New perspective in cementless total knee arthroplasty

Introduction

Total knee replacement is one of the most frequently performed procedures in orthopedic surgery. Arthritis is a common disease that is estimated to affect approximately 78.4 million adults until 2040. It is expected an increasing demand for total knee arthroplasty (TKA) due to the high number of arthritis patients among baby boomers by 2030 [1] Berger RA, Lyon JH, Jacobs JJ, Barden RM, Berkson EM, Sheinkop MB, Rosenberg AG, Galante JO. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop Relat Res. 2001 Nov;(392):196-207. doi: 10.1097/00003086-200111000-00024. PMID: 11716383.. TKA has been implanted with cemented and cementless fixation for many years. Cemented fixation has been considered the gold standard with high survival rate at long follow-up [2] Wojtowicz R, Otten V, Henricson A, Crnalic S, Nilsson KG. Uncemented trabecular metal high-flex posterior-stabilized monoblock total knee arthroplasty in patients aged 60 years or younger. Knee. 2024 Jan;46:99-107. doi: 10.1016/j.knee.2023.11.006. Epub 2023 Dec 8. PMID: 38070382.. Nevertheless, cemented fixation has still some bias considering the presence of a “weak” link represented by the polymethylmethacrylate interface. Uncemented knee replacements have been developed with the rational of offering a more durable biologic fixation without the potential of third-body wear from cement particles. Initially this was enthusiastically received but through the various decades cemented TKA remained the gold standard [3] Wilczyński M, Bieniek M, Krakowski P, Karpiński R. Cemented vs. Cementless Fixation in Primary Knee Replacement: A Narrative Review. Materials (Basel). 2024 Feb 29;17(5):1136. doi: 10.3390/ma17051136. PMID: 38473607; PMCID: PMC10933953..

Although several studies report similar outcomes between cementless and cemented TKA, a major concern remains aseptic loosening of the cementless tibial component [4] Berger RA, Lyon JH, Jacobs JJ, Barden RM, Berkson EM, Sheinkop MB, Rosenberg AG, Galante JO. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop Relat Res. 2001 Nov;(392):196-207. doi: 10.1097/00003086-200111000-00024. PMID: 11716383., which is particularly relevant in certain cohorts, especially women over 75 years of age with poor bone quality [5] Mosher ZA, Bolognesi MP, Malkani AL, Meneghini RM, Oni JK, Fricka KB. Cementless Total Knee Arthroplasty: A Resurgence-Who, When, Where, and How? J Arthroplasty. 2024 Mar 7:S0883-5403(24)00198-0. doi: 10.1016/j.arth.2024.02.078. Epub ahead of print. PMID: 38458333..

Another debated point was the pure implant cost which is generally higher for cementless TKA and has limited its use [6] Gandhi R, Tsvetkov D, Davey JR, Mahomed NN. Survival and clinical function of cemented and uncemented prostheses in total knee replacement: a meta-analysis. J Bone Joint Surg Br. 2009 Jul;91(7):889-95. doi: 10.1302/0301-620X.91B7.21702. PMID: 19567852.. Recently, it has been observed that the reduction of the overall procedural cost of implanting a cementless TKA has made net costs even more favourable than a cemented one [7] Lawrie CM, Schwabe M, Pierce A, Nunley RM, Barrack RL. The cost of implanting a cemented versus cementless total knee arthroplasty. Bone Joint J. 2019 Jul;101-B(7_Supple_C):61-63. doi: 10.1302/0301-620X.101B7.BJJ-2018-1470.R1. PMID: 31256655..

Cementless TKA procedure is associated with a surgical time reduction [8] Olivecrona C, Lapidus LJ, Benson L, Blomfeldt R. Tourniquet time affects postoperative complications after knee arthroplasty. Int Orthop. 2013 May;37(5):827-32. doi: 10.1007/s00264-013-1826-4. Epub 2013 Feb 16. PMID: 23417522; PMCID: PMC3631475., avoid cement-related thermal complications [9] Whitehouse MR, Atwal NS, Pabbruwe M, Blom AW, Bannister GC. Osteonecrosis with the use of polymethylmethacrylate cement for hip replacement: thermal-induced damage evidenced in vivo by decreased osteocyte viability. Eur Cell Mater. 2014 Jan 25;27:50-62; discussion 62-3. doi: 10.22203/ecm.v027a05. PMID: 24464728., and allows greater bone preservation with potentially more bone stock available at revision if well-ingrowth implant extraction is not detrimental [10] Dalury DF. Cementless total knee arthroplasty: current concepts review. Bone Joint J. 2016 Jul;98-B(7):867-73. doi:10.1302/0301-620X.98B7.37367. PMID: 27365463..

