The document discusses potential treatment options for bone loss following knee arthroplasty. It analyzes the causes of bone loss including mechanical loosening, infection, wear debris, and implant removal. Modular augmentation with metals or tantalum is presented as having advantages over allografts by providing more stable revisions, shortening surgical times, and decreasing complications like infection. While allografts can restore bone stock, their use has been limited by risks of failure, fracture, resorption, and higher infection rates compared to modular augmentation.

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Arch Orthop Trauma Surg
DOI 10.1007/s00402-014-1941-8
Knee Revision Surgery
Bone loss following knee arthroplasty: potential treatment options
Michele Vasso · Philippe Beaufils · Simone Cerciello ·
Alfredo Schiavone Panni
Received: 1 May 2013
© Springer-Verlag Berlin Heidelberg 2014
Conclusions Modular augmentation may significantly
reduce the need for allografting, whose complications
appear to limit the long-term success of knee revisions.
Keywords Revision knee arthroplasty · Knee
reconstruction · Bone loss · Augments · Tantalum ·
Allografts
Introduction
The optimal management of bone defects during revision
total knee arthroplasty (TKA) remains controversial, espe-cially
in case of large defects. Bone loss after TKA can
make implant alignment and the establishment of a stable
bone–implant interface extremely challenging. The vari-ability
in size and location of bone defects has led to the
development of a multitude of techniques aimed at restor-ing
physical integrity of the knee and supporting prosthetic
replacement: metal augments, metaphyseal tantalum cones
and porous sleeves, morcellized or structural grafts, and spe-cial
prosthetic components [1–3]. The knee surgeon should
know all possible causes of bone loss following knee joint
replacement, both to prevent and to manage them.
The purpose of this paper was to analyze the indications,
the results and the complications of the potential treatment
options used to manage bone loss within revision TKA.
Furthermore, possible causes of bone loss after TKA were
reviewed.
Etiology of bone loss
Several factors can be responsible for bone defects fol-lowing
the failure of a knee arthroplasty: primitive cause
Abstract
Introduction The management of bone loss is a crucial
aspect of the revision knee arthroplasty. Bone loss can hin-der
the correct positioning and alignment of the prosthetic
components, and can prevent the achievement of a stable
bone–implant interface. There is still controversy regarding
the optimal management of knee periprosthetic bone loss,
especially in large defects for which structural grafts, metal
or tantalum augments, tantalum cones, porous metaphyseal
sleeves, and special prostheses have been advocated. The
aim of this review was to analyze all possible causes of
bone loss and the most advanced strategies for managing
bony deficiency within the knee joint reconstruction.
Materials and methods Most significant and recent papers
about the management of bone defects during revision knee
arthroplasty were carefully analyzed and reviewed to report
the most common causes of bone loss and the most effec-tive
strategies to manage them.
Results Modular metal and tantalum augmentation
showed to provide more stable and durable knee revisions
compared to allografts, limited by complications such as
graft failure, fracture and resorption. Moreover, modular
augmentation may considerably shorten operative times
with a potential decrease of complications, above all infec-tion
which has been frequently associated to the use of
allografts.
M. Vasso (*) · S. Cerciello · A. Schiavone Panni
Department of Medicine and Science for Health, University
of Molise, Via Francesco De Sanctis, Campobasso, Italy
e-mail: vassomichele@gmail.com
P. Beaufils
Department of Orthopedics and Trumatology, Versailles “Andrè
Mignot” Hospital, Versailles Saint Quentin University,
Rue de Versailles 177, Le Chesnay, France

2. Arch Orthop Trauma Surg
of revision, mechanical loosening, chronic infection, wear
debris-induced osteolysis, implant and cement removal,
antibiotic spacer, spacer removal and delayed reimplanta-tion
of the prosthesis.
Primitive cause of revision
Primitive failure of primary TKA may be directly respon-sible
for bone loss, as it occurs because of a periprosthetic
fracture or subsidence of one or both the prosthetic compo-nents.
In these cases, bone loss often occurs regardless of a
well-defined biological or mechanical status.
Mechanical loosening
Mechanical loosening represents the most frequent cause
of failure of the modern TKAs [4, 5]. Mechanical loosen-ing
following TKA may be potentially determined by com-ponent
malalignment, prosthesis instability, patellofemoral
disorders, and other minor causes. All these factors may
produce knee periprosthetic bone loss by wear-induced
osteolysis (due to an increased asymmetrical loading and
the generation of shear stress), loosening and subsidence of
the femoral and/or tibial components, and stress shielding.
