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23 (); 113-117
doi:
10.1016/j.jor.2020.12.018

Is stemless implant fixation a valid option in total knee revision arthroplasty – Review of in vitro and in vivo studies

,
Department for Arthroplasty and General Orthopaedic Surgery, Asklepios Hospital of Orthopaedic Surgery Lindenlohe, Lindenlohe 18, 92421, Schwandorf, Germany

∗Corresponding author: H. Graichen. h.graichen@asklepios.com

Received: , Accepted: ,
Professor P K Surendran Memorial Education Foundation
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

Metaphyseal sleeves have shown an improved fixation in Revision Total Knee Arthroplasty (R-TKA) leading to a reduced aspetic loosening rate compared to other stem based fixation options. In the majority of these studies sleeve have been used with stems. Due to that is was not clear how much of this improved fixation could be rated to the sleeve and how much to the additional sleeves. In this review article we analysed the results of sleeve-only obtained in in-vitro or in-vivo studies.

In Vitro models showed independent of the set-up a dominant fixation of the sleeve, an additional stem was not adding a lot to the overall fixation. Undersized additional stems showed an increased micromotion and the stem tip, while distal engaging stems showed a proximal stress shielding effect. Very interestingly an increased BMI had not a significant effect on primary fixation of the sleeve. Reduced bone quality on the other hand had and this effect was increased in cases with an increased BMI.

In vivo results of sleeve-only patients showed comparable good results to sleeve and stem constructs. In particular on the femoral side the use of an additional stem is required only in a few scenarios. It has to be stated that the numbers of sleeves-only in rotating hinges is too low, to give any recommendation for this high constraint implants. Majority of cases was done with PS and VVC constraint. So far no in vivo data exist on the limitations of sleeve-only in patients with reduced bone quality and increased body weight.

In conclusion we can state, that Sleeve-only is an option for R-TKA. In majority of cases the aspetic loosening rate is as low as with additional stems. The borderlines in terms of constraint, bone quality and body weight need to be investigated in future in vivo studies. The in vitro results look so far encouraging.

Keywords

Metaphyseal sleeves
Revisions total knee arthroplasty
Primary fixation
Stems
Aseptic loosening
1

1 Introduction

Revision-Total Knee Arthroplasty (R-TKA) is a challenging procedure with a lot of different problems to solve. Bone defects and due that achieving a solid implant fixation is one of the most common problems, which also determines the long-term outcome in particular.1,2 According to the concept of zonal fixation,3 main fixation zones of revision implants are the diaphysis (zone 3) and metaphysis (zone 2). Reason for that is the fact that zone 1 is often compromised. That's why stems, cemented or uncemented are used in the great majority of R-TKA. Both types of stems have shown similar results in the literature,4–6 however, both are not achieving similar results in terms of aseptic loosening compared with primary TKA. In particular, in larger uncontained defects the results showed 6.5%–29% of aseptic loosening after 5–10 years7–10

To achieve improved fixation and due to that better long-term implant survival rates, additional fixation options, such as cones and metaphyseal sleeves have been introduced more than 10 years ago. The outcome studies showed very promising short- and midterm results for both constructs.11–14 Recently, the first 10 year follow-up of metaphyseal sleeves showed 97.8% implant survival15 and confirmed by that this low aseptic loosing rate. Although the names of sleeves and cones are often used in a similar manner, both constructs have fundamental differences in the way they work. Both constructs are used in larger defects and are fixed mainly in the metaphysis. Cones are for reducing defect size, and by that allowing an improved fixation of the cemented, stemmed implant. They are, however, not part of the implant and therefore they work as a filler for an indirect implant fixation. Multiple contact surfaces are created, such as bone-cone; cone-cement, cement-implant. Morgan-Jones et al. (2015) defined this as indirect, secondary fixation.3 The fixation principle of metaphyseal sleeves is different, as they are parts of the implant and by that a primary, direct fixation is achieved. Another very obvious difference is the fact that sleeves are made for cementless and cones for cemented implant fixation.

To differentiate between the relevance of sleeves and stems for fixation, a comparison of stem-only, sleeve -only and sleeve plus stem needs to be done. This kind of direct comparison under defined circumstances can be easily done in vitro. In vivo, however, a direct comparison study of such 3 groups does so far to our knowledge not exist. The difference between constructs can only be done by indirect comparison of the results of each construct.