Over the last few years, there has been a renowned interest in cementless TKA [11] Rodriguez S, Ranawat AS. The Future is Non-cemented Total Knee Arthroplasty: Volume Trends at the Hospital for Special Surgery. Indian J Orthop. 2021 Oct 2;55(5):1096-1100. doi: 10.1007/s43465-021-00508-0. PMID: 34629497; PMCID: PMC8487231.. Advantages at long-term for younger, more active and overweight patients has been demonstrated in the meanwhile [12], Abdel MP, Bonadurer GF 3rd, Jennings MT, Hanssen AD. Increased Aseptic Tibial Failures in Patients With a BMI ≥35 and Well-Aligned Total Knee Arthroplasties. J Arthroplasty. 2015 Dec;30(12):2181-4. doi: 10.1016/j.arth.2015.06.057. Epub 2015 Jul 2. PMID: 26220103.[13] W-Dahl A, Robertsson O, Lidgren L. Surgery for knee osteoarthritis in younger patients. Acta Orthop. 2010 Apr;81(2):161-4. doi: 10.3109/17453670903413186. PMID: 19968599; PMCID: PMC2852150.. Excellent implant survival of cementless TKAs has been observed with the recent designs and materials, although still with short follow-ups [14], Helvie PF, Deckard ER, Meneghini RM. Cementless Total Knee Arthroplasty Over the Past Decade: Excellent Survivorship in Contemporary Designs. J Arthroplasty. 2023 Jun;38(6S):S145-S150. doi: 10.1016/j.arth.2023.02.009. Epub 2023 Feb 14. PMID: 36791890.[15] Liu Y, Zeng Y, Wu Y, Li M, Xie H, Shen B. A comprehensive comparison between cementless and cemented fixation in the total knee arthroplasty: an updated systematic review and meta-analysis. J Orthop Surg Res. 2021 Mar 5;16(1):176. doi: 10.1186/s13018-021-02299-4. PMID: 33673850; PMCID: PMC7934367..

The development of new materials and different designs, especially for the tibial component, opens new perspectives for the use of cementless TKA as the potential new gold standard in a specific population [16] Polizzotti G, Lamberti A, Mancino F, Baldini A. New Horizons of Cementless Total Knee Arthroplasty. J Clin Med. 2023 Dec 30;13(1):233. doi: 10.3390/jcm13010233. PMID: 38202240; PMCID: PMC10780266..

Design of prostheses and coating materials

First generations of cementless TKAs showed several issues, mainly in the tibial side (Table 1 and 2). Common problems included short or inadequate primary fixation, patchy fixation surfaces with limited secondary fixation, disassembling of sintered coatings [4] Berger RA, Lyon JH, Jacobs JJ, Barden RM, Berkson EM, Sheinkop MB, Rosenberg AG, Galante JO. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop Relat Res. 2001 Nov;(392):196-207. doi: 10.1097/00003086-200111000-00024. PMID: 11716383.. Implant manufacturers have improved materials and designs of their cementless TKA portfolio through the years. It is the purpose of this paper to review the most modern and most representative cementless TKA options of the various companies in the market.

1. Materials

Hydroxyapatite (HA), a biocompatible osteoconductive ceramic composed of calcium phosphate (CaPO4), promotes de novo bone formation through its surface chemistry and topography. This property is advantageous in cementless TKAs, where HA coating applied to the metallic implant substrate enhances osseointegration by facilitating early bone apposition and subsequent conversion of the initial periprosthetic fibrous tissue into bone [17] Søballe K, Hansen ES, Brockstedt-Rasmussen H, Pedersen CM, Bünger C. Hydroxyapatite coating enhances fixation of porous coated implants. A comparison in dogs between press fit and noninterference fit. Acta Orthop Scand. 1990 Aug;61(4):299-306. doi: 10.3109/17453679008993521. PMID: 2402977.. This type of solution, also in combination with other materials, has been adopted by numerous companies, including ©Medacta International, ©Stryker (for femur only) and Adler Ortho®.