Moreover, sportive or lavorative activities involving squat-ting,
and kneeling postures in daily activities represent risk
factors for mechanical loosening of TKA [5].
Large numbers of wear particles detached from TKA
trigger and perpetuate particle disease, as highlighted by
progressive growth of inflammatory/granulomatous tis-sue
around the joint cavity. An increased accumulation of
osteoclasts at the bone–implant interface, impairment of
osteoblast function, mechanical stresses and increased pro-duction
of joint fluid contribute to bone resorption and sub-sequent
loosening of the implant [6].
Chronic periprosthetic infections
Infection remains the second most common cause of TKA
failure [5]. During chronic periprosthetic infections, cel-lular
mechanisms of osteolysis can be determined by (1)
the direct damage of infectious organisms and (2) the host
inflammatory response. Infectious bacteria produce a wide
variety of enzymes and toxins resulting in enzymatic deg-radation,
activation of fibrinolytic activity, vascular dam-age
and subsequent bone necrosis. Furthermore, bacterial
endotoxins (lipopolysaccharides) exert powerful effects
on a large variety of cells, including macrophages, neu-trophils
and B lymphocytes [7]. As a result of this activa-tion,
in addition to antibodies, host cells secrete a variety
of cytokines such as interleukin-1 (IL-1), granulocyte
and macrophage colonies stimulating factor (GM-CSF),
tumor necrosis factor (TNF), and IL-6 [7]. Some of these
1 3
cytokines are mainly involved in maturation and activation
of osteoclasts and macrophages, leading to osteolytic reac-tion
and bone resorption that make the prosthesis unstable
and needing revision [8].
Wear and osteolysis
Due to great improvements in implant and instrument
design, in manufacturing processes, and in surgical tech-nique
with expanding appreciation of the importance of
appropriate sizing, soft tissue balancing and joint line recon-struction,
polyethylene wear-induced osteolysis is no longer
the main factor of knee periprosthetic bone loss [4]. How-ever,
polyethylene wear remains a relatively frequent cause
of failure in modern TKA [9, 10]. Etiology of polyethyl-ene
wear in knee replacement is multifactorial: prosthetic
design, articular congruence, knee alignment, component
fixation, third body wear, manufacturing and sterilization
procedures, and thickness of the polyethylene itself [11].
The presence of articular polyethylene debris leads to
an inflammatory response by macrophages and histiocytes,
which induces activation of osteoclastic bone resorption,
resulting in periprosthetic osteolysis and possible implant
loosening [6, 12].
During metallosis following TKA, metal debris act simi-larly
to polyethylene debris. Metal debris cause the release
of cytokines by inflammatory cells (including IL-1, IL-6,
IL-8, TNF), resulting in chronic synovitis, osteoclastic
bone resorption, and periprosthetic osteolysis. A synergis-tic
action has been hypothesized between metal debris and
polyethylene debris in the activation of the macrophage
response, with an increase in cytokine release [6, 13].
Implant and cement removal
Prosthesis removal represents a further source of bone
loss. In the presence of a cementless prosthesis, removal
of a stable implant could cause significant bone loss, while
removal of a loosed implant generally preserves much
more bone stock. In the presence of a cemented prosthe-sis,
implant removal is usually easier because a detachment
usually occurs at the cement–metal interface. However,
removal of the bone cement can represent an additional
source of bone loss.
Once an infected prosthesis is removed, removal of all
necrotic and infected bone tissues is essential to eradicate
infection: therefore, accurate debridement may cause fur-ther
bone loss.
Antibiotic‑loaded spacer
Two-stage reimplantation involves the use of antibiotic-loaded
cement spacers to eradicate infection and preserve

3. Arch Orthop Trauma Surg
1 3
joint space. These spacers release microparticles of cement
into the joint, stimulating an inflammatory response of
the synovial membrane, with consequent damage to bone
and soft tissues. Moreover, the shear forces that are gener-ated
at the cement–bone interface during knee flexion are
responsible for additional erosion by friction of the host
bone. This occurs especially when the spacers (almost
exclusively the static spacers) are not perfectly shaped to
bone profiles of the distal femur and/or proximal tibia [14].
Significant bone loss of the metaphyseal spongiosa can
also occur after migration of an undersized static spacer. A
degree of osteopenia is finally caused by the partial immo-bilization
of the limb, which is necessary in patients treated
with static spacers [15, 16].
More recent articulating spacers allow weight bearing
and knee motion during the period following prosthesis
removal, thus reducing rigidity and osteopenia before reim-plantation
[17–19].
