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An increase in the utilization of metallic devices for orthopaedic interventions from joint replacement to fracture fixation has raised concern over local metal ion release and possible systemic sequelae due to dissemination of these ions. Our purpose was to determine whether serum titanium concentrations were elevated in patients who had previously received a locked volar distal radius plate. Our hypothesis was that the simple presence of titanium alone in a relatively fixed implant was not enough to raise serum titanium levels. Twenty-two potential subjects who had received a volar locked distal radius plate were identified through review of a single surgeon's operative logs. Eleven met inclusion criteria. Serum titanium levels were measured in these subjects and compared to both current and historical control groups. We found no difference between controls and our study group with the exception of one control subject who is employed as a welder. This is in contrast to previous studies from our institution which found increases in titanium levels in hip and spine implants. We conclude that a locking titanium volar distal radius plate does not raise serum titanium levels in this population.
A dramatic increase in the utilization of metallic devices for orthopaedic interventions from joint replacement to fracture fixation has raised concern over local metal ion release and the possible development of systemic sequelae due to dissemination of these ions. Several deleterious effects have been associated with increased metal ion levels including bone loss, prosthetic loosening, local tissue toxicity, hypersensitivity reactions, and even malignant cellular transformation.1,2 Considerable research supports elevated metal ion levels in the serum and urine of patients with metal-on-metal hip implants as well as in modular femoral stems and spinal instrumentation.3,4 Few studies, however, have examined whether fixed metallic implants, such as a locked volar distal radius plate, can also result in an increase in systemic metal ion levels.
All metal implants in vivo may undergo corrosion and wear which will result in the production of metal ions and surface degradation products.5-7 With fracture fixation devices such as intramedullary nails or volar plates, this phenomenon may be facilitated by micromotion of the implant, galvanic corrosion between materials of differing composition in close proximity, and fretting corrosion between the nail-screw or plate-screw interface.6,7 Most studies reporting on serum ion levels in patients have been in the context of a joint replacement device. With fracture fixation devices, which are used regularly in far younger patients than those commonly undergoing a total joint arthroplasty, there is the potential for significantly prolonged exposure to metal ions produced by that implant.
The shedding of metal ions greatly increases the total surface area in contact with the body. Locally, metal ions enter the cells and may alter the intracellular processes. Systemically, they undergo wider dissemination as both free ions and ingested particles that are transported to sites remote from the implant, including the spleen, regional lymph nodes, and the lungs, all of which may be adversely affected.7,8 Studies into possible carcinogenic effects have shown a correlation between chromosomal damage and elevations in degradation products and metal ions. This correlation appears to be dose-dependent and specific to the type of metal.7,9-11 Also, several studies have noted moderate elevations in hematopoi-etic malignancies in patients with hip arthroplasties.12-14 Since fracture fixation devices are generally amenable to removal, should elevations in local or systemic ions be discovered in association with fixed implants, patients may benefit from earlier removal of implants following fracture union.
We wished to determine whether serum titanium (Ti) concentrations in patients who had previously undergone open reduction and internal fixation of distal radius fractures using locked volar plates were elevated in comparison to control groups. We hypothesized that the mere presence of a titanium implant was not sufficient to significantly elevate serum titanium levels, but that device motion also is required for serum titanium to reach detectable levels.
This is a retrospective, non-randomized study comparing postoperative serum titanium concentrations in patients with a previously implanted unilateral volar distal radius locked plate.
The implant used in the current study was a DVR (distal volar radius) plate manufactured by Hand Innovations. It consists of a titanium plate with two distal rows of locked titanium screws and a variable length for the radial shaft where screws are of non-locking variety. In our study, we used exclusively three-hole plates with screws placed in all three proximal holes on the radial shaft. Motion of this device, theoretically, should be limited to only the three proximal non-locked screws which are stabilized by friction fit at the screw-plate-bone interface.
Potential subjects were identified through review of a single surgeon's operative logs and hospital billing codes. Patients deemed eligible for the study had previously undergone open reduction and internal fixation of a unilateral distal radius fracture with the previously described hardware construct. The patient's medical records were reviewed to ensure they had no other orthopaedic implants which might otherwise elevate titanium levels above that from the volar plate alone. Only patients with three-hole plates and all three proximal screw holes filled were included in our study. Subjects were contacted, consented to participate, and asked to provide a venous blood sample for trace metal analysis. Trace metal analysis was performed by a contract laboratory. Patient data was then compared to a control group previously established from prior ion studies within our department as well as to a current control group of volunteers free of any implanted metallic devices. The current control group was sent for evaluation with the same batch of samples from our study group in order to eliminate differences in laboratory analysis.
Venous blood samples were collected and processed from each subject. Venipuncture was performed with needles and syringes verified to be free of trace metal contamination. Blood samples were collected in SARSTEDT Monvetter (neutral) blood collection tubes via a Vacutainer Brand Safety-Lok 21G3/4 butterfly blood collection set with a Multi-Adapter (SARSTEDT 0197). A total of 30 ml was collected from each subject. To further limit possible contamination, the first 10 ml collected served as an apparatus washout and was discarded. Collected blood samples were allowed to clot for 30 minutes and then were centrifuged. The serum aliquots were collected and frozen at -80° C until processed for trace metal analysis.
