Adjunctive Fixation in Total Knee Arthroplasty Revision: Stems and Sleeves

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CHAPTER SYNOPSIS

The goals of adjuvant fixation in revision total knee arthroplasty are to enhance the mechanical stability and fixation of the prosthesis in the face of compromised bone stock. Fixation options include the use of cemented or cementless stems as well as metaphyseal filling sleeves. Little data exist, however, to guide the revision surgeon regarding which type of fixation is best. This chapter reviews the current indications, techniques, and review of the literature.

IMPORTANT POINTS

1

Stems are indicated in patients with compromised metaphyseal or diaphyseal bone stock.
2

Stems are indicated when femoral or tibial augments are used.
3

Stems and sleeves provide load-sharing capabilities and provide protection to host bone or allograft.
4

Sleeves provide rotational control of the prosthesis in patients with compromised metaphyseal bone and can be used as a substitute to larger allografts.
5

Controversy exists regarding the use of cemented or cementless fixation for stems and sleeves.

CLINICAL/SURGICAL PEARLS

1

Preoperative templating on both anteroposterior and lateral views is imperative. Stem length, diameter, alignment, and need for offset stems are determined ( Fig. 22-1 ).

FIGURE 22-1

Preoperative templating on both the anteroposterior (A) and lateral (B) views of the femur is essential to determine stem length and need for offset stems.
2

Preparation and placement of stems and sleeves require broad exposure in order to gain proper axial alignment in the intramedullary canal.
3

Metaphyseal broaches may be used to size and prepare metaphyseal bone for sleeves.
4

Host bone contact should be maximized with cementless sleeves to provide axial and rotational stability.
5

Trial stems and sleeves should be used and evaluated by intraoperative radiographs to ensure overall alignment and position of the joint line.

CLINICAL/SURGICAL PITFALLS

1

Stems should not dictate the overall position of the components.
2

In patients with metaphyseal or diaphyseal deformity, offset stems may be required.
3

Uncemented stems must be diaphyseal engaging stems in order to achieve appropriate fixation. Press-fit metaphyseal stems have been associated with higher failure rates ( Fig. 22-2 ).

FIGURE 22-2

Loose, malaligned nondiaphyseal engaging press-fit stem.
4

Cemented stems may be either fixed in the metaphysis or diaphysis depending on the amount of bone loss.

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HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

Revision total knee arthroplasty (TKA) is an increasingly common procedure. It is estimated that the burden of revision TKA could possibly increase 601% by 2030. Infection, instability, and aseptic loosening continue to be the major reason for failures in TKA. It is important, therefore, to determine the best surgical techniques to manage revision problems as they are encountered. Unfortunately, little comparative information exists to guide the revision surgeon concerning what type of fixation option is best.

The goals of adjuvant fixation in revision TKA are to enhance the mechanical stability and fixation of the prosthesis, to provide load-sharing capabilities, and to protect host bone or allograft. Intramedullary stem fixation occurs via either cemented to cementless means. Each type of fixation has advantages and potential pitfalls.

Recently, porous ingrowth and cemented metaphyseal sleeve technology have been introduced as an additional means of providing fixation in compromised metaphyseal bone ( Fig. 22-3 ). While no long-term data are available regarding their use, the concept and appeal of this technology have significantly increased their use in revision TKA.

INDICATIONS/CONTRAINDICATIONS

Indications for Stem Fixation

The goals of revision TKA include restoration of bone stock, long-term stability of implants, and, when possible, immediate weight-bearing and return to functional activity. Durable and long-term fixation of both the femoral and tibial components is dependent on component stability within the host bone. Revision TKA is often performed in patients with compromised host bone, making immediate- and long-term fixation challenging ( Fig. 22-4 ). Stems provide enhanced mechanical stability and improved fixation in the setting of compromised metaphyseal or diaphyseal bone stock.

There is general agreement that stems, whether cemented or cementless, should be used in all patients with compromised metaphyseal bone stock. No standard algorithm exists to determine when stem fixation is indicated. Each patient must be individually assessed with regard to remaining bone stock available for fixation. The Anderson Orthopaedic Research Institute (AORI) classification system ( Table 22-1 ) provides a useful way to classify bone defects and can be useful in determining the need for stems and sleeves. In Type I defects where there is intact metaphyseal bone and good cancellous bone at or near the normal joint line, it may be possible to use primary or revision components with our additional stem fixation. However, in patients with poor cancellous bone or where additional prosthetic constraint is needed, a stem should be used. In Type II and III defects, where there is damaged or deficient bone metaphyseal bone and significant loss of cancellous bone, the use of a cemented or cementless stem is indicated to provide additional fixation, bypass bone defects, and offload poor host bone. In addition, stems are indicated when augmentation is required on either the femoral or tibial side. When large structural allografts are used, additional stress protection and load-sharing capabilities are provided by the addition of intramedullary stems.