Spacer removal and prosthesis reimplantation
During the second phase of a two-stage reimplantation,
bone loss is caused by spacer removal, and by bone resec-tions
necessary for placement of the new prosthesis.
Removal of an articulating spacer is generally a simple
procedure: it does not require a dedicated instrumentation
and allows preservation of bone stock more than static
spacers. Once the spacer is removed, articular surfaces
have to be thoroughly debrided, with further bone loss.
As already mentioned, a variable amount of bone is sac-rificed
as the result of resections necessary for implantation
of the revision prosthesis. Wedges, augments and cones
require further bone resection to be positioned. Finally, use
of stem extensions could require debridement and curettage
of the femoral and/or tibial endomedullary canals.
Classification of the knee periprosthetic bone defects
Engh et al. [20] proposed the classification of the knee
bone defects according to the “Anderson Orthopaedic
Research Institute” (AORI). This classification defines the
extent and severity of the knee bone loss on the distal fem-oral
side (F1, F2, F3) and on the proximal tibial side (T1,
T2, T3). Type 1 defects (F1 or T1) are characterized by
intact metaphyseal segments, with only mild defects of the
spongiosa, no subsidence of the components and absence
of osteolysis. Type 2 defects present damaged metaphyseal
bone segments in one (F2A or T2A) or both (T2B or F2B)
femoral and/or tibial condyles. In particular, on the femoral
side subsidence of the components or osteolysis is distal to
the epicondyles; on the tibial side, subsidence or osteolysis
is up to or below the head of the fibula. Type 3 defects (F3
or T3) include major defects of the metaphyseal segments,
which are generally associated with partial or total insuf-ficiency
of the ligamentous structures. On the femoral side,
subsidence or osteolysis is proximal to the epicondyles,
thus being absent; on the tibial side, subsidence or osteoly-sis
is distal to the tibial tuberosity, often with serious prob-lems
of the knee extensor mechanism.
The AORI classification does not distinguish between
contained and non-contained defects. Contained or cavitary
defects have an intact cortical ring surrounding the area of
bone loss, while non-contained or segmental defects are
more peripheral and do not have a surrounding intact corti-cal
ring.
Historically, Rand [21] classified the bone defects in
relation to their symmetry, position and extent. An under-sized
tibial component could cause a symmetrical defect
linked to the subsidence of the middle part of the tibia. On
the other hand, an asymmetrical defect can be caused by
the angular mobilization of the tibial component, resulting
in an asymmetrical bone loss of the tibial plate. The loca-tion
of a bone defect can be defined as central or peripheral
relative to the integrity of the cortex. On the tibial side, a
central defect is usually due to the mobilization of an old
surface component, which leaves a peripheral border of
bone intact. A peripheral defect is associated with an angu-lar
deformity in the primary arthroplasty and is usually pos-terior
and medial in a varus knee. On the femoral side, the
bone loss associated with revision surgeries is distal, poste-rior,
or both. The extent of bone defects can be divided into
four types: minimum (type I), moderate (type II), extensive
(type III), and massive cavitary (type IV). The amount of
bone loss has to be evaluated after tibial and femoral resec-tions.
A minimum defect involves less than 50 % of a sin-gle
condyle, with a depth of less than 5 mm. A moderate
defect involves an area of 50–70 % of a single condyle,
with a depth of 5–10 mm. An extensive defect involves
more than 70 % of a condyle, with a depth greater than or
equal to 10 mm. Finally, a massive cavitary defect involves
the total disruption of one or both condyles and can be of
two types based on the presence (a) or absence (b) of an
intact peripheral rim.
Management of bone loss
For small, cavitary, type 1 defects according to AORI clas-sification
[20], cement, morcellized autografts and bone
substitutes can be sufficient. For larger, segmental, type 2
or 3 defects, impaction or structural grafts, augments, tan-talum
cones, metaphyseal sleeves, and special prostheses
have been advocated [1, 2, 22–26].
