The use of cement in revision total knee arthroplasty

Abstract

Despite the availability of modern implants and techniques, Revision Total Knee Arthroplasty (R-TKA) still poses a challenge to surgeons, particularly the management of bone loss/defects and the secure fixation of implants. Polymethylmethacrylate (PMMA) bone cement plays an important role for fixation as fully uncemented fixation in RTKA is rarely used. Cement can be employed as part of a full cementing construct or as a hybrid construct. While in fully cemented implants, the diaphyseal stem as well as any couplers or connectors in the metaphysis are cemented, in hybrid cementing, only the component parts at the joint surface and metaphysis are cemented, while the diaphyseal stem is fixed in a press-fit manner. In this article the literature on the in vitro as well on the in vivo results of both fixation options is reviewed.

Although the fixation mechanism of both constructs are different, radiographic and clinical survivorship appear similar for both techniques. Although there appears to be a trend towards a hybrid fixation method, the choice of which technique to employ in revision total knee arthroplasty will depend on the surgeons' familiarity with each technique as well as the factors peculiar to each patients anatomy.

1. Introduction

While the rates of revision total knee arthroplasty are variable across different registries, it is generally accepted that approximately 5–10% of all primary knee replacements will need revision for a variety of causes at 10 years after surgery.^1,2 Furthermore, with the increasing number of primary knee replacement surgeries done, and particularly, in younger and active patients; it is expected that more patients will eventually require a revision knee arthroplasty. The goals of a revision total knee arthroplasty (R-TKA) are similar to that of a primary knee replacement, but additional challenges are posed to the surgeon by the need to manage bone defects, as well as the need to achieve stable and secure fixation of the revision construct. These difficulties are attributed in large part to inadequate bone stock as a result of infection, osteolysis, stress shielding and implant removal. In addition, the need for increased varus/valgus constraint in the revision total knee construct as a result of ligamentous damage results in increased stresses across the implant-bone interval and necessitates the use of stemmed components to dissipate stresses. This results in a decrease in the durability of the revision construct. The use of stems can also help with implant alignment.³

1.1. Fixation strategies

The stable fixation of these revision implants during revision surgery can broadly be divided into where and how fixation is achieved. As popularised by Morgan-Jones et al., the distal femur and proximal tibia can be divided into 3 zones each, namely the epiphysis, metaphysis and the diaphysis. This represents 3 distinct areas where different methods can be used to secure the fixation of implants.⁴ This fixation can be achieved with or without the use of Polymethylmethacrylate (PMMA) bone cement.

The use of cement confers the benefit of cement interdigitation with the host cancellous bone, resulting in decreased micromotion and immediate stability of the implants, allowing the patient to weight bear immediately. Cementing an intramedullary stem increases the area of fixation, and allows for greater flexibility in the positioning and fixation of implants when there is an altered geometry of the medullary canal.⁵ This is particularly advantageous in cases where severe bowing of the tibia and femoral diaphysis precludes the use of a long press-fit stem. It is also useful in patients who are osteoporotic and have large, ectatic intramedullary canals.⁶ In revision surgery for prosthetic joint infections, cement gives the surgeon an opportunity for local antibiotic delivery. Cement fixation of stems decreases the risk of stem tip pain as well as the risks of fracture during stem preparation, as stems used without cement are often longer and larger.⁷

However, the use of cement fixation makes re-revision surgery difficult and may result in additional bone loss and increased risks of fracture when extracting a well-cemented component. Cement does not allow for a durable, long term biological fixation; and a cemented stem is also less useful as an aid for implant alignment. Furthermore, with the use of offset stems to help with optimal implant positioning and with novel stem materials and designs that can decrease stem tip pain; some of the traditional advantages of a cemented stem may be negated.^3,5, 6, 7, 8

When PMMA cement is used during revision surgery, we can broadly divide the cementing techniques into three categories: surface cementation, full cementation and hybrid fixation.³

Surface cementing results in the application of cement only to Zone 1 (epiphysis). Vince and Long reported the increased risk of failure with the use of increased constraint and surface cementation only.⁹ As such, uncemented fixation across the other two zones in the form of a press-fit stem or an uncemented metaphyseal fixation device is often used as well. Although fixation of implants in Zone 1 (epiphysis) without the use of cement has been regaining popularity in primary knee arthroplasty, its use is not routine during revision surgery, where most implants are still fixed to the epiphyseal surface with the use of cement.

In using the full cementing technique, revision components are fully cemented across all 3 zones; whilst in hybrid fixation, a press-fit stem is used with implants that are cemented only in the joint surface and the metaphysis.

2. Results

Despite the purported advantages and disadvantages of both cemented and hybrid fixation, the best method of fixation remains controversial.^10,11 A lack of high-quality evidence addressing this conundrum probably results from the heterogenous revision population, with substantial differences in the indication for revision surgery, the types of bone defects encountered, the strategies used to deal with the bone defects, as well as the size and lengths of the revision construct used. Most studies focus on the use of a hybrid cementing technique and head to head trials comparing the full cementing technique and hybrid technique are rare.

