Keywords
arthroplasty, replacement, knee - bone defects - homologous grafts - review
Introduction
The increase in the number of revision total knee arthroplasty (rTKA) surgeries can
be related not only to the increase in the absolute number of primary surgeries performed,
but also to several other factors such as the expansion of primary implant indications,
including younger and more active patients, as well as factors related to surgical
technique and implant durability.[1]
[2]
[3]
[4]
[5] In the United States, a 601% increase in the number of rTKAs is estimated between
2005 and 2030.[1] In Brazil, there is a lack of reliable data on the increase in the number of rTKAs.
Among the enormous challenges of this complex surgery, the adequate treatment of bone
defects is essential to obtain satisfactory and lasting results.[6]
[7]
[8] The cause of bone deficiency is usually multifactorial; however, aspects such as
previous pathology, the design of primary implants, the occurrence of osteolysis,
possible technical errors in the realization of the primary prosthesis or during the
removal of fixed implants and, also, the failure mechanism are frequently identified.[9]
[10]
[11]
[12]
Assessment of Bone Defects
Assessment of Bone Defects
Anteroposterior (AP) and lateral radiographs of the knee make it possible to assess
the design and size of prosthetic components, to analyze the type and quality of implant-host
fixation, to infer possible causes of failure, and to estimate the extent of bone
loss. Axial radiography of the patella allows the assessment of patellar alignment,
as well as the presence or absence of patellar component and/or bone defect.[13] Oblique radiographs can be useful in showing osteolysis, especially in implants
with a posterior-stabilized box. Panoramic views allow to analyze the limb alignment,
the presence of extra articular bone deformities, and the presence of possible synthesis
materials as well as the condition of the other joints.[12]
[13]
[14]
However, standard radiographs of the knee often underestimate, especially in the femur,[9]
[13] the extent of the bone defect identified intraoperatively after removal of implants
and debridement of fibrosis and necrotic tissues.[11]
[15] Computed tomography (CT) images show greater sensitivity and specificity in diagnosing
bone defects and osteolytic lesions that are difficult to observe on radiographs due
to the overlap of images of metallic components; however, due to the increased cost
and exposure to ionizing radiation, the routine use of CT is not recommended.[11]
[12]
[13]
[16]
The adequate treatment of bone defects aims to build a stable and lasting support
platform for implantation of the definitive prosthetic components and, if possible,
the restoration of bone stock. Concomitantly, it allows the correct alignment of the
prosthetic and limb components, as well as reestablishing the height of the joint
interline, thus restoring the tension of soft parts and load distribution to the host
bone and generating a joint reconstruction with good and stable function, and painless
too.[6]
[7]
[9]
[11]
Classification and Management Options for Bone Defects
Classification and Management Options for Bone Defects
Several distinct bone defect classification systems have been proposed to assist in
decision making. However, subjectivity and, therefore, low interobserver agreement
and limited accuracy in correctly estimating the size of bone defect are the main
criticisms of most classifications.[11]
[12]
[17]
The most widely used classification is that of the Anderson Orthopedic Research Institute
(AORI),[18] which describes the defects according to size, location, and impairment of soft-tissue
structures after the removal of components and debridement of devitalized tissues.
Defects in the femur and tibia are analyzed separately in three categories:
Type 1: it includes contained defects limited to the cancellous bone, without compromise
or cortical bone failure. It presents intact metaphyseal bone and, therefore, does
not compromise the stability of the revision components. In selected cases, revisions
can be effectively performed with primary implants,[19] although standard revision implants associated with the use of intramedullary nails
are the recommendation of most authors. Thus, this type of defect can be effectively
treated by filling with bone cement, sometimes associated with reinforcement with
screws. Bone grafting may represent a management option in this type of bone failure.