Bone grafts have been widely used in revision TKA
as being well suited to adapt to bone profiles without

4. Arch Orthop Trauma Surg
requiring excessive bone resections, and to transfer loads to
the underlying bone in a physiological manner. Autologous
grafts are generally used for the management of mild, con-tained
defects, and are used mainly in the form of cancel-lous
bone [27]. For larger defects, impaction or structural
allografts are needed. The advantages of structural allo-grafts
include relative cost-effectiveness, versatility, poten-tial
for bone stock restoration and potential for ligamentous
reattachment. However, many disadvantages have been
associated to the use of structural allografts: risk of dis-ease
transmission, nonunion, malunion, collapse or resorp-tion
of the graft [25]. Further disadvantages of structural
allografts are their availability and meticulous preparation
required to maximize surface contact between the allograft
and the host-bone interfaces [28]. Recently, impaction allo-grafts
have been advocated to address variable and irregular
defects that are commonly encountered in knee revisions;
moreover, impaction allografts could incorporate into host
bone and, successively, remodel and function like native
bone [29]. However, impaction allografting remains a time-consuming
1 3
and a technically demanding procedure [29].
Finally, a higher risk of periprosthetic infection has been
reported when using allografts [30].
Metal augments have been introduced in knee revision
surgery for the management of segmental bone defects.
Augments offer several advantages as compared to allo-grafts:
extensive modularity, quick and easy use with
decreased surgical time, great availability, and fewer com-plications
[22]. Modular metal and tantalum augmentation
allow a surgeon to produce a custom implant, re-establish
component levels (and therefore the anatomic joint line),
restore limb alignment, and balance soft tissues. Moreo-ver,
modular augmentation presents excellent biomechani-cal
properties, require minimal bone resection, and allow
immediate mobilization and loading [2]. Tibial augments
are either wedge or blocks shaped. Hemiwedges and hemi-blocks
can be used to fill small and asymmetric peripheral
defects, whereas full wedges and blocks can be used to cor-rect
axial alignment beneath the tibial tray or to substitute
for more extensive cortical bone loss elevating the tibial
baseplate (Fig. 1). Therefore, tibial augments can assist the
surgeon to recreate a flat platform, restore anatomic joint
line, and balance extension and flexion spaces.
Femoral augmentation has received less attention in the
literature. Current knee systems include femoral augments
of variable thicknesses for the medial and lateral condyles,
both distally and posteriorly or in combination. Poste-rior
femoral augments are particularly useful in restoring
proper anteroposterior dimension of the femoral com-ponent,
achieving the correct femoral component (extra)
rotation (Fig. 2), optimizing mediolateral bone coverage,
and addressing the extension-flexion mismatch as impact-ing
flexion gap. Distal femoral augments are useful in
Fig. 1 Full tibial blocks can be used for the management of exten-sive
cortical bone loss. Elevating the tibial baseplate helps to restore
anatomic joint line and reduces the polyethylene thickness, therefore
decreasing stresses at the insert locking mechanism
re-establishing the anatomic joint line, therefore impacting
extension gap. Trabecular tantalum augmentation has been
recently introduced in revision TKA for the management
of massive segmental bone defects. Trabecular tantalum
has been proposed to allow the restoration of bone stock by
promoting osseointegration; this may prove extremely ben-eficial
for younger patients, in whom a further revision is
likely [31, 32]. Tantalum cones can help restore the struc-tural
stability of the proximal tibial and/or distal femoral
metaphysis with severe type 2 or 3 bone defects (Fig. 3).
Cones can be used in combination with other metal aug-ments,
made of tantalum or other materials [2, 31]. Cones
are placed in direct contact with the host bone; prosthetic
components, eventually augmented, are then cemented on
the cones and on the metaphyseal bone (Fig. 4).
Press-fit metaphyseal sleeves represent a relatively
new strategy to manage structural defects in revision knee
arthroplasty. Taking advantage of biological fixation of
osseous integration, these components avoid potential com-plications
and the potential disease transmission of allo-grafts,
while providing a stabile scaffold for joint recon-struction.
Porous metaphyseal sleeves have been advocated
primarily for large tibial defects [1]. When the sleeve is
osseointegrated, it carries a portion of the axial load, effec-tively
protecting the epiphyseal fixation and improving the
rotational stability of the construct [33]. The primary dif-ference
between tantalum cones and porous sleeves is that

5. Arch Orthop Trauma Surg
1 3
the interface of the sleeve with the implant is created via
a Morse-tapered junction rather than with cement. A well-osseointegrated
sleeve or cone would more effectively
resist rotational stress than a cylindrical stem alone [33].