Several biomechanical and cadaveric studies have shown no differences in micromotion of revision implants with either cemented or uncemented stem.^12,13 However, others have shown a more stable fixation with a cemented stem when compared with a cementless stem of the same length. This was associated with less micromotion but with more stress shielding of the proximal tibia.¹⁴ The change in bone quality of the proximal tibia as a result of altered biomechanics may have an implication on failure and loosening of the tibia component.¹⁵ The altered bone stock of the bone in zone 1 may also affect subsequent re-revision surgery. Yet, in studies looking at the strain distribution at the proximal tibia, the use of a long hybrid construct results in a more equal and physiological strain distribution; favouring the use of a long hybrid stem over a shorter cemented stem. Some of the results in these biomechanical studies are mirrored in a clinical study by Heersterbeck et al.¹⁶ In their study, 32 patients were randomised into 2 groups, undergoing either an all cemented revision or a hybrid revision. Patients had similar degrees of bone defects and had similar construct lengths in both groups. Radiostereometric analysis of the patients’ radiographs was performed up to 24 months, and there were no significant differences in the amount of implant migration demonstrated between the two groups.

The presence of radiolucent lines around the stem have been reported around both all cemented and hybrid revision construct. When these radiolucent lines appear under the tibia tray, it may represent cancellous bone resorption as a result of stress shielding from a stem that is well fixed distally. These lines are common and have been reported in up to 61% of fully cemented stems and up to 74% of hybrid constructs. However, these lines are, for the most part, none progressive and are thought to have no clinical significance with respect to loosening.17, 18, 19

Objective assessment of the significance of these radiolucent lines can be performed using the Modified Knee Society Radiographic Scoring system. Gilliland et al. assessed 82 revisions performed for aseptic failures and found similar rates of radiographic failures between full cementing and hybrid cementing.¹⁰

Short term survivorship of up to 5 years is good in both groups. Praprosky et al. reported a 92% survivorship at 5 years using a hybrid technique. A multicentre retrospective study demonstrated that there was no significant difference in failure rates between cemented and hybrid fixation at an average follow-up of 76 months. Combining radiographic failures and re-revision rates, they found a failure rate of 6% in cemented tibia stems and 10% in cementless tibia stems. On the femur side, 8% of cemented stems and 9% of cementless stems failed.²⁰ More recently, a 2018 study comparing full cementing to hybrid cementing concluded that there was no difference in survivorship at 5 years (93% vs 94%).²¹ At 10-year follow-up, the same study found lower survivorship of 84% in the all cemented group compared to 94% in the hybrid group, although this difference was not found to be statistically significant. This result was also illustrated in a meta-analysis looking at the differences between the use of cemented and non-cemented stems in revision knee arthroplasty. At 5–10 years of follow-up, in another study there was a trend towards lower failure rates in the non-cemented group, although this result was also no statistically significant.¹¹ However, a more recent meta-analysis of more recent publications favoured the use of a hybrid fixation method.²² In the medium term, aseptic loosening was the most common cause of revision in the full cemented group while infection was the most common cause in the patients who have undergone hybrid fixation. At 10 years of follow-up, aseptic loosening was the most common cause of failure in both techniques.

Improvements in Knee Society Scores, KOOS scores and patient reported outcome measures appear similar in both techniques when comparison trials are done. Stem tip pain that is more common when cementless stems are used and occurs in 11–20% of patients.¹⁹ Stem tip pain has also been reported in patients with cemented stems, with some studies reporting rates similar to that of uncemented stems.^23,24 The use of larger, longer and non-slotted press-fit stems are risks factors for the development of stem tip pain. This may result in decreased patient satisfaction and a worsening of such scores. But the presences of stem tip pain is not exclusive to press-fit stems and can also occur when cemented stems are used as well.

PMMA cement is also frequently used to deal with small, shallow and contained defects, with or without the use of screw supplementation. These defects should generally be less than 5 mm deep and occupy no more than 50% of the tibia plateau or femoral condyle. Results of the management of bone defects using cement and screws have been good in both primary and revision total knee arthroplasty. In a study of 609 knees in which this technique has been utilised, Berend et al. reported a probability of survival of over 98% at 15 years of follow-up.²⁵

The use of metaphyseal fixation devices in Zone 2, namely metaphyseal sleeves and cones, have given surgeons the ability to deal with the problem of implant fixation as well as to manage bone loss at the same time. The survivorship of both metaphyseal sleeves and cones are excellent. Hanssen et al. reported a 95% revision free survival at 70 months with the use of metaphyseal cones, and revision free survivorship as high as 98% has been reported with the use of metaphyseal sleeves.²⁶ A variety of porous coating is usually applied to these metaphyseal fixation devices to allow for bony ingrowth and osteointegration. As such, while options are available in certain revision systems to implant a metaphyseal fixation device with cement, they are used in a press-fit manner without the use of cement most of the time. The indication for the use of a cemented sleeve is probably dependent on the choice of stem fixation. The use of contemporary cementing techniques with a fully cemented stem will interfere with the proper usage of a press-fit metaphyseal sleeve and will necessitate the use of a cemented sleeve.

3. Conclusion

The proper use of PMMA cement will allow a surgeon to deal with both bone defects and to secure revision components to the host bone. Currently available literature does not allow us to reach a conclusion on the superiority of one technique over the other. Nevertheless, while the overall data is similar in both techniques, the anatomy and host bone condition of an individual patient will probably dictate which method of fixation is suitable. This author prefers the use of a hybrid fixation technique in revision total knee arthroplasty, but preoperative planning and careful consideration of the patient's anatomy (such as bowing and existing bone stock) should be applied to each case. And in patients with such anatomical aberrations, then an all cemented construct may be more appropriate. While the conduct of further randomised controlled trials is difficult, it will give more information and allow the treating surgeon to select the most appropriate cementing technique.

Declaration of competing interest

None declared.