented
acetabular component with a cemented femoral component in 1994.
Enhancements were made to the prosthesis such as the
introduction of metal porous coating overlaid with
hydroxyapatite on the external surface of the cup, and an
improved face mounted introduction method subsequently.4 The
original Cormet cup design incorporated two sets of three
anti-rotation splines; two long splines with one small spline
above. It was found that the cups were occasionally difficult to
fully impact, especially in hard bone, and that in these cases
they sometimes did not fully seat in the prepared acetabulum.
The spline arrangement has been modified lately by removing the
superior spline and thinned down the two remaining splines in
profile (but with the overall length maintained) so that they
cut into the ischium and pubis more easily.1
The Cormet acetabular cup is equatorially
expanded - a 54 mm diameter cup has a diameter of 54 mm at the
pole and a diameter of 56 mm at the rim. Therefore, it allows a
perfect hemi-sphere to be reamed (54 mm diameter) for the
implant, which gives a 2mm press-fit at the mouth of the device
and a line-to-line fit at the pole. This results in improved
stress distribution to the acetabulum. Most current cementless
acetabular cup systems in Metal-on-Metal hip resurfacing now
utilise this hemispherical expansion principle, as the
advantages of a well-fixed press fit primary fixation are well
recognized.1,4
The management of younger patients with
abnormal hip anatomy leading to secondary osteoarthrosis is an
orthopaedic challenge. Long term outcome, safety, clinical
effectiveness and cost effectiveness of the Metal-on-Metal hip
resurfacing procedure in such patients is poorly understood. A
simple technique is described here to aid fixation of the
uncemented acetabular component in patients with shallow or
deficient sockets by rotating the acetabular component 1800 with
or without structural augmentation. This works satisfactorily by
utilising the ischio-pubic splines for superolateral socket
engagement.
Conservative hip arthroplasty with
resurfacing of the acetabulum and femoral head is an attractive
concept in young and active patients.2,4 Preservation of bone
stock is important for young patients who are likely to need
more than one operation in their lifetime. The closer is the
anatomy to normal, the better the function of resurfacing.
Achieving full seating of the acetabular component in
anatomically deficient sockets in patients with abnormal
coxanatomy can sometimes be technically difficult while
performing Metal-on-Metal hip resurfacing.This study supports
the resurfacing hip arthroplasty proponents as a practical and
potentially useful treatment method in young and active
arthritic hips with abnormal hip anatomy as well.
Conclusion:
In summary, Metal-on-metal resurfaced hips
with appropriate case selection can yield satisfactory results
in the young and active patients with abnormal coxanatomy. This
technique used in three patients with successful outcome and
averted the need of structural graft augmentation.
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