Modular stems can provide correct component position-ing,
enhance fixation, decrease stress at the bone–implant
interface in presence of severe and asymmetric bone loss
[34]. Elevated stress at the interface occurs when the col-laterals
are insufficient or absent, the bone–prosthesis inter-face
is reduced, metal augments are used, and osteotomy of
the tibial tuberosity is performed. When bone stock is quite
preserved, uncemented stems are preferred. The length and
diameter of the extension depend on the integrity of the
residual bone and the dimensions of the intramedullary
Fig. 2 Segmental defect of the postero-lateral femoral condyle
a should be managed with a metal augment, b to avoid intrarotation
of the femoral component and potential patellofemoral maltracking
and instability
Fig. 3 Massive metaphyseal tibial and femoral defects can be recon-structed
with highly porous tantalum cones. Tantalum cones have
been developed to prevent the incidence of nonunion and resorption
associated with structural allograft reconstructions
Fig. 4 Tantalum cones, with their potential for bony ingrowth, are
placed in direct contact with the host bone; the augmented prosthetic
components are then cemented onto the cones

6. Arch Orthop Trauma Surg
canal. Offset stems can assist with implant alignment when
the metaphyseal portion of the bone may not be directly
centered over the diaphysis [35]. Offset stems can prevent
mediolateral or anteroposterior components from protrud-ing,
enable achievement of the correct mechanical axis,
balance the spaces in extension and flexion through the
transfer of the components.
Materials and methods
The primary research question of this review was to deter-mine
the outcome of revision TKAs in which different
treatment options for bone loss management were used.
Outcomes of interest were revision implant survivorship,
failures of the different devices alternatively used, any
complication of the revision or of the devices used. An
advanced PubMed search was performed of the revision
knee arthroplasty literature. The search terms ‘‘revision
knee arthroplasty OR replacement”, “revision total knee”,
“bone loss OR defect”, ‘‘augment’’, “wedge”, “stem”,
‘‘tantalum cones’’, “sleeve”, “allograft”, and “bone graft-ing”
were used. Furthermore, the reference lists of retrieved
publications were checked manually for additional studies
that potentially met the inclusion criteria but had not been
found by the electronic search. Two investigators (M.V. and
S.C.) independently reviewed the literature to identify rel-evant
articles for this review. The reviewers independently
applied the criteria described above and below to the full
text of these articles to select articles for inclusion in this
review. An article was included if it represented a signifi-cant
study in which the outcome of the bone loss manage-ment
within revision TKA was reported. Studies involving
the treatment options for type 2 and/or 3 AORI bone defects
in revision TKA were included. Review articles, expert
opinions, surgical techniques, and abstracts from scientific
meetings were excluded. Duplicates were excluded, as well
as studies with less than 2 years of follow-up, finally result-ing
in 19 articles for the revision TKA. No relevant ran-domized
or comparative studies were found, so that only
Level IV, therapeutic case-series studies were included in
this review.
Results
The results of previous studies of revision TKA using dif-ferent
devices to manage type 2 and 3 AORI bone defects
are summarized in Table 1. Two authors (M.V. and S.C.)
extracted information from 19 revision TKA studies inde-pendently.
1 3
Informations extracted included study design,
number of knee revisions, bone loss treatment option, aver-age
follow-up, percentage of implant survivorship, and
complications. Non-progressive radiolucent lines around
implant or devices used for the management of bone loss
were not reported, not influencing clinical and functional
results in any study.
The use of allografts has shown higher incidence of
complications, and lower survivorship of the knee revisions
(Table 1). Naim et al. [29] prospectively studied 11 patients
with large tibial defects treated with impaction bone graft-ing.
None of the patients required secondary procedures
or further revisions. All radiographs showed incorporation
and remodeling of the graft. The only complication was a
superficial dysesthesia around the operative scar. However,
mean follow-up was only 2 years. Steens et al. [36] retro-spectively
analyzed 34 revision TKAs performed using
impaction grafting. The average follow-up was 4 years.
In five knees, there were no clear radiographic signs of
incorporation of the graft. Five other patients had compli-cations
due to aseptic loosening of their prostheses with
radiographic failure of the graft, leading to a periprosthetic
fracture in two cases. Lotke et al. [37] prospectively stud-ied
the results of 48 consecutive revision TKAs with sub-stantial
bone loss treated with impaction allograft. Average
follow-up was 3.8 years. There were six complications: two
periprosthetic fractures, two deep infections, and two patel-lar
clunk syndromes.