In this following review, we are therefore analysing whether this improved effect of fixation is achieved only when sleeves and stems are combined or whether it can also be achieved similarly in sleeves-only fixation, too. To achieve a fundamental insight this analysis is divided into 2 sections1: Analysis of in vitro data, and2 Analysis of in vivo studies. In the latter part we added also a chapter of potential limits of such a sleeves-only construct in clinical revision practice.

2

2 In vitro data

Traditional fixation is performed with stems. Those modular stems vary in length and thickness. They bypass the defect and reduce the stress at the implant-host interface by increasing the contact surface area. To achieve good long-term survival, initial press–fit is required in cementless stems. For long term fixation a constant loading of the bone around the implant is mandatory. An imbalance between osteoblastic and osteoclastic activity towards osteoclasts will result in implant loosening.16 The implant itself, however, is altering the load transmission within the tibial bone massively. To achieve proper fixation, the load transfer from implant to bone should stimulate osteoblastic activity leading to osteointegration and long term fixation.

2.1

2.1 Effect of tibial sleeves on primary stability

The effect of metaphyseal sleeves on fixation can be analysed at least in part in vitro. Of course, as osseointegration is a process that needs time and is based on the biologic process of osteoblastic activity, it can therefore not be studied in vitro. However, the important issue of primary implant stability and its relevant factors of implant stress and micromotion can be assessed in detail and under defined conditions. Different authors have created different bone defects according to the AORI classification.17 Interestingly independent whether it was a type 1, 2 a or 2b the value of an additional stem for reducing micromotion and stress is described to be very limited.18–21 The dominant role in primary fixation is played by the sleeve. This effect is found to be more or less independent of its size. Nadorf et al. described in their synthetic bone testing model that the most natural bone deformation could be observed in sleeve-only construct.19 This bone deformation was altered by an additional stem, the longer the more. On the other hand, it is described that an additional stem has the positive effect of load sharing, again the longer the more. For example, Completo et al. measured an increased load sharing along the stem if longer stems were used.22 However, in all those different testing models the effect of load sharing was small, therefore the consequence out of these studies was that in type I, IIa and IIb stems are of limited value for primary stability, and if one decides to use a stem, short stems should be preferred.

2.2

2.2 Effect of sleeve size

Awadalla et al. measured in their FE model an increase of contact area of 8% if the sleeve size was increased from 37 mm to 45 mm.21 The effect of further size increase was not described, however, as the sleeve size is growing constantly by 8 mm an additional increase of contact area of 8% can be assumed. Of course, in type 2b defects this contact area depends also on the defect size of the bone itself. The forces transferred from the implant to the bone were equal for both tested sleeve sizes. As the contact area in larger sizes is larger the composite peak strain (CPS) was reduced in larger sleeves. By adding a stem, a distal load transfer to the diaphysis was measured, however the differences described to be small and thought to be not clinically relevant.20,21

2.3

2.3 Effect of stem thickness and length

A distal supporting stem can offer additional fixation in zone 3. This is on the one hand an advantage, as it increases the contact area. On the other hand, this distal fixation is increasing the risk of proximal strain shielding19 and by that of reduced osseointegration.23 Thinner stems minimize the problem of proximal strain shielding, however, they have shown to have higher micromotion at the stem tip.19,21 This negative effect might influence osseointegration and can potentially explain the high rate of stem pain in undersized cementless stems.24 Nadorf et al. described that undersized stems increase implant bone flexibility.19 As the material properties of bone and stems are different, this can cause stem pain. They suggested that a reduction of stem stiffness might help to overcome this problem. Distal slotted stems might be a technical solution for that problem.

