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How to Do a Cementless Hip Arthroplasty
Klaus-Peter Günther, Firas Al-Dabouby, and Peter Bernstein
Introduction
Since the early 1960s, when Sir John Charnley was performing cemented total hip replacement (THR) regularly with
good results, techniques and component designs have been
improved substantially. At that time THR was mainly an
operation for elderly patients crippled with arthritis. Today,
however, young patients with hip disease increasingly hope
to restore their quality of life, which typically includes physically-demanding activities. As cement ﬁxation can break
down over time, there has been considerable effort and
research especially in trying to enhance the methods of ﬁxation. The goal was to create a living type of bond between
implant and bone, which would be longer-lasting and stronger than the cement-bone-interface. Advances in bioengineering technology have driven the development of cementless
hip implants with textured surfaces, which allow bone ingrowth. Recent studies suggest, that uncemented hips can
provide durable ﬁxation as well as cemented implants. In
addition, better materials and designs have allowed the use
of large-diameter bearings which provide an increased range
of motion with enhanced stability and very low wear. Less
invasive surgery can limit soft-tissue damage and might
facilitate accelerated discharge and rehabilitation. Currently,
studies are being performed to evaluate whether computerassisted surgery can contribute to reproducible and accurate
placement of implants, which is still a crucial factor for
long-term survival especially in uncemented THR.
We will brieﬂy describe the different anchorage concepts
of the most popular uncemented implants and available
Klaus-Peter Günther ()
Department of Orthopaedic Surgery, University Hospital Carl
Gustav Carus Dresden, Fetscherstr. 74, D-01307 Dresden,
Germany
e-mail: [email protected]
bearing materials. Then – after an overview on widely-used
surgical approaches – a very basic description of implantation technique, potential complications and rehabilitation
principles is provided. In order to compare different implant
and approach philosophies, a short summary of available
long-term studies will be presented.
As this lecture is focussing on conventional hip replacement, recent alternatives (surface replacement and shortstemmed implants such as “bone-preserving” prosthesis)
are not discussed in depth.
Implant Selection
Cementless Acetabular Cups
The rationale for cementless ﬁxation lies in the surface
structure of implant components that should allow bone
ongrowth. To secure a long-term ﬁxation of uncemented
implants, two important factors must be provided: primary
stability and secondary long-term osseointegration. Primary
acetabular stability is obtained by either inserting pressﬁt cups (with or without additional screws) or inserting
threaded cups (Fig. 1). To support osseointegration, most
current implants are made of pure titanium or a titaniumaluminum alloy. A rough surface area – produced by corundum blasting, titanium-plasma spray, titanium balls, nets or
other grid designs – is essential for osseointegration. To
allow for any osseous ongrowth, a 20 μm minimum porosity is required. To actually achieve osseointegration and
vascularization, porosity can be between 100 and 1,500 μm.
During the recent years, hydroxyapatite (HA) coating has
been advocated to improve and secure osseointegration.
HA-coating achieves the closing of micro-defects in the
implant-bone interface, thus preventing clefts for wear
debris entry.
G. Bentley (ed.), European Instructional Lectures. European Instructional Course Lectures 9,
DOI: 10.1007/978-3-642-00966-2_19, © 2009 EFORT
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Klaus-Peter Günther et al.
Fig. 1 Cementless press-ﬁt
cup and stem with proximal
ﬁxation (left side); threaded
cup and stem with
meta-diaphyseal ﬁxation
(right side)
Press-ﬁt Cups
Threaded Cups
Most press-ﬁt cups have a hemispherical design. The principle of implant press-ﬁt is based on force transmission
over the equator of the cup (mainly in the ilioischial direction) which requires:
● A 1–2 mm oversize of the implant diameter compared to
the reamed bone bed. When this difference is missed
(exact ﬁt technique), additional screwing might be necessary to secure primary implant ﬁxation. If the acetabular under-reaming exceeds 3–4 mm, the risk of acetabular
fracture rises.
● A ﬂat-bottom pole to avoid the rim bulging over the bony
circumference. This design allows for a more tilt-secure
position and is responsible for polar bone atrophy, which
itself demonstrates the new force transmission balance.
A circumferential closed bone rim avoids PE-distribution
to the bone bed.
● A certain surface porosity that ensures additional primary stability through friction.
The main advantage of threaded cups is an arbitrary selection of implant position, which can be helpful especially in
acetabular protrusion or hip dysplasia with poor bone quality. Additionally hemispherical threaded cups require less
bone resection than press-ﬁt designs.
Cup design and thread geometry are decisive for the
implant performance during the screw-in process and positioning. A conical-shaped threaded cup guarantees high tilting stability and requires a less exact preparation of the bone
bed [1]. However, threaded cup implantation requires good
sensing of insertion torque slope and the ﬁnal seating point
to achieve optimal stability and avoid overturning. In addition a correction of cup position after the ﬁrst threads –
which can be still applied in press-ﬁt cups – is not anymore
possible.
