Under optimal circumstances, a large structural acetabular graft will be
incorporated only at its margins. In cemented cups, the construct of bulk
graft and cup may fail when the graft collapses. However, in uncemented
acetabular reconstruction, bone-grafting plays a different role. Structural
bone-grafting is used to achieve a stable situation until definite
osseointegration has occurred. In addition to the primary stability of the
bone graft construct (the cup, additional screws, and the three-dimensional
surface structure of the cup), the placement of the construct against
autologous host bone is essential for obtaining secure osseointegration.
Therefore, if broader support on autologous bone can be achieved in total hip
arthroplasty in patients with developmental dysplasia of the hip, an elevated
hip center may be accepted even in combination with a structural bone
graft.
A high-quality anteroposterior pelvic overview radiograph
(Fig. 1) is essential for
preoperative planning and templating. For cup placement, the ideal position is
in the true acetabulum as far medial as possible and good support from
autologous bone should be planned. The resulting acetabular osseous defect can
be estimated. Also, extensive resection of the femoral neck should be planned
in order to provide a stronger graft. Often a preoperative drawing can be
helpful (Fig. 2).
Perioperative prophylaxis with antibiotics is achieved with 2 g of
cefazolin administered intravenously. All patients are placed in the supine
position, and the operation is performed through a transgluteal approach,
which permits continuous monitoring of the position of the pelvis. The patient
is placed flat to one side of the table so that the soft tissues of the
buttocks can fall posteriorly, and the hip is flexed approximately 30°
(Fig. 3). In patients in whom
extensive lengthening may be anticipated, it is useful to excise the capsule
completely. Relocation of the hip is facilitated in patients with
developmental dysplasia of the hip when the maximum neck resection possible is
used. After removal of the femoral head, the acetabulum is exposed with use of
Hohmann retractors.
Often the depth of the acetabulum is hidden by a large overhanging
osteophyte (Fig. 4). Excision
of the osteophyte with use of chisels may be helpful. The best landmark for
the identification of the true acetabulum is the acetabular teardrop
(Köhler teardrop), which can be identified by the overlying fat pad. The
first reamer is targeted at 90° to the horizontal axis of the body to
medialize the cup as far as possible by reaching the internal cortex of the
pelvis (Figs. 5 and
6). After removal of the
overhanging osteophyte, the underlying bone may be very soft. Especially with
new reamers, the preparation should be performed step-wise without too much
effort. Care also should be taken not to weaken a thin anterior wall. The
position of the reamer is then changed to the desired cup position, which will
give the surgeon a first impression of the portion of the cup that will remain
uncovered by bone. Use of the acetabular reamers in ascending series may
result in a mild elevation and lateralization because of the shape of the
anterior and posterior walls. This should be accepted since it will result in
broader coverage with autologous bone. Reaming is continued until the
anteroposterior diameter of the acetabulum is reached. Depending on the
quality of bone, only line-to-line reaming may be possible. With the last
reamer, the position of the cup may be simulated
(Fig. 7). The remaining
acetabular defect is exposed, and the outer cortex of the ilium is freed of
soft tissue for a short distance cephalad to the upper limit of the defect.
When sclerotic bone is encountered, it may be perforated by small drill-holes
or with a small chisel.
CRITICAL CONCEPTSINDICATIONS:All grades of developmental dysplasia of the hip, in which >20% of the
cup remains uncovered by bone when the cup is in an ideal position.When limb-lengthening of >3 cm is anticipated, an additional femoral
shortening procedure or a trochanteric osteotomy may be considered.CONTRAINDICATIONS:Primary and secondary osteoporosisA history of irradiation to the affected hipComplete collapse of the femoral headPITFALLS:Inadequate planning can result in missing instruments, inappropriate
implants, or unexpected leg-lengthening.Care must be taken not to drop the graft on the floor.The graft must be seated well. This may require reshaping of femoral neck
cortex.Graft fracture can be avoided by predrilling the screw-holes.Damage of the graft by the acetabular reamer can be avoided by first using
a small oscillating saw or a high-speed burr to prepare the acetabulum.Dislocation can be avoided by using an elevated liner and a 32-mm head.AUTHOR UPDATE:Instead of the original cups, a multiple-hole cup design is currently used
with a 32-mm elevated cross-linked polyethylene liner and a 32-mm alumina
femoral head (Biolox; CeramTec, Plochingen, Germany). The original
malleolar-type screws have been replaced by cannulated self-tapping 5-mm
titanium malleolar screws.
CRITICAL CONCEPTS
INDICATIONS:
All grades of developmental dysplasia of the hip, in which >20% of the
cup remains uncovered by bone when the cup is in an ideal position.When limb-lengthening of >3 cm is anticipated, an additional femoral
shortening procedure or a trochanteric osteotomy may be considered.
All grades of developmental dysplasia of the hip, in which >20% of the
cup remains uncovered by bone when the cup is in an ideal position.
When limb-lengthening of >3 cm is anticipated, an additional femoral
shortening procedure or a trochanteric osteotomy may be considered.
