Encyclopedia
Please note this is a comparison between Version 1 by Giuseppe Polizzotti and Version 2 by Lindsay Dong.
Considering the increasing number of young and active patients needing Total Knee Arthroplasty (TKA)A, orthopedic surgeons are looking for a long-lasting and physiological bond for the prosthetic implant. Multiple advantages have been associated with cementless fixation including higher preservation of the native bone stock, avoidance of cement debris with subsequent potential third-body wear, and the achievement of a natural bond and osseointegration between the implant and the bone that will provide a durable and stable fixation.
- cementless
- total knee arthroplasty
- survivorship
- biomaterials
1. Introduction
Total Knee Arthroplasty (TKA) has been widely recognized as the gold standard treatment for end-stage knee osteoarthritis [1]. This procedure is performed in more than 600,000 patients per year in the United States (US) and the number is projected to remarkably grow by 2030 [2].
The current literature is debatable regarding the efficacy and results of cementless TKA when compared to conventional cemented TKA. It has been often stated that press-fit fixation performs similarly or worse than cemented fixation depending on the selection criteria of patients [3][4][3,4]. Moreover, despite several cohort studies detecting comparable outcomes between the two types of fixations, higher costs have limited the widespread diffusion of cementless implants, leaving the conventional technique as the widely recognized gold standard [5][6][5,6].
One of the greatest concerns regarding cementless fixation was the increased risk of tibial component early aseptic loosening [7][8][9][10][7,8,9,10]. However, the development of new implant designs and materials has turned cementless fixation into an interesting and reliable option, especially in younger patients with good bone quality [11]. In addition, radiostereometric analysis (RSA) showed promising results that will be thoroughly analyzed in the following sections [12][13][12,13].
Despite the excellent reported outcomes of conventional cemented fixation, young and active patients have been frequently associated with a higher risk for implant revision, refs. [14][15][16][14,15,16] leading to a growing interest in a more durable fixation method.
2. Cementless Total Knee Arthroplasty
2.1. Surgical Technique Tips
Scholars start with tibia resection, using a 1.27 mm saw blade and scholars irrigate it with saline water at room temperature, while also trying not to spend so much time on the resection in order to not warm up the bone. Reducing the time for cutting, blade thickness, irrigation with saline water, and bone pre-cooling are very good tips to not overheat the bone. Minimizing heat shock is important because thermal necrosis at 60° can cause an immediate cellular depletion and a slow cell recovery [17]. After the resection, the tibia plane should be symmetric and flat. Distal femur resection is performed with the same irrigation and sawing technique. Once again, the flatness of the surface is primary to avoid no contact areas with the implant. After appropriate femoral sizing, different from the original technique, scholars start from chamfer resections and AP are made later on.
AP resections are parallel cuts and they are less sensitive to small micro-movements of the jig. After that, scholars complete the posterior condylar resection, changing the saw with a thinner one for the posterolateral bone resection in order to save the popliteus ligament.
The next step is the research of the optimal fit of the baseplate in tibial sizing, close to the cortical ream. After tibial sizing, scholars complete the tibia by reverse drilling where the bone is softer and normal drilling where the bone is harder. At the end, the impaction of the tibia baseplate should be symmetric: medial and lateral, anterior, and posterior. During the femur implantation, the surgeon must raise the hand while pushing the femoral component. The aim is to achieve no space area around the corner of the femoral component prosthesis, even if less than 2 mm of gap is accepted. Knee stability is tested throughout a complete ROM. At last, scholars use the intraoperative “pull-out lift-off” (POLO) test to check the appropriate tension of PCL.
2.2. Short Term Follow Up of a Novel 3D Printed Cementless TKA
One hundred and twenty-seven patients who underwent TKA during the period 2021 to 2022 at a institution were included in a prospective study. Seventy-seven patients received a cemented TKA and 60 patients received a 3D-printed cementless TKA (Figure 1). All the patients were evaluated at 3, 6, and 12 months by recording the VAS score, the Oxford Knee Score, the Knee Society Score, and the Forgotten Knee Score. No significant differences between the two groups were reported. The mean time to reach a VAS score < 3 was 6 months in 70% of the patients. The mean FJS was 67 at 3 months, 76 at 6 months, and 79 at 12 months post-operatively.
Figure 1.
Traser
® 3-D printed Permedica (GKS Prime Flex Traser).
2.3. Mechanical Characteristics of Cementless TKA
Considering the increasing number of young and active patients needing TKA [18], orthopedic surgeons are looking for a long-lasting and physiological bond for the prosthetic implant.
Multiple advantages have been associated with cementless fixation including higher preservation of the native bone stock, avoidance of cement debris with subsequent potential third-body wear, and the achievement of a natural bond and osseointegration between the implant and the bone that will provide a durable and stable fixation. This fixation is based on the migration of osteoblasts and mesenchymal cells towards the implant and the osseointegration through the roughened surface of the implant [19][20]. It has been reported that the minimum requirement for pore size is considered to be approximately 100 µm due to cell size, migration requirements, and transport. However, pore sizes >300 µm are recommended, due to enhanced new bone formation and the formation of capillaries.