Some Surgeons prefer cups with additional stabilization
through screws, pegs, rings, ﬁns, spikes or hollow cylinders. These modiﬁcations, however, can alter the mechanical responses of the acetabular host bone signiﬁcantly.
Several stem designs are available on the market. The stem,
is responsible for the ﬁxation of the prosthesis and for transmitting forces to the bone. Therefore in nearly all stem
types adaptive bone changes of the proximal femur can
Cementless Stems
How to Do a Cementless Hip Arthroplasty
be observed after several years and they vary according to
design geometry, biomaterials and surface texture. The
types of ﬁxation are epiphyseal (the femoral head is covered by a cup prosthesis), metaphyseal and meta-diaphyseal
(with straight or anatomically-shaped monoblock-prostheses
of different lengths, modular and custom-made prostheses)
and diaphyseal (using predominantly modular systems).
In primary cementless THR most stems are either straight
or anatomically-shaped monoblock-prostheses, which rely
on metaphyseal or meta-diaphyseal anchorage concepts
(Fig. 1):
● Proximal (metaphyseal) ﬁxation: The concept is based
on the preservation of proximal bone and ﬁxation without an attempt to ﬁll the canal distally. Although many
implants have been developed, one of the most popular
representatives of this philosophy in Europe is the
“Spotorno stem” [2]. It’s high initial stability depends
on a series of ﬂutes or ribs on the proximal anterior and
posterior aspects of the tapered, straight, grit-blasted
titanium stem which, with its rectangular cross-section,
provides an interference ﬁt in the femur. A slim diaphyseal part of the stem, without distal canal ﬁll, leads
to mainly metaphyseal load transfer without distal cortical hypertrophy as a result of stress-shielding.
● In contrast to the straight design of the Spotorno stem,
several other prosthesis are anatomically-shaped. Although these stems with a mild curvature do not show a
generally better survival, they are easier to implant with
the antero-lateral and anterior approach.
● In recent years, short-stemmed prostheses have been
developed, which claim neck-sparing and thus bonepreserving implantation. As this concept – as well as the
resurfacing technique – is still under observation, we
will not speciﬁcally address it within this article.
● Meta-diaphyseal ﬁxation: The classic representative of
this philosophy is the “Zweymüller” stem. This cementless, tapered, rectangular titanium stem was introduced
in the early eighties and the concept is still very popular in Europe [3]. The rectangular geometry avoids the
need to ream the femoral canal and advocators of this
concept argue, that the conservative bone preparation
reduces damage to the endosteal circulation. Cortical
thickening, however, could be observed in severeal
series and seems to be probably due to the concentration of focal stress in the transitional zone between the
stiff area around the stem and the elastic area distal to
the implant [4]. In spite of the frequency of this radiographic phenomenon, it is not related to stem loosening or inferior clinical outcome.
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Stems with diaphyseal ﬁxation are mostly modular and
mainly used in revision surgery. For primary THR they
offer an advantage of independent adjustment of anteversion, which can be important in deformed femora after a
history of dysplasia or femoral osteotomy. Conical stems
can also be implanted independent from the underlying
femoral anteversion and might therefore be indicated in
special situations.
All implants should provide a possibility to reconstruct
adequately the femoral offset. This can be obtained through
stem designs with different neck-stem angles, different offset versions (regular and increased offset) or modular neck
concepts.
Although different implant materials are available,
most cementless stems are made of titanium or titanium
alloys. The ﬂexibility of titanium stems seems to prevent
severe stress-shielding, as the Young’s modulus of elasticity of titanium is near to human bone. More rigid
implants made of other materials (e.g., cobalt-chromiumalloys) tend to produce higher rates of proximal stressshielding and distal cortical thickening especially with
diaphyseal ﬁxation.
Most cementless stems have some kind of surface modiﬁcation to enhance osseointegration. As in cementless cups
a rough surface area – produced by corundum blasting,
titanium-plasma spray, titanium balls, nets or other grid
designs – can stimulate osteoblast activity. Additionally,
some implants are also coated with Hydroxyapatite. As
proximal bone stress-transfer has been thought to be less in
association with proximally-coated stems as compared with
extensively-coated stems, the latter have nearly disappeared
from the market.
Bearing Materials
Survivorship of total joint arthroplasty depends on the durability of ﬁxation and durability of articulation. Therefore
not only the appropriate choice of cup and stem implants is
important, but also the bearing material. In cemented THR,
metal-on-polyethylene articular couple has been the most
widely-used. Polyethylene wear, however, has been identiﬁed as a major factor adversely inﬂuencing the durability of
joint replacement. Therefore alternative bearings with lower
wear rates have been developed and they offer improved
survival especially for young and active patients with higher
life expectancy, where cementless THR might be indicated.
All “hard-on-hard bearings” have been shown to be associated with reduced wear [5].