Metallic augmentations can also be an option to restore the joint interline.[6]
[10]
[11]
[12]
[15]
[19]
Type 2: it is characterized by considerable loss of metaphyseal bone, which will need
to be filled in during revision surgery. Defects can occur in only one femoral condyle
or tibial plateau and are referred to as type 2A. These defects are most often managed
with bone cement reinforced with a screw or non-porous metallic augmentations (wedge
or block) or, still, bone grafting and standard revision components with intramedullary
nails.[20] However, bone defects that affect both condyles or plateaus are classified as type
2B. In these more severe defects, more complex treatment and fixation options are
recommended. Thus, options with metaphyseal fixation, such as highly porous metal
cones (tantalum cones), or metaphyseal sleeves, or even homologous structural bone
grafting, are the most recommended options.[6]
[7]
[8]
[10]
[11]
[12]
[19]
[20]
[21]
[22]
Type 3: it has completely deficient metaphyseal bone, characterized by severe bone
loss that compromises the largest portion of the femoral condyle or tibial plateau.
These defects are often associated with detachments of the epicondyles and, consequently,
collateral ligaments, or even the patellar ligament. Normally, for appropriate treatment,
these defects require prosthetic implants with long intramedullary nail with diaphyseal
fixation, and options for defect management with metaphyseal fixation, such as trabecular
metal cones, or metaphyseal sleeve or, still, structural homologous graft. In cases
with detachment of the epicondyle and ligament insufficiency, blocked implants are
normally necessary. Customized implants, non-conventional or tumor prostheses can
be indicated for the management of large defects in which reconstruction is not possible.[6]
[7]
[8]
[10]
[11]
[12]
[19]
[21]
[22]
[23]
Thus, for an adequate treatment of bone defects during the performance of rTKA, the
accurate analysis of the quality of the host bone, the configuration (whether contained
or not contained), the size and location of the bone defect must be carefully analyzed.
However, currently, there is no option for managing bone failure that is ideal in
all circumstances. Therefore, several other factors, such as functional demand, presence
of comorbidities, life expectancy and experience of the surgeon must be evaluated
in the decision-making process and in the individual choice of the option employed.
However, restoration of bone stock is preferable in patients with the possibility
of future revisions.[24]
Bone Cement with or without Reinforcement with Screws
Bone Cement with or without Reinforcement with Screws
Bone defects involving less than 50% of the cancellous bone surface (ideally, less
than 10% of peripheral deficiency) and with a depth of less than 5 mm are traditionally
managed with methyl methacrylate. In short, this technique is best suited for small
bone defects, mainly, those contained.[17]
The use of bone cement is also advocated for the handling of defects with a depth
between 5 and 10 mm; however, the use one or more screws from 4.5 to 6.5 mm is recommended
to reinforce the construction, aiming to provide greater mechanical resistance to
the cement column and improve the load distribution to the host bone. In this case,
attention must be paid so that the screws do not remain in direct contact with the
definitive implant. Therefore, this technique can be indicated in the management of
AORI type-1 defects and, eventually, in selected cases AORI type 2A.[6]
[11]
[12]
[15]
[17]
Satisfactory results, in medium-term follow-up, in the treatment of bone defects in
the tibia, using cement reinforced with screws, were demonstrated by Ritter et al.,[25] although with a high incidence of non-progressive radiolucent lines. Therefore,
this technique was more often indicated for older patients with less functional demand,
due to the questioning regarding the long-term conservation of the biomechanical properties.[6]
[11]
[24] Posteriorly, Berend et al.[26] demonstrated high implant survival in patients with 20 years of surgery who underwent
primary arthroplasty with significant bone defects managed with methyl methacrylate
reinforced with screws. Additionally, the same authors evaluated patients who underwent
rTKA surgeries and demonstrated that the use of bone cement reinforced with screws
as well as the use of revision implants had the ability to restore knee biomechanics
and a 98.5% survival rate after 15 years. Thus, the authors guide the possibility
of using this technique to reduce costs without compromising the survival of the prosthesis.[27]
Modular Metallic Augmentation (Blocks and Wedges)
Modular Metallic Augmentation (Blocks and Wedges)
Modular metallic augmentations is indicated in the management of uncontrolled bone
defects, compromising more than 25% of the cortical contour and with a depth between
5 and 20 mm, or even when more than 40% of the implant surface is not supported by
the host bone.[11]
[12]
[15]
[28] In summary, modular metallic augmentations are most often indicated in the management
of AORI type 2 bone defects[11] and also employed in selected AORI type 3 cases in elderly patients with low physical
demand.[15]
[17]
The various revision implant systems present metallic augmentations of varying thicknesses,
sizes and shapes. They can be added to both the femoral and tibial components to fill
the bone defect in one or both tibial condyles or plateaus.