Trabecular Metal™ (Zimmer Inc., Warsaw, IN, USA), is a biomaterial made from tantalum with excellent mechanical and biological properties. This type of porous material was introduced in orthopedic surgery in 1997. It has several advantages: it’s flexible, strong enough for implants without needing a metal base and it has high coefficient of friction against bone (m ¼ 0.88), high volume (average 80%) and better-connected pores (550 μm) and low stiffness. Previous cell studies confirmed that osteoblast cells respond well to tantalum, supporting its long history as a safe biocompatible material [18], Bobyn JD, Pilliar RM, Cameron HU, Weatherly GC. The optimum pore size for the fixation of porous-surfaced metal implants by the ingrowth of bone. Clin Orthop Relat Res. 1980 Jul-Aug;(150):263-70. PMID: 7428231.[19], Bobyn JD, Poggie RA, Krygier JJ, Lewallen DG, Hanssen AD, Lewis RJ, Unger AS, O’Keefe TJ, Christie MJ, Nasser S, Wood JE, Stulberg SD, Tanzer M. Clinical validation of a structural porous tantalum biomaterial for adult reconstruction. J Bone Joint Surg Am. 2004;86-A Suppl 2:123-9. doi: 10.2106/00004623-200412002-00017. PMID: 15691117.[20] Cohen R. A porous tantalum trabecular metal: basic science. Am J Orthop (Belle Mead NJ). 2002 Apr;31(4):216-7. PMID: 12008853..

Among materials with characteristics suitable for the development of cementless prostheses, titanium is one of the most widely used and popular. Titanium is a very porous material and different studies show it promotes bone growth, proving osteoinduction and osteoconduction properties, and blood vessel formation [21], Asti A, Gastaldi G, Dorati R, Saino E, Conti B, Visai L, Benazzo F. Stem Cells Grown in Osteogenic Medium on PLGA, PLGA/HA, and Titanium Scaffolds for Surgical Applications. Bioinorg Chem Appl. 2010;2010:831031. doi: 10.1155/2010/831031. Epub 2010 Dec 23. PMID: 21234383; PMCID: PMC3017899.[22] Gastaldi G, Asti A, Scaffino MF, Visai L, Saino E, Cometa AM, Benazzo F. Human adipose-derived stem cells (hASCs) proliferate and differentiate in osteoblast-like cells on trabecular titanium scaffolds. J Biomed Mater Res A. 2010 Sep 1;94(3):790-9. doi: 10.1002/jbm.a.32721. PMID: 20336739.. One of the features to consider is the pore size, which must be approximately in the range between 100 and 600 microns. In fact, smaller pores lead to fibrous tissue growth instead of bone, while larger pores lead to slower and incomplete bone filling [18], Bobyn JD, Pilliar RM, Cameron HU, Weatherly GC. The optimum pore size for the fixation of porous-surfaced metal implants by the ingrowth of bone. Clin Orthop Relat Res. 1980 Jul-Aug;(150):263-70. PMID: 7428231.[23] Frosch KH, Barvencik F, Viereck V, Lohmann CH, Dresing K, Breme J, Brunner E, Stürmer KM. Growth behavior, matrix production, and gene expression of human osteoblasts in defined cylindrical titanium channels. J Biomed Mater Res A. 2004 Feb 1;68(2):325-34. doi: 10.1002/jbm.a.20010. PMID: 14704974.. Porosity should also be between 50-70%, to achieve a good balance between maximizing bone ingrowth and maintaining adequate mechanical strength of the implant. Several companies have developed proprietary materials with varying characteristics, starting from titanium. Products made from titanium have already been on the market for several years, such as Porocoat™ (DePuy Synthes). More recently, several companies are marketing products developed with different technique to give specific geometries and properties: 3D printing technology, such as Trabecular Titanium™ (LimaCorporate), Affixium™ 3DP Technology (DePuy Synthes), OsseoTi® Porous Metal (Zimmer Inc.), TiPor® and CoPor® (3D-Por® surface manufactured also in CoCrMo alloy) (Adler Ortho®), Tritanium® (©Stryker), Conceloc◊ (Smith&Nephew, Inc.), Truliant® Porous (Exactech, Inc.) ; Selective Laser Melting (SLM) technique, as Traser® (Permedica); titanium foam, as BioFoam (Microport Orthopedics, Inc), or spray, as Plasmapore® (Aesculap® B. Braun) and Mectagrip (©Medacta International).

2. Tibial component fixation type

As with the materials, different options have been developed for tibial component design, to obtain initial implant stability necessary to achieve adequate biological fixation in cementless TKA [24] Bhimji S, Meneghini RM. Micromotion of cementless tibial baseplates: keels with adjuvant pegs offer more stability than pegs alone. J Arthroplasty. 2014 Jul;29(7):1503-6. doi: 10.1016/j.arth.2014.02.016. Epub 2014 Feb 21. PMID: 24709524..