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Metal-on-metal bearings have wear rates that are 20–100
times lower than metal on conventional polyethylene. However, metal-on-metal articulations may lead to local adverse
responses (metallosis) and increased systemic levels of
cobalt and chromium. Therefore patients with kidney dysfunction, child-bearing age or known metal sensitivities
should not receive these couplings.
Ceramic-on-ceramic bearings have been in clinical use
for nearly 40 years. The wear rates are also very low, but
potential disadvantages are the risk of component fracture
(especially rim fractures due to impingement in cup malpositioning) and audible squeaking in a small number of
patients. Recently ceramic-on-metal bearings have been
introduced, which address these risks.
Finally “Highly Cross-Linked” Polyethylene bearings
have evolved into the most frequently used bearing material for total hip arthroplasty. The liners can be combined
with metal as well as ceramic heads and show signiﬁcantly
less wear than conventional polyethylene. Due to a still
limited observation time, we do not know enough at the
moment about potential long-term risks (i.e., ageing of the
material).
Although the combination of cups, heads and stems
from different manufacturers is theoretically possible, it
should be avoided! In case of material problems (i.e., early
component fracture) medical device directives acknowledge the responsibility of a manufacturer only if his certiﬁed implants had been combined. If surgeons combine
products from different manufacturers, they become liable
for the “new product”.
Surgical Technique
Indication for Cementless Implants
The ﬁrst step of cementless THR is always to check the
indication for this technique. Quantity as well as quality of
host bone must be good enough to guarantee primary stability of the implant as well as susequent osseointegration.
In patients with certain bone disorders or impaired bone
metabolism (e.g., osteoporosis, osteomalacia) or a history
of radiation exposure, initial bone strength and consecutive
biological response might not be sufﬁcient.
With regard to the cup it must be considered if primary
stability and circumferential bone contact can be achieved:
● Is the bone bed strong enough to resist the impaction
force of a 1–2 mm oversized implant?
● Is there enough structural support to relay forces through
the ischio-ilio-pubic columns of the acetabulum?
Klaus-Peter Günther et al.
● Is there any defect (e.g., in a dysplastic acetabulum)
which might impair primary stability through insufﬁcient contact area?
In order to achieve a proper stem position and long-term
ﬁxation, the following questions must be addressed:
● Is the cortical bone strong enough to resist proper broaching and impaction of a cementless stem?
● Is the shape of the medullary canal appropriate for the
selected stem type?
● Can previous osteotomies prevent proper broaching and
cortical stem contact?
● Does the design of the selected stem allow for adequate
reconstruction of offset and leg-length?
Generally, the implantation of cementless THR is more
appropriate in younger than in elderly patients, although
there are no evidence-based age limits. A deﬁnite indication can be the documented allergy against components of
bone cement.
Pre-Operative Planning
Proper pre-operative planning and templating is one of the
most important issues in THR. The choice of implants with
adequate design and size depends on correct radiographs.
For several reasons, an antero-posterior (a-p) view of the
pelvis together with an axial view of the involved hip is
mandatory. A weight-bearing a-p view of the pelvis allows
grading of osteoarthritis, evaluation of acetabular as well
as proximal femoral anatomy and proper measurement of
leg-length discrepancies (together with the clinical investigation, which determines the presence of contractures).
Modern computer programmes are offered for electronic templating (Fig. 2), but the elementary planning
steps can also be performed very easily with appropriate
drawing on template ﬁlms (Fig. 3).
Basic steps of planning are:
● Determination of correct hip centre: If possible, by projection from normal contra-lateral side. Alternatively,
(in dysplastic hips with high dislocation), through
determination of “true acetabular region” according to
Ranawat (1980): A perpendicular line with a length of
20% of the pelvic height is plotted on the vertical of the
Köhler line connecting the bottom of the teardrops. A
parallel line of the same length is then drawn laterally,
starting from the most proximal point of the ﬁrst segment. Finally, the end-points of these two segments are
connected with a line. The triangular area enclosed by
these lines deﬁnes the anatomically correct acetabular
region (Fig. 4).
How to Do a Cementless Hip Arthroplasty
Fig. 2 Pre-operative planning: example of electronic templating in a patient with hip osteoarthritis after failed pelvic osteotomy
Fig. 3 Conventional pre-operative planning in a patient with secondary hip osteoarthritis due to developmental dysplasia
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a
Klaus-Peter Günther et al.
b
Fig. 4 (a) Estimation of correct hip centre and “true acetabular
region” (see pre-operative planning) in a patient with hip dislocation due to acetabular dysplasia. (b) Post-operative radiograph
with reconstruction of correct hip centre via implantation of
bone- and screw-augmented press-ﬁt cup and conical stem
● Selection of appropriate cup size and position.
● Deﬁnition of femoral shaft axis and appropriate neckshaft angle (off-set).
● Determination of neck resection level and leg-length
adjustment.
exposure of the acetabulum, facilitating cup positioning
which may decrease rates of dislocation and the decreased
risk of sciatic nerve injury which is not close to the operative
ﬁeld. Critics of the direct lateral approach suggest that the
violation of the hip abductors may lead to delay in recovery
of abductor strength and late Trendelenburg gait.
