Initially popularized in the 1980s,¹,² cementless fixation for total knee arthroplasty (TKA) has enjoyed variable rates of success over the last 3 decades. Historical registry data demonstrate a relatively small percentage of usage internationally for cementless fixation in TKA, with slightly higher failure rate consistently observed with uncemented fixation.³ While arthroplasty surgeons have been relatively slow to embrace cementless fixation in TKA, interest has recently surged in large part due to the increasing incidence of TKAs performed in younger,⁴ more active, and more demanding patients. Additionally, recent improvements in biomaterials and robust implant designs to enhance initial component stability and osseointegration, improved polyethylene, and a better understanding of the failure mechanisms of past designs portend a bright future for cementless fixation in TKA. While cemented fixation has a well-established track record and remains the gold standard,⁵,⁶,⁷,⁸,⁹,¹⁰,¹¹ aseptic loosening with fragmentation and debonding of the cement interface continues to be a major failure mechanism.¹²,¹³,¹⁴,¹⁵ This is particularly concerning with TKA in young patients¹⁶,¹⁷ with whom a more durable biological fixation method holds the promise of improved longevity. Moreover, improved operating room and procedural efficiency via eliminating cement cure time can yield improved operating room efficiency and translate directly into healthcare dollars saved.¹⁸ It is documented that decreasing surgical procedure duration has a positive impact on postoperative infection rate, and this may be a potential advantage to cementless fixation in TKA.¹⁹ Additionally, the longevity of a biologic ingrowth interface may yield decreased long-term revision burden in patients who would have outlived traditional cemented fixation, particularly in younger more active patients.

Despite potential advantages, improved materials, and advances in design, cementless fixation remains controversial. Past failures in the early cementless implant designs are well documented and are often directly attributable to various design flaws or inferior biomaterials.²⁰,²¹,²²,²³,²⁴ Poor-quality polyethylene, inferior polyethylene locking mechanisms, tibial patch-porous coating,²⁵,²⁶ tibial screw augmentation, fatigue fracture of the femoral component,²⁷ and patellar failures²⁸,²⁹,³⁰ have all contributed to poor outcomes. Despite these early failures, certain cementless TKA designs have yielded excellent long-term results on par with those of cemented TKA.³¹,³²,³³,³⁴,³⁵ With the emergence of porous ingrowth metals and improved polyethylene, the current generation of modern cementless designs is an enticing option for fixation in TKA.

As with early generations of cementless total hip arthroplasty (THA), close clinical follow-up has identified several design-related failures associated with early cementless TKA systems. These unanticipated shortcomings of early designs underscore the significance of close clinical follow-up as new technologies and cementless TKA designs are introduced into the marketplace. The somewhat checkered history of cementless TKA has left us with a cache of knowledge which can be implemented to enhance future designs. In most systems, the femoral component has achieved reliable long-term fixation to bone in both in hybrid and cementless TKA constructs,³³,³⁶ while the tibial and patellar components remained problematic in many series²⁵,²⁶,²⁸,²⁹,³⁰ and are considered the “Achilles heel” of successful uncemented TKA.

Successful fixation on the femoral side has not been problematic and is attributed to the inherent mechanical stability obtained with multiplanar press-fit. Although fixation was not an issue, some early-generation cementless femoral component designs demonstrated catastrophic failures due to fatigue fracture of the thin regions of the implant.²⁷,³⁷ Additionally, designs with porous-coated femoral pegs have been shown to cause stress-shielding which can lead to loss of anterior femoral bone at revision surgery for cementless TKA systems. Early-generation femoral components, both cemented and cementless, were not designed to optimize patellar tracking³⁸,³⁹ and likely contributed to polyethylene wear and metal-backed patellar component failure frequently observed in series of early designs.

Tibial component fixation and design in cementless TKA continues to be the main area of focus for optimizing performance and outcomes. Early designs achieved fixation with short pegs which did not attain adequate initial mechanical stability for osseointegration, instead allowing deleterious micromotion, liftoff, and subsidence. The addition of stems or screws to augment initial tibial component stability has been shown in biomechanical studies to minimize micromotion and prevent tray liftoff. While
supplemental screw fixation can enhance initial stability, there has been reported failure of ingrowth and metaphyseal osteolytic lesions predominating around tibial screw tracks. Berger et al reported results in a series of 131 consecutive cementless Miller-Galante-1 (Zimmer, Warsaw, IN) with an ingrowth tibial interface and screw augmentation, finding 8% tibial aseptic loosening rate due to failure of ingrowth and a 12% incidence of osteolytic lesions around screw holes at a mean 11-year follow-up. The incidence of screw hole osteolysis is reported to be greater than 30% in some cementless tibial component designs and has been attributed to the screw holes acting as access channels for particulate debris to the proximal tibial metaphysis.

