Rationale

A press‐fit stem has the theoretical advantage of reduced bone loss with component insertion and ease of extraction if this becomes necessary. Concerns with uncemented stems include a lack of bone ingrowth, increased incidence of malalignment, and an increased incidence of stem tip pain.^10,11

Clinical comment

An uncemented total knee revision technique offers several advantages, including endosteal referencing and subsequent stabilization of the construct without the difficulty of future extraction compared to cemented fixation.¹⁰ Cementless revision TKA was originally described by Whiteside using a mixture of loosely packed cancellous allogeneic and autogenic morselized bone with a component that had fluted press‐fit titanium long stems and a sintered‐bead porous tibial under‐surface.¹²

Available literature and quality of the evidence

Five studies (levels II–III) are available to answer this question.

Findings

In his prospective series of 110 cases, Whiteside evaluated the results of cementless fixation and morselized allografting of metaphyseal defects at 60 to 127 months of follow‐up.¹² He described an apparent increase in radiodensity in the profile views of 31 tibias and 28 femora at postoperative intervals greater than 1 year, suggestive of bone remodeling. Only 1 tibial component was revised for loosening.¹² Hanna et al. reviewed 56 cases of revision TKA using Whiteside’s technique (cementless long‐stemmed components in combination with morselized bone graft) at a mean of 7.3 years (range 4–10 years), obtaining a 98% survival at 10 years. They reported a 9% reoperation rate including all‐cause revision.¹³

Further interest in uncemented components has increased in recent years with the advent of foam metal technology. These metals are made of elemental tantalum or titanium and are highly porous to allow for significant bio‐interlock. Foam metal has a modulus of elasticity similar to that of cancellous bone, allowing for a more physiological transfer of force from the implant to the bone interface. In 2015, Kamath et al. showed excellent medium‐term (minimum five years) results of a porous tantalum cone used in 15 cases with severe metaphyseal bone stock deficit.¹⁴ Although the authors have described the surgical technique with cementation of the tibial implant after the cone was impacted, it has also been used with allografts, bio‐composite scaffolding, or in a fully cementless fashion in more rare situations. These cones may increase bone loss during bone preparation, lead to stable long‐term fixation, and have predictable bony ingrowth with a reduction in proximal stress shielding.¹⁴

Stem tip pain remains a disadvantage of uncemented fixation. This issue can also occur with cemented stems but at a lower incidence.⁵ At a minimum follow‐up of two years, Barrack reported localized pain at the end of the stem in 11% of uncemented femurs and 14% of uncemented tibias.⁶ Methods to reduce stem stiffness with fluting or slots have been undertaken by some manufacturers to minimize stem tip pain. There is, however, limited evidence comparing fluted and nonfluted stems.^15,16

Concerns about proximal stress shielding with cementless fixation remain, especially if the stem is well fixed distally.^17–19 There is also no definitive answer on optimal stem size relative to the endosteal canal. Canal filling stems would seem to provide better initial stability and alignment compared to thinner dangling stems, but long‐term concerns regarding proximal stress shielding also remain with canal filling stems.^20–22

Theoretical concern exists with uncemented implants due to greater access areas for polyethylene wear debris to enter the metaphyseal bone compared to a cemented implant.²³ It is thought that cement offers an immediate barrier to third‐body debris that is absent with an uncemented prosthesis, especially in cases with increased levels of constraint. The presence of radiolucent lines and its potential association with loosening also remains a concern with uncemented prostheses.¹³ It has been demonstrated that when trying to encourage biological interlock, establishing secure initial stability is crucial.²⁴ Minimal tolerances to micro‐motion must exist if true osseointegration is to occur. Porous metals may have advantages over fiber metal coatings in this regard due to their rougher surfaces.²⁴

Finally, a long uncemented stem will not be useful in cases with severe deformities, marked osteopenia, or excessive femoral bowing. There is also an increased risk of periprosthetic fracture on stem insertion.²⁵ The basis of press‐fit stability is also reliant upon complete canal fill when significant proximal bone stock is absent.²⁶

Resolution of clinical scenario

• In the setting of severe bone loss, cement augmentation may be less than ideal. Uncemented revision TKA, alone or in combination with allografting, is an attractive option in these situations. Due to a lack of randomized controlled trials (RCTs) there is no ideal method and treatment should be individualized for each patient (level II–III).^27–29
  
• Application of foam metal technology to revision TKA has been applied with successful medium‐term outcomes (level III).^12,27
  
• It has yet to be characterized if an uncemented prosthesis is more or less susceptible to third‐body‐induced osteolysis in the long term (level III).¹⁹
  
• Uncemented stems may not be useful in cases of severe femoral or tibial shaft deformities or in cases of marked osteopenia. Increased risk of periprosthetic fracture has been reported in these types of cases (level III).^27,28