The antero-lateral approach addresses the intermuscular plane between the gluteus medius and tensor fascia lata.
The vastus lateralis muscle is left undisturbed. This approach
provides sufﬁcient anatomic orientation and exposure with
minimal dissection and without excessive retraction. There
is no danger of injury to the superior gluteal nerve or its
branches. Due to the intact attachment of the gluteus medius,
however, the insertion of straight stems (and reamers) can
be difﬁcult and might put the muscle under pressure. With
this approach the implantation of so-called “anatomic”
(curved) stems is preferred.
The anterior approach between sartorius and tensor fascia latae muscles is avoiding any tension on the abductors
at all. The acetabular exposure is very good and even the
femur can easily be accessed with the hip in extension and/
or traction. Care must be taken to avoid damage of cutaneous femoral nerve branches.
It is claimed that minimally-invasive surgical approaches
for THR reduce soft-tissue trauma, decrease post-operative
pain and blood loss, speed-up recovery and reduce the
length of the hospital stay. These new procedures either use
one small 6–10 cm incision through a posterior, lateral,
Choice of Surgical Approach
Many different surgical approaches to the hip joint have been
described. Currently, THR is most commonly performed via
a posterior, an antero-lateral or a direct lateral (transgluteal)
approach. Anterior as well as medial approaches are possible, but not as popular.
The posterior approach is considered to be associated
with less problems regarding gait, since the abductor muscles are not dissected and damage to the superior gluteal
nerve is very unlikely. Disadvantages are a less reliable cup
positioning and increased rates of dislocation. Adequate
soft tissue repair by re-attachment of posterior capsule and
external rotators, however, greatly reduces the relative risk
of dislocation using the posterior approach.
In the lateral approach a longitudinal incision of the
ﬁbres of the gluteus medius and minimus and the vastus lateralis muscles takes advantage of the tendinous junction of
these muscles over the greater trochanter. The incision
should not be extended too far cranially in order to protect
the superior gluteal nerve. Proposed advantages are the good
How to Do a Cementless Hip Arthroplasty
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Fig. 5 Simultaneous bilateral hip replacement through a minimally-invasive (anterior) approach. (a) Pre-operative and (b) postoperative radiographs
antero-lateral or anterior approach. The “two-incisionapproach” (a short posterior incision for placement of the
femoral component and an anterior incision for placement
of the acetabular component) is more popular in the U.S.A.
than in Europe. Controversy exists on whether these small
incision THRs are actually minimally-invasive. It is debated
whether a small skin incision that requires the application of
high forces on the soft tissues for exposure of the joint but
less muscle dissection will produce less overall trauma to
the patient than a larger incision with wider muscle dissection but with lower retraction forces. Another question is
whether decreased visualization provided by these techniques can ensure proper implant position and prevent neurovascular complications. A review of the literature to date
provides no convincing evidence of any signiﬁcant advantages of small incision THR compared with standard incision THR other than a shorter surgical scar [5].
There is also little evidence of the beneﬁt of one minimallyinvasive approach over another in the literature. We have
recently performed a prospective randomized trial to compare the functional outcome of two different less-invasive
approaches (anterior and antero-lateral) with the conventional lateral approach and could only observe minor functional differences [6]. We therefore offer surgery through a
minimally-invasive approach mainly for patients who
demand this technique as well as in patients with bilateral
simultaneous hip replacement (Fig. 5).
Basic Surgical Steps in Cementless THR
As the sequence of surgical steps depends at least partially
on the selected approach, we describe more general aspects
of cup and stem implantation and give some additional
remarks referring to different approaches when indicated.
Cup First or Stem First?
Most surgeons tend to perform a stepwise approach with preparing and implanting the acetabular cup ﬁrst followed
by broaching and implanting the femoral stem. While the
acetabular component inclination is relatively independent
from femoral geometry and should be targeted between 30
and 50° (“safe zone” according to Lewinnek et al. [7]),
proper anteversion of the cup depends at least partially on the
amount of femoral version. In cementless THR the positioning of the stem with regard to anteversion or retroversion is
more limited than in cemented implantation techniques, as
uncemented stems must follow the natural geometry of the
medullary canal to a certain degree. Therefore some surgeons
prefer to broach the proximal femur after neck osteotomy
ﬁrst and to estimate the stem anteversion before implanting
the acetabular cup. This offers the opportunity to adjust an
appropriate cup anteversion in cases with abnormal femoral
version and to avoid impingement and/or dislocation.
Femoral Neck Osteotomy
After the capsule of the hip joint has been exposed, a capsulotomy is performed with an electrical knife. In anterior,
antero-lateral and lateral approaches the anterior portion of
the capsule can be excised. In the posterior approach the
incision should leave an intact capsular ﬂap – together with
the released tendons of the short external rotators – which
can be repaired at completion of arthroplasty.