In the past, early tibial designs only had relatively small pegs, which did not guarantee adequate initial fixation. Screws and a central stem were added to try to improve stability and reduce micro-movement [25] Schwabe MT, Hannon CP. The Evolution, Current Indications and Outcomes of Cementless Total Knee Arthroplasty. J Clin Med. 2022 Nov 8;11(22):6608. doi: 10.3390/jcm11226608. PMID: 36431091; PMCID: PMC9693456..

At the beginning of the 21st century, one of the most widely used prostheses was NexGen Trabecular Metal™ Monoblock Tibial Component (Zimmer), characterized by monoblock baseplate made of porous tantalum featuring two 16-mm-long hexagonal pegs. Several options have developed from this type of tibial component, such as Persona® TM, from the same company, which also features a tibial component with two hexagonal pins, but without being a monoblock component [26] De Martino I, D’Apolito R, Sculco PK, Poultsides LA, Gasparini G. Total Knee Arthroplasty Using Cementless Porous Tantalum Monoblock Tibial Component: A Minimum 10-Year Follow-Up. J Arthroplasty. 2016 Oct;31(10):2193-8. doi: 10.1016/j.arth.2016.03.057. Epub 2016 Apr 12. PMID: 27172865.. LimaCorporate decided to start from this kind of design without a keel, unlike other tibial component choices on the market, to allow for bone preservation and easy removal procedure, if necessary. Physica TT Tibial Plate was developed with two central hexagonal pegs and an anterior spike with the aim of reducing micromotions [27] Quevedo Gonzalez FJ, Lipman JD, Sculco PK, Sculco TP, De Martino I, Wright TM. An Anterior Spike Decreases Bone-Implant Micromotion in Cementless Tibial Baseplates for Total Knee Arthroplasty: A Biomechanical Study. J Arthroplasty. 2023 Nov 22:S0883-5403(23)01163-4. doi: 10.1016/j.arth.2023.11.020. Epub ahead of print. PMID: 38000515..

An hystorical common option is the use of a single central keel, with different shapes depending on the company: GMK Primary (©Medacta International), ACS (Implantcast®), Genus (Adler Ortho®) and Columbus (Aesculap®BBraun). The most common design option employed by several companies is characterized by a central keel with four pegs or spikes. Several studies[24], Bhimji S, Meneghini RM. Micromotion of cementless tibial baseplates: keels with adjuvant pegs offer more stability than pegs alone. J Arthroplasty. 2014 Jul;29(7):1503-6. doi: 10.1016/j.arth.2014.02.016. Epub 2014 Feb 21. PMID: 24709524.[28], Carlson BJ, Gerry AS, Hassebrock JD, Christopher ZK, Spangehl MJ, Bingham JS. Clinical outcomes and survivorship of cementless triathlon total knee arthroplasties: a systematic review. Arthroplasty. 2022 Jun 3;4(1):25. doi: 10.1186/s42836-022-00124-9. PMID: 35655250; PMCID: PMC9164316[29] Ali MS, Mangaleshkar SR. Uncemented rotating-platform total knee arthroplasty: a 4-year to 12-year follow-up. J Arthroplasty. 2006 Jan;21(1):80-4. doi: 10.1016/j.arth.2005.04.018. PMID: 16446189. have shown better initial and long-term stability with this solution. Numerous companies have introduced this type of design, with different component shapes: Persona® OsseoTi® (Zimmer), GKS PRIME Flex TRASER (Permedica), Attune cementless knee system (DePuy Synthes) and its evolution Attune cementless Affixium™ 3DP Technology, Triathlon® Tritanium® (Stryker), Legion Conceloc◊ (Smith&Nephew, Inc.), Evolution® (Microport Orthopedics Inc.), Truliant® Porous Knee (Exactech, Inc.).