While screw holes provide access, the osteolytic process is likely multifactorial and tied to the polyethylene quality, polyethylene thickness, and integrity of the polyethylene locking mechanism. Hofmann et al reported no cases of screw track osteolysis in a series of 176 cementless Natural Knee prostheses (Zimmer, Warsaw, IN) at minimum 10-year clinical follow-up.³³ In the next iteration of this design, the Natural Knee II (Zimmer, Warsaw, IN) screw augmentation was found to be unnecessary by Ferguson et al.⁴⁰ This study evaluating 116 consecutive TKAs study demonstrated equivalent stability and ingrowth at average 67-month follow-up in cementless TKA both with and without screw fixation.⁴⁰

Tibial baseplates that contain patch-porous coating and/or smooth metal tracks separating pads of porous coating on the undersurface of the tibial tray allow a path of minimal resistance for egress of particulate wear debris and the subsequent development of osteolysis in the proximal tibia.²⁵,²⁶ Whiteside et al reported a high rate of osteolysis in the first-generation Ortholoc Modular tibial component (Wright Medical Technology, Arlington, TN), which contained such a configuration. When compared to the next-generation Ortholoc II tibial component (Wright Medical Technology, Arlington, TN) that utilized continuous porous coating, no cases of osteolysis in 675 cementless TKAs were identified. These clinical findings support that maintaining a circumferential and fully porous-coated cementless tibial tray is important to effectively seal off the tibial metaphysis from particulate debris and can prevent particulate egress and subsequent tibial lysis in cementless TKA tibial designs.

The most commonly reported complication in early cementless TKA designs was failure of cementless metal-backed patellar components.²⁰,²⁴,⁴¹,⁴² Failure mechanisms included dissociation of the metal-polyethylene interface,⁴¹ dissociation of the peg-baseplate junction due to lack of osseointegration of the baseplate,²⁴ and excessive polyethylene wear with subsequent metal-metal articulation,⁴² proliferative synovitis, and pain. These complications were linked to both component design as well as errant surgical technique such as excessive femoral component internal rotation. Berger et al²⁰ reported a 48% failure rate requiring reoperation for failed Miller-Galante (Zimmer, Warsaw, IN) cementless patellar components with the two failure mechanisms being failure of ingrowth and excessive polyethylene wear and metallosis.

Despite the early design failures and complications reported with cementless TKA, there are a number of designs that have obtained successful long-term results similar to cemented TKA with 10-year survival rates greater than 95% (Table 38-1). Hofmann et al reported on the cruciate-retaining (CR) cementless Natural Knee system (Zimmer, Warsaw, IN) that utilized a tibial tray with a stem and screw augmentation and a countersunk metal-backed patella, reported 99.1%, 99.6%, and 95.1% 14-year survivorship for the femoral, tibial, and patellar components, respectively.³³ As with most cementless systems, the majority of failures were attributed patellar edge wear, and the authors attributed the excellent long-term results to the asymmetric tibial component, coating the bone surfaces with autograft bone slurry and a countersunk patella component.³³

Whiteside reported the 10-year results of 163 CR Ortholoc I (Wright Medical Technology, Arlington, VA) cementless tibial and femoral components.³⁵ The tibial component had a fully porous-coated undersurface with a smooth central stem and smooth pegs, while the femoral component had porous coating on the distal surface; the anterior and posterior chamfers with a less rough and relatively smooth anterior and posterior condylar flanges to avoid transmitting axial forces to those bone regions. Considering loosening and infection as failure criteria, Whiteside reported a 97% at 10-year follow-up. However, 91 of the original 256 knees were lost to follow-up or had died prior to follow-up in this series.³⁵ Buechel et al reported the 20-year results of the Low Contact Stress (LCS, Depuy, Warsaw, IN) cementless CR meniscal bearing and rotating platform designs with a rotating-bearing cementless metal-backed patellar component.⁴³ Using revision for any mechanical reason, including bearing wear, survivorship of the cementless CR meniscal-bearing knee was 97% at 10-year and 83% at 16-year follow-up. Survivorship of the cementless rotating platform knee group was 98% at both 10- and 16-year follow-up. The tibial component was fully porous-coated and stabilized with a stem without screw augmentation. In the total 309 cementless tibial and femoral components, there was only one reported tibial component loosening and no femoral component loosening.⁴³ A report of 76 CR cementless Osteonics series 3000 (Osteonics, Allendale, NJ) total knee replacements documented a 100% survival rate at 10 years and 97% at 13 years.³⁴ The femoral and tibial components were both made of cobalt-chrome with cobalt-chrome beads on the undersurface, and the tibial components were stemmed and secured with supplemental screw fixation.³⁴