The femoral head is then dislocated (depending on the
approach anteriorly or posteriorly), and the neck of the
femur is osteotomized at the pre-determined level. In cases
where the femoral head is deformed or enlarged, it can be
broken into fragments to facilitate removal, removing the
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head piece by piece. Another alternative is to perform two
parallel cuts through the neck and remove the fragment inbetween the cuts ﬁrst. This can reduce tension and allows
removal of the head easily.
Then the distance between the lesser trochanter and the
performed cut is controlled by palpation in order to check
whether the pre-operatively planned level of neck osteotomy has been realized.
This is also a good moment to perform an additional
release of tight capsular remnants or contracted short external rotators in anterior, antero-lateral or lateral approaches
if necessary.
The femoral head should be kept for potential grafting
purposes during the following procedure.
Preparation of the Acetabulum and Cup Implantation
Long, curved, narrow, sharp Hohmann retractors are applied
to the anterior wall and the inferior acetabular notch, and the
femur is retracted posteriorly (in anterior, antero-lateral and
lateral approaches) or anteriorly (in the posterior approach).
Most surgeons now excise the capsule entirely from the
antero-superior rim and remove the labrum. It is essential to
get full exposure of the acetabular rim and the transverse
ligament in order to reach an optimal position of the cup. To
get an estimation of the adequate reaming depth, the acetabular fossa can be considered as reference point and therefore
should also be cleared of soft tissues. Sometimes a chisel
has to be used to remove osteophytes.
The acetabulum is prepared using spherical reamers of
increasing diameter. In routine cases we use reamers with
outside diameters measuring from 44 to 68 mm, incrementing
2-mm at each step. We start always with a 44 mm reamer,
which is pointing centrally to the bottom of the acetabulum.
Once central exposure of cancellous bone is achieved, we
continue with progressively larger reamers to remove the
subchondral plate until enough cancellous bone with adequate
blood supply is exposed. This ensures necessary activity of
inﬂammatory mediators and bone-forming cells in contact
with the implant surface as a pre-requisite for sufﬁcient bone
ongrowth. In average cases a penetration of the rim/circular
wall as well as the acetabular ﬂoor should be avoided. The
better the remaining bone stock, the better will be cup stability and secondary osseointegration. In acetabular dysplasia,
however, a mild medialisation of the cup even with a perforation of the medial wall is proposed by some surgeons.
In order to avoid cranialization of the implant, the inferior margin of the last reamer should be level with the
transverse ligament. After a horizontal direction of the ﬁrst
1–2 reamers (to ensure distal positioning) the remaining
Klaus-Peter Günther et al.
reamers are angulated at an inclination angle (abduction) of
about 45°. Prior to acetabular reaming the corresponding
diameter of the last reamer to the planned cup size must be
checked (depending on implants and bone quality some
manufacturers propose over- or even under-reaming by 1
or 2 mm in order to achieve stable cup seating).
When the desired reaming depth has been reached and
inspection conﬁrms appropriate bone quality, a trial cup can
be inserted to check adequate positioning. The trial cup – as
well as the deﬁnitive implant – should be positioned according to the “safe zone” [7].
● Inclination of 30–50° with reference to the transverse
teardrop line (higher inclination can lead to excessive
loading at the superior edge with liner wear and/or
instability)
● Anteversion of 10–30° depending on the anticipated antetorsion of the femoral components (less anteversion can
lead to ventral impingement in ﬂexion and/or dorsal instability, higher anteversion can lead to ventral dislocation)
Once an acetabular trial component – which should ﬁt
snugly – is placed to assess the coverage and optimum position, image intensiﬁer control can be performed. This is
especially helpful in obese patients where the position on the
operating table is difﬁcult to determine.
In a dysplastic acetabulum the lateral coverage can be
insufﬁcient. If less than 70% of the trial component is in
contact with bone, the stability can be improved by performing bony augmentation. For that purpose an appropriate
cortico-cancellous fragment is cut out of the femoral head
and ﬁxed to the cranial wall with two screws (Fig. 6).
It might also be necessary to remove inﬂamed synovial
tissue from arthritic cysts. If the cysts are large enough,
grafting by cancellous bone chips out of the preserved femoral head can be performed.
After removal of debris the deﬁnitive implant can be
seated.
Press-ﬁt cups are impacted with a heavy hammer. During
impaction, one should be aware of the correct position and
angulation. If in doubt, the position of the patient on the table
is checked again and even ﬂuoroscopy can be performed.
Conﬁrmation of stable seating is achieved by a combination
of acoustic (sound change during impaction) and tactile indicators (increasing resistance of the impactor against manual
movements). Some cup designs allow checking the approximation towards the central bone bed through the impactor’s
screw-hole. One should not try to maximize stability by overhammering as this will eventually result in loosening or
acetabular fracture. Adaption of pelvic bone to raising
mechanic stress can be supported by waiting intervals between
repeated hammerings.
