Titanium

Titanium alloy for orthopedic applications:  

Since its introduction in the early 1950s, the use of titanium and its alloys in orthopaedics has been primarily limited to the alloy Ti-6AI-4V and to unalloyed commercially pure (CP) titanium. Both of these materials were originally developed for military and industrial applications. In human body titanium is inert, meaning that it has only a limited ability to react with surrounding biological tissue. In contact with air, Titanium builds a resistive oxide layer which prevents titanium ions to be released and react with other molecules. Compared to cp titanium, Ti-6AI-4V develops a thicker oxide layer and decreases the risk of corrosion. In addition, Ti-6AI-4V features a higher tensile strength than CP titan [1].

• Commercially Pure Titanium (CP): Cp titanium was first used clinically in 1951 by Doctors Jergensen and Leventhal for fracture fixation bone screws and plates. They observed that the material exhibit good corrosion resistance and tissue tolerance, but marginal strength [2].
  
  Ti-6AI-4V: The alloy Ti-6AI-4V was first employed in the Soviet Union in 1959 in the Sivash total hip. During the early 1970s, Ti-6AI-4V replaced CP Titanium to increase the strength of nails, plates, screws, and endoprostheses being manufactured in England. In the mid- to late- 1970s, the extra low interstitial grade of Ti-6AI-4V was introduced in the United States for total hip femoral components [3].  

TMZF

TMZF™ alloy for ABG™II [4]:  

TMZF™ alloy was developed in 1986 by Stryker. Consisting of Titanium, Molybdenum, Zirconium and Ferrous (iron), it achieves a superior combination of flexibility, strength and notch resistance when compared to other alloys used in orthopaedic implants:  

• Increased Range of motion
• Increased Flexibility
• Increased Notch and Wear Resistance
• More biocompatible

Increased Range of Motion (ROM) and Strength  

• TMZF™ alloy is 20% stronger (has up to 20% higher yield strength) than Ti-6AI-4V (figure 1). The higher strength allows engineers to incorporate smaller stems and cross sections into the design. Smaller neck cross sections give patient greater range of motion and reduce the chance of impingement.   

Increased Flexibility

• TMZF™ alloy is 25% more flexible than Ti-6AI-4V (figure 2). Compared to other orthopaedic alloys, TMZF™ has a modulus of elasticity close to that of bone. Improved flexibility leads to a better stress transfer to bone and minimizes the potential for bone atrophy due to stress shielding. Besides it potentially reduces thigh pain for the patient.   

Increased Notch and Wear Resistance

• TMZF™ alloy has 47% greater notch resistance than Ti-6AI-4V. Notch resistance is the ability of a material to resist fracture with the presence of a surface imperfection such as a notch, section, crack, or scratch. Increased notch resistance provides better tolerance to surface stress concentration. TMZF™ demonstrates improved wear resistance reducing the potential for generation of particle wear debris. Increased notch and wear resistance builds a better foundation for implant longevity.

More biocompatible

• TMZF™ alloy does not include any aluminum or vanadium. While there have not been any clinically substantiated reports of problems stemming from the presence of the elements aluminum and vanadium in current titanium alloy, there are reported concerns based on potential toxicity, potential inhibition of apatite formation, and possible association with neurological disorders.  

Fig. 1: yield strength of TMZF compared to Ti-6AI-4V

Fig. 2: modulus of elasticity of different materials

Fig. 3: notch resistance of TMZF compared to Ti-6AI-4V

BACK to common Materials and Technologies

[1] Farthing TW. "The Development of Titanium and its Alloys". Clinical Materials, Vol.2, No.1, Feb. 1987
[2] Laing PG. "Clinical Experience with Prosthetic Materials"; Historical Perspectives, Current Problems and Future Directions. ASTM STP 684, pp. 199-211, 1979
[3] Semlitsch M. "Titanium Alloys for Hip Joint Replacements", Clinical Materials, Vol. 2, No.1, Feb. 1987
[4] Data on file at Stryker®