The metallic augmentations for the management of tibial defects are presented in wedge
or block form. In both options, it is usually necessary to prepare and remove additional
host bone for correct adaptation of the metal augmentation. Although there is a lesser
removal of additional bone with the use of metal wedges, the sheer force at the implant-bone
interface is greater and, consequently, more susceptible to mechanical failure. When
using block augmentation, bone removal is usually greater; however, it presents a
better load distribution to the host bone.[11]
[24]
[29] The possible bone loss after the use of modular augmentations must be filled in
with methyl methacrylate or by bone grafting.[15]
The use of symmetric metallic augmentation extensions in both the distal femur and
the proximal tibia frequently contribute to the restoration of the height of the joint
interline and, consequently, soft-tissue tensioning and equilibrium of the flexion-extension
balance. Posterior femoral augments are particularly useful in restoring the anteroposterior
dimension of the component and, consequently, in the stability of the flexion space;
however, the use of asymmetric posterior femoral augments may be necessary to ensure
proper external rotation of the component.[6]
[11]
The main advantages of using metallic extensions are the immediate load-bearing capacity,
it helps the rotational stability of the component, the reduction of surgical time
and presents less complications. The disadvantages, however, refer to the increased
costs with the implant, sometimes the need for additional resection of the host bone
and the fact of not restoring the bone stock. Other potential disadvantages refer
to the possibility of corrosion and the formation of wear debris at the modular augmentation
interface and prosthetic component, in addition to the possibility of the occurrence
of the stress shielding phenomenon due to the difference between the elasticity modules
of the metal and the host bone.[10]
[15]
[24]
[30]
[31]
Failures of metallic augmentations in performing adequate treatment of defects, most
often, occur when the surgeon underestimates the severity of bone deficiency and does
not identify the need to use defect treatment options with metaphyseal fixation.[11] Therefore, the tendency of modern modular augmentations is to use metals in highly
porous configuration, between 70 and 80%, given the benefits of having an elasticity
module closer to the host bone, greater friction and fixation capacity, in addition
to enabling bone growth and biological fixation.
Good or excellent results with the use of metallic augmentations to treat bone deficiencies
during the revision have been reported to vary from 84 to 98%,[15]
[31] although the effectiveness and durability of the technique is contested.
In a prospective medium to long follow-up of 79 patients with AORI defects, two treated
with metallic augmentations, although Patel et al.[31] have observed incidence of non-progressive radiolucent lines in 14% of cases, they
found durability of 92% after 11 years. Favorable results, with no complications or
loosening in 3 years, were also reported by Werle et al.,[32] with the use of 30 mm femoral metallic augmentation to treat femoral defects AORI
3. Contrarily, Hockman et al.[33] identified that even using modular augmentations in 89% of rTKA cases, structural
grafts were necessary in 48% of cases to effectively treat bone deficiency. They also
observed a greater number of failures in patients treated only with metallic augmentations,
resulting in a 79.4% durability in 8 years.
Impaction Bone Graft
The use of impaction bone graft is an effective option for the management and restoration
of bone stock in defects of various sizes and shapes, especially for those contained,
although good and durable results have also been demonstrated for not contained defects.[30]
[34]
[35] Autologous graft has osteoinduction, osteoconduction, and osteogenic capacity and
can be used, above all, in small disabilities due to limited availability and risk
of pain and complications at donor sites. Due to greater quantitative availability,
the homologous graft is the most frequently used, although it presents a potential
risk of disease transmission, fracture of the host bone during impaction and, also
the possibility of graft absorption with loss of support capacity.[12]
[17]
[30]
[34]
[35] Increased risk for infection and concern about immunological reaction are also related
to the homologous graft.[17]
The surgical technique requires careful debridement of the bone defect with the use
of a burr drill to remove the sclerotic bone from the periphery of the defect, thus
forming a viable bed for osteointegration. The initial stability of components with
the use of impacted bone graft is worrisome and is also influenced by the integrity
of the cortex, the size of the defect and the type of implanted intramedullary nail.
