Preoperative Planning
Preoperative planning is required in order to allow the correct sizes of
allograft and femoral component to be ordered. Routine radiographs are made to
determine the length of the deficient proximal part of the femur and hence the
approximate length of allograft that is required. It is prudent to order an
allograft that is longer than estimated. The outer diameters of the host femur
and allograft should be approximately the same. It is desirable not to have an
allograft with a diameter that is substantially wider than that of the host.
In fact, it is common for the outer diameter of the allograft to be smaller
than that of the host femur. Because of lysis and cavitation around the loose
femoral component, the relatively smaller allograft can be telescoped into the
host femur for 1 or 2 cm. This will enhance union and the stability of the
construct. It is important for the allograft canal to be sufficient to
accommodate the femoral implant to be used. Radiographs of the allograft are
also important for preoperative templating of the femoral implant. If
necessary, these radiographs can be made while the allograft is in the sterile
packaging to verify its size. Ideally, radiographs of the host femur and the
allograft should have the same magnification rates as the templates of the
implants that are selected. Otherwise, adjustments of sizing must be
performed, and for this it is necessary for the magnification rate of the
radiographs of both the allograft and the host femur to be known. The
preoperative limb-length discrepancy should be measured in order to determine
whether the limb length needs to be adjusted during the surgery.
Preparation of the Allograft-Prosthesis Composite
The allograft used in this procedure is stored at —70°C and, at
our institution, it is irradiated with 2.5 Mrad. Graft preparation is
performed concurrently on a separate surgical table by a second surgical team
while fracture exposure is being performed by the operating surgeon. We
recommend using fresh-frozen allograft from an American Association of Tissue
Banks-accredited tissue
bank3. The larger
banks process the bone in bactericidal and virocidal solutions before the bone
is deep frozen. This requires a class-10 cleanroom. Some banks provide
irradiated bone, which is 10% to 20% weaker, depending on the radiation
dose4. We have had
no experience with freeze-dried structural grafts, but they are weaker and
more brittle than deep-frozen grafts
are5. We prefer to
use a proximal femoral allograft to replace the proximal part of the femur,
but a distal femoral allograft will accept a larger implant and is used by
some surgeons. The allograft is thawed in 5% povidone iodine solution after
culture specimens have been taken. Once the bone has been thawed and stripped
of soft tissue, it is prepared for the femoral implant. The femoral neck is
divided about 1 cm proximal to the lesser trochanter, or even at the base of
the lesser trochanter, facilitating insertion of the implant and allowing room
to adjust the version. Lengthening of the limb is not carried out by means of
the neck cut, but rather by means of the selection of the length of the
allograft distal to the lesser trochanter. The allograft should be cut long
initially. A stable graft-host junction is necessary, and either a step-cut or
an oblique graft-host osteotomy can be used to obtain stability (Figs.
2 and
3). An oblique osteotomy is
easier to work with and allows for adjustment of the version without having to
make major changes to the osteotomy; it should be as long as possible, at
least 2 cm in length. Occasionally, there is enough of a canal diameter
discrepancy between the graft and the host that the graft can be telescoped
into the host canal for a couple of centimeters, making the step-cut or
oblique osteotomy unnecessary.
CRITICAL CONCEPTSINDICATIONS:Uncontained segmental femoral defects that extend for >8 cm into the
femoral diaphysis.Vancouver type-B3 periprosthetic femoral
fractures1.Post-tumor-resection reconstructions.Severe loss of proximal femoral bone stock rendering the distal fixation of
a long, uncemented femoral stem difficult, if not impossible.CONTRAINDICATIONS:Infection, unless the revision hip arthroplasty is performed in two
stages.Elderly patients with other comorbidities for whom immediate mobilization
and weight-bearing is indicated after the revision surgery.PITFALLS:Over-reaming of the allograft to get the prosthesis to press fit distally
should be avoided as the proximal allograft will require too much reaming to
accommodate the size of the prosthesis and will be weakened.The graft should not be cut too short at first; it should be cut long
initially and then trimmed to adjust limb length after trials.Cement should not be placed distally because doing so will compromise
host-graft junction union and also will make further revision difficult.The shell of the proximal part of the host femur should not be discarded.
