Biocompatibility of Titanium Implants in Beagle Dogs

Chuck RosenwasserMentors: Frank Raia & Mel RosenwasserColumbia Presbyterian Medical Center

Hypothesis

Titanium metal implants for fracture fixation generate different tissue responses than implants made of stainless steel.

Introduction

The goal of fracture treatment is to protect and improve the natural healing process. Internal fixation of long bones with plates preserves fracture reduction and prevents movement between fragments, which results in early restoration of anatomy and function to the extremity.

Introduction (cont.)

Typically stainless steel has been the metal of choice for fracture fixation with plates. Titanium has been used more recently for its enhanced biomechanical properties; however, case reports state that the use of titanium can cause complications including tendon rupture and severe inflammation of the tendon and/or surrounding tissue.

Materials and Methods

18 skeletally mature beagle dogs (female)

6 pure titanium 4-hole plates6 titanium alloy 6-4 (titanium-aluminum-

vanadium) 4-hole plates6 stainless steel 4-hole platesAll holes on the plates were 2.7mm in

diameter and all had 2.7mm screws made of corresponding metal.

Materials and Methods (cont.)

An osteotomy was performed on the distal right radius of each animal utilizing an oscillating saw and fixed utilizing one of the aforementioned plates. Post-surgery, the animals were allowed weight bearing as tolerated and the animals were followed for a three-month period with serial x-rays to establish healing. At three months, specimens of the overlying tendons and soft-tissue were harvested. The harvested tissue was stained using an H&E stain (hematoxylin and eosin).

Radius fixed with 4 hole plate and screws

Materials and Methods (cont.)

Analysis using histology and light microscopy allowed for grading of the inflammatory response to the metal used. Grading system was conducted on a 5-point scale, 0 being no inflammation and 5 being severe inflammation.

Inflammatory Cells per High Powered Field (40x)

# of Inflammatory Cells Score (on 5-point Scale)

0-2 0

3-5 1

6-10 2

11-20 3

21-50 4

50+ 5

Results

Each of the three surgical groups demonstrated significant differences in cell density and distribution. As shown in the chart, the stainless steel plates had the lowest average inflammation at 1.5.

Results (cont.)

Titanium, either alloy or pure, demonstrated more inflammation (3.4-3.7) without a statistically significant difference although a trend to increased inflammation was observed in the pure titanium.

Average Degree of Inflammation

00.5

11.5

22.5

33.5

44.5

5

Stainless

(n=6)

Ti Alloy

(n=6)

Titanium

(n=6)

Extensor tendons overlying a stainless steel plate

Extensor tendons overlying a titanium-vanadium alloy plate

Extensor tendons overlying a pure titanium plate

Discussion

Fractures are a common injury to both people and animals. Modern fracture care dictates that anatomic restoration is important to function recovery. Stainless steel fracture plates have been used for many years and with good results. Newer metals such as titanium and its alloys have theoretical advantages in material properties closer to native cortical bone.

Discussion (cont.)

Viscoelasticity is one such property and the titanium is less stiff, therefore, the bone cells at the fracture site would heal with better strength. These biomechanical advantages derived in bench testing required confirmation in a living system. Human trials utilizing pure titanium for fractured forearms demonstrated surprisingly poor results. These included marked, scar formation, tendon rupture, and loss of joint mobility.

Conclusion

Plates made of titanium and a titanium alloy cause more inflammation to surrounding tissue than do those made of stainless steel. This may help to explain complications involving tendons and other soft tissues described in the orthopedic literature.