Contained defects can be treated without major difficulties; however, for non-contained
defects, a shaped plate or metal mesh should be used to avoid graft leakage and to
increase the stability of the construction.[17]
[30]
[34] The intramedullary nail test must be properly positioned before the impaction of
bone particles between 3 and 5 mm in size to provide greater initial stability.[17]
[30]
[34] The test implants are removed, and the final intramedullary nail must be inserted.
The use of long press-fit nails can add initial stability to the system; however,
it can over-protect the load transmission graft and, consequently, there is a concern
to inhibit early incorporation. Therefore, many authors recommend the preferential
use of a cemented nail.[30]
[34]
In a study of 42 rTKAs, with an average follow-up of 3.8 years, treated with impacted
homologous graft, Lotke et al.[34] identified graft incorporation in all cases without failure of the implants. Similar
results were found by Naim et al.[36] by treating large tibial bone losses with impacted graft and short cemented nail
and demonstrating favorable clinical results and durability in the short-term. Conversely,
poor results with long-term follow-up (10 years) are demonstrated by Hilgen et al.[37] In this study, of the 29 patients treated with impacted graft and constricted implants,
14 required revision due to mechanical failure at a mean time of 5 years, and in all
these cases a lack of graft incorporation and reabsorption was observed during the
operation.
Structural Homologous Bone Graft
Structural Homologous Bone Graft
Structural bone graft from a tissue bank represents a cost-effective option for the
treatment of types 2 and 3 AORI bone defects, of varying shapes and sizes, in patients
with greater physical demand and future possibility of a new rTKA.[17]
The advantages of using the homologous graft consists of the capacity to restore bone
stock and provides adequate initial support to the implants, allows the reinsertion
of the epicondyles and avoids additional removal of the host bone.[17] However, in addition to the limited availability in our midst, this technique presents
the risk of non-union, resorption and graft fracture, long surgical time, as well
as the risk of disease transmission.[12]
The femoral head is the most widely used homologous graft, possibly because of its
ability to adapt to various formats of bone defects; however, segmental parts of the
distal femur and proximal tibia are also widely used. All the cartilaginous tissue
of the graft must be removed, as well as the cortical bone, with preference being
given to the use of cancellous bone. The part must be prepared with abundant irrigation
to remove the bone marrow components. Acetabular milling cutter is used to remove
sclerotic bone in order to potentiate graft-bone host contact and promote its incorporation.
Provisional fixation is performed with Kirschner wires to continue making bone cuts
with an oscillatory saw. The structural graft is customized to the bone defect. The
final fixation, if necessary, can be carried out with screws. The definitive implants
are cemented on the homologous graft[12]
[38] ([Figure 1]).
Fig. 1 (A) and (B) anteroposterior radiographs and aseptic loosening profile of total knee
prosthesis with marked osteolysis in the distal femur; (C) Intraoperative aspect of
the femoral bone defect; (D) Preparation of the graft with an acetabular cutter; (E)
Intraoperative appearance after debridement; (F) and (G) Postoperative radiographs
of the structural homologous graft fixed with screws in both condyles of the distal
femur and revision semi-constricted implants; (H) Intraoperative appearance after
using homologous bone graft.
In 46 rTKAs using homologous structural graft, Engh and Ammem[38] reported 91% of 10-year survival. Of these patients, four required a new surgical
approach. In two of them the graft was incorporated and in two others the graft was
removed due to infection. Similarly, Wang et al.[39] studied 30 reviews in which an average of 1.7 homologous femoral heads were used,
with an average follow-up of 76 months, and they did not observe graft failure at
the end of the evaluation. Conclusions favorable to the capacity of the homologous
graft as an adequate option for durable support were obtained by Chun et al.[40] when evaluating the clinical and radiographic results, with an 8-year follow-up
of 27 patients, 26 of whom showed no fractures or graft collapses or disease transmission.
