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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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