Serum samples from implanted and control subjects were sent for Ti analysis to a single contract laboratory which utilized high resolution inductively coupled plasma-mass spectrometry (ICP-SFMS) (SGAB Analytica, Lulea, Sweden). Serum samples were analyzed for Ti (isotopes 47 and 49) after 20-fold dilution (0.14M supra-pure HNO3 in DDIW) using ICP-SFMS operated in medium resolution mode. Instrumental drift was corrected using internal standardization (In) and quantification was done by external standardization. Quality control/assurance procedures included analysis of blank samples and serum control materials (SERO AS, Norway) were processed along with study samples. The detection limit reported was 0.25 mg/L (ppm). Additional details on operating conditions and measured parameters were reported by Rodushkin et al., 2001.15
Subgroup comparisons were made using analysis of variance (ANOVA) and student's t-test. A p-value of <0.05 was considered to be significant.
A total of 22 subjects were identified for potential inclusion in the study. Of the 22, one declined to participate and 10 were unable to be contacted or reached. A total of 11 subjects (8 females, 3 males) with a mean age of 63 years agreed to participate. Demographic data for our patients is listed in Table 1 including age, sex, height, weight, and time since surgery.
Trace metal analysis revealed that only one subject had a serum titanium concentration (0.58 μg/L) above the minimum detectable level (0.25 7mu;g/L). All controls also had levels below the detection limit except for a positive control that sustained daily titanium exposure due to welding and had a titanium level of 2.86 μg/L (Figure 1). Titanium levels in both historical and current controls as well as those individuals with volar plates were lower than those reported for two separate hip prostheses (one non-modular, one modular) as well as for those individuals with spinal instrumentation (Figures 2, ,3).3). No evidence of any implant loosening was found on postoperative imaging review.
Previous studies within our department have found increased serum titanium levels with both spinal instrumentation as well as modular and non-modular femoral total hip stems.3,4 Multiple studies have found increased cobalt (Co) and chromium (Cr) levels with metal-on-metal total hip bearings.16-18 Concern over the effect of these ions both in the form of local tissue reactions as well as systemically have led to numerous investigations into their effect with no conclusive results to date.
In our review of the literature, we were unable to find a study to show that a fixed titanium implant in the body does not result in elevated serum titanium levels. We felt it was important to determine whether the presence of a static titanium implant was significant enough to raise systemic titanium levels, or if other factors were required to generate significant increases in systemic titanium levels. Should evidence continue to mount regarding deleterious effects of increased local or systemic metal ion concentrations, this study would allow us to better stratify device safety protocols and develop guidelines for removal of fracture fixation devices if indicated.
The Hand Innovations DVR plate is a commonly implemented orthopedic implant used to treat fractures of the distal radius. Because it is a mostly fixed angle device made of titanium with motion only occurring at the non-locked radial shaft screw-plate interface, it is ideally suited to demonstrate that fixed titanium implants alone are not sufficient to cause serum ion elevations. While micromotion is possible at the plate-screw-bone interface, the friction fit at this site evidently is enough to disallow systemic ion elevations based on our results. Whether ions are produced at all or if production takes place but renal clearance occurs rapidly enough to prevent detection is not known based on our study. Regardless, it appears that titanium ion levels are essentially undetectable with the three-hole DVR model.
Several questions remain to be answered. Our study was able to evaluate systemic ion levels but we are unable to comment on whether local soft tissue concentrations are increased, and what, if any, effect this may have. In addition, because our data is specific to titanium, we are unable to stratify our results to other metal ions such as cobalt or chromium. These two ions are very important in the current controversy over metal-on-metal implants as they form the bearing surfaces for those prostheses. Unfortunately, there are currently no commonly used cobalt-chromium fixed implants that are free of motion for us to evaluate and establish as a control group for these metals like there is with the currently studied titanium plates. Finally, we are unsure if continued long term exposure of the studied device will eventually cause increased serum titanium levels. We would hypothesize that once fracture union occurs no further device motion would take place and therefore no further increase in titanium levels would result. Further studies are needed to verify this theory.
It is important to address several limitations of our study. First, it is retrospective in nature and we lack preoperative serum ion levels for comparison. Secondly, only one size of implant with a fixed amount of titanium was evaluated. A larger implant exposing the body to a higher amount of titanium could conceivably result in elevated ion levels. Further, we don't have a similar device exposed to movement to show that motion of the current implant could increase serum titanium levels. However, we feel that previous studies focusing on hip and spine implants showing increased titanium levels support this conclusion.3,4 Despite these limitations, we feel that our study demonstrates that the presence of a relatively fixed angle titanium device alone is not enough to cause detectable increases of systemic ion levels. This increases the applicability and confidence we will be able to place in future studies of titanium devices which do allow implant motion.
Our findings suggest that fixed titanium DVR plates do not result in a detectable increase in systemic exposure to trace metal ions. The absence of titanium elevations in this study population leads us to conclude that micro-motion at plate-screw-bone interfaces is not sufficient to yield a detectable increase in systemic titanium levels. These data establish that the presence of bodily titanium alone is not enough to generate detectable increases in serum titanium levels in contrast to data previously found in modular and non-modular femoral stems and spinal instrumentation. We propose that device motion may be necessary for increased serum titanium levels to occur.