Similarly, we did not observe fracture or collapse of the homologous graft in a short-term
assessment of 26 rTKAs with AORI types 2B and 3 defects; however, in three cases we
noticed mild-to-moderate graft absorption without compromising the support function
or implant failure, and one patient observed a non-union of segmental graft from the
distal femur, but without loss of structural function.[23]
However, doubts and concerns about the durability and maintenance of the structural
function of the graft in the long term are not completely clarified. Several studies
report the 10-year survival rate of revisions with a structural graft with a mean
of 74%.[6]
[41]
[42] Unsatisfactory results, however, have been reported by Bauman et al.[41] When evaluating 70 rTKAs, they found survival of 80.7% and 75.9% at, respectively,
5 and 10 years after surgery. Of the 16 cases of failure described, 8 cases were attributed
to graft failure, which occurred on average 42 months after surgery. In a systematic
review, evaluating 551 rTKAs with homologous graft and mean follow-up of 5.9 years,
the reported incidence of any type of graft failure was 6.5%. Deep infection occurred
in 5.5% of cases and aseptic loosening in 3.4%.[8]
Trabecular Metal Metaphyseal Cones and Metaphyseal Sleeves
Trabecular Metal Metaphyseal Cones and Metaphyseal Sleeves
Metaphyseal cones and sleeves represent a modern option for the management of large
bone defects, providing immediate structural support and potential biological fixation.
Metaphyseal cones come in a variety of sizes and models, allowing the treatment of
lesions of varying sizes and configurations. In short, they are indicated for the
treatment of AORI types 2 and 3 defects.[6]
[17]
[22] The lack of restoration of the bone stock, the need for additional removal of the
host bone for correct accommodation of the cones or sleeves and, if necessary, the
difficulty of removal due to biological fixation are the main disadvantages attributed
to this option.[6]
[11]
[22]
[43]
[44]
Proper implantation of both the tantalum cone and the sleeve require the preparation
of the host bone. Initially, the metaphysical cones were symmetrical and did not have
side specificity; however, with the evolution of the designs, the current cones are
asymmetric and can be metaphyseal or diaphyseal. A variety of implant systems can
be used with metaphyseal cones, but sleeves are specific implants.[6]
[7]
[12]
[17]
[45]
It is recommended that the intramedullary test nail be used to obtain correct alignment
and direction of the specific cutters to prepare the bed and better adaptation of
the cone or sleeve. A burr drill may also be necessary in this debridement. After
positioning the metaphyseal cone and repairing the defect, reconstruction proceeds
with the placement of prosthetic components. It is noteworthy that the rotation of
the cones should favor the better filling of defects and greater contact with the
host bone and, thus, they are independent of the rotation of the implants. Eventual
non-contact areas from the metaphyseal cone to the host bone should be grafted to
favor biological integration. The inner portion of the cones allows cementation of
the definitive prosthetic components. However, care should be taken with the use of
an offset stem for some systems, given the possibility of difficulties in fitting
to the metaphyseal cone ([Figures 2] e [3]).
Fig. 2 (A) and (B) Preoperative radiographs of the 2nd revision total knee arthroplasty
due to septic failure, with severe bone defect, especially in the proximal tibia;
(C) Intraoperative appearance with the test components of the metaphyseal cone and
tibial tray; (D) Intraoperative appearance with the tantalum cone implanted in the
tibia and with maximum contact with the host bone; (E) and (F) Postoperative radiographs
of the revision with contrite implants and metaphyseal cone in proximal tibia.
Fig. 3 (A) and (B) Preoperative radiographs of aseptic total knee arthroplasty failure with
severe distal femoral defect; (C) metaphyseal tantalum cone positioned to treat bone
defect; (D) Profile image of the definitive femoral component plus a tantalum cone
and distal and posterior femoral wedges; (E) and (F) Postoperative radiographs.