It should be used as a vascularized autograft to wrap around the host-graft
junction.One should not forget to consider femoral version when preparing step-cut
osteotomy.
CRITICAL CONCEPTS
INDICATIONS:
Uncontained segmental femoral defects that extend for >8 cm into the
femoral diaphysis.Vancouver type-B3 periprosthetic femoral
fractures1.Post-tumor-resection reconstructions.Severe loss of proximal femoral bone stock rendering the distal fixation of
a long, uncemented femoral stem difficult, if not impossible.
Uncontained segmental femoral defects that extend for >8 cm into the
femoral diaphysis.
Vancouver type-B3 periprosthetic femoral
fractures1.
Post-tumor-resection reconstructions.
Severe loss of proximal femoral bone stock rendering the distal fixation of
a long, uncemented femoral stem difficult, if not impossible.
CONTRAINDICATIONS:
Infection, unless the revision hip arthroplasty is performed in two
stages.Elderly patients with other comorbidities for whom immediate mobilization
and weight-bearing is indicated after the revision surgery.
Infection, unless the revision hip arthroplasty is performed in two
stages.
Elderly patients with other comorbidities for whom immediate mobilization
and weight-bearing is indicated after the revision surgery.
PITFALLS:
Over-reaming of the allograft to get the prosthesis to press fit distally
should be avoided as the proximal allograft will require too much reaming to
accommodate the size of the prosthesis and will be weakened.The graft should not be cut too short at first; it should be cut long
initially and then trimmed to adjust limb length after trials.Cement should not be placed distally because doing so will compromise
host-graft junction union and also will make further revision difficult.The shell of the proximal part of the host femur should not be discarded.
It should be used as a vascularized autograft to wrap around the host-graft
junction.One should not forget to consider femoral version when preparing step-cut
osteotomy.
Over-reaming of the allograft to get the prosthesis to press fit distally
should be avoided as the proximal allograft will require too much reaming to
accommodate the size of the prosthesis and will be weakened.
The graft should not be cut too short at first; it should be cut long
initially and then trimmed to adjust limb length after trials.
Cement should not be placed distally because doing so will compromise
host-graft junction union and also will make further revision difficult.
The shell of the proximal part of the host femur should not be discarded.
It should be used as a vascularized autograft to wrap around the host-graft
junction.
One should not forget to consider femoral version when preparing step-cut
osteotomy.
The greater trochanter is osteotomized and is removed from the allograft,
thereby allowing for reattachment of the host greater trochanter. If the
patient does not have a greater trochanter, then the allograft greater
trochanter should be left in place with a cuff of abductor muscle insertion
for attachment of the host abductors. Reaming of the allograft is then carried
out (Fig. 4). Reaming is
performed with straight rigid reamers for a straight implant or with flexible
reamers for a bowed implant. The calcar region is milled until the implant can
be seated. We ream the cortex only enough to allow insertion of the implant.
The host canal is almost always larger than the allograft canal, and if the
surgeon attempts to use an implant large enough to obtain a press fit
distally, then the allograft will have to be excessively reamed and will be
weakened as a result. We most commonly use a 13.5 or 14-mm-diameter stem,
which does not usually provide a press fit distally; a press fit is not
necessary as the implant is cemented into the allograft, and, once the
allograft-host junction unites, the entire construct is stable.
AUTHOR UPDATE:No changes in this technique have been made since the publication of the
original article.
AUTHOR UPDATE:
No changes in this technique have been made since the publication of the
original article.
As the implant is cemented into the allograft but not the host, we are
dependent on the stability of the graft-host junction to stabilize the
construct. Cementing proximally into the allograft and distally into the host
would interfere with graft-host union (by stress-shielding the graft-host
junction, leading to graft
resorption)6. Also,
cementing distally would compromise future revision surgery.