Increasing stem length is reducing distal relative micromotions, which is beneficial for osseointegration in distal areas. Strengthening the distal fixation is automatically weakening proximal fixation, as it is leading to an increase in proximal relative micromotions,19 in particular under varus/valgus loading conditions. This increase of micromotions further increases the risk of metaphyseal stress shielding. These biomechanical findings are in accordance with the description of clinical findings, in which fatigue fractures of distal fixing implants between stem and sleeve can occur and non-integrated tibial sleeves were observed.11,25

2.4

2.4 Effect of bone quality, BMI

In 2018, Awadall et al. measured in their FE model that an increase in BMI just led to a marginal increase of peak composite micromotion (CPM) and CPS around the sleeve.20 The main effect was measured around the stem, in particular in undersized stems. In a distal press fitting stem the effect of BMI again was minor. A larger effect was found for bone quality. As bone quality is changing in the entire bone, this effect was found in the entire tibia. In bone with reduced quality the effect of increasing BMI then gets more relevant. This effect again is most prominent in non-engaging distal stems. This is leading to a doubling of CPM values greater than 50 (= critical value for primary fixation) around an undersized stem from 21.7% to 42.7%. In larger, distal engaging stems a strain shielding effect in the proximal metaphysis compared to sleeve only was found.

2.5

2.5 Femur

Compared to tibial sleeves, the amount of biomechanical studies on femoral sleeves is very limited. However, the described effects of proximal metaphyseal fixation on tibial sleeves can probably be transferred 1 to 1 to the femur. As femoral sleeves have a larger size than tibial sleeves and as they are partially and fully coated available the coated contact areas for fixation are a lot larger than of tibial sleeves, which probably will pronounce the fixation effect of sleeves even more.

In accordance to this assumption, (Fonsecca et al.) showed recently for femoral sleeves that there is no significant difference between sleeve only and sleeve with stem construct in terms of primary fixation.26 They found no significant difference for micromotion, the amplitude in both scenarios was below 50–150 μm, which is suitable for bone ingrowth. Therefore, they recommended the stemless construct in all anatomical difficult situation with bowings or posttraumatic deformities.

Retrieval study showed that femoral sleeves have a larger surface area (21.3%) of bone ingrowth compared to tibial sleeves (14.7%) demonstrating that femoral sleeves without stems should work at least as good as tibial sleeves.27

2.6

2.6 Limitations of in vitro studies

The strength of these different in vitro studies is that the specific conditions for testing is clearly defined. For example, the type of bone defect that is tested. None of the models however can study the process of secondary osseointegration, which is however a relevant factor for implant longevity. All testing was performed with the implants in perfect alignment. What is the effect of malposition on primary fixation and long-term outcome? The same is the case for joint stability. What is the effect of an unbalanced joint on primary fixation? Is this effect more severe for flexion instability than for midrange? To simulate the effects of such often found clinical problems and their effect on implant fixation would be something to test in the future.

3

3 In vivo data

At the time when sleeves were introduced into the market, the company recommended to use them only with additionally stems. Therefore, in the beginning a sleeve-only construct was off-label use and due to that the number of revisions with sleeve-only had been very small and limited to specific cases for example with severe bone deformity. Majority of publications have mainly been on sleeves with stems. Multiple publications have shown a great bone ingrowth and described a low aseptic loosening rate.11,28,29 This was confirmed recently by Bonanzinga et al. in a systematic review, in which they have found an aseptiuc loosening rate of 0.7% after 45 months.13 Meanwhile the first long-term studies confirmed the promising midterm results.15

The number of cases and studies analysing the loosening rates of sleeves-only is comparable low. Within their larger series, some authors11,28–31 described some cases with sleeves only. Except Agarwal who found 2 cases with early loosening,28 all the other reported on excellent osseointegration and low aseptic loosening for this sleeve-only fixation too. However, until now only a few studies exist that have exclusively analysed their results of sleeve-only systematically on a larger number of cases.32–34 Cumulative all 3 studies have included almost 200 patients and showed an aseptic loosening rate between 0 and 1% after a follow-up of 37–58 months. Fig. 1a and 1b In the following paragraphs we want to summarise their findings and try to give recommendations for daily use of Sleeve-only:

Postoperative long leg a.p. Xray of R-TKA with stemless sleeves.
Fig. 1a Postoperative long leg a.p. Xray of R-TKA with stemless sleeves.
Postoperative lateral Xray of R-TKA with stemless sleeves.
Fig. 1b Postoperative lateral Xray of R-TKA with stemless sleeves.
3.1

3.1 Defect type

Majority of cases included in these 3 studies showed type 2 a and 2b defects, however, in a smaller percentage also type 1 and type 3 defects were included. Only Scior et al. excluded type 3 defects in their study.34 Independent of the type of bone defect the osseointegration was excellent, even in uncontained and type 3 defects.

