gms | German Medical Science

Introduction: Titanium is known to be the most biocompatible orthopaedic implant material and is therefore used as the material of choice in Germany. Though doubts exist concerning the biocompatibility of nickel-containing stainless steel the question can be raised whether the higher concentration of metallic wear, which is released from titanium implants, influences bone healing. Therefore the aim of this study was to compare implant materials from stainless steel and titanium, in a standardized osteosynthesis model.

Materials and methods:Transversal osteotomy of the tibia (gap 1mm) with consecutive plate osteosynthesis from either 316L stainless steel or commercially pure (cp-) titanium, was performed on 30 New-Zealand-white-rabbits. Full weight bearing without a cast was allowed postoperatively. Dynamics of bone formation were examined using the polychromatic fluorescend labeling according to Rahn (xylenolorange on day 11, calceingreen on day 21, alizarinkomplexon on day 34, tetracycline on day 49). Animals were sacrificed on day 56, and intensity of wear and inflammation in the implant-surrounding tissue was examined conventionally (particles (lymphocytes)/high power field (HPF) and immunehistochemically (anti- macrophage antibody). Results are presented as mean and standard error, significance level was set to p<0.05.

Results: The overall rate of newly formed bone was singnificantly lower (26,3%) in the cp-titanium animals compared to those in the 316L-group (30,7%). Regarding the course of bone formation, the highest intensity was also seen clearly later in animals with osteosynthesis from cp-titanium compared to those in the stainless steel group. Microscopically, there were significantly more wear particles in the connective tissue around cptitanium plates (14,1 (± 1,9) particles/HPF) compared to 316L (3,5 (±1,1) particles /HPF). Immunehistochemically, significantly more macrophages could be identified in the cp-titanium group (18,8/HPF; ± 2,7) compared to the 316L animals (8,3/HPF; ±1,5). Further, more lymphocytes could be counted in the connective tissue around the titanium implants (21,7/HPF) compared to steel (8,9/HPF). There was a strong statistical correlation in the cp-titanium group between the amount of particles and the severity of inflammation (K=0,72).

Conclusions: Surprisingly, these results show both a weaker and slower bone healing after osteosynthesis with cp-titanium implants. This could be caused by the higher amount of wear and the consecutively stronger inflammation in the connecitve tissue. In respect to these results, titanium implants should no longer be regarded to be superior to stainless steel under in vivo conditions.