2.4. First Generation of Cementless TKA
3-D printed Permedica (GKS Prime Flex Traser).
2.3. Mechanical Characteristics of Cementless TKA
Considering the increasing number of young and active patients needing TKA [18], orthopedic surgeons are looking for a long-lasting and physiological bond for the prosthetic implant.
Multiple advantages have been associated with cementless fixation including higher preservation of the native bone stock, avoidance of cement debris with subsequent potential third-body wear, and the achievement of a natural bond and osseointegration between the implant and the bone that will provide a durable and stable fixation. This fixation is based on the migration of osteoblasts and mesenchymal cells towards the implant and the osseointegration through the roughened surface of the implant [19,20]. It has been reported that the minimum requirement for pore size is considered to be approximately 100 µm due to cell size, migration requirements, and transport. However, pore sizes >300 µm are recommended, due to enhanced new bone formation and the formation of capillaries.
2.4. First Generation of Cementless TKA
First, the generation of cementless TKA has been associated with numerous design flaws that led to early failure. When evaluating the prosthetic components, the femoral component reached better outcomes than the tibial and patellar counterparts. Femoral component failures were mainly associated with fatigue fractures of the thin areas [21][30]. Moreover, other pitfalls included the use of sintered beads or mesh coating, non-continuous fixation surfaces, short pegs, poor polyethylene locking mechanisms, and sterilization methods, and the use of metal-backed patellar components that showed poor survivorship [9].2.5. New Materials
Innovations in technology and design have helped modern cementless TKA implants improve dramatically. The better coefficient of friction and reduced Young’s modulus mismatch between the implant and host bone have been related to the use of porous metal surfaces. Moreover, biologically active coatings have been used on modern implants such as periapatite and hydroxyapatite. These factors have increased the potential for ingrowth by reducing micromotion and increasing osteoconductive properties. New materials with better biocompatibility, porosity, and roughness have been introduced to increase implant stability. Hydroxyapatite (HA) represented a promising material with the potential to achieve biological fixation of implants. HA coating, in comparison to press fit fixation or porous coating, is an osteoconductive calcium phosphate molecule that can encourage the biological growth of the bone even in the presence of gaps or partially unstable conditions [22][31]. More recently, Trabecular Metal™ (Zimmer Inc., Warsaw, IN, USA) (Figure 2), a newer biomaterial made of tantalum, has been introduced as being similar in porosity to cancellous bone. It has been extensively associated with excellent mechanical and biological properties, including predictable ingrowth and osseointegration, primary stability, and maintenance of bone mineral density (BMD). However, clinical results at the mid-to-long-term follow-up with tibial monoblock components have been controversial [23][24][25][26][36,37,38,39].Figure 2.
Trabecular Metal™ (Zimmer Inc., Persona, cementless).
BIOFOAM (Microport Orthopedics, Inc., Arlington, TN, USA) is a cancellous titanium foam that can be manufactured to reach a porosity of up to 80% to increase mechanical properties. Cancellous titanium is a porous reticulated titanium material developed for load-bearing orthopedic implants with a compressive modulus similar to bone and it shows improved material properties with increased porosity and friction coefficient which enhances early stability and osseointegration [27][46].
A novel modular cementless tibial component (Triathlon® Tritanium®, Stryker Orthopedics, Mahwah, NJ, USA) has been introduced. It is made up of a highly porous titanium coating applied by 3-dimensional printing to create a biological fixation surface with a triangular keel and 4 cruciform 9-mm-long pegs coated solely at the base of each peg. This device has been compared in a cadaveric study with a two-peg TM monoblock baseplate reporting reduced rocking motions and liftoff, supporting higher potentials for biological fixation [28][48].
2.6. Implant Migration and RSA Analysis
Radiostereometric analysis (RSA) represents a valid method to evaluate implant fixation to bone and early migration, especially within the first two postoperative years, providing a prediction to long-term outcomes. Cementless fixation has shown a pattern of high initial migration called “settling”, followed by stabilization after approximately one year, compared with lower initial migration for cemented components [29][50]. However, cemented fixation can be affected by late degenerative processes to the cement mantle such as delamination that can compromise implant fixation [5].
Laende et al. [30][51] compared the long-term migration of 79 patients with cemented (58 TKA) and cementless (21 TKA) tibial components at a mean of 12 years postoperatively. The authors reported a significant correlation between one-year and long-term migration, especially for cementless components. In addition, the long-term migration was comparable but the inducible displacement (single-leg stance weight bearing) at 10 years was significantly higher for the cemented components (0.2 [range, 0.2–0.4] vs. 0.1 [range, 0.1–0.2]; p < 0.001), suggesting at least equivalent, if not superior, long-term fixation of the press-fit technique.