The metaphyseal sleeve fits the revision component, and the construction allows limited
internal or external rotation to adjust the rotation of the tibial tray and the metaphyseal
component. The definitive components are implanted with cement on the surface of the
tibial tray, leaving the spinal canal free of cement for biological integration. Eventual
removal of these porous devices can be quite difficult.[7]
[12]
[43]
[45]
[46]
Several clinical studies using tantalum cones for the management of bone defects during
rTKA have shown favorable initial results in a short follow-up, with the need for
reoperation in only about 1.1%.[43]
[44]
[47]
[48]
[49]
[50]
[51]
In a meta-analysis, evaluating 8 studies with 196 revision surgeries using 233 tantalum
cones, with a follow-up of up to 40 months, the authors identified only two cases
of aseptic loosening. The recurrence of infection after a two-stage exchange was the
main cause of reoperation.[20]
Systematic review of 20 studies including 812 metaphyseal cones was performed by Divano
et al.,[21] showing 94.55% survival in the short-to-medium-term follow-up. The incidence of
infection was 7.1%, while the rates of reoperation and revision were, respectively,
16.19% and 8.19%.
Kamath et al.[52] studied 66 reviews using tantalum cones in types 2 and 3 AORI defects, with minimum
follow-up between 5 and 9 years, and identified that 23% of the cones had incomplete
and non-progressive radiolucent lines and that 3% (two cones) had aseptic loosening.
Therefore, the revision-free survival was over 96%, thus demonstrating the maintenance
of favorable results in the medium and long terms.[52] Favorable medium-term results were also corroborated by Potter et al.[53]
These favorable results, however, were contested by Bohl et al.,[22] who compared reviews with the use of tantalum cones with the results of rTKA with
conventional implants without the use of cones, and concluded that there was no evidence
of superiority with the use of metaphyseal cones.
Similarly, Beckmann et al.[8] conducted a systematic review that compared 10 studies with 233 revisions managed
using tantalum cones with 17 studies involving 476 revisions that performed large
structural grafts. The authors pointed out that, although the results should not be
considered conclusive, there are strong indications of better results favorable to
the use of trabecular metal.
Short-term assessments of cementless metaphyseal sleeves have been studied by Alexander
et al.;[54] these proved to be a promising option for the treatment of types 2B and 3 bone defects,
being able to provide stable construction for fixation of implants.
In a prospective study, with a short-term follow-up of 83 rTKA, using 36 femoral and
83 tibial sleeves, 2 patients (2.7%) required revision for aseptic loosening on the
tibial side.[46] Satisfactory results, with osteointegration of all sleeves in the short term, were
also identified on the tibial side by Barnett et al.[45]
Non-Conventional Prostheses and Customized Mega Prostheses
Non-Conventional Prostheses and Customized Mega Prostheses
Unconventional or tumoral prostheses and customized megaprostheses are generally used
to replace the entire distal femur or the entire proximal tibia. Thus, they are usually
used in oncology, or to treat severe bone loss that is typically found in chronic
infection, or after multiple joint reconstruction surgeries, so they are usually atypical
indications.[12]
[17]
Customized implants are usually expensive, require a long time to produce, and often
have a high risk of infectious and mechanical complications.[17]
Fraser et al.[55] studied 247 patients treated with hinged megaprostheses for the treatment of severe
bone defects, demonstrating revision-free survival, after 8 years, of only 58%. Similarly,
Holl et al.[56] identified a high incidence of complications in 11 out of 20 patients who underwent
the placement of this type of implant, however without the need for amputation. These
results were corroborated by Barry et al.,[57] who demonstrated a high number of complications and reoperations with this treatment,
although, according to the authors, it is a viable option for salvage of the limb.
Final Considerations
Proper treatment of bone defects during TKA revisions is a fundamental principle for
obtaining satisfactory and long-lasting results. There are several management options
with their respective advantages and disadvantages, and there is no option for treating
bone failure that is ideal in all circumstances. Therefore, decision making and choice
of the method employed is individualized; however, the procedure should focus on the
objective of restoring bone stock in patients with the possibility of future revisions.