How to Do a Cementless Hip Arthroplasty
197
a
f
b
d
c
e
Fig. 6 Bony augmentation of the acetabulum in a patient with unilateral osteoarthritis due to hip dysplasia (a) primary reaming in the
true acetabular region (b) would lead to insufﬁcient cranial acetabular coverage of the cup (c). Screw ﬁxation of a cancello-cortical
fragment retrieved from the deformed femoral head (d) results in circular bony augmentation and adequate stability of the cup (e, f)
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Klaus-Peter Günther et al.
If no stable implant ﬁxation can be achieved, the following potential reasons should be checked:
● Is there still enough stable bony support on the anterior,
posterior and cranial rim?
● Has an acetabular fracture appeared?
● Has the right implant size been chosen?
● Was the impact position (angulation) of the implant
identical with the desired position?
● Does soft tissue prevent bony contact?
ment of the liner against the neck of the stem, which is
especially critical for hard bearings.
Prior to impaction of the liner, the shell must be thoroughly cleaned and soft tissue remnants at the circumference
removed. After impaction check carefully circumferential
seating of the liner and stable ﬁxation.
If no distinct reason for insufﬁcient stability can be identiﬁed
and the bone stock is good enough, repeated reaming to a
deeper position with the ﬁnally-used size can be tried. A larger
cup size or mild reduction of anteversion (to get better dorsal
support) can also be tried, if no fracture has occurred.
Some surgeons propose the application of additional
screws to enhance stability and many implants provide screw
holes for that purpose. Those screws should be placed in the
direction of the main force vector and not override the medial
wall nor the ischial foramen to avoid injury of major vessels
and nerves. We should be aware of the fact, however, that
additional screws change the pelvic strain distribution
(thereby potentially inﬂuencing secondary osseointegration)
and can lead to backside wear (particle transport through
screw holes). Finally a grossly unstable cup will never be
sufﬁciently ﬁxed by augmenting screws.
Threaded cups require basically the same acetabular
preparation as press-ﬁt cups. The deﬁnitive implantation
process is somewhat different, however. Because of thread
geometry it is not possible to correct implant angulation
during turning the cup. As the threads support good stability very early during impaction, sensing of the correct seating point is the most critical part of cup implantation. In
hemispherical designs it is more demanding to maintain the
correct angulation during turning than in conical cups.
Achievement of correct seating point and angulation, however, will always require a certain learning curve in threaded
as well as in press-it cups.
Exposure of the femur depends on positioning of the patient
and surgical approach. In anterior and lateral approaches,
the leg is externally rotated, in the postero-lateral approach
(lateral position) the leg is turned inwards (up to 90°) together
with bending and adduction of the hip. It is generally recommended to bend the knee joint 90° in order to use the lower
leg as a reference line for appropriate anteversion. A short,
narrow Hohmann retractor is applied to the posterior aspect
of the femur to protect the soft tissues and the skin from
damage during rasping.
The femoral canal is mostly prepared using a canal
ﬁnder and a series of chipped tooth broaches which increase
in size.
The canal ﬁnder (sometimes an awl) has to be inserted
laterally and slightly dorsal in order to avoid varus positioning of the stem. A good estimate for the entry point is
the piriformis fossa as it is normally in line with the medullary canal. To prepare the entry point, most manufacturers
provide a chisel, which removes a corticocancellous bone
block from the neck. While pushing the canal ﬁnder (awl)
into the medullary cavity, it must be pressed in the direction
of the greater trochanter. In straight stems it is sometimes
even necessary to remove a small piece of the trochanter
base from the femoral neck, as the medullary cavity has to
be opened more from dorsally than in anatomic (curved)
stems. In hips with a deformation of the trochanteric region
(i.e., after proximal femoral osteotomy) anatomic stems
can be easier to implant than straight stems (Fig. 7).
Then the bed for the stem is prepared, using rasps of
increasing size, until the highest possible degree of stability
is obtained. Mostly this process is started with the smallest
rasp available. Curved handles or even off-set handles help
to avoid contact with soft tissues. With the ﬁrst rasp, care
must be taken, to ensure a correct anteversion (usually
10–15°). This is necessary, as the sum of femoral and
acetabular anteversion should aim at 20–30° (in posterolateral approaches even a little bit more). Constant bending
of the lower leg (90° ﬂexion in the knee joint) helps to
determine the desired anteversion very precisely. In patients
with pathological anteversion or retroversion, a second
osteotomy more distal towards the lesser trochanter or
Liner Choice
Most cup implants offer several liner options (conventional
Polyethylene as well as hard bearings). The choice depends
on patient’s age and activity as well as Surgeon’s preference. Modern liners offer the advantage of optional elevated lips and compatibility with different head ball sizes
(mostly 28–36 mm) in order to improve the range of motion
and reduce wear. It must be re-emphasized, however, that
wrong cup position can lead to edge loading and impinge-
Preparation of the Femur and Stem Implantation
How to Do a Cementless Hip Arthroplasty
199
a
b
Fig. 7 Choice of femoral stem type: in hips with a deformity of the trochanteric region after femoral osteotomy (a), anatomic stems
might be easier to implant than straight stems (b)
removal of some cortical bone may be necessary. Another
option in these cases is, to change the prosthesis system and
implant a conical stem, which allows free rotation (Figs.