Concerning the use of structural allografts in revi-sion
TKA, Ghazavi et al. [38] reported only 67 % survi-vorship
at 5 years in 30 patients. Backstein et al. [39] had
one of the largest cohorts with 61 patients. The survival
rate at 5.4 years was 85.2 %, but the infection rate was
6.5 %. Clatworthy et al. [40] prospectively followed 52
revision TKAs with 66 structural grafts. Five knees had
graft resorption, resulting in implant loosening. Four knee
replacements failed because of infection, and two knees
had nonunion between the host bone and the allograft. The
survival rate of the allografts was 72 % at 10 years. Bau-man
et al. [41] reviewed 65 revisions in which large bone
defects were managed with bulk allografts. They reported
a 10-year revision survivorship of 76 %. Sixteen patients
(22.8 %) had failed reconstructions: eight failures of the 16
were secondary to allograft failure, three were secondary to
failure of a component not supported by allograft, and five
were secondary to infection.
Modular metal and tantalum augmentation has provided
more stable and durable knee reconstructions, with a lower
incidence of complications (Table 1). Historically, Rand
[21] reviewed 28 knees in 25 patients reporting good or
excellent results in 100 % of patients using metal augmen-tation
in revision TKA. In 22 knees with modular metal
wedges to augment tibial bone stock deficiency, Brand
et al. [42] reported no failures and no loosening of tibial
components after a mean of 3 years. No patient underwent
re-revision surgery. Haas et al. [43] reported an 8-year

7. Arch Orthop Trauma Surg
1 3
Table 1 The results of previous studies of revision TKA using different devices to manage type 2 and 3 AORI bone defects
References Study type Revisions Treatment option Average FU (years) Implant survivorship (%) Complications
Naim and Toms [29] Prospective case-series 11 Impaction grafting 2 100 Dysesthesia around the operative scar
Steens et al. [36] Retrospective case-series 34 Impaction grafting 4 85 Aseptic loosening with failure of the
graft (14.7 %), periprosthetic fracture
(5.9 %)
Lotke et al. [37] Prospective case-series 48 Impaction grafting 3.8 88 Infection (4.2 %), periprosthetic fracture
(4.2 %), patellar clunk syndrome
(4.2 %)
Ghazavi et al. [38] Retrospective case-series 30 Structural allografts 5 67 Infection (10 %), loosening of the
tibial component (6.6 %), fracture
of the graft (3.3 %), nonunion at the
allograft–host junction (3.3 %)
Backstein et al. [39] Retrospective case-series 61 Structural allografts 5.4 85.2 Infection (6.5 %)
Clatworthy et al. [40] Prospective case-series 52 Structural allografts 10 72 Infection (7.7 %), nonunion at the
allograft–host junction (3.9 %)
Bauman et al. [41] Retrospective case-series 65 Bulk allografts 10 76 Allograft failure (12 %), failure of a
component not supported by allograft
(4.6 %), infection (7.7 %)
Rand [21] Retrospective case-series 28 Metal wedges 2.3 100 None
Brand et al. [42] Prospective case-series 22 Modular metal wedges 3 100 None
Haas et al. [43] Retrospective case-series 67 Modular metal wedges and augments
press-fit modular stems
8 93 None
Werle et al. [44] Retrospective case-series 5 Large (30 mm) metal distal femoral
augments
3.1 100 None
Patel et al. [45] Prospective case-series 79 Modular metal augments 7 92 Aseptic loosening (7.6 %), infection
(2.5 %)
Wood et al. [46] Retrospective case-series 135 Metal augmentation and press-fit
modular stems
5 87 Aseptic loosening (1.4 %), infection
(1.4 %)
Panni et al. [35] Prospective case-series 38 Metal augments, porous tantalum
cones and press-fit modular stems
7 92 Instability (2.6 %), infection (5.2 %)
Meneghini et al. [47] Prospective case-series 15 Porous tantalum cones 2.8 100 None
Howard et al. [31] Prospective case-series 24 Porous tantalum cones 2.7 100 None
Lachiewicz et al. [32] Retrospective case-series 27 Porous tantalum cones and press-fit
modular stems
3.3 92 Aseptic loosening (3.7 %), infection
(3.7 %), femoral shaft fracture (3.7 %)
Rao et al. [3] Prospective case-series 26 Porous tantalum cones and press-fit
modular stems
3 100 None
Alexander et al. [1] Retrospective case-series 30 Porous titanium tibial sleeves 2.7 97 Infection (3.3 %), instability (3.3 %)

8. Arch Orthop Trauma Surg
survivorship of 92 % on 67 revisions for aseptic indica-tions,
performed with use of metal wedges and augments,
and not-cemented stems. Werle et al. [44] assessed the use
of large metal distal femoral augments to compensate for
severe bone deficiencies in revision TKA. Clinical and
functional scores significantly improved after implanta-tion
of femoral components with 30-mm distal femoral
augments. There was no radiographic evidence of loosen-ing,
and no implants had been revised at mean 37-month
follow-up. Patel et al. [45] described the results of type 2
bone defects treated with modular metal augments in 79
revision TKAs. The survival of the components was 92 %
at 11 years. The presence of non-progressive radiolucent
lines around the augment in 14 % of knees was not associ-ated
with poorer knee scores, range of movement, survival
of the component, or type of insert used. Wood et al. [46]
described the results of 135 revision TKAs performed for
both septic and aseptic failures. The Kaplan–Meier sur-vival
rate after 12 years was 87 % using press-fit modular
stems and metal augmentation. Panni et al. [35] recently
reported on 38 knee revisions, satisfactorily managed with
metal augments, tantalum cones and stem extension. No
allograft was used. The median follow-up was of 7 years,
therefore supporting the hypothesis that modular augmen-tation
could provide stable and durable revision total knee
arthroplasties. All metal augments and all tantalum cones
appeared well fixed radiographically at the final follow-up,
with no evidence of complications related to the modular
augmentation. In particular, on the immediate postoperative
radiographs, all nine porous cones appeared to be closely
apposed to the adjacent host bone of the proximal tibial and
distal femoral metaphysis.
