Are we ready to adopt cementless fixation in unicompartmental knee arthroplasty?

At a Glance

• Cementless UKA may reduce aseptic loosening and revision risk.
• Some cementless designs have shown concerning early failure rates.
• Patient selection and implant design remain critical to success.

Estimated read time: 5 minutes

Unicompartmental knee arthroplasty (UKA) remains an attractive alternative to total knee arthroplasty (TKA) for patients with isolated medial compartment osteoarthritis, offering preserved kinematics, lower perioperative morbidity, faster recovery, and potentially improved outcomes and overall patient satisfaction. While cemented fixation has been the gold standard, there has been increased adoption of cementless UKA over the last two decades, aiming to address one of the main causes of failure: aseptic loosening. Cementless implants now represent a substantial and growing proportion of UKA cases in certain parts of the world and have shown very promising results. The use of cementless UKA in North America remains limited, however, particularly amid recent studies that raise significant concerns. Are we now ready to adopt cementless UKA in North America?

Why consider cementless fixation?
One of the main concerns with UKA is a higher revision rate compared to TKA. Along with arthritis progression in the non-replaced compartments, aseptic loosening is a major cause of failure. Cementless designs can potentially address this issue as well as other concerns with cement use, such as progressive radiolucent lines, the risk of cement extrusion, and third body wear.

The decreased risk of loosening with cementless implants is corroborated in the literature. Indeed, while analyzing the indications for revision in medial UKA, Tay et al. found that the risk of aseptic loosening was more than six times higher in cemented versus cementless UKA. The UK National Joint Registry data showed a 26% reduction in revision rates with the use of cementless implants along with a significant, albeit less clinically relevant, increase in function as measured by the Oxford Knee Score. The New Zealand Joint Registry similarly showed reduced revision rates with cementless UKA. In a meta-analysis of 12 studies, Liu et al. also showed significantly improved outcomes with the cementless Oxford UKA, reduced radiolucent lines, and reduced revision rates. Moreover, the authors showed that using a cementless design saves about 10 minutes of operating room time. Indeed, cementless fixation allows for a more efficient operation, an additional advantage worth serious consideration.

What are the concerns with cementless fixation?
In a series of cementless UKA procedures, Bruni et al. reported failure and revision in approximately one quarter of their cases within six years, an unacceptably high early failure rate. The main reason for failure was aseptic loosening, with only one failure for fracture. At least two high-volume centers in the U.S. demonstrated similar concerns with a cementless UKA design that was available in the U.S. at the time. Bertrand et al. had a 12% revision rate within the first two years and reported the absence of any ingrowth at the implant-bone interface at the time of revision surgery. Vossen et al. similarly reported high early postoperative revision rates and lower outcomes when comparing the cementless design of the same implant to a hybrid technique. The implant in question has since been withdrawn from the market.

In a systematic review comparing cementless and cemented UKA, including 25 studies and more than 10,000 cases, Muhammad et al. showed a significantly reduced revision rate for cementless UKA; however, when performing a subgroup analysis by design, they lost that significant effect when excluding the Oxford knee. Thus, the advantages offered by the cementless Oxford knee demonstrated in the U.K. and New Zealand registries, as well as other studies and meta-analyses, may not necessarily extrapolate to other UKA designs. The reasons for the apparent superiority of the cementless Oxford design are not fully understood and are likely multifactorial. Potential contributors include its porous surface coating, which facilitates bony ingrowth; implant geometry that incorporates a tibial keel to reduce micromotion and increase the available ingrowth surface; and a mobile-bearing design that may decrease stress at the implant-bone interface, allowing more reliable biologic fixation. This design has been officially available in the United States for less than two years. The first study on cementless Oxford UKA in the U.S. was actually an Investigational Device Exemption (IDE) study led by Hamilton et al., who showed similar revision rates at five years between cemented and cementless designs in a multicenter randomized controlled trial.

In addition to the failure of ingrowth in designs without a long track record, another concern with cementless fixation is an increased risk of periprosthetic fracture, which is consistently reported across multiple studies. A nationwide cohort study from Denmark showed a threefold greater risk of early periprosthetic fracture within four months after cementless UKA compared to cemented UKA. Other identified risk factors for early periprosthetic fracture included female sex, age >70 years, body mass index >40 kg/m², and height <160 cm. the authors recommended opting for cemented fixation in elderly female patients older than 70 years old, especially if they are relatively shorter and or heavier, in an attempt to reduce the risk of early periprosthetic fracture. similarly, the norwegian arthroplasty register showed the risk of revision for periprosthetic fracture in cementless oxford uka within the first year to be 15 times higher; the authors recommended against the use of cementless uka, especially given the increased implant cost.

In a large database study in the U.S. matching cementless UKA to cemented UKA, researchers found periprosthetic infection rates 10 times higher and periprosthetic fracture rates eight times higher in cementless designs. Cementless UKA had significantly higher rates of revision at two years and 10 years. The increased rate of infection witnessed was also identified in the Norwegian Arthroplasty Register, which is another reason for concern. The cases included in this study were, however, before the Oxford cementless knee became readily available in the United States.

The bottom line
Ultimately, both fixation methods are valid and have different failure profiles, with a lower risk of periprosthetic fracture in cemented UKA and a higher potential survivorship with cementless UKA, along with reduced rates of aseptic loosening and radiolucent lines. Older patients with poor bone quality are likely still better suited for cemented fixation; in younger patients with good bone stock and increased life expectancy, cementless fixation should be considered, especially in the hands of a high-volume surgeon using an implant design with an established track record. Continued surveillance through the American Joint Replacement Registry, mirroring the granular fixation-specific reporting available in European and Australasian registries, will be essential to confirm whether the survivorship advantage seen abroad translates to North American practice patterns and case volumes.

Joseph A. Karam, MD, is an associate professor in the Department of Orthopaedic Surgery at the University of Illinois Chicago College of Medicine.

Seth A. Roge, MD, is an orthopaedic surgery resident in the Department of Orthopaedic Surgery at the University of Illinois at Chicago College of Medicine.

References

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