Cemented versus cementless fixation in total knee arthroplasty

Abstract

The question of whether to use cemented or cement-less fixation for a total knee arthroplasty (TKA) is still debated. Discouraging preliminary results of cement-less TKAs have determined the worldwide use of cemented implants. However, with the development of biotechnologies and new biomaterials with high osteoconductive properties, biological fixation is now becoming an attractive option for improving the longevity of TKAs, especially in young patients.

There is no evidence in the current literature to support the use of one method of fixation. The extensive clinical experience with cemented implants gathered over the years justifies their widespread use. New randomized clinical trials are necessary to compare cementless fixation based on the new ingrowth surfaces with standard cemented implants.

Introduction

The ideal fixation of a total knee arthroplasty (TKA) is still debated. The main question is whether the use of cement is more efficient than press-fit fixation in terms of ensuring durable stability. The use of cement in TKAs has been associated with excellent clinical outcomes and low rates of aseptic loosening at long-term follow-up, and it is the most widespread method of fixation in knee replacement. However, alterations of the bone/cement interface leading to osteolysis prompted orthopaedic surgeons to look for a new method of fixation that would avoid this complication, particularly in younger patients (1–3).

The basis for the use, since the mid-80s (both in Italy and in Europe), of cementless TKAs in young patients with adequate bone stock is the concept that osteo-conductive component surfaces, in the presence of a very active bone metabolism, show high biological properties. Many authors proposed a “hybrid” fixation technique, consisting of a cementless femoral component and a tibial component fixed with a cemented baseplate and a press fit keel (4,5). However, the demonstration, in short- and medium-term studies, of an high rate of early loosening related to micromotion led to a return to standard cemented TKAs (6,7) (Tab. 1). This problem was related to the first cementless designs and the geometry of the early components, characterized by poor osteoconductive surfaces or inadequate fixation devices (pins, screws). Modern implants incorporate effective solutions (porous coatings, plasma spray, rotating platforms) able to reduce stress conditions and micromotion at the bone/metal interfaces.

Table 1.

Trend analysis of the types of TKA fixation used during the decade 2001–2010. The data shows a progressive reduction in the number of cementless and hybrid fixed implants with respect to cemented TKAs (Data from RIPO Emilia-Romagna 2000–2010).

Year	% Cemented Implants	% Cementless Implants	% Cemented Tibial Components Only	% Cemented Femoral Components Only
2001	82.2	8.1	9.0	0.7
2002	78.8	9.0	11.8	0.4
2003	82.6	7.6	9.5	0.4
2004	88.0	7.4	4.0	0.6
2005	89.9	6.2	3.3	0.6
2006	90.7	5.3	3.6	0.4
2007	91.1	4.5	3.0	1.3
2008	91.2	4.2	2.2	2.4
2009	91.5	4.5	1.5	2.5
2010	93.5	4.5	0.9	1.1

Cemented versus cementless TKAs

At long-term follow-up, survival rates of up to 99% for cemented TKAs and 97% for cementless implants have been reported (4,8–10). However, the literature lacks studies that compare the two methods of fixation.

A meta-analysis of 15 studies showed a higher risk of aseptic loosening for cementless TKAs. However these studies were very heterogeneous in terms of patient characteristics and knee systems implanted. Furthermore, patients were not stratified by age and level of activity. Randomized clinical trials have not demonstrated a clear superiority of cemented TKAs over cementless implants, in terms of survival rates and clinical outcomes (10).

Khaw et al. (11), in a randomized controlled study, found comparable survival rates (95.3% for cemented TKAs versus 95.6% for cementless TKAs) in a cohort of 501 implants (227 cemented and 224 cementless) of the same design (PFC; DePuy, Warsaw, IN). Park at al. (12) analyzed clinical and radiographic results in a randomized controlled study of 50 patients undergoing a simultaneous bilateral knee replacement with implants of the same design (Nexgen; Zimmer, Warsaw, IN), which were cemented on one side and cementless on the contralateral side. The survival rate of the femoral components was found to be 100% for both implants, while the tibial plates showed a survival rate of 100% for the cemented TKAs, and 98% for the cementless TKAs. However, no significant differences were found in the clinical results (12). Other clinical studies have been performed to assess the best method of fixation, but to date no evidence exists to support the use of one over the other. Most of the case series reported in the literature present limitations, investigating heterogeneous patient samples, different implants, and first-generation porous surfaces that are not comparable in terms of bone ingrowth to the modern coatings.

Cementless implants and biological fixation

One of the main indications for using a cementless TKA is good bone quality with high metabolic activity, in order to promote biological fixation. Indeed, a younger age (under 65 years old) and an adequate bone stock are the most typical indications.

To ensure good primary stability of the implant, the bone resections must be performed accurately, avoiding any gaps between the host bone and the components. In cemented TKAs, small defects in resections can be easily filled by the cement mantle without affecting the stability (Tab. 2).

Table 2.