4b and 6f).
Progressive and step-wise rasping with increasing
dimensions now compresses the cancellous bone. The rasps
are inserted with small hammer blows and care is taken not
to fracture the cortex. If it is necessary, the cortex can even
be reamed. The desired stability of cementless stems is
based on a press-ﬁt-concept in cortical and cancellous
bone. It is therefore very important to get the best press-ﬁt
possible. Undersizing of the stem must be avoided, as this
can lead to subsidence and loosening over time. On the
other hand, oversizing bears the risk of damaging cortex
stability, which can lead to an intra-operative or early postoperative fracture.
If a stable position of the ﬁnal rasp has been reached, it
must be checked to ensure that the distance between the
proximal shoulder of the prosthesis and the greater trochanter
is equal to the pre-operatively templated position. If the
actual distance is shorter, the neck osteotomy can be repeated
in a lower position and a smaller rasp introduced. If the distance is higher than pre-operatively determined either a larger
rasp with a less deeper position or a long neck can be tried.
200
This is the opportunity to check alignment with a trial
reduction. For that purpose most systems offer trial necks
of different length and/or off-set, which can be inserted
into rasp holes after removing the handles. Once the trial
neck which corresponds to the pre-operatively planned offset is selected, a trial head can be positioned. After reduction of the trial prostheses, three main issues should be
checked:
● Range of motion
● Leg-length
● Stability
Although this can be performed clinically, we also control
the reconstruction under ﬂuoroscopy. The radiographic evaluation allows us to document, if the pre-operatively planned
off-set and leg-length reconstruction have been achieved. If
the alignment has to be changed, a repeat trial with heads of
different length (or even a different neck) is possible.
The range of motion is checked to avoid bony impingement and instability. Depending on the surgical approach,
especially external rotation in extension (anterior and lateral approaches) or internal rotation in hip ﬂexion (posterolateral approach) should be performed in order to simulate
anterior or posterior dislocation mechanisms.
After removal of the rasp, a prosthesis of the appropriate
size is inserted and driven into the medullary canal, until it is
completely stable. This manoeuvre has to be performed with
the necessary light touch, as most implants have a slightly
larger dimension than the corresponding rasp. Because of
the wedge mechanism an excessive load might be exerted in
addition. This load on the neck cortex – or the greater trochanter when a straight stem is implanted – can lead to a
fracture. It is therefore very important to adjust the force of
the hammer blows according to the bone quality. The hammer blows should be stopped immediately, if a change in the
sound of the blows from dull (cancellous bone) to sharp
(cortical bone) is perceived. This is one of the most critical
steps in cementless THR and can only be learned by
experience.
Rarely the stem needs to be removed intra-operatively
(i.e., when the position after insertion is different from the
previous rasp position). For this situation a speciﬁc extraction instrument should be available, which protects the
neck and cone of the stem. Then the prosthesis can be used
again after necessary changes (as for example repeated
rasping) have been performed.
After insertion of the stem, another trial reduction can
be performed with a test head as before (especially if the
ﬁnal level of the imlant shoulder is different from the level
of the rasp – indicating a different depth of insertion).
Finally the taper must be cleaned and dried thoroughly,
Klaus-Peter Günther et al.
before the deﬁnitive femoral head is mounted and tapped
into position. Before wound closure we perform another
range-of-motion as well as ﬁnal stability testing. A ﬁnal
ﬂuoroscopic control serves as post-operative radiographic
documentation of correct alignment and bone integrity.
Computer Navigation
Navigation is sometimes used in an effort to increase the
accuracy and consistency of hip arthroplasty component
position. Most recent studies have demonstrated equal or
superior accuracy in association with the use of navigation
systems as compared with manual techniques. It still has to
be evaluated, however, if patients have any clinical beneﬁt
from that improvement and under which circumstances
navigation is cost-effective. Therefore currently, navigated
THR cannot be recommended as a routine procedure [5].
Peri- and Post-Operative Management
Prophylaxis of Heterotopic Ossiﬁcation
To avoid heterotopic ossiﬁcation it is crucial to protect the
soft tissues throughout the whole procedure and to prevent
the apposition of bone fragments around the joint. We therefore remove meticulously any debris from acetabular reaming and femoral rasping prior to insertion of the implants,
trial reduction and ﬁnal reduction. Additionally patients
receive NSAIDs for 2 weeks post-operatively, if no contraindication exists.
Peri-Operative Antibiotics
As one of the major risks in THR is the development of
peri-prosthetic infection, we deliver a single-dose prophylaxis with cephalosporine intravenously.