CONTRAINDICATIONS:
Primary and secondary osteoporosisA history of irradiation to the affected hipComplete collapse of the femoral head
Primary and secondary osteoporosis
A history of irradiation to the affected hip
Complete collapse of the femoral head
PITFALLS:
Inadequate planning can result in missing instruments, inappropriate
implants, or unexpected leg-lengthening.Care must be taken not to drop the graft on the floor.The graft must be seated well. This may require reshaping of femoral neck
cortex.Graft fracture can be avoided by predrilling the screw-holes.Damage of the graft by the acetabular reamer can be avoided by first using
a small oscillating saw or a high-speed burr to prepare the acetabulum.Dislocation can be avoided by using an elevated liner and a 32-mm head.
Inadequate planning can result in missing instruments, inappropriate
implants, or unexpected leg-lengthening.
Care must be taken not to drop the graft on the floor.
The graft must be seated well. This may require reshaping of femoral neck
cortex.
Graft fracture can be avoided by predrilling the screw-holes.
Damage of the graft by the acetabular reamer can be avoided by first using
a small oscillating saw or a high-speed burr to prepare the acetabulum.
Dislocation can be avoided by using an elevated liner and a 32-mm head.
AUTHOR UPDATE:
Instead of the original cups, a multiple-hole cup design is currently used
with a 32-mm elevated cross-linked polyethylene liner and a 32-mm alumina
femoral head (Biolox; CeramTec, Plochingen, Germany). The original
malleolar-type screws have been replaced by cannulated self-tapping 5-mm
titanium malleolar screws.
The preparation of the graft may be challenging because of its complex
three-dimensional shape. The femoral head should be cleared of all osteophytes
and soft tissue (Fig. 8). The
biggest danger is that the graft may fall on the floor during manipulation;
therefore, an extra table should be provided and one experienced assistant
should hold the graft with a strong bone clamp. New medium-sized saw blades
should be used to shape the graft.
Our technique follows four steps:
Step 1: At an angle of about 120°, two cuts are made along the
inside of the cortex of the femoral neck to the depth of the head-neck
junction (Fig. 9).
A third perpendicular cut at the head-neck junction then allows removal of
a pie-shaped segment (Figs. 10
and 11).
Step 2: At the outer aspect of the graft, the margins of the head
overlapping the neck are trimmed (Figs.
12 and
13).
Step 3: The top portion of the head is then removed (Figs.
14 and
15).
Step 4: The short side of the L-shaped graft is trimmed in a
triangular form to remove the remaining cortical bone. After this cut, only
cancellous bone is left to face into the acetabulum (Figs.
16,
17, and
18).
The autograft is then positioned into the defect so that the long side of
the "L" is positioned laterally, and its inner aspect slides along
the outer cortex of the ilium (Fig.
19). If the graft is not seated completely, the anterior and
posterior parts of the neck may be trimmed a little to allow an optimum fit.
The autograft is then pressed against the ilium with a sharp-tipped bone
impactor (Fig. 20) and is
provisionally fixed with two (threaded) Kirschner wires
(Fig. 21). In the case of a
weak autograft and a sclerotic defect, predrilling with a long 2.0-mm drill
may be helpful. In the original technique, two AO cortical or malleolar screws
as long as possible, with or without washers, were used for the final
fixation. Depending on the stability of the fixation, it is not necessary that
the screws gain purchase of the inner table of the ilium. To avoid placing
screws that are too long, intraoperative fluoroscopy with an image-intensifier
may be helpful. During drilling for those screws, the autograft has to be
stabilized with the sharp-tipped bone impactor. Currently, we use 5.0-mm
cannulated titanium malleolar screws to facilitate this step (Figs.
22 and
23).
The acetabulum and the graft are then reamed with the last acetabular
reamers (Fig. 24).
Especially in soft bone before reaming, trimming of the cancellous part of
the graft with a small saw blade or a high-speed burr may prevent the graft
from getting damaged by a jammed reamer
(Fig. 25). Bone-graft slurry
from the acetabular reaming is used to fill in the gaps
(Fig. 26).
The hemispherical acetabular cup is seated with a limited or minimum
press-fit depending on the quality of bone and the size of the graft
(Fig. 27). Currently,
multiplehole cups are used to allow more options for screw fixation and to
improve visualization during seating of the cup. The cup is then secured with
use of at least two cortical or cancellous screws. In soft bone, the use of a
tap is recommended. However, care must be taken not to break the tap against
the malleolar screws of the graft.
The graft fixation screws are tightened once more after definitive
placement of the cup. Marginal osteophytes are resected. After lavage of the
implant, the polyethylene liner is inserted in the locking mechanism. Since
hips with developmental dysplasia have a tendency to dislocate, a 10°
elevated liner is used in all patients with an anticipated leg-lengthening of
up to 1.0 cm (Fig. 28). With
large grafts, portions of the front and back of the cup may be uncovered.
Where it is appropriate, the gaps can be filled with bone-graft slurry. Also
the back side of the structural graft can be palpated, and bone-graft slurry
may be used to fill in here. In the original technique, conventional
polyethylene liners were combined with 32-mm alumina heads
(Fig. 29). Currently, 32-mm
highly-cross-linked polyethylene liners are used in combination with 32-mm
alumina heads.
Postoperative mobilization commences on day 1. Over the ensuing twelve
weeks, partial weight-bearing of up to 20 kg with use of two lower-arm walking
supports is recommended.