3.2

3.2 Influence of constraint

Majority of cases included in these series had only PS constraint. Only a few hinges were included and as this number was so low, a final conclusion can not be made, whether the sleeve-only fixation can withstand the higher stresses over time in rotating hinges. Scior et al. found the only cases with aseptic loosening in cases with TC3 inserts.34 PS inserts showed no aseptic loosening in any of the 3 series.

3.3

3.3 Femur-tibia

Radiographic analysis of sleeves with stems showed better bone ingrowth with fewer radiolucent lines for femoral sleeves (3.4%) compared with tibial sleeves (8.9%).35 Scior et al. demonstrated a reduced aseptic loosening rate of femoral sleeves (100%) compared to tibial (96%).34 All the other sleeve-only studies showed no lucency of femoral sleeves. Reason for the better results of femoral can be the increased contact area of the femoral sleeves compared to tibial sleeves.

3.4

3.4 Bone quality/BMI

Unfortunately, no in vivo on both factors is available that could give some clinical tips on how to deal with sleeve-only fixation in very obese and/or osteoporotic bones.

3.5

3.5 Limitations of sleeve-only in daily practice

The Sleeve-only construct is a lot shorter than the one with an additional stem. The advantage of the longer construct is that it can guide the implant position in the right direction. In cases with straight bones this intramedullary guidance is very helpful. As the sleeve-only construct is a lot shorter the potential problem of malalignment is higher. This problem was reported by Göttsche et al. They observed in 51% of their cases an outside optimal alignment and a mean tibiofemoral alignment of 6° valgus.32 The other authors have not reported such problems, maybe because they used stems for preparation and trial implants, and only the original implant was stemless. On the other hand, the shorter length of sleeve-only can be of great help in all bowed bones. As the bowing is guiding longer constructs into malalignment, shorter constructs can stay proximal to the bowing. However, an additional extramedullary help for placing the short construct in the correct alignment is of great help. One option for this can be conventional extramedullary guides another one navigation. As all TKA-revisions are preformed tibia first, the position of the tibia is crucial and in particular for its correct placement the surgeon should have a standard that assures this.

Another problem of femoral sleeves is the fixed distance between the sleeve position and the distal joint line. In the great majority of cases this limitation can be solved by pre- and intra-OP measurement of correct joint line position. However, in larger defects in zone 2 it can become difficult to fix the sleeve at the right height for a proper joint line reconstruction. In the newer revision system, the number of sleeve sizes has been increased, which can help to overcome the problem. Additional bone grafting for minimizing the bone defect can be another option.

A general intra-OP complication that can occur independent whether stems are applied to the sleeves or not is a fracture during impaction of the broach or the original implant. Bonanzinga et al. described an intraoperative fracture rate of 3.1%. However, in 86% of these fractures, they were described to be non-displaced and did not require any additional surgical treatment.13

4

4 Conclusion

In multiple in vitro and in vivo studies sleeves have shown that they are capable of improving primary and secondary osseous implant fixation. This is also documented by very low rates of aseptic loosening. An additional stem is giving additional support in zone 3, however, they simultaneously increase the risk of potential proximal stress shielding. By that the risk of secondary loosening and/or fatigue fracture between stem and sleeve is increased.

Sleeve-only has several advantages, such as it achieves more natural bone deformation, reduced implant length and costs. The reduced length can be very helpful in bowed bones to overcome the problem of malalignment, on the other hand it is more difficult to achieve perfect sleeve position in sleeve-only constructs. Therefore, most surgeons use trial stems for preparation.

The most important finding of all in vitro analyses is the fact that the sleeves are the dominant implant part for fixation and stems are adding only a small bit in most of the cases. In vitro and in vivo the findings are very encouraging that sleeve-only will deliver similar good results as sleeve-stem constructs have shown. In particular on the femur the use of stems can be limited to a few cases. The effect of reduced bone quality has demonstrated to be important in FE models, in particular in combination with an increased BMI. Unfortunately, this problem has not been assessed in vivo and therefore no clear borderlines for sleeve-only constructs can be defined. However, if someone is in doubt the use of an additional stem is therefore still recommended. This stem should not be undersized, otherwise it has an increased potential for stem pain. The length of the stem should be minimal, otherwise a proximal stress shielding effect can occur, which can reduce the long-term survival of the sleeve (see Fig. 1a,b).

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