Before the implant is cemented into the allograft, the graft is
"triple washed" in 5% povidone-iodine solution, followed by 1%
hydrogen peroxide, and then bacitracin (50,000 units per liter of normal
saline solution). Finally, we use the hydrogen peroxide again as a drying
agent. The proximal femoral graft is dried with use of sponges that are passed
through the canal. The femoral component is cemented into the allograft on a
separate table. This ensures that no cement enters the graft-host junction. A
cement gun is used to insert the cement into the allograft, and the cement is
pressurized by plugging the canal distally with a finger. The implant is then
inserted, in the correct version, which has been predetermined (and marked)
along with the required length at time of the trial reduction. After the
implant is seated, the cement is cleaned from the distal part of the stem and
also from the surface of the osteotomy site with use of damp sponges. After
the cement has cured, the graft-implant composite is then ready for insertion
into the host (Fig. 5).
Additional fine-tuning of the length of the graft and the version of the
osteotomy site may be necessary, depending on the final trial reductions.
The Revision
The revision is carried out with the patient positioned on the uninvolved
side. A straight lateral incision is used, with incorporation of old scars if
possible. We prefer to use a trochanteric slide for
exposure7
(Fig. 6). An extended
trochanteric slide also can be used. Often, the proximal part of the femur is
so deficient that the trochanteric fragment is very thin, but it is important
to keep it in continuity with the abductors and the vastus lateralis. We have
modified the trochanteric slide to reduce the prevalence of posterior
dislocation8. We
leave the posterior capsule and external rotators intact by leaving about 1 cm
of the posterior part of the greater trochanter attached to the femur. After
the trochanteric slide osteotomy has been completed, the vastus lateralis
muscle is reflected from the septum anteriorly to the distal extent of the
anticipated coronal femoral split. The distal extent of the vastus reflection
is determined by preoperative planning and intraoperative visualization of the
junction of the deficient and healthy portions of the host femur. The
trochanter is retracted anteriorly, and the femur is then split in the coronal
plane down to the level considered to be healthy enough not to require
replacement by allograft. The femoral split is easily done with a saw or
osteotomes because the proximal part of the femur is so deficient. At the
level of healthy femoral bone, transverse cuts are made anteriorly and
posteriorly, each extending about a quarter of the way around the femur,
leaving the medial half of the femur intact. The deficient part of the femur
is then pried open with use of multiple osteotomes
(Fig. 7). At the level of the
horizontal cut, the medial half of the femur remains intact and can be used as
the step-cut or oblique osteotomy. Before the old femoral implant is removed
or dislocated, a pin is inserted into the iliac crest and a fixed point on the
host femur is identified and marked with a drill-hole. This point must be in
healthy host femoral bone distal to the allograft as it is a reference point
for measuring the limb length. The distance between the pin in the iliac crest
and the fixed point on the distal part of the host femur is measured and
noted. The preoperative limb-length discrepancy can then be used to adjust the
limb length, if appropriate, during surgery. The hip is then dislocated, and
the old femoral component is removed.
The deficient part of the femur is cleaned of residual cement and
granulation tissue. Any residual bone in the deficient proximal part of the
femur is left with the soft-tissue attachments intact so that it can be used
as a vascularized bone graft to wrap around the allograft, especially at the
graft-host junction, where it enhances union. The residual host bone proximal
to the junction does not replace the allograft, but it may reinforce it by
uniting to it. However, this does not determine the success of the allograft
as there is usually very little host bone left to wrap around the allograft.
The host bone that is wrapped around the junction is much more important
because it enhances union between host and allograft. The part of the host
femur distal to the split is gently reamed for the purpose of removing any
cement or granulation tissue distal to the split.