Meneghini et al. [47] reported on porous tantalum cones
for the management of large tibial bone loss at 15 revision
TKAs. Patients were followed for an average of 34 months.
At the last follow-up, all 15 cones showed evidence of osse-ointegration
1 3
with reactive osseous trabeculation at points of
contact with the tibia. There was no evidence of loosening
or migration of any of these tibial reconstructions at final
follow-up. Howard et al. [31] reported on tantalum cones
for the treatment of severe femoral type 3 bone loss at 24
knee revisions. The patients were followed for an average
of 33 months. All femoral cones appeared well fixed radio-graphically.
Lachiewicz et al. [32] retrospectively reviewed
27 patients who had 33 tantalum cones implanted during 27
revision TKAs performed for infection, aseptic loosening,
and wear osteolysis. The maximum follow-up was 7 years.
One knee with two cones was removed for infection. All
but one cone showed osseointegration. Clinical and func-tional
scores significantly improved at final follow-up.
Recently, Rao et al. [3] reported the results of 26 revision
TKAs using 29 trabecular metal cones. Patients were fol-lowed
for a mean of 36 months (24–49). No radiolucent
lines suggestive of loosening were seen around the trabecu-lar
metal cones, and by 1 year all the radiographs showed
good osteointegration. There was no evidence of any col-lapse
or implant migration. No complication was reported.
Alexander et al. [1] retrospectively reviewed 30 revision
TKAs, performed using a porous titanium tibial sleeve. The
mean follow-up was 2.7 years. Six patients had a repeat
operation though none were sleeve related. Only an implant
was revised. All radiographs at final follow-up showed
well-fixed components with osseous ingrowth. Seven
patients had end-of-stem pain, four of which resolved.
Discussion
The main finding of this review was that modular metal
and tantalum augmentation showed to provide more stable
and durable revision TKAs compared to allografts, limited
by complications as infection, fracture and resorption. The
clinical literature to support the impaction bone allograft
technique is still weak. Since 2006, impaction grafting has
been used for contained and uncontained large defects in
primary and revision TKA. This option has shown good
versatility in short follow-ups, although being time con-suming
and technically demanding [29]. Moreover, compli-cations
as infection and graft failure have been frequently
reported [36], which could limit the long-term success of
this procedure.
Structural allografts have been primarily used for mas-sive,
type 2 and 3 defects [48–50]. Concerns exist about the
long-term results of structural allografts due to their possi-ble
complications, namely, graft nonunion, collapse, resorp-tion
and infection [40, 51]. Structural allografts remain a
relative cost-effectiveness option that may be reserved for
patients with lesser functional demand to decrease the risk
of collapse or fracture of allograft before its complete incor-poration
into host bone [30, 49]. Structural allografts could
be suitable in younger patients who present high rates of
union while restoring bone stock for future revisions. Older
patients who need immediate ability to weight bear and
mobilize are not good candidates to allograft reconstruction.
The use of structural allografts could be limited in septic
revision since a higher risk of periprosthetic infection has
been reported when using allografts [30, 33, 40, 49]. Since
allografts need a well-vascularized metaphyseal host bone
to obtain a proper incorporation and remodeling and avoid
early resorption, the use of allografts could be limited in
large uncontained metaphyseal defects [33]. Moreover, graft
disincorporation and resorption could depend on the sterili-zation
process, which may compromise tissue biology and
biomechanics of allografts [49]. Finally, oversized allografts
could be complicated by altered vascularization leading to
graft fracture or early resorption [24, 48].

