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Surgical
procedure
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Revision
of acetabular cup loosening
The
surgical repair consists in removing the loose prosthesis
and excising the debris-filled granulomatous reactional
tissue causing the osteolysis. The bone damage repair can
then be achieved by graft. However, whatever the type of
graft (autograft, allograft, substitute), there is a chance
of secondary bony resorption.
The
bone repair can also be achieved through osteogenesis,
similar to a fracture callus, of living bony tissues, in
contact with stable prostheses. To do so, cement-less
prosthesis are required.
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 Pre-operative
planning
The
lesion are assessed by face-on pelvic Xrays and face-o, and
thre quarters alar and obturator hip Xray. For added
accuracy, a scan can be made in doubtful cases.
Pre-operating tracings help, on an x ray with
a known enlargement (most often 1.15), determine the size of
the acetabulum prosthesis. However, it often happens that
the bone damage be more important than expected, all the
more since the prosthesis, cement and damaged tissue
ablation may worsen the lesions. Therefore, a range of
prostheses with different sizes should be prepared before
the operation.
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Postero
lateral approach with a trochanteric bone
strip
In
lateral decubitus, the incision is longitudinal, centred
around the greater trochanteric. After slitting the fascia
lata in the direction of the fibres, draw the trochanter
strip disinserted, using an electrocautery. It is located in
the upper posterior part of the great trochanter. The
posterior tendon of the medium gluteus and the upper portion
of the pelvitrochanteric muscles are inserted there. In
order to achieve secure osteosynthesis, the bone fragment
should be large enough. It should be 1.5 to 2 cm thick, and
3 to 4 cm long. The longitudinal cut is performed using an
oscillating saw. The transversal cut is done using an
osteotome. A small angle of the lower line, forming a closed
angle with the longitudinal line, provide a better embedding
of the bar after the osteosynthesis. In line with the
longitudinal cut, the posterior tendon of the medium gluteus
is dissociated on 1cm. The quadratus femoris muscle inserted
in the lower part of the trochanteric structure is cut near
the femur, as usual. The strip length should not exceed 3 to
3 cm and does not affect the quadratus femoris insertion. If
the strip is extended in that area, the posterior part of
the femur neck will be weakened, which is not advisable. The
strip is separated from the femur using an osteotome or an
extractor, in order to incise the capsule lengthways using a
bistoury, from its insertion on the femur up to the
acetabulum edge. The retractor is placed in back of the
acetabulum, providing a field of vision on the joint, and
protecting the trochanter strip and the pelviotrochanteric
msucle during the hip dislocation, which is done according
to the usual method, by bringing the lower limb to an
internal flexion-adduction-rotation position. The approach
to the acetabulum is made easier by the resection of the
posterior edge of the greater trochanter, which usually
impairs the vision. At the end of the operation, the strip
and the tendons inserted into it are reinserted using a
metal wire, a special screw or a metal rod osteosynthesis
system. The rod should end in an anchor to its proximal end
and in a small distal fastening system buried in the vastus
lateralis.
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Acetabulum
prosthesis and deteriorated tissue ablation
The
loosened acetabularcup is usually easy to remove.
After
ablating the cup, clean the acetabulum cavity thoroughly.
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Fitting
the acetabulum prosthesis
First
identify the obturator hole location. The inside fibrous
tissue has been excised, in order to identify the vacuum
corresponding to the obturator hole. The acetabular
prosthesis should be placed right over the mark so as to
prevent a raising of the hip's rotation centre. The
acetabulum cavity is reamed, using a small size reamer
first. The reaming process should be done carefully and
conservatively. Its purpose is to open up the sclerotic
acetabulum bone in order to have a bleeding and living bone.
It also provides a hemispheric shape to the acetabulum and
helps determine the cavity diameter.
The technique then depends on the
extent of the damage : Grade of SOFCOT
COTATION
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GRADE
1 (good bone capital)
The
technique is similar to a first intention implantation : the
size of the reamer is increased until it fills the
acetabulum cavity and is stable in all planes. The diameter
of the last reamer determines the acetabulum diameter. In
order to achieve impaction stability, it is advisable to
look for a press fit effect by using a cup 2 mm larger in
diameter than the last reamer.
GRADE
2 (fragile or even pellucid continuous acetabulum + hole at
the bottom)
At
this point, the cavity should be made bigger and large size
cups should be used in order to achieve a direct peripheral
support on the living bone around the acetabulum . The
important thing for the impacted cup stability is the bone
continuity around the acetabulum ; it leans on the roof,
anterior and posterior columns and lower margin. This is
particularly important and the cup should be applied here
properly in order to prevent protrusion. A defect at the
bottom of the acetabulum cavity does not constitute a
problem if the edge is continuous.
Increase
the size of the reamers until the cavity is fill up. With
oval cavities, most often with greater vertical diameter, a
hemispherical reaming will make the front to rear diameter
bigger, which does not harm the stability. The biggest
stable reamer in all planes determines the acetabulum
diameter. The cup to be impacted is bigger by 2 mm.
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No bone
grafting
In
grade 2, grafts are not usually needed. Osteolytic defects
disappear through osteogenesis preventing the risk of
potential graft resorption. It helps reconstruct a
continuous acetabulum wall, thin but with sufficient
trophism. The large bone-prosthesis contact surface,
achieved through large size cups, allows a good spreading of
stress, preventing long term protrusion.
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GRADE
3 (disappearance of two walls)
At
this grade, impacted cups may be used. Even if the
acetabulum roof is highly deteriorated, it never disappears
completely, and there is always some bone at the top in the
thick iliac bone. The lower margin is also present. Usually,
the walls that disappear are the front and rear walls. In
most cases, in spite of the wall destruction, living bone
remains in the columns in front and in back of the bottom
defect. The objective is to press the cup on the remaining
bone ring. Use a reamer to gave, as above, a hemispheric
shape to the large cavity, and fasten the greatest possible
cup, using iliac screws. Cups up to 74 mm in diameter can be
used. Primary stability is achieved by screwing, and the
anterior and posterior walls are rebuilt (autograft,
lyophilised bone or bone substitute). These grafts affixed
to the cup have no immediate mechanical role.
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Hip rotation
centre
Does
the use of large cups lead to hip centre raising ? Schutzer
and Harris showed that the functional results were
satisfactory. Our experience shows that the osteolysis
usually extends to the bottom (lower margin), and to the top
(roof) ; therefore the hip rotation centre is not very
affected.
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Result after 5
years
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GRADE
4 (disappearance of two or more walls and / or
fracture)
At
this advanced destruction phase, a reinforcement and bone
grafting is needed
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