Post-Operative Rehabilitation
Our post-operative management in routine cases involves
protected full weight-bearing (with crutches) for 3–4 weeks.
After that time full weight-bearing without crutches is
encouraged. Physical therapy is performed to strengthen the
thigh and hip muscles. Depending on the surgical approach,
certain muscles might need protection (i.e., re-attached
external rotators in the postero-lateral approach or abductors in the lateral approach). In minimally-invasive anterior
How to Do a Cementless Hip Arthroplasty
or antero-lateral approaches there is no speciﬁc limitation
of range of motion.
Complications
Generally, the complications of cementless THR are very
similar to the comlications of cemented implantation tecniques. Therefore patients should be informed about speciﬁc risks of artiﬁcial joints (i.e., venous thromboembolic
disease, damage of neurovascular structures, dislocation,
peri-prosthetic infection, leg-length discrepancy, component loosening and heterotopic ossiﬁcation).
One speciﬁc issue is the prevalence of peri-prosthetic
fractures, which seems to be higher in cementless THR: In a
recent large cohort study risk factors associated with femoral
fractures and their effect on femoral stem survivorship were
determined. The incidence of proximal femoral fracture was
2.3%. Risk factors associated with fractures included an
antero-lateral approach, uncemented femoral ﬁxation and
female sex.
In case of intra-operative fracture most often cerclage
wiring is sufﬁcient. If the fracture occurs post-operatively,
treatment depends on the type of fracture and stability of
the implant.
While mal-positioning of the acetabular cup can lead
to edge load (increased wear), impingement and dislocation, the sequelae of stem mal-positioning are less clear.
Some surgeons have observed that stem mal-positioning,
particularly varus, has been associated with higher failure
rates. Min et al., however, reviewed a consecutive series
of THR’s performed with a cementless tapered-wedge
stem and a mean duration of follow-up of 7.7 years, where
the stem position was neutral in only 63% of the hips,
valgus in 21% and varus in 16%. No revision was necessary, there was no difference in the three groups in clinical
outcome (HHS or thigh pain) and similar bone re-modeling changes were observed in all patients, regardless of
stem position [8].
Implant Survival
The short- and medium-term results of modern cementless
THR are normally good and similar to those reported after
cemented THR, with respect to relief from pain and function. Mallory et al. reported on 2,000 consecutive arthroplasties with a tapered stem that were performed between
1984 and 2001. The rate of femoral stem survival was
98.6% at 5 years, 98.6% at 10 years and 96.6% at 15 years.
201
This success was attributed to the stem geometry and surface texture [9].
Long-term results with a follow-up of more than 10
years are only available for a limited number of uncemented
implants. Aldinger et al. reviewed a series of cementless,
double-tapered straight femoral stems (CLS) in 326 patients
at a mean follow-up of 12 years (10–15 years). The mean
age of the patients was 57 years (13–81). The overall survival was 92% and survival with femoral revision for aseptic loosening as an end-point was 95% [2].
The survival of cementless cups is still somewhat lower
than the stem survival. Considering the mode of primary
ﬁxation, results between press-ﬁt and threaded cups are
still controversial [1, 10]. Using revision for any reason as
an end point, 10–12 year survivorship rates from 93 to 99%
and 15–18 year survivorship rates from 83 to 88% seem to
be possible, especially in younger patients for both implant
types [11–14].
In patient cohorts with uncemented implants many factors can inﬂuence survivorship, such as geometry, materials, surface ﬁnishes and bearings. Other factors including
patient age and activity, surgical approach, expertise of the
Surgeon and study design may also add to baseline differences between studies.
Due to these limitations, National hip replacement
Registries seem to be a valid instrument to compare the
performance of different implants. In the most popular
Swedish Registry the number of documented cementless
THR is still signiﬁcantly lower than the number of cemented
arthroplasties. While the 10-year survival of all cementless prostheses in this registry is still somewhat lower than
that of cemented prostheses, certain cementless implants
show equal performance (i.e., CLS stems and Trilogy
cups). In the Finnish registry a recent analysis at a mean
follow-up of 12 years was performed [15]. The authors
found that cementless THRs, as well as the stems and cups
when analyzed separately, had a lower risk of revision for
aseptic loosening than did the cemented THRs in patients
with osteoarthritis who were 50–74 years-old. In patients
who were 75 years of age or older, there were no signiﬁcant differences in the results, other than the reduced risk
of revision for aseptic loosening of hydroxyapatite-coated
cementless cups compared with cemented all-polyethylene cups. Excessive wear of the polyethylene liner, however, resulted in numerous revisions of the modular
cementless cups in patients who were 55–74 years-old.
Thus, the long-term survival of the cementless THRs, with
revision for any reason as the end-point, did not differ
from that of the cemented THRs in any of the age groups.
In conclusion, modern-design threaded and press-ﬁt
cups as well as cementless stems show promising survival
202
rates. With the increasing use of hard bearings especially
in younger patients we can expect even further improvement.
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