Cemented Versus Cementless Stems

Options for stem fixation in revision TKA include cemented and cementless fixation ( Table 22-2 ). The advantages of cementless stem fixation include easy removal and preservation of bone stock if revision is required, fixation distal to the areas of damaged metaphyseal bone that is often encountered in revision surgery, and the potential for favorable support and load of an allograft prosthetic composite. The main disadvantage is that a cementless stem must engage the diaphysis in order to provide adequate fixation. This fixation may be limited in patients with poor diaphyseal bone stock. In addition, diaphyseal-engaging stems may dictate the position of the femoral and tibial component, leading to overhang and malalignment ( Fig. 22-5 ). This often may require the use of offset stems. There has also been concern related to end of stem pain with cementless stem fixation. Barrack et al. reported pain at the end of cementless tibial stems in 18.8% of cobalt chrome and 8% of fluted titanium stems.

TABLE 22-2

Advantages and Disadvantages of Cemented and Cementless Stems

Type of Stem Fixation	Advantages	Disadvantages
Cemented stems	Immediate fixation	Difficult removal
	Able to obtain fixation within metaphysic
	Will not dictate component position
	Local delivery of antibiotics
Cementless stems	Ease of removal	Must engage diaphysis for fixation
	Bypass deficient metaphyseal bone	Must engage diaphysis for fixation
	Favorable support with use of allograft prosthetic composite	May dictate component position
		End of stem pain

The advantages of cemented stem fixation include immediate fixation that is achieved at the time of the surgery, and the position of the components is not dictated by the bony alignments and provides better fixation in patients with poor diaphyseal bone stock. Additionally, it allows delivery of local antibiotics in the cement for patients at risk for infection or those patients with previous infection. The main disadvantage to cement fixation is difficult removal if revision surgery is required ( Fig. 22-6 ).

Biomechanics of Stem Fixation

Biomechanical issues with regards to stem fixation include the length of the stem, the type of fixation, concern for stress shielding, and micromotion. Several studies have focused specifically on the role of stress shielding with stem fixation. Initially, there were concerns that intramedullary stems led to stress shielding of the proximal tibia over the length of the stem and could affect the long-term fixation of the prosthesis. Brooks et al., however, showed that a 70-mm stem carries 30% of the axial load and concluded that stems are load sharing, and significant stress shielding is unlikely. Jazrawi et al., in a biomechanical model, showed no significant decrease in the proximal tibial stresses with either cemented or cementless stems. Several studies have focused on the concern for micromotion with regard to stem fixation. Stern et al., in a cadaveric study, showed that micromotion and migration were significantly less in cemented stems compared with a cementless stem construct. Bert and McShane in a biomechanical study, showed that fully cemented implants have less micromotion than implants where the tray was cemented and stems were press-fit. Recently, Jazrawi et al. showed that cemented metaphyseal-engaging stems have less micromotion than cementless stems of the same length and longer diaphyseal-engaging stems are required to achieve the same stability as a shorter cemented stem.

Indication for Sleeve Technology

Traditionally, large segmental or cavitary defects have been treated with bulk allograft. The main advantage of large bulk allografts are the potential for restoration of bone stock. There are, however, many drawbacks to their use. The correct size and shape allograft may be difficult to obtain. Preparation and fixation can be difficult and time consuming. Long-term fixation and incorporation of allograft to host bone are unpredictable. In one of the largest series of revision TKAs using structural allografts, Clatworthy and Gross et al. reported on 52 revision cases. At 5-year follow-up, the success rate was 92%. This dropped to 72% at 10 years.

The concept of metaphyseal sleeves is not new. The Noiles S-ROM rotating hinge prosthesis, originally designed in the 1970s underwent modification in the late 1980s and early 1990s to include metaphyseal filling metal sleeves. Barrack et al. and Jones et al. reported mid-term, excellent results with the S-ROM Modular, mobile-bearing hinge prosthesis in patients with severe knee problems. The advent of newer metal metaphyseal sleeves and segmental augments offer an alternative to structural allografts. While these augments do not restore bone stock, they are technically easier to use and do allow for immediate weight bearing and range of motion. They can be manufactured in various sizes and shapes to fit most standard patterns. These sleeves are available in both cemented and cementless versions.

Highly porous metal implants are now readily available for use in treating patients with metaphyseal defects on both the femur and tibia. Trabecular metal is a highly porous metal with high strength and low stiffness, comparable to cancellous bone. Its high biocompatibility and coefficient of friction allow for enhanced initial stability and the potential for long-term bony ingrowth. Because of their relative recent introduction, no set indications exist for the use of cemented or cementless metaphyseal sleeves. Metaphyseal sleeves may be used in Type II defects ( Table 22-3 ) to provide rotational control in the proximal tibia. In such instances, cancellous bone is often poor quality and a central defect may exist, thus preventing engagement of the tibial base plate keel into host bone and compromising rotational stability.

TABLE 22-3

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