Cementless implants: critical factors.

Good bone quality

Ensure high primary stability

Accurate bone resections

Early migration of tibial component

High cost

Integration of femur > tibia > patella

Radiostereometry analyses (RSA) have made it possible to understand the different migration patterns shown by the TKA components with the two different fixation methods. Cementless tibial baseplates may migrate early, i.e. in the first three months postoperatively, usually reaching stability after this interval; cemented tibial components, on the other hand, do not migrate in the immediate postoperative period, while they may show micromotion over 60 months (13). No differences have been demonstrated in the migration pattern of cemented with respect to cement-less femoral components (14).

Cementless implants are up to three times more expensive than cemented ones due to the high technology required to produce bioactive surfaces: supporters of cemented TKAs maintain that it is not reasonable to use an expensive cementless system that gives the same overall clinical results as a cheaper implant, even in younger patients.

However, using cementless TKAs is undoubtedly time-saving, it reduces the pneumatic ischemia time (there is no need for complete exposure of the trabecular bone ready to receive the cement), and finally it allows an easier bone-sparing revision in the event of failure.

Over the decades, in vitro studies have demonstrated that the use of rotating platforms in cementless TKAs is associated with a better tribologic performance and survival of the implant, related to the reduction of stresses at the bone/metal interface. Several studies in the clinical setting have also shown long-term survivorship of press fit TKAs with rotating platforms, ranging from 83% to as high as 99.4% (15–17).

Hybrid fixation, which combines a cemented component (generally the tibial plate) with a cementless one (usually the femoral component), has been proposed on the strength of the high osteoconductive properties of the modern component coatings. In a randomized controlled study, Gao et al. (14), using RSA, found similar results in terms of migration, clinical outcomes, and survival rates of 41 TKAs in young patients (<60 years) undergoing knee replacement (NexGen, Zimmer, Warsaw, USA): 22 with fully cemented implants and 19 with hybrid fixated implants. Yang et al. (18), following up 235 TKAs, performed with a hybrid fixation technique and using five different knee systems, reported a survival rate of 95% at ten years, and then of 92% at fifteen years. Cementation of the patellar component is crucial: it is now clear that cementless patellas are associated with a high risk of failure due to early loosening of the component.

Cemented implants

The extensive clinical experience with this method of fixation and the long-term studies reported in literature justify its worldwide use. Cementation allows an easier surgical technique, ensures greater primary stability as demonstrated by RSA studies, may be useful for the delivery of local antibiotics (given the diffusion of antibiotic-loaded cements), and, finally, may produce a barrier able to prevent the diffusion of wear particles over the periprosthetic bone tissue, known to be the most frequent cause of aseptic failure of knee implants. However, cemented fixation is not without drawbacks (Tab. 3).

Table 3.

Cemented implants: critical factors.

Third-body wear

Extra-articular impingement

Long surgical time

Complex revision

Bone thermal necrosis

Additional contact surfaces

Radiolucency at the bone-cement interface

Fat embolism

The use of cement usually involves specific steps, which have to be carefully performed: preparation, application on the bone or component surfaces, removal of residual cement, extensive washing. All these operations take time, and thus prolong the overall surgical time.

Several studies have addressed the risks of extra-articular impingement of the cement mantle on the tibial insert, and third body wear induction by the release of particles in the articular space. Noble et al. (19), in their observational study of 162 revision TKAs, showed significant abrasive wear in 35% of retrieved cemented components (versus 25% of retrieved cementless ones). However, the risk of residual particles after cementation may be prevented by thorough washing and cement removal before closing.

Moreover, thermal necrosis, which may be induced during the polymerization of the cement, carries a specific risk of tissue damage. The use of a cement mantle (generally 2 mm thick) introduces an additional surface (cement/bone plus cement/component) in the implant, increasing the risk of mobilization or of wear production (20). There is still a debate on which of the two interfaces is the source of failure: the cement/bone interface is generally suggested to be the critical zone. An important study of the complications of total hip arthroplasty demonstrated a high risk of fat embolism during the pressurization of the cement in the femoral canal (21). Even though there is no study of this kind in TKAs, it is reasonable to think that knee replacement may carry a similar risk. Clarke et al. (22) showed a significantly increased risk of deep venous thromboembolism in cemented TKAs with respect to cementless implants.

Finally, revisions of failed cemented TKAs are technically more demanding with respect to cementless implants, particularly on account of the frequent bone loss after removal of the components.

Future directions

There is still no evidence to support the use of cemented TKAs with respect to press fit implants. Longer follow-up studies are necessary to ascertain any clinical improvement of modern bioactive surfaces over traditional cemented TKAs. The study of the interactions between bone tissue and drugs active on bone metabolism is a brand-new field of interest. Even though, to date, only preliminary in vitro studies have been conducted, the results are encouraging, showing a favorable effect, in terms of bone stimulation and osseointegration of knee components, of drugs generally used in bone metabolism alterations (23).