9. Arch Orthop Trauma Surg
1 3
Modular augmentation (metal and tantalum) may signifi-cantly
reduce the need for allografting, whose complications
appear to limit the long-term success of the revision TKAs.
The major concerns with structural allografts are graft
resorption, mechanical failure and infection, along with the
considerable time and surgical skill required to obtain good
host–allograft interface [33]. Metal augmentation and tanta-lum
cones may simplify the knee joint reconstruction, mak-ing
it more reproducible due to their extensive modularity
associated to quick and easy use. Moreover, modular aug-mentation
may considerably shorten operative times with
a potential decrease of complications, above all infection
[32]. The coefficient of friction of porous tantalum is high,
allowing for a good primary implant stability and, therefore,
for immediate postoperative weight-bearing. The potential
for osteointegration of porous tantalum could favor its use
in younger patients with higher functional demand [31, 32].
Data also suggest that tantalum surfaces increase host white
blood cell activation and lower bacterial fixation, possibly
decreasing the risk of infection and therefore being suitable
in septic revisions [32]. Finally, modular augments and tan-talum
cones, with their excellent biomechanical properties,
could provide a well-functioning and durable knee joint
reconstruction also in the presence of severe large bone
defects, both in young and older patients [49]. Although the
clinical results using the metal augments are excellent, con-cerns
could exist about the use of augments relate to poten-tial
mid-term bone loss and fretting, or dissociation of the
modular components. Bone loss could occur because the
use of augments does not involve restoration of bone stock,
and may require further resection of bone to accommodate
the component. Use of the tantalum cones in the setting of
revision knee arthroplasty could be potentially associated
with all the usual complications that can occur in these dif-ficult
cases, including mechanical failure of the cones or
the prosthesis, aseptic loosening, instability and infection.
Metal augments such as tantalum cones may require fur-ther
bone resection too, needed to get an optimized fit of
the cone. Finally, the cost of these devices may limit their
availability and use in many countries which might not even
have access to all these new technologies [32, 33].
Recently, porous-coated metaphyseal sleeves have been
introduced to address these situations and have shown a
promising early outcome. Porous sleeves have been intro-duced,
in alternative to the tantalum cones, for the manage-ment
of severe metaphyseal bone defects, demonstrating
osseous ingrowth and presenting minimal complications,
and providing stable construct with biologic fixation [1].
The popularity of the porous sleeves and tantalum cones
has been driven by the efficiency of obtaining align-ment
while managing the defect and by the opportunity to
achieve non-cemented metaphyseal fixation. However, both
metaphyseal sleeves and cones incorporate with host bone
and are attached to the prosthesis by a mechanical interface
or cement, so that concerns persist regarding stress shield-ing
and difficulty of removal [2, 33].
Conclusions
The management of bone defects is a crucial aspect of revi-sion
TKA. Bone loss can hinder the correct positioning and
alignment of the prosthetic components, and can prevent
the achievement of a stable bone–implant interface. Knee
surgeon should know all possible causes of periprosthetic
bone loss and all techniques available to manage it during a
knee joint reconstruction.
The best management of severe type 2 and 3 bone
defects following TKA is still debating. Although time
consuming and technically high demanding, the use of
allografts remains a good and cost-effectiveness solution
for patients with a quite long life expectancy and lower
functional demand. The risk of graft failure, resorption and
infection limit the use of allografts for contained type 2 or
asymmetrical type 3 defects in aseptic revisions.
Modular metal and tantalum augmentation could reduce
the need for bone allografting, whose limitations and com-plications
appear to limit the long-term success of rTKAs.
Metal augments, tantalum cones and porous sleeves (dif-ferent
in shape and size) could help the surgeon to man-age
any type of bone loss, contained or uncontained type
2 and 3 defects, providing stable and durable knee joint
reconstruction. The potential for osteointegration of tan-talum
cone and porous sleeves makes these devices suit-able
for the use in younger patients with high functional
demand. Moreover, the primary stability and excellent
biomechanical properties of modular metal augmentation
allow immediate mobilization and full weight bearing in
older patients. Finally, the decreased infection rate and
the association with antibiotic bone cement of the modu-lar
augmentation make it selective in septic knee revisions.
The major concerns of metal augmentation are certainly
represented by elevated costs and difficult removal at
re-revision.
Conflict of interest None.
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