3. Femural coating

Metallic materials, inside the body, can be subject to corrosion and thus to the release of ions, which, in some cases may lead to hypersensitisation reactions. Various types of implant coatings are employed by manufacturers both to reduce sensitization issues and to smoothen rough surfaces such as titanium on the femoral component of cementless TKAs. Coatings are mave through various techniques, being physical vapor deposition (PVD) the most common one. One of the most effective surface treatments with excellent long-term survival results is OXINIUM® Oxidized Zirconium (Smith&Nephew). Titanium Nitride or Titanium Niobium Nitride has demonstrated excellent results as well to minimise ions release and reduce wear [30], Ragone V, Canciani E, Biffi CA, D’Ambrosi R, Sanvito R, Dellavia C, Galliera E. CoCrMo alloys ions release behavior by TiNbN coating: an in vitro study. Biomed Microdevices. 2019 Jul 4;21(3):61. doi: 10.1007/s10544-019-0417-6. PMID: 31273538.[31] Thienpont E. Titanium niobium nitride knee implants are not inferior to chrome cobalt components for primary total knee arthroplasty. Arch Orthop Trauma Surg. 2015 Dec;135(12):1749-54. doi: 10.1007/s00402-015-2320-9. Epub 2015 Aug 29. PMID: 26318754.: Bioloy® (Permedica), TiN (Implantcast®), SensiTiN (©Medacta International), TiNbN (Adler Ortho®), NitrX™ (Microport Orthopedics Inc). Another solution was developed by Aesculap® B. Braun with Advanced Surface (AS), a multilayer coating consisting of seven layers of which the most external includes a ceramization process.

Surgical technique and tricks & tips

Bone manipulation with motorized instruments may raise temperatures (45°C, 47°C and the most severe at 60°C) to a level which induces bone necrosis and cellular depletion. Reducing the heating to a minimum promotes a greater osteointegrative capacity of uncemented components. Furthermore, it has been shown that a mild heat shock (below 47°C) for the duration that occurs during surgical cutting can even promote the proliferation of osteoprogenitor cells [32] Dolan EB, Haugh MG, Tallon D, Casey C, McNamara LM. Heat-shock-induced cellular responses to temperature elevations occurring during orthopaedic cutting. J R Soc Interface. 2012 Dec 7;9(77):3503-13. doi: 10.1098/rsif.2012.0520. Epub 2012 Aug 22. PMID: 22915633; PMCID: PMC3481591.. There are several strategies to reduce the risk of thermal necrosis:

1. With preoperative cryocompression (1 hour at 5 degrees Celsius) it is possible to reduce the bone temperature at 20-23° on average (WAC 2024, Baldini et al) (Figure 1).
2. Using a 1.27 mm saw-blade, and irrigating with 0.9% NaCl physiological solution (Figure 2) cooled
3. Reduction of cutting time to a minimum and using thinner blade may further reduce the risk of heating [33] Firoozbakhsh K, Moneim MS, Mikola E, Haltom S. Heat generation during ulnar osteotomy with microsagittal saw blades. Iowa Orthop J. 2003;23:46-50. PMID: 14575249; PMCID: PMC1888392..

After resection, the plane of the tibia should be symmetrical and flat. Any recutting may introduce additional imperfections. Any asymmetry can reduce the support of the component and some areas will not be able to osteointegration [34] Delgadillo LE, Jones HL, Ismaily SK, Han S, Noble PC. How Flat Is the Tibial Osteotomy in Total Knee Arthroplasty? J Arthroplasty. 2020 Mar;35(3):870-876. doi: 10.1016/j.arth.2019.10.007. Epub 2019 Oct 9. PMID: 31694778.. Generally, the greatest difficulty encountered is ensuring the flatness of the resection of the posterolateral portion of the tibia.

During the preparation of the femur, the “chamfer first” technique (Figure 3) reduces the possibility of imperfections on the surface of the cuts, in fact the anterior and posterior cuts being parallel are less at risk of deviating the resection plane.

The posterolateral portion of the tibial plateau may be difficult to be exposed for vertical insertion on the tibial component. This space should always be cleared in order to avoid asymmetric engagement of the tibial pegs in the prepared holes (Figure 4).

Optimal adaptation of the base plate in the tibial sizing, close to the cortical layer provides additional useful surface for primary fixation (Figure 5).

Final preparation of tibial pegs may include reverse reaming if there are soft medullary bone parts in the four tibial quadrants (Figure 6). Cleaning every bone particle present on the bone platform and in the holes after preparation ensures a perfect engagement of the tibial plate. During femoral implantation, care must be taken in raising the implanting arm while pushing the femoral component to avoid malseating of the various surfaces. The goal is to achieve no gapping around the femoral component, although a gap of less than 2 mm can be accepted in certain zone (bone bridging during secondary ingrowth is commonly described) (Figure 7). After implantation, stability of the components during the full range of motion should be assessed both with the extensor mechanism dislocated and reduced (Figure 8).

Conclusion

Innovations in materials and designs of cementless knee implants have helped to increase their current popularity. Improvement of primary femur and tibia stability, rapid osteointegration, and promising mid-term results, lead to a progressively increased indications in several cohorts of patients.