At this point, the acetabular revision is performed
(Fig. 8). Once the acetabular
reconstruction is completed and a trial cup is in situ, the length of the
allograft can be determined. First, the femoral component length is chosesn to
allow at least four cortical diameters of implant beyond the anticipated
host-allograft junction. The femoral component can either be a one-piece
monoblock stem or a modular stem with a smooth taper; it is essential that the
stem is not intended to be used as a press-fit device. A distal press fit will
unload the graft-host junction, increasing the risk of nonunion.
The femoral implant is inserted into the host canal, without the allograft,
and is reduced into the trial cup (Fig.
9). With use of the pin in the iliac crest and the previously
placed drill-hole in the host femur, the limb length is measured
(Fig. 10). The length of
allograft, relative to the exposed length of the intended stem, can then be
determined. The allograft is cut slightly longer than the required length
(including the step-cut or oblique osteotomy), and a trial reduction is
performed with the implant and allograft together, but not cemented
(Fig. 11). The length of the
proximal femoral allograft may range from 9 to 25 cm (average, 15 cm). Further
adjustment of length and version (by trimming the step-cut or oblique
osteotomy site) may require multiple trial reductions. Once proper length and
version have been achieved, the implant is cemented into the allograft on a
separate table. Once the implant is cemented into the allograft, fine-tuning
of the version, stability, and length can still be carried out by trimming the
osteotomy site. When all of these parameters have been satisfied, the
allograft-prosthesis composite is inserted into the host and is fixed at the
junction with cerclage wires (Figs.
12 and
13). Any available remnants of
the residual host femur with its soft-tissue attachments is also cerclaged
around the proximal femoral allograft, particularly at the junction, to act as
vascularized autograft to enhance union
(Fig. 14). Any autogenous bone
that is obtained during the removal of the loose implant or during host bone
reaming can be added to the host-allograft bone junction as well.
Rotational stability at the graft-host junction is better achieved with a
step-cut osteotomy. The oblique osteotomy can also provide rotational
stability to some degree. If the junction is not perfectly stable, a cortical
strut is fixed to the junction with use of cerclage wires to serve as a
biological plate. We prefer a cortical strut because a plate and screws
weakens the allograft, but, if necessary, a plate is acceptable. The greater
trochanter is then attached to the allograft with two 1.6-mm stainless steel
cerclage wires (Fig. 15).
Drill-holes in the allograft are avoided if possible by placing the wires
distal to the lesser trochanter so that they will not migrate proximally. The
vastus lateralis muscle is reattached to the septum. The rest of the closure
is routine.
Figure 16 shows the
postoperative radiograph of the same hip shown in
Figure 1. Axial stability is
easier to achieve with proximal femoral allografts. Rotational stability can
be achieved with a step-cut or oblique osteotomy and reinforcement with
cerclage wires. Occasionally, there is a need for additional enhancement of
stability with a biological or metal plate. In the patient described here, a
cortical strut graft was used medially.
Postoperative Care
Postoperatively, patients are managed with intravenous antibiotics for five
days: 1 g of cefazolin is given intravenously every eight hours, or, if the
patient is allergic to penicillin, 300 mg of clindamycin is administered
intravenously every six hours. After the five-day course of intravenous
antibiotics, five days of oral antibiotics are given (cephalexin [500 mg four
times daily] or clindamycin [150 mg three times per day]). Patients with a
urinary catheter also should receive one dose of 80 mg of gentamicin
intravenously at the time of insertion of the catheter and then should receive
800 mg of sulfamethoxazole orally once per day until the catheter is removed.
At our institution, this regime of antibiotic prophylaxis is followed for all
patients undergoing revision surgery and the infection rate has been audited
to be 2.6%. Prophylactic anticoagulation with low-molecular-weight heparin is
continued for three weeks. The patient is kept on complete bed rest for three
days and then is kept non-weight-bearing on the affected side until there is
radiographic evidence of union of the graft-host junction, which usually
occurs at between six and ten weeks. No resisted abduction is allowed for six
weeks in order to allow for union of the greater trochanter to the
allograft.